US2035024A - Manufacture of paper for toweling and other purposes - Google Patents

Description

Patented Mar. 24, 1936 UNITED STATES PATENT-OFFICE MANUFACTURE OF PAPER FOR TOWELING AND OTHER PURPOSES Milton 0. Sclmr, Berlin, N. 11., assignor to Brown Company, Berlin, Maine N. H., a corporation of No Drawin Application April 0,1931,

Serial No. 528,229

6 Claims. (01. 91-68) This invention relates in its fundamental aspect to papers of high water absorptivity and yet possessing such a high degree of tenacity or integrity while wet as to resist effectively disin-' that the ordinary paper towels are of waterleaf variety, that is, contain nothing besides the cellulose pulp. The use of papermaking ingredients, 20 such as sizes and binders, in paper towels has beenabstained from, since it has been taken for granted that they detract from the capacity of the towels to absorb water. Generally speaking, this abstinence from the use of sizes or binders 25 is sound practice, since the water absorbing capacity of paper towels is as important, if not more so, than the wet strength of such towels.

I have now discovered that the controlled use of glue or gelatlne, especially in tanned condition, 30 in paper toweling may be of remarkable advantage, since this particular sizing agent has the ability of vastly appreciating the wet strength of paper toweling while depreciating its water absorbency comparatively little. In accordance 35 with the present invention, glue or gelatine is distributed through paper toweling in such a way that the finished article absorbs water like similar waterleaf toweling but is far more resistant to disintegration especially while wet. The ad- 4 vantage of using glue in paper toweling obtains up to a glue content of only about based on the dry weight of fiber, since when this maximum percentage is overstepped considerably, the increase in wet strength attributable to such over- 4 stepping is more than outweighed by the undesirable drop in water absorptivity. By remaining within an upper limit of about 5% glue content in the toweling, it is possible to achieve a multifold increase in the wet strength of the toweling 50 over its waterleaf wet strength without much decrease in its water absorptivity. This multifold increase in the wet strength of the towel is more than is necessary to render the towel resistant to disintegration even when put to vigorous 55 use in the wiping of wet hands. Accordingly,

there is no particular point in exceeding in the towel the limiting value of glue content mentioned, since the excess simply makesfor greater expense and an impairment of the ability of the towel to imbibe water. 5

While there may be various ways of incorporating the desired amount of glue in paper toweling, a simple, procedure open to ready application in usual paper making practice devolves about starting with a waterleaf web of toweling as it is removed in partially or completely dried condition from the dry end of a paper making machine.

The'web of toweling may be composed of, say,

kraft pulp, and possess a basis weight of, say, 37 pounds or thereabout. Assuming that one starts with a perfectly dry waterleaf web, the web may be passed through an aqueous glue solution whose glue content corresponds with that desired in the finished toweling. Forinstance, I may pass the web through an impregnating solution containing up to about 5% glue solids and preferably containing up to about /2% of a tanning agent such as formaldehyde, alum, or tannic acid. The solution-soaked web is then passed through squeeze rolls which may be adjusted to reduce the solution content of the web to a point where the web holds similar to those used at the dry end of the usual paper'machine. The dry toweling is characterized by an amazingly enhanced wet strength and a water absorptivity practically similar to that of the waterleaf paper used as a raw material. Indeed, the finished toweling containing only about 3% tanned glue, based on the weight of dry fiber, may be characterized by a wet strength about four to seven times as great as that of the waterleaf paper used as the starting material. 4

In the commercial application of my invention, the web of toweling may undergo such operations as ereping and/or embossing in the course of its manufacture, which operations are well known in paper towel manufacture. If desired. the dried, glue-impregnated web may be mechanlcal- 1y softened, as by being brought into facial engagement, while under tension with the edge of a so-called doctor blade. The softness and limpness of the web may also be enhanced by adding a softening agent, such as glycerine, soap, and alcohol, in relatively small amount to the glue solution. If desired, the glue solution may contain a small amount of suitable preservatives. for instance phenolic compounds of the type of sodium-ortho-phenyl-phenate, which permit the glue solution to stand for comparatively long periods without putrefaction.

The glue used as a raw material may be derived from various sources, such as bones, fish, or hides. The usual glues of commerce, including those which have heretofore sometimes been used in sizing papers, may serve as the raw material. In fact, any of the glues on the market, glues which have been chemically treated or purified so as to be more valuable for use in paper toweling, and glues which upon drying become substantially water-insoluble, may be selected for the purpose of my invention.

In accounting for the results which I secure, one should look to the structure or texture of the original waterleaf web and to the properties of the glue, especially in its state of distribution through the fibrous structure of the web. To begin with, the waterleaf web is made up largely of void spaces or pores rather than solid fibers. Even after the web has undergone impregnation with the glue solution and drying as heretofore described, it still possesses substantially its original volume of void spaces or pores. The small amount of glue incorporated through the web evidently forms exceedingly thin films or coatings on the individual fibers; and these thin films or coatings bind the fibers together with such tenacity at their regions of contact as to increase enormously resistance against separation of the fibers especially in the presence of water. Nevertheless, the glue, even when it is set in substantially water-insoluble condition, is apparently very easily wetted by water, by which I mean that water spreads easily over the films or coatings of glue rather than being shed therefrom. Inasmuch as the glue is distributed throughout the web and is present in such small amount that a large overall glue surface is exposed to contact with water without material loss in the total volume of the pores, the web of necessity must have a large capacity for water absorption. Doubtless, too, in addition to being wetted by water, the glue adsorbs and/orabsorbs the water 7 and then transmits water to the cellulose fibers, which, of course, are also capable of absorbing large amounts of water. Whether or not the foregoing explanation is accurate, insofar as concerns the structure of the towels of the present invention and the actions ensuing from their use, it is a fact that by following the procedure hereinbefore outlined, it is possible to produce paper towels whose wet strength is surprisingly high and whose water-absorptivity compares favorably with similar waterleaf toweling.

I am aware of the fact that it has been proposed to treat paper locally with glue or other agents for the purpose of reinforcing it against disintegration under the action of water, but the incorporation of glue as a continuous phase throughout the body of a waterleaf paper web, as hereinbefore described, possesses important features of superiority. To begin with, it is a relatively simple matter to incorporate glue throughout a waterleaf paper web, as the web need simply be dipped into a glue solution of appropriate strength to lead to the desired results. Again, the finished or dried paper is of uniform feel, absorptivity, and other qualities; and in realizing a given highwet strength in the paper, it is unnecessary to use a glue solution of such high glue conpaper. Indeed, as already stated, the glue solutions which I employ should be used at a glue content not exceeding about 5%, as solutions of higher solids concentration are likely to clog the surface pores and thereby interfere with a uniform impergnation of the waterleaf paper web; and even when they are sufiiciently fluid to become uniformly distributed throughout the web, the web will retain more than the desired amount of glue. This is attributable to the fast that, once the glue solution has entered uniformly into the web, the web tends to retain approximately its own weight of glue solution, even after being thoroughly squeezed.

I am not unmindful of the fact that in the early days of paper manufacture, glue alone was sometimes relied upon as a sizing material. In such case, however, the glue was used primarily to enhance the dry strength of the paper and to prevent the spread of ink thereon. The ink-resisting quality desired in the paper was realized by filling the pores of the paper substantialy entirely or largely with the glue substance, even though increase in strength of the paper began with the addition of only small quantities of glue and progressively increased as the amount of glue increased and the pores of the paper were filled. The desired filling of the pores of the paper .and the attendant high strength "and inhibition of the spread of ink were realized by the use of a relatively concentrated glue solution. When paper impregnated with such glue solution was dried, suflicient set glue remained in the pores of the paper to obstruct capillary channels therein and thus to prevent the spread of ink on the paper and the absorption of water thereby. In order to enhance the impermeability and strength of glue-sized paper, it was also the practice, in the early days of papermaking, to air-dry or loft-dry such paper under conditions permitting unrestrained shinkage and the accompanying closing of the pores in the paper. With the advent of beater or rosin-sizing, it became the practice to size the paper pulp to a considerable extent in the beater engine by disseminating rosin size throughout the pulp and then adding alum or other suitable precipitant to fix the resin on the pulp fibers. The sized pulp was then run off on a papermaking machine. When papers of unusually high strength and resistance to the spread of ink are currently demanded, a pre-sized and dried paper sheet is sometimes passed through a bath of sizing agent, such as a glue or starch solution, and redried. The second or surface-sizing treatment more perfectly fills the surface pores of the paper. All the paper-sizing procedures of the prior art, including the sizing of paper with glue, were thus carried out so as to produce papers of low waterabsorptivity.

It came as a distinct surprise to me that a waterleaf paper might be impregnated with glue in such amount that its water absorptivity remained unimpaired while its wet strength underwent a multifold increase, particularly when the paper so impregnated was dried with shrinkage largely restrained, as is common practice on drum driers of the usual paper machine type. The value of my invention as applied to paper towel manufacture was therefore substantiated repeatedly in order to make certain that accidental or fortuitous reasons were not responsible for the fruitful results initially secured.

I am using the expression glue in the specification and in the appended claims not only in the generic sense hereinbefore indicated, but also to include nitrogenous or protein glues, such as casein glues or glues prepared from albumens, for example blood albumen, to all of which the principles of the present invention may extend.

What I claim is:

1. A method which comprises dipping a porous, waterleaf web of paper into a glue solution containing less than 5% by weight of glue solids and containing a tanning agent for said glue to effect a soaking of such web with the solution,

squeezing the web until it contains only aboutits own weight of solution, and drying the squeezed web to remove its water content and to tan said glue and to render said glue temporarily water resistant.

2. A method which comprises dipping a porous, waterleaf web of paper into a glue solution containing less than 5% by weight of glue solids and containing a preservative against the putrefaction of said glue solution to effect a soaking of such web with said solution, squeezing the web until it contains only about its own weight of solution, and drying the squeezed web and rendering its glue content temporarily water resistant.

3. The method of preparing a soft flexible, porous sheet of paper which comprises impregnating a sheet of thin paper of open formation with a dilute solution of albuminous adhesive, removing a part of the solution to reopen the interstices of the paper while leaving a thin coating of adhesive on the fibers to bind them together at their junctions, and rendering said coating temporarily water resistant, whereby the resulting sheet is characterized by softness, flexibility, porosit and high wet strength.

4. The method of preparing a soft, flexible, porous sheet of paper which comprises impregnating a sheet of thin paper of open formation with rous sheet of paper which comprises impregnating a sheet of thin paper of open formation with a dilute solution of albuminous adhesive containing a tanning agent for such adhesive, removing a part of the solution to reopen the interstices of the paper while leaving a thin coating of adhesive on the flbers to bind them together at their junctions, and drying said sheet to set said adhesive coating and to cause its tanning by said tanning agent and to render it temporarily water resistant, whereby the resulting sheet is characterized by softness, flexibility, porosity and high wet strength.

6. The method of preparing a soft, flexible, porous sheet of paper which comprises impregnating a sheet of thin paper of open formation with a dilute solution of albuminous adhesive containing both a tanning agent and a softening agent for such adhesive, removing a part of the solution to reopen the interstices of the paper while leaving a thin coating of adhesive on the fibers