US 2761417 A
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Description (OCR text may contain errors)
Se t. 4, 1956 T. A. RUSSELL ETAL 2,761,417
MULTIPLE COATING APPARATUS Filed Feb. 25, 1955 CarleionRSanford INVENTORS ATTORNEX'S' United States Patent i MULTIPLE COATING APPARATUS Theodore A. Russell, Rochester, Richard M. Wilson, Penfield, and Carleton R. Sanford, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application February 23, 1955, Serial No. 489,861
4 Claims. (Cl. 118-410) The present invention relates to a new coating apparatus for applying multiple coatings to the surface of a moving Web, and particularly to a coating apparatus useful in carrying out the method of multiple coating a web described in U. S. application Serial No. 489,863, filed on even date herewith.
In said above-identified patent application there is disclosed a method of applying a plurality of separate coatings to the surface of a moving web which allows all of the layers to be applied to the web simultaneously while still maintaining a distinct layer relationship between the coatings after deposition. Essentially, it involves continuously forming each fluid composition into a layer of given thickness, bringing these layers into surface contact prior to the time they are applied to the surface of the web and then directing them in combined relation to a point of application where they are simultaneously applied to the web in the desired orientation and with no noticeable mixing or contamination at the interface of the layers.
The primary object of the present invention is to provide an apparatus by means of which this method of multiple coating a web can be carried out.
A further object is to provide a multiple hopper which forms each of several fluid coating compositions into individual layers and then brings them into surface contact prior to the time they are fed to a point of deposition where they are picked up on the surface of a moving web while the distinct layer relationship is maintained.
Another object is to provide a multiple feed hopper which is a combination of slide and extrusion types of hoppers wherein the separate coating compositions are individually formed into layers by both the slide technique and by extrusion, and after forming, the layers are combined in stratified relationship prior to the time they are applied to the surface of the web.
And another object is to provide a multiple feed hopper which comprises one or more extrusion type hoppers each adapted to form a separate coating composition into a layer, and one or more slide type hoppers each adapted to form a separate coating composition into a layer, said hoppers being combined and so arranged that the individual layers formed by each are combined with the others in stratified relationship without mixing prior to the time they are applied to the surface of a Web whereby all of said layers can be applied to the web surface simultaneously.
The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which:
Fig. 1 is a schematic showing of a coating apparatus including a multiple feed hopper constructed in accordance with the present invention;
Fig. 2 is a side view, partly in section, showing a dual 2,761,417 Patented Sept. 4, 1956 feed hopper constructed in accordance with one embodiment of the present invention and in operating association with a web to be coated thereby;
Fig. 3 is a view similar to Fig. 2 but showing another embodiment of the hopper adapted to feed three separate coating compositions to the coating point, two by extrusion and one by gravity; and
Fig. 4 is a vertical section of another embodiment of multiple feed hopper which is adapted to feed four separate coating compositions to the coating point, two by extrusion and two by gravity.
In the manufacture of supports or continuous webs which require the application of two or more separate coatings in superposed layer relationship on one surface thereof, it has been the customary procedure to place each of the coatings on the support in succession and to set and/ or dry each coating before the application of the next. Such a procedure has been deemed necessary in order to maintain a distinct relationship between the separate layers and to prevent mixing of the coatings or contamination of one by the other at the interface of the layers. It will be appreciated that such a procedure of applying a plurality of coatings to the surface of a support has been very time consuming and has involved the use of duplicate equipment for each coating. These two factors alone have added greatly to the expense of making such multiply coated supports.
In the above-mentioned patent application there is disclosed a method of coating which permits the simultaneous application of a plurality of separate coating compositions onto the surface of a web whereby the time and duplication of equipment involved in conventional coating procedures is reduced or eliminated, as the case may be. This novel method of coating is not dependent upon the use of any particular form of coating apparatus so long as it permits the formation of each of the coating compositions into layers of a given thickness and permits these layers to be brought into surface contact in the desired orientation prior to the time these layers are fed to the surface of the support in such combined relationship for simultaneous application to the surface. Experiments have shown that multiple coatings applied to the surface of a web in accordance with this method exhibit just as good results, both physically and chemically, so
far as distinct layer relationship is concerned as multiple coatings applied by the conventional technique of successively applying the coatings with a complete curing or drying of each one before application of the next.
The present invention relates to a particular type of apparatus adapted for carrying out this new method of multiple coating. Generally speaking, this apparatus includes a multiple feed hopper which, in this instance, is the combination of one or more extrusion hoppers with one or more slide hoppers so arranged that the separate coating compositions are first formed into individual layers and are then combined into stratified layer relationship prior to, or at, the time the combined layers are fed to a coating bead. The web, in moving across and in contact with this bead of coating, simultaneously picks up the combined layers of coating compositions on its surface and the layers of the separate coating compositions maintain their distinct layer relationship even after deposition on the web surface and up until the time they are completely dried.
Referring now to Figs. 1 and 2, there is shown an ap paratus constructed according to one embodiment of the present invention which was successfully used to apply two separate coatings to a support in the manufacture of photographic film. It comprises an extrusion type hopper, indicated generally at 10, combined with a slide type hopper, indicated generally at 11, in such a way that the layers L and L1 of separate coating composition formed by each are combined in surface relationship prior to, or at the time, .said layers enter a bead of coating 17 maintained between the discharge lips of the hopper and the surface ofaweb W continuously moved across and in contact with the head by a backing roll 13 which also serves to hold the web rigid and smooth at this point.
The extrusion hopper comprises a cavityinto which a fluid coating composition S is continuously supplied at a known rate through an inlet14 by a metering pump P of the constant discharge type. From the cavity 15 the coating composition is forced through an elongated narrow slot 16 which forms the composition into a layer L and directs it into the coating bead 17' maintained between the discharge lips of the hopperandthe web spaced therefrom and across which bead the web W is moved to pickup alayer of'coating therefrom. This bead technique of coating is well known in the coating art and is characterized by the formation of a puddle or bead" between the lips of the coating hopper and surface to be coated which tends to pileup or'puddle on that side of the coating device from which the web leaves. This pile up or head extends completely across the width of the web being coated and is generally referred to in the art as a coating head or a head of coating. In Fig. 2 we have shown the form of bead believed to exist with the present multiple slide hopper, as well as the paths taken by the individual layers of coating composition in passing therethrough. However, it is pointed out that this is merely a speculation since it has proven practically impossible to actually see what occurs within the bead. technique the coaing is not in fact deposited directly ontothe web surface by the hopper, but that the hopper merely maintains thecoating bead and the web is coated therefrom. With the bead technique of coating the actual thickness of the coating-laydown on a web moved thereacross will be determined by the action of the bead and will vary with the speed of web movement, the rate of supply of the coating compositions, etc. and will not necessarily be equal to the thickness of the ribbon of coating composition fed to the slide surface or the thickness of the layer formed in flowing down the slide surface.
The slide hopper comprises a cavity 18 into Whichanother fluid coating composition 8' is continuously fed at a known rate through inlet 19 by a metering-pump P. From this cavity coating composition S is fed through an elongated substantially horizontal slot 20 in the form of a ribbon and out onto a downwardly inclined slide surface 21 down which it flows by gravity to form the layer L1. The slide surface 21 intersects the upper wall of the discharge slot 16 of the extrusion hopper at an acute angle so that the layer L1, as it leaves the slide surface, is combined in surface relationship with the layer L as it emerges from the extrusion slot 16 at the time, or just prior to the time, the two layers enter the coating bead 17. This distinct layer relationship between the layers L and L1 must be maintainedduring the time the two move through the bead and after the two layers are picked up simultaneously on the surface of the web as it moves across and in contact with the bead, since an enlarged cross-section of the coated web after being dried showed that the two layers were distinct, extremely free of contamination or mixing at their interface, and possessed a relative thickness commensurate with the rate at which each composition was supplied to the hopper. Since, for reasons pointed out above, the thickness of the layers when deposited on the web may, and usually will, be different from the thickness of the same layers when they move into the bead, due to the bead action, the layers of coating after application to the web have been designated'by the same reference characters as the respective layers formed by moving down the slide surface or-be'ing extruded from slot 16 with theexception that the de posited-layers have been designated by a prime to" It can be seen that with this bead coating- 4 indicate that the thickness ofthe layers after deposition might be difierent than dun'ng the initial formation.
Although it is conceivable that the complete hopper could be made from a single block of metal or other material, in order to facilitate the fabrication of this device and to make it possible to clean it out when it is desired to change from one coating composition to another, it would be more practical to make the device up from a'number of separate pieces which can be assembled and disassembled. To this end we have shown this hopper composed of three separate blocks 23, 25"and'26 which can be held in assembled relation by any suitable means not shown. In the event the coating compositions used must be heated or cooled in order to keep them in a suitable fluid condition during passage through the hopper, the hopper, or the blocks making up the same, may be provided with interconnected conduits 31 and 32 through which a fluid heating or cooling-mediumcan be circulated. In the case of conduits 31 which are formed at the joint of two blocks, a gasket 33 may be inserted to obtain thenecessary liquid-tight joint.
Using a dual fe'ed hopper'of this type, a gelatino silver halide photographic emulsion and a protective coat of clear gelatin, as well as many other coating compositions well known in the photographic art, have been simultaneously coated onto different types of supports, including cellulose acetate, at different coating speeds. All coatings made have been excellent on the basis of micro cross-section tests made on the product after complete drying and in every case the photographic tests made of the coatings indicate that each one was within the tolerance range in comparison with the same product made in the conventional manner of'applying each coating'in succession with a complete drying of each coating before application of the next.-
The hopper 10 may be provided with any suitable form of adjustable mount so that the position of the lower end of the slide surface relative to the web being coated may be adjusted for the best results. To this end the hopper 10 may be carried by a frame 32' provided with bearings 33 rotatably mounted on the axle of the roll 13 to swing concentrically of the roll so that the position of the hopper as a whole may be shifted around the roll periphery, see Fig. 1. It is adapted to be locked in any adjusted position by clamping screw 34 engaging an arcuate slot 35 in the support 36. The hopper may be pivoted to the frame 32 for critical adjustment around the periphery of the roll, and may be slidably mounted on the frame for adjustment toward and from the roll'periphery by any suitable means not shown.
After the web W has been coated, it may be necessary to set and dry the coatings applied'thereto. In the manufacture of photographic film or paper, the coatings applied may be of the type which are'set by cooling prior to drying-in order to limit the amount of relative flow between the layers themselves or between the bottom layer andthe support. In such a case the web W after being coated can be passed through a chill box 37 and then through 'a drying chamber 38. If the coatings applied are of the type which do not require chillingbefore drying', then chill box 37 can be omitted or by-passed. The Web may be pulled from the drying chamber 38 by a feed or guide roller 39.
In Fig. 3 there is shown a triple feed hopperconstructed in accordance with the present invention by means of which three separate coatings have been simultaneously applied to the surface of a web. Structurally this hopper is practically identical with the dual feed hopper shown in Fig. 2, but difiers therefrom in that two extrusion hoppers are used in combination with a single slide hopper. This hopper comprises three cavities 50, 51 and 52 into whichseparate coating compositions 53, 54 and 55 are respectively.punip'ed'through inlets 56, 57 and 58,' respectively, by separate metering pumps P.' The coating composition 53 is extruded through an elongated narrow ing composition 54 is extruded through an elongated narrow slot 41 where it is formed into a layer 42. The discharge slots 59 and 41 meet at an acute angle so that layers and 42 being extruded therethrough are brought into surface contact at the time they issue from their respective slots and are thus combined in layer relationship prior to the time they enter the coating bead 17' maintained between the discharge lips of the hopper and the surface of web W to be coated.
The coating composition 55 is forced through a substantially horizontal elongated narrow slot 44 in the form of a narrow ribbon and out onto downwardly inclined slide surface 45 down which it flows by gravity and is formed into a smooth, uniformly thick layer 46. The slide surface 45 intersects the extrusion slot 42 at an acute angle at substantially the point where layers 40 and 42 come together so that the layer 46, as it moves off of the slide surface, is combined in surface relationship with layers 40 and 42 and the three layers move into the bead in this combination without mixing. As the web is moved across and in contact with the head of coating 17', it picks up the three layers 40, 42 and 46 of separate coating compositions and which are laid down on the surface of the web as distinct layers 49', 42' and 46. These layers, after deposition on the web, are primed because they may differ from the layers 40, 42 and 46 entering the bead so far as thickness is concerned due to the action of the bead, as pointed out above. As before, the temperature of the coating compositions while moving through the hopper may be controlled by flowing a fluid heating or cooling medium, as the need arises, through conduits 31' running through the hopper.
While visual inspection of micro cross-sections of the coated webs has shown that the several layers of coating composition do not mix while moving through the coating bead, it has been impossible to accurately ascertain the precise shape of the path each layer takes in moving through the bead. What we believe happens, however, is that in the dual hopper of Fig. 2 the extruded layer 1. backs into and fills the space 60 between the lip 61 of the hopper and the web W due to capillary attraction while the upper layer L1 is stretched up onto the leaving edge of the slide surface of the hopper due to the combined effect of capillary attraction and the frictional pull of the web. In the case of the triple feed hopper of Fig. 3 we believe that the upper and lower layers 46 and 40, respectively, act in the same way as the two layers of the Fig. 2 hopper. The middle layer 42, however, is believed to pass through the bead in a practically undeformed manner because it does not directly engage either the slide surface of the hopper or the surface of the web W so as to be affected by capillary attraction.
In Fig. 4 we have shown a hopper constructed in accordance with another embodiment of our invention and by means of which four layers of separate coating com positions may be simultaneously applied in distinct layer relationship to the surface of a web. This hopper comprises the combination of two slide type hoppers with two extrusion type hoppers. This hopper 64 includes four cavities 65, 66, 67 and 68 into which four separate fluid coating compositions may be continuously supplied at a known rate through inlets 69, 70, 71 and 72, respectively, e. g. by separate metering pumps P. The combined extrusion hoppers are structurally the same as those disclosed in U. S. patent application Serial No. 489,862, filed on even date herewith in the name of Russell. The two cavities 67 and 68 are separated by an adjustable partition 73 spaced from the top wall 74 so as to form a slot through which the coating composition entering cavity 67 may be forced to form it into a layer 75. The coating composition entering cavity 68 is directed into extrusion slot 76 along with layer 75 and is thereby formed into a layer 77 between one surface of layer 75 and the bottom wall of the extrusion slot 76. The two layers 75 and 77 pass through the extrusion slot 76 in combined surface relationship and are extruded in this combined relation into a bead 17 maintained between the surface of a web W and the discharge lip of the hopper. As before, the web is backed up and continuously moved across and in contact with the coating bead by means of a roll 13.
The fluid coating composition supplied into cavity 66 is forced through a narrow slot out onto a downwardly inclined slide surface 79 in the form of a ribbon. This ribbon of coating composition flows down the slide surface under the force of gravity and is thereby formed into a smooth and uniformly thick layer 89. This slide surface 79 merges with the upper wall of the discharge slot 76 of the extrusion hoppers at an acute angle so that layer 86 in leaving the end of the slide surface 79 is combined, in surface relation, with layers and 77 leaving discharge slot 76 just prior to, or at the time, said layers enter the bead of coating 17".
The fluid coating composition supplied into cavity 65 is forced through an elongated narrow slot 82 in the form of a ribbon and out onto a downwardly inclined slide surface 83 which is parallel to, and disposed above, slide surface 79. In moving down slide surface 83 under the force of gravity, the ribbon of coating composition is formed into a smooth uniformly thick layer 84 by the time it reaches slide surface '79. This layer then flows onto the top of the ribbon of coating composition forced out onto slide surface 79 and the two move down slide surface 79 together and into the head 17'. It will thus be seen that the four layers 75, 77, 8t] and 84 of the separate coating compositions are combined in surface relation just prior to, or at the time, the same enter the head of coating. These four layers are then simultaneously picked up on the surface of the web in the proper orientation and with no apparent mixing or contamination between the layers. The layers after application to the web will possibly differ from the layers fed into the coating head 17" only in thickness and velocity, be-
' cause of the bead action as pointed out above, and because of this possible difierence in thickness the layers after application to the web have been designated by the same reference characters as the layers entering the coating bead except that they have been primed Because of the size limitation caused by a line drawing, in order to show the separate layers as applied to the web surface, it has been necessary to show the combined coatings out of proportion to the thickness of the web to which they are applied. Rather than the thickness of the combined layers of coating being equal to, or an appreciable fraction of a part of, the thickness of the web to which they are applied, as is indicated by the drawings and particularly those embodiments including three or more coat-- ings, actually the thickness of the combined coatings would be only a small fractional part of the over-all thickness of the web. By way of a practical example of a coated web which this apparatus is adapted to handle very well, let us consider a color photographic film. The web in this instance might be a cellulose acetate support having a thickness of .003.008 inch. Each of the three color sensitive emulsion coatings might vary between a dry thickness of .0001.001 inch whereas the protective layer or layers separating the different emulsion layers might be as thin as one micron. The disclosed coating apparatus is particularly adapted to coating such thin layers, and it will be seen that even with four of the thickest layers applied to the web the combined thickness of the four coatings will be less than 4 the thickness of the web per se.
We are unable to explain why two or more layers of coating composition when simultaneously coated onto a web in accordance with the present invention do not mix but maintain a layer relationship as distinct and as free of mixing and contamination at the interface of the layers as when the same compositions are coated successively with a complete drying of each coating before the next 7 on'e'is applied thereto. the different coating compositions are physically or chemically non-compatible" because, as the examples show, the-same results are obtained if all of the coating compositions are identical both physically and chemically, except that a dye or carbon dispersion was incorporated in one to give visible proof of this phenomenon.
In attempting to explain the reason why the different layers of coating composition do not mix when coated according to the present invention, the question of whether it was'because a form of liquid motion known as laminar flow was involved as distinguished from a form of motion known as turbulent flow has been considered. According to the Reynolds theory of fluid motion (R. C. Binder, Fluid Mechanics, Prentice-Hall, 1943, p. 71), when two separate streams of water are passed through a pipe, they will stay separated due to a condition of laminar flow so long as the critical velocity is not reached and after the critical velocity is reached, the flow becomes turbulent and the streams will mix. Reynolds showed that the critical velocity depended on the diameter of the pipe, the velocity of the fluidsp-assing through the pipe, its density, and its viscosity, and that if these four factors were combined in one Way, and one way only, a function known as the Reynolds number would be obtained giving the critical velocity for the flow of a fluid through a pipe. While this theory might be applied to explain the reason why the separate layers do not mix in passing in combined relation through the exit slot in one of the disclosed extrusion type hoppers, on the basis that the flow is laminar because the Reynolds number is not high enough to reach the critical velocity, it does not seem to apply when the combined slide and extrusion hopper techniques are used, nor does it explain the maintained separation of the layers through the coating bead and after deposition on the webuntil they are dried, because the layers are not movingthrough a pipe nor are they totally confined in any way. The one explanation for this phenomenon which might'be advanced is that normally it takes an appreciable time for two solutions to mix even if they are brought together insuch a way as to provoke turbulence, and with applicants method of coating the difierent layers are not in combined layer relationshiplong enough, before being deposited on the web, to allow noticeable mixing to take place even if the conditions of flow are such as to be conducive to such a mixing. As to why the layers of coating maintain their separate relationship between the time they are deposited on the web and they are completely dried is inexplainable except in the case of those coating compositions which a-re capable of being set by chilling, heating, or by chemical action immediately after deposition on the web surface and prior to drying. Here again the element of time might be the critical factor since the time elaps'ing between the deposition of the layers on the web and the time the coating is dried is relatively short and perhaps'less than the time required for the coatings, or the materials dispersed therein, to diltuse into one another.
Whilewe have shown and described certain specific embodiments of our invention, we are aware that many modifications thereof are possible. Our invention, therefore, is not to be limited to the precise details shown and described but is intended to cover all modifications coming within the scope of the appended claims.
Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:
1. In an apparatus for simultaneously applying a plurality of fluid coating compositions to the surface or" a web in superposed and distinct layer relationship, the combination with a web guiding surface over which a web to be coated is adapted to be continuously moved while being held a smooth condition, of a multilayer hopper comprising a plurality of cavities, one for each coating composition, a pair of separated lips defining an elongated discharge slot directed toward but spaced from said web It is not based onthe fact thatguiding surface by an amountslightly greater thanth'e thickness of the Web to be coated; means for continuously extruding a separate'layer of' coating composition from certain of said cavities and through said discharge slot directly toward said web guiding surface and including a separate elongated duct connecting each of said cavities with said discharge slot whereby said layers are combined in strata relationship upon discharge from said discharge slot and are s iultaneously applied to the web in such combined relationship, and means for continuously form ing a layer of the other coating composition with the aid of gravity flow and combining them in strata relationship with the combined exfuded layers as they issue from said discharge slot, and including a downwardly inclined slide surface intersecting said discharge slot at an acute angle, and means for continuously feeding a layer of coating solution from each of said other cavities onto said slide surface at separated points above said discharge slot.
2. In an apparatus for simultaneously coating two fiuid compositions onto the surface of a Web in superposed and distinct layer relationship, the combination with a web guiding surface over which a web'to be coated is adapted to be continuously moved while being held in a smooth condition, of a multilayer hopper comprising a pair of separated lips defining a discharge slot between them, said lips spaced from and immediately adjacent the surface of the web to be coated and separated from one another in the general direction of movement of said web, two separate cavities, one for each coating composition, means for continuously extruding a layer of one coating composition dire'ctly toward the web to be coated and including a duct joining one of said cavities and said discharge slot, means for continuously forming a layeriofthe other coating composition with the aid of gravity flow and combining it with the extruded layer in surface relationship prior to application of the combined layers to the web, and comprising a downwardly inclined slide surface which forms a part of the uppermost of said two lips and intersects said discharge slot at an acute angle, and a duct counectin said other cavity with said slide surface at a point spaced above said discharge slot, and means for pumping said other composition from said other cavity through said duct and onto said slide surface, whereby the layer of coating composition formed upon moving down said slide surface solely under the influence of gravity is combined with the layer extruded from said discharge slot in strata relationship and thetwo layers are then simultaneously and directly applied to the surface of the web in combined relation.
3. A coating apparatus according to claim 2 characterized by the inclusion of means for applyin a third layer of fluid coating composition along with said two layers mentioned, said means comprising a third cavity, a layer forming duct connecting said cavity with said discharge slot and being directed into said slot at an acute angle to said other duct, and means for continuously feeding a third coating composition into said third cavity and through said duct connecting it with the discharge slot, whereby said third layer is combined in strata relationship with said first-mentioned layers at the time it leaves said discharge slot.
4. A multilayer hopper for feeding a plurality of fluid coating compositions in Stratified layer relationship to a coating point where they are adapted to be simultaneously applied to the surface of a web moving relative to said coating point and comprising a hopper provided with a plurality of separate cavities, one for each coating cornposition, a pair of lips separated to define an elongated discharge slot, a separate elongated layer forming duct connecting certain of said cavities with said discharge slot and said ducts relatively arranged so that the layers of coating composition issuing therefrom are combined in strata relation as they issue from said discharge slot; a downwardly inclined slide surface forming an exterior surface of one of said lips and intersecting the discharge positions into their respective cavities at a given rate comslot at an acute angle, whereby a layer of coating solution mensurate with the thickness desired in the different layers flowing down said surface unier the action of gravity is after coating.
adapted to combine in surface relationship with the combined layers issuing from said discharge slot and move to 5 References Cited in the file of this Patent the coating point in such strata relationship therewith; an UNITED S A PATENT elongated layer forming duct connecting each of the remaining cavities With said slide surface at separate points 2052695 Chlveton Sept" 1936 2,382,177 Schanz Aug. 14, 1945 spaced from one another and located above sa1d dlscharge 2 681 294 Be uin June 15 1954 slot; and means for continuously feeding the coating com- 10 g