US2639989A - Treatment of cellulosic pulps - Google Patents

Description

Patented May 26, 1953 fl-ICE TREATMENT 0F James H. Gonover, Chicago, 5111., zassignor 'to United States Gypsum Gompaqypflhicago lll a corpcrationof Illinois fNo Drawing. AmalieatiiinfApfiFZfi-IMG, Serial; No. 6645995 l ill of these' features 'are'so interrelated as to constitute onecomprehensive inventive concept, leading 'tothe' production of "fiber bo'ards, of the conventional"insulating board-type; but endowed with imprbved strength, stiffness, density, 1 and withother valuableproperties.

ln' the 'manufacture of fiber insulation boards, the fibrous'pulp'which is made of wood, bagasse, straw or 'other similar materials, is suspended in water, usually 99% -wate'r or more. The "dietended fibers are. thereafterideposited'on a'wi're screen either by gravitybr by-xsuction; by allowing the watertobe' drawn away through the-deposited 'fibrous -mass, thus resulting in a wet mat or' 'felted mass of fibers. The 'wet feltedinass' is then-ipressed by rollers or the rlike usuallybetween wool 'felts or wire "screens; to eliminate all the water possible "and to produce a compacted felted board'usually .about /2" thick or m'ore, whichrwh'en dried-"forms the insulation-ionbuilding board commonly used in building; construction as a 's'h'eathing, interior 'wall, or ceiling '1 covering.

In ithis type: of manufacturing; process it will be' evident thatthe drainage rate of the=fibrous ,pulp isrmost important, as otherwise only a very thin paiperdikesheetcan be formed.

The strength of the resulting board depends largely'on the=preparationoi the pulp. :If the fibers are :we11- beaten they holdmore: water and become hydrated, as it is known in the art. Hydrated pulp, :-however, becomes very slow draining, soth'at it'isfiormed inthick sheetsrwith difficulty, cannotbe; pressed to any degree withoutfdeformi'n'g or crushing Ithe-board,' andris difficult to dry. The dried product,-however,:is :stronger, harder and more. lumber-like. Hydrating pulp to any degree,-besides causingdifiicult processing; adds materially-to the expense ofpre- :paring the product.

;N.ormal= fiber board pu p, made? in accordance rwith theausualmeth ds c n: n yrbe s ie lyshw 12 drated if an 'ieconomical sprocess is to be maintamed.

3 Due to the *s ringy nature of the fiber when only 'slightl y hydrated, "it cannot be pressed to diig'h'er densities Ithan abiout 17 ,=-to 19 e pounds per cubic foot, and therefore lthBiDfDdllGt thus-produeed is limited @to r'elatively zs'oft insulation "boar'd products.

Accordingly, :it is wine :of the objects of the eres'ent mventi'on to' overcome the slowness of a hydrated pulpg so that denser and stro'nger-prodhots may be made, usingythe standard type of e uipment new used in the paper and I pulp t industry.

further object is to :produce :a fiber board. containing therein idistributeid Eli-me or other alkanne earthihydrexides.

-A Eu'rther 'objeot ts to a pro'vid'e a Eprocess 1 for mamngsuehabeam.

-A fur'th er objet is -to provide a process by means of which rubber or resin particles may be incoriiorated withtarpaperifurnish, and deposited upon the fibers thereof.

{Other objects will appear from the further and. more detailed description--which io1iows.

Phave discovered that-ifian-alkaline earth hydroxide, such as lime hydrate high calcium) or quicklime (since it slalres t'o lithe hydrate), or the hydroxide of hariumor strontium, isadded to ;fa'fcellulosic fibergsiispension the drainage rate or fffreehess *tif -the suspension is increased, making f it possible ;to use :a more 3 hydrated pulp without havin trouble "with formation of "the ,,r is'heet'or board 'mat on the forming inachine; the water vx'lilfiirain away -Inore easilyon the, screens or felts and the fibers will compact to a ,thinnferfsheeturider the "same pressi'ng conditions. "Inithie case" v pulp mats, these will shrink more ,in (the dryingfiop'erationand "the resultant 'Tdryfniat,willfhavefalhiigherdensity andgreater strength; thanan. untreated'mat subjected tothe ,same'ioperatin v ditions.

'Alt oughfithe scope-of the: invention is intended to i iric'lu'd an amounted: alkaline earth hydroxides, whichlwheni-added to ,a t'suspensioniof cellulosicl-fibers in-anyway will give any or all the above resultsto. any degreejthe. preferred method lto ,pre'dispersesuperfine T high calcium "quicklime in ,rwat'er, "and allow Tit Ito hydrate. When, for example,v makingpulplaboards such a dispersion ,is addeid to the hot 110 -1120 F.) fiber suspension or fur atsucharatefthat 'theamount ofmndissolved hm ydr-ate in the furnish will beat .lcas t about {of-the dry pulp and at su e h int in-rthej i-pr ocess that-the mixing before the mat is formed will be sufficient to give good dispersion of the alkaline earth hydrate. Hot slurry is preferred, in case of calcium hydroxide, because this hydrate is less soluble in hot water, which hence means less loss. In general about of the alkaline earth hydroxide will be the maximum that needs to'be used; although lower percentages will still produce decided increases in freeness. The addition of the alkaline earth hydrate has been found to increase the tendency of the furnish to develop foam to a varying degree, depending on the amount of rosin or rosin acids present; with pine pulp showing a greater tendency to foam than others. To reduce this tendency, an anti-foaming agent may be added with the alkaline earthhydrate and I have discovered that an agent must be used which does not react with the alkaline earth hydrate in any way, as this would have an adverse effect upon its action. Since alkaline earth hydrates are cationic in nature, it is preferred that a cationic type of anti-foaming agent be used, as these are less likely to be reactive toward the lime hydrate. Hydrochloric, acetic or other acid salts of long chain amines have been found satisfactory.

This type of material, being cationic in nature, will act as an anti-foaming agent against any foam caused by an anionic material. It is also a wetting agent, and would tend to destroy the sizing of the mat except that in the drying of the wet mat the acid component of the amine salt is driven off, leaving the amine, which is water-resistant. The acetic acid salt of such an amine breaks down more easily under heat and therefore is preferred over the others.

Rosin size is not well adapted to this process as a material to give the board water resistance. I prefer to use, instead, a cook starch-wax type of size having the wax emulsified inthe cooked starch.

A size, made up as follows, may be used:

Paraffin wax, emulsified therein 200 With this sizing material is it possible to obtain satisfactor water resistance, comparable with regular insulation board even in the alkaline water caused by the addition of the lime hydrate. This in itself is beneficial, since the board will not deteriorate as fast on aging as it would if it were acid.

The action of the lime or other alkaline earth hydrates is not fully understood, but it is believed that their action is similar to that which is obtained when a positively charged colloid is added to a colloid of opposite charge, namely a phenomenon of co-precipitation. The more hydrated the original pulp, the closer it approaches the properties of a negatively charged colloid and the more attraction it has for water, which causes the slower drainage rate or lower freeness. When the positively charged alkaline earth hydrate is added there occurs a co-precipitation action between it and the pulp. Since the water-attractive charges of the pulp are neutralized by the hydrate, the freeness or drainage rate increases. It has been found that an excess of hydrate may couse a decrease in freeness due to the filter plugging action of the felted fibers. Inthe formed or felted mass the attraction between the fiber and water of the hydrated pulp has been changed to an attraction between the pulp and alkaline earth hydrate. This mutual attraction of the co-precipitated mass of fibers and hydrate reduces the tendency of the fibers to spring back after being pressed to a certain thickness. In the drying operation the same attraction pulls the mass closer together, producing a higher density in the ultimate product. The increased strength of the dried product is also due to this fiber-to-hydrateto -fiber bond or attraction.

The process of the present invention may be applied to the usual method of making pulp insulation board, using as an added ingredient the alkaline earth hydroxide such as barium hydroxide, strontium hydroxide, and more particularly, calcium hydroxide. Because of its cheapness, the latter is preferred; and the further description is devoted to a process in which lime forms the source of the hydroxide. Thi may be either in the form of quick-lime (CaO) which is slaked in the course of the process, or in the form of so-called hydrated lime which is obtainable in dry form as an almost impalpable powder. A high calcium lime is preferred. When using other alkaline earth hydroxides, equivalent quantities should be used to produce the same degree of alkalinity. These quantities can be readily calculated from the atomic weights of barium and strontium as compared with that of calcium.

The process may be carried out as follows:

A furnish containing 1500 parts by weight (dry basis) of ground wood fibers, such, for example as cottonwood or willow, at a concentration of -1% (i. e. suspended in 150,000 parts of water) is worked, as in a beater or similar instrumentality, partially to hydrate the fibers. The furnish, preferably warmed to a temperature of about F., is then given an addition of about 360 parts of high calcium lime hydrate (Ca(OH)2), which latter is preferably first mixed with sufficient water to provide a cream-like slurry. About 1,000 parts of water will suffice. The addition of the hydrated lime will increase the apparent freeness of the furnish by an amount proportioned to the degree of hydration of the pulp. Either before or after the addition of the lime, a suitable amount of the above-mentioned starch-wax emulsion may be mixed with the furnish to yield about a 2% to 3% paraffin wax content in the finished board. The furnish is then fed to the headbox of a suitable forming machine and formed into a wet mat, from which the water is expressed by means of rolls, which act upon the mat through the intervention of a suitable traveling screen and wool felts. A regular Oliver board former forms an excellent apparatus in which to carry out the process; but it is not limited to the use of this particular machine, as Fourdrinier machines and other well known board formers may be used. As all these are so well known in this art, a detailed description thereof would serve no useful purpose.

After the free water has been expressed from the wet mats, they are cut into large sheets by the usual transversely traveling cutters, and elevated by the usual tipples into a multi-deck drier, such as a Coe drier, or the like, and dried to about 5% moisture content. They may then be cut into any desired dimensions.

The results obtained by the addition of the lime to the furnish are drastic and far reaching. Thus the freeness is increased, the board is thinner, much denser and has a greater strength. These iaeaaesc results will yary qdepending -;-on the amount 1' of lime-hydrate added; they-method:'ofeaddition; the

temperature of the waterlslurry;.thefle reeuof dispersion :of athe :hydrate particles and the --amo11nt of hydration lot thepulp. :5

If the. pulp were. more hydrated, then the/untreated freenesstwouldebe lower,-.-but-.t-he treated freeness would bet-approximatelyuthe: same, thus indicating more-strongly the :freeing actionoof I the. lime hydrate.

I.- have found: that-'slaked quiclclime or: lime. hy-

(irate may bensedwith.anyasuspension emulsion or colloidal SOIUtlOIITOf" an material, whichrhasva negative particle charge, "to fioccnlate it-he: ma-

terial and cause it to be retained by the pulp. In 15 of material added with the lime hydrate.

The mechanism of the above process is'similar to the action of lime on pulp. In this case the negative charge of the emulsified particlezand the pulp is neutralized by the lime so that they no longer repel each other, but rather are joined, ,or attached. by the limehydrate.

.In. this way a negatively charge'dirubber; emulsionmay be. used with lime inv the .p.ulp.treatment to increase the elasticity .or toughness of the mat. "Various negatively charged resin colloids may be used .to-increaselhardness and strength, and. so on; aslongasthe. material particlelhas a negative charge, the lime hydrate will. neutralize .the chargeandcausethe retention of the particle on jthe pulp. .If wood.,pulpdshydratedinto a state approachingacolloidal solution,.and.is then used with lime .in the! treatment .of pulp, the sameaction .occursand the strength of the resultant mat is increased :..considerably. This makes itpossible torefine the. base;.pulp arelatively small amount, .addapproximately a% of ,colloidalized pulp with lime,.and .obtain .a' mat considerably stronger. The. lime hydrate-also: re-

'6 whichda-isdiluted with foursadditionalparts of water. :ZIfhis. dispersion may, then beadded tothe pulp .-slurry,atsany point from. the vthickeners to the forming machine. Addition of: the Iii-neat the head-boxispreferred.

sAny sizing material, for example, the -starch- :wax-size described previously, maybe zaddedwith :thelime hydrate. or: separatelyv at any other point, .from the thickeners to the formingmachine. Good mixing I .of the size and hydrate with the pulpsshould be: insured before the mat is formed. sltt-isspreferred to add thelime hydrate-slurry 170:13116; pulp at such; a.- rate that l the undissolved portion of hydrate retainedeby. the fibers will be between 5% and 10% of the dry mat weight.

If it is desirablethat a foam depressant be added as previously mentioned, it may be'added with the size, with-the lime hydrate, or at any vother suitable or convenient point. The amount required is a fewtenths of l per cent.

In'thezformation of the mat on the forming machine cylinder or wire, the lime hydratetreattnient-gives the pulpthe property oflosingits :water more easily andcompacting to a thinner mat having a lower water content. In'the wet pressing operation it is also possible to compact thepulpflto a much higher density and a'lower water content than if ithad notreceived the hydrateitreatment. In the drying operation the mat shrinks to .a greater degree and'the dried mat, containing approximatelyfi ib of lime, will have .afdensity or: from.25 to 28' pounds. per cubic footas compared with a density of '16'to .l'l' pounds per cubic foot. for a mat made of the same pulpbutwithout the lime hydrate treatment, but otherwiseunder the sameforming conditions.

.The following table gives a comparison of the test resuitsonboards made on commercial equipment. 'Both mats were formed and made under identical conditionsexcept that the pulp forNoo l wastreated with-the lime hydrate slurry, while No.,2. had no lime added. Transverse strengths were found using -a 12' span.

sists the tendency of the colloidal pulp to-reduce the pulp ireeness.

If thepulpused-toform-these mats had been -more hydratedfithe results would have shown In the actual use of this lime hydratentreat- 2higher values.

merit in the wet forming process, any type of cellulose fiber may be used, but the degree of action of the lime depends on the point to which the fiber has been hydrated. If there isno hydration, the action as described will be negligible.

For purposes of definition in connection with the disclosure of the present invention, the term hydration means not plain refining or reduction to individual fibers, .lbut :fur-ther beating or *mechanicallyworking to a state in which the 'hydro- B5 gen :bonds of the .cellulose or lignocellulose 'mi- ,celles of the fibers are tbroken, giving unsatisfied charges or zvalences which "have an'attraction'for water-and give the pulpra gelatinized'appearance in'varying degree, depending on-theamount-of 7 hydration.

In theuse o'f the lime hydrate treatment inthe wet-forming process; the preferred-method is to predisperse 1 7 part of high calcium guicklim'e in 3 parts of= eOld-waterand allow it tohydratenafter Further tol'illustrate the-advantages obtained by thepractice of the-present lIlVQlltlOllybOQl'dS were made upboth with'and without theuse of the lime,'and the following results obtained:

Without With Limo Lime Freeness increase .*cc.;. none, 20 Drying shrinkage .lperccntn 12. 3 '20. 2 Thickness Whendry. 'nches 0. 467 0.367 Density, dry u ft 17.8 27. 7 Modulus oi-Runture. 339 998 Transverse strength .lbs. 24. 6 44. 8

It "willb'e noticed that the modulus of rupture increased by, about "300 percent. This is also reflected *in 'the large increase in transverse strength "andithe "far greater density. Boards made bythisprocessr can therefore be 'used "uner 1 conditions where ordinary insulation boards wouldprove inadequate.

To illustrate the effect of lime in showing a larger increase in freeness when the pulp is hydrated to a greater degree and to show the similar effect of the other alkaline earth hydroxides,

boards were made from pulp having a Schopper hydrate addition increased the freeness to 550 cc. and resulted in a board having a modulus of rupture of 2,060 pounds.

It can be seen from these results that a ligninfree or pure cellulosic pulp may be used in this process if it is hydrated as described previously by actually rupturing the fiber cell.

The examples given show the unusual results obtained with fiber boards used for structural purposes. Obviously the same type results may be expected in paper or other fiber products produced by wet-felting fibers, pressing and drying in a manner similar in principle to the methods disclosed. Certain classes of paper products,

It will be noticed that the lime caused a free ness increase of only 65 cc. on the unbeaten pulp as against 175 cc. with the beaten pulp. Both barium and strontium hydroxide gave the same freeness increase as lime on the beaten or hydrated pulp. All three alkaline earth hydroxides show an increase in modulus of rupture and density with the lime giving the highest values.

In order to show the suitability of a ligninfree or pure cellulosic type of pulp in this process and also to emphasize the need for hydration as described above, a series of boards were made of bleached sulfite pulp. In the following data, by swollen sulfite is meant bleached sulfite pulp which had been treated for 24 hours in 40 a solution of NaOH so that the fibers became swollen with absorbed water, thus giving chemically hydrated pulp without actual fiber rupture. This pulp was then washed free of caustic before using.

The same technique was employed as when making boards from a lignocellulosic pulp. The results are shown on the subjoined Table III.

such as glassine and fiber sheet cartons, where high strength coupled with dense structure and stiffness is important, can be vastly improved and made more economically using the methods as specified in this disclosure.

While the process has been described in connection with wet ground wood pulp made from cottonwood or willow, it is also applicable to pulps of other origins, which are hydrated to any degree as described previously, such as pine, poplar and other woods, which may have been pulped by boiling with water either at atmospheric or superatmospheric pressure, and with or without the aid of pulping chemicals. It is also applicable to the type of pulps obtainable by the so-called explosion process in which Wood chips are heated in high pressure steam and then suddenly released into atmospheric pressure surroundings.

From the above disclosure it will also be apparent that the use of the alkaline earth hydroxides enables a determination of the felting qualities and true hydration of any cellulosic pulp,

Table III Original Freencss Dry Den- Modulus of Type of Mat Freeness Increase sity Rupture Cc. Cc. Pounds/ft. Pounds l. Sulfite Fiber 720 26.3 279 2. Sulfite Fiber+Ca(OH)1 720 none 27.4 270 3. Sulfite Fiber Beaten From 720 cc.

Frecness To 200 cc. Freeness-I- Oa(OH)n 200 200 43.7 3,315 4. Sulfite Fiber Beaten as above Without Oa(OH)2 200 41.9 2, 425 5. Swollen Sulfitc+Ca(OH)2 720 13.5 6. Swollen Sulfite Fiber Beaten from Frceness of 720 cc. to 450 cc. Freeness+Ca(OH)z 450 100 38.0 2, 060

It will be noticed that the lime hydrate had no effect on the plain unbeaten sulfite fiber, giving no increase in strength or freeness, but in the case of #3 when the fiber was beaten, thus rupturing the fiber cell, to a Scho'pper freeness at 1% consistency of 200 00., the lime hydrate increased the freeness by 200 cc. and gave a modulus of rupture of 3,315 pounds. In the case of #5 the lime hydrate had no effect on the fiber which had been hydrated chemically without fiber rupture, but in the case of #6 when the same type fiber was beaten to a freeness of 450 cc., the lime 75 answer as calcium hydroxide (lime-hydrate) to a li y dra'ted pulp, the measured freenessror the pulp will be increased by an amount that is proper-L ti'onal to the degree of "true -hydration;

Bi measuring the 'freeness- -of-' a ulp by the hereinabove described method, a result is obtained which is a measure of the sum of the effect of the slowing action of the surface area of the pulp fibers and the water attraction of hydrated portion. This will give a certain free-ness value. If now a sample of the same pulp is treated with calcium hydroxide (say 5% thereof on the basis of the dry pulp at 1% consistency), and then tested for freeness, it will be found that that part of the original slowness which was occasioned by the hydration is neutralized, as a result of which the apparent freeness of the pulp will increase by an amount that is proportional to the degree of the true hydration of the pulp. greater the increase in freeness caused by the presence of the alkaline earth hydroxide, the greater must have been the degree of hydration of the pulp that was tested. It follows, also, that the greater the degree of hydration, the greater will be the felting strength of the fibers, and hence they will produce a stronger and denser product, such as paper or board.

As an example of the utilization of this method of testing the hydration of a pulp one ma3 proceed as follows:

The freeness of a certain pulp, as measured on a standard Schopper-Riegler tester was found to be 600 cc. Another sample of the same prulp, after treatment with calcium hydroxide, as hereinabove explained, then had a freeness of 665 cc., which is an increase of 65 cc. A mat made from such a pulp had a modulus of rupture of 282. The same pulp was then mechanically worked (beaten) so as to hydrate it to a freeness of only 350 cc. A sample of the thus beaten pulp was treated with calcium hydroxide and then tested for freeness, which now was found to 'be 525 cc., or an increase of 175 cc., as compared with an increase of only 65 cc. in the case of the unbeaten pulp. A mat made from the beaten pulp had a modulus of rupture of 615, or better than twice that of the unbeaten pulp. The degree of hydration was thus also indicated to be more than twice that of the original, unbeaten pulp.

There is thus provided a novel and very useful method for discriminating between slowness due to shortness of fiber and slowness due to real hydration; something which has not been possible by so simple means in the past.

Accordingly, and reserving to myself the reasonable adoption of equivalents and the use of the usual mechanical instrumentalities used in this art, I claim:

1. Process of making fiber board which comprises suspending ground wood fibers in water to form a fiber furnish, mechanically working said furnish to hydrate the fibers therein, adding enough lime, within the range of from about 1% to about 24% by weight of the dry fibers, to in- Hence the crease the"freeness 'of'tliefurnish "by "from about cc; to -about cc. overi'itsoriginal freen'es's, forming the resulting.. furnish int0 a wet' niat, compressing. the latter to": express free water therefrom,-- anddryingthe mat:

21LProcess;ofimakingfiberrboard which comprisesadding' to a.furnish containing hydrated lignocellulosie fibers a sufficient amoui'it of an alkaline earth. hydroxide, withinthe range-of from -about".'1%.to-about 24%1by weightfof the dry fibers'to increase thefreenessrof the furnish byfi'om about 65cc-to.about175' cc., and forming a" compressed..mat therefrom, and drying the 3 lProcessi. of makingfiber board which oom"- prises adding to a furnish containing hydrated lignocellulosic fibers a sufficient amount of calcium hydroxide, within the range of from about 1% to about 24% by weight of the dry fibers, to increase the freeness of the furnish by from about 65 cc. to about 175 cc., and forming a compressed mat therefrom, and drying the same.

4. Process of making high density high strength fiber insulation board which comprises suspending ground wood fibers in water to form a furnish containing partially hydrated fibers, adding, within the range of from about 1% to about 24% on the weight of the dry fibers, of an alkaline earth hydroxide sufficient to increase the freeness of said furnish by about from 65 cc. to about 175 cc., forming a wet mat from said furnish, compressing the mat to express free water therefrom, and drying the resulting mat.

5. Process of making fiber insulation board which comprises grinding raw wood in the presence of water to form a furnish having a Schopper-Riegeler freeness of from about 350 cc. to about 600 cc., adding enough of an alkaline earth hydroxide thereto, within the range of from about 1% to about 24% on the dry weight of the fiber, to increase the freeness of said furnish by from about 65 cc. to about 175 cc., forming a wet mat from the furnish, expressing free water from said mat, and drying the same.

6. A fiber insulation boand consisting of cellulosic fibers and from about 1% to about 24% by weight of an alkaline earth hydroxide, said board having a density of about 25 to 45 pounds per cubic foot, a modulus of rupture of about 900 to 3300, and a tensile strength of about 544 pounds per square inch.

7. A fiber insulation board consisting of lignocellulosic fiber and from about 1% to about 24% by weight of calcium hydroxide, said board having a density of about 25 to 45 pounds per cubic foot, a modulus of rupture of about 900 to 3300, and a tensile strength of about 544 pounds per square inch.

JAMES H. CONOVER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,048,110 Tingberg Dec. 24, 1912 1,372,118 Collier Mar. 27, 1921 1,630,635 Rawlins May 31, 1927 1,730,009 Kennedy Oct. 1, 1929 1,760,446 Skolnik May 27, 1930 1,765,774 Rose June 24, 1930 1,970,521 Harvey Aug. 14, 1934 1,978,022 Kirschbraun Oct. 23, 1934 2,022,010 Schopper Nov. 26, 1935 2,042,501 Buchanan et a1 June 2, 1936 (Other references on following page) 11 12 UNITED STATES PATENTS FOREIGN PATENTS Number Name Date Number Country Date 2,049,864 Rafton Aug. 4, 1936 743,872 France Apr. 7, 1933 2,067,876 Campbell Jan. 12, 1937 2,097,121 Fromm Oct. 26, 1937 5 OTHER REFERENCES 2,131,097 Drewsen Sept. 27, 1938 Pa r In ustry a d Pap r W d, Ap l 9 2,140,199 Mason Dec. 13, 1933 page ,1 7 44 Mason July 25, 1939 Technical Association Papers Series 22 (1939), 3 3 71 Fritz 3, 1942 pages 482 to 48 Series 23 (1940), pages 132 to 47, 73 Fritz 25, 1944 10 137. Series 25 (1942), pages 504 to 510. 2 3 3, 35 Booth b, 6 1945 Industrial and Engineering Chemistry, Janu- 2,375,245 Pretzel May a, 1945 r 1941, p s

2,376,687 Goldstein et a1 May 22, 1945 Boehm Paper Tra o rn l. May 9 0 pp- 2,376,688 Goldsbein et a1 May 22, 1945 2,416,447 Laughlin et a1 Feb. 25, 1947 15 p and Paper Manufacture, 1 DD. 944,

945 (1950) published by McGraw Hill, New York.

Claims (1)

1. PROCESS OF MAKING FIBER BOARD WHICH COMPRISES SUSPENDING GROUND WOOD FIBERS IN WATER TO FORM A FIBER FURNISH, MECHANICALLY WORKING SAID FURNISH TO HYDRATE THE FIBERS THEREIN, ADDING ENOUGH LIME, WITHIN THE RANGE OF FROM ABOUT 1% TO ABOUT 24% BY WEIGHT OF THE DRY FIBERS, TO INCREASE THE FREENESS OF THE FURNISH BY FROM ABOUT 65 CC. TO ABOUT 175 CC. OVER ITS ORIGINAL FREENESS, FORMING THE RESULTING FURNISH INTO A WET MAT, COMPRESSING THE LATTER TO EXPRESS FREE WATER THEREFROM, AND DRYING THE MAT.