WO1995012550B1

WO1995012550B1 - Deinking of recycled pulp

Info

Publication number: WO1995012550B1
Application number: PCT/US1994/012666
Authority: WO
Filing date: 1994-11-04
Publication date: 1995-06-08
Anticipated expiration: 1996-05-04

Abstract

A process for separating printing ink from recycled paper fiber (20) includes the steps of repulping recycled paper furnish with water in a rotary mixer (10) for about 5 minutes at a consistency of 6 % to 18 % with a mixing element (16) having a top speed no greater than 2,000 ft/min. This first stage repulping and mixing is followed by a second mixing stage of 20 to 45 minutes with a mixing element tip speed 2,500 to 4,000 ft/min. Agglomerated contamination particles in the resulting slurry are removed by centrifugal cleaning and slot screening (18).

Claims

AMENDED CLAIMS [received by the International Bureau on 12 May 1995 (12.05.95); original claims 1, 5, 9, 10, 17, 18 and 22 amended; remaining claims unchanged (5 pages)]

Claim 1. in a process for recovering fiber constituents from recycled fibrous cellulose material containing ink particles and other contaminants to be separated from the recovered fiber constituents which involves forming an aqueous slurry containing the recycled fibrous cellulose material and mixing the slurry with a mechanical agitator rotated about a substantially vertical axis to reduce the cellulose material to liberate fiber and contaminant particles therefrom into the slurry, the improvement which comprises mixing the slurry in a first blending stage at a relatively low agitator velocity for a first time interval and mixing the slurry in a second blending stage at a relatively high velocity of the same agitator as compared to that of the first blending stage and for a second time interval substantially longer than that of the first blending stage, whereby the ink particles and other contaminants in the resulting slurry are more readily separated from said fiber constituents.

Claim 2. The process of Claim 1 wherein said second blending stage time interval follows said first blending stage time interval.

Claim 3. The process of Claim l, wherein the slurry has a consistency of between about 6% and 18% .

Claim 4. The process of Claim 1, further comprising the step of adding an agglomeration agent to the slurry.

Claim 5. The process of Claim 1, wherein said relatively low velocity of said agitator is provided by a rotor having a tip speed of leββ than about 2000 ft/minute and said relatively high velocity includes a rotor tip speed of greater than about 2500 ft/minute.

Claim 6 The process of Claim 1 wherein said mechanically rotating agitation means comprises a turbine type rotor.

Claim 7. The process of Claim l wherein said ink particles and other contaminants are separated from said fiber constituents by screening and centrifugal cleaning.

Claim 8. The process of Claim 7 wherein said ink particles and other contaminants are separated by screens having 0.004 in. to 0.010 in. slotted openings.

Claim 9. The process of Claim 1, wherein ink particles and other contaminants separated from said slurry are agglomerated to an average particle size of at least about 0.15mm² and at least about 30% of such agglomerated particles are larger than about 0.10 mm².

Claim 10. A process for separating ink particles and other contaminants from the fiber constituency of recycled paper comprising the steps of forming an aqueous slurry from recycled cellulosic fiber sources having printing ink and other contaminants combined therewith, mixing said slurry with agitation means rotating about a substantially vertical axis at a first rotational velocity for such a period of time as to cause particles of said ink and other contaminants to separate from respective fiber support followed by mixing said slurry at a second rotational velocity of said agitation means to agglomerate separated ink and other contamination particles into and with larger contamination particles; and separating agglomerated ink and other contamination particles from the remainder of said slurry.

Claim 11. The process of Claim 10, wherein the slurry has a consistency of between about 6% and 18%.

Claim 12. The process of claim 10, further comprising the step of adding an agglomeration agent to the slurry.

claim 13. The process of claim ιo, wherein said first rotational velocity of said agitation means Is provided by a rotor having a tip speed of less than about 2000 ft/minute and said second rotational velocity includes a rotor tip speed of greater than about 2500 ft/minute.

Claim 14. The process of Claim 10 wherein said mechanically rotating agitation means comprises a turbine type rotor.

Claim 15. The process of Claim 10 wherein said agglomerated contamination particles are separated from the remainder of said slurry by screening and centrifugal cleaning.

claim 16. The process of Claim 15 wherein said agglomerated contamination particles are separated by screens having 0.004 in. to 0.010 in. slotted openings.

Claim 17. The process of Claim 10, wherein the average size of the agglomerated ink and other contamination particles separated from said slurry is at least about 0.15 mm² and at least about 30% of the agglomerated particles are larger than about 0.10 mm².

Claim 18. A process for recycling papermaking fiber having printer's ink and other contaminants combined therewith, said process comprising the steps of combining paper and water in a repulping vessel that is agitated by a vertical axis rotary mixing element, said paper including fiber support of ink and other contaminants; mixing said paper, water, ink and contaminants in said vessel to a slurry consistency of about 6% to about 18% at a mixing element tip speed of no greater than 2000 ft/minute for a first interval of time sufficient to εeparate ink and other contaminants from corresponding paper fiber support; increasing the tip speed of said mixing element to at least 2500 ft/minute for a second period of time sufficient to agglomerate ink and other particulate contaminants to an average agglomerated particle size of about 0.15 mm² or greater whereby at least 30% of said agglomerated particles are larger than about 0.10 mm²; and, separating said agglomerated particles from said slurry.

Claim__19. A process for recycling papermaking fiber as described by Claim 18 wherein said rotary mixing element is a turbine type rotor.

Claim_20. A process for recycling papermaking fiber as described by Claim 18 wherein said agglomerated particles are separated from said slurry by screening and centrifugal cleaning.

Claim 21. A process for recycling papermaking fiber as described by Claim 20 wherein said agglomerated particles are separated by screens having 0.004 in. to 0.010 in. slotted openings.

Claim 22. In a process for recycling the fiber constituency of printed paper having ink and other contaminants combined therewith wherein said ink contaminated paper is combined with water of approximately 130*F to 180ºF in a mixing vessel having a vertical axis rotary mixing element to form a slurry of about 6% to about 18% consistency to separate particles of ink and other contaminants from corresponding fiber support and subsequently screening and centrlfugally segregating said ink and other contaminant particles from said slurry, the improvement comprising the steps of driving said mixing element at a tip speed of no greater than 2000 ft/minute for an initial slurry mixing interval to separate said particles of ink and other contaminants from corresponding fiber support and subsequently increasing said mixing element tip speed to at least 2500 ft/minute for agglomeration of said fiber separated particles into larger combinations of said particles.

Claim 23. in a process for recycling the fiber constituency of printed paper as described by Claim 22 wherein said rotary mixing element is a turbine type rotor.

Claim 24. in a process for recycling the fiber constituency of printed paper as described by Claim 22 wherein said ink and other contaminant particles are segregated from said slurry by screens having 0.004 in. to 0.010 in slotted openings.

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STATEMENT UNDER ARTICLE 19

The present application was filed with 24 claims. Claims 1, 5, 9, 10, 17, 18 and 22 have been amended as set forth above to more particularly distinguish applicant's invention from unrelated prior art.

Applicant's invention relates to a hydrodynamic process for segregating ink particles from recycled paper. As described by the present amendments to applicant's claims, an aqueous slurry of fibrous material is formed by mixing recycled paper with water using a mechanical agitator rotated about a vertical axis. The agitator is driven at a relatively low agitator velocity for one mixing interval to liberate ink particles and other such contaminants from fiber substrate and at a relatively higher agitator velocity for another mixing interval resulting in more effective agglomeration of the liberated particles of ink and contaminants.

On a very basic level, practice of Applicant's invention requires at least a two-speed mixing vessel agitator drive.

The Holz et al reference cited in the International Search Report as relevant to applicant's invention does not mention deinking. The first stage of the Holz et al process is dry shredding. From the shredder, the paper shards enter a horizontal axis tumbler 30 for high consistency wetting. From the tumbler, pulp advances into a rub 70. The tub is agitated by a single speed rotor.

Holz et al relates no particular operating parameter to the separation or agglomeration of ink particles and other such contaminants. Furthermore, Holz et al reveals no multiple speed capacity respective to the vertical axis motor 84 or mixer wheel 82. Therefore, Holz et al fails to teach even the most rudimentary process elements of Applicant's invention. More importantly, the Holz εt al objectives are completely foreign to the deinking objectives of applicants' invention. Henricson et al '736 describes a waste paper repulping apparatus having a vertical axis rotating agitator. Additionally, the '736 Henricson et al apparatus includes an internal recirculation pump for high consistency (8% to 12%) repulping. Henricson et al '736 discloses no rotational speed change capacity for their vertical axis mixing element. Consequently, Henricson et al '736 could neither teach nor suggest a change in the same mixing element tip speed respective to successive mixing stages or any effect of this on the agglomeration of ink and other contamination particles. Moreover, Henricson et al '736 is not a deinking process disclosure. Henricson et al '736 is devoted exclusively to paper repulping as opposed to the separation of ink particles from a repulped slurry.

Henricson et al '444 likewise includes no mention of ink particle separation from a pulp slurry. The "cleaning" and "screening" described by Henricson et al '444 is directed to knots, shives and fiber bundles which are undesirable materials in a pulp slurry that are highly distinct from ink particles. The cleaning and screening system includes no repulping machine and, in particular, no variable speed, vertical axis, rotating agitators. The Henricson et al '444 cleaners are hydrodynamic centrifuges.

Thompson et al is directed to a waste paper deinking process wherein ink particles are first dislodged from wastepaper fiber by "dry fiberization". Thereafter, the fiberized material is slurried with water and agitated in a high consistency pulper or by disk refining to promote agglomeration. Thompson et al provides only a vague description of a "fiber kneading device" by which the fiber slurry is agitated. Thompson provides no suggestion of the two-stage mixing of a slurry batch by a vertical axis rotary agitator as set forth in Applicant's claims.

Thus, of the four references cited by the International Search Report as relevant to Applicant's claimed invention, only the Thompson et al reference relates to removing ink from paper fiber. However, Thompson et al does not even remotely suggest Applicant's two speed agitator process for promoting the agglomeration of ink and other contamination particles. Since none of the other references disclose either Applicant's process objective or equipment capable of carrying out that process objective, it necessarily follows that Applicant's invention is not an "obvious" combination of the references or in any way suggested by them.