US2982675A - Method of water- and grease-proofing paper products - Google Patents

Description

A. M. KAPRAL May 2, 1961 Filed May 8, 1956 METHOD- OF WATER- AND GREASE-PRO'OFING I PAPER PRODUCTS 1 Ales Maria Kapral, Kingsford, near Sydney, New South Wales, Australia, assignor to Process Methods Corporation, Chicago, Ill., a corporation of Illinois Filed May 8, 1956, Ser. No. 583,479

Claims priority, application Australia May 12, 1955 13 Claims. (Cl. 117-154) mixtures of paraffins and/or waxes with rubber-latex, resins, rosin, or metallic'soaps under various cond1t1ons,

frequently in .the molten state, but sometimes in the form of solutions or emulsions. j,

These known treating methods have, for instance, the following disadvantages; comparatively large quantities of wax or the like have to be applied to the paper. Penetration of the substances applied and their adhesion to the surface are not always adequate, so that the coating may peel off and goods wrapped therein are exposedto possible contamination. It may be difficult' or even impossible to incorporate into the coat additives such as flavors, insect repellents, preservatives, and the like. The coherentcoat closes the pores and prevents passage.

of air, so that the material to be wrapped cannot breathe. It is the object of the present invention to avoid these disadvantages and this is achieved according to the in vention, inter alia, by the impregnation of manufactured paper and cardboard with a substantially water-insoluble metallic salt of a long-chain carboxylic acid;

According to the'invention, printed, colored or plain paper or cardboard is impregnated with-asubstantially water-insoluble metallic salt or salts of a natural or syn-.

thetic long-chain saturated or-unsaturated oarboxylic acid or acids having a chainlength of at least 11 carbon atoms in the molecule, the metal having a valency of at least two and said metallic salt or salts being formed during the impregnation within oron the cellulose fiber ofthe 2 tured paper and cardboard and a specific embodiment of a machine unit for carrying said method into effect are hereinafter described, by way of example only, with reference to the accompanying diagrammatic drawings which show in Fig. 1 the machine unit in side elevation,

the method being further illustrated by a number of nonlimitative examples, and in Fig. 2 an alternative construction for a part of the machine.

In one embodiment of the method, the paper 'or cardboard-is treated in a firs-t step with a hot or boiling aqueous solution of an alkali metal and/or ammonium salt of such carboxylic acid, and in a second reaction step with an aqueous solution of a metal salt capable of forming with said first-mentioned salt or salts a substantially water-insoluble metal salt of the carboxylic acid, the metal of the salt having a valency of at least two. The aqueous solutions used in the first and second reaction steps may be applied to the paper or cardboard by dipping, rollercoating, brushing or spraying.

The long chain saturated or unsaturated carboxylic acid may be a synthetic fatty acid or a mixture of synthetic fatty acids having chain lengths of at least 11, obtained by oxidation of natural or synthetic hydrocarbons or by hydrogenation of carbon monoxide. Preferably however, it is a natural carboxylic acid having a "chain length from 12 to 20 carbon atoms. Suitable nat-,, ural fat ty acids are for instance, oleic acid, lauric acid,

myristi-c acid, palmitic'acid and stearic acid. Suitable alkali salts of these fatty acids are, for instance, sodium oleate, potassium stearate and ammonium stearate either alone or in mixture, but similar alkali salts of these and other fatty acids are also usable in the process.

vThese alkali salts are-dissolved in hot or boiling water, or'ifso desired, the 'aqueous'solution of an alkali salt of a fatty acid may be prepared shortly before use by saponificationin heat, Mom of the aforementioned fatty acids the 'p'resencelof, a suitable organic amine such as.tri-' paperor cardboard, preferably in the presence of am- A machine-unit suitable for waterand grease-proofing manufactured paper. and cardboardwith a"si1bstantially;--' water-insoluble metallic salt of a long-chaincarboxylic acid may comprise an endless conveyorbeltpervious to-i liquids and. adaptedzfor transporting sheets rofpaper. or cardboard, two or morethan two pairs ofscoatingrollers, the rollers of each pairbearing upon fiaid belt from opposite sides, ,and -said p'airs of rollers being in" game or orgamc salt, or salts of a metal havmgavalency" l spaced relationship to one anotherIfor' supplying to saidpaper or cardboard treating solutions being; respectively,

a hot aqueous solution of'an alkali salt ofa longechain carboxylic acid'with'or without other additions, and an aqueous solution of an inorganic or organic higher metal saltcapable of forming 'a substantially:water-insoluble metallic salt of a long-chain carbox'ylic 'acid, the unit further including a heating chamber for drying the paper .or cardboard after treatment.j= f I The methodof water 5 and grease proofirig 'manufacethanol-amine.

.Tests. have shown that itis of particular and une'xpected technical advantage. to add to the aqueous solution of an alkali salt of said fatty acid or acids a quanitity ofhexamethylene tetramine.' It has been found that suchsolutio'n tpenet'rates. quicker the minute pores and channels of the-cellulose fibers and produces an imsubsequentiheatatreatment;.1

If so desired, organic water-soluble dyestuffs may be added to the first solution, or may be applied to thezpape'r .1 after .the application. ofthe solution in. a separate produc tion step,;so;as:to give the paper apermanent colouring pram.

Subsequent to :suchv first; treatment, the: wet: paper flora I cardboard istreatedin a second st'ep:of the reaction either" once or repeatedly; with an aqueoussolutionofgan'inor "ofatfleastitwo; The" fatty acid salts of saidmetalsmust be; substantiallywinsoluble in 1 Water .and, if 1 intended for i usegin'connectiom-with .foodstufis; theymust anemone. andcompatible with legislation -relating to pure ffbodJ-ia SuitablemetaLl; salts are, :for instance, aluminum sulphate; v pdtassiumiealuininum:sulphate' ron sulphate and alumij nuni' acetat thapapaaac with the meatsaia aiaatieiiuy Patented May 2, 1961:

--ties.of-natural.or synthetic rubber latex with or without grease-proofingpaper and' cardboard ac'cqrdingqtolath t's -mtir b rseena nrz e tac hat; paper-' or "card?- or direct on the cellulose fibers, forming substantially'water-insoluble metal salts of fatty acids which are colloidally dispersed in the pores and capillaries of the cellulose fibers, an alkali salt being formed at the same time.

Itmay be of advantage, at this stage, to remove the alkali; salts fonned during the reaction by Washing, i.e. wetting the paper with water, and subsequent squeezing. However,- small quantities of salts may still remain in the pores and, therefore, sulphates and phosphates are preferred for instance to chlorides, as their sodium or potassium salts formed during the reaction are nonhygroscopic.

If ammonia salts of long-chain fatty acids are used in the first reaction step, ammonia being preferably in excess, andthe precipitation is brought about in the second reaction step by the use of aluminum acetate, then any danger of salts being hidden in the pores is practically eliminated, because ammonium acetate Which maybe formed is heat-volatile and acetic acid and ammonia will evaporate as a mixture during the subsequent drying process described hereafter.

After the chemical treatment is completed, the paper a or cardboard is dried by passing it through a heating chamber" at a temperature of up to about 400 degrees C. The paper may remain in the heating chamber for about 20 seconds to about 2 minutes, depending on the actual drying temperature.

The aforedescribed process renders anytype of paper Waterand grease-resistant, thin paper acquiring the ap-- pearance and some of the advantageous properties of a vegetable parchment. However, if cheap grades of paper, such as newsprint are used, such resistance may not be permanent and may decrease over a period of time.

According to a further feature of the invention this disadvantage is overcome and the permanency. of the impregnation is considerably improved by treating the paper prior to, during, or after the described chemical reaction with a selected protective colloid, such as alginic acid, a water-soluble salt of alginic acid, gluten, casein and the like. It is preferred however to add the protective colloid to the alkali solution used in the first reac tion step. 1

Alginic acid,its salts, gluten, and casein are capable ofacting as protective colloids as they envelop the particles of the Water-insoluble fatty acid salt and'thus act as stabilizers. JTherefore, practically permanent waterand grease-resistance of :the paper or cardboard is assured by such treatment. 1

The aforedescribedmethodof water and grease proofing of paper and :cardboard, in addition to-bein'g eco nomical has the further technical advantage, especially for theproduction of food wrappers, that certain substances can be added toxthe solutions, such as a specific perfume or aroma appropriate tothetype of productto be wrapped. and/or insect repellents, or fungicides, .or bactericides, or the like. propionate and/or digitalis-or like, glucosides may. be addeditothesolutiom. I

lfigadditionally,,imperviousness.to air is required,tit

is possible .to addito and to disperse in thealkali solution I of a fatty acid salt containing ammonia and/or an organicqamine used in the first. reaction step,.small guantivulcanizingLadditives.or,falternative1y, of 'aI-vinyl or of anothertresinemulsion; i 1 i A paper 'gtre'atedu according to the aforedescribed method.isnotLheatQseaIing, but a wrapper madeythereoffi cantbe rendered so.by;the application of heatisealingcorna pounds such as thermoplastic adhesives', gutta ,percha and ;they like to appropriate sectionslof theiwrappen,= L

Acpa ticul-ansadvantage .ofethe method of :Water-x! and.

Thus, for instance, .-.sodium is then dried as describedfinExample l.

I Solution A:

' 4 instances precludes its use in the food industry. Additionally, after treatment the paper will be practically-free of bacteria.

The following non-limitative examples serve to illustrate the methodaccording to this invention, of waterand grease-proofing manufacturedpaper and cardboard.

In each .of theseexamples the hot solution used for the first reaction step is termed solution A for the sake ofshortness and the'solution used in the 2nd reaction step is,"accordingly, termed solution B.

are dissolved. Sheets of paper are treated with the solution A eitherby dipping them into or by passing them through a bath containing the solution, or by roller coating or, alternatively, by spray application.

Solution .B contains 18 gms. of aluminum sulphate per 1 gallon of water. After the first treatment is completed thepaper-is passed through a cold bath consisting of solution B.- Also this second treatment can becarried out in various ways, egg. by coating the paper bymeans of rollers covered with rubber orplastic sponge-like material,; or by spraying. a a 7 Potassium stearate from solution A reacts with the aluminum sulphate fromsolution B and forms waterinsoluble aluminum stearate within, or direct on the cellulose fiber, the hexamethylene-tetramine aids thepenetration and improves the impregnation. I

.The paper is then dried by passing it through. a heating chamber. The temperature ofthe heated air entering the chamber is thermostatically controlled and kept.

Solution A:

27 gms. oleic acid,

9 sodium carbonate 9 gms. ammonium hydroxide and 4.5 gms. lhexamethylene-tetramine are added to -1 gallon of boiling water, whilst agitating- Thelpaper istreatcd with the solution A and-subsequently with a solution Boontaining-Q gms. of aluminum p0 The paper tassium sulphate in '1 gallon of cold Water.

.Exqmple. l

27 gms. stearic acid and 45 gms. ammonium hydroxide are dissolved while stirring in 1 gallon of boiling water. If so desired,9 gms. of hexamethylene-tetramine may I I be added to solution A.": However, this is not necessary,

asrammonium. hydroxide: isconsiderably in excess and penetration is" assured.

' The :papen-is' treated-"with, the first solution A and subsequently with .a cold solution B containing .9 gms. of *freshly, prepared aluminum acetate int 1 gallon of water." Thexpaperis thenadried. as described in Exfample-lr 1 I w Exarup le 4 agitation. infgl galloniof boiling lwater;

.; i i 1 gm .ste iql idg 1 gms. ammonium earbonataq and; 1' 9 hsaastethyleu t narninet;

27 gms. stearic acid,

9 gms. triethanolamine, 18 gms. ammonium hydroxide, and

I 9 gms. hexamethylene-tetramine.

Solution B consists of 4.5 gms. of aluminum sulphate and 4.5 gms. of aluminum acetate, in l-gallon of water.

Example 6 Solution A .is prepared by dissolving under agitation in 1 gallon of boiling water:

27 gms. stea ric acid, 18 gms. hexamethylene-tetramine, and 9 gms. ammonium hydroxide.

Solution B consists of 9 gms. of aluminum sulphate in 1 gallon of water. v

The method illustrated in any one of Examples 1 to 6 may be modified bythe addition to solution A, for the purposes set out above, of any one or more of the following: Synthetic or natural rubber latex, polyvinyl or like resin emulsions, flavors, perfumes, bactericides suchas digitalis or like glycosides, insecticides,-fungicides such as sodium propionate, preservatives", e.g.. sodium benzoate or sodium salicylate. f

Moreover protective colloids may be added to the ammoniacal fatty acid salt solution in order to increase the permanency of the water and grease-resistance of the paper or the like. It has been found that gluten, casein and alginic acid'are particularlysuitable protective colloids. Their use is exemplifiedin the following examples. Example 7 Solution. A:

27 gms. oleic acid,

9 gms. sodiumcarbonate,

9 gms. ammonium hydroxide,

4.5 gms. hexamethylene-tetramine, and

4.5 gms. gluten are added underagitation tol gallon of boilingwater. and the solution thus obtained is used for the first treatment. The second treatment and the drying are carried out as described in anyone :of Examples 1 to .6.

I I Example 8 Solution A: I I I 27 gms. s'tearic acid, I 45 gms. ammonium hydroxide,

1 I I 9 gms. gluten and I I .127gms. synthetic orv natural rubber latex g are'added under agitaiton to 1 gallon of boilingcwater. The colloidal solution A thus obtained is used: for the first treatment and .theprocess completed as'describedin any one of Examples lto 6.

Example 9 9 gms. of casein are mixed with 27' 'lgms. of water.

After standing for about 20 minutes during which time the .casein is allowed to swell, the casein paste is added the'solutions A described in Examples to any one of Example 1 alkali 'saltsolutions A of fatty acids used for the first treatment according to Examples 1 to 6. I

cally unchanged, the increase of weight being of the order of about 0.01 to 0.1 percent.

The accompanying drawing shows diagrammatically an apparatussuitable for use in carrying out the operations described above. In the drawing,

Fig.1 is a transverse sectional view of the apparatus assembly for handling paper products to carry out the method of this invention; and

Fig. 2 is a similarview of a modified form of a portion of the apparatus shown in Fig. 1.

The apparatus shown in the drawing substantially comprises an endless conveyor belt 1 which is pervious to liquid, means for feeding or conveying sheets vof paper one by one from a stack 2 onto said belt 1, two pairs of coating rollers 3, 4, and 5, 6 in spaced relationship to one another, and a drying chamber 7, the rollers of each of said pairs bearing upon the belt 1 from opposite sides andbeing associated with a supply for the solutions A and B, respectively, in such a manner that these solutions are applied to both sides of the paper.

The belt. 1 iscarried by two end rollers 8 and 9, one of which, e.g. roller 8, is a driving roller connected to a prime-mover (not shown). Additionally, the belt 1 is supported between its ends by idling rollers 10, 11 and 12. The belt 1 is made of corrosion-proof wire gauze, wire netting or perforated material. Preferably, the material used for the belt is stainless steel.-

Thesupported ends of the belt are arranged outside the drying chamber 7 which, in the form shown, is provided withadditional belts 1A and 1B below belt 1, the paper being transferred from each belt to the belt beneath by optional means, before leaving the chamber7 in adried end rollers 8 and 9 14 and 16, respectively, and/or; to the coating rollers 3 and5,re'spe ctively.' j f 'i The lower coating rollers 4- and 6 alsomay'each be,

f 'sired The troughs 15 and 17 and/or the liquid level therein may be adjustable. v

" 14.5 gms. ofalginic acid are added to any one of the 1 Solution A is supplied to the upper coating roller 3 substantially over its entire length from a suitable receptacle l4.- The lower roller 4 receives solution A from a trough 15 wherein it is rotatably supported,

Similarly, solution B is supplied to the upper coating roller 5 substantially over its entire length'from a receptacl116 whereas the lower roller 6 receivesjsolution B from a'trough17.

All coatlng rollers ,are preferably positively driven to ensure' -the, greatest possible uniformity of liquid transfer. In the formshown,the upper rollers 3 and 5 eachlcooperate withza' doctor roller 18 and 19, interposed, respectively, between the upper roller. and the receptacle above it, the doctor rollers 18, 19 serving to further equalize the quantityv and to improve the distribution-of isof advantage to sb ar'rangethe doctor rollers 18 and 19 I that they are adjustable with :respectto thereceptacles associated with. a doctor roller (not: shown), if so de- Preferably each pair of coating rollers 3, 4 '5, -6

-is associated with a pair of squeezing rollers; 20, 21

and 22, 23 respectively, which Ibear upon the upperrun of the belt 1" fromopposite sides and are properly spaced from the coating rollers-3', 4 and 5,6. The, squeezing/ rollers improve the distribution of liquid within- "and; over the paper and they remove surplus: liquid sired the means for grease-proofing-maybe associated di- ILA method of watereproofing paper. sheet material comprising the steps 'ofmoving 7 said material in a path throughlthe air, directly and positively' applying to at -least one face of .said paper sheet assaevs '7 latter maybe collected. in open troughs 24 and 25 situated below the respective pairs of squeezing rollers.

The ,belt 1, with the wet paper passes over the supporting and guiding; roller 12 into the heating chamber 7. Water sprays 26 and 27' arranged at that station, outside the chamber 7 above and below the belt 1, respectively, serve thepurpose of washing away watersoluble alkali salt formed on the sheets during the impregnation.

The heating chamber 7 is of optional size and shape. Air is supplied to it by a blower 28 and it is thermally or electrically heated within a chamber 29 before it enters the chamber 7 through a number of ducts. 3%, which discharge the hot air below the upper runs of the respective belts 1, 1A and 1B. Appropriate means may be provided for keeping the hot air entering the chamber7 substantially constant, e.g. at about 400 degrees C. V

The wet paper passed through the chamber 7 on the belt 1 is transferred from the latter to the belt 1A beneath it through a chute 31 which preferably accommodates a mechanically operated jockey or equivalent (not shown), and is therefore arranged outside the chamber 7. Similarly, the paper is transferred from the belt 1A to the belt 113 through a chute 32. .Finally the paper is discharged from the chamber 7 in dry or substantially dry condition by a suction device 33, and is collected at 34.

For economy, the hot and moist air, escaping the top of the chamber 7 through a flue 35 is passed through a condenser 36 from which the condensed water isremoved through anv outlet 37, while comparatively dry and warm air is returned to the chamber 29 via a down pipe 38 by the suctionof the blower or fan 28.

Fig. 2 shows an arrangement in which there is placed inthe trough a quartz crystal transducer 39 connected to an oscillator 40 capable of generating ultra-sonic oscillations which are fed to the crystal 39 through the cable 41. An air space 42 is left below the crystal. ,It has been found that the continuous agitation'of the solution by ultra-sonic frequencies leads; particularly when the solution contains ingredients, which-are not strictly speaking in solution, to a more even distribution of the components of the solution and thus to a more even distribution of them on the sheets of paper. It has also been found, although the reason for, it is not understood, that such agitation leads to a better penetration of the solution into'the paper. I

A 'I desire it to be understood'thatel do not .wish protection by Letters Patent to be limited to thevaforedescribed details as these are capable of further modification withl in the scope of the appendedclaims.

ibeltreat'ed in insoluble salt of said carboxylic acid,'one of said solutions containing hexamethylenetetramine, whereby said one face of said paper sheet material is impregnated in situ with said substantially water-insoluble salt of said carboxylic acid. in the presence of said hexamethylenetetramine in close association with the cellulose fibers at and near said face of said paper sheet material and said paper sheet material is-rendered elfectively waterproof andgrease-proof.

2. Method as claimed in claim 1, wherein the longchain carboxylic acid is selected from the group ofnatural fatty acids consisting of oleic acid, lauric acid, myristic acid, palm-itic acid and stearic acid. 4

3. Method as claimed in claim 1, wherein the substantially water-insoluble metallic salt of a carboxylic acid is formed in the presence of triethauolamine.

4. Method as claimed in claim 1, wherein the waterinsoluble metallic salt is an aluminum salt.

5. Method as claimed. in claim 1, wherein the waterinsoluble metallic salt is an iron salt.

6. Method as claimed in'claim 1, wherein the metallic salt capable of forming a substantially water-insoluble metallic salt of a carboxylic acid, used in the second reaction step is selected from the group of salts consisting of phosphates, sulphates and acetates.

7. Method as claimed in claim 1, wherein a protective colloid is added to the aqueous solution used in the first reaction step.

-8. Method as claimed in claim 7, wherein the protec?- tive colloid is selected from the group consisting of gluten, alginic acid, water-soluble salts of alginic acid and casein.

9. Method as claimed in clairn'l, wherein a polyvinyl resin emulsion is added to the aqueous solution used in .the :first reaction step..

10. Method as claimed in ,claim 1,;wherein a material selected fromthe group consisting of sodium propionate and glycosides is added to the aqueous solution used in the first reaction step.

11. Method as claimed in claim 1, wherein in the first reaction step the said aqueous solution is agitated by means of ultra-sonic vibrations.

12. A water-proof and grease-proof paper sheet produced by moving said material in a path through the air, directly and positively applyingto at least one face of said paper sheet material in a first reaction step a hot aqueousv solution of a compound selected from the group consisting of alkali metal salts and ammonium salts of'a long'chain carboxylic acid having a chain length of at least 11 carbon atoms in the molecule, and in 'a second reaction stepdirectly and positively applying to said one face of said paper sheet material an aqueous solution of a salt of a metal having a valencyofat-least .2 and reactive with said first-named. compound to form a substantially water-insoluble saltQof said. carboxylic acid, one of said solutions containing.hexamethylene j tetramine, whereby said one .face of said paper. sheet above are applied either to oneside or to both sides of.

the paperas it passes said section or sections. -If so de rectly with a printing machine:

Whatl claim is:'

material in a first reaction step a hot aqueous solution carboxylic acid having a chainl'ength of at-lea-st 11 carbon 5 paper sheet material an aqueous solution of ;a salt of a rnetal l1avinga valency of at least 2 andjreactive with said first-named compound to form a substautiallywaten' ,1; 'sheet; material an.a'queo'us solutionof a saltof ametalhavand grease-proofing material is impregnated in situ with said substantially water-insoluble salt of said carboxylic acid inthe presence 0f said hexamethylenetetramine, in close associa tion with the cellulose fibers at and near said face of said paper sheet materialand said paper sheet mate rial is renderedv effectively water-proof and grease-proof.

13. A. water-proof and grease-proof paper sheet producedby movinglsaid material in .a path through the'air,

- of a compound selected from the -group consisting of alkali; metal salts and animoniumsalts, of a long chain ato the rnolecule jand in; a .second reaction step directly and gpositively applying to .said one face) of said aqueous solution of acompound selected from the group consisting of alkali metal salts and ammonium salts of a long chain carboxylic acid h'a'ving a chain length o f-at least; 1.l car bon atoms in the molecule andselected'from the group consistingof oleic acid, myristic-acid, palmitic' acid'and stearic, acid, and in a secondreaction step directly and ;positively-applying to said one face-.of-said paper aesaevs ing a valency of at least 2 selected from the group consisting of phosphates, sulphates and acetates and reactive with said first-named compound to form a substantially waterinsoluble salt of said carboxylic acid, one of said solutions containing hexamethylenetetramine whereby said one face of said paper sheet material is impregnated in situ with said substantially water-insoluble salt of said carboxylic acid in the presence of said hexamethylenetetramine in close association with the cellulose fibers at and near said face of said paper sheet material and said paper sheet material is rendered elfectively waterproof and grease-proof.

References Cited in the file of this patent UNITED STATES PATENTS 10 Hoskins Oct. 3, 1922 Sellows et al Dec. 16, 1924 Grunbaum Feb. 11, 1930 Schroeder Nov. 3, 1931 Ellis June 26, 1934 Owen Nov. 27, 1934 Bucy Nov. 19, 1935 Hayden June 23, 1942 Warth et al. Dec. 29, 1942 Fiero et a1. Dec. 12, 1950 Cook et a1. July 15, 1952 Figdor Apr. 14, 1953 Arnold May 5, 1953 Copeman et al. Mar. 22, 1955 FOREIGN PATENTS Great Britain May 1, 1941

Claims (2)

1. A METHOD OF WATER-PROOFING AND GREASE-PROOFING PAPER SHEET MATERIAL COMPRISING THE STEPS OF MOVING SAID MATERIAL IN A PATH THROUGH THE AIR, DIRECTLY AND POSITIVELY APPLYING TO AT LEAST ONE FACE OF SAID PAPER SHEET MATERIAL IN A FIRST REACTION STEP A HOT AQUEOUS SOLUTION OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL SALTS AND AMMONIUM SALTS OF A LONG CHAIN CARBOXYLIC ACID HAVING A CHAIN LENGTH OF AT LEAST 11 CARBON ATOMS IN THE MOLECULE, AND IN A SECOND REACTION STEP DIRECTLY AND POSITIVELY APPLYING TO SAID ONE FACE OF SAID PAPER SHEET MATERIAL AN AQUEOUS SOLUTION OF A SALT OF A METAL HAVING A VALENCY OF AT LEAST 2 AND REACTIVE WITH SAID FIRST-NAMED COMPOUND TO FORM A SUBSTANTIALLY WATER-

11. METHOD AS CLAIMED IN CLAIM 1, WHEREIN IN THE FIRST REACTION STEP THE SAID AQUEOUS SOLUTION IS AGITATED BY MEANS OF ULTRA-SONIC VIBRATIONS.

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