US3337966A - Method and device for removing liquid from webs - Google Patents

Description

Aug,v 29, 1967 A. MEEUSSEN ET AL 3,337,966

' METHOD AND DEVICE FOR REMOVING LIQUID FROM WEBS Filed May 12, 1965 2 Sheets-Sheet 1 INVENTORS LOU/5 ACH/LLS MEEUSSEN W/LFP/ED FLO/V7 DE GEES? BY WATSON. COLE. GR/NDLE.& WATSON ATTORNEYS 1967 A. MEEUSSEN 'ET AL 3,337,963

METHOD AND DEVICE FOR REMOVING LIQUID FROM WEBS 2 Sheets-Sheet 2 Filed May 12, 1965 INVENTOR S LOU/S ACHILLES MEEUSSEN I WiLFR/ED FLORE/W DE GEES? BY W4 7' SON .COLE GR/NDLE & WATSON ATTORNEYS United States Patent 3,337,966 METHOD AND DEVICE FOR REMOVING LIQUID FROM WEBS Louis Achilles Meeussen, Mortsel-Antwerp, and Wilfried Florent De Geest, Berchem-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel, Belgium, a Belgian company Filed May 12, 1965, Ser. No. 455,066 Claims priority, application Great Britain, May 15, 1964, 20,428/ 64 13 Claims. (Cl. 34-42) This invention relates to the removal from a continuously moving web of liquid which is adhering thereto.

The term web as used in this specification denotes any flexible or undefonnable sheet or strip which can be continuously fed. The term includes paper, plastics, glass or other material in such form.

By adhering liquid we mean liquid present on the surface of the web as a result of condensation, adsorption or otherwise, this in contrast to the absorbed liquid which has penetrated into the body of the web.

The invention is particularly suitable for use in the drying of wet webs. By removing the liquid which is ad herent, or part of said liquid, according to the invention, the advantage is achieved that only the liquid (if any) which is absorbed by the web and/ or the remaining part (if any) of the adsorbed liquid, has to be removed in a subsequent step, e.g., by a dry air current, to complete the drying. Since the said absorbed and/or remaining adsorbed liquid is usually only a minor part of the initial total amount of liquid carried by the web, the time for drying the web will be considerably reduced.

The invention may also be used for the purpose of metering liquid coatings just applied to webs.

As the invention is more particularly intended for drying or metering the coatings of light-sensitive and other materials for use in photographic processes, reference is particularly made to such materials in this specification but it is to be understood that the invention has many other potential uses.

According to the present invention some at least of the liquid adhering to a web surface is removed therefrom by establishing a liquid bead between said adhering liquid and at least one passageway or channel leading away from the web path, and advancing the web longitudinally past said passageway or channel while maintaining said bead and allowing or causing liquid continuously to leave said surface and to move along said passageway or channel at least in part under the influence of surface tension effects.

The nature of the surface or surfaces of the or each passageway or channel and the cross-sectional dimension thereof may be such as to induce motion of the liquid by capillary attraction and it is in fact preferred to use one or more passageways or channels of capillary size. If, however, the said surface or surfaces are inherently not wettable or not sufficiently wettable by the liquid, the surface tension between the liquid and the said surface or surfaces may be increased by electrical or magnetic forces, preferably by an electrostatic field established between the part or parts defining the passage way(s) or channel(s) and the web. The requisite movement of the liquid may alternatively or in addition be assisted by gravitational force, and it is in fact preferred to carry out the invention so that flow of liquid from the web and along the passageway(s) or channel(s) takes place downwardly and to bring about continuous dis charge of liquid from the passageway(s) or channel(s) by gravity.

The expression passageway particularly includes a flow path defined by a tube or between opposed walls and 3,337,966 Patented Aug. 29, 1967 the term channel is used as being more particularly applicable to a surface groove or the like. It is particularly recommended to employ a passageway of slot-like cross section arranged with its longer cross-sectional dimension normal to the line of motion of the web. The or each such passageway may, e.g., extend over the full width of the web.

As will hereafter appear, removal of liquid from the surface of a web to which it adheres by maintaining a liquid bead between the adhering liquid and a part or parts located adjacent the web while the latter is longitudinally advanced past such part or parts is new in itself and gives useful advantages over the previous known methods of metering liquid coatings. The advantage is marked when the flow of liquid away from the location of the bead is effected or promoted by capillary forces but there may be cases in which the use of surface tension effects otherwise than for maintaining or assisting the maintenance of the bead is not necessary and the invention accordingly also includes any method wherein liquid adhering to a surface of a web is removed by maintaining a liquid bead by or with the help of surface tension effects between the liquid on said surface and 'at least one part located at a'spacing from the said surface such that said part would be out of contact with the liquid on the web were it not for said bead, and maintaining such bead while advancing the web and allowing or causing liquid to flow from the location of the bead so that the liquid forming the head is continuously replenished by liquid from the web.

The invention will be further described with reference to the accompanying diagrammatic drawings illustrating certain embodiments thereof which have been selected by way of example and which incorporate various other optional features of the invention not so far referred to. In the drawings:

FIG. 1 is a perspective view of a capillary.

FIG. 2 is a diagrammatic vertical view of a device for removing liquid from a web.

FIG. 3 is a diagrammatic vertical view of a device for removing liquid from a web, in which an electrostatic field is applied.

FIG. 4 is a diagrammatic vertical view of a device for removing liquid from both sides of a web, in which an electrostatic field is used.

FIG. 5 is a perspective view of another embodiment of the capillary.

FIG. 6 is a diagrammatic vertical view of an arrangement for removing liquid from coated photographic plates.

For carrying out the embodiment which will be described hereinafter, use Was made of a capillary which was constructed as follows.

Two glass slides 11 measuring 50 x 50 mm and having a thickness of 2 mm. were parallelly assembled by means of four strips 12 of triacetate film which were stuck two by two between two opposite edges of the slides. The strips measured 50 x 50 x 0.14 mm., so that a capillary was obtained with a width a of 0.3 mm., a length b of 40 mm. and a height 0 of 50 mm. The slides had a smooth surface and were Well-cleaned.

A first device which was used for demonstrating the invention is shown in FIG. 2. It comprises a lick-roller wetting system with a roller 13 and a tray 14, the capillary 15 as represented in FIG. 1, a pan 16, and an idler roller 17.

A common 35 mm. fihn web 18 which is perforated at both its edges is advanced, its emulsion side facing downwardly, over the rollers 13, 17, at a speed of 10 crn./s. in the direction of the arrow. The capillary 15 is so arranged, that a distance d of 0.5 mm. exists between the top of the capillary and the emulsion side of the web, and that the web is centrally guided over the capillary. The roller 13 partly turns in an aqueous solution in the tray 14, so that upon movement of the web 18, the emulsion side of the web will be wetted by the liquid which adheres to the roller 13. T minor amount of the liquid is absorbed by the emulsion layer of the film web whereas the greater part of the liquid superficially adheres, or in other words, is adsorbed, to the web.

The removal of the liquid adhering to the web starts by causing the wetted side of the web to briefly contact the top of the capillary. In its simplest way this was done by slightly pushing down the web between the two rollers until its wetted side contacted the capillary. Upon the returning of the web to its flat stretched state beween the two rollers, a liquid bead formed between the top of the capillary and the web.

Said liquid bead first increased somewhat as the web advanced, but thereafter the liquid penetrated into the capillary by the action of the surface tension of the liquid. The capillary will be wetted by the liquid which gradually penetrates therein until the lower opening of the capillary is reached. At that moment the liquid starts to leave the capillary in the form of droplets or in the form of a continuous liquid stream, and is received in the pan 16. When the web is lifted from the rollers 13 and 17 for visual inspection, it clearly appears that there is a considerable difference in the amount of liquid adhering to the web before, respectively after, the removing station.

The said difference in the amount of liquid adhering to the web was determined in a more accurate way by measuring the electrical current through said wet layer of the web in front of, respectively behind the capillary. To this end two sets of electrode pairs rubbing over the wet side of the web, each pair consisting of two stainless steel spheres of a diameter of mm. and being spaced from each other in the longitudinal direction of the web over a distance of 20 mm., were located at either side of the capillary.

A D.C. tension of 500 volts was applied to each set of electrodes. Before the capillary an electrical current of 40 A. and behind the capillary a current of 4 ,uA. was measured. With a second similar capillary being located a few centimetres behind the first capillary, the values measured before, respectively behind the capillary with the aid of identical electrodes and the same D.C. tension were 4 and 0.4 nA.

These values point out that each time about 90% of the liquid adhering to the web is removed by the capillary. It is clear that the absolute quantity of removed liquid decreases for each further capillary, and will tend finally to zero.

During the operation of the device it was observed that the liquid does not necessarily completely fill the capillary over'its full length, [1:40 mm., or at least over a distance corresponding to the width of the web, i.e. 35 mm., along its height c. When looking perpendicularly to the plane of the slides, one time a truncated cone-shaped liquid pattern was seen the smallest side directed downwardly and another time a pattern in the form of broad strings was seen. In any case, however, the removal of liquid occurred very uniform over the full width of the web. The perforations of the film did not lead to a rupture of the liquid bead, nor did they disadvantageously affect the removal of liquid along the longitudinal paths at either side of the web determined by the perforations.

The establishment of the liquid bead in the described device has also been performed in another way than by briefly pushing down the web between the rollers 13 and 17. According to a first modification the bead was established by using a small brush of marten hair which was held shortly against the back side of the capillary and which contacted with its extremity the wet layer of the web. Upon travel of the web the brush took up liquid from the web which after a few moments wetted the top of the capillary and then started penetrating into the capillary. At that stage the brush was removed and the device continued working.

It has to be noted that the width of the brush was only part of the width of the film web. This did not prevent the establishment of a liquid bead over the full width (35 mm.) of the film web.

According to another modification the bead was established by means of a small strip of film which Was inserted in the capillary at its lower opening and advanced upwardly until it contacted the web. The film strip acted as a scraper assembling liquid until a bead was established between the web and the capillary. At that moment the film strip was withdrawn. A strip of polyethylene terephthalate film was used having a thickness of 0.1 mm., and measuring 35 x 70 mm.

The technique of removing liquid from a web by means of a capillary according to the invention, represents important advantages over the known techniques comprising the use of squeegee roller pairs, scrapers such as a doctor blade, metering devices such as a trailing knife, etc.

First, there is no direct contact between the removing means and the web. In practice distances will be used varying between some tenths of a millimeter and a few millimeters. As a consequence thereofany risk of mechanical damaging of the side of the web containing the liquid to be removed, is avoided.

Second, when the web is not completely fiat in the transverse direction, relatively great differences will exist between the web and a closely adjacent removing device such as a doctor knife. Since the capillary according to the invention is relatively much further removed from the web than the known removing devices, the relative distance differences in case of a web being not completely fiat will be much smaller. As a consequence thereof, the removal of liquid in the transverse direction of the web occurs very uniformly, even in cases when the web is not fiat.

A second embodiment of the invention is represented in FIG. 3.

The device comprises a metal backing roller 20 which is covered with an electrically insulating layer 21, a capillary 15 similar to that represented in FIG. 1, a potential source 22, and a copper electrode 23.

A web 18 similar to that which was used in the device 7 of FIG. 2 is advanced over the free-turning backing roller 20 with the wetted side facing downwardly. A clearance d=0.5 mm. exists between the web and the top of the capillary 15 which is located under the roller 20.

The liquid head between the web 18 and the capillary 15 is established by applying a voltage difference between the backing roller 20 and the capillary 15.

To this end, the metal backing roller 20 is electrically insulated from the other metal parts of the device by journalling its shaft in insulated bearings. Means are provided for connecting the shaft of the backing roller to one terminal of the potential source 22. The other terminal of said source is electrically grounded.

Also grounded is a strip of copper foil 23, having a thickness of 0.1 mm. and measuring 30 x 50 mm., which is inserted in the capillary as shown in FIG. 3 and the ex tremity of which remains at a distance e:1 mm. beneath the top of the capillary.

The potential difference between the backing roller 20 and the electrically conductive foil 23 in the capillary creates an electrostatic field which traverses the gap be tween the web and the capillary. The said electrostatic field establishes a liquid head between the web and the capillary, since an amount of liquid is literally struc against the top of the capillary. Upon the establishment of said liquid bead the surface tension causes the liquid to wet the walls of the capillary and thereby to penetrate into the capillary. Finally the liquid leaves the capillary by the force of gravity. In case the distance d is too great to maintain the liquid bead between the web and the capillary, the potential difierence between the backing roller and the copper foil may not be removed.

The distance e is not critical. The mentioned measure of keeping the extremity of the copper foil within the capillary was only taken for preventing the thin flexible foil from being distorted or bent. It is evident that in case the said distance 2 is increased, the applied voltage shall be raised accordingly. In the present case an A.C. voltage of 1000 volts (RMS value), 50 kc. was continuously applied.

The thickness of the electrical insulation 21 on the backing roller 20 amounted to 1 mm. Its object is to prevent any electrically conductive path between the backing roller and the foil 23 which would seriously set down the potential difference, and consequently reduce the electrostatic field. Such conductive path could e.g. be formed by liquid passing through the perforations of the web, by a web which would completely be penetrated by the liquid, etc.

It is to be understood that such insulating layer on the roller 20 is not indispensable and if one is sure that an electrically conductive path cannot arise, the said layer may be omitted.

Hitherto no details have been given about the wetting power of the liquid to be removed. The following discussion of the physics of surface wetting may be useful in connection with the selection of the capillary and the conditions in which it will be used in carrying out the present invention, but the invention does not depend on these statements of theory.

In the introductory part of the description it has been mentioned that the capillary should be wettable by the liquid to be removed. As a matter of course, said condition applies to the inner wall of the capillary.

Said wetting is a conditio sine qua non, since without wetting no capillary rise can occur, and consequently no tendency will exist for the liquid to leave the web. The classic example of a non-Wetting liquid is e.g. mercury which is depressed in a glass tube.

It is known that the wetting power of a liquid depends on its surface tension. In case of a capillary the influence of said factor is expressed by the formula giving the capillary rise in tubes:

wherein h is the height of rise; T the surface tension of the liquid, 0 the angle of contact, D the sepecific gravity of the liquid, r is the radius of the tube and g is the acceleration of gravity (Principles of Physics I, by F. W. Sears, 1964, Addison-Wesly Press, Inc., Mass, U.S.A.).

In such capillary the height of rise is nothing else than v the state of equilibrium between the upwardly directed force at the meniscus in the capillary, and the downwardly directed force representing the weight of the liquid column;

In the capillaries represented in the foregoing embodiments said state of equilibrium cannot occur since instead of a rise of liquid, there is actually a fall. This explains the continuous discharge of liquid from the capillary.

The dimensions of the capillary 15 which have an efl ect on the removal of liquid from the web, are the width a and the height 0. When reducing the width a the capillary effect increases but the resistance to the passage of liquid increases as a consequence of the smaller cross-section. When reducing the height c of the capillary, the capillary effect decreases accordingly, but the resistance for the passage of liquid decreases also.

The distance d between capillary and web is less critical. The main object of said distance is to prevent the capillary from directly touching the web.

The linear speed of the web has also to be taken into account, of course, and in each case a given speed cannot be exceeded without disadvantageously influencing the removal of the liquid from the web.

Finally, the addition of surfactants to the liquid adsorbed on the web may be considered for decreasing the surface tension and enhancing the spreading of the liquid.

In the embodiment of FIG. 3 the use of an electrostatic field for the establishment and/or the maintaining of the liquid bead between the web and the capillary has been described. It should be noted that the electrostatic field, besides its effect on the liquid bead, has also a secondary effect which is not neglectable, viz. an increase of the wetting power of the liquid. This is briefly explained as follows.

Each heterogeneous system of matter possesses at each surface of matter or interface between different phases, a particular amount of free energy. A change in the sur face state supposses that free energy is withdrawn from or added to the system. In that connection a change in the free surface energy is referred to. Free surface energy is potential energy and therefore is table to perform work.

For a particular system, the total free surface energy depends on the size of the considered surface and of the free, or more specifically, of the physico-chemical free binding energy unit of surface. Hence a process which strives for reducing the contact surface or for reducing the magnitude of the free surface energy per unit of surface will occur spontaneously. In a contrary case, energy will have to be added to the system. Such addition of energy occurs by applying an electrostatical charge. The above-mentioned method has further been described in detail in the co-pending United States application 150,820.

In order to show that the good removal of liquid from the web has to be attributed to the effect of capillarity and not to the back wall of the capillary acting in some way as a scraper although not in direct contact with the web, a capillary was used consisting of two parallelly spaced plates of about the same dimensions as those represented in FIG. 1. The parallel distancing of both plates was performed by means of some spacers in such a way that the front plate could be removed, the back plate remaining in place. After some time, when the capillary was continuously removing liquid from the'web, the front plate of the capillary was removed without changing the position of the back plate. The removal of liquid decreased immediately to only a fraction of the quantity which was removed before.

A third embodiment of the invention is represented in FIG. 4.

A film web which is wetted at both sides is advanced by means, not shown, in the direction of the arrow. The web passes between two capillaries 15 which are located at 45 in respect of the web 18 and mutually at about The capillaries are made of an electrically insulating material and a copper wire 30 extending across the length of the capillary and running parallel at a distance of some millimeters to the top of the capillary, has been provided in a groove in one plate of each capillary. Both wires are connected to one terminal of the potential source 22, the other terminal of which is grounded. The grounding of the liquid layers on the web may occur by grounding the supply of liquid to be applied to the web, by making the web pass over grounded metal rollers etc. The grounding of said liquid layers is schematically indicated by the ground point 31 on the figure.

For the width a of the capillaries as well as the distance d, we refer to the foregoing explanations in this respect.

The potential source 22 may be used for only establishing the liquid bead between the web and the capillaries, or it may be used for establishing and maintaining or stabilizing the liquid beads.

The tension of the source 22 as well as the frequency of it may be varied between large limits. An A.C. tension will be mostly more effective than a DC. tension of the same magnitude. Care should be taken that no ionization occurs since otherwise the web or given layers coated thereon may be damaged or affected disadvantageously.

In case important currents arise (greater than say 10 ma.), the voltage diflerence may break down so that the electrostatic field is considerably reduced. This effect can be avoided by preventing the electrodes from direct contact with the liquid. In the embodiment of FIG. 3 this prevention has been performed by the insulating layer 21. In the present embodiment, the electrodes 30 may be insulated or incorporated in the insulating capillary material to suit the same purpose. The establishment of the electric field may also be performed by other means than by the incorporated wires 30. Use may be made of capillaries, at least one wall of each being covered with an electrically conductive layer, e.g. a vacuum coated layer, which in its turn may be covered with an electrically insulating layer.

Still another embodiment of the invention is represented in FIG. 5.

A 35 mm. film web, its wetted emulsion side turned upwardly is advanced by means, not shown, in the direction indicated by the arrow. The web passes underneath a capillary 15 which is constituted by two parallelly spaced members. The members are made out of copper plate of a thickness of 1.5 mm. and shaped as illustrated by the figure. The distance between both members amounts to 0.6 mm. and is obtained by joining the plates at some points .at their periphery with soft soldering spots 26. The edge 27 of the capillary runs parallel to the web at a distance of 0.5 mm.

As described hereinbefore, the removing of the liquid from the web starts by making the web briefly contact the adjacent edge of the capillary. Upon the returning of the web to its initial distant position, a liquid bead forms between the edge 27 of the capillary and the web.

As the web advances, the liquid rises in the capillary until it starts to spread out over a width greater than the width of the web. The liquid starts to fill the ledges 28 of the capillary, and finally leaves the capillary in the form of droplets or of a continuous stream at the extremities 29 at either side of the web.

It is clear that, contradictory to the previous embodiments, in the present one a really capillary rise takes place.

The height to which the liquid will rise in the capillary before the liquid starts to leave the capillary by the force of gravity depends on the distance a between the plates, the surface tension of the liquid, etc.

The present form of capillary may be used in connection with the forms shown in FIGS. 1 to 3, so that even in this embodiment, when the Web travels horizontally, liquid which is adherent to a web at both its sides may be removed.

It is evident that also in the present embodiment an electrostatic field may be applied for establishing or maintaiuing the liquid bead between the web and the capillary.

To this end the copper capillary may be connected to one pole of a source of E.M.F., and an insulated electrode which is located under the web at the height of the capillary will be connected to the other pole.

For the sake of completeness it may yet be mentioned that the removal of the liquid from the capillary may as well be performed by other means instead of by the force of gravity, e.g. by maintaining a reduced pressure at the outlet opening of the capillary, by creating an electrostatic field between the outlet opening of the capillary and a lower located electrode, etc.

The examples given hereinbefore generally relates to the removal of liquid from webs.

More particularly the method according to the invention is suited for the removal of processing liquid which is adherent to film and paper webs which are being processed. In removing according to the invention the adherent liquid from the web as it passes from one bath to another, e.g. from the developer to the fixing bath, or from the fixing to the bleaching bath, the rinsing between the respective baths may be shorter and more effective. Especially in the case of high speed photography which is done in the field, e. g. in mobile units for military purposes, the hQIEr processing time and the reduced quantities of rinsing liquid are interesting. When finally removing a great deal of the adherent liquid before the web passes into the drying section, also the time for drying the web is considerably reduced as mentioned already in the introductory part of the description.

Another particular application of the invention resides in its use for post-metering the coating thickness of low viscous liquid compositions onto webs.

According to this technique more coating composition is applied to the web at the coating station than actually is required. At some distance behind said station means is provided for removing part of the coating composition so that the remaining part of the composition corresponds to the required wet quantity per square unit. Known metering means are the air-knife, the trailing knife, the metering roll, etc.

All of said known metering devices possess a number of specific inconveniences and it may be interesting to consider if in a given case, the substitution of an existing metering device by the capillary removing means according to the invention, would not constitute some improvement.

As a specific characteristic of the capillary removing means according to the invention has already been mentioned the absence of direct contact with the web. Further interesting points are its small dimensions which permit to locate it at hardly accessible areas, or to locate it close to the coating station, and moreover the possibility of using an electrostatic field and even controlling to some extent the removal of composition from the web by means of the magnitude of the electrostatic field.

Returning to the possibility of locating the capillary close to the coating station, we refer to British patent specification 953,704 filed Sept. 9, 1959 by Research Laboratories of Australia Limited. Said specification claims a method of coating surfaces which consist in delivering the coating material through a delivery nozzle disposed at an angle to the surface being coated and withdrawing surplus material from the coating zone by a suction nozzle also angularly inclined to the surface being coated and facing the delivery nozzle, the coating material being thus caused to follow a curved path between the delivery nozzle and the suction nozzle which extends into theplane of the surface being coated.

For the withdrawal of surplus material, the suction nozzle may advantageously be replaced by a capillary removing means according to the invention. The pump for removing coating composition through the suction nozzle may then be omitted.

Sinoe said pump is responsible for the formation of foam in forcing air in the supply of coating composition contained in the supply tank, it is clear that the formation of foam will be reduced.

Another application of the invention which has given very good results in practice is described hereinafter.

In the manufacture of photographic glass plates, the light-sensitive emulsion is coated on the glass plates while the latter are closely ranged against each other on a continuously and horizontally advancing conveyor belt. After the emulsion has been applied to the top side of the plates, the coated layer has to gel before the plates can be removed from the conveyor belt for placing into racks whereafter they are put into the drying section. The gelling occurs in making the plates horizontally run over a felt conveyor belt, which is soaked with water at a temperature of 3 C.

In this way the backside of the plates becomes quite wetted. When the plates leave the gelling felt belt and are transferred to the dry conveyor belt, a relatively great quantity of water remains adhering to the backside of the plates. When the plates are removed from the conveyor belt, their backsides are still considerably wet. During the drying process, the water at the backside of the plates contracts, and forms droplets and stripes which leave stains after drying. Although the said stains in no way impair the technical quality of the photographic plates, they are considered as a serious shortcoming in appearance.

It has now been found that a capillary removing means according to the present invention permits to reduce the mentioned drawback considerably.

The arrangement which was used in practice is diagrammatically shown in FIG. 6.

A coated glass plate 35 is just leaving the wetted felt conveyor belt 36 and is already partly supported by the dry conveyor belt 37. Between the two conveyor belts three capillaries 38 are provided, each consisting of two glass plates with a width of 104 cm., a height of cm., a thickness of 3 mm. and a relative spacing of 0.4 mm. The top edges of the plates are bevelled as shown in the said figure and the distance between the path followed by the backside of the plates and the top of the capillaries amounts to 1 mm.

In each capillary a small strip 39 of polyethylene terephthalate film with a thickness of 20 mm. is provided which extends about 1 mm. above the capillary.

The object of said strip is to establish the liquid bead between the wet backside of the glass plate and the capillary, at the moment the front edge of the plate passes over the capillary.

The coating apparatus wherein the present arrangement was provided operated at a coating speed of 6 LIL/min. The obtained results were very successful in that only very small drying spots remained on the backside of the plates after drying.

In the examples given hereinbefore, capillaries were considered consisting of two closely spaced flat walls, running parallel to each other. It is to be noted that this form of capillary is not limitative for the invention. Any other composition or structure representing the efiect of capillan'ty may be considered for performing the invention.

So the use of two closely spaced plates which slightly diverge from the entry opening, substantially triangular shaped closely spaced plates with their bases constituting the entry opening, and their tops constituting the outlet point, etc. may be envisaged.

'Further cellular materials with open cell structure may be provided between the walls constituting the capillary or even they may be partly or completely used as capillary means without any further wall means. Materials which may be used to this end are rigid cellular polymers such as polyvinyl chloride and polyethylene, flexible cellular polymers such as styrene butadiene latex, polyvinyl chlo-' ride and polyurethane, natural cellular products such as cellulose.

What we claim is:

1. The method of removing excess liquid from the surface of a moving web wet with said liquid by the steps compnsmg:

(1) Arranging at a fixed locus at least one capillary channel, each such channel having one end situated at a point below the other end;

(2) Passing said web along a path bringing one surface of the web in close spaced proximity to the upper end of said channel, at least that portion of such path adjacent said upper end being fixed and extending at an angle relative to said channel, the clearance between the web surface and upper channel end being such as to preclude contact between the surface and channel end but to maintain the liquid layer on said surface in contact with said channel end, whereby capillary and gravitational forces combine to move the liquid through said channel; and

(3) Collecting the liquid emerging from the lower end opening.

2. The method of claim 1 wherein the clearance between the web surface and the upper channel end normally exceeds the normal thickness of the liquid layer on said web surface but is less than the distance the surface tension of said liquid will support a bead extending between the liquid layer and said channel end.

3. The method of claim 2 wherein a bead is struck between said liquid layer and said channel end by temporarily reducing the clearance between the web surface and channel end to less than the liquid layer thickness and then returning the clearance to its normal distance.

4. The method of claim 2 wherein said head is struck between said liquid layer and said channel end by creating an electrostatic field between said channel end and the liquid on the web surface.

5. The method of claim 1 wherein the capillary opening in contact with the liquid on said web extends substantially across the width of the web.

6. The method of claim 5 wherein said capillary channel is continuous across substantially the entire web width.

7. The method of claim 1 wherein each such capillary channel has a substantially regular internal dimension from one end to the other.

8. The method of claim 1 wherein the movement of the liquid through said capillary is promoted by maintaining an electrostatic field between the liquid in said channel and an electrical conductor disposed on the opposite side of said web from said capillary channel.

9. The method of claim 1 including the step of contacting said web surface at a point on said path downstream of said capillary channel with a current of dry air.

10. A device for removing surplus liquid from a moving web wet with such liquid, which comprises means for guiding said web along a path at least a portion of which is fixed, means defining at least one capillary channel having two generally opposed ends, one of which ends lies below the other, said channel defining means being so arranged relative to the fixed path portion that the channel defined thereby extends generally at an angle to said path portion and has the uppermost end thereof in close spaced, non-contacting proximity to the web surface, and means for receiving the liquid emerging from the lowermost channel end.

11. The device of claim 10 including an electrical conductor associated with said capillary-defining means, an electrical conductor disposed in close proximity on the opposite side of said web from said capillary defining means and extending substantially across said web, in-

UNITED STATES PATENTS 2,234,697 3/1941 Hickman 3418 X 2,436,028 2/1948 Wiegerink 3495 X 3,009,257 11/1961 Scott 34-71 KENNETH W. SPRAGUE, Primary Examiner.

Claims (1)

1. THE METHOD OF REMOVING EXCESS LIQUID FROM THE SURFACE OF A MOVING WEB WET WITH SAID LIQUID BY THE STEPS COMPRISING: (1) ARRANGING AT A FIXED LOCUS AT LEAST ONE CAPILLARY CHANNEL, EACH SUCH CHANNEL HAVING ONE END SITUATED AT A POINT BELOW THE OTHER END; (2) PASSING SAID WEB ALONG A PATH BRINGING ONE SURFACE OF THE WEB IN CLOSE SPACED PROXIMITY TO THE UPPER END OF SAID CHANNEL, AT LEAST THAT PORTION OF SUCH PATH ADJACENT SAID UPPER END BEING FIXED AND EXTENDING AT AN ANGLE RELATIVE TO SAID CHANNEL, THE CLEARANCE BETWEEN THE WEB SURFACE AND UPPER CHANNEL END BEING SUCH AS TO PRECLUDE CONTACT BETWEEN THE SURFACE AND CHANNEL END BUT TO MAINTAIN THE LIQUID LAYER ON SAID SURFACE IN CONTACT WITH SAID CHANNEL END, WHEREBY CAPILLARY AND GRAVITATIONAL FORCES COMBINE TO MOVE THE LIQUID EMERGING FROM THE LOWER END (3) COLLECTING THE LIQUID EMERGING FROM THE LOWER END OPENING.

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