US2936468A

US2936468A - Apparatus for washing film

Info

Publication number: US2936468A
Application number: US579095A
Authority: US
Inventors: Robert J Iverson
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1956-04-18
Filing date: 1956-04-18
Publication date: 1960-05-17
Anticipated expiration: 1977-05-17

Description

y 1960 R. .1. IVERSON 2,936,468

APPARATUS FOR WASHING FILM Filed April 18, 1956 2 Sheets-Sheet 1 17 I8 8 Q? m lint-i 2 o :31

INVENTOR ROBERT JOHN IVERSON May 17, 1960 R. J. IVERSON APPARATUS FOR WASHING FILM 2 Sheets-Sheet 2 Filed April 18. 1956 INVENTOR ROBERT JOHN I VERSON United States Patent:

2,936, l68 APPARATUS FOR WASHING FILM Application April 18, 1956, Serial No. 579,095

8 Claims. (Cl. -93) This invention relates to treating and washing a traveling web of sheet material, particularly at high speeds. The invention will be described for continuously washing a web of gel regenerated cellulose film. However, it should be understood that the principle of operation makes this invention applicable to the continuous'liquid treatment of traveling webs in general. Washing gel regenerated cellulose film involves passing the web of film through wash tanks containing water in serpentine fashion, under rolls within the tanks and over transfer rolls above the tank. The method is not completely satisfactory due to the development of film tension caused by water drag. As the speed of the process increases, tension increases. Since undue tension may cause film breaks anddoes cause poor physical properties in the ultimate regenerated cellulose film, the standard process is not satisfactory for high speed casting of film. Furthermore, increased speeds and high solution drag promote the formation of edge folds, i.e. the tendency of the film to fold back upon itself at the running edges, thus reducing the useful width of the film.

The object of the invention is to wash impurities from gel regenerated cellulose film rapidly and effectively while imposing a minimum tension on the film. Another ob ject is to provide an apparatus for washing a traveling web of gel regenerated cellulose film, the apparatus characterized by efiiciency, simplicity and economy. Other objects will appear hereinafter.

The objects are accomplished by an apparatus for doing the following: coating the web of, gel regenerated cellulose film on both surfaces with a layer of wash liquid; maintaining the liquid in contact with the web for a period of time sufiicient to permit the diffusion of impurities from the web to the wash liquid layer; removing thecontaminated wash liquid layer from the web; reapplying a portion of the removed contaminated liquid to the web; and repeating the coating removal and reapplication steps until the desired degree of purity is obtained.

In the equipment previously described comprising a tank containing wash solution, submerged rolls within the tank and transfer rolls above the tank, the web of film passing under the submerged rolls and over the transfer rolls in a substantially vertical, alternately ascending and descending path, the present invention involves an additional piece of equipment which comprises an elongated 'L-shaped angle composed of a horizontal surface and a vertical surface placed above the tank transverse to the ascending path of the web; scraping means mounted on the horizontal surface of the angle adapted to contact a moying surface of the web and to remove liquid there: from; and means for'mixing and re-applying a portion of the removed liquid to the moving surface of the web. In preferred practice the scraping means comprises a bladehaving a width at; least equal to the width. of the web mounted on the horizontal surface of the angle, spaced from'both surfaces o'frthez'angle and extending beyond the edge of the horizontal surface of the angle. The means for mixing and re-applying liquid comprises a three-sided trough formed by dams fastened at each end of the blade in combination with the vertical surface of the angle. A substantial portion of the liquid scraped from the surface of the film flows through the space between the blade and the horizontal surface of the angle, then up through the space between the rear edge of the blade and the vertical surface of the angle into the trough. The liquid in the trough is re-applied above the blade to the surface of the moving web. A minimum of two such scraping means is required, one for each surface. However, the invention is applicable to a plurality of scrapers to obtain additional purification.

The objects and advantages of the invention will become more apparent from the following description when considered with the accompanying drawings in which:

Figure 1 is a diagrammatic illustration of a process of this invention.

Figure 2 is a view in perspective of a preferred apparatus including an illustration of the process embodying the principle of this invention.

Figure 3 is a side elevation of one embodiment of the apparatus with the scrapers shown in section, the sectional view taken along 33 of Figure 2.

Referring to the figures, a web of gel regenerated cellulose film, F, issuing from the conventional desulfuring bath (not shown) is washed by passing it under a series of freely rotatable

lower rolls

11, 12, 13, and 14 submerged within wash water in

tanks

15 and 16 and over positively driven upper rolls 17, 18, i9, 20, and 21. The rolls are disposed to carry the web in a substantially vertical, alternately ascending and descending path of travel.

Between the lower rolls and upper rolls are

scrapers

22 and 23, each disposed to contact opposite surfaces of the traveling film, F, during the films ascending path. The scrapers which are shown in greater detail in Figures 2 and 3 are each composed of an elongated L- shaped stainless steel angle 24, a stainless steel blade 25 bolted on the upper horizontal surface of the angle 24 by bolts 26 and separated from the horizontal surface of the angle 24 by shims 27 associated with the bolts. Stain: less steel dams 28 are fastened to both ends of the blade 25 to maintain the solution in the trough formed by the angle, blade and dams.

In a specific embodiment, gel regenerated cellulose film, .004 inch thick and 55 inches wide, was cast from a viscose solution in a standard casting .machine at a speed of yards per minute. After leaving the de,- sulfuring tank which contained hot dilute caustic solution, the film was washed in the apparatus described above.

The submerged rolls were placed within the tank so that the film dipped into the tank only 4 inches below the Water level. The lower scraper blade contacted the film about 27 inches above the center line of the submerged roll. The upper scraper blade was 21 inches above the lower scraper blade. The lower bladewas arched in the horizontal plane to impart a. bow of about inch per 6-foot length. The distance between center lines of submerged rolls and upper transfer rolls was 6 feet. The L-shaped angles were each 1 inches x 1%, inches x /s inch. Each blade was 1 /2 inches x 5 inch and was bolted on the horizontal surface of the angle to leave a space of inch between the back edge of the blade and the vertical surface of the angle. The blade projected an average of beyond the edge of the horizontal surface of the angle. The bite of the scraper blades into the traveling web of film, which correspondg to the displacement of the travelingweb. froma truly vertical path, was 1 to 2 inches. The bolts holding the blade to the angle were spaced 4 inches apart with .032 inch shims separating the blade from the horizontal surface of the angle. The scrapers were tilted so that the scraper blade formed an angle of degrees with the horizontal plane,

The combination of the speed of the film, the wiping action of the scrapers and the dimensions of the apparatus served to provide wash solution in the reservoir or trough above the blade, which solution was re-applied to the surface of the film. This is illustrated in Figures 2 and 3. The blade projection and the bite of the blade into the film determines the amount of liquid removed from the surface of the film and the film speed provides a velocity head that forces solution through the opening between the angle and the blade. Part of the solution never reaches the opening but remains on the bottom surface of the angle eventually draining back into the tank. From the mode of operation it is evident that the flow of liquid into the mixing trough, which is dependent on velocity head, is favored by high film speeds.

The process reduced drag on the film substantially over the standard wash process at the same speed. Furthermore, the performance of the process, evaluated in terms of purification, at 135 yards per minute compared favorably with a standard process run at only 75 yards per minute.

The surprising success of this invention may be ex? plained by the following theory, which theory should not limit the scope of the invention. After a traveling web containing impurities has passed through a Wash solution, it retains wash liquid on its surfaces. The retained wash liquid, however, is not uniformly contaminated, but is more highly contaminated closest to the surface of the web. For the sake of simplicity, we shall assume two layers of wash liquid exist on each surface of the web; an interfacial layer that is highly contaminated and an outer, more dilute layer. Washing occurs in two steps; impurities first dilfuse from the web into the interfacial layer, and then diffuse into the outer layer. However,

the higher concentration of impurities in the interfacial layer repels the further diffusion of impurities from the web. By momentarily removing both layers from the surface (by scraping), then mixing the layers (in the trough) and re-applying a portion of this mixed liquid, a more dilute layer is formed at the interface. The impurities from the web can then resume difiusion into the interfacial layer.

The dimensions of the apparatus are somewhat flexible but a useful guide is offered in the table below:

Emhodi- Preferred ment Range Over-all Dimensions:

Dip of Film into Tank, inches 4 4.3 Distance Between Lower Scraper and .Center Line of Submerged Roll,

Other factors such as the Width and thickness of the scraper blade, the shape of the shims, the bolt spacing, etc., should be selected to provide sturdy equipment While offering the minimum resistance to the fiow of liquid into the trough.

' The dimensions are selected to provide an optimum combination of washing-'eflieiency and low tension on the film-at all film speeds, and particularly at film speeds of yards per minute and higher. The clip of film into the tank, the distances between scrapers and between scraper and submerged roll, the bite of the scraper into the film and the aforementioned arch or bow in the lower scraper blade also contribute to reducing folds and wrinkles along the running edges of the traveling web of film.

The invention is useful in the washing and treating of traveling webs of sheet material, particularly washing gel regenerated cellulose film. It is extremelyuseful when floor space is at a premium. The invention provides improved washing efiiciency at high speeds without resorting to deeper wash tanks, longer wash tanksor more wash tanks.

As many widely different embodiments can be made without departing from the spirit and scope of this in vention, this invention is not limited except as defined in the appended claims.

What is claimed is:'

1. In an apparatus for continuously washing a traveling web of gel regenerated cellulose film comprising a tank adapted' to contain wash liquid; rolls within the tank adapted to be submerged in the liquid and transfer rolls above the tank, the web of film passing under the submerged rolls and over the transfer rolls in a substantially vertical, alternately ascending and descending path, the improvement which comprises an elongated Lshaped angle composed of a'subst-antially horizontal surface, and a substantially vertical surface disposed at least 4 inches above the liquid level in the tank, transverse to the as; cending path of the traveling web of film; scraping means mounted on the substantially horizontal surface of the angle to contact a surface of the traveling web and to remove liquid therefrom,. said scraping means mounted on the substantially horizontal surface of the angle in'such a manner as to provide a passage for flow of liquid between said scraping means and said substantially vertical and'horizontal surfaces to mix and re-apply a portion of the removed liquid to the surface of the traveling'web'.

2. An apparatus as described in claim 1 wherein the scraping means comprises a blade having a width at least equal to the width of the travelingweb mounted on the substantially horizontal surface of the angle, spaced from both surfaces of the angle and extending at least A inch beyond the edge of the substantially horizontal surface of the angle.

3. An apparatus as described in claim 2 wherein the mixing and re-applying means comprises a three-sided trough formed by fastening dams to each side edge of the blade.

4. In an apparatus for continuously washing a traveling web of gel regenerated cellulose film comprising a. tank adapted to contain wash liquid, rolls within the tank adapted to be submerged in the liquid and transfer rolls above the tank; the web of film passing under the submerged rolls and over the transfer rolls in a substantially vertical alternately ascending and descending path, the improvement which comprises a pair of elongated L-shaped angles, each composed of a substantially horizontal surface and a substantially vertical surface, one angle disposed at least 4 inches above the liquid level in the tank, transverse to the ascending path of the traveling film and adapted to face one surface of the film, the

other angle disposed at least 6 inches above the first angle,

transverse to the ascending path of the traveling film and adapted to face the opposite surfaceof the film; a blade having a width at least equal to the width ofthe travelcal and horizontal surfaces into said trough, said trough adapted to mix and to re-apply a portion of the removed liquid to the surface of the traveling web.

5. An apparatus as in claim 4 wherein the blade on the -lwer L-shaped angle is arched in the horizontal plane to impart a bow of about inch per 6 foot length.

6. An apparatus as in claim wherein both L-shaped angles are tilted upwardly to form an angle between the blade and the horizontal plane of up to 15' degrees.

7. An apparatus as in claim 4 wherein the L-shaped angles are disposed so that the blades displace the traveling web of film 1-2 inches from a substantially vertical path.

8. In an apparatus for continuously washing a traveling web of gel regenerated cellulose film comprising a tank adapted to contain wash liquid; rolls within the tank adapted to be submerged in the liquid and transfer rolls above the tank, the web of film passing under the submerged rolls and over the transfer rolls in a substantially vertical, alternately ascending and descending path; the improvement which comprises an elongated L-shaped angle composed of a substantially horizontal surface and a substantially vertical surface disposed above the liquid level in the tank, transverse to the ascending path of the traveling web of film; scraping means mounted on the substantially horizontal surface of the angle to contact a surface of the traveling web and to remove liquid therefrom, said scraping means mounted, on the substantially horizontal surface of the angle in such a manner as to provide a passage for flow of liquid between said scrap ing means and said substantially vertical and horizontal surfaces to mix and re-apply a portion of the removed liquid to the surface of the traveling web.

References Cited in the file of this patent UNITED STATES PATENTS McAlpine et al. Apr. 7, 1953

Claims

1. IN AN APPARATUS FOR CONTINOUSLY WASHING A TRAVELING WEB OF GEL REGENERATED CELLULOSE FILM COMPRISING A TANK ADAPTED TO CONTAIN WASH LIQUID AND TRANSFER ROLLS ADAPTED TO BE SUBMERGED IN THE LIQUID AND TRANSFER ROLLS ABOVE THE TANK, THE WEB OF FILM PASSING UNDER THE SUBMERGED ROLLS AND OVER THE TRANSFER ROLLS IN A SUBSTANTIALLY VERTICAL, ALTERNATELY ASCENDING AND DESCENDING PATH, THE IMPROVEMENT WHICH COMPRISES AN ELONGATED L-SHAPED ANGLE COMPOSED OF A SUBSTANTIALLY HORIZONTAL SURFACE AND A SUBSTANTIALLY VERTICAL SURFACE DISPOSED AT LEAST 4 INCHES ABOVE THE LIQUID LEVEL IN THE TANK, TRANSVERSE TO THE ASCENDING PATH OF THE TRAVELING WEB OF FILM, SCRAPING MEANS MOUNTED ON THE SUBSTANTIALLY HORIZONTAL SURFACE OF THE ANGLE TO CONTACT A SURFACE OF THE TRAVELING WEB AND TO REMOVE LIQUID THEREFROM, SAID SCRAPING MEANS MOUNTED ON THE SUBSTANTIALLY HORIZONTAL SURFACE OF THE ANGLE IN SUCH A MANNER AS TO PROVIDE A PASSAGE FOR FLOW OF LIQUID BETWEEN SAID SCRAPING MEANS AND SAID SUBSTANTIALLY VERTICAL AND HORIZONTAL SURFACES TO MIX AND RE-APPLY A PORTION OF THE REMOVED LIQID TO THE SURFACE OF THE TRAVELING WEB.