US1921953A - Apparatus for making sheets or films - Google Patents

Description

Aug. 8, 1933. L. T. STEPHENS APPARATUS FOR MAKING SHEETS OR FILMS Filed Nov. 29, 1930 Patented Aug. 8, 1 933 UNITED STATES APPARATUS roa MAKING SHEETS mars Levi T. Stephens, Rochester, N. Y., minor to Eastman Kodak Company, Rochester, N.

Corporation of New York Application November 29, 1930 Serial No. 499,048

6 Claims.

My invention relates to apparatus and processes for making sheets or films from viscous compositions, and more particularly to a spreading device adapted to effect the spreading of the viscous composition onto a continuously moving sheeting or receiving surface. The viscous composition may be a gelatinous material or any other material which when spread into a thin layer will dry to form sheets such as cellulose esters and cellulose ethers, known in the art as dopes.

Among the objects of my invention is to provide a simple, inexpensive, and efficient spreading device adapted to produce film or sheets of uniform thickness and quality. It is an object of my invention to provide a spreading device so constructed that the dope wets the receiving surface at a point distinct from the point where the film is formed.

Another object of my invention is to avoid the formation of air bubbles or similar imperfections in the sheet or film by rolling or puddling the dope on the receiving surface prior to the formation of the sheet or film.

Another object of my invention is to provide a spreading device which will insure an even distribution of the dope whereby sheets may be produced having an even texture and thickness.

Another object of my invention is to provide apparatus for feeding dopes to a capillary pool on a moving receiving surface, the movement of which draws the dope out into sheet form and in which the amount of dope fed to the capillary pool controls the thickness of the resulting film.

Other objects and advantages of my invention will appear from the following description when read in connection with the accompanying drawing and its scope will be pointed out in the 40 appended claims.

Referring to the drawing in which like reference characters denote like parts throughout,-

Fig. 1 is a diagrammatic side elevation partly in section and on a reduced scale, of a typical film making apparatus in which my invention may be embodied, the hopper being exaggerated in relative size for the sake of clearness.

Fig. 2 is a fragmentary sectional view of a hopper embodying one form of my invention.

My improved dope hopper is illustrated as applied to a fihn machine of the rotary drum type in which a base 10 supports a bearing 11 for the shaft 12 of a wheel or drum 13. The peripheral facing 14 of the drum 13 forms an endless dope receiving surface and moves during rotation in the direction of the arrow 15 from the dope applying station 16 to a stripping station 17 and then back to the dope applying station 16.

As is well understood in the art, the dope is applied to the receiving surface 14 in a thin 6 layer or film 18 which dries as the drum rotates and is later stripped ofi at the stripping station 17 and removed over the roller 19.

In order to obtain a film of uniform thickness and free from air bubbles and slugs, I so construct my hopper that the dope 20 wets the receiving surface 14 at a point21 separated from the film forming point 22 and forms a capillary pool 23 on the receiving surface 14. As hereinafter described this pool functions as a conditioning pool by puddling the dope immediately before it is drawn into sheet form.

The depth of the capillary pool 23 is determined by the distance the lower end of the movable blade 24 is spaced from the receiving surface 14. The depth of the pool may be varied by adjusting the movable blade 24 by means of the threaded member 25 passing through the frame 26 of the hopper.

A second movable blade 27 is positioned within the hopper and is adapted to control the flow of the dope 20 to the capillary pool 23. The lower end of the plate 27 cooperates with the opposite wall of the hopper to form a throat or restricted passage through which the dope must pass on its way to the capillary pool on receiving surface 14. This blade is also adjustable through the threaded member 28 mounted in the frame 26 of the hopper. The rear of the pool 23 is maintained at the wetting point 21 by the blade 29 carried by the rear side of the hopper and its spacing from the receiving surface 14 is adjusted by raising or lowering the hopper as a whole in any well known manner as now practiced in the art.

When the machine is in operation the dope 20 flows onto the receiving surface 14 and wets it at the point 21. The movement of the surface 14 carries the dope under the movable blade 24 which tends to hold the dope in a capillary pool and the movement of the drum puddles or rolls the dope in this pool so as to maintain an even mixture and to lessen the tendency of the dope to slug. By slug I mean the tendency of the dope to form lumps of slightly hardened dope which have less solvent than the major portion of the dope, and which may tend to interfere with flowing a smooth, even sheet on the dope receiving surface. The skin tension of the capillary pool at the point of the blade 24 tends to hold the done in the pool while the capillary attraction of the moving receiving surface 14 tends to carry the dope in the pool along with it with the result that a film of a definite thickness is formed on the receiving surface. The thickness of this film is affected by the depth of the pool and the viscosity of the dope, but is primarily determined by the rate of movement of the receiving surface and the size of the restricted passage between the end of the blade 27 and the wall of the hopper. In other words, the amount of dope removed from the pool is controlled by the amount of dope fed to the pool.

Since the pool of dope has considerable mass, it is unaffected by air currents and gives a film of uniform thickness without waves or air bubbles I have found that if the depth of the pool is three to four times the thickness of the film being formed that the best results are obtainable although other ratios will give suitable results under certain conditions. I have also found that very good results are obtained when the length of the pool is approximately five times its depth, although my invention is not to be limited to these dimensions of the pool since a pool of almost any workable size will give satisfactory re-.

sults.

While I have illustrated and described the preferred embodiment of my invention, I do not desire to be limited thereby as many changes and modifications will be obvious to those skilled in this art without departing from the spirit of my invention or the scope of the appended claims.

What I desire to secure by Letters Patent of the United States is:

1. An apparatus for the manufacture of film, the combination with a continuous dope receiving surface adapted to receive continuous motion in -a uniform direction, of a dope hopper having an extended fiat surface substantially parallel to the receiving surface and spaced therefrom such a distance that dope must necessarily 'contact with said fiat surface and said receiving surface, and a restricted passage in said hopper for supplying dope between and into contact with said fiat surface and said receiving surface to form a capillary pool.

2. An apparatus for the manufacture of film in which dope is coated on an endless receiving surface adapted to receive continuous motion in a uniform direction, a hopper for supplying dope to said surface, a fiat surface associated with said hopper, said fiat surface being spaced from said receiving surface such a distance that dope from said hopper must necessarily contact with said-fiat surface and said dope receiving surface forming a pm! of dope whereby said movable dope receiving surface may draw out a thin layer of dope from said pool.

3. An apparatus for manufacturing film ineluding a continuously rotating drum having a dope receiving surface, a dope hopper mounted in spaced relation to said drum, and adapted to supply dope thereto, a surface spaced a slight distance from the dope receiving surface of said drum and carried by said hopper so positioned as to necessarily contact with dope fed from said hopper to said receiving surface whereby a pool of dope is formed, the rotation of said drum being adapted to draw a layer of dope from said pool.

4. An apparatus for manufacturing film in which liquid dope is coated on a smooth surface and stripped therefrom when dry, including a a continuously rotating drum, a member having an extended fiat surface substantially parallel to the surface of the drum being so spaced therefrom as to necessarily contact with dope passing to the drum and adapted to maintain a pool of liquid dope between the fiat surface and the drum, a hopper for supplying dope to the pool and arestricted passage between the hopper and the pool, said restricted passage being of less cross section than the area between said fiat surface and said drum.

5. In an apparatus for forming a film from dope of known viscosity, a hopper having at the bottom thereof a restricted opening, a smooth continuous surface movable beneath said hopper whereby the hopper may deposit dope thereon, one wall of the hopper being continued from the opening a substantial distance and the end thereof being spaced from the surface by adistance so small that dope passing from the hopper to the receiving surface must necessarily contact therewith and so that the skin tension at such point will keep intact a pool of dope of said known viscosity completely filling the space between said surface and said extended wall.

6. In an apparatus for forming a film from dope of known viscosity, a hopper having at the bottom thereof a restricted opening, a smooth continuous surface movable beneath said hopper whereby the hopper may deposit dope thereon, the space between one wall of the hopper and the surface constituting a pocket one end of which is open to the opening in the hopper and spaced from said hopper by such a distance that dope passing from the hopper to' the continuous surface must contact therewith whereby the pocket may be kept full of dope, and the edge of the pocket further from the hopper being spaced from the surface by a distance so small that the skin tension at such point will keep intact a pool of dope of said known viscosity completely filling the pocket from which a layer of dope may be deposited on said smooth continuously moving surface.

LEVI T. STEPHENS.

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