US2150250A - Process for casting films - Google Patents

Description

1955 3 Sheets-Sheet l 1N VENTOR. W

c. SCOTT PROCESS FOR CASTING FILMS Filed July 25,

March 14; 1939.

Mmh '14, 1939. c. SCOTT 2,150,250

PROCESS FOR CASTING FILMS Filed July 25, 1955 5 Sheets-Sheet 2 7/ K 33 m 3a 2a 4 Z5 INVENTOR.

March 14, 1939. C COTT 2,150,250

v PROCESS FOR CASTING FILMS Filed July 25, 19:55- 3 Sheets-Sheet 3 INVENTOR.

Patented Mar. 14, 1939 UNITED STATES PATENT OFFICE PROCESS FOR. CASTING FILMS Clyde Scott,East Orange, N. J. Application-July 25, 1935, Serial No. 33,000

14 Claims.

This is a continuation in part of my application, Serial Number 666,358, filed April 15, 1933, for Process and apparatus for casting film's.

The invention to which the following description relates deals with improvements in methods and apparatus for continuously casting film in sheet or strip form from solutions of cellulose such as nitrocellulose, acetylcellulose, cellulose ether, or like material. I have found that the film is improved and its production facilitated by maintaining an accurate and close control of the conditions under which the operation is carried out. Furthermore, this controlling operationis facilitated by improvements in the mechanism relating to the casting operation, the surfaces upon which the film is deposited and the subsequent operations by which the film is produced in final form.

In the rapid production of film it has been found that the successful application of currents of warm air or other evaporating media to the film during its conditioning, has necessitated the use of high-boiling solvents or mixed solvents containing high-boiling components and that this presents a difficulty in the tendency of the newly deposited films to ripple, wrinkle or web when brought into contact with such evaporating currents.

It. is an object of my invention to make possible the use of less expensive low-boiling solvents through the establishment'of a quiescent atmosphere. In this manner it is even possible to add to these lowboiling solvents considerable quantities of diluents without deterioration of the desirable qualities in the film so formed. As an example, the evaporation of a cellulose acetate film may be carried out successfully in a quiescent atmosphere of solvent vapors in which lowboiling acetone is the dominant solvent although mixed or diluted with as much as 50% of its weight of benzol.

It is characteristic of many cellulose ester or ether solutions that their viscosity may be varied and controlled by mechanical treatment alone. As an incident of my invention I have prepared highly concentrated cellulosic solutions by such forms of treatment as heating, agitation and filtration while hot in order that the solution may be purified, rendered uniform throughout and its viscosity sufiiciently diminished to permit satisfactory deposit in the form of extremely thin films of desired predetermined thickness.

In order to obtain highly concentrated cellulose solutions particularly of cellulose acetate, acetone or solvents such as the like which have a natural tendency to lower the viscosity of such solutions may be supplemented with heat to obtain fluent solutions containing a higher concentration of solids than would otherwise be possible.

The working temperature of solutions and 5 apparatus is important. Diffusion in cellulosic solutions is ordinarily a very slow process, but is accelerated by rise of temperature. A homogeneous solution remains so only as long as the different portions are maintained at the same tem- 10 perature. When one portion of an initially homogeneous solution is kept at a different temperature from the other portions the solution becomes heterogeneous, the colder portion becoming more cencentrated than the warmer part, 15 while dissolved substance tends to diffuse from the warmer into the colder zone of the solution.

The viscosity of cellulose nitrate solutions is a very important property, especially so in solutions adapted for film-forming by casting and evapo- 20 rating processes. Great variations are noted in these solutions with changingtemperatures. Viscosity is related tomolecular complexity, and there is no doubt that in solutions of high viscosity the molecular complexes are comparatively 25 large. It is possible to trace a direct connection between the viscosity of such solutions and the mechanical and chemical treatments to which they have been subjected. The viscosities are diminished by treatment which the substance or 3 its raw material undergoes, such as heating the mixture and heating the finished cellulosic solution.

My herein described process permits of a wider range or scope of forming films by casting and evaporating methods than is possible by other means. For example, whenan endless belt or drum is employed the viscosity of the film-forming component must permit of great fluidity. The solvents must be sufiiciently volatile to per- 40 mit the deposited solution to set quickly and the resultant film to be stripped off or removed from the casting-surface before one complete cycle of the casting-surface has been made. In heretofore proposed apparatus and processes the filmforming solutions are deposited upon supports having an even, close or polished surface to which the film, when fully dried, will not adhere. It is, as a rule, deposited upon the casting-surface to within about one or two inches from the edges of the support and upon drying, the film immediately leaves or separates from the casting-surface (particularly at the edges), due to lack of adhesion. Films produced by endless-belt, or drum apparatus are usually of dimensions of from 0.003 to 0.007 or 0.008 of an inch thick. The great difiiculty of producing and stripping thinner films, due to the separation from the casting-surface at the edges, prevents the satisfactory production of films thinner than 0.003 of an inch in thickness. Obviously very heavy gauge thick films cannot be produced by such means in continuous operation even though a plurality of means be provided as has been proposed for depositing successive layers, primarily on account of the limited area available for drying purposes.

The method of applying the solution to the casting surface in-a pool from which the film is withdrawn permits the solution to come in contact with the guide-strips at the side for an extent many times greater than the thickness of the final film. The result is that this wetting of the guide-strips by the solution forms an extended attaching edge with greatly increased adhesion. This bond with the guide-strips remains, during the drying and subsequent treatment of the film. on the casting surface. It follows that there is an improved holding effect which maintains the film under tension, fiat against the surface of the casting surface. This permits complete drying without danger of curling and successive coating solutions may be applied without impairing the uniformity of the film or distorting it.

Because of the ability of the guide-guard strips on my machine to retain thoroughly dried films (and particularly very'thin and very thick films) in intimate contact with and upon the plane surface of the travelling-supports, it becomes possible to cast very thin multi-layer laminae i. e., composite films of one to two one-thousandths of an inch thick and dry under ten.- sion each successive layer without the films separating from the support at the edges, and without substantial distortion, wrinkling, warping or curling of the film during the process of manufacture or after removal from the casting-surface.

In the depositing of this film I have provided an improved discharge hopper by which the solution is first maintained in the proper condition of low viscosity and then delivered in accurately measured quantities as is desired in order to produce a suitable film.

Among the objects of my invention is the provision of an improved casting surface which is mechanically advanced past the above mentioned hopper. In the use of this casting-surface it is maintained at the proper temperature in conformity with the temperature of the solution so that the evaporation of the film will not be disturbed by local temperature changes which might cloud the film or produce irregularities or blemishes therein.

Another object of my invention to provide improved means in the form of. guide strips by which substantially the full surface area of the casting-surface is rnade available for the film and the necessity of trimming wastage from the latter is minimized to a great extent.

As an incident of this object of my invention it is to be noted that the device provides means by which the film, when once cast on the surface, is held rigidly in place without distortion, warping or curling and may thus be subsequent ly treated by the deposition of successive layers of similar or dissimilar material thereon.

Among the further objects of my invention is the completion of the film-forming operation by subjecting the solution'when cast to travel along an upward gradient opposite to the direction in which the solution is first applied, in an atmosphere of the solvent used in the film and kept at a degree of saturation and moderate temperature that will permit the evaporation of the film in the most effective and prompt manner.

The film produced by this invention may be the subject of a further successive deposition by which its Water-proof, moisture-proof or fireproof properties will be improved or modified. As a final step the invention contemplates the conditioning of the film as a continuous strip or in shortened sections in a conditioning chamber.

In order to illustrate one preferred form which my invention may take, the following drawings are shown for the purpose of example only of a machine by which the above and other related objects may be satisfactorily attained. In the drawings Fig. 1 is a top plan view of the improved machine;

Fig. 2 is a side elevation thereof;

Fig. 3 is a side elevation showing the adjustment in inclination of the casting machine;

Fig. 4 is an end elevation;

Fig. 5 is a top plan View of the improved hopper.

Fig. 6 is a side elevation thereof;

Fig. 7 is an end elevation of the same;

Fig. 8 is a vertical section on the line 8-8 of Fig. 6;

Fig. 9 is an enlarged transverse detailed section of the casting element and associated parts;

Fig. 10 is an enlarged view of the hopper discharge shown in Fig. 8;

Fig. 11 is a fragmentary detail side View of the casting plate and its mounting and Fig. 12 is a longitudinal section of the casting surface drive means.

The casting machine consists generally of a device for advancing a series of casting plates to form a continuous surface on which the cellulose solution or the like may be deposited and subsequently treated. In the drawings this machine is shown to consist in a stand or table II having at one end a pair of trunnions 12. Between these trunnions I? there is a table which extends for the full length of the stand I I. table I3 is supported at the other end of the stand by means of a pair of standards I l which are locked in adjusted position to the stand H.

A cross bar I5 at this end of the stand forms a journal for the lifting screw l6, one end of which is manipulated by the hand wheel H. The upper end of the lifting screw it supports the cross bar l8 beneath the table 13 and serves to lift the latter to give it any desired inclination or gradient. In this way the left or discharge end of the table i3 is raised relatively to the opposite end an amount dependent upon the operating factors ofthe casting machine such as the viscosity of the material, the rate of travel of the casting-surface and the rate of evaporation.

The table l3 has a series of transverse shafts H) which carry a pair of parallel spaced endless conveyor chains 20, 20 by means of appropriate sprocket-wheels. or the like. This may form one endless conveyor connecting the opposite ends of the table 13 or the conveyors may be arranged in overlapping relation serving successive zones along the table and delivering the casting plates from one conveyor or zone to another. One of the transverse shafts I9 is provided with a driven wheel 2| by which the conveyor or series of conveyors is causedto operate. The conveyor chains 2|] are provided at appropriate distances with engagement pins 22 by which the casting plates are I advanced along the length of the table.

The casting plates consist of polished glass or metal plates 23 which rest at their side edges on appropriate tracks or shoes and are advanced by means of transverse metal bars 24 also resting upon the shoes and being engaged by the pins 22. As is shown in the drawings the metal bars 24 are of substantially the same thickness as the glass casting plates but are undercut or rabbeted along one edge to accommodate the pins 22. The lengths'of the plates 23 and bars 24 are such as to provide a continuous top surface upon which the solution may be cast or caused to flow.

In those instances where it is feasible and desirable to use a metal casting plate it may take the form of a plate similar to the glass plate 23 except that the opposite ends are rabbeted to accommodate the pins 22.

Referring to Fig. 9 it will be seen that the casting plate 25 is urged in a forward direction by the pins 22. The plate rests upon an accurately proportioned shoe or track 21 which in turn is mounted on the side member of the table I3.

The table l3 also carries along its upper side edge a curbing 28 and above that an inwardly extending flange 29. This flange begins in advance of the point where the solution is deposited on the casting-surface and. may continue into the subsequent zone of evaporation.

A guard strip 30 having a U-shaped cross-section is provided to be carried along the side edges of the casting plate 25. This guard strip 30 fits snugly against the side wall of the curbing 28 but there is suflicient vertical clearance between the flange 29 and the side member of the table I3 to prevent the guard strip from binding against either the flange or the side member of the table and the overlap of the strip 30 with the side edges of the casting plate 23 compensates for variations in the horizontal direction.

These guard strips 38 are of the same length as the individual casting plates 25 and travel with the plates from the point of their placement on the conveyor to the opposite end of the machine.

The vertical adjustment of the shoe or track 21 insures a straight line of travel for the casting plates while the curbings 28 prevent lateral movement of the plates.

The casting operation is carried out along a portion of the table l3 which is equipped with a suitable cover to form a chamber for the solvent vapors. As illustrated in Figs. 1 and 2 this chamber comprises panels 32 which latter extend along the sides, ends and top of the frame to form a relatively closed chamber 33. Panels 32 are illustrated as being of framed sheet glass sothat the casting operation can be observed readily. The ends of the chamber 33 are open at the bottom sufiiciently to permit the introduction and withdrawal of the casting plates or similar elements without substantial loss of the solvent vapors or the production of undesirable air currents.

The chamber 33 is provided with suitable means, not illustrated, for its temperature control and for the withdrawal of excess vapors produced from the evaporation of the film solution. In this way these vapors are recovered and the solvent made available for use again while the rate dryer or other device by which the film is further and finally treated.

In the delivery of the film from the chamber 33 it may pass as a continuous strip or web or may be cut into pieces of the desired length. In the latter case the sections of the casting surface will be made of the selected length so that the individual sections of the casting surface together with the film deposited thereon will be 7 transferred to the chamber 34.

One standard 35 is bolted or otherwise attachedto each side member l3 of the frame and extends upwardly within and above the chamber 33. These standards provide guides and supports for the casting hopper 36. This hopper includes a pair of end walls 31 and a rear wall 38. The end walls 31 have yokes 39 by which the hopper is slidingly held by the standards35. Each end wall 31 has bolted thereon a bar 48 which extends beyond the front of the end wall 31 and has a rearward extension 4|. This extension 4| is screwthreaded at the point'which overlies the end of the standard 35. The extreme end of the extension 4| carries a gauge 42.

Vertically extending through each extension 4| is an adjustment screw 43 the lower end of which rests upon a bearing in the end of the standard 35. The upper end of the adjustment screw 43 carries a handwheel 44 the edge of which is calibrated.

The adjustment screw 43 supports the weight of the hopper and its load on the ends of the standards 35 and the hopper is prevented from movement in any but a vertical direction by means of the yokes or guides 39. The spacing of the hopper with respect to the casting-surface is indicated by the gauge 42 and the calibration of the handwheels 44 so that a close control can be made of each end of the hopper and a uniform spacing for the casting film thus maintained.

The top 45 of the hopper has an opening 46 through which the inlet 41 of the film solution projects.

The top 45 also supports a heating coil 48 the convolutions of which extend generally through the body of the film solution and serve to maintain it at such a degree of temperature as will lower its viscosity and control the conditions under which the solution will be delivered with greatest efiectiveness. The back wall 49 of the hopper is formed of a panel which is hinged at the top and the lower end is free to move inwardly with respect to the rear wall 38.- The rear wall 38 has a depositing lip 58 toward which a corresponding lip 5| on the back wall 49 is adapted to be spaced, both lips serving to reinforce the sheet metal walls 38 and 4|]. In this way a delivery slot is established through which a thin stream of the film solution passes to the casting-surface.

' The upper edge of the wall 49 has two or more hinged brackets 52 by which the wall is suspended .pivotally :on the cross bar 53. The cross bar, in turn, is freely journalled in bars 54 on the ends .31 and carries calibrated dials 55. The free ends of the brackets 52 .are apertured to carry adjustment screws 55. The heads of the screws 56 rest upon the free ends of the brackets 52 and carry operating levers 51. The lower ends of the screws 55 pass through screw-threaded openings in. a bar 58 which in turn extends transversely of the hopper between the bars 43. In this way the adjustment of the screws 56 will cause the wall 49 and the lip 5| to vary the size of the discharge slot. When operating circumstances demand, an operating handle 59 mounted on wall 59 may be used to move the latter inwardly until the discharge slot is entirely closed. It is to be understood that the side edges of the wall 49 will come in such close contact with the end walls 3'! of the hopper as to prevent undesirable discharge of the solution at these points.

It is not intended primarily that the discharge from the hopper will control directly the operation of depositing the film but mainly will serve as a feeder for the solution. The solution pass-- ing from the hopper flows backwardly and forms a slight pool on the casting-surface :due to the upward slope of the latter. The deep end of the pool is formed by a baffle 60 which extends in front of the feeding lips 56, 51 and for the full width of the hopper of the end Walls 31. A cross plate 6! connects the end walls 31, 3'! and is vertically slotted as at 52. The baffle 68 has adjustment screws 53 extending horizontally therefrom and passing through the slots 62 in plate 6|. Lock-nuts M are used to adjust the position of the bafile 50 relative to the discharge end of the hopper and also to control the clearance of the lower edge of the bafile 60 with respect to the casting plates passing thereunder.

In place of individual casting plates 23 the endless conveyor 20 may have a casting-surface or member carried directly thereon. Such a casting member will be in the form of an endless belt of flexible material. The coated surface of this conveyor belt is smoothly polished to provide an appropriate casting-surface which will hold the solution during the evaporation of the film.

Such a casting-surface may also be equipped as desired with flanges or ledges upon its side edges which will operate similar to the guide strips 3!! to hold the edge of the film while drying.

The operation of this device may be briefly described as the continuous presentation to a discharge hopper of a casting-surface which may either be continuous or in suitable removable sections. This casting-surface or member is brought to uniform temperature with the solution and the conditions in chamber 33 so that the operation of evaporation of the solvent will not be attended by undesirable efiects such as occur when a composite film comes in contact with a plate of a different temperature causing a differential solidification and separation out of the film of that component which solidifies at a temperature lower than the remaining com.- ponents.

The casting plate 23 as it is advanced to the hopper is equipped with the guide strips 3i) which prevent the lateral spread of the solution deposited.

The solution is discharged from the slot in the base of the hopper and between walls 37 and 38 and the panel 49. The rate of discharge is accurately controlled by the adjustment of the dis.-

charge lips'50 and 5|. The solution on discharge spreads laterally into. contact with the guide strips 30 and drains downwardly to the baflle 60. The bafile 60 causes the solution to accumulate in a shallow pool, the upper surface of which extends slightly to the left of the lip 50 as: shown in Fig; 8,

Due to the upward slope of the casting plate 23 and its continuous movement toward the upper end of the conveyor, there is a tendency for the solution to flow in the opposite direction from that of the casting plate and to return to the pool. This action insures first, an adequate deposit of the solution upon the casting plate regardless of variation in viscosity and immediately thereafter the draining of excess solution to the pool so that the desired thinness of the film may be attained and its upper surface remain quite flat.

In the course of the travel of the plate together with the deposited film solution through the chamber 33, there is produced an evaporation of the solvent dependent upon the rate of travel, the temperature maintained and the surface tension or degree of saturation of the solvent which is permitted to remain in the chamber. The film, therefore, dries or evaporates uniformly. There is no tendency for the surface of the film to dry too fast and form a coating through which .the solvent cannot escape from U The film on reaching the discharge end of the chamber 33 will be sufficiently hardened to permit it to be cut into sections defined by the size of the casting plates. The latter with the film still adhering both to the plates and to the guide strips may then be transferred to the conditioning chamber 34.

Where the conveyor itself carries the casting surface, the conveyor may be extended to pass through the conditioning chamber 34 and thus carry the film in a continuous: strip.

In like manner the chamber 34 may extend for sufficient distance to permit the use of a second or subsequent discharge hopper. Thus the film deposited from the first hopper may be partially or substantially evaporated and coated with a second film of the same or a different film solution and the composite film evaporated prior to reaching the discharge point from the conveyor.

Through the procedure outlined above and by means of the machine as described, provision is made for casting laminated sheets and strips in continuous operation and for drying the sheets thoroughly between successive coatings. The firmness With which the films are held under tension on the surface of the casting element and the particular atmosphere of solvent vapors maintained reduces the likelihood of surface irregularities such as craters and pits. The accurate control-of the conditions of temperature permits the casting of pre-heated solutions at elevated temperatures and upon pre-heated casting surfaces.

The provision of the chamber of solvent vapors is of primary importance as permitting the use of inexpensive low-boiling solvents in conjunction with inexpensive diluents. At the same time it is a great improvement in preventing blushing which would be'otherwise caused by precipitation of moisture. It will also be evident that such a controlled atmosphere during evaporation prevents surface-sealing and pin-holes.

By causing the solution to accumulate first in a pool of substantial depth and in contact with the guide strips, the latter are thoroughly wet to form an edge contact with the film which remains throughout the subsequent operations.

Where the solution contains oxidizing products, glycerol, phthalate resins or drying oils, which require baking or other heat treatment to dry, the upwardly inclined travel through the heated chamber of solvent vapors is of particular advantage. r

The mechanism above described will thus be seen to be suitable for the continuous production of films of various types and kinds. While one particular form of the device has been described, many variations in structural details and operation are comprised within the scope of the inven-- tion and as defined by and limited to the following claims. x

What I claim is:

1. The process of casting film in sheet or strip form which comprises depositing a film-forming solution uniformly over a casting surface, said casting surface having means to contact said filmforming solution at the sides or edges thereby causing the sides or edges of the deposited solution to be engaged and held against retraction, evaporating volatile solvent therefrom, said engagement being maintained-during evaporation of volatile solvent of the film-forming solution to the extent that the film is held under tension and against the casting surface during and after the formation of said film.

2. The process of casting film which comprises flowing a film-forming solution of suitable characteristics upon a casting surface, causing its opposite edges to be anchored in proximity to the surface, evaporating volatile solvent therefrom, maintaining such engagement until evaporation of volatile solvent has substantially ceased therefrom, and then removing the film so produced.

3. ,The process of casting film which comprises depositing a film-forming solution uniformly over a casting surface, said casting surface having meansto contact said film-forming solution at its opposite sides or edges, said means causing the sides or edges of the deposited solution to-be engaged and securely anchored in proximity to said surface, evaporating volatile solvent therefrom and maintaining said anchorage during the evaporation of volatile solvent and formation of film.

4. The process of casting multi-layer composite films of predetermined thickness which comprises depositing a known quantity of film-forming solution uniformly over a casting surface, said casting surface having means to contact film-forming solutions at opposite sides or edges and anchor said solutions and hold same in place without distortion during the evaporation of volatile solvent therefrom, uniformly depositing thereupon subsequent layer or layers comprising known quantities of film-forming solutions, uniformly drying said composite film under tension and finally removing the substantially dry composite film from the casting surface.

5. The process of casting film which comprises depositing a film-forming solution uniformly upon a fiat casting surface travelling in continuous movement along an upward gradient opposite to the direction in which the solution is first applied, within a regulated quiescent atmosphere comprising a regulated concentration of solvent vapors, partially evaporating volatile solvent from said film-forming solution within said atmosphere, removing the forming film from said atmosphere and depositing said film and said casting surface within a conditioning chamber, subjecting said film to evaporating media therein, and finally removing said film from said casting surface.

6. The process of casting film in sheet or strip form in continuous progressive operation which comprises uniformly depositing upon a moving flat casting surface a film-forming solution con tained in a discharge hopper supported adjustably above and across said casting surface, said casting surface being adapted to travel in continuous movement along an upward gradient, draining excess solution to a pool, evaporating volatile solvent and then removing from the" casting surface the film so produced.

7. In the process of forming films and evaporating volatile liquid solvent therefrom steps comprising depositing a film forming solution uniformly upon a casting surface within a relatively closed chamber comprising a quiescent atmosphere wherein the concentration of gaseous solvent vapor is regulated as to the mass per unit volume, said casting surface having means to contact said solution at its opposite sides or edges,

contacting said solution with said means to form attaching edges and cause said edges of said solution to be engaged and held against retraction, subjecting said solution within said chamber to the influence of temperature and pressure adapted to convert liquid into its vapor, subjecting said solution withinsaid chamber to the influence of vapor saturated to a degree adapted to substantially regulate the tendency of said solution to form vapor, said vapor being saturated substantially with the liquid from said-solution from which solution said vapor is derived, evaporating volatile solvent from said solution within said chamber to form a film engaged upon said casting surface, said engagement being maintained during the evaporation of volatile solvent to the extent that the film is held under tension and against the casting surface during and after the formation of said film, uniformly intensifying the strength of said film while held under tension upon said casting surface within said chamber by a regulated rate and a regulated degree of substantially uniform evaporation of liquid from said film, removing said film upon said casting surface from said chamber, depositing said film and said casting surface within a conditioning chamber, subjecting said film within said conditioning chamber to the influence of temperature and pressure adapted to evaporate substantially all volatile solvent remaining in said film and adapting said'film to receive subsequent coating or coatings of similar or dissimilar film forming substance.

8. In the process of forming films and evaporating volatile liquid solvent therefrom steps comprising depositing a film forming solution from a pool uniformly upon a fiat surface travelling in continuous movement along a uniform upward gradient opposite to the direction in which the solution is first applied within a relatively closed chamber comprising a wherein the concentration of gaseous solvent vapor is regulated as to the mass per unit volume, said casting surface having means to contact said solution at its opposite sides or edges, contacting said solution with said means to form attaching edges and cause said edges of said solution to be engaged and held against retraction, draining excess solution to said pool, subjecting said solution within said chamber to the influence quiescent atmosphere of temperature and pressure adapted to convert liquid into its vapor, subjecting said solution within said chamber to the infiuence of vapor saturated to a degree adapted to substantially regulate the tendency of said solution to form vapor, said vapor being saturated substantially with the liquid from said solution from which solution said vapor is derived, evaporating volatile solvent from said solution within said chamber toform a film engaged upon said casting surface, said engagement being maintained during evaporation of volatile solvent to the extent that the film is held under tension and against the casting surface during and after the formation of said film, uniformly intensifying the strength of said film while held under tension upon said casting surface within said chamber by a regulated rate and a regulated degree of substantially uniform evaporation of liquid from said film.

9. In the process of forming composite films and evaporating volatile liquid solvent therefrom steps comprising depositing a film forming solution from a pool uniformly upon a flat casting surface travelling in continuous movement along a uniform upward gradient oppositeto the direction in which the solution is first applied within a relatively closed chamber comprising a quiescent atmosphere wherein the concentration of gaseous solvent vapor is regulated as to the mass per unit volume, draining excess solution to said pool, evaporating volatile solvent from said solution within said chamber to form a film upon said casting surface, depositing thereupon within said chamber a second film forming solution to form a composite film, subjecting said solutions within said chamber to the influence of temperature and pressure adapted to convert liquid into its vapor, subjecting said solutions within said chamber to the influence of vapor saturated to a degree adapted to substantially regulate the tendency of said solutions to form vapor, said vapor being saturated substantially with the liquid from said solutions from which solution said vapor is derived, uniformly intensifying the strength of said film upon said casting surface within saidchamber by a regulated rate and a regulated degree of substantially uniform removal of unneeded liquids from said film, removing said composite film upon said casting surface from said chamber, depositin said film and said casting surface within a conditioning chamber, subjecting said film within said conditioning chamber to the influence of temperature and pressure adapted. to evaporatesubstantially all volatile solvent remaining in said. film, and

then removing said film from said casting surface.

10. The process of making multi-ply composite film, comprising uniformly applying one or more layers of film-forming material dissolved in volatile solvent to an area of a film base layer on a casting surface, said base layer being firmly affixed at its opposite edges and securely held under tension against said casting surface, evaporating volatile solvent, and removing the composite film so formed from said casting surface.

11. The process of casting film which comprises flowing a film forming solution of suitable characteristics upon a casting surface; causing its opposite edges to be anchored in proximity to the surface; solidifying said film forming solution to form a film; maintaining said edge engagement until solidification has been substantially effected; and then removing the film from the cast ing surface.

12. The process of casting film which comprises flowing a film forming solution of suitable characteristics upon a casting surface; causing its side edges to be anchored in proximity to the surface; solidifying said film forming solution to form a film; maintaining said engagement of the side edges of the film until solidification has been substantially effected; and then removing the film from the casting surface.

13. The process of casting film in sheet or strip form in continuous progressive operation which comprises flowing a film forming solution upon a casting surface moving in an upwardly inclined gradient; engaging the edges of the film in proximity to the casting surface to hold said film against retraction; removing solvent from the film forming solution to solidify the film; and then removing the formed film from the casting surface.

14. The process of forming composite film in sheet or strip form in continuous progressive operation which comprises flowing a film forming solution upon a casting surface moving in an up wardly inclined gradient; engaging the edges of the film in proximity to the casting surface to hold said film against retraction;- removing solvent from the film forming solution to solidify the film; flowing a second film forming solution on said solidified film on said upwardly inclined gradient; engaging the edges of the second deposited film to hold said second deposited film against retraction; removing solvent from said second deposited film forming solution to solidify the film; and removing the composite film from the casting surface.

CLYDE SCOTT.

Images