U.S. patent application number 12/004847 was filed with the patent office on 2008-08-28 for process for preparation of aqueous suspensions of mineral loads, aqueous suspensions of mineral loads obtained and their uses.
Invention is credited to Maurice Husson, Christian Jacquemet, Eugene Vorobiev.
Application Number | 20080203008 12/004847 |
Document ID | / |
Family ID | 29797481 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080203008 |
Kind Code |
A1 |
Husson; Maurice ; et
al. |
August 28, 2008 |
Process for preparation of aqueous suspensions of mineral loads,
aqueous suspensions of mineral loads obtained and their uses
Abstract
The invention concerns a process for the preparation of aqueous
suspensions of fluid mineral matter, which are able to be pumped
and conveyed by the end user 5 immediately after the filtration
stage, possibly followed by a compression, which process comprises
filtration in two separate stages. The invention also concerns
aqueous suspensions of mineral matter obtained and their uses.
Inventors: |
Husson; Maurice; (Chalons en
Champagne, FR) ; Jacquemet; Christian; (Lyon, FR)
; Vorobiev; Eugene; (Compiegne, FR) |
Correspondence
Address: |
AMSTER, ROTHSTEIN & EBENSTEIN LLP
90 PARK AVENUE
NEW YORK
NY
10016
US
|
Family ID: |
29797481 |
Appl. No.: |
12/004847 |
Filed: |
December 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10520471 |
Jan 7, 2005 |
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PCT/FR2003/002254 |
Jul 16, 2003 |
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12004847 |
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Current U.S.
Class: |
210/350 |
Current CPC
Class: |
C01P 2004/62 20130101;
C01F 11/185 20130101; C01P 2006/22 20130101; B01F 3/20 20130101;
C09C 1/021 20130101; B01F 3/1207 20130101 |
Class at
Publication: |
210/350 |
International
Class: |
B01D 33/052 20060101
B01D033/052 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2002 |
FR |
0209015 |
Claims
1-5. (canceled)
6. An aqueous suspension of fluid mineral matter, which are able to
be pumped and conveyed by the end user immediately after the
filtration stage, possibly followed by a compression, characterised
in that it contains 0.01% to 10%, preferentially 0.1% to 2% by dry
weight of dispersant relative to the dry weight of mineral matter
to be filtered, and in that it is obtained by the process as
claimed in any of claims 1 to 5.
7. An aqueous suspension of mineral matter as claimed in claim 6,
characterised in that the mineral matter is chosen from among
natural calcium carbonate such as the various chalks, calcites,
marbles, or again chosen from the synthetic calcium carbonates such
as the calcium carbonates precipitated at different stages of
crystallisation, or from the mixed carbonates of magnesium and
calcium such as the dolomites, or from magnesium carbonate, zinc
carbonate, lime, magnesia, barium sulphate such as barita, calcium
sulphate, silica, the magnesio-silicates such as talc,
wollastonite, clays and other alumino-silicates such as the
kaolins, mica, metal or alkaline-earth oxides or hydroxides such as
magnesium hydroxide, iron oxides, zinc oxide, titanium oxide,
titanium dioxides in the anatase or rutile forms, and mixtures of
them, and moreover mixtures of talc and calcium carbonate.
8. The aqueous suspension as claimed in claim 6 for use in the
fields of paper, paint, water treatment, such as in the fields of
purification muds, detergency, ceramics, cements or hydraulic
binders, public works, inks and varnishes, gluing of textiles, and
more particularly in the field of paper, ceramics, paint and water
treatment.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns the technical sector of
mineral loads, such as notably the paper production field and in
particular paper coating and mass-loading of paper, or the fields
of paint, water treatment such as notably the field of purification
muds, detergency, ceramics, cements or hydraulic binders, public
works, inks and 10 varnishes, gluing of textiles or any type of
industry requiring the use of concentrated pigment suspensions, and
concerns more particularly the fields of paper, water treatment,
paint and ceramics.
[0002] In a more particular manner, the invention concerns a
process for preparation of aqueous suspensions of mineral loads or
pigments with a satisfactory rheology used in the various
abovementioned fields.
BACKGROUND OF THE INVENTION
[0003] To accomplish the industrial applications in the above
fields, it is necessary to produce suspensions of mineral loads,
notably calcium carbonates, with an excellent rheology, i.e. with a
low viscosity during the period of storage to facilitate
manipulating and application of them, and as high as possible a
mineral matter content, in order to reduce the quantity of water
handled.
[0004] During production of these aqueous suspensions of mineral
loads satisfying the abovementioned criteria, some processes lead
to weakly concentrated aqueous suspensions of mineral or organic
matter.
[0005] These suspensions must then be concentrated to offer them to
the end user who use the aqueous suspensions or to eliminate the
solvents present when these loads are used in a powder form.
[0006] One of the means known currently is to concentrate these
suspensions by a filtration process, but these filtrations have
until the present day led to cakes which are so compact that it is
necessary firstly to add the dispersant after the filtration stage
and secondly to use a high mechanical energy to return them to
suspension or convey the concentrated suspensions.
[0007] Thus, patent application WO 00/39029 teaches those skilled
in the art that a process to prepare an aqueous suspension of
calcium carbonate consists in following the filtration stage with a
thermal concentration stage and then with a stage of use of
mechanical energy to return the mineral particles to suspension,
with the addition of dispersant after the filtration stage.
[0008] Thus, the filtering of suspensions not containing any
dispersant is known (Solid-liquid filtration and separation
technology, A. Rushton, A. S. Ward, R. G. Holdich, 1996;
Filtration: Equipment selection Modelling and process simulation,
R. J. Wakeman, E. S. Tarleton, 1999; Practice of filtration, J. P.
Duroudier, 1999), but the disadvantage is that cakes which are
produced are difficult to re-disperse.
[0009] A process involving the introduction, into an aqueous
suspension of calcium carbonate, of half the quantity of dispersant
before filtering the said suspension, and the addition of the other
half after the filtration stage, is also known (JP 53-025646) in
order to obtain a highly concentrated suspension of calcium
carbonate.
[0010] Those skilled in the art are also familiar with another
document (GB 1 482 258) which reveals a process for the preparation
of aqueous suspensions of precipitated calcium carbonate (PCC)
using a dispersant before the stage of concentration by a
filtration in a single stage, but this process has two major
disadvantages.
[0011] The first consists of the need to use a pressure of over 17
bars to be able to filter and of the obligation to use very
particular dispersive facilities to disperse the cake obtained.
[0012] The second disadvantage of the said method lies in the fact
that large quantities of dispersant are found in the filtrate,
which generates environmental and ecological problems, and
industrial wastes treatment problems or problems of recirculation
of the water used in the remainder of the process, and which also
generates cost problems given the large quantities of dispersant
used.
[0013] Similarly, patent GB 1 463 974 describes a method for
filtration in a single stage leading to the same disadvantages as
those mentioned above.
[0014] Thus, the techniques known to those skilled in the art lead
them to use the dispersant agent either in full after the
filtration, or half before the filtration stage and the other half
after the filtration stage, or again in using the dispersant agent
before the filtration stage but with the need to use firstly a
large quantity of dispersant agent generating the abovementioned
disadvantages, and secondly a very particular dispersive
facility.
[0015] Generally, all these techniques known on today's date have
the disadvantage that they result in great difficulty in returning
the cake to suspension if it is desired to obtain highly
concentrated suspensions of dry matter having a satisfactory
rheology.
SUMMARY OF THE INVENTION
[0016] Thus, one of the aims of the invention is to offer a process
for preparing aqueous suspensions of loads and/or mineral pigments
with a satisfactory rheology, i.e. to offer a process for preparing
fluid aqueous suspensions of mineral matter, which are able to be
pumped and able to be conveyed by the end user immediately after
the filtration stage, possibly followed by a compression, using
small quantities of dispersant, and allowing a check of the
quantities of dispersant present in the filtrate with a view to
obtaining near-zero quantities of dispersant present in the
filtrate.
[0017] Near-zero quantities of dispersant present in the filtrate
means that the end of the second stage corresponds to the
appearance of the dispersant in the filtrate. This appearance of
dispersant in the filtrate is quantified by a measurement of
electrical conductivity.
[0018] This process of preparing, as claimed in the invention,
aqueous suspensions of fluid mineral matter, able to be pumped and
able to be conveyed by the end user immediately after the
filtration stage, with small quantities of dispersant used, and
allowing control of the quantities of dispersant present in the
filtrate, is characterised by the fact that it comprises a
filtration in two separate stages, possibly followed by a
compression.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 shows a diagram of the filtration process conducted
in two stages.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In a more particular manner, these two separate stages of
filtration consist of a first stage in which a pre-layer is formed
using no dispersant agent, followed by a second stage continuous
with the first in the presence of one or more dispersant agents,
and in an even more particular manner followed by a second
filtration stage containing 0.01% to 10%, preferentially 0.1% to 2%
by dry weight of dispersant relative to the dry weight of the
mineral matter to be filtered.
[0021] When this pre-layer has been formed, the water of the
pre-layer is replaced, in the second stage, by the water of the
second stage containing one or more dispersant agents such that the
dispersant or dispersants are spread uniformly throughout the whole
of the filtration cake.
[0022] It should be noted that during the entire filtration period
the pressure applied has a value of around that commonly used in
the traditional filtration processes. In an even more particular
manner, this process as claimed in the invention is characterised
in that the quantity of dispersant agent present in the filtrate is
controlled and limited by a continuous measurement of electrical
conductivity of the filtrate and in that the filtration stage is
stopped as soon as the electrical conductivity of the filtrate
increases. This stoppage of filtration at the time when the
electrical conductivity increases corresponds to a near-zero
quantity of dispersant present in the filtrate.
[0023] Thus, the process as claimed in the invention enables
aqueous suspensions of fluid mineral matter to be obtained
directly, which are able to be pumped and able to be conveyed
immediately after the filtration stage, possibly followed by a
compression, using small quantities of dispersant and with
near-zero quantities of dispersant present in the filtrate.
[0024] To do so, the dispersant agent or agents used are chosen
either from the dispersants commonly used in the field of
suspension of mineral loads such as, for example, polyphosphates,
polyacrylates, whether functionalised or not, or any other polymer
with a dispersant function, or from the anionic, cationic,
non-ionic or zwitterionic surface active agents.
[0025] The process of preparing aqueous suspensions of mineral
matter as claimed in the invention is characterised in that the
mineral matter may be chosen from natural calcium carbonate
including notably the various chalks, calcites or marbles, or
chosen from the synthetic calcium carbonates such as precipitated
calcium carbonates at different stages of crystallisation, or from
the mixed magnesium and calcium carbonates such as dolomites, or
from magnesium carbonate, zinc carbonate, lime, magnesia, barium
sulphate such as barita, calcium sulphate, silica, the
magnesio-silicates such as talc, wollastonite, clays and other
alumino-silicates such as kaolins, mica, metal or alkaline earth
oxides or hydroxides such as magnesium hydroxide, iron oxides, zinc
oxides, titanium oxides, titanium dioxides in its anatase or rutile
forms, and mixtures of them such as, notably, mixtures of talc and
calcium carbonate.
[0026] Preferentially, the mineral matter is chosen from natural
calcium carbonate, synthetic calcium carbonate also called
precipitated calcium carbonate, titanium dioxide in its anatase or
rutile forms, kaolin, aluminium hydroxide, clays or their
mixtures.
[0027] An additional aim of the invention is to develop an aqueous
suspension of mineral matter which is fluid, able to be pumped and
conveyed by the end user immediately after the filtration stage,
possibly followed by a compression.
[0028] This aqueous suspension of mineral matter as claimed in the
invention is characterised in that it contains 0.01% to 10%,
preferentially 0.1% to 2% by dry weight of dispersant relative to
the dry weight of mineral matter to be filtered, and in that it is
obtained by the process as claimed in the invention.
[0029] In a more particular manner, it is characterised in that the
mineral matter may be chosen from among natural calcium carbonate,
including notably the various chalks, calcites, marbles or again
chosen from the synthetic calcium carbonates such as precipitated
calcium carbonates at different stages of crystallisation, or again
from the mixed carbonates of magnesium and calcium such as the
dolomites, or from magnesium carbonate, zinc carbonate, lime,
magnesia, barium sulphate such as harita, calcium sulphate, silica,
magnesio-silicates such as talc, wollastonite, clays and other
alumino-silicates such as kaolins, mica, metal or alkaline-earth
oxides or hydroxides such as magnesium hydroxide, iron oxides, zinc
oxides, titanium oxides, titanium dioxides in its anatase or ruble
loans, and mixtures of them such as, notably, mixtures of talc and
calcium carbonate.
[0030] Finally, another aim of the invention concerns the use of
aqueous suspensions as claimed in the invention in the fields of
paper, paint, water treatment such a notably the field of
purification muds, detergency, ceramics, cements or hydraulic
binders, public works, inks and varnishes, gluing of textiles or
any type of industry requiring the use of concentrated pigment
suspensions, and concerns more particularly the use of aqueous
suspensions as claimed in the invention in the fields of paper,
water treatment, paint and ceramics.
[0031] The scope and interest of the invention will be better
perceived thanks to the following examples which cannot be
restrictive.
EXAMPLE 1
[0032] This example illustrates the invention and concerns the
filtration of an aqueous suspension of natural calcium carbonate
and more particularly of a Champagne chalk of median diameter 2
micrometers.
[0033] To accomplish this, 286.8 grams of the chalk suspension is
used with a dry matter concentration equal to 20.3% and, as
filtration equipment, an item of laboratory equipment of the
company CHOQUENET consisting: [0034] of a polypropylene frame with
a chamber 2.2 cm wide and with a section of 25 cm [0035] of two
steel plates, one of which fixed, with flutes on the inner face, by
which the filtrate is collected, [0036] of two joints which provide
sealing between the plates and the frame, [0037] of two
polypropylene filtrating membranes from the company SEFAR FYLTIS
(ref.: F 0149 AN)
[0038] The filtration chamber (CF) can be supplied successively by
a tank R1 containing the suspension of the pigment to be
concentrated, and then by a second tank R2 containing the same
suspension as before, to which will be added a quantity of
dispersant Co required to obtain a concentrated cake (ES.sub.2),
and which can easily be removed, i.e. a cake with a sufficient
consistency to be removed from the filtration chamber in a single
element. Another alternative consists in R2 containing only a
dispersant solution.
[0039] The filtration process proper is conducted in two separate
stages (see diagram 1): [0040] 1/during a first stage, a pre-layer
from suspension 1 is formed on the filtrating membranes, [0041]
2/followed by a second stage, in which filtration is undertaken
from suspension 2 containing the dispersant.
[0042] In the second stage, the water contained in the pre-layer is
replaced by water loaded with dispersant contained in suspension 2,
such that at the end of the filtration stage the dispersant is
spread uniformly throughout the entire filtration cake.
[0043] Each of the filtration stages is undertaken under a 5 bar
pressure.
[0044] The filtration stage is followed by a compression stage
under a pressure of 15 bars, and enables a filtration cake of
dryness ES.sub.2 to be obtained.
[0045] The filtration cake is then subjected to a weak shearing to
obtain a suspension also called fluid "slurry".
[0046] This stage is undertaken using a standard laboratory
mechanical agitator of type RAYNERI filled with an adapted
blade.
[0047] When the suspension is homogeneous, we measure its viscosity
(visco 2) using a Brookfield.sup.T''' viscometer of the RVT type
fitted with an adapted module.
[0048] The suspension as claimed in the invention, obtained by the
process as claimed in the invention described above and using 0.2%
by dry weight, relative to the dry weight of dry chalk, of an
ammonium polyacrylate of molecular weight by weight equal to 4,500
g/mole, is then an aqueous suspension of chalk with a dry matter
concentration of 76.8% and a Brookfield.TM. viscosity of 2,900 mPas
measured at 10 revolutions per minute and of 518 mPas measured at
100 revolutions per minute.
[0049] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 170.6 grams of filtrate. The content of
dispersant in the filtrate is then near-zero.
[0050] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the 40 end user immediately after the filtration
stage.
[0051] After 8 days' storage of the suspension as claimed in the
invention, a new measurement of Brookfield.TM. viscosity is taken
after agitating the flask containing the said suspension. A
Brookfield.TM. viscosity is then obtained of 3,770 mPas measured at
10 revolutions per minute and of 645 mPas measured at 100
revolutions per minute, showing that the suspension obtained is
fluid, and able to be pumped and conveyed, even after eight days'
storage.
EXAMPLE 2
[0052] This example illustrates the invention and concerns the
filtration of an aqueous suspension of natural calcium carbonate
and more particularly of a marble of median diameter of 0.75
micrometer.
[0053] To accomplish this, with the same operating method and the
same equipment as in example 1, firstly 173.2 grams of the aqueous
suspension of marble is used, the dry matter concentration of which
is 27.6% and secondly 0.5% by dry weight, relative to the dry
weight of marble, of a sodium polyacrylate called Coatex DV 834, to
obtain directly an aqueous suspension of marble the dry matter
concentration of which is 72.1%, and the Brookfield.TM. viscosity
of which is 635 mPas measured at 10 revolutions per minute and 240
mPas measured at 100 revolutions per minute.
[0054] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 114.5 grams of filtrate. The dispersant
content in the filtrate is near-zero.
[0055] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
[0056] After storage of 8 days of the suspension as claimed in the
invention, a new Brookfield.TM. viscosity measurement is undertaken
after agitating the flask containing the said suspension. A
Brookfield'''' viscosity is then obtained of 1,930 mPas measured at
10 revolutions per minute and of 550 mPas measured at 100
revolutions per minute, showing that the suspension obtained is
fluid, and able to be pumped and conveyed, even after eight days'
storage.
EXAMPLE 3
[0057] This example illustrates the invention and concerns the
filtration of an aqueous suspension of precipitated calcium
carbonate (PCC) of median diameter 0.9 micrometer.
[0058] To accomplish this, with the same operating method and the
same equipment as in example 1, firstly 156 grams of the aqueous
suspension of PCC is used, the dry matter concentration of which is
24% and moreover 1.0% by dry weight, relative to the dry weight of
PCC, of a sodium polyacrylate of molecular weight by weight equal
to 10,000 g/mole, to obtain directly an aqueous suspension of PCC
the dry matter concentration of which is 65.9% and the
Brookfield.TM. viscosity of which is 4570 mPas measured at 10
revolutions per minute and 930 mPas measured at 100 revolutions per
minute.
[0059] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 123.7 grams of filtrate. The dispersant
content in the filtrate is then near-zero.
[0060] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
EXAMPLE 4
[0061] This example illustrates the invention and concerns the
filtration of an aqueous 15 suspension of natural calcium carbonate
and more particularly of a marble of median diameter 0.6
micrometer.
[0062] To accomplish this, with the same operating method and the
same equipment as in example 1, firstly 226.4 grams of the aqueous
suspension of marble is used, the dry matter concentration of which
is 20.9%, and moreover 1.0% by dry weight, relative to the dry
weight of marble, of a sodium polyacrylate called Coatex DV 834, to
obtain directly an aqueous suspension of marble the dry matter
concentration of which is 70.0%, and the Brookfield.TM. viscosity
of which is 1,500 mPas measured at 10 revolutions per minute and
670 mPas measured at 100 revolutions per minute.
[0063] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 177.7 grams of filtrate. The content of
dispersant in the filtrate is then near-zero.
[0064] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
[0065] After 8 days' storage of the suspension as claimed in the
invention, a new measurement of the Brookfield' viscosity is taken
after agitating the flask containing the said suspension. A
Brookfield'''' viscosity is then obtained of 1,840 mPas measured at
10 revolutions per minute and of 750 mPas measured at 100
revolutions per minute, showing that the suspension obtained is
fluid, and able to be pumped and conveyed, even after eight days'
storage.
EXAMPLE 5
[0066] This example illustrates the invention and concerns the
filtration of an aqueous suspension of titanium dioxide sold by the
company Elementis under the name RHD2.
[0067] To accomplish this, with the same operating method and the
same equipment as in example 1, firstly 390.9 grams of the aqueous
suspension of titanium dioxide is used, the dry matter
concentration of which is 24.2%, and moreover 0.3% by dry weight,
relative to the dry weight of titanium dioxide, of a copolymer sold
by the company Coatex under the name Coatex BR3, to obtain directly
an aqueous suspension of titanium dioxide, the dry matter
concentration of which is 74.2%, and the Brookfield.TM. viscosity
of which is 1,100 mPas measured at 10 revolutions per minute and
460 mPas measured at 100 revolutions per minute.
[0068] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 288.5 grams of filtrate. The dispersant
content in the filtrate is then near-zero.
[0069] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
[0070] It is also advantageously used in the paint field.
EXAMPLE 6
[0071] This example illustrates the invention and concerns the
filtration of an aqueous suspension of kaolin sold by the company
Imerys under the name SPS.
[0072] To accomplish this, with the same operating method and the
same equipment as in example 1 are used, firstly 229.1 grams of the
aqueous suspension of kaolin is used, the dry matter concentration
of which is 23.9%, and moreover 0.2% by dry weight, relative to the
dry weight of kaolin, of a sodium polyacrylate of molecular weight
by weight equal to 4,500 g/mole, to obtain directly an aqueous
solution of kaolin the dry matter concentration of which is 68.0%,
and the Brookfield.TM. viscosity of which is 1,590 mPas measured at
10 revolutions per minute and 655 mPas measured at 100 revolutions
per minute.
[0073] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 167.7 grams of filtrate. The dispersant
content in the filtrate is then near-zero.
[0074] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
EXAMPLE 7
[0075] This example illustrates the invention and concerns the
filtration of an aqueous solution of aluminium hydroxide sold by
the company Martinswerk under the name 50L 104.
[0076] To accomplish this, with the same operating method and the
same equipment as in example 1, firstly 201.0 grams of the aqueous
suspension of aluminium hydroxide is used, the dry matter
concentration of which is 25.3%, and moreover 0.25% by dry weight,
relative to the dry weight of aluminium hydroxide, of a copolymer
of molecular weight by weight equal to 3,500 g/mole, and consisting
of acrylic acid and of methoxy-polyethylene glycol methacrylate of
molecular weight 2,000, having been completely neutralised using
soda, to obtain directly an aqueous suspension of aluminium
hydroxide, the dry matter concentration of which is 71.8%, and the
Brookfield.TM. viscosity of which is 230 mPas measured at 10
revolutions per minute and 230 mPas measured at 100 revolutions per
minute.
[0077] The filtration stage is stopped when the electrical
conductivity of the filtrate measured using an HI 8820N
conductivity meter from Hanna Instruments (Portugal) increases,
i.e. after having collected 144.2 grams of filtrate. The dispersant
content in the filtrate is then near-zero.
[0078] The suspension thus obtained is fluid, and able to be pumped
and conveyed by the end user immediately after the filtration
stage.
EXAMPLE 8
[0079] This example concerns the use of an aqueous solution of
mineral load as claimed in the invention in the paper field, and
more particularly concerns the measurement of the optical
properties of the suspension of example 4 obtained as claimed in
the invention, and more particularly the determination of the value
of the capacity for diffusion of the visible light of the aqueous
suspension of example 4, together with the intrinsic brilliancy
values of the pigment obtained by filtration.
[0080] This capacity for diffusion of visible light is expressed by
a light scattering factor S which is the Kubelka-Munk factor for
diffusion of light, determined by the method well known to those
skilled in the art described in the publications of Kubelka and
Munk (Zeitschrift fur Technische Physik 12, 539, (1931)), of
Kubelka (J. Optical Soc. Am. 38(5), 448, (1948) and J. Optical Soc.
Am. 44(4), 330, (1954)).
[0081] To accomplish this, a sheet of synthetic paper sold by the
company Arjo Wiggins Teape under the name Synteape is used.
[0082] Before being coated using a coating machine of the Hand
Coater model KC202 type, this sheet of paper of dimension 26
cm.times.18 cm, and of specific weight 60 to 65 g/m.sup.2, is
weighed and then subjected to a light radiation of wavelength 457
nm on a black plate using an Elrepho.TM. 3000 spectrophotometer
from Datacolor (Switzerland) to determine the reflectance factor
R.sub.b of the uncoated paper on a black background.
[0083] The suspension for testing, formulated with a binder (12
parts styrene-acrylic binder (Acronal S360D) for 100 g dry weight
of mineral load for testing) is then applied on this pre-weighed
paper sheet using a coating machine of the Hand Coater model KC202
type.
[0084] The sheet of paper thus coated with different layer weights
of between 5 and 50 g/m.sup.2 is then subjected to light radiation
of wavelength 457 nm using an Elrepho.TM. 3000 spectrophotometer
from Datacolor (Switzerland) on a black plate to determine the
reflectance factor of the paper on a black background R.sub.o and
on a pile of at least 10 non-coated sheets of paper to determine
the reflectance factor of the coated papers on a white background
R.sub.1, where r is the reflectance factor of the pile of uncoated
sheets of paper.
[0085] The reflectance factor R.sub.sc of the layer alone, on a
black background, is then determined using the following
formula:
R sc = R 1 R b R o r ( R 1 - R o ) rR b + R b - r ( 1 )
##EQU00001##
together with the transmission T.sub.sc of the layer
T sc 2 = ( R o - R sc ) ( 1 - R sc R b ) R b ( 2 ) ##EQU00002##
[0086] From these two quantities it is possible to calculate a
theoretical reflectance value R.sub.oo for a layer of infinite
thickness given by the following formula:
1 - T sc 2 + R sc 2 R c = 1 + R oo 2 R oo ( 3 ) ##EQU00003##
[0087] Thus, from this formula the light scattering factor S of the
pigment under study may be calculated for each layer weight, given
that, for a layer weight P,
45 S . P . = 1 b coth - 1 ( 1 - aR sc ) bR sc where a = 0.5 ( 1 R
oo + R oo ) and b = 0.5 ( 1 R oo - R oo ) ##EQU00004##
[0088] This light scattering factor S is traced according to the
layer weight and the value S for a layer weight of 20 g/m.sup.2 is
determined by interpolation.
[0089] In the present case the value S obtained is 157 m.sup.2/g
and is entirely comparable to the values obtained for suspensions
of calcium carbonate of the prior art obtained according to the
traditional means of thermal concentration.
[0090] In addition, the 75.degree. C. TAPPI brilliancy of the sheet
of paper previously coated is determined before calendering by
passing the coated paper into the Lehmann.TM. laboratory
glossmeter. For paper coated using the coating color containing the
aqueous suspension of calcium carbonate of example 4a 75.degree. C.
TAPPI brilliancy of 63.5 is obtained.
[0091] The coated paper is also calendered using a
super-calendering machine with 9 areas of contact between the two
rollers, sold by Kleinewefers.
[0092] The 75.degree. C. TAPPI brilliancy is then 69.3.
* * * * *