EP0793747A1

EP0793747A1 - Methods for pulping and deinking

Info

Publication number: EP0793747A1
Application number: EP95941475A
Authority: EP
Inventors: Don R. Scott; William J. Fondow; Albert S. Kelly; David C. Grantz
Original assignee: Black Clawson Co
Current assignee: Thermo Black Clawson Inc
Priority date: 1994-11-21
Filing date: 1995-11-20
Publication date: 1997-09-10
Also published as: WO1996016222A1; EP0793747A4; BR9509797A; JP2001500572A; CA2203676A1

Abstract

Methods of recycling office waste paper of the type having ink and laser printed thereon. The wastepaper is simultaneously pulped and ink particles dispersed by kneading (2) the waste paper in the form of a high solids content aqueous mixture or sludge. After the simultaneous pulping and dispersing, no additional dispersion step is needed to form deinked paper stock. The high solids content aqueous mixture sludge is diluted and forwarded to wet deinking separation devices such as froth floatation unit (12) or the like. The thus treated pulp is washed (18) and results in the formation of a high quality pulp stock (20) ready for bleaching and/or paper making procedures.

Description

METHODS FOR PULPING AND DEINKING

Field Of The Invention The present invention pertains to methods for pulping and deinking cellulosic materials such as office waste paper.

Background Of The Invention The use of recycled office waste papers as a precursor source for paper making fibers has become increasingly popular. Recyclable office waste paper often contains ink and laser jet print particles. The latter actually exist as a multiplicity of particles or carbonized specs along the waste paper surface. The former may be described as comprising a mixture of pigment or organic dye, binder and solvent. Of course, in order to recycle such office waste, the ink, including laser print particles, must be removed in order to provide high quality pulp stock for production of high brightness papers .

Traditionally, deinking is accomplished with chemical additives and a plurality of mechanical process steps including the sequential steps of thickening the pulp, dispersing the ink particles in the thickened pulp in a kneading machine or the like, followed by diluting the kneaded pulp. Then the pulp is forwarded to a flotation cell where the dispersed ink particles are separated via air froth flotation or the like on the surface of the pulp slurry.

The aforementioned deinking processes normally contemplate usage of a repetition of the thickening, dispersing, and flotation steps. This accordingly presents an imposing capital expenditure especially with regard to the thickening (i.e. washing) machines since these are large machines, requiring excessive floor space, and are expensive to purchase. The same detriments exist for the dispersing step since the performance of these steps again requires expensive equipment. U.S. Patent 4,668,339 (Terry) discloses a process for dry deinking of secondary fiber sources wherein air dry secondary fiber batches are shredded to produce discrete fibers and fines. The fines include ink bearing fines or ink particles which are "dry" separated from the fibers via vacuum/screen arrangements.

Additionally, wet deinking or cleaning steps may be interposed between this dry shredding and the subsequent pulping of the fibers in an aqueous slurry.

Despite the efforts of the prior art, there remains a need for a process for deinking used office waste paper that will minimize the need for employment of successive thicken, disperse, flotation steps so that capital expenditure for this equipment will accordingly be minimized. A more specific need exists for a deinking process in which pulping and ink dispersion may be achieved simultaneously by use of the same equipment so that pre-pulping treatments such as those taught by the '339 patent supra. may be eliminated.

Summary Of The Invention

These and other objects are met by the present invention. Basically, the inventive methods pertain to the discovery that raw office waste paper of the type imprinted with ink and laser jet print can be simultaneously pulped and deinked in a high solids content, viscous aqueous mixture.

This step of simultaneous pulping and deinking may be carried out without any upstream pretreatment steps. Raw, untreated waste paper, such as office waste paper, is subjected to a kneading or shearing action in a viscous aqueous mixture having a solids content of greater than 20 wt.% solids. Use of more water in the mixture than that specified actually retards the mechanical kneading or shearing action of the waste paper as it is frictionally kneaded or sheared by the machine action and action of the high solids waste paper itself rubbing against other waste paper.

Use of this simultaneous pulping and deinking step has proven successful in separating the waste paper into a homogenous mass of substantially discrete fibers and dispersing the ink and laser printed particles throughout this mass so that about 90% or greater of the ink and laser printed particles are reduced in size to about 160 micron or less in diameter. Ink particle reduction to such small sizes has in the past resulted in successful ink particle separation using conventional flotation separation and washing techniques.

After the simultaneous pulping and dispersion step in accordance with the invention, the need for a subsequent dispersing step is drastically reduced. This presents tremendous savings in machine cost and floor space requirements.

After the waste paper has been simultaneously pulped and ink dispersed therein, the high solids viscous mixture may be diluted to a concentration of about 2 to 5% solids for passage through a coarse screen having openings on the order of 0.050" to 0.125" whereby large impurities will be maintained on the screen and accordingly purged from the process stream.

Downstream from the coarse screen, the process stream may be further diluted to about 0.8 to 1.0% solids and forwarded to a centrifugal cleaner wherein high specific gravity impurities are separated from the pulped, process stream. A variety of other separatory devices may be employed downstream from the initial centrifugal cleaning step, ending in a final washing and thickening stage that provides a 5 to 12% solids deinked pulp stock ready for bleaching and/or feed to the paper making fourdrinier or cylinder machine.

The invention will be further described in conjunction with the following detailed description and appended drawing.

Brief Description Of The Drawing

Figure 1 is a schematic flow diagram illustrating a process in accordance with the invention; and

Figure 2 is a schematic view partly in side elevation and partly in section of a preferred pulping and kneading apparatus used in the process.

Detailed Description Of The Preferred Embodiments Turning now to Fig. 1, raw, untreated office waste paper is fed to pulping and kneading station 2. Water is added to result in a high solids content viscous mixture having greater than about 20 wt.% solids, preferably between about 20-80 wt.% solids. At this station, the waste paper is formed into a homogenous mass of substantially discrete fibers and dispersed ink particles, the latter of which are dispersed throughout the homogenous high solids content mixture.

The type of device to be used as the simultaneous pulping and kneading station 2 is not critical. A variety of machines will suffice. For example, in addition to the twin screw arrangement shown, conventional ball mill, banbury, Hobart mixers and Lannoye kneader-pulpers and other mixing or kneading devices may also be mentioned. For the simultaneous pulping and ink (including laser jet print particles) dispersion step, the important criteria are that a high solids content aqueous mixture be mechanically subjected to compression and shearing action. It is thought that the high solids content requirement improves the shearing action especially and, in contrast to the normal low solids (i.e. 5-8%) or medium solids (8-20%) dispersion or kneading processes, imparts a frictional force on the waste paper, thereby improving ink particle dispersion and particle size reduction.

Based upon presently available data, it is desired to perform the simultaneous pulping and dispersion step at a solids content of 20-80 wt.%. More preferably, the solids content will be 30-70 wt.% with the range most preferably being 40-60 wt.%. Preliminary data suggest that about 50% solids is optimum.

The presently preferred apparatus for the step of simultaneous pulping and dispersing is shown in Figure 2. This is a specially designed "Hi-Con" pulper sold by Black Clawson Company, Middletown, Ohio. This pulper is described in detail in U.S. Patent 4,535,943, the disclosure of which is incorporated by reference herein. With specific attention to Figure 2, the pulper includes pulping tub, generally designed 110, having a bottom wall comprising an extraction plate 112 surrounded by tapered wall portion 113 and a generally cylindrical side wall 114 extending upwardly therefrom.

Below the extraction plate 112 is an annular accepts chamber 115 having a tapered bottom 116 and an outlet pipe 117 having a conventional control valve (not shown) . An additional outlet 118 is provided for reject material too large for passage through the extraction plate 112. A rotor, generally designated 120, is mounted centrally of the bottom wall for rotation about a substantially vertical axis. The rotor 120 is preferably driven by an electric motor (not shown) in a manner well- known in the art and disclosed, for example, in Couture U.S. Patent No. 4,109,872, disclosure of which is incorporated herein by reference. Extending upwardly from the rotor hub of the rotor 120 is a feed screw 130 which includes a core section 131 forming an upwardly tapering continuation of the rotor hub. This apparatus provides necessary compressive and shearing forces on the high solids, viscous aqueous mixture so as to effectively transform raw office waste or the like into a mass of substantially discrete fibers with ink and other friable contaminants substantially uniformly dispersed throughout the fibrous mass.

Another suitable apparatus for station 2 is described in U.S. Patent 4,993,649, the disclosure of which is incorporated herein by reference. This device is a twin screw device in which the screws rotate in opposite directions. Each screw shaft is tapered in its diameter, and, in the preferred embodiment, the tapers are disposed in opposite directions. That is, the taper direction for one of the screws extends from left to right (large o.d. to smaller o.d.) whereas the other screw taper (large o.d. to smaller o.d.) extends from right to left.

Other machines which may be used with some modification to effect simultaneous pulping and dispersion include those depicted in U.S. Patents 3,533,563 (Eriksson) ; 3,064,908 (Hjelte) ; 4,284,247 (Eriksson) ; 4,339,084 (Eriksson) ; 4,393,983 (Eriksson) ; 4,586,665 (Eriksson); 4,732,335 (Eriksson) ; 4,732,336 (Eriksson); and 4,655,406 (Eriksson) . The disclosures of these patents are incorporated by reference herein. Turning back to Figure 1, in the device 2, the ink particles, including laser jet ink particles are dispersed and reduced to size whereby about 90% or greater of the particles, after working in the device 2, have particle diameters of about 160 microns or less. The high solids content pulped and dispersed ink mixture 3 is then diluted to a solids concentration of about 2 to 3% and forwarded to purge screen 4 located downstream from device 2. Screen 4 has apertures that are suitably sized to remove larger debris and waste from the process stream so that the slurry can be pumped and processed further.

After the process slurry is forwarded through the purge screen, it may be diluted to a solids consistency of about 1-1/2 to 2% and is then injected into a liquid cyclonic cleaner 6 of the type well known in the art in which liquids/solids separation is effected via centrifugal action with the higher specific gravity articles "the heavies" exiting at the bottom and the desired, cleaned pulped slurry leaving at the top of the device. These devices are commercially available from The Black Clawson Company, Middletown, Ohio under the "Ultra-Clone" trademark.

The slurry is then fed to coarse screen 8 and fine screen 10 located downstream from liquid cyclone cleaners 6. The coarse screen may for instance comprise screen openings of about .050 inches to .125 inches and the fine screen having openings of about .004 to .010 inches. Located downstream from screen 10 is a wet separation step, namely air froth flotation device 12. This may for example be a IIM-BC Flotator available from Black Clawson. This device comprises air inlet 24 which forms bubbles in the vat to aid in floating ink and other floatable contaminants to the surface of the liquid where they are separated via weir 22. The separation efficacy of these machines benefits the formation of small particle sizes and from good separation of the particles from the paper fibers. The slurry may then be further diluted to about

0.5% to 1.0% solids and fed to liquid cyclonic cleaner stations 14,16, which may comprise, respectively, "X-Clone" and "Ultra-Clone" cyclonic cleaners available from Black Clawson. These, of course, provide further cleaning, removing ink and other contaminants that may remain in the slurry.

As shown, the slurry exiting cyclone cleaning station 16 is forwarded to washer 18 which may, for instance, be a "D.N.T." washer available from Black Clawson. Here the influent slurry is usually fed to the washer at about .5% to 1.0% solids with the resulting washed paper stock 20 exiting the washer being on the order of about 9 to 12% solids. The washed stock 20 is ready for paper forming operations or bleaching and/or neutralizing processes prior to paper formation.

In another embodiment (not shown) the high solids content viscous mixture exiting station 2 may be diluted and then fed through a coarse screen followed by a fine screen. Then, it may be fed through a cyclonic cleaner train similar to 14,16 shown in Fig. 1, followed then by a flotation cell 12 and washer 18.

It is to be understood that in accordance with one aspect of the invention, the office waste paper containing secondary fibers is fed to the pulping and dispersion station 2 without any need for pre-pulping whatsoever (i.e. there is no pulping station upstream from station 2) . Additionally, it is noted that the waste paper may be fed to station 2 in the form of bales, without any pretreatment, or it may be sorted, shredded or in loose form. If desirable, chemical additives, gases, or steam may be added before or during the step of simultaneous pulping and dispersing at station 2.

It is apparent that the disclosed process eliminates or drastically reduces the need for traditional multiple thicken, disperse and float method steps. Stated differently, after the simultaneous pulping and dispersing step, no subsequent ink dispersion step is needed prior to formation of the paper stock 20. Also, save for the use of the washer 18 to form the paper stock 20, no additional washing or thickening is required.

While the invention has been described primarily with regard to its use in conjunction with office waste paper, it is noted that other recyclable fiber sources may be included. For example, old magazines and old newspapers may also be processed in accordance with the invention. All of these are within the scope of the phrase "secondary fibers" which phrase should be construed to include all non-virgin fiber sources.

Additionally, although the present disclosure has emphasized the desirable attributes of simultaneously pulping and deinking secondary fibers, the invention can be more generally viewed as involving simultaneous pulping and dispersion of other easily friable contaminants. Included within the ambit of the phrase "friable contaminants" are such items as thermoplastic coatings, varnishes, sizes, plasticizers, as well as the inks including xerographical and laser print inks as referred to above. Accordingly, use of the simultaneous pulping and dispersion step has proven successful in transforming the waste paper into a homogenous mass of substantially discrete fibers, separating adhering particles from the fibers, and dispersing the friable particles throughout the mass so that a large majority (i.e. about 70% and greater, preferably 90% or greater) of the particles are reduced in size to about 160 microns or less in diameter.

While there are shown and described presently preferred embodiments of the invention, it is to be understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

- -CLAIMS- -

1. Method of treating secondary fibers including ink containing waste paper comprising simultaneously pulping said waste paper and dispersing ink particles therefrom in a high solids content aqueous mixture having a solids content of greater than about 20wt% solids, said method being devoid of any step of pre-pulping said waste paper prior to said step of simultaneously pulping and dispersing wherein said step of simultaneously pulping said waste paper and dispersing ink particles therefrom comprises kneading said secondary fibers, said method further comprising subsequent to said step of simultaneously pulping and dispersing, diluting said kneaded secondary fibers with water and subsequently wet separating said ink particles from said diluted secondary fibers, and wherein said method is devoid of any additional step of dispersing said ink.

2. Method of treating secondary fibers including ink containing waste paper comprising simultaneously pulping said waste paper and dispersing ink particles therefrom in a high solids content aqueous mixture having a solids content of greater than about 30 wt.% solids.

3. Method of deinking secondary fibers containing ink particles thereon comprising concurrently pulping said waste paper to form a homogenous mass of substantially discrete fibers and dispersing said ink particles in said mass by kneading said waste paper in a high solids content aqueous mixture comprising at least about 30 wt.% solids.

4. Method as recited in claim 3 further comprising washing said waste paper after said step of concurrently pulping and dispersing, said step of washing being the only washing subsequent to said step of concurrently pulping and dispersing.

5.. Method for making a pulp stock for use in paper making processes; comprising

(a) providing raw waste paper material including ink particles thereon; (b) concurrently pulping said raw waste paper and dispersing said ink particles by kneading said raw waste paper in a high solids aqueous mixture having at least about 30 wt.% solids to form a waste paper pulp; and

(c) subsequently diluting said waste paper pulp formed as a result of said step (b) .

6. Method as recited in claim 5 wherein subsequent to said step (c) said process is devoid of any additional step of dispersing said ink and laser printed particles prior to formation of said paper stock.

7. Method as recited in claim 6 wherein subsequent to said step (c) said process comprises washing (d) said diluted waste paper pulp, said washing step (d) being the sole washing step performed in said process subsequent to said step (b) and prior to formation of said paper stock.

8. Method as recited in claim 5 further comprising wet separating solids from said diluted waste paper pulp formed as a result of step (c) .

9. Method as recited in claim 8 wherein said separating comprises passing said diluted waste paper pulp formed as a result of step (c) through a cyclonic cleaner.

10. Method of treating waste paper having friable contaminants components thereon, said method comprising simultaneously pulping said waste paper and dispersing said friable contaminants in an aqueous mixture having a solids content of greater than about 30% solids.