U.S. patent application number 10/123425 was filed with the patent office on 2002-11-07 for process for preparing precipitated calcium carbonates.
This patent application is currently assigned to Solvay Soda Deutschland GmbH. Invention is credited to Dillenburg, Helmut, Kinnen, Andreas, Nover, Christoph, Schinninger, Kurt.
Application Number | 20020164280 10/123425 |
Document ID | / |
Family ID | 7893535 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020164280 |
Kind Code |
A1 |
Kinnen, Andreas ; et
al. |
November 7, 2002 |
Process for preparing precipitated calcium carbonates
Abstract
A process for the preparation of precipitated calcium carbonate
by introducing CO.sub.2 into milk of lime, in which the milk of
lime is first ground, and then the CO.sub.2 is introduced to
precipitate the calcium carbonate.
Inventors: |
Kinnen, Andreas; (Xanten,
DE) ; Dillenburg, Helmut; (Rheinberg, DE) ;
Schinninger, Kurt; (Hallein, AT) ; Nover,
Christoph; (Rheinberg, DE) |
Correspondence
Address: |
CROWELL & MORING, LLP
Intellectual Property Group
P.O. Box 14300
Washington
DC
20044-4300
US
|
Assignee: |
Solvay Soda Deutschland
GmbH
|
Family ID: |
7893535 |
Appl. No.: |
10/123425 |
Filed: |
April 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10123425 |
Apr 17, 2002 |
|
|
|
09476111 |
Jan 3, 2000 |
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Current U.S.
Class: |
423/432 |
Current CPC
Class: |
C01F 11/181 20130101;
Y02P 20/141 20151101 |
Class at
Publication: |
423/432 |
International
Class: |
C01F 011/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 2, 1999 |
DE |
199 00 021.2 |
Claims
What is claimed is:
1. A process for the preparation of precipitated calcium carbonate
with reproducible application-related properties, said method
comprising the steps of: subjecting milk of lime to specific
grinding treatment to obtain ground milk of lime, and thereafter
introducing CO.sub.2 into the ground milk of lime to precipitate
the calcium carbonate.
2. A process for the preparation of precipitated calcium carbonate
according to claim 1, further comprising the steps of: continuously
measuring the viscosity of the milk of lime during the specific
grinding treatment, and controlling the grinding in response to the
measured viscosity to regulate the quality of the ground milk of
lime.
3. A process for the preparation of precipitated calcium carbonate
according to claim 1, wherein the specific grinding is controlled
to produce ground milk of lime having a viscosity of at most 2500
mPas.
4. A process for the preparation of precipitated calcium carbonate
according to claim 2, wherein the specific grinding is controlled
to produce ground milk of lime having a viscosity of at most 2500
mPas.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a process for the preparation of
precipitated calcium carbonate which is suitable as a functional
filler and is distinguished by defined properties. One typical
field of application is the use of the precipitated calcium
carbonate as a filler in plastisols, such as underbody sealants for
automobiles.
[0002] The precipitated calcium carbonate in this case is capable
of controlling the flow behavior of the plastisols. Thus, by using
the calcium carbonates which are suitable in each case, plastisols
having very differing flow behaviors can be prepared. Depending on
the intended application, high, medium or low flow limits may be
desired. The flow limit according to Bingham in the plasticiser
mixture is usually quoted as a typical characteristic for the
application-related suitability of calcium carbonates as fillers.
The ability of the precipitated calcium carbonate to control the
flow limits is influenced, inter alia, by the nature of the burnt
lime used for producing the milk of lime and by the slaking
operation.
[0003] Finely dispersed calcium carbonate is either prepared from
naturally-occurring raw materials by mechanical preparation, or
chemically, e.g. by precipitation.
[0004] Usually, precipitated calcium carbonate is prepared by
introducing CO.sub.2 into milk of lime
Ca(OH).sub.2+CO.sub.2.fwdarw.CaCO.sub.3+H.sub.2O
[0005] The properties of the precipitated calcium carbonate depend,
for example, on the chemical composition of the limestone used or
on the burning conditions.
[0006] Preferably so-called soft-burned lime is used to prepare
precipitated calcium carbonate. To this end, limestone is burned at
a temperature of 1000 to 1250.degree. C.
[0007] Among other characteristics, the ability of burnt lime to
react with water is used to characterize it. The so-called VEC
value (Vlocit d'Extinction de Chaux) is measured. In this case, the
heating rate of a defined water/burnt lime mixture is measured.
Typical VEC values for burnt lime which is suitable for the
preparation of precipitated calcium carbonate are above 3.degree.
C./min.
[0008] To prepare the milk of lime, the burnt lime is reacted with
water, for example in a slaking drum, whereupon a Ca(OH).sub.2
suspension, so-called milk of lime, forms. The milk of lime usually
has a solids content of 70 to 220 g/liter Ca(OH).sub.2, a viscosity
of 30 to 1500 mPas and an average particle diameter of less than 50
.mu.m.
[0009] Milk of lime is used, for example, to neutralize waste
water, or to prepare soda or precipitated calcium carbonate.
[0010] One drawback of the previously known processes for preparing
precipitated calcium carbonate is that it has hitherto not been
possible to satisfactorily control the application-related
properties of the precipitated calcium carbonate, in particular as
a rheological additive, due to its average grain size, grain size
distribution and particle form.
[0011] U.S. Pat. No. 3,920,800 describes a process for the
preparation of precipitated calcium carbonate of high purity.
According to the method described, an aqueous calcium hydroxide
slurry (milk of lime) is ground in the presence of CO.sub.2 at a
temperature of at most 100.degree. C. The calcium carbonate formed
by the reaction of the calcium hydroxide with the CO.sub.2 is free
of calcium hydroxide. The particle size of the calcium carbonate is
controlled by means of the temperature during the grinding process.
At temperatures of approximately 30.degree. C., very small
particles are obtained, and at temperatures of approximately
80.degree. C. larger calcium carbonate particles are obtained.
SUMMARY OF THE INVENTION
[0012] It is the object of the invention to provide a process for
preparing precipitated calcium carbonate (CCP) having defined,
reproducible properties.
[0013] This and other objects are achieved in accordance with the
invention in that the milk of lime is ground before the CO.sub.2 is
introduced to precipitate the calcium carbonate.
[0014] Known mills may be used for grinding the milk of lime.
Preferably bead mills are used. Suitable grinding beads include, in
particular, zirconium oxide grinding beads having a diameter of 0.4
to 2 mm.
[0015] The grinding result is greatly influenced by the fineness of
the beads.
[0016] The grinding effect is furthermore controlled by the speed
of the mill, the residence time of the milk of lime in the mill and
the resulting specific energy input.
[0017] The average particle size of the Ca(OH).sub.2 particles in
the milk of lime or the viscosity of the milk of lime can also be
measured as a measured parameter indicating the success of
grinding.
[0018] The course of the wet grinding can also be followed by
measuring the grain distribution of the calcium hydroxide or by
measuring the viscosity of the milk of lime at a defined
concentration and temperature.
[0019] According to the invention, the viscosity of the milk of
lime is measured and used to control the mill. The viscosity should
be measured without difficulty, e.g. continuously, and the mill
throughput or the speed of the mill, and hence the resulting
quality of the milk of lime, can be controlled automatically by
means of a corresponding control circuit.
[0020] In one embodiment of the invention, the milk of lime is
ground to a viscosity of at most 2500 mPas. A higher viscosity
should be avoided, since otherwise the introduction of the
precipitating gas is not optimally possible.
[0021] Therefore, for the purposes of the invention, the viscosity
of the ground milk of lime should be set such that the milk of lime
can flow readily, so that the precipitating gas can be dispersed
homogeneously. The grinding furthermore makes it possible to adjust
the viscosity of the milk of lime such that calcium carbonate with
application-related properties which are desired in each case, in
particular as a rheological additive, can be prepared. Thus,
depending on the intended purpose, CaCO.sub.3 can be prepared in a
consistent quality which is suitable as a high functionality
constituent of mixtures for e.g. polymers, polymer preparations,
plastics, coating compounds, sealing compounds, paper or paints, in
particular printing inks.
[0022] After grinding, the milk of lime is supplied to a container
into which CO.sub.2 is introduced to precipitate the calcium
carbonate and is homogeneously dispersed in the milk of lime.
[0023] Surprisingly, it has been discovered that the properties of
the precipitated calcium carbonate can be reproduced if the milk of
lime is first ground, and then CO.sub.2 is introduced to
precipitate the calcium carbonate.
[0024] If precipitated calcium carbonate from non-ground milk of
lime is compared with that from ground milk of lime, it is apparent
that the grinding has an influence on the reaction rate, on the
average particle diameter of the CCP and on the use-related
properties of the CCP.
[0025] It has been discovered that a decreasing particle size in
the milk of lime also involves a reduction in the average particle
diameter of the CCP.
[0026] It has furthermore been discovered that the precipitation
time is decreased by about 20% by using the milk of lime ground
according to the invention.
[0027] The viscosity-controlled wet grinding of the milk of lime
according to the invention makes it possible to significantly
influence the flow limit of the CCP-filled plastisols, i.e. to
adjust them specifically. It has been found that the flow limit is
a function of the specific energy introduced during grinding, or of
the viscosity of the milk of lime after grinding. It was therefore
discovered that the properties of the CCP can be reproducibly
influenced by specifically adjusting the viscosity of the milk of
lime.
[0028] The undesirable influencing of the properties of the CCP by
undefined fluctuations in the nature of the burnt lime and of the
slaking operation are cancelled out by the grinding of the milk of
lime according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] The following examples are intended to illustrate the
invention in further detail without restricting its scope.
1 Examples 1-6: Burnt lime was slaked in a slaking drum: Lump size
2-5 cm VEC: 4.8.degree. C./min The resulting milk of lime was
ground and characterized: solids content 150 g/liter average
particle diameter D.sub.50: 4.4 .mu.m
[0030] Grinding Conditions:
[0031] horizontal attrition mill
[0032] grinding chamber volume 5 liters
[0033] 22 kW motor power
[0034] grinding bodies:
[0035] spheres of zirconium silicate
[0036] diameter 1.0-1.6 mm
[0037] filled volume: 4.8 liters
[0038] The tests were performed at a constant speed of 1990 rpm.
The residence time of the milk of lime in the mill was varied.
Different specific energy inputs resulted from this.
[0039] Calcium carbonate was produced from the resulting ground
milk of lime by introducing CO.sub.2-containing gas:
2 Precipitation conditions: Precipitation temperature: 18.degree.
C. CO.sub.2 concentration in the 30% by volume precipitating gas:
Gas stream: 1 m.sup.3/hour per 10 liters milk of lime Duration of
precipitation: see table Subsequent treatment: 2% fatty acid
Grinding CCP precipitation CCP Specific energy Milk of lime
Duration of CCP particle (kWh/t) relative Viscosity Milk of lime
precipitation diameter Example to dry product (mPas) D50 (.mu.m)
(min) dp (nm) 1 0 45 4.4 98 70 2 23 50 4.4 94 71 3 31 105 3.2 92 66
4 113 135 2.8 83 62 5 254 860 2.1 79 63 6 307 1120 1.8 77 61
[0040] It is apparent that the viscosity of the milk of lime and
the average particle diameter of the milk of lime can be controlled
specifically by the wet grinding. This means that the duration of
precipitation of CCP can be reduced to 20%. The particle diameters
of CCP are reproducibly adjusted.
3 Examples 7-12: Preparation of an underbody sealant: Plasticiser,
dioctyl phthalate 55 g Plasticiser, diisononyl phthalate 60 g
paste-making PVC, Solvic 374 MIB 70 g paste-making PVC, Solvic 266
SF 30 g CaCO.sub.3, in accordance with Examples 1-6, 70.0 g
respectively, coated with fatty acid UV-stabilizer, IRGASTAB 17 MOK
2.0 g Adhesion promoter, Euretek 505 4.0 g Drying agent, calcium
oxide 5.0 g Example Flow limit (Pa) 7 40 8 48 9 80 10 89 11 157 12
200
[0041] CCP from Examples 1-6, respectively, was used in each case
to produce underbody sealants corresponding to the formulation
described. It becomes clear that the flow limit of the CCP-filled
plastisol can also be specifically controlled by wet grinding the
milk of lime.
4 Example 13: Preparation of an offset-printing ink Pigment,
flushed, Eurolith Blue 25.0% by weight CaCO.sub.3, in accordance
with Example 4, 15.0% by weight coated with fatty acid Printing
oil, Haltermann, PKWF 4/7 12.0% by weight Binder, Uroset 48.0% by
weight Result Flow limit 31 Pa Viscosity at shear rate 3/sec 9.4
Pas Depth of color C 53 Gloss 60.degree. 71%
[0042]
5 Example 14: Preparation of polyurethane compounds, 2-component
system Polyol, Desmophen 1150 150 g CaCO.sub.3 in accordance with
Example 6, 60 g coated with fatty acid Titanium dioxide pigment
(rutile), 3 g Tiona Rcl-535 Dry paste, Baylith L Paste 15 g
Adhesion promoter, Acronal 700L 1 g Plasticiser, Mesamoll II 35 g
Polyurethane activator 1 g Isocyanate 3 g Result Flow limit
according to Bingham 220 Pa Viscosity at shear rate (100/sec) 6.1
Pas Pot life 26 min Adhesion good Dispersion quality/grindometer
<35 .mu.m
[0043]
6 Example 15: Preparation of silicone compounds For testing, a
non-curing silicone compound was produced which corresponds to a
2-component system, but the catalyst required for curing was not
added. Silicone polymer 60 g CaCO.sub.3 according to Example 2, 38
g coated with fatty acid Plasticizer 2 g Result Flow limit
according to Casson 900 Pa Viscosity at shear rate 5/sec 280 Pas
Dispersion quality/grindometer <35 .mu.m
[0044] The foregoing description and examples have been set forth
merely to illustrate the invention and are not intended to be
limiting. Since modifications of the disclosed embodiments
incorporating the spirit and substance of the invention may occur
to persons skilled in the art, the invention should be construed
broadly to include all variations falling within the scope of the
appended claims and equivalents thereof.
* * * * *