US2309609A - Apparatus for making regenerated cellulosic film - Google Patents

Description

Jan. 26, 1943 J. E. BRANDENBERGE'R ETAL 2,309,609

APPARATUS FOR MAKING REGENERATED CELLULOSIC FILM Filed Jan. 20, 1940 Jarquejfdwz'lz Bra/2116721662962" r Henri fem! NVENTORS @etenie .F 26,

AARATUS FGR MAKETG REGENERA CELLULOSIC FE Application January 20, 1940, Serial No. 314,810

2 Claims. (Cl. 18-15) This invention relates to regenerated cellulosic film, especially to the manufacture of continuous webs from viscose. More particularly it appertains to improvements in the guiding and handling of the sheet material through the casting machine, whereby regenerated cellulose pellicles having improved transparency, durability and surface characteristics are obtained.

The present invention is an improvement in the current method of manuiactuting regenerated cellulose film in a continuous manner from viscose as disclosed in United States Patent No. 1,548.864 (Brandenberger). This general procedure, which is particularly well suited to a commercial scale operation, involves continuous extrusion of a sheet of cellulose xanthate solution (viscose) through a narrow slot directly into a coagulating (and/or regenerating) bath, where it is kept until it has acquired the mechanical strength necessary to withstand the subsequent treatments which it receives in the following sections of the casting machine.

After the web has become strong enough, it is removed from the coagulating bath and passed through a converting smtion (usually a liquid bath which causes the cellulose xanthate to be regenerated to cellulose). After leaving the converting bath, the web is subjected to a series of treatments such as washing, desulfuring, washing, bleaching (or dyeing, depending upon the use which is to be made of the product), and washing, preferably in the order named.

These last mentioned treatments, like the coagulating and converting treatments, are conveniently carried out by passing the continuous web through vats containing the corresponding treating liquid.

It is customary to provide for softening the cellulose web by passing it through an aqueous solution of glycerol after it leaves the last Washing bath and before it is dried. As a final step in the manufacture, the cellulosic sheet material is dried (usually by passing it over heated rolls) and collected in mill rolls for storage, transportation. etc.

In transporting the cellulosic web through the baths in the aforementioned procedure, two very serious problems are encountered. .The first is the cost of the lower rolls, which must 'be made of non-corrosive material because many of the bath solutions are strongly acid. The

cheaper acid-proof materials, such as glass, cannot be used because they are brittle and/or do not have the mechanical strength necessary to withstand the driving torque, shock, etc., to

which such rolls are subjected. The second problem is the mechanical difliculty encountered in preventing leakage of the bath about the driving axle of the roll where it extends through the side of the vat or tank containing' the bath.

A proposed solution of both problems (German Patent 567,990) involves removal of the lower rolls and their replacement with small glass rods. In such an installation the stuffing boxes, packing glands and the like are eliminated. and by rigidly securing the glass guides, their brittleness is of considerably less importance.

Such an apparatus has not proved successful in high speed operations with wide webs. The webs bind upon such rods, and there is undesirable slippage ,over the top driven rolls. When this slippage over the top rolls is prevented by grooving them (in accordance with the teachings of German Patent 583,543) undesirable tensions are set up in the web and streaks, scratches and other blemishes appear in the web surface. The various physical properties, such as tear resistance, deformational changes with changes in relative humidity, and the like, of cellulose sheet prepared under such high tensions are undesirably anisotropic. In addition to this nonuniformity, low resistance to tear and the detrimental changes in dimension accompanying the variation in relative humidity, such cellulose sheet material has generally exhibited low durability and presented a surface which was either tacky or which had a tendency to stick to adjacent surfaces when stored under pressure for any length of time.

It was an object of this invention to provide improvements in the manner of, and means for, handling delicate pellicles in an aqueous treating medium. Further objects were to provide means for controlling the transportation of gel regenerated cellulose webs through the liquid of treating baths, to provide means for preparing cellulosic Webs at higher speeds than were heretofore possible or attainable, and to provide improved lower guiding members for the continuous production of cellulose film. A general advance in the art. and other objects which will appear hereinafter, were also contemplated.

It has now been found that it is possible to prepare regenerated cellulose film in a continuous and highly satisfactory manner if lower nonrotating guide members, presenting a curved surface of from 1.25 to 2.5 inches in radius to the cellulosic web, are provided in the wet end tanks. The film is adequately lubricated 'by the layer of the bath liquid between it and the guide, and

as a result it rides smoothly thereover without scratching.

It is possible, with lower guides of such dimensions and operating characteristics, to use very sensitive and accurate driving means for the supporting rolls operating out of contact with the liquid of the drying bath. Such (upper) rolls may, for instance, be equipped with individual variable speed drives of a suitable nature.

From the following description and specific examples, in which are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode fOr carrying out the invention, it will be apparent how the forev going objects and related ends are accomplished. The written description is amplified by the accompanying drawing, in which:

Figure 1 is an isometric view illustrating the manner of guiding a gel regenerated cellulose film through a treating bath;

Figure 2 is'a side elevation of the wet end tanks utilized in the production of regenerated cellulose film, the tanks being shown in section Referring now to Figure 1, the numeral I represents a continuous web of gel regenerated cellulose. The material passes over a roll I02 mounted in suitable brackets, one of which is shown at I 0|. This roll guides the web down into a treating tank I03, where it passes around a lower guide roll I04. Such rolls are ordinarily 4 inches in diameter. In this figure a showing of the liquid in the tank has been omitted for the sake of clearness.

Pass ng to Figure 2, the various treating tanks are indicated by the numerals I through I5. These vats are conventional, being of the character described in U. S. A. Patent No. 1,548,864. After leaving tank I5, the film is usually passed over drying rolls (not shown) preliminary to being wound into mill rolls: The numeral I00 shows the gel film in each of these baths. The positively driven upper guide rolls are shown at I02, and circular stationary lower guides are indicated by the numeral I e The roll I in Figure 3 is of the size commonly employed in the art. It is suitably apertured at 305 to receive means for supporting and preventing rotation of the same. While merely stopping the known lower guide rolls enables the objects-of the present invention to be satisfactorily accomplished, it is also possible to use guides of much smaller diameter, as for example, the ceramic rod I having an aperture for supporting means at 405 as illustrated in Figure 4. The use of a circular guide member may not be desirable in all instances, and it has been found that a bar having a somewhat wedge-shaped appearance, such as that illustrated at I in Figure 5, may be used satisfactorily. An aperture for connection of supporting means with the guide Jill is provided at 505.

In Figure 6 there is illustrated at GM an elongated guide having an aperture 605 for supporting means, flattened sides and arcuate surfaces (for guiding the web). Such a guide member has the advantage that it may, by being turned through an angle of 180, be reversed to present a new guiding surface. This is sometimes desirable where a portion of the guide has become roughened.

In any of .the aforementioned embodiments a slight deviation from a true circle cross section will be found satisfactory, although the true circle form has given the best results.

The type of apparatus for the manufacture of film from viscose and the like illustrated in the aforementioned patent, is equipped throughout the treatment vats with rotating lower guide members for the gel film. It has now been found that, when these machines are operated in such a way that the gel film when passing through the treatment baths is always maintained at a minimum of tension and the lower guide members in the bath are.f 1eld stationary, superior results are obtained, both in operation and in the properties of the resultant film. The best results have been obtained when the upper guide and supporting members are rotated at a surface speed corresponding to the rate of travel of the web corrected for shrinkage in the machine direction, and when the lower guide and supporting members are cylindrical in form and have a diameter in the range of 6 centimeters to 12.7 centimeters (about 2 /2 to 5 inches). These dimensions appear to be critical. The 6 centimeter diameter given above seems to be a practical minimum.

The desired speed for the upper rolls may be obtained in a satisfactory manner by individual variable speed drives capable of adjustment for the particular requirements, or the maintenance of a constant and uniform torque upon the rolls by means of a suitable form of light friction clutch between each roll and its source of power. Both types of apparatus are well known in the art.

If desired, the rotating rolls can be made to transfer the web thereover more positively by making grooves therein, by providing it with small dome-shaped button-like knobs, and by related departures from smooth surfaces.

It is essential that the surface of the lower guide members be smooth, and of such material that corrosion by the substances present in the treating bath or in the film will not take place. The surface shoulder also be of such a nature that dirt and solid materials, especially colloidal sulfur, will not adhere thereto.

A film of liquid seems to form between the surface of the web and the surface of the lower guide member during treatment. This film of liquid acts as an extremely efficient lubricant, and gives sufficient separation of the surfaces to prevent scratching by small particles of for eign material.

Preferably the lower guide members have perfectly smooth glass surfaces, but polished stainless steel, hard rubber, soft rubber, or phenol formaldehyde resin surfaces have been found satisfactory.

cellulose webs.

The tension on the film should not exceed 20 pounds for a sheet of 132 centimeters (52 inches) width. This is approximately four-tenths of a pound per linear inch of film width. The minimum tension is only that required to guide the web through the bath, and amounts approximating 3 pounds for the 52 inch sheet are common. These tensions are for an operating speed of 50 meters per minute. Variations within the scope of the invention will be readily apparent to those skilled in the art.

The surprising discovery that there was a critical curvature for a stationary lower guide surface in the wet end of a viscose casting machine with which the treating bath liquids could cooperate to furnish suflicient lubrication to enable the continuous webs to be guided thereover without undesirable tension, has led to a great advance in the processing of gel regenerated As a result,-an improved product which can be manufactured at greatly improved rates of processing and with general economies, is possible. This discovery has ledto a greatly simplified and more eflicient method of practicing the general processes described in the aforementioned United States patent. The present invention permits better tension control on the web in its passage through the treating baths. It has also materially reduced the maintenance and operating costs of this type of machine. snarling of the web around guide members has been prevented, and the formation of scratches and other surface imperfections in the finished web have-been almost completely eliminated.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in theappended claims.

We claim:

1. An apparatus for treating gel regenerated cellulose film which comprises a tank containing a treating liquid, upper and lower guide members, the upper guide members being posi 'tively driven knobbed rolls and the lower guide 2. A viscose sheet casting machine compris ing liquid treating baths and means for guiding the continuously cast cellulosic sheet in a sinuous path therethrough, said machine having upper positively driven knobbed guide members above and lower smooth guide members in the liquid baths, which lower guide members are non-rotating and 4.5 inches in diameter.

JACQUES EDWIN BRANDENBERGER. HENRI FENAL.

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