1. The use of at least one depolymerized carboxylated cellulose solution for preparing an aqueous Precipitated Calcium Carbonate (PCC) slurry by slaking of a material containing calcium oxide in water, followed by carbonation of the milk of lime thus obtained, said depolymerized carboxylated cellulose solution exhibiting a solids content of between 25 wt.% and 40 wt.%, based on the total weight of the solution, and a molecular weight Mw of between 10 000 g/mol and 40 000 g/mol.

2. The use as claimed in claim 1, according to which said depolymerized carboxylated cellulose exhibits a polydispersity index PI of between 2 and 10.

3. The use as claimed in either of the preceding claims, according to which said depolymerized carboxylated cellulose is partially or completely neutralized by means of one or more neutralizing agent(s) chosen from the group consisting of sodium hydroxides, calcium hydroxides, magnesium hydroxides, potassium hydroxides and amines.

4. The use as claimed in any one of the preceding claims, in which said depolymerized carboxylated cellulose solution is present in the slaking water of the material containing calcium oxide.

5. The use as claimed in any one of the preceding claims, according to which said material containing calcium oxide and the water are mixed in a weight ratio ranging from 1:1 to 1:12.

6. The use as claimed in any one of the preceding claims, according to which said depolymerized carboxylated cellulose solution is used in combination with at least one slaking additive. 34

7. The use as claimed in the preceding claim, according to 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, the sodium salt of diethylenetriaminepentaacetic acid, gluconates, phosphonates, sodium tartrate, sodium lignosulfonate, calcium lignosulfonate and their mixtures.

8. The use as claimed in any one of the preceding claims, according to which the milk of lime has a Brookfield viscosity ranging from 1 mPa.s to 1000 mPa.s at 25°C, at 100 rev/min.

9. The use as claimed in any one of the preceding claims, according to which the PCC slurry has a Brookfield viscosity of less than or equal to 1000 mPa.s at 25°C, at 100 rev/min.

10. The use as claimed in any one of the preceding claims, according to which the precipitated calcium carbonate slurry obtained has a dry solids content of at least 10 wt.%, based on the total weight of the slurry.

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,
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:
*Repeat boxes in case of more than one entry
*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
2
The present invention relates to the use of a depolymerized carboxylated cellulose for
preparing an aqueous Precipitated Calcium Carbonate (PCC)slurry, said depolymerized
carboxylated cellulose optionally being used in combination with at least one slaking
additive.
Background of the invention
Calcium carbonate is one of the most widely used additives in the paper, paint and plastics
industries. Natural Calcium Carbonate (NCC) is,for example,used as mineral filler in
numerous applications.For its part, Precipitated Calcium Carbonate (PCC) can be
manufactured tailor-made in terms of morphology and particle size, which confers other
properties on the materials which contain it. Scalenohedral Precipitated Calcium Carbonate
(S-PCC) is used in particular as mineral filler in combination with cellulose fibers in filler
applications in paper.
The processes forthe production of PCC comprise the steps consisting of the slaking of a
material containing calcium oxide (generally known as "quicklime")with water, so as to
produce a calcium hydroxide slurry (generally known as "milk of lime"), followed by the
subsequent synthesis of the calcium carbonate by circulating carbon dioxide through said
resulting calcium hydroxide slurry. Such processes produce PCC slurrieshaving a low dry
solids content. Consequently, these processes generally comprise an additional concentration
step in order to obtain a PCC slurry exhibiting a higher dry solids content, which is
advantageous during the transportation of the PCC slurry. Nevertheless, such additional
concentration steps are energy-consuming and cost-intensive and necessitate having to resort
to a specific item ofequipment (for example a centrifuge, requiring high maintenance).
Furthermore, the use of such items of equipment can result in the destruction of the structure
of the PCC formed, as is in particular the case with S-PCC prepared in the form of clusters.
Processes for the preparation of PCCin the presence of different additives are described in the
literature.
3
A certain number of documents are concerned with the preparation of PCC in the presence of
negatively charged polymers, for example (meth)acrylic acid polymers.
In particular, the document WO 2005/000742 A1 relates to a process for the preparation of
lamellar PCC comprising the steps consisting in forming a calcium hydroxide slurry,
carbonating said slurry, and in adding apolyacrylateto the slurry before the end of the
carbonation in order to precipitate the lamellar calcium carbonate.
Also, the unpublished patent application EP 14166751.9,filed on behalf of the present
applicants, relates to the use of a combination of at least one water-soluble polymer(for
example a polyacrylic acid) and of at least one slaking additive in a process for the
production of an aqueous precipitated calcium carbonate slurry.
Other documents describe the use of positively charged additives prepared, for example, from
monomeric units having a quaternary amine.
The unpublished patent applicationFR 15 51690, filed on behalf of the present applicants,
relates to the use of a cationic polymer, optionally in the presence of a slaking additive, in a
process for the production of an aqueous precipitated calcium carbonate slurry. The invention
described in this document makes it possible to prepare PCCslurries having cationic surface
charges, even at alkaline pH values.
Finally, other documents are concerned with the use of at least partially biosourcedadditives.
For example, the patent application WO 2007/067146 A1 describes a process for the
preparation of PCC in the presence of starch or ofcarboxymethylcellulose (CMC).
The document EP 2 868 716relates to the use of depolymerized carboxymethylcellulosefor
helping in the grinding of mineralsfor the purpose of preparing an aqueous slurryof mineral
particles.
4
The paper by Sonobeet al.entitled Polymorphism, size and shape control of calcium
carbonate crystals in the presence of a polyelectrolyterelates to the carbonation conditions
according to which crystallographic modifications of the calcium carbonate can be obtained
by means of polyacrylatesor of neutralized CMC.
The document US 2013/0312925 relates to the improvement in the mechanical or optical
properties of paper by employing different polysaccharides, including CMC,during the
preparation of PCC subsequently used during the preparation of paper.
Objects of the invention
One object of the present invention is to provide a solution for the production of PCC slurries
using an additive of biosourced origin, that is to say not resulting from fossil energy. This
step comes within a conceptof green chemistry and of sustainable development.
Another object of the present invention is to provide a solution for the production of PCC
slurries having, for example,a high dry solids content, without having recourse to an
additional step of thermal or mechanical concentration.
Another object of the present invention is to provide a solution for the production of PCC
slurries having a high dry solids content possessing viscosities which can be easily managed,
that is to say a solution which makes it possible to increase the dry solids content of PCC
slurries, while preventing an increase in the viscosity of the slurries.
It is also desirable for said solution not to negatively affect the kinetics of the carbonation
step and/or not to detrimentally affect the crystallographic structure of the PCC.
Another object of the present invention is to provide a solution for the preparation of PCC
slurries to be useddirectly as mineral filler in a process for the manufacture of paper.
5
Brief description of the invention
The present invention relates to the use of at least one depolymerized carboxylated cellulose
solution for preparing an aqueous Precipitated Calcium Carbonate (PCC)slurry by slaking of
a material containing calcium oxide in water, followed by carbonation of the milk of lime
thus obtained.
According to one embodiment of the present invention,said polymerized carboxylated
cellulose solution exhibits a solids content of between 25 wt.%and 40 wt.%, based on the
total weight of the solution.
According to another embodiment, said depolymerized carboxylated cellulose exhibits a
molecular weight Mw of between 10 000 g/moland 40 000 g/mol.
The present invention relates, in addition, to the use of a combination of at least one
depolymerized carboxylated cellulose solution and of at least one slaking additive in a
process for the production of an aqueous precipitated calcium carbonateslurry.
The present invention also relates to the use of at least one depolymerized carboxylated
cellulose solution for preparingPrecipitated Calcium Carbonate (PCC)in the dry form, by
slaking of a material containing calcium oxide in water, carbonation of the milk of lime thus
obtained and at least drying of the PCCslurry.
Detailed description of the invention
Definitions
For the purposes of the present invention, the terms cited belowshould be understood as
having the following meanings:
6
"Material containing calcium oxide" is understood to mean a mineral or synthetic material
having a calcium oxide content of at least 50 wt.%, for example of at least 75 wt.%, or of at
least 90 wt.% or also of at least95 wt.%, based on the total weight of the material containing
calcium oxide.
"Mineral material" is understood to mean a solid substance having a defined inorganic
chemical composition and a characteristic crystalline and/or amorphous structure.
"Natural Calcium Carbonate (NCC)" is understood to mean a calcium carbonate obtained
from natural sources, such as limestone, marble or chalk, and subjected to a wet and/or dry
treatment, such as a grinding, a sieving and/or fractionation, for example using a cyclone or a
sorter.
"Precipitated Calcium Carbonate (PCC)" is understood to mean a synthetic material generally
obtained by precipitation subsequent to the reaction of carbon dioxide and of calcium
hydroxide (hydrated lime) in an aqueous medium or by precipitation of a source of calcium
and of a source of carbonate in water. Moreover, the precipitated calcium carbonate can also
be the product which makes it possible to introduce calcium and carbonate salts, calcium
chloride and sodium carbonate, for example in an aqueous medium. The PCC can be in the
vaterite, calcite or aragonite form. PCCs are described, for example, in the 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" or "solids content" of a
liquid composition is a measure of the remaining amount of material after evaporation of all
the solvents or of water.
Throughout the present document, the "particle size" of the precipitated calcium carbonate or
of the other particulate materials is described by its particle size distribution. The value dx
represents the diameter for which x wt.% of the particles have a diameter of less thandx. This
means that the value d20is the particle size at which 20 wt.% of all the particles have a
diameter of less than the value d and the valued98is the particle size at which 98 wt.% of all
the particles have a diameter of less than the value d. The value d98is also known as "top cut".
7
The value d50is known as the weight medium particle size, that is to say that 50 wt.% of the
particles have a diameter of less than or greater than this particle size. For the purposes of the
present invention, the particle size is indicated as being the weight medium particle size d50,
unless otherwise indicated. Use may be made, in order to determine the weight medium
particle sized50 orthe particle size of the top cut d98, of a Sedigraph 5100 or 5120 device from
Micromeritics, USA.
A "specific surface according to the BETmethod (SS)", within the meaning of the present
invention, is defined as being the surface area of the precipitated calcium carbonate particles
divided by the weight of the PCC particles. As used here, the specific surface is measured by
N2adsorption using BET isotherms (ISO 9277:1995) and is indicated in m2
/g.
Within the meaning of the present invention, "stable in an aqueous slurry having a pH of 12
and a temperature of 90°C" means that the polymeric additive retains its physical properties
and its chemical structure when it is added to an aqueous slurryhaving a pH of 12 and a
temperature of 90°C. For example, the polymeric additive retains its dispersingqualities and
is not depolymerized or degraded under said conditions.
For the purposes of the present invention, the term "viscosity" or "Brookfield viscosity"
refers to the Brookfield viscosity. The Brookfield viscosity is measured using a Brookfield
viscometer (RVT type) at 25°C ± 1°Cat 100 rev/min using an appropriate spindle and is
indicated in mPa.s.
For the purposes of the present invention, "water-soluble" materials are defined as being
materials which, when they are mixed with deionized water and filtered through a filter
having a pore size of 0.2 µm at 20°C in order to recover the liquid filtrate, result in a weight
of less than or equal to 0.1 g of solid material recovered after evaporation of 100 g of said
liquid filtrate between 95°C and 100°C. "Water-soluble" materials are defined as being
materials resulting in a weight of greater than 0.1 g of solid material recovered
afterevaporation of 100 g of said liquid filtrate between 95°C and 100°C.
8
A "slurry", within the meaning of the present invention, comprises insoluble solids and water,
and optionally other additives. It is capable of containing large amounts of solids and thus of
being more viscous and of having a greaterdensity than that of the liquid from which it is
formed.
The term "comprising", as used in the present description and the present claims, does not
exclude other elements. For the purposes of the present invention, the term "consisting of" is
regarded as being a preferred embodiment of the term "comprising". If a group is defined
hereinafter as comprising at least a certain number of embodiments, it should also be
understood that it describes a group which preferably consists only of these embodiments.
The terms "which can be obtained" or "which can be defined" and "obtained" or "defined" are
usedinterchangeably. For example, this means that, unless the context stipulates otherwise,
the term "obtained" does not indicate that an embodiment has to be obtained by the sequence
of steps following the term "obtained", even if such a limited understanding is always
included by the term "obtained" or "defined" as a preferred embodiment.
Depolymerized carboxylated cellulose and process of the preparation
"Carboxylated cellulose" is understood to mean a cellulose which has been chemically
modified and comprises carboxyl units, for example carboxymethyl –CH2-COOH units.The
carboxylatedcellulose is, at least partially, of biosourced origin. It can be supplied in the
powder form or in the solution form, for example in the aqueous solution form.
According to one embodiment of the present invention, the carboxylated cellulose is
carboxymethylcellulose.
In the context of the present invention, use is made of a carboxylatedcellulose which has been
depolymerized in order to exhibit a molecular weight optimal for the present application. This
is because the inventors demonstrate that the use of anon-depolymerized CMC does not make
it possible to increase the dry solids content of the milk of lime while maintaining a viscosity
which allows the slurry to be handled.
9
In the context of the present invention, the terms "polymeric additive" and "depolymerized
carboxylated cellulose" are used equivalently.
According to one embodiment of the present invention, said depolymerized carboxylated
cellulose solution is obtained according to a process described in the patent application
WO 2015/063402. In particular, said depolymerized carboxylated cellulose solution can be
obtained according to a process comprising:
1) a depolymerizationstep, according to which:
1a) a carboxylated cellulose to be depolymerized exhibiting a degree of substitution of
between 0.2 and 2 is available,
1b) a reactor containing water is heated to a temperature of between 50°Cand 85°C (limits
included), for example to a temperature of between 75°Cand 85°C (limits included),
1c) the carboxylatedcellulose to be depolymerized and a peroxide are gradually and
simultaneously added to a reactor while maintaining the temperature according to 1b),
and
1d) after addition of all of the reactants according to 1c), the temperature of the mixture is
maintained according to 1b) until the peroxide has been completely consumed,
2) a step of cooling the mixture to a temperature of less than 75°C, for example to a
temperature of less than 70°C, and
3) optionally a step of neutralization of the mixture.
According to one embodiment of the present invention, the depolymerized carboxylated
cellulose exhibits a molecular weightMw of between 10 000 g/moland 40 000 g/mol, for
example between13 000 g/moland 35 000 g/molor,for example, between 13 000 g/moland
25 000 g/mol.
The molecular weight of the depolymerized carboxylated cellulose can be determined by Size
Exclusion Chromatography (SEC) or Gel Permeation Chromatography (GPC). This methodis
described in particular in the patent application WO 2015/063402. In addition, a precise
measurement example is given in the experimental part of the present patent application.
10
The polydispersity index PI corresponds to the distribution of the molecular weights of the
different macromolecules within the cellulose obtained. If all the macromolecules exhibit a
similar molecular weight Mw, the PI index decreases and approaches the theoretical value
of1. If, on the other hand, the macromolecules exhibit different molecular weights, the PI
index increases.
According to one embodiment of the present invention,said depolymerized carboxylated
cellulose exhibits a polydispersityindex PI of between 2 and 10, for example of between 3
and 5.
According to one embodiment, the depolymerized carboxylated cellulose is providedin the
form of a solution.
According to one embodiment of the present invention, the depolymerized carboxylated
cellulose solution exhibits a solids content of greater than25 wt.%, for example of between
25 wt.%and 40 wt.%, based on the total weight of the solution; or a solids content of greater
than 30 wt.%, for example between 30 wt.% and 40 wt.%, based on the total weight of the
solution,orfor example between 31 wt.% and 35 wt.%.
According to one embodiment of the present invention, said depolymerized carboxylated
cellulose is partially or completely neutralized by means of one or more neutralizing
agent(s)chosen from the group consisting of sodium hydroxides, calcium hydroxides,
magnesium hydroxides, potassium hydroxides and amines.
Material containing calcium oxide
The aqueous PCC slurryis prepared by slaking of a material containing calcium oxide CaO.
Thus, in the process for the production of an aqueous precipitated calcium carbonate slurry, a
material containing calcium oxide is provided. Said material containing calcium oxide can be
obtained by calcining a material containing calcium carbonate. Calcination is a heat treatment
process applied to the material containing calcium carbonate in order to bring about a thermal
decomposition resulting in the formation of calcium oxide and carbon dioxide gas. The
11
materials containing calcium carbonate which can be used in such a calcination process are
those chosen from the group comprising precipitated calcium carbonates, natural minerals
containing calcium carbonate, such as marble, limestone and chalk, and minerals containing a
mixture of alkaline earth metal carbonates comprising calcium carbonate, such as dolomite or
fractions rich in calcium carbonate originating from other sources. It is also possible to
subject a waste material containing calcium carbonate to a calcination process in order to
obtain a material containing calcium oxide.
Calcium carbonate decomposes at approximately 1000°C to give calcium oxide (commonly
known as quicklime). The calcination step can be carried out under conditions and using
items of equipment well known to a person skilled in the art.As a general rule, the
calcinationcan be carried out in furnaces or reactors (sometimes known as kilns) of various
designs, in particular shaft furnaces, rotary kilns, multiple hearth furnaces and fluidized bed
reactors.
The end of the calcination reaction can be determined, for example, by monitoring the change
in density, the residual content of carbonate, for example by X-ray diffraction, or the
reactivity of the slaking by standard methods.
According to one embodiment of the present invention, the material containing calcium oxide
is obtained by calcining a material containing calcium carbonate, for example chosen from
the group consisting of precipitated calcium carbonate, natural minerals containing calcium
carbonate, such as marble, limestone and chalk, minerals containing a mixture of alkaline
earth metal carbonates comprising calcium carbonate, such as dolomite, or their mixtures.
For reasons of effectiveness, it is preferable for the material containing calcium oxide to have
a minimum content of calcium oxide of at least 75 wt.%, preferably at least 90 wt.% and
particularly preferably 95 wt.%, based on the total weight of the material containing calcium
oxide. According to one embodiment, the material containing calcium oxide consists of
calcium oxide.
12
The material containing calcium oxide can consist of just one type of material containing
calcium oxide. Alternatively, the material containing calcium oxide can consist of a mixture
of at least two types of materials containing calcium oxide.
The material containing calcium oxide can be used in the process of the invention in its
original form, that is to say in the raw material form, for examplein the form of more or less
large chunks. Alternatively, the material containing calcium oxide can be ground before use.
According to one embodiment of the present invention, the material containing calcium
carbonate is in the form of particles having a weight medium particle size d50ranging from
0.1 µm to1000 µm and, for example, from 1 µm to 500 µm.
Use of the depolymerized carboxylated cellulose
The present invention relates to the use of a depolymerized carboxylated cellulose for
preparing a Precipitated Calcium Carbonate (PCC).
More specifically, the present invention relates to the use of a depolymerized carboxylated
cellulose solution for preparing a Precipitated Calcium Carbonate (PCC)in the dry form or in
the form of an aqueous solution or aqueous slurry.
The processes for the production of an aqueous PCC slurrygenerally comprise the steps
consisting in (i) preparing a milk of lime by mixing water and the material containing
calcium oxide, and optionally the at least one slaking additive, and (ii) carbonating the milk
of lime obtained in step (i) in order to form an aqueous precipitated calcium carbonate slurry.
"Carbonating" is understood to mean circulating carbon dioxide within the calcium hydroxide
Ca(OH)2slurry, so as to form precipitatedcalcium carbonate CaCO3.
According to the present invention, at least onedepolymerized carboxylated cellulose solution
is used for preparing an aqueous Precipitated Calcium Carbonate (PCC)slurry by slaking of a
material containing calcium oxide in water, followed bycarbonation of the milk of lime thus
obtained, said depolymerized carboxylated cellulose solution exhibiting a solids content of
between 25 wt.% and 40 wt.%, based on the total weight of the solution, and a molecular
weight Mw of between 10 000 g/moland 40 000 g/mol.
13
Slaking step
In the first step of the process for the production of PCC, that is to say "the slaking step"
(called step i) above), a milk of lime is prepared by mixing water, the material containing
calcium oxide, the depolymerized carboxylated cellulose and optionally the at least one
slaking additive.
The reaction of the material containing calcium oxide with water results in the formation of a
milky calcium hydroxide slurry, better known under the name of milk of lime. Said reaction
is highly exothermic and is also known in the art as "lime slaking".
According to one embodiment, said depolymerized carboxylated cellulose solution is present
in the slaking water of the material containing calcium oxide.
According to one embodiment of the present invention, the temperature of the water, which is
used in the slaking step, that is to say the temperature of the water which is used for the
slaking of the material containing calcium oxide, is adjusted in order to be within the range
extending from 0°C to 100°C, for example from 1°C to 70°C orfrom 2°C to 50°C or from
30°C to 50°C or from 35°C to 45°C. It will appear obvious to a person skilled in the art that
the initial temperature of the water is not necessarily the same as the temperature of the
mixture prepared in the slaking step as a result of the highly exothermic nature of the slaking
reaction and/or of the mixing of substances having different temperatures.
According to one embodiment of the present invention, the slaking step of the process
comprises the steps consisting in:
a1) mixing the depolymerized carboxylated cellulose solution with water and optionally the
at least one slaking additive, and
a2) adding the material containing calcium oxide to the mixture of step a1).
14
According to one embodiment, step a1) is carried out at a temperature of between 0°C and
99°C, for example between 1°C and 70°C or between 2°C and 50°C orbetween 30°C and
50°C or between 35°C and 45°C.
According to another embodiment of the present invention, the slaking step of the process
comprises the steps consisting in:
b1) mixing the material containing calcium oxide, the depolymerized carboxylated cellulose
solution and optionally the at least one slaking additive, and
b2) adding water to the mixture of step b1).
According to yet another embodiment of the present invention, in the slaking step of the
process, the material containing calcium oxide, the depolymerized carboxylated cellulose,
optionally the at least one slaking additive and water are mixedsimultaneously.
According to yet another embodiment of the present invention, the at least one slaking
additive is added before or after the slaking step of the process.
The depolymerized carboxylated cellulose solution can be added in the slaking step in its
entirety or in several parts, for example in two, three, four, five or more parts.
The slaking step of the process can be carried out at ambient temperature, that is to say at a
temperature of 20°C ± 2°C, or at an initial temperature of between 30°C and 50°C orbetween
35°C and 45°C. As the reaction is exothermic, the temperature generally reaches a
temperature of between 85°C and 99°C during step i), preferably a temperature of between
90°C and 95°C. According to a preferred embodiment, step i) of the process is carried out by
mixing or by stirring, for example with mechanical stirring. The appropriate item of
equipment for the mixing or the stirring of the process is known to a person skilled in the art.
15
The progression of the slaking reaction can be observed by measuring the temperature and/or
the conductivity of the reaction mixture.
The inventors have found, with surprise, that the addition of a specific depolymerized
carboxylated cellulose as defined above and optionally of a slaking additive as defined above,
before or during the slaking step of a process for the production of PCC, can make possible
the preparation not only of a milk of lime having a low dry solids content but also of a milk
of lime having a high dry solids content. This is because it is advantageous to note that,
according to one aspect of the invention, by carbonating said highly concentrated milk of
lime, it is possible to obtain an aqueous PCC slurry which also has a high dry solids content.
Consequently, the process of the present invention does not require an additional
concentration step in order to obtain a PCC slurryhaving a high dry solids content.
According to one embodiment of the present invention, the milk of lime of the slaking step
has a dry solids content of at least 15 wt.%, for exampleranging from 15 wt.% to 45 wt.% or
for examplefrom 20 wt.% to 40 wt.% or for example from 25 wt.% to 37 wt.%, based on the
total weight of the milk of lime.
According to one embodiment of the present invention, the milk of lime of the slaking step
has a Brookfield viscosity ranging from 1 mPa.s to1000 mPa.s at 25°C, for example from
5 mPa.s to 800 mPa.s at 25°C or for example from 10 mPa.s to 500 mPa.s at 25°C, as
measured at 100 rev/min.
In the context of the present invention, additional water can be introduced during the slaking
reaction in order to control and/or maintain and/or reach the desired dry solids content or the
desired Brookfield viscosity of the milk of lime.
The slaking step of the process can be carried out in the form of a batchwise, semibatchwise
or continuous process.
16
In the slaking step, the material containing calcium oxide and the water can be mixed in a
weight ratio ranging from 1:1 to 1:12, for example from 1:2 to 1:12, for example from 1:2.5
to 1:6.
According to one embodiment, said depolymerized carboxylated cellulose solution is used in
combination with at least one slaking additive.
In this case, the at least one slaking additive can be chosen from the group consisting of
organic acids, organic acid salts, sugar alcohols, monosaccharides, disaccharides,
polysaccharides, gluconates, phosphonates, lignosulfonates and their mixtures.
According to one embodiment, the at least one slaking additive is chosen from the group
consisting of sodiumcitrate, potassiumcitrate, calcium citrate, magnesium citrate,
monosaccharides, disaccharides, polysaccharides, sucrose, sugar alcohols, meritol, citric acid,
sorbitol, the sodium salt of diethylenetriaminepentaacetic acid, gluconates, phosphonates,
sodium tartrate, sodium lignosulfonate, calcium lignosulfonate and their mixtures.
Carbonationstep
In thisstep of the process for the production of PCC, that is to say the carbonation step(called
step ii)above), the milk of lime obtained on conclusion of the slaking step is carbonated in
order to form an aqueous precipitated calcium carbonate slurry.
The carbonation is carried out by means and under conditions well known to a person skilled
in the art. The introduction of carbon dioxide into the milk of lime rapidly increases the
concentration of carbonate (CO3
2-) ions and calcium carbonate is formed. In particular, the
carbonation reaction can be easily controlled by taking into account the reactions involved in
the carbonation process. The carbon dioxide dissolves, according to its partial pressure, to
form carbonate ions via the formation of carbonic acid (H2CO3) and of hydrogencarbonate
(HCO3
-
) ions which are unstable in alkaline solution. During the continuous dissolution of the
carbon dioxide, the hydroxide ions are consumed and the concentration of carbonate ions
increases until the concentration of dissolved calcium carbonate is greater than the solubility
product and the solid calcium carbonate precipitates.
17
According to one embodiment of the present invention, the carbonation is carried out by
incorporating pure carbon dioxide gas or industrial gases containing at least 10 vol.%of
carbon dioxide in the milk of lime.
The progression of the carbonation reaction can be easily observed by measuring the
conductivity and/or the pH. In this regard, the pH of the milk of lime before the addition of
carbon dioxide will be greater than 10, generally of between 11 and 12.5, and will continually
decrease until a pH of approximately7 is obtained. The reaction can then be halted.
The conductivity slowly decreases during the carbonation reaction and then rapidly decreases
to reach low values when the precipitation is complete. The progression of the carbonation
can be monitored by measuring the pH and/or the conductivity of the reaction mixture.
According to one embodiment of the process for the production of PCC, the temperature of
the milk of lime obtained on conclusion of the slaking step, which is used in the carbonation
step,is adjusted in order to be within the range extending from 20°C to 60°C and for example
from30°C to 50°C. It will be clearly apparent to a person skilled in the art that the initial
temperature of the milk of lime is not necessarily the same as the temperature of the mixture
prepared in the carbonationstep as a result of the exothermic nature of the carbonation
reaction and/orof the mixing of substances having different temperatures.
According to one embodiment of the process for the production of PCC, the carbonation step
is carried out at a temperature of between 5°C and 95°C, for examplefrom 30°C to 70°C and
for example from 40°C to 60°C.
The carbonation step of the process can be carried out in the form of a batchwise,
semibatchwise orcontinuous process. According to one embodiment, the process for the
production of PCC involving the slaking and carbonationsteps of the process is carried out in
the form of a batchwise, semibatchwise or continuous process.
18
According to one embodiment of the present invention, the process for the production of PCC
does not comprise a step of concentrating the aqueous precipitated calcium carbonate slurry
obtained in the slaking and carbonation steps of the process.
Thus, the present invention relates to the use of depolymerized carboxylated cellulose in a
process for the preparation of PCC, more specifically in the step of preparation of a milk of
lime which has to be subsequently carbonated.
Without wishing to be committed to any one theory, it may be thought that the affinity of the
PCC particles formed during the process described above with the cellulose fibers or fibrils of
the paper sheet is improved as a result of the use of said depolymerized carboxylated
cellulose during the process for the production of PCC. This is because, when the
depolymerized carboxylated cellulose is present during the step of slaking of the material
containing calcium oxide in order to form the PCC, it may be thought that the depolymerized
carboxylated cellulose is incorporated within the PCC particles and thus plays a binding role
between these PCC particles and the fibrous mat of the cellulose used to form the paper sheet.
According to one embodiment of the present invention, the use of depolymerized
carboxylated cellulose during the process for the preparation of PCC confers, on the aqueous
PCC slurries produced, a zeta potential of less than 0 mV but greater than the zeta potential of
a PCC prepared in the presence of negatively charged polymers, for example (meth)acrylic
acid polymers, in particular those described in the application WO 2005/000742 A1, which
remains an advantage for the filler application.
According to another embodiment, the aqueous PCCslurries obtained using the
depolymerized carboxylated cellulose are characterized in that they have a zeta potential of
less than 0 mV, for example of between 0 mV and -40 mV, for example between 0 mV
and-30 mV.
According to one embodiment, the use of depolymerized carboxylated cellulose during the
process for the preparation of the PCC confers, on the aqueous PCC slurries produced, a
Mütek charge of less than 0 μeq/g.
19
According to another embodiment, the aqueous PCC slurries obtained by using the
depolymerized carboxylated cellulose are characterized in that they exhibit a Mütekcharge of
less than 0 μeq/g, for example of between 0 µeq/g and -1 μeq/g or between 0 µeq/g and
-0.8 μeq/g.
According to one embodiment of the present invention, the depolymerized carboxylated
cellulose is added during the first step of the process for the production of PCC, that is to say
that the depolymerized carboxylated cellulose is added before or during the slaking step. The
milk of lime, known to a person skilled in the art, obtained by slaking of a material
containing calcium oxide with water generally has a pH of between 11 and 12.5, measured at
a temperature of 25°C, according to the concentration of the material containing calcium
oxide in the milk of lime. Given that the slaking reaction is exothermic, the temperature of
the milk of lime can reach a temperature of greater than 80°C, for example of between
80°Cand 99°C. According to one embodiment, the depolymerized carboxylated cellulose,
used in the context of the present invention, is chosen so as to be stable in an aqueous slurry
having a pH of 12 and a temperature of 90°C. Within the meaning of the present invention,
"stable in an aqueousslurry having a pH of 12 and a temperature of 90°C" means that the
polymeric additive retains its physical properties and its chemical structure when it is added
to an aqueous slurryhaving a pH of 12 and a temperature of 90°C. For example, the
polymeric additive retains its dispersing qualities and has not degraded under said conditions.
According to one embodiment of the present invention, the depolymerized carboxylated
cellulose is added in an amount ranging from 0.01 wt.% to 2 wt.%, for example from
0.02 wt.% to 1 wt.% and for example from 0.05 wt.% to 0.5 wt.%, based on the total weight
of the material containing calcium oxide.
Slaking additive
In the first step of the process for the production of PCC (or slaking step), at least one slaking
additive can be used in addition to the depolymerized carboxylated cellulose.
20
Thus, according to one embodiment, said depolymerized carboxylated cellulose solution is
used in combination with at least one slaking additive.
The at least one slaking additive can be chosen from the group consisting of organic acids,
organic acid salts, sugar alcohols, monosaccharides, disaccharides, polysaccharides,
gluconates, phosphonates, lignosulfonates and their mixtures.
According to one embodiment of the present invention, the at least one slaking additive is
chosen from the group consisting of sodium citrate, potassiumcitrate, calcium citrate,
magnesium citrate, monosaccharides, disaccharides, polysaccharides, sucrose, sugar alcohols,
meritol, citric acid, sorbitol, the sodium salt of diethylenetriaminepentaacetic acid,
gluconates, phosphonates, sodium tartrate, sodium lignosulfonate, calcium lignosulfonate and
their mixtures. According to a preferred embodiment, the at least one slaking additive is
sodium citrate and/or sucrose.
According to one embodiment of the present invention, the at least one slaking additive used
consists of just one type of slaking additive. Alternatively, the at least one slaking additive
used can consist of a mixture of at least two types of slaking additives.
The at least one slaking additive can be added in an amount ranging from 0.01 wt.% to
2 wt.%, based on the total amount of material containing calcium oxide, for example in an
amount ranging from 0.05 wt.% to 1 wt.%, for examplefrom 0.06 wt.% to 0.8 wt.% or for
example from 0.07 wt.% to 0,5 wt.%.
The addition of a slaking additive can be of use in controlling the size of the PCC particles
and their crystalline morphology without affecting the viscosity of the aqueous slurry.
As was mentioned above, the inventors have found, with surprise, that the addition of a
depolymerized carboxylated cellulose as defined above, optionally in combination with the
addition of a slaking additive before or during the slaking step of a process for the production
of PCCs, can make possible the preparation of a PCCslurryhaving a high dry solids content.
It is also believed that the omission of a concentration step improves the quality of the PCC
21
particles produced, given that the surface damage of the particles, which may occur during
the concentration step, is avoided. It is also estimated that said PCC slurrycan be further
concentrated up to a solids content of 52 wt.%with acceptable viscosities, for example
Brookfield viscosities of less than or equal to 1000 mPa.s at 25°Cand at 100 rev/min.
Additional steps of the process
The process for the production of precipitated calcium carbonate can comprise additional
steps.
The milk of lime can be sieved in order to remove oversized particles. An appropriate sieve
can comprise, for example, a sieve having a sieve size of 100 µm to 700 µm, for example
approximately 100 µm orapproximately 300 µm. According to one embodiment of the
present invention, the milk of lime is sieved after the slaking step and before the carbonation
step, for exampleusing a sieve having a sieve size ranging from 100 µm to 300 µm.
The process for the production of precipitated calcium carbonate can further comprise an
additional step of separation of the precipitated calcium carbonate from the aqueous
slurryobtained on conclusion of the carbonation step.
For the purposes of the present invention, the expression "separation" or "separating" means
that the PCC is removed or isolated from the aqueous slurryobtained in the carbonationstep of
the process. Any conventional separating means known to a person skilled in the art can be
used, for example a mechanical and/or thermal means. Examples of mechanical separation
processes are filtration, for example by means of a drum filter or of a filter press,
nanofiltration or centrifugation. An example of a thermal separation process is a process for
concentrating by application of heat, for example in an evaporator.
The PCC obtained can be transformed, for example deagglomerated or subjected to a dry
grinding step. It can also be wet ground in the form of a slurry. If the PCC is subjected to
dewatering, dispersing and/or grinding steps, these steps can be accomplished by methods
known in the art. Wet grinding can be carried out in the absence or in the presence of a
grinding aid agent. Dispersants can also be included in order to prepare dispersions, if
appropriate.
22
The process for the production of precipitated calcium carbonate can further comprise an
additional step of drying the precipitated calcium carbonate, for example separated
precipitated calciumcarbonate obtained on conclusion of the separating step described above.
The term "drying" refers to a process according to which at least a portion of the water is
removed from a material which has to be dried, so that a constant weight of the "dry" material
obtained at 120°C is achieved. Furthermore, a "dry" material can in addition be defined by its
total moisture content which, unless otherwise indicated, is less than or equal to 1.0 wt.%,
preferably less than or equal to 0.5 wt.%, more preferably less than or equal to 0.2 wt.%and
particularly preferably of between 0.03 wt.%and 0.07 wt.%, based on the total weight of the
dry material.
In general, the drying stepcan be carried out using any appropriate item of drying equipment
and can, for example, comprise thermal drying and/or drying under reduced pressure, using
an item of equipment such as an evaporator, a flash dryer, an oven or a spray dryer, and/or
drying in a vacuum chamber.
The drying step results in a dry precipitated calcium carbonate having a low total moisture
content which is less than or equal to 1.0 wt.%, based on the total weight of the dry
precipitated calcium carbonate.
The precipitated calcium carbonate obtained by the process of the invention can be posttreated,
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 fatty acid phosphoric esters.
According to one embodiment of the process for the production of PCC, the precipitated
calcium carbonate obtained has a weight medium particle sized50ranging from 0.1 µm to
100 µm, for example from 0.25 µm to 50 µm, for example from 0.3 µm to 5 µm and for
example from 0.4 µm to 3.0 µm.
23
The precipitated calcium carbonate can have an aragonite, calcite or vaterite crystalline
structure or mixtures of these structures. Another advantage of the present invention is that
the crystalline structure and the morphology of the precipitated calcium carbonate can be
controlled, for example by adding seed crystals or other structure-modifying chemical
products. According to a preferred embodiment, the precipitated calcium carbonate obtained
by the process of the invention has a clustered scalenohedral crystalline structure.
The BET specific surface of the precipitated calcium carbonate obtained by the process
according to the present invention can range from 1 m2
/g to 100 m2
/g, for example from
2 m2
/g to 70 m2
/g, for example from 3 m2
/g to 50 m2
/g, for example from 4 m2
/g to 30 m2
/g,
measured using nitrogen and the BET method in accordance with the ISO 9277 standard.The
BET specific surface of the precipitated calcium carbonate obtained by the process of the
present invention can be controlled by using additives, for example surface-active agents,
which involve shearing during the precipitation step or subsequently at high mechanical shear
rates, which results not only in a small particle size but also in a high BET specific surface.
According to one embodiment of the present invention, the precipitated calcium
carbonateslurryobtained has a dry solids content of at least 10 wt.%, for example ranging
from 20 wt.% to 50 wt.%, for example from 25 wt.% to 45 wt.% orfor example from 30 wt.%
to 40 wt.%, based on the total weight of the slurry.
According to one embodiment of the present invention, the PCC slurry has a Brookfield
viscosity of less than or equal to 1000 mPa.s at 25°C, for example of less than or equal to
800 mPa.s at 25°C or for example of less than or equal to 600 mPa.s at 25°C, as measured at
100 rev/min.
Another aspect of the present invention relates to the use of a combination of at least one
water-soluble polymer and of a slaking additive in a process for the production of an aqueous
precipitated calcium carbonate slurry, in which:
24
- the depolymerized carboxylated cellulose solution exhibits a solids content of between
25 wt.% and 40 wt.%, based on the total weight of the solution, and a molecular weight of
between 10 000 g/mol and 40 000 g/mol, 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 their mixtures.

25
EXAMPLES
1. Measurement methods
The measurement methods employed in the examples are described below.
Brookfield viscosity
The Brookfield viscosity of the aqueous slurries was measured after one hour of production
and after one minute of stirring at 25°C ± 1°Cat 100 rev/min using a Brookfield viscometer
of RVT type equipped with an appropriate disc spindle, for example a 2 to 5 spindle.
pH measurement
The pH of a slurry or of a solution was measured at 25°Cusing a Mettler Toledo Seven Easy
pH meter and a Mettler Toledo InLab® Expert Pro pH electrode. A three-point calibration
(according to the segmentation method) of the instrument was carried out first using
commercially available (from Sigma-Aldrich Corp., USA) buffer solutions having a pH of 4,
7 and 10 at 20°C. The pH values given are the final values detected by the instrument (the
measurement is terminated when the signal measured differsby less than 0.1 mV from the
mean over the last 6 seconds).
Particle size distribution
The particle size distribution of the PCC particles prepared was measured using a Sedigraph
5100 device from Micromeritics, USA. The method and the instrument are known to a person
skilled in the art and are commonly used to determine the grain size of mineral fillers and
pigments. The measurement was carried out in an aqueous solution comprising 0.1 wt.%of
Na4P2O7. The samples were dispersed using a high-speed stirrer and ultrasound. No other
dispersing agent was added for the measurement of the dispersed samples.
26
Dry solids content of an aqueous slurry
The dry solids content of the slurry (also known as "dry weight") was determined using an
MJ33 Moisture Analyzer from Mettler-Toledo, Switzerland, with the following settings:
drying temperature of 160°C, automatic halting if the weight does not vary by more than
1 mg over a period of 30 seconds, standard drying of 5 g to 20 g ofslurry.
Specific surface (SS)
The specific surface was measured using the BET method in accordance with the ISO 9277
standard using nitrogen, followed by conditioning of the sample by heating at 250°Cfor a
period of 30 minutes. Before carrying out these measurements, the sample is filtered on a
Büchner funnel, rinsed with deionized water and dried overnight in an oven at a temperature
of between 90°Cand 100°C. Subsequently, the dry filtration cake is meticulously ground in a
mortar and the resulting powder is placed in a moisture analysis balance at 130°Cuntil a
constant weight is obtained.
Specific carbonation time
The monitoring of the conductivity, which slowly decreases during the carbonation reaction
and then rapidly decreases to reach a minimum value, therefore indicating that the reaction is
complete, was used to determine the time necessary to make possible complete precipitation.
The specific carbonation time (min/kg ofCa(OH)2) was determined by the following formula:
Specific carbonation time =
105
.Tf
W.DSCMoL
in which:
- Tf (min) is the time necessary to complete the carbonation of the milk of lime, as
determined by monitoring the conductivity,
- W (g) is the weight of the milk of lime introduced into the carbonation reactor, and
- DSCMoL (%) is the dry solids content by weight of the milk of lime.
27
Measurementof the charge - Mütek
The measurement of the charge is carried out using a Mütek PCD 03 device equipped with a
Mütek PCD titrator.
From 0.5 g to 1 g of dry PCC is weighed in the plastic measuring cell and diluted with 20 ml
of deionized water. The displacement piston is put in the "on" position. While the piston
oscillates in the cell, there is a wait for the flow current between the two electrodes to
stabilize.
The sign of the measured value displayed on the screen indicates whether the charge of the
sample is positive (cationic) or negative (anionic). A polyelectrolyte of opposite charge
having a known charge density is added to the sample as titrating agent (either 0.001N
sodium polyoxyethylene sulfate or 0.001N pDADMAC). The charges of the titrating agent
neutralize the existing charges of the sample. The titration is interrupted as soon as the point
of zero charge (0 mV) is reached.
The consumption of the titrating agent in mLis used as basis for the subsequent calculations.
The amount of specific charge q [eq/g of slurry] is calculated according to the following
formula:
a = (V * c) / w
V: volume of titrating agent consumed [l]
c: concentration of the titrating agent [eq/l] or [µeq/l]
w: weight of the weighed slurry [g]
a: amount of specific charge [eq/g ofslurry] or [µeq/g ofslurry]
Zeta potential
In order to measure the zeta potential, a few drops of PCC slurryare dispersed in a sufficient
amount of serum obtained by mechanical filtration of said slurryin order to obtain a slightly
cloudy colloidal suspension.
28
This suspension is introduced into the measuring cell of the Zetasizer Nano-ZS device from
Malvern which directly displays the value of the zeta potential of the PCC slurryin mV.
2. Preparation of a depolymerized CMC
The process for the preparation of the depolymerized CMC according to the invention
comprises three steps: a depolymerization step, a cooling step and a neutralization step.
Depolymerization step
800 g of bi-permuted water and 0.017 g of FeSO4.7H2O catalyst are introduced into a oneliter
reactor. The reactor is heated to 80°C ± 2°C. There is then injected, for 2 h 45, a 35 wt.%
hydrogen peroxide solution at 189 mg/min and also CMC (Sigma-Aldrich with the reference
419281, Mw = 250 000 g/mol, DS = 1.2) in aliquots of 25 g every 15 minutes (continuous
process). The reaction is allowed to continue for 2 h 30 after the end of the injections. It is
confirmed that all of the hydrogen peroxide has been consumed.
Cooling step
The reactor is cooled to 70°C. The pH as measured in the reactor is 4.4.
Neutralization step
A 10% NaOHsolution is introduced so as to achieve a pH of 7.4.
Characterization of the depolymerized CMC thus obtained:
VBat t0 (mPa.s) = water
VBof the depolymerized CMC solution obtained (mPa.s) 725
SC (wt.%) 33.9
Total duration of process 4 h45
Mw (g/mol) 13 310
PI 4
29
Method for determination of the molecular weight (Mw) and PI index of the
depolymerized CMC:
The molecular weight of the CMCis determined by Size Exclusion Chromatography(SEC) or
Gel Permeation Chromatography (GPC).
Such a technique employs in the case in point a liquid chromatography device of the
WatersTM brand having a detector. This detector is a refractometric concentration detector of
the WatersTM brand.
This liquid chromatography appliance has a size exclusion column suitably chosen by a
person skilled in the art in order to separate the different molecular weights of the
CMCsstudied. The liquid elution phase is an aqueous phase adjusted to pH 9.00 with 1N
sodium hydroxide containing 0.05M of NaHCO3, 0.1M of NaNO3, 0.02M of triethanolamine
and 0.03% of NaN3.
In a detailed manner, according to a first step, the CMC solution is diluted to a solids content
of 0.9% in the dissolution solvent of the SEC, which corresponds to the liquid elution phase
of the SEC, to which 0.04% of dimethylformamide, which acts as a flow marker or an
internal standard, is added. Filtration is then carried out through a 0.2 µm filter. 100 µl are
subsequently injected into the chromatography device (eluent: an aqueous phase adjusted to
pH 9.00 with 1N sodium hydroxide containing 0.05M of NaHCO3, 0.1M of NaNO3, 0.02M
of triethanolamine and 0.03% of NaN3).
The liquid chromatography device contains an isocratic pump (WatersTM 515), the flow rate
of which is adjustedto 0.8 ml/min. The chromatography device also comprises an oven which
itself comprises, in series, the following system of columns: a precolumn of WatersTM Guard
Column Ultrahydrogel type with a length of 6 cm and an internal diameter of 40 mmand a
linear column of WatersTM Ultrahydrogel type with a length of 30 cm and an internal
diameter of 7.8 mm. For its part, the detection system is composed of a refractometric
detector of WatersTM 410 RI type. The oven is brought to a temperature of 60°Cand the
refractometer is brought to a temperature of45°C.
30
The chromatography device is calibrated with sodium polyacrylate powder standards with
different molecular weights certified for the supplier: Polymer Standards Service or
American Polymer Standards Corporation.
3. Preparation of Precipitated Calcium Carbonate (PCC):
A milk of lime was prepared by mixing, with mechanical stirring, water and different
polymer additives, optionally in the presence of a slaking additive (for example dry sodium
citrate, NaCi), at an initial temperature of between 40°C and 41°C (the amounts of polymer
additives and optionally of slaking additives are shown in table 1 below). Subsequently,
calcium oxide (quicklime raw material from Golling, Austria) was added with stirring. The
mixture obtained was stirred for 25 min and then sieved through a 200 µm sieve.
The milk of lime obtained was transferred into a stainless steel reactor, in which the milk of
lime was cooled to 50°C. The milk of lime was then carbonated by introducing an air/CO2
mixture (26 vol.% of CO2 and a flow rate of 23 l/min). During the carbonation step, the
reaction mixture was stirred at a speed of 1400 rev/min. The kinetics of the reaction was
monitored by inline pH and conductivity measurements.
Exemplified polymer additives:
P1 = depolymerized CMC prepared according to 2 (according to the invention),
P2 = non-depolymerized CMC - Blanose ® Ashland 12M8P (degree of substitution 1.2 and
molecular weight 395 000 g/mol) (outside the invention), and
P3 = sodium polyacrylate (outside the invention) - Mw = 4270 g/mol, PI = 2.3 (Mw and PI
determined according to the unpublished patent application EP 14166751.9).

31

Polymer
additive
Amount of polymer
additive
wt.% CaO
Slaking
additive
Amount of
slaking
additive
wt.% CaO
Solids content
of the milk of
lime
wt.%]
1 OINV none -- NaCi 0.1 25.2
2 OINV none -- NaCi 0.1 16.2
3 INV P1 0.15 NaCi 0.1 28.1
4 OINV P2 0.15 NaCi 0.1 28.1
5 OINV P3 0.15 NaCi 0.1 29.5
Table 1 Characteristics of the milks of lime
(INV: according to the INVention - OINV: Outside the INVention)
The characteristics of the milks of lime and of the aqueous PCC slurries prepared are
described in table 2 below.
Test
Viscosity of
the milk of
lime (mPa.s) at
100 rev/min
Carbonation
time (min/kg of
Ca(OH)2)
Solids
content of
S-PCC
wt.%]
Viscosity of
S-PCC (mPa.s)
at 100 rev/min
Zeta
potential
(mV)
Mütek
(μeq/g)
D50
(μm)
SS
(m2
/g)
1 OINV Viscosity of the milk of lime excessively high Not measured
2 OINV 23 44.2 20.5 20 + 5.5 0.1 1.6 4.7
3 INV 410 47 36.6 597 -29.1 -0.5 1.5 4.7
4 OINV Viscosity of the milk of lime excessively high - effect Not measured
5 OINV 329 46.5 37.6 940 -35.2 -0.9 1.3 5
Table 2 Characteristics of the milks of lime and of the aqueous PCC slurries
(INV: according to the INVention - OINV: Outside the INVention)
32
The results recorded in table 2 show that the use of a slaking additive alone results in a milk
of lime having a high Brookfield viscosity (test 1) and that it is not possible to increase the
dry solids content of the milk of lime (wt.%) while preventing the increase in the viscosity of
the slurry (comparison of test 1 and of test 2).
On the other hand, sample 3 according to the invention confirms that the viscosities of the
milk of lime and of the PCC slurry which are obtained are compatible with the anticipated
use of the PCC thus obtained, that is to say PCC slurries having a Brookfield viscosity of less
than or equal to 1500 mPa.s at 25°C, for example of less than or equal to 1000 mPa.s at 25°C
or of less than or equal to 600 mPa.s at 25°C, at 100 rev/min.
Furthermore, the kinetics of carbonation and the crystallographic structure of the PCC
prepared (results not provided) are similar to those obtained with a process involving the use
of an anionic polymer (polymer P3 outside the invention, solely by way of comparison).
33
WE CLAIM:
1. The use of at least one depolymerized carboxylated cellulose solution for preparing an
aqueous Precipitated Calcium Carbonate (PCC) slurry by slaking of a material
containing calcium oxide in water, followed by carbonation of the milk of lime thus
obtained, said depolymerized carboxylated cellulose solution exhibiting a solids
content of between 25 wt.% and 40 wt.%, based on the total weight of the solution,
and a molecular weight Mw of between 10 000 g/mol and 40 000 g/mol.
2. The use as claimed in claim 1, according to which said depolymerized carboxylated
cellulose exhibits a polydispersity index PI of between 2 and 10.
3. The use as claimed in either of the preceding claims, according to which said
depolymerized carboxylated cellulose is partially or completely neutralized by means
of one or more neutralizing agent(s) chosen from the group consisting of sodium
hydroxides, calcium hydroxides, magnesium hydroxides, potassium hydroxides and
amines.
4. The use as claimed in any one of the preceding claims, in which said depolymerized
carboxylated cellulose solution is present in the slaking water of the material
containing calcium oxide.
5. The use as claimed in any one of the preceding claims, according to which said
material containing calcium oxide and the water are mixed in a weight ratio ranging
from 1:1 to 1:12.
6. The use as claimed in any one of the preceding claims, according to which said
depolymerized carboxylated cellulose solution is used in combination with at least
one slaking additive.
34
7. The use as claimed in the preceding claim, according to 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, the sodium salt of
diethylenetriaminepentaacetic acid, gluconates, phosphonates, sodium tartrate, sodium
lignosulfonate, calcium lignosulfonate and their mixtures.
8. The use as claimed in any one of the preceding claims, according to which the milk of
lime has a Brookfield viscosity ranging from 1 mPa.s to 1000 mPa.s at 25°C, at
100 rev/min.
9. The use as claimed in any one of the preceding claims, according to which the PCC
slurry has a Brookfield viscosity of less than or equal to 1000 mPa.s at 25°C, at
100 rev/min.
10. The use as claimed in any one of the preceding claims, according to which the
precipitated calcium carbonate slurry obtained has a dry solids content of at least
10 wt.%, based on the total weight of the slurry.