US3179555A - Process for de-inking printed waste paper - Google Patents

Description

United States Patent This is a continuation-in-part of our application filed July 19, 194-8, SN. 39,428 (now Patent 2,743,178, granted April 24, 1956) and SN. 579,237, filed April 19, 1956, now abandoned.

This invention relates to a process of de-inking waste paper, and particularly waste newspaper stock. While the process may be readily used to de-ink various chemical types of waste paper stock or pulp, it is particularly suitable for the de-inking of waste newspaper, which heretofore has been very difiicult to successfully and economically de-ink on a commercial basis. Therefore, the process as hereinafter described will be particularly applicable to the de-inking of waste newspaper stock.

Many different processes have been proposed for deinking waste newspapers so that the paper may be rendered into a pulp for re-use in forming paper or other cellulosic products. These known processes, however, are expensive, laborious, time-consuming and complicated.

Therefore, it is the principal object of the present inven tion to provide a process for de-inking waste paper that is capable of producing a better result, but, nevertheless, reduces the amount and number of materials employed, the time and cost of operation, and the labor and equip-: ment required.

In Patent 2,743,178 the use was disclosed and claimed of a process comprising forming an aqueous slurry of shredded waste newsprint stock having a consistency of from one to four percent of fiber by weight. A suitable water soluble salt yielding or giving anion having a valency of at least 4 or greater and which induces a zeta potential of the same charged sign as the ink particles and which differs from that of similarly charged particles of the material by factor of at least 4-, was then added to the slurry to thereby effect a substantial separation of the ink particles from the material particles. Such salts were NH4P207, Na (PO Th(NO Th(NO or K Fe(CN) In certain aqueous electrolyte solutions of the slurry, the pulp and ink particles acquired an electrostatic charge, and by the addition to the slurry of a salt as just defined, the cellulose and ink particles acquired electrostatic charges of like sign, but diifering in magnitude, and the electrostatic relation between the particles became repellent in nature, the cellulose fibers acquiring a small positive or negative charge and the ink particles acquiring a highly positive or negative charge to thereby bring about and eifect a substantial separation of the ink particles from the material particles.

A detergent of a suitable type to emulsify the separated ink particles and retain them in suspension and separated from the material particles was also added to the resulting slurry. The detergents used were of such character that, at a temperature of 150 F. to 190 F., they remained completely dispersed through the mix and did not rise to the surface to cause or aid foaming; this served to loosen the ink binder, and to emulsify the ink particles after their separation from the paper and permit them to be removed from the pulp by washing. The time of agitation was typically /2 to 2 hours.

It was subsequently observed, however, that when such a slurry was subjected to rapid mechanical mixing (e.g., with a 4000 rpm. high sheer, bar-type, electric mixer) the pulp would be defibered (egi, in 30 seconds) to such;

an extent that (before the chemicals were added or uniformly dispersed) mechanically dislodged ink particles would be mechanically beaten into the defibered pulp,

so as to become more permanently embedded than was the original printing. In other words; these transplanted? or mechanically embedded ink. particles proved to be harder to dislodge than was the primary printing, and

such impregnation is especially diflicult to reverse at low temperature. But if then the chemicals were added and the temperature raised (both to promote dispersion of the chemicals and their detergent action on the ink), a hy-' dration of the cellulosic material could occur which (if,

unchecked) ultimately produced a slow-draining pulp;

if this was converted to paper it had the characteristics of a gelatinous, brittle kind of sheet (not usable as news stock).

medium which already contained our chemicals (uniformly dispersed), detergency can take effect before this transference-impregnation becomes set. Heating 1 does not then have an unfavorable elfect--it may hasten the de-inking, but in some cases it may be unnecessary, and

indeed, when using distilled or soft water, even the;

detergent may be omittedt l Thus it is another object ofthe invention to prov ide a. process for de-inking waste paper at low temperature that produces a pulp substantially equal in color, brightness, and strength, to that of the original pulp. I 3

It is a further object of the invention to provide a process for de-inking waste paper that comprises Sim plicity of organization, economy of requirements, etlia ciency of operation and superiority of result.

Other objects, advantages and features ofour invention will become apparent as the description proceeds, in conjunction with the disclosures of our cited prior applications which are here specifically incorporated by reference. Further technical discussion of the general Subject may be found in Modern Pulp and Paper Making, by G. S. Witham, Sn; Deinking of Waste, Paper-Tappi Monograph Series-No. 16 (1956); Mechanical Pulp: ing Manual-Tappi Monograph SeriesN=o. 21 (1960) Mechanical beaters are used both to break down the sheet structure of shredded paper and to mix intimately the chemical reactants with the pulp. For this purpose a certain elevation of temperature may likewise promote both dispersion and reaction (thus reducing treatment time). However, prolonged heating or cooking eventually produces hydration of the pulp, reducing its utility.

, for paper making by destroying its strength or tear resist-i ance.

Such hydration, with its attendant increased vis-. cosity of the pulp, also slows down the paper making machines. In general, the number of times the reconstituted paper can be folded, varies inversely with the time of beating the pulp as occurs in conjunction with its deinking. Hence modern beating machines have been directed to achieve the fastest efficient heating or mixing action, and heat has been used to hasten the process. For such reasons it is not desirable for the pulp to be in the de-inking media for more than two hours (and less as the temperature is elevated). 1

High speed mixers may be considered as thosemachines (generally electric motor driven) which operate from about 50-60 r.p.m. (Holland beater) to 3000 rpm. (Tappi Standard disintcgrator). At the latter speed, (dry) shredded newspaper freshly added to aqueous medium is substantially (e.g., 5%) defibered in about 30 seconds. In a Holland beater, the same amount of defibering may take 3 minutes (varying somewhat with the size of the batch, etc.).- In either event, however, this defibering is visually evident (unless there was an obscuring quantity Patented Apr. 20, 1965.

However, it was then discovered that, when; mixing was carried out :less forcefully, or in aqueousarraeee of dirt originally occurring in the newsprint). If the present de-inking salt has not become thoroughly dispersed through the bath prior to its initial amount of defibering, it is then extremely diflicult for the de-inking to take place since the beater has already (secondarily) embedded displaced ink particles in the pulp.

In marked contrast, when the designated salt is thoroughly dispersedthrough the aqueous bath-either before the shredded paper is added, or prior to this mechanical transplant-embedding of ink particles caused by the mixer-the subsequent beating and defibration does not result in the ink becoming reseated. In such case, de-inking may be effected without anyapplication of heat (ambient room temperature) and in as little as 20 minutes. Likewise, the need of a detergent varies considerably, depending somewhat upon the character of ink being removed. Thus oil-based ink is readily removed by our de-inking salts without added detergent, if the present sequence of first adding salt and then paper is followed.

As before, paper is first cleaned (it necessary) and the consistency of the (cleaned) aqueous-paper mix is ad justed to a paper concentration of from one to four perthe dry weight of the paper may be used. For hard 7 water, additional detergent may be added to offset the effects thereof. It must be of such a character that, at the temperature'maintained, it will remain completely dispersed entirely through the mix and will not rise to the surface to cause or aid foaming at any temperature within the range employed. The detergent serves two purposes; namely, to loosen the ink binder, and to emuls'ify the ink particles after their separation from the paper so that the ink particles will be separated from the pulp by washing.

One example of a suitable detergent is C-cetyl betaine, an internal quaternary ammonium salt of amino acid derivative of cetyl alcohol. Other detergents, such as sulfonated esters of C15-C13 alcohols might be used, as well as amino acid derivatives of such alcohols.

In addition to the specific examples of our pending application: 400 g. waste newspaper were added to 20,000 g. water already containing 16 g. tetrasodium pyrophosphate and 4 g. C-cetyl betaine; with a Holland beater at a temperature of 66 F. and a mixing time of only 20 minutes, the de-inked pulp had a GE. brightness of 48%. Other effective detergents used for deinking include a mixture of methylene bis (trichlorophenol) and pine oil (Genie); reaction products of ethylene oxide with octylphenol (Triton X-100 for lower temperature and Triton X-102 for higher temperature); ditertiary acetylenic glycol in 2-ethyl hexanol (Surfynol 104A); Z-ethylhexanol sodium sulfate (Tergitol); and many others too numerous to mention herein. Other salts used successfully in place of tetrasodium pyrophosphate, in these experiments, are hexametasodium phosphate and tripolysodium phosphate.

.The present sequence of dispersing the salt (and detergent) prior to making a slurry of the printed paper has its principal effectiveness below about 150 F. when the ink particles have not become secondarily embedded (due to rapid mixing in the absence of salt or detergent). Above this temperature the electric charge of the de-inking salt (zeta potential) exerts more force on the (secondary) attached ink particles to readily loosen them. In other words, at elevated temperature, the sequence of mixing is not critical for tie-inking, but the effect of heat on the '4 pulp (as well as its greater cost) is 'not desirable. For some inks, an upper limit of about F. is preferred.

We claim:

1. The process of de-inking printed material which comprises mechanically mixing in aqueous medium (a) printed and shredded waste newsprint stock material and (b) a water soluble salt yielding an ion having a valency of at least 4, and which induces a zeta potential of the same charged sign as the ink particles and which diifers from that of similarly charged particles of the material by a factor of at least 4, said mixing being effected at a rate producing uniform dispersal of said salt prior to substantial defibration of said material and prior to substantial mechanically transplanted-embedding of ink particles in said material, continuing mechanical mixing of said material and medium thereby to effect permanent separation of the ink particles from the material particles, and removing the separated ink particles from the slurry.

2. The process of the preceding claim 1 wherein said type to emulsify separated ink particles and retain the same in suspension separated from the pulp particles.

4. The process of the preceding claim 3 wherein said detergent comprises C-cetyl betaine;

5. The process of the preceding claim 3 wherein said detergent comprises sulfonated esters of S -C aicohols.

6. The process of de-inking printed material which process comprises mixing in aqueous medium (a) a detergent of a suitable type to emulsify separated ink particles and retain the same in suspension separated from the pulp particles, and (b) a water soluble salt yielding an ion having a valency of at least 4, and which induces a zeta potential of the same charged sign as the ink particles and which differs from that of similarly charged particles of thematerial by a factor of at least 4, then (c) adding printed and shredded waste newsprint stock material to form a slurry with said aqueous detergent and salt to thereby effect a substantial separation of the ink particles from the material particles, while subjecting such mass to a temperature of from ambient room temperature to about F. for a predetermined period of time and agitating the mass during said period; and removing the separated ink particles from the slurry.

7. The process of de-inking material as set forth in claim 6, in which the mass after its subjection to said temperature is brought into contact with spaced electrodes to which is applied an electric potential difference of approximately 1.8 to 2.4 volts per inch of linear distance between said electrodes, so as V to substantially complete the separation of the ink particles from the material fibers without permitting, however, an electrolysis, whereupon the separated ink particles are removed from the slurry and mass with the water.

8. The process of the preceding claim 6 wherein said temperature is from ambient room temperature to abou 130 F.

References fitted by the Examiner UNITED STATES PATENTS DONALL H. SYLVESTER, Primary Examiner. MORRIS O. WOLK, Examiner.

Claims (1)

1. THE PROCESS OF DE-INKING PRINTED MATERIAL WHICH COMPRISES MECHANICALLY MIXING IN AQUEOUS MEDIUM (A) PRINTED AND SHREDDED WASTE NEWSPRINT STOCK MATERIAL AND (B) A WATER SOLUBLE SALT YIELDING AN ION HAVING A VALENCY OF AT LEAST 4, AND WHICH INDUCES A ZETA POTENTIAL OF THE SAME CHARGED SIGN AS THE INK PARTICLES AND WHICH DIFFERS FROM THAT OF SIMILARLY CHARGED PARTICLES OF THE MATERIAL BY A FACTOR OF AT LEAST 4, SAID MIXING BEING EFFECTED AT A RATE PRODUCING UNIFORM DISPERSAL OF SAID SALT PRIOR TO SUBSTANTIAL DEFIBRATION OF SAID MATERIAL AND PRIOR TO SUBSTANTIAL MECHANICALLY TRANSPLANTED-EMBEDDING OF INK PARTICLES IN SAID MATERIAL, CONTINUING MECHANICAL MIXING OF SAID MATERIAL AND MEDIUM THEREBY TO EFFECT PERMANENT SEPARATION OF THE INK PARTICLES FROM THE MATERIAL PARTICLES, AND REMOVING THE SEPARATED INK PARTICLES FROM THE SLURRY.