U.S. patent number RE36,424 [Application Number 09/012,245] was granted by the patent office on 1999-12-07 for method for producing pulp from printed unselected waste paper.
Invention is credited to Jean-Marie Clement.
United States Patent |
RE36,424 |
Clement |
December 7, 1999 |
Method for producing pulp from printed unselected waste paper
Abstract
A waste paper recycling process relates to the treatment of a
mixture of waste paper containing non-cellulosic contraries and
printing inks, in order to release the contraries from the fibers
and further to separate them from the stock in order to produce
re-usable pulp for the production of paper and board. The invention
has to do with new and useful improvements in methods for first
removing the non-ink contraries from the fibrous mass and second
releasing and then removing the ink particles from the said fibrous
mass. The invention is directed to the treatment of the fiber
slurry produced during the ink separation stage, after the ink
releasing stage has been applied. One aim of the process is to
allow both the use of the fibers and the mineral fillers contained
in that slurry, for pulp and board making, and the use the
solids-free water contained in the same slurry as the washing
liquid in the previous ink-separation treatment, thus closing the
fibers and the water circuits. This process includes chemical and
thermo-mechanical treatments, starting under alkaline conditions,
which may become neutral at the end of the process.
Inventors: |
Clement; Jean-Marie (20147
Milano, IT) |
Family
ID: |
11303060 |
Appl.
No.: |
09/012,245 |
Filed: |
January 22, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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054951 |
Apr 27, 1993 |
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600012 |
Oct 18, 1990 |
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482623 |
Apr 6, 1983 |
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Reissue of: |
822943 |
Jan 27, 1986 |
04780179 |
Oct 25, 1988 |
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Foreign Application Priority Data
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Apr 19, 1982 [IT] |
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67514/82 |
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Current U.S.
Class: |
162/5; 162/55;
162/8; 162/7 |
Current CPC
Class: |
D21B
1/325 (20130101); D21B 1/32 (20130101); D21C
5/025 (20130101); Y02W 30/646 (20150501); Y02W
30/64 (20150501); Y02W 30/648 (20150501) |
Current International
Class: |
D21B
1/00 (20060101); D21B 1/32 (20060101); D21C
5/02 (20060101); D21F 005/02 () |
Field of
Search: |
;162/4,5,7,8,55 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1078557 |
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Jun 1980 |
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CA |
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92124 |
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Oct 1983 |
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EP |
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1031536 |
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Jan 1951 |
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FR |
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2417580 |
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Feb 1978 |
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FR |
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2406692 |
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Oct 1978 |
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FR |
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2421241 |
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Mar 1979 |
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FR |
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2433609 |
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Jul 1979 |
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FR |
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2441680 |
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Nov 1979 |
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FR |
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1761864 |
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Feb 1971 |
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DE |
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2413159 |
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Oct 1974 |
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DE |
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2413278 |
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Nov 1975 |
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DE |
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26641 B2 |
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Sep 1975 |
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JP |
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20563 B2 |
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Jun 1977 |
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JP |
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40850 |
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Mar 1980 |
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JP |
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7512806-6 |
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May 1979 |
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SE |
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689 278 |
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Mar 1953 |
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GB |
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1463776 |
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Feb 1977 |
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GB |
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1525947 |
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Sep 1978 |
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GB |
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2017780 |
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Oct 1979 |
|
GB |
|
2030186 |
|
Apr 1980 |
|
GB |
|
2036603 |
|
Jul 1980 |
|
GB |
|
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|
Primary Examiner: Hastings; Karen M.
Attorney, Agent or Firm: Wolf, Greenfield & Sacks,
P.C.
Parent Case Text
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of reissue application Ser. No.
08/054,951 filed Apr. 27, 1993, entitled METHOD FOR PRODUCING PULP
FROM PRINTED UNSELECTED WASTE PAPER, now abandoned, which is a
continuation of reissue application Ser. No. 07/600,012, filed Oct.
18, 1990, now abandoned, which is an application for reissue of
U.S. Pat. No. 4,780,179 issued Oct. 25, 1988, which
.Iaddend..[.This.]. is a continuation of co-pending application
Ser. No. 482,623 filed on Apr. 6, 1983, now abandoned.
Claims
I claim:
1. A method of treating a mixture of printed and contaminated waste
paper in order to produce a pulp for use in the manufacture of
paper and paperboards, said waste paper containing non-ink
contaminants including stickies, which method comprises:
(a) forming a first aqueous fibrous suspension of said waste paper
at room temperature by applying specific mechanical energy lower
that 50 KW.H/Ton to form a pumpable slurry and to release
substantially all of the non-ink contaminants including the
stickies, from the surface of the paper and without dispersing such
non-ink contaminants as finely divided particles throughout the
fibrous suspension;
(b) removing substantially all of the non-ink contaminants
including the stickies, which have been released without dispersal
as finely divided particles from the first fibrous suspension by
screening and cleaning at room temperature to form a second aqueous
fibrous suspension substantially free of the non-ink contaminants
including the stickies;
(c) after the step of removing the non-ink contaminants softening
the ink vehicles and weakening their binding with the surface of
the fibers by submitting the second fibrous suspension at a
consistency of more than 15% to the simultaneous actions of (A) a
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one deinking agent under strong
alkaline conditions having a pH of at least 9; and
(d) detaching the ink particles from the surface of the fibers and
dispersing them into the second fibrous suspension by submitting
the second fibrous suspension to the simultaneous actions of (A)
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more that 15% and (C) at least one chemical dispersing agent, under
strong alkaline conditions having a pH of at least 9 whereby higher
specific energy inputs and higher temperatures are used to detach
the ink particles from the fibers of the second fibrous suspension
after removal of the non-ink contaminants than are used on the
first fibrous suspension before removal of the non-ink
contaminants;
(e) limiting the total duration of the ink softening and detaching
steps (c) and (d) to a range between 2 and 10 minutes and
(f) removing the detached ink particles from the second fibrous
suspension to provide a brightness of at least 59 ISO the final
pulp.
2. The method of claim 1 wherein the specific energy applied to the
fibrous suspension during the forming step (a) is applied for
approximately 20 minutes.
3. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are conducted at a pressure higher than the
atmospheric pressure.
4. The method of claim 1 wherein the total duration of the ink
softening and detaching steps (c) and (d) is kept between 3 and 5
minutes.
5. The method of claim 1 wherein the total specific energy applied
during the ink softening and detaching steps (c) and (d) is about
80 KW.H/Ton.
6. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are performed simultaneously in a single
apparatus.
7. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are performed separately in two different pieces
of equipment.
8. The method of claim 1 wherein the removing of the ink particles
from the fibrous suspension is achieved by washing.
9. The method of claim 1 wherein the alkalinity of the fibrous
suspension in steps (c) and (d) is obtained by adding any one of
the following chemicals:
sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium
hydroxide, sodium carbonate, sodium phosphate, sodium
tripolyphosphate, sodium pyrophosphate, sodium silicate.
10. The method of claim 1 wherein an oxidizing agent is added
during the ink softening and detaching steps (c) and (d).
11. The method of claim 1 wherein a bleaching action is performed
during the ink softening and detaching steps (c) and (d).
12. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are performed simultaneously in a triturator.
13. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are performed simultaneously in a
disintegrator.
14. A method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are performed separately in a steaming chamber
followed by a disperser.
15. The method of claim 1 wherein the step of removing the ink
particles from the fibrous suspension is achieved by froth
flotation.
16. The method of claim 1 wherein the step of removing the ink
particles from the fibrous suspension is achieved by washing and
froth flotation.
17. The method of claim 1 wherein the alkalinity of the fibrous
suspension in steps (c) and (d) is obtained by adding a mixture of
chemicals selected from the group consisting of, sodium hydroxide,
potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium
carbonate, sodium phosphate, sodium tripolyphosphate, sodium
pyrophosphate, sodium silicate.
18. The method of claim 1 wherein the ink softening and detaching
steps (c) and (d) are achieved at a consistency between 25% and
30%. .Iadd.
19. A method of treating a mixture of printed and contaminated
waste paper in order to produce a pulp for use in the manufacture
of paper and paperboards, said waste paper containing non-ink
contaminants including stickies, which method comprises:
(a) forming a first aqueous fibrous suspension of said waste paper
at ambient temperature by applying specific mechanical energy lower
than 50 KW.H/Ton to form a pumpable slurry and to release
substantially all of the non-ink contaminants including the
stickies, from the surface of the paper and without dispersing such
non-ink contaminants as finely divided particles throughout the
fibrous suspension;
(b) removing substantially all of the non-ink contaminants
including the stickies, which have been released without dispersal
as finely divided particles from the first fibrous suspension by
screening and cleaning at ambient temperature to form a second
aqueous fibrous suspension substantially free of the non-ink
contaminants including the stickies;
(c) after the step of removing the non-ink contaminants, softening
the ink vehicles and weakening their binding with the surface of
the fibers by submitting the second fibrous suspension at a
consistency of more than 15% to the simultaneous actions of (A) a
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more then 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one deinking agent under strong
alkaline conditions having a pH of at least 9;
(d) detaching the ink particles from the surface of the fibers and
dispersing them into the second fibrous suspension by submitting
the second fibrous suspension to the simultaneous actions of (A)
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one chemical dispersing agent, under
strong alkaline conditions having a pH of at least 9 whereby higher
specific energy inputs and higher temperatures are used to detach
the ink particles from the fibers of the second fibrous suspension
after removal of the non-ink contaminants than are used on the
first fibrous suspension before removal of the non-ink
contaminants;
(e) limiting the total duration of the ink softening and detaching
steps (c) and (d) to a range between about 1 and 5 minutes; and
(f) removing the detached ink particles from the second fibrous
suspension to provide a brightness of at least 59 ISO to the final
pulp..Iaddend..Iadd.20. A method of treating a mixture of printed
and contaminated waste paper in order to produce a pulp for use in
the manufacture of paper and paperboards, said waste paper
containing non-ink contaminants including stickies, which method
comprises:
(a) forming a first aqueous fibrous suspension of said waste paper
at a low temperature by applying specific mechanical energy lower
than 50 KW.H/Ton to form a pumpable slurry and to release
substantially all of the non-ink contaminants including the
stickies, from the surface of the paper and without dispersing such
non-ink contaminants as finely divided particles throughout the
fibrous suspension, the low temperature being sufficiently low to
maintain rigidity of non-ink contaminants having a lowest melting
point so that the lowest melting point non-ink contaminants will
not extrude through screens;
(b) removing substantially all of the non-ink contaminants
including the stickies, which have been released without dispersal
as finely divided particles from the first fibrous suspension by
screening and cleaning at the low temperature to form a second
aqueous fibrous suspension substantially free of the non-ink
contaminants including the stickies;
(c) after the step of removing the non-ink contaminants softening
the ink vehicles and weakening their binding with the surface of
the fibers by submitting the second fibrous suspension at a
consistency of more than 15% to the simultaneous actions of (A) a
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one deinking agent under strong
alkaline conditions having a pH of at least 9;
(d) detaching the ink particles from the surface of the fibers and
dispersing them into the second fibrous suspension by submitting
the second fibrous suspension to the simultaneous actions of (A)
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one chemical dispersing agent, under
strong alkaline conditions having a pH of at least 9 whereby higher
specific energy inputs and higher temperature are used to detach
the ink particles from the fibers of the second fibrous suspension
after removal of the non-ink contaminants than are used on the
first fibrous suspension before removal of the non-ink
contaminants;
(e) limiting the total duration of the ink softening and detaching
steps (c) and (d) to a range between about 1 and 5 minutes; and
(f) removing the detached ink particles from the second fibrous
suspension to provide a brightness of at least 59 ISO to the
final
pulp..Iaddend..Iadd.21. A method of treating a mixture of printed
and contaminated waste paper in order to produce a pulp for use in
the manufacture of paper and paperboards, said waste paper
containing non-ink contaminants including stickies, which method
comprises:
(a) forming a first aqueous fibrous suspension of said waste paper
at a low temperature by applying specific mechanical energy lower
than 50 KW.H/Ton to form a pumpable slurry and to release
substantially all of the non-ink contaminants including the
stickies, from the surface of the paper and without dispersing such
non-ink contaminants as finely divided particles throughout the
fibrous suspension, the low temperature being sufficiently low to
maintain rigidity of non-ink contaminants having a lowest melting
point so that the lowest melting point non-ink contaminants will
not extrude through screens;
(b) removing substantially all of the non-ink contaminants
including the stickies, which have been released without dispersal
as finely divided particles from the first fibrous suspension by
screening and cleaning at the low temperature to form a second
aqueous fibrous suspension substantially free of the non-ink
contaminants including the stickies;
(c) after the step of removing the non-ink contaminants softening
the ink vehicles and weakening their binding with the surface of
the fibers by submitting the second fibrous suspension at a
consistency of more than 15% to the simultaneous actions of (A) a
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% and (C) at least one deinking agent under strong
alkaline conditions having a pH of at least 9;
(d) detaching the ink particles from the surface of the fibers and
dispersing them into the second fibrous suspension by submitting
the second fibrous suspension to the simultaneous actions of (A)
high temperature between 85.degree. and 130.degree. C., (B) high
shear forces substantially corresponding to a specific mechanical
energy of more than 50 KW.H/Ton applied at the said consistency of
more than 15% And (C) at least one chemical dispersing agent, under
strong alkaline conditions having a pH of at least 9 whereby higher
specific energy inputs and higher temperature are used to detach
the ink particles from the fibers of the second fibrous suspension
after removal of the non-ink contaminants than are used on the
first fibrous suspension before removal of the non-ink
contaminants;
(e) limiting the total duration of the ink softening and detaching
steps (c) and (d) to a range between 2 and 10 minutes; and
(f) removing the detached ink particles from the second fibrous
suspension to provide a brightness of at least 59 ISO to the final
pulp..Iaddend.
Description
FIELD OF THE INVENTION AND REVIEW OF THE PRIOR ART
Recycling of waste paper is possible only after most of the non
cellulosic contaminants have been removed from the fiber mass.
These contaminants may have been introduced during the printing
steps (carbon black, pigments, ink vehicles, ink fixating polymers,
etc. . . ), during converting, (varnishes, coats, binders,
wrapping, etc. . . ) and later during the collecting phase
(metallic pieces, plastics, soils and dirt of any kind).
Removing of the contraries generally occurs based on chronological
dimensional sequences, through screening, magnetic separation,
first in dry conditions and later in aqueous suspension.
The fiber mass is then screened through perforated plates and finer
contraries are removed by centrifugal and centripetal cleaners.
The ink particles are not substantially removed during the
preceding steps, and this operation is achieved in two steps: (a)
detaching the ink particles from the fiber surface, through the
combined action of chemicals, temperature and mechanical shear
forces and (b) removing these particles from the pulp slurry.
Generally, all the contraries including the ink particles, are
released from the fibers during the defibering phase. The waste
paper is treated in a pulper, under alkaline conditions at
50.degree.-60.degree. C. temperature, in order to be well defibered
and transformed into a pumpable slurry. An alternative to this
process is to operate the pulper in cold conditions, then thicken
the pulp above 15% consistency, then heat the pulp with steam at
60.degree. C. introducing at that point the de-inking and bleaching
chemicals. The pulp then remains in a reaction tower during 2-3
hours without any mechanical action.
The first drawback of these techniques is that all contaminants are
submitted to the thermal treatment, including the ones which have
low melting points, such as binders, hot melts, plastics and other
"stickies". By this way, they become dispersed and cannot be
removed any more by the conventional means, and will precipitate
again on paper machine elements such as doctor blades, wires,
felts, pipe walls, etc. . . , creating operating problems and loss
of efficiency.
A second drawback is that these ink-releasing techniques have a
weak action on the modern inks such as the rotooffset inks, where
ink vehicles are made of synthetic resins which form an insoluble
polymer on the surface of the fibers. The same consideration
applies for xerocopy printed paper and varnished papers, where
temperatures in the range of 60.degree. C. will provide neither any
softening of the ink vehicles nor any weakening of the bondings
between the fibers and these vehicles.
An other limitation of these techniques is that it is not possible
to increase the temperature of the ink releasing step, because the
combination of the alkalinity and the temperature during a long
time will result in an unacceptable yellowing of the pulp,
specially if some groundwood is present in the mixture to be
treated.
Ink removing techniques in use to-day are essentially two:
floatation and washing.
In flotation, the diluted fiber slurry is intensively mixed with
air after a hydrophobe ink collector has been added. Then stock is
naturally deaereted and air bubbles collect the ink particles
during the upwards travel to the surface. The resulting black foam
is then collected and treated separately through centrifuges, then
disposed of;
In washing, a very old and well known process, the finest dispersed
particles are removed through several dilutions and squeezing
cycles, generally arranged as a counter-current cascade
configuration. The effluent of the first squeezing sequence
contains all the free fine ink particles, but also a great quantity
of fine cellulosic fibers and most of the mineral fillers, and are
sewered and treated according to the local pollution
regulations.
Some other ink removing techniques exist, such as solvent
extraction but have not been followed by wide indutrial
application, due to high production cost and low quality of the
produced pulp.
In the U.S. Pat. No. 4,076,578 Puddington et Al. recall the
fundamental concept of de-inking: (a) releasing ink from the paper
fiber by mean of chemicothermomechanical treatment and (b)
separating of dispersed ink particles from the pulp, then proposes
a different method to achieve this goal, through absorption of the
ink particles onto the surface of solid particles, followed by the
removal of said particles from the pulp, and then removal of the
ink from those solids.
Nowadays, none of the above mentioned processes has asserted itself
because each of them presents some drawbacks.
The flotation is a low consistency process (between 1% and 2%) and
thus involves high volumes of pulp, with consequent high investment
cost. Also, the nature of this process is essentially
physico-chemical and thus its stability is greatly related to the
sability of the composition of the waste paper, the type of fibers
(chemical or mechanical), the type and content of mineral filler,
the calcium ion concentration. Consequently, the brightness of the
de-inked pulp shows undesired high fluctuations. These brightness
variations are also accompanied by all composition variations
coming together with the raw material (waste paper), without any
possibility of control or continuous measurement and
monitoring.
To-day, it is generally admitted that the first condition for the
good operation of a modern fast papermachine is the constancy of
operating parameters, the most important one being the composition
of the stock feeding the machine. Unfortunately, it is not possible
to control the composition of a waste paper lot as easily as a
virgin pulp bale. For this reason, the efficiency decrease of
high-speed paper machines using high percentages of flotation
de-inked pulp is mainly caused by the uncontrolled variations of
the stock composition rather than by the brightness (or de-inking
efficiency) variations. This problem can be solved using selected
classified waste paper, at a price which makes the de-inked pulp
uncompetitive respect to the virgin pulp, assuming that such type
of waste is available.
Finally, the flotation process needs to be continuously controlled,
on a three shift basis, by highly specialized chemical experts
using sophisticated instrumentation and laboratory, thus
appreciably increasing the production cost.
The washing process involves simpler, cleaner, and easier to
control equipment, in particular when washing occurs at
consistencies between 3% and 15%.
This process does not require any specialized control and it is
admitted that not only the quality (cleanliness and strength) of
the washed pulp is definitely higher than for the floated pulp, but
this quality is much more constant and less sensitive to raw
material variations of composition, thus offering a higher
"runability" of the pulp in the paper machine room.
In fact, the principle of washing on a perforated plate
statistically says that elements having a smaller size than the
plate openings should pass through the plate. It appears that the
variations of composition of the stock to be de-inked (fines,
groundwood, mineral fillers) will reverberate on the fraction lost
through the plate, giving a final product almost constant in
quality, if not in quantity. This principle allows for the use of
unselected waste paper, a lower quality product having a much lower
cost and higher availability.
On the other hand, this process needs a much higher quantity of
water, and produces the equivalent higher quantity of effluents
which still contain a great quantity of valuable products,
cellulosic short fibers, mineral fillers, mixed together with the
undesired ink. Besides that direct loss, it is necessary to
consider the indirect cost due to the abatement of the pollution
created by the solids contained in the effluents.
In conclusion, it can be said that if flotation de-inking presents
high investment and operating cost together with low constancy of
the quality of the final product, washing de-inking also shows a
high similar cost of the product due to both the intrinsical low
yield of the process and the pollution abatement cost.
In order to minimize the negative aspects of each one of these
basic processes, their supporters have proposed several
combinations of them, keeping in mind to produce only one de-inked
pulp starting from one waste paper mixture.
In the French patent application No. 79 19392, M. Fritz Zeeb of
Voith Cy. suggests to remove the fine fibers fraction together with
the mineral fillers from a flotation de-inked pulp, using screens
and strains arranged as washing elements. This process, which is
only summarily described without any example, seems to add up both
costs and drawbacks of flotation and washing.
In the TAPPI magazne, vol. 63, No. 9, September 1980, M. Lothar
Pfalzer of the same Voith Cy., while recalling the same concept
(page 116, FIG. 3), specifies that the fine fiber fraction and
mineral fillers are centrifugated and then disposed of and lost. It
also appears from this publication that the effluent is totally
sedimented after having been floculated by addition of aluminum
sulfate, but it is also specified that a good dispersion of the ink
particles can be obtained at high and well controlled pH. These two
statements are rather contradictory and make this concept hardly
applicable in practice.
M. Pfalzer also suggests the opposite philosophy (page 114, FIG.
1), which consists of a total flotation followed by a total
sedimentation of the effluents of a conventional washing process.
For the same reasons as above, which are: the low yield of the
washing process, the non-compatibility between ink dispersing high
pH and aluminum sulfate sedimentation low pH, the addition of the
costs and drawbacks of each individual process, this proposal has
not been applied on an industrial scale.
In the French patent application No. 78 29637, M. Calmanti of
Montedison Cy. suggests in a more simple way to separate the ink
particles from the fine fibers and the mineral fillers contained in
the effluents of a washing process, by means of a simplified
flotation process where no chemicals are added. It is also stated
that the chemicals added at the begining of the process (pulping
stage) will also provide for the ink collecting function. In this
process, the so called "clarified" effluents which actually contain
most of the fibers and mineral fillers lost during the washing
step, are totally recycled ahead of the process.
A tentative application of this process had to be quickly abandoned
for two reasons. At first, it has not been possible to obtain a
satisfactory selective removal of the ink during the flotation,
because of the antagonistic functions of the two chemicals mixed
together at the pulper: (a) dispersing of the ink needed during
washing, (b) coagulation of the ink needed during flotation. So,
too much fibers and fillers were floated together with the ink
resulting in a quick overloading of the sewer system, and immediate
shut down of the plant.
Second, it has not been possible to recirculate continuously ahead
of the washers, an effluent which contains most of the fines and
fillers lost by the same washers. This total recirculation has
quickly resulted in (a) a drop of the brightness due to the poor
ink removal efficiency and (b) an unacceptable drop of the
hydraulic capacity of the thickening elements. Both can be
attributed to the saturation of the circuit with fines and fillers,
dimensions of which are of the same order of magnitude than the ink
particles.
In the Italian patent application No. 26944 A/80, M. Calmanti
recalls the same principle, where the effluents at a concentration
of 0,14% would be selectively floated with the only addition of
air, and then totally recycled ahead of the process together with
their suspended solids. M. Calmanti nevertheless suggests to
install a "quick" flotation, a third flotation, installed ahead of
the washing process. This configuration does not seem to bring any
answer about the two basic previous problems; (a) how is it
possible to have the best dispersion together with the best
coagulation, (b) how is it possible to avoid the saturation, the
clogging of the thickening elements, and the loss of the ink
removal efficiency, due to the recirculation of the fines and the
fillers together with the effluent.
GOALS OF THE INVENTION
The present invention aims to provide a practical and integral
industrial process which allows to produce, in a continuous way and
starting from a mixture of unselected waste papers, three separate
products, namely:
(a) a totally cleaned and de-inked pulp having constant and
controlled brightness and fiber classification, having a very low
and constant fillers content;
(b) a totally cleaned and de-inked pulp having a fine fiber
classification and a very high fillers content, these two
parameters being variable in both quality and quantity;
(c) an effluent which does not practically contain suspended
solids, which has not been submitted to any pH reversion, which
does not contain any floculation or sedimentation chemical agent,
and thus is immediately and totaly re-usable as the dilution and
washing liquid during the ink removal step of the de-inking
phase.
A further aim of this invention is to provide a practical and
advantageous improved method for de-inking these grades of printed
papers and boards which cannot be correctly de-inked by
conventional methods.
An other aim of this invention is to provide a practical and
advantageous method which allows high quality paper and board at
high speeds using the low quality waste grades which could not be
used for such noble purpose when treated by conventional
methods.
The invention is also directed to the application of modified and
purposely adapted ink removal processes, such as washing, selective
separation, flotation, coagulation, filtration, onto the high
ink-content slurry produced by the primary ink removal process.
The invention also aims to allow for the use in paper making of the
by-products of a washing de-inking process, either on the paper
machine which will use the primary pulp, or on a different paper
machine.
An object of this invention is to provide a to create a constant
and controlled composition of the pulp used for paper making, which
can be different from the composition of the incoming waste paper
mixture. This object is achieved by pumping controlled flows of
each one of the two components and mixing them ahead of the paper
machine(s) in the desired percentage; the capacities of the chests
act as buffers between waste paper and paper machine stock
compositions.
An other object of this invention is to increase the value of the
by-product (the secondary pulp) by the fact that good long fibers
can be extracted from the main line in order to optimize the
operation both of the selective separation of the ink and of the
filtration on fiber mat.
A further object of this invention is to accomplish the selective
separation of the ink at a stage where this ink is highly
concentrated (approximately three times more than in the main
pulp), thus increasing the efficiency of the chemicals.
An ulterior object of this invention is to achieve the selective
separation of the ink (which is the more delicate operation of the
whole recycling process), in a satellite circuit of reduced
capacity (approximately one third of the flow through the main
line), thus being easier to operate and requiring lower investment
cost.
This invention then aims to insure the highest possible constancy
of quality of the primary pulp, by the fact that the variations of
fines and fillers contents will instantaneously reverberate on the
fraction produced by the satellite circuit, which in turn can also
be stabilized by mean of a thorough mixing and high retention time
in the final buffer chest.
With these and other aims and objects, the nature of which will
become more apparent, a fuller understanding of this invention will
be gained by reference to the following detailed description and
the appended claims.
DESCRIPTION OF THE INVENTION
The following detailed description, together with the attached
schematic flow-sheet, refers to one preferred practical application
of the invention, although other procedures can also be
applied.
Following the flow-sheet, the bales of waste paper (1) are loaded
into a pulper (2) by means of a loading mechanism, together with
the recycled water and eventual caustics in order to bring the pH
at values above 7. It is possible but not mandatory to introduce
part or all of the quantity of dispersing chemicals required by the
ink-releasing action, during the pulping operation.
The pulp is then diluted using recycled water and pumped through
one or several stages of screens and cleaners (3) in order to
release contraries and contaminants from the paper surface, and
further remove them from the pulp slurry.
When the de-inked pulp is used for high quality paper production or
on high-speed machines, such as light weight coating base or
newsprint, this operation must be done in the same way it is done
with chemical or mechanical virgin pulps, using the same equipment
and operating parameters. In particular, the best results have been
obtained through a combination of pressurized slotted screens
equipped with 0.3 mm. slot width working at 1% consistency followed
by 4 inch size cleaners working at 2,8 bars pressure drop and 0,6%
consistency in the first stage.
It is anyhow of paramount importance that the temperature of the
stock be kept as low as possible so that the low melting point
contaminants will remain rigid and will not extrude through the
slotted screens and thus be eliminated by the screens. This pulp is
then thickened (4) to the consistency required by the ink releasing
process. The effluents produced by this thickening stage can easily
be recycled, as they are cold and do not contain much fibers and
very little ink. At the beginning of the following ink-releasing
step (5) chemicals are mixed together with the fiber suspension.
Caustics are added in order to raise the pH up to 9-10, together
with oxydizing agent (such as hydrogen peroxide), and stabilizers
(such as sodium silicate), and dispersing agents (surfactants, etc.
. . ). The basic parameters of this process, - temperature,
pressure, specific energy, chemicals dosing - will be determined in
order to insure the optimum detachment of the ink particles from
the surface of the fibers together with their finest dispersion
inside the pulp.
In the following examples, this operation has been made in a
kneader, also called triturator, which permits the temperature to
be brought to the desired value (i.e. above the melting point of
the ink vehicles) within few seconds and simultaneously applies
very strong shear forces at high consistency and in presence of
de-inking agents.
The principle of the operation is that at first, the combined
actions of ink-releasing chemicals and temperature
(90.degree.-130.degree. C.) will soften the ink vehicles and weaken
the bondings between the same and the fibers, and then the combined
actions of ink-dispersing chemicals and intense shear forces will
detach and finely disperse these particles inside the fiber
suspension. The high consistency (20-30%) allows to treat very low
volumes of pulp in small machines during a very short time (2-3
minutes), .Iadd.for example 1 to 5 minutes or 2 to 10 minutes,
.Iaddend.thus avoiding the yellowing of the pulp and increasing the
efficiency of the chemicals.
This pulp then remains 5 to 20 minutes in a latency chest (6), at a
consistency between 2% and 5%. It may then be deflaked (7) in order
to thoroughly separate the fibers bundles one from the other, and
thus facilitate the ink removal from the slurry.
The fibrous suspension finally goes through the ink removal process
(8) which can be advantageously composed of multi-stage,
counter-current, high consistency washing. The number of stages is
choosen according to the quantity of ink to be removed and to the
desired final brightness. The extraction of the water is conducted
through strains of perforated plates, the dimensions of the
openings of which will be selected in order to allow for a given
quantity of fibers to be carried away together with the effluent,
thus ensuring the optimum operation of both the following ink
selective separation process, and the final filtration of the
recovered satellite secondary pulp.
In case a filler-free secondary pulp is desired, the effluents from
the washing step (8) can advantageously be strained again on one or
several fine mesh filters (9). By this means, it is possible to
remove at each filter stage up to 80% of the mineral fillers
contained in that slurry. In such a case, the finest fraction must
be sent to a conventional alkaline clarifier (10) and then be
disposed of. The clarified fraction is then returned ahead or after
the following ink selective separation step (11), according to the
operating parameters of this last process (consistency,
temperature), and according to the required brightness.
The necessary chemicals are also introduced ahead of this step. In
case this process is a selective flotation, ink collectors such as
fatty acids or their sodium or calcium soaps can be added, taking
care to insure a mixing time of about 5 minutes at a temperature of
about 35.degree. to 45.degree. C.
It may be worthy to recall that the dispersing agent used during
the washing step has a negative effect both on the coagulation
produced by the collecting agents during the flotation step, and on
the drainability (freeness) of the fibrous suspension during the
filtration step. It will be good to inactivate or neutralize these
agents for example by precipitation with calcium chloride or
calcium hydroxide. The precipitation of the sodium silicate will
also contribute to increase the brightness of the secondary pulp
through the formation of a precipitated mineral filler. It has also
been observed that the quantity of mineral fillers removed together
with the foam during the flotation step may vary from 30% up to 70%
according to the operating parameters of the process: flotation
time, temperature, pulp consistency, dosing and type of chemicals.
The rejected foam containing the ink is then pumped to centrifuges
or filter-presses and disposed of. The loss of solid particles has
been observed to be between 10% and 20% of the flow of secondary
pulp, which means about 3% to 6% of the total quantity of pulp
feeding the washing step (8).
It has also been observed that the maximum efficiency of the ink
removal has been reached at much higher consistencies that the ones
recommended by the suppliers of the cells. For example, a cell
designed to work at 1% has shown best results between 1,5% and 2%.
This peculiarity allows for the treatment of lowest quantities of
effluents, using higher consistencies during washing, and larger
holes in the extractors perforated plates.
When the requested concentration for the ink selective separation
process is higher (say 0,5% or more) than the maximum concentration
which can be given to the effluent of the washing step, some heavy
stock can be advantageously extracted from the latency chest (6).
In this case, the small quantity of long fibers added to the
secondary pulp will help in forming the filtering mat in the final
filtration step (12).
The selective separation of the ink (11) can also be a process
based on adsorption of the ink upon the surface of non-soap solids,
as recommended by Ira Puddington et Al. in the U.S. Pat. No.
4,076,578.
The de-inked slurry leaving the process (11) is then filtered on
fibrous mat up to at least 4% consistency, possibly above 10% in
order to remove from the final secondary pulp the maximum possible
quantity of dissolved salts.
In case this pulp contains a very high quantity of ground-wood
fines and fillers (such as mixtures of newsprint and magazine
paper), the pH ahead of the filtration step has to be dropped down
to values below 8, by addition of sulfuric acid (preferably to
aluminum sulfate), under intense mechanical agitation (as could be
the suction side of a centrifugal pump), and after some long fibers
extracted from the washed final primary pulp has been added to the
the satellite slurry to be filtered.
It has been observed that the application of equipment such as
Polydisk or Waco Filters to the thickening process (12) has
permitted to produce clear filtrate having less that 100 ppm
suspended solids and consequently totally re-usable in the pulping
(2), cleaning (3) and washing (8) processes without any further
clarification.
The final thickened secondary pulp leaving (12) must then be
brought to a pH compatible with the following use by addition of
sulfuric acid or aluminum sulfate, always under intense mechanical
agitation, and can be stored in a buffer chest according to the
final use.
EXAMPLES
The following examples will illustrate three different applications
of the general procedure previously described, using different
mixtures of waste paper and producing different grades of paper and
board. Measurements of brightness were made with an Elrepho meter
with 457 mm. light filter, according to I.S.O. standards. Chemicals
dosings are expressed in percent by weight of the chemical at 100%
concentration relative to the weight of total solids in the line
where said chemical is added. Sodium silicate is considered at
38.degree. Be and the Removink F and L as supplied.
EXAMPLE 1
The raw material is a mixture of over-issued newspapers and
telephone books (white and yellow pages) in a ratio approximately
50/50. The de-inked pulps are used for the production of newsprint
and telephone directory papers (white and yellow), on only one high
speed paper machine.
In this installation, the pulper has a capacity of 46 m.sup.3
containing 2.700 kg of waste paper. Each batch takes 30 min.
Dilution water is coming from the effluent of the thickening
process (4) and make-up is made using clear filtrate from the
Polydisk filter (12). One percent of sodium hydroxide is added in
the pulper together with 1% of a de-inking agent such as Removink L
8001 supplied by Chemicarta SPA, Milano. .Iadd.This pulping step
typically is performed at ambient or room temperature.
.Iaddend.When this cold pulping operation is finished, the stock is
pumped through turboseparator, screens and cleaners, at
consistencies starting around 4% and ending at about 0,6%.
The turboseparator is equipped with a perforated plate having 3 mm.
diameter holes and the rejected stock is then sent to a vibrating
flat screen also having 3 mm. holes, the rejects of which are
disposed of.
The accepted stock from the turboseparator is then diluted from 3%
down to 1% before it passes through pressurized slotted screens
fitted with 0,30 mm. slot width. The rejected stock is processed
through a second stage screen having the same slot size, and
rejects of the same go to a vibrating flat screen, rejects of which
are disposed of.
The accepted stock from the first stage of screens is then diluted
down to 0,6% consistency and processed through a conventional
battery of 4 stages of Triclean cleaners. The light and the heavy
rejects of the 4th stage are disposed of.
The total loss of both high and low consistency turboseparating,
screening and cleaning is varies between 6% and 9% by weight,
depending upon the
degree of contamination of the waste paper.
No more stickies or hot melts can be seen in the pulp, and a visual
inspection is confirmed by the Sommerville test, which shows less
than 0,2% of shives. At that point, the pulp is totally cleaned and
the only remaining contaminant is the printing ink. The pulp is
then thickened up to 30% consistency in two steps, using a disk
filter up to 10-12% and then a screw press up to 30%.
Characteristics of the pulp are: brightness=40.degree.-45.degree.
ISO, freeness=50.degree.-55.degree. SR, filler content=6-8%,
temperature=20.degree.-25.degree. C. The ink releasing step (5) is
achieved in a kneader under the following operating conditions:
temperature=95.degree.-98.degree. C., sodium hydroxide=1,5% ,
sodium silicate=4% , hydrogen peroxide=1,8% , specific energy=80
KW.H/Ton during 3 minutes. The brightness of the pulp at the end of
the treatment is 50.degree.-55.degree. ISO, and freeness is
60.degree.-65.degree. SR. The pulp is then diluted using all the
flow of effluents coming from the second stage of washers, then
squeezed up to 12% in the first washing stage.
These washers are composed of inclined screws (better known as
Rice-Barton or Baker's screws), where the pulp is drained under
continuous and vigorous agitation through perforated plates having
1,4 mm. diameter holes, in order to produce an effluent having
approximately 0,8-1% consistency.
The thickened stock is then processed through two other similar
counter current washing steps and the final usable pulp presents
the following characteristics: brightness=59.degree.-60.degree.
ISO, freeness=46.degree.-50.degree. SR, filler content 2-3%,
consistency=12-14%. This pulp represents 78% by weight of the
quantity of pulp feeding the washers (8). The balance 22% is going
to the satellite circuit with the first stage effluent which shows
brightness=35.degree.-40.degree. ISO, filler content=20-25%,
freeness=80.degree. SR.
The capability for the ink of being removed from the fibers
contained in the effluent has beenverified in the laboratory as
follows: an effluent sample has been hyperwashed under fresh water
shower on a 200 mesh wire ,and a handsheet has been made, showing a
brightness of 56.degree. ISO, which is very similar to the
brightness of the final primary pulp. This effluent has then been
mixed together with 4% of a special ink-collecting agent purposely
designed for this application by Chemicarta SPA, Milano, and kept
for 5 min. under agitation at 30.degree. C.
The mixture is then processed through one single stage conventional
flotation cell, Voith open type, during 15 min.. The loss of weight
through the cell is 15-20%, which means only 3-4,5% respect to the
total quantity of pulp entering the washers. We have found that
addition of 0,5% to 1% of calcium chloride or calcium hydroxide
together with the collector, ahead of the flotation, helps
controlling the foam and the ink coagulation when low ash content
pulps are processed.
The total alkalinity is then dropped down to pH=7-8 with addition
of 1% of sulfuric acid on the suction side of the centrifugal pump
feeding the disk filter (12). At this point, the pulp shows a
brightness=53.degree.-56.degree. ISO, a filler content=15-20% and a
freeness=78.degree.-80.degree. SR.
The disk filter (12) is a Polydisk filter sized according to a
specific filtering factor=20 liters/min./m2. Besides this unusual
value, it is also necessary to feed the mat-peeling showers with
air instead of water, in order to reach the maximum possible
consistency of the discharged pulp.
Using the above mentioned parameters, a final consistency of 8% to
10% could be obtained and the clear filtrate shown less than 100
ppm average suspended solids, measured on paper filter, black
label.
The pulp is then brought to pH=6 and sent to a buffer chest having
8 hours total retention time. From this point, it is then pumped to
the mixing chest of the paper machine at controlled flow rates
according to the paper grade actually produced and in function of
the mean composition of the secondary pulp.
The clear filtrate from the Polydisk filter is then totally
recycled in order to dilute the stock ahead of the third washing
stage and make-up is provided by fresh industrial water which does
not contain aluminium ions.
The application of such a process in a paper mill having one single
paper machine offers the following advantages:
(a) possibility to maintain constant freeness and ash content
during a grade run, independently from the incoming waste paper
characteristics, thus allowing the paper machine to run at maximum
speed and efficiency;
(b) possibility to achieve very quick grade change, exactly as
whenusing virgin pulp and fillers, without the need to intervene a
long time before in the waste paper plant, thus permitting an
easier and more constant operation of that plant;
(c) possibility to always use the highest possible quantity of
recycled fibers in the paper, by the free disposal of each one of
the two fractions and their use in the optimum way.
(d) possibility to produce totally cleaned pulps having the same
standards of cleanliness than virgin pulps and thus offering the
highest possible runability in the paper machine room, particularly
being free of any "sticky" or "hot melt" or ink vehicle free
particle.
EXAMPLE 2
The raw material is a mixture of printed continuous stationary ,
old books and office file, in a ratio 50/50.
The de-inked pulp is used to produce, on three distinct paper
machines: (a) light weight machine-glazed wrapping papers, (b) fine
papers for writing and printing, including wood containing printing
grades, (c) stationary and continuous print-out papers.
The operation is similar to example (1) up to the thickening step
(4), although it is not necessary to add any chemical
agent--caustics or de-inking agent--during the pulping step (2).
When entering the ink-releasing step (5), the pulp has a
brightness=60.degree. ISO, a freeness=40.degree.-45.degree. SR, and
a filler content=20%.
The ink-releasing equipment is the same as for example (1) but
operating parameters are as follow: Removink L8001=0,3%; hydrogen
peroxyde=0,5%, sodium hydroxyde=1%, sodium silicate=3%. All other
parameters remain unchanged. At the end of the process, the pulp
has shown a brightness increase of 2.degree. ISO and freeness did
not show any appreciable variation.
The pulp is then washed by mean of three washing stages as for
example (1), but the design of the perforated plates are different:
the first stage is fitted with 2 mm. diameters holes, the second
and the third stages are equipped with 1,4mm. diameter holes. Also
the feed consistency of the washing stages is different, being
2,5%. With these parameters, the final washed primary pulp has
shown following characteristics: brightness=75.degree. ISO, filler
content below 3%, freeness 27.degree.-30.degree. SR.
The effluent leaving the first washers has a consistency between 1%
and 1,2%, a filler content=60%, brightness=50.degree. ISO, and
freeness=70.degree. SR.
The flotation cell used in this application is a high consistency
Swemac type, and heavy stock has been pumped from chest (6) and
mixed together with the effluent before the flotation, in order to
raise the consistency up to 1,5%. In this way, the two lines
(primary by washing and secondary by flotation) have exactly the
same solids flow rate, or the same capacity in tons/day, but
produce two pulps having opposite characteristics. This extraction
also procures long fibers which will help the final filtration
(12).
This extraction could have been done using washed pulp and this
would have increased the brightness of the secondary pulp. But in
such a case, the washing equipment would have to be sized for 30%
more capacity, which is not a worthy choice in our case.
The flotation is then conducted with only 2% of the same collector
(Removink F) and the retention time through the cell is only 10
min., thus producing a loss of weight of 10% (which means 5% of the
total pulp).
After acidification at pH=8 ahead of the disk filter, the pulp
shows a brightness=70.degree. ISO, a filler content=35-40%, a
freeness=65.degree.-70.degree. SR.
The Polydisk filter can be sized using a filtering factor=25
liters/min./m2, and produces an effluent containing 70-100 ppm
suspended solids. The other steps of this application are similar
to the ones described in example (1).
The application of such a process in a paper mill having several
paper machines as in this example is offering the following
advantages:
(a) possibility to produce a pulp having physical and cleanliness
characteristics similar to the ones of a virgin chemical pulp, thus
usable for the production of fine light weight papers, with good
Yankee dryer glazing capabilities;
(b) possibility to produce a pulp having physical and optical
characteristics of a mixture of fine chemical and/or ground-wood
pulp, and mineral fillers, thus usable for the production of
printing papers where high opacity and smoothness are
requested.
(c) possibility to mix these two pulps together in a ratio which
can be very much different from the original one coming together
with the raw material.
EXAMPLE 3
The raw material is a mixture of low quality printed waste,
containing old books, office waste and stationary, and some
newspapers and magazines, in variables proportions.
The mill has one multiply board machine, and produces high quality
folding box board, which can be on-machine coated and must show an
excellent multicolour offset printing aptitude. The white top liner
is composed of 100% de-inked primary pulp and the underliner uses
the secondary pulp, mixed with other pulp.
Pulping is conducted in a continuous way with the same parameters
as for example 1. The cleaning and screening treatment (3) is
simplified and composed of centrifugal high-density cleaners,
followed by a turboseparator, working at 3% consistency. The
following thickening stage is also simplified and composed of
inclined screws producing pulp at 15% consistency, followed by a
screw press. The finest contaminants will be detached and better
dispersed during the ink-releasing step (5) and then carried away
with the effluent during the washing stage. They will remain in the
secondary pulp thus contributing to add weight and volume to the
board, as the underliner does not need to be particularly
cleaned.
The pulp entering the ink-releasing and dispersing step shows a
brightness=50.degree. ISO, a filler content=25-30%. The operating
parameters are the same as for example (1), but the brightness
drops down to 46.degree.-48.degree. ISO.
The following washing step has only two stages, which are fed at
2,5% consistency. The perforated plates of the inclined screws have
1,6 mm. diameter holes, and it has been found that the
characteristics of the effluent are very similar to the one of
example 1.
The washed primary pulp shows a brightness=68.degree. ISO, a filler
content=4% and a freeness=45.degree.-50.degree. SR. The fine
cleaning of the primary pulp is achieved with the cleaners and the
screens installed ahead of the board machine, which is sufficient
to reach the desired quality. It must be said that the contaminants
have been thoroughly dispersed in the kneader (5) and most of them
have left this primary pulp during the washing step.
The satellite circuit is also simplified because the brightness of
the underliner has only a third-order influence on the final
brightness of the coated board. We have observed that a brightness
of the underliner secondary pulp in the 50.degree. ISO range was
sufficient to insure the required brightness 80.degree. ISO of the
coated board, providing that the top liner primary pulp has
70.degree. ISO. Thus, the flotation time has been reduced below 10
min. and the dosing of the collector has been kept below 2%. We
have also observed that it was possible to run without any chemical
when lower quality grades are produced, but no compromise can be
applied on the dispersion effect, because black spots in the
underliner are always visible even through the coated top
liner.
The application of such a process to the production of stratified
board is offering the following advantages:
(a) possibility to totally replace chemical pulp or high quality
selected unprinted waste paper by a low value and large
availability raw material;
(b) simplification of the main line by eliminating the fine
screening and cleaning equipment;
(c) increase of the total yield, by transferring in the secondary
pulp (and then in the underliner or in the middle ply) all finely
dispersed contaminants which are not acceptable in the top
liner.
* * * * *