US2147213A - Paper-making process - Google Patents

Description

Feb. 14, 1939. D. K. PATTILLocH PAPER MAKING PROCESS Filed May 27, 1937 NQQQQQ 14 Q do? NNN @zal Patented Feb. 14, 1939 'UNITED Y STATES PATIENT. OFFICE PAPER-MAKING PROCESS Application May 27, 1937, Serial No. 144,975

11 Claims.

The present invention relates -to an improvement in a process for incorporating starch with paper during its formation, for the purpose of enhancing the strength of the paper, to improve its formation,and to endow it 'with superior qualities as compared with paper made from the same grade of ber but in the absence of the starch.

One of the major objects of the present invention is to co'ordinate the addition of the starch and the starch-precipitating chemicals so as to obtain the maximum benefits from the starch addition and particularly to avoid those difliculties which have hitherto stood in the way of i5 successful incorporation of starch with paper bers during the formation of a paper web on a paper-making machine.

A further object of the invention is to time the addition of the starch and the starch-precipitating chemicals so as to secure the maximum benefits from the starch addition while avoiding those inconveniences and difficulties which arise in the course of the operation of a papermaking machine by reason of the great many variableswhichare encountered during the operation thereof, such for example asthe variables introduced into the operation by the dilution at the mixing box of a paper plant where white water, fresh water, or a mixture of the two in varying proportions is mixed with the concentrated stock derived from the beater.

A further object of the invention is to insure the retention of starch in the forming paper web, which involves beating gelatinized starch with* paper fibers in a beater to form a starchcontaining furnish, subsequently diluting this furnish to the point of maximum dilution at which it is ready to pass to the wire of the papermaking machine and at the point of maximum dilution, and while the stream is freely flowing, adding thereto, in the order named, aluminum sulfate and an alkaline materialfrom the group consisting of sodium aluminate, sodium metasilicate and sodium sesquisilicate, or their equiva- 45 lerliits, as for example the corresponding potassium sa s.

A still further object of the invention is to coordinate the above mentioned operations so as to A' insure the presence in the diluted furnish at all 5o times of the proper amount of potential aluminum hydroxide or alumino silicate forming reagents, properly proportioned to the amount of starch present in the diluted furnish to insure the precipitation and bonding to the fibers of the 55 starch which was added in the beater.

Still another object of the invention is to control the above mentioned operations so that a fairly constant hydrogen-ion concentration will be maintained in the diluted furnish which passes to the Wire of the paper-making machine, the alkaline material from the grou'p consisting of sodium aluminate, sodium metasilicate, and sodium sesquisilicate, being added at a constant rate which is proportional to the rate of paper production on the Wire and Vwhich rate is related to the amount of starch present in the furnish and the operating conditions, nature of stock, etc., the aluminum sulfate being added at a varying rate in accordance with the hydrogen-ion concentration of the furnish actually flowing to the head box of the paper-making machine, so that there will always be present in the diluted furnish the correct amount of aluminous-precipitateforming reagents to precipitate the starch in the furnish and to bond the same to the paper fibers, thereby retaining the starch in the finished sheet.

Other objects of the invention will become apparent from the further description hereinbelow and the hereunto appended claims.

It has already been proposed, by myself as well as others, to introduce starch into paper during its formation. In some of these prior art processes dry starch has been fed into the flowing stream of paper furnish just prior to the admission of? the furnish to the head box of the paper machine while also controlling the hydrogen-ion `concentration of the flowing stream. It will be noticed, however, that in such a prior art process as for example that disclosed and claimed in my prior Patent No. 1,907,440, of May 9, 1933, the starch was the nal ingredient added, and this starch was in the raw condition. It has been found, however, that the retention of starch when thus fed raw is quite insuicient and that considerable quantities of starch are lost in the white water which passes through the Wire of the machine and that, even though white water return is used, the retention of the starch is insuicient, particularly because it is notprpperly bonded to the paper fibers. In another one of my previous patents, No. 2,036,882, of April 7,

1936, I have described a process in whichA gelatinized starch and aluminum sulfate are added to a beater containing paper-making bers and beaten therein to form a ber furnish, this furnish, after discharge from the beater, having sodium aluminate or sodium metasili'cate added thereto in order to precipitate aluminum hydroxide or an aluminous silica compound, which carries down the starch and causes its adherence to the bers. This last mentioned process has proved successful because it so co-ordinates the order of addition of these materials-namely, the starch and the precipitating agentsas to insure the bonding of the starch to the fiber. It has been found, however, in many paper mills where this process has gone into use, that the rate of dilution of the stock at the mixing box varies from time to time during the operation of the machine, particularly as to the proportions and chemical condition of white water and fresh water us'ed for diluting the stock or furnish, such as it solids-content, colloidality and the like. Furthermore, when simultaneously sizing the fibers in the beater by means of the well known method of adding a rosin soap or size and precipitating the same with yalum or aluminum sulfate, yadditional aluminum sulfate is employed to react with the subsequently added sodium aluminate, but the excess aluminum sulfate -in the beater is subject to considerable, practically uncontrollable variations. This is caused by the fact that the aluminum sulfate requirements of the size will vary from batch to batch, and in the making up in a commercial beater there will be unavoidable variations in the actual amount of paper fibers present, due to variations in the weight of pulp bales. Furthermore, the excess alum hasya distinct tendency to react'with the bers and to become adsorbed thereon, so that it will not be present in properly ionized condition in solution in the water phase of the furnish.

In commercially carrying out my prior process of l Patent No. 2,036,882, the control was so operated as to maintain a constant hydrogen-ion concentration equivalent to about pH 5.5 to pH 5.7 at the head box of the machine. In order to accomplish this,the sodium aluminate had been added in a varying stream of a solution of constant strength, say 10%, the stream being directed into the dilute stream of furnish flowing between the mixing box and the head box of the machine. However, inasmuch as the addition of the sodium aluminate decreases the hydrogen-ion concentration (hence raises the pH), it was also found that there would be insuillcient starch retention and that the increased Mullen strength of the paper would not be apparent 0n careful inventigation it was discovered that the reason for this was that sufdcient alum had been bonded by the bers, used up by the size, or rendered inert by constituents of the water, so that there would be an insufficient amount of properly ionized aluminum sulfate in the furnish at the time the sodium aluminate was added. I found. as a result of careful tests, that a really successful bonding of starch to the paper bers can be accomplished only'if the ,siach is precipitated by the correct and proper am droxide or aluminum-silica I complex, thispre cipitation taking place at a carefully controlled hydrogen-ion concentration.

I have therefore lconceived and developed a marked improvement in a process generally laid down in my prior Patent No. 2,036,882, in that I have modified the procedure in the following respects: Instead of adding the alum to the beater, as I have hitherto done, I now do one of two things I either add a part of the alum to the beater andthe rest of it to the flowing stream of furnish atits point of ultimate dilution or add it all to the diluted furnish, and only then, after I am sure that `the right amount of properly ionized aluminum sulfate is present in the diluted furnish, do I add the sodium aluminate or other precipit of aluminum hy-l tant. To accomplish this I add the starch to the beater, the starch being in the gelatinized condition, which may be accomplished by boiling or by chemical means, or it may be a modified starch capable yof gelling in water, thus producing a starch-containing furnish. This I pass through the Jordan and then tov the mixing box of the paper-making machine, where the stock which had been at a concentration of about .4% in the beater is diluted with white water and/or fresh water to a consistency of about 1/2%. The stock is then allowed to flow through an open launder or pipe to the screens and head box of the papermaking machine. Into this flowing stream of starch-containing furnish I feed, by means of an automatic electrically controlled feeding device, a constant volume of a, say, 10% solution of sodium aluminate or equivalent precipitant, the rate of addition of this solution being in proportion to the rate at which paper is being made. feet ahead of the point of addition of, for example, the sodium aluminate I add a solution, of say 10%, of aluminum sulfate, in the form known in this art as paper-makers alum, the addition of which solution however is varied in accordance with the hydrogen-ion concentration as measured at the head box of the machine. How this controlis accomplished will be described in greater detail in connection with the hereunto annexed drawing, which is, respectively:

Fig. 1, a diagrammatic ilow sheet of my present improved process; and

Fig. 2, a similar flow sheet illustrating my prior process of Patent No. 2,036,882, so that the diilerence between the two processes can be most accurately and easily made apparent.

Describing my present invention in connection with Fig. 1, it will be seen that I have provided a beater 3, having thereon indicated that the consistency of the fibers is at about 4%. Into this beater there is fed an appropriate amount of starch 4 and, if desired, sufiicient alum 5 to take care of the precipitation of size which might have been used. I prefer however to add only a slight excess oir alum at this point. Where I mention alum, it is of course to be understood that I mean the so-called paper makers alum. The beater furnish at about 4% consistency and containing an amount of starch which forexample very advantageously can be equal to 4% of the dry weight of the fibers, but which may vary from 2% up to about 10%, depending upon the results desired, is. after proper beating, sent through the Jordan 6 and thence directed to the mixing box 1, at which point it is diluted by means of white water, fresh water, or a mixture of the two,

coming from the white-water collecting sump t, being pumped to the mixing box 1 by means of the pump 9 through the pipe I 0. The fresh-water supply has been diagrammatically illustrated as being a tank II, although ofcourse it will be obvious that this is merely the regular source of water supply of the mill. In the mixing box 'I the furnish is diluted to a. consistency of about and in that condition will ilow through the launder or pipe I2 toward the head box I3. 'I'here is provided a tank I4 of, say, 10% alum solution, this solution being fed through the pipe I5 and the automatic control valve I6 into the launder I2, as indicated in the drawing. The valve I6 is under the control of a hydrogen-ion control device which is a standard piece of equipment consisting of an electrical instrument Aand a suitable thermionic tube amplifier and is diagrammatically indicated at I1, the electrode I0 of the Afewv instrument being immersed in the head box Il. The valve I6 therefore will open and close in accordance with the alum requirements of the operation. A little further down along the launder or pipe on its way to the head box, sayat a distance of from 3 to 10 feet, there is the point of introduction of 'the sodium illuminate, or other precipitant, which iiows from the storage tank I9 through the pipe 2Il and through the flow-control meter 2I.v This flow-control meter is connected through the electrical control 22 with the operai:-`

ing mechanism which controls thevspeed oi.' the wire 23. concentration and is fed at such a rate that if, for example, the rate of paper production is 1600 pounds of dry paper per hour, it will feed approxithe presses and driers 24 and finally reeled up on a reel 25.

The range of starch to paper may be from 2% to but it has been found that the addition of about 4% of starch yields the greatest practicalreturn for thev moneyv expended. In other words, the benefits obtained with that percentage of starch are at their best. dium aluminate maybe from 1% to l%%, or substantially in the ratio above set forth, the

percentage of other precipitants mentioned being Vwhen using sodium aluminate should show a pH of from about 5.5 to 6 in the head box ofthe machine, while with sodium metasilicate or sesquisilicate it is better to work out a pH of about 6.8, but at any rate the furnish should not be allowed to become alkaline. as this might deleteriously affect thhe size `which might'have been addedin the beater. By size I mean, of course the usual sodium compound of rosin as precipitated by aluminumsulfate in an insoluble form on 'the fiber.

In order to exemplify the difference between my present process and that which I have described in my previous Patent No. 2,036,882, I shalliust briefly review this patent in connection with Fig. 2 of the present specification, corresponding figures being used, properly primed to distinguish from my present invention. Where the numbers are not primed, the arrangement and de\.es are the same.l Referring to Fig. 2, therefore, I provide a beater 3 in which the fibers are at a consistency of about 4%, adding gelatinized starch 4, so that there will be about 4% The precipitant solution is at about 10% The mount of soi of starch onthe dry weight ofthe fibers in the beater. I also incorporate alum 5 in the beater. but there is no otherpoint of addition of alum in this priorprocess. In other words, I put all the alum which I intend to use right into the beater and beat it with the starch and the fibers.

'I'he mixture in the beater, which then consists of fibers, gelatinized starch and alum (and also any size with which the fibers may have been treated), is fed through the Jordan Ii into the mixing box I of the machine, where it is diluted 'with water flowing through the pipe I 0. under the influence of pump 9, this water being either fresh water, white water, or a mixture thereof, exactly as in the `case' of Fig. 1. The .diluted stock. at a consistency of about 1/2%, flows through the launder or pipe I2 and receives an addition of precipitant from the tank I9, this solution iiowing throughl the line 20. and the valve. 2|', which in this case is under the control of the electrical control device I1' which has its electrode I8 in the headv box I3 of the machine. The

precipitant thus reacts' with the alum already present in the diluted furnish to precipitate the alum, forming an alumino'us precipitate. By reason of the white water returned and the great variation in the amount of fresh water with which the latter is diluted, the condition of the lstock variesfrom time -to time as it flows through the launder or pipe I2. If everything is working properly, of course, my prior process gives excellent results, and the Mullen strength of the paper, which ordinarily may be only about 26,

will be raised toas high as 42 to 43, based upon a -pound'bond paper. However; when operating in accordance with myV prior process just described, it has often happened that', although the was properly controlled at about 5.7 and the precipitantwas added strictly in accordance with the reading of-theacntrol instrument II and the setting of the valve 2I', the`Mullen test would suddenly drop to as low as for no apparent reason. I have now found that the reason for this was that, due to the variation in white water return and also due to variables in the making up of the beater furnish, there would be an insuicient amount of properly ionized aluminum sulfate in the 1/2% diluted stock in the launder or pipe I2' to react with the precipitant. Obviously, if there is not enoughI aluminum sulfate, the lprecipitant will raise the pH of the solution in the head box, and hence the electrical control .will throttle down the amountl of precipitant fed, as otherwise, because of its alkalinity, the pH would continue to rise. Naturally, it there were insumcient aluminum sulfate, there would also be insuicient precipitant, so that there would be a precipitation of the aluminousl compounds of only diminished amount, which would be insuiilcient lproperly to precipitate the starch.

This condition I have now completely remedied closed herein in connection with Fig. 1, where I insure the presence of the proper amount of alum by feeding the sodiumraliminate or other' herein named precipitating reagent at a constant rate directly proportioned to the production rate by practicing the invention which I have disof the machinefbut. feed alum ahead of the precipitant into/the flowing stream of diluted stock under the control of the control instrument I'I and valve I 6. In this way I can'maintain the sizing and other chemicals, however, are weighed,y

and hence usually are present in the predetermined quantities. The ratio of these chemicals to the ber will thus vary considerably, and there are thus introduced into the operation a number of unpredictable varia-bles. Furthermore, size varies from time to time, and hence the alum requirements for precipitation likewise vary. Further variables are introduced into the operation by the nature of the water employed. for diluting the stock after its removal from the beater, i. e., in the 4mixing box 1. Obviously if all white water is us'ed and this has, for instance, a pH of 5.8, there will be one effect, and if all fresh water is used and this has a pH, say, of 7.2, there will be another effect, with a further variation caused when mixtures of freshand white Water are employed. The white water contains colloidal matter, while the fresh water i`s usually fairly free from such material but also differs from the white water, and on different days, in total solids content, hardness, etc.

By operating as hereinabove described, however, I can overcome these variations, which from a commercial point of view is of paramount importance and constitutes what I believe to be the greatest single advance in this particular field that has been made to date.

,There is also another )very important advantage in operating as I have herein described, and that lies in the fact that I not only can increase the Mullen strength ofv the paper but also its tearing strength, folding endurance, and tensile strength. Therea'son for this is that, by precipitating the starch onto the fibers, I obtain an e'ect which is quite analogous to the hydration of the fibers; that is to say, the stock becomes less free, which gives a better formation and. a stronger sheet, as is well known. Formerly, and Without the use of my invention, it was necessary to beatthe bers for a much longer time and to subject them to more severe jordaning in order to hydrate them. In so doing, while they would increase in diameter due to their having imbibed sufficient water to effect thehydration or gelatinization, they were, at the same time, reduced in length, and it is the length of ber's that controls ,the tear, fold and tensile strength, while the hydration effect controls the Mullen strength and to some extent the wet tensile strength. By my present process, however, I can boat the fibers for a much shorter length of time and subject them` to a less vigorous Jordan treatment, because I do not have'to depend upon beating and jordaning for the hydration and gelatinization effect, and by thus reducing the mechanical preparatlon of the fiber I get a far better ber length, which naturally improves the above mentioned qualities of the paper.

Just as an example of how greatly the present invention is capable of increasing the wet tensile strength of the paper product, it may be mentioned that in a recently developed wet strength test, the wet strength was increased about 2000%. This test is made by obturating the bottom of an open 3inch cylinder about 24 inches high with a disk of the paper to be tested and then filling the cylinder to a predetermined height with water at 70 F., not less than 3.0 kilo- Vgrams of water being used, so that the paper is thus subjected to a dead weight of this amount of water over the entire area of the 3inch disk. The time when the paper breaks under this load is measured in minutes and seconds. A given grade of butchers wrapping paper made by customary methods had a test of 9 minutes, but'when the same stock was made into paper with the use of the present invention it required 190 minutes, or an increase of 181 minutes, equal to 2000%.,

Inorder to complete the disclosure, I am here mentioningthe approximate chemical formulas of the precipitants employed by me. Thus the nsodium aluminate is a commercially obtainable product and has the formula Na-2A12O4. The available commercial' grade usually gives the following approximate Ichemical analysis:

' `Per cent Soluble silica, SiOz 0.50 Sodium hydroxide, NaOH excess 7.99 Sodium carbonate, Na2CO3 1.04 Sodium aluxninate, NazAlzOi 87.13 Insoluble 1.42 Sodium potassium tartrate 1.92

The sodium metasilicate and sesquisilicate are also commercial products. Sodium metasilicate is a definite chemical compound having the formula Na2SiO3.5H2O. It has been describedtogether with a number of its other hydrates in United States Patent No, 1,898,707. Sodium sesquisilicate has a molecular formula of anazozsiommzo and contains about 36.89% NazO, 23.83% SiOz, and 39.27% water. It is described in United States Patent No. 1,948,730. An alternative formula is Na3HSiO4.5H2O. Obviously, I can use more than one of these materials, i. e., the aluminate 'and'the silicate, at the same time, introducing them separately, or together, or each under its own control.

Summing up my invention, therefore, it not only assures a better grade of paper with the same amount of ber and a. paper which is of improved physical properties, such as Mullen burst' ing strength, tear strength, 'folding endurance and tensile strength, but which also has a closer and better formation and smoother surface, and which is far superior inA every respect. The essential point to be remembered is that I have now solved the dimculties which have hitherto acccmpanied the carrying out of my prior inventions, in that I have successfully overcome the many variables which are encountered in the commercial operation of a. paper machine, and

cate thereto to form an aluminous precipitate by f the substantially complete reaction of both added ingredients in the furnish but keeping the furnish on the acid side of neutrality, whereby the starch is precipitated upon the i'lbers, and forming a paper web therefrom.

2. The improvement in incorporating starch in paper during its formation which comprises the steps of mixing gelatinized starch with paper fibers to form a furnish containing ilbers at about 4% consistency, diluting this furnish after removal from the beater to a consistency of about 1/2%, owing the diluted furnish toward the wire of a paper-making machine and while thus flowing adding, successively, aluminum sulfate anda precipitant from the group consisting of sodium aluminate, sodium metasilicate and sodium sesquisilicate thereto in substantially stoichiometri cally balanced amounts to form thereon an aluminous precipitate by the reaction of both added ingredients but keeping the furnish on the acid side of neutrality, whereby the starch is precipitated onto the iibers, and forming a paper web therefrom.

3. 'I'he improvement in incorporating starch in paper during its formation which comprises the steps of mixing in a beater, cellulosic fibers, water and starch to form a paper furnish containing fibers and gelatinized starch, transferring this furnish continuously to a point of dilution and then diluting it to a consistency suitable for web formation, flowing the diluted furnish toward the wire of a paper-making machine and while thus owing introducing thereinto a precipitant from the Agroup consisting of sodium aluminate, sodium metasilicate, and sodium sesquisilicate, at a constant rate predetermined by the rate. of paper production of the machine, measuring the hydrogen-ion concentration of the furnish as it enters the head box of the machine and adding a solution of aluminum sulfate to the ilowing furnish at a point ahead of that of the introduction of the precipitant in an amount sumc'ient to react therewith so as to. maintain the predetermined hydrogen-ion concentration at the head box, whereby a sufiicient amount of aluminous precipitate will be formed in the furnish properly to bond the starch to the fibers, the hydrogen-ionconceni,

tration hereinabove mentioned being that corresponding to a pH of from about 5.5 to 6.8.

4. The improvement in incorporating starch in paper during its formation which comprises the steps of beating paper-making bers in a beater with from about 2% to 10% of gelatinized starch based on the dry weight of the fibers, subsequently diluting the resultant starch-containing furnish to substantially its ultimate consistency, and then adding separately thereto stoichiometrically balanced amounts of aluminum sulfate and aprecipitant from the group consisting of sodiumaluminate, sodium metasilicate and sodium sesquisilicate to precipitate the starch, while keeping the furnish thereby at a pH of from about 5.5 to 6.8. l

, bond the starch to the fibers, while maintaining `oi the diluted furnish just prior to the addition diluted furnish toward the wire in a stream and ksodium aluminate, suiiicient additional aluminum .a predetermined hydrogen-ion concentration of from about pH 5.5 to 6.8 at the head box of the machine.

6. The improvement in incorporating starch in paper during its formation which comprises the 5 steps of beating paper-making fibers in a beater with the addition of from about 2% to 10% of gelatinized starch based on the dry weight of the fiber, diluting the thus produced starch-containing furnish to a consistency suitable for paper- 10 web formation, a `d prior to its introduction into the head box of `t e paper-making machine add, ing aluminum sulfate and sodium m'etasilicate thereto in stoichiometrically balanced amounts l to precipitate suiiicient aluminous precipitate to 15 bond the starch to thebers, while maintaining a predetermined hydrogen-ion concentration of from about pH 5.5 to 6.8, at the head box of theV machine.

7. The improvement in incorporating starchin npaper during its formation which comprises the steps of beating paper-making bers in a beater with the addition of from about 2% to 10% of gelatinized starch based on the dry weight of the fiber, diluting the thus produced starch-containu ing furnish to a consistency suitable for paperweb formation, and prior to its introduction into the lhead box of the paper-making machine adding aluminum sulfate and sodium sesquisilicate thereto" in stoichiometrically balanced amounts n to precipitate sufficient aluminous precipitate to bond the starch to the bers, while maintaining a hydrogen-ion concentration of from pH 5.5 to about pH 6.8 at the head box of the machine.

8. The process of making paper containing u starch which comprises the steps of beating papermaking fibers and gelatinized starch in a beater together with aluminum sulfate to produce a starch-containing fiber furnish, diluting the same to its final consistency suitable for web formation and adding thereto an amount of aprecipitant from the group consisting of sodium aluminate, sodium metasilicate and sodium sesquisilicate, based on the rate of paper production, while augmenting the aluminum sulfate content of the precipitant so as to insure the presence in the diluted furnish of sufiicient aluminum sulfate to react with all of the precipitant, and to maintain the hydrogen-ion concentration of the furnish on the acid side of neutrality.

9. In the process of making paper containing starch which comprises the steps of beating paper-making fibers and gelatinized starch in a beater `with aluminum sulfate to produce a fiber furnish containing X% of starch, and, after re moval from the beater, diluting the furnish tothe ultimate consistency at which it is to be fed to the wire of a paper-making machine, iiowing the adding thereto Y% of sodium aluminate at a rate adjusted to the speed of paper production per hour, the. ratio of X to Y being as about 3.5:1. and also feeding into said stream, ahead of the sulfate to insure the Apresence of a suilicient amount thereof to react with all of the sodium aluminate,. the control of the addition of said beater' with aluminum sulfate to produce a ber l furnish containing X% of starch, and, after removal from the beater, diluting the furnish to the ultimate consistency at ,which it is to be fed to the wire of a paper-making machine, flowing the diluted furnish toward the wire in a stream and adding thereto Y% of sodium metasilicate at a rate adjusted to the speed of paper production per hour, the ratio of X to Y being as about 2.5 1, and

also feeding in to said stream, ahead of the sodium metasilicate, sumcient additional aluminum sulfate to insure the presence of a sumcient amount thereof to react with a1l`\of the sodium metasilicate, the control of the addition of said aluminum sulfate being based on a maintained hydrogen-ion concentration of about pH 6.8 at the head box of the paper machine.

11. In the process of making paper containing starch which comprises the steps `oi? beating paper-making bers and gelatinized starch in a vminum sulfateto insure the presence of a suilicient amount thereof to react with all of the sodium .sesquisi1icate, the control oi' the addition of said aluminum sulfate being based on a maintained 15 hydrogen-ion concentration of about pH 6.8 at the head box of the paper machine.

DONALD K. PATI'ELOCH.

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