METHOD FOR PROCESSING MIXTURES OF SECONDARY FIBERS AND MECHANICAL PULPS

METHODE DE TRAITEMENT DE MELANGES COMPOSES DE FIBRES SECONDAIRES ET DE PATE MECANIQUE

English 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.

Claims

The embodiments of the invention in which an exclusive property or privilege is
claimed are defined as follows:

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.

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

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~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.