Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
BIOLOGICAL METHOD OF DEINKING PRINTED WASTEPAPER
NAMES OF INVENTORS
TAE JIN EOM
STEVEN SAY-KYOUN OW
FIELD OF THE INVENTION
The present invention relates to a method of deinking
printed wastepaper.
CROSS-REFERENCE TO OTHER APPLICATIONS
This application is a Divisional Patent Application
of Canadian Patent Application Serial No. 2,032,256, filed
December 14, 1990.
BACKGROUND OF THE INVENTION
Deinking of pulp fibre is essentially a laundering or
cleaning process in which ink is considered to be the dirt.
Chemicals along with heat and mechanical energy, are
used to dislodge the ink particles from fibers and to disperse
them in the aqueous medium. The ink particulars are then
separated from the pulp fibers, either by washing or flotation
or by using a modern hybrid process that combines the two
elements.
The chemicals used for the conventional deinking
process are surfactants which function as detergents to remove
ink from fiber, keep the ink particles dispersed to prevent
redisposition on the fibers, and provide a foaming action for
the froth flotation of ink particles.
A typical surfactant is a long chain molecule with a
hydrophobic part to the one end and a hydrophillic part to the
other end. The hydrophobic part may consist of fatty acid,
fatty alcohol, alkylphenols or other oil soluble surfactants.
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The hydrophillic part of the deinking surfactant
usually consists of anion molecules such as carboxyl acid salts
or sulfonic acid salts and nonionic molecules such as
polyoxyethylenated chains.
The typical surfactants commonly used in the washing
and froth flotation deinking process are: sodium and potassium
salts of strait chain fatty acid (soap), linear
alkylbenzenesulfontate (LAS), olefine sulfonate, long chain
fatty alcohol, polyoxyethylenenated alkylphenols,
alkylphenolethoxylates, and polyoxyethylenated strait chain
alcohols.
The major disadvantage of using these surfactants in
the deinking process is excess foaming in the subsequent pulp
stock flow and paper making process lines. In addition, some of
the above surfactants are resistant to biodegradation in the
effluent treatment stages causing a serious environmental
problem.
In the froth flotation deinking process, a collector
is added to agglomerate ink into large particles and attach them
to the air bubbles. Collectors are required for effective
flotation and are usually anionic long-chain fatty acid soap.
Fatty acid collectors are precipitated with calcium ions to form
larger, insoluble ink particles and collector particles. With
injection of air in the flotation cells, the agglomerated ink
particles adhere to the bubbles, rise to the surface and are
skimmed off from the system.
Major disadvantages of the flotation method using the
fatty acid collector is a pitch deposition and calcium scaling
problems in the subsequent stock lines and paper making
equipment. Besides the surfactants, other chemicals are caustic
soda, sodium silicate, metal ion chelating agents and hydrogen
peroxide.
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The hydrogen peroxide bleaching agent has to be added
in order to prevent a pulp colour yellowing caused by the
additions of caustic soda and to improve brightness of pulp
fibers.
With the advance in the modern printing and
photocopying technology, conventional deinking with the aid of
surfactants encounters serious problems with the wastepaper
printed with the use of heavily coated, highly polymerized, or
nonimpact inks, such as ultraviolet, heatset, Xerox, laser and
ink jet. These inks usually contain cured polymer resins which
bind ink particles so strongly on the fiber surface that it is
impossible to dislodge the ink completely during the wastepaper
defiberizing (pulping) stage with the conventional deinking
chemicals. Excess heat and mechanical energy are also required
along with the ineffective conventional chemicals.
In the conventional flotation deinking process for
newsprint wastepaper a major technical problem is experienced
with fine ink particles embedded in the fibre bundles and
between fibrils which are almost impossible to remove from the
fibers by a washing and/or flotation process.
SIJNlN.fARY OF THE INVENTION
This invention provides a new and much improved
method of deinking printed wastepaper. This method is effective
in newsprint deinking, as well as the deinking of wood free
printed wastepaper such as whiteledger, laser printed,
xerographic copypaper and computer printout wastepaper.
This invented deinking method is to remove ink
particles with the use of biological activity of enzyme on the
cellulose fiber surface and a dispersing function of enzyme
protein on ink particles.
In contrast to the conventional method no alkali and
deinking surfactants are required although some surfactants can
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be used along with the enzyme to enhance the deinking
efficiency. In the froth flotation process the fatty acid
collectors are not required. Since caustic soda is not used in
the newsprint deinking, hydrogen peroxide bleaching agent is not
also required for yellowing prevention.
The elimination of the fatty acid collector in this
biological deinking process will solve the persistent pitch and
scale deposition problem associated with the conventional
flotation process using the fatty acid type soap and calcium
salts and silicates.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
This method will now be described.
Printed Wastepaper, such as old newsprint or printed
wood free wastepaper, is disintegrated in a conventional pulper
(consistency 4-7%) or in a high consistency pulper, 12-15%, at
the water temperature ranging from room temperature up to 60 C.
The addition level of enzyme is 0.005% to 5.0% based on dry
weight of wastepaper, pH of the stock slurry is adjusted in the
range of 3.0 to 8Ø As compared to the conventional pulping
process using caustic and surfactants in pulping, the process
using enzymes can be completed in a relatively short period and
ink particles are completely separated from the fiber surface
and dispersed well. The dispersed inks are removed out of pulp
fibers by conventional washing process equipment such as a
vibration screen and a drum washer without the aid of detergent
surfactants. The ink particles dispersed with the action of
enzyme protein can be also selectively removed out of the
diluted pulp slurry with conventional flotation equipments in
which air is injected into the pulp to provide bubbles to pick
up the particles. No fatty acid collector is required in the
case of waste newsprint. A small amount of fatty acid collector
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may be added to enhance the ink removal efficiency in the case
of laser-printed wastepaper.
This biological deinking process is to lower pulping
energy to a large extent since the addition of enzyme results in
5 a reduction in pulping time, as compared to the pulping in the
absence enzyme, of almost 50% reduction. The observed faster
and easier pulping in the presence of enzyme may be attributed
to an unique biological activity of enzyme which is effective to
debond the fiber bonding and dislodge the inks bonded on the
fiber surface as well as within the fibrils. A partial
enzymatic hydrolysis of cellulose within micro structure of
fiber surface may occur during the pulping stage. This
biological activity of enzyme takes out fine ink particles
embedded within fiber bundles, fibrils and fines which have been
impossible to be taken out by conventional deinking chemicals.
According to this biological deinking method of old
newsprint the addition of hydrogen peroxide to prevent the fiber
yellowing is not required, which will result in a substantial
reduction of deinking chemical cost as compared to the
conventional deinking process using caustic soda, hydrogen
peroxide, chelating agent and sodium silicates.
It should be pointed out that the physical strength
properties of the resulting pulp fiber prepared by this invented
method are found to be higher than those of the corresponding
pulp prepared by the conventional method, in addition to the
much higher resulting pulp brightness. The enzyme addition does
not appear to degrade the fiber strength, instead improving the
fiber strength for reasons that are as yet unknown.
Example 1.
Deinking of old newsprint with a cellulolytic enzyme.
A sample of old newsprint wastepaper was added to a
pulper which was filled with 40 C water at the consistency of 4%
and a cellulase was dissolved at the dosage level of 0.1% based
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on oven dry weight of wastepaper. The wastepaper was soaked for
minutes and then disintegrated for 5 minutes. After a
complete disintegration of wastepaper, one half of the pulp
slurry was diluted to a 1% consistency.
5 The diluted pulp slurry was moved to an air flotation
cell and then the dispersed ink particles were removed out of
the pulp slurry by skimming off a froth containing ink particles
out of the cell while injecting air through a porous plate. The
flotation time for the complete removal of the ink froth was one
10 minute.
The other half of the pulp slurry was washed on a
laboratory vibration screen to remove the dispersed ink
particles.
The resulting recycled pulp fibers obtained by the
flotation and the washing step were evaluated for pulp
brightness and mechanical strength properties. To compare this
enzyme treated deinking pulp to the conventional deinking pulp,
the same sample of wastepaper was treated in the pulper with the
addition of 1.0% NaOH, 0.3% HO, 3% sodium silicate solution
(water glass), 0.8% of SERFAX MT-90 (Trademark) (fatty acid
soap) and 0.2% IGEPAL 660 (Trademark) based on oven dry weight
of wastepaper. The pulping time was 10 minutes for a complete
disintegration. After diluting to 1% consistency, the dispersed
ink particles were removed by the flotation method with the
laboratory flotation cell as described above.
As shown in Table 1, the brightness of the pulp
deinked with enzyme was much higher than that of the pulp
deinked with the conventional chemicals and the mechanical
strength of the enzyme-deinked pulp was also superior to that
pulp deinked with the fatty acid collector and the dispersant
(IGEPAL 660 TM). The microscopic observation revealed that the
pulp prepared by the present invention contained more long fiber
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fractions and has smoother fiber surface and looked less
mechanically damaged.
Table 1.Comparison of properties of recycled pulp by method of
present invention and the conventional method.
brightness tensile index tear index
($) (N.m/g) (mN.m/g)
KONP AONP KONP AONP KONP AONP
flotation 47.1 45.2 28.9 32.4 11.7 13.6
present
method
washing 50.3 48.6 29.3 32.9 11.8 14.1
SERFAX MT-90TM 45.1 38.4 30.1 32.8 10.8 13.1
KONP: Korean old newspaper
AONP: American old newspaper
The enzyme treated pulp gave cleaner and brighter pulp
with the washing as compared to the flotation ink removal.
The enzyme addition appeared to accelerate the wastepaper
disintegration to a large extent. When the old newspaper was
disintegrated in the conventional pulper at the 4% consistency,
the addition of 0.5% enzyme reduced the pulping time from 5
minutes (no enzyme addition) to 30 seconds for a complete
disintegration as shown in Table 2.
Table 2.Relation between enzyme addition and disintegration
time.
Enzyme (%) 0.5 0.1 0
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disintegration 30> 60-120 300<
time (sec)
Example 2.
Deinking of laser CPO (computer printout) with
cellulolytic enzyme.
It is almost impossible to achieve a complete removal
of laser beam cured ink particles from laser CPO wastepaper with
the conventional deinking chemicals, because the ink particles
are so strongly adhered to the fiber surface that alkali and
general deinking surfactants in the conventional deinking
chemicals are not able to dislodge and disperse in the pulp
water slurry.
A sample of laser CPO wastepaper was added to water
in a laboratory high consistency pulper at the consistency of
12.5% and a cellulase was added to the water at the dosage level
of 0.2% based on the dry weight of paper. At stock water
temperature of 20-35 C, the pulping was carried out for 20
minutes. The completely disintegrated pulp slurry was diluted to
0.5% and then dispersed ink particles were removed out of the
pulp slurry using the laboratory flotation cell as explained in
Example 1. In this case, to increase the ink removal efficiency
and selectivity a small amount of the conventional fatty acid
collector, SERFAX MT-90 (trademark), of 0.3% based on dry weight
of wastepaper was added prior to the air flotation and the
flotation time was 3 minutes. To compare to enzyme deinked
pulp, the conventional deinked pulp was prepared by the same way
but the different chemical conditions as follows:
1% NaOH on dry weight of wastepaper
0.1% IGEPAL 660 Tm dispersant
0.8% SERFAX MT-90 '
pulping temperature : 50 C
pulping time : 30 minutes
calcium salt addition to the flotation cell: 200 ppm
flotation time : 3 minutes
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The brightness and the strength properties of the
resulting pulp samples were compared in Table 3.
As shown in the table, the image analysis of the
paper samples indicates that the number of the residual ink
particles was much less, about 10 times, for the pulp deinked
with the enzyme and the tensile strength was also higher as
compared to the pulp prepared with the conventional chemicals.
A recycled chemical pulp of high quality in terms of
dirt count and fiber strength properties can be obtained with
the use of enzyme in a combination of a small amount of fatty
acid collector by the flotation method.
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Table 3.Comparison of pulp properties recycled by the method of
present invention and conventional method.
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brightness dirt amount tensile index
(o) (count/area) (N.m/g)
10 enzyme: MT-90-
(0.3%) 79.0 450 34.3
MT-90 (90%) 80.6 4,330 26.3
Example 3.
Deinking of waste newsprint by pectinolytic enzyme.
As the same method to example 1, the waste newsprint
containing 0.1% of pectase was soaked for 10 minutes at 40C and
disintegrated for 5 minutes. Diluting the disintegrated pulp to
1%, the ink particles are removed by flotation for 1 minute.
As shown in Table 4, the brightness and tensile
strength of paper sheet prepared by the method of the present
invention are improved.
Table 4.Comparison of the method of using pectinolytic enzyme
with conventional method.
brightness tensile index
M (N.m/g)
present method 44.2% 33.3%
MT-90 (0.8%) 38.4% 32.8%
