US1971274A - Manufacture of water-repellent papers of high wet strength - Google Patents

Description

Patented Aug. 21, 1834 "PATEN'D osmosmnurscruns 0F WATER-REPELLENT rsraas or men war srasucrn George A. Richter and Milton 0. Schur, Berlin,

assignors to Brown Company, Berlin,

N. 11., a corporation of -Maine No Drawing. Application September 2, 1932, 861181 N0- 631,497

17 Claims.

There are various water-repellant papers now on the market, wherein paraflin wax or the like is used to impart to the paper its property of shedding or repelling water. Such papers are i .usually made by saturating and/or coating a base sheet of paper with paraflln wax or like material, which prevents water from entering into and weakening the paper base. The adequacy of such paper in service depends upon maintaining the illm of saturant interlacing the fibers or the coating perfect or unbroken, since, if the fiber or coating becomes cracked or otherwise damaged, water will penetrate into the paper base, cause a softening and swelling of the fibers, and may eventually give rise to rupture of the sheet, especially when it is subjected to handling or is under other stress. In accordance with the present invention, we associate regenerated cellulose with the paper base. as well as saturate it and/or provide it with a coating of paramn wax or equivalent 'water-repellant material. A paper so made is highly resistant to disintegration in the presence of water, for the reason that even though the coating of paraffin wax on the fibers or on the surface of the sheet is imperfect to begin with,

or develops imperfections in use, the regeneratedcellulose present in the paper base will tend to 'preserve' the sheet against rupture by the water entering "thereinto on account of the imperfections in the wax phase. Indeed, the presence of with the paper sheet at any suitablestage of its manufacture, as by using viscose and regenerating'cellulose therefrom under the influence of-heat and/or suitable chemicals. For instance,

a viscose solution may be applied to the nascent web of paper while it is still pursuing its course through the'papermaking machine. A convenient place of application on the papermaking machine is at the last pair of wet press rolls, whose pressure can be controlled so as to leave only the desired amount of viscose in the web. Or the partially or completely dried paper web may 53 be passed through 'a bath of viscose solution,

then through squeeze rolls, and finally over a bank of heated drying drums. The regeneration of the cellulose from the-viscose may take place under the influence of the heat'of the drying drums, particularly when an appropriate chemical, such as boric acid, isadded to the viscose for the purpose .of promoting regeneration under heat. On the other hand, the viscose-impregnated web may be passed through a bath of suitable cellulose-regenerating chemical, such as. an alum solution or chlorine water, and, if desired,-through a bath of wash water, before it is finally led over the heated drying drums. The use of chlorine water or similar oxidizing medium tends to destroy odoriierous sulphur com- 7 pounds liberated from the viscose through the regeneration of cellulose therefrom.

The dry paper containing regenerated cellulose is not water repellent, but, on the contrary, imbides water quite freely, especially when it contains only a small percentage of regenerated cellulose and is otherwise substantially unsized. In accordance with the present invention, such paper is treated with parailin wax or like water-repellent material in any suitable manner. That is to say, the-wax may be put on the paper sheet in a heat-liquefied condition by the ordinary waxing machine, which is equipped with a vat containing a bath of the molten wax, through which the paper travels, 35 and with means for removing excess wax from the surfaces of the sheet. The paper sheet acquires a smooth, continuous film or coating of wax, which does not detract from-the wetstrengthening function of the regenerated cel- 'lulose distributed through the body of the paper. The regenerated cellulose is, in fact, inert with: respect to the wax and is substantially unaffected by the temperature conditions under which the wax is applied in molten condition 96 to thepaper, or by'such solvent media as mightbe used in dissolving the waxso as to permit its application in the formof a solution under atmospheric temperature conditions.

The paper base may be made from any able paper making pulp, such as kraft pulp, sulphite pulp, or the like. The paper is made from such pulp as ordinarily, excepting that it is preferable to omit the use of sizing or other materials, which would inhibit a rapid diffusion 105 of viscoseinto and throughout the body of the paper. The pulp itself may, however, be beaten or hydrated sumciently to ensure a paper sheet of good texture, strength, and other mechanical properties. In some instances, it may be ll.

suit- 100 desirable to add a paper size, such as gelatine or glue, as well as viscose, to the paper. In such case, the gelatine or glue maybe incorporated into the paper sheet along with the viscose, as a single mixed impregnant, although, if desired, the gelatine or glue solution may be introduced into. a paper' with which regenerated cellulose has been previously associated in comparatively small amount. Glycerine may advantageouslybe added to the paper so as to increase its softness and pliability, especially when.

the paper is sized with gelatine or glue/as hereinbefore described. The glycerine may be used alone or in admixture with the viscose and/or gelatine, glue, or other sizing agent. Aside from the fact that the sizing agent supplements thethe paper, where it exercises the desired function of shedding or repelling water, and further for vending edibles associated with water.

that with agiven usage of wax a thicker and more effective barrier against the penetration of water into the sheet is realized than when the wax has been partially consumed or taken up by the internal. fibrous structure of the s'heet.

As already indicated, it is important that the water-repellent material appear on the finished paper as a substantially continuous film or coating. This result is had when the water-repellent material is used in a continuous molten or dissolved state. Paraflin wax, for example, is preferably applied in molten condition, although it might be used in the form of a solution in suitable solvent media. It is possible to secure the desired result through the use of aqueous dispersions or emulsions of paraffin or other wax only when the dispersed or emulsified particles are subsequently fused in situ on the paper by heat, so" as to cause their coalescence into a. continuous, protective phase.

If the finished paper is designed for use in'contact with fruits, vegetables, or other edibles, the wax is preferably of such 'anature that it will not impart an objectionable taste or odor to the edibles. The wax would then be preferably in the class of paraflin, in so far as concerns its odorlessness and tastelessness.

' The principles of the present invention extend to paperboard or other comparatively thick papers such as are used in making ice cream cartons or boxes, oyster pails, or other containers The need for reinforcing such thick papers with an internal phase of regenerated cellulose, however,

is usually less than in those instances where the paper base is comparatively thin and flexible and is used in connections where the paper,

In some instances, the wax may be added in.

water-dispersed condition to the body of the paper, either alone or together with the viscose. For instance, the paper may be impregnated with a viscose solution mixed with an aqueous paraflin wax emulsion. If desired, the mixed composition may additionally contain another sizing agent, such as rosin size or other soap. The rosin size or other soap may, in fact, constitute the dispersing or stabilizing ingredient for the aqueous paraflin emulsion. The impregnated paper may be dried in the usual manner on steam-heated drier drums, which serve additionally to cause more or less fluxing and coalescence of the dispersed wax-particles. In such instances, too, the dried paper may be given an additional waxing by leading it through a bath of molten paraffin wax, as previously described. The viscose and/or wax emulsion to be incorporated intothe body of the paper may be added to the bulk stock in the beater engine and then undergo precipitation and fixation on the fibers through the. action thereupon of alum or equivalent acid salt or other acid reagent. The paper formed from a stock which has acquired the regenerated cellulose and dispersed wax at the same stage or at difierent stages of papermaking, beginning with the beater engine and ending with the finished sheet of paper containing both these ingredients, may advantageously receive on its surface a substantially continuous coating of wax, as already indicated.

The various methods hereinbefore described yield a paper of such high wet strength and water repellency that it can be soaked in water for one or two days or even longer and yet retain its high wet strength. In this respect, our novel paper resembles parchment paper, but it has the advantage thereover that it does not take up water as readily and is hence to be preferred for such uses as fabrication into bags or sacks designed to hold wet or moist materials, such as coal.

We claim:

1. As an article of manufacture a paper impregnated throughout with regenerated cellulose and enveloped by wax over substantially all of its surface.

2. As an article of manufacture, a paper containing both regenerated cellulose and war throughout the body thereof and coated with war over substantially all of its surfaces.

3. As an article of manufacture adapted for use in contact with edibles, a paper substantially all of whose surfaces carry a substantially continuous coating of wax and whose fibrous body portion contains therethroughout regenerated cellulose acting to reenforce it against disintegration by the action of such water as may enter thereinto through an imperfection in said coating 4. As an article of manufacture, a paper substantially .all of whose surfaces are coated witl paraffin wax and containing regenerated cellulos4 distributed throughout its fibrous body.

.5. As an article of manufacture, a paper substantially all of whose surfaces are coated witl paraffin wax and whose interior contains distributed therethroughout regenerated 0811111051 and a paper size serving to keep said wax essentially only on the surface of the paper.

6. As an article of manufacture, a paper sub stantially all of whose sm'faces are coated wit] paraflin wax and whose interior contains dis tributed therethroughout regenerated cellulos and glue.

7. As an article of manufacture, a paper sub stantially all of whose surfaces are coated wit] paraflin wax and whose interior contains dis tributed therethroughout regenerated cellulose glue, and glycerine.

8. A process which comprises associating re generated cellulose and wax with paper, and thei depositing a substantially continuous coating 0 wax on substantially all of the paper surfaces.

9. A process which comprises impregna paper with an aqueous liquor containing both viscose and dispersed. wax, drying the paper, and submersing the paper in a bath of molten was.

10. A process which comprises impregnating paper with an aqueous liquor containing both viscose and dispersed wax, drying the paper and fiunng its wax content, and submersing the paper in a. bath of molten was.

11. In procexs which comprises impregnating paper with an aqueous liquor containing both emme generated cellulose, glue and glycerine with we terleaf paper and then depositing a substantiai is continuous coating of wax on substantially oi the paper surfaces.

15. A process which comprises treating a water leaf paper with viscose, regenerating cellul from the viscose in situ in the paper. treating the paper with glue, drying, and depositing a a 2 t stantially continuous coating of wax on sub em tially all or the paper surfaces.

16. A process which comprises first associating regenerated cellulose with waterleai paper and then submersing the paper in a bath oi molten wax to form a substantially continuous coating of wax on substantially all oi the paper surfaces.

1'1. A process which comprises first asociatimg about we to 2% oi regenerated cellulose with waterleat paper and then submersing the paper inabathoimoitenwantofiilresidual poresipi said paper and to form a substantially continuous coatng oi waxon sutantally all of the paper surfaces.

GRGE A. i

TON 0. a