Note: Descriptions are shown in the official language in which they were submitted.
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Method for reducing negative effects of natural pitch contaminants in both
pulping
and papermaking operations
The invention relates to resin and pitch control agents, which are aqueous,
non-
film forming, polymer dispersions and to a process for preventing the
deposition of
pitch particles in cellulosic pulp suspensions, by use of such polymer
dispersions.
Cellulosic pulps contain a considerable proportion of organosoluble matter
which
is generally referred to as resin or pitch. The resins are extracted from the
wood
during the pulping process and constitute a significant nuisance in cellulosic
suspensions because the resin particles are sticky, tend to agglomerate and
form
adherent deposits on the pulping and papermaking machinery. The removal of
water during papermaking is normally carried out using a type of fabric mesh,
commonly referred to as machine wires or felts. Resin or pitch deposits clog
and
block the small openings in the fabrics inhibiting drainage and causing sheet
defects, such as holes in the finished paper. Deposits which accumulate on the
internal surfaces of pulp and backwater chests can suddenly be released and
displayed as resin lumps in the paper sheet. Larger lumps can break the paper
sheet in the machine, leading to loss of production.
For years there have already been products supplied as passivating agents for
treating pulp contaminants such as resin or pitch. These dissolved products
are
intended to make the surface of the tacky impurities more hydrophilic and
hence
keep them more wettable, thereby reducing the affinity for hydrophobic
surfaces.
Hydrophobic surfaces are present on, for example, wires, felts and rollers;
hydrophobizing is boosted further by coating, with sizing agent or defoamer,
for
example, thereby further promoting the attachment of pitch.
In certain cases, resins and pitch do not cause any problems in papermaking,
if
.. they do not agglomerate. To prevent agglomeration, various methods are
known
for chemically modifying the pitch particles that have remained in the stock
stream
and the adsorption thereof on support materials, such as machine wires.
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In the context of these problems, the procedures below have been adopted in
practice, but lead only to partial success.
On the one hand, dispersion may take place, with the aim of changing the
charge
on the pitch by means of anionic and nonionic dispersants. This forms
colloidal,
anionically charged or nonionic particles which counteract agglomeration and
deposition. The wetting properties of the dispersant are very important in
this case,
since the pitch is hydrophobic.
Alternatively, according to the literature, the tack of the pitch can be
reduced in the
following ways:
- Fixing of the strongly anionic contaminants by means of strongly cationic
fixatives (formation of what are called polyelectrolyte complexes; the
reaction
product then adsorbs on the anionic fiber).
- Absorption on pigments of high specific surface area (e.g., talc,
modified clay,
mica, smectite, bentonite), often with subsequent flocculation by means of
polymers in order to bind separable macroflocs.
- Enveloping (masking) with nonionic hydrophilic polymers (polyvinyl
alcohol) or
zirconium compounds, more particularly zirconium acetate and ammonium
zirconium carbonate.
Known strongly cationic fixatives include polyethyleneimine (PEI),
polydiallyldimethylammonium chloride (polyDADMAC), polyvinylamine (PVAm),
polyaluminum chloride (PAC), polyacrylarnide (PAAM), polyamine, etc. The
sphere
of action of fixatives extends from about 1 rim to 50 micrometers in terms of
the
particle size of the pitch, depending on the nature and modification of the
chemicals used.
Materials with a low surface energy (wires, felts, roller surfaces) exhibit a
more
hydrophobic behaviour and therefore possess a high affinity for hydrophobic
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compounds, such as resins and pitch, thereby resulting in contamination of the
wires and hence to defects and/or reduction in the dewatering performance of
felts.
Adsorbents used are, in particular, various types of talc with specific
surface
modifications and particle-size distribution, which on account of their
hydrophobic
and organophilic surface are capable of attaching to adhesive constituents and
entraining them with the paper. Particles of adhesive encapsulated in this way
have less of a tendency to deposit on hot machinery parts.
Protein solutions are also employed as agents for masking sticky impurities.
The pitch agglomerates tend to deposit on machinery parts, wires, cloths,
drying
cylinders, and this consequently leads to marks, holes, and instances of web
sticking, and consequently to breakages in the wet section and drying section
in
the course of winding and rewinding or in the course of printing.
DE-102009035884.6 / EP 2 462 278 by Clariant discloses a method for reducing
negative effects of adhesive synthetic contaminants in systems of substances
comprising waste paper. In waste paper the main problem are the pitch
agglomerates (stickies) which lead to a deposit on the machinery parts.
In contrary in the process for producing cellulosic pulp suspensions the
negative
effects are caused by natural pitch contaminants in both pulping and
papermaking
operations. These contaminants tend to deposit during the production on the
cellulosic material and lead to ugly black spots.
In order to prevent resin deposits talc has been known in the prior art to
prevent
and control pitch deposits. Using talc to control pitch deposits, however, has
certain disadvantages. For instance, the system is highly sensitive to shear.
Talc,
moreover, has poor retention properties and frequently causes clogging of the
felts. Talc may adversely affect resin sizing, and stabilizes foam. The two
inorganic
products, talc and bentonite, require laborious dispersion.
4
There continues to be a need for improvement in reducing the tackiness of
natural
pitch and resin particles.
Summary
Surprisingly, the tackiness of pitch can be reduced considerably through the
use of
specific polymer dispersions.
In certain embodiments there is provided a method for inhibiting pitch
deposition on
pulping and papermaking equipment or machinery in the processing of wood pulp
comprising adding to a wood pulp slurry containing natural pitch an effective
amount
of polymer dispersion comprising a component A and a component B, wherein
component A is a homopolymer and/or copolymer of acrylic acid and/or its alkyl
esters, or methacrylic acid and/or its alkyl esters, styrene and/or
methylstyrene, vinyl
acetate, itaconic acid, glycidyl methacrylate, 2-hydroxyalkyl (meth)acrylate,
methacrylamide, N-hydroxyethyl(meth)acrylamide, dimethacrylate monomers,
1,3-butylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene
glycol
dimethacrylate, propylene glycol dimethacrylate, dipropylene glycol
dimethacrylate,
4-methyl-1,4-pentanediol dimethacrylate, divinylbenzene and/or
trivinylbenzene, and
component B is an aqueous solution of a styrene copolymer with acrylic acid,
maleimide and/or maleic anhydride.
In certain other embodiments there is provided a use of an aqueous polymer
dispersion comprising a component A and a component B, component A being a
homopolymer and/or copolymer of methyl methacrylate, acrylate and/or styrene
and
component B being an aqueous solution of styrene copolymer with acrylic acid,
maleimide and/or maleic anhydride, for coagulating and detackifying pitch
particles in
the processing of pulp and paper.
Detailed Description
The invention provides an aqueous polymer dispersion and the use thereof in a
method for reducing sticky contaminants in the processing of wood pulp and in
the
papermaking procedure, which involves adding an aqueous polymer dispersion
comprising a component A and a component B for passivating and detackifying
the
pitch particles, component A being a homopolymer and/or copolymer of acrylic
acid
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and/or its alkyl esters, more particularly its methyl, ethyl, butyl, isobutyl,
propyl, octyl,
decyl, 2-ethylhexyl esters;
or methacrylic acid and/or its alkyl esters, more particularly its methyl,
ethyl, butyl,
isobutyl, propyl, octyl, decyl, 2-ethylhexyl esters;
styrene and/or methylstyrene;
vinyl acetate;
itaconic acid;
glycidyl methacrylate;
2-hydroxyalkyl (meth)acrylate;
methacrylamide;
N-hydroxyethyl (meth)acrylamide
dimethacrylate monomers, such as, for example, 1,4-butylene glycol
dimethacrylate, 1,3-butylene glycol dimethacrylate, ethylene glycol
dimethacrylate,
diethylene glycol dimethacrylate, propylene glycol dimethacrylate, dipropylene
glycol
dimethacrylate, 4-methyl-1,4-pentanediol dimethacrylate;
divinylbenzene and/or trivinylbenzene
and component B being an aqueous solution of a styrene copolymer with acrylic
acid, maleimide and/or maleic anhydride.
Component A is a hydrophobic homopolymer and/or copolymer of the above-stated
monomers having a very high glass transition temperature or softening
temperature
(Tg), preferably methyl methacrylate or styrene. The glass transition
temperature of A
is preferably above 70 C, more particularly above 90 C, very preferably
above
.. 100 C.
Component B is a styrene copolymer with (meth)acrylic acid, maleimide and/or
maleic anhydride. Component B is preferably a copolymer of styrene and acrylic
acid. Component B preferably has a molecular weight of between 3000 g/mol and
15 000 g/mol, more particularly 3000 and 7000 g/mol.
Particularly preferred is an aqueous dispersion with particle sizes of less
than
150 nm, preferably less than 120 nm.
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The aqueous polymer dispersion may be applied in combination with calcium and
or magnesium salts, often naturally occurring in the processing water.
Hardness
salts insolubilise component B, leading to the de-stabilisation of the tiny
emulsion
particles. The agglomerated emulsion particles are now more hydrophobic and
associate readily and preferentially with any pitch particles in the pulp. The
harder
emulsion particles reduce the tackiness of the pitch and increase the
softening
temperature. Hard agglomerates show much less tendency to deposit on
machinery.
In certain embodiments, the aqueous polymer dispersion comprises pulp and/or
paper making process water having a water hardness of less than an amount in
the
range of 15- 20 dH, for example, less than 20 dH.
Where water hardness levels are very low, there may not be sufficient
electrolyte to
initiate de-stabilisation of the emulsion particles. The aqueous polymer
dispersion
may therefore be optionally applied in combination with component C, a
cationic fixative, which promotes coagulation of the emulsion particles in the
cellulosic fibre slurry. Component C is preferably selected from the following
group:
polyethyleneimine (PEI), polydiallyldimethylammonium chloride (polyDADMAC),
polyvinylamine (PVAm), polyaluminum chloride (PAC), zirconium salts,
polyacrylamide (PAAM), polyamine and polyamideamine.
The present invention allows Component C to be added during pulp or paper
manufacture, either before, after or together with the aqueous polymer
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dispersions. When Component C and aqueous polymer dispersions are pre-mixed
before being added to the fibrous slurry, the particle size increases and the
the
process of destabilisation is initiated. This premature destabilisation is
described
with the term "pre-crashing".
It is not essential but preferential to dilute both components before
combining them
in a pre-crashing application. For aqueous polymer dispersions of the present
invention, a dilution of 1 to 20 % (based on dry content) is preferred, more
preferably 1 to 5 %. For Component C, a dilution of Ito 10 % (based on dry
content) is preferred, more preferably Ito 5 %. The ratio of the diluted
components is controlled using individual dosing pumps and, immediately after
blending, the combined components are passed through a static mixer and then
into the suction side of a pulp transfer pump, in order to facilitiate
efficient
distribution within the fibrous slurry.
In order to boost the efficiency of the polymer dispersion of the invention
and its
stability, it is further possible to add a further component D optionally in
the form of
a surfactant.
Further to components A, B, and/or D, the polymer dispersion comprises
water (component E).
In one preferred embodiment the aqueous dispersion comprises
2 % to 50 %, preferably 5 % to 30 % of component A,
1 % to 30 %, preferably 3 % to 10 % of component B,
0 % to 0.3 %, preferably 0 % to 0.2 % of component D, and
96 A to 17.7 %, preferably 90 % to 45 % of water (component E).
All percentages here relate to A) by weight.
In the presence of Ca2+, the aqueous dispersion constitutes a self-coagulating
nanodispersion. The polymer dispersion of the invention attaches to the
hydrophobic sticky particles, incorporating them into the precipitating
polymer
dispersion and thus detackifying them (Fig. 1).
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Examples:
Example 1 (version with methyl methacrylate)
A 2 I reactor with stirrer and reflux condenser was charged with 739.5 g of
deionized water and 419.3 g of 25 % strength solution of styrene-acrylic acid
copolymer, this initial charge then being heated to 85 C with stirring under
a
nitrogen atmosphere.
Feed stream I:
384.8 g of methyl methacrylate
Feed stream II:
1.99 of ammonium peroxodisulfate
136.39 of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 318.2 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 24.1 %
D = 53 nm
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Example 2 (version with methyl methacrylate + crosslinker)
A 2 I reactor with stirrer and reflux condenser was charged with 739.5 g of
deionized water and 419.3 g of 25 % strength solution of styrene-acrylic acid
copolymer, this initial charge then being heated to 85 C with stirring under
a
nitrogen atmosphere.
Feed stream I:
370.9 g of methyl methacrylate
19.5 g of glycidyl methacrylate
Feed stream II:
1.9 g of ammonium peroxodisulfate
136.3 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 318.2 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 24.9 %
= 40 nm
Example 3 (version with methyl methacrylate + second crosslinker)
A 2 I reactor with stirrer and reflux condenser was charged with 740 g of
deionized
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water and 419 g of 25 % strength solution of styrene-acrylic acid copolymer,
this
initial charge then being heated to 85 C with stirring under a nitrogen
atmosphere.
Feed stream I:
.. 370 g of methyl methactylate
19 g of ethylene glycol dimethacrylate
Feed stream II:
2 g of ammonium peroxodisulfate
136 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 318 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 25 %
= 40 nm
Example 4 (version with styrene)
A 2 I reactor with stirrer and reflux condenser was charged with 739.5 g of
deionized water and 419.3 g of 25 % strength solution of styrene-acrylic acid
copolymer, this initial charge then being heated to 85 C with stirring under
a
nitrogen atmosphere.
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Feed stream I:
384.8 g of styrene
Feed stream II:
5 1.9 g of ammonium peroxodisulfate
136.3 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
10 separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 318.2 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 24.5 %
D = 61 nm
Example 5 (version with colloid + surfactant)
A 2 I reactor with stirrer and reflux condenser was charged with 1111 g of
deionized water, 310 g of 25 % strength solution of styrene-acrylic acid
copolymer,
and 3 grams of lauryl sulfate, this initial charge then being heated to 85 C
with
stirring under a nitrogen atmosphere.
Feed stream I:
387 g of methyl methacrylate
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Feed stream II:
2 g of ammonium peroxodisulfate
88 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 80 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
.. and average particle size (D), is given below:
SC = 24 %
D = 50 nm
Example 6 (styrene-methyl acrylate copolymer
A 2 I reactor with stirrer and reflux condenser was charged with 739.5 g of
deionized water and 420 g of 25 % strength solution of styrene-acrylic acid
copolymer, this initial charge then being heated to 85 C with stirring under
a
nitrogen atmosphere.
Feed stream I:
1939 of styrene
193 g of methyl methacrylate
Feed stream II:
2 g of ammonium peroxodisulfate
136 g of deionized water
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When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 318.2 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 30.0 %
= 70 nm
Example 7 (styrene-maleic anhydride as component B)
A 2 I reactor with stirrer and reflux condenser was charged with 400 g of
deionized
water and 750 g of 14 % strength solution of styrene-maleic anhydride
copolymer,
this initial charge then being heated to 85 C with stirring under a nitrogen
atmosphere.
Feed stream I:
390 g of methyl methacrylate
Feed stream II:
2 g of ammonium peroxodisulfate
130 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream II were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
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retention of the reaction temperature. The pumps were flushed with 318.2 g of
deionized water. After that, the reaction mixture was cooled to room
temperature
and filtered on a filter having a mesh size of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 29.6 %
D = 70 nm
Example 8 (high colloid fraction)
A 2 I reactor with stirrer and reflux condenser was charged with 21.1 g of
deionized water and 750 g of 25 % strength solution of styrene-acrylic acid
copolymer, this initial charge then being heated to 85 C with stirring under
a
nitrogen atmosphere.
Feed stream I:
390 g of methyl methacrylate
Feed stream II:
29 of ammonium peroxodisulfate
130 g of deionized water
When an internal temperature of 85 C had been reached, feed stream I and feed
stream ll were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 3 h 30, with
stirring and
retention of the reaction temperature. The pumps were flushed with 80 g of
deionized water. After the end of both feed streams, the mixture was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
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The characterization of the copolymer obtained, in terms of solids content
(SC)
and average particle size (D), is given below:
SC = 44 %
= 80 nm
Example 9 (styrene-acrylic acid copolymer with Tg of about 30 C)
A 2 I reactor with stirrer and reflux condenser was charged with 433 g of
deionized
water, and 3 grams of lauryl sulfate (30 % strength solution), this initial
charge
then being heated to 80 C with stirring under a nitrogen atmosphere.
Feed stream I:
5 g of ammonium peroxodisulfate
62 g of deionized water
Feed stream II:
400 g of styrene,
260 g of butyl acrylate,
10 g of methacrylic acid,
11 g of surfactant solution (lauryl sulfate, 30 %),
384 g of deionized water
When an internal temperature of 80 C had been reached, feed stream I and feed
stream ll were metered continuously into the polymerization batch via two
separate feeds, beginning simultaneously, over a period of 4 h, with stirring
and
retention of the reaction temperature. The pumps were flushed with 235 g of
deionized water. After the end of both feed streams, the system was left to
after
react at the reaction temperature for a further 25 minutes. After that, the
reaction
mixture was cooled to room temperature and filtered on a filter having a mesh
size
of 160 pm.
The characterization of the copolymer obtained, in terms of solids content
(SC)
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and average particle size (D), is given below:
SC = 37 %
= 185 nm
Tg = 30 C
5
