US2464784A - Film forming solution of cellulose acetate - Google Patents

Description

Patented Mar. 1949 2,464,784 FILM FORMING SOLUTION or CELLULOSE CETATE Russell P. Easton, Binghamton,

N. Y., asslg'nor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application August 9, 1945, Serial No. 609,931

1 Claim. l This invention relates to the manufacture of sheets, films or foils composed of cellulose organic esters and other film forming materials. More particularly, the invention relates to a method of facilitating the removal of such sheets, films, and foils from the surface ,upon which they are cast. a

In the manufacture of sheets, foils, or films from high molecular, water insoluble film-forming materials such as cellulose organic esters ranging from-.001 to .05 of an inch in thickness, and of any suitable width, the cellulose organic ester is dissolved in a suitable solvent and a plasticizer added to make a composition which in the parlance of the trade is called a dope. This dope is cast on the surface of a slowly rotating wheel or drum having a smooth nickel or chrome plated surface, or on the surface of an endless metallic band, and the solvents removed from the deposited material by means of heated air. Finally, the dried'or cured material is stripped from the casting surface in the form of a continuous sheet which is wound upon a shaft for storage or further use, such as for coating with emulsions to form photographic film. Notwithstanding that the bulk of the solvent has been removed from the film when it reaches-the point where it. is

stripped from the casting surface, difliculty is experienced in the removal of the material from the casting surface. In some instances, depending upon the nature of the plasticizer employed, the cast film or foil adheres so tightly to the casting surface that it requires considerable force to remove it. This causes the film to strip off in an unsteady manner with considerable jerking. Vibrations are set up-and the surface of the film or foil develops crosswise markings which distinctly impairthe quality of the' resulting product. The adhesion may be so great in some cases as to cause small portions of the film to be torn away from the main body of the material and left upon the casting surface.

In order to obviate the above difliculties, it has been suggested that considerable care be exercised in selecting the plasticizer for the cellulose organic ester. The plasticizer selected should be of a high boiling point so that it will remain in the foil at the end of the drying span. For photographic film, the plasticizer selected must be photographically inert and resistant to hydrolysis. It must not lower the flexibility nor increase the water sensitivity of the film or foil. The plasticizers which are generally suggested for use by the art in this connection are, for ex-, ample, triphenyl phosphate, trinaphthyl phos- 2 phate', tricresyl phosphate, tricresyl thiophosphate, naphthyl diamyl phosphate, trixylyl phosphate, dlmethyl phthalate, isobutyl phthalate,

dibutyl phthalate, methyl cyclohexyl acetatephthalate, methylphenoxy ethyl phthalate, acetyl tributyl citrate, tributyl citrate, hydrophthalic acid diethyl ester, octyl phenyl ether, orthophthalic acid diethyl ester, mixtures of oand .p-toluene ethyl suifonamides and the like. It is possible by selecting a plasticizer from this group to correlate its properties and the amount used with the particular cellulose ester employed, to obtain foils or films which have the requisite tensile strength to furnish pliability and the like. However, despite the care exercised in selecting such plasticizers and irrespective of the improvements obtained in the physical properties by the use thereof, the diiiiculty in stripping the film or foil from the casting surface is not overcome. The principal object of the present invention is to avoid the above mentioned difficulties and to provide a means whereby such films, sheets, or foils may be stripped from a casting surface with ease and without impairment of their quality.

Another object is to provide an improved method of stripping cellulose organic esters and other film-forming substances from a casting surface.

These and further objects will become apparent in the following description.

1 I have discovered that I am enabled to achieve the objects of the present. invention by selecting a combination of plasticizers which not only acts as a plasticizer for the film-forming material and imparts the aforesaid desirable physical characteristics thereto, but also aids in the stripping of the cast film or foil after drying or curing. This combination consists of a mixture of a trialkyl phosphate and a common plasticizer which is normally. employed in plasticizing cellulose organic esters.

Any trialkyl phosphate may. be employed pro- "vided, however, that each alkyl group therein contains at.least 5 carbon atoms. Examples of suitable phosphates are triamyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, triclecyl phosphate and the like. The plasticizing agent generally employed in plasticizing cellulose esters which with the trialkyl phosphate is critical to the success of the invention is exemplified by triphenyl phosphate, trinaphthyl phosphate, tricresyl phosphatefdioctyl phosphate, tricresyl thiophosphate, trixylyl phosglycol di-2-ethyl hexoate, triethylene glycol di- 2-ethyl butyrate and the like.

The mixture of the aforesaid components is added directly to the high molecular weight filmforming material, to the solvents employed in dissolving the same, or to the solution of said film-forming material in a suitable solvent or solvent mixture. The amount of trialkyl phosphate employed is in the ratio of 0.5 to 3 parts by weight to approximately 3 to 5 parts by weight of any common plasticizer for each 10 to 20 parts by weight of the film-forming material. The most desirable ratio of plasticizer mixture, however, is 0.8 part by weight of trialkyl phosphate to 3.2 parts by weight of the common plasticizer for each 16 parts by weight of the film-forming material.

The use of trialkyl phosphates alone renders the plasticized film-forming dope unsuitable for casting purposes. The partially dried or cured foil or film does not adhere sufllcientiy to the casting drum beforethe drum or other circular casting means has made a complete revolution to the guide roll which leads to a'drying chamber. As a result thereof, the partially dried film or foil slips from the under surface of the casting drum and falls to the ground. on the other hand, the commonly used plasticizers when employed per se lead to an impairment of the film and.strip. However, by the combined effect of both on the film-forming materialythe desired result is achieved. Just how each component of the plasticizing m xture contributes to the unitary action has not been ascertained. That both cooperate by exerting a definite influence on each other and on the high molecular weight film forming material, however, is not open to dispute.

The trialkyl phosphates employed in accordance with the present invention are prepared by reacting a phosphorous oxyhalide, e. g., phosphorous oxychloride with a hydroxy alkyl compound such as, for example, n-amyl alcohol, isoamyl alcohol, 2-pentanol, 3-pentanol, d-amyl alcohol. amylene hydrate, l-hexanol, 2-hexanol, 2 methyl l-pentanol, 3,3-dimethyl-2-butanol, 2,3-dimethyl-2-butanol, l-heptanol, l-octanol, l-nonanol, l-decanol, and the like, and have the following general formula:

R--O-P=O R-O/ wherein R is an alkyl group ranging from to carbon atoms.

The trialkyl phosphates having the foregoing general formula are available commercially and inmost instances are viscous oils'or solid resins at room temperature. They are readily soluble in the high molecular weight film-forming materials and in most normally liquid solvents such as alcohols, i. e., methyl, ethyl, propyl, butyl, amyl and the like, and ketones such as acetone, methyl ethyl ketone, diethyl ketone, and the like, aromatic hydrocarbons such as benzene, toluene, xylene and the like, and chlorinated hydrocarbons such as chiorobenzene, chloroform, methy lene chloride, chlorinated kerosene and their mixtures with alcohols and ketones asabove and esters such as dibutyl acetate, diamyl acetate, cellosolve commonly used in lacquer solvents.

In practicing the present invention. any unplasticized film forming material may be employed, such as a cellulose organic ester. for example, cellulose acetate. cellulose formate. cellulose propionate, cellulose butyrate, cellulose acetate-propionate, celulose' acetate-butyrate. and the like, or cellulose nitrate, or film-forming polymers, such as polyvinyl chloride, copolymers of vinyl chloride-vinyl acetate, copolymers of vinyl chloride-vinylidene chloride, polyamides, superpolymers and the like.

The nature of the solvent or solvent mixture employed in preparing dopes of the above-listed cellulose organic esters and film-forming polymers is immaterial so long as it dissolves or is compatible with the plasticizing mixture of the present invention. This fact can be ascertained readily by a simple experiment.

For a fuller understanding of the nature and objects of the invention, reference is made to the following examples which are given merely to further illustrate the invention, and they should not be regardedas limiting it. All the parts are by weight.

Example I A solution or dope is made up as follows:

- Parts Cellulose acetate (containing 58% acetic acid) l6 Trioctyl phosphate 0.8 Triphenyl phosphate 3.2 Methyl alcohol 8.0 Methylene chloride 72 This solution was cast upon the polished periphery of a drum to form a layer which upon drying would produce a film of about 0.008 of an inch in thickness. The partially dried film was removed with ease when taken up by the guide roll leading to the drying chamber.

The advantages of the invention were brought home by contrasting the above procedure with the following, illustrating the effect of adding a common plasticizer to a cellulose organic ester dope from which a film is cast.

7 Parts Cellulose acetate (containing 58% acetic acid) 16 Triphenyl phosphate 4 Methyl alcohol 8 Methylene chloride 72 Example 11 Parts Cellulose acetate-propionate 20 Triamyl phosphate 1.2 Tricresyl phosphate 4.0 Acetone 75 Example III 4 Parts Copolymer of vinyl chloride-vinyl acetate Tridecyl phosphate 0.6 5 Dibutyl phthalate 2.8 Methyl alcohol 8.0 Methylene chloride 1 80 The solutions of Examples II and III when cast resulted in satisfactory films, which were 10 readily removed and did not possess any undesirable characteristics.

It is evident that the solutions or dopes prepared in accordance with this invention are not limited for casting on a peripheral surface, but

are also capable of being cast on endless metallic belts to give films, foils, or sheets which are clean ly stripped from the casting surface.

While the present invention-has'been described in considerable detail with reference to preferred procedures and materials, it is to be understood that the invention is not limited thereto and that numerous variations may be made in the procedures herein described. All such modifications and variations are within the scope of the invention as defined by the appended claim.

Iclaim:

A film-forming solution or cellulose acetate consisting essentially of about 16 parts of cellulose acetate, an organic solvent therefor in an amount suitable for strip casting, about 1 part of trioctyl phosphate, and about 4 parts of triphenyl phosphate.

' RUSSELL P. EASTON.

REFERENCES orrnn The following references are of record in the file of this patent:

'UNITED STATES PATENTS