US2236648A - Process for the production of foils or films of cellulose triacetate - Google Patents

Description

April 1, 1941. NAGEL r 2,236,648

PROCESS FOR THE PRODUCTION OF FOILS 0R FILMS OF CELLULOSE TRIACETATE Filed March 6, 1936 Kuer M651.

JOSEF 65/5 [VOW/6' SCHEFFEE 9 KIfL Men/5e Patent ed Apr. 1,1941

' rnocnss FOR THE PRODUCTION or FOILS on FILMS or cnnwnosn mmcnra'm Kurt Nagel, Josef Seib, Ludwig Scheifer, and Karl Werner, Mains-Mombach, Germany, assignors, by mesne assignments, to Chemical Marketing during its coagulation.

Company, Inc., New York, N. Y.

Application March 6, 1938, Serial No. 67,554

In Germany March 6, 1935 9 Claims.

The present invention relates to a process and able permanence of form so that damage by tearing during the process is avoided.

Further objects and advantages of the invention, will appear more fully from'the followin description particularly when taken in conjunc- 'tion with the accompanying drawing which tating agent. No practical procedure for producing films or foils by this method has heretofore been discovered. Products of this nature have generally been cloudy or turbid, and at times brittle, and their surfaces have been marked by longitudinal or transverse striations which rendered them unfit for any practical use.

We have discovered that these defects can'be avoided by the process to be described below. This process consists essentially in using solutionsof cellulose triacetate in which the celluv lose triacetate contains at least 59% acetyl, calculated as acetic acid, in combined form, and in which the catalyst .has been rendered inactive directly after the termination of acetylation. Furthermore, the precipitating liquid into which the cellulose triacetate is introduced contains not more than and preferably from 7% to 20% of acetic acid. A film produced in this manner, after it has been washed and dried, has a surface'which'ls free from striations and cloudiness. In no other manner can these defects be avoided. Q

In carrying out the process in practice, solutions of cellulose triacetate whichhave been primarily stabilized are suitable.

A further feature of the process is that the strength and lustre of the films is considerably increased, if the temperature of the precipitating bath is kept as low as possible, and especially below C. Where very low temperatures are used; a pouring device in the nature of a slotted nozzle is preferably used, because of the tendency forms a part thereof, and which discloses an apparatus for carrying out the invention.

In the drawing:

Fig. 1 shows a portion, diagrammatically and in section, of anapparatus' forcarrying out the invention.

Fig. 1a shows a continuation of the same device, the right hand side of Fig. 1a corresponding to the left hand side of Fig. 1.

As shown in the drawing, the apparatus comprises a bath of precipitating liquid in which is arranged a roll 9 which extends above the level of the surface of the liquid. A nozzle, such as a slotted nozzle I0, is arranged'adjacent the top of the roll 9. Within the bath l are arranged idler rolls ll, 12, i3. Washing bathsZv and 3 are arranged as shown in series with the bath I. A roll i4 is arranged between baths 5 and 2 and a roll 20 between baths 2 and 3. In the bath 2 are arranged idler guide rolls I 5, l6, l1, i8, i9 and in the bath 3 guide rolls 2!, 22, 23. The drying device 4 consists of a substantially closed chamber having an inlet 6' and an outof the solution which is being poured to solidify.

Since at low temperatures the rate of precipitation is reduced considerably, it is possible for the adjacent cells of the cellulose to arrange themselves in parallel relation throughout-the film. this arrangement being essential both for strength and for complete transparency to light. It is especially advantageous to stretch the film If the above conditions are observed it is possible to obtain a completely precipitated foil from a solution which contains 10% or more of cellulose triacetate. Solutions of such high concentration produce a foil which .has a considerlet If. In one wall of the drying chamber 6 adjacent the bath 3 is arranged a rol1-24 and inthe opposite wall a roll 32. Within the chamber are a plurality of guide and pressing rolls 25,

2t, 21, 28, 29, 30and 3|.

Next to the drying chamber 6 are arranged a pair oi washing baths 5 and 6- (Fig. la). Bath 5 is arranged 'adjacentthe roll 32, and between baths 5 and 8 is a roll 38. Within the bath 5 ,are guide rails 33, 34, as, as, 31 and in the bath I 6 are guide "rolls 39, 40, ll. 1 represents the second drying chamber having an inlet 1' and an outlet 1", this being a closed chamber in one wall of which adjacent the bath 6 is arranged a roll. 42. Within the chamber are guide rolls 43, ll, 5, l8, l1 and I8, and adjacent theother wall of the chamber is a guide roll '50. Adjacent the outlet slot- 5i near the guide roll 50 in the wall of chamber 1 is a take-up roll. or reel 8 driven in a suitable manner by 'a friction clutch.

The use of this arrangement will be clear from the following examples:

I Example I The starting material is an a'cetylated solution of cellulose triacetate, the cellulose triacetate containing about 61% acetyl,calculated as acetic acid. This material is produced by the use of suitable quantities of a weak catalyst. The weak catalyst is first neutralized, the excess acetic anhydride is converted into approximately 95% acetic acid, and the solution is stabilized by heating for several hours at 80 C. to 100 C. This solution which contains about 15% cellulose triacetate is filtered and de-aeZ'atedL It is then fed to the nozzle I so as to be spread in the form of a film on the roll 9. The film so produced is carried by the roll 9 into the bath I containing a 7% aqueous solution of acetic acid. If a foil of a thickness of 0.02 mm. is-to be formed, the foil should remain on the roll 9 in the bath for a period of about 30 seconds so that it will attain sufilcient permanence of form to be removed from the roll 9 without injury. The concentration of the bath may vary up to about 20% acetic acid, but if this limit is ex-' ceeded irregularities in the surface of the film and longitudinal striations are likely to be produced. The bath l is maintained preferably at room temperature.

After the film passes out of the bath I it may be dried or washed in any suitable manner, preferably in the manner described below in connection with the remainder of the apparatus.

Example If An acetylated solution is produced using from to of sulphuric acid as the acetylation catalyst. The cellulose triacetate in this solution contains about 62.5% acetyl, calculated as acetic acid. The catalyst is neutralized and the excess fatty acid anhydride removed by adding 5% to 10% (calculated on the weight of the solution) of methanol chloride or formic acid. The solution is then filtered and de-aerated, while it is maintained at a temperature between 30 C. to 50 C. to avoid any undesirable increase in the viscosity. The material is expressed through a slotted nozzle, at a pressure of several atmospheres, into a precipitating solution or coagulating bath comprising a solution of acetic acid in water, which is maintained at a temperature of from 0" C. to 5 C. Because the foil is exposed on both sides to the material of the bath, 5 to 10 seconds contact with the material of the bath coagulates the foil sufiiciently so that it may be handled for passage to a further coagulating and washing bath.

With respect to the purpo es and advantages of the washing and drying arrangements now to be described, the following features of interest should be noted.

During the process, precaution should be taken to prevent any free inorganic acids, which may be formed through the splitting of easily saponifiable catalyst residues of the cellulose acetate, from passing into the precipitating bath and accumulating therein.

If desired, materials may be added as softening agents to the solution to be poured. These softening agents should be such as will not be dissolved from the material of the freshly poured foil by the precipitating agent. For example, triphenyl phosphate and tributyl phosphate may be added in amounts as high as 100% of the triacetate in the solution. Triacetine, ethyl phthalate, and the like, on the other hand, are easily dissolved by the precipitating bath.

According to the process, we have found that the removal of the last traces of acetic acid from glycerin, di-glycerin, or glucose, these agents may be incorporated in the foil before it is dried. The quantity of softening agent may be regulated by varying the concentration of such agent in the washing bath.

A further feature of the invention consists in removing the principal portion of the water contained in the foil, before the final step of drying it by heat, by washing the film with an organic solvent which is easily miscible with water but does not exert a swelling action on the film. Methanol is suitable for this step. 1 When the film is dried in this manner after treatment with methanol no creases caused by shrinkage occur on drying. Even extremely thin foils may be rolled without damage after such a treatment.

Referring now to the drawing, in which the dot and dash lines indicate the path of the film, a film formed and precipitated for example as described above in Example I may pass from the roll 9 over the rolls H, l2, l3 and I4 into the bath 3. This bath for instance may contain water for washing the film. The foil'passing over rolls I5, I 9, l1, l8, l9 and 30 then enters the washing bath 3 which may contain either water or an organic liquid such as methanol. The foil then passes over roll 24 into the first drying chamber 4. Air is blown through this chamber into contact with the film on the rolls 35 to 3|, and this air escaping through the outlet ll may be carried to a recovery device for removing any organic liquid therefrom. By regulating the humidity and fiow of the air, the amount of drying produced in the drying chamber 4 may be controlled.

The foil then passes out of the chamber over roll 32 to a bath 5 of water in which any residual acid is washed out. After being guided by rolls 33, 34, 35, 39 and 31 through the bath 5 the film passes over roll 33 to a bath 6 in which it is guided by rolls 39, 40 and ll. This bath may contain either water or methanol. When the bath contains water, water soluble softening agents such as glycerin, di-glycerin or glucose may be included and thus introduced into the foil. If the bath contains an organic liquid, it is possible to introduce either dyes which are soluble in alcohol or benzol, or softening agents such as alkyl phosphates or phthalic esters. By varying the concentration of the material and the time the foil remains in the bath the quantity of any material taken up by the foil may be regulated.

The roll 32 may be arranged so as to regulate the width of the film, so that, if shrinkage has occurred in the width of the films during the drying, they will be 'again expanded before they enter is guided by pressure and guide rolls. 43 to .iil.

The film then passes through theslot ii to the drum! where it is wound up into a roll.

By the inclusion of softening agents or dyes in the material of the bath 8 it is possible to incorporate such materials into the foil just before its final drying. However, such materials also may be included just before the intermediate drying by introducing them into the bath 3. It is also desirable to have the precipitating bath and washing baths operate on the countercurrent principle. For this purpose the individual washing baths may be connected with each with water, and then with an organic liquid other and with the precipitating bath by conduits, such as for Example 52, 53. These conduits may be provided with manually or automatically regulated valves 54, 55. By passing the water through bath 5, andthen through bath 2 to the bath l, the acetic acid dissolved from the film acts as a precipitating agent in the precipitating bath.

While we have described herein 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 I 1. A process for the production of foils or films of cellulose triacetate, comprising forming a film of acetylated solutions of cellulose triacetate, 'in which the cellulose triacetate has an acetyl content of at least 59%, calculated as acetic acid,

and in which the catalyst has been rendered inactive substantially directly after termination of the acetylation, and introducing such film into an aqueous precipitating bath which contains.

from 7% to 20% of acetic acid, washing out and drying the'film thus obtained.

2. A process according to claim 1 in which the temperature of the precipitating bath is below 30 C. 3. Aprocess according to claim 1 in which the acetylated solution contains at least 10% of cellulose triacetate.

4. In a process according to claim 1, the washing out and drying steps consisting of first washing the film, subjecting the film to a partial intermediate drying, further washing the film to remove residual acid therefrom, and then further drying the film.

5. In a process according to claim 1, said washing out step comprising introducing the film into a bath which contains water soluble softening agents, whereby such softening agents are.

' miscible with water which doesnot exert a swelling action on the film.

7. Process according to claim 1 in which said washing out step comprises introducing the film V into a bath of water and thereafter into a bath of an organic liquid miscible with water which does not exert a swelling action on the film, said last bath -containing a softening agent.

8. Process for the production of foils or films from cellulose triacetate, comprising forming a film of acetylated solutions containing at least 7 10% of cellulose triacetate, in which the cellulose triacetate has an acetyl content of at least 59% calculated as acetic acid and in which the catalyst has been rendered inactive directly after termination of. the acetylation and introducing such film into an aqueous precipitating bathwhich contains from 7% to'20% of acetic acid and which isat a temperature ofless' than 30 C., then introducing the film thus obtained into a washing bath containing water, then partially drying the film, then introducing the film into a second washing bath containing water to remove residual acid therefrom, then introducing the film into' a bath of an organic liquid which is soluble in water but which does not exert a swelling action on the film, and then drying the film.

9. A process for-the production-of foils or films of cellulose triacetate, comprising forming a film of acetylated solutions of cellulose triacetate, in

which the cellulose triacetate has an acetyl con- .tent 01' at least 59%, calculated as acetic acid,

in which the catalyst has been rendered ,inactive substantially directly after termination of the acetyla'tion and containing a softening agent which cannot be dissolved out of the film by an aqueous precipitating bath which contains 1% to 20% of acetic acid, and introducing such film into an-aqueous precipitating bath which contains from 7 to 20% 01. acetic acid, washing out and drying the film thus obtained.

' KURT NAGEL.

JOSEF SEIB. LUDWIG SCHEFFER. KARL WERNER.

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