US2115044A - Apparatus for casting films - Google Patents

Description

` 'April 26, 193s. Cl SCOTT 2,115,044

APPARATUS FOR CASTING FILMS @Home/n April 26, (jl SCOTT Y APPARATUS FOR CASTING FILMS V Filed March 16, 1934 5 Sheets-Sheet 2 HV'A @Hom/wig April 26, 1938. C. SCOTT 2,115,044

APPARATUS FOR CASTING FILMS Filed March 16,1954 f 3 Sheets-Sheet 3 Snvcnfoz @513% twfvlm Patented Apr. 26, 1938 unirsi) STATES PATENT OFFICE y Application March 16,

14 Claims.

This invention is in part a continuation of my co-pending application, Serial Number 666,358, filed April 15, 1938 for Method for casting films.

The invention to which the following description relates, deals with. improvements in apparatus for continuouslycasting lm ini sheet or strip form from solutions of cellulose or like material. I have found that the lm is improved and its production facilitated by maintaining an accurate and close control of the conditions under which the operation is carried out. Further, this controlling operation is 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.

The working temperature of solutions and apparatus is important. Diffusion in cellulosic solutions is ordinarily a very slow process, but may be accelerated by rise in temperature. A homogeneous solution remains homogeneous and of the same viscosity only so long as the diierent parts are maintained at the same temperature. When one part of the initially homogeneous solution is kept at a different temperature from the vother parts, the solution becomes heterogeneous insofar as flowability is concerned, the colder part becoming more concentrated and viscous, and the warmer portion more dilute and thinner flowing, while the dissolved substances diffuse from. the warmer into the colder portion of the solution. By means of the apparatus forming the subject matter of this invention these disadvantages are substantially overcome, with the result that more uniform films are obtainable as to composition and physical characteristics, and the operationV may be made continuous with the formation of films of indenite length and of great uniformity in composition.

My herein described apparatus involves a proccss wherein a wide scope of forming lms is permissible, irrespective of the chemical composition of the cellulosic portion of the nlm, when cast according to the methuods herein described with the apparatus herein illustrated.

For example, when an endless belt or drum is employed the viscosity of the film-forming component must permit of great fluidity. The solvents or solvent combination must be sufliciently volatile so that the deposited solution will have a denite, known and controllable speed of evaporation and hence time of setting, in order that the' solid or solids deposited from the solution may be stripped from the casting surface before 1934, Serial No. 715,897

one complete cycle of the casting surface has been made.

In heretofore proposed apparatus, the filmformng solutions have been deposited upon supports having an even, close or vpolished surface 5 to which the lm in the dried condition will not adhere, or at least adhere so tenaciously as to be removable with difficulty. It is, as a rule, deposited upon the casting surface to within one or n two inches from each edge of the support, and upon drying, the film immediately detaches or separates from the casting surface (particularly at the edges), due to lack of adhesion or deficiency in adhesion.

Films produced by endless belt, or drum appal5 ratus are usually of dimensions of from 0.003 to 0.007 or 0.008 of an inch in thickness. One of the major difficulties in producing Vand stripping thinner lms, due to the separation from the casting surface from the edges, prevents the sat- 20 isfactory production of lms 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 for depositing successive layers, as has been proposed, and this is because of the limited area available for drying purposes. Y

The method of applying the solution to, the .y A

casting surface in a pool from which the lm 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 lm. 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 lm on the casting surface. It follows that there is an improved holding effect which maintains the film under tension, flat 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 iilm or distorting it.

Because of the ability of the guide-guard strips on my machine to retain thoroughly dried lms (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 tension each successive layer without the films separating from low viscosity and then delivered in accurately' measured quantities as is desired in order to make a suitable lm. n

Among the objects Vof Ymy invention isthel provision o-f an improved casting surface which is mechanically advancedrpast the above mentionedY hopper. InV the use of this casting-surface it is Y maintained at thev proper temperature in. conformity with the temperature of the solution so that the evaporationV of the film will Vnot be disturbed by localtemperature changes which might cloud the lm Y'or produce irregularities or` blemishes in it. Y Another object of my invention is tov provide Y improved means in the form of guide strips by is to be noted` that the devicezprovides means by Y or curlingand mayY thus be subsequently treated Y by the' deposition of successivezlayers of similar orV which the full'surfac'e area ofthe casting-surface is made available. for -the lm and thelnecessity of trimming wastage from the latter is minimized toagreatextent.y` i

As an incidentof this object of my invention it whichthe lm, whenV once cast on the surfaces, is held rigidly in place without distortion, warping dissimilar material.

Among the further the completion of the film-forming operation by Ysubjecting the solution when cast to travel along;

an upward gradient-opposite to the direction in which the solution isrrst applied, in van atmosphere of the solvent used in the Iilm and kept at a degreeof saturation and moderate temperature that will permitl the evaporation of the film inthe most effective and prompt manner.

The lm produced by this invention may bethe subject of a further successive deposition; by which its Waterproof, moisture-proof or fire-proof properties will :be improved ormodii'led. yAsa final step the invention contemplatesV the conditioning of the lm as a continuous Vstrip' orinshortened 70 Y casting plate and itsrmounting and sections-in a conditioningchamber. Y 't In order to illustrate the preferred'formrwhich myv invention may take, I have shown in thefollowing drawings, for the purpose of example only, a machine by which the above and other related objects may beattained. In the drawings 1 is a top plan view of the improved machine; Y f

Fig. 2 is a side elevation thereof;

Fig. 3 is a, side elevation showing the adjust- Y ment in inclination of the casting machine;

Fig. 4 is Van end elevation;

Fig. 5 is a top plan view of the improved hopper; Y Fig. 6 is a side elevation thereof; l

Fig. 7 is an end elevation of the same; 'Y

Fig. 8

Fig. 6; Y Y V Y Y 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; Y Y

Y Fig.` 11 is av fragmentarydetail side view of the FigllZ is a longitudinal section of the'casting surface drive means. f Y I Thecasting machine consists generally of a de- V vicev for advancing a seriesofcasting plates to objects of my invention is is a verticalsection on'the line 8-8 of form a continuous surface on which the cellulose solution may be deposited and subsequently treated. In the drawings this machine is shown to consist in a stand or table I I having at one end a pair of trunnions I2. Between these trunnions I2 there is a table which'extends for the full length of the stand II. This table I3 is supported at the other end of the stand by means of a pair of standards I 4 which arelocked in adjusted position tojtherstand II.V A cross bar I 5 at this end of the stand forms a journal for the lifting screw I 6, one end of whichk is manipulated by the hand wheel I1. The upper end ofthe lifting screw I6 supports the cross bar I8 beneath the table I3 and serves tolift 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 tothe 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'castingsurface and the rate of evaporation. j

The table I3 has a series of transverse shafts I9 which carry a pair of parallel spaced endless conveyor chains 20,120 by means of appropriate 20 are provided at appropriate distances withfen- Ysprocketwheels or the like. Y This may form one l Vendless conveyor connecting the opposite ends of drivenv n gagement pins 22 by which the casting plates Vare Y advanced along the length .of the table.

The casting plates consistof polished glass orVV metal plates 23 which rest at their sideV edges on'appropriate tracksor shoes and are advanced byY means of transverse metal bars 24 also rest- 22. As is shown in the drawings the metal bars ing upon the shoes and being engaged by the pins Y;

24 /are of substantially 'the same thickness as the glass casting plates but areundercut or 'Yi-low.,

In those instances whereit is feasible and de-V "sirable to use a metal casting plate it maytake the form of a plate 25, (not shown in drawing);4 the opposite ends o-f which are rabbeted as shown inv26 (not shownv indrawing) to accommodate thepinsl22. Y Y l' Referring to Fig. 9 it will be seen that Ythe casting plate 25 is urged in a forward direction by the pins 272. proportioned shoe or track 21 which in turn is mounted on the side member of the table I3.

The table I3 also carries along'its upper side edge a curbing 28 and above that an inwardly extending flange 29. This Vflange begins in advance of the point where the solution is deposited on the casting-surface and maycontinue into the subsequent zone of evaporation.V A guard strip 30 having a U-shapedcross-section is provided to be carried along the side edges of the casting plate 25; This guard strip 30 vfits snuglyv against Vthe side wall of the curbing `28 but Vthere is sufficient vertical clearance between theiiange 29 and the side member of the table I3 to prevent the guard strip from 'binding against either the ilange or the side member of the tableV rab-beted along one edge to accommodate the1 The plate rests upon an accurately Y and the overlap of the strip 30'with the side edges of the casting plate 23 compensates for variations in the horizontal direction. r

These guard strips 30 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 I3 which is equipped with a suitable cover to form a chamber for the solvent vapors. iAs 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 so that the casting operation can be observed readily. The ends of the chamber 33 are open at the bottom suiiciently 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 of evaporation is also controlled by changes in the vapor tension. f

The casting plates with the deposited film may be subjected to further treatment before being removed from the closed chamber, for example, by the deposit of one or more subsequent film laminae of the same or dissimilar character, either prior to or subsequent to the substantial completion of the evaporation from the originally deposited film. L

The lm, either of single or multiple layers, is discharged from the chamber 33 into a conditioning chamber 34 which may be a mechanical dryer or other device by which the lm 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 transferred to the chamber 34.

4One standard 35 is bolted or otherwise attached to each side member I3 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 33. l'Ihe end walls 31 have yokes 39 by which the hopper is slidingly held by the standards 35. Each end wall 31 has bolted thereon a bar 40 which extends beyond the front of the end Wall 31 and has a rearward extension 4I. This extension 4| is screw-threaded at the point which overlies the end of the standard 35. 'I'he 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. 'I'he upper end of the adjustment screw 43 carries a handwheel 44 the edge of which is calibrated.

. a feeder for the solution.

The adjustment screw 43 supports the weight of the hopper and its load on the ends of the standards 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 on the handwheels 44 so that a close control can be made oi' each end of the hopper and a uniform spacing for the casting nlm thus` maintained.

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

The to-p 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 effectiveness. 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 tothe rear wall 38. The rear wall 38 has a depositing lip 5U 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 33 and 40. In this way a delivery slot is established through which a thin stream of the nlm 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 58. The heads of the screws 55 rest upon the free ends of the brackets 52 and carry operating levers 51. 'I'he lower ends of the screws 5S 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 53 will cause the wall 49 and the lip 5l to vary the size of the discharge slot. When operating circumstances demand, an operating handle 53 mounted on wall 49 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 31 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 The solution passing 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 baiile 60 which extends in front of the feeding lips 55, 5I and for the full width of the hopper of the end walls 31. A cross plate 6I connects the end walls. 31, 31 and is vertically slotted as at 52. The baffle 6B has adjustment screws E3 extending horizontally therefrom and passing through the slots 62 in plate 6i. Locknuts 54 are used to adjust the position of the bafe B relative to the discharge end of the hopper and also to control the clearance of the lower edge of the baffle 50 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 issmoothly polished to provide an appropriate. casting-surface which will ho-ld the rsolution'during the evaporationof the nlm.A

Such a casting-surfacemay also be equipped f as desired with flanges orledges upon its side `edges either be continuous or in'suitableV removable sections. This castingsurface or member is brought'to uniform temperature with the solution and the conditions in chamber 33 so'that the operation of evaporation of the solventV will not .beYV attended by undesirable eifects such Yas The solution is discharged from the slot in the base of the hopper and between walls 31 and38 .and the'panel 49. The rate of discharge is ac'- curately controlled by the adjustment of the dis-Y The solution on dischargeY charge lips and 5I. l Y spreads laterally into contact with the guide strips 30 and drains downwardly tothe baiile 5D. The bailie E0 causes the Ysolution to accumulate in Ya shallowA pool, the upper surface Vof Ywhich extends slightly'to the left of the lip 5D'as shown in Fig. 8.

Due to the upward slope of the casting plate 23 and lits continuous movement towardV the upper end of the conveyor, there is a tendency for the solution to ow in the opposite directionYY from vthat ofthe casting plate and to return to the pool. This action insures'iirst, an adequate deposit ofthe solution upon the casting plate regardless of variationrin viscosity and immediately 'thereafter the draining of excess solution to the pool so that the desired thinness of the nlm may be attained and its upper surface remainquite hat. Y

In the course of thetravel of the plate together u with the deposited nlm solution through the rcharn- It is also Vpossible in this Yway to regulate the evaporation Without producing a` current or draft of air which might injure the desired surface ofthe film.

The nlm on reaching the discharge end of the chamber 33 will be VVsufiiciently hardened tcrpermit it to be cut into sections dened by the size of .the casting plates. VQ'Ihe latter with thehn still Yadhering both to the plates and to the guide strips may then be transferred to the conditioning chamber34. Y' f I Where the conveyor itself carries the casting surfacefthe conveyor may be extended to pass through the conditioning chamber 34 and thus carry the film in a continuous strip.

In like mannerthe chamber 34 may extend for suflicient distance to permit the useof a second or subsequent discharge hopper. ThusY the film deposited from the rst hopper may bepar- Y tiallyv or substantially evaporated and'coated'with a second fllm of the same or a different nlm solution and the composite nlm evaporated prior to reaching Vthe discharge point fromrthe conveyor. 'Y

Through the procdure outlined above and by means of the machine as described, provision is made forcasting laminated sheets and strips in continuous operation and for .drying the sheets Ythoroughly between successive coatings.' The firmness With whichthe films areheld under ten.

sion on the surface of the Ycastingelement and the particular atmosphereof solvent'vapors maintained reduces the likelihood of surface irregularities such as craters and pits. The accurate control of the conditions Vof temperature permits the casting of pre-heated solutions at elevated temperatures and upon pre-head casting surfaces. The provision of the chamber of solvent vapors is of primary importance as permitting the userof inexpensive low-boiling solvents in conjunction with inexpensive diluents. At the same time it is a great improvement in preventing Yblushing whichV Y would .be otherwise caused by precipitation of i moisture. It will also be evident that such a controlled atmosphere Yduring evaporation prevents surface-sealing and pin-holes.

By causing the solution to accumulate iirst in a. Y

throughout the-subsequent operations'.

Where the solutionrcontains oxidizing products,Y

glycerol, phthalate resins orY drying oils, which require baking or other heat treatment to dry,;

f the upwardly inclined travel `through the heated chamber of solvent vapors is of. particular advan-y tage.

The mechanism above described will thus'be seen to be suitableY for the continuous production.

of lrns of various types and kinds. .While one Yparticular form of the device has Vbeen described,

many variations in structural detailsY andoperation are comprised within the scope of theI invention as defined by the following claims.

What I claim is:- Y Y i 1. A lm casting machine comprising'a mov.

able casting surface, iilm retaining membersV onV the side edges of said surfacaand means Vfor depositing a film solution on the surface between and in contact withsaid retaining members, said.

forming compounds against retraction.

2. A lrn casting machine comprising a casting surface, Vmeans for moving said surfaceY longitudinally and upwardly, detachable anges on Ving they film attached to the surface and said flanges, said chamber comprising a regulatable atmosphere of solvent vapors,and means forV withdrawing said surface from the lchamber and depositing same into a conditioning chamber.

4. A ,film casting machine comprising a movable casting surface having means for adjustably Ylifting one end, and a discharge hopper for film solution, supported above and across said surface.'

retaining Vmembers being adapted to hold nlm- 5. A film casting machine comprising a movable casting surface having means for adjustably lifting one end, a hopper for film solution supported adjustably above and across said surface.

6. A film casting machinecomp-rising an adjustable movable casting surface having means for adjustably lifting one end, a hopper for lm solution supported adjustably above and across said surface, and means for varying the rate of discharge from said hopper.

7. A film casting machine comprising an adjustable movable casting surface having means for adjustably lifting one end, a hopper for lm solution sup-ported adjustably above said surface, a discharge outlet from said hopper extending uniformly across said surface and means for varying the size of said outlet. Y

8. A lm casting machine comprising a movable casting surface having means for adjustably lifting one end, a hopper for film solution supported above and across said surface, means for varying the discharge from said hopper and means for controlling the temperature of the solution in the hopper.

9. A casting surface adapted to receive one or more evenly applied uniform coatings of similar or dissimilarv nlm-forming solutions and hold same against retraction, said casting surface having means at its opposite sides or edges adapted to firmly hold the forming and formed film rigidly in place without substantial distortion of the nlm, said surface being adapted by said means to receive and retain said coatings over substantially the full surface area of said casting surface.

l0. A lm casting machine comp-rising a casting surface movable upwardly in a straight, slightly inclined direction, means for depositing a film solution on said surface, and a relatively closed chamber into which said film solution passes and through which the said surface moves during and subsequent to the deposit of the film.

11. A iilm casting machine comprising a casting surface movable upwardly in a straight, slightly inclined direction, means for depositing a film solution on said surface, a relatively closed chamber into which said film solution passes and a baffle supported adjustably and across said surface for maintaining a shallow pool of solution through which the surface moves.

12. In an apparatus of the kind described comprising means for continuously moving a casting surface upwardly in a straight, slightly inclined direction, a hopper for film solution supported adjustably above and across said surface, means for varying the discharge from said hopper, and a relatively closed chamber into which said lm solution passes.

13. A film casting machine having means for conveying and mechanically advancing a series of casting plates which form a continuous top surface under a discharge hopper, said conveyor being provided with means to engage said casting plates on the under side thereof and advance said plates in a forward direction, a series of casting plates having means on the under side thereof to accommodate said conveyor engaging means, regulatable means for depositing lm solution upon said surface, and a relatively closed chamber into which said film solution passes.

14. In anl apparatus of, the kind described comprising means for continuously moving a casting surfacel upwardly in a straight, slightlyinclined direction, means for depositing a lm solution on said surface, means to partially evaporate volatile solvent from said deposited solution to form a film within a relatively closed chamber, a conditioning chamber, means to subsequently substantially completely evaporate Volatile solvent from said film within said conditioning chamber.

CLYDE SCOTT.

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