U.S. patent application number 13/293262 was filed with the patent office on 2012-03-08 for process for grinding minerals in aqueous dispersion using a dispersing agent comprising homopolymers and/or copolymers of (meth)acrylic acid.
Invention is credited to Marianne Creamer, Robert Krasnansky, Joseph Manna, Daniele Cristina Santos.
Application Number | 20120059106 13/293262 |
Document ID | / |
Family ID | 40635802 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120059106 |
Kind Code |
A1 |
Creamer; Marianne ; et
al. |
March 8, 2012 |
Process for Grinding Minerals in Aqueous Dispersion Using a
Dispersing Agent Comprising Homopolymers and/or Copolymers of
(Meth)Acrylic Acid
Abstract
The process of the present invention produces an aqueous
dispersion of mineral materials, suitable for use in pigments and
other coatings, by introducing a fully neutralized dispersing agent
to an aqueous dispersion of coarse mineral materials, grinding the
aqueous dispersion and, during grinding, adding a partially
neutralized dispersing agent to the aqueous dispersion. The process
of the present invention produces aqueous dispersions of very fine
particles, having a solids content of at least 75% by weight, based
on the total weight of the aqueous dispersion, and wherein 95% or
more of the particles are below 2 microns.
Inventors: |
Creamer; Marianne;
(Warrington, PA) ; Krasnansky; Robert; (Le Rouret,
FR) ; Manna; Joseph; (Quakertown, PA) ;
Santos; Daniele Cristina; (Jacerei, BR) |
Family ID: |
40635802 |
Appl. No.: |
13/293262 |
Filed: |
November 10, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12454790 |
May 22, 2009 |
8076403 |
|
|
13293262 |
|
|
|
|
Current U.S.
Class: |
524/425 ;
524/447; 524/451; 524/547 |
Current CPC
Class: |
C01P 2006/12 20130101;
C01P 2006/22 20130101; C09C 1/405 20130101; C09C 1/028 20130101;
C01P 2004/61 20130101; C09C 1/3676 20130101; C09C 1/42 20130101;
C01P 2004/51 20130101; C09C 1/402 20130101; C09C 1/40 20130101;
C09C 1/021 20130101; C09C 3/041 20130101 |
Class at
Publication: |
524/425 ;
524/547; 524/447; 524/451 |
International
Class: |
C08K 3/26 20060101
C08K003/26; C08K 3/34 20060101 C08K003/34; C08L 43/02 20060101
C08L043/02 |
Claims
1. A dispersion of particulate mineral solids in a medium
containing water and at least one dispersing agent, wherein the
dispersing agent comprises a water soluble, phosphonate terminated
polymer of acrylic acid with a weight average weight of from 2,000
to 10,000 and wherein 95% or more of the particulate mineral solids
has a particle size of less than 2 micrometers and said dispersion
has a solids content of at least 75% by weight, based on the total
weight of the dispersion.
2. The dispersion of claim 1, wherein said mineral comprises at
least one mineral selected from the group consisting of: calcium
carbonate, aluminum silicate, kaolin, talc, and titanium
oxides.
3. A dispersion of particulate mineral solids in a medium
containing water and at least one dispersing agent, wherein the
dispersing agent comprises a water soluble, phosphonate terminated
polymer of acrylic acid and has the formula: ##STR00003## wherein A
is a polymer derived from units comprising ethylenically
unsaturated monomers; B is a hydrogen, phenyl, C.sub.1-C.sub.6
alkyl, or is a polymer consisting of ethylenically unsaturated
monomers; X is hydrogen, an alkali metal, an alkaline earth metal,
ammonium or an amine residue, wherein the ethylenically unsaturated
monomers are selected from the group consisting of: acrylic acid,
methacrylic acid, maleic acid, maleic anhydride, a sulfonic
unsaturated monomer and an unsaturated polymerizable monomer having
a COOH group, and wherein the at least one dispersing agent
comprises: (a) from 55% to 80% by weight acrylic acid, (b) from 20%
to 45% by weight methacrylic acid, and (c) from 0% to 10% by weight
of at least one monomer selected from the group consisting of:
maleic acid, maleic anhydride, a sulfonic unsaturated monomer and
an unsaturated polymerizable monomer having a COOH group, wherein
the weight percents are based on the total weight of the dispersing
agent and the total of the percentages of components (a), (b) and
(c) does not exceed 100.
4. The dispersion of claim 3, wherein said mineral comprises at
least one mineral selected from the group consisting of: calcium
carbonate, aluminum silicate, kaolin, talc, and titanium
oxides.
5. The dispersion of claim 3, wherein the at least one dispersing
agent comprises: (a) from 55% to 75% by weight acrylic acid, (b)
from 25% to 45% by weight methacrylic acid, and (c) from 0% to 10%
by weight of at least one monomer selected from the group
consisting of: maleic acid, maleic anhydride, a sulfonic
unsaturated monomer and an unsaturated polymerizable monomer having
a COOH group.
6. A process for producing a dispersion of mineral materials
suitable for use as pigments, comprising the steps of: (A)
preparing a mixture comprising water and a mineral to be ground,
comprising particles and said mixture having at least 75% solids
content by weight, based on the total weight of the mixture; (B)
grinding the mixture in the presence of at least one dispersing
agent; and (C) continuing grinding said dispersion until 95% or
more of the mineral particles have a minimum dimension below 2
microns, wherein the at least one dispersing agent is selected from
one or more water soluble, phosphorus-containing polymers having
the formula: ##STR00004## wherein A is a polymer derived from units
comprising ethylenically unsaturated monomers; B is a hydrogen,
phenyl, C.sub.1-C.sub.6 alkyl, or is a polymer consisting of
ethylenically unsaturated monomers; X is hydrogen, an alkali metal,
an alkaline earth metal, ammonium or an amine residue, wherein the
ethylenically unsaturated monomers are selected from the group
consisting of: acrylic acid, methacrylic acid, maleic acid, maleic
anhydride, a sulfonic unsaturated monomer and an unsaturated
polymerizable monomer having a COOH group.
7. The process of claim 6, wherein said mineral comprises at least
one mineral selected from the group consisting of: calcium
carbonate, aluminum silicate, kaolin, talc, and titanium
oxides.
8. The process of claim 6, wherein the at least one dispersing
agent comprises: (a) from 55% to 80% by weight acrylic acid, (b)
from 20% to 45% by weight methacrylic acid, and (c) from 0% to 10%
by weight of at least one monomer selected from the group
consisting of: maleic acid, maleic anhydride, a sulfonic
unsaturated monomer and an unsaturated polymerizable monomer having
a COOH group, wherein the weight percents are based on the total
weight of the dispersing agent and the total of the percentages of
components (a), (b) and (c) does not exceed 100.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for producing
aqueous dispersions of finely ground minerals suitable for use in
pigments by using water soluble phosphinate terminated homopolymers
and/or copolymers of acrylic acid/methacrylic acid as a dispersion
aid during grinding. The present invention also relates to the
dispersions produced by said process.
BACKGROUND OF THE INVENTION
[0002] The use of mineral materials for preparing industrial
products for the paint industry, for coating paper, fillers for
rubbers and synthetic resins etc. is well known and represented in
the prior art. Such mineral materials include, for example, calcium
carbonate, sulphate and silicate, as well as aluminum silicate,
kaolin, talc and titanium oxides. When used as pigments, such as in
paper coatings, solid particles of one or more mineral materials
are suspended in water, along with binding agents, dispersing
agents, thickeners, coloring agents and, possibly, other additives.
Such coatings must have a low viscosity which remains stable
throughout the storage, transport and coating processes to
facilitate handling and application, as well as the highest
possible solids (mineral) content to reduce the amount of heat and
time required to dry the coating material.
[0003] It is difficult to use some mineral materials, such as the
calcium compounds, as pigments because the particles do not
naturally disperse, nor remain dispersed, sufficiently. Such
mineral substances are typically converted to useful form by
grinding into very fine aqueous dispersions in which the
constituent particles are as small as possible, i.e., typically
smaller than a few microns. Moreover, even when such mineral
materials are initially successfully ground and dispersed in an
aqueous dispersion, there is often a tendency for the mineral
solids to form a gel, which increases the viscosity of the
dispersion, sometimes to the point of being useless for the
intended application.
[0004] To enhance dispersion and reduce gel formation in
dispersions of mineral materials, one or more grinding and/or
dispersing agents (hereinafter referred to collectively as
"dispersing agents") are often introduced into the mineral
dispersion before and/or during grinding. For example, it is well
known to use water soluble acrylic polymers and/or copolymers, of
low molecular weight, totally or partially neutralized by various
neutralizing agents, as the dispersing agents. See, e.g., French
Patent Nos. FR2488814 and FR2603042, and European Patent Nos.
EP0100947, EP0127388, EP0129329, EP0542644, EP0100948 and
EP0542643.
[0005] U.S. Pat. No. 4,868,228 discloses grinding agents in aqueous
dispersions of mineral materials, and, in particular, the use of
such grinding agents to produce low viscosity aqueous dispersions
of mineral solids. The grinding agents are described to be acrylic
acid polymers and/or copolymers that are completely neutralized by
at least one neutralizing agent having a monovalent function and at
least one neutralizing agent having a polyvalent function. This
reference teaches that the only fraction of acrylic alkaline
polymers and/or copolymers of which the specific viscosity lies
between 0.3 and 0.8 delivers the maximum required characteristics
of a grinding agent. The resulting aqueous dispersions contain at
least 70% solids and at least 95% of the mineral particles have a
greatest dimension less than 2 microns.
[0006] French Patent No. FR2488814 discloses a process using
acrylic alkaline polymers and/or copolymers for preparing an
aqueous dispersion of mineral substances with a high solids
concentration of very fine mineral particles of which 95% have a
dimension less than 2 microns, and of which 75% at least have a
dimension less than 1 micron, and also having a viscosity much
lower than that previously obtained. FR2488814 also teaches that
the only fraction of acrylic alkaline polymers and/or copolymers of
which the specific viscosity lies between 0.3 and 0.8 delivers the
maximum required characteristics of a grinding agent. However, it
was also observed that the viscosity of the resulting dispersions
was not, in fact, stable over time, and that eight days after
grinding, the viscosity increased by two to five times the
viscosity that had been measured immediately after grinding was
completed.
[0007] U.S. Pat. No. 6,395,813B1 discloses dispersions of solid
particles in water formed by grinding using water soluble
phosphonate-terminated homopolymer and/or copolymer to form
dispersions of fine particles, 70% or more of which are below 2
microns, and 70% or more are below 1 micron. U.S. Pat. No.
6,395,813B1 teaches that such dispersing agents having a weight
average molecular weight of from 2000 to 6000 are especially
preferred.
[0008] It would be advantageous to have a grinding process which
produced a mineral dispersion of low initial viscosity, high solids
content and having minimal viscosity increases (i.e., minimal gel
formation) over time.
SUMMARY OF THE INVENTION
[0009] The present invention provides a process for producing a
dispersion of mineral materials suitable for use as pigments. The
mineral(s) may be calcium carbonate, aluminum silicate, kaolin,
talc, and/or titanium oxides. The process comprises the steps of:
(A) preparing a mixture comprising water and a mineral be ground,
comprising particles and said mixture having at least 75% solids
content by weight, based on the total weight of the mixture; (B)
introducing a fully neutralized dispersing agent into the mixture,
in an amount of from 0.1% to 0.5% by weight, based on the dry
weight of the mineral present in the mixture; (C) grinding the
mixture to produce an aqueous dispersion; (D) introducing into the
dispersion, during grinding, at least two portions of a partially
neutralized dispersing agent, which has been at least 30%
neutralized, based on equivalents of acid groups, wherein the total
of the portions is from 0.2% to 1.0% by weight, based on the dry
weight of the mineral present in the mixture; and (E) continuing
grinding the dispersion until 95% or more of the mineral particles
have a minimum dimension below 2 microns. For example, the
dispersion may be ground for at least 110 minutes.
[0010] Each of the fully neutralized and partially neutralized
dispersing agents is selected from one or more water soluble,
phosphorus-containing polymers having the formula:
##STR00001##
wherein A is a polymer derived from units comprising ethylenically
unsaturated monomers; B is a hydrogen, phenyl, C.sub.1-C.sub.6
alkyl, or is a polymer consisting of ethylenically unsaturated
monomers; X is hydrogen, an alkali metal, an alkaline earth metal,
ammonium or an amine residue, wherein the ethylenically unsaturated
monomers are selected from the group consisting of: acrylic acid,
methacrylic acid, maleic acid, maleic anhydride, a sulfonic
unsaturated monomer and an unsaturated polymerizable monomer having
a COOH group, and wherein each of said fully neutralized and
partially neutralized dispersing agents comprises: (a) from 55% to
80% by weight acrylic acid, (b) from 20% to 45% by weight
methacrylic acid, and (c) from 0% to 10% by weight of at least one
monomer selected from the group consisting of: maleic acid, maleic
anhydride, a sulfonic unsaturated monomer and an unsaturated
polymerizable monomer having a COOH group, wherein the weight
percents are based on the total weight of the dispersing agent and
the total of the percentages of components (a), (b) and (c) does
not exceed 100. The dispersing agents have a molecular weight of
from 2,000 to 10,000, based on (weight/number) average molecular
weight.
[0011] In one embodiment, the at least two portions of a partially
neutralized dispersing agent total from 0.2% to 0.8% by weight,
based on the dry weight of the mineral present in the mixture. For
example without limitation, the at least two portions may comprise
a plurality of portions, a first group of which comprises two
separately introduced portions which total 0.3% by weight of the
partially neutralized dispersing agent and a second group of which
comprises four separately introduced portions which total 0.5% by
weight of partially neutralized dispersing agent, based on the dry
weight of the mineral present in the mixture.
[0012] The present invention also provides a dispersion of
particulate mineral solids in a medium containing water and at
least one dispersing agent, wherein the dispersing agent comprises
a water soluble, phosphonate terminated homopolymer of acrylic acid
with a weight average weight of from 2,000 to 10,000 and wherein
95% or more of the particulate mineral solids has a particle size
of less than 2 micrometers and said dispersion has a solids content
of at least 75% by weight, based on the total weight of the
dispersion.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The process of the present invention produces an aqueous
dispersion of mineral materials, suitable for use in pigments and
other coatings, by introducing a fully neutralized dispersing agent
to an aqueous dispersion of coarse mineral materials, grinding the
aqueous dispersion and, during grinding, adding a partially
neutralized dispersing agent to the aqueous dispersion. The
dispersing agents are water soluble, phosphorous-containing
polymers. The process of the present invention produces aqueous
dispersions of very fine particles, having a solids content of at
least 75% by weight, based on the total weight of the aqueous
dispersion, and wherein 95% or more of the particles are below 2
microns. Such aqueous dispersions are suitable for use in the
fields of coating of paper, as well as those of paint, ceramics,
drilling fluids, fillers for synthetic resins and rubbers,
detergent and any other field using said suspensions such as
notably cements, plasters and other fields of application in the
construction industry.
[0014] Whether fully or partially neutralized, the dispersing
agents are water soluble, phosphorous-containing polymers having
the formula:
##STR00002##
wherein A is a polymer derived from units comprising ethylenically
unsaturated monomers; B is a hydrogen, phenyl, C.sub.1-C.sub.6
alkyl, or is a polymer consisting of ethylenically unsaturated
monomers; X is hydrogen, an alkali metal, an alkaline earth metal,
ammonium or an amine residue. The ethylenically unsaturated
monomers are selected from the group consisting of: acrylic acid,
methacrylic acid, maleic acid, maleic anhydride, a sulfonic
unsaturated monomer and an unsaturated polymerizable monomer having
a COOH group. Each of said fully neutralized and partially
neutralized dispersing agents comprises (a) from 55% to 80% by
weight acrylic acid, (b) from 20% to 45% by weight methacrylic
acid, and (c) from 0% to 10% by weight of at least one monomer
selected from the group consisting of: maleic acid, maleic
anhydride, a sulfonic unsaturated monomer and an unsaturated
polymerizable monomer having a COOH group. The weight percents are
based on the total weight of the dispersing agent and the total of
the percentages of components (a), (b) and (c) does not exceed 100.
For example, in one embodiment, the dispersing agents may comprises
(a) from 55% to 75% by weight acrylic acid, (b) from 25% to 45% by
weight methacrylic acid, and (c) from 0% to 10% by weight of at
least one monomer selected from the group consisting of: maleic
acid, maleic anhydride, a sulfonic unsaturated monomer and an
unsaturated polymerizable monomer having a COOH group.
[0015] The dispersing agents have a weight average molecular weight
of from 2,000 to 10,000, such as from 3,000 to 6,000. Although
stable dispersions with a low viscosity can be obtained with
dispersing agents of a higher molecular weight, there is an
increased tendency for gel formation with polymers of molecular
weight above 6000 which may be disadvantageous in some
applications.
[0016] The acrylic acid polymers and/or copolymers suitable for use
as dispersing agents are produced by polymerization using known
processes, in an aqueous, alcoholic, hydroalcoholic, aromatic or
aliphatic medium, from acrylic acid and at least one of the
following monomers and/or comonomers: methacrylic acid, itaconic
acid, crotonic acid, fumaric acid, maleic acid, isocrotonic acid,
aconitic acid, mesaconic acid, sinapic acid, undecylenic acid,
angelic acid, hydroxyacrylic acid, and also acrolein, acrylamide,
acrylonitrile, esters of acrylic and methacrylic acids and in
particular dimethylaminoethyl methacrylate, the imidazoles,
vinylpyrolidone, vinylcaprolactame, ethylene, propylene,
isobutylene, di-isobutylene, vinyl acetate, styrene,
alphamethylstyrene, and methylvinylketone. Where the dispersing
agent is a co-polymer of acrylic acid, the other monomer is
preferably maleic acid or maleic anhydride, methacrylic acid, or
any unsaturated polymerisable monomers having a COOH group.
Furthermore, the water soluble dispersing agent is preferably a
phosphonate terminated co-polymer of acrylic acid and methacrylic
acid. Such polymers may be made, for example, according to U.S.
Pat. No. 4,046,707, U.S. Pat. No. 5,376,731, U.S. Pat. 5,077,361
and U.S. Pat. No. 5,294,686.
[0017] The polymerization medium may be water, methanol, ethanol,
propanol, isopropanol, the butanols or dimethylformamide,
dimethylsulfoxide, tetrahydrofurane, acetone, methylethylketone,
ethyl acetate, butyl acetate, hexane, heptane, benzene, toluene,
xylene, mercaptoethanol, tert. dodecylmercaptan, thioglycolic acid
and its esters, dodecylmercaptan, acetic acid, tartaric acid,
lactic acid, citric acid, gluconic acid, glucoheptonic acid,
2-mercaptopropionic acid, thiodiethanol, halogenated solvents such
as carbon tetrachloride, chloroform, methylene chloride, methyl
chloride, and the ethers of monopropyleneglycol and
diethyleneglycol.
[0018] The neutralizing agent used to fully or partially neutralize
the acrylic polymer dispersing agent may have a monovalent or
bivalent function, for example, without limitation, sodium
hydroxide or magnesium hydroxide, or it may be a mixture of
monovalently and bivalently functional neutralizing agents.
[0019] The dispersed or suspended solid mineral material may be any
particulate solid which is sufficiently chemically inert to be
dispersed or suspended in an aqueous medium. The particles are
generally inorganic, and substantially insoluble in water. Examples
include, but are not limited to, calcium carbonate, aluminum
carbonate, clays, kaolin, talc and metallic oxides.
[0020] The dispersion medium may be water, or a water-containing
solution. This medium may also contain alcohols, glycols,
surfactants or wetting agents.
[0021] The dispersion produced by the process of the present
invention provides at least two important advantages, namely, a
reduction in viscosity of the dispersion and a reduction in the
tendency of the dispersion to form a gel particularly in fine
particle dispersions. In addition, these benefits are obtained for
systems in which the percentage by weight of the solid particles in
the dispersion is high, for example greater than 70%, such as, for
example, greater than 75%, and the particle size is fairly
uniformly very fine, i.e., 95% or more of the particles are below 2
microns.
[0022] To achieve the aforesaid resulting product, the process of
the present invention involves multiple-step additions of totally
neutralized and successively partially neutralized dispersing agent
polymer dosages (wherein it is at least 30% percent neutralized
base on equivalents, of acid groups) to promote the reduction in
the tendency of dispersion to form gel, lower initial viscosity and
obtain dispersion in which the percentage by weight of solid
mineral particles is at least 75%, based on the total weight of the
dispersion.
[0023] There are various methods for grinding mineral material,
such as, for example, calcium carbonate, disclosed in the
literature. As is understood by persons of ordinary skill in the
art, the grinding typically involves use of a grinding material
comprising very fine particles which is introduced to the aqueous
suspension containing the aqueous medium, the mineral material to
be ground and the dispersing agent. For example, the grinding
material may have grain size between 0.20 millimeters ("mm") and 4
mm. The grinding material is generally is generally made of
materials such as silicon oxide, aluminum oxide, zirconium oxide or
mixtures of these or synthetic resins of great hardness, steels,
etc. However, the apparatus and particular method of physically
grinding the aqueous dispersion is not limited in accordance with
the process of the present invention.
[0024] The time necessary to reach satisfactory fine-ness of
mineral after grinding varies according to the nature and amount of
mineral to be ground, grinder material hardness and size (aluminum
oxide, zirconium oxide are preferred), process of stirring used,
temperature, amount of dispersing agent and their addition rate and
finally the degree of neutralization during the process.
[0025] The process of the present invention, as well as the aqueous
dispersion produced thereby, will be further clarified by the
following information and examples.
EXAMPLES
TABLE-US-00001 [0026] TABLE 1 Dispersing agent compositions used in
the following examples Chain Regulator/ Composition Initiator used
to make % Dispersing Agent (weight %)* dispersing agent Solids pH
MW.sub.w Commercially Available A 100 AA Isopropanol/Sodium 43.5
7.0 7000 initiator B 100 AA Isopropanol/Persulfate 45.0 4.0 7000
initiator C 100 AA Isopropanol/Persulfate 45.0 7.0 7036 initiator
Homopolymers 1 100 AA Sodium metabisulfite/ 49.22 3.98 3151 Sodium
Persulfate 2 100 AA Sodium Hypophosphite/ 49.93 4.21 3234 Sodium
Persulfate 3 100 AA Phosphorous Acid/ 47.96 5.62 3437 Sodium
Persulfate Copolymers 4 AA/MAA//70/30 Sodium Hypophosphite/ 47.70
4.26 3406 Sodium Persulfate 5 AA/MAA//70/30 Sodium Hypophosphite/
49.82 4.02 3866 Sodium Persulfate 6 AA/MAA//70/30 Sodium
Hypophosphite/ 47.89 4.3 4793 Sodium Persulfate 7 AA/MAA//75/25
Sodium Hypophosphite/ 46.93 4.25 3433 Sodium Persulfate 8
AA/MAA//75/25 Sodium Hypophosphite/ 46.53 4.05 3971 Sodium
Persulfate 9 AA/MAA//75/25 Sodium Hypophosphite/ 46.69 4.26 4789
Sodium Persulfate 10 AA/MAA//65/35 Sodium Hypophosphite/ 46.33 4.29
3495 Sodium Persulfate 11 AA/MAA//65/35 Sodium Hypophosphite/ 47.18
4.33 3879 Sodium Persulfate 12 AA/MAA//65/35 Sodium Hypophosphite/
47.26 4.27 4623 Sodium Persulfate *Abbreviations are as follows: AA
= acrylic acid, and MAA = methacrylic acid.
[0027] Dispersing agents A, B and C were prepared using a method
well known to those skilled in the art using a persulfate initiator
and isopropyl alcohol (IPA) as the chain transfer agent. Dispersing
agents 2 and from 4 to 12, inclusive, were prepared using sodium
hypophosphite (NaHP) as the chain transfer agent. Dispersing agent
1 was prepared using sodium metabisulphite (SMBS) and dispersing
agent 3 is phosphonate containing polymer of the present invention
and was prepared using phosphorous acid (H.sub.3PO.sub.3) as the
chain transfer agent.
[0028] Each of experiments in the following examples was performed,
generally, in accordance with the following basic procedure:
[0029] The dispersion was prepared by first adding the amount of
0.2% of totally neutralized polymer dispersing agent to water,
mineral clay and grinding media (balls) into a stainless steel
double wall beaker to be ground.
[0030] The resulting aqueous solution was stirred at a rate of
1400-1600 rpm for the first 5 minutes, and then at a rate of
1400+/-10 rpm for additional 5 minutes to complete 10 minutes.
[0031] The total amount 0.8% of partially neutralized dispersing
agent was divided into equal parts and added, one at a time,
successively, every 5 minutes, over the remainder of grinding time,
which totaled 110 minutes, or until the desirable particle size of
95% less than 2 microns was achieved.
[0032] The solids content (% by weight based on the total weight of
the aqueous dispersion), particle size (in microns, or .mu.m) and
final pH and viscosity of the aqueous dispersion were measured
immediately after grinding time (at T.sub.0).
[0033] Lastly, gel tendency and viscosity were measured using a
conventional Brookfield type viscosimeter.
[0034] The weight percents of dispersing agents reported
hereinafter as having been added to the aqueous dispersions is
based on the dry weight of the dispersing agent added compared to
the dry weight of the mineral material in the dispersion.
Example 1
[0035] Measurement of Viscosity and Gel Tendency for Dispersions of
Calcium Carbonate of Particle Size at least 95% less than 2 microns
using homopolymer (100 AA) with different end-groups. Gel tendency
and viscosity were measured after each of 1 hour (T.sub.1), 24
hours (T.sub.24), and 144 hours (T.sub.144).
[0036] For each of four experiments (one each with a different
dispersing agent, A+B, 1, 2 and 3), 0.2% by weight of fully
neutralized dispersing agent in solution was added to the aqueous
dispersion before commencement of grinding. During grinding,
partially neutralized dispersing agent was added as follows: a
total of 0.3% by weight added in 2 separate steps, and a total of
0.5% added in 4 separate steps. The results are provided in Table 2
below and demonstrate that phosphinate terminated homopolymer, in
particular, dispersing agent 2 which is in accordance with the
present invention, provides significant lower initial viscosity and
lower gel tendency after 1 hour than dispersants combination A+B
and phosphonate or sodium metabisulphite (SMBS) end-group
polymers.
TABLE-US-00002 TABLE 2 Dispersing Grinding time Part size distrib.
Solids Viscosity Gel (Spindle C) Agent (min) % < 2 .mu.m % <
1 .mu.m (wt %) pH (S4 - 100 rpm) T0 T1 T24 T144 A + B 121 97.2 64.1
76.0 8.5 794 12.2 18.2 43.8 68 1 128 97.0 65.5 71.8 9.1 >2000 --
-- -- -- 2 115 96.5 63.1 76.0 8.7 568 6.7 15.6 >140 >140 3
114 96.6 63.9 76.0 9.0 >2000 94.3 -- >140 >140
Example 2
[0037] Measurement of Viscosity and Gel Tendency for Dispersions of
Calcium Carbonate of Particle Size at least 95% less than 2 microns
use phophinate terminated copolymers at different composition ratio
(AA/MAA) and molecule weight. Gel tendency and viscosity were
measured after each of 1 hour (T.sub.1), 24 hours (T.sub.24), 168
hours (T.sub.168), and 28 days (T.sub.28d).
[0038] The 15 calcium carbonate dispersions listed below were
prepared using the same grinding process described above, where
0.2% by weight of fully neutralized dispersing agent in solution,
was added to the aqueous dispersion before commencement of
grinding, followed by addition during the grinding time of
partially neutralized dispersing agent in the following amounts: a
total of 0.3% added in 4 separate steps and a total of 0.5% added
in 7 separate steps. The results of these 15 experiments are
reported in Table 3 below and demonstrate that the dispersing
agents according to the present invention, i.e., acrylic/methacryl
acid phosphinate terminated copolymers, added in accordance with
the process of the present invention, produce aqueous dispersions
with equal or lower increases of viscosity after 168 h than
commercially known dispersing agents (i.e., combination A+B and
C+B). In particular, for aqueous dispersions of mineral materials,
having solids content of at least 76% solids, pH of 8.6, and at
least 96% of the mineral particles being 2 microns or less, which
are produced with phophinate terminated polymers as dispersing
agents, the gel tendency is lower than for dispersions of
equivalent characteristics but produced using non-phophinate
terminated polymers as the dispersing agent.
TABLE-US-00003 TABLE 3 Brookfield Viscosity Gel Tendency Dispersing
Grinding Time Particle Size Solids (100 rpm) (Spindle C) MW.sub.w
Agent (min) % < 2 .mu.m % < 1 .mu.m (%) pH T.sub.0 T.sub.168
h-T.sub.0 T>.sub.28 d-T.sub.0 T.sub.1 T.sub.24 T.sub.168 3433 7
113 96.4 62.7 76.0 8.5 484 3050 5480 11.9 76.8 >140 3406 4 110
96.0 61.9 75.9 8.6 390 2150 3060 8.0 23.4 137 A + C 113.5 97.1 64.0
76.0 8.6 646 2080 3220 13 33 78 3495 10 110 95.7 61.9 75.9 8.5 374
1930 3470 8.1 19.1 105 4793 6 116 97.1 63.1 76.0 8.5 530 1540 2420
10.9 22.4 50.3 3855 5 113 96.2 62.6 76.0 8.5 406 1490 -- -- 16.9 41
3866 5 114 96.6 63.3 76.1 8.6 420 1420 2540 7.4 16.3 45.8 3879 11
112.5 96.9 63.6 75.9 8.5 408 1390 2080 7.2 14.4 43.9 4789 9 116
96.5 62.8 76.1 8.5 476 1260 2030 9.1 16.8 36.7 A + B 113.5 96.2
62.8 76.1 8.6 592 1210 1910 12.3 21 34 3971 8 112 96.0 61.9 76.0
8.4 414 1170 1860 6.7 12.0 37.4 3855 5 113 96.9 63.3 76.1 8.6 402
1060 2410 6.3 10.7 29.2 3866 5 110 96.4 62.0 76.1 8.7 372 1060 1660
6.1 9.4 24.5 4623 12 108 95.6 61.5 75.9 8.5 356 990 1760 6.8 10.6
23.8 3879 11 108 95.6 61.2 75.9 8.5 344 680 1360 5.4 8.3 15.7
[0039] It is further noted that, in general, the results are
enhanced when a dispersing agent comprising a copolymer composition
with at least 25% methacrylic acid (by weight based on the total
weight of the polymer) and weight average molecule weight above
3500. As shown in the Examples 1 and 2, the phosphinate terminated
dispersing agent, when introduced according to the process of the
present invention, provides stable dispersions even after standing
one week or 28 days.
[0040] It will be understood that the embodiments of the present
invention described hereinabove are merely exemplary and that a
person skilled in the art may make variations and modifications
without departing from the spirit and scope of the invention. All
such variations and modifications are intended to be included
within the scope of the present invention.
* * * * *