US2130149A - Process for the production of cellulose ester foils or sheets - Google Patents

Description

Sept. 13, 1938.

PROCESS FOR THE PRODUCTION OF CELLULOSE ESTER FOILS OR SHEETS Filed March 6, 1956 swam ow Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF CEL- LULOSE ESTER FOILS 0R SHEETS Deutsche Goldvormals Roessler, Germany Application March 6,

und Silber Scheideanstalt,

Frankfort-on-the-Main,

1936, Serial No. 67,553

In Germany March 6, 1935 6 Claims.

The invention relates to a process and apparatus for the production of cellulose ester foils or sheets, and more particularly to the production of such foils in a plurality of layers by pouringmethods.

In the past, efforts have been made to produce multiple layer cellulose films by pouring a layer on a previously poured and dried layer. This process, however, has required a long period of drying for each layer, and it has been impossible to carry it out except by the use of diiferent solvents and different cellulose derivatives for each individual layer. It has been difiicult in such processes in any event to avoid solution of the .base layer by the solvent present in the liquid material which is being poured on to form the second layer.

According to the present invention, a completely homogeneous foil or film is obtained by first forming a base by the wet pouring method from a cellulose ester solution and precipitating this base, then pouring a second layer on the first layer, precipitating the second layer in a suitable bath, and then washing and drying the product. In the same manner a plurality of layers may also be applied.

It is particularly advantageous to pour the second layer on the base layer at the time when the base layer, through the action of the precipitating bath, has just attained a state of nascent stability of form, that is, when it is no longer subject to deformation by slight external forces. Particularly good adhesion of the layers is ob tained in this manner. We believe that such adhesion is produced by the fact that the colloidal chemical state of the base layer at this particular period in its formation permits the newly poured layer of solution to combine favorably with the material of the base, but prevents excessive penetration of the solvent of the solution being poured on into the base because of the high amount of precipitant in the base, so that the base layer itself is not dissolved or softened to a suificient extent to be injured.

Various modes of carrying out the process of the present invention, and apparatus for that purpose, will be described. For example, according to one modification, the cellulose ester solution may be poured on an endless band and then passed through a precipitating bath to form a base layer, and then the second layer may be applied to the base while it is still on the support. The two layers are then passed through the precipitating bath until sufficient precipitation has occurred to give stability of form t0 the fi m, and

the two-layer film is then withdrawn from the bath and passes to the washing and drying apparatus. According to a second modification, however, the first layer is poured on a support, then when it reaches the condition of nascent stability of form is removed from the support and itself employed as the support for the formation of further layers which may be applied to one or both sides. This method is particularly advantageous inasmuch as it submits the first layer to the action of the precipitating bath from both sides, so that this limiting layer, particularly in a multiple layer film, is precipitated homogeneously with the layers on both sides thereof.

The base. layer which serves as a supporting layer may also be produced by allowing the cellu lose ester solutions to pass directly into a precipitating bath.

Further objects and advantages of the invention will appear from the following description, particularly when taken in conjunction with the accompanying drawing, which forms a part thereof, and which shows apparatus for carrying out the invention.

In the drawing:

Figs. 1 to 3 show different modifications of apparatus for use in the process, diagrammatically and in section.

The arrangement shown in Fig. 1 consists of a bath F, in which a precipitating liquid is present, for example, up to the level a. In this bath are arranged three rolls or drums, l, 2 and 3 of acid proof material, arranged to rotate on parallel axes. These rolls preferably extend slightly above the level of the liquid and rotate in the directions indicated by the arrows. At the top of each roll are arranged pouring slots or nozzles 4, 5 and 6 cooperating with the rolls l, 2 and 3 respectively. 1, 8, 9 and I0 represent idler rolls, the purpose of which in guiding the film will be described below. We may also provide rollers W1, W2 and W3 engaging the periphery of the rolls I, 2, and 3 respectively. These rolls may be positively driven and thus serve to drive the rolls 5, 2 and 3.

They are arranged at points angularly spaced from the nozzles in a direction opposite the direction of rotation of the rolls l 2 and 3. Their function as pressure rolls will be described below.

In the use of the device shown, the film moves in the manner shown by dot and dash lines and in the direction indicated by the various arrows. A layer of cellulose ester solution, for example a solution of cellulose tri-acetate, is poured through the nozzle 4 onto the surface of the d um The film thus spread on the surface moves with the rotation of the drum into the liquid of the precipitating bath. When the film thus formed is sufficiently precipitated to have a certain amount of stability, it moves off the roll as indicated by the dot and dash lines and passes to the roll 2, on which it is pressed by the roll W2. The nozzle 5 then forms a second layer on the first layer or base which is itself in a nascent state of stability. The two superposed layers are then carried by rotation of the drum 2 down into the liquid of the bath, where the second layer is precipitated. The film then passes over the idler roll I to the drum or roll 3, where, as will be observed, the uncoated side of the base layer is exposed. The roll Ws'presses the two layers against the roll 3. The nozzle 6 applies a layer to the oppositeside of the base layer, and the three-layer film is then carried down again into the solution, over the rolls 8 and 9, and up over the guide roll I out of the bath. From this point the film is carried over to the washing'baths and the drying devices, which may be of any known type.

Preferably the rolls I, 2 and 3 are so arranged that their relative speed may be adjusted, so that variations in operating conditions can be compensated for. The distance between the rolls is so chosen that the layer produced on any roll reaches the next roll in the required state of stability of form, that is, the state in which it has just reached sufiicient stability to resist slight outside forces tending to deform it.

The advantage of the rolls W1, W2 and W3, which rotate in directions opposite to the rolls I, 2 and 3, is that by means of these rolls the film is freed of any precipitating liquid, which might adhere thereto from the bath, before it reaches the nozzle, and also is pressed smooth before the next layer is applied by the succeedin nozzle. Furthermore, it is not necessary to provide all of the rolls I, 2 and 3- with highly polished surfaces, as only the roll I on which the solution is poured directly requires such a surface. By suitable construction of the surfaces of the rolls, various surface effects might be obtained.

Obviously, we do not wish to be limited to the specific arrangement described above. For example, the first film layer or base might be produced in a different precipitating bath, or each pouring step can be carried out in a separate bath.

The following example indicates the manner in which the invention may be carried out using the apparatus shown in Fig. 1.

Example I A primary cellulose tri-acetate solution, having an ester content of about 14%, which may be produced according to known processes, is applied by the nozzle 4 on the drum I to a thickness of about 0.08 mm. The precipitating bath consists of an aqueous solution of acetic acid. The film so produced passes from the roll I in the manner described to the roll 2, and there a second layer is applied by means of a pourer or nozzle having a slot of 0.28 mm. width, so as to form on one side of the thin film a thicker layer of the same material. After passing under the roll I the film then passes beneath the nozzle 6, where a still thicker layer is poured on, since this nozzle has a width of 0.45 mm. The rolls 8, 9 and I0 then carry the film on for further treatment, as for example washing and drying. The final dried product has a thickness of 0.08 mm.

The operation may be carried out at a relatively high speed.

Fig. 2 shows a second form of the device for carrying out the invention. Rolls I3 and I4 extend slightly above the level of the liquid in the bath F and are provided with nozzles I5 and I6 respectively. Idler rolls II, I1 and I8 serve for Example II A tri-acetate film of 0.1 mm. thickness is produced inia separate precipitating bath. While it is still moist and in a state of nascent stability of form, it passes over the idler roll II and beneath roll I2 to drum I3. Nozzle I5 applies a layer of a thickness of 0.22 mm. of a 12% solution ofcellulose tri-acetate. The resulting film is then carried by the roll l3 into the precipitating solution, for example a 15% solution of acetic acid in water. The resulting film passes to the drum I4 beneath the roll W, where a second layer is applied by the nozzle I6 on the opposite side of the base film. This layer then passes through the coagulating bath beneath roller I1 and out over roll I8. The resulting product is washed and. dried and a film of a thickness of 0.06 mm. is produced.

The invention above described is of special importance, as it has heretofore been impossible to produce these films in a single operation by the wet pouring method. The precipitation of a thick poured layer proceeds quite slowly, and especially irregularly. In the past therefore it has been necessary to produce thin films separately and then to cement these together with suitable apparatus. Such a method is much more expensive than a single continuous process, and it is practically impossible in this fashion to produce films of true mechanical or optical uniformity. It has been almost impossible to avoid the production of air bubbles or other faults in the films, and this lack of uniformity increases the greater the number of layers required.

The present invention, however, makes it possible to produce films even of considerable thickness by a wet pouring method in a single process, such films being absolutely homogeneous and adherent. Even in the production of films of ordinary thickness, for example of 0.02 to 0.04 mm., the present invention makes it possible to operate more rapidly, as a part of the precipitation of the applied layers may take place in the washing bath. Thus with a machine of the same size it is possible to operate at a higher speed and with greater efiiciency.

The cellulose ester solutions used in the process preferably have an ester content of from 8% to 25%.

According to a further feature of the process, it is possible to produce films having strata of different characteristics for special purposes. For example, various color effects may be obtained by coloring one or more of the solutions which are poured by the nozzles to form the layers of the film.

An arrangement for producing such afilm is shown for instance in Fig. 3. This consists of a bath F of precipitating material in which two rolls I9 and 20 are mounted extending above the level of the liquid. An endless band 2|, for example of metal, passes around the rolls [9 and 2D and beneath an idler roll 24. Nozzles 22 and 23 cooperate with the rolls l9 and 20 respectively. An idler roll 25 is also provided. This device is used for instance as described in the following example:

Example III A primary cellulose tri-acetate solution, with an ester content of about 14%, and containing also of copper bronze, is poured by the nozzle 22 on the metal band 2|. This band carrying the layer so formed then dips into the solution, which may be a 25% aqueous solution of acetic acid. The layer passes around the drum 20 on the band 2| and beneath the nozzle 23, where a tri-acetate solution which contains an addition of some suitable pigment is poured onto the first firm. The film then passes under the roll 24 through some of the precipitating liquid, and the two-layer film is there stripped ofi of the band 2 l, and led ofi over idler 25 to the washing and drying mechanism. A film having a metallic appearance, with a brilliant lustre on one side and a dull lustre on the other, is obtained.

While we have described some embodiments of our invention, we wish it to be understood that we do not intend to limit ourselves thereby except within the scope of the appended claims.

We claim:

1. A process for the production of cellulose ester foils, comprising pouring a cellulose ester solution to form a film, subjecting the film so formed to the action of a precipitating linuid until the film has attained a nascent stability of form, and then pouring a solution of the same cellulose ester on the film to form a layer thereon.

2. A process for the production of cellulose ester foils, comprising forming a film of cellulose ester,

subjecting the said film to the action of a precipitating liquid until it has reached a state of nascent stability of form, and then pouring a solution of the same cellulose ester on the film to form a foil therewith.

3. A process for the production of cellulose ester foils, comprising pouring on one side of a film of cellulose ester, which has been precipitated by the wet method to a state of nascent stability of form, a solution of the same cellulose ester, and precipitating such solution.

4. A process for the production of cellulose ester foils, comprising pouring on one side of a film of cellulose ester, which has been precipitated by the wet method to a state of nascent stability of form, a solution of the same cellulose ester, precipitating such solution by the wet method to form a layer, pouring a solution of the same cellulose ester on the other side of such first film, to form a layer thereon, and precipitating by the wet method said second layer.

5. A process for the production of cellulose ester foils, comprising pouring a film of cellulose ester, subjecting the film so formed to the action of a wet precipitating liquid until the film has attained a nascent state of stability, then pouring a solution of the same cellulose ester upon the film which has attained a nascent state of stability, and precipitating such solution by the wet method. 1

6. A process for the production of cellulose triacetate foils comprising forming a film of cellulose triacetate, subjecting the film so formed to the action of a wet precipitating liquid until the film has attained a nascent state of stability, then pouring a cellulose triacetate solution upon the film which has attained a nascent state of stability and precipitating such solution by the wet method.

KURT NAGEL. LUDWIG SCHEFFER.

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