US2036377A - Process of treating cellulose derivative sheets - Google Patents

Description

Aprill 7, 1936..

J. B. WELLS if:

PROCESS OF TREATING CELLULOSE DERIVATIVE SHEETS Filed May 26, 1933 AIROUTLET.

HOT AIR INLET.

elected Apr '7, W3

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This invention. relates to processes oi lecturing cellulose ester products and more er ticularly to processes for treating cellulose ester sheet material with various solutions or susnensions to import improved properties thereto. Specifically, thev invention relates to the treutment of sheeting particularly thin sheeting, hrolo only while it is in u relatively plastic condition end contains a. considerulolc proportion oi" solvent and in all events heiore it lies heen removed irons the surface upon which it wus originally cost. in the manufacture of cellulose derivative sheeting e. suitable solution. oi e cellulose ester is spread or flowed upon scestins surtuce, end the solvents removed therefrom by evu ooreticu. Que oi the most commonly employed methods is to maize up 2. cellulose ester solution or done of the proper composition and viscosity by dissolving the cellulose ester in appropriate solvents end ieedine; this done irom e. hopper, regulated to give the desired thickness, upon the suriuce ot a slowly rotating casting wheel. The solution hows out upon the curious oi the wheel end no the latter rotates a current oi sir or other sultehlc evaporative medium is hroueht in coutoct with the sheet thus termed, cousins; the solvent to he evaporated therefrom. Before the wheel has rotated through or complete revolution most oi the solvents hove evaporated and the sheet is then in o. condition in which it may he stripped from the suriace oi? the wheel uud subjected to curing treatment to iurther reduce its residual solvent content and bring its choreoteristics within the desired rouge.

it is often desired to treat-sheeting produced in this manner to impart to it certein properties such as to impart color or to treat the muteriul with various solutions for the purpose oi coating or lubricating it and for muny other purposes. It has heretofore been the practice to carry out such treatment, either alter the sheet hus'heen completely cured, or at some stage of the curing operation, that is; alter the sheet has been removed from the casting surface. Such treatment has been attended with varying degrees oi success, depending somewhat upon the nature and thickness oi the sheet end the nature oi the solution or liquid applied .thereto. However, the results obtained, for example, in applyins solutions or suspensions of colored material to cellulose derivative sheeting have not been wholly satisfactory due-to lack of proper penetration of the coloring or other'solutlon into the cured sheet and to the very marked tendency of the material to wrinkle. 50 marked has been (or in this wrne tendency, particularly with the ter types oi cellulose derivative sheeting de signed for wrapping purposes, that it has loeeri oructicslly out oi the question to eerily coloring or other types of treeting solutions to this type oi material. 7

it is the principal object oi the present invention to overcome the shove mentioned difilcuities end to provide processes in which cellulose deriv utive sheeting may he treated with various impresenting solutions or suspensions end in which no wrinkling or other adverse distortion of the materiel takes place. 0 A specific ololect of the in vention is to provide u process for coloring thin cellulose derivative sheetingby application ct e solution or suspension of coloring mutter. ohiects will hereinuiter appear.

The invention is more iully set forth in the lot lowing description tulteu in connection with the 'uccou'ioanying drawing! in which hits numerals are spelled to like ports and in which,

his. l is a diaerumnuutic sectional elevation of on unnarutus tor the manufacture and treatment of cellulose derivetive sheets in accordance with the invention, u portion oi the epparstus being hrolseu away to more clearly show the internal structure.

it is u irsernentury sectionul elevation oi as portion oi the apparatus shown in Fig. i iilustrot" J the upnlicutlon oi on impregnating or coutinu solution to the cellulose derivative sheeti i s. 3 end i are fragruentery elevationel views in nurtial section looting toward the wheel end in c, direction at right angles to that oi li ies. i end 2, illustrating the lower port of a casting wheel end the method icy which a, striped product may he produced in accordance with specific enmtiodiments oi the invention.

Although relatlne portly to the coloring or r dyeing oi cellulose ester sheeting, considered in its loroeder aspects, the invention includes troutins u cellulose clerivotive sheet with e solution or .ursnenslou to import color or anti-static or other desired properties thereto, 'ttihcn using on upptus such as that illustrated in Fig. i, l have discovered that this treatment of the cellulose derivative material may be best accomplished by cool the solution to the sheet at about the point where it has been carried through one half, of a revolution on the casting wheel, although I do not limit myself to application of the solution at any particular point in the rotation of the wheel, specltying only'that' the solution isto he lit applied to the sheet before removal from the casting surface.

I wish to emphasize that my process is especially characterized by this fact, i. e., that the sheeting is impregnated with a dissolved or suspended material before removal from the surface upon which it is cast-and that the dissolved or suspended components of the treating liquid .is

deposited on or in the surface of the sheeting. and remains in the finished product.

As pointed out above, the liquids usually employed for dyeing or otherwise treating cellulose derivative sheeting have a decided tendency to cause wrinkling, buckling or distortion thereof. This is particularly true of liquids having a direct solvent action on the cellulose derivative material, although certain nonsolvent liquids produce distortion due to their swelling action on the material. I have discovered that only when the treating liquid is applied to the sheet while still adhering to the casting surface can the desired properties be imparted thereto without wrinkling or buckling. Even extremely thin types of sheeting are amenable to treatment by my process without any undesirable distortion whatever.

As will be readily understood, the original sheet-forming cellulose ester solution or dope is spread upon the casting surface and immediately begins to lose solvent by evaporation. The solvent will of course evaporate from the outer surface of the dope much more rapidly than it does from that portion next to the casting surface or, in other words, it tends to skin over, leaving that portion next to the casting surface in a relatively more highly plastic condition than the outside. progressively as the casting surface rotates and the sheet tends to lose more and more of its solvent with the result that itshrinks to a certain extent and thereby clings very closely to the casting surface and lies perfectly flat thereon. 1 have found that if the treating solution is now applied to the surface of the sheet it will penetrate at least the outer portions or layers thereof, but since the sheet is then shrunk tightly onto the casting surface, it willcontinue to cling closely thereto and will not tend to wrinkle or buckle as would be the case if the treating liquid were applied after it had been removed therefrom. As a matter of fact, I have found that, once the thin sheet has been removed from the casting surface, it cannot be successfully treated with impregnating liquids without wrinkling or buck- It will'be apparent from a consideration of the facts just stated, that a sheet may be readily colored by applying suitable dye solution thereto in the manner just specified. Although per meation of the sheet by the solution will be relatively more complete when employing as the solvent for the coloring matter an active solvent of the cellulose ester material, the process is, to all intents and purposes, equally successful when the solvent is merely a swelling agent for the ester. This fact enables me to employ both solvents and non-solvents, although, I prefer to employ a cellulose ester solvent rather than a non-solvent. It is of course possible to use a mixture of solvents and non-solvents and to control the solvent action of any given mixture by increasing or decreasing the amount of diluting non-solvent in the mixture. Even a non-solvent treating solution may be used where the solution adheres sufficiently well to the sheeting. Typical suitable This initial curing action takes place non-solvent liquids are toluene, benzene and heroin.

The particular solvent or non-solvent employed in making up my treating solution will of course depend largely upon the nature of the sheeting being treated, and to a certain extent, upon the added components of the treating liquid. If it is desired, for example, to dye the ordinary hydrolyzed cellulose acetate sheeting, a liquid comprising 50% acetone and 50% methyl alcohol may be employed. Other appropriate solvent liquids comprise a mixture of ethylene chloride and alcohol, ethyl acetate, ethylene chloridetertiary amyl alcohol,.acetone-methyl cellosolve (monomethyl ether of ethylene glycol), and many others. When dealing with cellulose acetate-propionate, solvent liquids include ethylene chloride, ethyl acetate, methyl ethyl ketone and others. It will of course be understood that the nature of cellulose ester material of the sheet must be taken into consideration when making up the treating liquid and. the components of this liquid will be selected upon the basis of their solvent or swelling action with respect to a given cellulose ester. The solubility of these esters in various agents differ, not only with the particular solvent, but also with the degree of hydrolysis of the ester and with amount of acyl group present in the ester molecule. The effect of varying degrees of hydrolysis on the solubility of mixed cellulose esters is more fully explained in the co-pending application of C. J. Malm and C. F.

Fletcher, Serial No. 551,546 filed July 17, 1931.

In the case of the fully esterified mixed esters the solubility in a given solvent depends upon the ratio of the amounts of the different acyl groups in a given ester as more fully set forth in the application of C. J. Malm and G. F. Nadeau, Serial No. 659,698, filed March 6, 1933.

While I find it convenient to illustrate my invention by reference to cellulose acetate sheet, it is in no sense limited to the treatment of this material, but broadly applicable to the dyeing or other treatment of sheeting produced from a wide variety of single or mixed cellulose esters, such as cellulose nitrate, cellulose propionate, cellulose nitrate, cellulose acetate-propionate, cellulose acetate-butyrate, cellulose acetate-stearate and many others.

It is also to be understood that the cellulose ester solutions from which the sheeting is cast may contain any suitable plasticizers. In the case of cellulose acetate appropriate plasticizers include monoacetin, triacetin, monochlornaphthalene, camphor, tricresyl phosphate, triphenyl phosphate, pentaerythritol tetracetate and many others known tothose skilled in the art.

While I have just referred to the use ofsolutions or suspensions of coloring matter and to the coloring of cellulose ester sheeting, my invention is in no sense limited to this specific treatment as it is equally applicable to the treatment of sheet material for many other purposes as will be more fully set forth. I may, for example, wish to apply thin coatings of various solid materials to the surface of the sheeting. I may, for example,'desire to apply certain lubricatingmaterials to the surface of thin cellulose ester material designed for wrapping purposes to enable this type of sheeting to be more rapidly passed through packaging machinery, or to treat the surface of a cinematographic film support with a lubricating agent to enable it to be more easily passed through a projection apparatus.

In the case of wrapping material it has been proposed in the U. S. patent to Alfred D. Slack and Albert A. Young, No. 2,011,348, issued on application Serial No. 673,038, flled May 26,1933.

to treat this type of sheeting with a solution of an agent which will prevent'the accumulation of static charges on its surface and will also lubricate the material. In this case, the sheeting is treated with a dilute solution of stearic acid in a cellulose ester non-solvent. I have found that such a process may be most eflectively carried out in accordance with the invention if the solution is applied to the sheeting before it has been stripped from the casting surface. I may in this manner also employ various solutions of inorganic salts for improving the anti-static properties of the material such as Glaubers salt, lithium chloride, stannic chloride and. in fact, almost any metallic salts which increase its electrical conductivity.

The practice of my invention will best be illustrated by reference to a typical example which is included merely for purposes of illustration and in no sense as a limitation thereof.

Referring now to the drawing, the numeral i designates a. casting wheel mounted in suitable bearings f and provided with a suitable coating surface 3, preferably consisting of several different metallic layers plated one on top of the other. The numeral t designates a hopper comprising a V-shaped container provided with a stationary blade and an adjustable blade t actuated by a suitable device, such as thumb screw l, for regulating the thickness of the stream of cellulose derivative solution or dope ii flowing from the hopper onto the surface'of thewheel.

The wheel i is completely surrounded by a casing 9 through which a current of heated air passes in the direction indicated by the arrows, the air being supplied to the casing by a blower or other appropriate means (not shown) through the hot air inlet i0, and, after passing around the casing to the opposite side is evacuated therefrom by the air outlet ll.

The numeral l2 designates a curing section directly connected to the casing t and, in fact, forming an extension or continuation thereof. The section if is divided by a partition it into two compartments i l and IS. The compartment it is provided with a series of idle rolls l5 over which the sheet is passed after being stripped from the casting surface. The second compartment lltof the curing section is provided with drying or curing drums ll over which the sheet is carried after leaving the idle rolls l5 of compartment i4. Guide rolls l8 serve to convey the cured sheet to the wind-up roll l9 positioned opposite the door 20 through which the finished material may be removed when desired.

The hot air inlet pipe l0 supplies both compartments l4 and i6 of the curing section l2 with heated air which is led from these compartments by the air outlets 2| and 22, respectively.

Numeral 23 designates a hopper or tank, preferably' positioned at the lowest point of the casting surface, and partially or wholly enclosed bythe air casing 9. The hopper 23 may be provided with a suitable cover to prevent excessive evaporation of its contents and is provided with a -cylin'drical applicator roll 25 rotatably mounted therein and adapted to be partially submerged in a body of treating solution 26 and to convey a thin film of this solution into close proximity with the surface of the casting wheel as roll I rotates in the direction indicated by the arrow at the upper part of the figure, the roll 25 being driven in the direction indicated by the arrow appearing thereon. The hopper 23 is supplied with treating fluid'through the inlet pipe 32 controlled by valve 33, the fluid, if desired, circulat-.

ing through the hopper and being discharged therefrom through outlet pipe 34. It will ofcourse be understood that both the casting wheel and the applicator roll are driven by appropriate mechanism, not shown.

Referring now to Fig. 2 which illustrates the method of application of the treating solution to the support or film and in which the relative sizes of the various elements have been somewhat exaggerated for the sake of clearness, it

will be seen that the applicator roll 25 dipping in the solution 26 carries up a portion thereof and applies it to the surface of the film 28 in the form of a bead fl. It will thus be seen that the roll is positioned just close enough to the surface of the wheel to provide for maintaining this relatively fine head of solution in constant contact with the film surface.

Referring to Fig. 3, the numeral 29 designates a special type of roll for applying parallel colored stripes to the cellulose derivative sheet material, the roll 29 dipping in the body of fluid 26 in the same manner as illustrated in Fig. 2 and applying the colored solution or suspension as a plurality of small beads. l

In Fig. 4 there is illustrated a. still different type of roll 30 for application of diagonal stripes to the sheeting. The operation of this roll 3b is in all respects similar to the operation of the roll .29 shown in Fig. 3, except that the fluid 726 is carried up along the outside of the spiral ii and is machined so that it is substantially parallel with the surface of the wheel l and, as in the two previous instances, is spaced at small distance therefrom. W'hen emplo this type of roll it is necessary that the roll turn in the di rection indicated by the arrow thereon, that is,

in a direction such that the treating solution roll moves at the point of contact in the same direction and at the same peripheral speed as the sheet to which it is applied' As shown in the drawing, the hopper 23 is mounted so as to protrude into the air casing 9, but since the hopper is of less width than the width of the wheel casing i, the air passing through the casing may pass around the hopper and is not obstructed thereby. In some cases it may be desirable to form the walls of the casing i so as to protrude outwardly to provide additional space on either side of the hopper 23 for thepassage of the air through the casing.

Although I have shown a single hopper adapted for the application of one treating or impregnating solution at a time, I may employ a. plurality of hoppers to provide for the successive application of a number of different solutions or suspenslons to the sheet. For example, it may be derolls and containing the desired color, mounted one ahead of theother at the bottom of the wheel casing and appropriately spaced. In such an arrangement the first hopper will supply one color which will be carried up onto the surface of the sheet by means of an appropriate roll simtion is as follows.

ilar to roll 25, while each succeeding hopper and its r011 will supply additional colors 'as desired. It will, of course, be necessary to space the respective hoppers at such a distance from one another as will permit a sufficient amount of evaporation or' drying out of solvent contained in the coloring liquids to take place to prevent running or smudging. Such details of construction and operation are obviously within the province port or even emulsioned film for the purpose of edge marking and involving the use of -various forms of edge marking rolls. An example of the latter. process is contained in the co-pending application of K. C. D. Hickman, Serial No. 362,844, filed May 13, 1929.

Although the carrying out of my process will be fairly evident from a consideration of the several figures of the drawing, briefly stated, the opera- A cellulose ester dope, for example, a solution consisting of one part by weight of the acetone-soluble variety of cellulose acetate dissolved in four to six parts by weight of acetone is placed in the hopper 4 from which it is fed in suitable thickness and at an appropriate temperature to the surface of the coating wheel I. As the wheel rotates in the direction indicated by the arrow, a thin layer of solution is continual-v ly spread upon the wheel and solvents are rapidly evaporated therefrom by the current of heated air passing around the wheel surface through the casing 9. This evaporation takes place progressively until the'sheet contains, say, only .a few percent of solvents in which condition it may then be readily stripped from the wheel and passed through the curing section. When the sheet reaches the lowermost position in the casing it meets solution 26 carried up by the rotating roll 25 and is readily permeated thereby. When the solution 26 contains dyes or other coloring matter, for example, these are carried well into the body of the film and, in fact, may in some cases completely penetrate the full thickness of the film. Not only is the sheet penetrated by the solution, but, due to the fact that it clings closely to the casting surface when the treating solution is applied thereto, it has no tendency to wrinkle or buckle away from the coating surface and, in fact, has exactly the opposite tendency, that is, a positive tendency to shrink closer thereto and lie perfectly flat thereon. It is this fact that makes possible the successful treatment of even extremely thin sheeting by my process.

The treated sheet, after stripping from the casting surface, is subjected to any desired curing operation, such as by carrying it through the various compartments of the curing section I 2 where it is subjected to an additional current of warm air to remove any residual solvents and to give the film its proper shrinkage characteristics.

As pointed out above, the invention is of rather broad scope and includes various types of film treatment. As indicated, one ofthe most important applications is in the coloring of thin sheeting. A suitable solution for color treatment may comprise the following:

Butyl acetate 100 The above solutiorris of course only typical of many'which may be employed for cellulose acetate or other types of cellulose ester thin sheeting. In addition to acetone-soluble dyes other dyes such as the following may be successfully employed.

Color Index No.

In addition other coloring material, such as suspensions of various finely divided vegetable and mineral coloring matters, metallic powders such as gold, silver and bronze powders, pigments such as titanium dioxide, lithopone, baryta, and other materials may be employed.

If it is desired to impregnate or coat the cellulbse derivative sheeting with solid material such as stearic acid, in accordance with the procedure outlined in the above mentioned Slack and Young application, the following formula may be employed:

Grams Stearic acid -4 40 Acetone 700 Butyl acetate 260 As above indicated, in some cases it may be desirable to impregnate the sheeting in this manner with a solution of a metallic salt such as lithium or stannic chloride to give it anti-static properties. The salt may be applied in the form of a separate solution or may be added to a coloring solution. For example, when employing a separate solution for this purpose, it may con tain 2% lithium chloride and 5% glycerine dissolved in a mixture of 10% water and acetone.

If it is desired to render the sheeting hygroscopic, glycerine may be incorporated with a given treating solution, this being carried into the interior of the sheet and being retained thereby after curing is completed.

The invention also includes applying coatings or layers of various materials to the sheeting. It may, for example, be desired to apply a thin coating of gelatin in which case the treating solution may comprise a few percent of gelatin dissolved in a mixture of acetone and water in which the acetone preferably predominates. Coatings of cellulose esters may also be applied in accordance with the invention. For example, I may coat a sheet of cellulose acetate with cellulose nitrate by applying a dilute solution of the nitrate in methyl alcohol or in a mixture of methyl alcohol and acetone. In any of these cases, in accordance with the invention, the sheeting is treated before removal from, and therefore clinging closely to, the casting surface and the liquid is such that it slightly attacks the plastic material or at least penetrates thereinto.

The invention is to be distinguished from known processes involving the application of solutions as suspensions to the surface of sheeting to build up a thin layer thereon as in such processes, not only is a definite and distinct layer or stratum built up by such treatment, but there is no appreciable penetration or permeation of Fuchsin Y 677 Spirit red 258' Acid green L 666 Malachite green 657 Oil orangeE 24; Methanil yellow; -138 Fast wool yellow 3 g 636 ,Fast wool blue B 209 Spirit blue 689 Spirit nigrosine 864 lit lit

aoeasvv the sheet by the liquid. Furthermore, in these cases the sheet is not treated until the sheet is stripped from the wheel whereas according to the present invention the treatment can be carried out only before the sheet is stripped from the casting surface.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. The process which comprises casting a cellulose ester solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and treating the sheet before removal from the casting surface and while the sheet contains an appreciable amount oi residual solvent with a dye solution.

2. The process which comprises casting a cellulose ester solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and treating the sheet, before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent with a dye dissolved in a liquid containing an active solvent of the cellulose ester.

3. The process which comprises casting a cellulose ester solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and treating the sheet, before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent with a dye dissolved in a liquid containing an active solvent of the cellulose ester and a non-solvent.

t. The process which comprises casting a ce1lulose ester solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and treating the sheet before removal from the casting surface and while the sheet contains all appre ciable amount of residual solvent with a solution at a lubricating agent.

5. The process which comprises casting a cellulose estersolution in the form ot a sheet on an appropriate allowing the sheet to set by evaporation of solvent therefrom and treating the sheet before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent with a solution oi stearic acid.

6. The process which comprises casting a cellulose acetate solution inthe form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and treating the sheet, before removal from the casting surface and while the sheet contains an appre-' ciable amount of residual solvent with an acetone solution of dye.

7. The process of applying color in the term of stripes to cellulose derivative sheeting which comprises applying a dye solution thereto in the form of a plurality of beads before the sheeting is removed from the surface on which it is cast and while the sheeting still contains an appreciable amount of residual solvent.

8, The process 01 coloring cellulose acetate sheeting which comprises applying to the sheeting before removal from the surface on which it is cast and while still containing an appreciable amount of residual solvent, a colored solution which contains a liquid which substantially pene trates the body of the sheeting and permanently deposits the color within the structure thereof.

9. The process of making a cellulose ester sheeting having a permanent gelatin coating thereon which comprises casting a cellulose ester solution in the form of a sheet on an appropriate surface, allowing the sheetto set by evaporation of solvent therefrom, and applying to the sheet before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent, a gelatin solution containing a liquid which penetrates into the body of the sheet.

10. The process of making a cellulose organic ester sheeting having a permanent gelatin coating thereon which comprises casting a cellulose organic ester solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and

applying to the sheet before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent, a gelatin solution containing a liquid which penetrates into the body of the sheet.

11. The process of making a cellulose nitrate sheeting having a permanent gelatin coating thereon which comprises casting a. cellulose nitrate solution in the form of a sheet on an appropriatesurface, allowing the sheet to set by evaporation of solvent therefrom, and applying to the sheet before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent, a gelatin solution containing a liquid which penetrates into the body of the sheet.

l2. The process of making a cellulose acetate sheeting having a permanent gelatin coating thereon which comprises casting a cellulose acetate solution in the form of a sheet on an appropriate surface, allowing the sheet to set by evaporation of solvent therefrom, and applying to the sheet before removal from the casting surface and while the sheet contains an appreciable amount of residual solvent, at gelatin solution containing a liquid which penetrates into the body of the sheet.

JACKSON B. WELLS.

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