US2215136A - Manufacture of wet-strengthened paper - Google Patents

Description

Patented Sept. 17, 1940 Milton 0. Schur, Berlin, N. 11., assignor to Brown Company, Berlin, N. 11., a corporation of Maine No Drawing. Application July 19, 1937,

- Serial No. 154,465

This invention relates to the manufacture of wet-strengthened paper, that is, paper of markedly higher wet-strength than ordinarily. While not restricted thereto, it deals especially with wet-strengthened paper of substantially unimpaired absorptivity and hence of particular value for those uses for which it is important that a paper possess an absorptivity comparable to that of waterleaf paper and yet be of markedly I higher wet-strength, than that of waterleaf paper.

While it has been found that specific sub-. stances, notably regenerated cellulose and gelatine, can be incorporated into paper in controlled amount conducive to a wet-strengthened absorpi5 tive paper product, yet a long-continued quest for other agents capable of wet-strengthening paper while substantially preserving its absorptivity has shown what was to be anticipated,

- namely, that numerous binders or sizes capable of increasing the wet-strength of paper to a significant extent are so water-repellent as to destroy-in effect the absorptivity of the paper and that water-soluble or water-absorbing binders, although capable of enhancing the dry strength of the paper and preserving to a noteworthy degree the absorptivity" of the paper, are generally of little value in improving the wetstrength of the paper.

I have discovered that 39 be made to function exceedingly well as a wet strengthening agent in paper ,without detracting unduly from the absorptivity of the paper, provided that the gum is properly alkalinized or activated with an alkaline solution.- It is preferable to alkalinize the gum in situ in the paper; and, to this end, an alkaline solution may be applied to the gum-containing paper web while the web is still on the papermaking machine, for instance, on its way to the drier, or it may be applied to the predried, gum-containing paper web and t web redried. While aqueous solutions of various alkaline compounds, including caustic soda, caustic potash, andsimilar hydroxides, are effective and can be used as activating media for the gum, it is considered preferable at the present time to usesolutions of comparatively mildly alkaline compounds, such as borax and sodium carbonate, for it has been found that a paper product of the desired high wet-strength and other qualtities is realized with a pH value little greater than 7 in the finished paper product and that it is easyto obtain such desired slight alkalinity even with dilute alkaline solutions of such comparatively 56 mild alkaline compounds as have no appreciable locust bean gum can gum. While the 5 Claims. ((31. 92-21) effect on the skin. Thus, when the finished paper product is to serve as towels, paper handkerchiefs or other skin wipes, the presence thereinv of borax or similar mildly alkaline compound in amount to impart suitable alkalinity thereto 5 has no noteworthy eifect on the skin.

The locust bean gum useful for the purposes hereof is available on the market as a fine white powder that lends itself nicely to incorporation into papermaking stock without any conditioning 10 treatment whatever and isx well retained by the stock. This is evidently attributable to the fact that the powder particles swell promptly in cold water and hence become intimately attached to and/or enmeshed in the fibers of 5 the papermaking stock while in aqueous suspension and while the water of suspension is being drained from the thin web of stock on the .papermaking machine. It thus becomes possible to add the powdered gum to the papermaking stock in the beater engine, in the head box, or at any other convenient place in the course of papermaking and thus, while otherwise pursuing essentially a conventional papermaking practice, to produce a paper sheet throughout which the gum is substantially uniformly distributed.

Because the gum can be dissolved in weakly alkaline water, it is most surprising that a weakly alkaline solution activates the gum so that it exerts extraordinary wet-strengthening effect on paper. The fact is, however, that mere spraying of weakly alkaline solution on the- -wet,- gum-containing web on its way to the dry end of the papermaking machine or mere clipping of the predried, gum-containing paper web in weakly alkaline solution followed by redrying yields a finished paper product whose wet-strength is vastly greater than that of a similar paper product lacking the activated 40 present invention compre- I hends the impregnation of a paper web in dried or moist conditionwith an aqueous solution of the gum, yet solutions of the gum are highly viscous even at very low gum content so that they do not ordinarily lend themselves very well to use in uniformly. impregnating the web; and

it is, moreover, more expedient from the .standpoint of a papermaker to add the powdered gum 6 v as such to the papermaking stock, particularlyv .as the powdered gum can be quickly and uni-; V iormly dispersed throughout the stock with ex-, cellentretention by the stock of the water swollen gum particles throughout subsequent papermaking operations and alkalinizing treatthat the use of excessive borax solution might ment. have the eifect of leaching out some of the gum,

For making papers of high absorbency as a simflar predried, gum-containing paper sheet. well as markedly supernormal wet-strength, as was sprayed with borax solution of 1% strength a little as 1% to or even less of the locust in the amount of only 150%. based on the weight a bean gum, based on the dry weight of the paperof the dry gum, and the sprayed sheet redried, in making stock, may be used pursuant to the preswhich latter case it was found that the wet-tenent invention. If desired, however, the gum sile-strength of the dried product had risen to may be used for the purposes hereof in amount 2.0% pounds. All of the dried, mildly alkalinized,

10 up to about 5% or in even greater amount, gum-containing paper products were, however, although it is usually preferable to stay within characterized by a wet-strength many times that I an upper limit of gum usage of about 5%, based of a paper sheet similarly made but of waterleaf on the dry weight of the papermaking stock, in character, that is, containing no gum. Indeed, producing paper products of the absorptivity the similar waterleaf paper sheet had a wet-tendesired for such an article as paper toweling. she-strength of only 0.20 pound. It might be 15 The papermaking stock used for the purposes noted that the dried, mildly alkalinized, gum-conhereof may comprise any one or a mixture of varitaining paper products hereof were of substanous cellulosic fibers, such as sulphite pulp, kraft ti lly unimpa r d water absorbency in t s nse pulp, wood pulp refined t high alpha, cell los that they imbibed water practically as freely and and it is to be observed that, because of the whit'epurposes as toweling need hence h rdly .be ness of the locust bean gum, it does not: detract tres edfrom t whlteness of bl h d papermaklng In testing the paper products hereof for their stock into which it is incorporated, wh n a, wet-tensile-strength, the method is to moisten a 35 paper product of highest absorbency is desired strip /2 inch Width by e s of a camel's hair and the papermaking stock is being suspended in brush pp d into Water d subjecting e s r p water in a beater engine, the beater roll is operthus moistened or brushed transversely at the ated in such away and for such a period of time pl p te o e to the te si e-strength-testing 3? as to 'do little more than individualize the fibers or ma hi h wet-t ns -s re th re ord d y smooth out the stock sufllciently to enable the I the n'lhehlne p se s t e oad n pounds which formation therefrom of a uniformly textured the m s n d ip 1' /2 inch W d h n ppo sheet on the papermaking machine. In other at the rupture breaking p 7 words, the stock is not beaten or hydrated with a It is to he understood that the exemplary P uview toward developing a paper sheet of the relaeedllles hereinbefele given e u j t to wide tively high density requirements of bond, writing, variation without departing from the p it or or ledger papers. On the contrary, the beater scope of t e vent on r o s efin by t engine is operated essentially as a mixer to bring appended claims. Thus, it isp s l p y e I about uniform suspension of the pulp fibers in the inventive Drinclples hereof in making P pe Prod-- 40 water and uniform dispersion of the gum particles n s of Wi y Varying is Wei ht and compact- 4g throughout the suspension, assuming that the n n pt for m ny uses besides that of powdered gum is added to the stock while in the taking 9' Water While resisting t t onbeater-engine rather than at a later stage of instance-n Wet-strengthened, absorptive D paper making, say, whileit is flowing as a stream per product hereof containing locust bean gum as 145 to the papermaking machine, the wet-strengthening agent may undergo a sec- 5 Typical procedures carried out accordant with ondsry impregnation with water-repellent matethe present invention involved the use of a mixrials of oleagin us. resinous. y tureture of equal parts by weight of bleached sulphite Thus, t ay he mp egnated with parafllp wax or and bleached kraft wood pulps. After the mixed e like to produce a epe lent paper sheet pulps were suspended in water with very littl suitable for use as a lettuce crate-liner, for wrap- 5 hydration thereof to produce a uniform pulp sus- P E- l In such a e spheres of use. i pension of appropriate consistency for paper mak-' is d r e that the Water coming from? the ing, namely, of about 1% fiber content, locust melted iceinwhich the heads-of lettuce or bundles bean gum was added as a'flne powder to the sus-' of celery are p k d e ep ll d by thepaper-liner .55 pension in amount to yield a paper sheet contain- Wrap ra n: gum, based on the dry weight of the pulp. So far as concerns the alkalinization of a pre- Specifically, the powdered gum was dispersed unir e p per W b n i ing the locust bean gum. formly in the dilute pulp suspension at the head it is possible, as already indicated, to use any box of the paper-making machine. The sheet proalkaline solution capable of imparting to the pa- .60. duced on the papermaking machine, which had a per a pH value greater than 1. It is thus seen on basis weight of about 22 pounds, was pressed and that alkaline s lutions, of wid ly v rying alkalindried in the. usual way on the papermaking lty or s e are use ul for the purposes hereof machine. The dried papersheet containing locust aiforded with alkalis or alkaline compounds-of 85 bean gum, based on the dry weight of fiber, was many different kinds, 'even though for somepur- .05 dipped into an aqueous borax solution of 1% poses, such as toweling, it is preferable t t um-l the dried, weakly alkalinized product had a wetprovided by such mildly alkaline con; unds a I tensile-strength of 1.4 pounds. When a solution borax. The amount of alkaline solution used to 1 71! of 1% strength was prayed onto a similar preactivatethe gum in situ in the gum-containing 7o dried, gum-containing paper sheet in an amount paper'web is 3180' subject to wide variation, but of 300%, based on the weight -of the dried sum, it is ener lly Preferable to apply no more alka and the sprayed sheet redrled, it was found that line solution to the web than is necessary to wet the drIedQWeakIy kalinized product'had a wetor alkalinize the web substantially uniformly g; tensile-strength of 1.8 poun Sincejit appeared throughout while avoiding dripping or drainage alkalinizationor treatment with alkaline solu-' tion is dried or redried at elevated temperature, as on the steam-heated drier drums of a papermaking machine. It is thus seen that the process hereof can be practiced while a sheet of paper is being made at the customary high papermaking speeds and the resulting continuous sheet of paper containing the gum can be activated or brought to the desired high wet-strength by a1- kalinization while such sheet is pursuing its high speed continuous course from the station of alkalinization, through the drier, and thence to the reel.

I claim:

l. A method of making a paper product of high wet-strength, which comprises forming paper from paper-making stock containing powdered locust bean gum in an amount not more than about based'on the dry weight of the stock; and alkalinizing the resulting paper with an aqueous solution of an alkaline compound.

2. A method of making a paper product 01' high.

wet-strength, which comprises forming paper from paper-making stock containing powdered locust bean gum substantially uniformly dispersed therethrough in. an amount not more than about 5%, based on the dry weight of the stock, wetting the resulting paper with an alkaline soelevated temperature.

lution of suflicient alkalinity to impart thereto a pH value greater than '7, and drying the alkalinized' paper.

3. A method of making an absorptive paper product of high wet-strength, which comprises incorporating into .substantially unhydrated' papermaking stock not more than about 5% of powdered locust bean gum, based on the dry weight of the stock, forming paper from the resulting stock, alkalinizing the paper substantially uniformly with an aqueous solution of a mildly alkaline compound, and drying the paper.

4.. A method of making an absorptive paper product of high wet-strength, which comprises incorporating into substantially unhydrated papermaking stock about 4% to 1% of powdered locust bean gum, based on the dry weight 01 the stock, forming paper from the resulting stock, wetting the paper substantially uniformly with a solution of borax, and drying th paper.

5; A method of making a paper roduct of high wet-strength, which comprises incorporating-into papermaking stock powdered locust bean gum in an amount not more than about 5%, based on the dry weight of the stock, forming paper from the resulting stock, spraying the paper with a solution of mildly alkaline compound in amount to wet the paper substantially uniformly throughout while substantially avoiding the extraction of the gum therefrom, and drying the paper at MILTON- o.