U.S. patent application number 10/841262 was filed with the patent office on 2004-12-16 for process for the production of paper.
Invention is credited to Carr, Duncan S..
Application Number | 20040250972 10/841262 |
Document ID | / |
Family ID | 36773838 |
Filed Date | 2004-12-16 |
United States Patent
Application |
20040250972 |
Kind Code |
A1 |
Carr, Duncan S. |
December 16, 2004 |
Process for the production of paper
Abstract
The invention relates to a process for the production of paper
which comprises (i) providing a main aqueous flow containing
cellulosic fibers; (i) introducing one or more retention components
into the main aqueous flow to form a main aqueous flow containing
one or more retention components; (iii) providing a diluting
aqueous flow; (iv) introducing a low molecular weight cationic
organic polymer into the diluting aqueous flow to form a diluting
aqueous flow containing a low molecular weight cationic organic
polymer, the low molecular weight cationic organic polymer having a
weight average molecular weight up to 5,000,000; (v) introducing
the diluting aqueous flow containing a low molecular weight
cationic organic polymer into the main aqueous flow containing one
or more retention components to form a resulting aqueous flow; and
then (vi) ejecting the resulting aqueous flow onto a wire and
dewatering the resulting aqueous flow to form a web of paper.
Inventors: |
Carr, Duncan S.; (Neenah,
WI) |
Correspondence
Address: |
Michelle J. Burke
Akzo Nobel Inc.
Intellectual Property Department
Dobbs Ferry
NY
10522
US
|
Family ID: |
36773838 |
Appl. No.: |
10/841262 |
Filed: |
May 7, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60469010 |
May 9, 2003 |
|
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Current U.S.
Class: |
162/164.1 ;
162/168.3; 162/175; 162/181.7 |
Current CPC
Class: |
D21H 21/10 20130101;
D21H 23/24 20130101; D21H 17/20 20130101 |
Class at
Publication: |
162/164.1 ;
162/175; 162/181.7; 162/168.3 |
International
Class: |
D21H 021/10 |
Claims
1. A process for the production of paper which comprises (i)
providing a main aqueous flow containing cellulosic fibers; (i)
introducing one or more retention components into the main aqueous
flow to form a main aqueous flow containing one or more retention
components; (iii) providing a diluting aqueous flow; (iv)
introducing a low molecular weight cationic organic polymer into
the diluting aqueous flow to form a diluting aqueous flow
containing a low molecular weight cationic organic polymer, the low
molecular weight cationic organic polymer having a weight average
molecular weight up to 5,000,000; (v) introducing the diluting
aqueous flow containing a low molecular weight cationic organic
polymer into the main aqueous flow containing one or more retention
components to form a resulting aqueous flow; and then (vi) ejecting
the resulting aqueous flow onto a wire and dewatering the resulting
aqueous flow to form a web of paper.
2. The process of claim 1, wherein the main aqueous flow has a
higher consistency than the diluting aqueous flow.
3. The process of claim 1, wherein the diluting aqueous flow is
white water obtained by dewatering the resulting aqueous flow.
4. The process of claim 1, wherein the retention components are
selected from the group consisting of microparticle retention
systems and retention systems comprising at least two organic
polymers.
5. The process of claim 4, wherein the retention components
comprise at least one cationic organic polymer and anionic
silica-based particles.
6. The process of claim 5, wherein the cationic organic polymer is
cationic starch or cationic acrylamide-based polymer.
7. The process of claim 1, wherein the low molecular weight
cationic organic polymer has a weight average molecular weight
within the range from 500,000 to 3,000,000:
8. The process of claim 1, wherein the low molecular weight
cationic organic polymer is a chain-growth polymer.
9. The process of claim 1, wherein the low molecular weight
cationic organic polymer is a homopolymer or copolymer based on
diallyldimethylammonium chloride.
10. A process for the production of paper on a paper machine
containing a dilution headbox which comprises (i) introducing one
or more retention components into a main aqueous flow containing
cellulosic fibers, and feeding the obtained main aqueous flow into
the dilution headbox; (ii) introducing low molecular weight
cationic organic polymer having a weight average molecular weight
up to 5,000,000 into a diluting aqueous flow and feeding the
obtained diluting aqueous flow into the dilution headbox; (iii)
mixing the obtained main aqueous flow with the obtained diluting
aqueous flow in the headbox to form a resulting aqueous flow; and
(iv) ejecting the resulting aqueous flow onto a wire and dewatering
the resulting aqueous flow to form a web of paper.
11. The process of claim 10, wherein the retention components
comprise two or more components which, when used in combination,
give better retention than is obtained when not adding the
components.
12. The process of claim 10, wherein the retention components are
selected from the group consisting of organic polymers, organic
polymers in combination with aluminium compounds, and organic
polymers in combination with inorganic microparticles.
13. The process of claim 10, wherein the low molecular weight
cationic organic polymer has a weight average molecular weight
within the range from 500,000 to 3,000,000.
14. The process of claim 10, wherein the diluting aqueous flow is
white water obtained by dewatering the resulting aqueous flow.
15. The process of claim 10, wherein the paper machine produces
paper at a speed of from 300 to 2500 m/min.
16. The process of claim 10, wherein it comprises recycling of
white water and introduction of from 0 to 30 tons of fresh water
per ton of dry paper produced.
17. The process of claim 10, wherein the retention components
comprises at least one organic polymer containing one or more
aromatic groups.
18. The process of claim 10, wherein the low molecular weight
cationic organic polymer is a homopolymer or copolymer based on
diallyldimethylammonium chloride.
Description
RELATED APPLICATION
[0001] This application claims priority based on U.S. Provisional
Patent Application No. 60/469,010, filed May 9, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for the
production of paper in which papermaking additives are introduced
into a cellulosic stock before it is ejected from a headbox onto a
wire and dewatered to form a web of paper.
BACKGROUND OF THE INVENTION
[0003] In the papermaking art, an aqueous suspension containing
cellulosic fibers and optional fillers and additives, referred to
as stock, is fed into a headbox which ejects the stock onto a
forming wire. Water is drained from the stock so that a wet web of
paper is formed on the wire, and the web is further dewatered and
dried in the drying section of the paper machine.
[0004] Retention agents are usually introduced into the stock in
order to increase adsorption of fine particles, e.g. fine fibers
and filler particles, onto the cellulosic fibers so that they are
retained with the fibers on the wire. A wide variety of retention
agents are known in the art, examples of which include anionic,
non-ionic, amphoteric and cationic organic polymers of different
molecular weights, inorganic materials, and combinations thereof.
Due to incomplete retention, the water obtained by dewatering the
stock and the wet web, referred to as white water, contains fine
particles not being retained on the wire and the white water is
usually recirculated in different flow circuits.
[0005] In paper machines having a dilution headbox, white water is
used to dilute the stock within the headbox. Hereby the flow of
high consistency stock is diluted with a low consistency flow
originating from the white water. The headbox can have a series of
mixing sections or dilution lines distributed over the width of the
headbox. White water is injected into the mixing sections to
locally control the stock dilution thereby forming a variable
consistency profile leaving the slice opening at a constant volume
flow. The dilution headbox design provides better control of paper
properties; by adjusting the amount of dilution, i.e. the ratio of
high consistency flow to low consistency flow, at a plurality of
points of the dilution headbox across the machine, the basis weight
of the web can be controlled in an improved manner and rendered
essentially uniform in a cross machine direction. However, notably
when using high performance retention agents, it has been
experienced that the papermaking process and the properties of the
paper produced are still not completely satisfactory, which has
been attributed to inadequate pitch deposition control.
[0006] Problems caused by pitch build-up on papermaking machinery
and formation of pitch globules in the final paper in the
production of all types of paper has previously been recognized.
Pitch generally refers to emulsified hydrophobic organic compounds.
Pitch can be defined as the sticky, resinous materials that are
released from wood during the pulping process. Pitch has also come
to include sticky materials which arise from components of coated
broke and recycled fibers, such as adhesives, and are often
referred to as stickies and tackies. In paper mill process waters,
pitch exists as unstable, colloidal dispersions of hydrophobic
particles. Therefore, typical papermaking process conditions, such
as hydrodynamical and mechanical shear forces and abrupt changes of
temperature as well as chemical environment and equilibrium, may
cause the colloidal pitch particles to agglomerate within the
cellulosic suspension or deposit on the surfaces of the wire or
other equipment. This may lead to quality defects in the finished
product, such as formation of spots or holes and a poor quality
paper surface, and shortened equipment life, runnability problems,
paper machine downtime and, ultimately, lost profit for the mill.
These problems are magnified in paper mills with high level of
process water closure, such as extensive white water
recirculation.
SUMMARY OF THE INVENTION The present invention is generally
directed to a process for the production of paper which
comprises:
[0007] (i) providing a main aqueous flow containing cellulosic
fibers;
[0008] (ii) introducing one or more retention components into said
main aqueous. flow to form a main aqueous flow containing one or
more retention components;
[0009] (iii) providing a diluting aqueous flow;
[0010] (iv) introducing a low molecular weight cationic organic
polymer into said diluting aqueous flow to form a diluting aqueous
flow containing a low molecular weight cationic organic polymer,
said low molecular weight cationic organic polymer having a weight
average molecular weight up to 5,000,000;
[0011] (v) introducing said diluting aqueous flow containing a low
molecular weight cationic organic polymer into said main aqueous
flow containing one or more retention components to form a
resulting aqueous flow; and then
[0012] (vi) ejecting said resulting aqueous flow onto a wire and
dewatering said resulting aqueous flow to form a web of paper.
[0013] The present invention is further directed to a process for
the production of paper on a paper machine containing a dilution
headbox, the process comprising:
[0014] (i) introducing one or more retention components into a main
aqueous flow containing cellulosic fibers, and feeding the obtained
main aqueous flow into the dilution headbox;
[0015] (ii) introducing low molecular weight cationic organic
polymer having a weight average molecular weight up to 5,000,000
into a diluting aqueous flow and feeding the obtained diluting
aqueous flow into the dilution headbox;
[0016] (iii) mixing the obtained main aqueous flow with the
obtained diluting aqueous flow in the headbox to form a resulting
aqueous flow; and
[0017] (iv) ejecting the resulting aqueous flow onto a wire and
dewatering the resulting aqueous flow to form a web of paper.
[0018] The invention is also directed to a process for the
production of paper from an aqueous suspension containing
cellulosic fibers, and optional filler, which comprises introducing
one or more retention components into the suspension followed by
introducing into the suspension a low molecular weight cationic
organic polymer having a weight average molecular weight up to
5,000,000, and thereafter forming and draining the suspension on a
wire.
DETAILED DESCRIPTION OF THE INVENTION
[0019] According to the present invention it has been found that
pitch problems can be reduced by the introduction of additives into
a stock in a certain manner before it is dewatered on a wire to
form the web of paper. This finding is particularly applicable to
papermaking processes where paper is produced on a paper machine
with a dilution headbox. It has also been found that pitch
deposition in the papermaking system can be better controlled
according to the present invention. It has further been found that
the process of this invention renders possible production of paper
with improved properties.
[0020] Dilution headboxes generally can be described as devices
comprising at least one inlet for a first partial volume flow, at
least one inlet for a second partial volume flow, at least one
section for mixing the partial volume flows to form a mixture
volume flow, and at least one outlet for ejecting the mixture
volume flow. Preferably the dilution headbox comprises a plurality
of such inlets, sections and outlets across its working width.
Examples of suitable dilution headboxes include those disclosed in
U.S. Pat. Nos. 4,909,904; 5,196,091; 5,316,383; 5,545,293; and
5,549,793.
[0021] The term "main aqueous flow", as used herein, refers to the
main flow of stock containing cellulosic fibers, and optional
filler, entering the headbox which has a high consistency
(hereafter HC), i.e. a high solids content, HC stock, thereby
representing the high consistency flow (hereafter HC flow). The
consistency of the HC flow can be within the range of from 0.1% to
3.5% by weight, preferably from 0.3% to 2.2% and more preferably
from 0.4% to 1.9%. The term "diluting aqueous flow", as used
herein, refers to the aqueous flow which is used to dilute the HC
flow and which, in relation to the HC flow, has a low consistency
(LC), i.e. a low solids content, LC stock, thereby representing the
low consistency flow (hereafter LC flow). The consistency of the LC
flow can be within the range of from 0-1.5% by weight, preferably
0.002-0.9%, and more preferably 0.005-0.8%, with the proviso that
the consistency of the LC flow is lower than that of the HC flow.
Preferably, in the headbox, the HC flow is mixed and diluted with
the LC flow, for example just before the turbulence generator, to
form a resulting flow which is discharged onto the wire for
dewatering. The volume ratio of HC flow to LC flow can be within
the range of from 99:1 to 50:50, preferably from 97:3 to 60:40,
more preferably from 95:5 to 75:25 and typically about 85:15. As
conventional in dilution headbox designs, the volume ratio of HC
flow to LC flow preferably is varying at a plurality of points of
the headbox across its width in order to adjust the amount of
dilution, thereby enabling better control of the basis weight cross
profile of the paper web formed. Preferably the partial volume
flows, i.e. the HC flow and the LC flow, are mixed in the headbox
to form a resulting HC/LC mixture volume flow which is ejected from
the headbox and which is essentally constant in a cross-machine
direction.
[0022] The aqueous LC flow used for dilution can be selected from
fresh water, white water and other types of aqueous flows that are
recycled in the process. The diluting LC flow may contain fiber
fines and filler, and it may be treated by means of any
purification step before being fed into the headbox. Examples of
suitable steps that can be used for purifying or clarifying aqueous
flows of these types include filtration, flotation, sedimentation,
anaerobic and aerobic treatment. Preferably, the LC flow is white
water containing, for example, cellulosic fines, extractives and
other materials released from wood during the pulping process as
well as filler and other additives introduced into the HC flow but
not retained on the wire. The white water used is preferably
obtained by dewatering the stock and/or the wet web on the wire,
and it may be clarified as mentioned above before being fed into
the dilution headbox. The LC flow usually has a composition that is
different from that of the HC flow. When filler is used in the
process the filler content of the LC flow usually differs from that
of the HC flow; the LC flow normally has a higher filler content,
expressed as percentage of the dry substance of the flow, than the
HC flow.
[0023] In addition to the HC flow and the LC flow entering the
headbox as described above, there can be at least one additional
flow entering the headbox in accordance with the present invention.
The additional flow is preferably a flow that contains water alone.
The additional flow may also be a flow of stock or pulp, the
consistency and/or composition of which differs from that of the HC
flow.
[0024] The retention component(s) to be introduced into the HC flow
according to this invention may be a single retention agent or a
retention system, for example any of those defined hereinafter. The
single component can be any component functioning as a retention
agent, preferably a cationic polymer such as, for example, any of
those defined herein. In this embodiment, the amount of the
component introduced into the main aqueous flow should be
sufficient so as to give better retention than is obtained when not
adding the component.
[0025] In a preferred embodiment of this invention, there is used a
retention system. The term "retention system", as used herein,
refers to two or more components, or agents which, when being added
to a stock, give better retention than is obtained when not adding
the two or more components, or agents. The components of retention
systems are preferably selected from two or more organic polymers
and one or more organic polymers in combination with aluminium
compounds and/or inorganic microparticles.
[0026] In a preferred embodiment of the invention, there is used a
microparticle retention system. The term "microparticle retention
system", as used herein, refers to a retention system comprising a
microparticulate material, or microparticles, such as, for example,
anionic inorganic particles, cationic inorganic particles and
organic microparticles, as defined herein. The microparticulate
material is used in combination with at least one further
component, usually at least one organic polymer, herein also
referred to as a main polymer, preferably a cationic, amphoteric or
anionic polymer. Anionic microparticles are preferably used in
combination with at least one amphoteric and/or cationic polymer,
whereas cationic microparticles are preferably used in combination
with at least one amphoteric and/or anionic polymer. Preferably the
microparticies are anionic inorganic particles. It is further
preferred that the microparticles are in the colloidal range of
particle size. The retention system, e.g. systems comprising
microparticles, can comprise more than two components; for example,
it can be a three- or four-component retention system. Examples of
suitable additional components of this type include, for example,
aluminium compounds and low molecular weight cationic organic
polymers. Usually retention systems, including microparticle
retention systems, also give better dewatering than is obtained
when not adding the components, and the systems are commonly
referred to as retention and dewatering systems.
[0027] In another preferred embodiment of the invention, there is
used a retention system comprising one or more cationic organic
polymers and one or more anionic organic polymers. Preferably such
a retention system includes a cationic organic polymer having one
or more aromatic groups and/or an anionic organic polymer having
one or more aromatic groups, as defined herein.
[0028] Anionic inorganic particles that can be used according to
the invention include anionic silica-based particles and clays of
the smectite type. Anionic silica-based particles, i.e. particles
based on SiO.sub.2 or silicic acid, including colloidal silica and
different types of poly-silicic acid and polysilicates, are
preferably used. Anionic silica-based particles are usually
supplied in the form of aqueous colloidal dispersions, so called
sols. Examples of suitable silica-based sols according to the
invention may also contain other elements, for example nitrogen,
aluminium and boron. Such elements may be present as a result of
modification using organic nitrogen-containing organic compounds,
aluminium-containing compounds and boron-containing compounds,
respectively. These compounds may be present in the aqueous sol
and/or in the silica-based particles. Examples of suitable
retention and dewatering systems comprising anionic silica-based
particles are disclosed in U.S. Pat. Nos. 4,388,150; 4,927,498;
4,954,220; 4,961,825; 4,980,025; 5,127,994; 5,176,891; 5,368,833;
5,447,604; 5,470,435; 5,543,014; 5,571,494; 5,584,966; 5,603,805;
and 6,379,500, which are all hereby incorporated herein by
reference.
[0029] Anionic silica-based particles preferably have an average
particle size below about 50 nm, preferably below about 20 nm and
more preferably in the range of from about 1 to about 10 nm. As
conventional in silica chemistry, the particle size refers to the
average size of the primary particles, which may be aggregated or
non-aggregated. The specific surface area of the silica-based
particles is preferably above 50 m.sup.2/g and more preferably
above 100 m.sup.2/g. Usually, the specific surface area is up to
about 1700 m.sup.2/g and preferably up to 1000 m.sup.2/g. The
specific surface area is measured by means of titration with NaOH
in known manner, e.g. as described by Sears in Analytical Chemistry
28(1956):12, 1981-1983 and in U.S. Pat. No. 5,176,891, after
appropriate removal of or adjustment for any elements or compounds
present in the sample that may disturb the titration like aluminium
and boron species. The given area thus represents the average
specific surface area of the particles.
[0030] In a preferred embodiment of the invention, the anionic
inorganic particles are silica-based particles having a specific
surface area within the range of from 50 to 1000 m.sup.2/g and
preferably from 100 to 950 m.sup.2/g. Preferably, the anionic
inorganic particles are present in a silica-based sol having an
S-value in the range of from 8 to 45%, preferably from 10 to 35%,
containing silica-based particles with a specific surface area in
the range of from 300 to 1000 m.sup.2/g, preferably from 500 to 950
m.sup.2/g, which particles can be non-aluminium-modified or
aluminium-modified, preferably surface-modified with aluminium. The
S-value is measured and calculated as described by lier &
Dalton in J. Phys. Chem. 60(1956), 955-957. The S-value indicates
the degree of aggregate or microgel formation and a lower S-value
is indicative of a higher degree of aggregation.
[0031] In yet another preferred embodiment of the invention, the
anionic inorganic particles are selected from polysilicic acid,
optionally reacted with aluminium, having a high specific surface
area, preferably above about 1000 m.sup.2/g. The specific surface
area can be within the range of from 1000 to 1700 m.sup.2/g and
preferably from 1050 to 1600 m.sup.2/g. In the art, polysilicic
acid is also referred to as polymeric silicic acid, polysilicic
acid microgel, polysilicate and polysilicate microgel, which are
all encompassed by the term polysilicic acid used herein.
Aluminium-containing polysilicic acid is commonly referred to as
polyaluminosilicate and poly-aluminosilicate microgel, which are
both encompassed by the term polysilicic acid used herein.
[0032] Clays of the smectite type that can be used in the process
of the invention are known in the art and include naturally
occurring, synthetic and chemically treated materials. Examples of
suitable smectite clays include montmorillonite/bentonite,
hectorite, beidelite, nontronite and saponite, preferably bentonite
and especially such which after swelling preferably has a surface
area of from 400 to 800 m.sup.2/g. Examples of suitable clays
include those disclosed in U.S. Pat. Nos. 4,753,710; 5,071,512; and
5,607,552, which are hereby incorporated herein by reference, the
latter patent disclosing mixtures of anionic silica-based particles
and smectite clays, preferably natural bentonites. Cationic
inorganic particles that can be used include cationic silica-based
particles, cationic alumina, and cationic zirconia.
[0033] Examples of suitable organic polymers for use as a retention
agent or part of a retention system according to this invention
include anionic, non-ionic, amphoteric, or cationic polymers, they
can be derived from natural or synthetic sources and they can be
linear, branched or cross-linked, e.g. in the form of
microparticles. Preferably the polymer is water-soluble or
water-dispersable.
[0034] Examples of suitable cationic polymers include cationic
polysaccharides, e.g. starches, guar gums, celluloses, chitins,
chitosans, glycans, galactans, glucans, xanthan gums, pectins,
mannans, dextrins, preferably starches and guar gums; examples of
suitable starches including potato, corn, wheat, tapioca, rice,
waxy maize, barley, etc.; cationic synthetic organic polymers such
as cationic chain-growth polymers, e.g. cationic vinyl addition
polymers like acrylate-, acrylamide-, vinylamine-, vinylamide- and
allylamine-based polymers, and cationic step-growth polymers, e.g.
cationic polyamidoamines, polyethylene imines, polyamines and
polyurethanes. Cationic starches and cationic acrylamide-based
polymers are particularly preferred cationic polymers, both as
single retention components as well as in retention systems with
and without anionic inorganic particles. Examples of suitable
cationic organic polymers having one or more aromatic groups
include those disclosed in WO 02/12626. The weight average
molecular weight of the cationic organic polymer can vary within
wide limits depending on, inter alia, the type of polymer used, and
usually it is above 2,000,000, more often above 3,000,000,
preferably above 5,000,000. The upper limit is not critical; it can
be about 600,000,000, usually 150,000,000, and preferably
100,000,000.
[0035] Examples of further suitable cationic polymers that can be
introduced into the HC flow according to the invention include
cationic organic polymers having a low molecular weight. Such
cationic organic polymers include those commonly referred to as
anionic trash catcher (hereafter ATC). The weight average molecular
weight of the ATC cationic organic polymer is usually at least
2,000, preferably at least 10,000 and more preferably at least
50,000, and it is usually up to 2,000,000 and often up to
1,500,000. Examples of suitable ATC's include linear, branched and
cross-linked polymers, usually highly charged, which can be derived
from natural and synthetic sources. Examples of suitable ATC's
include low molecular weight degraded polysaccharides, e.g. those
based on starches, guar gums, celluloses, chitins, chitosans,
glycans, galactans, glucans, xanthan gums, pectins, mannans,
dextrins, preferably starches and guar gums; examples of suitable
starches including potato, corn, wheat, tapioca, rice, waxy maize,
barley, etc.; cationic synthetic organic polymers such as cationic
chain-growth polymers, e.g. cationic vinyl addition polymers like
acrylate-, acrylamide-, vinylamine-, vinylamide- and
allylamine-based polymers, for example homo- and copolymers based
on diallyldialkyl ammonium halide, e.g. diallyldimethyl ammonium
chloride, as well as (meth)acrylamides and (meth)acrylates; and
cationic step-growth polymers, e.g. cationic polyamidoamines,
polyethylene imines, polyamines, e.g. dimethylamine-epichlorhydrin
copolymers, and polyurethanes.
[0036] Examples of suitable anionic organic polymers according to
the invention can be selected from step-growth polymers,
chain-growth polymers, polysaccharides, naturally occurring
aromatic polymers and modifications thereof. Examples of suitable
anionic step-growth polymers include anionic benzene-based and
naphthalene-based condensation polymers, preferably
naphthalene-sulphonic acid based and naphthalene-sulphonate based
condensation polymers; and addition polymers, i.e. polymers
obtained by step-growth addition polymerization, e.g. anionic
polyurethanes. Examples of suitable anionic chain-growth polymers
include anionic vinyl addition polymers, e.g. acrylate- and
acrylamide-based polymers comprising anionic or potentially anionic
monomers like (meth)acrylic acid and paravinyl phenol (hydroxy
styrene). Examples of suitable naturally occurring aromatic
polymers and modifications thereof, i.e. modified naturally
occurring aromatic anionic polymers, according to the invention
include lignin-based polymers, preferably sulphonated lignins, e.g.
lignosulphonates, kraft lignin, sulphonated kraft lignin, and
tannin extracts. Examples of other suitable anionic organic
polymers having one or more aromatic groups include those disclosed
in WO 02/12626. The weight average molecular weight of the anionic
polymer can vary within wide limits dependent on, inter alia, the
type of polymer used, and usually it is at least about 500,
preferably above about 2,000 and more preferably above about 5,000.
The upper limit is not critical; it can be about 600,000,000,
usually 150,000,000, preferably 100,000,000 and more preferably
10,000,000.
[0037] The term "step-growth polymer", as used herein, refers to a
polymer obtained by step-growth polymerization, also being referred
to as step-reaction polymer and step-reaction polymerization,
respectively. The term "chain-growth polymer", as used herein,
refers to a polymer obtained by chain-growth polymerization, also
being referred to as chain reaction polymer and chain reaction
polymerization, respectively.
[0038] Aluminium compounds that can be used according to the
invention include alum, aluminates, aluminium chloride, aluminium
nitrate and polyaluminium compounds, such as polyaluminium
chlorides, polyaluminium sulphates, polyaluminium compounds
containing both chloride and sulphate ions, polyaluminium
silicate-sulphates, and mixtures thereof. The polyaluminium
compounds may also contain other anions, for example anions from
phosphoric acid, sulphuric acid, organic acids such as citric acid
and oxalic acid.
[0039] Preferred retention systems according to the invention
comprise:
[0040] (i) anionic silica-based particles in combination with
cationic starch, cationic guar gum or cationic acrylamide-based
polymer, optionally in combination with anionic organic particles
and/or ATC and/or aluminium compound;
[0041] (ii) anionic silica-based particles in combination with
anionic chain-growth polymer, preferably anionic acrylamide-based
polymer in combination with cationic organic polymer and/or
ATC;
[0042] (iii) bentonite in combination with cationic
acrylamide-based polymer, optionally in combination with ATC and/or
aluminium compound;
[0043] (iv) cationic polysaccharide, preferably cationic starch, in
combination with anionic step-growth polymer, preferably anionic
naphthalene-based condensation polymer; optionally in combination
with ATC and/or aluminium compound;
[0044] (v) cationic polysaccharide, preferably cationic starch, in
combination with naturally occurring aromatic anionic polymer and
modifiations thereof, preferably sulphonated lignin, optionally in
combination with ATC and/or aluminium compound;
[0045] (vi) cationic chain-growth polymer, preferably cationic
acrylamide-based polymer, in combination with anionic step-growth
polymer, preferably anionic naphthalene-based condensation polymer,
optionally in combination with ATC and/or aluminium compound;
and
[0046] (vii) cationic chain-growth polymer, preferably cationic
acrylamide-based polymer, in combination with naturally occurring
aromatic anionic polymer and modifiations thereof, preferably
sulphonated lignin, optionally in combination with ATC and/or
aluminium compound;
[0047] (viii) cationic chain-growth polymer, preferably cationic
acrylamide-based polymer, in combination with ATC; and
[0048] (ix) cationic chain-growth polymer, preferably cationic
acrylamide-based polymer, in combination with anionic organic
particles.
[0049] In the process of the invention, the retention component(s)
is/are introduced into the HC flow which is to be mixed with the LC
flow, preferably in the headbox, thereby introducing the
component(s) into the resulting aqueous flow in the dilution
process. When using a retention system comprising more than one
component, the components can be added to the stock flow in
conventional manner, preferably at different points and in any
order. When using a retention system comprising anionic inorganic
particles and a cationic polymer, it is preferred to add the
cationic polymer to the HC stock flow before adding the
microparticulate material, even if the opposite order of addition
may be used. When using a retention system comprising cationic and
anionic organic polymers, it is preferred to add the cationic
polymer to the HC stock flow before adding the anionic polymer,
even if the opposite order of addition may be used. It is further
preferred to add the first component, e.g. the cationic polymer,
before a shear stage, which can be selected from pumping, mixing,
cleaning, etc., and to add the second component, e.g. the anionic
inorganic microparticles or organic polymer, after that shear
stage. When using a low molecular weight cationic organic polymer
as an ATC, it is preferably introduced into the HC stock flow prior
to or simultaneous with other retention component(s). When using an
aluminium compound, it is preferably introduced into the HC stock
flow prior to or simultaneous with other retention
component(s).
[0050] The components of the retention system are introduced into
the stock to be dewatered in amounts which can vary within wide
limits depending on, inter alia, type and number of components,
type of stock, type of filler, filler content, point of addition,
etc. Generally the components are added in amounts that give better
retention than is obtained when not adding the components. When
using anionic inorganic particles as a microparticulate material,
the total amount added is usually at least 0.001% by weight, often
at least 0.005% by weight, based on dry substance of the stock. The
upper limit is usually 1.0% and preferably 0.6% by weight. When
using anionic silica-based particles, the total amount is
preferably within the range of from 0.005 to 0.5% by weight,
calculated as SiO.sub.2 and based on dry stock substance,
preferably within the range of from 0.01 to 0.2% by weight. Organic
polymers, e.g. cationic and anionic polymers, are usually added in
total amounts of at least 0.001%, often at least 0.005% by weight,
based on dry stock substance. The upper limit is usually 3% and
preferably 1.5% by weight. When using a low molecular weight
cationic organic polymer as an ATC, it can be introduced into the
HC stock flow in an amount of at least 0.01%, based on dry stock
substance, preferably the amount is in the range from 0.05% to
0.5%. When using an aluminium compound in the process, the total
amount introduced into the stock to be dewatered is dependent on
the type of aluminium compound used and on other effects desired
from it. It is for instance well-known in the art to utilize
aluminium compounds as precipitants for rosin-based sizing agents.
The total amount added is usually at least 0.05%, calculated as
Al.sub.2O.sub.3 and based on dry stock substance. Preferably the
amount is in the range of from 0.08 to 2.8%, more preferably in the
range from 0.1 to 2.0%.
[0051] According to the present invention, a low molecular weight
cationic organic polymer is introduced into the LC flow to be mixed
with the HC flow, preferably in the dilution headbox. Examples of
suitable low molecular weight (hereafter LMW) cationic organic
polymers include linear, branched and cross-linked polymers,
usually highly charged, which can be derived from natural and
synthetic sources. Examples of suitable LMW cationic organic
polymers include LMW degraded polysaccharides, e.g. those based on
starches, guar gums, celluloses, chitins, chitosans, glycans,
galactans, glucans, xanthan gums, pectins, mannans, dextrins,
preferably starches and guar gums; examples of suitable starches
including potato, corn, wheat, tapioca, rice, waxy maize, barley,
etc.; LMW cationic synthetic organic polymers such as cationic
chain-growth polymers, e.g. cationic vinyl addition polymers like
acrylate-, acrylamide-, vinylamine-, vinylamide- and
allylamine-based polymers, for example homo- and copolymers based
on diallyidialkyl ammonium halide, e.g. diallyldimethyl ammonium
chloride, as well as (meth)acrylamides and (meth)acrylates; and LMW
cationic step-growth polymers, e.g. cationic polyamidoamines,
polyethylene imines, polyamines, e.g. dimethylamine-epichlorhydrin
copolymers, and polyurethanes. The weight average molecular weight
of the LMW cationic organic polymer is usually at least 100,000,
preferably at least 500,000 and more preferably at least 1,000,000,
and it is usually up to 5,000,000, preferably up to 3,000,000 and
more preferably up to 2,000,000. Usually, in case a cationic
organic polymer is added to the HC flow as a retention agent or
part of a retention system, the weight average molecular weight of
the LMW cationic organic polymer added to the LC flow is lower than
that of the cationic organic polymer added to the HC flow.
[0052] The LMW cationic organic polymer is usually added to the LC
flow in an amount of at least 0.01%, based on dry substance of the
stock to be dewatered. Preferably, the amount is in the range of
from 0.05 to 1.0%, more preferably in the range from 0.1 to
0.5%.
[0053] In a preferred embodiment of this invention, subsequent to
introducing the LC flow containing the LMW cationic organic polymer
into the HC flow containing one or more retention components to
form the resulting aqueous flow, no further retention components
are introduced into the resulting aqueous flow. The formation of
the resulting aqueous flow preferably takes in the dilution
headbox, but may also take place outside the headbox.
[0054] The process of this invention is applicable to all
papermaking processes and cellulosic suspensions, and it is
particularly useful in the manufacture of paper from a stock that
has a high conductivity. In such cases, the conductivity of the
stock that is dewatered on the wire is usually at least about 1.5
mS/cm, preferably at least 3.5 mS/cm, and more preferably at least
5.0 mS/cm. Conductivity can be measured by standard equipment such
as, for example, a WTW LF 539 instrument supplied by Christian
Berner. The values referred to above are determined by measuring
the conductivity of the resulting aqueous flow that is ejected onto
the wire to be dewatered. High conductivity levels mean high
contents of salts (electrolytes) which are usually derived from
materials used to form the stock, from various additives introduced
into the stock, from the fresh water supplied to the process, etc.
Further, the content of salts is usually higher in processes where
white water is extensively recirculated, which may lead to
considerable accumulation of salts in the water circulating in the
process.
[0055] The present invention further encompasses papermaking
processes where white water is extensively recycled, or
recirculated, i.e. with a high degree of white water closure, for
example where from 0 to 30 tons of fresh water are used per ton of
dry paper produced, usually less than 20, preferably less than 15,
more preferably less than 10 and notably less than 5 tons of fresh
water per ton of paper. Fresh water can be introduced in the
process at any stage; for example, fresh water can be mixed with
cellulosic fibers in order to form a suspension, and fresh water
can be mixed with a thick suspension containing cellulosic fibers
to dilute it so as to form a thin suspension that is fed into the
headbox as a high consistency flow.
[0056] The process according to the invention is used for the
production of paper. The term "paper", as used herein, of course
include not only paper and the production thereof, but also other
web-like products, such as for example board and paperboard, and
the production thereof. The process can be used in the production
of paper from different types of suspensions of cellulosic fibers,
and the suspensions should preferably contain at least 25% and more
preferably at least 50% by weight of such fibers, based on dry
substance. The suspensions can be based on fibers from chemical
pulp, such as sulphate and sulphite pulp, thermomechanical pulp,
chemo-thermomechanical pulp, organosolv pulp, refiner pulp or
groundwood pulp from both hardwood and softwood, or fibers derived
from one year plants like elephant grass, bagasse, flax, straw,
etc., and can also be used for suspensions based on recycled
fibers. The invention is preferably applied to processes for making
paper from wood-containing suspensions. The suspension also contain
mineral fillers of conventional types, such as, for example,
kaolin, clay, titanium dioxide, gypsum, talc and both natural and
synthetic calcium carbonates, such as, for example, chalk, ground
marble, ground calcium carbonate, and precipitated calcium
carbonate. The stock can of course also contain papermaking
additives of conventional types, such as wet-strength agents, stock
sizes, such as those based on rosin, ketene dimers, ketene
multimers, alkenyl succinic anhydrides, etc.
[0057] Preferably the invention is applied on paper machines
producing wood-containing paper and paper based on recycled fibers,
such as SC, LWC and different types of book and newsprint papers,
and on machines producing wood-free printing and writing papers,
the term wood-free meaning less than about 15% of wood-containing
fibers. The invention is also applicable for the production of
board on single layer machines as well as on machines producing
paper or board in multilayered headboxes, and on machines with
several headboxes, in which one or more of the layers essentially
consist of recycled fibers. In machines using multi layer
headboxes, or several headboxes, in which one or more of the layers
are produced with a headbox of the dilution type, the invention can
be applied to one or more of these layers. Preferably the invention
is applied on paper machines running at a speed of from 300 to 2500
m/min and more preferably from 1000 to 2000 m/min.
[0058] The invention is further illustrated in the following
example which, however, is not intended to limit the same. Parts
and % relate to parts by weight and % by weight, respectively,
unless otherwise stated.
EXAMPLE
[0059] The process of this invention was tested using different LMW
cationic organic polymers as additive to the LC stock.
[0060] Paper was produced from a cellulosic suspension on a paper
machine utilizing a dilution headbox to make SC grades. Retention
agents were added to the HC stock; first 0.8 kg/ton based on dry
furnish of dimethylamine-epichlorhydrin copolymer with a weight
average molecular weight of about 1 million and then 0.36 kg/ton
based on dry furnish of cationic polyacrylamide with a weight
average molecular weight of 4.6 million. The LC stock was obtained
by draining the stock.
[0061] 500 ml of LC stock was added to a Dynamic Drainage Jar and
mixed at 1000 rpm for 15 seconds, and then LMW cationic organic
polymer was added to the stock and mixed for 30 seconds. For blank
tests, the LC stock was added to a Dynamic Drainage Jar and mixed
at 1000 rpm for 45 seconds without the addition of LMW cationic
organic polymer. The obtained LC stock was then drained and the
filtrate was collected and passed through a 1 micron filter. An
Ocean Optics S2000 UV spectrophotometer with a fast scanning rate
was used to measure the UV absorption as a representation of the
pitch content of the filtered fraction.
[0062] Several LMW cationic organic polymers were tested at the
same dry dosage (4 kg/ton based on LC stock dry substance,
corresponding to about 2 kg/ton based on total dry substance reel
tonnage) and the results outlined below.
[0063] LMW-1 was a dimethylamine-epichlorhydrin copolymer with a
weight average molecular weight of about 120,000;
[0064] LMW-2 was a dimethylamine-epichlorhydrin copolymer with a
weight average molecular weight of about 1,000,000;
[0065] LMW-3 was a polydiallyldimethylammonium chloride with a
weight average molecular weight of about 680,000; and
[0066] LMW-4 was a polydiallyldimethylammonium chloride with a
weight average molecular weight of about 1,800,000.
[0067] Compared to the blank test, all the processes according to
the invention showed a reduction in UV absorbtion. The most
effective process according to the invention was the one employing
the polydiallyldimethylammonium chloride with a weight average
molecular weight of about 1,800,000.
[0068] The tests are summarised in Table 1, showing UV absorbance
at different wavelengths for the processes according to the
invention and the blank corresponding to the prior art.
1TABLE 1 UV absorbance at different wavelengths. UV Absorbance
Wavelength nm Blank LMW-1 LMW-2 LMW-3 LMW-4 241.21 2.68 2.656 2.683
2.636 2.647 244.96 2.707 2.744 2.707 2.671 2.657 248.7 2.705 2.61
2.603 2.499 2.454 252.44 2.586 2.427 2.403 2.296 2.243 256.18 2.555
2.345 2.352 2.228 2.156 259.91 2.575 2.376 2.37 2.255 2.181 263.64
2.607 2.454 2.441 2.328 2.293 267.37 2.692 2.545 2.567 2.488 2.438
271.1 2.728 2.666 2.649 2.588 2.575 274.82 2.71 2.682 2.66 2.642
2.623 278.54 2.687 2.706 2.666 2.64 2.633 282.26 2.654 2.653 2.639
2.621 2.596 285.97 2.634 2.59 2.582 2.534 2.496 289.68 2.476 2.331
2.318 2.212 2.164 293.39 2.05 1.838 1.823 1.715 1.661 297.09 1.672
1.463 1.453 1.359 1.31 300.8 1.433 1.239 1.23 1.144 1.101 304.49
1.284 1.104 1.096 1.017 0.98 308.19 1.172 1.005 0.998 0.927 0.892
311.88 1.073 0.916 0.91 0.844 0.813 315.57 0.97 0.826 0.817 0.757
0.73 319.26 0.868 0.733 0.727 0.673 0.648 322.94 0.768 0.643 0.638
0.589 0.567 326.62 0.672 0.558 0.553 0.509 0.49 330.3 0.576 0.473
0.468 0.431 0.415
* * * * *