US2275716A - Process of casting plastic sheeting - Google Patents

Description

, continuous.

. Patented Mar. 10, 1942 P BOCESS OF CASTING PLASTIC SHEETING Gustave B. Bachman, Lafayette, Ind., and Carl N. Behrndt, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application September 15, 1939, Serial No. 295,088

3 Claims. (Cl. 106-181) This invention relates to the casting of sheeting from plastics, such, for instance, as cellulose esters, methacrylate resins, polyvinyl acetal resins, polyvinyl acetate, or butyl resinic lactone. The preparation of butyl resinic lactone is described in the copending application of J. G. McNally and R. H. Van Dyke, Serial No. 248,496. The casting of sheeting, such as photographic film base, wrapping tissues, etc., from plastics, such, for instance, as cellulose esters, is well known. A solution of plastic and plasticizer, in a volatile solvent or solvent mixture, is spread in a thin, uniform layer on a, highly polished the dope by adding it to the plastic during the surface, and the solvent allowed to evaporate.

In the most common form of casting, the plastic solution or "dope is spreadon a nickel or chromium-plated surface which forms the periphery of a rotating wheel, so that the casting process is The wheel is of large diameter, so that by the time the wheel has made approximately, three-fourths of a rotation after the spreading of the dope on its surface, the solvent has evaporated to a sufficient extent to set the resulting film and permit of stripping it from the casting surface. A certain amount of tension is usually necessary to strip the film from the casting surface. In some cases the tension required is so severe that the film is damaged in stripping, small pieces being pulled from the surface of the film, or the film being torn.

We have discovered that the stripping of plastic sheeting from the casting surface may be facilitated, so that littleor no tensionis required to strip it, by incorporating in the surface of the sheeting adjacent to the casting surface a dialkyl ester of sulfosuccinic acid, either in its free form or in the form of an alkali metal salt, e. g. the sodium salt. The dialkyl esters of sulfosuccinic acid, and their salts, are described in U. 8. Patent 2,028,091. For example, the diamyl, dihexyl,

I paringthe solution of sulfosuccinic acid dialkyl ester, or its salt, may be acetone, methanol, or any other volatile solvent for the sulfosuccinic acid ester which is not injurious to the plastic solution or dope. A 4% solution of sulfosuccinic 55 "ester of sulfosuccinic acid,"

acid ester may suitably be used. This percentage is illustrative only, and we are not to be limited thereby.

When the dialkyl ester of sulfosuccinic acid, or its salt, is incorporated in the plasticsolution or dope, we may use from 0.05% to 5%, approximately. of the sulfosuccinic acid ester, calculated on the weight of the plastic (cellulose ester or resin).

Instead of adding the sulfosuccinic acid ester directly to the dope, we may incorporate it in preparation of the plastic. For instance, in the case of cellulose acetate, it may be introduced during acetylation or pretreatment, or in a wash previous to, or following, acetylation. In the case of polymeric resins, it may be added just prior to or during the polymerization.

Mixtures of any of the dialkyl esters of 'sulfosuccinic acid, or their salts, in any desired proportions, may, of course,;be used.

Incorporation of a salt of a dialkyl ester of sulfosuccinic acid into a plastic dope has an additional beneficial effect in certain cases. Partially hydrolyzed lower fatty acid esters of cellulose, particularly the esters of wood pulp cellulose, often exhibit an inflated viscosity in organic solvents, such as dry acetone, which is believed to be due to the ash content of the esters as explained in U. S. Patent No. 2,126,489 of Malm. The proportion of mineral salt, particularly of calcium salt causing this "salt effect may be (and usually is in a well washed product) only a small fraction of one percent based on the cellulose ester, such as would be imparted by washing the cellulose ester in natural water instead of salt-free water. We have found that by the incorporation of 0.1% to 5% of a salt of a dialkyl ester of sulfosuccinic acid into such a cellulose ester dope or solution, the viscosity is reduced, the amount of this reduction beingproportional to the salt effect which had been exerted upon the cellulose'ester.

This power ofl'cancelling the effect of mineral salts is also possessed by the salts of the alkyl substituted aromatic sulfonic acids, such as are stated to be useful as antiherents in the copendmg application of c. J. Stand and can. Bachman, SerialNo. 231,916, filed September 27, 1938. The alkyl substituted aromatic sulfonic acids and their salts may also be applied, in solution, to the casting wheel for facilitating stripp' ne of plastic films, as well as incorporated in the dope.

In the appended claims. by the term dialkyl we mean to include not only the tree esters, but their alkali metal salts.

be secured by Letters Patent of the United States is.

a plasticizer, and a diaikyi ester of sulfosuccinic acid.

2. A solution. in a volatile organic-solvent, of

a cellulose ester and a plasticizer, adapted to be 10 What we claim as our invention and desire to 1. A composition comprising a cellulose ester,

- cast on a casting surface to form transoarent sheeting, containing, as a. substance for facilitating stripping of the sheeting from the casting surface, from 0.05% to 5% of a dia1kyl ester of sultosuccinic acid.

3. A transparent sheet comprising a cellulose ester, a plasticizer, and a dialkylester oi. sulfosuocinic acid.

GUSTAVE B. BACHMAN; CARL N. BEHRND'I.