US2166711A - Moistureproof cellulosic sheeting - Google Patents

Description

18,1939. BEACH v 2 166,711

MOISTUREPROOI" CELLULOS IG SHEETING Filed Jul 17, 1931 i @319 4 I gmmms A/OIEIYANEBEACH.

Patented July 18, 1939 UNITED STATES 2,166,711 MOISTUKEPROOF OELLULOSIO SHEET ING Norman F. Beach, Rochester, N. Y., assignor, by

mesne assignments, to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application July 1'1, 1931, Serial No. 551,491

1'? Claims.

This invention relates to the manufacture of thin cellulosic sheeting and more particularly to a waterproof and moistureproof form of such sheeting which is transparent, flexible and non- 5 tacky. It also relates to the manufacture-of a specific type of composition for application to this class of sheeting to render it highly water-resistant.

It is known that paper, cloth, and various other types of fibrous and similar cellulosic materials may be rendered impenetrable or impermeable to water and other liquids by impregnating them with compositions containing gums, waxes, oils, or other materials. It is known that many compositions containing cellulose derivatives, gums, waxes, plasticizers, and other ingredients have been formulated and used as coating compositions for many purposes. For example, it has I been proposed to waterproof a regenerated cellulose sheet material by applying a composition containing a cellulose derivative base and various ingredients of a waterproofingcharacter. The present invention is not concerned broadly with either waterproofing or with compositions therefor except as it relates to .a particular class of base sheet treated with a new and improved composition which renders it molstureproof as well as waterproof, said composition being much simpler in constitution than known compositions in that v 3'0 it contains no base materal such as cellulose nitrate. I

It has been found that thin sheets of cellulose acetate and similar types of colloidized cellulosic compositions make excellent material for wrapping or packaging a large variety of articles due to the fact that it is relatively'tough and strong, yet flexible, and is highly transparent as well as being impermeable to dust and other foreign matter. Under some conditions cellulose acetate, for example, as ordinarily produced without being specially treated may be said to possess a certain degree of resistance to the penetration of moisture, but I have found that it is not sumciently water-resistant to permit its use for purposes wheresubstantially complete imperm'eabib.

ity is necessary. For example, if water comes in contact with the untreated material it would'- not ordinarily penetrate or be absorbed immediately, as would occur with cloth, paper, or other fibrous materials, buirif water were to remain for any appreciable length of time on the surface it would be found that it had penetratedv the interiorofthesheet. Ithasalsobeer'ifoundthst. water vapor will gradually pass through'untreatedcelluloscacetstesheetingwitboomparative ease. .These properties of the untreated sheeting accordingly render it unsatisfactory for I use in wrapping or packaging products or mate,- rials which must be kept substantially free from moisture. It is, therefore,-a highly desirable re- 5 suit and a distinct advance in the art to render thin sheeting made from cellulose acetate, waterand moistureproof and to dose has opened up a wide and entirely new field of uses for this valuable material. I

It is the principal object of my invention to provide a means of rendering thin sheets of cellulose acetate and similar colloldized organic cellulose ester compositions waterproof and moistureproof. A further object is to provide a wrapping or packaging material which is, not only waterproof and molstureproof, but also highly transparent, flexible, odorless and non-tacky.- A still further object is to provide a waterand moistureprooflng coating composition suitable for 20 application to cellulose acetate and similar materials which is simple to compound and apply and contains a less number of ingredients than have heretofore been considered necessary in such a composition. Other objects will appear '25 hereinaften.

These objects are accomplished by the following invention which, in its general aspects, may be said to consist in-the formulation of a coating composition comprising a mixture of a gum and 30 a wax dissolved in a sovent and, if desired, having optional ingredients such as plasticizers and other agents, and the application of this composition to a thin sheet of cellulose acetate, whereby said sheet is rendered waterand moistureproof, while 35 at the same time its flexibility and transparency are preserved and its other essential and valuable. properties not adversely affected.

In carrying out my invention I employ a composition comprising essentially a wax and a gum 40 or resin, or various mixtures of wax and gum. or resin dissolved in a common solvent.

As examples of waxes which I have found satisfactory may be mentioned paraflln, ceresin, beeswax, pimela, lanolin, spermacetl, montan, 45 bayberry, vasell'ne, Japan, candelilla and Chinese wax, any of which may be used singly or in combination with one another or with other waxes of this general nature which are known to or in various combinations, and also with other gums and resins.

The various properties of the finished product, such as waterproofness, moistureproofness, fiexibility, and transparency may be controlled by varying the proportions of the ingredients mak-,

ing up the moisture proofing composition in accordance with the particular qualities desired. With regard to the waterproofing quality of the composition it may be said in general that the higher the proportion of wax to gum or resin, the greater will be the water resistant properties, although it is, of course, necessary to control the proportions of the various ingredients in such a way that a clear, homogeneous and continuous film is produced when applied to a thin sheet of cellulose acetate. The ratio of wax to gum and resin, as well as the proportion of solvent or solvents employed may be varied within rather wide limits, depending uponthe requirements of the particular material produced, but I prefer to keep the wax content of the composition less than 55% and the gum or resin content above 45% although I may use even as highas 78% wax with 22% gum or resin and still produce good results. These percentages are, of course, based on the total solids, and not on the composition as a whole. I have found that the more wax present in the composition, the more friable will be the coating on the finished sheet. On the other hand, the more gum or resin present, the better will be the adhesive properties of the composition as a whole, but if the proportion of gum or resin isincreased beyond certain limits, the coating when applied will have a tendency tobecome ohjectionably tacky. I have also found that as the ratio of wax to resin is decreased, the. practical difficulties encountered in applying the composition are decreased and the resulting protective coating is harder and less subject to inJury from friction, but is less eii'ective as a waterproofing layer. For many purposes compositions containing even as low a ratio of wax to resin as 1:20

have been found useful as a water resistant material.

I The gum-wax compositions of my invention may be applied to the surface of the thin cellulose acetate sheeting in a variety of ways. For example, the gum or resin and wax may be melted and applied in a molten state. The preferred method, however, is to dissolve the gum and wax in a suitable solvent and apply this solution in any suitable manner, such as by spraying. immersion, or by means of ,application rolls. The immersion method of application is usually to be preferred, especially where it is desired to coat both sides of the base sheet.

- I may employ as solvents those which will dissolve both the wax and gum or resin, but which are non-solvents for cellulose acetate. Among these may be mentioned benzene, toluene, xylene, naphtha, gasoline, carbon tetrachloride, ethylene dichloride, trichlorethylene, and petroleum ether. Any of these solvents may be used either singly or in suitable mixtures with each other, or with other suitable solvents in varying'proportions so long as a solvent for the cellulose acetate itself is not thus produced. when applying compositions containing a high ratio of wax to resin I prefer to use a solvent or solvent mixture con- .taining relatively high boiling constituents such as xyleneor toluene, and to carry out the drying at a temperature ranging from 50 to 105 C., although a wider range of drying temperatures may be used with good results. It maybe that the drying temperatures employed should be controlled in accordance with the known properties of the cellulose acetate base sheet and should not be high enough to cause any softening and stretching of the sheet as it progresses through the coating machinery. The particular type of solvent used will in every case be selected with reference to the particular type of cellulose acetate or other material forming the base sheet.

It is to be understood that the preferred type of cellulose acetate described in the examples and in connection with which the above list-of solvents is stated to be suitable is an acetone-soluble variety and of high precipitation value, such as that disclosed in the application of Albert F. Sulzer, Serial No. 353,649, filed April 8, 1929.

As optional ingredients which may be incorporated into my waterproofing composition, although not essential to the purposes of my invention, may be mentioned various plasticizers such as tricresyl phosphate, triphenyl phosphate, benzyl benzoate, ethyl benzoate, butyl benzoate, monochlornaphthalene and others. I may also incorporate softeners, such as non-drying oils, among which may be mentioned castor oil and olive oil. I may also use certain drying oils, typical examples of which are rapeseed oil, linseed oil, and cotton seed oil. If a colored coating is desired, various oil-soluble dyes may be added. Likewise, flavoring materials and perfumes may be incorporated in the composition depending upon the use to which the finished product is to be put.

In the following examples, I have set forth several of the preferred compositions of my invention which are included merely for purposes of illustration and not as a limitation.

Example 1.--A mixture of 40% candelilia wax and 60% ester gum was dissolved in toluene until the resulting solution contained 15% solid matter by weight. This solution was appliedv to both sides of a thin sheet of cellulose acetate by means of a subbing operation using application rollers, such as those illustrated in Figure 1 of the drawing. During this operation the sheet was moved at a uniform rate of 3 feet per minute past the subbing rollers, the drying temperature being maintained at about 55 C. In this manner a uniform transparent coating of the gum-wax composition, having a thickness of the order of 0.00001" was obtained on both surfaces of the sheeting. The untreated base in this case had a moisture transmission of 1.5 to 1.0 milligrams per square 7 centimeter per hour. The coating operation was found to render the sheet 250 times more resistant to penetration by water vapor than before treatment.

Example II.-A coating solution was made up containing V2% by weight ester gum and by weight of a 139 parafiln dissolved in a solvent comprising 50% by weight of'toluene and 50% by weight of solvent naphtha having a boiling point of 60-70 C. and consisting largely of normal hexane. This was applied by immersion to a thin sheet of cellulose acetate having a thickness of .001", the sheetingbeing passed through the coating solution at the rate of 10 feet per minute and dried by passing through a drying chamber maintained at a temperature ranging from 50 C. to 105 C. The resulting coated sheeting possessed excellent moisture resistance, the permeability tomoisture measured as milli grams of moistureper square centimeter per hour being only .0021 as compared to 1.5 milligrams for Example IIL-A coating solution was made up containing 1%% by weight paraflin having a melting point of 139 F. and 1%% by weight ester gum dissolved in a solvent comprising 50% toluene and 50% of the above mentioned solvent naphtha. This was applied by immersion to a thin sheet of cellulose acetate having a thickness of .001", the sheet being passed through the coating solution at the rate of 10 feet per minute and dried as in Example 11 at a temperature ranging from 50 C. to 105 C. The resulting coated sheeting possessed exceptionally good moisture resistance, the material permitting the passage of only .0018 milligram of water per square centimeter per hour.

Example IV.--A mixture containing 66% candelilla wax and 34% ester gum was dissolved in toluene until the resulting solution contained 10% solid matter by weight. When applied to a thin base sheet of cellulose acetate having a thickness of .001 under the conditions described in Example III it was found to have a permeability expressed in milligrams of water per square centimeter per hour of only .002.

Example V.--A base sheet of cellulose acetate having a thickness of .001" was coated with a solution containing 4.5% solids, said solids comprising 22% ester gum and 78% of 139 paramn dissolved in a solvent comprising 85% toluene and 15% ethylene chloride. The sheet was coated successively on both sides, the drying of the first coating being carried out at a temperature of approximately 70 C. and the second coating being dried at a temperature of 60 C. Upon examination, the material was found to transmit only .007 milligram of water per square centimeter per hour.

Example W.--A coating composition containing 70% by weight gum dammar and 30% by weight of 139 paraiiln was made up by melting the gum and paraflin to a uniform consistency. This composition was applied in a hold condition to a base sheet of cellulose acetate of .001" thickness having originally a permeability of 1.5 to 1.0 milligrams per-square centimeter per hour. The permeability was found to be reduced by application of this coating material to only .035 milligram. 3:

Figure 1 is a diagrammatic representation or one form of apparatus for carrying out the'invention, in which the sheet is coated on both sides simultaneously by immersion.

Figure 2 is a detail ole. conventional form of scraping device for removing excess coating iiuicl and insuring uniform application to the surface of the sheet.

Figure 3 is a diagrammatic representation of an optional iorm oi apparatus for applying the coating to one or both sides of the sheet.

I Referring to the drawing in detail, in Figure 1 4 the numeral I designates a sheet oi thin cellulose acetate which is fed from a supply roll 2 over a guide roll 3, whence it passes under an immersion roll 4 through. a bath of coating .fluid 0 of the desired composition contained in immersion vat 6. The vat 6 is provided with means for raising or lowering (not shown) with respect to immersion roll 4 so that the sheet material may be immersed in the fluid to varying depths or, ii occasion requires, maybe removed entirely from contact therewith. Numerals I and 8 designate conventional scraper bars sdiustably mounted either on or above the vat i in such manner that they may be moved horizontally toward or away from the sheet I depending upon the degree of contact with.

or scraping effect desired. Numeral I designates a drying chamber for evaporation of the solvents and may be provided with any well known means for maintaining the desired temperature. Such means may, for example, comprise a blower or any equivalent device for passing a heated current of dry air downwardly through the chamber 9. There should preferably be providedmeans for continuously removing the vaporized solvents from the drying air which is drawn through the chamber 9. I0 represents a drum over which the coated sheet I passes after emerging from the drying chamber 9 while II is a wind-up roll provided with conventional mechanism (not shown) for producing the desired tension upon the sheet.

Assuming the process to be in operation, the sheet I leaves the supply roll 2, passes over the uide roll 3, and thence under immersion roll 4. When the vat 6 is raised to the proper height, which generally placesthe guide roll 4 well beheath the surface of the fluid 5, the sheet I will be entirely immersed and, due to the fact that the fluid flows freely into the V-shaped opening between the down-coming and up-going portions,

the sheet will be simultaneously coated on both sides. After emerging from the bath 5 the sheet passes up through scraper bars I and 8 and into drying chamber 9 where solvents are removed by evaporation. The dry sheet then passes over drum I0 and is wound upon wind-up roll II.

In Figure 2 which shows a sectional detail of the scraping mechanism, the sheet I passes up through the opening between the rounded con tact portions l2 and I3 of the scraper bars I and 8. The scraper bars I and 8 are provided with slots i4, bolts l5 cooperating therewith, and providing a means for horizontal adjustment of the bars with resulting variation of the width of'the opening between the rounded portions I 2 and i3.

Figure 3 shows diagrammatically an optional method of application of the coating. The numeral l6 designates a supply roll from which the base sheet passes between subbing roll I! and squeeze roll I8 and over guide rolls 2'0 and 2|. Chamber I9 is a drying chamber provided with means for maintaining the desired temperature as in the case of chamber 9 of Figure l. The roll I8 may be provided.with a proper adjusting mechanism to vary the distance between the two rolls so that'varying degrees of squeezing action may be obtained. The numeral 22 is a vat which contains a coating fluid 23 'which is carried up by roll I9 for application to the base sheet. 20 is a subbing roll similar to roll I9 and having squeeze roll 25 positioned thereover and cooperating there! containing coating fluid 21 of composition similar to fluid 23. for coating the other side of the sheet. 28 is a drying chamber also provided with means for maintaining the desired temperature and means for continuous removal of solvent vapors.

28 represents a vat similar to vat 22 also 29 is a wind-up roll for the finished material which is preferably provided with mechanism (not shown) for producing the proper tension upon sheet I7.

Assuming the operation to be carried out by the use of the apparatus of. Figure 3, the sheet I! leaves the supply roll it and passes between subbing roll 19 and squeeze roll I8. Roll is picks up fluid from 23 and carries it into contact with the under side of sheet l'l, roll It being adjusted with relation to roll I! so that excess material is continuously removed. The sheet then passes to guide roll 20 having the proper thickness of coating superimposed thereon. After passing guide rolls II and II, the sheet passes through a similar operation employing rolls 2 and II, this second operation providing a coating for the opposite side of the sheet. The coated sheet is then passed carrying out my invention may vary without departing in any way from the scope of my invention. Such variations in the apparatus to conform to other modes of operation will be apparent to those skilled in the art towhich this invention relates. For example, the vats 6, 22 and 26- may be provided with means for maintaining the coating fluid-in a liquid condition, such as steam Jackets surrounding them or heating coils immersed in the liquid contained therein.

As indicated by the above description of typical coating operations, the base sheet may be coated on one or both sides, or may be given successive coatings. In any case, the resulting extremely thin outer layer 'will consist of a simple two-component mixture of gum and wax adhering to the sheet and preventing the transfusion of moisture while at the same time rendering the material waterproof in the ordinary sense. In coating only one side of the base sheet, an apparatus such as that of Figure 3 will be suitable, the second set of coating rolls being dispensed with.

One of the many advantages of the invention is that my improved water-resistant coating is of such character thatit enables me to readily Join or seal the edges of the coated sheeting by simply bringing them together and applying heat and pressure. ing of each of the surfaces will fuse and flow together or coalesce, while the pressure brings 0 them into even more close relation and thereby I6 alcohols, such as diacetone alcohol: aromatic ke-- causes the sheets to adhere to one another. Since both the acetate sheet and the coating material are transparent, a neat and transparent seal results. The fusibility of the coating. as well as its strongly adherent character after fusion and cooling, make possible the use of finished sheeting for the manufacture of a large variety of containers such as cigar wrappers, food packages, and many other articles.

It has also been found that the waterproof sheeting of my invention is readily susceptible of being united or joined by applying various solvents to the portions of the material it is desired to unite and bringing them into close contact- As in the case of simple heat sealing, such as described in the proceeding paragraph, heat and pressure is advantageously used to cause those portions of the moisture-proof surface which have been softened or partially dissolved by the solvents to coalesce and, upon evaporation of the solvent, to form a strong uniform, and t joint or seal. The heat will, of course, evaporate oi! the solvent and leave only'themingled or coalesced portion of the respective sheets adhering and thereby forminga uniform bond between them.

Among the solvents which have been found suitable for them oftbissolvent sealingmaybe included alcohols of both the aliphatic and aromatic series and containing one or more hydronl groups such as methyl, ethyl and normal butyl alcohol, glycerol, benzyl alcohol and cyclohexanol: derivatives of alcohols. such as esters of mono or polyhydric alcohola typical examples of which are ethyl acetatemonoacetin and diacetin; keto Under the influence of heat the coateither alone or in combination. requisite of such liquids is that they should be tones, such as acetophenone, benaophenone, and cyclohexanone; mixed ether-esters of aromatic or aliphatic acids, such as ethoxy ethyl phthalate; mixed ether alcohols, such as the monobutyl ether of ethylene glycol and the monoethyl ether of ethylene glycol; diacyl derivatives of dihydroxy alcohols, such as glycol diacetate; monoacyl derivatives of the monoalkyl ethers of glycol, such as derived'from the monoethyl ethers of ethylene glycol and others. The discovery that the above mentioned compounds may be used for this purpose is not to be understood as forming part of my invention since this is the invention of C. J. Staud and William O. Kenyon and is described and claimed in their U, S. Patent 1,925,509.

In the above examples I have disclosed the coating of acetate sheeting having a thickness of the order of .001", but it is entirely feasible to moistureproof sheeting of greater or less thickness by my method. For instance sheeting having a thickness of .002 to .003" or even more may be molstureproofed in accordance with my invention and satisfactorily employed for many purposes. The thickness of the coating deposited on the sheeting may also be varied as desired, although I have found that in coating a base sheet having a thickness of .001" it is preferable to keep the thickness of the water resistant layer somewhere in the vicinity of .00001.

It is to be understood that the list of waxes, gums, and resins included herein is intended merely to be illustrative, for it is evident that many other waxes, gums, and resins may be used in formulating my improved. waterproofing composition.

The same holds true in the case of the solvents. since many others than those listed may be used The principal substantially non-solvents for cellulose acetate. Either high or low boiling solvents may be used but, in general, when using a high ratio of wax to resin it is advantageous to use a relatively high boiling solvent.

As regards the control of flexibiity of the finished product, this is governed largely by the amount of plasticizer used in the cellulose acetate base sheet but varying proportions of plasticizer may also be incorporated in the coating composition itself, if desired, although the effect here would be to plasticize the coating layer rather than the sheet itself.

Various other optional ingredients may be used in making up the moistureprooflng composition of my invention. For example, various spiritsoluble and oil-soluble dyes, aluminum flakes, gold leaf, pearl essence and other coloring materials may be included in the moistureprooflng composition or may be incorporated directly in the ester dope from which the base sheet is produced. Perfumes or flavoring material may be used, depending upon the use to which the finished product is ultimately to be put. Furthermore, various ultra-violet filters, such as those described in the U. B. patent to Richardson and Stand 1,958,714. may be advantageously used in the manufacture of moistureproof sheeting which is to be used for the wrapping of delicately tinted articles which have been dyed with compounds which are fugitive to ultra violet light.

pmofquality of the material is of particular imin which it is necessary to retain moisture. The' same property is of equal importance in the manufacture ofcontainers for materials from which moisture must be excluded. The coated cellulose acetate sheet is almost perfectly transparent, and this quality is of particular advantage, since inspection of the contents of packages may be easily made without unwrapping. My product, although strong and sufliciently tough for most uses as a wrapping material, may be torn with comparative case. This is particularly advantageous when using the material for enclosing cigarette packages, cigars, and the like. I have also found that due to its lower density over known analogous products, it has a much greater covering power per pound. Furthermore, the flexibility may be readily controlled to meet the particular demands of the use to which it is to be put.

Although there are several tests for determining the permeability or ability of the material to permit the passage of moisture, I prefer to use a method briefly described as follows: A weighing bottle containing a weighed amount of a water absorbing agent (magnesium perchlorate trihydrate) is placed 'in a crystallizing dish and thereafter a diaphragm of the sheeting is cemented over the mouth of the dish. It is then placed in an atmosphere saturated with water vapor at a temperature between 85 and 95 F. After the proper length of time, the diaphragm is removed and the weighing bottle transferred to a balance and weighed. The permeability, or gain in moisture, is expressed in milligrams per square centimeter per hour.

It is to be understood that the terms gum and resin are used herein and in the claims interchangeably, and when reference is made to a gum it is to be taken for the purposes of my invention as also including both the natural and synthetic resins. Furthermore, although the specific examples above given are directed to sheeting composed of organic esters of cellulose it is to be understood that I am not to be limited thereby, as my invention is applicable to thin sheeting composed of any cellulosic material to which the gum-wax coating wili adhere well,

such, for instance, as that which is commonly known as viscose or regenerated cellulose. The term cellulosic material is. therefore, intended to include all forms of colloidizeol cellulosic materials ordinarily employed in this art.

What I claim as my invention and wish to secure by Letters Patent is:

1. An article of manufacture comprising a thin, flexible, transparent colloidized cellulose or-- ganic ester sheet coated with a film of a moisture resisting composition the film-forming constituents of which consist, essentially oi a mixture of a wax and a gum. V

2, An article of manufacture comprising a thin flexible transparent sheet of cellulose acetate coated with a film of a moisture resisting composition, the fllm-forming constituents of which consist essentially of a mixture of a wax and a guru, the ratio of wax to gum being between'about 40:60 and 78:22.

3. An article of manufacture comprising a thin flexibie transparent sheet of cellulose acetate coated with a film of a moisture resisting composition, the film forming constituents of which consist essentially of a mixture of wax, a guru position,

consist essentially of approximately 50% 4, An article of manufacture comprising a thin flexible transparent sheet of cellulose acetate coated with a fllm of a moisture proofing composition, the fllm-forming constituents of which consist essentially of ester gum and wax, the

ratio of wax to gum being between about 40:60 and 78:22.

5. An article of manufacture comprising a thin flexible transparent sheet of cellulose acetate coated with a fllm of a moistureprooflng composition, the film-forming constituents of which consist essentially of approximately 50% by weight of a wax and about 50% by weight of a gum.

6. An article of manufacture comprising a thin flexible transparent sheet of cellulose acetate coated with a film of a moistureprooflng comthe film-forming constituents of which y weight of ester gum and about 50% by weight of parafiin.

7. An article of manufacture comprising a thin flexible transparent base sheet of cellulose acetate having a thickness of about .001" coated with a film of a molstureproofing composition, the filmforming constituents of which consist essentially of approximately 55% wax and about gum.

B. A moistureproofing composition adapted for rendering cellulose acetate sheets moistureproof but not greasy or tacky, the film-forming constituents of which consist essentially of a wax,

a guru and a plasticizer, the ratio of wax to gum being between about 40:60 to 78:22 and a solvent therefor which is a non-solvent for cellulose acetate.

9. A moistureprooflng composition adapted for rendering cellulose acetate sheets moistureproof but not greasy or tacky, the film-forming constituents of which consist essentially of a wax and ester gum, the ratio of wax to gum being between the limits 40:60 and 78:22.

10. A moistureproofing composition adapted for rendering cellulose acetate sheets moistureproof but not greasy or tacky, the film-forming constituents or which consist essentially of approximately by weight of ester gum and about 50% by weight of paraffin, dissolved in a solvent comprising about 50% toluene and about 50% solvent naphtha.

for rendering cellulose acetate sheets moistureproof but not greasy or tacky, the film-forming constituents of which consist essentially of a wax.

and a gum, the ratio of wax to gum being between about 40:60 to 78:22, and a solvent therefore which is a non-solvent for cellulose acetate.

14. An article of manufacture comprising a.-

thin, flexible, transparent colloidized cellulose acetate sheet coated with a film of a moistureresisting composition, the film-forming constituents oi. which consist essentially of a mixture of a wax and a gum.

15. An article of manufacture comprising a thin, flexible, transparent sheet oi cellulose organic ester coated with a fllm of a moistureresisting composition, the film-forming constituents of which consist essentially of a mixture oiawaxandagum,theratiooi'waxtogum being between about 40:60 and 78:22.

16. An article of manufacture comprising a thin, flexible, transparent sheet of cellulose organic ester coated with a fllm o! a moistureconstituents of which consist essentially 'of a 10 mixture of ester gum and wax:

NORMAN 1*. BEACH.

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