US2041285A - Paper sizing - Google Patents

Description

May 19, 1936.

J. A. DE CEVV PAPER SIZING Filed Sept. 28, 1955 INVENTOR.

.JU/)50N A. DECEW ATTORNY,

@GQ www@ Patented May 199 1936 sTATEs PATENT orf-ICE 2,041,285 PAPER SIZING l .'indson A. De Gew, Mount'Vei-non, N. Y. Application September 2E, 1933,-Serial No. 691,420

. it claims. This invention relates to peper sizing which is a complicated operation on account of the varied conditions under which paper is made. Paper sizing consists primarily in the preparation of a t 'sizing material consisting chiefly 'of rosin and soda in the form of a partially saponied solution. or emulsion which becomes effective as a sizing agent after 'it has been acidied by an acid salt such as sulphate of alumina. The essential ingredients"\th at produce the effect called sizing, are rosin and alumina, which may be combined in innumerable ways to produce dierent degrees of water resistance or no sizing effect whatever.

The chemical composition and the physical form of the rosin emulsions and the chemical analysis of the coagulantl have a bearing upon the sizing'results but these are not the most important factors in the sizing process, because they can be made to react upon'each other in such a 20 manner as to ,produce good sizing results, a partial sizing result or no sizing.

The important factors in sizing paper are that the resinous material be'spread uniformly over the surface of the fibers; that it be precipitated thereon with the alum solutions in a manner to give the material its maximum colloidal property; that these colloidal properties be not destroyed before the stock reaches the paper machine; that all alkalinity of the precipitate must be removed and the precipitate must not be acidied to such a degree that its operties will be destroyed .when

the paper is being dried where the heat of the driers can decompose the excess alum solution `into free acid and alumina.

Paper can be sized with rosin-and alum in so many ways with different degrees of emciency that there are many unexpected results that have never been properly understood or explained. For instance, while it has been known that all uncoagulated sizing materials containing rosin are alkaline and in the form in which they are mixed with the paper stock they contain freeV alkali, and that some vsizing materials have more free alkali than others, still the majority vof paper mills first add their size and then the alum in the beaters. Thus it has not been made known. or appreciated before that when the size is added to a neutral pulp in a beater the free alkali is absorbed by the pulp and, the amount of alum, required to size the paper does not-depend upon the reaction between the alum and the size,- but is governed by the acidity required to remove the alkali from the fiber under the conditions of temperature, concentration and time for reaction that exist.

(Cl. B21-21) This is the normal condition in sizing practice and therefore, the average mill is obliged to use from two to three times the amount of alum actually required to size the paper. But the mill operator finds that if the alum is reduced, the fibers remain alkaline and the paper is unsized. If the" mill happens to be following the practice that occasionally exists, of adding the alum first, and then the rosin size, it obtains the following results: if the size emulsion is added to the paper stock in the beater after the alum, it is immediately coagulated locally at the point at ,whichA it is added, and the precipitated size is then distributed by mixing with the rest of the pulp. In most cases Where this is done, there is no sizing eilect produced in the paper, but in some Y cases a sizing eect can be obtained if the size is mixed with the stock quickly enough, such as would be obtainedby the action of a Jordan, but only by the .use of more rosin than 20.

should be required.

'Ihe value of a sizing process does not depend `upon whether or not it sizes paper but'upon whether it sizes paper in a wasteful or in an economic manner. So, among others, one object of this invention is to reduce the amount of alum used in sizing paper. The invention is based upon my discovery that the efciency of the sizing can beimproved by adding the sizing ingredients to the paper in a way that produces certain new 3G chemical reactions that produce the highest efficiency in the sizing of paper. The process of `this invention eliminates the danger of the size being coagulatedbefore it is mixed with the stock.

It brings about the sizing reaction rapidly and under controlled acidities and time factors and in a degree of concentration of paper stock that enables the reaction to be completed before the stock passes to the paper machine.

The essential part of this invention is consld-k ered to be the continuous mixing of the size with the pulp before coagulation thereof under cons ditions which do not allow time for the free al kali in the size to bel absorbed by the pulp fibers, and the rapid coagulation of the size onto the .bers by adding it to an alum solution' mixed with bers where the pH of such alum solution is controlled within certain limits.

For the better understanding of how this invention may be carried out the drawing accompanying this specification showsrdiagrammatil cally 'a flow sheet of a paper sizing plant, on which legends aroused to indicate the various pieces of usual equipment commonly found in av paper mill. 55

That is the drawing shows atypical paper sizing plant having a beater, a beater chest, a machine chest, a. machine head box, a screen, a

breast roll and paper machine, all as is usual.,

chest and head box of the paper machine without.

any Jordan being present. The novel features of the invention reside 'in the relationship of the special chemical reactions obtained by the sen quence of loperations described.

The process may be practiced by adding a stream of sizing emulsion or solution to the stream of slightly acidied or neutral pulp in a manner whereby these materialsare mixed together as they pass from the beater chest to the machine chest. 'I'he alum solution is added continuously to the machine chest where it becomes diluted and mixed with the stock and the precipitated size. The sizing reaction is continuous inasmuch as the mixture of size and paper stock are continually reacting in the machine chest with the mixture consisting of (1) acidifled fibers, (2) acidiiied sizing precipitates and (3). diluted alum solution made basic by its continuous reaction with the size. l

This is an entirely new sizing reaction to be made use of knowingly. It involves a new combination of conditions that can be maintained consistently and that is entirely independent of 40 the existence of a Jordan in the paper mill, al-

though the reactions should take place within certain limits. These limitations are that the size must be mixed with the pulp without coagulation. If the mixture of size with the acidifled or neutral pulp is alkaline, then the size should be coagulated before the fibers have time to become alkaline. The reaction with the alum takes place in the undiluted stock in the machine chest. The size is not precipitated directly by the fresh alum solution, but by a partially acidified mixture of fibers and precipitated rosin size and an alum solution having a pH of over 4.

More particularly, J'uSt sufficient alum or papermachine water is added to the paper stock inthe beater to remove all alkalinity from the bers. If they are already acidlfled by prior treatment, this is not required. The coloring matter may be added to the stock in the beater, but not the sizing ingredients. After being beaten, the. stock is discharged into a chest called the beater chest. From here, it is pumped to a head box where it ows by gravity to a Jordan if used and if not used it is discharged into a pipe carrying it to the machine chest.

In carrying out my process, the size .is mixed with the pulpat some point in its continuous flow contact can be regulated toavoid this. The mix- 75 ture a: pulp and uncqsumtnd sin is that cls charged into the machine chest. The alum for coagulating the size is discharged in a continuous stream into the machine or coagulation chest, where it maintains the acidity required for the chemical reaction. Ordinary commercial alum 'has an acid reaction represented by a pH of from 3.0 to 3.5. If the size is coagulated by an alum solution of this acidity, the colloidalvand physical properties of the precipitate'are injured. After the stream of size is mixed with the stream of pulp, the pH is between 6 and 8 and the pH of the pulp in the machine chest into which the uncoagulated size is discharged is between 4.0 and 5.4. In a mixture of size and pulp having a pH of 6, thev size does not coagulate for a long time. In a mixture of size and pulphaving a pH of 8 there is still free'ialkali, but this alkali is not absorbed by the iiber, within the time limits of contact allowed by this process.

In my process, therefore, the alum is added to the pulp mixture in the machine chest in just suflcient quantity to maintain the acidity of the pulp at a pH of vover 4 and preferably less than 5.4. The use of these limits contributes deiinitely to the eiciency of this process. As the stream of stock mixed with the uncoagulated size is discharged into the machine chest, the size is very quickly and completely coagulated for the process is similar to adding a stream of size into an alum solution, where the reaction is many times faster than adding a stream of alum to a size solution. `This is probably the explanation why so much less alum is required when using this process.

The reason that this process is operative in spite of thex rapid coagulation of the size is the fact that the size is already mixed with the pulp fibers before coagulation, and the pH of the coagulating alum has been raised and the alum made more basic. Although the rate of reaction between the size and alum is faster than can be successfully obtained in a beating engine, nevertheless the reactions are all uniform and under control, because the acidity of the pulp in the machine chest is uniform and under control.

The prior treatment of the bers to remove all alkalinity that may be present is a step that assures the uniformity of the reaction ,which would not be possible if the pulp van'ed from an It is evident that the chemical reaction, contemplated bythis process,

can not be Iobtained in a beater unless the beater is being fed withpulp continuously, which is seldom the case. It is also evident that this reaction can not be obtainedv by throwing alum and size alternately and in batches into a chest containing paper stock. The chemical reaction in this process is also different from that which would be obtained by mixing together simultaneously a stream of pulp fibers, a stream of size solution, and a stream of alum solution.

- Any kind of sizing solution may be used withv this process, and it is especially valuable when a size is being used that has a considerable amount of free alkali, as such a size .is often very troublesome when used in beater sizing. If an' ordinary size emulsion is mixed with neutral pulp, the pH of the mixture will be about 9. This mixture will soon produce an alkaline ber diilicult to size, and such a size should not be mixed with the pulp more than a few seconds before it is coagulated. This is impossible to accomplish in a beater. When alum is added to such a mix- 7.5

amines ture 'of alkaline size and pulpl ina. beater, the

rateof reaction is slow, requiring a large excess of alum to be used to complete the reaction and to acidify the pulp amounting generally' to from.

2% to 4% of alum by weight of thenber.

-Bymy process, bond and Writing papers and many others can be sized with not over 1%. of alum by weight oi the ber. And I also ilnd that my process requires from one-half to one-third mixing of the alum solution mustbe proportioned to the rate of reaction between the size and alum.

" action that takes place at` one-half per cent is the amount of alum generally required by pres# ent methods in beater sizing to produce the saine results. A

Although I have described a, process where the coagulation .of the size takes place in the machine chest, which is themethod most suited to ordinary mill conditions, it would be possible to carry out this process by .using other mixing means. The size may be mixed withthe pulp within the Jordan, if used, or in a small mixing device or both. The alum may be mixed with thepulp in any mixing device replacing the machine chest or a stream of alum may be added to a stream of size and pulp, provided the pH oi-the alum solution is over.4.2 or if a very quick mixing action immediately follows. The rate of The rate of reaction increases as the pH is lovrered. The rate ofreaction is also slower as the concentrations are decreased. As the pulp is transferred from the beater chest to the machine chest, there is practically no dilution of the stock, but the stock pumped from the ma.- chine' chest is discharged either onto the paper machine screens or'into sand traps on its way to the screens, and 'assoon as itis discharged, it is diluted with a large amount of water being returned fromfiie paper machine'. 'I'he stock is diluted from about 3% consistency to about one-half per cent consistencyg The chemical renot completed within the time that it takes for the pulp to pass through the screens and `onto I the machines, and if it is attempted to coagulate the size in this dilute condition, a large amount oi froth is produced.

l am therefore, limiting my process to the coagulating of the size before the pulp is 4diluted for screening, if the ordinary paper making equipment is used. 'My process would operate successfully, however, if a special tank were installed into which the diluted stock were discharged either before or after screening 'and into which the stream of alum could be poured, and when the size could be coagulated and the reac- .tion -completed before the diluted pulp was' returned to the machine chest. Now, if the alum'solution added for the coagulation'ofithe size is combined with this stream of stock returning to the chest and it meets in the chest, the stream of pulp coming from the beater chest containing the size, there is no chance for vai-iations in the chemical, reaction. The.alum is diluted with; pulp where the chemical reaction is already complete and just4 sumcient-alum is used to maintain the pH of the solution desired vfoi-'proper coagulation which is generally about 4.6 although it will operate within the limits given in this specication.

I claim: l. A method of sizing paper which comprises mixing' a stream of size with a stream of nonalkaline pulp fibers;` and beforeV the ibers can.v absorb the. alkali from the size, 'discharging the mixture into a chest containing pulp, precipitatedsize, .and alum, while additional alum is continuously added to said chest.

2. A method of sizing paper which comprises mixing a. stream of size with a stream of slightly acidiiied pulp bers; and before the size is coagulated, discharging the mixture into a chest containing pulp, precipitated size and alum while 15 y additional alum is continuously addedto said chest.

3. A method oi sizing paper which comprises mixing a stream o f size with a stream of slightly acidiiid pulp bers; and before the size is coi agulated, discharging the mixture into a chest containing pulp, precipitated size and alum While additional alum is continuously added to said chest to maintain the pH in said tank at some point between 4 and 5.2. 25

4. A step in a method oi sizing paperwhich comprises adding a stream of paper pulp containing a mixture of slightly acldified pulp fibers and an alkaline size solutionyto a chest containing acidied ber, precipitated size and an alum solution While additional alum is continuously added to said chest.`

`5. A method of sizing paper which includes the steps oi discharging continuously a fresh mixture of a weakly alkaline size and a. non-alkaline pulp, into a. mimng chest containing pulp fibers Vthatare already acidied byfthe continuous adf dition of alum to a pH. of between 4 and 5.2.

6. A method of sizing paper which includes the continuous addition to a chest ol. a mixture 4@ of anon-alkaline Ypulp and a. weak alkaline size and the continuous addition of an alum. solution^ to the chestin sumcient quantity to coagulate the size within the chest.

7. A method of sizing paper when using pulp ibers that have been prepared by an alkaline process, which comprises the steps 'of treatingl 'the bers with a sumcient amount. of papermakers alum to remove the internal alkali from the iibers, then continuously adding a stream ci' 5@ sizing material to a stream-o the pulp and before the bers can absorb the alkali from the size, the size is coagulated by the continuous additionof a stream of alum.

8. A' method of sizing paper pulp 'which in- 55 cludes the continuous mixing of a sizing solutien with paper making bers that have been preyiously slightlyacidifled'by treatment with a fresh alum. solution and immediately' coagulatingthe size by the continuous additiorrof alum.

9. A stepV in themethod of sizing paper pulp which comprises mixing sizing solutioniwlth a stream of-puip bers, discharging the mixture into a "g vat and coagulating the size in the vat by the onstant addition of a. stream of alum which maintains the pH in the vat at between d and 5.2.

- 1Q. A step in the method-of sizing paper pulp which vcon'iprises mixing an aqueous stream of 70 pulp bers containing uncoagulatedsize with a stream. of pulp bers containing coagulated size, and alum and which ismaintained at a pH of from 4 to 5.2 by the continuous addition of alum. i JUDSON A. DE GEW.I 75

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