US2975754A - Multiple coating apparatus - Google Patents

Description

March 21, 1961 s. E. WRIGHT MULTIPLE COATING APPARATUS 2 Sheets-Sheet 1 Filed Oct. 2'7, 1958 S. E. WRIGHT MULTIPLE COATING APPARATUS March 21, 1961 2 Sheets-Sheet 2 Filed 001:. 27. 1958 Sian leyEMTrighi INVENTOR.

Stanley E. Wright, Fairport, N.Y., assignor to Eastman 1 Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Oct. 27, 1958, Ser. No. 769,881

4 Claims. (Cl. 118-407) The present invention relates to hoppers to be used for applying simultaneously two or more layers of aqueous colloidal dispersions to a moving web of film base, paper, plastic sheeting, etc., said layers being applied in thicknesses varying one to another, and having different compositions resulting from the addition of varying amounts of solids, such as silver halide grains, matting agents, color couplers, gelatins, pigments, dyes, etc.

This invention relates to a multiple slide hopper for use in carrying out the method of multiple coating disclosed in U.S. Patent 2,761,791. Specifically, it is a modification of features disclosed in U.S. Patent 2,761,419 which relates to the basic multiple slide hopper.

The objects of this invention are: (1) to greatly extend the range of relative layer thickness which may be applied;

simultaneously to the surface of a web using a multiple slide hopper, and (2) to make possible the handling of fluid coating compositions containing higher proportions of granular solids, such as silver halide grains, matting agents, color couplers,.p-igments, etc., than is possible by the use of previously disclosed multiple coating apparatus, while at the same 'timemaintaining uniformity of layer undisturbed by differential movement of individual granular particles.

The novel features that I consider characteristic of my 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 understoodfrom the following description when read in connection with the accompanying drawings, in which: Fig. 1 is aschematic sectional view of a web coating apparatus, and including a multiple slide hopper con- United States Patent struc'ted in accordance with one embodiment of the present I invention and adapted to feed two fluid coating compositions to the coating bead;

Fig. 2 is an enlarged sectional view of the upper portion of the hopper shown in Fig. l in combination with the web supporting device and the web to be double coated;

Fig. 3 is a view similar to Fig. 1, but showing another embodiment consisting of a double slide hopper adapted to simultaneously feed three fluid coating compositions to the coating bead; v

Fig. 4 is a view similar to Fig. 3, but showing another formof slide hopper for simultaneously feeding three fluid coating compositions to the coating bead;

Fig. 5 is an enlarged view of the embodiment shown in Fig. 4, and showing the manner in which the individual layers of the three coating compositions are formed and combined in the slide hopper and how they move through.

the coating bead for application onto the web surface; and

Fig. 6 is a vertical sectional view of a slide hopper constructed in accordance with still another embodiment of the present invention and adapted to feed fourdifferent coating compositions to the coating bead.

Generally speaking, the present invention consists of a coating hopper having one or more slide surfaces so arranged as to carry by gravity flow two or more different,

2,975,754 Patented Mar. 21, 1961 slot at the upper edge of a slide surface or surfaces in such a position that two or more fluid coating compositions issuing therefrom form a stratified layer arrangement which will then proceed by gravity flow down the sloping slide surfaces to the coating bead across and in contact with which a web is continuously moved to pick up a multiple coating from the bead.

Referring now to Figs. 1 and 2, there is shown an apparatus constructed in accordance with one embodiment of the present invention which was successfully used to apply two separate coatings to a support in the manufacture of photographic film. Here there is shown a double slide hopper 10 having a cavity 11 into which one fluid coating composition S is continuously pump-ed at a given rate by a metering or constant discharge'pump P. The, coating composition S is then forced from cavity 11; through a narrow distributing or discharge slot 12 in the; form of a ribbon and out onto a downwardly inclined slide; surface 13 down which it flows by gravity in the form; of a layer 14 into a coating bead 15 formed between the surface of the web W to be coated and the lip or end 16 of the slide surface. The web W is backed up at this point by a roll 17 which may serve as a means for continuously moving the web across and in contact with the bead 15 as well as serving as a means for supporting and holding the web smooth while passing across the head of coating.

. This bead technique of multiple coating is well known in the art and is disclosed fully in the above-noted Patents 2,761,791 and 2,761,419. It need only be mentioned here that the bead 15 extends completely across the width of the web W being coated and that the surface of the web W in moving across and in contact with the bead picks up the layers of coating therefrom. It can be seen that with this bead coating technique the coating is not in fact deposited directly onto the web surface by the hopper, but that the hopper merely maintains the coating bead and the web is coated therefrom. With the bead technique of coating, the actual thickness of thecoatinglaid down on the web moved thereacross will be determined by the action of the bead and will vary with the speed ofmovement of the web and the metered flow rates of the coating compositions from their discharge slots and will not necessarily be equal to, or directly dependent upon, the

thickness of the ribbon of coating composition fed to the j slide surface or the thickness of the layer formed in flow- '1 arrangement of these two distributing or discharge slots 12 and 20 that the present slide hopper diflersfrom those shown in U.S. Patent 2,761,419. Whereas in the. .1 patented hopper each of the discharge slots is separated'j by a slide surface down which a layer of. coating flows v by gravity before joining a layer extruded from a lower 1,; slot, in the present invention the exit ends of the two; distributing or discharge slots 12 and 20 meet at a common line to form a common slot 21 at the top of the slide surface 13. Coating composition S is delivered through discharge slot 12 at a metered rate of flow, while In accordance with 3 simultaneously a second coating composition S is delivered through slot 20 at a metered rate of flow, which may be less than, equal to, or greater than the flow rate for composition S. The two compositions flow in a stratified layer system 14 and 14' down slidesurface 13 and form a Stratified coating bead 15, see Fig. 2. In Fig. 2 an attempt has been made to show in detail the layer thickness relationship which might occur throughout the flow path. The ratio of layer thicknesses on the web W is directly proportional to the metered flow rates delivered from the discharge slots 12 and 20. However, the ratio of layer thicknesses on the slide surface 13 may vary from the metered rates due to physical property differences between the fluid coating compositions which maycause difierential layer velocities while flowing by gravity. In leaving the coating bead 15, and on the moving web W, the layers regain the metered rates of thickness. 011 the web W the absolute thickness of each layer is a function of the metered rate of liquid flow and the linear speed of the web. The distribution or discharge slots 12 and 20 only perform the function of feeding the fluid coating compositions S and S respect'ively, uniformly from end to end of the slide surface 13, and do not perform a metering function. Therefore, the same slot width can be used for agreat range of flow rates with the metering of flow rates being accomplished in the liquid supply system ahead of the distributing slots. The width ofcommon slot 21 formed by the meeting of distribution slots 12 and 20 is sub: stantially equal to the sum of the widths of slots 12 and 20.

As mentioned a'b0ve,-.the novel feature of this embodh ment of the present invention is the manner in which the two coating compositions are simultaneously delivered to the slide surface 13 by distributing slots 12 and 20.

This is particularly useful when the upper layer of liquid 1 is to be very thin. In this situation, when the system of tandem slides disclosed in U-.S. Patent 2,761,419 is used, the surface tension, viscosity and setting characteristics of the liquid and the ability of the liquid to wet the slide surface while flowing. alone down the upper slide surface maycause the edges to draw in toward thecenter, making the layer narrower than desired and causing an undesirable thickening in the edge areas. In extreme cases, the liquid may even solidify on the slide surface,- ca'using interference with thesmooth sheet-like flow necessary to produce a uniform coating. By use of the apparatus disclosed in- Figs. 1 and 2,- the coating composition S can be extruded fromdischarge slot 20 into a thin layer and be deposited directly onto the layer of composition S extruded from slot 12, traveling with it to the coating bead 15 without edge withdrawal and the thickening etfect above mentioned. 7 Commercialcoatingshave been made with this embodiment of slide hopper having an upper layer wet thickness of- .28 mil. This is approximately'one-half themin-imum thickness possible with the same coating compositions using the tandem slide hopper disclosed'in US. Patent 2,761,419. Ex=

perim'ental coatings using this new slide hopper have been made with an upper layer wet thickness of .14 mil.- The hopper may: be provided with conduits C through which a hot or cold fluid may be circulated for the purpose of maintainingthe temperature of the coatingcompositions in the hopper cavities such as to promote proper coating thereof.

After'the we'b has been coated, it may be necessary to set and dry thecoatings applied thereto. In the manufacture of photographic'film-or paper, the coatings appliedmaybe of the'type which will set by cooling prio'r'to drying in order to limit the amount of relative flow between'the layers themselves-or between the-bottom layer and the'support: Insucha case-the wehW" after being.coatedcan=be;passed-through achill box B and thendhrough the dryingchamber- D. If' the coatings applied are of the type which do not require chillingi before drying, the chill box B can be omitted or bypassed. The web may be pulled from the drying chamber D by a feed or guide roll R.

Another embodiment of my invention is shown in Fig. 3. In this embodiment a third distributing or discharge slot 25 has been added to the embodiment shown in Figs. 1 and 2 in order to deliver another layer of fluid coating composition S onto extended slide surface 26 coplanar with slide surface 13' so as to form a threelayer Stratified head 15' and produce athree-layer coating on the moving web W. The coating composition S is continuously fed into a third cavity 27 by a metering pump P". Inasmuch as that portion of the hopper above discharge slot 25 for feeding the coating compositions forming the upper two layers is the same as that shown in Figs. 1 and 2, the parts thereof are designated by the same reference characters as the corresponding parts of the Fig. 1 and 2 embodiment except that they are primed. In this embodiment, any grouping of layer thickness is possible. However, as in the first embodiment, the meeting line of the two upper distribution or discharge slots 12' and 20 makes possible the application of an extremely thin top surface layer. By the addition of more distribution slots and slide surfaces, more layers may be simultaneously applied using the same method for the top two layers.

Another application of the novel feature of this invention is used in the embodiment shown in Figs. 4' and 5. In this case a coating composition 8;, is fed from cavity 30 through a discharge slot 31 onto a slide surface 32. At the same time fluid coating compositions S4" and S are fed from cavities 33 and 34, respectively, through discharge slots 35 and 36 onto slide surface 37. The discharge slots 35 and 36 meet in a common line or slot at the top of slide surface 37 so that the ribbons of liquid 8.;- and S issue therefrom in stratified layer relationship. The layer of composition S issuing from slot 31, after flowing down slide surface 32, joins and moves onto the top of the two layers of composition issuing from slots 35 and 36 to form a three-layer stratified flow on slide surface 37, see Fig. 5, proceeding then through the stratifiedbead at" and onto the web W moving across and in contact therewith to pick up a three-layer coating, see Fig; 5. It will be seen that this arrangement of distributing slotsallows the middle layer of coating compositions; to be extruded through slot 35 directly betweentlie upper and lower layers of coating compositions 8 and S respectively, without the necessity for flowing by gravity in contact with a" slide surface. Many coating compositions, suchas colloidal dispersions containing high concentration of granular solids, such as silver' halide, matting ma'terials;etc;, aresubject to non uniforrn'layer formation caused by the retarded progress of the'larger particles in contact with the'slide surface of the hopper. By the use of this embodiment of the invention the center layer, coating composition S issuing from the discharge slot 35 may be insulated from physical damage'which might result f'rom cont-act'with the slide surface 37 by the bottomla'yer of coating composition S which"may be nongranular. At the same time, the upper' layer of coating composition S3 reaching the common meeting line of discharge-slots 35 and 36'viadischarge" slot 31 and slide surface 32, serves to seal themiddle layer of coating composition'S from contact with the surrounding air, thus preventing: damage by 'air' current and air-borne dirt particlesdurihg'passage to" and through the coating head 15''. Fig. 5 shows the layer conformation in this embodiment ine'nlarged detail. Y

Another us'eof' the novel feature of'this inve'ntionis incorporated in the embodiment shown in'Fig. 6 which is a modification'o'f the"Fi g-.-4 and 5 embodiment'and has the corresponding partsfdesipated by the same'reference' numerals primed. In'this embodimentan additional discharge'slot-40'intr'oduce's a fourth coating composition s ffroni cavity 41 into the stratified layer system at the crete layers which can be applied common meeting line or slot at the top of slide surface 37. In this case, neither the layer of coating composition 8,; issuing from discharge slot 35' or the layer of coating composition 8.; issuing from discharge slot 40 comes into contact with the slide surface 37 or the surrounding air.

Further variations may be made by providing additional discharge slots and slide surfaces above the common meeting line of two or more discharge slots so that two or more layers may overlay the critical layer or layers which must be protected from contact with a slide surface and/or the surrounding air. The number of disby variations of the invention appear to be limited only by the necessary structural rigidity of the hopper for maintaining uniform distributing slot conformation, the number of available supply sources for the coating compositions used, and the capacity of the equipment necessary for processing the multiple coating to the final dry state.

While I have shown and described certain specific embodiments of my invention, I am aware thatmany modifications thereof are possible. My 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 my invention, what I 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 of a web in superposed and distinct layer relationship the combination with a web guiding surface over which the web -to be coated is adapted to be continuously moved and held in a smooth hopper comprising condition; of a multiple layer slide an exposed slide surface inclined downwardly toward the web guiding surface and terminating in a lip spaced from the guide surface by an amount 2. An apparatus according to claim 1 characterized by i the fact that the exit ends of each of said discharge slots slightly greater than the thickness of the web to be coated;

wall means forming a discharge slot extending from the interior of said hopper at an acute angle to said slide surface and having an'exit end opening onto said slide surface at a point spaced above said lip to provide an uninterrupted and exposed slide portion below said exit end down which a layer of a fluid coating composition extruded therefrom flows by gravityto form a smooth layer of uniform thickness; second wall means forming a second discharge slot extending from the interior of said hopper and having an exit end opening onto said slide surface above the exit end of said first discharge slot and merging therewith into a common slot in said slide surface whereby a layer of fluid coating composition extruded from said second slot flows onto the upper surface of the layer extruded through said first slot and the two layers flow down said uninterrupted slide portion by gravity flow in stratified relation with the layer of coating composition issuing from the first slot supporting thelayer of coating composition issuing from the second slot and maintaining the latter layer out of physical contact with said slide portion, and the layer of coating composition issuing from the second slot acting to seal said other layer from contact with the surrounding atmosphere as they issue'onto and slide down said exposed slide portion, and means for continuously feeding a fluid coating composition into each of said discharge slots at a predetermined rate commensurate'with the thickness desired for each of said layers after coating.

extend transversely of said exposed slide portion in parallel side-by-side relation and merge at the upper end of said slide portion into a common slot whose width is equal substantially to the sum of the individual widths of said two slots, the upper edge of the exit end of said first discharge slot and the lower edge of the exit end of said second discharge slot being joined by a substantially sharp edge forming a common part of said two well means. a v

3. In an apparatus for simultaneously applying a plurality of fluid coating compositions to the surface of a web in superposed and distinct layer relationship, the combination with a web guiding surface over which the web to be coated is adapted to be continuously moved and held in a smooth condition; of a multiple layer slide hopper comprising an exposed slide surface inclined downwardly toward the web guiding surface and terminating in a lip spaced from the guide surface by an amount slightly greater than, the thickness of the web to be coated; wall means defining a plurality of discharge slots, extending from the interior of said hopper and each having an exit end opening onto said slide surface through which the separate coating compositions are adapted to be extruded in the form of layers, said discharge slots being so arranged that said" exit ends thereof merge into a common slot in said slide surface spaced above said lip to provide an uninterrupted exposed slide portion below said common slot down which layers extruded from said discharge slots flow by gravity in stratified relation, said common slot having a width equal substantially to the sum of the widths of said discharge slots whereby the individual layers of coating composition issuing from said individual discharge slots merge in and issue from, said common slot in stratified relation; and means for continuously feeding a fluid composition into each of said discharge slots at a predetermined rate commensurate with the thickness desired for each of said layers after coating.

4. An apparatus according to claim 3 and including further wall means defining another discharge slot extend-v ing from the interior of the hopper and having an exit end opening onto said slide surface through which another fluid coating composition is adapted to be extruded in the form of a layer; the exit end of said last-mentioned discharge slot being disposed above said common slot to provide a second uninterrupted exposed slide portion References Cited in the file of this patent UNITED STATES PATENTS Russell et al. Sept. 4, 1956 Russell Sept. 4, 1956 Russell Sept. 4, 1956

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