US2580161A - Process of deinking printed waste paper - Google Patents

Description

Patented Dec. 25, 1951 UNITED STATES Cornelius Clarence Driessen, Little Chute, Wis.

No Drawing. Application March 13, 1947, Serial No. 734,545

1 Claim.

This invention relates to improvements in the de-inking of waste printed paper. a While the price of propely sorted waste paper varies considerably from time to time, the average price over a long period of time is not sumciently lower than the price of virgin pulp to permit the profitable performance of many of the presently known de-inking processes. Most of such processes are commercially unsatisfactory because: they are too costly, they produce a pulp which is not of suflicient brightness and cleanliness, or they require unusual and expensive equipment for their practice. Such processes are costly because of the type and large quantity of chemicals needed. They fall to initially free enough ink, irreversibly color the fibers, or leave carbon agglomerates, all or each of which cuts the brightness of the recovered pulp. Generally they require large volumes of water for their operation. This has the two-fold effect of making the final removal of the ink more difficult and also requires the use of expensive and unconventional mechanical equipment.

It is an object of this invention, therefore, to provide a commercially practical process of deinking waste printed paper.

Another object of the invention is to provide a process for de-inking printed waste paper and recovering pulp or finished stock having a bright ness .and cleanliness higher than that heretofore attained by any de-inking process.

A still further object of this invention is to provide a process for de-inking printed waste paper which utilizes standard conventional equipment generally available in paper-making mills.

These objects are obtained by treating printed waste paper pulp with a truly colloidal forming solution in which the pigment will become and remain completely dispersed for a long time and which will pass through filter paper. Once the carbon is dispersed, the removal of the liquid by filtering or pressing leaves the pulp free from the ink and without agglomerated particles of the ink enmeshed in the fibers. It has been discovered that by using sodium hydroxide (caustic soda), sodium hypochlorite (with the weight of the hypochlorite in excess of the weight of .either J the caustic soda or soap), and sodium palmitate (soap) to pulp the waste printed paper, the ink was completely dispersed in a colloidal solut on and remained in such state for weeks without breaking. Such colloidal solution could be filtered or pressed from the pul leaving it free from ink. The particles of carbon being colloidal pass oil with the liquid and are not enmeshed in the fibers of the remaining pulp. While carbon does remain to the extent that a portion of the initial liquid is not removed, it cannot be seen even under a microscope and affects only the brightness of the pulp.

A theory for this phenomenon has been advanced by technical leaders in colloidal chemistry and paper chemistry who are of the opinion that the sodium hypochlorite contributed to such colloidal dispersion either by its action on the soap or jointly with the soap and caustic soda. In any event, experiments show that the ink is completely dispersed and easily removable by conventional washing equipment to an extent not possible when other combinations were used. To test the essentialness of the sodium hpochlorite, trial runs were made without using sodium hypochlorite. First, to obtain the equivalent degree of carbon dispersion as that obtained when all the substances are used, over four times as much caustic soda was required. The use of this much caustic soda resulted in an alkalinity pH of 11.6. This irreversibly darkened the grounded fibers present in the pulp to a dull yellow or India tint. As this could not be bleached thereafter, using conventional methods, the operation was of no commercial interest.

Experiments shown that the alkalinity pH in the pulping treatment should be between 8.5 and 10.5 in order to accom lish the dispersion of the carbon and prevent the irreversible darkening of the groundwood fibers. The process herein described may be readily controlled within these limits. It is believed that the sodium hypochlorite, by its action on either the soap or caustic soda, or both. causes the formation of a truly colloidal solution without the use of excessive and damaging amounts of the alkali.

In addition to its action on the dispersing of the carbon, the sodium hypochlorite also acts (particularly in the presence of caustic soda and sodium soap) to bleach any groundwood fiber and unbleached chemical pulp fiber. It also accelerates the penetration of the paper stock by the pulping solution.- Tests have shown that old telephone books in large packages may be dropped into the pulp vat without opening and the penetration of the cooking liquors when the mass is being ag tated was perceived to be faster than that otherwi e obtained.

In practice of the invention, a pulping vat known as a Liebeck pulper, having a capacity of handling a charge of waste paper of approximately three thousand pounds of actual fiber in a dry state, is used. It is first half filled with soft 3% water or with hard water treated with thirty pounds or one per cent of the weight of the charge, of sodium carbonate. About sixty pounds, or two per cent of the weight of the charge, of caustic soda and one hundred and twenty pounds, or four per cent of the weight of the charge, of the soap is then added. The soap may be inthe form of a solution, chips, or other form. After this solution is heated to 115 F. a three thousand pound charge of waste printed paper is added. The mass is then agitated until the larger masses of paper have been broken down and circulation uniform. The solution of sodium hypochlorite is then introduced while agitation continued. This solution is made by the trezl' ffnt of one hundred and ninety-five pounds of caustic soda with one hundred and fifty pounds of chlorine. This is a ratio of one hundred and thirty pounds of caustic soda and one hundred pounds of chlorine for each ton of the charge. The agitation continues for a few minutes while the cooking liquors thoroughly penetrate the pulp and the dispersion of the carbon completed. These proportions of chemicals usually result in a pH ofbetween 8.5 and 10.5. However, a test is made and if the alkalinity is not within these limits the amount of caustic soda should be altered to bring it within such limits.

Since the carbon is now completely dispersed in the liquid and will pass off with it, it is only necessary to remove from the fiber as much liquid as practically possible. To accomplish this the material is pumped through a screw press which dewaters the pulp to approximately thirty-three per cent solids. This dewatering or high density wash is accomplished in conventional screw presses and a very moderate amount of water is utilized. This reduces the loss of short fiber to an from the use of other methods of de-inking.

There are modifications of the preferred embodiment. For example, half or more than half of the solution of sodium hypochlorite may be initially added with the caustic soda and soap and the remainder added after the first wash. The pulp is then given a second dewatering or wash which further reduces the amount of colloidalized carbon.

To obtain the best results the soaps should be salts of saturated fatty acids which have molecular structures of less than eighteen carbon atoms in a line or chain length. However, a sodium soap of unsaturated fatty acids, such as oleic and linoleic acid, have been found satisfactory. In the acids with the number of straight chain carbon atoms less than six, the detergent properties are not so pronounced and their efiectiveness as a de-inking agent is likewise less. Tests show that whenever rosin or abietic acid soap is used, eighteen per cent of the weight of the charge was required to give complete dispersion of the ink and a pH of eleven was found to exist. This irreversibly darkened the groundwood fibers and proved commercially impractical.

In place of the caustic soda the process may be used with sodium carbonate (soda ash), sodium silicate (water glass), sodium phosphate, or any other water-soluble alkali capable of creating a hydrogen ion concentration of approximately pH 10.5 when used in the quantities specified.

. When the preferred embodiment of the invention is used, the brightness of the finished groundwood stock has been found to be at least three points brighter on a standard brightness tester than the best results reported by leading authorities in the field and results of other deinking processes on printed waste paper containing groundwood. One point in brightness is considered worth approximately $10.00 per ton of paper on the scale of prices prevalent before 1939. The brightness and cleanliness of the finished stock and the absence of carbon agglomeration in such stock make it a commercially desirable product.

While the preferred embodiments of the invention have been described in detail, it is to be understood that the details of procedures, the arrangement of steps, the proportion of ingredients and like factors, may be considerably varied without departing from the spirit of the invention or the scope of the following claim:

I claim:

The process of de-inking printed waste paper which comprises preparing an aqueous solution containing a water soluble alkali, soap in the form of a sodium salt of a fatty acid having more than six and less than eighteen carbon atoms in a line, and sodium hypochlorite as the sole essentially active ingredients, said hypochlorite being made from caustic soda and chlorine, the weight of said alkali, soap, caustic soda, and chlorine not including the solution being proportioned to the dry weight of the fiber of the paper to be de-inked substantially as follows: alkali 2%; soap 4%; caustic soda 6.5%; chlorine 5%; heating said solution to a temperature consistent with easy formation of pulp by agitation, introducing a predetermined charge of waste paper into said solution and agitating it to form a pulp, maintaining said mass at a hydrogen ion concentration of a pH value of from 8.5 to 10.5, and removing colloidali ed carbon from said mass.

CORNELIUS CLARENCE DRIESSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,112,887 Burby Oct. 6, 1914 1,226,735 Wright May 22, 1917 1,247,757 Wante Nov. 27, 1917 1,555,674 Kellner Sept. 29, 1925 1,568,664 Geisler Jan. 5, 1926 1,576,994 Plumstead Mar. 16, 1926 1,727,722 Lewis Sept. 10, 1929 1,925,372 Darling Sept. 5, 1933 1,933,228 Snyder Oct. 31, 1933 1,991,823 Snyder Feb. 19, 1935 1,992,977 Wells Mar. 5, 1935 2,107,297 Kauffmann Feb. 8, 1938 2,191,431 Kauffmann Feb. 20, 1940 2,200,622 Hines May 14, 1940 2,359,891 Brallier et al. Oct. 10, 1944 OTHER REFERENCES Deinking of Paper by West, published by Institute of Paper Chemistry, Appleton, Wisconsin (1943), pages 5 to 10.

Printing Inks by Ellis, published by Reinhold Publishing Corp., New York (1940), pages 480 to 483.