US2046553A - Film drying method and apparatus - Google Patents

Description

July 7, 1936.I D, H. EDWARDS FILM DRYING METHOD AND APPARATUS Filed April 20, 1934 /N VEN TOR 0A wo H. [0n/A205 ATTOENE Y Patented? July v, 193e UNIT-ED STATES P.1,5lf'l"E `1l`J-T CFFICE t 2,046,553 u FILM name ME'rnon AND APPARATUS pavia n. Edwards, Kenmore, N. Y.; assignor'to- Du Pont Cellophane Companm- Inc., New Y/ork,

- y N. Y., a. corporation of Delaware l Application April `20, 1934, Serial No. 721,515

a claims. (el. 347-24) This invention relates to the continuous dry'- ing of sheets or films. More particularly, it ,re-

` lates to the drying of sheets or lms formed in -a gel state and susceptible to shrinkage and strains during drying.l For convenience, the invention will be discussed in termsof regenerated cellulose but it is obvious that it is equally applicable .to other gel lm's cast from aqueous solutions including glycolv cellulose and similar cellulose ethers, wet cast cellulose acetate, gelatin, casein,'etc, Such sheets lor. films of regenerated cellulose are widely used for packaging various materials unless the lm is capable of properly following its track, the machine either becomes jammed or. stopped or unserviceable packages are produced. A very considerable amount of atten- -tion has been given tothe manufacture of the wrapping tissue to insure its proper working in such machinery.

In addition, such sheets or lms may be processed through multi-color printing machines.

'I'he success of such machines depends on perfect registration of the sheet or lm. If in dry- 35 ing, the lm has shrunk more on one side than on the other, the path of this lm through the printing machine will be curved instead of straight and it will be impossible to secure good results.

Again, such sheets or films of regenerated cellulose are used for making windowbags in combination with paper. In machines for producing such bags in the most economical manner, the overlap of paper and regenerated cellulose sheet Will be small. Unless the two sheets are in perfect registration at all times, a number ofbags will be defective. It has been found that lack of uniformity in drying regenerated cellulose lms will produce 5 strains 'in the illm which will produce a product that will be neither flat nor straight, nor will it function properly. This undesirable condition of the lm may be defined as not straight in the sense that a hundred feet of ilni laid-on a table '55, wm not ne m substantiauy a straight une. n r

and such packaging and wrapping is usually done some'of Athe varlationsit may be deiined as not at in the sense that if the hundred feet of lm were stretched between two -end supports, a cross section of the i'llm will be a curved line instead of substantially a; straight horizontal line.

Heretofore gel sheets or films of regeneratedcellulose have been' continuously dried bypass- V ing over a series of rotating heated hollow rollers. In the prior art, the rollers over which the lm f has passed have been internally heated by means of hot water. To secure the maximum heating has not been found satisfactory in drying mate rial such as regenerated cellulose because at atmospheric or higher pressures, steam gives relatively high temperatureswhich adversely aiect the hlm. At reduced pressures and lower temperatures, the uniformity of drying across thesheet has been poor, and in particular the film is drier at the steam inlet end than at the opposite end. It is signicant to note that gel structures,

such as regenerated cellulose, are very sensitive" compared to paper, and experience in the paper art aiords. no basis for speculation in this art.

An object of this invention is to produce sheets or lms of the character referred to that are substantially uniformly iiat and straight when -stretc'bhed taut. A further object is to produce sheets or films of non-fibrous cellulosic material that are substantially uniformly iiat and straight when stretched taut. A still further object is to produce sheets or lms of regeneratedcellulose that are substantially uniformly at and straight when stretched taut. A still further object is to eliminate expensive and intricateuidother machinery. Other objectsl will appear as hereinafter.

These objects are accomplished by the following invention which comprises-a drying apparatus for a continuous moving sheet or nlm. This invention resides in the development of drier rollers internally heated with hot water, or other fluid heating medium, which rollers uniformly dry .such materials `as sheets of regenerated celluloseand yield sheets of marked iiatness.y The invention specically resides inA the discovery that `by running the rollers only partially `filled withwater stagnation, orv stratification of the water does not occur and uniform heating of the rollers is provided at a `favorable low temperature relative to steam. I prefer torun the rollers approximately half full of water since this makes for simple design and operation but it is understood that this invention contemplates any percentage filling of the rollers. as will insure' the desired uniformity of heating. For the purpose of this specification, I mean rollers which are 25 to 85 per cent filled, and preferably from 40 to 5,0 .per cent.

`In the drawing, Fig. 1 isa side elevation of the drying end of a nlm-producing machine; Fig. 2-

is a longitudinal sectional view `of a drying .roller which may be used in the practice of the invention; Fig. 3 is aside view taken in section along the line 3-3 of Fig. 2.

In the making of regenerated cellulose'sheets such as areused as wrapping tissu, a sheet is cast from viscous coagulated, regenerated. and then processed as by .desulfurlng, bleaching, washing and glycerinating. The wet film is then dried by passing over rotating heated rollers-and is then wound on a take-up roll. The dlrying end ofthe machine and thev take-up roll are' shown in Figfl, and since the arrangement of rollers, shown in Fig. i, is conventional, it need not be discussed further in detail.

Various forms oi drying rollers may be used in the practice of this invention. Describing the invention with reference to the drawing, rollers I ,which constitute the lower drying rollers shown in Fig. 1 are hollow to permit the introduction and retention of the heating iiuid and may be made of any suitable material. The upper rollers of the drier are frictionally driven by tires from positively rotated lower rollers and ordinarilyV receive heat indirectly from the positively heated lower rollers. 'I'he heating iluid, ordinarily water, although any other suitable liquid heating medium may be used, is introduced into the rollers I from any suitablereservoir 2,

` through pipe 3 having an extension d extending into the rollers I. The rollers! are rotatably supported at one end .5 in any suitable bearing 8 and are rotated by power. from any suitable source at their ends 5. The other end of the rollers, designated 1, is rotatably supported in any suitable bearing B and has an inside diameter 'somewhat larger than that of pipe d in orderto permit the heating uid to pass out of the roller I continuously into any suitable receiver 9;'

If desired, pipe 4 may be supported at. its inner end by any suitable means, e. g., by supporting it by the roller I' adjacent end 5, in order to prevent sagging, or any other suitable/means for preventing sagging may be used. l

Hot water is ,continuously` introduced into the vroller-I; its exact height, that is, the constant level of -watr which is maintained within the roller, may be controlled either by the rate ofv accesso quently the hot water circulates freely and sef necessary, the lowering, for example,

sequent saving in fuel cost.

production rates.

oi' the opening between pipe '4 and end i of the roller, or both.

To secure a more even temperature distribution across the rollerfpipe d is provided with a series of holes Illthroughout that portion of 5 the pipe which is enclosed by the roller to distribute the hotv water more evenly throughout the interior of the-roller. Holes i0 may be varied in size and arrangement depending on` the .width and/or thickness of the film to be dried. l04

These holes may be situated on any or all sides of pipe d, but, preferably, only on the uppermost side thereof. The size and spacing of the holes are then properly adjusted and a suiiicient head of water furnished; a series of hot water 15 and cause the heating liquid to impinge directly 25 against the upper inside surface of the roller. To obtain this edect, it may be advisable to bend l the pipe 4v upward adjacent roller end 'I so as to `raise it substantially above the water level throughout. J 30 Referring to Fig. 2, it will be seen that when the roller is full of water, that portion of the water adjacent to the interior surface I2 of the roller might have a tendency to travel around with the relier, while the Awater adjacent to pipe 35 d would circulate out of the rollerthrough the exit pipe 1. Thus, there would be' a ring, adjacent to surface I2, of comparatively cold water, which would not. circulate. Under these conditions, the drying of the nlm depends a great deal on ambient air conditions in the drying room. which conditions are subject to considerable iluctuation. 'With the roller only partially full of water, there is no opportunity for the water to travel around with the roller, and conse-[4*5 cures even heating eifects throughout the roller. Operating in this manner, the water also exerts a scrubbing action on the interior surface of the roller.v Due to these advantages, it is `even possible to operate the dryer rollers at lower temperatures than have heretofore been conside the neighborhood of 6 to 8 degrees C.. with a con- A further advantage of lthe invention resides in a very simple construction, as compared with prior'art construction using rollers adapted to be completely lled with water and requiring perect Joints, necessitating very exact i r in order to prevent leakage of the water.

When regenerated cellulose nlm is dried accordingto this invention, the product obtained is substantially completely and uniformly dat and of substantially uniformv moisture content throughout. Because of its uniform iiatness, illiiil run through subsequent processing operations, such as coating, slitting, laminating, printing, and others, is so .processed at less cost and ter im Moreover, sheets or nlm so dried. are well adapted to use in modern high vspeed mapping machinery and insure rapid operation and perfect packages. Furthermore, this method lof ldrying 7laosaess oi' its emcient and uniform application of the heating medium permits operating the drier rollers at a somewhat lower temperature. This results in fuel economy and in a better lm since it is known that the higher the drying temperal as opposed to the fittings required in heating under conditions where the rollers are full of heating medium. This secures a very considerable economy in design and in maintenance and power consumption.

VWhile the invention has been described with respect to the use of a liquid heating medium, speclcally water, it may be advisable under certain conditions to introduce steam as the heating medium.` In such event, the steam must be used lunder conditions which cause it to condense to water continuously, the water, after vthe drier rollers have become partially lled to a sumcient level, being continuously removed Vin the same way as when hot water is introduced into the rollers as the heating medium.

Any variation or modiication which conforms to the spirit of the invention is intended to be included within the scope of the claims.

I claim:

1. A roller for drying gel pellicles comprising a hollow cylindrical body, means tor passing a heating liquid into said hollow body, said means having a plurality of openings for evenly distributing said liquid along the length of said body, and over-iiw means for preventing said liquid from occupying more than 50% and less than 40% of the volume of said hollow bodv, said plurality' of openings all being positioned in the upper surface of the rst named means so that the liquid issuing therefrom will be directed against unlled sections of said "e m" f whereby said roller is maintained at a constant, uniform temperature throughout.

2. Inv an apparatus for making cellulosic pellicles, means for forming a gel pellicle of nonibrous, cellulosic material, a plurality of rollers for drying said pellicle, said rollers comprising hollow cylindrical bodies, means for evenly distributing a heating liquid along the internal length of said bodies, and axially positioned overow means for preventing said liquid from occupying more than 50% and less than 40% of the volume of said bodies, said iluid distributing means comprising an element having a plurality of openings all of which are positioned` in the vupper surface of said element so that the liquid issuing therefrom will be directed against uniiiled sections of said bodies, whereby said rollers are maintained at a constant. uniform temperature throughout.

3. In a'method for the production ci noniibrous transparent, cellulosic pellicles of bicellular structure from aqueous alkaline celiulosic solutions which are coagulable in an acid coagulating bath, and which are Vsubjected. while in their coagulated or regenerated gel state to puriication, the step which comprises removing the moisture from said gel pellicles by passing the wet pellicles into contact with a rotating. heated, cylindrical surface which is maintained at a constant uniform temperature by maintaining a body of heating liquid solely in contact with the lowermost 40% to 50% of the internal side of said surface. and spraying the internal upper unnlled portion of said surface with a heating liquid throughout the length thereof.

DAVID E. EDWARDS.

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