US2005742A - Process for deinking imprinted paper - Google Patents

Description

June 25, 1935. P. R. HINES PRocEss FOR DEINKING IMPRINTED PAPER Original Filed July 27, 1932 m /d m m F f M /l w .m i m /2 m .f J W Patented June 25, A1935y UNITED STATES PATENT oFFlCrE j` Vacosmz rRocEss Foa DErNxrNG mmm i PAPER .Pierre a. Hines, romand, om.

'Continuation of 4application Serial No. 625,209, July 27, 1932.` This application'MayZS, 1934,

ASerial No.l 727,577 11 claims. 'rms application is med in ccntmuauon and completion of my application filed July 27, 193,2, Serial No. 625,209,a1lowed January 15, 1934.

The object of my invention is rto provide an efficient and practical process for removing carl"non inks from imprinted paper.

Waste imprinted paper may readily be reconverted into stock, but beforesuch stock may again be usedv for making paper, the imprinted ink must `be removed. In other words, the paper must be inking of the-paper.

My invention hasfor its purpose to providea process adaptable for de-inking papers Aof all classes-newspapers, sgmagazines, ledgers and bookswith a negligibleloss ofv thepaperstOck and filler, and without deleterious effectupon the fiber composing the de-inked stock.

The carbon particles of the ink with which paper has been imprinted may be loosened from the paper fibers of imprinted paper and I'have discovered that when the carbon particles have been freed from the fiber, they may then beremovedl by flotation in the form of a froth,'so'as to leave the fibers cleaned of the inkas a residuum.

By flotation I refer to a process similar'toA that employed for separating .minera1; Vbut before flotation can be accomplished the stock rmust-be suitably prepared which preparation .constitutes one of the essential steps of my invention.

I will nowA describe my invention bythe various steps which it comprises.

Refining and` cooking Describing first the refining and cooking treatment of waste magazines, ledger and book papers, my process for de-inl-ring imprinted paper is as follows: l

By refining I mean the separation of the fibers from each other, (defiberizing) andproducing stock suitable forv making paperon a papermachine.

The paper is first dusted, and `preferably shredded. Shredding facilitates the reconvertirg of the paper into stock. The shredding operation may be convenientlyl performedy ina hammer mill, or paper shredder available.

vthe ink has been freed; y y `brought to a proper `consistency, foriiotation. The .flotation operation yisimpedeci by too, thiclc; lstock and too thin a stock,requires too.V much The shredded paper may y Y l y and ,refined by either one of two vWell-lrnovvn methods; `namely/,by the lcirculating Icookingtank method,.or the rotary-cooker rnethod,but

be '.cooked, beaten,

4the cookingperiodmay-be reduced, with a Vview Ato economyjln-steam and timeytojfrom 2 to 3 hours. For the'complete removalof inkfromthe fiber yis not essential in carrying out .rny deinking process, sincebothcarbon particles and ink-encrusted fibers are removed together :from the stock .by the subsequent de-inking steps.

vThe stock may be cooked vvitlrsorne.allnrli,y not lexceeding the equivalent vofs-4% y ofy ;caustic ..soda,

for this may be used, for example 4vcausticpgsjoda,

rmixture of lime, (calcium oxide)` :and vsodium silicate. The proportions of said chemicals-.are based on the dry weight of. thelpaperfstock. The consistency ofthe stock-duringthe cookingkstep is generally 4-6%.

LThe cooking, beating,

separation of theV carbon particles from th'e paper fibers and ller. K

rrIifnewspaper only isto Abe defiberizeciv and rel and refining. effects *thel defiberization ofthe stociaand facilitates the fined, rthe, above-described` processv maybe ,mo'd- A'fied' by proceeding as follows:

The newspapers are sorted, 4dusted and weighed, then preferably are shredded with yone o! thev usual shreddersfin common use, and then.; is refined by thoroughly .beating in a ."broke' beater or beatercommonly-,used in papermiils, or may be agitated in a tanky by, afpump,v rnechanical impeilers, or .similarmeans ',Inzthede-inkingof newspapers, it ,is prefer-VVA v)able that the temperature of the beater-.water `be-lcept at from 140to 1,60y degrees z-F. News-- paper. defiberizes more `easilyinqfyater., of lthat temperature.

r lApproximately 25^30i1bs. of caustic soda, andy four pounds Yof sodium vsilicate per ton'of-dry weight .of newspapersr areaddedto the beater.

The. paper vispbeaten or agitated. for ..45-60. niin.- y

utes at a consistency of, appror`1Vma`te`ly-I 3%.

Consistency for. flotation The defiberizedandrefined stoclrz. from which fromV lthe-fiber must be `flotation cell capacity. A ,consistency of 1 -11A,%, v(8() lao-100 parts of water to one of original paper by dry weight) is'desirable. Due to variations in sizing, certain .waste .pa-

-Y flotation.

pers require longer cooking and reiiningthan others. In any event it is desirable to operate the dotation process continuously at a constant rate, and an agitated storage tank should be provided for the stock after it has been brought to a proper consistency, so that the flow of stock to the flotation apparatus may be maintained at a vsteady volume.

VI'locculation of ink and dispersion of jlller The higher grade papers such as magazines. ledgers, and books are heavily sized with rosin, emulsifled waxes and similar materials. The inks are incorporated with linseed oil and dryers, and the ink is dried by oxidation. When sized papers are cooked with an alkali, the size and oils are saponified. I have found that the carbon ink particles freed by the refining and cooking are dispersed due to the soaps present in the cooking liquor. 'I'he dispersion of the ink particles retardsA and hinders their removal by flotation, and therefore they should be flocculated, prior to I have further discovered that the carbon ink particles may be flocculated, if the pH value is above 7.0, by adding burnt lime (calcium oxide), magnesium oxide or similar reagent. The lime and similar salts precipitate the sodium soaps which causes the ink particles to flocculate. Approximately pounds of burnt lime per ton of original or dry weight of paper is sufllcient for average No. l books and old magazines.

The dispersion of the mineral fillers in the paper retards their tendency to float oil' in the froth. I have found either sodium silicate or starch suitable dispersing agents when Ythe pH value of the stock is above 7.0. Sodium silicate may be added at the rate of 10 lb. or less per ton of original dry weight of paper. If soluble starch is used, it may be used in amounts not exceeding 8 1b. per ton of dry paper.

Either lime or sodium silicate may be substituted for an equivalent amount of other alkali to assist in the cooking and refining operation.

If the stock has a pH value of less than 7.0 the addition of 4-10 lb. per ton of dry paper, of an acid, such as sulphuric, or one of the alum salts may be used to flocculate the ink and disperse the filler.

Eectz'ng frothing and collecting by a suitable agent I Vhave discovered that the volume of froth from paper stock increases with the pH value from 7.0v upwards. If the pH value is below 7.0 it is necessary to use a large amount of frothing reagent `of the heavier type as hereinafter specified. k

The soaps formed in refining and cooking with an alkali of sized papers, also contribute to froth formation, since a small amount of size, from a paper-makers standpoint, Vi'orrns a relatively `large amount of frothing agent, from a flotation Rosins and similar soaps have two extremes;

by a reagent such as sulphurlc acid; also by the removal of the cooking liquor thus lowering theV pH value as well as reducing the amount of saponifled products present. The removalV of cooking liquor may be accomplished by filtering or similar means immediately following the cooking and refining step. The volume of froth may also be reduced by the addition of 4-8 lb. of kerosene or similar reagent per ton of dry Weight of paper treated, and this is probably the most practical method. It is usually desirable to modify the type of froth bythe addition of one to two pounds per ton of dry paper, of a light frothing reagent, such as cresylic acid, pine oil, or one of thehigh boiling point synthetic alcohols, known commercially as Du Pont Frothers.

Newsprint contains little or no size, and rarely fillers. The carbon inks are incorporated with mineral and fish oils and are dried by absorption. Newsprint is made with a. large proportion of ground wood pulp which containstannic acid. Tannic acid is toxic and prohibits froth formation. Hence it is difficult to obtain a sufficiently vigorous froth by a normal amount `of/frothing agent. I have found a suitable froth may be obtained by raising the pH value of the stock to 8.5-9.0 in combination with frothing reagents. The lighter frothing reagents may be used in amounts of approximately four pounds per ton of dry weight of paper. The heavier frothing reagents such as Barrets No. 4 coal taroil, pine tar oil, hardwood creosotes may also be used, and it will be found advantageous to add these during the cooking and refining stage, thus to thoroughly incorporate them in the stock. The Du Pont 'Frothers" are particularly good for newsprint.

' It will be seen from the above that there are highly sized and coated papers producing voluminous flotation froths,y and newsprint giving insufficient flotation froths when the stock is cooked and refined by alkaline processes. The above discoveries will enable those skilled in the art of flotation not only to handle'thre above classes, but to intel-V ligently treat intermediate and special classes of old papers, to be de-inkedbymy method.

If the paper stock to be de-inked has a pH value of below 7.0, flotation reagents both light and heavy, and in combination, mayV be Yused atthe rate of 8 lb. and upwardsper ton of Vdry paper.

The froth bubblesshould be polygonal in shape with enough toughness to carry over well, Vand breaking down to liquid readily. The volume of froth should be less than 20%- of the total Volume of stock being floated, anda smaller volume is better. augmented as above mentioned for producing eilicient separation and removal of -the ,ink par,

Tough and persistent froths heavily enwith filler, orroe-like froths by any of the means above A thin or Weak froth must beY veniently ascertained by trial `and test in a Cil flber and filler are not floated oi! in the froth and no separation attained. This is most conlaboratory flotation machine.

The high boiling point synthetic alcohols (commercially known as Du Pont Frothers) mentioned above under frothing reagents, also have excellent collecting properties for carbon ink particles.

Kerosene or similar products have excellent collecting properties, as well as being useful in modifying excessive froths, and it works well 4in connection with the Du Pont Frothers.

Sodium cleate if used in'small amounts is an excellent collector of ink, but if used Vin large amounts disperses the carbon ink particles. If newsprint is to be de-inked sodium oleate may be added to the cooking step in the amount of two pounds or less per ton of dry paper. It has good detergent properties, as well.

Equal parts of amyl acetate and butyl alcohol have good collecting properties for carbon ink particles, and are excellent modifiers of heavy' and voluminous froths; Two pounds or less of each per ton of dry paper should be used.

If the paper stock being floated has a pHvalue of below '7.0, potassium ethyl xanthaie dissolved in ethyl chlor carbonate (commercially known as Minerec) is a good collector.

Since only a relatively small amount of some reagent is to be thoroughly incorporated in a very large amount of paper stock of the consistency required, the stock should be agitated for two to threeminutes prior to flotation. This is termed conditioning in flotation work, and the stock from the storage chest may be pumped continuously to an agitating chest or tank of sufficient size to give proper conditioning time. If the stock requires the addition of water to dilute it to a proper consistency for flotation, the stock and water may be delivered continuously at constant rate to the conditioning tank, and the reagents added continuously at a constant rate at the same time by means of flotation reagent feeders.

It will be appreciated by those skilled in the art of flotation that the reagents may be added at other convenient points to take advantage of other properties or to give longer conditioning time, or to intensify the flotation operation at some later stage in flotation. Removal of ink particles by flotation operation stock is introduced first in the'third compartment,

the first froth produced will be found heavier in ink than the froth from thevsucceeding compartments of the flotation machine. i

The froth produced in the machine raises freed ink clots, and inky fibers from the stock, also some clean fiber and filler are entrained in the froth.

The stock passes thru the remaining compart-r ments of the flotation machine, and finally is discharged as a de-inkedstock but with most of the mineral filler still in it.

` The froth from the third and successive compartments of the flotation machine is returned to the nrst compartment and flows through the second compartment to the third, where it JoinsY and Wasted. It also saves clean fiber and Iflller which have become entrained in the froth by returning the latter to the circuit. In this way the fiber and filler loss is confined substantially to very dirty fibers andl filler material which have ink clots adhering to them, which Ifound to be about 2% to 5% of the original dry weight of paper.

In short, my flotation method may consist of 'two steps. The first step called roughing, uses a dense, heavy collecting froth; the last compartments, in this'case, acting as safety traps catching the occasional inky fiber and carbon particles which may have escaped; at the same time some clean fiber. .'I'he second step is theretreatment of the first froth termed cleaning. The second froth is rich in inky fibers and carbon' particles, and low in entrained clean fiber and filler, as a lesser numberk of ber and particles are the wrong direction to stay in the closed circuit until they are finally rejected. K

In case a straight pneumatic flotation cell is used, thefroth from the rougher cell is sent to a smaller cleaner cell, and the froth from the latter is rejected, and the stock the cleaner" cell is returned to the feed of the first or rougher" cell.

The selection of the proper size of flotation machine should be made so as to give a frothing time in the first treatment of at least six to eight minutes. The specific gravity of the stock may, for practical purposes, be taken as 1. lPaper stock stays in suspension for long periods compared to ore pulps and the vigorous actionv required in the mineral industry to keep the vheavy minerals in suspension isrnot required in deinking paper.

The first froth generally breaks down readily into a stock ofv approximately the same consistency as the original stock treated by flotation.

down the rougher cell froth before re-treatment in the cleaner cell with beneficial effects as lower consistencies assist the cleaner cell action appreciably.

In flotation work sometimes a third cleaning is done, and there are a number of combinationsof cleaner and rougher cells used in flotation work as will suggest itself to anyone skilled in the art o f flotation.

Removal of flotation reagents The de-inked stock may then be filtered upon one of the well-known types of filters to remove flotation reagentsand lightlyY washed, prior to bleaching or subsequent operations commonly employed for converting .the stock into paper.

The filtrate may be used for diluting the cooked F `Spray water may be used to assist in breaking and refined stock coming to the chest prior to flotation, thus saving water in bringing the stock to the required density. This filtrate carries'the soluble reagents left in the stock and the amount 'of new reagents required is only that necessary to bring up the lstoel: to the original amounts specified. This also saves very nne filler in the filtrate or white water which may have escaped the filtering or de-watering operation. The experienced operator will be able to Judge from conditions in the flotation machine, and the characteristics of the froth, the` necessary changes in amount of reagents when using returned filtrate water.v y 4 While it is desirable that a high percentage of the ink be freed from the fibers, itis notan essential to my method that the cooking be carried to the point where all the ink is absolutely freed and separated from the fiber, as the froth will pick up, and remove ink encrusted bers as wel as the carbon ink particles. Y l

The rejected froth and inky bers may be washed and used for board or other stock where whiteness is of no importance.

A laboratory flotation machine furnishes results which are dependable for controlling full scale results and may be used to determine in advance the best practice for operating under local or specialc'onditions. f

Illustrations of practcal'operatiou of my de-'inkv ing method Invde-inking old No. l magazines, the magazines are sorted for elimination of foreign matis rapidly circulated by a large stock pump exterior to the tank; the heating is accomplished by live steam. The cooking is generally in'batches.

A 6% consistency stock is furnished to the cooker togetherv with 4% of caustic soda and 1% of burnt lime (calcium oxide). yThe temperature is brought up with steam to i90-210 degrees F. and the stock rapidly circulated for 3-4 hr. determined by test or sample to see the stock is thoroughly defiberized.

The cook is then discharged toga storage chest from which it is pumped at a constant rate by a stock pump to a conditioning chest. Water or filtrate from the finished stock is added at a constant rate to maintain the consistency in the conditioner at 11/4 Reagents are then added at a constant rate by means of reagent feeders in the. following amounts *perA ton of dry paper: eight pounds of kerosene, one pound of B24 Du Pont Frother and two pounds of soluble starch. The conditioning tank should be. of such size as to give three minutes conditioning time prior to notation. The conditioned stock is preferably pumped by a stock pump so that a constant rate of 'feed to the flotation maybe maintained. ,y

The conditioned stock'issent tol av rougher type of pneumatic flotation cell of such, size as to give six minutes flotation time.

The first or rougher froth is sent by means of a launder to a cleaner cell of the pneumatic type, and the froth is well sprayed with wash water to .break down the froth. The cleaner. cell'froth'isv roughly deckcred, and the inky material wasted. Any coarse fiber caught by the decker due to operating errors may vthen bereturnedfor retreatment. 1 A.

The cleaned stockv from the rougher cell is sent to a filter, and the filtered stock is then sent for a lightbleach' to the bleachery,

'I'he stock from the cleaner cell may be sum- `ciently bright to be mixed with the clean stock from the rougher cell. If not, it is returned to the first or rougher cell for re-treatment.

The nitrate or white water from the filter il delivered to a storage tank. and may be used to dilute cooked stock in the conditioning tank. and

for froth sprays., excess' being wasted.

The following is an illustration of the application of my method for de-inking old newspapers.

'I'he newspapers are sorted roughly for elimination of foreign matter and any undesirable waste paper. l

The sorted newspapers are-then shredded pref-f erabjly in a wet type hammer mill, using water to carry the paper through the hammer mill,

. and into a circulating tank cooker.

The newspapers are cooked at a consistensy of about 3% with 25 lb. of caustic soda, and four pounds of sodium silicate per ton of dry newspaper. The temperature is maintained at 140 deg. F. andthe cook rapidly circulated for one hour. Y i

The deberized stock is discharged to a storage chest, and from there pumped at constant ratelto a conditioning tank. 'I'he stock is diluted to a consistency of l 1/.,% in the conditioning tank. Sufficient caustic soda is added to give a pH rvalue of 9.0. to the 11A% consistency stock. Four pounds of the Du Pont Frothers isarlded per ton of newsprint. The conditioner tan-lt is of such size as to give three minutes-agitation prior to entering the flotation circuit.

The conditionedstock is then fed to a pneu. matic cell of suflcient size to giveG-minutes otation time, the rst or rougher froth going to ay cleaner cell, thev second or cleaner cell froth going direct to sewer or Waste. The stock from the cleaner cell is returned to the head of the rougher cell for re-treatment.

The clean stock from the rougher cell is sent to a paper-mill decker and de-Wateied. The dewatered clean stock is then sentv to storage chests. If any of the newspapers are brown from ageing, zinc hydrous sulphlte may be used to brighten the stock, otherwise it is ready for paper.

The white water from the deckers issent to a storage tank for use in diluting cooked stock in the conditioning tank, for spray Water, and any excess is wasted.

I claim:

1. vThe process'of de-inking paper which coinprises refining andv cooking the stock, with a chemical adapted to free substantially the ink particles from the pulp fiber, until tests show the stock to be deiberizedY and the fiber substantially freed from ink particles, eiiecting occulation of lthe ink particles, and dispersion of other constituents by an agency selected relatively to the pH value of the stock,'eiecting frcthing and collecting by a suitable agent, vand removing the ink particles by froth flotation method. Y f

2. The process of de-inking paper which comprises rening and cooking the stock, with a chemical adapted-to .free substantially the ink particles from the pulp-fiber, until tests show the stock to be defiberized andthe fiber substantially freed from ink particles, bringing the stock to a suitable consistency, effecting occulation of the ink particles, and dispersion of other constituents by an agency selected relatively to the pH value of theY stock, effecting frothing and collecting by a. suitable agent, and removing the ink particles by froth flotation method.

3. The process of de-inking paper which comprises refining and cooking 4the stock, with a 75 chemical adapted to free substantially the ink particles from the pulp fiber, until tests show the stock to be deiiberized and the fiber substantially freed from inl: particles, bringing the stock to a consistency of approximately 80 to 100 parts of Water to one part per dry weight of paper treated, effecting fiocculation ofthe ink particles, and dispersion of other constituents by an agency selected relatively to the pH Value of the stock,

effecting frotliing and collecting by a ysuitable agent, and removing the ink particles by froth flotation method.

4. The process of de-inking paper which comprises refining and cooking the stock, with a chemical adapted to free substantially the ink particles from the pulp fiber, until tests show `the stock to be dcfiberized and the fiber substantially freed from ink particles, bringing the stock to a suitable consistency, effecting flocculation of the ink particles, and disp-ersion of other constituents by an agency selected relatively to the pH value of the stock, effecting frothing and collecting by a suitable agent, and removing the ink4 particles by froth flotation method including roughing and cleaning stages.

5. The process of de-inking paper which comprises refining and cooking the stock, with a chemical adapted to free substantially the ink particles from the pulp fiber, until tests show the stock to be defibcrized and the fiber substantially freed from ink particles, bringing the stock to a suitable consistency, effecting flocculation of the ink particles, and dispersion of other constituents by an agency selected relatively to the pH value of the stock, effecting frothing and collecting by a suitable agent, removing the ink particles by iiotation operation, and removing fiotaticn reagents from cleaned stock.

6. The process of de-inking imprinted paper which comprises macerating the imprinted stock, adding, While agitating the stock, agents having alkaline, dispersing and collecting properties, cooking the paper stock until tests taken from the stock show the fiber to be substantially freed from ink particles, agitating the paper stock With a collecting agent, and a gelatinous material, reducing the paper stock With Water to a low density, adding a frothing agent, the relative amounts of paper stock and agents above named beingdetermined as hereinbefore described, producing frothing to effect flotationand thus the final separation of the inky froth from the paper stock, and removing the froth produced.

'7. The process of cle-inking imprinted paper containing ground Wood and/or heavy filler which comprises refining and partially deliberizing the stock with a mild cook, reducing the Stock with Water to a low density, adding, while agitating, agents having dispersing and collecting and frothing properties, producing froth oy tation and thus the partial separation of inky froth from the paper stock and removing the froth produced, screening out oi the filler and fine fiber from the stock, subjecting the paper to a further strong cook until tests taken from the stock show the fiber to be substantially freed from inky particles, again reducing the stock with water to a low density, adding, While agitating, further agents having dispersing and collecting properties, the relative amounts of paper stock and agents above named being determined as hereinbefore described; and producing. a frothing in the presence of a. frothing agent, thus to effect the final separation of inky froth from the paper stock, and removing the froth produced.

8. The process of de-inking imprinted paper which consists in deiiberizing the stock, adding agents having detergent and collecting properties, cooking the paper stock until tests taken show the stock deflberized and the fiber substantially freed from ink particles, reducing the l stock with Water to low density, the relative amounts of stock and agents above named being determined as hereinbefore described, producing frothing in the presence of a frothing agent, whereby to effect iiotationand thus the final separation of the inky froth from the paper stock and removing the froth produced.

9. The process of de-inking imprinted paper which consists in deiiberizing the stock, adding agents having detergent dispersing and collecting properties, cooking the paper stock until tests taken show the stockdefiberized and the fiber substantially freed from ink particles, reducing the stock with water to low density, the relative amounts of stock and agents above named being determined as hereinbefore described, producing frothing in the presence of a frothing agent, whereby to effect notation and thus the final separation of the inky froth from the paper stock and removing the froth produced.

10. The process 0f de-inking imprinted paper which consists in defiberizing the stock, adding agents having detergent and collecting properties, cooking the paper stock until tests taken show the stock defiberized and the fiber substantially freed from ink particles, reducing the stock with water to low density, the relative amounts of stock and agents above named being determined as hereinbefore described, producing frothing inthe presence of a frothing agent, whereby to effect flotation and thus the final separation 0f the inky froth from the paper stock, controlling excessive frothing by a modifying agent, and removing the froth produced.

11. The process described by claim 8 including regulating the pH value by a suitable agency.

PIERRE R. HINES.

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