U.S. patent application number 09/741300 was filed with the patent office on 2001-06-28 for silica-based sols.
Invention is credited to Greenwood, Peter, Johansson-Vestin, Hans E., Linsten, Magnus Olof.
Application Number | 20010004927 09/741300 |
Document ID | / |
Family ID | 27240269 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004927 |
Kind Code |
A1 |
Greenwood, Peter ; et
al. |
June 28, 2001 |
Silica-based sols
Abstract
The invention relates to an aqueous silica-based sol comprising
a nitrogen-containing organic compound and silica-based particles
with a specific surface area of at least 300 square meters per gram
of silica. The invention further relates to a process for the
production of an aqueous silica-based sol comprising a
nitrogen-containing organic compound which comprises incorporating
a nitrogen-containing organic compound into a silica-based sol
containing silica-based particles with a specific surface area of
at least 300 square meters per gram of silica. The invention also
relates to the use of an aqueous silica-based sol comprising a
nitrogen-containing organic compound and silica-based particles
with a specific surface area of at least 300 square meters per gram
of silica as a flocculating agent in the production of pulp and
paper and in water purification. The invention further relates to a
process for the production of paper from an aqueous suspension
containing cellulosic fibers, and optional fillers, which comprises
adding to the suspension (i) an aqueous silica-based sol comprising
an organic nitrogen-containing compound and (ii) at least one
charged organic polymer, forming and draining the suspension on a
wire.
Inventors: |
Greenwood, Peter; (Goteborg,
SE) ; Linsten, Magnus Olof; (Kungalv, SE) ;
Johansson-Vestin, Hans E.; (Kungalv, SE) |
Correspondence
Address: |
Lainie E. Parker
Akzo Nobel Inc.
Patent and Trademark Department
7 Livingstone Avenue
Dobbs Ferry
NY
10522-3408
US
|
Family ID: |
27240269 |
Appl. No.: |
09/741300 |
Filed: |
December 19, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60172893 |
Dec 21, 1999 |
|
|
|
Current U.S.
Class: |
162/168.3 ;
162/175; 162/181.6; 516/83; 516/84; 516/87 |
Current CPC
Class: |
D21H 17/68 20130101;
C02F 2103/28 20130101; B01J 13/0034 20130101; C02F 1/56 20130101;
C01B 33/149 20130101; C02F 1/545 20130101; B01J 13/0039 20130101;
D21H 21/10 20130101 |
Class at
Publication: |
162/168.3 ;
162/175; 162/181.6; 516/83; 516/84; 516/87 |
International
Class: |
C01B 033/141; B01F
017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 1999 |
EP |
99850204.1 |
Aug 24, 2000 |
SE |
0002986-8 |
Claims
1. Aqueous silica-based sol comprising a nitrogen-containing
organic compound and silica-based particles with a specific surface
area of at least 300 square meters per gram of silica and having an
S-value within the range of from 10 to 60%.
2. The aqueous silica-based sol of claim 1, wherein it contains
silica-based particles with a specific surface area of from 550 to
1700 square meters per gram of silica.
3. The aqueous silica-based sol of claim 1, wherein the
nitrogen-containing organic compound has a molecular weight below
1,000.
4. The aqueous silica-based sol of claim 1, wherein the S-value is
within the range of from 15 to 40%.
5. The aqueous silica-based sol of claim 1, wherein it has a
specific surface area in the range of from 150 to 250 square meters
per gram of aqueous sol.
6. The aqueous silica-based sol of claim 1, wherein it has a silica
content in the range of from 10 to 60% by weight.
7. The aqueous silica-based sol of claim 1, wherein it has a pH of
from 8 to 13.
8. The aqueous silica-based sol of claim 1, wherein the
nitrogen-containing organic compound is an amine containing from 2
to 12 carbon atoms.
9. The aqueous silica-based sol of claim 1, wherein the
nitrogen-containing organic compound is a quaternary amine.
10. The aqueous silica-based sol of claim 1, wherein the
nitrogen-containing organic compound is selected from the group
consisting of propylamine, butylamine, cyclohexylamine,
ethanolamine, 2-methoxyethylamine, diethylamine, dipropylamine
diisopropylamine, diethanolamine, pyrrolidine, triethylamine,
triethanolamine, N,N-dimethylethanolamine, tetraethanol ammonium
hydroxide, tetraethanol ammonium chloride, methyltriethanolammonium
hydroxide, methyltriethanolammonium chloride,
dimethyldiethanolammonium hydroxide, dimethyldiethanolammonium
chloride, choline hydroxide, choline chloride,
dimethylcocobenzylammonium hydroxide, dimethylcocobenzylammonium
chloride, tetramethylammonium hydroxide, tetramethylammonium
chloride, tetraethylammonium hydroxide, tetraethylammonium
chloride, tetrapropylammonium hydroxide, tetrapropylammonium
chloride, diethyldimethylammonium hydroxide,
diethyldimethylammonium chloride, triethylmethylammonium hydroxide,
triethylmethylammonium chloride, aminoethylethanolamine, piperazine
and derivatives thereof, and mixtures thereof.
11. The aqueous silica-based sol of claim 10, wherein the
nitrogen-containing organic compound is selected from the group
consisting of triethanolamine, diethanolamine, dipropylamine,
aminoethylethanolamine, 2-methoxyethylamine,
N,N-dimethylethanolamine, choline hydroxide, choline chloride,
tetramethylammonium hydroxide, tetraethylammonium hydroxide, and
tetraethanol ammonium hydroxide.
12. The aqueous silica-based sol of claim 1, wherein the
nitrogen-containing organic compound contains at least one oxygen
atom.
13. Aqueous silica-based sol comprising a nitrogen-containing
organic compound and silica-based particles with a specific surface
area of at least 700 square meters per gram of silica.
14. The aqueous silica-based sol of claim 13, wherein the
nitrogen-containing organic compound has a molecular weight below
1,000.
15. The aqueous silica-based sol of claim 13, wherein it has an
S-value within the range of from 15 to 40%.
16. The aqueous silica-based sol of claim 13, wherein it has a
specific surface area in the range of from 150 to 250 square meters
per gram of aqueous sol.
17. The aqueous silica-based sol of claim 13, wherein it has a
silica content in the range of from 10 to 60% by weight.
18. The aqueous silica-based sol of claim 13, wherein it has a pH
of from 8 to 13.
19. The aqueous silica-based sol of claim 13, wherein the
nitrogen-containing organic compound is an amine containing from 2
to 12 carbon atoms.
20. The aqueous silica-based sol of claim 13, wherein the
nitrogen-containing organic compound is a quaternary amine.
21. The aqueous silica-based sol of claim 13, wherein the
nitrogen-containing organic compound is selected from the group
consisting of propylamine, butylamine, cyclohexylamine,
ethanolamine, 2-methoxyethylamine, diethylamine, dipropylamine
diisopropylamine, diethanolamine, pyrrolidine, triethylamine,
triethanolamine, N,N-dimethylethanolamine, tetraethanol ammonium
hydroxide, tetraethanol ammonium chloride, methyltriethanolammonium
hydroxide, methyltriethanolammonium chloride,
dimethyldiethanolammonium hydroxide, dimethyldiethanolammonium
chloride, choline hydroxide, choline chloride,
dimethylcocobenzylammonium hydroxide, dimethylcocobenzylammonium
chloride, tetramethylammonium hydroxide, tetramethylammonium
chloride, tetraethylammonium hydroxide, tetraethylammonium
chloride, tetrapropylammonium hydroxide, tetrapropylammonium
chloride, diethyldimethylammonium hydroxide,
diethyldimethylammonium chloride, triethylmethylammonium hydroxide,
triethylmethylammonium chloride, aminoethylethanolamine, piperazine
and derivatives thereof, and mixtures thereof.
22. The aqueous silica-based sol of claim 21, wherein the
nitrogen-containing organic compound is selected from the group
consisting of triethanolamine, diethanolamine, dipropylamine,
aminoethylethanolamine, 2-methoxyethylamine,
N,N-dimethylethanolamine, choline hydroxide, choline chloride,
tetramethylammonium hydroxide, tetraethylammonium hydroxide, and
tetraethanol ammonium hydroxide.
23. The aqueous silica-based sol of claim 13, wherein the
nitrogen-containing organic compound contains at least one oxygen
atom.
24. Aqueous silica-based sol having a specific surface area of at
least 100 square meters per gram of aqueous sol and comprising a
nitrogen-containing organic compound and silica-based particles
with a specific surface area of at least 300 square meters per gram
of silica.
25. The aqueous silica-based sol of claim 24, wherein the
silica-based particles have a specific surface area of from 550 to
1700 square meters per gram of silica.
26. The aqueous silica-based sol of claim 24, wherein the
nitrogen-containing organic compound has a molecular weight below
1,000.
27. The aqueous silica-based sol of claim 24, wherein it has an
S-value within the range of from 15 to 40%.
28. The aqueous silica-based sol of claim 24, wherein it has a
specific surface area in the range of from 150 to 250 square meters
per gram of aqueous sol.
29. The aqueous silica-based sol of claim 24, wherein it has a
silica content in the range of from 10 to 60% by weight.
30. The aqueous silica-based sol of claim 24, wherein it has a pH
of from 8 to 13.
31. The aqueous silica-based sol of claim 24, wherein the
nitrogen-containing organic compound is an amine containing from 2
to 12 carbon atoms.
32. The aqueous silica-based sol of claim 24, wherein the
nitrogen-containing organic compound is a quaternary amine.
33. The aqueous silica-based sol of claim 24, wherein the
nitrogen-containing organic compound is selected from the group
consisting of propylamine, butylamine, cyclohexylamine,
ethanolamine, 2-methoxyethylamine, diethylamine, dipropylamine
diisopropylamine, diethanolamine, pyrrolidine, triethylamine,
triethanolamine, N,N-dimethylethanolamine, tetraethanol ammonium
hydroxide, tetraethanol ammonium chloride, methyltriethanolammonium
hydroxide, methyltriethanolammonium chloride,
dimethyldiethanolammonium hydroxide, dimethyldiethanolammonium
chloride, choline hydroxide, choline chloride,
dimethylcocobenzylammonium hydroxide, dimethylcocobenzylammonium
chloride, tetramethylammonium hydroxide, tetramethylammonium
chloride, tetraethylammonium hydroxide, tetraethylammonium
chloride, tetrapropylammonium hydroxide, tetrapropylammonium
chloride, diethyldimethylammonium hydroxide,
diethyldimethylammonium chloride, triethylmethylammonium hydroxide,
triethylmethylammonium chloride, aminoethylethanolamine, piperazine
and derivatives thereof, and mixtures thereof.
34. The aqueous silica-based sol of claim 33, wherein the
nitrogen-containing organic compound is selected from the group
consisting of triethanolamine, diethanolamine, dipropylamine,
aminoethylethanolamine, 2-methoxyethylamine,
N,N-dimethylethanolamine, choline hydroxide, choline chloride,
tetramethylammonium hydroxide, tetraethylammonium hydroxide, and
tetraethanol ammonium hydroxide.
35. The aqueous silica-based sol of claim 24, wherein the
nitrogen-containing organic compound contains at least one oxygen
atom.
36. Process for the production of an aqueous silica-based sol which
comprises incorporating a nitrogen-containing organic compound in a
silica-based sol containing silica-based particles with a specific
surface area of at least 300 square meters per gram of silica and
having an S-value in the range of from 10 to 60%.
37. The process of claim 36, wherein the nitrogen-containing
organic compound has a molecular weight below 1,000.
38. The process of claim 36, wherein the aqueous silica-based sol
contains silica-based particles with a specific surface area of
from 550 to 1700 square meters per gram of silica.
39. The process of claim 36, wherein the aqueous silica-based sol
obtained is concentrated to a specific surface area in the range of
from 150 to 250 square meters per gram of aqueous sol.
40. The process of claim 36, wherein the nitrogen-containing
organic compound is an amine containing from 2 to 12 carbon
atoms.
41. The process of claim 36, wherein the nitrogen-containing
organic compound contains at least one oxygen atom.
42. Process for the production of an aqueous silica-based sol which
comprises incorporating a nitrogen-containing organic compound in a
silica-based sol containing silica-based particles with a specific
surface area of at least 700 square meters per gram of silica.
43. The process of claim 42, wherein the nitrogen-containing
organic compound has a molecular weight below 1,000.
44. The process of claim 42, wherein the aqueous silica-based sol
contains silica-based particles with a specific surface area of
from 550 to 1700 square meters per gram of silica.
45. The process of claim 42, wherein the aqueous silica-based sol
obtained is concentrated to a specific surface area in the range of
from 150 to 250 square meters per gram of aqueous sol.
46. The process of claim 42, wherein the nitrogen-containing
organic compound is an amine containing from 2 to 12 carbon
atoms.
47. The process of claim 42, wherein the nitrogen-containing
organic compound contains at least one oxygen atom.
48. Process for the production of an aqueous silica-based sol which
comprises incorporating a nitrogen-containing organic compound in a
silica-based sol containing silica-based particles with a specific
surface area of at least 300 square meters per gram of silica and
concentrating the aqueous silica-based sol obtained to a specific
surface area of at least 100 square meters per gram of aqueous
sol.
49. The process of claim 48, wherein the nitrogen-containing
organic compound has a molecular weight below 1,000.
50. The process of claim 48, wherein the aqueous silica-based sol
contains silica-based particles with a specific surface area of
from 550 to 1700 square meters per gram of silica.
51. The process of claim 48, wherein the aqueous silica-based sol
obtained is concentrated to a specific surface area in the range of
from 150 to 250 square meters per gram of aqueous sol.
52. The process of claim 48, wherein the nitrogen-containing
organic compound is an amine containing from 2 to 12 carbon
atoms.
53. The process of claim 48, wherein the nitrogen-containing
organic compound contains at least one oxygen atom.
54. Process for the production of paper from an aqueous suspension
containing cellulosic fibres, and optional fillers, which comprises
adding to the suspension an aqueous silica-based sol comprising an
organic nitrogen-containing compound and at least one charged
organic polymer, forming and draining the suspension on a wire.
55. The process of claim 54, wherein the sol contains silica-based
particles with a specific surface area of at least 300 square
meters per gram of silica.
56. The process of claim 54, wherein the charged organic polymer
comprises a cationic starch and/or cationic polyacrylamide.
Description
[0001] The present invention generally relates to silica-based sols
comprising an organic nitrogen-containing compound which sols are
suitable for use as drainage and retention aids in papermaking.
More particularly, the invention relates to silica-based sols, a
process for the production of silica-based sols, and a process for
the production of paper in which silica-based sols are used as
additives.
BACKGROUND
[0002] In the papermaking art, an aqueous suspension containing
cellulosic fibres, 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 through the forming
wire so that a wet web of paper is formed on the wire, and the
paper web is further dewatered and dried in the drying section of
the paper machine. Drainage and retention aids are conventionally
introduced into the stock in order to facilitate drainage and to
increase adsorption of fine particles onto the cellulosic fibres so
that they are retained with the fibres on the wire.
[0003] Silica-based particles are widely used as drainage and
retention aids in combination with charged organic polymers like
anionic and cationic acrylamide-based polymers and cationic and
amphoteric starches. Such additive systems are disclosed in U.S.
Pat. Nos. 4,388,150; 4,961,825; 4,980,025; 5,368,833; 5,603,805;
5,607,552; 5,858,174; and 6,103,064; and International Patent
Applications WO 00/66491 and WO 00/66492. These systems are among
the most efficient drainage and retention aids now in use.
[0004] Silica-based particles suitable for use as drainage and
retention aids are normally supplied in the form of aqueous
colloidal dispersions, so-called sols. Such commercially used
silica-based sols usually have a silica content of about 7-15% by
weight and contain particles with a specific surface area of at
least 300 m.sup.2/g. Sols of silica-based particles with higher
specific surface areas are usually more dilute to improve storage
stability and avoid gel formation.
[0005] It would be advantageous to be able to provide silica-based
sols with further improved drainage and retention performance and
even better stability. It would also be advantageous to be able to
provide a process for preparing silica-based sols exhibiting
improved drainage, retention and stability properties. It would
also be advantageous to be able to provide a papermaking process
with improved drainage and retention.
THE INVENTION
[0006] In accordance with the present invention there is provided
amine-modified silica-based sols which are suitable for use as
drainage and retention aids in papermaking. The term "drainage and
retention aids", as used herein, refers to one or more components
(aids, agents or additives) which, when added to a papermaking
stock, give better drainage and/or retention than is obtained when
not adding the said one or more components. The amine-modified
silica-based sols of the invention result in improved drainage
and/or retention when used in conjunction with charged organic
polymers. Hereby the present invention makes it possible to
increase the speed of the paper machine and to use a lower dosage
of additives to give a corresponding drainage and/or retention
effect, thereby leading to an improved papermaking process and
economic benefits. The silica-based sols of the invention further
exhibit very good stability over extended periods of time, notably
very high surface area stability and high stability towards
gelation, and hence they can be prepared and shipped at high
specific surface areas and high silica concentrations. The sols
have improved capability to maintain the high specific surface area
on storage at high silica concentrations.
[0007] The present invention thus relates to silica-based sols
comprising an organic nitrogen-containing compound, the preparation
of such sols and their use, as further defined in the appended
claims. The invention also relates to a process for the production
of paper from an aqueous suspension containing cellulosic fibres,
and optional fillers, which comprises adding to the suspension a
silica-based sol comprising an organic nitrogen-containing compound
and at least one charged organic polymer, forming and draining the
suspension on a wire, as further defined in the appended
claims.
[0008] The silica-based sols according to the invention are aqueous
sols that contain anionic silica-based particles, i.e. particles
based on SiO.sub.2 or silicic acid, including colloidal silica,
different types of polysilicic acid, polysilicate microgels,
colloidal borosilicates, aluminium-modified silica or aluminium
silicates, polyaluminosilicate microgels, and mixtures thereof. The
particles are preferably colloidal, i.e. in the colloidal range of
particle size, and preferably amorphous or essentially amorphous.
The silica-based particles suitably 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, particle size refers to the average size of the
primary particles, which may be aggregated or non-aggregated.
[0009] The silica-based sols according to the invention contains an
organic nitrogen-containing compound, for example an amine which
can be selected from primary amines, secondary amines, tertiary
amines and quaternary amines, the latter also referred to as
quaternary ammonium compounds. The amines can be aromatic, i.e.
containing one or more aromatic groups, or aliphatic; the aliphatic
amines usually being preferred. The nitrogen-containing compound is
preferably water-soluble or water-dispersible. The amine can be
uncharged or cationic. Examples of cationic amines include acid
addition salts of primary, secondary and tertiary amines and,
preferably, quaternary ammonium compounds, as well as their
hydroxides. The organic nitrogen-containing compound usually has a
molecular weight below 1,000, suitably below 500 and preferably
below 300. Preferably, a low molecular weight organic
nitrogen-containing compound is used, for example those compounds
having up to 25 carbon atoms, suitably up to 20 carbon atoms,
preferably from 2 to 12 carbon atoms and most preferably from 2 to
8 carbon atoms. In a preferred embodiment, the organic
nitrogen-containing compound has one or more oxygen-containing
substituents, for example with oxygen in the form of hydroxyl
groups and/or alkyloxy groups. Examples of preferred substituents
of this type include hydroxy alkyl groups, e.g. ethanol groups, and
methoxy and ethoxy groups. The organic nitrogen-containing
compounds may include one or more nitrogen atoms, preferably one or
two. Preferred amines include those having a pKa value of at least
6, suitably at least 7 and preferably at least 7.5.
[0010] Examples of suitable primary amines, i.e. amines having one
organic substituent, include alkylamines, e.g. propylamine,
butylamine, cyclohexylamine, alkanolamines, e.g. ethanolamine, and
alkoxyalkylamines, e.g. 2-methoxyethylamine. Examples of suitable
secondary amines, i.e. amines having two organic substituents,
include dialkylamines, e.g. diethylamine, dipropylamine and
di-isopropylamine, dialkanolamines, e.g. diethanolamine, and
pyrrolidine. Examples of suitable tertiary amines, i.e. amines
having three organic substituents, include trialkylamines, e.g.
triethylamine, trialkanolamines, e.g. triethanolamine,
N,N-dialkylalkanolamines, e.g. N,N-dimethylethanolamine. Examples
of suitable quaternary amines, or quaternary ammonium compounds,
i.e. amines having four organic substituents, include
tetraalkanolamines, e.g. tetraethanol ammonium hydroxide and
tetraethanol ammonium chloride, quaternary amines or ammonium
compounds with both alkanol and alkyl substituents such as
N-alkyltrialkanolamines, e.g. methyltriethanolammonium hydroxide
and methyltriethanolammonium chloride, N,N-dialkyldialkanolamines,
e.g. dimethyldiethanolammonium hydroxide and
dimethyldiethanolammonium chloride, N,N,N-trialkylalkanolamines,
e.g. choline hydroxide and choline chloride,
N,N,N-trialkylbenzylamines, e.g. dimethylcocobenzylammonium
hydroxide and dimethylcocobenzylammonium chloride,
tetraalkylammonium salts, e.g. tetramethylammonium hydroxide,
tetramethylammonium chloride, tetraethylammonium hydroxide,
tetraethylammonium chloride, tetrapropylammonium hydroxide,
tetrapropylammonium chloride, diethyldimethylammonium hydroxide,
diethyldimethylammonium chloride, triethylmethylammonium hydroxide
and triethylmethylammonium chloride. Examples of suitable diamines
include aminoalkylalkanolamines, e.g. aminoethylethanolamine,
piperazine and nitrogen-substituted piperazines having one or two
lower alkyl groups of 1 to 4 carbon atoms. Examples of preferred
organic nitrogen-containing compounds include triethanolamine,
diethanolamine, dipropylamine, aminoethylethanolamine,
2-methoxyethylamine, N,N-dimethylethanolamine, choline hydroxide,
choline chloride, tetramethylammonium hydroxide, tetraethylammonium
hydroxide and tetraethanol ammonium hydroxide.
[0011] The molar ratio of SiO.sub.2 to N of the silica-based sols
is usually from 1:1 to 50:1, suitably from 2:1 to 40:1 and
preferably from 2.5:1 to 25:1.
[0012] The specific surface area of the amine-modified aqueous
silica-based sols of the invention is suitably at least 90
m.sup.2/g aqueous sol, i.e. based on the weight of aqueous sol,
preferably at least 100 m.sup.2/g aqueous sol, more preferably at
least 115 m.sup.2/g aqueous sol and most preferably at least 150
m.sup.2/g aqueous sol. Generally, the specific surface area of the
aqueous sol obtained can be up to about 300 m.sup.2/g aqueous sol,
suitably up to 250 m.sup.2/g aqueous sol, preferably up to 240
m.sup.2/g aqueous sol.
[0013] The specific surface area of the silica-based particles is
suitably at least 300 m.sup.2/g SiO.sub.2, i.e. based on the weight
of SiO.sub.2, preferably at least 400 m.sup.2/g SiO.sub.2 and most
preferably at least 550 m.sup.2/g SiO.sub.2, notably at least 700
m.sup.2/g SiO.sub.2. Generally, the specific surface area of the
particles can be up to about 1700 m.sup.2/g SiO.sub.2. In a
preferred embodiment of the invention, the specific surface area of
the silica-based particles is up to about 1000 m.sup.2/g SiO.sub.2,
suitably from about 550 to 950 m.sup.2/g SiO.sub.2. In another
preferred embodiment of the invention, the specific surface area of
the silica-based particles is from about 1000 to 1700 m.sup.2/g
SiO.sub.2, suitably from 1050 to 1500 m.sup.2/g SiO.sub.2.
[0014] The specific surface area can be 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 the
organic nitrogen-containing compound and any other compounds
present in the sample that may disturb the titration like aluminium
and boron species. When expressed in square meters per gram of
aqueous sol, the specific surface area represents the specific
surface area that is available per gram of aqueous silica-based
sol. When expressed in square meters per gram of silica, the
specific surface area represents the average specific surface area
of the silica-based particles present in the sol.
[0015] The silica-based sols usually have an S-value within the
range of from 10 to 60%, suitably from 15 to 50%, preferably from
15 to 40% and most preferably from 20 to 35%. The S-value can be
measured and calculated as described by Iler & Dalton in J.
Phys. Chem. 60(1956), 955-957. The S-value, which is affected by
silica concentration, density and viscosity of the silica-based
sol, can be seen as an indication of the degree of particle
aggregation or interparticle attraction and a lower S-value
indicates a higher degree aggregation.
[0016] The silica-based sols should suitably have a silica content
of at least 3% by weight but it is more suitable that the silica
content is within the range of from 10 to 60% by weight and
preferably from 12 to 40% by weight. In order to reduce storage
facilities and to simplify shipping and reduce transportation
costs, it is generally preferable to ship high concentration
silica-based sols but it is of course possible and usually
preferable to dilute the sols to substantially lower silica
contents prior to use, for example to silica contents within the
range of from 0.05 to 5% by weight, in order to improve mixing with
the furnish components.
[0017] The viscosity of the silica-based sols can vary depending
on, for example, the silica content of the sol, specific surface
area of the silica-based particles and the organic
nitrogen-containing compound used. Usually, the viscosity is at
least 1.5 cP, normally within the range of from 2 to 100 cP,
suitably from 2 to 70 cP and preferably from 2.5 to 40 cP. The
viscosity, which is suitably measured on sols having a silica
content of at least 10% by weight, can be measured by means of
known technique, for example using a Brookfield LVDV II+
viscosimeter. The pH of the silica-based sols according to the
invention is usually from 7 to 14, suitably from 8 to 13 and
preferably from 9 to 12.
[0018] The silica-based sols of this invention are preferably
stable. The term "stable silica-based sol", as used herein, refers
to silica-based sols which when subjected to storage or ageing for
one month at 20.degree. C. in dark and non-agitated conditions
exhibit an increase in viscosity of less than 100 cP. Suitably the
viscosity increase, if any, is less than 50 cP and preferably less
than 30 cP when the sols are subjected to the above conditions.
[0019] In addition to the nitrogen-containing compound, the
silica-based sols according to the invention may also contain other
elements, for example aluminium and boron. Such elements may be
present as a result of modification using aluminium-containing and
boron-containing compounds, respectively. If aluminium is used, the
sols can have a molar ratio of SiO.sub.2 to Al.sub.2O.sub.3 within
the range of from 4:1 to 1500:1, suitably from 8:1 to 1000:1 and
preferably from 15:1 to 500:1. If boron is used, the sols can have
a molar ratio of SiO.sub.2 to B within the range of from 4:1 to
1500:1, suitably from 8:1 to 1000:1 and preferably from 15:1 to
500:1.
[0020] The aqueous silica-based sols according to the invention can
be produced by incorporating a nitrogen-containing compound, for
example any of the ones described above and having the above
characteristics, into a silica-based sol, optionally followed by
concentration of the silica-based sol. The silica-based sol to be
used suitably contains anionic silica-based particles. Preferably
the particles are colloidal and amorphous or essentially amorphous.
The specific surface area of the silica-based particles is suitably
at least 300 m.sup.2/g SiO.sub.2, i.e. based on the weight of
SiO.sub.2, preferably at least 400 m.sup.2/g SiO.sub.2 and most
preferably at least 550 m.sup.2/g SiO.sub.2, notably at least 700
m.sup.2/g SiO.sub.2. Generally, the specific surface area of the
particles can be up to about 1700 m.sup.2/g SiO.sub.2. In a
preferred embodiment of the invention, the specific surface area of
the silica-based particles is up to about 1000 m.sup.2/g SiO.sub.2,
suitably from about 550 to 950 m.sup.2/g SiO.sub.2. In another
preferred embodiment of the invention, the specific surface area of
the silica-based particles is from about 1000 to 1700 m.sup.2/g
SiO.sub.2, suitably from 1050 to 1500 m.sup.2/g SiO.sub.2. The
silica-based sol to be used in the process usually has an S-value
within the range of from 10 to 60%, suitably from 15 to 50%,
preferably from 15 to 40% and most preferably from 20 to 35%.
[0021] The aqueous silica-based sol to be used in the process
according to the invention usually has a pH within the range of
from 1 to 11. In one preferred aspect of this invention, the pH of
the aqueous silica-based sol to be used is within the range of from
1 to 4, usually an acid silica-based sol or polysilicic acid. In
another preferred aspect of this invention, the pH of the aqueous
silica-based sol to be used is within the range of from 4 to 11,
suitably from 7 and most preferably from 8 up to 11.0, preferably
up to 10.5.
[0022] Acid silica-based sols can be prepared starting from a
conventional aqueous silicate solution like alkali water glass,
e.g. potassium or sodium water glass, preferably sodium water
glass. The molar ratio of SiO.sub.2 to M.sub.2O, where M is alkali
metal, e.g. sodium, potassium, ammonium, or a mixture thereof, in
the silicate solution or water glass is suitably within the range
of from 1.5:1 to 4.5:1, preferably from 2.5:1 to 3.9:1, and pH is
usually around 13 or above 13. Suitably a dilute silicate solution
or water glass is used which can have an SiO.sub.2 content of from
about 3 to about 12% by weight, preferably from about 5 to about
10% by weight. The silicate solution or water glass is normally
acidified to a pH of from about 1 to about 4. The acidification can
be carried out in known manner by addition of mineral acids, e.g.
sulphuric acid, hydrochloric acid and phosphoric acid, or
optionally with other chemicals known as suitable for acidification
of water glass, e.g. ammonium sulphate and carbon dioxide. However,
it is preferred that the acidification is carried out by means of
an acid cation exchanger which, among other things, lead to more
stable products. The acidification is preferably carried out by
means of a strongly acid cation exchange resin, for example of
sulfonic acid type. It is preferred that the acidification is
carried out to a pH of from about 2 to 4, most preferably from
about 2.2 to 3.0. The obtained acid sol, or polysilicic acid,
contains particles with a high specific surface area, normally
above 1000 m.sup.2/g SiO.sub.2 and usually around about 1300 to
1500 m.sup.2/g SiO.sub.2. Acid silica-based sols can also be
prepared by acidification of an alkaline silica-based sol, for
example by means of acidification as described above.
[0023] The organic nitrogen-containing compound is then
incorporated into the acid sol, optionally in combination with
alkali, e.g. lithium hydroxide, sodium hydroxide, potassium
hydroxide and ammonium hydroxide, or an aqueous silicate solution
as defined above. The organic nitrogen-containing compound and the
alkali can be added simultaneously, either separately or in
admixture, or sequentially, e.g. addition of nitrogen-containing
compound followed by addition of alkali. The amount of organic
nitrogen-containing compound is usually such that the
above-mentioned molar ratio of SiO.sub.2 to nitrogen (N) is
obtained. The pH of the organic nitrogen-containing compound
modified silica-based sol is usually from 7 to 13, suitably from 8
to 12.5 and preferably from 9 to 12.
[0024] In a preferred embodiment of the invention, the silica-based
sol obtained after incorporation of the organic nitrogen-containing
compound is further concentrated. Concentration can be carried out
in known manner such as, for example, by osmotic methods,
evaporation and ultrafiltration. The concentration is suitably
carried out to produce silica contents of at least 10% by weight,
preferably from 10 to 60% by weight, and more preferably from 12 to
40% by weight. The concentration is further usually carried out so
that the silica-based sol obtained in the process has a specific
surface area of at least 90 m.sup.2/g aqueous sol, i.e., based on
the weight of aqueous sol, suitably at least 100 m.sup.2/g aqueous
sol, preferably at least 115 m.sup.2/g aqueous sol and most
preferably at least 150 m.sup.2/g aqueous sol. Generally, the
specific surface area of the aqueous sol obtained can be up to
about 300 m.sup.2/g aqueous sol, suitably up to 250 m.sup.2/g
aqueous sol, preferably up to 240 m.sup.2/g aqueous sol.
[0025] According to the present process, silica-based sols, notably
stable silica-based sols, having the above characteristics can be
prepared and the produced sols exhibit good storage stability and
can be stored for several months without any substantial decrease
of the specific surface area and without gelation.
[0026] The organic nitrogen-containing compound modified
silica-based sols of this invention are suitable for use as
drainage and retention aids in papermaking. The silica-based sols
can be used in combination with organic polymers which can be
selected from anionic, amphoteric, non-ionic and cationic polymers
and mixtures thereof, herein also referred to as "main polymer".
The use of such polymers as drainage and retention aids is well
known in the art. The polymers can be derived from natural or
synthetic sources, and they can be linear, branched or
cross-linked. Examples of generally suitable main polymers include
anionic, amphoteric and cationic starches, anionic, amphoteric and
cationic guar gums, and anionic, amphoteric and cationic
acrylamide-based polymers, as well as cationic poly(diallyldimethyl
ammonium chloride), cationic polyethylene imines, cationic
polyamines, polyamidoamines and vinylamide-based polymers,
melamine-formaldehyde and urea-formaldehyde resins. Suitably the
silica-based sols are used in combination with at least one
cationic or amphoteric polymer, preferably cationic polymer.
Cationic starch and cationic polyacrylamide are particularly
preferred polymers and they can be used singly, together with each
other or together with other polymers, e.g. other cationic polymers
or anionic polyacrylamide. The molecular weight of the main polymer
is suitably above 1,000,000 and preferably above 2,000,000. The
upper limit is not critical; it can be about 50,000,000, usually
30,000,000 and suitably about 25,000,000. However, the molecular
weight of polymers derived from natural sources may be higher.
[0027] When using the silica-based sols in combination with main
polymer(s) as mentioned above, it is further preferred to use at
least one low molecular weight (hereinafter LMW) cationic organic
polymer, commonly referred to and used as anionic trash catchers
(ATC). ATCs are known in the art as neutralizing and/or fixing
agents for detrimental anionic substances present in the stock and
the use thereof in combination with drainage and retention aids
often provide further improvements in drainage and/or retention.
The LMW cationic organic polymer can be derived from natural or
synthetic sources, and preferably it is an LMW synthetic polymer.
Suitable organic polymers of this type include LMW highly charged
cationic organic polymers such as polyamines, polyamideamines,
polyethyleneimines, homo- and copolymers based on diallyldimethyl
ammonium chloride, (meth)acrylamides and (meth)acrylates. In
relation to the molecular weight of the main polymer, the molecular
weight of the LMW cationic organic polymer is preferably lower; it
is suitably at least 1,000 and preferably at least 10,000. The
upper limit of the molecular weight is usually about 700,000,
suitably about 500,000 and usually about 200,000. Preferred
combinations of polymers that can be co-used with the silica-based
sols of this invention include LMW cationic organic polymer in
combination with main polymer(s), such as, for example, cationic
starch and/or cationic polyacrylamide, anionic polyacrylamide as
well as cationic starch and/or cationic polyacrylamide in
combination with anionic polyacrylamide.
[0028] The components of the drainage and retention aids according
to the invention can be added to the stock in conventional manner
and in any order. When using drainage and retention aids comprising
a silica-based sol and an organic polymer, e.g. a main polymer, it
is preferred to add the polymer to the stock before adding the
silica-based sol, even if the opposite order of addition may be
used. It is further preferred to add the main polymer before a
shear stage, which can be selected from pumping, mixing, cleaning,
etc., and to add the silica-based sol after that shear stage. LMW
cationic organic polymers, when used, are preferably introduced
into the stock prior to introducing the main polymer.
Alternatively, the LMW cationic organic polymer and the main
polymer can be introduced into stock essentially simultaneously,
either separately or in admixture, for example as disclosed in U.S.
Pat. No. 5,858,174, which is hereby incorporated herein by
reference. The LMW cationic organic polymer and the main polymer
are preferably introduced into the stock prior to introducing the
silica-based sol.
[0029] In a preferred embodiment of this invention, the
silica-based sols are used as drainage and retention aids in
combination with at least one organic polymer, as described above,
and at least one aluminium compound. Aluminium compounds can be
used to further improve the drainage and/or retention performance
of stock additives comprising silica-based sols. Suitable aluminium
salts 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, organic acids such as citric acid and oxalic acid.
Preferred aluminium salts include sodium aluminate, alum and
polyaluminium compounds. The aluminium compound can be added before
or after the addition of the silica-based sol. Alternatively, or
additionally, the aluminium compound can be added simultaneously
with the silica-based sol at essentially the same point, either
separately or in admixture with it, for example as disclosed by
U.S. Pat. No. 5,846,384 which is hereby incorporated herein by
reference. In many cases, it is often suitable to add an aluminium
compound to the stock early in the process, for example prior to
the other additives.
[0030] The components of the drainage and retention aids according
to the invention are added to the stock to be dewatered in amounts
which can vary within wide limits depending on, inter alia, type
and number of components, type of furnish, filler content, type of
filler, point of addition, etc. Generally the components are added
in an amount that give better drainage and/or retention than is
obtained when not adding the components. The silica-based sol is
usually added in an amount of at least 0.001% by weight, often at
least 0.005% by weight, calculated as SiO.sub.2 and based on dry
stock substance, i.e. cellulosic fibres and optional fillers, and
the upper limit is usually 1.0% and suitably 0.5% by weight. The
main polymer is usually added in an amount of at least 0.001%,
often at least 0.005% by weight, based on dry stock substance, and
the upper limit is usually 3% and suitably 1.5% by weight. When
using an LMW cationic organic polymer in the process, it can be
added in an amount of at least 0.05%, based on dry substance of the
stock to be dewatered. Suitably, the amount is in the range of from
0.07 to 0.5%, preferably in the range from 0.1 to 0.35%. When using
an aluminium compound in the process, the total amount introduced
into the stock to be dewatered depends on the type of aluminium
compound used and on other effects desired from it. It is for
instance well known in the art to utilise 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. Suitably the amount is in the range of from
0.1 to 3.0%, preferably in the range from 0.5 to 2.0%.
[0031] In a preferred embodiment of the invention, the process is
used in the manufacture of paper from a suspension containing
cellulosic fibers, and optional fillers, having a high
conductivity. Usually, the conductivity of the stock that is
dewatered on the wire is at least 0.75 mS/cm, suitably at least 2.0
mS/cm, preferably at least 3.5 mS/cm. Very good drainage and
retention results have been observed at conductivity levels of 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 suitably determined by
measuring the conductivity of the cellulosic suspension that is fed
into or present in the headbox of the paper machine or,
alternatively, by measuring the conductivity of white water
obtained by dewatering the suspension. High conductivity levels
mean high contents of salts (electrolytes) which can be derived
from the cellulosic fibres and fillers used to form the stock, in
particular in integrated mills where a concentrated aqueous fibre
suspension from the pulp mill normally is mixed with water to form
a dilute suspension suitable for paper manufacture in the paper
mill. The salt may also be derived from various additives
introduced into the stock, from the fresh water supplied to the
process, or be added deliberately, 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.
[0032] The present invention further encompasses papermaking
processes where white water is extensively recirculated (recycled),
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, suitably less than 15, preferably
less than 10 and notably less than 5 tons of fresh water per ton of
paper. Recirculation of white water obtained in the process
suitably comprises mixing the white water with cellulosic fibres
and/or optional fillers to form a suspension to be dewatered;
preferably it comprises mixing the white water with a suspension
containing cellulosic fibres, and optional fillers, before the
suspension enters the forming wire for dewatering. The white water
can be mixed with the suspension before, between simultaneous with
or after introducing the drainage and retention aids. Fresh water
can be introduced in the process at any stage; for example, it can
be mixed with cellulosic fibres in order to form a suspension, and
it can be mixed with a suspension containing cellulosic fibres to
dilute it so as to form the suspension to be dewatered, before or
after mixing the stock with white water and before, between,
simultaneous with or after introducing the components of drainage
and retention aids.
[0033] Further additives which are conventional in papermaking can
of course be used in combination with the additives according to
the invention, such as, for example, dry strength agents, wet
strength agents, optical brightening agents, dyes, sizing agents
like rosin-based sizing agents and cellulose-reactive sizing
agents, e.g. alkyl and alkenyl ketene dimers and ketene multimers,
alkyl and alkenyl succinic anhydrides, etc. The cellulosic
suspension, or stock, can also contain mineral fillers of
conventional types such as, for example, kaolin, china clay,
titanium dioxide, gypsum, talc and natural and synthetic calcium
carbonates such as chalk, ground marble and precipitated calcium
carbonate.
[0034] The process of this 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 cellulosic
fibre-containing sheet or 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 cellulose-containing fibres and the suspensions
should suitably contain at least 25% by weight and preferably at
least 50% by weight of such fibres, based on dry substance. The
suspension can be based on fibres from chemical pulp such as
sulphate, sulphite and organosolv pulps, mechanical pulp such as
thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp
and groundwood pulp, from both hardwood and softwood, and can also
be based on recycled fibres, optionally from de-inked pulps, and
mixtures thereof. The pH of the suspension, the stock, can be
within the range of from about 3 to about 10. The pH is suitably
above 3.5 and preferably within the range of from 4 to 9.
[0035] The invention is further illustrated in the following
Examples which, however, are not intended to limit the same. Parts
and % relate to parts by weight and % by weight, respectively, and
all solutions are aqueous, unless otherwise stated.
EXAMPLE 1
[0036] A sodium hydroxide stabilized silica sol containing silica
particles with a specific surface area of around 800 m.sup.2/g
SiO.sub.2 was deionized with a cationic ion-exchange resin
saturated with hydrogen ions. The resulting acid silica sol had a
pH of 2.6, SiO.sub.2 content of 9.15% by weight and contained
silica particles with a specific surface area of 820 m.sup.2/g
SiO.sub.2 and an S-value of about 27%.
[0037] To 5000 g of this acid silica sol was added 239 g of a 34%
choline hydroxide solution under agitation for about 20 seconds,
resulting in an amine stabilized aqueous silica sol with a molar
ratio of SiO.sub.2 to N of 11:1. In order to reduce the smell from
the choline hydroxide, 5.0 g of limonene was added. The final
silica-based sol had a pH of 10.8, SiO.sub.2 content of 8.73% by
weight, S-value of 20% and contained silica particles with a
specific surface area of 820 m.sup.2/g SiO.sub.2.
EXAMPLE 2
[0038] Sodium waterglass with a molar ratio of SiO.sub.2 to
Na.sub.2O of 3.4 was diluted to about 6% by weight SiO.sub.2 and
treated with a cationic ion-exchange resin saturated with hydrogen
ions. The obtained acid silica sol, or polysilicic acid, had a pH
of 2.4, SiO.sub.2 content of 5.7% by weight and contained silica
particles with a specific surface area of 1350 m.sup.2/g SiO.sub.2
and an S-value of about 32%.
[0039] To 2000 g of this polysilicic acid was added 120 g of a 34%
choline hydroxide solution under agitation for 2 seconds, resulting
in an amine stabilized aqueous silica-based sol which had a pH of
10.4, SiO.sub.2 content of 5.4% by weight, molar ratio SiO.sub.2 to
N of 5.5:1, S-value of 28% and contained silica particles with a
specific surface area of 1330 m.sup.2/g SiO.sub.2.
EXAMPLE 3
[0040] A sodium hydroxide stabilized silica sol was deionized in
the same manner as in Example 1 resulting in an acid silica sol
which had a pH of 2.4, SiO.sub.2 content of 9.15% and contained
silica particles with a specific surface area of 850 m.sup.2/g
SiO.sub.2.
[0041] To 2000 g of this acid silica sol was added 90 g of a 25%
solution of tetramethylammonium hydroxide under agitation for 2
seconds. The obtained silica-based sol had a pH of 10.4, SiO.sub.2
content of 8.75%, molar ratio of SiO.sub.2 to N of 12:1, S-value of
19.5% and contained silica particles with a specific surface area
of 850 m.sup.2/g SiO.sub.2.
EXAMPLE 4
[0042] A dilute sodium waterglass solution was ion-exchanged in the
same manner as in Example 2. The resulting polysilicic acid had a
pH of 2.4, SiO.sub.2 content of 5.8% by weight and contained silica
particles with a specific surface area of 1365 m.sup.2/g
SiO.sub.2.
[0043] To 10000 g of this polysilicic acid was added 552 g of a 25%
solution of tetramethylammonium hydroxide under agitation for 20
seconds. The resulting amine stabilized alkaline silica sol, which
had an SiO.sub.2 content of 5.4% and a molar ratio SiO.sub.2 to N
of 6.7:1, was concentrated by ultrafiltration to a stable
silica-based sol which had a pH of 10.5, SiO.sub.2 content of 13.4%
by weight, S-value of 27% and contained silica particles with a
specific surface area of 1140 m.sup.2/g SiO.sub.2.
EXAMPLE 5
[0044] A sodium hydroxide stabilized silica sol was deionized in
the same manner as in Example 1 resulting in an acid silica sol had
a pH of 2.5, SiO.sub.2 content of 8.7% by weight and contained
silica particles with a specific surface area of 860 m.sup.2/g
SiO.sub.2.
[0045] To 1750 g of this acid silica sol was added 70 g of a 35%
solution of tetraethylammonium hydroxide under agitation for 1
second. The obtained amine stabilized alkaline silica-based sol had
a pH of 10.8, SiO.sub.2 content of 8.4% by weight, molar ratio
SiO.sub.2 to N of 15:1, S-value of 21% and contained silica
particles with a specific surface area of 930 m.sup.2/g
SiO.sub.2.
EXAMPLE 6
[0046] A sodium hydroxide stabilized silica sol was deionized in
the same manner as in Example 1 resulting in an acid silica sol
with a pH of 2.4, SiO.sub.2 content of 8.9% by weight and silica
particles with a specific surface area of 820 m.sup.2/g
SiO.sub.2.
[0047] To 2000 g of this acid silica sol was added 214 g of a 20%
solution of tetrapropylammonium hydroxide under agitation for 15
seconds. The obtained aqueous silica-based sol had a pH of 10.7,
SiO.sub.2 content of 8.1% by weight, molar ratio SiO.sub.2 to N of
14:1, S-value of 24% and contained silica particles with a specific
surface area of 820 m.sup.2/g SiO.sub.2.
EXAMPLE 7
[0048] A sodium hydroxide stabilized silica sol containing silica
particles with a specific surface area of around 800 m.sup.2/g
SiO.sub.2 was deionized in the same manner as in Example 1
resulting in an acid silica sol with a pH of 2.6, SiO.sub.2 content
of 9.3% by weight and contained silica particles with a specific
surface area of 795 m.sup.2/g SiO.sub.2,
[0049] To 2000 g of this acid silica sol was added 192.4 g of
triethanolamine under agitation for 10 seconds. The obtained
silica-based sol had a pH of 9.0, SiO.sub.2 content of 8.5%, molar
ratio SiO.sub.2 to N of 2.4:1, S-value of 15% and contained silica
particles with a specific surface area of 795 m.sup.2/g
SiO.sub.2.
EXAMPLE 8
[0050] To 2000 g of the acid silica sol according to Example 7 was
added 30.1 g of triethylamine under agitation for 10 seconds. The
obtained silica-based sol had a pH of 10.2, SiO.sub.2 content of
9.15%, molar ratio SiO.sub.2 to N of 10.4:1, S-value of 25% and
contained silica particles with a specific surface area of 800
m.sup.2/g SiO.sub.2.
EXAMPLE 9
[0051] A sodium hydroxide stabilized silica sol was deionized in
the same manner as in Example 1 resulting in an acid silica sol
with a pH of 2.8, SiO.sub.2 content of 9.3% by weight and contained
silica particles with a specific surface area of 860 m.sup.2/g
SiO.sub.2.
[0052] To 2000 g of this acid silica sol was added 68.1 g of
N,N-dimethyletanolamine under agitation for 5 seconds. The obtained
silica-based sol had a pH of 10.1, SiO.sub.2 content of 9.0%, molar
ratio SiO.sub.2 to N of 4:1, S-value of 26% and contained silica
particles with a specific surface area of 860 m.sup.2/g
SiO.sub.2.
EXAMPLE 10
[0053] A sodium hydroxide stabilized silica sol with specific
surface area around 800 m.sup.2/g was deionized in the same manner
as in Example 1 resulting in an acid silica sol which had a pH of
2.6, SiO.sub.2 content of 9.1% by weight and contained silica
particles with a specific surface area of 880 m.sup.2/g
SiO.sub.2,
[0054] To 2000 g of this acid silica sol was added 103 g of
diethanolamine under agitation for 2 seconds. The obtained amine
stabilized alkaline silica sol had pH of 10.1, SiO.sub.2 content of
8.65%, molar ratio SiO.sub.2 to N of 3:1, S-value of 22% and
contained silica particles with a specific surface area of 875
m.sup.2/g SiO.sub.2.
EXAMPLE 11
[0055] To 2000 g of the acid silica sol according to Example 10 was
added 40.4 g of diethylamine under agitation for 2 seconds. The
obtained silica-based sol had a pH of 11.4, SiO.sub.2 content of
8.92%, molar ratio SiO.sub.2 to N of 6.5:1, S-value of 22% and
contained silica particles with a specific surface area of 880
m.sup.2/g SiO.sub.2.
EXAMPLE 12
[0056] To 2000 g of the acid silica sol according to Example 10 was
added 32.4 g of diisopropylamine under agitation for 2 seconds. The
obtained silica-based sol had a pH of 11.0, SiO.sub.2 content of
8.95%, molar ratio SiO.sub.2 to N of 9.5:1, S-value of 25% and
contained silica particles with a specific surface area of 885
m.sup.2/g SiO.sub.2.
EXAMPLE 13
[0057] To 2000 g of the acid silica sol according to Example 10 was
added 32.5 g of pyrrolidine under agitation for 2 seconds. The
obtained silica-based sol had a pH of 11.1, SiO.sub.2 content of
8.95%, molar ratio SiO.sub.2 to N of 6.6:1, S-value of 25% and
contained silica particles with a specific surface area of 880
m.sup.2/g SiO.sub.2.
EXAMPLE 14
[0058] To 2000 g of another deionized silica sol, which had pH of
2.8, SiO.sub.2 content of 9.3% and contained silica particles with
a specific surface area of 860 m.sup.2/g SiO.sub.2, was added 35.5
g of dipropylamine under agitation for 2 seconds. The obtained
silica-based sol had a pH of 10.6, SiO.sub.2 content of 9.10%,
molar ratio SiO.sub.2 to N of 8.8:1, S-value of 30% and contained
silica particles with a specific surface area of 855 m.sup.2/g
SiO.sub.2.
EXAMPLE 15
[0059] To 2000 g of acid silica sol according to Example 10 was
added 33.7 g of ethanolamine under agitation for 2 seconds. The
resulting silica-based sol had a pH of 10.1, SiO.sub.2 content of
8.95%, molar ratio SiO.sub.2 to N of 5.5:1, S-value of 24% and
contained silica particles with a specific surface area of 870
m.sup.2/g SiO.sub.2.
EXAMPLE 16
[0060] To 2000 g of the acid silica sol according to Example 10 was
added 30 g of cyclohexylamine under agitation for 2 seconds. The
resulting silica-based sol had pH of 10.4, SiO.sub.2 content of
9.0%, molar ratio SiO.sub.2 to N of 10:1, S-value of 24% and
contained silica particles with a specific surface area of 880
m.sup.2/g SiO.sub.2.
EXAMPLE 17
[0061] To 2000 g of another deionized silica sol, which had pH of
2.8, SiO.sub.2 content of 9.3% and contained silica particles with
a specific surface area of 860 m.sup.2/g SiO.sub.2, was added 59.1
g of 2-methoxyethylamine under agitation for 2 seconds. The
obtained silica-based sol had a pH of 10.2, SiO.sub.2 content of
9.0%, molar ratio SiO.sub.2 to N of 3.9:1, S-value of 28% and
contained silica particles with a specific surface area of 850
m.sup.2/g SiO.sub.2.
EXAMPLE 18
[0062] To 1500 g of deionized silica sol, which had pH of 2.8,
SiO.sub.2 content of 9.3% and contained silica particles with a
specific surface area of 860 m.sup.2/g SiO.sub.2, was added 66.1 g
of aminoethylethanolamine under agitation for 5 seconds. The
obtained silica-based sol had a pH of 10.5, SiO.sub.2 content of
9.0%, molar ratio SiO.sub.2 to amine of 3.6:1, S-value of 26% and
contained silica particles with a specific surface area of 875 m2/g
SiO.sub.2.
EXAMPLE 19
[0063] In the following tests, drainage and retention performance
of silica-based sols according to Examples 1 to 18 were tested.
Drainage performance was evaluated by means of a Dynamic Drainage
Analyser (DDA), available from Akribi, Sweden, which measures the
time for draining a set volume of stock through a wire when
removing a plug and applying a vacuum to that side of the wire
opposite to the side on which the stock is present. Retention
performance was evaluated by means of a nephelometer by measuring
the turbidity of the filtrate, the white water, obtained by
draining the stock.
[0064] The stock used was based on a standard fine paper furnish
consisting of 60% bleached birch sulfate and 40% bleached pine
sulfate. 30% calcium carbonate was added to the stock as filler and
0.3 g/l of Na.sub.2SO.sub.4.10 H.sub.2O was added to increase
conductivity. Stock pH was 8.4, conductivity 0.46 mS/cm and
consistency 0.29%. In the tests, the silica-based sols were tested
in conjunction with a cationic polymer being a cationic starch
having a degree of substitution of about 0.042. The starch was
added in an amount of 12 kg/tonne, calculated as dry starch on dry
stock system, and the silica based sols were added in amounts of
0.25, 0.5 and 1.0 kg/tonne calculated as dry silica on dry stock
system.
[0065] The silica-based sols according to the invention were tested
against two silica-based sols, Ref. 1 and Ref. 2, used for
comparative purposes. Ref. 1 is a silica-based of the type
disclosed in U.S. Pat. No. 5,368,833 which had an S-value of about
25%, SiO.sub.2 content of 8%, specific surface area of 72 m.sup.2/g
aqueous sol and contained silica particles with a specific surface
area of about 900 m.sup.2/g SiO.sub.2 which were surface-modified
with aluminium to a degree of 5%. Ref. 2 is a silica sol with an
S-value of 36%, SiO.sub.2 content of 10.0%, molar ratio SiO.sub.2
to Na.sub.2O of 10:1, specific surface area of 88 m.sup.2/g aqueous
sol and containing silica particles with a specific surface area of
880 m.sup.2/g SiO.sub.2.
[0066] The stock was stirred in a baffled jar at a speed of 1500
rpm throughout the test and chemical additions to the stock were
conducted as follows:
[0067] i) adding cationic polymer followed by stirring for 30
seconds,
[0068] ii) adding silica-based particles followed by stirring for
15 seconds,
[0069] iii) draining the stock while automatically recording the
drainage time.
[0070] Table I shows the results obtained when using varying
dosages (kg/tonne, calculated as SiO.sub.2 and based on dry stock
system) of silica-based sol. Without addition of chemicals, the
stock showed a drainage time of 20 seconds and a turbidity of 490
NTU. With addition of cationic starch only, 12 kg/tonne, calculated
as dry starch on dry stock system, the stock showed a drainage time
of 15 seconds and a turbidity of 70 NTU.
1 TABLE I Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.25 kg/t 0.5 kg/t 1.0 kg/t Ref. 1 12.20/43
10.40/40 8.76/37 Ref. 2 11.60/45 9.83/44 8.28/37 Example 1 9.11/38
7.19/30 5.74/28 Example 2 8.65/38 6.79/35 5.76/-- Example 3 9.34/40
7.30/34 6.30/28 Example 4 8.82/39 6.97/36 5.86/31 Example 5 --/--
7.74/37 --/-- Example 6 --/-- 8.98/38 --/-- Example 7 10.3/42
8.77/37 6.66/33 Example 8 10.3/42 8.31/36 7.02/33 Example 9 9.90/--
8.80/-- 7.90/-- Example 10 10.00/-- 8.21/-- 7.07/-- Example 11
10.00/-- 8.04/-- 7.28/-- Example 12 9.87/-- 7.97/-- 6.85/-- Example
13 9.60/-- 7.85/-- 6.30/-- Example 14 10.70/-- 8.80/-- 7.80/--
Example 15 10.70/-- 8.80/-- 7.51/-- Example 16 10.30/-- 8.13/--
6.75/-- Example 17 10.50/-- 8.80/-- 7.70/-- Example 18 10.60/--
9.20/-- 8.20/--
EXAMPLE 20
[0071] In the following tests, drainage and retention performance
of the silica-based sol according to Example 3 was further
evaluated. The procedure according to Example 19 was followed
except that a different stock and different cationic polymers were
used.
[0072] The furnish was based on 70% cellulosic fibres and 30% clay
filler. The fibres consisted of about 70% bleached thermomechanical
pulp, 10% stoneground pulp, 10% bleached birch sulphate and 10%
bleached pine sulphate pulp. The pulp and filler was dispersed in
water to a consistency of 1.5 g/l. In the water was included 25 g/l
of bleach water from a bleaching plant containing dissolved organic
disturbing substances and calcium chloride (CaCl.sub.2.10 H.sub.2O)
in an amount to give a conductivity of 5 mS/cm.
[0073] The silica-based sols were used in combination with a highly
cationic low molecular weight polyamine, which was added in an
amount of 0.5 kg/tonne, calculated dry polymer on dry stock system,
and a cationic polyacrylamide, which was added in an amount of 1.0
kg/tonne, calculated dry polymer on dry stock system. The polyamine
was added to the stock system followed by stirring for 15 seconds
and then the cationic polyacrylamide and silica-based sol were
added according to the procedure of Example 19. The silica based
sols were added in amounts of 0.25, 0.5 and 1.0 kg/tonne calculated
as dry silica on dry stock system.
[0074] Table II shows the results obtained when using varying
dosages (kg/tonne, calculated as SiO.sub.2 and based on dry stock
system) of silica-based sol. Without addition of chemicals, the
stock showed a drainage time of 22 seconds and a turbidity of 100
NTU. With addition of solely 1 kg/tonne cationic polyacrylamide,
calculated as dry polymer on dry stock system, the stock showed a
drainage time of 16 seconds and a turbidity of 55 NTU. With
addition of 0.5 kg/tonne cationic polyamine and 1 kg/tonne cationic
polyacrylamide, calculated as dry polymers on dry stock system, the
stock showed a drainage time of 11 seconds and a turbidity of 50
NTU.
2 TABLE II Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.25 kg/t 0.5 kg/t 1.0 kg/t Ref. 1 12.20/48
11.00/47 9.90/45 Ref. 2 12.30/47 10.70/43 9.18/41 Example 3
10.10/40 8.08/39 6.27/40
EXAMPLE 21
[0075] Sodium waterglass with a ratio SiO.sub.2 to Na.sub.2O of
3.4:1 was diluted to around 6% SiO.sub.2 and treated with a
cationic ion-exchange resin saturated with hydrogen ions. The
obtained polysilicic acid had a pH of 2.5, SiO.sub.2 content of
5.6%, and contained silica particles with a specific surface area
of 1300 m.sup.2/g SiO.sub.2.
[0076] To 5000 g of this polysilicic acid was added 353.5 g of a
34% choline hydroxide solution under agitation for 5 seconds,
resulting in an amine stabilized alkaline silica-based sol with a
pH of 10.8, SiO.sub.2 content of 5.26% and molar ratio SiO.sub.2 to
N of 4.6. This sol was concentrated by vacuum-evaporation to a
stable silica-based sol which had an SiO.sub.2 content of 13.9% by
weight, S-value about 30% and a specific surface area of 169
m.sup.2/g aqueous sol (measured after 40 days) and contained silica
particles with a specific surface area of 1215 m.sup.2/g SiO.sub.2
(measured after 40 days). The viscosity was essentially constant
during these 40 days; initially 11.8 cP and 11.0 cP after 40
days.
EXAMPLE 22
[0077] To 5000 g of the polysilicic acid according to Example 21
was added 347.2 g of a 35% tetraethylammonium hydroxide solution
under agitation for 5 seconds. The resulting amine stabilized
alkaline silica sol had a pH of 10.8, SiO.sub.2 content of 5.26%
and molar ratio SiO.sub.2 to N of 5.7:1. This sol was concentrated
by vacuum-evaporation to a stable silica-based sol which had an
SiO.sub.2 content of 20.0%, viscosity of 9.9 cP and specific
surface area of 250 m.sup.2/g aqueous sol, and contained
silica-based particles with a specific surface area of 1250
m.sup.2/g SiO.sub.2. After storage for 40 days, the sol showed a
viscosity of 8.2 cP, S-value of 43% and specific surface areas of
239 m.sup.2/g aqueous sol and 1195 m.sup.2/g SiO.sub.2.
EXAMPLE 23
[0078] To 5000 g polysilicic acid having a SiO.sub.2 content of
5.1% prepared in a manner similar to Example 21 was added 114 g of
dipropylamine under agitation for 5 seconds. The obtained amine
stabilized alkaline silica-based sol had pH of 10.8, SiO.sub.2
content of 5.0% and molar ratio SiO.sub.2 to N of 3.8:1. This sol
was concentrated by ultrafiltration to a stable silica-based sol
which had an SiO.sub.2 content of 14.8%, specific surface area of
196 m.sup.2/g aqueous sol and contained silica particles with a
specific surface area of 1320 m.sup.2/g SiO.sub.2.
EXAMPLE 24
[0079] To 5000 g polysilicic acid having a SiO.sub.2 content of
5.5% prepared in a manner similar to Example 21 was added 229.8 g
aminoethylethanolamine under agitation for 5 seconds, resulting in
an amine stabilized alkaline silica sol with a pH of 10.3,
SiO.sub.2 content of 5.2% and molar ratio SiO.sub.2 to N of 2:1.
This sol was concentrated by vacuum-evaporation to a stable
silica-based sol with an SiO.sub.2 content of 13.6% and specific
surface areas of 170 m.sup.2/g aqueous sol and 1255 m.sup.2/g
SiO.sub.2.
EXAMPLE 25
[0080] A sodium hydroxide stabilized silica sol having a SiO.sub.2
content of 15% by weight, S-value of about 50% and containing
silica particles with a specific surface area of 500 m.sup.2/g
SiO.sub.2 was deionized in the same manner as in example 1
resulting in an acid silica sol exhibiting a pH of 2.9, SiO.sub.2
content of 14.8% by weight and specific surface area of 490
m.sup.2/g SiO.sub.2.
[0081] To 4000 g of this acid sol was added 414.5 g of a 35%
solution of tetraethylammonium hydroxide under agitation for 5
seconds, resulting in an amine stabilized alkaline silica-based sol
with a pH of 12.1, SiO.sub.2 content of 13.4% and molar ratio
SiO.sub.2 to N of 10:1. This sol was concentrated by
vacuum-evaporation to a stable silica-based sol exhibiting a
SiO.sub.2 content of 40%, specific surface areas of 224 m.sup.2/g
aqueous sol and 560 m.sup.2/g SiO.sub.2.
EXAMPLE 26
[0082] The drainage (dewatering) and retention performance of the
silica-based sols according to Examples 21-24 was investigated in a
manner similar Example 19. The results are set forth in Table
III.
3 TABLE III Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.25 kg/t 0.5 kg/t 1.0 kg/t Ref. 1 12.1/49
10.2/43 9.1/43 Ref. 2 11.8/50 10.2/50 9.0/42 Example 21 9.3/36
7.4/34 6.9/34 Example 22 10.3/45 9.3/42 8.8/41 Example 23 10.8/44
8.8/42 8.1/37 Example 24 10.0/44 8.7/40 7.9/38
EXAMPLE 27
[0083] To 1024 g of polysilicic acid having a pH of 2.7 and
SiO.sub.2 content of 5.84% by weight, prepared in a manner similar
to Example 21, was added 37.1 g of a 75% by weight solution of
choline chloride under agitation resulting in a molar ratio of
SiO.sub.2 to N of 5.0. To this mixture was added 99.6 g of 3M NaOH
under agitation. The obtained silica-based sol had a pH of 11.0,
SiO.sub.2 content of 5.1% by weight, and contained silica particles
with a specific surface area of 1010 m.sup.2/g SiO.sub.2.
EXAMPLE 28
[0084] To 1068 g of polysilicic acid according to Example 27 was
added a mixture of 39 g of a 75% solution of choline chloride and
99.6 g of 3M NaOH under agitation. The obtained silica-based sol
had a pH of 11.0, molar ratio SiO.sub.2 to N of 5.0, SiO.sub.2
content of 5.2% by weight and contained silica-based particles with
a specific surface area of 1175 m.sup.2/g SiO.sub.2.
EXAMPLE 29
[0085] To 50 g of polysilicic acid according to Example 27 was
added 0.9 g of a 75% solution of choline chloride under agitation
resulting in a molar ratio SiO.sub.2 to N of 10.0. The obtained
mixture was added to 9.5 g of 3M NaOH under agitation. The obtained
silica-based sol had a pH of 10.0.
EXAMPLE 30
[0086] 50 g of polysilicic acid according to Example 27 was added
to a mixture of 0.9 g of a 75% by weight solution of choline
chloride and 9.5 g of 3M NaOH under agitation. The obtained
silica-based sol had a pH of 10.1, molar ratio SiO.sub.2 to N of
10.0 and SiO.sub.2 content of 4.8% by weight.
EXAMPLE 31
[0087] To 50 g polysilicic acid according to Example 27 was added
0.9 g of a 75% by weight solution of choline chloride under
agitation resulting in a molar ratio SiO.sub.2 to N of 10.0. To
this mixture was added 20.0 g of a water glass solution containing
9.2% by weight SiO.sub.2 under agitation resulting in a
silica-based sol with a pH of 10.1 and SiO.sub.2 content of 6.6% by
weight.
EXAMPLE 32
[0088] The drainage (dewatering) and retention performance of the
silica-based sols according to Examples 27-31 was investigated in a
manner similar Example 19 except that calcium chloride was added to
the stock to increase the conductivity to 2.0 mS/cm and that the
cationic starch was added in an amount of 10 kg/tonne, calculated
as dry starch on dry stock system. The results are set forth in
Table IV.
4 TABLE IV Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.5 kg/t 1.0 kg/t Ref. 1 25.5/120 21.4/104
Example 27 23.4/116 16.1/83 Example 28 23.1/115 14.5/91 Example 29
22.3/102 16.2/85 Example 30 20.9/98 14.4/78 Example 31 23.0/110
17.3/87
EXAMPLE 33
[0089] An alkali stabilized silica sol was treated with a strong
cation exchange resin in acid form and after the treatment the
silica sol had a pH of 2.6, SiO.sub.2 content of 16.2% by weight
and specific surface area of 500 m.sup.2/g. To 2530 g of this
silica sol was added 294 g of tetraethanol ammonium hydroxide under
rapid agitation for about 5 seconds resulting in an amine
stabilized silica-based sol with a pH of 11.1, SiO.sub.2 content of
14.5% by weight and molar ratio SiO.sub.2 to N of 4.9:1. The
viscosity was 4.6 cP and specific surface area 500 m.sup.2/g. The
obtained product was used for drainage performance testing.
[0090] It was possible to concentrate this product by evaporation
of water to a SiO.sub.2 content of 38.8% by weight. The
concentrated product had essentially the same specific surface area
and could be stored for 6 weeks without gelling. The concentrated
product could easily be diluted and showed the same good
performance in drainage as the non-concentrated product.
EXAMPLE 34
[0091] In the following tests, drainage performance of the
non-concentrated silica-based sol according to Example 33 was
tested in the same manner as in Example 19. The stock was the same
as in Example 19, but calcium chloride was added in an amount to
increase the conductivity to 2.0 mS/cm. Stock pH was 8.4 and
consistency 0.3% by weight. Cationic starch dosage was 12 kg/t,
calculated as dry starch on dry stock. The silica-based sol
according to Example 33 was tested against Ref. 3, which is a
silica sol with an S-value of about 50, SiO.sub.2 content of 15.0%
by weight, specific surface area of 75 m.sup.2/g aqueous sol and
containing silica particles with a specific surface area of about
500 m.sup.2/g of SiO.sub.2. The results are set forth in Table
V.
5 TABLE V Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.25 kg/t 0.5 kg/t 1.0 kg/t Ref. 3 28.0 23.9
17.8 Example 33 26.2 22.6 17.4
EXAMPLE 35
[0092] To 3000 g of a polysilicic acid having a pH of 2.6,
SiO.sub.2 content of 5.7% by weight and specific surface area of
1270 m.sup.2/g was added 200 g of tetraethanol ammonium hydroxide
under rapid agitation for about 5 seconds resulting in an amine
stabilized silica-based sol with a pH of 9.9, SiO.sub.2 content of
5.4% by weight and molar ratio SiO.sub.2 to N of 3:1. The viscosity
was 3.2 cP and specific surface area 1160 m.sup.2/g. The obtained
product was used for drainage performance testing.
[0093] It was possible to concentrate this product by evaporation
of water to a SiO.sub.2 content of 14.5% by weight. The
concentrated product was storage stable for more than 2 months and
showed the same good drainage performance as the non-concentrated
product.
EXAMPLE 36
[0094] In the following tests, drainage performance of the
non-concentrated silica-based sol according to Example 35 was
tested in the same manner as in Example 19. The stock was the same
as in Example 19, but calcium chloride was added in an amount to
increase the conductivity to 2.0 mS/cm. Stock pH was 8.4 and
consistency 0.3% by weight. Cationic starch dosage was 12 kg/t,
calculated as dry starch on dry stock. The silica-based sol
according to Example 35 was tested against Ref. 2. The results are
set forth in Table VI.
6 TABLE V Drainage time (sec)/Turbidity (NTU) at SiO.sub.2 dosage
of Silica-based sol 0.25 kg/t 0.5 kg/t 1.0 kg/t Ref. 2 25.4 21.0
14.9 Example 35 22.7 17.4 13.8
* * * * *