U.S. patent application number 09/949503 was filed with the patent office on 2002-09-12 for retention system.
Invention is credited to Ovenden, Cherie, Thompson, Russell Martin, Williams, Kevin Michael, Wiseman, Nicholas, Xiao, Huining.
Application Number | 20020124979 09/949503 |
Document ID | / |
Family ID | 9899038 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020124979 |
Kind Code |
A1 |
Ovenden, Cherie ; et
al. |
September 12, 2002 |
Retention system
Abstract
There is provided a method for flocculating one or more
particulate materials present in a dispersion, the method
comprising contacting the dispersion with (i) fibrous cationic
colloidal alumina microparticles; and (ii) a cationic polymer
and/or a non-ionic polymer.
Inventors: |
Ovenden, Cherie; (Chester,
GB) ; Xiao, Huining; (Fredericton, CA) ;
Wiseman, Nicholas; (Manchester, GB) ; Thompson,
Russell Martin; (Octel, GB) ; Williams, Kevin
Michael; (Cheshire, GB) |
Correspondence
Address: |
FAY, SHARPE, FAGAN,
MINNICH & McKEE, LLP
Seventh Floor
1100 Superior Avenue
Cleveland
OH
44114-2518
US
|
Family ID: |
9899038 |
Appl. No.: |
09/949503 |
Filed: |
September 7, 2001 |
Current U.S.
Class: |
162/158 ;
162/168.1; 162/175; 162/181.4 |
Current CPC
Class: |
B01D 21/01 20130101;
C02F 2209/06 20130101; D21H 17/375 20130101; D21H 17/455 20130101;
D21H 17/44 20130101; C02F 1/56 20130101; C02F 1/5236 20130101; D21H
17/675 20130101; D21H 21/10 20130101; C02F 2103/28 20130101 |
Class at
Publication: |
162/158 ;
162/168.1; 162/175; 162/181.4 |
International
Class: |
D21H 021/00; D21H
017/34; D21H 017/24; D21H 017/63 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2000 |
GB |
0021971.7 |
Claims
1. A method for flocculating one or more particulate materials
present in a dispersion, the method comprising contacting the
dispersion with (i) fibrous cationic colloidal alumina
microparticles; and (ii) a cationic polymer and/or a non-ionic
polymer.
2. A method according to claim 1 wherein the dispersion is aqueous
based.
3. A method according to claim 1 or 2 wherein the dispersion
comprises or is components of papermaking stock.
4. A method according to claim 3 wherein the papermaking stock is a
pulp of a hardwood or of a softwood, or a combination thereof.
5. A method according to claim 4 wherein the pulp is selected from
pulps of the chemical, mechanical, recycled, semi-chemical and
thermomechanical types, or mixtures thereof.
6. A method according to any one of the preceding claims wherein
the one or more particulate materials are flocculated on a fibrous
material.
7. A method according to claim 6 wherein the fibrous material
comprises or is fibrous cellulose.
8. A method according to any one of the preceding claims wherein
the dispersion is contacted with a composition comprising (i)
fibrous cationic colloidal alumina microparticles; and (ii) a
cationic polymer and/or a non-ionic polymer.
9. A method according to any one of the preceding claims wherein
the cationic polymer is selected from polyacrylamide, polyethylene
imine, polyamines, polycyandiamide formaldehyde polymers,
amphoteric polymers, diallyl dimethyl ammonium chloride polymers,
diallylaminoalkyl (meth)acrylate polymers, and dialkylaminoalkyl
(meth)acrylamide polymers, a copolymer of acrylamide and diallyl
dimethyl ammonium chloride, a copolymer of acrylamide and
diallyaminoalkyl (meth)acrylates, a copolymer of acrylamide and
dialkylaminoalkyl (meth)acrylamides, a polymer of dimethylamine and
epichlorohydrin, and natural and semi-synthetic polymers including
cationic starch.
10. A method according to any one of the preceding claims wherein
the non-ionic polymer is selected from polymers formed from at
least one monomer chosen from acrylamide, methacrylamide, and
N-tertiary butyl acrylamide.
11. A method according to any one of the preceding claims wherein
the charge density of the cationic polymer is no greater than
60%.
12. A method according to any one of the preceding claims wherein
the molecular weight of the cationic/non-ionic polymer is no
greater than 30,000,000, preferably 500,000 to 30,000,000, more
preferably 1,000,000 to 30,000,000, more preferably 5,000,000 to
30,000,000.
13. A method according to any one of the preceding claims wherein
the polymer:microparticle ratio is from 10:1 to 1:10, preferably
2:1 to 1:2, more preferably approximately 1:1.
14. A method according to any one the preceding claims wherein the
dispersion is contacted with the cationic alumina prior to contact
with the cationic polymer and/or the non-ionic polymer.
15. A method according to any one of claims 1 to 13 wherein the
dispersion is contacted with the cationic polymer and/or non-ionic
polymer prior to contact with the cationic alumina.
16. A method according to any one of claims 1 to 13 wherein the
dispersion is simultaneously contacted with the cationic polymer
and/or non-ionic polymer and the cationic alumina.
17. A method according to any one of the preceding claims wherein
the dispersion has a pH of from 3to 10.
18. A method for retention and/or drainage of a papermaking stock
as defined in any one of the preceding claims.
19. A method according to claim 18 wherein the papermaking stock
has a concentration of pulp of up to 20 wt. %.
20. A method according to claim 19 wherein the papermaking stock
has a concentration of pulp of 1-2 wt. %.
21. A method according to claim 19 wherein the papermaking stock
has a concentration of pulp of 3-5 wt. %.
22. Use of fibrous cationic colloidal alumina microparticles for
flocculating one or more particulate materials present in a
dispersion characterised by the features of any one of claims 1 to
17.
23. A composition comprising (i) fibrous cationic colloidal alumina
microparticles; and (ii) a cationic polymer and/or a non-ionic
polymer.
24. Paper or a paper product obtained or obtainable using the
invention as defined in any one the preceding claims.
25. A flocculated particulate material obtainable by the method
according to claim 1 or any claim dependent thereon.
26. A method as substantially hereinbefore described with reference
to any one of the Examples.
27. A use as substantially hereinbefore described with reference to
any one of the Examples.
28. A composition as substantially hereinbefore described with
reference to any one of the Examples.
29. A paper or a paper product as substantially hereinbefore
described with reference to any one of the Examples.
30. A flocculated particulate material as substantially
hereinbefore described with reference to any one of the Examples.
Description
[0001] The present invention relates to a retention system. In
particular the present invention relates to a method for
flocculating one or more particulate materials present in a
dispersion. The present invention utilises fibrous cationic
colloidal alumina microparticles.
[0002] Retention aids are employed to bond papermaking stock
components together and reduce loss to white water by either
coagulation or flocculation of small particles, and then entrapment
or attachment of the flocs onto the larger cellulosic fibres.
Papermaking stock is essentially a suspension of particles ranging
from 2-3 mm down to a few nanometers in dimensions, the
distribution of which depends on the type of filler used and the
degree of refining and cleanliness of the pulp.
[0003] Charge neutralisation is the predominant mechanism in
coagulation of small particles in papermaking stock. Retention has
been recognised for many years as one of the most important aspects
of papermaking. Careful application of retention aids may provide
many process benefits and economic benefits, such as optimised
wet-end running conditions, improved paper properties, maximised
raw material yield, and reduced effluent load.
[0004] In recent years trends in paper and board production have
contributed to the need for improved retention systems. These
trends have included the need for better paper quality, higher
machine speeds, greater filler levels, the use of mechanical pulps
and recycled fibres and of course environmental pressures. This
drive to improve sheet quality, increase paper machine
productivity, and control rising furnish costs continues to
escalate the demands placed on wet end chemistries.
[0005] Papermaking often compromises one desirable benefit in order
to gain more of another desired benefit. An example of this is use
of single high molecular weight polymer drainage/retention aids on
paper machines. Simple (single polymer) retention aid systems often
lack flocculation power under highly turbulent conditions. To
obtain high retention of fines on high-speed paper machines,
dual-polymer or microparticle retention systems have been
developed. Dual-polymer retention aid systems have gained
popularity particularly for the manufacture of low basis weight
papers (e.g., tissue paper) or filler-containing papers (fine
paper, magazine paper) under severe retention conditions.
[0006] Dual-polymer systems have been used for many years with
varying degrees of success. Generally speaking, they have comprised
of a combination of the low molecular weight cationic polymer, such
as a polyamine, and a high molecular weight polyacrylamide. The
cationic polymer is normally added early in the stock to neutralise
much of the anionic material present and create an environment in
which the polyacrylamide can function effectively. The
polyacrylamide functions by bridging flocculation and there may be
a need to compromise between optimum retention and paper
properties.
[0007] Microparticulate retention aid systems are normally based on
negatively charged inorganic colloids and positively charged
synthetic or natural polymers. The main difference between the
systems is usually the type of microparticle used. Currently used
commercial anionic microparticulate retention aid systems
include
[0008] Compozil--colloidal silica used in conjunction with cationic
starch (available from EKA Nobel AB, Sweden); and
[0009] Hydrocol--sodium montmorillonite (bentonite clay) used with
cationic polyacrylamide (available from Ciba, UK).
[0010] The performance of chemical flocculants as retention aids in
papermaking may depend on factors such as the point of addition and
the shear levels experienced. A high shear level often leads to the
break-up of flocs formed, which is beneficial for paper formation,
but it also leads to the detachment of fillers deposited on fibres
and thus reduces filler retention. A high degree of reflocculation,
especially with regard to the flocculation of fillers to fibres
when the shear subsides is therefore a desirable characteristic of
a retention aid system. This ability to reflocculate after floc
breakage is a feature normally ascribed to the
microparticle-containing flocculant systems.
[0011] In commercial microparticle systems, strong flocculation of
fillers and fibres is first achieved by addition of the cationic
component, which is normally a high molecular weight polymer (e.g.,
cationic starch or cationic polyacrylamide). After periods of high
shear, e.g., in pumps, screens, and pipe constrictions, during
which flocs are partly disrupted to floc fragments, the flocs can
reform when the high shear subsides. Close to the headbox, the
negatively charged particle sol is added, which leads to greater
flocculation through charge interaction with the cationic polymers
adsorbed onto particle surfaces.
[0012] The results of microparticulate coagulation can be very
significant and even dramatic when compared to standard retention
aid systems. They may include improved retention (stronger
flocculation), faster dewatering (drainage) on the wire and press
section of the paper machine, greater overall control and
flexibility and improved paper properties.
[0013] The retention of filler particles is of great economic and
process benefit. However, it also poses a complicated problem and
it is difficult to predict the effect of changes in the wet-end of
the papermaking system on the retention of filler. Selection of the
best retention aid programme depends on the type of fillers used,
filler loading, anionic trash content, type and amount of starch,
whether the sheet is sized or not, and the mechanical shear of the
machine, etc. Consideration also has to be given to the level of
retention desired, and the corresponding loss in formation
allowable. Increasing the use of retention agents leads to higher
chemical costs, so the payback in terms of increased productivity
and filler saving is a factor. Reliable selection of a suitable
retention aid system is largely dependent on the chemistry of the
system.
[0014] To-date much of the literature on microparticle applications
in the papermaking industry has concerned anionic microparticles
used in conjunction with a high molecular weight cationic polymer.
However, a synthetic cationic polymeric microparticle with a range
of particle sizes and charge densities has been used as a retention
aid for negatively charged fibres and positively charged
precipitated calcium carbonate particles [H Ono and Y Deng, 1996
CPPA International Paper and Coating Chemistry Symposium, Canada,
pp 175-184, Jun. 11-13 (1996)].
[0015] Colloidal silica has previously been treated to make it
cationic, and used as a retention aid system in conjunction with
either an anionic or cationic polymer [K Moberg, TAPPI Papermakers
Conference Proceedings, Volume 1, 115-127, (April 1993), TAPPI
Press, Atlanta, Ga.]. This system has not been commercialised.
[0016] Cationic colloidal silica microparticles, where aluminium
atoms have replaced some of the surface silica, are also known.
U.S. Pat. No. 4,798,653 describes a system where anionic
polyacrylamide is used with a cationic silica sol, where the
polyacrylamide dosage ranges from 0.01 to 1.0% w/w, and the
microparticle between 0.01 and 2.0% w/w. It is recommended that the
polymer has a medium to high molecular weight and low charge
density.
[0017] A similar cationic colloidal silica is described in U.S.
Pat. No. 4,946,557. This teaching uses a cationic polyacrylamide.
The order of addition of the two components is largely influenced
by the size of the silica particles. Better results are reported
with small silica particles when the polymer is added first, but
for larger particles the silica should be added first.
[0018] Silica-containing anionic microparticulate systems can be
expensive in use. Moreover, silica sols rendered cationic by
incorporation of polyvalent metallic ions (e.g., Al.sup.3+) in the
silica surface are unstable with respect to disproportionation
under normal conditions of use and either have to be prepared and
used quickly or require the use of additional stabilising
components such as phosphate, carbonate, borate and the like. [U.S.
Pat. No. 4,798,653; U.S. Pat. No. 4,946,557].
[0019] A major disadvantage of bentonite-containing anionic
microparticulate systems is that bentonite
(Na.sup.+-montmorillonite) is classed as a carcinogen, so
particular care must be taken in its handling and transportation [K
Johnson, In: 51st APPITA Annual General Conference Proceedings, pp
325-328, Apr. 28-May 2, 1997].
[0020] The present invention alleviates problems of the prior
art.
[0021] Aspects of the present invention are defined in the appended
claims.
[0022] The present invention aims to provide a cationic fibrous
alumina colloidal compound or composition useful in retention,
drainage and dewatering of papermaking that is stable in storage,
safe to use and cost-effective.
[0023] The present invention aims to provide a method to improve
the effectiveness in retaining the fine mineral fillers such as
clay or calcium carbonate with paper fibres using a new inorganic
cationic microparticulate retention system based on a synthetic
water-based fibrous colloidal alumina with a high surface
charge.
[0024] The present invention aims to provide a drainage/retention
aid that is less shear- and pH-sensitive as compared to
conventional high molecular weight cationic acrylamide-derived
polymers.
[0025] The present invention may provide a composition comprising
(i) fibrous cationic colloidal alumina microparticles; and (ii) a
non-ionic polymer and/or cationic polymer, and a method for using
the same or the constituents thereof to improve the effectiveness
in retaining the fine mineral fillers such as clay or calcium
carbonate with paper fibres using a new retention system based on a
synthetic water-based fibrous colloidal alumina with a high surface
charge.
[0026] The present invention may provide a drainage/retention aid
composition comprising (i) fibrous cationic colloidal alumina
microparticles; and (ii) a cationic polymer and/or a non-ionic
polymer and a method for using the same or the constituents thereof
that is less shear- and pH-sensitive as compared to conventional
drainage/retention aides comprising high molecular weight cationic
acrylamide-derived polymers.
[0027] The present invention may provide a new inorganic cationic
microparticulate retention composition comprising (i) fibrous
cationic colloidal alumina microparticles; and (ii) a cationic
polymer and/or a non-ionic polymer, and a method for using the same
or the constituents thereof to improve the effectiveness in
retaining fine mineral fillers such as clay or calcium carbonate
with paper fibres.
[0028] The present invention may provide a synthetic water-based
colloidal alumina composition with high positive surface charge and
controllable particle size and a method for using the same or the
constituents thereof. The composition may be useful in wet-end
papermaking processes, particularly for the retention of fine
particulate fillers such as clay or calcium carbonate.
[0029] The flocculant system of the present invention (i.e. a
composition comprising (i) fibrous cationic colloidal alumina
microparticles; and (ii) a cationic polymer and/or a non-ionic
polymer and the method for using the same) was found to be
relatively resilient to shear stress and insensitive to common
papermaking process pH variations. This new flocculant system and
method was found to give comparable results to a commercial anionic
microparticle system in terms of retention and sheet formation when
compared on a pilot paper machine and in the laboratory.
[0030] The flocculant system and method of the present invention is
stable under normal conditions of storage and use and does not
present handling problems nor require application of additional
stabilising components.
[0031] Unlike most other microparticles used in the papermaking
industry, the flocculant system of the present invention is
cationic and fibrous in shape. Consequently, there is little or no
conformational changes of the alumina fibres once adsorbed or for
reduced effects from penetration into the pores of cellulosic
fibres, due to the rigid structure of the alumina particles.
[0032] Furthermore, the other advantages of using the flocculant
system of the present invention instead of water-soluble retention
aids include more effective patch formation on adsorption and
higher charge density which may be easily controllable by the
synthesis chemistry.
[0033] The total cationic demand of the pulp furnish in papermaking
can be reduced by using cationic microparticles and there is no
accumulation of the microparticles in a closed white water system
because of the strong adsorption of the cationic sol onto
negatively charged substrates. The presence of anionic polymer will
form a co-bridge with the adsorbed cationic microparticle, which
will significantly increase flocculation efficiency.
[0034] Alumina
[0035] In the present specification by the term "fibrous" it is
meant products which are composed of fibres.
[0036] The term "fibre" is used in accordance with the customary
meaning and includes fibrils and aggregates of fibrils which form
relatively long thread-like structures.
[0037] The term "fibril" is used to refer to products which when
viewed under the electron microscope appear to be single particles
as opposed to structures formed of aggregates of a number of
separate members. The term "fibrous" encompasses materials in which
the fibrils are discrete and relatively unaggregated.
[0038] Preferably the fibrils are particles with an aspect ratio of
.gtoreq.3:1, preferably .gtoreq.20:1 and/or preferably with a
uniformity of diameter along the length of the particle. Depending
on the specific process conditions used in preparation, the fibrous
alumina may be in the form of fibrils or small fibres which have
one or more dimensions in the colloidal range. Such fibrils can
form aggregates of larger fibres made up of assemblies of fibrils
disposed parallel to the length of the fibres. Such fibrous alumina
as used in the present specification will preferably have the
boehmite crystal lattice.
[0039] In the present specification by the term "cationic" it is
meant that the compound/composition is ionic and has a positive
charge.
[0040] In the present specification by the term "colloidal" it is
meant a heterogeneous system consisting of one substance (the
disperse phase) finely divided and distributed throughout a second
substance (the continuous phase). Generally speaking, the disperse
phase has dimensions in the range of 1 to 1000 nm (1 .mu.m).
[0041] In the present specification by the term "alumina" it is
meant any compound consisting essentially of aluminium and oxygen
(i.e. aluminium oxide).
[0042] The alumina may be .alpha.-alumina, .beta.-alumina,
.gamma.-alumina or a mixture thereof. Preferably the alumina is
acicular (fibrous) boehmite alumina (.alpha.-alumina). In this
aspect preferably the acicular (fibrous) boehmite alumina
(.alpha.-alumina) may be obtained under acidic hydrothermal
conditions (according to U.S. Pat. No. 2,915,475 or WO
97/41063).
[0043] Preferably the alumina is fibrillar hydrated
.alpha.-alumina, known as boehmite alumina (formula: .alpha.-A1OOH)
or basic alumina monohydrate, optionally obtained in accordance
with a process described in WO 97/41063. The fibrils each consist
of a crystal of boehmite alumina. The particles contain
surface-bound acetate groups (chemisorbed CH.sub.3COO.sup.-) and
have a high positive surface charge which is responsible for the
colloidal stability of the system and the other useful properties
of the product. In water, these cationic boehmite colloid particles
are stabilised by electrical double-layer repulsion.
[0044] In the present specification by the term "microparticles" it
is meant particles having an average maximum dimension of 1000
nm.
[0045] Preferably the "microparticles" are non-deformable particles
(spherical, plate-like or fibrous in shape)
[0046] Neither the particle size nor surface charge of the cationic
microparticles is, alone, critical to the performance of the
present invention. The present invention is advantageous provided
the microparticles can disperse and be dispersed in the suspension,
such as an aqueous pulp suspension, and can readily interact with
the components which are present in the suspension.
[0047] The microparticles of the present invention may form or be
in the form of water-insoluble dispersions. In such dispersions the
microparticles any exist both as discrete particles and aggregates
of said particles.
[0048] In a preferred aspect the microparticles have surface area
of greater than 50 m.sup.2/g.
[0049] The microparticles may be in one aspect of the present
invention inorganic colloidal particles.
[0050] The particle size nor surface charge of the cationic
microparticles is not, per se, critical to the invention provided
that the microparticles can disperse and be dispersed into an
aqueous pulp suspension and readily interact with the anionic
components which are present in the aqueous pulp suspension or the
non-ionic and cationic substances of the invention.
[0051] Preferably the alumina is prepared according to the methods
exemplified in WO 97/41063 or PCT/GB99/02841.
[0052] Preferably the alumina is made from isolated solid basic
aluminium acetate or other similar aluminium containing salt or
starting material under acidic hydrothermal conditions.
[0053] Cationic/Non-Ionic Polymer
[0054] The cationic polymer may be selected from polyacrylamide,
polyethylene imine, polyamines, polycyandiamide formaldehyde
polymers, amphoteric polymers, diallyl dimethyl ammonium chloride
polymers, diallylaminoalkyl (meth)acrylate polymers, and
dialkylaminoalkyl (meth)acrylamide polymers, a copolymer of
acrylamide and diallyl dimethyl ammonium chloride, a copolymer of
acrylamide and diallyaminoalkyl (meth)acrylates, a copolymer of
acrylamide and dialkylaminoalkyl (meth)acrylamides, a polymer of
dimethylamine and epichlorohydrin, and natural and semi-synthetic
polymers including cationic starch.
[0055] The cationic polymer may be selected from water-soluble
copolymers of acrylamide or methacrylamide which carry or are
capable of carrying a cationic charge when dissolved in water. The
cationic copolymers include the following examples: copolymers of
(meth)acrylamide with dimethylaminoethyl methacrylate (DMAEM),
dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate
(DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary
ammonium forms made with dimethyl sulfate or methyl chloride,
Mannich reaction modified polyacrylamides, diallylcyclohexylamine
hydrochloride (DACHA HCl), diallyldimethylammonium chloride
(DADMAC), methacrylamidopropyltrimethyla- mmonium chloride (MAPTAC)
and allyl amine (ALA).
[0056] Copolymers of dialkyl aminoalkyl(meth)acrylates (in cationic
form) and (meth)acrylamide may be used as the cationic polymer of
the present invention. As discussed in U.S. Pat No. 5,571,380 it is
known in the polymer art that acrylamide-containing polymers may
contain a minor amount of acrylic acid or acrylic acid salt mer
units due to inadvertent hydrolysis of some acrylamide mer units,
even though the polymer is not subjected to conditions that would
hydrolyze a substantial proportion of the acrylamide. It is
believed that the presence of a minor proportion of hydrolyzed
acrylamide mer units (or hydrolyzed methacrylamide mer units) will
disable the performance of a cationic polymer that otherwise meets
the requirements for use in the present process. Further, it is
believed that the presence of up to about 5 mole percent anionic
mer units in the polymer is not harmful to the polymer's
performance. Hence the term "cationic" as used herein includes
polymers containing a minor amount of anionic mer units, although
of course the primary nature of the polymer remains cationic.
[0057] The charge density of the cationic polymer may be no greater
than 60%.
[0058] The non-ionic polymer may be selected from polymers formed
from at least one monomer chosen from acrylamide, methacrylamide,
and N-tertiary butyl acrylamide.
[0059] The molecular weight of the cationic/non-ionic polymer may
be no greater than 30,000,000, preferably 500,000 to 30,000,000,
more preferably 1,000,000 to 30,000,000, more preferably 5,000,000
to 30,000,000.
[0060] Composition
[0061] Preferably the cationic/non-ionic polymer:alumina ratio may
be from 10:1 to 1:10, more preferably from 2:1 to 1:2, yet more
preferably approximately 1:1.
[0062] The method of the present invention may contact one or more
additional components with the dispersion. These components may
also be present in the composition of the present invention. These
components include cationic starch (including potato starch, and
maize starch), fillers, sizing additives (including alum and
rosin), pitch control agents, extenders (including anilex),
biocides and brightening agents.
[0063] Possible inorganic or mineral fillers include alkaline
carbonates, such as calcium carbonate, titanium dioxide, kaolin
clay, and the like. The amount of inorganic filler typically
employed in a papermaking stock is from about 10 to 30 parts by
weight of the filler, as CaCO.sub.3, per hundred parts by weight of
dry pulp in the slurry. The amount of filler may, at times, be as
low as about 5, or even about 2, parts by weight, or as high as
about 50, or even 80 or 90, parts by weight, per hundred parts by
weight of dry pulp in the slurry.
[0064] Method
[0065] As described above the flocculant system and method of the
present invention was found to be relatively resilient to shear
stress and insensitive to pH variations. Therefore the components
of the present invention may be contacted with the dispersion at
any point of a paper making process including contact with the
thick stock, the thin stock or at high shear points. The dual
system of the present invention was found to give comparable
results to a commercial anionic microparticle system in terms of
retention and sheet formation when compared on a pilot paper
machine and in the laboratory.
[0066] The dosage amount of cationic microparticles and/or the
cationic polymer and/or non-ionic polymer, used in this invention,
is not, per se, critical to the performance of the present
invention. Generally the dosage is controlled to be in an amount to
flocculate the suspended matter Those of ordinary skill in the art
can readily determine suitable dosage amounts by conventional
means. Thus, whilst the exact dosage amount for a particular system
can vary widely depending on the nature of the system, the amount
of suspended matter and the degree of drainage or retention
desired. In general the dosage, based on the dry weight of
suspended matter amount, can range:
[0067] for the alumina, from 0.005 to 3% w/w, preferably from 0.01
to 2% w/w
[0068] for the cationic polymer and/or non-ionic polymer combined,
from 0.001 to 0.5 weight percent, preferably from 0.01 to 0.3%
w/w.
[0069] The alumina and the cationic polymer and/or non-ionic
polymer may be contacted with the dispersion in any order. For
example, the dispersion may be (i) contacted with the alumina and
subsequently with the cationic polymer and/or non-ionic polymer,
(ii) contacted with the cationic polymer and/or non-ionic polymer
and subsequently with the alumina, (iii) simultaneously contacted
with the alumina and the cationic polymer and/or non-ionic polymer.
The order of addition of the alumina and the cationic polymer
and/or non-ionic polymer may have some influence on the obtained
effect. In a preferred embodiment of this invention the alumina is
generally added first and the cationic polymer and/or non-ionic
polymer added subsequently.
[0070] The method of the present invention can be carried out over
a wide pH range, for example at a pH of from 3 to 10. In a
preferred aspect, the suspension has a pH of from 4 to 9.
[0071] Parer/Pulps
[0072] The present invention is suitable for use with pulps of both
hardwoods, softwoods and non-wood (e.g. straw) or combinations
thereof. Pulps of the chemical, mechanical, recycled, semi-chemical
or thermomechanical types are suitable for treatment in accordance
with the present process.
[0073] The pulp may have a net charge which anionic, cationic or
neutral.
[0074] The dispersion of the present invention may be pulp stock of
various concentration. The pulp stock may have a concentration of
pulp of up to 20 wt. %. The pulp stock may be a thin stock (for
example having a concentration of 1-2 wt. %) or a thick stock (for
example having a concentration of 3-5 wt. %).
[0075] The present invention is suitable for use in the preparation
of a wide range of paper types including newsprint, fine paper and
board.
[0076] We have found the present invention to be advantageous in
providing useful wet-end papermaking properties, particularly for
the retention of fine particulates.
[0077] The invention will now be described, by way of example only,
with reference to the accompanying drawings in which:
[0078] FIG. 1 shows a graph;
[0079] FIG. 2 shows a graph;
[0080] FIG. 3 shows a graph; and
[0081] FIG. 4 shows a graph.
[0082] The following preparations and examples are included herein
as further description and are illustrative of the present
invention.
EXAMPLES
[0083] Flocculation Experiments
[0084] Octasol.TM. is a cationic colloidal alumina marketed by The
Associated Octel Company Limited, UK. A Photometric Dispersion
Analyser (PDA 2000, Rank Brother, UK) and Dynamic Drainage Jar
(DDJ) were used to examine the effectiveness of different
Octasol.TM. samples at flocculating filler particles, in particular
clay, in both the absence and presence of papermaking fibres. The
use of Octasol.TM. in conjunction with a range of different
polymers was examined.
[0085] The polymers used were:
1TABLE 1 Polymer Product Description Polymer Type Commercial Name
Charge Density Molecular Weight Non-ionic Calgon Hydraid N/A High
Polyacrylamide 6696EZ Cationic Allied Colloids High Cationic High
Polyacrylamide Hydrocol 864
[0086] The flocculation studies carried out were:
[0087] 1. All Octasol.TM. samples with clay alone, at dosages of
0.1% to 3.0% w/w on clay, in the absence of fibres. An optimum
Octasol.TM. dosage was determined for the basis of the experiments,
and the relationship between Octasol.TM. particle size,
electrophoretic mobility and flocculating ability was examined.
[0088] 2. At the optimum dosage from Step 1, four Pilot Plant
Octasol.TM. samples were used with a non-ionic and cationic
polymer, increasing the ratio of polymer to Octasol.TM. from 0.25:1
to 1:1. Clay was used in the absence of fibres. The order of
component addition was also examined, initially by looking at the
effect on one Octasol.TM. sample. Once an optimum ratio of polymer:
Octasol.TM. had been determined a more detailed look at the effect
of addition order was carried out.
[0089] 3. At the dosages, ratios and addition orders predefined in
Step 2, four Pilot Plant samples were used with the non-ionic and
cationic polymers with both clay and fibres. The polymers were the
same as those used in Step 2, and detailed in Table 1.
Example 1
Clay Flocculation Induced by Octasol.TM. and Cationic Polymer
Cationic Polymer Dosage
[0090] The Octasol.TM. dosage was held constant at 0.7% w/w on clay
and the cationic polymer dosage varied between 0-0.7% w/w on clay.
The effect of the use of the polymer alone at each dosage was also
examined. The cationic polymer used was Hydrocol 864, a high
molecular weight polyacrylamide (12 million) with a high charge
density of about 40% DS.
[0091] FIG. 1 for the cationic polymer shows that although the
turbidity of the dual component system is improved over the
Octasol.TM. alone, and at the higher dosages of polymer that there
is moderate synergy between the polymer and Octasol.TM..
[0092] FIG. 2 shows the relative floc sizes of the cationic polymer
dual component system using the V.sub.rms/V calculations. It can be
seen that at the lower polymer dosages of between 0.1-0.4% w/w on
clay (ratios 1:4 and 1:2), the calculated floc size from
V.sub.rms/V is smaller than that when Octasol.TM. is used alone. As
the polymer dosage increases above this, the floc size grows, until
at the highest dosage studied where there appears to be floc
shrinkage evident.
[0093] Addition Order
[0094] The effect of the addition order was examined at ratios 1:2
for samples PP3, 4 and 6, and at 3:4 for sample PP1, since at these
dosages some moderate synergy was observed between the two
components. For all four Pilot Plant Octasol.TM. samples studied,
adding Octasol.TM. after the cationic polymer gave a quicker
response than if Octasol.TM. is added to the clay first, but with
little difference in the final turbidity, as seen in Table 2.
[0095] The speed of response in Table 2 was calculated by the
increase in DC value of the PDA output between 120 and 130
seconds.
2TABLE 2 Comparison of Addition Order with Octasol .TM. and
Cationic Hydrocol 864 Speed of Response (dDC/dt)* Final Relative
Turbidity PP1 PP3 PP4 PP6 PP1 PP3 PP4 PP6 Octasol .TM. 0.035 0.027
0.011 0.032 0.09 0.11 0.14 0.12 Added First Octasol .TM. 0.151
0.195 0.778 0.856 0.05 0.14 0.18 0.19 Added Second *dt = 10
Seconds
[0096] Effect of Octasol.TM. Properties
[0097] Table 3 shows a summary of the final relative turbidity and
V.sub.rms/V values for when the cationic Hydrocol 864 is used in
conjunction with Octasol.TM.. For this data, the polymer was added
as the first component and the polymer: Octasol.TM. ratio was 1:2
with Octasol.TM. at 0.7% w/w on clay, even for PP1.
3TABLE 3 Comparison of Octasol .TM. and Cationic Hydrocol 864
Induced Clay Flocculation Hydrocol PP1 PP3 PP4 PP6 864 Mobility
6.240 6.16 7.750 6.31 (.mu.m.cm/Vs) Particle Size 1.524 1.49 1.491
0.174 (.mu.m) Relative 0.220 0.14 0.180 0.190 0.19 Turbidity
V.sub.rms/V 0.110 0.03 0.010 0.070 0.04
Example 2
Clay Flocculation Induced by Octasol.TM. and Non-ionic Polymer
Non-ionic Polymer Dosage
[0098] The Octasol.TM. dosage was held constant at 0.7% w/w on clay
and the non-ionic polymer dosage varied between 0-0.7% w/w on clay.
The effect of the use of the polymer alone at each dosage was also
examined. The non-ionic polymer used was Hydraid 6696EZ, a very
high molecular weight polyacrylamide.
[0099] FIG. 3 shows the relative turbidity of the clay suspension
with varying non-ionic polymer dosage. As can be seen, the addition
of the non-ionic polymer reduced the turbidity below that for the
single Octasol.TM. system with no polymer. There is a little
synergistic effect observed between the two components, as the
turbidity of the dual component system is only slightly reduced
below that of the polymer alone. The best synergy is perhaps seen
at polymer: Octasol.TM. ratio of 1:2.
[0100] FIG. 4 shows the relative floc sizes of the non-ionic
polymer dual component systems respectively using the V.sub.rms/V
calculations. It can be seen that at the lower polymer dosages of
between 0.1-0.4% w/w on clay (ratios 1:4 and 1:2) the calculated
floc size is smaller than that when Octasol.TM. is used alone. As
the polymer dosage increases above this, the floc size grows, until
at the highest dosage studied where the flocs appear to shrink.
[0101] Addition Order
[0102] The effect of the order of addition of the two components
was studied at polymer: Octasol.TM. ratio of 1:2, since at these
dosages the greatest synergy between components was observed.
[0103] For all four Pilot Plant Octasol.TM. samples studied, adding
Octasol.TM. after the non-ionic polymer gave a quicker response
than if Octasol.TM. is added to the clay first, although a slightly
higher final relative turbidity was obtained with samples PP4 and
PP6, as seen in Table 4.
[0104] The speed of response in Table 4 was calculated by the
increase in DC value of the PDA output between 120 and 130
seconds.
4TABLE 4 Comparison of Addition Order with Octasol .TM. and
Non-ionic Hydraid 6696EZ Speed of Response (dDC/dt)* Final Relative
Turbidity PP1 PP3 PP4 PP6 PP1 PP3 PP4 PP6 Octasol .TM. 0.029 0.022
0.005 0.031 0.19 0.19 0.20 0.14 Added First Octasol .TM. 0.099
0.098 0.755 0.799 0.12 0.13 0.27 0.23 Added Second *dt = 10
Seconds
[0105] Effect of Octasol.TM. Properties
[0106] Table 5 shows a summary of the final relative turbidity and
V.sub.rms/V values for when the non-ionic Hydraid 6696EZ is used in
conjunction with Octasol.TM.. For this data, the polymer was added
as the first component and the polymer: Octasol.TM. ratio was 1:2
with Octasol.TM. at 0.7% w/w on clay.
5TABLE 5 Comparison of Octasol .TM. and Non-ionic Hydraid 6696EZ
Induced Clay Flocculation Hydrocol PP1 PP3 PP4 PP6 6696EZ Mobility
6.240 6.16 7.750 6.31 (.mu.m.cm/Vs) Particle Size 1.524 1.49 1.491
0.174 (.mu.m) Relative 0.120 0.13 0.270 0.230 0.32 Turbidity
V.sub.rms/V 0.030 0.04 0.050 0.050 0.05
Example 3
Clay Flocculation in the Presence Of Fibres Flocculation Induced by
Octasol.TM. and Polymers
[0107] The four Pilot Plant Octasol.TM. samples, PP1, PP3, PP4 and
PP6, used previously were used at a dosage of 0 7% w/w on clay
(0.14% w/w on o.d. fibre) as part of a dual component flocculation
system with the non-ionic and cationic polymers, for clay in the
presence of fibres.
[0108] Octasol.TM. and Cationic Polymer
[0109] Cationic Hydrocol 864 polymer was used with Octasol.TM. in
this study. The Octasol.TM. dosage was fixed at 0.7% w/w on clay,
and the polymer at 0.35% w/w on clay for PP3, PP4 and PP6, and at
0.525% w/w on clay for PP1, giving a polymer: Octasol.TM. ratio of
1:2 (or 3:4 for PP1). In each case, the cationic polymer was added
to the pre-mixed clay and fibre suspension as the first component,
prior to the addition of Octasol.TM..
[0110] A summary of the relative turbidities of the dual component
Octasol.TM. and cationic Hydrocol 864 systems can be found in Table
6.
6TABLE 6 Comparison of Octasol .TM. and Cationic Hydrocol 864
Induced Clay Flocculation with Fibres Relative Turbidity Component
(.tau..sub.f/.tau..sub.i) Hydrocol 864 0.10 Hydrocol 864 with PP1
(ratio 3:4) 0.11 Hydrocol 864 with PP3 (ratio 1:2) 0.15 Hydrocol
864 with PP4 (ratio 1:2) 0.18 Hydrocol 864 with PP6 (ratio 1:2)
0.11
[0111] From Table 6, it can be seen from the very low relative
turbidity value that the use of the cationic Hydrocol 864 alone
gives very good flocculation of clay in the presence of fibres. The
dual component systems with Octasol.TM. as the second component
also give good relative turbidities. However, it seems that the use
of Octasol.TM. slightly impairs the performance of the polymer as
the relative turbidity increases. This could be due to cationic
charge inundation resulting in a slight re-stabilisation of the
clay and fibre suspension.
[0112] Octasol.TM. and Non-Ionic Polymer
[0113] Non-ionic Hydraid 6696EZ polymer was used with Octasol.TM.
in this study. The Octasol.TM. dosage was fixed at 0.7% w/w on clay
and the polymer at 0.35% w/w on clay, giving a polymer: Octasol.TM.
ratio of 1:2. In each case, the non-ionic polymer was added to the
pre-mixed clay and fibre suspension as the first component, prior
to the addition of Octasol.TM..
[0114] A summary of the relative turbidities of the dual component
Octasol.TM. and non-ionic Hydraid 6696EZ systems can be found in
Table 7.
7TABLE 7 Comparison of Octasol .TM. and Non-ionic Hydraid 6696EZ
Induced Clay Flocculation with Fibres Relative Turbidity Component
(.tau..sub.f/.tau..sub.i) Hydraid 6696EZ 0.43 Hydraid 6696EZ with
PP1 (ratio 1:2) 0.34 Hydraid 6696EZ with PP3 (ratio 1:2) 0.39
Hydraid 6696EZ with PP4 (ratio 1:2) 0.41 Hydraid 6696EZ with PP6
(ratio 1:2) 0.40
[0115] Table 7 shows that the performance of the non-ionic polymer
either alone or with Octasol.TM. is not so effective as that of the
cationic polymer alone. However, the combination of Octasol.TM.
with the non-ionic polymer provides a synergy between the
components, as the effect on the relative turbidity is greater than
for either of the single components. In this case, the non-ionic
polymer is able to interact in a positive way with the cationic
Octasol.TM. as there is less repulsion between the two components
than with the cationic polymer.
[0116] All publications mentioned in the above specification are
herein incorporated by reference. Various modifications and
variations of the described methods and system of the invention
will be apparent to those skilled in the art without departing from
the scope and spirit of the invention. Although the invention has
been described in connection with specific preferred embodiments,
it should be understood that the invention as claimed should not be
unduly limited to such specific embodiments. Indeed, various
modifications of the described modes for carrying out the invention
which are obvious to those skilled in chemistry or related fields
are intended to be within the scope of the following claims.
* * * * *