US2443222A - Process for waxing paper - Google Patents

Description

Patented June 1948 PROCESS FOR WAXING PAPER Samuel Bergstein, Cincinnati, Ohio, assignor to Robert Morris Bergstein and Frank David Bergstein, trustees No Drawing. Application February 23, 1945, Serial N0. 579,493

My invention relates to the application of Waxes or waxlike compounds in molten condition to packages or to packaging materials. Packaging materials are customarily fibrous sheet stocks such as paper or paperboard; and the primary purpose of a coating or application of a wax or waxlike composition is to provide protective qualities such, for example, as moisture-vapor proofness. Because fibrous sheet stocks are absorbent in nature, waxy materials when applied to them in molten form tend to be absorbed or partially absorbed and to this extent fail to provide the desired protective characteristics. For optimum results it is necessary that the Wax remain on the surface of fibrous sheet stocks in the form of a continuous, and therefore imperforate and impervious, film. Any absorption of the coating tends to disrupt the continuity of such a film and to increase the quantity of coating substance required to secure proofness.

For example, on an impenetrable surface approximately 7 pounds of wax will cover an area of 1000 square feet with a film approximately /1000 of an inch thick. I have found that a uniform continuous surface film of wax which is only /1000 of an inch thick is sufficient to provide moisture proofness. But the ideal continuity of the film has not hitherto been obtainable in applying wax to the surfaces of fibrous stocks. So much Of the wax penetrates or soaks into the fibrous structure that a reasonable degree of moisture proofness is normally obtainable only through the application of two or three times the amount of wax mentioned above, and in some instances is not obtainable at all with commercial amounts of wax.

Also, as is wel1 known, the penetration of wax into the surface of paper or paperboard produces an undesirablediscoloration of it, as will be discussed more at length hereinafter.

The principal objects of my invention are the provision of a mode of enhancing film formation with wax or waxlike substances applied in molten form, without increasing the cost of the product or its manufacture in any significant way and with consequent economy of coating material and the avoidance of discoloration and other disadvantages.

These and the more specific objects of my inyention which will be set forth in the ensuing '7 Claims. (Cl. 11760) Waxy substance while permitting a good bond of of fibrous material, as by a light spray of water, immediately prior to the application of the molten waxy compositions, and by applying the compositions in molten form in a' manner coordinated with the wetting as hereinafter set forth, I am able very greatly to lessen or to eliminate altogether the penetration of the Wax substances into the surface of the fibrous sheet stock. I have found further in the practice of my process that inherent film forming characteristics in the Waxy compositions employed become very much less important and that it is entirely possible to form continuous films from substances which inherently possess poor film forming characteristics as applied to absorbent surfaces.

The bare presence of water in or on the surfaces of paper or paperboard is not sufficient for the purposes of my invention. Instead, both the quantity and disposition of the applied water must be controlled at the time the molten coating composition is applied. It is possible to add too much water to fibrous sheet stocks so that the surface becomes too wet to permit the formation of an adequate film even with coating compositions having strong film forming characteristics. The addition of too much water to fibrous sheet stocks, or the provision of too much water on their surfaces prevents the proper anchorage of any film which is formed. It is undesirable also in that it tends to weaken the sheets and may entail a subsequent drying operation. With too little Water or Where the water, irrespective of its quantity, is substantially wholly absorbed into the body of the fibrous sheet stock, adequate films will not be formed unless excess quantities of coating substances having strong film forming characteristics are employed.

I have found, however, that excellent results may be obtained by Wetting the surfaces of fibrous sheet stocks with a relatively very small quantity of water uniformly and quickly applied and then immediately coating the surfaces with the molten waxy materials. In my process the effect is as though at the instant of the application and chilling of the molten waxy substance the water itself formed a barrier film at the surface of the fibrous material, preventing penetration of the the coating with the fibrous material. Yet the quantity of water applied is so small that the sheet stock does not require subsequent drying operations nor is there any tendency for vaporized water to blow holes in the applied coating.

The condition of the water film is an evanescent one, requiring that the coating be done 1m- By adjusting the spray heads as they unifomnly apply moisture to the surface of the sheet just before the sheet passes into or :beneath'th'e surface of a bath of molten waxy comp H fore the composition is appliedet-o surfaces by roller coating or printing means, a condition of operation can readilyhe arrived at Q11. Qti s befib ussh et and maintained, which will result in the produce tion of a continuous and imperforate filrn' with minimum penetration of the sheet stochby the.

waxy substance. The precise quantity of water mnle e wi vary-somewha with h a r n? wi -aeae h brmisl hea to k; t. ua ess operating conditions can r-eadilytbe arrived at and ma aain d in t r s tfq j' h abwe- I now give certain examples 'offor ms. whichthe nr e i a my a tn lqnjmay. ake it e n m da hed at t ese. re lu at el Emample 1- One. o'fthe most widely usedgradesv of paperboaid forfolding boxes is .fna'de; entirely. or in large part orjwaste .pape'ifQand' "lsknown as chip board. Ih; the m nufacture of finany types of packages, ula'rlyj f for. the lfood, industry and g for such 1 sasjmeapg onucts;ba er-moods n the likejitisdsirabl gwaxyofie orfboth suriac'eslof this' sortof paperboard. vvneniajmolten waif, or Vila ycornp'osition is fappljied td'chi'pv board by proce'dui'es I customar m1 the industry; the penetrati'dii of. the jl'nolteii. and .now mgjwax causes a decidd. darkening. anddisol" ationbf t e, board, whichjisunslghtlyljand i'rabl, particularly for ."paickagfesfcontaining "food 'pm1ut Some chipboard's. are made with a linerfoif. gunmen} ef'oi a "grad stock, but evennere the. banetration .wa l'as 'ap'fili'ed inlthe. usual. wayQissuch as. to. cause whatfl is" known as'fa 'stri'ke through. The Wag; tendslto inake. theIsurfa'fc'eIliner mega transparent "and the iiarkei'color o the bod or a an s ows" through it. Indeedwith lined ho rdsvzaxing' has tendency to. cause. uneven or s'pldtchy darkening or l thelsurfac'e,WhiChiis Iaddi aoa ny' undesirable. "Bantam food products, it nasjbeen the'practice in the; past ft'o'f u e' .a solid board made or expensive'and' v1 g ii'b'leahed'piilp. where" the board was to be] "axed."

' To manufacture packages." from] paperboard Wherethev protective.characteristics of ax are des red, onepractice has been, mm-x bulk paper boa din sheets or rolls from; which aQnumber 0f units '01:. individual carton blanks farefthereafter out... Another practice has been toirrjnthe tar; ton blanks themselves an d thereafter 'vvax'fthein, individually .by passing. the. blanks between apair Qr.. m11ers,.cne,.or both fof .IWhich Icarryi a. surface filn iof the molten.wax, ,supplie d tothe rolls from, a heated fountain; The'thickness oi the waxfilm I on the, surfaces. of ther'olls ispcontfolled'bya docto rblade.

' When paperboard in. either oithese forms is, waxed, in. addition to the undesirable darkening. or disc oration 'p-reviously' noted; the porous. nature 'of the' 'stock ca sesa. large amo nt of. the wagctoZ. b el absorbe d by jthe sheet, making, it .difiicult; iaahie e-a ent ai pusijtiaej lm i the 'surfaces-ohmiclboard'from-bne .or both sides, as

the case may be, with a controlled amount of Water. I have found that I can secure continuous and. impcr fgrate films with Very much smaller quantities ofwax than have hitherto been reat ired-to achieve proofness, and that I can do this Withoutan'y rea-Lstaining or discoloration of the board Hence .Lmay not only use lined boards instead of the more expensive virgin pulp boards of mea uautasut \I may also employ chip boards a 61 other cheap fibrous materials, the uncoated surfaces of which would be acceptable commercially for the intended uses.

Lh vehere n oved aussed he applicat on of thawa Thenian er o lap lica it toilthawax s ot. mitm e cent hat ts u dmeierahly perm on o o h 7 q antity pliedto .e iec he .eoa om e 1 i n m p ation, and; x: p ha t heu sd ot ba man-p ie s-tqinvqlve h at n Qf hepape hq rd to, ahis-h. emperatu e for e at l pro on ed pr d o ime. 1 he waxmam -desired; e. annli ahy n ayine- But f the p p rboard a t-blanks; re miss dhrou h a bathof molten waxysubstanca; i-t ia de table h t he t oit vel be a h rt neso t. he p i do a fiy .Q& i ..-@nu eg n. o. .cengeal. and t in; mn ar t na aqn ist ner eiq he har c er t t t Wa r. lm-des ribed a are r destroy d. For h sason .:-n .ier.ae er coating operatiqnofthe kind described;

wmle2-- le ia f i t fi a g n tvegetable i. s i hq ea a a' ke I ou t the application or my. presentproc int greaseproo'f. compositions mom-gage. product:

I find that when the pap'erzldripa erboard I reaiea. ith etsin' i eal:

a substantial broadening of the temperature ranges at which successful results are achieved.

Example 3 'while the reverse side of the sheet is the one treated with a waxy composition for protective purposes. When a light weight sheet, such as an 18 or 24 pound sulphite paper is waxed in the customary way, any substantial absorption of the wax is likely to cause it to penetrate entirely through the paper. In some instances this tends to increase the transparency of the paper, which is undesirable, and in other instances a mottled appearance is produced. In any event, a striking of the waxy substance through the paper tends to interfere with printing upon the opposite side.

Paper is customarily waxed while in the form of a continuous Web. It is unwound from a parent roll and is passed over a coating roller which is partially submerged in a fountain containing molten paraffiin or other waxlike substance. After the wax has been thus applied, the web is either cut apart into sheets or rewound preparatory to further processing.

In accordance with my invention, I can follow the same general procedure in applying wax to the web but immediately prior to its application by the coating roll I treat the web with a spray of water as has been described. Penetration of the wax into the paper is very substantially lessened or is eliminated entirely, preserving the appearance of the paper, as will be evident. Also in my practice, it is possible to obtain a light weight paper bearing a uniform protective waxlike film upon one surface while the other surface remains sufficiently free from wax to present a suitable surface for printing or other decorative processes. I am also enabled, in accordance with my invention, to apply much heavier coatings of wax to one side of thin paper without harming appearance or the ability of the other side to accept printing inks.

Ewample 4 It is a practice in certain branches of the packaging industry to dip finished, filled and closed cartons or containers into a bath of molten wax or waxy substance so as to secure an all over external protective film on the finished package. This may be done for moisture proofness or to prevent the infiltration or escape of external or internal gases.

My invention is suitable for use in conjunction with such treatments. I find that if a suitably sealed paperboard carton is first passed through a fine spray or mist of water vapor and is thereupon immediately immersed in a molten bath of waxy substance under the conditions hereinabove set forth, the wax treatment becomes very much more effective for essentially the same reasons as have been pointed out in connection with my other examples. Since the wax is unable to penetrate the surface barrier formed by the water under the conditions taught above, it forms a more uniform and continuous external film, providing the maximum protection with the minimum of coating material. Again, undesirable staining or discoloration of the package is avoided.

I have further discovered that it is possible,

without. interfering with the obtaining of, the effects described above, to add other materials to the water so as to obtain additional advantages. The water may thus be used as a vehicle to introduceinto .the sheets materials which remainingafter the dispersion or evaporation of the water, produce secondaryor residual effects. For example, a percentage of glycerin may be added to and mixed with the water. This does not interfere with they formation of the desired barrier to the penetration of molten waxy substances; .but the glycerin remainingin the sheet .acts as aplasticizer and imparts added flexibility to the finished product. This is of especial importance in connection with light weight papers. Again, a small percentage of a water soluble, grease-proof resin such as polyvinyl alcohol may be added to the water which is to be sprayed upon the paper or paperboard. The pressure of the resin does not adversely affect the action of the water in preventing penetration of the wax; but the grease proofness of the sheet is augmented by the residual resin so introduced.

Excep-ting for the actual cost of additives, there is no extra operation or additional labor in providing such secondary advantages since no additional step or operation is involved.

By my invention as herein described, I have provided a simple and highly effective mode of insuring the formation of a uniform and continuous surface film of wax or waxlike compounds on fibrous or other normally highly absorbent materials. Modifications may be made in my invention without departing from the spirit of it. Having thus described my invention in certain exemplary embodiments, what I claim as new and desire to secure by Letters Patent is:

1. A method of waxing a web of paper stock to provide on a surface thereof an imperfora-te superficial film of a coating wax, solid at room temperatures, with a minimum amount of such coating wax, which comprises applying to the said surface a light superficial film of water no more than sufiicient to form an imperforate film on said surface, and immediately thereafter applying said coating wax in a molten state to said surface before said water film is absorbed into said surface.

2, A method according to claim 1 in which said water contains polyvinyl alcohol.

3. A method according to claim 1 in which a plasticizer for said coating wax is mixed with said water.

4. A method according to claim 3 in which said plasticizer is glycerin.

5. In a process of applying to a surface of paper stock a coating of a wax, which is solid at room temperatures, the steps of quickly and uniformly applying to said surface a light superficial film of water no more than sufficient to form an imperforate film on said surface, and immediately applying thereto a molten coating wax before substantial absorption of said water into the surface of said paper stock can take place, under conditions to promote immediate chilling thereof.

6. In a process of applying to a surface of a web of paper stock a wax coating, solid at room temperatures, the steps of producing a continuous movement of said web, continuously spraying water evenly over said whole surface in an amount no more than sufilcient to form an initial imperforate film of water substantially wholly superficially thereon, and immediately applying a molten coating wax to said surface and