CA2036313C

CA2036313C - Method for processing mixtures of secondary fibers and mechanical pulps

Info

Publication number: CA2036313C
Application number: CA 2036313
Authority: CA
Inventors: Kwei-Nam Law
Original assignee: Individual
Current assignee: LAW KWEI NAM
Priority date: 1991-02-14
Filing date: 1991-02-14
Publication date: 1995-12-12
Anticipated expiration: 2011-02-14
Also published as: CA2036313A1

Abstract

A novel method, based on the rubbing action in a refiner, for disintegration and deinking mixtures of recovered or secondary fibers, primarily used newspapers and printing-writing papers, and mechanical pulps, such as stone groundwood pulp, refiner mechanical pulp, thermomechanical pulp, chemithermomechanical pulp and chemimechanical pulp, permitting to produce a new grade of pulp furnish of better quality and more economical for the production of newsprint without the use of conventional deinking equipment, is described.

Description

~ 2036313 METHOD FOR PROCESSING MIXTURES OF
SECONDARY FIBERS AND MECHANICAL PULPS

BACKGROUND OF THE INVENTION
This invention relates to a method for processing secondary fibers, particularly from used newspaper and printing-writing paper, wherein said secondary fibers are processed in mixtures of mechanical pulps such as s~one groundwood, refiner mechanical, thermomechanical, chemith~rmomechanical and chemimechanical pulps.
A secondary fibers recycling process usually consists of three main steps:
deinking the raw material or used paper, removal of cont~min:~nt~ such as org~nic and inorganic foreign materials and separation of ink particles from fibers. Thedeinking stage is a chemi-thermo-mechanical process in which the raw m~t~i~l~
are subjected to chemical and mechanical actions in an aqueous milieu at an elevated temperature. The deinking stage lasts from about 30 to 60 minutes Or longer and the gentle mechanical agitation of the relatively dilute pulp slurry is not efficient to dislodge all ink particles from the fibers and to completely di.h~te~d~e the raw material. The incomplete deinking effect would reduce pulp quality, while the inadequate disintegration of the raw material would require addittonal mechanical treatment.

THEORY OF THE INVENTION
The present invention is based in part upon the theory that the rubbing action in a refiner between stiff mechanical pulp fibers and softer and ~ore flexible secondary fibers can improve the deinking and disintegration efficiency of the latter, that co-refining help develop fiber properties of both the mechanical ?
-~363~
pulp and the secondary fibers, and that in-refiner bleaching can improve brightness of the resulting pulp furnish. The benefits derived are:
(a) good quality furnish for the m~nllf~çtllre of new~.inl, (b) lower capital and operatiing t;~enses than those associated with a separate mechanical pulping line and a separate secondary ~lbers processing line;
(c) this hybrid process can be incoporated into the existing mills producing newsprint furnish.

SUMMARY OF THE INVENTION
The objective of this invention is to produce novel fibrous pulps suitable for newsprint production from mechanical pulps and secondary fibers. According to this invention, the mechanical pulps can be a stone groundwood pulp, a refiner mechanical pulp such as che.~ h~ni~l, chçmithc. "I~"~fch~nir~l and thermomechanical pulps. The said secondary f1bers comprise principally used newspaper ;md used printing and writing papers.
In accordance with the theory of the present invention the ref~rred mechanical pulps are produced in the manner known to the pulp and paper industry and are washed to remove the residual chemicals that may present in thepulping process and the extractives such as fatty acid, resin and other soluble materials from the pulp in order to improve the subsequent treatment stages. Themechanical pulps are then thickened to a predetermined consistency prio~ to subsequent blending with the secondary fiber raw materials. The referred seconda,~
fiber raw m~tl ri~lc are first disintegrated in a pulper, cleaned to remove the heavy rejects such as metals, sand and plastics, etc., and thickened to a predet~.rmined consistency prior blending with the referred mechanical pulps. The treated 2~ 3~ 3~3 secondary fiber raw materials are blended, in various proportions according to the desired product quality, with the thickened mechanical pulps. In the mixing stage, bleaching chemicals such as hydrogen peroxide, sodium hydroxide, sodium silicate, Magnesium sulfate andlor the chelating agents such as DTPA (diethylene triaminepentaacetic acid) and EDTA (ethylene diaminetetraacetic acid) are added to improve the pulp brightness as well as the deinking efficiency. The pulp mixtureimpregnated with bleaching agents is preheated to a temperature suitable for thebleaching reaction to occur, prior to be refined in an industrial refiner in one or more stage(s) under atmospheric pressure. The refined mixture is then screened to eliminate large rejects, cleaned to remove dirts, and washed to separate the dislodged ink particles from the fibers. The washed pulp furnish is then delivered to the papermaking line.

DESCRIPTION OF THE INVENTION
The process according to the invention can be carried out in the manner illustrated in flow diagram 1, wherein a mechanical pulp 2 preferably having a freeness (drainage) of about 150 mL or higher (C~n~ n standard freeness) is washed 4 and thickened 6 in ways known to the pulp and paper industry, and wherein a raw material 8 of secondary fibers preferably of used n~w~apel and/or used printing and writing papers is dishltegrated 10 in a standard e~luiplllent known as pulper, cleaned 12 using a heavy rejects cleaner or high density cleaner known to the secondary fibers industry, and thickened 14 in a manner known in the prior art. The said mechanical 6 and the said secondary fibers raw material 14 are 2S blended 16 together in various proportions according to the desired properties of the end product. In the blending stage 16, a bleaching solution 18 containing, in cc,mbillalion, hydrogen perioxide, sodium hydroxide, sodium silicate, magnesium ~G~6313 sulfate, chelating agent such as ethylene diaminetetraaceatic acid (EDTA) or diethylene triaminepentacetic acid (DTPA), and/or soap and detergent. The said impregnated pulp mi~ c; 16 is preheated 20 to a temperature ranging from about 30C to about 90C, preferably about 60 to 80C, which is suitable for the bleaching reaction to occur, and for a time from about S to 60 minutes, preferably for about 10 to 20 minlltes. The preheated pulp mi~ e 20 is refined 22, under atmospheric pressure, in an industrial refiner suitable for carrying out secondary refining, in accordance with the refining conditions known to the pulping industry.
The refined pulp mi~lule 22 is screened 24 in a known way to elimin~te the largerejects, cleaned 26 with known equipments to remove the dirts, and washed 28 using known techniques to separate the dislodged ink particles from the fibrous m~t-ri~l The said washed furnish 28 is suitable for papermaking such as newspl;llt manufacture.

Claims

1. A process for the treatment of secondary fiber raw materials with mechanical pulps, wherein said secondary fiber raw materials are disintegrated, cleaned and blended, bleached and refined with said mechanical pulps.

2. A process according to claim 1, wherein said secondary fiber raw materials are principally used newspaper and used printing and writing papers.

3. A process according to claim 1, wherein said mechanical pulps comprise stone groundwood pulp, refiner mechanical pulp, thermomechanical pulp, chemithermomechanical pulp, chemimechanical pulp made from lignocellulose-containing materials such as softwoods and hardwoods.

4. A process according to claim 1, wherein said secondary fiber raw materials are, prior to bleaching and refining, disintegrated and cleaned to remove the heavy rejects such as metals, sands and rocks, and plastic materials, etc.

5. A process according to claim 1, wherein said cleaned secondary fiber raw materials are blended with said mechanical pulps, prior to said bleaching and said refining, to give a mixed furnish.

6. A process according to claim 1, wherein said mixed furnish is impregnated with a bleaching solution containing, in combination, hydrogen peroxide, sodium hydroxide, sodium silicate, magnesium sulfate, chelating agent such as diethylene triaminepentaacetic acid (DTPA) or ethylene diaminetriacetic acid (EDTA), and soap or detergent.

7. A process according to claim 1, wherein said chemical impregnated mixed furnish is preheated by steaming or microwaving or other heating means to a temperature ranging from about 30°C to about 90°C, preferably from about 60°C to about 80°C, and for a time ranging from about 5 to 60 minutes, preferably for about 10 to 20 minutes.

8. A process according to claim 1, wherein said heated mixed furnish is refined, under atmospheric pressure, in one or more stage(s).

9. A process according to claim 1, wherein said refined mixed furnish is screened to eliminate large rejects, cleaned to remove dirts and washed to separate the dislodged ink particles from said mixed furnish.