US2159007A

US2159007A - Composite article and method for producing same

Info

Publication number: US2159007A
Application number: US737792A
Authority: US
Inventors: Charch William Hale; Dorothy E Bateman
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1934-07-31
Filing date: 1934-07-31
Publication date: 1939-05-23
Anticipated expiration: 1956-05-23

Description

Patented. May 23, 1939 PATENT OFFICE OOMPOSI'I'E ARTICLE AND METHOD FOR BRODUOING SAME William Hale Church and Dorothy It. Bateman, Bui'lalo, N. Y., asslgnors, by means assignments, to E. I. du Pont do Nemours a Company, Wilington. Del, a corporation oi Delaware No Drawing. Application July 31, 1934, Serial 8 Claims.

This invention relates to the art of coating and it particularly pertains to the production of moistureproof, coated, non-fibrous, celluiosic wrapping tissues, in which the surface coating tenaciously adheres to or is anchored to the cellulosic base, even when the tissue is placed in direct contact with water or when used as a wrapping directly in contact with products containing large amounts of water or moisture for prolonged periods of time.

Sheets or films of regenerated cellulose have been rendered moistureproof by coating with a moistureprooflng composition comprising in its preferred and common form a cellulose derivative, a wax or wax-like material, a blending agent and a plasticizer. These coated sheets are very eflectivc as a wrapping material for products such as bread cake, candy, cigars or the like, which it is desired to maintain in substantially their original fresh condition without any change in moisture content. Such sheets, however, are unsuited for use as a wrapping material directly in contact with products having a very high water or moisture content, such as butter, cheese, wet or frozeniish, ice cream or the like, when they are stored for appreciable and substantial periods of time, since under such conditions the moistureproof surface coating tends to loosen and/or flake off, impairing the moistureproof property of the wrapping material and producing an unsightly appearance.

It is an object of the present invention to produce coated articles in which the coating is securely anchored to the base material.

It is a further object of the invention to produce articles having a cellulosic base to which is securely anchored a surface coating.

A still further object of the invention pertains to the molstureproofing oi non-fibrous base material wherein the moistureproof coating is securely anchored to the base.

.Another object of the invention comprises the production of non-fibrous, cellulosic wrapping tissues having a molstureprooiing coating which is securely attached or anchored to the base even when subjected to the action of substantial quantitles of water over long periods oi time.

An additional object comprises the production of transparent, flexible, moistureproof material adapted for use as a wrappin tissue directly in contact with products having a high water or moisture content, which it is desired to maintain in substantially their original state, characterized in that the moistureprooflng coating, after drying, is substantially permanently secured to Renewed August 4. i938 the base by means of a substantially insoluble synthetic resin.

Other objects oi the invention will appear hereinai'ter.

Various methods for applying the. principles of 5 the invention have been discovered, for example, the anchoring effect may be obtained by (A) applying the synthetic resins to the cellulosic base sheet from an aqueous solution containing either the individual compounds such as phenol and formaldehyde, which will condense to form the resin, or containing a water-soluble incompletely condensed, tacky or sticky synthetic resin, the resin being completely condensed or polymerized on the base sheet to form the insoluble, non-tacky resin, the surface coating being subsequently applied; (B) by applying to the cellulosic base sheet an anchoring coating. comprising a synthetic resin in which the condensation of the resin-forming compounds has reached an intermediate state in which the condensation product is still sticky and tacky and soluble in organic solvents, the resin being applied from organic solvent solution, the polymerization then being permitted to continue on the base sheet until the condensation product has reached a tack-free and substantially insoluble form, the surface coating then being applied; (C) by dissolving orrotherwlse distributing in the cellulosic solution fromwhlch the him is cast, e. g. viscose, materials which will be co-precipitated when the fllm is cast and which will subsequently yield insoluble, tack-free resins, casting the film and then applying the surface coating. Various ways of carrying out these methods will be described in detail below, it being understood that the examples given are illustrative and are not intended to unduly limit the scope of the invention.

By the expression anchor or equivalent thereof used herein is'meant the securing of the suriace coating imposed on the base in such a way that the resulting product will withstand the deleterious eflect of water or moisture and the surface coatlng will not loosen and/or flake oil from the base when the product is directly in contact with water or moisture for appreciable and substantial periods of time, c. g. for a period of several weeks or more.

For the purposes of this specification and claims, we define moistureproof materials as those which, in the form of continuous, unbroken sheets or films, permit the passage 0! not more than 690 grams of water vapor per 100 square meters per hour, over a period of 24 hours, at approximately 39.5 0. plus or minus 0.5 0., the

relative humidity of the atmosphere at one side of the film being maintained at least at 98% and the relative humidity of the atmosphere at the other side being maintained at such a value as to give a humidity diflerential of at least 95%.

Moistureproofing coating compositions are defined as those which, when laid down in the form of a thin, continuous, unbroken film applied uniformly as a coating with a total coating thickness not exceeding 0.0005" to both sides of a sheet of regenerated cellulose of thickness approximately 0.0009", will produce a coated product which is moistureproof.

For the purposes of experimental tests, especially for those materials adaptable as coating compositions, moistureproof materials include those substances, compounds or compositions which, when laid down in the form of a continuous, unbroken film applied uniformly as a coating with a total coating thickness not exceeding 0.0005" to both sides of a sheet of regenerated cellulose of thickness approximately 0.0009", will produce a coated sheet which will permit the passage therethrough of not more than 690 grams of water vapor per 100 square meters per hour over a period of approximately 24 hours, at a temperature of 395 C. plus or minus 0.5 C. (preferably 39.5" C. plus or minus 025 C.), with a water vapor pressure diiferential of 50-55 mm. (preferably 53.4 plus or minus 0.7 mm.) of mercury. For convenience, the number of grams of water vapor passed under these conditions may be referred to as "the permeability value." An uncoated sheet of regenerated cellulose having a thickness of approximately 0.0009" will show a permeability value of the order of 6900.

From the foregoing, it is apparent that under the conditions set forth, 'a moistureproofed regenerated cellulose sheet is capable of resisting the passage of moisture of water vapor therethrough at least ten times as effectively as the uncoated regenerated cellulose sheet.

The objects of the invention are accomplished by the following invention which, in one of its phases, contemplates a cellulosic base, a surface coating comprising essentially a cellulose derivative, and an anchoring agent comprising a synthetic resin applied to and/or incorporated in the cellulosic base either as an intermediate condensation product which is still tacky and soluble in organic solvents or, alternatively, soluble in water, or as a mixture of the water-soluble compounds which condense subsequently to form the resin, the condensation reaction then being permitted to take place until the resin has completely polymerized to a tack-free, substantially insoluble state.

A. Anchoring by means of synthetic resins introduced from aqueous solution The preferred form of the invention, whereby an extremely effective anchoring of a surface film to a base film may be accomplished, comprises applying the synthetic resin onto the base from an aqueous medium. In accordance .with this form of the invention, the aqueous solution to be applied to the base film comprises either a solution of the individual resin-forming compounds, for example, a phenol and an aldehyde, or, alternatively, an aqueous solution of an incompletely condensed synthetic resin which is still soluble in water, the intermediate resin, after deposition onto the base film, being capable, at

' elevated temperatures in the presence of a condensing agent or catalyst, if desired, of condens- 7 and at temperatures not excessively high.

ing to form an insoluble, non-tacky resin. After applying the intermediate resin to the film. the film is then subjected to temperatures sufficiently high to cause the formation therein and thereon of the resin in a tack-free and insoluble state during the drying of the ceiluiosic sheet.

Resins suitable for application to the nonfibrous base sheet, according to this method of the invention and having the characteristics desirable in an anchoring medium, are resins of the phenol-aldehyde and urea-aldehyde types.

Resins contemplated as suitable for application as coatings for this preferred form of the invention are resins capable of rapid formation at temperatures under 200 6., preferably capable of formation in 5 minutes or less at temperatures C. or less, substantially insoluble and unaffected by water and organic solvents such as those employed in surface coating compositions, preferably substantially colorless at least in very thin films which are preferably less than 0.0001" in thickness and formed by the reaction of substances which are themselves sufllciently watersoluble to yield aqueous solutions of the necessary concentration.

Combinations of resin-forming materials which may be employed in dilute aqueous solution to produce a suitable resin as an anchoring medium in or on the celluloslc sheet include meta-cresol and formaldehyde, resorcinol and formaldehyde, phloroglucinol and formaldehyde, orcinol and formaldehyde, phenol and formaldehyde, methyl-phloroglucinol and formaldehyde, resorcinol monomethyl ether and formaldehyde, preferably in each instance with an alkaline condensing agent such assodium hydroxide, potassium hydroxide, sodium carbonate or, in some cases, an amine like ethylene diamine; or a suitable aqueous solution may contain urea, theourea, melamine, or other sufficiently water-soluble carbamide or cyanuric acid derivative and formaldehyde with an acidic or alkaline condensing agent, preferably the former. Formaldehyde maybe replaced by other water-soluble and reactive aldehydes such ase acetaldehyde, glyoxal, or the like, in aqueous solutions of either phenolaldehyde or aldehyde-amino resin-forming materials. In most cases, however, formaldehyde is more satisfactory as reacting more readily with the phenol, carbamide or cyanuric acid derivative in question. Of course, phenolic compounds other than the ones herein named may be used in aqueous solutions designed to produce substantially insoluble phenol-aldehyde resins in or on a non-fibrous cellulosic sheet, but the phenolic compounds mentioned have been found most suitable with respect to water-solubility and conversion to substantially insoluble resins quickly It should also be noted that phenolic compounds having two or more hydroxyl groups meta to each other react with aldehydes to produce substantially insoluble resins much more quickly and at lower temperatures than phenol itself, for example, or a polyhydric phenol with two or more hydroxyl groups not meta to each other.

In introducing a urea-formaldehyde resin into or on the non-fibrous cellulosic sheet, it is much more convenient to employ in place of an aqueous solution of urea, formaldehyde and a condensing agent, an aqueous solution of dimethylol urea, which is a water-soluble condensation product of urea and formaldehyde formed in an alkaline medium, with a condensing agent which will impart to the solution a pH between 3 and 5,

til

such as salicylic acid, gluconic acid, or ammonium thiocyanatc, for instance.

In employing aqueous solutions of resin-torming materials, we prefer dilute solutions, preferably of such concentration that the total weight or resin-iorming materials is between 1.5 and 3 per cent and the weight of condensing agent, it used, between 0.01 and 0 .15 per cent, although, of course, solutions more or less concentrated in resin-forming materials or condensing agent may be used 11' desired. In these solutions, a desirable molar ratio of phenol to aldehyde is approximately 1 to 3 and a suitable ratio oi carbamide to aldehyde is 1 11101 of carbamide to 2-3 mols of aldehyde, although it is understood that these ratios may be varied in any desirable manner without departing from the essential procedure of forming in or on a non-fibrous cellulosic sheet a substantially insoluble resin by causing to react by means of elevated temperatures, preferably with a condensing agent, materials capable of forming the resin and introduced into or on the cellulosic sheet from their aqueous solution.

The term "carbamide, as used throughout the specification and. claims, is meant to include carbamide derivatives and derivatives of cyanuric acid.

As a base, this invention contemplates any smooth, dense, substantially non-porous, nonfibrous, cellulosic sheet, film or tubing precipitated from an aqueous cellulosic dispersion or solution, or from a solution of a cellulose ester or ether in an organic solvent or mixture of solvents. This includes sheets or films of regenerated cellulose, whether precipitated from solutions of viscose, cuprammonium, or any other aqueous solutions or dispersions of cellulose, and also sheets or films of such cellulose esters and ethers as are precipitated from aqueous solutions or dispersions, such as glycol cellulose, cellulose glycollic acid, methyl or ethyl cellulose of low alkyi content, cellulose phthalic acid and other similar cellulose products described by these terms; also sheets or films of cellulose acetate, cellulose propionate, cellulose butyratc, ethyl cellulose, benzyl cellulose or any other ester or ether of cellulose precipitated from a solution of the cellulose derivative in an organic solvent or solvent mixture. It is, of course, understood that this invention does not contemplate as a base cellulose esters or ethers in the stage of esterification or etheriflcation which renders them soluble in the solvents employed in the surface coating to be applied. However, there are many degrees of est-erification or etheriiication with corresponding degrees of solubility in various solvents, and this invention does comprehend sheets or films of cellulose esters or ethers at stages of esterification or etherification in which they are soluble in certain organic solvents or solvent mixtures and yet are insoluble in the organic solvents employed in the surface coating solution. When any given coating composition is applied to such sheets or films, said coating composition will not penetrate therethrough and will normally result in asuriace coating.

In certain cases of coated materials, this invention also contemplates as a base cellulosic threads or fibers, whether natural fibers such as cotton, linen, jute, ramie, hemp, or the like, or synthetic fibers precipitated from aqueous cellulosic dispersions or solutions, or from solutions of cellulose derivatives in organic solvents. It will be understood, however, that the preferred form or the invention comprises its application to non-fibrous cellulosic sheets or him: and the detailed description of the invention will be so limited. a

As a surface coating this invention contemplates any flim-iorming composition, preferably a moistureproof composition, having a cellulose derivative base or a base consisting of an ether resin, a vinyl resin, rubber, a rubber-like material, rubber derivative, or product resulting from the chemical treatment of rubber, any of which bases may be modified by the addition or blending agents, waxes or wax-like materials, plasticizers, et cetera. Cellulose derivatives suitable for use as a coating base include cellulose nitrate, cellulose acetate, ethyl cellulose, benzyl 'cellulose, or the like. By the term, ether resin" is meant a resin during the production of which ether linkages are formed and resulting from the reaction of polyhydric phenols with aliphatic polyhalides, such as, for example, the resin formed by the reaction of dihydroxydiphenyl propane and B,B'-dichlorodiethyl ether in the presence of alkali. Among the vinyl resins, we prefer a resin composed of 60 per cent vinyl chloride and -i 0 per cent vinyl acetate although various other vinyl resins are suitable for use in coating compositions. As rubber-like materials, rubber derivatives or products resulting from the chemical treatment of rubber may be mentioned thermoprene, a thermoplastic, unsaturated hydrocarbon derived from rubber hydrocarbon, described in detail by H. L. Fisher in "Industrial & Engineering Chemistry, vol. 19, No. 12, page 1325, hydrogenated rubber, polymerized chloro- 2-butadiene-l,3, chlorinated rubber, those products known under the trade names "Pliolite" and "Plioi'orm, the reaction products of rubber and stannic chloride, ferric chloride, boron fluoride. chlorostannic acid, etc., described in detail by Thies and Clifford in "Industrial and Engineering Chemistry, vol. 26, page 123, or thelike. The surface coating may be applied to the cellulosic material. from solution in organic solvents or from a melt, depending upon the nature of the cellulosic material to be coated and the composition of the coating employed. In the preierred form, for coated cellulosic sheet or film materials, the surface coating is a moistureproof coating comprising a cellulose derivative, a wax or wax-like material or other moistureprooiing agent, a blending agent and a plasticizer, and is applied from solution in organic solvents.

In order that the finished non-fibrous cellulosic sheet may be of the desired softness, a softener such as glycerine may be incorporated in the aqueous solution of resin-forming materials. Varying amounts of suitable dyes may also be added to the solutions The aqueous solution of resin-forming materials may be applied to the non-fibrous cellulosic sheet by dipping or immersing the sheet in the solution, by brushing or spraying the solution on the sheet or by applying it to the sheet by rollers or by any other convenient means. Moreover, the solution may be applied either to the cellulosic sheet in the gel condition, that is, after the same has been coagulated and at least partially regenerated but before being dried, or to the finished, dry cellulosic sheet. In any case, after the application of the aqueous solution of resin-forming materials to the cellulosic sheet, the excess solution is removed from said cellulosic sheet by squeeze rolls or any known means, preferably to such an extent that an amount of III weight of the cellulose remains in the cellulosic sheet. The amount of substantially insoluble resin present in or on the finished dry cellulosic sheet depends upon the concentration of the aqueous solution of resin-forming materials used and upon the amount of this solution removed from the sheet by squeeze rolls or other means prior to the drying of the sheet, but, in the preferred form of this invention, ranges from2 to 12 per cent of the weight of the sheet, although it may be desirable for certain purposes to have present in or on the cellulosic sheet amounts of resin greater or less than those included within these limits.

The amount of heat required to convert the resin-forming materials, applied to the cellulosic sheet from an aqueous solution, to a substantial ly insoluble resin varies, of course, with the individual resin and the materials employed to produce it. From the standpoint of convenient operation and effect upon the cellulosic sheet, it is usually desirable to effect the formation of the resin in a comparatively brief period of 5 minutes or less at temperatures under 100" C. It is possible, however. to vary the time and temperature rather widely to suit the requirements of special resins without unfavorably affecting the quality of the cellulosic sheet. Temperatures very much under 100. sometimes as low as 40 to 50 C., are oftai sufficient and desirable to cause resinformation in or on the sheet when a period of time longer than 5 minutes is employed. Moreover, a temperature much higher than 100 (3., even as high as 180' C. can be applied for a very brief interval to a cellulosic sheet wet with an aqueous solution of resin-forming materials to bring about the formation of the desired substantially insoluble resin without damaging the cellulosic sheet. The necessary heat may be applied by bringing the cellulosic sheet into contact with heated dryer rolls or other heated surfaces or by leading the sheet through a heated atmosphere or in any other manner. In some cases, where the formation of the resin from the materials used in the aqueous solution is slow and it is undesirable to employ a high temperature to speed up the resin-formation, the reaction can be completed in the short time and at the desired only moderately elevated temperature by allowing the solution of resin-forming materials to stand or "age for several hours before applying it to the cellulosic sheet. Presumably, at least, the initial condensation of the resin-forming materials takes place in the solution before its introduction to the cellulosic sheet and thereby shortens the time required for completing the reaction to form a substantially insoluble resin in or on said sheet.

In its preferred and simplest form for producing non-fibrous cellulosic sheet or film materials, capable of securely anchoring a surface coating, this invention contemplates applying the dilute aqueous solution of resin-forming materials to the cellulosic sheet in the gel condition directly on the casting machine, as, for example, in the manufacture of regenerated cellulose sheeting. This can be done conveniently by dissolving the resin-forming materials in the desired amounts directly in the bath commonly used to provide a softening treatment and containing the aqueous solution of glycerine or other softener for the cellulosic sheet, allowing the gel sheet to be led through said bath and subsequently dried in the usual manner. The resulting sheet can then be 9,109,007 solution equal to between 3 and 4 times thecoated with a moistureproof surface coating which will remain anchored to the sheet for a period of days or even weeks even in direct contact with water or moisture.

It will be apparent from the foregoing that this invention constitutes a marked departure from and improvement over previous processes for producing moistureproof non-fibrous cellulosic sheets in which the moistureproof surface coating firmly adheres or is anchored to the cellulosic sheet even in direct contact with water or moisture. This process is simple, eliminating the inconvenience and expense of two coating operations and requiring no additional equipment since the anchoring medium consisting of a substantially insoluble resin results from treating the cellulosic sheet with an aqueous solution of resinformlng materials during the regular process for producing the cellulosic sheets. Moreover, the finished sheet, containing a substantially insoluble resin therein or thereon, whether before or after the application of a surface coating. is completely odorless. Furthermore, cellulosic sheets having a substantially insoluble resin present therein or thereon by reason of the treatment described by this invention are capable of retaining extremely well a surface coating with a cellulose derivative base or a base consisting of an ether resin, a vinyl resin, rubber, a rubber-like material, rubber derivative, or product resulting from the chemical treatment of rubber (preferably a moistureproof surface coating). These surface coatings adhere or anchor tenaciously to such cellulosic sheets even in direct contact with water for periods of weeks and are very suitable for use as a wrapping in direct contact with products having a high moisture or water content such as butter. cheese, wet or frozen fish, ice cream or the like. In addition, non-fibrous cellulosic sheets containing therein or thereon a substantially insoluble resin, according to this invention, have various uses in themselves without the application of a surface coating. By reason of the unique surface which they possess. for instance, they are particularly adapted for certain types of printing and embossing and for various other uses which will at once suggest themselves. Moreover, this invention supplies a method of laminating together non-fibrous cellulosic sheets. Two or more non-fibrous cellulosic sheets wet with an aqueous solution of resinforming materials such as described by this invention can be caused to adhere very firmly by superimposing them one sheet upon the other and drying them thus under pressure at elevated temperatures sufllcient to cause the formation of the substantially insoluble resin.

The following examples illustrate the anchor ing of a coating to a base by the use of a solution of resin-forming components.

Example L-A sheet of regenerated cellulose in the gel condition which has been cast from viscose. desulfured, bleached and washed free from impurities in the usual manner in the casting machine and is ready for the softening treatment, is led through an aqueous glycerine bath which in addition to 4% per cent by weight of ghrcerine normally used for softening also contains one per cent by weight of resorcinol, 2 per cent by weight of commercial formaldehyde (that is, 0.8% H200) and 0.02 per cent by weight of sodium hydroxide, which solution has been allowed to age at room temperature for 12 hours or more before using. The sheet of regenerated cellulm is in contact with the aqueous solution of glycerine, resorcinol and formaldehyde for from 10 to 20 seconds, after which the excess solution is removed from the sheet by means of squeeze rolls which reduce the water content of the sheet to between three and four times the weight of the cellulose, after which the sheet of regenerated cellulose, wet with the solution of resin-forming materials and glycerine, is ready to be dried. During the drying, water is removed from the sheet of regenerated cellulose and the resin-forming materials react under the influence of the heat employed for the drying to form a substantially insoluble resin in or on the sheet.

Drying may be carried out according to the usual method for drying regenerated cellulose sheeting on the casting machine by bringing the sheet directly from the squeeze rolls into contact with heated rolls and drying the sheet at temperatures between 60 and 90 C. However, there may be a tendency for the substantially insoluble resin, formed by the reaction of the resinforming materials, to be deposited on the dryer rolls as they become wet with the solution of resin-forming materials from the wet cellulosic sheet passing over them. This deposit of resin may flake off from time to time on the fresh cellulosic sheeting passing over the rolls, thereby imparting a faintly mottled appearance to the dry uncoated sheet.

Therefore, in this preferred example the regenerated cellulose sheet wet with the solution of resin-forming materials and glycerine, after passing through the squeeze rolls and before coming into contact with the dryer rolls is first given a preliminary partial drying out of contact with any surface by passing the sheet through air heated to an elevated temperature by means of a suitable arrangement of gas burners or electric heaters, whereby the moisture content of the sheet is reduced to any desired extent, for instance, from /3 to /2 its initial water content before coming in contact with the dryer rolls. The partially dried cellulosic sheet is then led over the heated rolls of the casting machine in the usual manner to complete the drying operation and to complete the formation of the substantially insoluble resin in or on the sheet.

The resulting sheet of regenerated cellulose with a substantially insoluble resin therein or thereon may be rehumidified if necessary to bring it to the desired moisture content and is then coated with a moistureproofing composition of the following formula:

Per cent Nitrocellulose 6.44 Gum dammar 2.17 Dibutyl phthalate 2.40 Paraflin (M. P. 60-6l C 0.52 Zinc stearate 0.17 Ethyl acetate 55.85 Toluene 28.70 Ethanol 3.59 Acetone 0.15 Benzene 0.01

The sheet is passed through the moistureproofing composition, the excess of which is removed by scraping or any suitable means and the coated sheet is dried at a temperature above the melting point of the wax, after which the finished, coated sheet may be again conditioned to bring it to the desired moisture content. The resulting product is a coated sheet of regenerated cellulose which is transparent, flexible, odorless and moistureproof, and to which, by reason of the presence in or on the cellulosic sheet of a substantially insoluble resin, the moistureproof surface coating adheres or is anchored very tenaciously even when the sheet is in direct contact with water or is used as a wrapping directly in contact with products containing large amounts of water or moisture, such as butter, cheese, wet or frozen fish, ice cream, or the like, for very substantial periods of time.

Example II A sheet of regenerated cellulose in the gel condition which has. been cast from viscose, desulfuted, bleached, and washed free from impuritiesin the usual manner on the casting machine and.is ready for the softening treatment, is led through an aqueous glycerine bath which, in addition to /2% by weight of glycerine, which is present for softening purposes, also contains 3 per cent by weight of dimethylol urea and 0.1 per cent byweight of salicylic acid, and which has been allowed to stand for 48 hours at room temperature before using. The sheet of regenerated cellulose is allowed to remain in contact with the aqueous solution of glycerine and dimethylol urea for from 10 to 20 seconds after which the excess solution is removed from the sheet by means of squeeze rolls so that the water content of the sheet is reduced to between three and four times the weight of the cellulose. The celiulosic sheet wet with the aqueous solution of glycerine and dimethylol urea is then dried according to the usual procedure for drying regenerated cellulose sheeting by passing it over the heated dryer rolls of the casting machine. In this case, however, the temperature of the dryer rolls is kept below 0., preferably between 40 and 50 C. After drying the cellulosic sheet is conditioned if necessary to bring it to the desired moisture content and is then coated with a moistureproofing lacquer of the following composition:

Per cent Nitrocellulose 6.44 Gum dammar 2.17 Dibutyl phthalate 2.40 Parafiin (M. P, 60-61 C 0.52 Zinc stearate 0.17 Ethyl acetate 55.85 Toluene 28.70 Ethanol 3.59 Acetone 0.15 Benzene 0.01

The sheet is passed through the moistureprooiing composition, the excess of which is removed by scraping or other suitable means, and the coated sheet is dried above the melting point of the wax, after which the finished sheet may be conditioned again to bring it to the desired moisture content. The resulting coated sheet of regenerated cellulose is flexible, transparent, odorless, colorless and moistureproof, and retains its moistureproof surface coating very tenaciously for appreciable and substantial periods of time even in direct contact with water or as a direct wrapping for products containing large amounts of water or moisture.

Example III.-A sheet of regenerated cellulose treated with an aqueous solution of glycerine, resorcinol, formaldehyde, and sodium hydroxide and dried according to the procedure in Example I and ready for the application of the surface coating, is coated with a moistureproofing composition comprising a solution of ethyl cellulose, paraflin, a blending agent and a plasticizer.

Example IVFA sheet of regenerated cellulose treated with an aqueous solution of glycerine, resorcinol, formaldehyde and sodium hydroxide and dried according to the procedure in Example I and ready for the application of the surface coating is coated with a moistureprooflng composition comprising a vinyl resin (60% vinyl chloride and 40% vinyl acetate), a wax and a plasticizer.

Example V.--A sheet of regenerated cellulose treated with an aqueous solution of glycerine, resorcinol, formalderyde and sodium hydroxide and dried accordang to the procedure in Example I, and ready for the application of the surface coating is coated with a composition comprising essentially the ether resin prepared by condensing dihydroxydiphenyl propane and B, B-dichlorodlethyl ether in alkaline solution, and a wax.

Example VL-A' finished or dry sheet of glycol cellulose is immersed in an aqueous solution containing 0.75% phloroglucinol, 1.5% commercial formaldehyde, 87%, (that is, 55% H260). and 0.015% sodium hydroxide. The excess solution is removed from the sheet which is dried at an elevated temperature, preferably between 70 and 90 C., and the resulting dried sheet is coated with a composition comprising essentially Pliolite and a wax.

Example VII.-A sheet of cellulose acetate is immersed in the aqueous solution described under Example VI, dried and coated with a moistureprooi' coating comprising, essentially, the ether resin formed by the reaction of dihydroxydlphenyl propane and B,B'-dichlorodiethyl ether in alkaline solution, and a wax.

Example VIII.--A sheet of regenerated cellulose is passed through an aqueous solution containing one per cent by weight of m-cresol, 2 per cent by weight of commercial formaldehyde (37%) and 0.02 per cent by weight of sodium hydroxide which has been allowed to stand for 48 hours at room temperature before using. The excess solution is removed and the sheet dried almost completely at 90 C., then subjected to a very brief heating of 5 seconds, or preferably less, at a temperature of 180 C., after which the sheet is cooled, humidified, and coated with a moistureprooflng composition comprising a solution of nitrocellulose, paramn, gum damar and dibutyl phthalate.

B. Use of soluble synthetic resins deposited from a non-aqueous solution An alternative method of anchoring a surface coating to a cellulosic base can be effected by applying to the base a solution in an organic solvent of an intermediate, tacky, or sticky, incompletely condensed or polymerized synthetic resin, and subsequently completing the condensation thereof to obtain a tack-free, substantially insoluble resin and then aplying the surface coating.

This form of the invention contemplates the use of base sheets, films, or tubing, such as have been described under A above.

The surface coating which may be used in accordance with this method is capable of wide variation, for example, the coating may comprise a cellulosic derivative base such as cellulose nitrate, cellulose acetate, ethyl cellulose, benzyl cellulose, or the like, which may be modified as desired by the addition of blending agents, waxes, plasticizers, etc. Preferably, this invention contemplates 9. molstureproofing coating comprising in the preferred and common form a cellulose derivative, a wax or wax-like material, a blending agent and a plasticizer. For further variation in the character of the surface coating, see the dis- *cussion under "A".

In accordance with this alternative method, an undercoat of a synthetic resin is applied to the lmse from a solutoin in an organic solvent or mixture of solvents, the resin which is dissolved in the solution being sticky or tacky, only partially condensed, polymerized or hardened, and being capable after deposition on the base sheet or film of being completely condensed, polymerized, or hardened to a substantially insoluble, tack-free form under the influence of heat and, if desired, in the presence of a catalyst.

We prefer to use for the anchoring undercoat partially condensed, polymerized or hardened synthetic resins which condense, polymerize or harden completely to a tack-free, substantially insoluble stage in extremely thin coatings, preferably less than 0.0001 inch in thickness, in a period of a few minutes at an elevated temperature preferably not exceeding 125 degrees 0., and it is desirable that the period be five minutes or less and the temperature be between 90 degrees and '1 degrees C. However, different resins will require different conditions and the time and temperature may be varied according to the nature of the particular resin used. Thus, for instance, a longer time at a lower temperature may be employed to effect the desired result with a given resin which in a shorter time would require a much higher temperature. It is, of course, understood that any of the well-known catalysts may be used with the partially condensed, polymerized or hardened resin to accelerate its conversion to a final hardened, substantially insoluble form on the cellulosic sheet.

of the partially condensed, polymerized or hardened resins available, we prefer to use those with at least a fair degree of flexibility in order to obtain undercoats which do not form visible cracks on the cellulosic sheet when it is creased or crinkled. It is often impossible, however, successfully to use resins which are commonly regarded as somewhat brittle since for the purposes of this invention they are applied to the cellulosic sheet in such extremely thin layers that they flex with the sheet whereas thicker layers, of several ten-thousandths of an inch thickness, for example, would crack visibly if sharply bent. It is also preferable to employ for the anchoring undercoat partially condensed, polymerized or hardened synthetic resins which are substantially colorless in films of several ten-thousandths o1 an inch thickness or less and which are substantially odorless after having been condensed, polymerized or hardened and which are substantially free from drying oils, drying oil acids or other drying oil derivatives.

As has been stated, the synthetic resin undercoat is usually extremely thin, preferably less than 0.0001 inch in thickness, being often as thin as 0.00001 to 0.00003 inch in thickness, so that the thickness of the resin-coated cellulosic sheet is not appreciably greater than that of the original sheet. To obtain resin undercoats of the requisite degree of thickness, the partially condensed, polymerized or hardened synthetic resin may be applied from solution in a suitable solvent or mixture of solvents, such as acetone, ethanol, butanol, ethyl acetate, benzene, toluene, amyl acetate or the like. The resin solution may be of any suitable consistency as determined by the apparatus employed and the thickness of the coating desired. In practice, solutions containing between 5 and per cent solids have been found convenient. Application of the resin solution to the cellulosic sheet may be made by immersing the sheet in the solution or by brushing or spraying the solution on the sheet or by applying the solution to the sheet by rollers or any other convenient means," after which the coating is smoothed and the excess removed in any suitable manner.

The partially condensed, polymerized or hardened synthetic resins suitable for use as an anchoring undercoat according to this alternative form of the invention are not limited to the phenol-aldehyde resins exclusive of all other types (although the phenol-aldehyde type is preferred), but rather include resins of any type which answer the requirements of being capable of application to the cellulosic sheet in a. soluble, tacky, partially condensed, polymerized or hardened stage and of subsequent further complete condensatlon, polymerization or hardening to a final tack-free, substantially insoluble form on the sheet.

As specific resins suitable for use as anchoring undercoats according to this invention may be cited certain phenol-formaldehyde resins known under the trade name "Durez" and also a resin formed by the interaction of dihydroxy-diphenylpropane and formaldehyde.

If for any reason it is desired to modify the characteristics of any specific partially condensed, polymerized, or hardened synthetic resin or of the anchoring undercoat which said resin forms on the cellulosic sheet, for example with respect to flexibility, hardness or color, certain other materials may be combined with the synthetic resin in question. These include natural resins and resirr'acids, such as, for example, rosin and hydrogenated rosin, other synthetic resins, oils and oil acids, fats, waxes and wax-like materials, drying oils and drying oil acids. dyes or the like. These materials may be combined with the partially condensed, polymerized or hardened synthetic resin either by addition along with the other ingredients during the preparation of the resin itself or by addition to the solution of said resin in organic solvents after it has reached the partially condensed, polymerized or hardened stage and is ready for application to the cellulosic sheet. It is to be clearly understood, however, that in the case of additions of drying oils or drying oil acids to the synthetic resins, the anchoring efi'ect depends upon the completion of the condensation, polymerization or hardening of the partially condensed, polymerized or hardened synthetic resin to the final tack-free, substantially insoluble form on the cellulesic sheet. It is also to be noted that if the addition to the synthetic resin undercoat is a wax or wax-like material there results after the completion of the condensation, polymerization or hardening of the synthetic resin on the cellulosic sheet, a coating of the resin which not only is firmly anchored to the cellulosic sheet even in direct contact with water or moisture but which also exhibits mois' tureproofness.

The following examples illustrate the anchoring of films by the use of a solution of a soluble resin:

Example IX .-The resin to be employed as the anchoring intermediate coating or undercoat is prepared by condensing dihydroxydiphenyl-propane and formaldehyde in alkaline solution at room temperature and isolating the viscous liquid resulting upon acidification of this solution. For

example, one molar equivalent of dihydroxydiphenyl-propane (M. P. 157 C.) is dissolved in an aqueous alkaline solution containing 2 molar equivalents of sodium hydroxide, 3.25 molar equivalents of commercial formaldehyde (37%) are added and the clear solution allowed to stand for two days at room temperature. The mixture is then acidified and the viscous, practically colorless liquid which separates is washed acid-free and the water removed in a vacuum oven. This viscous liquid is a resin which at this stage is only partially condensed, polymerized or hardened and which requires additional heating to complete its condensation, polymerization or hardening to a. tack-free, substantially insoluble form. It is now dissolved in ethyl alcohol to give a solution which will contain from '7 per cent to 33 per cent resin depending upon the type ofcoating to be employed.

A coating of this ethyl alcohol solution of partially condensed, polymerized or hardened resin is applied to a finished sheet of regenerated cellulose by passing the sheet through the solution, removing the excess by means of a suitable scraping mechanism to such an extent that the dried resin coating on the sheet will not exceed 0.0001 inch in thickness, and thereafter drying the coated sheet at 110 C. until all the solvent has been removed from the sheet and the resin coating has become hard and tack-free and substantially insoluble. The resin-coated cellulosic sheet is then cooled and rehumidifled to the desired moisture content, after which the moistureproof surface coating is applied by passing the cellulosic sheet through the moisture-proofing bath, removing the excess by means of a suitable scraping mechanism and drying at a temperature above the melting point of the wax in the moistureproofing composition. After drying, the moistureproof coated cellulosic sheet is again cooled and reconditioned to the desired moisture content. The moistureprooflng bath used in this example has the following composition:

Per cent Nitrocellulose 5.21 Gum dammar 3.22 Dibutyl phthalate 2.30 Paraflin (M. P. 61 C.) 0.88 Zinc stearate 0.10 Ethyl acetate 45.76 Toluene 35.63 Ethanol 6.23 Acetone 0.67

The moistureproof sheet of regenerated cellulose produced by this procedure is transparent, flexible, odorless and colorless and retains its moistureproof surface coating tenaciously even in direct contact with water or moisture for prolonged periods of time so that it is admirably suited for use as a wrapping material employed directly in contact with products containing large amounts of water or moisture such as butter, cheese, wet and frozen fish, ice cream or the like, even when these products are to be stored for appreciable periods of time.

Example X .Riegenerated cellulose sheet material is coated with a 15 per cent ethanol solution of a commercial product marketed under the designation Durez Serial No. 1622-R-2" which product is essentially a partially set up phenol: formaldehyde resin advanced in its polymerization or condensation only to a stick or tacky stage. After being passed through the solution the cellulosic sheet is freed of excess solution by scraping or any convenient means so that the resin coating remaining on the sheet after drying will not exceed 0.0001 inch in thickness and is thereafter dried for several minutes at C. until the ethanol has been volatllized and the resin has been converted to a tack-free, substantially insoluble condition. The resin-coated cellulosic sheet is then cooled and rehumidifled to the desired moisture content, after which it is coated with a moistureproofing composition comprising a solution of ethyl cellulose, a wax, a blending agent and a plasticizer, and, after removing the excess coating solution by suitable means, dried at a temperature above the melting point of the wax in the moistureprooilng composition, cooled and again rehumidified to the desired moisture content.

The resulting moistureproof cellulosic sheet is transparent, flexible, odorless and colorless and its moistureproof surface coating is so securely anchored to the basic cellulosic sheet by virtue of the immediate coating or undercoat of synthetic resin that said mostureproof cellulosic sheet can be very successfuly used in direct contact with water or moisture. Moreover, the process described in the above example employs synthetic resins which are easily reproducible with desired characteristics.

0. Anchoring by means of synthetic resins dissolved or otherwise distributed in the cellulosic film-forming solution It has furthermore been discovered that an effective anchoring of a coating to a cellulosic base film may be accomplished by incorporating in the liquid film-forming material from which the base is cast, for example, in the aqueous alkaline cellulose xanthate solution used for the casting of regenerated cellulose wrapping tissues by the viscose process, alkali-soluble, incompletely condensed or polymerized synthetic resins which are subsequently precipitated simultaneously with the cast sheet. In addition to incorporating a synthetic resin in the cellulosic sheet in the aforesaid manner, the resin-containing non-fibrous cellulosic sheet may also be treated with an aqueous solution of a substance capable of further polymerization on heating or oi inter-action with the incompletely condensed or polymerized synthetic resin in the cellulosic sheet or of liberating formaldehyde or capable of two or of all of these functions. After drying, the cellulosic sheet is ready for the application of the surface coating, preferably a moistureproof coating, in the usual manner. The process may be directly applied to existing equipment used in the manu facture of cellulosic sheets.

Carrying out this modification of the invention, in its preferred form, there will be produced an article comprising a cellulosic base, a, surface coating consisting essentially of a cellulose derivative or an ether resin, and an anchoring medium comprising a synthetic resin dispersed throughout the cellulosic base, and precipitated with it, from an aqueous, alkaline cellulosic dispersion or solution.

As a base this invention contemplates any smooth, dense, non-fibrous, cellulosic sheet or film precipitated from an aqueous alkaline cellulosic dispersion or solution. By this, we include sheets or films of regenerated cellulose and of such cellulose esters and ethers as are precipitated from aqueous solutions or dispersions, such as glycol cellulose, cellulose glycollic acid, methyl cellulose and ethyl cellulose, cellulose phthalic acid and other similar cellulose products described by these terms. When any given coating composition is applied to such cellulosic sheets or films, the coating composition will not penetrate therethrough and will normally result in a surface coating.

The surface coating applied to the synthetic resin-containing base, in accordance with this form of the invention, may be of the same character as has been discussed for the surface coating under A above.

As an anchoring medium the instant invention contemplates any alkali-soluble, acid-insoluble, incompletely c'o densed or polymerized synthetic resin which as been dispersed uniformly throughout the cellulosic sheet by dissolving it in the aqueous, lkaline cellulosic solution or dispersion from which the sheet is to be cast and thereafter precipitated in and simultaneously with the cellulosic sheet by means of the acid precipitating bath. Resins of the phenol-aldehyde and polybasic acid-polyhydrlc alcohol types (commonly known as Glyptals") have been found particularly suitable for use as anchoring media in this manner. In addition to alkali-solubility and acid-insolubility, it is desirable that the resin to be incorporated in the cellulosic sheet be capable of further condensation or polymerization during the drying of the cellulosic sheet and that it be sufficiently condensed or polymerized that after the drying of the cellulosic sheet at elevated temperatures it does not impart a sticky feel to the dry cellulosic sheet containing it. It is also desirable that the resins used in the practice of this] invention be substantially colorless, at least in very thin films. As specific resins which when incorporated in the cellulosic sheet by dissolving them in the aqueous alkaline cellulosic solution or dispersion from which the sheet is to be formed, impart to said sheet the property of securely anchoring a surface coating may be mentioned phenol-formaldehyde or resorcinol-formaldehyde resins in suitable stages of condensation or polymerization, resins formed by the condensation of dihydroxydiphenyl propane and formaldehyde in alkaline solution, and polybasic acid, polyhydric alcohol resins such as. for example, the condensation product of glycerol, glycol, and adipic acid.

The resin to be employed as an anchoring medium is either added to the aqueous alkaline cellulosic solution or dispersion-directly, preferably in finely divided form if it is a solid, and stirred until completely dissolved in the cellulosic solution or dispersion, or the resin may be first dissolved in dilute sodium or ammonium hydroxide and the resulting alkaline solution of resin added to the cellulosic solution or dispersion with thorough mixing. Any desired amount of resin may be incorporated in the cellulosic sheet although from 5 to 25 per cent by weight of resin on the basis of the total solids in the sheet is sufficient to give satisfactory anchorage. Moreover, amounts of resin in excess of 25 per cent by weight of the solids in the finished sheet often result in a somewhat weakened and less flexible sheet.

After the resin has been dissolved and well mixed in the aqueous alkaline cellulosic solution or dispersion, the cellulosic sheets are cast, coagulated, regenerated, washed and bleached, in the usual manner, softened if desired and dried at elevated temperatures, preferably not above 110 C.

If it is desired to obtain still more permanent (ill anchorage of the surface coating to the cellulosic sheet than is obtained by the incorporation of a resin in the cellulosic sheet containing the synthetic resin dispersed therein, after being bleached and washed free of impurities but before being dried, may be further treated by passing it through an aqueous solution of a compound capable on heating of polymerizing further or of inter-acting with the incompletely condensed or polymerized resin in the sheet or of liberating formaldehyde or of two or all of these functions. Thus dilute aqueous solutions of dimethylol urea. monomethylol urea, hexamethylenetetramine, water-soluble condensation products of thiourea and formaldehyde or cyanuric acid and formaldehyde and many similar compounds may be employed to good advantage. These compounds may be employed in aqueous solutions of widely varying concentrations, limited, of course, by their solubility, but dilute solutions of from i to per cent by weight and preferably of 2 to 4 per cent by weight are very suitable. If a softener for the cellulosic sheet is to be used, such as glycerine, for example, it may very conveniently be incorporated in the aqueous solution under discussion and be applied to said sheet simultaneously with the water-soluble compound designed to improve anchorage. It is probable that such water-soluble compounds as dimethylol urea, hexamethylenetetramine, water-soluble thiourea or cyanuric acid resins or the like still further improve the anchorage of cellulosic sheets containing incompletely condensed or polymerized synthetic resins therein by reason of their ability to liberate formaldehyde which may react with the resin in the sheet or by reason of their own ability to condense or polymerize further which makes possible interaction with the resin in the cellulosic sheet. In either case the result would be a substance on the surface of the cellulosic sheet chemically bound to the resin dispersed throughout the sheet. After the application of such aqueous solution of a substance capable on heating of liberating formaldehyde, further condensing or polymerizing, or of interacting with the resin in the cellulosic sheet or of two or all of these functions, the excess solution is removed from the sheet by squeeze rolls or other s table means so that the amount of solution remaining in the sheet is be tween 3 and 4 times the weight of the sheet and the sheet is then dried at an elevated temperature, preferably under 110 C. in any desired mannet.

The dried non-fibrous cellulosic sheet containing therein a synthetic resin incorporated as described according to this last-named alternative method, with or without having been subsequently treated prior to the drying with an aqueous solution of a compound capable on heating of establishing a chemical union with the resin in the cellulosic sheet, is then ready for the application of a surface coating, preferably a moistureproof surface coating, and is capable of anchoring said coating for substantial periods of time even when directly in contact with water or moisture.

From the foregoing, it will be apparent that this invention constitutes a marked departure from, and improvement over, previous processes for producing moistureproof non-fibrous cellulosic sheets in which the moistureproof surface coating firmly adheres to the cellulosic sheet even in direct contact with water or moisture. This process is simpler and less expensive in operation. By adding the anchoring material to the aqueous alkaline cellulosic solution or dispersion before the cellulosic sheet is cast, the expense and inconvenience of two coating operations are eliminated and a non-fibrous cellulosic sheet ready for the surface coating and capable of anchoring it is produced on the regular machinery, as for example by the usual process for manufacturing regenerated cellulose sheets, without any additional equipment or change in procedure. The optional application to the resin-containing cellulosic sheet, prior to drying, of an aqueous solution of a substance capable at the elevated temperature employed to dry the sheet of further condensation or polymerization. of interacting with the incompletely condensed or polymerized resin in the cellulosic sheet, of liberating formaldehyde or of two or all these functions. may be carried out in one of the tanks of the casting machine, usually the one containing the softening bath, so that here again no additional operation or equipment is needed. Moreover, resin-containing non-fibrous cellulosic sheets precipitated from an aqueous alkaline solution or dispersion and thereafter coated with a cellulose derivative or ether resin topcoat, preferably a moistureproofing coating comprising a cellulose derivative or ether resin, a wax or wax-like material, a blending agent and a plasticizer, constitute coated sheets the surface coating of which is well anchored to the cellulosic sheet and adheres to it tenaciousiy for substantial periods of time when in direct contact with water or when used as a wrapping directly in contact with products having a high water or moisture content such as butter, cheese, wet or frozen fish, ice cream or the like. These coated sheets, in which the anchoring effect is achieved by the presence of a synthetic resin in the cellulosic sheet, have the additional advantage of being free of odor. Furthermore, the uncoated non-fibrous cellulosic sheets containing a synthetic resin, made according to this invention, have various uses in themselves. Regenerated cellulose sheets so prepared differ from ordinary regenerated cellulose sheets with respect to surface deformation et cetera and are therefore peculiarly suited for certain types of printing and embossing, for instance, and for numerous other uses which will at once suggest themselves.

The following examples illustrate modes of anchoring coatings to bases by incorporating synthetic resins or resin-forming materials into the solution from which the base is cast.

Example XI.The resin incorporated in the cellulosic sheet as an anchoring medium is prepared by condensing dihydroxydiphenyl propane and formaldehyde in alkaline solution at room temperature and isolating the viscous liquid resulting upon acidification of this solution. For example, one molar equivalent of dihydroxydiphenyl propane (M. P. 157 C.) is dissolved in an aqueous alkaline solution containing 2 molar equivalents of sodium hydroxide; 3.25 molar equivalents of commercial formaldehyde 137%) are added and the clear solution is allowed to stand for 2 days at room temperature. The mixture is then acidified and the viscous, practically colorless liquid which separates is washed acidfree and dried in a vacuum oven. This viscous liquid is a resin which is only partially condensed, polymerized or hardened and requires further heating to complete its condensation, polymerization or hardening. It is now dissolved in 10 per cent sodium hydroxide to form a solution containing a known weight of 'resin which will preferably range from to per cent by weight.

A sumcient quantity of sodium hydroxide solution of the resin is added to a solution or viscose containing TV-2% cellulose so that the resin ent in the cellulosic sheets formed from the viacose solution will be about 10% of the total solids in the sheet. After thorough mixing 0! the resin solution in the viscose and deaeration oi the resulting mixture the resin-containing viscose is cast into sheets in the usual manner. These sheets are washed, bleached and washed again and then led through an aqueous solution containing 4 per cent by weight 01' dimethylol urea. The excess solution is removed from the sheet by squeeze rolls so that the sheet subsequently contains between 3 and 4 times its weight of solution and the sheet is then dried at temperatures between 65 and C. by passing it over heated rolls. After being cooled and humidified the sheet is coated with a moistureprooflng composition of the following formula:

Per cent Nitrocellulose 5.21 Gum dammar 3.22 Dibutyl phthalate 2.30 Paraflin (M. P. 60-61 C.) 0.88 Zinc stearate 0.10 Ethyl acetate 45.76 Toluene 35.63 Ethanol 6.23 Acetone 0.67

The cellulosic sheet is passed through this bath. the excess bath removed by a suitable scraping mechanism and the sheet dried at a temperature above the melting point of the wax in the moistureproofing composition. After drying the moistureproof coated celiulosic sheet is again cooled and humidified if necessary to the desired moisture content.

Example XII.A suflicient quantity of the resin described in Example XI is dissolved in a viscose solution so that the cellulosic sheets formed from the solution contain about 10 per cent of the resin based on the solid content of the sheets. After thorough mixing and deaeration the resincontaining viscose is cast into sheets, bleached and washed free of impurities in the usual manher and dried at temperatures between 65 and 95 C. After being cooled and humidified, the sheet is coated with a composition comprising essentially a wax or wax-like material and the ether resin resulting from the reaction of dihydroxydiphenyl propane and B,B'-dichlorodiethyl ether in alkaline solution. The excess coating composition is removed from the sheet by scraping or any suitable means and the sheet is dried at a temperature above the melting point of the wax employed in the coating composition.

Example XIII .In place of the ether resin used in Example XI, a phenol-formaldehyde resin marketed under the designation, Liquid Durez 550, is added to the viscose solution in the same amount and exactly the same procedure followed throughout as in Example XI.

Example XIV.As an anchoring medium an incompletely polymerized resin 01 the glyptal type made by the reaction of glycerol, glycol and adipic acid is incorporated in the cellulosic sheet in the manner described in the preceding examples by dissolving in the viscose sunicient resin to form 15 per cent of the total solids in the finished cellulosic sheet and before drying passing the sheet through a 4 per cent by weight aqueous solution of dimethylol urea. The finished, dry cellulosic sheet thus prepared is coated with a presmoistureprooilng composition comprising a solution of nitrocellulose, paramn, gum damar and dibutyi phthalate.

It will be seen from a study of the various alternative methods described under the headings A", 3" and "(7 above that the present invention may be applied with great efliciency and economy to the production of composite films in which the surface coating is securely anchored to the base so as to withstand the destructive action oi large amounts 01' water or moisture for prolonged periods or time. In particular, moistureproof films made from regenerated cellulose and the like by coating processes, having a high degree of resistance to deterioration when under the influence of large amounts of water, are produced in accordance with the principles oi this invention.

It will be understood that the various details involved in the preceding discussion 0! the invention may be modified in a number 0! diii'erent ways. Any variation or modification, however, which conforms to the spirit of the invention is intended to be included within the scope o! the claims.

We claim:

1. A wrapping tissue comprising a transparent, non-fibrous, celiulosic base sheet, a transparent moistureprooi coating on said base sheet, a transparent anchoring medium between said base sheet and said moistureproot coating. said anchoring medium comprising a synthetic resin taken from the class consisting of a phenol-aldehyde resin and a urea-aldehyde resin which is substantially unafl'ected by water and the solvents used in the moistureprooi coating.

2. A wrapping tissue comprising a transparent, non-fibrous, cellulosic base sheet, a transparent moistureprooi coating on said base sheet, a transparent anchoring medium between said base sheet and said moistureprooi coating, said anchoring medium comprising a synthetic resin taken from the class consisting of a phenol-aldehyde resin and a urea-aldehyde resin which is substantially unaifected by water and the solvents used in the moistureprooi coating, said anchoring medium being incorporated throughout the body of the base sheet. A

3. A wrapping tissue comprising a transparent, non-fibrous, cellulosic base sheet, a transparent moistureproof coating on said base sheet, a transparent anchoring medium between said base sheet and said moistureprooi' coating, said anchoring medium comprising a synthetic polyhydric phenol-aldehyde resin which is substantially unafieeted by water and the solvents used in the moistureprooi' coating.

4. In a process for producing a transparent, anchored, moistureproo! wrapping tissue the steps comprising applying an anchoring medium composed oi a synthetic resin taken from the class consisting of a phenol-aldehyde resin and a ureaaldehyde resin on a transparent, non-fibrous, cellulosic base sheet, and applying a transparent moistureproof coating on said anchoring mediumcontaining base sheet, said resin, in the finished wrapping tissue, being transparent and substantially unaii'ected by water and solvents used in the moistureprooi coating.

5. In a process tor producing a transparent, anchored, moistureproof wrapping tissue, the steps comprising applying an anchoring medium composed of a synthetic, polyhydric phenol-aldehyde resin on a transparent, non-fibrous, cellulosic bale sheet, and applying a transparent moistureprooi coating on said anchoring medium-containing base sheet, said resin in the finished wrapping tissue, being transparent and substantially unailected by water and solvents used in the moistureprooi coating.

6. In a process for producing a transparent, anchored, mcistureprooi wrapping tissue, the steps comprising dissolving a resin-forming material taken from the class consisting of a phenolaldehyde resin-forming material and a ureaaldehyde resin-forming material in an aqueous solution, applying said solution of resin-forming materials en's. transparent, non-fibro cellulosic base sheet, converting said resin-taming materials to a transparent, insoluble resin, and applying a transparent, moistureprooi coating on said resin-treated base sheet.

'1. In a procea i'or producing a transparent, anchored, moistureproot wrapping tissue the steps comprising dissolving a phenol and an aldehyde in an aqueous solution. applying said solution of a phenol and an aldehyde on a transparent, nonflbrous, cellulosic base sheet, converting said phenol and aldehyde to a transparent, insoluble resin, and applying a transparent, moistureproo! coating on said resin-treated base sheet.

8. In a process for producing a transparent, anchored, moistureprooi wrapping tissue the steps comprising dissolving a carbamide and an aidehyde in an aqueous solution, applyi said solution of carbamide and aldehyde on a transparent, non-fibrous, cellulosic base sheet, converting said carbamide and aldehyde to a transparent, insoluble resin, and applying a transparent. moistureprooi coating on said resin-treated base sheet.

WILLIAM HALE CHARGE. DOROTHY B. BATELEAN.

CERTIFICATE OF CORRECTION.

Patent No. 2,159,007. May 25, 1939.

WILLIAM HALE CHARCH, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 1,0, for "of water" read or water; same page, second column, line ?9-L ,O, for "theourea" read thiourea; line 15, for "ase" read as; page 6, first column, line 12, for "formalderyde" read formaldehyde; line 15, for "accordang" read according; same page, second column, line 6, for "solutoin" read so1ution;'line 1+}, for the word "impossible" read possible; page 7 second column, line 35, for "moisture-proofing" read mois'tureproofing; line 75, for "stick" read sticky; page 9, first column, line 3, after the word "sheet" insert alone, the. cellulosic sheet; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 1 th day of July, A. D. 1959.

Henry Van Arsdale (S l) Acting Commissioner of Patents.