US3289632A - Cascade coating apparatus for applying plural layers of coating material to a moving web - Google Patents

Description

Dec. 6, 1966 F. c. BARSTOW 3,289,632

CASCADE COATING APPARATUS FOR APPLYING PLURAL LAYERS OF COATING MATERIAL TO A MOVING WEB Filed Oct. 2, 1965 2 Sheets-Sheet 1 INVENTOR. WM C WW4 r "/2 %M ATTORNEYS D 1966 F. c. BARSTOW 3,289,632

CASCADE COATING APPARATUS FOR APPLYING PLURAL LAYERS OF COATING MATERIAL TO A MOVING WEB Filed Oct. 2, 1963 2 Sheets-Sheet 2 INVENTOR.

M? ATTORNEYS United States Patent 3,289,632 CASCADE COATING APPARATUS FOR APPLYING PLURAL LAYERS 0F COATING MATERIAL TO A MOVING WEB Frederick C. Barstow, Sudbury, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Filed Oct. 2, 1963, Ser. No. 313,262 1 Claim. (Cl. 118-412) The present invention relates to coating and, more partircularly, to a novel coating apparatus adapted to apply one or more layers of individually uniform thickness to a web. Still more particularly, it relates to a novel cascade coating device adapted for continuously applying one or simultaneously applying a plurality of layer-s, of individual- 1y uniform thickness, to a continuously moving flexible support or web.

In general, in the manufacture of coated webs, films and the like, the production of a continuous structure of standard and uniform width provides optimum utilization of facilities and materials. However, it has been characteristic of web coating processes, wherein one or more coatings of relatively viscous solutions are applied, in a continuous manner, to a Web, that edge bead formation, that is, an excess of coating material disposed at the lateral edges of the coated area and a deficiency of coating material contiguous to the edge bead, provides decreased yeld of acceptable coated web and generally requires an additional operation, within the coating procedure, to obviate this defect.

In the production of various coated webs, the coating solution components, for example, thecoating solutions employed in the fabrication of photographic film units, are relatively expensive per unit area and, if recoverable at all from defective portions of the web, require relatively complicated and expensive procedures to effect salvage of such components. Furthermore, the discontinuities in coating thickness, resultant from edge bead formation, provide distinct disadvantages when coating layers are required to be chilled and/ or dried within exact parameters of time and/ or temperature for optimum product properties. For example, in the production of photographic film units, the edge bead area of the coating, having a greater thickness than the central portion of the web, requires a relatively longer period of drying and/or higher temperature coefficients. In continuous coating processes therefore, these requirements may necessitate more complex drying equipment to compensate for the required temperature gradients or increased drying capacity employing decreased coating speeds and additional drying facilities. Where increased drying capacity is the means chosen in order to insure that the lateral edge beads are dried, the corollary result is, in general, sacrificing of optimum drying conditions With respect to the remaining portions of the coated web and subjecting this area of the coating to excess heat contact.

The mechanical devices generally employed in the art, for example, doctor blades, scrapers, calender rolls, and the like, have been singularly unsuccessful in obviating the problem of edge bead formation in the production of coated Webs possessing at least one, and preferably a plurality of, relatively thin, fragile and unstable coating layers, such as are necessitated to provide photographic film units. Such contact devices, in addition to the propensity of inducing surface defects, provide, in general, objectionable effects upon the sensitometry of the resultant film when employed in their production. Under these circumstances, the most effective procedure has been to remove or trim the lateral edges of the coated web, subsequent to the coating process, by various cutting or slitting devices, with the concomitant coating and drying problems and wastage previously described.

The mere presence of the nonuniformities provided by the edge bead may result in various types and degrees of damage to the coated web, as, for example, curled or turned edges resultant in torn web edges during subsequent wind up and handling, in addition to limiting the web capacity of a roll retaining same.

It is therefore an object of the present invention to provide a novel coating apparatus particularly adapted for the continuous application of a coating material, to a web, in a relatively uniform coating thickness. Another object is to provide a novel coating apparatu of relatively simple construction, elemental in operation, requiring substantially no maintenance, possessing no moving parts, and is particularly adapted for the simultaneous and contiguous deposition of a plurality of coating solutions, in layerwise uniform thickness, on a continuous web. A further object is to provide a novel cascade coating device particularly adapted for the continuous, simultaneous and contiguous deposition of a plurality of photographic coating solutions, in layerwise uniform thickness, on a moving flexible web. A still further object is to provide a novel cascade coating device particularly adapted for the con tinuous application of a plurality of uniformly thick, contiguous aqueous colloidal solutions to the surface of a continuously moving web. A still further object is to provide a novel cascade coating device particularly adapted to prevent edge bead building during the continuous application of one or more coating solutions to the surface of a travelling web.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claim.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a schematic sectional view of one embodiment of a preferred cascade coating apparatus of this invention showing the simultaneou deposition of a plurality of contiguous and uniform layers on the surface of a continuous web;

FIG. 2 is an exploded perspective view of the preferred cascade coating apparatus of FIGURE 1 constructed in accordance With the present invention; and

FIG. 3 is a sectional perspective view of the coating apparatus of FIG. 2 in assembled relationship.

The conventional cascade coating apparatus or slide hopper, in general, performs its coating operation by metering a coating solution or liquid through a narrow slot, or orifice, which distributes the solution uniformly across the top of a downwardly inclined slide surface or plane. The layer of coating solution moves down the slide surface, by gravity, so as to supply an even and steady ribbon of coating solution to the terminal or lip edge of the slide surface. The web to be coated is moved across and in contact with the solution ribbon adjacent the lip edge of the coating device, to pick up the layer of coating solution.

Slide hoppers adapted to simultaneously deposit a plurality of contiguous layers are disclosed, for example, in US. Patent No. 2,761,419, issued September 4, 1956, and possess a slide surface having a plurality of separated, substantially parallel distributing slots, whereby separate coating solutions may be metered from individual supplies and distributed uniformly across the inclined slide surface. Each of the respective coating solutions flows, by gravity, down the inclined surface and then, in superposed relationship, onto the top of the layer issuing from the "next lower orifice present on the slide surface. Finally, all layers flow in combined, striated ribbon relationship from the last slide surface to the point of deposition, where they are simultaneously picked up on the surface of a web moved continuously across the point of deposition.

It has now been unexpectedly found that cascade coating devices, of the type described, retaining hereinafter specified guide members on the lateral edges of the slide surface, facilitates the production of coated webs of uniform coating thickness.

Specifically, it has been discovered that a cascade coating device, which facilitates the deposition of a coating solution having a uniform transverse thickness, may comprise the following construction. A first means or member, such as a block, providing a downwardly inclined plane surface which terminates in a transverse edge, or lip, adjacent the point at which a coating solution is deposited on a travelling web. Fluid distributing means such as a distributing orifice, slot or hole, extending through the first member and spaced from the transverse edge, for conducting a layer of coating solution onto the plane surface. An uninterrupted slide surface, below the orifice, over which a layer of distributed coating solution is adapted to flow, by gravity, and means for confining opposite longitudinal edges of the solution as it flows downwardly onthe slide surface as, for example, a pair of guide members mounted on, or integral with, the first member adjacent opposite longitudinal edges of the slide surface. The guide members possess facing surfaces, Which extend in the direction of flow, perpendicular to the slide surface and cooperate therewith to provide a channel extending in the same direction. Additionally, the guide members preferably possess means for selective adjustment of the height or elevation which the facing surfaces extend from their associated slide surface.

During employment of the cascade coating device, the height of facing surfaces is substantially equal to the height of coating solution traversing the associated slide surface and for some unknown reason facilitates the deposition of a coating solution, on a travelling web, having a uniform transverse thickness.

'For the simultaneous application of a plurality of coating solutions, to a continuous web, at a single point of deposition, it has been found that a cascade hopper, constructed according to the following parameters, facilitates the continuous coating of a. plurality of layers having uniform thickness layerwise.

The cascade hopper includes a first means or member having a downwardly inclined plane surface terminating in a transverse edge, adjacent to the point of coating solution deposition on a travelling web. The first member has a plurality of separated, substantially'parallel fluid distributing means, as, for example, slots extending through the first member, for conducting a plurality of separate coating solutions, which may be metered from individual supplies and distributed uniformly across the inclined plane surface. The lowermost of the distributing slots is spaced from the transverse edge and the remaining distributing slots spaced above this lowest slot. Each distributing slot is spaced from each other slot to provide an uninterrupted slide surface below each slot, over which the layer of coating solution discharged therefrom flows, by gravity. In the case of all but the lowest slot, the respective layers of coating solution flow until they reach the next lower slot and there flows onto the top of, and along with, the layer of coating solution discharged from the next lowest slot. Means are provided for confining opposite longitudinal edges of the solutions as they flow downwardly on the slide surfaces, as, for example, a pair of guide members mounted on, or integral with, the first member adjacent opposite longitudinal edges of each uninterrupted slide surface. i Each of the pairs of guide members possesses facing surfaces, extending in the direction of flow perpendicular to the slide surface, which cooperate with its associated slide surface to provide a channel extending in the direction of solution fiow. Individual means are provided for selective adjustment of the height the facing surfaces extend from their associated slide surface.

During employment of this coating device, the respective facing surfaces of each pair of guide members are adjusted to be substantially equal to the total height of coating solution material traversing its associated slide individual, contiguous coatings to a travelling Web, for

the production of photographic film. I

As shown, a cascade coating device 1, which While conceivable that it could be constructed from a single blank of dimensionally stable material, for example, metal or plastic, is shown as comprising a plurality of individual blocks 2 to 5, which are suitably fabricated, or machined, in order that they may be assembled, as shown, to provide the reservoirs, slots, channels, and positional arrangement, further detailed hereinafter.

Individual blocks 2 to 5 may be held in assembled relationship by any suitable fastening means, such as bolt 6 and nut 7 combinations extending through co-ordinated channels 8.

In the event that the coating compositions employed are of the type which require maintenance of limited temperature parameters, in order to facilitate coating same, hopper 1 may be provided with conduits, through which an appropriate heat exchange fluid medium, for example, water, may be continuously circulated. As shown, such conduits may comprise interconnected inlet channels 9, continuously feeding a heat exchange fluid into a plurality of reservoirs 10, retained in individual blocks 3 to 5, which, in turn, continuously drain into interconnected outlet channels 11.

Hopper 1 may be provided with any suitable form of adjustable mount so that the position of terminal edge 12 of lowermost slide surface 13, relative to the web 14, may be adjusted for optimum coating results. As shown, hopper 1 may be pivotably mounted on frame 15, by a clamping screw (not shown) engaging in arcuate slot 16, for critical adjustment. of angle between the hoppers slide surface and the web, and to swing in concentric relationship to back-up roll 17, such that the position of the hopper as a whole may be pivoted for critical adjustment around the periphery of the roll.

Subsequent to the coating of web 14, in the production of photographic film it may be necessary to set and/ or 'dry the coatings applied thereto. In such case, web 14 1 subsequent to being coated may be passed through chill box 18 and/or then through drying chamber 19. Web 14 may then be conveniently removed from the drying chamber by windup roll 20.

As shown, a three-slide hopper 1 is detailed, by the use of which three separate layers of the same or different fluid coating compositions may be simultaneously applied to the surface of web 14.

Structurally, hopper 1 possesses a plurality of coating reservoirs 21 to 23 into which separate fluid coating compositions 24 to 26, respectively, are continuously pumped, at given rates, by individual metering, or constant discharge, pumps (not shown) through inlets 27 to 29, interconnected with channels 30 to 32, and directly supplying the reservoirs. Each coating composition 24 to 26 is then forced from its reservoir, through narrow vertical slots 33 to 35, in the form of a ribbon and out onto downwardly inclined slide surfaces 13, 36 and 37, respectively, down which they flow by gravity in the form of layers 38 to 40, to terminal lip 12, and then onto the surface of web 14.

Web 14 is backed up at the point of deposition by backup roll 17 which may serve as a means of continuously moving the web across, and in contact with, striated coating layers 38 to 40 and serves as a means for supporting and holding the web in a smooth condition for takeup of the contiguous coatings.

In assembled relationship, slide surfaces 13, 36 and 37 of hopper 1 are substantially coplanar so that upon continuous extrusion of the coating materials, solution 26 issuing from distributing slot 35 flows layerwise down slide surface 37 up on top of solution 25 issuing from slot 34, and the two solutions then flow together down slide surface 36 up on top of solution 24 issuing from slot 33, and the three solutions then flow together, in striated relationship, down slide surface 13, and from lip 12 onto the surface of travelling web 14.

Blocks 2, 3 and 4 each have a pair of guide members which, as shown, may comprise a pair of substantially rigid rectilinear projections 41 and 42, 43 and 44, and 45 and 46, mounted adjacent opposite longitudinal edges 47 and 48, 49 and 50, and 51 and 52 of slide surfaces 13, 36 and 37. Each of the pairs of guide members possesses facing surfaces 53 and 54, 55 and 56, and 57 and 58, respectively, in coplanar relationship and extending in the direction of solution flow perpendicular to the slide surface, to provide a cooperating channel extending in the direction of coating solution flow.

The guide members possess means for being mounted on their respective blocks and adapted to provide selective adjustment of the height the facing surfaces extend from their associated slide surface, such as the set screw 59 and shim 61 combination shown.

During coating operations, the facing surfaces of each pair of guide members are adjusted to be substantially equal to the total height of coating solution, traversing the channel provided between the facing surfaces and their associated slide surface, in order to provide to the web a coating having a uniform transverse thickness layerwise.

The relative height of each layer of coating material on the slide surface is dependent upon the rate at which it is pumped into its respective reservoirs.

For setting the height each pair of facing surfaces extend from their associated slide surface, the specific height of coating solution cascading down the respective slide surface may be determined employing the formula:

1 Q sine 011 B 433[ p wherein B=solution height in inches; =solution viscosity in centipoises;

=solution density in grams/cmfi;

Q=volumetric flow rate of solution in cubic centimeters per minute per inch; and

a=the angle of the coating head from the horizontal.

Subsequent to coating operation, any one or more stages of the hopper may be simultaneously or individually cleaned, in assembled relationship, by charging a cleaning solution or fluid through respective inlets 27 to 29, ohannels 30 to 32, reservoirs 21 to 23 and discharging the fluid through the individual channel 62 interconnecting an outlet part 63 and the reservoir of a stage selected to be cleaned.

The cascade coating devices of the present invention are adapted to effect deposition of coating compositions employing aqueous and/or organic solvent diluents. In general, the coating composition comprises at least a film-forming polymeric material dissolved in, or dispersed in, an appropriate solvent. As will be recognized, the composition may additionally contain any of the ap- 6 propriate conventional coating aids and adjuncts, to facilitate coating of the specific compositions selected.

The present invention has been found to be particularly useful in the coating of the aqueous coating compositions employed in the fabrication of photographic film.

In general, such compositions comprise at least an aqueous solution or dispersion, especially colloidal dispersion, of a natural polymeric material such as gelatin, albumin, agar-agar, etc., and/or a synthetic polymeric material such as a water-soluble and/or permeable polyamide, a polyvinyl alcohol, etc. Additionally, one or more of the compositions may contain photosensitive silver halides, antifoggants, sensitizing agents, preservatives, stabilizers, coating aids, developing agents, matting agents, antihalation agents, and/or color-providing materials such as dyes and the like, etc., generally in solid or particulate form.

For the production of black-and-white film employing the apparatus of the present invention, a web may have coated thereon a plurality of layers, in striated relationship, which may include one or two gelatino silver halide photosensitive emulsion layers and an over-coating of, generally, gelatin, as an antiabrasion layer.

The production of multicolor film such as that disclosed in the copending US. application of Edwin H. Land et al., Serial No. 565,135, filed February 13, 1956, however, may comprise effecting the deposition of eight or more contiguous layers, each within uni-form parameters, on a web. These film units generally comprise a Web which carries a red-sensitive gelatino silver halide emulsion stratum, a green-sensitive gelatino silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum, having dispersed in water-immiscible organic solvents and contained in separate permeable gelatin layers, behind them, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer. Gelatin or other interlayers also may 'be positioned between the red-sensitive emulsion stratum and the magenta dye containing layer and between the greensensitive emulsion stratum and the yellow dye containing layer, and an outer layer, for example, of gelatin, may be positioned on the surface of the blue-sensitive emulsion stratum.

Although the apparatus of the present invention may be employed to effect coating of solutions having an extensive range of viscosities that is, any coating solution which will flow on a slide surface, in general, the solutions most effectively coated by means of the present invention comprise aqueous colloidal compositions having a viscosity of not less than about 10 to about 200 cps., at 40 C., and may have a solids content of up to about 30%.

While the present invention has been specifically described as applied to a cascade coating device adapted to effect coating of a single layer or three layers in striated form, it will be readily apparent, from the foregoing description, that the invention is equally applicable to any cascade coating hopper adapted to effect the coating of a travelling web, with one or more layers of coating solution, at a single point of deposition. For example, in the production of the aforementioned photosensitive color film, the present invention has been successfully employed in cascade coating devices, of the type described, for coating up to, and including, the nine contiguous layers previously described.

The web designated in the drawings as 14 may comprise any of the various types of conventional flexible supports, for example, paper and polymeric films of both synthetic types and those derived from naturally occurring products. Suitable materials include paper; polymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers; polyvinyl acetal; polyamides such as nylon; polyesters such as polymeric films derived from ethylene glycol terephthalic acid; .and cellulose derivatives such as cellulose acetate, triacetate, nitrate, propionate, butyrate, acetate-propionate, or acetate-buyrate.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

A cascade coating device for simultaneously feeding a plurality of coating solutions in superposed and distinct layer relationship, to a point of deposition, where they are deposited onto the surface of a web moving relative thereto, which comprises, in combination:

(a) a first member having a downwardly inclined plane surface terminating in a transverse edge adjacent said point of deposition;

(b) a plurality of distributing orifices, one for each coating solution, extending through said first member for conducting a layer of coating solution onto said plane surface, the lowermost of said orifices being spaced from said transverse edge and the remaining of said orifices spaced above said lowermost orifice and from each other to provide an uninterrupted slide surface below each of said orifices, over which the layer of coating solution discharged therefrom flows, by gravity, in the case of all but the lowermost orifice, to the next lowest orifice and flows onto the top of, and along with,

the layer of coating solution discharged therefrom, and, in the case of the lowermost location, before it reaches said transverse edge;

(c) a pair of guide members mounted on said first member adjacent opposite longitudinal edges of each of said slide surfaces said members having facing surfaces extending in the direction of flow, perpendicular to said slide surface, and cooperating with said slide surface to form a channel extending in said direction of flow, said facing surfaces adjacent adjoining longitudinal edges of said slide surfaces extending in coplanar relationship; and

((1) means for mounting said guide members on said first member for selective adjustment of the height said facing surfaces extend from their associated slide surface.

References Cited by the Examiner UNITED STATES PATENTS 1,787,140 12/1930 Campbell 118-325X 1,906,471 5/1933 Lambacher 11s 325 X 1,932,727 10/1933 Faulkner 118-407 2,761,419 9/1956 Mercieretal 11s 412 2,809,129 10/1957 Peterson 118-324X CHARLES A. WILMUTH, Primary Examiner.

I. P. McINTOSH, Assistant Examiner.

Images