US1986291A - Manufacture of absorbent waterlaid webs of felted fiber - Google Patents

Description

not into which it may enter.

Patented Jan. 1, 1935 ,QI'PAT MANUFACTURE OF ABSORBENT WATER LAID WEBS 101 FELTED-FIBERT Milton 0. Schur, Berlin, N. H., assignor to Brown Company, Berlin, N. H., a'corporation of Maine f Application November 23,"'193 3 Serial No;689,467 v No Drawing.

Y I 10. Claims.

' 'This invention relates'to the manufacture of porous and absorbent waterlaid webs offelted fiber on Fourdrinier or other paper-making machines from suitable aqueous fiber suspensions or s'o-called paper-'making stocks. tive of this inventio'n'is the economical production, more especially from cellulose fiber of the ful for various purposes 'in'the arts, depending upon' the qualities imparted thereto by the particular binder used as the impregnant. Inasmuch as'the' present" invention devolves f more particularly about the manufacture of the felt base, I shall dwell thereuponand indicate only in a general way the sort of impregnated prod- When the production of webs or felts of a porous and absorptive character is attempted .on the usual paper-making machinespfor instance, a Fourdrinier machine, difliculties are likely to arise. "The seriousness of the dimculties met with varies, depending upon the particular paper-making stock delivered'to the machine and the porosity and absorbency sought inthe resultin'g'webs or felts. In any event, however, one is faced with the problem, of operating a pa'per-makingmachine having a ,dry end or driersection of given length andcapacity so that it will be productive of Webs or felts of the appropriate dryness at its rated capacity or at as great a capacity as possible. In order to get therated capacity out of a given papermaking machine, it is necessary to dewa'ter the web or felt as much as possible through, the action of squeeze rolls at the wet end of the machine. Such practice, however, leads to'webs or felts of excessive density or compactness with most kinds of paper-making stock and this may be true even when the stock is comparatively 'free as,for instance, when it includes a large or preponderant proportion of substantially unhydrated wood pulpof high alpha cellulose con tent. The possibility of by-passing-the squeeze rolls at the wet end of the paper-making machine'is obviously to beavoided, if possible, since such'prac'tice requires either an expensive enlargement of the dry end of' the machineor a sacrifice in the production of the machine. A greater steam consumption is inevitable as a The objec at the same time the-I production of,,webs or result of .such practice, as also, the' problem rupture or. other damage throughlthe machine.

I havefound that in thelfabricationof porous and absorptive webs, it is distinctlydesirable to" 'ad dto the paper-making stock at any stage ofits transformation into webs or felts,;but before drying, suitable surface-tens'ion-reducing:reagents, preferably water-soluble ones, as in the form,of-

'of running a weaker and SOg iCr -Web wthout I aqueous solutions of-water-soluble soaps oraqueous solutions of water-miscible. liquids of .the

nature of alcohol, acetone, etc. This desirability resides'in the fact that when sucl -agents are added to. the stockfand the web is dried in the presence of suchagent, itsdensityorcompactness is, markedly lessthan when such agent is even when the web is ,dewatered by, the action of squeeze rolls at the wet. end of the machine to substantially the fullest extent possible, ,be-, fore it is dried. Thepractice of the present invention hence makes possible the operation} of a Fourdrinierv or other typical papermaking, machines substantially attheir rated capacities and felts whichffor many purposes, have the appropriate porosity and absorbency. It is my belief that the undesirably high density orcompactness that the'web acquires when manufactured in the ordinary way is duenot only to the squeez 'ing which the web receives but also tothe contractile, i. e.,' shrinkingforcesi, set up :by the water as it evaporates from the web on the dryer. These ,contractile ,;;;fpr,ces are believed to vary with the, surface-tension of thewaterduring the drying. operation." Byproviding in the'wet web an agent which reduces the action. of surface-tension during the subsequent drying operation, shrinkage of theweb and the accompanying reduction ,of porosity and absorbency therein can be, reduced so as. to conduce -to webs of the desired character even when material squeezing pressure is exerted on the Wet web by the squeeze rolls at the wet end of the machine and/or when the paper-making stock is unfavorable inthe absence of a surface-tension-reducing' reagent to webs of the desired character. Depending uponthepressure exerted on the. wet, web and the nature of the papermaking'stock, itis possible by thepracticc of the present invention toproduce webs of a wide variety of desirable compactnesses, wherefore,

fomitted and further that this fact holds true while the principles of the present invention are applicable to greatest economic advantagewhen the wet web is dewatered to amaximum content 2; in V before drying, they also obtain when less dewatering is so accomplished, for instance, even when no dewatering is so accomplished, as in stantially unbeaten or-unhydrated refined wood pulp; 8% beaten waste paper; 24% beaten rags; 3% raw potatostarch; sufficient water to form a suspension for delivery to a Fourdrinierff-map-chine, say, asuspe'nsion of about%% 'to 1% solids content. r I

The foregoing ingredients were first mixed in a beater engine under conditionstopreserve the substantially unhydrated condition of the refined woodpulp', which was ofthe unbleached variety having an alpha cellulose content of about 94%. The thick aqueousmixture produced in the beater engine was then diluted with .water to' the consistency appropriate for feltmaking on a Fourdrinier machine and was run off. on such a machine. The wet'web formed fromlthe" stock was carried by the'usual carrier felt through the press rolls of the *machine which was set to squeeze the web-suificiently hard to remove substantially' all the extractable water therefrom and thereby permit the machine. to be run at a high capacity, Between the press rolls, a 1% solutionof ammonium oleate" was sprayed onto the wet web and the rate of addition; of such soapfsolution to the web was controlledso as tofinfuse about 0.8% to 1% of soap into'the dried web. The web {delivered from the dry end of the machine had a basisweight, of 220 and a-compa'ctness of 44. A web made in exactly'the samef'way; but-which did not undergo soaping; before'the drying operation, had a compactnessofi5'7; 'andth is higher compactness'was refiec'ted in a harder and stiffer web; The difference ,inquality between the two webs was readily'discernible by merely feeling them.

Indeed; samples of the-two webswere handed to a number of persons unskilled in the artjand they invariably had no trouble whateverjin picking out the'web of the present invention as being distinctly softer and bulkier than the webs made as ordinarily. 7

It is, of course, possible to use aqueous solu tions of various water-soluble soaps, such as the ammonium, sodium and'potassium' soaps of various fatty acids, such as stearic, palmitio and oleic, as the fsurface-tension-reducing reagents in accordance with my invention. Solutions may also be used containing other wetting-out agents, such as Turkey red oil, monopole oil, or other sulphonated oils, and a great variety of reagents are available in the comparatively recent commercial development of wetting-out agents comprised of sulphonated naphthalene, usually having side-chains, or sulphonated fatty alcohols. The solutions may be used at various concentra tions, although dilute solutions of, say, about 0.5% to 2% strength are generally to be preferred, since they effect the required surfacethereby in the dried web can be regulated so as to be extremely small, say, about 0.5% to 2%. When volatile liquids like alcohol and acetone serve as the surface-tension reducing reagents, they are volatilized during the drying of the web with the result that the dried web is substantially'devoid'of such-agents. The effect of the surface-tension-reducing reagent maybe had by its addition to the paper-making stock at any time before the drying operation. Thus, the agent may be added to the bulk papermaking stock and/or to the wet web as it is passing over the suction boxes and/or, as already described, to the wet web as it is proceeding to or between'the' press rolls. Any of the waters paper-making stock, the machine may be 0perated with a closed white-water system so as to avoid loss of the agent; When a solution of such agent is added to the wet web at the suction boxes'or at the squeezerolls, the water containing such agent sucked or squeezed from the web. may be recovered and used as the vehicle 'for'making afresh solution of such agent.

By adjusting the pressure on the squeeze-rolls at the wet end of the machine, it is possible to practicemy'in'vention to produce webs orfelts of av compactness ranging from about 20 to 55.

The lowest compactness value represents that attainablewhen little or no squeezing of the web is done at the wet end of the machine and when the web is .made from a suitable paper-making stock, say, one. consisting substantially only of refined wood pulp having an alpha cellulose contentof about '93 to 96% or higher andin a practically unhydrated condition. The highest compactness value represents that attainable when maximum squeezing of the' web is done atthe wet end of the machine and when the papermaking stock, like that-given-in the foregoing example, includes asubstantial proportion of hydrated cellulose fibers and even binders such as starch. ,Within the foregoing range of com- I pactness, the websmay be handled satisfactorily "and can be impregnated quickly and uniformly the uppers of']shoes. Webs at the upper end of the compactness range can alsobe impregnated with rubber latex compositions and then dried to produce artificial leathers possessed of the 'stifiness requisite for such articles as welt inner soles. Webs in the intermediate zone or at the upper end of the compactness; range can be bituminized most satisfactorily and to a high bitumen content to produce sheet material of valuein the roofing and flooring industries. The foregoing are merely cited as being illustrative of "only a few of many impregnated products in which the porous and absorbent webs or felts produced accordant with my invention may enter. I have hereinbefore referred to definite compactnessvalues as being indicative of the density or compactness of webs fabricated according to my invention. These values of compactness are obtained by dividing the basis weight of the web in pounds by its thickness in the compactness value really represents the fixi'cmfma multiplyin'gby' arms 16-}. The expression "basis weight to which! havealso alluded as a definite value'is known -:in papermaking circles as, representing the weight in pounds of 480 sheeta whose dimensions .are- 24x36 inches, this being equivalent to 2,880

square feet of sheetm'aterial, In other words,

weight of fiber per unit volume of sheet material. I t a I a aware of the fact that it has been proposed to introduce saponaceous or foam-generating. materials, into aqueous pulp suspensions for Such practice. leads. to a dry, bulky mass of fibers of such bulkiness' as to disintegrate under light stresses and are unsatisfactory in many importantfinstances for many practical impregnation treatments, especially continuous treatments. In the practice of myinven'tion, even when I add water-soluble. soaps to the bulk. paper-making stock, I keep such stock substantially free from gas bubbles V and foam so as to avoid improper felting of that'lis, an ordinary web once dried, cannot,

.however, be restored toamaterially less comthe fibers on accountof interference by the gas bubbles or foam. I am also aware. of the fact that it has been proposed to soapprefabricated waterleaf paper such as is to serve for toweling Ior similar purposes with aqueous soap in solu- 'tions and' the n to redry the paper, the soap being thus added for the purpose of imparting. the quality of 'emollients to the paper. @A comparatively compact prefabricated paper web,

pact, condition by the action of'a soapsolution thereupon,'since the effect of compression and of shrinka'geon the web once it has beendried cannot be undone'to any great extentdn this way. ,The fact of thematter-is that a paper intended'for toweling or similar usemust have a compactness much greater than the webs produced according to my invention falling into a compactness range of about 20 to 55, since otherwise they would tend to disintegrate 0r pulp up in wet hands. Waterleaf paper toweling made from kraft pulp is said to contain aslight soap residue from the production of the kraft pulp, but this soap residue is .of, a resinous practically insoluble nature as can be readily appreciated from the fact that it is not dissolved and removed during the thorough washing operation which kraft pulp must necessarily undergo. The slight soap residue in kraft pulp hence does not function measurably as a surface-tension-reducing agent and, in any event; does not constitute a positive addition to the pulp but an occlusion that naturally and inevitably results from kraft pulp manufacture. It is hence possible to realize the results of the present in,- vention by depending upon the slight amount of resinous soap occluded on kraft pulp, so that should ordinary kraft pulp or kraft pulp refined to high alpha cellulose content be used in papermaking stock and the results of the present invention be, desired from such stock, a solution of water-soluble soap or other surface-tensionreducing reagent must be used in the very same way as hereinbefore described, Nor aretheresults obtained by the practice of my invention possible of attainment when rosin soap or size is added to the paper-making furnish as is cus- 1,o'se,ao1

ftomarily ease; in, the manufacture of a great variety of .papers asginsuch ,case the soap or size is precipitated or insolubilized by a suitable reagent, usuallyalum, and hence does not exist as a surface-tension-lowering reagent during the drying of-thepaper web. 1 I

I have spoken about adding the surface-tension- -reducing reagent to the, paper-making stock at any stage of paper-making,-butbeforedrying. In saying: this I mean that this addition is effected before drying has proceeded to a stage i where the action of surface-tension and shrinkage on the web has-,takentplaceto, a aterial 'eictent. In other words, the expression but before/dry as used in the foregoing description and in thelappended claims, is to be construed as comprehending the addition of surface-tension-reducing reagents partway down thedrier,

that is, while the-web still contains suflicient water to be benefited by thesurface-tension-reducins reagents, as such practice would be effective for the, purposes of the present invention even though it would be comparatively less'efilcientu I i So far as concerns certain subject-matter, the instant applicationis acontinuation in part of my application SerialNo. 495,785, filed November 14, 1930.

, I,claim:---

1. In the fabrication of a porous and absorb-] ent waterlaidfelt involving the formation of such .felt from-an aqueous suspension of a feltmaking furnish, containing cellulose fiber, those steps which'coinprise adding at any stage, of feltfabrication, butv before drying, to the wateras'sociated with the'flber a 'surface-tension reducing agent while 'keeping such-water substan- ;,tially freefrom gas bubbles and foam, 'deWatering the felt to dryness and controlling the com position. of the furnish and/or the stateof hydration of the cellulose fiber used insltne furnish and/or the conditions under which the"'dewaterving"operation; is performed so as,topr oduce a feltof a compactness of about '20 to 55, said corm. .pactness being determined bydividing the basis weight of the felt in poundsby its thickness in inches and multiplying by the factor 10-4. 2. In the fabricationof ,a porous and absorbent waterlaid felt involving: the formation or such felt from an aqueous suspension of a feltmaking furnishcontaining cellulose fiber, those steps which comprise adding at any, stage, of felt fabrication, but beforedrying, tothe waterassociated with the fiber a surface-tension-reduc-' ing agent whilekeeping such water substantially free from gas bubbles and foam, said surfacetension-reducing agent being selected from a class consisting of water-soluble soaps, wettingout agents, alcohol,'and-acetone, dewatering the felt to dryness, and controlling the composition of the furnish and/or'the state of hydration of v waterlaid felt involving the formation of such felt from an aqueous suspension of a felt-making furnish, those steps which comprise includ-.-

ing cellulose fiber of high alpha cellulose content as an ingredient of the furnish, adding atv any stage of felt'fabrication, but before drying,

I ness ininches torthe water associated with such fiber a watersoluble soap while eeping suchwater-substan tially free from gas: bubbles andfoam, dewater ingthe felt todryness, and contro1ling'th'e'com position of .the furnish and/or the State of -hy-' dration of the cellulose fiber used inthe furnishand/or the conditions under whichthe dewatering operation isp'erform'edso ast'oproduce a felt of a'compactnessmf about 20 to 55, said compactness'beingi determined by dividing the entwater-laid felt involving the formation or such felt from an'aqueous suspension of a feltmaking furnish containing cellulose'fiber, those steps which comprise addingat any stage of felt fabrication, but before drying, tothe water as-* sociated withthe fiber ammonium oleate'while keeping such' 'water substantially free from gas bubbles and foam, *dewateringthe felt'to dry-' ness, and controlling the composition of the furnishand/or'the state of hydration of the "cellu lose fiber used in the furnish and/or the conditions under which the dew'atering'operation" is performed so as to. produce'a felt of a compactness of about 20 to '55, said compactness being determined by dividing the'b'asis weight of the felt in pounds by its thickness in and multiplying by the factor V 5. In the fabricationiof a' porous and absorbent, waterlaid felt involving the formation of "inches such felt from'an aqueous suspension of a felt- "of: the felt-making furnish substantially unhymaking furnish, those steps which comprise including as the preponderantzfibrous ingredient drated refined wood pulp of an alpha cellulose content of at least about 93%, adding to'the wet felt at any stage 'of'its fabrication, but before drying,a surface-tension-reducing agent,

ed agent, thereby producing a felt of compactness of about'20 to 55; said compactness being determined by dividing the basis weight of thefelt in pounds by its thickness in inches and multiplying by the factor 10*. v

6. 'In the fabrication of a'porous and absorbent waterlaid felt involving the formation of such felt from an aqueous suspension 'of a feltmaking furnish, and the squeezing of the freshly formed wet felt before it -isdried,'those steps which comprise including as the prepo'nderant fibrous ingredient of the felt-making furnish substantially unhydrated refined wood pulp of an alpha cellulose content of at least about 93%, adding an aqueous soap solution to the freshly formed wet felt, squeezing the wet felt, and drying the squeezed felt in the presenceof such added soap solution, thereby producing a felt of a compactness of about to 55, said compactness fbeing determined by dividing the basis weight ofthe felt in pounds by'its thickness in inches and multiplying by the factor 107 '7. In the fabrication of a porous and absorbent waterlaidfelt involving the formation of such hiined by dividing the basis weight of the felt in pounds by its thickness in inches'and multiplying by the factor 10-3;

8.-A porous and absorbent waterlaid fibrous felt falling within a range of compactness of about20'to 55 and containing up to only about 2% of the residue of a solution of a waterdetermined by dividing the basis weight of the felt i'n'pounds by its thickness in inches and multiplying by the factor 10 o '9. A porous and absorbent waterlaid fibrous felt falling within a range of compactness of about 20 to 55 andcontaining not more than about 0.5%" to 2%" of the residue ofa solution of a'water-soluble soap, based on the dryweight and dryingthe felt em nceofsuch addof thefelt, said compactness being determined by dividing the basis weight of the felt in pounds by its thickness in inches and multiplying by the factor 10 10. A porous and absorbent waterlaid fibrous solution of ammonium oleate, based'on the dry weight of the felt, said compactness being determined by dividing the basis weight of the felt in pounds by its thickness in inches and multiplying by the factor 10- a MILTON 0-. SCHUR.