US2370332A - Treatment of cellulose mixed esters - Google Patents

Description

Patented Feb. 27, 1945 OFCELLULOSE MIXED ESTERS' TREATMENT Howard A. Tanner, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y.,

a corporation of New Jersey No Drawing. Application March 14, 1941,

Serial N0. 383,369

13. Claims, (Ql. 106-171) This invention relates to the manufacture oi sheeting and photographic film base and more particularly to a method of treating cellulose mixed organic acid esters employed as the base of\the sheeting and film base whereby the adhesion of the sheet or film is reduced, and whereby no viscosity change is produced in the solution from which the sheet or film base is coated.

Photographic films and similar films and thin sheeting commonly employed for wrapping materials are usually prepared from cellulose esters by coating 2. solution of the cellulose ester onto a smooth coating surface and then stripping oil? the film or sheet after the solvents have been partially evaporated. In the case of single esters no great difliculty has been experiencedin stripping the formed film or sheet from the coating surface. However, when cellulose mixed organic acid esters were coated from solvent solutions and in particular from chlorinated solvents in accordance with the gel dope process described in Fordyce application Serial No. 245,023, filed December-10, 1938, now U. S. Patent No. 2,319,055, issued May 11, 1943, appreciable difficulty was experienced from time to time with the adhesion of the sheet or film to the coating surface. In some instances such adhesion caused particles of the film to be pulled away or the film to be torn with the result that the product was unusable.'

Various attempts were made to overcome this adhesion of the mixed ester sheets. It was finally found that if the mixed ester were treated with an aqueous sodium or potassium soap solution that the adhesive characteristic of the resuiting-film base or sheet. could be controlled. However, if the soap treated mixed ester were made into a coating solution in a chlorinated solvent, the improvement in adhesive control was oflset by a persistent drift in solution viscosity. It was found that on standing the solution would gradually turn to. a gel. This viscosity change greatly interfered with production of sheets by the above mentioned gel dope process. This is a phenomenon which is frequently encountered The instant application describes an improved method whereby a soap treatment may be employed to control the adhe'siveness or the cellulose mixed ester sheets as'well as theviscosity of the coating solution particularly when employing chlorinated solvents.

An object of the present invention is a method of reducing the inherent sticking tendency of films, foils and sheets made of cellulose mixed organic acid esters.

Another object of the invention is a method for reducing the adherence of cellulose mixed ester sheets to sheet forming surfaces.

A further object of the invention is a method of reducing the adherence of cellulose mixed ester sheets and film base without producing a tendency for viscosity increases in the solution from which the sheet or film base is coated.

In accordance with the invention these and other objects are attained by soaking the cellulose mixed organic acid ester in an aqueous sodium or potassium soap solution to thoroughly wet the ester with the soap solution. The soap solution is then drained of! and the ester rinsed in distilled water to remove all but a minor per 1 cent of the sodium or potassium soap solution. The washing is carried out sufficiently that no more than 1%. preferably no morethan 0.5% of the soap remains in the cellulose ester. Ordinarily at least 0.1 oi. soap is retained by the cellulose ester aftengthe washing operation. The mixed ester is now washed with artificially hardened water containing one or more soluble salts of when alkalimetal salts (such as sodium stearate) V are .present in solutions of cellulose esters in soldyents containing chlorinated hydrocarbons. The

alkali metal ion evidently initiates or catalyzes a breakdown of the chlorinated solvent liberating acidic materials which cause the ester to decompose. This eflect may be prevented by the addition of small amounts ot'a weakly acidic material such as stearic acid or boric acid to represilhe formation of alkali metal ions.

metals such as calcium, magnesium, zinc, aluminum and copper thereby changing the residual sodium or potassium soap to the corresponding metal soap which is insoluble and of weaker basicity than soaps of potassium. The ester is then drained free of th'giartificially hard ened water and thoroughly rinsed with distilled water to remove the soluble sodium or potassium.

salts. .This leaves only minor quantities of insoluble metal soaps in the ester which do not react with chlorinated solvents to increase the solution viscosity or cause it to gel. The ester is then dried and mixed in a solvent to form a cellulose mixed organic acid ester coating solu tion. The solution may then be coated by the process disclosed inFordyce et al. application Serial No. 335,336, filed May 15, 1940,-now'Patent No. 2,295,394, into films and sheeting. ifthe solvent is a chlorinated solvent of the type described therein, or by the process described in Davidson Patent 2,051,201 it the solvent is acetoneor other such non-chlorinated solvent.

I have found that by the instant method a sheet or film of a greatly reduced adherence tendency may be made. The product is of good clarity, has a pleasant smooth feel, and slides easily over itself or other surfaces and will freely strip from the coating surface. When chlorinated solvents are employed there is no viscosity change over long periods of time.

The soap solution is preferably a pure dilute solution of sodium stearate soap or a similar soap such as sodium or potassium palmitate and pieate. The concentration of soap in the soap solution does not appear critical and may be in the range of approximately .05 to The soaking treatment may vary from fifteen minutes to several hours. Ordinarily the temperature of the A soap solution may be that ofthe room although it may be raised somewhat, if desired. If chlo rinated solvents are employed the final washing is generally continued until only 0.1 to 0.2% of invwsoluble' metal soap, based on the weightof the cellulose mixed ester, remains heldby the mixed ester.

The following are typical examples of how my invention may be applied in forming thin sheetin! or film base but are not to be considered as limitations thereof.

Example I A cellulose acetate butyrate containing 19% acetyl and 27% butyryl was repeatedly .washed with distilled water after which the acetate butyrate was covered with distilled water and boiled for several hours. It was then again washed several times after which it was covered with 20 times its weight of distilled water and given a soap treatment. This involved heating the water to about 140-150 R, and then adding with stirring a quantity of warm (150 F.) l0% soap solution to result in a concentration of .05.l% sodium stearate in the water. After one hour at;

tained at a temperature of 140 F. This results in a double decomposition reaction and the residual sodium stearate left in the mixed ester is transformed to insoluble aluminum stearate and the sodium combines with the chloride. The water is then drained off and the mixed ester is washed thoroughly with hot distilled water such as described in Fordyce et a1. application Serial No. 335,336, new U. S. Patent Number 2,295,394, issued Sept. 8, 1942, the film exhibited no tendency to adhere to the coating wheel and was easily stripped therefrom.

Example II ,The treated ester was dissolved in 85% propylene dichloride and 15% methyl alcohol and coated on a clean glass surface. The cured film showed no adhesion to the glass surface and was easily stripped therefrom. Portions of the solution not coated showed no tendency to increase in viscosity or to gel.

Example 111 A cellulose acetate butyrate containing 31% acetyl and 15% butyryl was treated with the washing and soap treatment described in Example I with the exception that a 0.1% magnesium sulfate solution was employed in place of the aluminumchloride solution in which case the residual sodium stearate is changed to insoluble magnesium sulfate and the sodium removed as sodium sulfate. When thoroughly dried the ester was put in solution in a solvent mixture of 300 parts of propylene chloride and 100 p rts of ethylene chloride by mixing the ingredients with stirring at 70 C. The solution was then formed into film support by the process and apparatus deand dried. The drying operation employed is to contrifuge the mixed ester, until it contains only about three times its weight of water, after which it is placed ina drier and dried at about 180 F. to a moisture content of approximately 0.5%.

For film manufacture, the cellulose, acetate butyrate thus-treated with the soapsolutionwas dissolved ina solvent mixture consisting of by weight of propylene chloride and 10% methyl alcohol to a solvent ratio of about 6:1. Dibutyl phthalate was added as plasticizer to the extent of 25 parts for parts of cellulose ester. The dope Ml: prepared by mixing thoroughly at a somewhat elevated temperature such as scribed in Fordyce application Serial No. 335,335, now Patent No. 2,295,280. No difliculty was exp'eriencedin stripping-the formed film from the coating surface. Portions of the solution not coated exhibited no viscosity increase or gelation tendency.

Example IV -A cellulose acetate propionate containing 30% acetyl and 14.5%. propionyl was treated accord ing to the'procedure shown in Example I. This ester was made into a coating solution in 600 parts by weight of a solvent mixture composed of 53% by weight of propylene chloride and 47% by weight of amyl alcohol and 10% triphenyl phosphate based on the weight of the ester. When coated according to the process described in Fordyce application Serial No. 335,335, now U. S. Patent Number 2,295,280, issued September 8, 1942, no appreciable adherence of the film to the coating wheel was noted. The viscosity of this solution did not-increase on standing.

A small percentage of the insoluble soap based.

solution after the ester and solvent have been .mixed will not produce the same result as is obtained by soaking the ester itself in a soluble soap 1''. and was then filtered. It was found that even after prolonged standing there was no tendency for the solution to increase in viscosity or to gel. when supplied to a film coating machine 2,370,332 without diminishing other desirable character this case the solution should be formed into the sheeting soon after it is made up otherwise the solution will exhibit a. viscosity increase. Furthermore, if acetone or some other solvent which does not have a gelling action or at least as active a gelling action as do chlorinated solvents the hardened water wash may be omitted and the reduction of the adhesiveness of the sheetby the soap treatment will be obtained.

My invention is applicable toany suitable cel-' lulose mixed organic acid ester such as cellulose acetate propionate, and cellulose acetate butyrate, cellulose propionate butyrate, cellulose acetate propionate butyrate, cellulose acetate stearate, cellulose acetate palmitate, cellulose acetate laurate and the'like.

The salts employed to harden the distilled water may be aluminum chloride, stannous chloride, copper sulfate, zinc sulfate and magnesium sulfate. The zinc and tin salts are less desirable since they seem to cause haze in the'sheeting.

In the accompanying claims the term sheeting" is meant to include sheeting such as that employed for wrapping purposes as well as that employed for photographic film base.

While I have found that potassium and sodium soaps are very satisfactory for use in carrying out this invention I may'in general employ any water soluble soaps including ammonium soaps.

Iclaim:

l. The method of preparing a cellulose mixed organic acid ester coating solution which comprises treating the ester forming the base of the solution with an aqueous soap solution selected from the group consisting of sodium and potassium soap. solutions, washing the soap'from the ester with distilled water until 0.1 to 1% of soap based on the weight of the ester remains, treating the ester with artificially hardened water con taining soluble salts of one or more metals selected from the group consisting of calcium, magnesium, zinc, aluminum and copper, washing the ester substantially free from the soluble alkali metal salts, drying the ester and mixing the ester and a plasticizer in a solvent t form a solution;

2. The method of preparing a cellulose acetate butyrate coating solution which comprises treating the ester forming the base of the solution with an aqueous soap solution selected from the. group consisting of sodium and potassium soap- 3. The method of preparing a cellulose acetate propionate coating solution which comprises treating the ester forming the base of the solution with an aqueous soap solution selected from the group consisting of sodium and potassium soap solutions, washing the soap from the ester with distilled water until 0.1 to 1% of soap based on the weight of the ester remains, treating the ester with artificially hardened water containing soluble salts of one or more metals selected from the group consisting of calcium, magnesium, zinc,

aluminum and copper, washing the ester substantially free from the soluble alkali metal salts,

drying the ester and mixing the ester and a plasticizer in a solvent to form a solution.

4. The method of reducing the adhesive properties of a. cellulose mixed organic acid ester without increasing its tendency to gain in viscosity when in solution in organic solvents which comprises treating the mixed ester with an aqueous soap solution, and washing the soap from the ester with a solvent of the soap until 0.1 to 0.5% of soap based on the weight of the ester remains.

5. The method of reducing the adhesive properties of a cellulose mixed organic acid ester without increasing its tendency to gain in viscosity when in solutionin organic solvents which comprises treating the ester with an aqueous soap solution selected from the group consisting of a sodium soap solution and a potassium soap solution, washing the soap from the ester with distilled water until 0.1 to 1% of soap based on the soluble salts of one or more metals selected from the group consisting of calcium, magnesium, zinc.

aluminum and copper, and washing the ester substantially free from the soluble alkali metal salts.

6. Cellulose mixed organic acid ester sheeting containing 0.1 to 0.2% of an insoluble metal soap therein.

9. Cellulose mixed organic acid ester sheeting taining 0.1-0.2% of a magnesium soap therein.

13. The method of reducing the adhesive properties of a cellulose mixed organic ester without increasing its tendency to gain in viscosity when in solution in organic solvents, which comprises treating the mixed ester with an aqueous soap solution, and washing the soap from the ester with distilled water until 0.1-0.5% of soap, based on the weight of the ester, remains.

HOWARD A.