-~ 20322~~
The present invention rH~iates to a method of de inking
printed wastepaper.
BACKGROUND OF THE INVENTION
Deink.ing of pulp fibre is essential iy a launder ing or
cleaning process in which ink is considered to be the dirt.
Chemicals along with heat and mec:han:icai energy, are
used to dislodge the ink pari_icles from fibers and to
IG disperse them in the aqueous medium. Tree ink particulars are
then separated from the pulp fibers; either. by washing or
flotation or by using a modern hybrid process that combines
the t:wo 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.
2G
A typical surfactant is a long chain molecule with a
hydropt~ot~ic part to tale one end and a hydrophilic part to the
other end. Tile hydrophobic part may be consist of fatty
ac:.id, fatty alcohol , alkylpheruo.is or other of l soluble
surfactants.
The hydrophilic part of ttie deinking surfactant usually
consists of anion molecules such as carboxyl acid salts or
sulfonic acid salts and nonionic molecules such as
3G polyoxyethylenated chains.
The typical surfactants c~ammon.ly used in the washing
and froth flotation deinking- process are; sodium a.nd
potassium sa.l.ts of strait chain fatty acid (soap); linear
alkyloenzenesulfontate (LAS); o7_efine sulfonate, long chain
_. 2~~~~~~
2
fatty alcohol, polyoxyethylenenated alkylphenols;
alkyiphenolethoxylate~~, and palyoxyethylenated strait chain
alcohols.
The Ma jor disadvantage of using the~~e surfactants in
tree deinking process is excess foaming in the subsequent pulp
stock flow and paper making process Lines. 7n addit:ian, some
of tile above surfactants are re~;istant to biodegradati.on in
the eff luent treatment: stages causing a serious environment=al
problem.
In tt~e froth flotation deinking process; a collector is
added to agglomerate ink into large particles and attach them
to the air bubbles. Co.ll.ectors are required fc~r effective
flotation and are usually anionic long-chain fatty acid soap.
rr~atty acid collectors are precipitated with calcium ions to
form larger, insolub3.e ink. particles and collector particles.
With injection of air in 1=he flotation cells; floe
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 tree subsequent stock lines and paper
making equipment. Besides the surfactants; other chemicals
are caustic soda, sodium silicate, metal ion chelating agents
and hydrogen peroxide.
The hydrogen peroxide blea~::hing agent has to be added
in order to prevent a pulp colour yellowing caused by flue
additions of caustic soda and to improve brightness of pulp
fibers.
With t_he advance in the modern printing and
photocopying technology; conventional deinking with the aid
-- 2032~~u
3
of surfactants encounters serious problems with the
wastepaper printed with the use of heavily coated, highly
polymerized; or nonimyact 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
wi th the convent Tonal deinking c:kiemica is . Exc:ess~ heat and
mechanical energy <are also required along witkr the
ip ine.ffect ive conventional ckiemicals.
In the convent Tonal f lot<it ion de inking process for
newspririt wastepaper a major technical problem is experiencHd
witki fine ink particles embedded in the fibre bundles and
i5 between fibrils whicki are almost impossible t:o remove from
the f fibers by a washing and,/or f lotat ion process .
SUNI~~1ARY OF THE INVENTION
This invention provides a view and much improved method
2p of deinking printed wastepaper. This method is effective in
newsprint deinking, as well as the deink.ing of wood free
printed wastepaper sucks as whiteledger, laser printed,
xerographic copypaper and c:omputerr printout wastepaper.
25 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.
3p In contrast to the conventional method no alkali and
de.inking surfactants are required although some surfactants
can 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
20322~u
4
in tile newsprint deinking, hydro~zen peroxide bleaching agent
is not also required for yellowing prevention.
Tine elimination of the fatty acid collector in this
biologica.i deinking process will solve the pers=istent pitch
and scale deposition problem associated with the conventional
flotation process using the fatty acid type soap and c:al.cium
salts and silicates.
i0
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The method will now be described.
Printed Wastepaper, such as old newsprint or printed
wood free wastepaper, is disintegrated in a conventional
pulper (consistency ~~-'19F;) or in a high consistency pulper;
12-158;, at the water temperature ranging from room
temperature up to 60 ~. The addit:i.on level of enzyme is
0.00584 to 5.09F; based on dry weic3ht of wastepaper; pH of the
stock slurry is adjusted in thc~ 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
we i 1 . The dispersed inks are removed out of pu ip f fibers by
conventional washing process equipment such as a vibration
screen and a drum washer without the a.id of detergent
surfactants. The ink particles dispersed with t: he ac t:i.on of
enzyme protein can be a.l.so 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. i3o fatty acid col.iector is required
in the case of waste newsprint. A small amount of fatty acid
collector may be added to enhance the ink removal eff_i.ciency
in the case of laser-printed wastepaper.
2032~~~
This biologi.cai deinki.ng process is t_o lower pulping
energy to a large extent sine trte addition of enzyme results
in a reduction in pulping time, a-s compared to tire 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 unit;ue b-iologic:al activity o.f enzyme which
is effective to debond tire fiber bonding and dislodge the
inks bonded on the fiber surface as well as within the
fibrils. A partial enzymatic hydrolysis of cellulose within
i0 mic:ro st:ructure 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 i-mpossible to be take out by convertti.onal
deinking chemicals.
i5
According to this biological deinking method of old
newsprint t:he addition of hydrogen peroxide to prevent the
fiber yellowing is not required, which will result in a
substantial reduction of deinkin.g chemical cost: as compared
20 tc~ the conventional de inking process using caustic soda,
hydrogen peroxide; cheiat.ing ager~t and sodium silicates.
It should he pointed out that the phys.ica.l strength
properties of the resulting pulp fiber prepared by this
25 invented method are found to b~e higher than t=hose of ttte
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 fox reasons
Op that are as yet unknown.
.35
203225fi
6 ' "
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 on oven dry weight of wastepaper. The
wastepaper was soaked for 10 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.
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 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% H O, 3%
,
sodium silicate solution (water glass), 0.8% of SERFAX MT-
, 0 (Trademark) (fatty acid soap) and 0.2% IGEPAL
9
(Trademark) -660 based on oven dry weight of wastepaper.
The pulping time was 1.0 minutes for a complete
disintegration. After diluting to 1% consistency,
_m_ ~~32256
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 de.inked
with the conventional chemicals and t=tie mechanical strength
of the enzyme-deinkecl pulp was also superior to that. pulp
deinked with the fatty acid collector and the di.spersant
{IGEPAL 660). The microscopic oioservation revealed that the
pulp prepared by the present invention contained more long
fiber fractions and has smoother fiber surface and looked
less mechanically damaged.
i5 Table 1. Comparison of properties of recycled
pulp by method of pre~:ent invention and
the conven-tional met_had.
brightness tensile index tear index
( ~; ) ( N.m/g ) { mN.m ,lg)
KONP AONP KONP AONP KONP AONP
flotation 4?.1 45.2 28.9 32.4 1I.? 13.6
preserrt _..__.._..__.______.__.__..____._. r._.___. _.____.__ ___
____.___~___._.__~___._____._____.____.._.._....__..__. _._
method
washing 50.3 48.6 29.3 32.9 11.8 1.4.1
SERFAX MT-90 45.1 38.4 30.1 32.8 10.8 13.1
,~0 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.
20~22~6
The enzyme addition ap~~eared to accelerate tine
wastepaper disintegration to a large extent. When the old
newspaper was disintegrated in the conventional pulper at the
4°c; consistency, the addition of 0.5:K enzyme reduced the
pulping time from 5 minutes (no enzyme addition) to 30
seconds for a complete disintegrat ion as shown in Table 2 .
Table 2. Relation between enzyme addition and
disintegration time.
Enzyme ( 96 ) 0.5 0.1 0
disintegration 30> 60-120 3OO<
time ( sec )
- _._...__. _._._.__~____._. ____._._ _..__._ __...____._.._____..___..
_____~..__.___._____.___._.__ __.._..___._____.______
Example 2.
Deinking of laser CPO (,computer printout) with
cellulolytic enzyme.
It is almost impossible ac:h:ieve a complate removal of
laser beam cured ink particles from laser CPO wastepaper with
t:he conventional de>inking rhemica.Is, because the ink
particles are so strongly adhered to the f. fiber surfacie 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 waste>paper was added to water in
a laboratory high consistency pulper at the consistency of
12.5~C; and a cellu.iase was added to thH water at the dosage
level of 0.2gr; based on the dry weight of paper. At stock
water temperature of 20-35 C; the pulping was carried out for
2U322~6
9
20 minutes. The completely dig>integrated pulp slurry was
diluted to 0.5~ and than 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 tHle lIlk
removal efficiency and selectivity a small amount of the
conventional fatty acid collector, SERFAX NT-90; of 0.39F;
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, tile conventional deinked pulp was
prepared by the same way bL~t the different chemical
conditions as follow:
1~; NaOH on dry weight of wastepaper
0.19r; IGEPAh 660 disoersant
0.89f; SERFAri MT-90
pulping temperat=ure . 50 C
pulping time : 30 minutes
calcium salt addition to tine flotation cell: 200 ppm
flotation time . 3 minutes
The brightness and the :strength properties of tree
resulting pulp samples were compared in Tahle 3.
As shown in the of the paper
tab3.e, the
image analysis
samples indicates that the number of the residual i.nk
particles was much less; about 10 times; for pulp deinked
the
wi th the enzyme and tare tensi le st rerrgth
was also higher as
compared to the pulp prepared with tire conventional
chemicals.
A recycled chemical pulp of high duality in terms of
dirt count and fiber strength properties can be obtained with
,~0 ttre use of enzyme in a combinat ion of a small amount of fats=y
acid collector by the flotation method.
Table 3. Comparison of pulp properties recyc..ied
by the method of present invention and
conventional method.
1~ 2~32~~~
brightness dirt amount tensile index
1 {count,/area) {N.mjg)
enzyme : MT-90- { 0 . 39k ) '19 . 0 450 34 . 3
MT-90 { 90°6 ) 80 . 6 4 ; 330 26 . 3
Fxampie 3.
Deinkinc,~ of wast.-e newsprint by pectinolytic enzyme.
As the same method t=o example 2; tine waste newsprint
containing 0.191, of pectase was soaked for 10 minutes at 40C
i5 and disintegrated for 5 minutes. Diluting the disintegrated
pulp to i9K; 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 the method of using
pect.inolytic enzyme with c:onvent_ional
method.
brightnes~> tensile index
} { N.m,ig )
present method 44 . 29k 3 3 - ~3~'0
3O
_______..___________....___..__r_.~..___._____.________.___.___.....__._...____
._._._.______._ __.__._....____._._______._. ...__._.._..
MT-90 { 0 . 896 } 38 . 49F; 32 . 896
