US2051201A - Film making machine and method - Google Patents

Description

Aug. 18, 1936. A. J. DAVIDSON FILM MAKING MACHINE AND METHOD 2 Shets-Sheet 1 Filed April 10, 1954 Aug. 18, 1936. I x, DAVIDSQN 2,051,201

FILM MAKING MACHINE AND METHOD Filed April 10, 1934 2 Sheets-Sheet 2 l l\- 4.51/15 /J 1 I 1 I Patented Aug. 18, 1936 UNITED STATES FILM MAKING MACHINE AND METHOD Arthur J. Davidson, Rochester, N. Y., assignor to Eastman Kodak Company,-Roehester, N. Y., a corporation of New York Application April 10, 1934, Serial No. 719.917

'lClaims.

This invention relates to the art of making film base or sheeting by coating solutions of cellulosic material onto a smooth moving surface such as a belt or wheel and more particularly to an improved process for maintaining the proper conditions at the beginning of the coating operation and to an improved type of apparatus for accomplishing this result.

As is well known to the art, cellulosic film or sheeting is formed by spreading a thin coating of the desired material, generally a solution of a cellulose ester such as cellulose nitrate or cellulose acetate in suitable solvents, onto an appropriate surface and permitting or causing the solvents to evaporate therefrom. The method generally employed consists in feeding the solution or dope from an appropriate feeding device ontothe"polishedmetallic surface of a slowly rotating'wheel or drum. The solvent evaporates from the film more or less progressively as the wheel turns until (in less than a complete revolution) sufficient solvent has been removed to admit of the film being removed therefrom and conveyed to a wind-up or carried over other rolls 5 or drums for further treatment.

The device usually employed for feeding the solution to the wheel comprises a v-shaped hopper provided with blades mounted at an angle to one another at the apex of the V and at least .one of which is adjustable with respect to the other so as to provide a means of controlling the thickness of the dope stream and therefore the sheet being formed. Such a device is shown inconventional form in U. S. Patent 1,900,873 issued on March 7, 1933 to Henry E. Van Derhoef.

It has been found that serious difficulties often arise. from the tendency of the cellulose ester solutions to form slugs or encrustations on the edges of either one or both of the hopper blades, since, when these slugs form, they project down into the dope stream and give rise to uneven coating and the formation of streaks in themished product which render it unfit for use. These difficulties are more serious in the manufacture of the thinner types of sheeting and film support than in the thicker material and may even result in the production of holes or voids in the product.

Work which I have done shows that this slugging action is due to the fact that small amounts of the cellulose ester solution creep along the outer surfaces of the blades as it flows out of the hopper instead of being carried along in the dope stream on the wheel. .The solvent evaporates from these small portions of dope and cause them to solidify, thus forming slugs. These slugs tend to increase in size due to further accretions of dope and eventually become sufficiently large to project below the edges of the blades and cause the disastrous results above referred to.

My invention accordingly has as its principal. object to overcome the above mentioned diiliculties and to provide a method for insuring uninterrupted and even coating of the cellulose ester solutions in film and sheet making. An- 10 other object is to provide an improved type of device for accomplishing this result. Another object is to provide a method of making cellulose ester sheets or films inwhich the solvent vapor in the immediate vicinity of the feeding 15 device is maintained at such a concentration as will prevent the formation of accretions of solidified material at that point. A further ob-" ject is to provide a device for enclosing a portion of the feeding device and maintaining in 20 the enclosed portion a solvent-saturated atmosphere. Other objects will appear hereinafter.

My invention will be made clear from the following specification and the accompanying drawings in which like numerals refer to like 25 parts and in which: 7

Fig. 1 is an elevational view, partly in section showing the improved type of dope feeding device of my invention mounted in operative position on a film or sheet forming machine.

Fig. 2 is an enlarged sectional elevation of the feeding device of Fig. 1 showing the liquid reservoirs and vapor chambers surrounding'the hopper blades.

Fig. 3 is a plan view of the device shown in 35 Fig. 2 with part of the wheel housing broken away to more clearly illustrate the position of the hopper with respect to the wheel.

Fig. 4 is an elevational view along the line 4-4 of Fig. 2 with one of the adjustable gates or partitioning members removed and a portion of the end wall of one of the enclosing chambers broken away to show the internal construction of the chamber and its relation'to the top of the filmforming wheel. v

Fig. 5 is a plan view in partial section taken on the line 5-5 of Figs. 2 and 4, illustrating the circulation or movement of the solvent vapors in the vicinity of. the hopper blades, the back blade being shown in full section and the position of the front blade in relation thereto being shown in a dotted line.

Fig. 6 is a fragmentary sectional view of the lower part of the hopper illustrating the'manner in which slugs tend to form on the hopper blades of devices not employing my invention.

Referring to the drawings. the numeral l designates a device for feeding the cellulosic solution or dope which, for example. may be a solution of cellulose nitrate or acetate in a suitable solvent, such as acetone or other liquid, to the surface of the wheel 'or drum 2 This feeding device may hereinafter conveniently be referred-to as a "dope hopperl'vthe cell'ulosic solution as dope-and thejwheel or drum as theficoating wheel, since these are the terms customarily employed in the art. The hopper may be adjustably mounted, or suspended, over thewheel by means (not shown) in such manner that it may be lowered to, or raised from, the coating surface as occasion may require.

The hopper i as shown comprises a V-shaped trough provided at the lower part of its rear wall 2 with a blade 4 set into a recess in the hopper wall. Cooperating with the blade 4 is a blade, fitting into a recess in the opposite wall I and provided'with a plurality 'ofadiusting screws 1 by which it may be moved toward or away from the blade 4, thereby regulating the thickness of the stream of-dope which flows from the I hopper onto the coating surface. ,Itwill be noted that these blades project downwardly into the space below the hopper and that even in the "case of the back blade 4 there is always a small space between the edge of the blade and the wheel surface.

According to one form of the invention, the body of the hopper may be provided with internal chambers or reservoirs I and I for storing a supply of liquid solvent l2 fed thereto through It should be noted that under ordinary conditions of operation these reservoirs are not necessary to the proper functioning of the device, since all that-is required to accomplish the abovementioned objects of the invention is to provide a confined and segregated solvent-saturated atmosphere in the immediate vicinity of the lower portions of the hopper blades as will be more fully set forth below.

Referring to Figs. 4 and 5 the hopper frame, which may be in the form of a single casting or other convenient construction is so formed as to provide side chambers II which form passages for the solvent vapors to circulate or at least pass freely between the chambers I and 2. The lower walls of these chambers or passages I! are provided with sealing strips i4 which serve the double purpose of preventing escape of solvent from the interior of the device and providing antifrictional contacts between the hopper and the sides of the rotating wheel.

Numerals II, Figs. 2 and 3, designate gate or partitioning members adapted to be raised or lowered by means of thumb-screws I 0 operatingin internally threaded bosses II on the hopper frame. Rigidly, but removably attached to the members I! are members ll. preferably of wood. and provided with a covering of suitable textile fabric or other soft material. The numerals I I 'indicate guide members projecting from and integral with the hopper providing vertical guiding channels 2| within which the gate members move.

' Numeral 24 designates a casing for wheel 2 provided with inlet 28 and outlet 24 for the ingress and'egress of air or any other suitable evaporative medium. It will be noted that the internal chambers 2| and 22 of the'hopper have 6 no communication with the wheel casing except what is provided by regulation-of the gate blades 4 and s are adjusted to give'the desired thickness of mm. The solution flows out uponlthe surface of the wheel which rotates slowly in the so direction indicated bythe arrow. Evaporation of solvent takes place immediately and continues e less Pms wvelvas the mm is carried around by the wheel through less than a com- I I plete revolution until at some predetermined point 8 the film thus formed, which may be designated by numeral 21, can be removed therefrom and conveyed to other apparatus for further treatment or to n wind-uprl able solvent selected according tofthe particular cellulosic material employed in the dope. Assuming for purposes of illustration that acelluloss acetate dope is employed, the solvent may be acetone, the level of the liquid being brought to a Just below the tops of the vapor conduits II. If

desired, any form of constant level devices con nected to a suitable source of supply may be employed for automatically maintaining the solvent e level at the desired point in the reservoirs. One 0 suitable form of such a device is illustrated in Fig. 7 and comprises a feed line 22 connected to. a suitable source of supply (not shown) passes through cap 22 and is provided with valve 8.. This valve is controlled by lever 2| and provided with slot 22 in which cam 22 attached to rod 24 is adapted to move. Rod 24 is attached at its lower end to float 25 which rises and falls with the level of liquid in the reservoir. and admitting more solvent by opening valve II when the liquid level drops below a predetermined point. Op-

tionally, heating means such as coils in which warm water or other liquid circulates may also be provided for increasing the rate of evaporation of the solvent.

The vapors of solvent pass through the conduits l2 and down into the chambers 2| and 22 where they are confined within the space formed by the wheel surface, the walls of the chambers 2i and 22 and by gate members I. As indicated by the arrows in Fig. 5, the solvent vapor circulates or moves from one chamber to the other through the'passages it thus insuring at all times a concentrated solvent atmosphere for both the front and back hopper blades. The atmosphere surrounding the blades is thus automatically kept as nearly saturated at the temperature prevailing in the apparatus, as is possible.

As indicated above. the level of solvent in the reservoirs should never rise above the tops of the 70 conduits 12 as otherwise drops of liquid solvent would drop downupon either the wheel surface or the forming film and cause spots or other defects in the product. In other words, in accordance with the principles of my invention, there It Thereservoirs 2 andl are filled with suit-:- 3 I should always be a suillcient amount of solvent present at the blades to keep them free from slugs or encrustations of'dope, but the solvent should always be present in the form of vapor rather than liquid.

By keeping the blades surrounded by solvent vapor I have found that the slug formation above referred to and further illustrated in Fig. 6 is entirely eliminated. This is apparently accounted for by the fact that as soon as any of the dope commences to creep and solidify along the outer surface of either blade, it meets an atmosphere of solvent of such concentration as immediately to redissolve it. What actually happens is probably that the solvent in the vaporladen atmosphere in the immediate vicinityof the edge of the blade acts to keep the dope at that point at all times in solution so that it never even has an opportunity to start a slug or solid encrustation. Whatever the explanation, I have found that by employing the above device and maintaining a saturated or nearly saturated solvent atmosphere in the immediate vicinity of the hopper blades, slug formation is entirely obviated and the film forming operation is thereby rendered much more efiicient and economical than otherwise possible due to elimination of streaking and the consequent wastage of material. It might be supposed from the fact that solvents are constantly evaporating from the stream of dope at the hopper that sufficient solvent would be present at that point to prevent the formation of slugs, but experience has shown this is not the case and slugging has always been blade I is more susceptible of slug formationthan the front blade 5 because of the-fact that it gen erally lies closer to the coating surface and thus permits only a minor quantity of solvent vapor emanating from the dope stream to pass back of the blade, and even this small amount of vapor, were it not for the provision of the enclosing means herein described, would be quickly dissipated. Although there is normally a much greater quantity of solvent vapor in the vicinity of the front blade, since it is in closer proximity to the dope stream, yet it has been found that this is insumcient to prevent accretions at the edge or on the back surface of this blade.

If for any reason it is desirable to have an amount of solvent corresponding to less than a saturated atmosphere, the gate member I! may be raised sufilciently to permit the escape of a portion of the solvent. It should be noted in this connection that the forward gate members I5 must always be adjusted upwardly or downwardly to correspond with the thickness of film or sheeting being produced. These members are, of course, never positioned so close to the wheel surface as to contact with it-or with the surface of the forming film, although they are maintained as closely thereto as is consistent with safety.

It will be seen that I have provided a means of completely enclosing or segregating that portion of the dope hopper which is in the immediate vicinity of the blades and of maintaining therein and in contact with the blades an atmosphere substantially saturated with or at least containing a high concentration of solvent vapor which completely eliminates any form of encrustation or slugging.

It will of course be apparent that many changes may be made in the above described structure and in its specific mode of operation within the scope of my invention. It may, for example, be desirable to employ only one solvent reservoir and this may be located adjacent to either the front or backwhopper blades, since the side passages It will serve to convey the solvent vapor from one chamber or blade surface to the other. It may also be desirable, when two reservoirs are employed, to connect them by means of a conduit or to provide any other type of connection between them in order that both may be filled through a single port.

Although I have described my invention with reference to the manufacture of cellulose acetate or nitrate films or sheeting, it is equally applicable to the production of such products from any type of cellulosic solutions such as those of the higher single organic esters of cellulose including cellulose propionate, cellulose butyrate and the mixed organic esters such as cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate stearate, and others, the solvent employed for producing the vapor-laden atmosphere in any given case being selected upon the basis of its solvent power with respect to the particular ester dealt with. The solvent employed need in-the form of solvent chambers in the hopper frame, which device may be especiallydesirable n n c s i e' h n 'irnes o film or she tin due*"to"the"hi'gher coating speeds employed, my invention resides broadly in providing a confined, solvent-saturated atmosphere in the immediate vicinity of the lower ends of the hopper blades, regardless of whether the solvent vapor is merely accumulated in this confined space from evaporation from the dope stream itself or derived from an independent source.

Furthermore, while 1 have illustrated my invention as applied to a circular type of coating surface. namely a wheel surface, it will be apparent that the invention is equally adaptable (with slight modifications well within the province of one skilled in the art) to a fiat coating or film forming surface such as that of a metal belt passing continuously underneath the hopper in a horizontal direction as shown in U. S. Patent to Stevens et al. No. 573,928.

It will be apparent that I have provided a novel method and means of preventing the formation of slugs or encrustations of solidified material on or in the vicinity of the blades of a dope hopper, thereby precluding the possibility of streak formation, tearing or voids in the film or sheeting during its manufacture and eliminating one of the most prolific sources of shut-downs and waste of time and materials.

What I' claim as my invention is:

1. In a film or sheet-forming device comprising means for feeding a fiowable cellulosic solution to a moving film-forming element adjacent thereto, the combination of means forming an enclosing chamber for the feeding portion of the feeding means and means for supplying said chamber with solvent vapor.

2. In a film or sheet-forming device, the combination with a hopper provided with cooperating blades positioned in and projecting through an orifice thereinadapted to regulate the fiow of a cellulosic solution from said hopper to a filmforming element moving-below and in close prox-' imity thereto, of means for enclosing a portion of the coating surface and that portion of the hopper from which said blades normally project, and means for supplying solvent vapor in the space formed by"said enclosing means.

thickness, walls continuous with said hopper projecting there beiow and forming substantially vapor-tight chambers around a portion of the wheel surface, said walls being provided with internal reservoirs forocontaining a supply of liquid solvent, conduits for conveying solvent vapor from" said reservoirs to the vapor chambers, and

' adjustable partitioning means operating in vertical-recess in the hopper walls for controlling I the concentration of solvent vapor in said chambers. I 4 v -4.- In the process of making film or sheeting by feeding "a fiowable cellulose derivative solution from a container through a restricted orifice therein onto a film-forming surface located withi in an enclosed space containing an atmosphere of solvent vapor, the step which comprises keeping the edges of the orifice free from encrustations of solidified cellulose derivative material by enclosing and segregating a portion ofthe atmosphere of the enclosed space in the immediate vicinity of and surrounding the point of feed of the solution, and maintaining in said segregated portion a higher concentration of solvent vapor than in the remainder of the enclosed space.

5. In the process of making film or sheeting by feeding a fiowable cellulose derivative solution from a container through a restricted orifice therein onto a film-forming surface located within an enclosed space containing an atmosphere of solvent vapor, the step which comprises keeping the edges of the orifice free from encrustations oi solidified cellulose derivative material by enclosing and segregating a portion of the atmosphere of the enclosed space in the immediate vicinity of and surrounding the point of feed of the solution, and maintaining in said segregated portion a substantially saturated atmosphere of solvent vapor.

6. In the process by feeding a flowable cellulose derivative solution between, and in contact with, thicknessregulating means through which the solution is conveyed onto a film-forming surface located within an enclosed space containing anatmosphere of solvent vapor, the step which comprises of making film or sheeting keeping the, edges-of the regulating means free summation t;s li fledvac ulese.de vative, material by enclosing and segregating a portion of the enclosed space in the immediate vicinity ofthe regulating means, and maintaining in said segregated portion and in contact with the regulating means, a substantially saturated atmosphere of solvent vapor.

7. The process of making film or sheeting by feeding a fiowable cellulose derivative solution from a container provided with blades between which the solution fiows onto a film-forming surface located within an enclosed space containing an atmosphere of solvent vapor, the step which comprises keeping the blades free-fromencrustations of solidified cellulose derivative material 35 by enclosing and segregating a portion of the enclosed space in the immediate vicinity of the blades, and maintaining in said segregated portion and in contact with those portions of the surface of the blades which are adjacent to, but out of direct contact with, the dope stream, a substantially saturated atmosphere of solvent vapor.

ARI'HUR J; DAVIDSON.

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