Note: Descriptions are shown in the official language in which they were submitted.
21a278~
WO9S/12026 PCT/GB94/0235
Treatment of Cellulosic MatQrial and
Compositions for use in this
This invention relates to the de-inking of waste
paper. In this specification we use the term "paper" to
be generic to cellulosic sheet materials including filled
and unfilled papers and paper board.
It is st~Ard practice to reclaim waste paper to
allow the reclaimed paper fibres to be used as part or all
of the stock of subsequent paper production. The waste
paper needs to be de-inked and it is standard practice to
achieve this by forming a pulp from the waste paper in an
aqueous medium that includes de-inking chemicals, and
separating the ink from the pulp. This separation may be
by, for instance, wAching and/or flotation.
lS A typical de-inking process can comprise forming a
pulp of the paper in the presence of the de-inking
chemicals so as to disperse the ink into the pulp and then
subjecting the resultant pulp to flotation to provide a
Reject fraction that contains the floated ink compo~nts
with a minimum of paper fibres, and an Accept fraction
contA;ni~g the paper fibres with a minimum of the ink
components and the Accept fraction is then thickened to
provide stock or other material that may be used for paper
manufature, optionally after further conventinal
treatments.
Typical chemical processes for de-inking are described
in U.S. 1,925,372, 2,525,594, 4,347,099 and 4,780,179, and
FR 2,281,456. As is apparent from these publications,
typical de-inking chemicals have comprised a complex
mixture of chemicals. Generally they include a
significant amount of alkaline material, with sodium
silicate, hydroxide and carbonate frequently being
proposed.
The literature shows that the pH of the resultant pulp
during the de-inking process is usually high, for instance
above 9 and most usually above 10. Exposing the
cellulosic fibres to this degree of alkalinity tends to
WO95112026 pcTlGBs4lo23so
2152782
cause yellowing of the fibres and so it is generally
necessary to add a peroxide as a bleaching agent.
It is also known to include various other additives.
The use of certain polycarboxylic acid polymers to
activate de-i~king processes is described in GB-A-
2,178,079.
In U.S. 4,347,099 it is proposed to use a mixture of
sodium hydroxide, hydrogen peroxide, a carboxylic polymer
(usually polyacrylic acid or, preferably, poly hydroxy
acrylic acid), dispersants such as anionic, cationic or
non-ionic surface active agents, and other additives such
as collectors, foaming agents, alkali silicates and pH
regulators. The use of this complex and highly alkaline
mixture is undesirable since the liquor that results from
the de-inking process can cause environmental disposal
problems. Neutral de-inking systems have the advantage
that they reduce the risk of unwanted bleaching of the
fibres and they have the advantage that they are more
environmentally acceptable, especially because the effluent
can be substantially neutral. Unfortunately such systems
are not always as efficient as would be desired.
A de-inking system which has been commercialised under
the trade name Ennesco D is described in WO90/10749 and
apparently consists solely of a mixture of sodium carbonate
and sodium phosphate, optionally with hydrogen peroxide.
The use of this can reduce some environmental problems but
it introduces others, since the presence of large amounts
of dissolved phosphate in the de-inking liquor is
environmentally undesirable. It is possible to operate
this system at a lower pH, for instance around pH 8.
We have described in our application PCT/GB93/00780
(not published at the priority date) processes in which
pulp is formed from the waste paper in an aqueous medium
that has a pH of between 6 and 9 and that is substantially
free of dissolved phosphate and that includes an ink
dispersing amount of a dispersing agent which is preferably
a polycarboxylic acid. It is stated that the pH is
21~27~2
WO95/12026 PCT/GB94/02350
preferably buffered to a value in the range 6.5 to 8 and
the preferred dispersing agent is low molecular weight
polyacrylic acid.
Various inks may be present in the paper that is to be
de-inked and many of them comprise a binder and pigment.
Many of the binders dissolve or soften sufficiently in the
presence of the de-inking chemicals and/or during the
pulping stage in order to release the pigment as a
dispersion in the pulp. For instance many binders are
alkali-soluble or alkali-swellable and the alkaline
conditions prevailing in a conventional de-inking pulp will
be sufficient to release the ink from the paper fibres and
to release the pigment from the binder. As a result, the
~ pulp has finely dispersed pigment throughout it and a test
of a good de-inking process is the whiteness of a sheet
made from the Accept fraction, optionally after w~shing it.
The finely dispersed pigment has a tendency to cause an
overall grey colouration if the de-inking process is
inefficient.
~ 20 However in addition to the problem of overall
greyness, there is also a problem of visible sFDc~c in a
sheet made from the Accept fraction. These specks arise
when the ink particles on the paper that is to be de-inked
are resistant to the de-inking chemicals and the pulping
conditions as a result of the particles comprising a
pigment and a binder that is sufficiently resistant to
these conditions that ink particles retain their integrity
and appear as specks in the Accept fraction (hereinafter
referred to as a resistant binder). For instance a binder
that is soluble or swellable at pH 9 sufficient to release
pigment particles at that pH may not adequately release
them when the pulping and de-inking process is conducted at
a lower pH. Accordingly de-inking at relatively neutral pH
values (for instance pH6 to pH8.5) can incur the
disadvantage that ink binders that might release pigment
during the pulping process in alkaline pulping are
resistant during the neutral pulping such that they do not
WO9~112026 21~ ~ 7 8 ~ PCT/GB94/02350
release the pigment. Thus the ink particles may be
resistant to dispersion of the pigment (hereinafter
referred to as resistant ink particles) during neutral
pulping even though they might swell and release the
pigment during alkaline pulping.
A particular problem arises when the ink is applied by
laser printing or by Xerographic or other photocopying
t~chniques since ink deposits bonded by the binders used in
these processes have a t~n~ncy to be released from the
pulp but to remain as dispersed particles of bonded
pigment. Binders that are chemically cross linked are
liable to promote this problem. The ink particles can be
relatively large and so have a severe tendency to remain
-trapped by the fibres in the Accept fraction in preference
to being floated with any dispersed pigment in the Reject
fraction. As a result, sheets made from the Accept
fraction may have very good whiteness (as a result of good
removal of any dispersed pigment by the de-inking process)
but may have a significant number of visible specks (as a
-20 result of resistant ink particles remaining in the Accept
fraction). Accordingly, neutral de-i~king processes have
advantages from an environmental point of view but have
disadvantages in that binders that might swell in alkaline
de-inking are resistant binders in neutral de-inkinq
thereby leading to increased speck contamination, and speck
contamination is additionally an increasing problem because
of the increased amounts of laser or photocopier printed
papers in paper waste.
There is therefore a need to find a way of improving
neutral de-inking processes so as to reduce the speck
contamination in the Accept fraction due to resistant
binder, especially due to laser or photocopier inks, while
maint~in; ng good whiteness.
A process according to the invention for de-inking
paper carrying ink particles comprising a binder, which is
preferably resistant, and a pigment comprises forming a
pulp of the paper and thereby dispersing the particles in
- wossll2o26 21 5 2 7 8 ~ PCT/GB94/02350
the pulp often substantially without release of the pigment
from the particles, subjecting the pulp to flotation and
thereby forming a Reject fraction con~ ing the ink
particles and an Accept fraction, and thirk~ni~g the Accept
fraction, and in this process the pulping is conducted at
a pH of from 6 to 8.5 in the presence of an anionic polymer
formed from water-soluble ethylenically unsaturated monomer
or monomer blend comprising ethylenically unsaturated
carboxylic acid and that promotes dispersion of the ink
particles in the pulp, and the flotation is conducted in
the presence of a cationic surfactant that promotes
preferential flotation of the ink particles into the reject
fraction.
Thus in the invention the flotation step is optimised
by the use of cationic surfactant so as to obtain optimum
flotation of the resistant ink particles and we generally
find that it is possible to do this without adversely
affecting the whitene~R due to dispersion of pigment in the
pulp .
- 20 In some ins~ceC it is desirable to subject the pulp
to a plurality of flotation stages in which event one of
the flotation stages may be optimised for removing
dispersed pigment in the Reject fraction and another
flotation stage may be optimised for removing resistant ink
particles in the Reject fraction. For instance the
surfactant may be added to the Accept fraction from a
previous flotation stage so that dispersed pigment is
primarily removed during the previous flotation stage and
the resistant particles are primarily removed during the
later flotation stage.
It is also possible to conduct a pulping and flotation
de-inking process to remove dispersed ink and then to
conduct pulping on the Accept fraction from the first
process followed by flotation to remove resistant ink
particles, or the process can be conducted the other way
round.
Wo95/12026 2 1 ~ 2 7 8 2 PCT/GB94/02350
The de-inking process of the invention is a
substantially neutral de-inking process, that is to say the
pulping is conducted at a pH which is substantially
neutral, namely with a pH in the range of around 6 or 6.5
to 8 or 8.5. Often the pH is in the range of around 6.5
to 7.5 or 8.
The pH value is the pH of the pulp during the pulping
process, i.e., after the inclusion of any de-inking
additives that are incorporated in the pulp in order to
promote de-inking. Alkaline pulping is conducted in the
presence of materials such as sodium phosphate, sodium
hydroxide and/or sodium silicate and often with peroxide as
a bleach. Although small quantities of such materials can
- be included, provided the pH stays within the substantially
neutral range, in the invention the pulping is preferably
conducted in the substantial absence of such alkaline
materials. Some bleaching chemicals can be included if
necessary, or a subsequent bleach step can be added, but
preferably the pulping is conducted in the substantial
- 20 absence of peroxide or other bleaches.
Preferably the pulping is conducted in the presence of
a buffer for providing the pulp with the desired pH, which
is 6 to 8.5, often 6.5 to 8.
Although it is possible for the process to be
conducted utilising sodium carbonate and sodium phosphate
with the anionic polymer, preferably the process is
conducted in the substantial Ahs~nce of phosphate.
Conventional buffers such as sodium carbonate and/or sodium
bicarbonate, for instance as described in PCT/GB93/00780,
are preferably used.
When buffer material or other material is being
included to control or adjust the pH of the pulp, the
proportions of buffer or other material and polymeric
dispersing agent, on a dry weight basis, are generally 1:5
to S:l by weight, most preferably 2:1 to 1:2.
The anionic polymer that must be incorporated in the
pulping composition may be an anionic dispersing agent or
WO95/12026 ~1 5 2 7 ~ 2 PcT/Gss4/023so
an anionic anti-redeposition aid. It must be a water
soluble polymer.
Its molecular weight (measured by gel permeation
~ chromotography) should normally be above l,000 and
generally above 2,000. It is usually unnecess~ry for it
to be above 200,000 or 150,000 and generally it is below
lO0,000. For instance it is often below 50,000. Best
results are generally obtained when the molecular weight is
in the range 2,000 to 20,000. However good results can
also be obtained at higher values, e.g., 75,000 or higher.
If it is desired to provide the de-inking chemicals in
solid form, it is convenient for the molec~ r weight to be
sufficiently high to facilitate the formulation of the
product as a solid, in which event the molec~lAr weight is
lS generally above 5,000 and frequently in the range 7,000 to
20,000. However when the de-inking chemicals are
formulated as a solution the molecular weight can be lower.
Best results are often obtained in the range 2,000 to
lO,000, often around 2,500 to 6,000.
- 20 The monomeric material from which the polymeric
dispersing agent is formed preferably comprises
ethylenically unsaturated carboxylic acid. This can be
methacrylic acid, maleic acid, crotonic acid, itaconic acid
or any of the other polymerisable carboxylic acids, but
preferably it is acrylic acid or a mixture of acrylic (or
sometimes methacrylic) acid with maleic acid (frequently
including anhydride). The acrylic acid or other
carboxylic monomeric material can be polymerised alone or
with sulphonic monomer such as 2-acrylamido methyl propane
sulphonate (AMPS, U.S. trade mark), vinyl sulphonate or
(meth) allyl sulphonate, and/or it can be copolymerised
with non-ionic monomer, especially acrylamide.
Generally the carboxylic monomer constitutes at least
50% by weight of the monomers and preferably the polymer is
formed from carboxylic monomer alone or a blend consisting
of carboxylic and sulphonic monomers. Suitable polymers
include polyacrylic acid, copolymers of this with maleic
WO95/12026 21 ~ 2 7 8 2 PCT/GB94/023S0
anhydride, and copolymers of acrylic acid with 10-50% by
weight AMPS.
The polymer preferably has polydispersity below 2,
preferably below 1.8 and most preferably below 1.5, and
generally above 1.1, for instance as described in EP
129,329.
Other dispersing agents can be included in the pulping
process in order to improve results.
Suitable dispersing agents that can be used include
cellulosic derivatives, polyphosphonates, bentonites, and
sequestering agents.
Suitable cellulosic derivatives include cellulose
ethers, such as methyl cellulose, and carboxy methyl
cellulose.
15Suitable bentonites include the various swelling clays
that are referred to colloquially as bentonites, including
true bentonite, Fuller's Earth, hectorite and various
swelling montmorillonites, such as activated calcium
montmorillonite.
20Suitable sequestering agents are amino carboxylic acid
sequestering agents, such as ethylene diamine tetro acetic
acid and nitrilo tri acetic acid.
Suitable mixtures of two or more of the dispersing
agents include mixtures of one of the described polymeric
dispersing agents, especially polyacrylic acid or a
copolymer of acrylic acid with maleic acid (including
anhydride) or AMPS, with a polyphosphonate or sequestering
agent or CMC or methyl cellulose.
The components in such mixtures typically are present
in proportions ranging from 1:3 to 3:1 by weight.
The amount of dispersing agent that is required for
optimum performance can be selected by routine
experimentation and is normally in the range 0.01 to 1% by
weight based on the dry weight of the pulp, generally 0.05
to 0.5%.
The cationic surfactant is preferably added to the
pulp after the pulping process so as to promote
WO95/12026 2 1 5 2 7 8 2 PCT/GB94/02350
preferential fiotation in the pulp. However it is also
possible for some or all of the cationic surfactant to be
included in the pulping process. For instance it may be
included initially in the water into which the waste paper
is pulped or it may be added with the polycarboxylic acid
and any other de-inking chemicals during the pulping
process.
The cationic surfactant that is used in the invention
can either be a true cationic surfactant (in the sense that
it is cationically charged at the time it is added to the
pulp) or it can be a free base surfactant which we believe
can become cationically charged by interaction with the
polycarboxylic or other dispersing agent or other component
of the pulp.
Suitable materials that can be used include
ethoxylated fatty amines and fatty diamines and quaternary
fatty ammonium com~ou.lds (i.e., quaternary ammonium
compounds including at least one fatty group). The fatty
groups can be naturally O~UL ing or synthetic fatty
yLo~, generally containing 6 to 24, often 8 to 18, carbon
atoms. The fatty group is often alkyl. Ethoxylate fatty
amines are preferred.
The cationic surfactant can be a surfactant that
includes both cationic and anionic y~vU~ (i.e.,
amphoteric) but preferably it is wholly cationic.
The formation of the pulp may be conducted in the
presence of additional materials but a particular advantage
of the invention is that the chemicals used for it can
consist essentially only of the dispersing agent, buffering
alkali, optional surfactant and optional flotation aids and
collectors. Peroxide or other bleach can be included if
desired, but an advantage of the invention is that it is
usually unnPcpcs~ry. Accordingly the liquor resulting
from the de-inking is relatively free of materials that
would create environmental problems during disposal.
The de-inking process can be carried out in broadly
conventional manner, except for the choice of the de-inking
WO95/12026 21~ 2 7 8 2 PCT/GB94/02350
chemicals, as described above. The de-inking chemicals
can be included in the aqueous liquor into which the waste
paper is initially pulped, or the waste paper can be pulped
to form an aqueous pulp into which the de-inking chemicals
are then incorporated.
The waste paper preferably includes photocopy
(xerographic) and/or laser ink printed paper, for instance
in an amount of 10 to 100%, often 50 to 100%, of the waste
paper. The process is of particular value for de-i nki n~
office waste.
The overall de-inking process generally comprises a
series of stages, typically consisting of an initial
maceration or pulping stage (preferably conducted under
very high shear), a screening stage to remove grit and
oversized particles, one or more flotation stages, and a
thickening stage to form a clean pulp that can either be
used as such or that may be drained to form a dried pulp.
Typical de-i nki n~ ~,oc~see are described in more detail
in, for instance, ~An~hook for Pulp and Paper Technologists
by G.A.Smook.
Thickening can be conducted on thickening drums in
conventional manner, for instance to raise the solids
content of the pulp from a concentration suitable for
flotation to a concentration suitable for recycling to
paper manufacture, for instance 5 to 15% dry weight. The
Accept fraction from flotation may be subjected to w~chin~
with water or an aqueous solution of surfactant before or
after thick~ni n~ .
The following are examples of the invention. In these
examples the following de-inking components are used.
A 50:50 mix of sodium polyacrylate molecular weight
around 5,000 and sodium carbonate
D Ethoxylate fatty amine cationic surfactant
E C12 alkyl quaternary ammonium salt catinic surfactant
F Amphoteric cationic surfactant
G Sodium lauryl sulphate anionic surfactant
H Sodium dioctyl sulpho succinate non-ionic surfactant
WO 95/12026 2 1 5 2 7 8 2 PCT/GB94tO2350
Exam~le 1
A series of de-inking procecseæ was conducted. In
each process 1.5kg of waste paper carrying either laser
print or Xerox (trade mark) print was pulped with 0.2%
(based on the dry weight of waste) of de-inking component
A and 10 litres of water under neutral conditions. The
pulp was diluted to 1% and a sample was taken for speck
analysis. The results of this analysis are quoted in
column of Table 1.
10In this, and in all instances where a sample was taken
for speck analysis, the sample was made into a h~n~cheet,
dried and a visual speck count of the dried hAn~che~t was
made. The results were assessed on a scale of 1 to 10
- where 10 is the worst (highest number of specks) and 1 is
lS the best (lowest number of specks).
In those instances where surfactant was to be added,
it was then added to the pulp in an amount of 0.125%. The
pulp, with or without surfactant, was then floated in a
laboratory Voith flotation cell for 2 minutes. The Reject
was scraped off the surface and the Accept after 10 minutes
was sampled. Speck counts were made on each sample and
the results are in column 2 of Table 1.
The 1% Accept after 10 minutes was thickened to 10%
over a 710~m sieve and the thickene~ stock was sampled and
a speck count was made. The results are in column 3 of
Table 1.
Table 1
Additives Laser Xerox
1 2 3 1 2 3
Blank 10 9 9 10 9 9
Soap 10 5 4 10 9 9
A 10 9 8 10 8 8
A + D 10 3 2 10 4 4
A + E 10 3 2 10 3 3
A + F 10 5 4 10 6 6
A + G 10 4 4 10 6 6
A + ~ 10 6 5 10 7 7
WO95/l2026 PCT/GB94/02350
2 15 2~ ~ ~ 12
It is apparent from these results that the cationic
surfactants D and E give particularly good results.
Exam~le 2
Laser printed paper and xerographic printed paper was
pulped with 0.2% of de-inking component A at neutral
conditions (around pH7.4 or 7.5), diluted, treated with
surfactant, and subjected to flotation all broadly as
described in Example 1. The dirt area of the hand sheet
was recorded in parts per million by image analysis and the
brightness was recorded. The results are set out in Table
2, in which columns 1, 2 and 3 have the same meanings as in
Example 1.
Table 2
Dirt Area Brighteners
Laser 1 2 3 1 2 3
A 20354 6618 4887 73.575.3 76.2
A + D 10467 80.5 96.6 74.276.7 79.9
A + E 14235 475 733 73.276.1 79.3
A + F 10193 274 258 72.775.4 80.8
A + G 22560 2222 902 69.273.3 76.4
A + H 11192 628 306 71.774.0 78.6
Xero-
graphic
A 10129 10290 10411 74.474.4 75.1
A + D 9525 1087 483 73.175.4 79.4
A + E 8470 523 668 75.475.4 77.6
A I F 9058 684 854 76.276.8 80.7
A + G 11812 1876 1957 73.978.4 76.8
A + H 11304 1232 790 73.274.9 78.9
These results demonstrate the low speck area and the
satisfactory brightness values that can be obtAine~ using
the cationic surfactants. The amphoteric cationic
surfactant gives a low speck value on the laser paper but
is not so efficient on the xerographic paper.
The results also demonstrate the good brightness
values obtainable in the invention, and in this respect the
amphoteric cationic surfactant gives good results.
- WO9S/12026 ~ 5 2 7 8 2 PCT/GD~1J~2350
13
In this test the non-ionic surfactant H also gives
reasonably good dirt area and brightness values, but not as
good as the best cationic surfactant. However in the
prPc~ing example the non-ionic surfactant gave less
S satisfactory results.
The data shows that the use of the cationic surfactant
does give valuable results on a variety of papers,
especially on laser and xerographic papers.
According to another aspect of the invention, the
pulping is conducted at a pH of 6 to 8.5 in the presence of
an anionic polymer as desribed above, and non-ionic
surfactant is then added to the pulp in order to promote
preferential flotation of the resistant ink particles into
the reject fraction. In this aspect of the invention, the
cationic surfactant can be omitted.
In another aspect of the invention, the pulping is
conducted in the presence of an anionic polymer as
described above and the flotation is conducted in the
presence of a cationic or non-ionic surfactant that
- 20 promotes preferential flotation of the resistant ink
particles into the reject fraction, but in this process the
pulping is con~llcted at an alkaline pH, for instance up to
9 or 9.S. Thus the pulping can be conducted in the
presence of an alkali, optionally with a bleach. The
alkali is typically selected from sodium silicate and
sodium hydroxide and sodium phosphate. The bleach is
typically hydLo~en peroxide.
In another aspect of the invention, the pulping is
conducted at a pH of 6 to 8.5 as described above and the
flotation is conducted in the presence of a cationic or
non-ionic surfactant as described above, and the pulping is
conducted in the presence of a blend of sodium carbonate
and sodium phosphate instead of or in addition to the
anionic polymer.
