US2613579A - Sizing and bleaching a wet web - Google Patents

Description

FIP8589 Patented Oct. 14, 1952 UNITED fifo ewandaliN- SR. t'"

Robert L. McEwen, wiuie s in ',my essigno to Buffalo .Electro-Chemical ti e he ,Noinrawiiie- APDiicatiodAHg The present invention relates to :the manufacture of a sized, bleached, paper sheet and more particularly to a method ofmanufacturing such a sheet wherein the sizing and bleaching operation proceedsubstantially concurrently.

Recent improvements in -paper-making tech nclogy indicate that obtainment of better brightness of paper stock is probablybest performed upon the paper-making machine, ascontrasted to-bIeac'hing the pulp stock itself. "Examples-of this improved technique are described in Patent No. 2,150,926 granted-on'March' 21,1939 to -Kaunmann and Wolfe, and in Patent No. 2,125,634 granted on August 2, 1938 tdHeritage. These improvements in the brightening of-paper show that brightened paper stock can "bepro'duced economically and with little change in the'normal paper manufacturing procedureby applying the brightening or bleaching agent, preferably a peroxide, to the formed paper sheet while it is on the paper-making'machine.

These suggestions generally indicate that best results in paper bleaching-are obtained by application of the brightening agent to :the 00113011! dated paper sheet and subsequently removing moisture as, forinstancepbypassing the sheet over the drying element normally associated with the conventional paper-makingmachine.

Howevenin this type of operation, difliculty has been experienced in producing papers which are sized sufficient ly or which are properly sized to resist moisture penetration and to retain a sharp printing impression ora-sharp penand ink impression without feathering. Even where the normal quantities of usualor conventional size are present in the paper, the usual alkal-ies associated with the alkaline peroxide solution used upon the machine, to obtain bleached or brightened paper,;appear to destroy the'sizing properties of the material addedfor sizing-purposes. Many attempts have been made to overcome this deficiency in sheets resulting'from the machine bleaching with but indifferent 'fiuccess.

Thus, attempts have been made to increase the amount and type of sizing in thebeatenyet it has been found that in either case the alkaline p r xi solut llreduce the fiefiectivenes of r d str y the siz ng in :the sheet to the depth to which the alkaline bleach Lliquor penetrate s. Secondly, it has been attempted tofirst bleach the sheet with alkaline peroxide and thereaiter add an amount of size sufficient'to restorethe desired degree .of sizing ,requiredu- Howeven a procedure of this type is not generallyzapplicable to the various types and weights ni'paper'es e eiam. ioteer itzelz fected and even destroyed upon application t e of e Sizing olut on, esul g p oduction of unsal'able paperstock. The decrease in the t s ne ho e-s iproduce an. undu y r 'p rc ntage of brea ag :"I some case ea-lled"". ll n diflic lties are icund A u he disadvantage offlrstybleac; the paper sheet on the machine and subseguently sizing the ea d paper is t at the employme t o y f t e ention ,sizesythe'nape has a end qy't revert i -0191i by reason, p s ibl of some chemical action between the residual hemi a s fro eachintfsflufion an e added size T is i -rar i u arly no iceable i the employment of casein and also the emp qy e. o-n ledzaii m w shxboth u u sizingitreatments. p

' The ap lication of-thesiz ns agent subsequen to he ppli ation of h b aqn liqu r. ,mor over, may result in a lea hi. 011301 12 16 a ti e bleaching ingredient f om-t eimn eenated shee n the ain body o t e size olution, thereby resultinginbleaching'inefiiciency.

Re e e-p oc u and a ly n thes b as in mount nsi erablyinexpess, i t atnormally mp oye isu as i the production f hard sized shee s results n ei he the d struction of the e or the produ t nn a pa e which i bstant ally repe lent t t e bleaching s ution, in which'case the efficiency is reduced to such an extent that little or no bleaching occurs.

Where substantial amounts of wax emulsion e d d' ot e bea er as a .siaingagent, it has be n found that the g antit ef wax-so ids nec y o produ a si ed-endumac n bleached sheet sucnthat ,thepaper perties. aBQ-highly und si abl b eau e. thesh e s limit ess. fl ppy, and t o soft, :jahcl the. sheet ,..-in.-many instances, is not receptive to ink. Whereexcessive Quantities of. waxlare incorporated in ltheish et-t she t is then relativelyrepellentito theta ueoi bleaching solutiqnusubsequentl-y applied thereto.

The objects of the present invention are to overcome the many difiiculties encountered heretofore in the productionpi mach ne blea h pap ln. 1 i I l gi lalso an ob e t o., ymmim not-only th brightness of machineb eeched pape bu also ipfimprpve the quality of sizing r efjgiIt. isaisoan object of the intention 1531111113811 unvv sheet; moreover, most papers are of such lig ht Weight that the sheet structure-is adversely af- 'lency of the previously described ink.

writing, from unsized or slack-sized sheets which H may have been partially sized in the beater.

In accordance with the principles of the present invention, the alkaline.peroxidesolution and an inert Wax Size are iddedrsimultaneously u Thesame pul'p as described in Example I was to the formed sheet as it progresses through the machine. In general, the point of application of the mixture of alkaline peroxide and wax-size formed paper is greater than about 10% That;

treating emulsion of wax and peroxideis prepared from any suitable Waxjsizeas, for instance, the generally employed pa'r'afiin or microcrystalline' wax in emulsion form and'an alkaline peroxide, The resulting emulsion may, contain any desired amount of waxsolids as, for instance,

from about10.l to several percent 'or more as,'for instance, 5% The choice 'of this concentration will, of necessity, be, dictated by; the amount of sizing agent ,to be employed upon the particular sheet and the weight ofj the sheet. In general,

the amount of wax 'de'siredin'the sheet will be that quantity sufiicient 'to sizei the sheet to a degree where it will receive the hk, either in liquid or paste form, without feathering, and to "a degreeinsufiicien't t6 cause skipping or, repel- The' following examples aregiven as merely illustrative of the principles of theinv'ention and are not to be deemed limitative thereof as, obviously, there willf be many variations in the weight 'of paper'produced,'ithe"amount of size to'be added to the paperand the'jjdegree of brightening desired, it being understood that the 'inventionis applicable "generallyto the productin ofjsubstanti ally all types of 'paper h t 1 Example Iv i A pulp stock was prepared from bleached sulfite pulp and unbleached mechanicalor ground wood pulp, and paper was prepared from the pulp on a conventional Fourdrinier paper machine. The pulp stock had been treated in the beater with 1.25% rosin based on the weight of the dry pulp. The finished paper as discharged from the machine possessed a brightness of 49.5 asmeasured in*the usual manner with a photoelectric colorimeter. The sheets so produced, although sized, would feather to ink toa slight degree.

. amp I e. a

The same stock as described in Example I was used in preparation of an additional portion of paper except that a bleachingsolutioncontaining hydrogen peroxide and trisodiumphosphate was applied -to'ea' ch faee of the paper sheet jimmediately-precedingthe'driers; Theamount of the .had, a ,brightness of .58 units. brightness oifz';the1 sheet was increased 8.5 units,

4 bleach solution employed was such that 1.4% of hydrogen peroxide (100 volume basis), and 0.8% trisodiumphosphate, each based on the weight of bone dry paper, was applied. The dry calendered sheet discharging from the machine Although the the brightened sheet feathered extremely badly and was of no value whatsoever from the ink reception standpoint.

I A V Example III used to produce' an additional amount of paper which was treated with the amount and type of bleachin a'en'ta'nd alkali s ecified in Exam le will be one at which the moisture content of the g g p p II; "However, there was mixed with the alkaline bleach-solution sufficient emulsified wax so that, upon application of thebleach-wax size solution -to,,the paper sheet, there was also appliedto the sheet 025% wax solids based on the weight QfLb n .-.d y.paper.-.

the mixed wax emulsion-alkaline peroxide solutionwas applied to the paper sheet while the latter stilhcontained a substantial amount of water, that is in advance of, the driers, both the wax and the peroxide were able topenetrate below, the surface ofsthe sheet and the resulting sheet'was-brightened.9,7 units above that of-the untreated stock of Example I. The finished sheet was. also sufficiently sized as, when tested with pen and ink, this sheet showed no feathering nor was; any skipping of the ink apparent, the writing. beingcontinuous It will'be understood that-the amount of-wax to be employed willbe entirely dictated by the typeof pulp used andthe type of paper desired to be produced I-Iowever, in general, it has been found that inoperating in accordance with the present invention, and applying wax size simultaneouslywith the alkaline perixide to a slack sized sheet, in general, at least, 0.1% wax solids should be applied to the sheet, based on the dry weightof theLSheet Thislower limit will, of

course, vary: dependingupon the amount of beatersizing in the sheet, the type of pulp employed, .the.; operating speeds of the machinery, andythe weightlof the paper as, in some instances,-0.1% will'lbeinsufiicient to size the sheet to pen and ink. The-upp er limit of the amount of .wax will also vary but will generally be found tobe in the neigh borhood of to 1% wax solids on abone drybasis. Quantities in excess ofthis amount; produce pversizing, greasiness or unctuousness through the paper with resultant floppy sheets, and too great an excess tends to produce awax coating rather than a wax sizing. ,1he ,amount of peroxide to be employed will "depend upon lthe previousfihistory of the pulp, thatis whether'the same be a bleached, purified pulpf pr an .unbleached,- ground wood pulp, or mixtures of various typesof pulp, and also upon thei'degree of bleaching desired in the finished p'aperiproduct. "The amount of hydrogen peroxide 'calculatedjaSflOO volume hydrogen peroxide mayfvary from about 05% to 10% or even higherif The mixed peroxide wax emulsion may coritain penetrant's, or wetting agents to aid in carryingthe solution into the sheet as well as tinting 'agents, starches, etc. In addition to hydrogen peroxide-"the solution should contain an alkali "and preferably should be made alkaline with aiphosphatz-i such as trisodiumphosphate, sodiurripyrophosphate or the meta phosphates such*as'-hexametaphosphate. It is found that oxide are unsuited for the simultaneous bleaching and sizing of paper sheets, and best bleaching and sizing results are obtained by employing a phosphate as the primary alkali in conjunction with hydrogen peroxide.

The peroxide-wax emulsion is best prepared by adding the previously dispersed and diluted wax to the alkaline peroxide solution. The wax may be of any suitable type, such as paraflin wax or micro crystalline wax, prepared by well known emulsifying operations.

By addition of the wax-peroxide emulsion to the formed slack sized sheet prior to its entrance into the drier, a minimum amount of moisture need be removed from a, sheet by the drier while, at the same time, the peroxide solution and the particles of wax are able to penetrate the sheet to the desired degree and to efiect simultaneously the desired bleaching and the desired degree of sizing.

It will be noted that by the simultaneous application of the wax size and peroxide solution, to additional brightening action is obtained.

What is claimed is:

1. The method of sizing and bleaching a sheet of paper consisting in applying to a formed paper sheet containing at least about 10% moisture, an aqueous solution consisting essentially of hydrogen peroxide made alkaline with a phosphate of sodium and a dispersion of wax in amount to add about 9 to 5% wax, and from 0.5% to 10% hydrogen peroxide based on the weight of dry paper and thereafter passing the so treated sheet over heated drying rolls to dry the same, whereby penetration of said wax below the surface of the paper will occur without cansing the surface to be ink-resistant.

the usual alkalies employed with hydrogen per- 2. The method of sizing and bleaching a formed paper sheet which consists in applying to the sheet, while the same contains excess moisture, an aqueous solution consisting essentially of hydrogen peroxide made alkaline with a phosphate of sodium and a dispersion of wax in amount to add about 6% to 5% wax, and from 0.5% to 10% hydrogen peroxide based on the weight of dry paper and thereafter drying the sheet. I

3. The method of preparing a bleached, sized sheet of paper which consists in applying to a formed paper sheet, before said sheet has been fully dried, an aqueous composition consisting essentially of hydrogen peroxide made alkaline with a phosphate of sodium and a dispersion of wax and in amount to add about to 5% wax and 0.5% to 10% hydrogen peroxide based on the weight of dry paper, and thereafter drying the sheet at an elevated temperature whereby the same is bleached and properly sized for ink writing-and printing.

ROBERT L. McEWEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 52,788 Gwymi Feb. 20, 1866 1,797,048 Clapp Mar. 17, 1931 1,957,370 Thomas May 1, 1934 2,020,328 Raiton Nov. 12, 1935 2,125,634 Heritage Aug. 2, 1938 2,150,926 Kaufimann Mar. 21, 1939 2,510,595 McEwen et a1 June 6, 1950 bill'mbfl EiUUl