Patented Dec. 24, 1946 2,412,947 res PATENT OFFICE; 2,412,941 par cas'rma common or onnwnosr: scam-rs Gilbert w. Brant, Buffalo, N. Y., assignor to n. I. du Pont de Nemours A‘: Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 19, 1944, Serial No. 518,887 5 (Cl- 106—181) 1 This invention relates to improvements in the manufacture of cellulose acetate ?lm. More par ticularly, this invention relates to ‘an improved cellulose acetate composition suitable for dry casting by conventional methods, and which after evaporation of the major portion of the ‘solvent, glycollic acid, mixed others, etc., are suitable for the purposes 01' my invention. ' The amount of cellulose ether incorporated in the film-forming composition Ifnay be varied quite widely. Useful results may be obtained with as little as 0.1% based on the total weight of the can be easily stripped from the casting surface. Heretoi'ore, in the manufacture or cellulose solid comprising the ?lm-forming composition, ing surface.- Materials used for this purpose are weight unless otherwise indicated. although in some cases as much as 5% may be used advantageously without changing the essen acetate ?lms by the evaporative casting method, it has been customary to add to the casting dope, 10, tial character of the cellulose acetate ?lm. To further illustrate this invention, the fol a small amount of material to render the par lowing speci?c example is given. Parts are by tially dried ?lm readily strippable from the cast 1 usually electrically conductive in character. Example 7 When this type ?lm is used for electrical pur 16 A cellulose acetate casting solution was pre poses as, for example, covering on wires. the in pared by dissolving 74.8 parts of acetone-soluble sulation resistance is very markedly impaired due cellulose acetate (about 54.5% combined acetic to the presence of the electrically conductive acid), 0.2 part of ethyl cellulose (about 49% stripping agent. On the other hand,’ when an attempt is made to dry-cast cellulose acetate ?lm 20 ethoxy content) and 25 parts of dibutyl phth‘al ate in 300 parts of acetone. Alter thoroughly from solutions containing no stripping agent, the mixing, ?ltering and deaerating. the dope was removal of the partially dried ?lm from the cast spread out on a heated, smooth, nickel-surfaced ing surface requires so much tension that the casting plate by means or a doctor kniie to a uni ?lms are badly distorted and not infrequently are torn, and may even cause an interruption in the 25 form and constant thickness. When the solvent continuity of the process. _ It is, therefore, an object of this invention to provide a new cellulose acetate ?lm-forming com position which ls free of electrically conductive had substantially completely evaporated, the ?lm was stripped vfrom the plate and the stripping tension noted. It was iound that the tension required to strip the ?lm from the plate was only about 120 grams whereas a ?lm similarly materials and therefore capable of producing a 30 ' formed from a like composition but containing ?lm having desirable electrical properties and no ethyl cellulose or other stripping agent re without casting dimculties. A further object is quired a. stripping tension of about 250 grams. to provide a method for decreasing the adhesion Similarly it was found that by taking cellulose between freshly dry-cast cellulose acetate ?lm acetate butyrate or cellulose acetate propionate and the casting surface. Still another object is 35 the stripping tension could be markedly improved to prepare electricallynon-conducting cellulose by incorporating a small amount of ethyl cellu acetate dry-cast ?lm which is easily removable lose in the casting solution. For example, ?lm from the casting surface. Other objects will be apparent from the description thatfollows. compositions comprised of about 71% cellulose I have found that if a small amount of a wa ter-lnsoluble cellulose ether which is not com with 4% ethyl cellulose and 25% dibutyl phthal acetate butyrate or cellulose acetate propionate ' ate as a plasticizer were found to strip easily and patible with cellulose acetate is incorporated in with only about 11% of the tension required if the cellulose acetate casting solution, .the parti the composition contained no ethyl cellulose or ally dried ?lm i'ormed therefrom is easily stripped 45 other stripping agent. Likewise a cellulose ace from the casting surface with greatly reduced tate composition containing 4% benzyl cellulose tension. ' ‘ was found to strip with only about V3 of the ten By the term “cellulose acetate” as used sion required to strip a similar ?lm containing throughout this speci?cation, I not only include no benzyl cellulose or other stripping agent. the simple ester but cellulose acetate mixed esters Not only does a small amount of the water? so long as the substituent groups are predomi insoluble cellulose ether greatly improve the nantly acetate. strippability ‘of cellulose acetate ?lm from metal Any of the cellulose ethers which are insoluble casting surfaces, such as nickel, chromium, stain in water and incompatible with cellulose acetate, less steel, etc., but the ?lm produced has good e. g., ethyl cellulose, benzyl cellulose, cellulose 55 slip on its casting surface side. This is another 9,412,947 3 , . important advantage of this invention because cut sheets of ?lm piled up or a roll of ?lm can be separated from the adjacent surfaces with much less di?iculty than was heretofore possible . 4 - a cellulose acetate con?linlnl. as a strip agent, from 0.1% to 5% of a water-insoluble cellulose ether not compatible with cellulose acetate. 2. An organic solvent, dry casting solution of a cellulose acetate containing, as a strip agent, from 0.1% to 5% or ethyl cellulose. lose acetate, particularly if plasticized, are usu 3. A dry casting solution of cellulose acetate ally sized with a size containing electrically con dissolved in acetone and containing, as a strip ductive materials in order to obtain enough slip agent, from 0.1% to 5% of a water-insoluble to cause' adjacent surfaces to slide and wind up without wrinkling and to‘ prevent sticking or 10 cellulose ether not compatible with cellulose acetate. ‘ blocking. Furthermore, the absence of an elec 4. A dry casting solution of cellulose acetate trolyte in the cellulose acetate ?lm, makes it and a plasticizer dissolved in acetone and con generally suitable for electrical purposes where taining, as a strip agent, from 0.1% to 5% of high insulation resistance and high dielectric in the case of many ?lms. Thin ?lms ‘of cellu strength are needed. As many apparently widely different embodi ments of this invention may be made without de parting from the spirit and scope thereof, it is to be understood that this invention is not lim ited to the speci?c embodiments thereof except :0 as de?ned in the appended claims. I claim: 1. An organic solvent, dry casting solution of ethyl cellulose. . 5. A dry casting solution consisting of 74.8 parts by weight of acetone-soluble cellulose acetate, 25 parts of dibutyl phthalate, 0.2 part of ethyl cellu lose, and 300 parts of acetone. GILBERT W. BRANT.