F O R M 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
PRODUCTION OF PRECIPITATED CALCIUM CARBONATE
2. APPLICANT(S)
(a) NAME
(b) NATIONALITY
(c) ADDRESS
COATEX
FRENCH Company
35, RUE AMPÈRE,
F-69730 GENAY,
FRANCE
3. PREAMBLE TO THE DESCRIPTION
PROVISIONAL
The following specification describes invention
COMPLETE (√)
The following specification particularly describes the invention
and the manner in which it is to be performed
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble – “I/We claim”
on separate page)
6. DATE AND SIGNATURE ( to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on the separate page)
Note:
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*To be signed by the applicant(s)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and country
*Strike out the column which is/are not applicable
This form is digitally signed.
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The present invention relates to the use of a cationic polymer in a method for producing
precipitated calcium carbonate, said cationic polymer being optionally used in combination
with at least one slaking additive. Thus, the invention relates to a method for producing
precipitated calcium carbonate, comprising the use of a cationic polymer, optionally in
combination with at least one slaking additive.
Background of the invention
Calcium carbonate is one of the most commonly used additives in the paper, paint and
plastics industries. While naturally occurring Ground Calcium Carbonate (GCC) is usually
used as a mineral filler in many applications, synthetical Precipitated Calcium Carbonate
(PCC) may be tailor-made with respect to its morphology and particle size allowing these
materials to fulfil other functions.
Scalenohedral Precipitated Calcium Carbonate (S-PCC) notably is used as a mineral filler in
combination with cellulosic fibres in wet-end applications.
Commonly known PCC production methods comprising the steps of slaking quicklime with
water and subsequently precipitating calcium carbonate by passing carbon dioxide through
the resulting calcium hydroxide suspension, produce only PCC slurries with low dry solids
content. Therefore, these methods typically comprise a subsequent concentration step in order
to obtain a more concentrated PCC slurry, which is of interestfor the transport of the PCC
slurry. However, such additional concentration steps are energy-consuming and costintensive
and require an equipment such as a centrifuge, which is expensive and needs high
maintenance. Furthermore, mechanical dewatering methods using centrifuges may destroy
the structure of the formed PCC, for example in case of clustered scalenohedral PCC.
Methods for preparing PCC in the presence of different additives are described in the
literature.
Document US 2011/158890 A1 describes a method to manufacture PCC involving the use of
a comb polymer, which reduces the carbonation time of the PCC.
Document WO 2005/000742 A1 is directed to a method for preparing platy PCC comprising
the steps of providing a suspension of calcium hydroxide, carbonating said suspension, and
adding a polyacrylate to the suspension prior to the completion of the carbonation to
precipitate platy calcium carbonate.
Document EP 0 281 134 relates to a cationic pigment dispersion which is suitable in
particular for preparing papercoating compositions and contains (a) a pigment compound
which is composed of ground and/or precipitated calcium carbonate, kaolin, calcined kaolin,
titanium dioxide, zinc oxide, satin white, aluminumhydrosilicate or mixtures thereof, (b) a
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cationised polymer which surrounds the pigment particles as a protective colloid and has
been obtained from hydrophilic polyacrylates or polymethacrylates, degraded starches or
degraded modified starches, methylcelluloses, hydroxymethylcelluloses,
carboxymethylcelluloses, degraded alginates, proteins and/or polyvinyl alcohol and which
bringsthe Zeta potential of the dispersion containing the enrobed pigment particles to the
isoelectric point or into the cationic range, and optionally (c) a cationic polymer or a
quaternary ammonium compound as a dispersing agent for the colloid-enrobed and cationised
pigment particles.
Document US 2006/0137574 A1 relates to a pigment composition, comprising at least one
calcium carbonate chosen from rhombohedral calcium carbonate and ground calcium
carbonate, at least one anionic dispersing agent present in an amount sufficient to
overdisperse the at least one calcium carbonate and at least one cationic polymer.
Document WO 06/109171 A1 relates to PCC pigments, to be used in paper coating
formulations to manufacture coated high-quality matt papers, in particular for inkjet
applications. Method for preparingthese PCC pigments, using a reduced flow rate of a carbon
dioxide-containing gas in the PCC carbonation step, produces stable and porous agglomerates
of PCC having unique properties and structure, this step being followed by aconcentration
step to increase the dry solids content, said concentration being conducted without the use of
a dispersing aid agent or with a cationic dispersing aid agent.
Document US 2005/0221026 A1 relates to a thermal ink jet recording paper, incorporating
dewatered and ground Precipitated Calcium Carbonate (PCC). Precipitated calcium carbonate
is dewatered and ground in the presence of an amphoteric or anionic dispersing agent to
produce a high dry solids content PCC composition.
Unpublished patent application EP 14166751.9 filed in the name of present applicants relates
to the use of a combination of at least one water-soluble polymer and at least one slaking
additive in a method for producing an aqueous suspension of precipitated calcium carbonate.
Document FR 2934992 relates to the use, for the manufacture of a precipitated mineral
matter, of at least one particular copolymer. This copolymer would reduce the carbonation
time and thus increase the yield of the method of manufacture.
Document WO 2007/067146 A1 discloses a method for preparing PCC using starch or
carboxymethylcellulose during the calcium hydroxide carbonation.
Document WO 2010/093092 A1 describes a method of CO2 capture by the precipitation of
calcium carbonate in the presence of an amine polymer.
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Summary
An object of the present invention is to provide a solution for the production of PCC slurries,
for example with high dry solids content, without an additional thermal or mechanical
concentration step.
Another object of the present invention is to provide a solution for the production of high dry
solids content PCC slurries witheasily manageable viscosities, that is to say a solution making
it possible to increase the dry solids content of PCC slurries, while preventing theincrease of
the slurries’viscosity.
It is also desirable that said solution does not affect the kinetics of the carbonation step in a
negative way and/or does not impair the crystallographic structure of the PCC.
Another object of the present invention is to provide a solution for preparing PCC slurries
with cationic surface charges, even at alkaline pH.
Another object of the present invention is to provide a solution for preparing PCC slurries to
be directly used as a mineral filler in a paper-making method.
The present invention relates to the use of at least one cationic polymer in a method for
producing an aqueous suspension of precipitated calcium carbonate, said method comprising
the steps consisting in:
i) preparing a milk of lime by mixing water, a calcium oxide containing material and said
at least one cationic polymer, the calcium oxide containing material and water are
mixed in a weight ratio from 1:1 to 1:6 and
ii) carbonating the milk of lime obtained from step i) to form an aqueous suspension of
precipitated calcium carbonate.
Thus, the invention relates to a method for producing precipitated calcium carbonate,
comprising the use of a cationic polymer, optionally in combination with at least one slaking
additive, said method comprising the steps consisting in:
i) preparing a milk of lime by mixing water, a calcium oxide containing material and said
at least one cationic polymer, the calcium oxide containing material and water are
mixed in a weight ratio from 1:1 to 1:6 and
ii) carbonating the milk of lime obtained from step i) to form an aqueous suspension of
precipitated calcium carbonate.
The product comprising the precipitated calcium carbonate obtained with the use of a cationic
polymer according to the present invention may be a paper, a paper product, an ink, a paint, a
coating, a plastic, a polymer composition, an adhesive, a building product, a foodstuff, an
agricultural product, a cosmetic product or a pharmaceutical product.
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The present invention also relates to the use of a combination of at least one cationic polymer
and at least one slaking additive in a method for producing an aqueous suspension of
precipitated calcium carbonate.
Detailed description
It should be understood that for the purposes of the present invention, the following terms
have the following meaning:
A "calcium oxide containing material", in the meaning of the present invention,may be a
mineral or a synthetic material with a content of calcium oxide of at least 50wt.-%, preferably
75 wt.-%, more preferably 90 wt.-% and most preferably 95wt.-%relative to the total weight
of the calcium oxide containing material. For the purposes of the present invention, a
"mineral material" is a solid substance with a definite inorganic chemical composition and
characteristic crystalline and/or amorphous structure.
"Ground Calcium Carbonate" (GCC), in the meaning of the present invention, is a calcium
carbonate obtained from natural sources, such as limestone, marble or chalk, and subjected to
a wet and/or dry treatment such as grinding, screening and/or splitting, for example by means
of a cyclone or sorter.
Throughout the present document, the "particle size" of precipitated calcium carbonate or
other particulate materials is described by its particle size distribution. The value dx represents
the diameter for which x% by weight of the particles have diameters less than dx. This means
that the d20 value is the particle size at which 20wt.-% of all particles have diameters lessthan
the d value, and the d98 value is the particle size at which 98wt.-% of all particles have
diameters lessthan the d value. The d98 value is also designated as "top cut". The d50 value is
thus the weight median particle size, i.e. 50 wt.-% of all particleshave diameters less than or
morethan this particle size. For the purposes of the present invention, the particle size is
indicated as weight median particle size d50 unless indicated otherwise. For determining the
weight median particle size d50 value or the top cut particle size d98 value, a Sedigraph 5100
or 5120 device from the company Micromeritics, USA, may be used.
"Precipitated Calcium Carbonate" (PCC), in the meaning of the present invention, is a
synthetic material, generally obtained by precipitation following thereaction of carbon
dioxide and calcium hydroxide (hydrated lime) in an aqueous environment or by precipitation
of a calcium and a carbonate source in water. Additionally, precipitated calcium carbonate
may also be the product making it possible to introduce calcium and carbonate salts, calcium
chloride and sodium carbonate, for example, in an aqueous environment. PCC may be in the
vaterite, calcite or aragonite form. PCCs are described, for example, in documents EP 2 447
213 A1, EP 2 524 898 A1, EP 2 371 766 A1.
For the purposes of the present invention, the "dry solids content" of a liquid composition is a
measure of the amount of material remaining after all the solvents or water have been
evaporated.
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The "cationic polymer" used in the method of producing an aqueous suspension of
precipitated calcium carbonate, in the meaning of the present invention, is defined as a
polymer or a copolymer with at least monomer units with a net positive charge and making it
possible to produce a PCC slurry with a Zeta potential greater than 0 mV, for example a Zeta
potential of between 0 mV and 50 mV. According to one embodiment, the cationic polymer
used in the present invention consists of monomer units with a quaternary amine, for example
at least 50 mol.-% of monomer units with a quaternary amine.
With reference to the "cationic polymer" used in the method of the present invention, the
term "specific viscosity" is defined as the difference of the relative viscosity as measured
at a determined temperature minus 1.
A "BET Specific Surface Area" (SSA), in the meaning of the present invention, is defined as
the surface area of the precipitated calcium carbonate particles divided by the mass of PCC
particles. As used herein, the specific surface area is measured by N2 adsorption using the
BET isotherm (ISO 9277:1995) and is indicated in m2/g.
In the meaning of the present invention, "stable in an aqueous suspension with a pH of 12 and
a temperature of 95°C" means that the polymer maintains its physical properties and chemical
structure when added to an aqueous suspension with a pH of 12 and a temperature of 95°C.
For example, the polymer maintains its dispersing qualities and is not depolymerized or
degraded under said conditions.
For the purposes of the present invention, the term "viscosity" or "Brookfield viscosity"
refers to Brookfield viscosity. The Brookfield viscosity is measured by means of a Brookfield
(Type RVT) viscometer at 25°C ± 1°C at 100 rpm using an appropriate spindle and is
indicated in mPa.s.
For the purposes of the present application, "water-soluble" materials are defined as materials
which, when mixed with deionised water and filtered on a filter with a 0.2 m pore size at
20°C to recover the liquid filtrate, provide a mass of less than or equal to
0.1 g of recovered solid material after evaporation between 95°Cand100°C of 100 g of said
liquid filtrate."Water-soluble" materials are defined as materials leading to a mass of greater
than 0.1 g of recovered solid material after evaporation between 95°Cand100°C of 100 g of
said liquid filtrate.
A "suspension" or "slurry", in the meaning of the present invention, comprises insoluble
solids and water, and optionally other additives, and usually contains large amounts of solids
and, thus, is more viscous and may be of higher density than the liquid from which it is
formed.
sp 
7
Unless specified otherwise, the term "drying" refers to a method according to which at least a
portion of water is removed from a material to be dried such that a constant weight of the
obtained "dry" material at 120°C is reached. Moreover, a "dry" material may be further
defined by its total moisture content which, unless specified otherwise, is less than or equal to
1.0wt.-%, preferably less than or equal to 0.5wt.-%, more preferably less than or equal to
0.2wt.-% and most preferably between 0.03 wt.-% and 0.07wt.-%relative to the total weight
of the dry material.
The "total moisture content" of a material refers to the percentage of moisture (i.e.water)
which may be desorbed from a sample upon heating to 220°C.
Where the term "comprising"is used in the present description and claims, it does not exclude
other elements. For the purposes of the present invention, the term "consisting of" is
considered to be a preferred embodiment of the term "comprising". If hereinafter a group is
defined to comprise at least a certain number of embodiments, this is also to be understood to
disclose a group, which preferably consists only of these embodiments.
Where an indefinite or definite article is used when referring to a singular noun, for example
"a", "an" or "the", this includes a plural of that noun unless something else is specifically
stated.
Terms like "obtainable" or "definable" and "obtained" or "defined"are used interchangeably.
For example, this means that, unless the context clearly dictates otherwise, the term
"obtained" does not indicate,for example,that an embodiment must be obtained,for example,
by the sequence of steps following the term "obtained" even though such a limited
understanding is always included by the terms "obtained" or "defined" as a preferred
embodiment.
The present invention relates to the use of a cationic polymer in a method for producing
Precipitated Calcium Carbonate (PCC).
The method for producing an aqueous suspension of PCC comprises the steps consisting in(i)
preparing a milk of lime by mixing water, the calcium oxide containing material, the at least
one cationic polymer and optionally the at least one slaking additive and (ii) carbonating the
milk of lime obtained from step (i) to form an aqueous suspension of precipitated calcium
carbonate.
The at least one cationic polymer at least consistsof monomer units with a net positive
charge, for example monomer units with a quaternary amine, and makes it possibleto produce
a PCC slurry with a Zeta potential greater than 0 mV, for example a Zeta potential of between
0 mV and 50 mV. According to one embodiment, the cationic polymer used in the present
invention consists of monomer units with a quaternary amine, for example at least 50 mol.-%
of monomer units with a quaternary amine.
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The at least one slaking additive may be chosen from the group consisting of organic acids,
organic acid salts, sugar alcohols, monosaccharides, disaccharides, polysaccharides,
gluconates, phosphonates, lignosulfonates and mixtures thereof.
In method step(i), the calcium oxide containing material and water may be mixed in a weight
ratio from 1:2.5 to 1:6, for example from 1:2.5 to 1:4.
The use according to the invention of a cationic polymer in the methodfor producing PCC, in
particular S-PCC, is advantageous for wet-end applications. Indeed, the cationic polymer
brings cationic charges to the PCC slurries, which in combination with anionic cellulosic
fibresof the paper pulp improve the mineral filler retention.
The details and preferred embodiments of the useaccording to the inventionwill be set out in
more details hereinafter.
Calcium oxide containing material
In step i) of the method for producing an aqueous suspension of precipitated calcium
carbonate, a calcium oxide containing material is provided.
Said calcium oxide containing material may be obtained by calcining a calcium carbonate
containing material. Calcination is a thermal treatment method applied to calcium carbonate
containing material in order to bring about a thermal decomposition resulting in the formation
of calcium oxide and gaseous carbon dioxide. Calcium carbonate containing materials which
may be used in such a calcinationmethod are those chosen from the group comprising
precipitated calcium carbonates, natural calcium carbonate containing minerals such as
marble, limestone and chalk, and mixed alkaline earth carbonate minerals comprising
calcium carbonate such as dolomite or calcium carbonate rich fractions from other sources. It
is also possible to subject a calcium carbonate containing waste material to a calcination
method in order to obtain a calcium oxide containing material.
Calcium carbonate decomposes at about 1,000°C to calcium oxide (commonly known as
quicklime). The calcination step may be carried out under conditions and using equipment
well-known to the person skilled in the art. Generally, calcination may be carried out in
furnaces or reactors (sometimes referred to as kilns) of various designs including shaft
furnaces, rotary kilns, multiple hearth furnaces and fluidized bed reactors.
The end of the calcination reaction may be determined, for example, by monitoring the
density change, the residual carbonate content, for example by X-ray diffraction, or the
slaking reactivity by common methods.
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According to one embodiment of the present invention, the calcium oxide containing material
is obtained by calcining a calcium carbonate containing material, preferably chosen from the
group consisting of precipitated calcium carbonate, natural calcium carbonate minerals such
as marble, limestone and chalk, mixed alkaline earth carbonate minerals comprising calcium
carbonate such as dolomite and mixtures thereof.
For reasons of efficiency, it is preferred that the calcium oxide containing material has a
minimum calcium oxide content of at least 75 wt.-%, preferably at least 90wt.-% and most
preferably 95wt.-%relative to the total weight of the calcium oxide containing material.
According to one embodiment, the calcium oxide containing material consists of calcium
oxide.
The calcium oxide containing material may consist of only one type of calcium oxide
containing material. Alternatively, the calcium oxide containing material may consist of a
mixture of at least two types of calcium oxide containing materials.
The calcium oxide containing material may be used in the method of the invention in its
original form, i.e. as a raw material, for example, in form of smaller and bigger chunks.
Alternatively, the calcium oxide containing material may be ground before use. According to
one embodiment of the present invention, the calcium carbonate containing material is in
forms of particles with a weight median particle size d50 from 0.1 μm to 1,000 μm and
preferably from 1 μm to 500 μm.
Cationic polymer
The present invention relates to the use of at least one cationic polymer in a method for
preparing PCC, more precisely in the step of preparing a milk of lime which is to be
carbonated thereafter. The cationic polymer is defined in the context of the present invention
as having at least monomer units with a net positive charge, for example monomer units with
a quaternary amine. In addition, said polymer allows the production of a PCC slurry with a
Zeta potential greater than 0 mV, for example a Zeta potential of between 0 mV and 50 mV.
According to one embodiment, the cationic polymer used in the present invention consists of
at least monomer units with a quaternary amine, for example at least 50 mol.-% of monomer
units with a quaternary amine.
According to one aspect of the present invention, the cationic polymer may be a polymeric
amine, such as a polymer of quaternary amines or a polymer of amines that may be converted
to quaternary aminesorcombinations thereof.
The cationic polymer may also contain at least two different cationic monomers or contain a
cationic monomer and other non-ionic or anionic monomers.
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Suitable monomers of the cationic polymer comprise one or more monomers chosen from
water-soluble polyolefins containing quaternary ammonium groups which may be in the
polymer chain, for example, epichlorohydrin/dimethylamine copolymers (EPI/DMA), alkyl
or dialkyldiallylammonium halides, such as dimethyldiallyl ammonium chloride (DMDAC),
diethyldiallyl ammonium chloride (DEDAC), dimethyldiallyl ammonium bromide
(DMDAB) and diethyldiallyl ammonium bromide (DEDAB),
methylacryloyl-oxyethyltrimethyl ammonium chloride (METAC),
acryloyl-oxyethyltrimethyl ammonium chloride (AETAC),
methacryloyl-oxyethyltrimethyl ammonium methosulfate (METAMS),
acryloyl-oxyethyltrimethyl ammonium methosulfate (AETAMS),
methacrylamido-propyltrimethyl ammonium chloride (MAPTAC) or
acrylamido-propyltrimethyl ammonium chloride (APTAC).
Other additional exemplary monomers comprisedimethylaminoethylacrylate,
dimethylaminoethylmethacrylate and dimethylaminopropylmethacrylamide. Exemplary
polymers also comprise products of polymerization of any of the above listed cationic
monomers with non-ionic monomers such as acrylamide, methacrylamide or
N,N-dimethylacrylamide.
Exemplary cationic polymers comprisepoly(diallyldimethylammonium chloride)
(pDADMAC), poly(2-(trimethylamino)ethyl methacrylate) (pMADQUAT), copolymers of
quaternary dimethylaminoethyl acrylate, copolymers of quaternary dimethylaminoethyl
methacrylate and copolymers of epichlorohydrin/dimethylamine (EPI/DMA).
Other cationic polymers comprise condensates of formaldehyde with melamine, urea or
cyanoguanidine. The cationic polymers useful in the present invention also comprise
copolymers of the aforementioned cationic monomers with non-ionic monomers, such as
acrylamide, methacrylamide, vinyl acetate, vinyl alcohol, N-methylolacrylamide or diacetone
acrylamide, and/or anionic monomers, such as acrylic acid, methacrylic acid, AMPS or
maleic acid.
Such copolymers are herein so-called "cationic" since part or their monomer units present a
net positive charge, for example at least 40 mol.-% or at least 50 mol.-%. According to one
embodiment, the overall net charge of these polymers is positive.
According to one aspect of the present invention, the at least one cationic polymer is a
poly(diallyldimethylammonium chloride) (pDADMAC) or a poly(2-(trimethylamino)
ethyl methacrylate) (pMADQUAT).
According to another aspect of the present invention, the at least one cationic polymer
contains monomers with at least one quaternary ammonium group chosenfrom the group
consisting of methylacryloyl-oxyethyltrimethyl ammonium chloride (METAC),
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acryloyl-oxyethyltrimethyl ammonium chloride (AETAC), methacrylamido-propyltrimethyl
ammonium chloride (MAPTAC), acrylamido-propyltrimethyl ammonium chloride (APTAC)
and 2-methacryloxyethyltrimethyl ammonium chloride (MADQUAT).
According to another aspect of the invention, the at least one cationic polymer contains
monomers of acrylic acid, methacrylic acid, maleic acid, alkyl acrylate, alkyl methacrylate
and acrylamide or methacrylamidewith alkyl substituted or not.
According to another aspect of the present invention, the at least one cationic polymer
consists exclusively of monomers with at least one quaternary ammonium group chosenfrom
the group consisting of methylacryloyl-oxyethyltrimethyl ammonium chloride (METAC),
acryloyl-oxyethyltrimethyl ammonium chloride (AETAC), methacrylamido-propyltrimethyl
ammonium chloride (MAPTAC), acrylamido-propyltrimethyl ammonium chloride (APTAC)
and 2-methacryloxyethyltrimethyl ammonium chloride (MADQUAT).
According to one aspect of the present invention, the at least one cationic polymer may have
a weight average molecular weight (Mw) ranging from about 1,000 g/mol to about 5,000,000
g/mol, as determined by Size Exclusion Chromatography (SEC). According to another aspect
of the present invention, the at least one cationic polymer may have a molecular weight of at
least about 1,000 g/mol, such as a molecular weight of at least about 2,000 g/mol, of at least
about 5,000 g/mol, of at least about 10,000 g/mol, of at least about 25,000 g/mol, of at least
about 50,000 g/mol, of at least about 100,000 g/mol, of at least about 250,000 g/mol, of at
least about 500,000 g/mol or of at least about 1,000,000 g/mol. Physical mixtures of cationic
polymers containing different cationic moieties or mixtures of cationic polymers having
different average molecular weights and distributions are also considered.
The specific viscosity of the at least one cationic polymer may also reflect its weight average
molecular weight. According to one aspect of the present invention, the specific viscosity of
the at least one cationic polymer varies between 1 and 20, for example between 1.5 and 10.
According to one embodiment of the present invention, the cationic polymer gives a Zeta
potential higher than 0 mV to the aqueous suspensions of PCC produced.
According to another embodiment, the aqueous suspensions of PCC obtained with the use of
the cationic polymer are characterized in that they have a Zeta potential higher than
0 mV, for example between 0 mV and +50 mV, for example between 0 mV and +40 mV.
According to one embodiment, the at least one cationic polymer gives a Mütek charge higher
than 0μeq/g to the aqueous suspensions of PCC produced.
According to another embodiment, the aqueous suspensions of PCC obtained with the use of
the cationic polymer are characterized in that they present a Mütek charge higher than
0μeq/g, for example between 0 μeq/g and +8 μeq/g.
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According to the present invention, the at least one polymer defined above is added during
step i) of the method for producing PCC, i.e. the polymer is added before or during the
slaking step. As known to the skilled person, the milk of lime obtained by slaking of a
calcium oxide containing material with water has usually a pH between 11 and 12.5 at a
temperature of 25°C, depending on the concentration of the calcium oxide containing
material in the milk of lime. Since the slaking reaction is exothermic, the temperature of the
milk of lime typically reaches a temperature between 80°C and 99°C. According to one
embodiment of the present invention, the at least one polymer of the use according to the
invention is chosen such that it is stable in an aqueous suspension with a pH of 12 and a
temperature of 95°C. In the meaning of the present invention, "stable in an aqueous
suspension with a pH of 12 and a temperature of 95°C" means that the polymer maintains its
physical properties and chemical structure when added to an aqueous suspension with a pH of
12 and a temperature of 95°C. For example, the polymer maintains its dispersing qualities
and is not depolymerized or degraded under said conditions. The absence of any
depolymerization or degradation of the polymer may be determined by measuring the amount
of free monomers in the milk of lime and/or the obtained aqueous suspension of PCC.
According to one embodiment of the present invention, the amount of free monomers in the
milk of lime is lower than 0.1 wt.-%, preferably lower than 0.05wt.-%, more preferably lower
than 0.01 wt.-% and most preferably lower than 0.005wt.-%relative to the total amount of the
at least one polymer provided in stepi).
According to one embodiment of the present invention, the at least one cationic polymer used
in step i) of the method consists of one type of polymer only. Alternatively, the at least one
polymer of step i) may consist of a mixture of at least two types of polymers.
According to one embodiment of the present invention, the at least one cationic polymer is
added in an amount from 0.01 wt.-% to 0.5 wt.-%, preferably from 0.02 wt.-% to
0.4wt.-% and more preferably from 0.05 wt.-% to 0.35 wt.-%relative to the total weight of
the calcium oxide containing material.
The at least one cationic polymer may be provided in the form of a solution or as a dry
material. According to one embodiment, the at least one cationic polymer of step i) is
provided in the form of an aqueous solution with a polymer concentration from 1 wt.-% to 70
wt.-% and preferably from 2wt.-% to 60wt.-%relative to the total weight of the aqueous
solution.
The cationic polymers of the present invention are obtained through known radical
polymerization methods in solutions, in direct or invert emulsions, in suspensions or through
precipitation in appropriate solvents, in the presence of known catalyst systems and transfer
agents or through mediated radical polymerization methods, preferentially through
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nitroxide-mediated polymerization (NMP) or cobaloxyme-mediated polymerization, atom
transfer radical polymerization (ATRP) or sulfur derivative-mediated radical polymerization,
said sulfur derivatives being chosen from among carbamates, dithioesters or trithiocarbonates
(RAFT) or xanthates.
Slaking additive
In step i) of the method for producing PCC, at least one slaking additive may be used in
addition to the cationic polymer.
In this case, according to one embodiment, the preparation of the milk of lime according to
step i) additionally consistsinmixing at least one slaking additive.
The at least one slaking additive may be chosen from the group consisting of organic acids,
organic acid salts, sugar alcohols, monosaccharides, disaccharides, polysaccharides,
gluconates, phosphonates, lignosulfonates and mixtures thereof.
According to one embodiment of the present invention,the at least one slaking additive is
chosen from the group consisting of sodium citrate, potassium citrate, calcium citrate,
magnesium citrate, monosaccharides, disaccharides, polysaccharides, sucrose, sugar alcohols,
meritol, citric acid, sorbitol, sodium salt of diethylene triaminepentaacetic acid, gluconates,
phosphonates, sodium tartrate, sodium lignosulfonate, calcium lignosulfonate and mixtures
thereof. According to a preferred embodiment, the at least one slaking additive is sodium
citrate and/or saccharose.
According to one embodiment of the present invention, the at least one slaking additive of
step i) consists of one type of slaking additive only. Alternatively, the at least one slaking
additive of step i) may consist of a mixture of at least two types of slaking additives.
The at least one slaking additive may be added in an amount from 0.01 wt.-% to 2wt.-
%relative to the total amount of calcium oxide containing material, preferably in an amount
from 0.05 wt.-% to 1 wt.-%, more preferably from 0.06 wt.-% to 0.8wt.-% and most
preferably from 0.07 wt.-% to 0.5 wt.-%.
The addition of a slaking additive may be useful to control the size of the PCC particles and
their crystalline morphology without affecting the viscosity of the aqueous suspension.
Method step i)
In step i) of the method for producing PCC, a milk of lime is prepared by mixing water, the
calcium oxide containing material, the at least one cationic polymer, and optionally the at
least one slaking additive.
14
According to the invention, in step i),the calcium oxide containing material and water are
mixed in a weight ratio from 1:1 to 1:6. In a preferred manner, the calcium oxide containing
material and water are mixed in step i) in a weight ratio from 1:2.5 to 1:4.
According to one embodiment, the calcium oxide containing material and water are mixed in
step i) in a weight ratio from 1:2.5 to 1:6.
The reaction of the calcium oxide containing material with water results in the formation of a
milky calcium hydroxide suspension, better known as milk of lime. Said reaction is highly
exothermic and is also designated as "lime slaking" in the art.
According to one embodiment of the present invention, the temperature of water, which is
used in mixing step i), i.e. the temperature of water which is used to slake the calcium oxide
containing material, is adjusted to be in the range from 0°Cto100°C, for example from 1°C to
70°C or from 2°C to 50°C or from 30°C to 50°C or from 35°C to 45°C. It will be apparent to
the person skilled in the art that the initial temperature of water is not necessarily the same
one as the temperature of the mixture prepared in step i) due to the highly exothermic
character of the slaking reaction and/or due to the mixing of substances with different
temperatures.
According to one embodiment of the present invention, method step i) comprises the steps
consisting in:
a1) mixing the at least one cationic polymer with water, optionally the at least one slaking
additive and
a2) adding the calcium oxide containing material to the mixture of step a1).
According to one embodiment, step a1) is carried out at a temperature between0°Cand 99°C,
for example between1°Cand70°C or between2°Cand50°C or between30°Cand50°C or
between 35°Cand45°C.
According to another embodiment of the present invention, method step i) comprises the
steps consisting in:
b1) mixing the calcium oxide containing material, the at least one cationic polymer, and
optionally the at least one slaking additive and
b2) adding water to the mixture of step b1).
According to still another embodiment of the present invention, in method step i) the calcium
oxide containing material, the at least one polymer, optionally the at least one slaking
additive, and water are mixed simultaneously.
15
According to still another embodiment of the present invention, the at least one slaking
additive is added before or after step i) of the method.
The at least one polymer may be added in step i) in one portion or in several portions.
According to one embodiment, in step i), the at least one cationic polymer is mixed with
water, the calcium oxide containing material and the at least one slaking additive by adding
the at least one cationic polymer in one portion or in two, three, four, five or more portions.
Method step i) may be carried out at room temperature, i.e. at a temperature of 20°C ± 2°C,
or at an initial temperature between 30°Cand 50°C or between 35°Cand45°C. Since the
reaction is exothermic, the temperature typically reaches a temperature between 85°Cand
99°C during step i), preferably a temperature between 90°C and 95°C. According to one
preferred embodiment, method step i) is carried outby mixing or stirring, for
exampleundermechanical stirring. Suitable method equipment for mixing or stirring is known
to the person skilled in the art.
The progress of the slaking reaction may be observed by measuring the temperature and/or
conductivity of the reaction mixture. It may also be monitored by turbidity control.
Alternatively or additionally, the progress of the slaking reaction may be inspected visually.
The inventors surprisingly found that the addition of a cationic polymer as defined above and
optionally a slaking additive as defined above, before or during the slaking step of a method
for producing PCC may allow the preparation of a milk of lime not only with a low dry solids
content but also with a high dry solids content. It is indeed interesting to note that, according
to one aspect of the invention, by carbonating said highly concentrated milk of lime, an
aqueous suspension of PCC may be obtained which has also a high dry solids content. As a
result, the method of the present invention does not require any additional concentration step
in order to obtain a PCC suspensionwith a high dry solids content.
According to the present invention,the calcium oxide containing material and water are
mixed in a weight ratio from 1:1 to 1:6, for example from 1:2.5 to 1:6 or from 1:2.5 to 1:4.
According to one preferred embodiment, in step i), the calcium oxide containing material and
water are mixed in a weight ratio from 1:3 to 1:5.
According to one embodiment of the present invention, the milk of lime of step i) has a dry
solids content of at least 15 wt.-%, preferably from 15 wt.-% to 45 wt.-%, more preferably
from 20 wt.-% to 40 wt.-% and most preferably from 25 wt.-% to 37 wt.-% relative to the
total weight of the milk of lime.
According to one embodiment of the present invention, the milk of lime of step i) has a
Brookfield viscosity from 1mPa.sto 1,000 mPa.s at 25°C, more preferably from 5
mPa.sto800mPa.s at 25°C and most preferably from 10 mPa.sto500 mPa.s at 25°C.
According to one embodiment, the Brookfield viscosity is measured at 100 rpm.
16
In the context of the present invention, additional water may be introduced during the slaking
reaction in order to control and/or maintain and/or achieve the desired dry solids content or
Brookfield viscosity of the milk of lime.
Method step i) may be carried outin the form of a batch, semi-continuous or continuous
method.
Method step ii)
In step ii) of the method for producing PCC, the milk of lime obtained from stepi) is
carbonated to form an aqueous suspension of precipitated calcium carbonate.
The carbonation is carried out by means and under conditions well-known by the person
skilled in the art. The introduction of carbon dioxide into the milk of lime quickly increases
the carbonate ion (CO3
2-) concentration and calcium carbonate is formed.Particularly, the
carbonation reaction may be readily controlled considering the reactions involved in the
carbonation method. Carbon dioxide dissolves according to its partial pressure forming
carbonate ions via the formation of carbonic acid (H2CO3) and hydrogen carbonate ions
(HCO3
-) being unstable in alkaline solution. Upon continued dissolution of carbon dioxide,
hydroxide ions are consumed and the concentration of carbonate ions increases until the
concentration of dissolved calcium carbonate exceeds the solubility product and solid
calcium carbonate precipitates.
According to one embodiment of the present invention, in step ii), the carbonation is carried
out by incorporating pure gaseous carbon dioxide or technical gases containing at least 10
vol.-% of carbon dioxide in the milk of lime.
The progress of the carbonation reaction may be readily observed by measuring the
conductivity, turbidity and/or pH. In this respect, the pH of the milk of lime before addition
of carbon dioxide will be higher than 10, usually between 11 and 12.5 and will constantly
decrease until a pH of about 7 is reached. At this point the reaction may be stopped.
Conductivity slowly decreases during the carbonation reaction and rapidly decreases to low
levels, when the precipitation is completed. The progress of the carbonation may be
monitored by measuring the pH and/or the conductivity of the reaction mixture.
According to one embodiment of the method for producing PCC, the temperature of the milk
of lime obtained from step i), which is used in step ii), is adjusted to be in the range from
20°C to 60°C and preferably from 30°C to 50°C. It will be apparent to the person skilled in
the art that the initial temperature of the milk of lime is not necessarily the same one as the
temperature of the mixture prepared in step ii) due to the exothermic carbonation reaction
character and/or due to the mixing of substances with different temperatures.
17
According to one embodiment of the method for producing PCC, step ii) is carried out at a
temperature between 5°Cand95°C, preferably from 30°C to 70°C and more preferably from
40°C to 60°C.
Method step ii) may be carried outin the form of a batch, semi-continuous or continuous
method. According to one embodiment, the method for producing PCC involving the method
steps i) and ii) is carried out in form of a batch, semi-continuous or continuous method.
According to one embodiment of the present invention, the method for producing PCC does
not comprise any step of concentratingof the aqueous suspension of precipitated calcium
carbonate obtained fromsteps i) to ii) of the method.
As already mentioned above, the inventors surprisingly found that the addition of a cationic
polymer as defined above optionally in combination with the addition of a slaking additive
before or during the slaking step of a method for producing PCC may allow the preparation
of a PCC suspension with a high dry solids content. It is also believed that the omission of
aconcentration step improves the quality of the produced PCC particles, since surface
damages of the particles, which may occur during the concentration step, are avoided. It was
also found that said PCC suspension may be further concentrated to a solids content of 52
wt.-% at acceptable viscosities, for example Brookfield viscosities of less than or equal to
1,000 mPa.s at 25°C and 100 rpm. Generally, this maynot be done with PCC suspensions that
are obtained by conventional PCC production methodscomprising a concentrating step
because the viscosity of said suspension would reach a non-pumpable range.
According to one embodiment of the method for producing PCC, the obtained precipitated
calcium carbonate has a weight average particle size d50 from 0.1 μm to 100μm, preferably
from 0.25 μm to 50 μm, more preferably from 0.3 μm to 5.0 μm and most preferably from
0.4 μm to 3.0 μm.
The precipitated calcium carbonate may have aragonite, calcite or vaterite crystalline
structure or mixtures thereof. Another advantage of the present invention is that the
crystalline structure and morphology of the precipitated calcium carbonate may be controlled,
for example by addition of seed crystals or other structure modifying chemical products.
According to one preferred embodiment, the precipitated calcium carbonate obtained by the
methodof the invention has a clustered scalenohedral crystalline structure.
The BET specific surface area of the precipitated calcium carbonate obtained by the method
according to the present invention may be from 1 m2/g to 100 m2/g, preferably from 2 m2/g to
70 m2/g, more preferably from 3 m2/g to 50 m2/g, especially from 4 m2/g to 30 m2/g,
measured using nitrogen and the BET method according to ISO 9277 standard.The BET
specific surface area of the precipitated calcium carbonate obtained by the method of the
18
present invention may be controlled by the use of additives, for example surface active
agents,which involve shearing during the precipitation step or thereafter at high mechanical
shearing rates not only leading to a low particle size, but also to a high BET specific surface
area.
According to one embodiment of the present invention, the obtained suspension of
precipitated calcium carbonate has a dry solids content of at least 10wt.-%, preferably from
20 wt.-% to 50 wt.-%, more preferably from 25 wt.-% to 45 wt.-% and most preferably from
30 wt.-% to 40 wt.-%relative to the total weight of the suspension.
According to one embodiment of the present invention,the suspension of PCC of step ii) has a
Brookfield viscosity of less than or equal to 1,000 mPa.s at 25°C, more preferably less than
or equal to 800mPa.s at 25°C and most preferably less than or equal to 600 mPa.s at 25°C.
The Brookfield viscosity may be measured at 100 rpm.
Another aspect of the present invention relates to the use of a combination of at least one
water-soluble polymer and one slaking additive in a method for producing an aqueous
suspension of precipitated calcium carbonate, in which:
- the at least one cationic polymer at least consists of monomer units with a net
positive charge, for example monomer units with a quaternary amine and making it
possibleto produce a PCC suspensionwitha Zeta potential greater than 0mV and
- the slaking additive is chosen from the group consisting of organic acids, organic acid
salts, sugar alcohols, monosaccharides, disaccharides, polysaccharides, gluconates,
phosphonates, lignosulfonates and mixtures thereof.
Additional steps of the method
The method of the present invention may comprise additional steps.
The milk of lime may be screened in order to remove oversize particles. A suitable
sievemaycomprise, for example, a sievewith a sieve sizefrom 700 μm to 100 μm, for example
about 100 μm or about 300 μm. According to one embodiment of the present invention, the
milk of lime is screened after step i) and before step ii), preferably with a sieve with a sieve
sizefrom 100 μm to 300 μm.
The method for producing precipitated calcium carbonate may further comprise a step iii) of
separating the precipitated calcium carbonate from the aqueous suspension obtained from
step ii).
For the purposes of the present invention, the expression "separating" means that the PCC is
removed or isolated from the aqueous suspension obtained from step ii) of the method. Any
conventional means of separation known to the person skilled in the artmay be used, for
19
example mechanically and/or thermally. Examples ofmechanical separation methods are
filtration, for example by means of a drum filter or filter press, nanofiltration or
centrifugation. An example ofa thermal separation method is aconcentrationmethod by the
application of heat, for example in an evaporator.
The obtained PCC may be transformed, for example, deagglomerated or subjected to a dry
grinding step. It may also be wet ground in the form of a suspension. If the PCC is subjected
to dewatering, dispersion and/or grinding steps, these steps may be accomplished by
procedures known in the art. Wet grinding may be carried out in the absence or in the
presence of a grinding aid agent. Dispersants mayalso be included to prepare dispersions if
desired.
The method for producing precipitated calcium carbonate may further comprise a step iv) of
drying the separated precipitated calcium carbonate obtained from stepiii).
In general, the drying step iv) may be carried out using any suitable drying equipment and
may, for example, comprisea thermal drying and/or a drying at reduced pressure using an
equipment such as an evaporator, a flash drier, an oven, a spray drier and/or drying in a
vacuum chamber.
Drying stepiv) leads to a dry precipitated calcium carbonate with a low total moisture content
which is less than or equal to 1.0wt.-%relative to the total weight of the dry precipitated
calcium carbonate.
The precipitated calcium carbonate obtained by the methodof the invention may be
post-treated, for example during and/or after a drying step with an additional component.
According to one embodiment, the precipitated calcium carbonate is treated with a fatty acid,
for example stearic acid, a silane or phosphoric esters of fatty acids.
Finally, the invention also relates to the use of at least one cationic polymer in a method for
producing an aqueous suspension of precipitated calcium carbonate obtained according to the
invention.
20
EXAMPLES
1. Measurement methods
In the following, measurement methods used in the examples are described.
Brookfield viscosity
The Brookfield viscosity was measured after one hour of production and after one minute of
stirring at 25°C ± 1°C at 100 rpm using anRVT type Brookfield viscometer equipped with an
appropriate disc spindle, for example a spindle 2 to 5.
pHmeasurement
The pH of a suspension or solution was measured at 25°C using a Mettler Toledo Seven Easy
pH meter and a Mettler Toledo InLab® Expert Pro pH electrode. A three-pointcalibration
(according to the segmentation method) of the instrument was first made using commercially
available buffer solutions having pH values of 4, 7 and 10 at 20°C (from Sigma-Aldrich
Corp., USA). The reported pH values are the endpoint values detected by the instrument (the
endpoint was when the measured signal differs by less than 0.1 mV from the average over the
last 6 seconds).
Particle size distribution
The particle size distribution of the prepared PCC particles was measured using a Sedigraph
5100 apparatus from the company Micromeritics, USA. The method and the instrument are
known to the person skilled in the art and are commonly used to determine grain size of
mineral fillers and pigments. The measurement was carried out in an aqueous solution
comprising 0.1wt.-% of Na4P2O7. The samples were dispersed using a high speed stirrer and
ultrasound. For the measurement of dispersed samples, no otherdispersing agent wasadded.
Dry solids content of an aqueous suspension
The suspension dry solids content (also known as "dry weight") was determined using a
Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following
settings: drying temperature of 160°C, automatic switch off if the mass does not change by
more than 1 mg over a period of 30 sec, standard drying of 5 g to 20 g of suspension.
21
Specific Surface Area (SSA)
The specific surface area was measured via the BET method according to ISO 9277 standard
using nitrogen, followed byconditioning of the sample by heating at 250°C for a period of 30
minutes. Prior to such measurements, the sample is filtered within a Büchner funnel, rinsed
with deionised water and dried overnight at a temperature between 90°C and100°C in an
oven. Subsequently the dry filtration cake is ground thoroughly in a mortar and the resulting
powder is placed in a moisture analysis balance at 130°C until a constant weight is reached.
Specific carbonation time
The monitoring of the conductivity, which slowly decreases during the carbonation reaction
and rapidly decreases to a minimal level, thereby indicating the end of the reaction, was used
to assess the time needed to perform the complete precipitation. The specific carbonation
time (min/kg of Ca(OH)2) was determined by the following formula:
Specificcarbonation time =
105 . Tf
M . SCMoL
in which:
- Tf (min) is the time needed to complete the carbonation of the milk of lime, as
determined by monitoring the conductivity,
- M (g) is the weight of the milk of lime introduced into the carbonation reactor and
- SCMoL (%) is the weight dry solids contentof the milk of lime.
Specific viscosity of the polymer
The term "specific viscosity" in the meaning of the present invention is defined as the
difference of the relative viscosity as measured at a given temperature minus 1.
The relative viscosity as used herein is the quotient of the solution viscosity and the solvent
viscosity .
 1 sp rel  

0 
0    rel
22
where the solvent viscosity is defined as the viscosity of the pure solvent at a given
temperature (for example20°C or 25°C) and the solution viscosity is defined as the
viscosity of the polymer dissolved in the pure solvent at a given temperature and at a given
polymer concentration (for example 50 g/L).
However, to determine the relative viscosity it is sufficient to measure the elution time t (of
the polymer solution) and t0 (of the solvent) at a given temperature (for example20°C or
25°C) if the boundary conditions are constant. Therefore, the relative viscosity may be
defined as:
and, thus, the specific viscosity may be defined as:
More precisely, the specific viscosity of the polymer was obtained from an aqueous polymer
solution with a polymer concentration of 50g/L in a NaCl solution (120 g/L), the pH of the
polymer solution being possibly adjusted with ammonia to be within the range from 6 to 7.
The elution times t and t0 were measured at 25°C± 0.2°C, using a viscosimetric tube USA
KIMAX (reference: size 100 n°46460 B2).
t0: In order to determine t0, an aqueous NaCl solution was prepared by using reverse osmosis
water, the NaCl solution with a concentration of 120 g/L.
t: In order to determine t, 2.5 g of the dry polymer was combined with 50 g of reverse
osmosiswater and 6 g of NaCl in order to obtain a homogenous solution.
The elution times t and t0 were measured at 25°C ± 0.2°C and was calculated according to
the above-mentioned formulae.
Charge measurement – Mütek
The charge measurement was carried out using a Mütek PCD 03 device equipped with a
Mütek PCD titrator.
0.5 g to 1 g of dry PCC is weighed in the plastic measuring cell and is diluted with 20 mL of
deionised water. Put the displacement piston on. While the piston oscillates in the cell, wait
until the streaming current between the two electrodes stabilize.
0 

0 t
t
rel 
1
0
 
t
t
sp 
sp 
23
The sign of the measured value shown on the display indicates whether the charge of the
sample is positive (cationic) or negative (anionic). An oppositely charged polyelectrolyte of
known charge density is added to the sample as a titrant (either sodium polyoxyethylene
sulfate 0.001 N or pDADMAC 0.001 N). The titrant charges neutralize existing charges of
the sample. Titration is discontinued as soon as the point of zero charge (0 mV) is reached.
Titrant consumption in mL forms the basis for further calculations. The specific charge
amountq [eq/g of slurry] is calculated according to the following formula:
q = (V * c) / m
V:consumed titrant volume [L]
c: titrant concentration [eq/L] or [μeq/L]
m: mass of the weighed slurry [g]
q: specific charge amount [eq/g of slurry] or [μeq/g of slurry]
Zeta potential
For measuring the Zeta potential, a few drops of the PCC suspension are dispersed in a
sufficient amount of serum obtained by mechanical filtration of said suspension in order to
obtain a colloidal suspension which is slightly cloudy.
This suspension is introduced into the measuring cell of the Zetasizer Nano-ZS apparatus
from Malvern, which directly displays the value of the Zeta potential of the PCC suspension
in mV.
2. Example
A milk of lime was prepared by mixing under mechanical stirring water with cationic
polymers P1 to P5 (if available) and/ora slaking additive (for example dry sodium citrate,
NaCi) (if available), at an initial temperature between 50°C and 51°C (the amounts of slaking
additives and polymers are indicated in Table 2 below). Subsequently, calcium oxide
(quicklime raw material from Golling, Austria)was added. The obtained mixture was stirred
for 25min and then screened through a 200 μm sieve.
The obtained milk of lime was transferred into a stainless steel reactor, in which the milk of
lime was cooled down to 50°C. Then the milk of lime was carbonated by introducing an
air/CO2 mixture (26 vol.-% CO2), flow rate of 23 min/L. During the carbonation step, the
reaction mixture was stirred with a speed of 1,400 rpm. The kinetics of the reaction were
monitored by online pH and conductivity measurements.
24
Polymer additives exemplified:
P1 = MADQUAT (according to the invention)
Specific viscosity: 2.66
P2 = 70% Madquat/30% Maptac(according to the invention)
Specific viscosity: 2.19
P3 = 70% Madquat/30% Maptac (according to the invention)
Specific viscosity: 1.68
P4 = 50% Madquat/50% acrylic acid (according to the invention)
Specific viscosity: 2.87
P5 = pDADMAC (according to the invention)
Specific viscosity: 9.98
P6 = sodium polyacrylate(outside the invention) - Mw = 4,270 g/mol, PDI= 2.3(Mw and PDI
determined according to unpublished patent application EP 14166751.9).
Polymer
additive
Cationic
polymer
amount
wt.-%CaO
Slaking
additive
Slaking additive
amount
wt.-%CaO
Solids Content
Milk of Lime
wt.-%]
1 OI no -- NaCi 0.1 25.2
2 OI no -- NaCi 0.1 15.7
3 INV P1 0.15 NaCi 0.1 25.2
4 INV P2 0.15 NaCi 0.1 25.0
5 INV P3 0.15 NaCi 0.1 24.9
6 INV P4 0.15 NaCi 0.1 25.5
7 INV P5 0.15 NaCi 0.1 25.5
8 OI P6 0.15 NaCi 0.1 29.9
9 INV P1 1 NaCi 0.1 23.3
Table 1 Characteristics of the prepared milks of lime (INV: according to the INVention - OI:
Outside the Invention)
25
The characteristics of the prepared milks of lime and aqueous PCC suspensions are described
in Table 2 below.
Tests
Solids
Content
S-PCC
wt.-%]
Viscosity
of the
milk of
lime
(mPa.s)at
100 rpm
Carbonation
time (min/kg
Ca(OH)2)
Viscosity
of the
S-PCC
(mPa.s)
at 100
rpm
Zeta
potential
(mV)
Mutek
(μeq/g)
D50
(μm)
SSA
(m2/g)
1 OI
Too high viscosity –
not manageable
- - - - -
2 OI 20.2 20 52 20 +4.9 -0.2 1.5 4.7
3 INV 31.2 204 53 202 +0.1 +2.3 1.9 4.7
4 INV 32.1 83 46 225 +8.8 -3.2 1.4 5.2
5 INV 32.3 74 46 175 +0.2 -0.1 1.4 6.3
6INV 32.6 64 45 994 +0.2 -0.6 1.5 5.0
7 INV 33.6 164 47 1380 +30.5 +2.2 1.4 4.9
8OI 37.2 294 46 573 -10.5 -0.9 1.3 5.0
9 INV 29.8 441 46 191 +5.9 +5.9 1.5 5.9
Table 2 Characteristics of the PCC suspensions (INV: according to the INVention - OI:
Outside the Invention)
The results compiled in Table 2 show that the use of a slaking additive alone leads to a milk
of lime witha high Brookfield viscosity (sample 1) and that it is not possible to increase the
solids content of the milk of lime (wt.-%) while at the same time preventing increases of the
slurry viscosity (comparison of sample 1 and sample 2).
In contrast, samples 3 to 7 and 9 of the inventionconfirm that the viscosity of the obtained
milk of lime and PCC suspension is totally in linewith the intended use of the PCC so
obtained that is to say suspensions of PCC with a Brookfield viscosity of less than or equal to
26
1,500 mPa.s at 25°C, more preferably less than or equal to 1,000mPa.s at 25°C for samples 3
to 6 and 9 and most preferably less than or equal to 600 mPa.s at 25°C for samples 3 to 5 and
9.
Additionally, the kinetics of carbonation and the crystallographic structure of the prepared
PCC (results not shown) are similar to the ones obtained with a method involving the use of
an anionic polymer (P6 polymer outside the invention, for comparison only).
27
WE CLAIM
1. A method for producing an aqueous suspension of precipitated calcium carbonate,
comprising the use of at least one cationic polymer and the steps consistingin:
i) preparing a milk of lime by mixing water, a calcium oxide containing material and said
at least one cationic polymer, the calcium oxide containing material and water are
mixed in a weight ratiofrom 1:1 to 1:6 and
ii) carbonating the milk of lime obtained from step i) to form an aqueous suspension of
precipitated calcium carbonate.
2. The method according to claim 1, for which the at least one cationic polymer consists of
monomer units with a net positive charge, for example monomer units with a
quaternary amine.
3. The method according to one of the preceding claims, for which in step i), the calcium
oxide containing material and water are mixed in a weight ratio from 1:2.5 to 1:6 or
from 1:2.5 to 1:4.
4. The method according to one of the preceding claims, for which the preparation of the
milk of lime according to step i) additionally consists inmixing at least oneslaking
additive.
5. The method according to one of the preceding claims, for which the at least one slaking
additive is chosen from the group consisting of sodium citrate, potassium citrate,
calcium citrate, magnesium citrate, monosaccharides, disaccharides, polysaccharides,
sucrose, sugar alcohols, meritol, citric acid, sorbitol, sodium salt of diethylene
triaminepentaacetic acid, gluconates, phosphonates, sodium tartrate, sodium
lignosulfonate, calcium lignosulfonate and mixtures thereof.
6. The method according to one of the preceding claims, for which the milk of lime of step
i) has a Brookfield viscosity from 1mPa.sto 1,000 mPa.s at 25°C, at 100 rpm.
28
7. The method according to one of the preceding claims, for which the suspension of PCC
of step ii) has a Brookfield viscosity of less than or equal to 1,000 mPa.s at 25°C, at
100 rpm.
8. The method according to one of the preceding claims, for which the obtained suspension
of precipitated calcium carbonate has a dry solids content of at least 10wt.-% relative to
the total weight of the suspension.
9. The method according to one of the preceding claims, for which the at least one slaking
additive is added in an amount from 0.01 wt.-% to 2wt.-%relative to the total amount of
calcium oxide containing material.
10. The method according to one of the preceding claims, for which the temperature of
water, which is used in mixing step i), is adjusted to be in the range from 0°Cto 100°C
(limits excluded).
11. The method according to one of the preceding claims, for which the temperature of the
milk of lime obtained from step i), which is used in step ii), is adjusted to be in the
range from 20°C to 60°C.
12. A use of at least one cationic polymer in amethod for producing an aqueous suspension
of precipitated calcium carbonate which is defined according to one of the preceding
claims.