US3058151A - Cellulose film treating system - Google Patents

Description

Oct. 16, 1962 c. J. GONSALVES 3,058,151

CELLULOSE FILM TREATING SYSTEM Filed Aug. 30, 1960 IN V EN TOR.

CONRAD J OSEPH GONSALVES BYE; 2

ATTORNEYS United States Patent 3,058,151 CELLULOSE FlLM TREATHNG SYSTEM Conrad Joseph Gonsalves, Arnhem, Netherlands, assignor to N.V. Onderzoekingsinstituut Research, Arnhem,

Netherlands, a corporation of the Netherlands Filed Aug. 30, 1960, Ser. No. 52,853 Claims priority, application Netherlands Sept. 26, 1956 Claims. or. 18-15) This invention relates to a cellulose film treating system, and relates more particularly to a method and apparatus for the treatment of sheets, films and small ribbons of cellulosic material in continuous form.

Cellulosic sheets, films and small ribbons, hereinafter referred to as films, are normally produced by extruding a suitable cellulosic solution through a narrow slit or extrusion 'die of predetermined size and shape into a bath of liquid where coagulation or regeneration of the cellulosic solution takes place. While the method and apparatus of this invention are advantageous in the treatment of all kinds of films, they will be described in con nection with the treatment of regenerated cellulose films produced from viscose, but it is to be understood that this invention is not to be limited thereto.

In a prior method of producing regenerated cellulose film, a viscose solution is extruded under pressure through a suitable orifice, such as a narrow slit or die of the desired shape, under the surface of a bath of coagulating liquid. From the coagulating bath, the resultant film is subjected to several subsequent operations; including purification and finishing baths, usually over a system of guiding members in said latter baths so that the film passes therethrough in a zig-zag path. The film is then taken up on a suitable Winding device.

This and similar methods often have the disadvantage that the film leaving each bath drags along from the bath an adherent liquid mantle. It is undesirable for several reasons that the liquid is taken along. Thus, the liquid which is taken from the bath must be replenished by new liquid by an amount which is generally greater than the amount required to replenish the bath as a result of the treatment of the film. Moreover, a part of the liquid taken out of the bath by the film will enter into the next treatment bath as a result of which this treatment bath will be exhausted unduly rapidly. The latter will be more evident in the case where, for instance, an acid and an alkaline bath directly succeed each other. It is also undesirable for the film to carry along bath liquid for the adherent liquid is never distributed over the film in a uniform manner. Furthermore, the contacting time during which the film is subjected to the action of the bath liquid will not be the same in such a case for all parts of the film, and also the mechanical stress on the film is also uneven. As a result of this, difierences in properties will occur between different parts of the film.

In order to overcome all of the foregoing disadvantages, methods and devices have been proposed which were aimed to limit the quantity of liquid which was taken out of the bath. For example, it was proposed to pass the film as the film left the bath between two wipers made from a flexible material. In another expedient the film was passed through a pair of squeezing rollers to squeeze out the excess of liquid. Both of these expedients had disadvantages. Thus, by the necessary contact between the wipers or the squeezing rollers and the film the danger was present that the film will be damaged. These damages were caused by unevenness in or at the surface of the wipers or rollers by which pits or scratches were formed in the film surface.

Another disadvantage consists in that the wipers or the squeezing rollers give rise to an increase in tension in the moving film which tension increase is detrimental to the film. In spinning a film from viscose, the film leaving the coagulating bath is still soft; accordingly, it is desirable to keep the tension of the film as low as possible to prevent undue strain thereon.

It is accordingly an object of this invention to provide an improved method and apparatus for preparing film which will be free from the foregoing and other disadvantages.

Another object of this invention is the provision of an improved method for preparing film wherein the film leaving a treating bath has the liquid removed therefrom without damage to the film.

A further object of this invention is the provision of an improved apparatus for removing liquid from film leaving a treating bath without damage to the film and without undue tension thereon.

Still another object of this invention is the provision of films having characteristics of uniformity and which are free from mechanical damage.

Other objects and advantages of this invention, together with certain details of construction and combinations of parts of the apparatus, will appear from the following detailed description.

The above objects are accomplished in accordance with this invention by passing the film through the liquid coagulating or treating bath at high velocity, preferably at a velocity of more than meters per minute, and then, on leaving the bath, passing the film freely between a pair of plates which extend across the whole width of the bath or at least are of substantially the same width as the film. The plates extend partly into the bath liquid at an angle to the surface thereof, and form, at least with their lower edges, a narrow slit-shaped passage for the film.

It has been found that with a suificiently narrow adjustment of the slit and a sulficiently high film velocity at very satisfactory stripping of the adherent liquid mantle from the film is obtained. However, the vertical distance between the plates should be such that any direct contact between the film and the plates is avoided so that no danger exists for mechanically damaging the film.

In addition to the holding back of the adherent liquid on the film, it also has been found that there is produced a very slight increase in the film tension. in many cases, however, the film tension is considerably less than in the case where no measure whatsoever is taken in order to remove the adherent bath liquid.

It is necessary that the plates reach partly into the liquid of the bath and partly extend above the liquid surface thereof. The advantages of applicants invention will not be obtained if the plates are entirely submerged in the liquid or if they extend entirely above said liquid.

It has been surprisingly found that the narrowest slit width S between the plates may not exceed a certain limit C If the width S of the slit remains below this limit C then on increasing the film velocity V there will be reached a point where the liquid mass present between the plates will suddenly disappear. Above this critical film velocity there is a change in the flow pattern of the liquid in and around the slit, and it appears that the plates surprisingly wipe almost the entire adherent liquid mantle from the film. 3

It has been found that this effect is obtained at a film velocity which meets the mathematical relation wlierein S represents the width of the slit, i.e. the distance between the plates at the point Where the slit is formed, which always has to be less than a critical value C and wherein C and C represent constants which in turn are functions of the thickness of the film, the nature of the surface of the film and the plates, the shape of the plates, the specific gravity and the viscosity of the liquid.

In practice, the constants C, and C may be easily determined by one skilled in the art. For this purpose the width S of the slit is first varied at one definite high film velocity V until the width S equaling C has been found, at which the liquid level in the slit between the plates goes down. By subsequently varying the velocity V at a narrower adjustment of the width S of the slit until there is again the situation at which the liquid level in the slit goes down, the constant C may be determined so that for this case the critical width of the slit and the critical film velocity are found. It has been found that the operable widths of the slit need not be particularly narrow, nor do they need to meet very strong requirements of accuracy. As a result a very good wiping effect is readily obtainable with simple means.

The effect of the method of this invention may be strongly influenced by the flow pattern of the liquid in the aftertreatment bath in the vicinity of the plates. Thus, it has been found that more adherent liquid is removed from the film with a less critical shape of the slit and at lower film velocities by suitably guiding the bath liquid. According to this invention it is preferred that at the lower edges of the plates the path of the liquid which does not pass the slit-shaped passage is gradually deflected.

The apparatus for treating films in accordance with the method of this invention comprises a liquid container open at the top and with means in the container for guiding the film through the liquid of the bath.

According to this invention, the apparatus is provided near the point where the film leaves the liquid container and at either side of the film path two plates extending over the whole width of said film being treated, which plates partly reached into the bath liquid and which form, at least with their submerged edges, a narrow slit-shaped passage for the film. The plates extend partly above the liquid level in the liquid container.

As has been explained these plates serve as a wiper in a surprisingly satisfactory manner at a certain adjustment of the slit width and at a certain film velocity. This effect is obtainable with flat as well as curved plates and also with parallel as Well as a diverging arrangement of said plates.

According to apparatus of this invention, the desired action of the plates as wipers may be obtained most simply and also in the greatest degree if the two plates are blade-shaped and have a form which beginning at the submerged edges of the plates gradually deflect upwardly from the film path.

It has been found that said films made by the method and apparatus of this invention show a greater uniformity and less mechanical damage than films which have been manufactured according to usual methods.

In order to understand this invention more fully, reference is made to the accompanying drawing in which:

The FIGURE is a vertical section or" an apparatus incorporating a preferred embodiment of this invention.

Referring to the figure of the drawing, a film 1 of regenerated cellulose is formed by extruding a viscose solution through a casting slit 2 which is adapted to be submerged below the upper surface of a spinning or coagulating bath liquid held in a suitable container 4. The casting slit 2 is an element of a casting head 5, diagrammatically shown, to which viscose solution is supplied from a suitable source through a conduit 6. The formed film is passed substantially vertically downward, then around guide rod 7 suitably mounted in the container 4 after which it is passed upward in an oblique path. After leaving the spinning bath the film is passed via a deflecting or guide roller 8 to and through several aftertreatment baths (not shown) and finally collected on a roller of a winding device (likewise not shown).

Two blade-shaped plates 9 and 10 are arranged across the whole width of the spinning bath or at least the whole width of the film 1 at the point where the film leaves the spinning bath. These plates 9 and 10 form an upwardly broadening slit which is closed at either side by two side walls (not shown). The plates 9 and 10 are upwardly deflected horizontally according to a gradual profile and are thinly tapered downwardly.

Specifically, where the film had a width of about 200 cm. at the plates 9 and 10 and a thickness of about 0.15 mm., and the distance between the plates, ie the width of the slit, was 0.9 mm., it was found that with a film velocity of 75 meters per minute the wedge-shaped space hounded by the plates 9 and 10 was entirely filled with liquid. At the same time a quite considerable quantity of liquid was taken along by the film.

After the film velocity had been increased to 110 meters per minute, it was found that the wedge-shaped space was entirely free from liquid and that the liquid mantle entrained by the film was hardly perceptible. This was also accompanied by an especially uniform and turbulence-free flow of bath liquid along the outer sides of the plates 9 and 10.

Film tensions measured behind the roller 8 were uniform and remained, on an average, at a lower level than the film tensions which were similarly observed in the absence of the plates 9 and 10. Moreover, in the latter case the tensions being measured fluctuated to such an extend that it was hardly possible to obtain what could be called an average film tension.

An important advantage of this invention is that it provides a simple and expeditious system of producing films having great uniformity of thickness and free from physical imperfections.

While this invention has been described with particular reference to a preferred method of and apparatus for carrying out its practice, other embodiments will be apparent to those skilled in the art. It is therefore intended to limit the invention only by the scope of the appended claims.

What is claimed is:

I. In a method of continuously passing a cellulose film through an aqueous liquid treating bath and out of the same, the steps of passing the film through the liquid at a high velocity, and before removing the film from the liquid passing said film freely through a narrow horizontal slit formed of spaced and substantially parallel surfaces extending across the whole width of the film and submerged only partly in the liquid.

2. The method of claim 1 wherein the film passes though the liquid at a velocity of at least meters per minute.

3. In a. method of continuously passing film through a liquid treating bath and out of the same, the steps of passing the film through the liquid at a high velocity, and before removing said film from liquid, passing the same freely through a horizontal slit formed of curved spaced surfaces extending across the whole width of the film and submerged only partly in said liquid, the curvature of the surfaces being such as to cause the liquid not entering the slit to be deflected.

4. A device for wet treating cellulose films comprising a container for the aqueous treating liquid, and, at a point where the treated film is adapted to leave the liquid container, two substantially parallel plates, of a width at least the width of the film, carried by said container, said plates being spaced from each other to form a narrow slit-shaped passage for the film, the construction and arrangement being such that the plates only partly reach into the liquid of the container.

5. The device of claim 4, wherein the plates are curved, such as to form a narrow slit-shaped passage, which diverges from a constant width progressively in upward direction.

6. The device of claim 4, wherein a guide for the film is mounted in the container in the prolongation of the slit-shaped passage.

7. A device for casting cellulosic films, comprising means for extruding a viscose solution into a coagulating bath to form a film, a container for holding an aqueous coagulating liquid, a guide rod for guiding said film mounted in said container and, at a point where the treated film is adapted to leave the liquid container, two substantially parallel plates, of a width at least the width of the film, carried by said container, said plates being 10 spaced from each other to form a narrow slit-shaped passage for the film, the construction and arrangement being such that the guide rod is in the prolongation of the slit and that the plates only partly reach into the liquid of the container. I

References Cited in the file of this patent UNITED STATES PATENTS 1,901,273 Taylor Mar. 14, 1933 2,062,795 Pike Dec. 1, 1936 2,536,093 Coleman et al. Jan. 2, 1951 2,536,186 Keller Jan. 2, 1951 2,659,102 Rarick Nov. 17, 1953 2,852,808 Sowter et a1. Sept. 23, 1958 2,914,419 Oganowski Nov. 24, 1959 :UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,058,151 October 16, 1962 Conrad Joseph Gonsalves It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent shouldread as corrected below.

In the heading to the printed specification, line date of priority, for "septa 26, 1956" read Sept. 26,.

(SEAL) Attest:

ESTON G. JOHNSON Attesting Officer DAVID L. LADD Commissioner of Patents

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