US2322827A - Coating hopper - Google Patents

Description

June 29, 1943. I E. K. CARVER 2,322,827

COATING HOPPER Filed Dec. 29, 1939 FIGJ. F104; 12 x 22 1 IIW 'I IIW g F 9' 17 ]l lt WL l U 95 28 FIG. 2

Has.

v INVENTOR .priate feeding device onto the polished metallic of the V to form a coating slot. Usually one of a other so as to provide a means of controlling the Patented a... 29, 1943 UNITED STATES PATENT osncs Eastman Kodak Company, Rochester corporation of New Jersey Application December 29, 1939, Serial No. 311,588

4 Claims.

This invention relates to coating hoppers for coating solutions of cellulose material onto a smooth moving surface such as a belt or wheel to form a continuous sheet or him, and more particularly to an improved coating hopper adapted- 5 to coat photographic 'film support and the like from the new type of solution which is coated on a relatively col'd belt or wheel to congea'i the solution to form a gel-like him rather than coated on a hot wheel, as commonly practiced, to dry out the solvent.

As is wellknown to the art, cellulose film or sheeting is formed by spreading a thin coating of the desired material, generally a solution of a cellulose ester such as cellulose acetate in a suitable solvent, onto an appropriate heated surface and causing the solvent to evaporate therefrom. The method generally employed consists of feeding the solution or dope from an approsurface of a slowly rotating wheel or drum. The

a solvent evaporates from the film more or less' progressively as the wheel turns. In less than a complete revolution suflicient solvent has been evaporated to permit the film to be removed from the wheel and conveyed to a wind up or carried over other. rolls or drums for further curing treatment. I

The device usually employed for feeding the solution to the coating wheel comprises a i V shaped hopper provided with spaced apart blades I mounted at an angle to one another at the apex these blades is adjustable with respect to the 33 thickness of the dope stream and, therefore, the sheet being formed.

Such hoppers are very staisfactory for-coatingmany kinds of cellulosic solutions. However, when an attempt was made to coat what will be 40 hereinafter termed a gel dope" from such a hopper onto a cold wheel various unforeseen diiiicultles arose. The invention will perhaps be better understood if the characteristics and nature of as" "gel dope" are explained. In short,these types 4 of dope can be maintained as fluids at temperatures above C. and when allowed to cool to or below a critical temperature between 10-50 0., depending on the composition, they form transparent gels which remain homogeneous through- 50 out the gelling operation. This gelation occurs within approximately 20 C. of'the flowable solution point. When the gels are first formed they do not adhere strongly to the cooled wheel and although the gelled film contains relatively large rounding th which air cur 'the coating wli-eel, could be amounts of solvent, i. e. an amount of solvent equal to or greater than the weight of the cellulose ester, it is sufllciently strong and resistant inconsequential. When the regular type hopper was employed in coating the gel dopes onto .a cold wheel, the proximity of the hopper slot to the cold wheel caused a sufiicient temperature drop in the hopper-lips to permit formation of slugs on the edges of one or both of the hopper lips. These slugs project into the dope stream and give rise to uneven coating and the formation of streaks in the finished product. In forming photographic film base such imperfections are of course very undesirable. I

Various expedients were tried to eliminate the slug formation due to the chilling eflect of the cold'roll 'on the hopper lips. The difficulty was finally overcome by, raising the hopper. lips from the normal height of one inch above the coating wheel to two inches above the wheel and suropper lips by an enclosure from rents, particularly the cold air from minimized or substantially excluded.

Although these changes in the operation and construction of th'e hopper eliminates the cunculty of slug formation from the chilling eii'ect of the wheel, it was soon found that another unforeseen diiliculty is introduced. by these ggjchanges which'is as great if not even more of a disadvantage than slug formation.

It was found that under'the new operating conditions it was dimcult to coat a sheet or film support of a desired width. For example, it was found that a dope hopper which will coat a sheet 50 inches wide from a tsl'ot-bi) inches long would only coat 'a sheet offlinisupport onto the cold wheel of about 48 inches wide. This change in width was caused by the relatively long drop from the slot to the wheel which permitted the surface tension of the gel dope to drag in the edges of the wheel.

It was attempted to correct this diiiiculty by stream before it reached the coating i using a 5l /.inch hopper to coat a 50 inch sheet. However, this did not solve the problem since to a predetermined width.

In accordance with the invention these and other objects are attained by employing a hopper which has thin metal rods, needles or blades adjacent the ends of the hopper slot and extending therethru which guide the edges of the gel dope straight'down and prevent its necking in due to surface tension. These guide rods may be spaced from and extend down through the slot in the'hopper, or they may be fastened to the ends of the hopper. When using gel dopes'which change within a particularly small temperature range from a fluid to a solid, slugging may oc-,,

cur on the guides. In such cases I may substitute for metal guides, guides made'fror'n a porous material such as balsa wood. A "solvent for the gel dope is caused to flow from a reservoir through the porous balsa wood toward the stream of gel dope so as to form a continuous layer of solvent over the surface of the balsa wood guides. The dope will adhere to this continuous layer of solvent which, in turn, adheres to the guides, and flows down evenly upon the coating surface. The continuous flow of the solvent will overcome any'tendency for slugs to form on the guides.

The invention will be more clearly understood by reference to the following detailed description and associated drawing in which:

Fig. 1 is a front sectional view in elevation of a portion of an ordinary coating hopper positioned above a coating wheel and having a gel dope solu'tion flowing from the hopper slot onto the relative position of the guide rods and the hopper slot;

Fig. 5 is an end elevational view in section of the second type of my improved coating hopper in which a strip of porous balsa wood is employed as the guide for the gel dope guide;

Fig. 6 is a portion of a front elevational view in section of the second type of my improved coating hopper taken on the line 66 in Fig. 5. Fig. 7 is a bottom view of a portion of the hopper taken on the lines 1-1 of Fig. 6 showing more clearly the balsa wood guide in relation to the coating slot.

Referring to Fig. 1 there isshown a portion of an ordinary type of hopper 3 heretofore used rotating wheel and form a sheet 16 thereon. As

shown at ll when employing this type of hopper to coat gel dope the solution tends. to neck in as it leaves the coating slot. It therefore is imv possible to coat a sheet from such a hopper which will be of a predetermined and desired width.

Referring to Fig. 2 there 'is shown an improved coating hopper from which a fllm support from gel dope of a predetermined width can be made- As shown in this drawing the improved hopper is represented at 20 and comprises slanting side walls 2! and 22 having a heating jacket 23 and 24 positioned therein. The lower projections or lips 25 and 26 of these walls are suitably spaced apart to form a coating slot 21. A solution guide member 28 is removably positioned near the end i of coating slot 21. The guide member 28 is suitably attached to rod 29 and can be raised or lowered by raising or lowering rod 29 which is slidably mounted on the end wall 30 of the hopper by members 3| and 32. As is indicated in this drawing the solution l5 tends to adhere to the guide 28 and flow downward to the rotating coating wheel 33 positioned therebelow. Baflles 35 and 36. attached respectively to walls 2| and 22 serve to shield the stream of dope from undemounted on the inside of the hopper by members 38 and 39 operates to regulate the flow of the solution down the guide 28. A cover 4i! is suitably placed on the hopper to prevent foreign. materials from falling in the coating solution.

It will be understood that a guide rod is positioned at each end of the coating slot as shown more clearly in Fig. 3. The solution i5 is shown flowing from slot 21 and following the guides 28 on either end of the slot downward to contact the coating wheel 33 and form asheet iii. A slight tendency to neck in after the solution leaves the end of the guide rods 28 may occur as shown at M. This, however, is negligible and the hopper slot can be adjusted to a length which will produce a sheet of a desired width within small limits of error.

Referring to Fig. 5 there is shown a side elevational view in section of a modification of my improved coating hopper 55 in which a strip of porous balsa wood is employed as the guide for the gel dope. As shown in this drawing, the hopper 45 comprises walls 46 and 41 having heating jackets 68 therein. Cover plate 49 is placed on the hopper. A coating slot 5| is formed between the lower extremities of walls 46 and 41 through which the solution flows downward toward coating wheel 6|. Bailies 52 and 53 extend along the length of the slot and extend downward toward the coating wheel 6! and serve to restrict air currents from contacting the dope stream. In place of the metal guides 28 shown in Figs. 2, 3 and 4, in the present modification, there is substituted a strip of porous balsa wood 54. This strip of balsa wood is countersunk in the end wall-of the hopper and is flush therewith as shown more clearly in Figs. 6 and '7. Under the optimum operating conditions, hereinafter described, the gel dope will flow out of slot 5| as shown more clearly in Fig. 7 and follow the balsa wood guide down to the coating wheel 6| as shown in Figs. 5 and 6. To assure the adherence of the gel dope to the balsa wood guide as well as to',prevent slugs from forming thereon, it is desirable to keep the surface of the balsa wood covered with a thin layer of a solvent 59 for the gel dope. This will wet the surface of the balsa wood and gel dope will tend to adhere to the solvent and therefore follow the balsa wood guide downward toward the coating wheel and form a sheet 60. The solvent employed to wet the balsa wood guide is conducted to the side away from the dope stream 50 in suflicient quantities to flow through the porous wood by a conduit 55 contained in the end wall 55 as shown particularly in Figs. 6 and 7. A funnel 53 may be employed to introduce the solvent into the conduit 55.

To form a film support by the apparatus shown in Figs. 2, 3 and 4 an appropriate gel dope solution, for example iiooparts of cellulose acetate butyrate containing 33.2% acetyl and 11.9% butyryl in 700 parts by weight of' a solvent mixture composed of 60% by weight of propylene chloride and 40% of ethylene chloride is added to the hopper and by means of the heating Jacket is maintained above approximately 60 C. as a fluid. The coating wheel 33, by means not shown, is maintained at a cool temperature of approximately 14 C. The coating wheel 33 is caused to slowly rotate and a thin stream ofyhot dope i5 is permitted to flow from slot 21. The gel dope solution would normally neck inas shown in Fig. 1 were the guides 23 not employed. Because of the guides the dope will travel straight downward to contact the coating wheel 33 in a stream of the desired width as indicated most clearly in Fig. 3. when the dope stream reaches the cold wheel it will gel under the influence'of the lower temperature and form a transparent sheet.

This gel dope solution may be coated from the apparatus described in connection with Figs. 5, 6 and 7 by maintaining the solution in the hopper at 60 C. andpermitting it to flow out of the slot and down the balsa wood guides to contact the cold revolving wheel 5| in a stream of the desired width. The balsa wood guides are wetted by adding a 60-40 propylene chloride-ethylene chloride solvent mixture to the conduit 55 from which it will soak through to the face of the balsa wood as shown in Fig. 6 at 59. On reaching the cold wheel 52 the solution will change to a gel and form a transparent sheet having the desired width.

Usually on leaving the coating wheel the transparent gel like film is conducted to suitable drying apparatus, not shown, to further reduce the solvent content to a minimum. This is possible without employing high temperatures for the structure of the gel like film is such that it will readily release the volatile solvent.

Other gel dope solutions such as are disclosed in the copending applications Serial Nos. 245,- 020,; 245,021; 245,022; 245,023 filed Dec. 10, 1938; and Serial No. 275.712 filed May 25, 1939 may be employed in my improved coating hopper for forming film support of a predetermined width.

What I claim is:

1. In a film or sheet forming device, a hopper having a slot therein for feeding a film forming solution to a moving film forming surface positioned thereunder, solution guide members positioned near the ends of the slot extending from within the slot downward toward but out oi contact with the film forming surface for guiding the solution to the film forming surface ina stream width substantially equal to the length of the slot.

2. In a film or sheet forming device, a hopper having a slot therein forfeeding a film forming solution to a moving film forming surface positioned thereunder, solution guide members positioned near the ends of the slot extending from within the slot downward toward but out of contact with the film forming surface for guiding the solution to the film forming surface in a stream width substantially equal to the lengthof the slot, and means forming an enclosing chamber around the slot and guides extending from the vicinity of the hopper slot toward the film forming surface.

3. In a film or sheet forming device, a hopper having a slot therein for feeding a film forming solution to a moving film forming surface positioned thereunder, solution guide memhers positioned near the ends of the slot and out of contact therewith extending from within the slot downwardtoward but out of contact with the film forming surface for guiding the solution to the film forming surface in a stream width substantially equal to the length of the slot, and means forming an enclosing chamber around the slot and Euides extending from the vicinity of the hopper slot toward the film forming surface.

4. In a fllm or sheet forming device, a hopper having a slot therein for feeding a film forming solution to a moving film forming surface positioned thereunder, solution guide members positioned adjacent theyends of the slot extending from within the slot downward toward, but out of contact with. the film forming surface for guiding the solution" to the film forming surface in a stream width substantially equal to the length of the slot, and means for adjusting the position of said guide members toward and away from said film forming surface.

' EMMETI' K. CARVER. v

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