US2138325A - Process of making neutral sized paper - Google Patents

Description

Patented Nov. 29, 1938 UNITED? STATES PATENT oEFi-CE 1 raocsss or MAKING NEUTRAL size!) 1 i i PAPER Walter A. Nivling, Newton Center; Mass.

No Drawinl.

Application March 26, 1936, Serial No. 71,058

Claims. (oi. sis-4o) '10 The advantage of resistance to the penetration of ink or water and particularly to hot water longenough to adequately meet commercial or industrial requirements is obvious.

The presentjcommercial methodof obtaining the desireddegree of resistance to ink or water is to add from one to five per cent of a solution or emulsion oi rosin soap to the paper fibers while they are suspended in from twenty to two hundred times'their weight of water. This addition 50 of rosin soap is followed or preceded by the addition of alum. The amount. of alum required varies from an equal to two to three times the weight of the rosin used. Rosin soap (sodium resinate) reacts chemically with the alum to 25 form an aluminum resin complexcommonly described as aluminum resinate. This aluminum resinate is 'water repellent and when deposited on the paper fibers or mechanically interlocked among the paper fibers gives to the finished 80 paper the desired ink or water resistance. r

The obtaining of the desired degree of ink or water resistance consistently is 'one of the greatest problems of the paper manufacturer. Diffioulty in obtaining satisfactory ink or water 35 resistance. commonly described as sizing, arises from variousinterfering substances and condit ons. For example. hard waters containing calcium or magnesium, or returned-white waters gradually building up excessive amounts of 40 sodium sulphates,- interfere with theformation of the desired ink or water resistant aluminum resinat-e. High temperatures existin in intake water or built up by prolongedbeatinz r at y increase the difllculty of obtainlngsatisfa'ctory 45 ink or water resistant sizing. Hi h OH or alkalinity of the water in which the fibers are suspended greatly interferes with proper sizing. Other factors make ink or water resistant sizing of the fibers while they are in suspension dif- 50 ilcult. Even ver act ve, agitat on such as Jordaning reduces and at times destroys the effectiveness of rosin sizing if this be done prior or incident to the Jordaning operation.

Another improvement in the quality of paper 55' not possible by methods now employed but made posslbl e by my new method which I will describe hereafter is that of correcting two-sidedness of paper. Twosidedness is an inherent quality of all papers whether these papers are sized or not. This two-sidednessisdue in part at least to ex- 5 istin'g methods of making paper,' particularly by, the'use of the Fourdrinier wire. In th'e Four drinier wire, method of forming the sheet of paper, the paper making fibers in suspension in approximately two hundred times their weight 10 'of water are flowed onto a moving screen wire through which'the water. drains, aided first by the vibration of the wire and'later by the aid of suction boxes and sometimes with the further aid of a suction couch roll. In this removal of the 1 water, there is also removed some of the finer fibers and other suspended matter from the side of the paper adjacent 'to the wire. Obviously, the top side of the sheet is more compact because the paper fibers already deposited form a screen or rnat whichretains and thus makes the top surface more' dense in comparison with the wire surface of the sheet. 'This inherent two-sidedness results in not only a less dense sheet but also a less well-sized sheet on thewire side. When paper fibers aredyed in, the heaters and then formed on the wire, this two-sidednessis immediately apparent to the eye when the top. side and reverse side are brought into the same plane of view. Obviously two-sidedness is most noticeable on a colored or filled sheet. This twosided sheet when dried and submitted to surface sizing consequently absorbs the surface sizing more on one side than on the other. This further augments the differences due to two-sidedness. Curl and buckle are largely due to twosidedness which aiTects the rate of moisture absorption when the finished paper is exposed to an atmosphere of higher orlower humidity as in the print shop. This is the cause of many complaints and losses to the paper maker.

By the new process described herein the difficulties due to two-sidedness are largely overcome. The two-sidedness is corrected by, a

double application of my new sizin solution which combines both water or ink resistant sizing and surface sizing. Obviously, if in the first sizing step in my new process there still remains some two-sidedness' due to the. inherent difference in the formation of the twosides, this iscorrected by the second application of my new sizing. Since the first .application produces a very measurable degree of water and ink resistance, and since this degree of water and ink resistance or coloring is different on the two sides,

simultaneously.

acidity which results it follows that there will be a difference in the absorption of the second application thus equalizing and overcoming the difierence existing before. This is quite impossible with the present method of sizing. This point becomes distinctly noticeable if the dyeing and sizing are applied The first application may still show a difierence in the degree of coloring but whenthe second application is madesowing to a difierence in absorption due to the two-sidedness, the amount absorbed is reversed and both sides will then show the same depth of color shade. For the same reason, the amount of size on the two sides will be the same thus greatly reducing the tendency to curl and buckle. This will be apparent to anyone skilled in the art of paper making.

To overcome these various difilculties and oth ers such as foaming, foam spots, pitch troubles, choking of screen wires and felts, etc., my plan provides for the forming of the desired aluminum resinate in a vat separate from that in which the fibers are suspendeda'nd adding this aluminum resinate to the fibers after they have been substantially formed into their final position and after approximately eighty-five to ninety per cent or more of the water in which the fibers were previously suspended has been removed. To do this and obtain satisfactory ink or water resistant sizing and a paper free from harmful from the chemical inter-i reaction between rosin soap and alum as now used, it is essential that the aluminum resinate or its equivalent shall be formed and retained in a colloidally fine state of sub-division so that it may properly penetrate and deposit on all the fiber faces and interfaces. It is also essential that the by-product acidity be neutralized. While various methods of applying sizing to the paper web'after it has been at least partially formed have previously been proposed, none of them as far as I am aware have produced satisfactorily sized paper and nonebf them have solved the problems of two-sidedness or of cor recting the acidity of the fibers. I

For the purpose of describing this invention, when the term colloidal solutions or colloidal suspensions is employed, it will sufiice to describe "colloidal solutions or colloidal suspensions as those in which the substances dissolved or suspended are of sufilciently small particle size to permit light to pass through'or between the particles to such an extent as will permit type to be read through a half-inch depth of the liquid, cooled'to room temperature and aged for from two or four hours or more. This bespeaks a particle size sufilciently small to permit free penetration into the pores of the papers commercially known as newsprint paper, wrapping paper, writing paper, including bonds and ledger papers. I

Colloidal dispersions of aluminum resinate as above described can then be added to the web of paper or other paper articles and will penetrate freely. 'I'he water coincidentally added may be removed by any of the usual drying processes. The application of colloidally' fine aluminum resinate may be made by adding to the fibers while they are suspended in water in the heaters or at the head box or other inter-' mediate point since the aluminum resinate particlesare attracted to and held by the fibers.

It isv preferable, however, to add the suspension of aluminum resinate either on the wire at the suction couch roll or at the dandy roll since if destructive effect on areas added at either of these points ninety percent of the water previously used will have been removed with the advantage of attaining greater economy and avoiding difficulties incident to sizing in the presence of a large excess of water. The application may also be made at the press rolls or any desired point along the bank of driers, or if desired, the application may be made as that of the usual surface sizing procedure. It is preferable in many cases particularly with very light papers, to give some preliminary sizing in the heaters, so that when the size is applied to the web there will not be too great absorption, which would result in weakening the web or undesirably adding to the drying operation. For this preliminary sizing it is preferable to follow what is one standard practice, that is, to add the rosin to the pulp first and then to precipitate it with alum, taking care that an excess of thelatter be not used.

One way of making the desired colloidally, finely divided aluminum resinate is to dissolve the rosin soap (sodium resinate plus free unsaponified resin) together'witlra suitable protective colloid in water in such proportions so that there will be from one-quarter to three per cent of resin and from one to ten per cent of the protective colloid present. In these varying proportions it is desirable to correlate the amount of colloid to rosin so that will not be present in more than five times the amount of original rosin which enters'into the sizing compound. The solution so prepared is mixed with an equal volume of a solution containing a like amount of the protective, colloid together with a soluble aluminum salt such as for example papermakers alum. The amount of alum or other soluble aluminum salt may vary from one-half to twice or more times the dry weight of the rosin soap used; v

By the term protective colloid", I mean that of the many substances known as colloids, choice shall be made of such as will eflectively prevent the reaction product, aluminum resinate, from aggregating into large particlesize, generally described as flocs.

Several materials maybe used as protective colloids such as, for example, animal glue, gum arabic, casein or soluble starch. I have found the widely used soluble starch gum material known in the trade as "Hercules Gum well suited for serving as a protective colloid.

When the two solutions, one containing thi. rosin soap together with the protective colloid; the othereontaining the alum together with the protective colloid, are mixed, the chemical interreaction forming the aluminum resinate takes place in whole or in part and more aluminum resinate. is formed during the drying process. It is almost universally found necessary to use more than the theoretical amount of alumor other' aluminum salt to dissociate the sodium resinate. This excess alum ionizes, forming an acid state. This acidity weakens the paper fiber not only during the process of paper making but continuing after the paper has been [dried with the strength and folding quality of the paper. I f To overcome this undesirable acidity, various alkaline reactingsubstances have been proposed to neutralize the acidity, such as caustic soda, soda ash, bicarbonate of soda, borax, sodium alum-inate, triethanolamine and others. Paper manufacturers have used these various alkalies but their use is attended with great danger since, ifsuch an amount of any of the alkalies above mentioned is used as will neutralize the acidity, a secondary reaction takes place whereby at least part of the aluminum resinate is decomposed with more or less complete sacrifice of the desired ink or water resistant sizing.

After much investigation, I have found that if ammonium hydrate is used in the presence of a suitable colloid not only can enough be used to completely neutralize the free acidity but even a marked excess may be used with the result that harmful acidity is overcome without the destruction of the aluminum resinate. found that several times the amount of ammonium hydrate necessary to neutralize the acidity may be used, if in the presence of a suitable colloid, without any harmful effect on or decomposition of the ink or water resistant aluminum resinate. This has the great advantage of permitting the addition of a satisfactory neutralizing alkali without requiring the attendance of.

a chemist since by a simple testing with suitable indicators or even by the slight odor of ammonia, the man in the mill can produce the desired result without fear of harmful excess since an excess of ammonium hydrate will be evaporated during the drying and the finished paper will be quite neutral. This has long been desired for all paper and more particularly for permanent record papers. droxide can be more accurately determined by the usual methods of determining the hydrogen ion concentration, the measure of which is commonly referredto as the pH value. pH value of the sizing bath is at least 6.5 there will be sufficient ammonia for the purpose, although it is preferred to maintain the pH slightly higher than this in order to insure against loss of ammonia harmful residual acidity of the fibers.

The ammonia not only neutralizes the acidity of the paper web, but also acts to preserve the sizing dispersion in the colloidal condition best suited for use. It is well known that surface sizing baths become less efficient 'uponprolonged contact with the paper fibers, probably due to the taking up of acids from the paper fibers, and the use of ammonia as above described has proved to be advantageous in maintaining the bath in effective condition.

It will be apparent that the materials used may be replaced by equivalents and that the proportions above mentioned are typical only. Aluminum acetate or various alums or other aluminum salts may replace paper makers alum; sodium stearate may replace sodium resinate; ammonium resinate may replace sodium resinate; other colloids may replace the soluble starch Hercules; the ammonium hydrate may be replaced by another volatile alkali; and the particular method outlined for making and blending the reacting chemicals and colloids may be changed, and the proportions may be changed as may be more convenient or found best suited for the particular type of paper being made. Dyestuffs may be added to color the paper as part of the process described above andv either or both the sizing and the coloring may be done in several stages as, for example, part may be added while the paper making fibers are in a free flowing state of suspension, and a subsequent sizing and/or coloring may be made at any convenient point during the drying or the papermay be dried andsubsequently sized and/or sized and In fact, I have The amount of ammonium hy- Provided the by evaporation and to neutralize to anyone skilled inthe art colored'in one or two steps as,

may be found most convenient or desirable, without departing from the spirit of my invention.

My claims on which I desire to secure Letters Patent are: v

l. A process of sizing a paper web which comprises subjecting the formed and at least partially dried web to an aqueous sizing bath consisting of the reaction product of one-eighth to one and a half makers alum in an amount equal to one half to twice the amount of rosinsoap, one to ten percent of a protective'colloid, there being not more than ten times the amount of protective colloid as rosin, and ammonium hydroxide in suflicient amount to maintain a substantially non-acid reaction in that portion of the bath in contact with the fibers/throughout such period of contact, and thereafter drying the web to remove water and excess ammonia andto pro-- duce a substantially neutral dried web.

2. In a process of obtaining a sized, substantially neutral web, the steps comprising subjecting the web forming fibers to the action of an aqueous bath containing a colloidal dispersion of aluminum resinate, a protective colloid, and ammonium hydroxide in sufficient amount to preserve in that portion of the bath in contact with the fibers a pH of at least 6.5 throughout suchperiod of contact, and thereafter drying the web to remove water and excess ammonia and to produce a substantially neutral dried web.

3. In a process of obtaining a sized web free from the harmful acidity resulting from rosin sizing, the steps comprising subjecting the web forming fibers to the action of an aqueous bath containing a colloidal dispersion of the reaction product of sodium resinate and alum, a protective colloid, and ammonium hydroxide in sufiicient amount to maintain a non-acid reaction in that portionof the bath in contact with the fibers throughout such period of contact, and thereafter drying the web to remove water and excess ammonia and to produce a substantially neutral dried web. 7

4. In a process of obtaining a sized, substantially neutral paper web substantially free from two-sidedness, the steps comprising subjecting the paper forming fibers to the action of an aqueous bath containing a colloidal dispersion of the'reaction product of rosin soap and alum,

a protective colloid, and, ammonium hydroxide in suflicient amount to maintain a non-acid repercent of rosin soap and paper action in that portion of the bath in contactwith the fibers throughout such period of contact, at least partially drying the web, subjecting both sides of the web a second time to the action of another aqueous bath containing a colloidal dispersion of the reaction product of rosin soap and alum, and thereafter drying the web to remove water and excess ammonia and to produce a substantially neutral web.

5. In a process of obtaining a sized paper web substantially free from acidity which comprises forming the fibers into at least partial web form, subjecting the fibers of the web thus formed to the action of an aqueous bath containing a colloidal dispersion of aluminum resinate, a protective colloid, and ammonium hydroxide in suiiicient amount to maintain in that portion of the bath in contact with the fibers a pH of at least 6.5

throughout such period of contact, and thereafter