US2390695A - Method of treating paper stock - Google Patents

Description

Patented Dec. 11, 1945 METHOD OF TREATING PAPER STOCK John 0. Dean, Douglaston, and Roy T. Edwards, New York, N. Y., asslgnors to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application April 25, 1942,

Serial No. 440,488

4 Claims.

This invention relates to a process for removing ink and pitch from paper pulp or waste paper in the beater stage.

Many'types of paper are manufactured partially or entirely of waste paper. This paper, in many instances, has been printed upon with conventional printing inks. Since most inks are black, the presence of the pigment tends to throw the reworked stock off-shade to a pronounced dirty gray color. This is frequently objectionable, and for that reason, steps are often taken to remove the ink during the reworking operation. A further objection is that the presence of the ink in the waste paper may complicate subsequent paper making operations. Foaming difiiculties are frequently encountered, and are often attributed to the presence of rosin in the printing ink. Expensive foam control measures must then be taken, or the ink must be removed.

Present methods of de-inking are crude and only partially effective. The most widely used is extraction with kerosene. This solvent is added to the reworked stock in the beater after it has been thoroughly wet-back and broken down to a uniform pulp. Beating is continued until the solvent is completely dispersed throughout the pulp. The pulp is then washed to remove solvent and ink, but complete removal is impossible due to the affinity of the pulp for the mixture. The net effect of this method is to distribute the ink more uniformly, and also to complicate paper making by the presence of objectionable kerosene vapors. D

Recourse has been made to the use of emulsi fiers to assist in this removal. Attempts have been made to utilize a blend of solvent and emulsifier. Such blends might be termed ,emulsifia'ble solvents, since on addition to water an emulsion of solvent in water is formed. Experiments have shown that they are ineffective, due to the fact that the droplets of solvent are completely surrounded withwater, and are prevented from mixing with th water-insoluble inks in the pulp. Consequently, ink removal is poor, and in fact, is less than with straight solvent. An alternate procedure is to add emulsifier to a heater which has been treated with straight solvent. This method is more effective than either of the above, but fails chiefly due to the inability of the emulsifler to completely remove solvent and ink which is firmly bound to the paper fibres. Large quantitles of solvents will scour the pulp satisfactorily, but th cost is prohibitive, and the pulp is softened and thus degraded.

Pitch. removal from virgin pulp is analoy nus to the de-inking of waste paper. Chemical pulpmaking processes extract considerable quantities of naturally occurring resins from the pulp, but in few instances result in a pitch-free stock. For many grades of paper, contamination of the cellulose with small quantities of pitch is not objectionable. Such instances include grades sized with from /4,% to 3% or over of rosin. However, in'the manufacture of tissue papers and other unsized or lightly sized grades, pitch is objectionable. It tends to deposit upon the screens and rolls of the paper machine, and causes imperfect formation and frequent shutdowns for removal. Pitch troubles are combatted by the addition of solvents, such as de-odorized kerosene, to the stock to prevent agglomeration of the pitch, or by the use of small amounts of ahnn 'to set the resin firmly on the fibres.

This invention has for its object the provision of an effective method capable of removing ink, pitches, resin, and similar materials from paper stocks. A particularly important object is the provision of an effective process for de-inking recovered paper stocks under conditions economically permitting the attainment of a high color in the finished stocks.

This invention is based upon a novel process usinga product applicable for the de -inking of waste paper and the removal of pitch from paper pulp. The process consists of utilizing a reverse phase emulsion (water-in-oil) to extract the ink, and then causing the emulsion to reverse phase to an oil-in-water emulsion which is easily washed from the stock. Such a procedure overcomes the difilculties of the methods now in use. The ink is readily extracted, since the product functions as a solvent, and removal after reversion of phase is facilitated because the original emulsion carries sufiicient emulsifier to carry both the solvent and the extracted ink or pitch.

The novel product contains solvent, emulsifier,

and electrolyte, and water. The following materials may b employed in such a product.

SoZvent.'Any water-immiscible solvent may beemployed, including petroleum distillates, coal tar distillates of all types, chlorinated solvents such as carbon tetrachloride, orthodichlorobenzene, trichloroethylene, etc. Kerosene is preferred due to its low cost, satisfactory solvent power, and relatively high flash point.

Emulsifier.As emulsifiers, any of the group of soaps, mineral oil sulfonates, esters, glycerides, or the like may be used. Examples are sodium or potassium oleate, sodium salt of a mineral oil Examples I to V inclusive. With Examples I to V inclusive, the change of phase is accomplished by added alkali as will be observed later. With Example VI, the alkali required for phase reversal.

is present, but inactiveuntil the change is pro.-

moted by heating.

upon addition of alkali its action is destroyed,

and the emulsion reverses phase. Useful electrolytes include salts of bivalent and trivalent metals and certain organic acids Examples are aluminum sulfate,potassium sulfate, magnesium sulfate, calcium chloride, ferric or ferrous sulfates, oxalic acid, acetic acid, citric acid, lactic acid, etc.

The treating or de-inking reagent, as applied to the pulp is the reverse phase (water-ln-oil), emulsion. Such emulsions are relatively well known, and a few examples of such emulsions, particularly suitable for such use, follow:

' Water soluble mineral oil sulfonates 2.5 Kerosene 40.0 Epsom salt (magnesium sulfate) 2.0 Water 48.0

Other representative formulae which may be used are as follows:

De-inking and lie-pitching procedure The following procedure is followed in using these emulsions: The stock in the beater, either waste. paper or virgin pulp, is brought to a point where it is thoroughly wet-out and digested. The

- pulp-'more fibre and less water-is formed. This Example III Weight percent Oil soluble mineral oil sulfonates -4. 10.0 Kerosene 40.0 Epsom salt I 1.0 Water 49.0 Example IV v Weight percent Sodium oleate 8.0 Carbon tetrachloride 10.0 Kerosene 30.0 Epsomsalt 2.0 Water 50.0 EwampleV a Weight percent Mineral oil sulfonates 10.0 Coal tar solvent naphtha (xylol) :50.0 Oxalio acid 1.0 Water 39.0

Example VI V Weight percent Diglycol oleate' 7.0 Kerosene 25. Orthodichlorobenzene 25.0 Trisodium phosphate a. 3.0 Water -40.0

The manufacture of the above emulsion consists essentially of the following The solvent, and emulsifier are mixed in one container;' and.

the water and salt or acid, (electrolyte), in a second. With vigorous agitation the aqueoussolution is added to the solvent solution, and stirring is continued until the product is' made homoeeneous. I

In Example VI a formula is given which is set up on a basis unique as compared to preceding thus unusual, and since, even with virgin pulp, V

' simply by heating to, a proper degree.

pH of thestock is lowered to below 6.5. A pH of 4.5 is preferred, althoughthis is not essential. At this point the reverse-phase emulsion is added and allowed to mix intimately with the stock. Between 2 and 50 gallons of emulsion may be used for one ton of dry pulp, although the preferred quantity is between 10 and 20 gallons, depending upon the condition of the pulp to be treated.

For de-inking waste paper, more needed than for the removal of pitch.

After the emulsion has been thoroughly mixed ,emulsion is with the stock and has dissolved the ink or the pitch, the stock is neutralized and rendered slightly alkaline with caustic soda, soda ash, trisodium phosphate or the like. Any pH above 7.0 is, satisfactory after neutralization, although a pH of 8.0-8.5 is preferred. The contents of the beater may be heated to facilitate the reversion of phase, but this is not always essential. After the emulsion has reversed completely, it is washed from the stock in the usual manner.

When using a self-reversing emulsion such as that of Example VI, where sufficient alkali for. phase reversal is incorporated in theformula, but remains inactive untilthe application' of heat, the phase reversal will, of course, be accomplished With the emulsion of Example VI, the phase reversal will be accomplished by heating to aboutlfiflfF. to F,

It will thus be seen that while the process here disclosed'may make use of solvents and emulsi fiers known and presently used for the same overall purpose, it makes use of those materials in a new andfar more effective way, in that where pitchy materials, (and ink is such a pitchy material) must be dissolved, the reagent has a high capability of reaction in; that "it presents an external phase selectively capable of attacking the pitch and ink, yet, when it comes'to removing the reagent, it has been converted to a highly water miscible state.

Certain coinmentsare or, interest. The operationmay be conducted either in a heater or in a pulp digestor. vantageously-in a pulp digestor. Here a heavier is advantageous in that when the emulsion is inverted by the addition of alkali'a moreconcem' trated oil-in-water emulsion results than if the operation is conducted in a beater with a less concentrated pulp. The more concentrated emulsions are more stable and are 'more easily washed from the pulp..

'In formulae like that of Example VI care" should be taken-not to. use themwith pulps of very low pH since with such stocks the alkalinity of the formula upon heating may not beenough to overcome the acidity of thestock. Of course, where this condition is. known. to exist, proper adjustment of-the electrolyte proportion in the formula can be made totakecare ofjthe condition. Since most reworked stocks are not It can be conducted more ad-- when one is removing pitch, the recirculated white water" tends to hold the acidity at optimum levels, this unusual condition does not often obtain.

In proportioning the amount of emulsion to be used, the concentration shouldbe adjusted upon the basis of water present in stocks. With beater stocks, the proportions of 2 to 50 gallons per ton of dry pulp, preferred ranges being -20 gallons per ton should be used, and with more concentrated stocks these proportions should be adjusted with regard to the amount of water present to arrive at water/emulsion ratios of the same magnitude as those indicated for beater stocks.

We claim:

1. That method for the removal of pitchy materials from paper pulp stocks comprising the steps of contacting the stock while in a digested and acid condition with an invert emulsion of a solvent for suchpitchy material to substantially dissolve the pitchy material therein, then changing the phase relationships of the-emulsion and washing the emulsion, containing dissolved pitch, from the stock.

2. That method for the removal of pitchy materials from paper pulp stocks, comprising the steps of admixing with the wet-out, acid, and

, digested stock an emulsion of the water-internal type, comprising a water-immiscible solvent for the pitchy material, an emulsion forming material, and an emulsion inverting electrolyte inactive under alkaline conditions, dissolving and removing said pitchy materials by the use of said invert emulsion, then causing reversion of the emulsion to a water-external typ and washing the emulsion and contained pitchy material from the pulp stock.

3. That method for the removal of pitchy materials from paper stocks comprising bringing the stock to a hydrogen ion concentrationof below about 6.5, adding thereto a water-intemal type.

of emulsion comprising a solvent agent for the pitchy material, substantially removing said pitchy material from said stock by the use of said emulsion then bringing about reversion of the emulsion to the water-external type, and removing said emulsion and contained pitchy material from said-stock.

4. That method for the removal of pitchy materials from paper stocks comprising bringing the stock to a digested and acid condition, adding thereto a water-in-oil emulsion stable under acidic conditions and agitating it with the stockv to dissolve and remove pitchy material therefrom, then bringing the stock to an alkaline condition and inverting the emulsion to an oil-internal condition and washing the emulsion from the stock.

JOHN C. DEAN.