U.S. patent application number 14/891767 was filed with the patent office on 2016-05-26 for method of producing a pigment containing, cationic, high solids aqueous dispersion, aqueous dispersion containing pigments, and use thereof.
The applicant listed for this patent is EP-Pigments Oy. Invention is credited to Esko Aarni, Sami Haakana, Ilkka Tamminen, Jarmo Tolonen, Jorma Viitanen.
Application Number | 20160145807 14/891767 |
Document ID | / |
Family ID | 51178954 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160145807 |
Kind Code |
A1 |
Aarni; Esko ; et
al. |
May 26, 2016 |
METHOD OF PRODUCING A PIGMENT CONTAINING, CATIONIC, HIGH SOLIDS
AQUEOUS DISPERSION, AQUEOUS DISPERSION CONTAINING PIGMENTS, AND USE
THEREOF
Abstract
A method of producing an aqueous dispersion of a pigment, and
the aqueous dispersion of the pigment and the uses of the aqueous
dispersion of the pigment. In the present method, an inorganic
pigment is dispersed in water, in the presence of a dispersing
agent. According to the present invention, the inorganic pigment
comprises cationic calcium carbonate, especially precipitated
calcium carbonate, which is dispersed using a cationic biopolymer,
such as starch, in order to prepare an aqueous dispersion, the
solids content of which is approximately 30-75% by weight. The
dispersion generated can be used, among others, as pigment or
filler for ink-jet paper.
Inventors: |
Aarni; Esko; (Espoo, FI)
; Haakana; Sami; (Espoo, FI) ; Tamminen;
Ilkka; (Espoo, FI) ; Tolonen; Jarmo; (Espoo,
FI) ; Viitanen; Jorma; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EP-Pigments Oy |
Espoo |
|
FI |
|
|
Family ID: |
51178954 |
Appl. No.: |
14/891767 |
Filed: |
May 19, 2014 |
PCT Filed: |
May 19, 2014 |
PCT NO: |
PCT/FI2014/050378 |
371 Date: |
November 17, 2015 |
Current U.S.
Class: |
106/409 ;
106/447; 106/465; 162/175 |
Current CPC
Class: |
D21H 17/29 20130101;
D21H 19/385 20130101; B41M 5/52 20130101; D21H 19/54 20130101; B41M
5/5236 20130101; B41M 5/5218 20130101; D21H 21/16 20130101; D21H
23/56 20130101; B41M 5/5245 20130101; D21H 17/675 20130101 |
International
Class: |
D21H 19/38 20060101
D21H019/38; D21H 17/29 20060101 D21H017/29; D21H 17/67 20060101
D21H017/67; D21H 19/54 20060101 D21H019/54; D21H 21/16 20060101
D21H021/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2013 |
FI |
20135532 |
Claims
1. A method of producing an aqueous dispersion of a pigment,
wherein the inorganic pigment is dispersed into water in the
presence of a dispersing agent, characterised in that the inorganic
pigment comprises cationic calcium carbonate, which is dispersed
using a cationic biopolymer in order to produce a stable dispersion
which has a solids content of approximately 30-75% by weight.
2. The method according to claim 1, wherein the dispersion obtained
remains stable for a period of at least 2 weeks, more preferably
for at least 4 weeks, most preferably for more than 6 weeks.
3. The method according to claim 1, wherein dispersing the mixture,
which comprises a dry pigment or an aqueous slurry or aqueous paste
of the pigment, a dispersing agent and possibly water, by directing
shear forces at the mixture.
4. The method according to claim 1, wherein the solids content of
the dispersion is 50-60% by weight, preferably approximately 57% by
weight.
5. The method according to claim 1, wherein the pigment to be
dispersed is in the form of a dry pigment, an aqueous slurry of the
pigment or an aqueous paste of the pigment.
6. The method according to claim 1, wherein introducing into the
dispersion of a pigment, charge state of which is not rendered
anionic during the time between the production and the dispersion
of the pigment.
7. The method according to claim 1, wherein the surface area of the
calcium carbonate pigment is approximately 5-100 m.sup.2/g, in
particular approximately 10-50 m.sup.2/g.
8. The method according to claim 1, wherein the pigment comprises
calcium carbonate and another, in particular a light-scattering
pigment, such as titanium dioxide, kaolin, gypsum, silicate-based
material, talc or a different calcium carbonate.
9. The method according to claim 1, wherein the pigment consists of
calcium carbonate.
10. The method according to claim 1, wherein the pigment consists
of a porous calcium carbonate material, in particular it consists
of a calcium carbonate material, the particles of which are formed
of calcium carbonate agglomerates.
11. The method according to claim 1, wherein the pigment comprises
or consists of precipitated calcium carbonate.
12. The method according to claim 1, wherein the cationic
biopolymer is a cationic, modified, substituted starch or a
cationic sorbitol or maltodextrin.
13. The method according to claim 1, wherein the modified,
substituted starch comprises cationic, nitrogenous substituents,
such as amine or amide groups.
14. The method according to claim 1, wherein the nitrogen content
of the modified starch is approximately 0.1-2% of its dry
weight.
15. The method according to claim 1, wherein the degree of
substitution of the modified starch is 0.1-0.2, preferably
approximately 0.16.
16. The method according to claim 1, wherein the pigment is
precipitated calcium carbonate that has been dried after the
process of the production of the precipitated calcium
carbonate.
17. The method according to claim 1, wherein the pigment is an
aqueous slurry or aqueous paste of calcium carbonate, obtained by
filtering the dilute aqueous slurry of precipitated calcium
carbonate, which slurry is generated during process of the
production of pigment, is precipitated calcium carbonate.
18. The method according to claim 1, wherein the aqueous dispersion
is prepared without adding a polyelectrolyte, such as polyacrylate,
before dispersion, during dispersion or after it.
19. The method according to claim 1, wherein a dispersion is
prepared, the aqueous phase of which is essentially
polyacrylate-free, especially its polyacrylate content is lower
than 0.1%, most suitably lower than 0.01%, especially lower than
0.001%, of the dry matter content of the dispersion.
20. The method according to claim 1, wherein the aqueous dispersion
comprises a cationic starch derivative approximately 0.1-2.0% by
weight, especially approximately 0.5-0.99% by weight, of the dry
weight of the dispersion.
21. The method according to claim 1, wherein the pigment content of
the aqueous dispersion is approximately 30-75% by weight,
preferably 50-60% by weight, most preferably approximately 57% by
weight, and the dispersing agent content of the aqueous dispersion
is 0.2-5.0% by weight, preferably 0.5-3.0% by weight, most
preferably 0.7-1.5% by weight, in particular approximately 0.7% by
weight.
22. The method according to claim 1, wherein the dry pigment or the
aqueous slurry or aqueous paste of the pigment, the dispersion
agent and, if needed, water, is directed into the dispersion unit,
which is typically a disintegration device operating according to
the impact-repulsion mill principle.
23. The method according to claim 1, wherein an aqueous dispersion
is prepared, the Z-potential of which is at least +1 mV, at a pH
value of 9.5 and a dry matter content of 20%.
24. An aqueous dispersion which comprises an inorganic pigment and
a dispersion agent, wherein the inorganic pigment comprises
cationic calcium carbonate, that the dispersion agent comprises a
cationic biopolymer and that the solids content of the aqueous
dispersion is approximately 30-75% by weight, preferably 50-60% by
weight, most preferably approximately 57% by weight.
25. The aqueous dispersion according to claim 24, wherein the
dispersion is stable, especially the dispersion remains stable for
a period of at least 2 weeks, preferably a period of at least 4
weeks, most preferably a period of over 6 weeks.
26. The aqueous dispersion according to claim 24, wherein the
mixture which comprises a dry pigment or an aqueous slurry or an
aqueous paste of the pigment, a dispersing agent and possibly
water, is dispersed by directing shear forces at the mixture.
27. The aqueous dispersion according to claim 24, wherein the
particle size of the dispersed particle is in the nano-range,
typically 20-400 nm, more preferably over 20 and less than 250 nm,
especially 40-200 nm, in particular 40-100 nm.
28. The aqueous dispersion according to claim 24, wherein the
aqueous phase of the dispersion is essentially polyacrylate-free,
especially its polyacrylate content is lower than 0.1%, most
suitably lower than 0.01%, preferably lower than 0.001%, of the dry
matter content of the dispersion.
29. The aqueous dispersion according to claim 24, wherein the
Z-potential of the dispersion is at least +1 mV, at a pH value of
9.5 and a dry matter content of 20%.
30. The aqueous dispersion according to claim 24, wherein the
surface area of the calcium carbonate pigment is approximately
5-100 m.sup.2/g, especially approximately 10-50 m.sup.2/g.
31. The aqueous dispersion according to claim 24, wherein the
pigment comprises calcium carbonate and another, especially a
light-scattering pigment, such as titanium dioxide, kaolin, gypsum,
silicate-based material, talc or a different calcium carbonate.
32. The aqueous dispersion according to claim 24, wherein the
pigment consists of calcium carbonate.
33. The aqueous dispersion according to claim 24, wherein the
pigment consists of porous calcium carbonate material, especially
it consists of a calcium carbonate material, the particles of which
are formed of calcium carbonate agglomerates.
34. The aqueous dispersion according to claim 24, wherein the
pigment comprises or consists of precipitated calcium
carbonate.
35. The aqueous dispersion according to claim 24, wherein the
modified, substituted starch comprises cationic,
nitrogen-containing substituents such as amine or amide groups.
36. The aqueous dispersion according to claim 24, wherein the
nitrogen content of the modified starch is approximately 0.1-2% of
its dry weight.
37. The aqueous dispersion according to claim 24, wherein the
degree of substitution of the modified starch is 0.1-0.2,
preferably approximately 0.16.
38. The aqueous dispersion according to claim 24, wherein the
pigment is precipitated calcium carbonate, which has been dried
after the process of the production of the precipitated calcium
carbonate.
39. A dispersion according to claim 24, wherein the pigment content
of the aqueous dispersion is approximately 30-60% by weight,
preferably 50-60% by weight, most preferably approximately 57% by
weight, and the dispersing agent content of the aqueous dispersion
is 0.2-5.0% by weight, preferably 0.5-3.0% by weight, most
preferably 0.7-1.5% by weight, in particular approximately 0.7% by
weight, calculated from the dry weight.
40. A use of a dispersion according to claim 24 as a paper or
cardboard filler, in which case the dispersion is, if needed,
diluted with water and directed into the headbox of the paper or
cardboard machine.
41. A use of a dispersion according to claim 24 as a paper or
cardboard filler, without the use of a separate retention
agent.
42. A use of a dispersion according to claim 24 for surface-sizing
of paper or cardboard, in which case the dispersion is mixed into a
cationic starch that is suitable for conventional surface-sizing,
and the mixture is applied to the dried web.
43. A use of a dispersion according to claim 24 for the coating of
paper or cardboard, in which case the dispersion is mixed into a
coating paste, which is then applied to the dried web.
44. A use of a dispersion according to claim 24 as a pigment or
filler for ink-jet paper.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of and
incorporates by reference subject matter disclosed in International
Patent Application No. PCT/FI2014/050378 filed on May 19, 2014 and
Finnish Patent Application No. 20135532 filed May 17, 2013.
TECHNICAL FIELD
[0002] The present invention relates to production of cationic
pigments, especially aqueous dispersions which have a high dry
matter content. In particular, the present invention relates to the
method for example for the production of an aqueous dispersion
which is used in the production of paper or cardboard.
[0003] The present invention also relates to the aqueous dispersion
that comprises pigments, and the use of the aqueous dispersion.
BACKGROUND ART
[0004] The pigments which are used as paper and cardboard fillers
are added, in the form of an aqueous dispersion, into the pulp
slush in the headbox of the machine. Good retention of the pigments
(adhesion to pulp fibres) usually requires the use of retention
agents. If the pigment used is precipitated calcium carbonate, PCC,
which is prepared in the vicinity of the paper or the cardboard
mill, and which is generated, in the form of a slurry that
comprises 20-25% of solid matter, during the process of the
production of pigment, a separate retention agent is not
necessarily needed, because the PCC particle has a cationic surface
charge, in which case it adheres well to the anionic fibre
network.
[0005] Transportation of a PCC slurry which is dilute, i.e. which
comprises approximately 20-25% of solid matter, over long distances
is out of the question for cost reasons. If the PCC is going to be
used far from its place of production, the PCC slurry is typically
concentrated for example by centrifuging it to a higher percentage
of solid matter, after which the slurry is dispersed with an
anionic dispersing agent, and the resulting aqueous dispersion that
has a high dry matter content is transported to the place of
application. Alternatively, it is possible to dry the dispersion to
a dry anionic pigment. When the dispersion or the aqueous slurry
that is made from the dry anionic pigment is added into the pulp
slush, a cationic retention agent must be added, too.
[0006] Also, when ground calcium carbonate, GCC, is used, it is
usually delivered to the application in the form of a dispersion
having a high solid matter content, and in which case an anionic
agent has been used as the dispersing agent. Alternatively, the GCC
is delivered to the application in the form of an anionic pigment
which is stabilised by means of a dispersing agent. Thus, a
cationic retention agent is also needed when GCC is used.
[0007] Various dispersions and slurries of PCC are already known.
Thus, the WO application publication 9730220 describes a method of
producing paper which is filled with PCC, in which case a cationic
polymer, for example starch, is mixed into the PCC slurry, before
the mixture is added into the pulp slurry. After that, a retention
agent is added into the pulp slurry. The resulting mixture is not
stable.
[0008] EP application publication 0 790 135 describes a solution of
producing paper which is suitable for ink-jet printing technology.
A surface layer is applied onto the paper web, which layer
comprises a cationic pigment. The surface layer is comprised of an
aqueous suspension of the pigment and a binder. The percentage of
the binder in the mixture of the aqueous dispersion of the pigment
and the cationic binder is significantly high, and it is not
possible to add the binder for example into the headbox of the
paper machine, and thus use it as paper filler. This aqueous
dispersion is not stable either.
[0009] US patent publication 8197641 describes a paper filler, the
use of which requires that an aqueous slurry is formed of it, into
which slurry another aqueous dispersion is added. After that, an
aqueous slurry of starch is added, too. The resulting aqueous
slurry is not stable. Moreover, use of the previously described
mixture requires the addition of a retention agent.
SUMMARY OF THE INVENTION
[0010] The purpose of the present invention is to provide a stable,
aqueous dispersion which has a high dry matter content and which
comprises pigments and which is to be used in the paper and
cardboard industry, in which aqueous dispersion the surface of the
pigment that is used as a filler is cationic, and the retention of
which to the negatively charged pulp fibres is good and proceeds
without a separate retention agent.
[0011] In particular, the purpose is to provide a dispersion, the
stability of which is so good that pigment precipitation does not
occur even during a storage period of several weeks, even though
the viscosity of the dispersion is relatively low.
[0012] Another purpose is to provide a dispersion which, when used
for surface-sizing of paper, gives the paper a good
printability.
[0013] A further purpose is to provide a dispersion which, when
used for coating of paper, gives the paper good optical properties,
good colour densities and facilitates the rapid drying of printing
ink.
[0014] The present invention is based on the idea that an aqueous
dispersion which comprises pigments can be produced by using a
method in which either a dry pigment or an aqueous slurry or paste
of the pigment, having a pigment content of approximately 30-75% by
weight, is dispersed by using a dispersing agent and possibly an
additive, in order to generate a stable dispersion. In the present
invention, the dispersing agent used is cationic, modified starch.
The additive used is for example water.
[0015] The present invention provides an aqueous dispersion which
has a high dry matter content, and which comprises pigments and a
dispersing agent, which aqueous dispersion is characterised in that
the dispersing agent is a cationic polymer, for example a native
polymer or a polymer derived thereof, in particular a modified
starch.
[0016] The new dispersion can be used as paper or cardboard filler,
in which case, if needed, the dispersion is diluted with water and
directed into the headbox of the paper or cardboard machine.
[0017] The dispersion can also be used for surface-sizing of paper
or cardboard, in which case the dispersion is mixed into a cationic
starch that is suitable for conventional surface-sizing, and the
mixture is applied to the dried web.
[0018] A third application is the coating of paper or cardboard, in
which case the dispersion is mixed into a coating paste, which is
applied to the dried web.
[0019] More specifically, the method according to the present
invention is a method of producing an aqueous dispersion of a
pigment, wherein the inorganic pigment is dispersed into water in
the presence of a dispersing agent, characterised in that the
inorganic pigment comprises cationic calcium carbonate, which is
dispersed using a cationic biopolymer in order to produce a stable
dispersion which has a solids content of approximately 30-75% by
weight.
[0020] The aqueous dispersion according to the present invention
comprises an inorganic pigment and a dispersion agent, wherein the
inorganic pigment comprises cationic calcium carbonate, that the
dispersion agent comprises a cationic biopolymer and that the
solids content of the aqueous dispersion is approximately 30-75% by
weight, preferably 50-60% by weight, most preferably approximately
57% by weight.
[0021] The uses include a use of a dispersion as a paper or
cardboard filler, in which case the dispersion is, if needed,
diluted with water and directed into the headbox of the paper or
cardboard machine; a use of a dispersion as a paper or cardboard
filler, without the use of a separate retention agent; a use of a
dispersion for surface-sizing of paper or cardboard, in which case
the dispersion is mixed into a cationic starch that is suitable for
conventional surface-sizing, and the mixture is applied to the
dried web; a use of a dispersion for the coating of paper or
cardboard, in which case the dispersion is mixed into a coating
paste, which is then applied to the dried web; and a use of a
dispersion as a pigment or filler for ink-jet paper.
[0022] Considerable advantages can be achieved with the present
invention. Thus, as the results below demonstrate, by using
cationic starch as a dispersing chemical, excellent stability and
fluidity properties are achieved. The results also show that, when
cationic pigments are used together with cationic surface starch,
it is possible to improve the ink-jet printability, for example,
regarding the sharpness of the printing quality. The opacity of the
dispersed dry matter is excellent when dry.
[0023] The dispersion according to the present invention remains
stable for a period of at least 2 weeks, preferably for at least 4
weeks. This provides a significant advantage, because the
dispersion can be stored for a certain period of time, i.e. for
several weeks. In this case, the dispersion can be prepared in a
particular plant, from where it is then delivered to different end
users, typically paper and cardboard mills. Thus, the end users do
not have to invest in dispersing apparatus and high expertise in
dispersing technology.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 shows schematically alternative ways of dispersing
the pigments, according to the method of the present invention,
and
[0025] FIG. 2 shows the ink-jet print quality on a surface-sized
paper, with different surface-sizing agents.
DETAILED DESCRIPTION
[0026] As described above, according to the new technology, in the
production of an aqueous dispersion that comprises pigments, either
a dry pigment or an aqueous slurry or a paste of the pigment, the
pigment content of which is approximately 30-75% by weight, is
dispersed by using a dispersing agent and possibly together with an
additive, in order to generate a stable aqueous dispersion having a
high dry matter content. A cationic biopolymer is used as the
dispersing agent.
[0027] The pigment content of the aqueous dispersion is preferably
50-60% by weight, especially approximately 57% by weight.
[0028] The dispersion generated by the present method remains
stable for a period of at least 2 weeks, more preferably for at
least 4 weeks, most preferably for more than 6 weeks.
[0029] In this patent application a stable dispersion means that at
maximum approximately 15%, especially at maximum approximately 10%,
more preferably at maximum 5%, in particular at maximum 1% of the
solid matter of the dispersion precipitates during the observation
period, in which case the observation period means a period of at
least 2 weeks, preferably at least 4 weeks, most preferably more
than 6 weeks.
[0030] The dispersion is preferably carried out in such a way that
shear forces are directed at the mixture which comprises a dry
pigment or an aqueous slurry or paste of the pigment; dispersing
agent and possibly water.
[0031] The particle size of the dispersed pigment can be in the
nano-range, typically 20-400 nm, more preferably more than 20 and
less than 250 nm, especially 40-200 nm, in particular 40-100 nm.
The pigment particle size can also be larger than this. Thus, the
initial material used can be PCC products or structured pigments
having a particle size in the micrometre range. Examples of these
products are polynuclear, typically of regular shape, for example
particle clusters and particle agglomerates, which comprise several
interconnected, in particular spherical calcium carbonate
particles. The size (maximum diameter) of the structures of
polynuclear clusters or similar products, i.e. the agglomerates or
clusters, may be even 6000 nanometres, typically at maximum 4000 nm
and especially at maximum 2500 nm, most suitably approximately 1500
nm.
[0032] Based on the above, the particle size of the particles to be
dispersed is thus generally 20-4000 nm, most preferably 20-2500 nm
and especially 40-1500 nm.
[0033] Here, the particle size means the diameter of particles
after they have been changed into spherical bodies.
[0034] Preferably, the pigment to be dispersed is in the form of a
dry pigment, an aqueous slurry of the pigment or an aqueous paste
of the pigment.
[0035] In one embodiment, a pigment is introduced into the
dispersion, the charge level of which pigment is not rendered
anionic at any stage during the time between the production and the
dispersion of the pigment. It is thus possible to entirely avoid
the use of separate anionic chemicals, such as polyacrylates.
[0036] However, in the prior art, a product generated in the
production of calcium carbonate is treated to render it anionic
before dispersion. The WO application publication 9730220
explicitly states that, before the PCC slurry can be mixed with the
suspension, it is necessary to mix into the slurry an amount
cationic polymer that is needed for the cationisation (page 9, line
23). In the case of the WO publication, the amount to be added must
be significant, which indicates the anionic nature of the
slurry.
[0037] In many applications, the pigment should have a good dry
opacity.
[0038] In one embodiment that fulfils the above requirement of dry
opacity, the surface area of the calcium carbonate pigment is
approximately 5-100 m.sup.2/g, especially approximately 10-50
m.sup.2/g.
[0039] Examples of porous calcium carbonate materials, which are
suitable for this application as well as for other applications,
include those which are comprised of calcium carbonate material,
the particles of which are composed of calcium carbonate
agglomerates or clusters. These are described for example in EP
patent 0 944 551, according to which the precipitated calcium
carbonate crystals (PCC crystals) are in the form of polynuclear,
typically regular, usually spherical clusters, which comprise
several interconnected, in particular
spherical calcium carbonate particles having a particle size of
approximately 40-400 nm, typically approximately 40-200 nm.
[0040] The clusters described in that particular patent have
numerous internal reflection surfaces which improve the opacity of
the pigment and the filler.
[0041] The pigment can be used as such but it is of course possible
to use structured pigments, i.e. calcium carbonate, together with
light-scattering pigments. In this way, it is possible to increase
the diffuse reflections of light, in which case the probability
increases that light beams hit a reflecting surface.
[0042] EP patent 0 944 551 also describes a method of producing
porous pigments, i.e. in that case calcium carbonate clusters. The
publication is herewith incorporated by reference.
[0043] The cationic biopolymer which is used in the production is
preferably a cationic, modified, substituted starch or cationic
sorbitol or maltodextrin.
[0044] A specific example worth mentioning is a suitable, modified,
substituted starch that comprises cationic, nitrogen-containing
substituents, such as amine or amide groups.
[0045] The nitrogen content of the modified starch is for example
approximately 0.1-2% of its dry weight.
[0046] In a more preferable embodiment, the degree of substitution
of the modified starch is 0.1-0.2, especially approximately
0.16.
[0047] The technology can be applied to various pigments,
especially to mineral pigments. Examples are calcium carbonate,
such as precipitated calcium carbonate (PCC) or ground calcium
carbonate (GCC); talc; gypsum; titanium dioxide; and kaolin.
[0048] More preferably, the present solution is applied to PCC,
especially to a PCC that has been dried after the production
process of the PCC.
[0049] According another preferred embodiment, the present solution
is applied to an aqueous slurry or an aqueous paste of PCC, which
is obtained by filtration of the dilute PCC aqueous slurry that
comes from the production process of the PCC.
[0050] In a third embodiment, the pigment is dry PCC or GCC or an
aqueous slurry or an aqueous paste of PCC or GCC, having a pigment
content of 30-60% by weight, and the dry pigment or pigment slurry
or paste is stabilised by using an anionic dispersing agent.
[0051] In one embodiment, [0052] the pigment content of the aqueous
dispersion is approximately 30-75% by weight, preferably 50-60% by
weight, most preferably approximately 57% by weight, and [0053] the
dispersing agent content of the aqueous dispersion is 0.2-5.0% by
weight, preferably 0.5-3.0% by weight, most preferably 0.7-1.5% by
weight, in particular approximately 0.7% by weight.
[0054] One possibility is to direct the dry pigment or the aqueous
slurry or aqueous paste of the pigment, the dispersing agent and,
if needed, water, into the dispersing unit, which is typically a
disintegration device operating according to the impact-repulsion
mill principle.
[0055] The resulting dispersion can be used as a paper or cardboard
filler, in which case, if needed, the dispersion is diluted with
water and directed into the headbox of the paper or cardboard
machine.
[0056] The dispersion can also be used as a paper or cardboard
filler without the use of a separate retention agent.
[0057] In one embodiment the dispersion is used for surface-sizing
of paper or cardboard, in which case the dispersion is mixed into a
conventional cationic starch that is suitable for surface-sizing,
and the mixture is applied to the dried web.
[0058] The dispersion can also be mixed into the coating paste,
which is applied to the dried web.
[0059] The dispersion of the pigment can be carried out in various
ways, for example according to the process schematised in FIG.
1.
[0060] As described above, the aqueous dispersion is prepared
without the addition of a polyelectrolyte, such as polyacrylate,
before, during or after the dispersion. Thus, in one embodiment, a
dispersion is prepared, the aqueous phase of which is essentially
polyelectrolyte-free. For example, the polyacrylate percentage is
lower than 0.1%, most suitably lower than 0.01%, especially lower
than 0.001%, of the dry matter content of the dispersion.
[0061] In a preferred embodiment, the aqueous dispersion obtained
comprises a cationic starch derivative approximately 0.1-2.0% by
weight, especially approximately 0.5-0.99% by weight, of the dry
weight of the dispersion.
[0062] The new technology allows the production of for example an
aqueous dispersion, the Z-potential of which is at least +1 mV, at
a pH value of 9.5 and a dry matter content of 20%.
[0063] According to one embodiment, in the method of producing the
pigment slurry, a inorganic pigment is dispersed into water in the
presence of a dispersing agent, in which case the inorganic pigment
comprises cationic calcium carbonate, which is dispersed by using a
cationic biopolymer in order to generate an aqueous slurry, the
solids content of which is approximately 30-75% by weight, and in
which case the cationic calcium carbonate is a dry cationic
precipitated calcium carbonate, which is obtained by drying the
slurry coming from the production of the precipitated calcium
carbonate. It is possible to add water into the dry PCC, before
dispersion.
[0064] Because the solids content of the dispersion according to
the present invention is considerably high, also somewhat larger,
micro-sized pigment particles may be present in the dispersion,
along with the nano-sized pigment particles, without impairing much
the stability of the dispersion.
[0065] More preferred embodiments are examined with reference to
the drawings.
[0066] Production of a dry cationic pigment and production of a
dispersion of a cationic pigment as a two-stage process
[0067] The slurry coming from the production of pigment (PCC), the
solids content of which slurry is 24%, is fed along the pipe 11
into the centrifuge 1, where some of the water is removed. The
paste-like PCC slurry having a solids content of approximately 50%
is removed from the centrifuge. The paste is fed along the pipe 12
to the dryer 4, and the product 5 which exits from the dryer along
the pipe 13 is nearly 100% a dry cationic pigment (PCC), which can
be delivered as such for use. In the place of use or at the
producer of the pigment, it is possible to slurry the dry cationic
pigment in a desired amount of water, to feed a dispersing agent
into it and to disperse it. The resulting product is a cationic PCC
dispersion having a typical solids content of approximately
50%.
[0068] Dispersing of an anionic pigment in water together with a
cationic, modified starch, in order to form a cationic pigment
dispersion
[0069] PCC slurry having a solids content of 24% is fed into the
centrifuge 1, where some of the water is removed. The PCC slurry
which is removed from the centrifuge along the pipe 16 typically
comprises approximately 50% of solids and it is directed to the
disperser 3, to which is added an anionic dispersing agent. The
dispersed slurry is directed by line 17 to the dryer 4, where it is
dried. The resulting product, a dried anionic pigment (PCC), is a
commercial product which is known per se.
[0070] A dry anionic pigment produced in a way which is known per
se can be modified, for example, either in the place of use of the
pigment or at the producer of the pigment, to a cationic aqueous
dispersion of pigment having a high dry matter content. The dry
anionic pigment is slurried in a desired amount of water, a
dispersing agent is fed into it and then it is dispersed. The
resulting product is a cationic dispersion of PCC, having a typical
solids content of approximately 50%.
[0071] Although the anionic PCC pigment itself is useful as paper
filler, it is advantageous to modify the pigment to be cationic as
described above, because the retention of the cationic pigment is
good and does not necessarily require the use of a retention
agent.
[0072] Ground calcium carbonate (GCC) is also delivered in the form
of a dry anionic pigment or a dispersion of an anionic pigment.
These products can also be rendered cationic in the way described
above.
[0073] The following non-restrictive examples illustrate the new
technology.
Example of Slurry Production
[0074] A PCC slurry having a low dry matter content was prepared,
which slurry was filtered to form a paste that has a high dry
matter content. This was dispersed by using a cationic modified
starch (Vector 20157, Roquette) as the dispersion agent. The
viscosity of the prepared cationic aqueous dispersion of the PCC
having a high dry matter content, was 430 cP. The product was
stored in an IBC container for a period of 4 weeks. After storage,
it was found that the aqueous dispersion of the PCC having a high
dry matter content had not settled, and the viscosity of the slurry
was measured and found to be 100 cP.
Example 1
The Effect of the Pigment Content and the Dispersing Agent Content
on the Viscosity and the Stability of the Dispersion
[0075] The pigment used in the experiment was dry PCC. The pigment
was dispersed in water using a cationic modified starch (Vector
20157; Roquette) as the dispersing agent. The viscosity was
determined by means of a Brookfield rotational viscometer, at 100
rpm (Br100) and 50 rpm (Br50). The unit of measurement of viscosity
is mPa s. The precipitation tendency of the dispersion was measured
by pouring the dispersion into a 100 ml calibrated beaker that has
a diameter of approximately 2.0 cm, and then observing how the
height of the bright water column (mm) increases over time, for a
period of 2, 7 and 14 days.
[0076] The results are shown in Table 1. The table shows that the
dispersion, which has a pigment content of 57% and a dispersing
agent content of 0.7%, has a good stability (low settling, and no
observed change as a function of time) and a viscosity within a
suitable range.
TABLE-US-00001 TABLE 1 7 Dispers. Viscosity Viscosity 2 days days
14 days agent, % Pigment % Br100 mPas Br50 mPas pH mm mm mm 0.5
50.19 336 528 8.76 4 4 4 0.5 54.2 1364 2220 9 1 1 1 0.5 58.2 6700
9860 8.5 0.5 0.5 0.5 0.7 50.07 100 118 8.57 1 5 8 0.7 53.9 207 246
8.5 1 4 4 0.7 57.9 172 226 8.52 0.5 0.5 0.5 0.9 49.9 225 246 8.78 1
2 4 0.9 54.1 177 210 8.85 0.5 0.5 2 0.9 58.1 892 1624 8.57 0.5 0.5
0.5 1.1 50.1 155 180 8.6 1 1 1.5 1.1 53.9 297 348 8.6 0.5 0.5 1 1.1
57.9 1590 2360 8.75 0-0.5 0-0.5 0.5 1.3 50 259 308 8.5 0-0.5 1 1
1.3 53.9 396 466 8.62 0-0.5 0.5 0.5 1.3 58.1 3280 5840 8.59 3 3
4
[0077] Table 2 shows the viscosity of the dispersion as a function
of time. The pigment was dispersed in water using a cationic
modified starch (Vector 20157; Roquette) as the dispersing agent.
The viscosity was determined by means of a Brookfield rotational
viscometer, as above. The dispersion that has a pigment content of
57.5% and a dispersing agent content of 0.7%, has a suitable
viscosity, which does not change much as a function of time.
TABLE-US-00002 TABLE 2 Time, h Viscosity, Br100, mPas Viscosity,
Br50, mPas 0 170 240 1 350 412 2 404 428 3 370 396 4 398 420 5 380
396 6 500 700 11 320 470 23 336 504 30 504 700 48 404 462
[0078] Tables 1 and 2 show that the modified starch used renders
the dispersion a good stability and good flow properties.
Example 2
Ink-Jet Printability of Surface-Sized Paper
[0079] The cationic PCC pigment dispersion, which was prepared from
a semi-dry filter cake, by using a modified starch (Vector 20157)
as the dispersing agent, was mixed into a conventional cationic
starch that is used for surface-sizing. Three tests were carried
out, namely 1) a control, where the surface had been treated
exclusively with cationic surface starch; 2) anionic pigment was
added into the surface starch; 3) cationic pigment was added into
the cationic surface starch. The mixtures were applied onto the
surface of paper, and ink-jet printing was carried out.
[0080] The imprints of the experiments are shown in FIG. 2. It can
be seen that the sharpest print quality was obtained in test no. 3,
in which cationic pigment was used. This shows that the use of
cationic pigment in the surface-sizing agent of paper improves the
ink-jet printability of paper, because it prevents the printing ink
from spreading and being mixed into other printing inks.
Example 3
Ink-Jet Printability of Coated Paper
[0081] The cationic PCC pigment dispersion, which was prepared from
a semi-dry filter cake, by using modified starch (Vector 20157) as
the dispersing agent, was mixed into a coating colour. The results
were compared to the commonly used titanium dioxide pigment. Three
tests were carried out. A coating paste comprising 15% of titanium
dioxide was used as a control (Test 1). In Test 2, half of the
titanium dioxide, and in Test 3 all of the titanium dioxide was
replaced with a cationic PCC pigment that is described above. The
papers were coated, an ink-jet printing was carried out and the
coated papers and the imprints were tested. Table 3 shows the
results.
TABLE-US-00003 TABLE 3 Test 1, Test 2 Test 3 control 7.5% TiO.sub.2
0% TiO.sub.2 15% TiO.sub.2 7.5% cat. 15% cat. 0% cat. PCC PCC PCC
Optical Brightness, % 89.2 90.1 92.4 properties Fluorescence 2.6
3.6 6.0 Opacity, % 96.7 96.6 96.8 -- -- -- -- -- Inkjet test Colour
density 1.08 1.14 1.23 results Blue Colour density 0.93 0.95 1.06
Magenta Colour density 0.79 0.83 0.92 Yellow Colour density 2.92
2.92 2.96 Black Drying rate 6.2 5.0 3.8 (60 s); .DELTA.R20
[0082] The improved fluorescence (i.e., the difference in
brightness as measured under UV light conditions and under normal
light) is due to the reduced titanium oxide content of the coating
colour. The optical density of the coating colours blue, magenta,
and yellow were significantly increased by the cationic PCC. The
drying of the printing ink was accelerated by the cationic PCC. The
decrease in brightness of white paper, which was pressed against
the printed surface, was lower than in the control test.
[0083] The present invention is not intended to be limited to the
above embodiments, which are only examples. The present invention
is intended to be widely applied within the scope of protection of
the claims below.
[0084] The dispersion according to the present invention is a kind
of an initial product, which can be used for many different
purposes in the end-user facility, such as paper or cardboard
filler, a component of the surface-sizing agent for paper or
cardboard, or a component of the coating paste of paper or
cardboard. This fact is particularly significant for the material
logistics of paper or cardboard mills, because only one acquired
initial product is needed to produce a variety of end products.
[0085] Because the dispersion remains stable and the particles of
the dispersion remain cationic, it is possible to use the
dispersion directly as a filler by feeding it (possibly diluted in
water), without retention agents, into the headbox of the machine.
The dispersion is also, for example when mixed into cationic
starch, very well suited for surface-sizing of paper. Use of the
pigment of the dispersion in the surface-sizing agent of paper
improves the printability of the paper, particularly the ink-jet
printability, because it prevents the printing ink from spreading
and mixing into other printing inks.
[0086] When used in the paper coating, the pigment of the
dispersion provides better optical results (i.e. better brightness,
fluorescence and opacity) than provided by titanium dioxide. The
print quality of the ink-jet printing printed in this way on coated
paper is also better than the printing quality when using titanium
dioxide, and printing ink dries faster.
[0087] While the present disclosure has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this disclosure may be made without
departing from the spirit and scope of the present disclosure.
* * * * *