US2828240A

US2828240A - Packaging material

Info

Publication number: US2828240A
Authority: US
Inventors: Robert De S Couch; Yezek Milton
Original assignee: General Foods Corp
Current assignee: General Foods Corp
Priority date: 1954-10-22
Filing date: 1954-10-22
Publication date: 1958-03-25
Anticipated expiration: 1975-03-25
Also published as: GB805975A; DE1049695B

Description

March 25, 1958 R. DE s. coucH ET AL 2,828,240

PACKAGING MATERIAL 'Filed oct. 22, 1954 Sm wmmjxm United Sm O PACKAGING MATERIAL Robards s."^co1ielrv and-Milton# Yezek;=-Bt tle creek, v Mich., as sjgnors to General Foods Corporation, White Plains, N. Y., a corporation of Delaware uApplicationOetoberZ, 1954, Serial No. 464,169

12 'Claims. i(Cl. 154-138) This invention relates toximproved packagingmate'rial .1. 4especiallynadapted forense-in retail-,packaging or cartoning A of goods-thatfmust be-protectedagainst .loss' 'ofmoisture f. .to or'absorption of rmoistureffrom outsidethejpackage.

Much-timel and attention: have,beenidevotedttoltheletvelopment of retail packagesofaithe'v@type 4'characterized above." vIn general, suchtpackagesshould-haveV arr'attrac- -tive external-dress--and-appearance,-yet at-the sameti-me fftheyjshouldf bejhfighlyf resista/nt'Ltof,the*v transfer ofmoisture orawatenqvapor. As a rule-, these.requirementshavelheen met' byY vfmultiple"packages'A im"Whichf-printedcjcardboard cartons are the principal elements and protectionag'ainst water vapor transfery (WX/Tf) ist-increased by liners and/ or single or double overwraps of foil, cellulosic films such as cellophane, vglasvsine, waxedsulphitepapers, and the like. But such arrangerr'ients are expensive, bthas to material .costand ,as to the/expense ofinsertingand/or overvvrapping-.and then ,closing the successive layers of packaging v`.materia1,.withfthe result that desirable protection against water vapor transfer is often sacrificed in the interest of feconomy. As .tan illustration, breakfast cereals are com- '^m'only. marketed vtoclayfinprintedvcardb'oard cartons" havling singlenlwaxed" and -heat-sealedsulphite i overwrapsg although the' WVTproperties vof such packagesrarefnolmore ,A than faird to beginwith anddeteriorateArapidlyewhenlhe packages are jarred' during handling.

Efforts have accordingly-been rnadetonprovde-l by laminations a single sheet 'which willmeet"all"`of the'aforementioned requirements and "if possible provideimproved WVT characteristics at the same time. "'For example, some degree of success-ha`ssebeen attained by laminating two sheets of cardboard together with a moisture-resistant adhesivelsu'ch as microcrystallineewax; but for good results the wax must be specially selected and/or modified so that it becomes tacky before too much can be absorbedby the Aboard. Otherwise excessive quantities of laminant are, absorbed with the resultsthat the board may lbecome so greasy that it can not be printed satisfactorily, and theamount of laminantremainingonthesurface.may @be insuicient and too unevenly distributed, toffform a f-good bond. 'C Onthe fother hand, eventhough-:satisfactory lamination is obtained,'the"WV'If propertiesfobtained in this Waydo not'fprovide-the-vdesiredimprovementvv over r cartons :with waxed; paper overwraps as. describedfabove. We vhave found that' if theboard isu first impregnated as setforth hereinafter; it maythenbe laminated `to paper 2,828,240 4Patented Mar. 25, 1958 fire :fftWi-thfSubstantial;zelimination't*ofnthe vdiflcultieswzset Aforth boveifand production? of anidmproved 'product as :regards I Wy'lsploperesf? Asta rule: the; impregnated :board :forms htwinside ofitheicarton fora; vpackage::and -rwillwbe so con- 5 V idenedzhereiilaifter; although-- fthisiis f 'not necessarilyerthe "Qase. .rhesotherplyf off; the-fflaminated product,l .which Snallyswill bed-herouterrply 'ofrthe' package, may-'beine more; thanapapelefprinted flike :the: usual: carton Vor, overwrap.geBynvintue; ofthe,simpregnation1 of thew board-`ply, ;,.fsszlaminantizis requiredfiwbilev aebetter bond is obtained, and notably superior WVT characteristics .can be provided .zA-:s asf setiforth in;.detail .'below.

.ffl-he:hoard:;f,ormingf.:theinnerl ply of ithe laminatedma- ".tjerial may-:be anyof va'awide varietyV of known vkindszf-,for Xample-tboadsz-fmadefrom pure :chemical pulps such as n:bleached:.andmnbleached kraft, soda and sulphite board; 1.boardsifmadefromfsemichemical'fpulpsuch` as corrugat- -:ingrmediumi-boardyandr bleached .semif-chemic'al aboard; if beardnade' from wastewmaterials :such as :chip boardfand @aiuta-hoard; ,and-board made from combinations ofiswaste, groundwoodzand'zhemical pulpsrsnchzfaseWhitefPatent 'xicoated pnewsfboarmadouble; Manila linedwnews, groundwood Lcenterg and double. bleached :linedfwasteeground- "f Wod center-aboard. .':Such v'boardfis normally .specified in ffweightjfper thousand'square :feet -zandzl incpoints thickness .KonexpointaOOldnch); on this-basis-any of-:thesabove types of board in the range of'-20L.l60;lbs.t.and 5`.40;.point laf-may? .bez-suitable: ffor" useedepending iupon the:y size of the ,11s,-package,; theweght and physical :form Jofi ythe =-.enclosed 3Q: materiaLgand `the conditions.tofwhichi-thefpackageis'to be subjected.

.The :bardaselectedtfor' thefinner'ply :isf then impregnated before lamination. Generally speaking,: any;=suitableirn .z `:pregnant can :beaemployedzwhichf provides, goodf IWVT 35.;f:properties; rex-amples are -parafln vwax, fmicrocrystalline zrwaxes; .-polyethyleney asphalt, p olyamides, :.-andffthe' like. 'f iBy; impregnated-wwe meanunot merelyfsthatz-the :board is surfacelcoatedgfbutthatethe,voids Vand. intersticesxfwithin the boardaaretilled with the impregnant to azsubsta'ntial :adepthahelow theasurfacesgofzthe board. A .surface coatk:fing: alone:tdoesvnotfiprovide L a :satisfactory product. If made thick enough to provide in effectanotherzvplyoffthe .Je Acoating materialfeper se,jtheifamountfrequired:isfexcessive; besides the1.coating-materiali` tends-fte '-fbel-dri-venr intof'the 5t i oardfuneverily?` during: subsequent processing. 'ofthe flami- .eanatedestructureyresultingl:in a= tendencyfzto delamination :vor fab least-:weakened: r esistance::tozwater. vapor transfer La1at,:';'rai:ld; mfi points'rfand thus-in amen-uniform product. 0h73 huszzthezboard should carryfia'tlfleastiflfbynweight of :f-impregnant; the-majorportion"vofiwhicl'ly isI impregnated l t into-fthe `materiale int..athen-senseik described above 1=as"dis :tinguished from .aasurface coating.` Infact, there needA be :mo=srface;coating11atall,v although itis not necessary. to

.= take 'speciali painsto avoid it.

f. Preferably theu-boardl isi -treated underco'nditions such wfaszpressure-for; vacuumewhich caused the impregnantto be f. driven.: thoroughly into: themboard. f-` By2-such preferred 1 methods board-can Ibe'causedy toSabsorbAf-as1=rnuchv as :230+3`5%fby\weight= of iimpregnant, the voids and inter- Vastices intV the :product being substantially 'allV lledf Withimpregnant. For the types, weights and calipers of boards here involved, this condition of substantially full impregnation requires the absorption of at least 20% by weight of impregnant. As shown by the test results set forth hereinafter, such full impregnation prior to lamination results in outstandingly good WVT properties.

The other ply of the laminated material (usually buit not necessarily the outer ply of the package) comprises a suitable paper, in most cases a paper capable of being printed, in the range of 8-90 lbs. (basis 24 X 36-500: 3000 sq. ft.). Various kinds of paper are known, and as examples any of the following can be used: papers made from chemical pulps including sulphate papers, sulphite papers, sulphate-'sulphite combination papers, andV soda pulp papers, rtliese various papers being either uncoated'or coated on one' or both sides with a coating comprising clay, titaniumdioxide, and binder; papers made from chemical pulp or chemical pulp and groundwood combinations, coated or uncoated, which have been calen-Y dered or suplercalendered such as publishing papers, glassine, supercalendered sulphite papers, machine finish sulphite-sulphaite papers, and machine finish and machine glazed sulphite-sulphate papers; and other materials such as cellulosic films including cellophane and cellulose acetate, foil and the like.

The laminlant is applied to one or both surfaces to be laminated and .these surfaces are then juxtaposed in any suitable manner, with or withouit heat and/or pressure as may be appropriate to the particular impregnants and' laminants involved. VVarious procedures and apparatus for laminating materials together are well known in the art and need not be set forth in detail. For quantity production, of course, it will be desirable to laminate strips or sheets running continuously over rolls, the larninantY being applied by spraying, dipping or brushing as may be most convenient. Suitable laminants include, forexample,.microcrystalline waxes alone or with added polyethylene, butyl rubber, polyisobutylene, and/or parain;

paraffin; polyethylene 200G-21,000 N. W.); vinyl acetate emulsions; polyamides; butyl rubber emulsions; and like moisture-proof adhesives.

The accompanying drawing illustrates diagrammatically one embodiment of the invention, but it is to be expressly understood that said drawing is by way of example only and is not to be taken as a deiinition of the limits of the invention, reference being had to the appended claims for this purpose.

In the drawing, the board which is to be impregnated and form the inner ply is drawn from any suitable sup-l ply, preferably in the form of a continuous web or strip 1, and passes through a suitable evacuated chamber 2 containing a bath 3 of hot liquid impregnant. The strip is caused to move through the bath by means such as the

guide rollers

4, 5, and 6, dipping under the surface of the bath and them emerging from the bath before leaving the evacuated chamber.

Beyond the vacuum chamber, the desired moistureresistant adhesive is applied to the strip and distributed over its surface by any suitable means as indicated by the arrow 7. Then while the moving strip with its impregnant and adhesive is kept hot by heating means 8 disposed along the path of travel, the paper that is to form the outer ply is drawn from any desired source, preferably in the form of a continuous web or strip 9 which passes around a roller 10 intoa path parallel to that of the strip 1. The two strips 1 and 9 are then suitably pressed together, as by passing them between rollers 11, 12 completed, the laminated strip or web leaving the rolls at 12.

In the following tests, impregnated 8 pt. and 10 pt. bleached kraft board was laminated to a paper coated on both sides with clay and binder or with clay, binder and titanium dioxide (basis 25 x 38-500; equivalent to 54.5# per 3000 sq. ft.). These kraft boards were imweb of the board through a vacuum chamber immersed in a bath of melted parain.-. vOne side of the board was then coated with Quaker State amber microcrystalline wax by means of a laboratory coating applicator, the temperature of the microwax being 2lO-230 F. and the impregnated board being heated to 220 F. tto slow the solidilcation of the microwax and produce a ber-tearing bond between the board and p-aper. The paper ply was placed on the hot laminant and pressure applied by means of a rubber roller. For comparison plain (non-impregnated) board was laminated to Ithe same coated paper in a similar manner except that the board was coated with microwax while coldand the board and applied paper heated for 15-20 seconds before pressing. Also some of the plain and impregnated board was double laminated by coating it with microwax on the reverse side and laminating it to 30# printing sulphite.

Analysis of board before and after impregnation .Y

Results Analysis 8 pt. 10 pt.

Plain Impreg- Plain Impregnated nated Weight/M sq. ft pounds.. 44. 4 55. e Calip 0. 0079 0. 010 stiffness-MD 33 71 (Taber)-CD 20 44 -Total Wax/M sq. it .pounds.. 9. 7 13.6 Percent Impregnation 21.8 24.5

. WVT-gms./100 sq. in./ 24 hours:

Flat .grams.- 2. 1 1. 2 Fold l.' grams-. 5. 5 3. 0

1 The fold used for WVT analysis consisted of creasing each sample four times. Two creases, one inch apart, ran in the machine direction; the other two were similar running in the cross direction of the board or perpendicular to the first two. One score in each direction was prebroken and the other two 180.

TABLE #2 Analysis of 8 pt. single laminations Results Analysis Y Plain Impregnated Weight/M sq. t. V .lbs 57. 7 66. 2 Caliper inches 0.0113 0. 0115 Stiiness-MD 85 100 (Taber)-CD. 44 53 Weight of Laminant/M sq. it.-- 6. 8 7. 8 WV s sq 111/24 hours 1 sel'ratue #1. Y

- TABLE #3 Analysis 'of 8 j pit. doublre `laminations p Results Analysis Y Plain Impregnated Weight/M sq. n n..- so. o 79. 2 ipet 0. 0140 0. 0144 Stinness-MD 132 110 (Taber)-GD 86 80 Weight of Laminant/M sq. it. lbs-. 13. 1 9. 8 WVTf-gms/IQO sq. 1117./24 ho Flal; gms.- 0. 84 0. 22 Fold 1 g1ns 1. 20 0. 35

1 se Table #1.

TABLE #4 Analysis of 10 lpt. single laminations ases-,24o

(3) 1 oz. bleached kraft .eartonlined with waxed '25# sulphite and overwrapped with waxed 25# sulphite.

'(21) s oz, ehip board carton with waxed 'glassiiie liner Results 5 and waxed A25# siilphite overwrap. Analysis '(5) .S1/12oz. chip .board carton with waxed laminated Plain Impreg- .glassine liner .and waxed 25# sulphite overwrap. Dated a(6) 6oz. chip board c'arton with waxed v25# s lilphite 1 4 Vliner .anddouble Aoyerwitap of Reyseal .05.0 Ifoil O ggig 0 1'34 10 and waxed 25# .fsulphite 156 Soin'e of the rcartons were vpacked in shipping catons WmghmLmtMSq- "35g: 3 4 and subjected todrp tesis (1oz. size-L6 drops of 48 WVT-gms./100 sq. 111./24 hours: 2 0 13 inertes; V8 oz. size-'6 'drops f 30 inches); thereafter all lat ?`gm=s" gjgg @34 cartons were stored at 10() F. Aand approximately 80% 15 R. H. and moisture analyses made from time to time ,See Table-#1 with the following results: TABLE "#8 Resultsof moisture analysis-1 oz. study unhandled "Iercent'Moisture Content After Various Hours in Storage 510mm storage 22 4s 68 88 114e 165. 231 334 aekage Combination;

Impreg.-Isinglelam 2.13' 3.7 4.2 '4.'7' .Plainfl-single lam-- 3.6 3.7 5.2 4.1 Impreg.|dbl la 2.3y 3.2, 3.4 3..8 2.9 3.3l -6.0 5.7

'10vrwrap. 'TABLE #5 .'ITA'BLE` #9 n-alyss of 10 pt -oubl-e lama/t'om' 35 Results of moisture analysis-#1 l'ozfistudyfdrop tested f PerentMoist-ure Content Attei- Begins. Var1o1s;Honrsin Storage Analysis Pun I a laeg' 40 HoursinSt0rage. :22 :43 1,68 88 114 165 f f lbs" 8737 g4 2 PaekageCombination: i t

sq t mches-. 0.0180 0.0167 ImPfeg-:l-Smelelam 2.3 3.0 .4.3 fStitness 251` 275 Plam-l-Smgle 1am-- 2.7 3.124 `5,0 (Tbe-CD 147 145 Impreg.+dbl. 1am- 24 3.2 .jl weight ofLaminantpwsq-n ibs '14.4` 18.8 gl-lggell-- 22 WVgmsl10sq-mJ24 hour? m 0 32; 0.12 45 P1aincm.+ i b1.ow 3.8 4.4, 5. s Fldl gms 0,57 0,33 P13111 ctn-llmeri'ow -3-2 40 4*.9

lsee Table #1. TABLE #10 Percent Moisture Content After Various `Hours in Storage with two sheets waxed 25# sulphite.

Results of. moisture analysis-% l oz. studyuhandled Percent Moisture Content After Various Hours in Storage Results of moisture analysis-6 oz. study unhandled Percent MoistureContent After Various Hours in Storage Hours in storage r12a 2er asa 551 624 Package Combinations:

Impreg.+dbl. 1am 1. 8 2. 2 3 .4 4, 5 Y 4. 8 Plain ctn.+liner+foil-l-OW 1. 6 1. 7 2.1 2.7 V3. 0

A For purposes of comparison, it is convenientrto find by interpolation in the above data the time required for the moisture content to increase fromme giveirinitialY value to a selected nal Value. In considering breakfast cereals, it is appropriate to use for this purpose a range of 3.5-5.5% moisture corresponding generally to a critical range beyond which breakfast cereals lose crispness noticeably.

In the above manner, taking Table #7 as a standard of comparison, it is found that in all cases the laminated cartons provide superior moistend to "ture protection. Among the laminated structures, by far TABLE #i4 Moisture pickup at 909 F. and 85% VRH Vafter 35 days storage Moisture Pickup (Percent) Carton Gelatin Starch Dessert Pudding (Original (Original s Moisture Moisture Paran Imprcgnated Board Y Y 10.25 6.12 Parainn Impreguated Board with Paratiin Coated Paper Overwrap 2. 03 2. 06 Paratin Impregnated Board Laminated to Paper with Mierocrystalline Wax 0. 59 1.06

From the foregoing data it is evident that the invention Y provides a new packaging or cartoning material offering marked advantages in the packaging of goods requiring protection against loss of moisture to or absorption of moisture from the outside atmosphere. In summary,

Y theseadvantages reside in the fact that the single laminated sheet provides at least as good WVT properties as were obtainable heretoforeV with cardboard cartons and waxed paper overwraps, and especially in the further fact that these properties are not materially aiected by handling of the packages whereas prior types of lined l-oz. package l(b) of and overwrapped cartons rapidly lose a large if not major proportion of their original and intended WVT properties as the result of normal and unavoidable commercial handling. In addition, ofcourse, the single laminated sheet is simplerl andeasier to handle than multiple prior cartons plus liners and/ or overwraps, both in packagingrthe lgoods by the manufacturer and in opening the packages for use of the goods by thelcustom'er. At the Ysame time there is no loss of attractiveness or adverse the best protection was afforded by those using parainimpregnated bleached kraft. The single laminated struc- 40 ture of this type Was better than the/plain V(nonimpregnated) laminated structure 'and nearly 200% better than the standard. The double-laminated impregnated material was much better than the single-laminated 45 impregnated material as would be expected. Y

Drop'test handling had little or'no' eifecton the laminated cartons, but resulted in marked decreases in the protection afforded by theunlaminated structures. Thus While specialtypesof the latter having'both waxed liners and waxed overwrapsV afforded very good protection bcfore handling, they were no better than the single-laminated impregnated stock after drop testing. After handling, the latter provided approximately eight times better protection than the assumed standard.

Similar conditions were found with kthe larger cartons. In the 8-oz. and 51A-oz. sizes the` unhandledlaminatedimpregnated cartons were about equal tothe Vplain carton having both liner and overwrap; after dropntesting, however, the single-laminated impregnated carton was 10% better and the double-laminated impregnated material was 100% better.` In the 6-02. size, no drop tests were made.

Since commercially distributed packages are subjected to handling equivalent to that provided by the drop tests described above, it is evident that a fair evaluation of relative moisture protection can be obtained only after handling. The consistent'rnarked superiority of the laminated-impregnated structures, as compared with both'the larninated-non-impregnated structures and the' cartons r tested one per week for seven weeks:

effect on the external dress or appearance of the packages, since as already indicated the outer paper ply may be printed in any desired manner.. Thus by laminating a printed paper web to'an impregnated board web, a laminated material is obtained that can be formed into cartons having the advantagesset forth above together with elimination f liners and overwraps.

It is to ne understoood,V of `course,`that the invention is not restricted to' the details of the foregoing description and examples and that reference should be had to the appended claims for a definition of its limits.

What is claimed is:

l. A process for making laminated packaging material highly resistant to theV transfer -of water vapor therethrough which com-prises impregnating board which is to form one ply by forcing a moisture-resistantv impregnant amounting to at least 10% by weight of the board into the boardY under pressure so that the major portion thereof is absorbed by the board beneath its "surface, juxtaposing a flat ply of said board and a second ilat ply of paper, and laminating said previously impregnated board and paper together by interposing a moisture-resistant Vadhesive distributed over the. juxtaposed at faces of said plies and pressing the plies together.

2. The process-dened in claim 1 in which the amount of said impevg'nantl is from 20% to 35% by weightof the Y board.

3. A process for making laminated packaging material highly resistant to the .transfer of water vapor therethrough which comprises juxtaposing two at' plies, Aone comprising 5-40 point board in the range of `20 160 lbs. weight per thousand square feet and previouslyirnpregnated with a moisture-resistant material amounting to at least 10% by weight of the board the major portion of which is absorbed into the board beneath its opposite surfaces-the other ply comprising paper in the 7- range of 8-90 lbs. weight per'threethousandsquare feet,

coating the juxtaposed surface of one ofsaid plies with a moisture-resistant adhesive material distributed substantially uniformly over said surfaces, and pressing the plies together.

4. The process defined in claim 3, said impregnant being paraiiinic Wax and said adhesive being microcrystalline wax.

5. The process defined in claim 4, the amount of parafl'inic wax being in the range of 2035% by weight of the board.

6. The method of making laminated cartoning material which comprises forcing parain under pressure into a sheet of approximately 8-10 point kraft board with 20- 35% by Weight of parain to form one ply, juxtaposing a at sheet of said board ply with a second at ply comprising a sheet of printing paper of approximately 8-90 lbs. weight per three thousand square feet, interposing rnicro-crystalline wax as an adhesive between the paper and previously impregnated board, and distributed substantially uniformly over their juxtaposed ilat surfaces and pressing them together while maintaining said parain in a molten condition during lamination.

7. A laminated packaging material comprising a ply of -40 point board in the range of 20-160 lbs. per thousand square feet in weight, said board being impregnated with a moisture-resistant impregnant amounting to at least by weight of the board and the major portion thereof lling the voids in the board beneath its opposite surfaces, a second ply comprising paper in the range of 8-90 lbs. per three thousand square feet in weight, :and a moisture-resistant laminating adhesive material interposed between said impregnated board ply and said paper ply, said plies being juxtaposed and adhesively united over their entire area by said interposed adhesive material.

8. A laminated packaging material comprising a ply of 5-40 point board in the range of 20-160 lbs. per thousand square feet in weight, said board being impregnated with a moisture-resistant impregnant amounting to at least 10% by weight of the board and the major portion thereof filling the voids in the board beneath its opposite surfaces, a second ply comprising paper in the range of 8-90 lbs. per three thousand square feet in weight, said paper being printed on one side to form the external surface of a package, and a moisture-resistant laminating adhesive material interposed between said impregnated board ply and the other side of said paper ply, said plies Ibeing juxtaposed and adhesively united over their entire area by said interposed adhesive material.

9. A laminated packaging material as defined in claim 8, said impregnant comprising paranic wax.

10. A laminated packaging material as defined in claim 8, said adhesive material comprising microcrystalline wax.

11. A laminated packaging material as defined in claim 8, said impregnant being paran and said adhesive material being microcrystalline wax.

12. A laminated material for making moisture-resistant cartons `comprising a ply of approximately 8-10 point kraft board impregnated with 20-35% by weight of paranic wax, the major portion of said impregnant filling the voids in the board beneath its opposite surfaces, a second ply of printing paper in the range of 8-90 lbs. Weight per three thousand square feet, said plies being joined throughout substantially their entire area by interposed microcrystalline wax as an adhesive.

References Cited in the iile of this patent UNITED STATES PATENTS 395,645 Anderson June 1, 1889 1,217,819 Peterson Feb. 27, 1917 1,408,746 Kick Mar. 7, 1922 1,618,491 Taliaferro Feb. 22, 1927 2,158,754 Hodgdon May 16, 1939 2,290,741 Eckert July 21, 1942 2,296,171 Magill Sept. 15, 1942 2,376,899 Bulatkin May 29, 1945 2,434,106 Flood et al. Jan. 6, 1948 2,568,349 McKee Sept. 18, 1951 FOREIGN PATENTS 542,079 France May 11, 1922 464,751 Great Britain Apr. 23, 1937

Claims

3. A PROCESS FOR MAKING LAMINATED PACKAGING MATERIAL HIGHLY RESISTANT TO THE TRANSFER OF WATER VAPOR THERETHROUGH WHICH COMPRISES JUXTAPOSING TWO FLAT PLIES, ONE COMPRISING 5-40 POINT BOARD IN THE RANGE OF 20-160 LBS. WEIGHT PER THOUSAND SQUARE FEET AND PREVIOUSLY IMPREGNATED WITH A MOISTURE-RESISTANT MATERIAL AMOUNTING TO AT LEAST 10% BY WEIGHT OF THE BOARD THE MAJOR PROTION OF WHICH IS ABSORBED INTO THE BOARD BENEATH ITS OPPOSITE SURFACES, THE OTHER PLY COMPRISING PAPER IN THE RANGE OF 8-90 LBS. WEIGHT PER THREE THOUSAND SQUARE FEET, COATING THE JUXTAPOSED SURFACE OF ONE OF SAID PLIES WITH A MOISTURE-RESISTANT ADHESIVE MATERIAL DISTRIBUTED SUBSTANTIALLY UNIFORMLY OVER SAID SURFACES, AND PRESSING THE PLIES TOGETHER.
4. THE PROCESS DEFINED IN CLAIM 3, SAID IMPREGNANT BEING PARAFFINIC WAX AND SAID ADHESIVE BEING MICROCRYSTALLINE WAX.