US2200622A - Deinking of printed paper - Google Patents

Description

Patented May 14, 1940" UNITED STATES PATENT OFFICE Pierre R. Hines, Portland, Ores.

No Drawing. Application August 19, 1936, Serial No. 96,819

1 Claim. (01. 92-13) My invention relat t th art of hi king whichfurther are flocculated or precipitated with printed paper in which the flotation process i great difliculty; hence constitute an impediment l y t remove t particles after in the flotation step, therefore their formation ing been loosened from the cellulose fiber and in the p p r i n f he S ock for flotation 5 filler. By flotation process I mean froth flota- Process m be prevented tion as performed in a froth flotation machine A higher recovery is Obtained y t t tha and described in my Patent No. 2,005,742, dated y a se d s h art f paper m kin June 25, 1935, entitled Process for deinking paper. s constantly demanding ner and bri hter My present invention has for its particular finished prodll T flotation p ess r del lll purpose the elimination of all soaps from the inking Printed paper employed prior to my mmacerated stock; because, as I have discovered, m v ment h r in d s d, gives app mat ly the presence of soap prevents the employment ofv 00101 of 66-53 With reference to n sia the flotation process S ce fully white as a 100% standard. A slightly brownish The deinkin of printed paper by flotation murky color is also observed in the top layers process is entirely different than efiecting of the water when the stock settles, whichIfound inking by the washing process. The removal of to be caused by Stable Soaps Well pe s d- I ink particles from leached, or cooked (which are have discovered that y preventing the fo masynonymous terms) macerated waste paper by tion of stable soaps, together-with the substanthe washing process requires exactly the oppotier! removal o h Soluble ly Washing, nd

site condition than required for th flotation the precipitation and flocculation of unstable 20 process. The washing process requires the disp e 0010! Of recovered S oc c be persion of the ink particles in order to obtain raised to 73-74% compared With magnesia W ite, efiicient results, and soaps perform that funcd, furthermore, with grea Simplicity n the tion; thus facilitate the removal of the ink parflotation machine oper arlld uniformity n ticles together with dirt by washing the macerthe resllltsl 25 ated stock. On .the other hand, the flotation y'p e consists i coarsely shredding the process demands the flocculation of the ink parpaper into small pieces, for example one to three ticles and their removal; Since soaps "are strong inches q r pp x y, n lea hin thes dispersion reagents, their presence in the mac- ShredSln a S Preferably hot alkaline q erated leached stock must be substantially pm- By the leaching step ink particles are merely 30 vented. This may be done by the proper cono sened but not freed from the pap s trol of the leaching step as hereinafter dethe ink particles still cling to the shreds- The scribed. I shreds are merely put in such condition that The particular object of my invention is to the ink particles which they carry may be readas provide an efficlent simpleprocess by which such ily freed by my process. This condition of the control in the leaching step may be eflected. 7 paper shredsmanifests itself by the feel of a In the leaching step the" loosening of the ink sample taken from the leached macerated paper particles from the fiber and the fiberization of stock. The paper shreds are-not to be defiberized the paper mass is accomplished by the aid or until after removal of the soapy liquors, for if an alkaline liquor. Old paper stock contains condeflberized prior to such removal, thenthe re- 40 siderable saponlfiable material such as rosin size moval of the soapy liquors by draining or filterand'linseed oils in the inks. Leaching produces ing and washing is rendered impracticable for note single soap but a mixture of soaps. 1 commercial purposes, due to the fact that the From a flotation standpoint these soaps may filler constituent ofpaper-usually consisting of be grouped into three classes: First, soluble soaps, china. clay and calcium carbonate-tends to form 45 that is soaps completely soluble in water, hence a cake'practically impervious to the passage of readily .removed by draining or filtering followed soapy liquor, by washing; second, insolubleQunstabl soaps After the leaching p' d the e oval of in which there is a higher ratio of rosin or rosin the soluble soaps. the shredsmay be defiberized dissolved in soaps. These soaps are easily fioccuto detach the ink particles from the fiber and lated or precipitated by burnt lime or equivalent thus effect their sep io f o each her. The reagent, thus placing them in a condition harmstock is then ready for conditioning preparatory less in the flotation step; third, stable soaps to the flotation step. The soluble soaps may be which once formed cannot be sufiiciently rereadily removed by simple draining and washso moved by draining or filtering and washing and. ing without loss of appreciable amounts of paper as fiber. Some insoluble soap is alsoremoved as an emulsion in the drained liquors, but appreciable amounts of insoluble soaps remain and will finally reach the flotation circuit and unless precipitated or flocculated will interfere with the carrying out of the flotation step efficiently. The unstable soaps may be readily flocculated or precipitated by simple means such as conditioning with burnt lime, for example. Flocculated and precipitated soaps do not interfere with the flotation of the ink particles freed from the fiber.

The formation of stable soaps must be prevented in the initial preparation of the stock which may be accomplished by limiting the leaching time of the shreds.

I obtain best results by using for the leach a strong alkaline liquor-equivalent in strength to caustic solution of 12 Baum at 62,Fahr.-preferably used hotthat is with a temperature of 140-208" Fahr. And the leach must be limited to a period of approximately 30 minutes. The reason for limiting the leach to 30 minute periods is, as my experiments have shown, that during such limited period stable soaps are not formed, but if the leaching period be extended beyond 30 minutes, stable soaps are very apt to be formed almost instantly.

Objection may be found in the increase of the strength of the leaching liquor as mentioned, since such would increase the cost if new liquor were used for each treatment; but since the alkali for making up the initial liquor is necessarily in excess of the amount consumed in the leaching process, I find that by draining the shreds after. the leaching treatment, and returning the recovered liquor to the leaching bath, the latter may be maintained at proper strength without excessive alkali cost.

The leached shreds must then be thoroughly washed with water, with agitation, to cause the water to permeate into the body of the shreds and displace the soaps. This step must also be limited to approximately 45 minutes, for repeated tests made by me have demonstrated that if this washing step be extended beyond 45 minutes, some stable soap is likely to be formed.

Caustic soda or soda ash may be employed for making the leaching liquor. Caustic soda forms a relatively larger amount of soluble soap than soda ash, but the tendency to form stable soap is greater than with the use of soda ash.

When caustic soda is employed and the leaching time is carefully controlled, as mentioned, followed by draining, and water washing of the leached stock for removal of soluble soap, defiberizing, the leached shreds in suitable apparatus, and conditioning with a suitable flocculating and precipitating agent, then the floatation step will recover a high percentage of fiber and filler, and the de-inked stock will have a brightness of 73% to 74%, compared with magnesium white as The resulting froths are moderate in volume, easily controlled, and show a characteristic end-point of clear, fragile bubbles, indicating that the ink removal has been completed.

If soda ash is employed under the like conditions, a larger amount of unstable soaps reach the flotation circuit, causing a lower recovery of filler. But the finished product will be 1 to 2 points higher in whiteness, as determined by a colorimeter. Soda ash has less tendency to form stable soaps than caustic soda.

When soda ash is to be used for making up the leaching liquor. the same control as described with respect to the use of caustic soda must be followed, but a larger quantity of soda ash than caustic soda must be employed for making up the leaching liquor. The amount of soda ash used must give a liquor of about 2 Baum at 66 Fahr.

Precipitation and flocculation of the unstable soaps are always essential, and are readily effected by conditioning 15 minutes or less with calcium oxide (burnt lime), calcium chloride, sodium chloride (common salt), and similar flocculating agents prior to the flotation step. The flocculation of the soaps at the same time flocculates the dispersed ink particles, which are then readily removed by flotation, as described in my said patent.

I claim:

In the process of deinking printed paper comprising leaching of the stock with an alkaline liquor having strength equivalent to 24% caustic soda and a ratio of 12-15 parts of water by weight to one part of air-dried paper treated, and removal of the freed ink particles by froth flotation, the improvement which comprises preventing the dispersion of the ink particles due to the presence of soaps, soluble, insoluble, unstable and stable, by limiting the leaching to a period less than 30 minutes, thereby restraining the forming of stable soaps, removing only the soluble soaps by filtering and washing, limiting the washing to less than forty-five minutes, and precipitating and fiocculating both these soaps and ink particles, the unstable insoluble soaps, by the addition of burnt lime prior to the separation of the ink particles from the other paper constituents by the froth flotation step.

PIERRE R, HINES.