U.S. patent application number 14/924626 was filed with the patent office on 2016-02-18 for aluminum phosphate or polyphosphate particles for use as pigments in paints and method of making same.
The applicant listed for this patent is Bunge Amorphic Solutions LLC, Universidade Estadual de Campinas. Invention is credited to Joao de Brito, Fernando Galembeck.
Application Number | 20160046782 14/924626 |
Document ID | / |
Family ID | 35943444 |
Filed Date | 2016-02-18 |
United States Patent
Application |
20160046782 |
Kind Code |
A1 |
Galembeck; Fernando ; et
al. |
February 18, 2016 |
ALUMINUM PHOSPHATE OR POLYPHOSPHATE PARTICLES FOR USE AS PIGMENTS
IN PAINTS AND METHOD OF MAKING SAME
Abstract
An aluminum phosphate or polyphosphate-based pigment product is
made by a process comprising contacting phosphoric acid with
aluminum sulfate and an alkaline solution to produce an aluminum
phosphate based product; and optionally calcining the aluminum
phosphate based product at an elevated temperature, wherein the
process is substantially free of an organic acid. The aluminum
phosphate or polyphosphate-based pigment is amorphous. The
amorphous aluminum phosphate or polyphosphate characterized by a
bulk density of less than 2.30 grams per cubic centimeter and a
phosphorus to aluminum mole ratio of greater than 0.8. The
composition is useful in paints and as a substitute for titanium
dioxide
Inventors: |
Galembeck; Fernando;
(Campinas, BR) ; de Brito; Joao; (Cajati,
BR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bunge Amorphic Solutions LLC
Universidade Estadual de Campinas |
White Plains
Campinas |
NY |
US
BR |
|
|
Family ID: |
35943444 |
Appl. No.: |
14/924626 |
Filed: |
October 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12705293 |
Feb 12, 2010 |
9169120 |
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14924626 |
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11215312 |
Aug 30, 2005 |
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12705293 |
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Current U.S.
Class: |
524/417 ;
423/306; 423/311 |
Current CPC
Class: |
C08K 3/32 20130101; C08K
2003/327 20130101; C01B 25/45 20130101; C01B 25/36 20130101; C01B
25/40 20130101 |
International
Class: |
C08K 3/32 20060101
C08K003/32; C01B 25/45 20060101 C01B025/45; C01B 25/36 20060101
C01B025/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2004 |
BR |
PI0403713-8 |
Claims
1. A method of making amorphous aluminum phosphate comprising the
steps of: combining phosphoric acid with aluminum sulfate and
sodium hydroxide to react and form a suspension comprising an
amorphous aluminum phosphate precipitate; filtering the suspension
to isolate the precipitate; and drying the precipitate at a
temperature less than about 130.degree. C.
2. The method as recited in claim 1 wherein the amorphous aluminum
phosphate has a bulk density that is less than about 2.1 g/cc.
3. The method as recited in claim 1 where the amorphous aluminum
phosphate has an average individual particle radius size from about
5 to 80 nanometers.
4. The method as recited in claim 1 wherein the amorphous aluminum
phosphate consists of sodium aluminum phosphate.
5. The method as recited in claim 1 wherein the dried precipitate
is substantially free of open pores.
6. The method as recited in claim 1 wherein dried precipitate
comprises particles having closed voids.
7. The method as recited in claim 1 wherein the amorphous aluminum
phosphate has a bulk density that is less than about 1.99 g/cc.
8. The method as recited in claim 1 wherein the dried precipitate
has a macropore volume that is substantially less than 0.1
cc/gram.
9. The method as recited in claim 1 wherein during the step of
combining, the phosphoric acid, aluminum sulfate, and sodium
hydroxide are combined simultaneously.
10. The method as recited in claim 1 wherein after the step of
combining, adding further sodium hydroxide to the mixture.
11. The method as recited in claim 1 further comprising the step of
washing the precipitate after the filtering step.
12. The method as recited in claim 1 further comprising before the
step of drying, adding a dispersant to the precipitate.
13. The method as recited in claim 12 wherein the dispersant is
sodium tetrapyrophosphate.
14. A chemical composition comprising the amorphous aluminum
phosphate made according to claim 1 combined and uniformly
dispersed within a binding polymer.
15. The chemical composition as recited in claim 14 wherein when
the chemical composition is dried to form a film has a structure
characterized by enmeshed binding polymer and amorphous aluminum
phosphate.
16. A method of making amorphous aluminum phosphate comprising the
steps of: combining phosphoric acid with aluminum sulfate and
sodium hydroxide to form a mixture; reacting the mixture to form a
suspension comprising amorphous aluminum phosphate precipitate;
isolating the precipitate from the suspension; washing the isolated
precipitate; and drying the precipitate at a temperature less than
about 130.degree. C.
17. The method as recited in claim 16 wherein the amorphous
aluminum phosphate consists of sodium aluminum phosphate.
18. The method as recited in claim 16 wherein the amorphous
aluminum phosphate has a bulk density that is less than about 2.1
g/cc.
19. The method as recited in claim 16 wherein the dried precipitate
comprises particles having closed voids.
20. The method as recited in claim 16 wherein after the step of
drying, the amorphous aluminum phosphate has a macropore volume of
substantially less than 0.1 cc/gram.
21. The method as recited in claim 16 comprising combining the
phosphoric acid, aluminum sulfate, and sodium hydroxide
simultaneously.
22. The method as recited in claim 16 further comprising before the
step of drying, adding a dispersant to the precipitate.
23. The method as recited in claim 22 wherein the dispersant is
sodium tetrapyrophosphate.
24. A chemical composition comprising the amorphous aluminum
phosphate made according to claim 16, wherein the amorphous
aluminum phosphate is further combined with a binding polymer to
form the chemical composition.
25. The chemical composition as recited in claim 24, wherein the
amorphous aluminum phosphate has a bulk density that is less than
about 2.1 g/cc, and wherein the chemical composition when dried to
form a film has a structure characterized by interpenetrating
phases of binding polymer enmeshed with amorphous aluminum
phosphate.
26. A method of making a chemical composition comprising amorphous
aluminum phosphate, the method comprising the steps of: combining
phosphoric acid with aluminum sulfate and sodium hydroxide to form
a mixture; reacting the mixture to form a suspension comprising an
amorphous aluminum phosphate precipitate; filtrating and washing
the suspension to isolate the precipitate into a cake; forming a
dispersion of the washed cake; drying the cake to form amorphous
aluminum phosphate particles; and adding the amorphous aluminum
phosphate to a binding polymer to form the chemical
composition.
27. The method as recited in claim 25 wherein the amorphous
aluminum phosphate has a bulk density that is less than about 2.1
g/cc.
28. The method as recited in claim 25 wherein during the step of
forming a dispersion, a phosphate-based dispersant is used.
29. The method as recited in claim 25 wherein when in powder form
the amorphous aluminum phosphate has an average individual particle
radius size of between 5 and 80 nanometers.
30. The method as recited in claim 25 wherein after the step of
combining, adding further sodium hydroxide to the mixture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is continuation of and claims priority to
U.S. patent application Ser. No. 12/705,293, filed Feb. 12, 2010,
now U.S. Pat. No. 9,169,120, issued Oct. 27, 2015, which is a
divisional of U.S. patent application Ser. No. 11/215,312 filed
Aug. 30, 2005, now abandoned, which claimed priority to Brazilian
Patent Application No. PI0403713-8, filed on Aug. 30, 2004, which
applications are herein incorporated by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to methods of making hollow particles
of aluminum phosphate, aluminum orthophosphate and aluminum
polyphosphate. This invention further relates to use of such
particles as pigments in paints.
BACKGROUND OF THE INVENTION
[0003] Titanium dioxide is the most common white pigment due to its
strong ability to backscatter visible light, which is in turn
dependent on its refractive index. Substitutes for titanium dioxide
have been sought, but the refractive indexes of both the anatase
and rutile forms of this oxide are much higher than those of any
other white powder, due to structural reasons.
[0004] Titanium dioxide pigments are insoluble in coating vehicles
in which they are dispersed. The performance properties of such
titanium dioxide pigments, including its physical and chemical
characteristics, are determined by the particle size of the pigment
and the chemical composition of its surface. Titanium dioxide is
commercially available in two crystal structures: anatase and
rutile. Rutile titanium dioxide pigments are preferred as they
scatter light more efficiently and are more stable and durable than
anatase pigments. Titanium dioxide scatters light in two ways:
refraction and detraction. The decorative and functional attributes
of titanium dioxide, due to its refraction and diffraction
capabilities, make it a highly desirable pigment. However, titanium
dioxide is known to be an expensive pigment to manufacture.
Accordingly, there is a need for a more affordable substitute for
titanium dioxide as a pigment.
[0005] As mentioned, a desired feature of titanium dioxide is its
large capacity of spreading (or scattering) the visible light. This
property is the result of its high refraction index, together with
the absence of electronic transitions in the visible part of the
spectrum. Many attempts have been carried out to replace the
titanium dioxide, partially or totally in its applications as
pigment. However, the refraction indices of its two forms, anatase
and rutile, are difficult to obtain by other white solid substances
(Handbook of Chemistry and Physics, CRC Press, 57th ed., 1983).
Thus, the search for new white pigments led to the search of
systems with other light spreading mechanism. Multiphase media,
which present a large variation of the refraction index, may
operate as light spreaders.
[0006] The current options for manufacturing processes of pigments
or paints that result in a film containing "pores" in the internal
part of the particles or between the particles and the resin is
also quite limited. Some techniques for hollow particle preparation
have been described in the literature, however, most techniques
involve the manufacturing of spheroidal hollow and polymeric
particles by polymerization in emulsion. An example is the study of
N. Kawahashi and E. Matijevic (Preparation of Hollow Spherical
Particle of Itrium Compounds, J Colloid and Interface Science
143(1), 103, 1991) on the recovering of the polystyrene latex with
basic itrium carbonate and subsequent calcination in high air
temperatures, producing hollow particles of itrium compounds.
[0007] The preparation of hollow particles of aluminum
metaphosphates by chemical reaction between the sodium
metaphosphate and aluminum sulfate, followed by thermal treatment,
was described by Galembeck et al. in Brazilian Patent BR 9104581.
This study referred to the formation of hollow particles of
aluminum phosphate synthesized from sodium phosphate and aluminum
nitrate. As mentioned, the two pigments, aluminum phosphate and
metaphosphate, can be used to replace a large part of TiO.sub.2 in
paints based on PVA latex or acrylic emulsions.
[0008] Brazilian Patent BR 9500522-6 of Galembeck et al. describes
a way of making a white pigment from a double aluminum and calcium
metaphosphate, obtained directly by a chemical reaction between the
aluminum metaphosphate and calcium carbonate particles in a
polymeric latex emulsion type aqueous medium. This patent extended
the previous results to calcium salts that, from the environmental
point of view, are advantageous due to their full atoxicity.
[0009] Several publications discuss the synthesis of aluminum
phosphate materials primarily for use as a catalyst support
including crystalline and amorphous forms. Many of these methods
yield highly porous and crystalline forms and few thermally stable
amorphous compositions. Examples of such materials are described in
U.S. Pat. Nos. 3,943,231; 4,289,863; 5,030,431; 5,292,701;
5,496,529; 5,552,361; 5,698,758; 5,707,442; 6,022,513; and
6,461,415. There exists a need, however, for aluminum phosphate
with hollow particles, particularly for a powder that could be
manufactured with relative ease.
SUMMARY OF THE INVENTION
[0010] The subject of this invention is the product and process of
making an amorphous aluminum phosphate or polyphosphate
characterized by a bulk density of between 1.95 and 2.30 grams per
cubic centimeter and a phosphorus to aluminum mole ratio of greater
than 0.8. The aluminum phosphate or polyphosphate may be in slurry
form. Also, the aluminum phosphate or polyphosphate may be in
powder form and, for example, have one to four voids per particle
of amorphous aluminum phosphate or polyphosphate powder. The powder
form of the product may comprise an average individual particle
radius size of between 10 and 40 nanometers. The aluminum phosphate
or polyphosphate may be used as an ingredient in a paint, and
preferably, as a substitute (in part or in whole) for titanium
dioxide. The product may also be used as an ingredient in a
varnish, printing ink, or plastic. The aluminum phosphate or
polyphosphate may be dried at temperatures below 130.degree. C.,
and even at room temperature, to produce a powder that contains
10-20 water weight percent.
[0011] The amorphous aluminum phosphate or polyphosphate pigment
may be made by contacting phosphoric acid with aluminum sulfate and
an alkaline solution, either simultaneously or otherwise, and
optionally calcining the aluminum phosphate based product at an
elevated temperature, wherein the process is substantially free of
an organic acid. The mixture has a pH in the range from about 4.0
to about 4.5.
[0012] The process of making a the amorphous aluminum phosphate or
polyphosphate generally comprises the following steps: combining
phosphoric acid, aluminum sulfate, and sodium hydroxide into a
suspension; filtrating and washing said suspension into a cake;
dispersion of the washed cake; drying of the cake; polymerization
of the dry product; and micronization of the product.
BRIEF DESCRIPTION OF THE DRAWING
[0013] FIG. 1 is a transmission electron photomicrograph of a
sample of the inventive material using 25 eV inelastic scattered
electrons.
[0014] FIG. 2 is a bright field transmission electron micrograph of
the inventive material.
[0015] FIG. 3 is a bright field transmission electron micrograph
demonstrating "necking."
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0016] In the following description, all numbers disclosed herein
are approximate values, regardless whether the word "about" or
"approximate" is used in connection therewith. They may vary by 1
percent, 2 percent, 5 percent, or, sometimes, 10 to 20 percent.
Whenever a numerical range with a lower limit, R.sup.L and an upper
limit, R.sup.U, is disclosed, any number falling within the range
is specifically disclosed. In particular, the following numbers
within the range are specifically disclosed:
R=R.sup.L+k*(R.sup.U-R.sup.L), wherein k is a variable ranging from
1 percent to 100 percent with a 1 percent increment, i.e., k is 1
percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50
percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97
percent, 98 percent, 99 percent, or 100 percent. Moreover, any
numerical range defined by two R numbers as defined in the above is
also specifically disclosed.
[0017] The invention described in this patent relates to
non-crystalline solids, as opposed to the large majority of
inorganic industrial chemicals, including those products currently
sold as crystalline aluminum phosphates or polyphosphates. The CAS
number most often given for aluminum phosphate products is
7784-30-7, but this refers to a stoichiometric, crystalline solid.
There are not yet CAS numbers specifically assigned to amorphous
aluminum phosphates, following a search in the ACS SciFinder.RTM.
retrieval system.
[0018] Amorphous (i.e., non-crystalline) solids exhibit differences
from their crystalline counterparts with a similar composition, and
such differences may yield beneficial properties. For example, such
differences may include: (i) the non-crystalline solids do not
diffract x-rays at sharply defined angles but may produce a broad
scattering halo instead; (ii) the non-crystalline solids do not
have well defined stoichiometry, thus they can cover a broad range
of chemical compositions; (iii) the variability of chemical
composition includes the possibility of incorporation of ionic
constituents other than aluminum and phosphate ions; (iv) as
amorphous solids are thermodynamically meta-stable, they may
demonstrate a tendency to undergo spontaneous morphological,
chemical and structural changes; and (v) the chemical composition
of crystalline particle surface and bulk is highly uniform while
the chemical composition of surface and bulk of amorphous particles
may show large or small differences, either abrupt or gradual. In
addition, while particles of crystalline solids tend to grow by the
well-known mechanism of Ostwald ripening, non-crystalline particles
may expand or swell and shrink (de-swell) by water sorption and
desorption, forming a gel-like or plastic material that is easily
deformed when subjected to shearing, compression or capillary
forces.
[0019] As mentioned, one aspect of the invention described herein
is a synthetic process that produces non-crystalline aluminum
phosphates with unique properties. When a dispersion of such
particles dries under air at room temperature or up to 120.degree.
C., nanosized particles are formed that have a core-and-shell
structure. Such particles may be observed by analytical electron
microscopy. Moreover, these particles contain many voids dispersed
as closed pores in their interior. The cores of the particles are
more plastic than the respective shells of the particles. This
phenomenon is evidenced by growth of the voids upon heating, while
the perimeter of the shells remains essentially unaltered.
[0020] Another aspect of the invention consists of the development
of a new product and manufacturing process to form hollow particles
of aluminum phosphate and polyphosphate to be used as a pigment.
More specifically, this aspect of the invention relates to a new
pigment obtained through the reaction of the phosphoric acid,
particularly industrial-grade phosphoric acid, with aluminum
sulfate under controlled pH and temperature conditions. The
reactant may be filtered, dispersed, dried, calcinated, and
micronized for usage as pigment in paints, including in house
acrylic paints. Such pigments may be used in other products and
applications, such as paints, plastics, varnishes, printing inks,
etc.
[0021] As described herein, many have sought the formation of voids
within particles, but it is a difficult objective to obtain because
the majority of solids form open pores upon drying, and such open
pores do not contribute to paint opacity or hiding power. The
hollow particles formed within aluminum phosphate or polyphosphate
confer beneficial characteristics, both physically and chemically,
that can be used in many different applications. One aspect of the
inventions described herein is to produce aluminum phosphate or
polyphosphate with such hollow particles in order to take advantage
of such beneficial characteristics.
[0022] The aluminum phosphate particles described herein
demonstrate surprising and unique properties. For example, the
aluminum phosphate particles present voids, even when the particles
are dried at room temperature, or up to 130 degrees Celsius.
Preferably, the particles are dried between 40 degrees Celsius and
130 degrees Celsius. More preferably, the particles are dried
between 60 degrees Celsius and 130 degrees Celsius. Even more
preferably, the particles are dried between 80 degrees Celsius and
120 degrees Celsius. In addition, the aluminum phosphate particles
have a core-and-shell structure. In other words, these particles
have shells chemically different from their cores. This property is
evidenced by several different observations. First, the
energy-filtered inelastic electron images of the particles in the
plasmon region (10-40 eV), as measured by a transmission electron
microscope, show bright lines surrounding most particles. The
contrast seen in plasmon micrographs depends on local chemical
composition, and in this regard, a core-and-shell particle
structure can be observed from an examination of the micrograph in
FIG. 1.
[0023] Next, the presence of voids within particles, as
demonstrated in FIG. 2, dried at rather low temperatures are due to
the fact that the particles lose weight by de-swelling, while their
skins do not undergo contraction. Such voids, or hollow particles,
are made possible if the plasticity of the particle core is higher
than that of the shell. Additional indications of the formation of
the hollow particles are observed by heating the particles by
concentrating the electron beam on the particles. Large voids are
then created within the particles, while their perimeter undergoes
little change. Even further indication of the presence of closed
voids, or hollow particles, is the bulk density of aluminum
phosphate prepared by the process described herein, which is in the
1.95-2.27 g/cm.sup.3 range when measured at a water content of
approximately 15-17%, as compared to the 2.5-2.8 g/cm.sup.3 values
recorded for aluminum phosphate dense particles. Preferably, the
bulk density is less than 2.50 g/cm.sup.3. More preferably, the
bulk density is less than 2.30 g/cm.sup.3. More preferably, the
bulk density is less than 2.10 g/cm.sup.3. More preferably yet, the
bulk density is less than 1.99 g/cm.sup.3.
[0024] The aluminum phosphate particles, as prepared according to
the process described herein, may be dispersed in latex in the
presence of crystalline particulate solids. If a film is cast using
this dispersion, highly opaque films are produced. The highly
opaque films are produced even in the case of thin single layers of
particles. Experimental evidence for film opacity is obtained by
using amorphous aluminum phosphate as a replacement for titanium
dioxide (i.e., TiO.sub.2). Titanium dioxide is the current standard
white pigment used by almost all manufacturers involved in latex
paint formulations. A standard styrene-acrylic latex paint was
prepared using a usual load of titanium dioxide and it was compared
to a paint wherein fifty percent of the titanium dioxide load was
replaced by amorphous aluminum phosphate. This comparison was made
in two different paint-testing laboratories. The optical
measurements taken from films drawn using the two paints
demonstrate that aluminum phosphate may replace titanium dioxide
producing films while preserving the optical properties of the
film.
[0025] The surprising results and high effectiveness of the novel
aluminum phosphate discussed herein is related in part to its
relatively small particle size. Such smaller particle sizes allow
the particles to distribute extensively in the film and to
associate intimately with the resin and with inorganic paint
fillers, thereby creating clusters that are sites for extensive
void formation when the paint dries. The present aluminum phosphate
shows this tendency to form closed voids, or hollow particles, to
an extent that has not been previously observed for aluminum
phosphates, polyphosphates or any other particles. In some
embodiments, the particles of aluminum phosphate or polyphosphate
are substantially free of open pores while containing a number of
closed pores. As a result, in such embodiments, the macropore
volume is substantially less than 0.1 cc/gram.
[0026] Opacification of water-based paint films using aluminum
phosphate in some embodiments of the invention involves unique
features. The wet coating film is a viscous dispersion of polymer,
aluminum phosphate, titanium dioxide and filler particles. When
this dispersion is cast as a film and dried, it behaves differently
from a standard paint (below the critical pigment volume
concentration, CPVC). In a standard paint, the low glass transition
temperature (Tg) resin is plastic at room temperature and
coalesced, so that the resin film fills pores and voids. A paint
formulated with aluminum phosphate, however, can exhibit a
different behavior. The closed pores form, as described herein, and
contribute to the film hiding power.
[0027] The effectiveness of the aluminum phosphate or polyphosphate
described herein can be compared to the particles of aluminum
phosphate prepared by Hem et al. (see FIG. 3). The dry particles
described therein do not show small voids. In addition, the
particles undergo large morphological changes upon heating. The
extensive formation of "necks," as observed in the work of Hem et
al., is particularly interesting. Such necks are an indication that
the particle surfaces are very deformable, as opposed to rigid
particles that demonstrate the beneficial properties provided by
the invention described herein.
[0028] The aluminum phosphate or polyphosphate in pigments can be
prepared and used in at least one of the following forms: as a
slurry pulp (dispersion of high content of solids, which flows
under the action of gravity or low pressure pumps) with 50% or more
of solids; as dried and micronized aluminum phosphate with 15% of
humidity; and also in the polymeric form as calcinated and
micronized aluminum polyphosphate. The aluminum phosphate or
aluminum polyphosphate, used as a white pigment, can replace
titanium dioxide in dispersions in aqueous medium, such as
polymeric latex emulsion. The phosphorus:aluminum molar ratio of
the aluminum phosphate is preferably between 0.6 and 2.5. More
preferably, the phosphorus:aluminum molar ratio of the aluminum
phosphate is in the range of between 0.8 and 2.3. More preferably
yet, the phosphorus:aluminum molar ratio of the aluminum phosphate
is in the range of between 0.8 to 1.2.
[0029] As discussed, an aspect of the invention is a novel process
of manufacturing hollow particles of aluminum phosphate or aluminum
polyphosphate that may be used in different applications, including
white pigment in the formulations of paints based on aqueous
polymeric latex. The process is described in the following general
steps. One of skill in the art will recognize that certain steps
may be altered or omitted altogether. The steps include:
preparation of the main reagents used in the process, such as
diluted solution of phosphoric acid, diluted solution of aluminum
sulfate, and diluted solution of sodium hydroxide or ammonium
hydroxide; simultaneous and controlled addition of the reagents in
a reactor equipped with a sloshing system to keep the homogeneity
of the mixture during the process; control, during the addition of
the reagents in the reactor, of the temperature and pH (acidity) of
the mixture and, mainly, the reaction time; filtration of the
suspension, with approximately 8.0% of solids and separation of the
liquid and solid phases, in an appropriate equipment; washing out
of the impurities present in the filter cake with slightly alkaline
aqueous solution; dispersion of the washed cake, containing
approximately 35% of the solids, in an adequate disperser; drying
of the dispersed pulp in a turbo-dryer; micronization of the dried
product to an average granulometry of 5.0 to 10 microns; and
polymerization of the dried product by thermal treatment of the
aluminum phosphate in a calcinator.
[0030] There are several ways to prepare the main reagents in this
process. As mentioned, one source of phosphorus for the
manufacturing of aluminum phosphate and of the aluminum
polyphosphate is the fertilizer grade phosphoric acid, from any
origin, as it is clarified and discolored. For example, a
commercial phosphoric acid containing approximately 54% of
P.sub.2O.sub.5 may be chemically treated and/or diluted with
treated water resulting in a concentration of 20% P.sub.2O.sub.5.
Also, as an alternative to this process (instead of fertilizer
grade phosphoric acid or purified phosphoric acid), salts of
phosphorus as orthophosphates or as polyphosphates can be used.
[0031] Another reagent for the process is the commercial aluminum
sulfate. The aluminum sulfate may be obtained from the reaction
between the alumina (hydrate aluminum oxide) with concentrated
sulfuric acid (98% H.sub.2SO.sub.4), and then clarified and stored
at a 28% concentration of Al.sub.2O.sub.3. For the reaction to have
a favorable kinetics, the aluminum sulfate is diluted with water
treated at 5.0% of Al.sub.2O.sub.3. As an alternative for this
process, the source of aluminum can be any other salt of aluminum,
as well as aluminum hydroxide or aluminum in metallic form.
[0032] The neutralization of the reaction is carried out with a
sodium hydroxide solution, which may be commercially purchased in
different concentrations. A concentration of 50% of NaOH may be
purchased and diluted. For example, in the first phase of the
reaction, when the initial reagents are being mixed, the sodium
hydroxide may be used in the concentration of 20% of NaOH. In the
second phase of the reaction, due to the need of a fine-tuning of
the product acidity, a sodium hydroxide solution with 5.0% of NaOH
may be used. As an alternative neutralizer, ammonium hydroxide or
sodium carbonate (soda ash) may be used.
[0033] In one embodiment of the invention, a chemical reaction
results in the formation of aluminum orthophosphate or of aluminum
orthophosphates (Al.sub.2(HPO.sub.4).sub.3 or
Al(H.sub.2PO.sub.4).sub.3. The reaction, as described, is carried
out through the mixture of the three reagents, i.e., phosphoric
acid solution, aluminum sulfate solution, and sodium hydroxide
solution. The reagents are dosed in a reactor, typically containing
a sloshing system, during a 30-minute period. During the addition
of the reagents in the reactor, the pH of the mixture is controlled
within a 4.0 to 4.5 range and a reaction temperature, between
35.degree. C. and 40.degree. C. The reaction is completed after 15
minutes of the reagent mixture. In this period, the pH of the
mixture may be adjusted at 5.0, with the addition of more diluted
sodium hydroxide. In this embodiment, the temperature is preferably
below approximately 40.degree. C. At the end of the reaction, the
suspension formed should contain a molar relation between the
phosphorus:aluminum elements in a 0.8 to 1.2 range.
[0034] After the formation of the aluminum orthophosphate, the
suspension containing around 6.0% to 10.0% of solids, with a
maximum approximate temperature of 45.degree. C., and density in a
1.15 to 1.25 g/cm.sup.3 range, is pumped to a conventional filter
press. In the filter press, the liquid phase (sometimes referred to
as the "liquor") is separated from the solid phase (sometimes
referred to as the "cake"). The wet cake, containing approximately
35% to 45% of solids, and still possibly contaminated with the
sodium sulfate solution, is kept in the filter for washing cycle.
The filtered concentrate, which is basically a concentrated
solution of sodium sulfate, is extracted from the filter and stored
for future usage.
[0035] In one embodiment of the invention, the washing of the wet
cake is performed in the filter itself and in three process steps.
In the first washing ("displacement washing") the largest part of
the filtered substance that is contaminating the cake is removed.
The washing step is performed using treated water over the cake at
a flow rate of 6.0 m.sup.3 of water/ton of dried cake. A second
washing step, also with treated water and with a flow of 8.0
m.sup.3 of water/ton of dried cake, may be carried out to further
reduce, if not eliminate, the contaminants. And, finally, a third
washing step using a slightly alkaline solution may be carried out.
Such third washing step may be performed for the neutralization of
the cake and to keep its pH in the 7.0 range. Finally, the cake may
be blown with compressed air during a certain period of time.
Preferably, the wet product should present between 35% and 45% of
solids.
[0036] Next, in this particular embodiment of the invention, the
cake dispersion may be processed in such a way that the filter
cake, wet and washed, and containing approximately 35% of solids,
is extracted from the press filter by a conveyor belt and
transferred to a reactor/disperser. The dispersion of the cake is
aided by the addition of a dilute solution of sodium
tetrapyrophosphate.
[0037] After the dispersion step, the product is then dried, when
the aluminum phosphate "mud," with a percentage of solids within
the 30% to 50% range, is pumped to the drying unit. In one
embodiment, the water removal from the material can be carried out
with drying equipment, such as a "turbo dryer" type through an
injection of a hot air stream, at a temperature of 135.degree. C.
to 140.degree. C., through the sample. The final humidity of the
product should preferentially be kept in the 10% to 20% of water
range.
[0038] In certain embodiments of the invention, the next step of
the process would include product calcination. In this step, the
orthophosphate of the dry aluminum, as Al(H.sub.2PO.sub.4).sub.3,
is condensed by a thermal treatment to form a porous aluminum
polyphosphate, that is (Al(H.sub.2PO.sub.4).sub.3).sub.n, where "n"
can be any integer greater than 1, preferably, n is greater than or
equal to 4. More preferably, n is greater than or equal to 10. Even
more preferably, n is greater than or equal to 20. Preferably, n is
less than 100. Even more preferably, n is less than 50. This
process step is carried out by heating the phosphate aluminum, in a
spray-drier type calcinator, in a temperature range of 500.degree.
C. to 600.degree. C. After the polymerization, the product may be
cooled quickly and sent to the micronization unit. At this point,
product micronization step may be carried out. Finally, the
resulting product that leaves the drier (or the calcinator) is
transferred to the grinding and finishing unit, ground in a
micronizer/sorter, and its granulometry kept in the 99.5% range
below 400 mesh.
[0039] The aluminum phosphate or the aluminum polyphosphate, after
the thermal treatment, can be applied as white pigment in the
formulation of home paints, based on water, due to its
self-opacification property in latex, PVA, and acrylic films, due
to the formation of particles with hollow structures with high
light spreading capacity, during the paint drying process.
[0040] Various paints can be formulated using the aluminum
phosphate or polyphosphate made according to various embodiments of
the invention as a pigment, alone or in combination with another
pigment, such as titanium dioxide. A paint comprises one or more
pigments and one or more polymers as the binder (sometimes referred
to as "binding polymer"), and optionally various additives. There
are water-borned paints and non-water-borne paints. Generally, a
water-borne paint composition is composed of four basic components:
binder, aqueous carrier, pigment(s) and additive(s). The binder is
a nonvolatile resinous material that is dispersed in the aqueous
carrier to form a latex. When the aqueous carrier evaporates, the
binder forms a paint film that binds together the pigment particles
and other non-volatile components of the water-borne paint
composition. Water-borne paint compositions can be formulated
according to the methods and components disclosed in U.S. Pat. No.
6,646,058, with or without modifications. The disclosure of such
patent is incorporated by reference in its entirety herein. The
aluminum phosphate or polyphosphate made according to various
embodiments of the invention can be used to formulate water-borne
paints as a pigment, alone or in combination with titanium
dioxide.
[0041] A common paint is latex paints which comprises a binding
polymer, a hiding pigment, and optionally a thickener and other
additives. Again, the aluminum phosphate or polyphosphate made
according to various embodiments of the invention can be used to
formulate latex paints as a pigment, alone or in combination with
dioxide. Other components for making a latex paint is disclosed in
U.S. Pat. No. 6,881,782 and No. 4,782,109, which are incorporated
by reference herein in its entirety. By way of illustration,
suitable components and methods for making latex paints are briefly
explained below.
[0042] In some embodiments, suitable binding polymers include
emulsion copolymerized ethylenically unsaturated monomers including
0.8% to 6% of fatty acid acrylate or methacrylate such as lauryl
methacrylate and/or stearyl methacrylate. Based on the weight of
copolymerized ethylenic monomers, the polymeric binder comprises
0.8% to 6% fatty acid methacrylate or acrylate where preferred
compositions contain 1% to 5% of copolymerized fatty acid acrylate
or methacrylate having an aliphatic fatty acid chain comprising
between 10 and 22 carbon atoms. Preferred copolymer compositions
are based on copolymerized fatty acid methacrylate. Lauryl
methacrylate and/or stearyl methacrylate are preferred and lauryl
methacrylate is the most preferred monomer. Other useful fatty acid
methacrylates include myristyl methacrylate, decyl methacrylate,
palmitic methacrylate, oleic methacrylate, hexadecyl methacrylate,
cetyl methacrylate and eicosyl methacrylate, and similar straight
chain aliphatic methacrylate. Fatty acid methacrylates or acrylates
typically comprise commercial fatty oils coreacted with methacrylic
acid or acrylic acid to provide primarily the dominant fatty acid
moiety methacrylate with minor amounts of other fatty acid
acrylates or methacrylates.
[0043] Polymerizable ethylenically unsaturated monomers contain
carbon-to-carbon unsaturation and include vinyl monomers, acrylic
monomers, allylic monomers, acrylamide monomers, and mono- and
dicarboxylic unsaturated acids. Vinyl esters include vinyl acetate,
vinyl propionate, vinyl butyrates, vinyl benzoates, vinyl isopropyl
acetates and similar vinyl esters; vinyl halides include vinyl
chloride, vinyl fluoride, and vinylidene chloride; vinyl aromatic
hydrocarbons include styrene, methyl styrenes and similar lower
alkyl styrenes, chlorostyrene, vinyl toluene, vinyl naphthalene,
and divinyl benzene; vinyl aliphatic hydrocarbon monomers include
alpha olefins such as ethylene, propylene, isobutylene, and
cyclohexene as well as conjugated dienes such as 1,3-butadiene,
methyl-2-butadiene, 1,3-piperylene, 2,3 dimethyl butadiene,
isoprene, cyclohexane, cyclopentadiene, and dicyclopentadiene.
Vinyl alkyl ethers include methyl vinyl ether, isopropyl vinyl
ether, n-butyl vinyl ether, and isobutyl vinyl ether. Acrylic
monomers include monomers such as lower alkyl esters of acrylic or
methacrylic acid having an alkyl ester portion containing between 1
to 12 carbon atoms as well as aromatic derivatives of acrylic and
methacrylic acid. Useful acrylic monomers include, for example,
acrylic and methacrylic acid, methyl acrylate and methacrylate,
ethyl acrylate and methacrylate, butyl acrylate and methacrylate,
propyl acrylate and methacrylate, 2-ethyl hexyl acrylate and
methacrylate, cyclohexyl acrylate and methacrylate, decyl acrylate
and methacrylate, isodecylacrylate and methacrylate, benzyl
acrylate and methacrylate, and various reaction products such as
butyl phenyl, and cresyl glycidyl ethers reacted with acrylic and
methacrylic acids, hydroxyl alkyl acrylates and methacrylates such
as hydroxyethyl and hydroxypropyl acrylates and methacrylates, as
well as amino acrylates and methacrylates. Acrylic monomers can
include very minor amounts of acrylic acids including acrylic and
methacrylic acid, ethacrylic acid, alpha-chloroacrylic acid,
alpha-cyanoacrylic acid, crotonic acid, beta-acryloxy propionic
acid, and beta-styryl acrylic acid.
[0044] In other embodiments, polymers useful as component (a), the
"binding polymer", of the latex paints are copolymerization
products of a mixture of co-monomers which comprise monomers
selected from styrene, methyl styrene, vinyl, or combinations
thereof. Preferably co-monomers comprise (more preferably consist
essentially of) at least 40 mole percent of monomers selected from
styrene, methyl styrene, or combinations thereof and at least 10
mole percent of one or more monomers selected from acrylates,
methacrylates, and acrylonitrile. Preferably, the acrylates and
methacrylates contain from 4 to 16 carbon atoms such as, for
example, 2-ethylhexyl acrylate and methyl methacrylates. It is also
preferable that the monomers be used in a proportion such that the
final polymer has a glass-transition temperature (Tg) greater than
21.degree. C. and less than 95.degree. C. The polymers preferably
have a weight-average molecular weight of at least 100,000.
[0045] Preferably, the binding polymer comprises interpolymerized
units derived from 2-ethylhexyl acrylate. More preferably, the
binding polymer comprises polymerized units comprising from 50 to
70 mole percent of units derived from styrene, methyl styrene, or
combinations thereof from 10 to 30 mole percent of units derived
from 2-ethylhexyl acrylate; and from 10 to 30 mole percent of units
derived from methyl acrylate, acrylonitrile, or combinations
thereof.
[0046] Illustrative examples of suitable binding polymers include a
copolymer whose interpolymerized units are derived from about 49
mole percent styrene, 11 mole percent alpha-methylstyrene, 22 mole
percent 2-ethylhexyl acrylate, and 18 mole percent methyl
methacrylates with a Tg of approximately 45.degree. C. (available
as Neocryl XA-6037 polymer emulsion from ICI Americas, Inc.,
Bridgewater, N.J.); a copolymer whose interpolymerized units are
derived from about 51 mole percent styrene, 12 mole
percent.alpha.-methylstyrene, 17 mole percent 2-ethylhexyl
acrylate, and 19 mole percent methyl methacrylates with a Tg of
approximately 44.degree. C. (available as Joncryl 537 polymer
emulsion from S.C. Johnson & Sons, Racine, Wis.); and a
terpolymer whose interpolymerized units are derived from about 54
mole percent styrene, 23 mole percent 2-ethylhexyl acrylate, and 23
mole percent acrylonitrile with a Tg of approximately 44.degree. C.
(available as Carboset.TM. XPD-1468 polymer emulsion from B.F.
Goodrich Co.). Preferably, the binding polymer is Joncryl.TM.
537.
[0047] As described above, the aluminum phosphate or polyphosphate
made according to various embodiments of the invention can be used
to formulate latex paints as a pigment, alone or in combination
with another pigment.
[0048] Suitable additional hiding pigments include white opacifying
hiding pigments and colored organic and inorganic pigments.
Representative examples of suitable white opacifying hiding
pigments include rutile and anatase titanium dioxides, lithopone,
zinc sulfide, lead titanate, antimony oxide, zirconium oxide,
barium sulfide, white lead, zinc oxide, leaded zinc oxide, and the
like, and mixtures thereof. A preferred white organic hiding
pigment is rutile titanium dioxide. More preferred is rutile
titanium dioxide having an average particle size between about 0.2
to 0.4 microns. Examples of colored organic pigments are phthalo
blue and hansa yellow. Examples of colored inorganic pigments are
red iron oxide, brown oxide, ochres, and umbers.
[0049] Most known latex paints contain thickeners to modify the
Theological properties of the paint to ensure good spreading,
handling, and application characteristics. Suitable thickeners
include a non-cellulosic thickener (preferably, an associative
thickener; more preferably, a urethane associative thickener).
[0050] Associative thickeners such as, for example, hydrophobically
modified alkali swellable acrylic copolymers and hydrophobically
modified urethane copolymers generally impart more Newtonian
rheology to emulsion paints compared to conventional thickeners
such as, for example, cellulosic thickeners. Representative
examples of suitable associative thickeners include polyacrylic
acids (available, for example, from Rohm & Haas Co.,
Philadelphia, Pa., as Acrysol RM-825 and QR-708 Rheology Modifier)
and activated attapulgite (available from Engelhard, Iselin, N.J.
as Attagel 40).
[0051] Latex-paint films are formed by coalescence of the binding
polymer to form a binding matrix at the ambient paint application
temperature to form a hard, tack-free film. Coalescing solvents aid
the coalescence of the film-forming binder by lowering the
film-forming temperature. The latex paints preferably contain a
coalescing solvent. Representative examples of suitable coalescing
solvents include 2-phenoxyethanol, diethylene glycol butyl ether,
dibutyl phthalate, diethylene glycol,
2,2,4-trimethyl-1,1,3-pentanediol monoisobutyrate, and combinations
thereof. Preferably, the coalescing solvent is diethylene glycol
butyl ether (butyl carbitol) (available from Sigma-Aldrich,
Milwaukee, Wis.) or 2,2,4-trimethyl-1,1,3-pentanediol
monoisobutyrate (available from Eastman Chemical Co., Kingsport,
Tenn., as Texanol), or combinations thereof.
[0052] Coalescing solvent is preferably utilized at a level between
about 12 to 60 grams (preferably about 40 grams) of coalescing
solvent per liter of latex paint or at about 20 to 30 weight
percent based on the weight of the polymer solids in the paint.
[0053] The paints formulated in accordance with various embodiments
of the invention can further comprise conventional materials used
in paints such as, for example, plasticizer, anti-foam agent,
pigment extender, pH adjuster, tinting color, and biocide. Such
typical ingredients are listed, for example, in TECHNOLOGY OF
PAINTS, VARNISHES AND LACQUERS, edited by C. R. Martens, R. E.
Kreiger Publishing Co., p. 515 (1974).
[0054] Paints are commonly formulated with "functional extenders"
to increase coverage, reduce cost, achieve durability, alter
appearance, control rheology, and influence other desirable
properties. Examples of functional extenders include, for example,
barium sulphate, calcium carbonate, clay, gypsum, silica, and
talc.
[0055] The most common functional extenders for interior flat
paints are clays. Clays have a number of properties that make them
desirable. Inexpensive calcined clays, for example, are useful in
controlling low-shear viscosity and have a large internal surface
area, which contributes to "dry hide". But, this surface area is
also available to trap stains.
[0056] Because of their tendency to absorb stains, it is preferable
that calcined clays are used in the paints of the invention only in
the small amounts required for rheology control, for example,
typically as less than about half of the total extender pigment, or
are not used at all. The preferred extenders for use in the paints
of the invention are calcium carbonates; most preferred are
ultra-fine ground calcium carbonates such as, for example,
Opacimite (available from ECC International, Sylacauga, Ala.),
Supermite. (available from Imerys, Roswell, Ga.), or others having
particle size of approximately 1.0 to 1.2 microns. Ultra-fine
calcium carbonate help to space titanium dioxide optimally for hide
(see, for example, K. A. Haagenson, "The effect of extender
particle size on the hiding properties of an interior latex flat
paint," American Paint & Coatings Journal, Apr. 4, 1988, pp.
89-94).
[0057] The latex paints formulated in accordance with various
embodiments of the invention can be prepared utilizing conventional
techniques. For example, some of the paint ingredients are
generally blended together under high shear to form a mixture
commonly referred to as "the grind" by paint formulators. The
consistency of this mixture is comparable to that of mud, which is
desirable in order to efficiently disperse the ingredients with a
high shear stirrer. During the preparation of the grind, high shear
energy is used to break apart agglomerated pigment particles.
[0058] The ingredients not included in the grind are commonly
referred to as "the letdown." The letdown is usually much less
viscous than the grind, and is usually used to dilute the grind to
obtain a final paint with the proper consistency. The final mixing
of the grind with the letdown is typically carried out with low
shear mixing.
[0059] Most polymer latexes are not shear stable, and therefore are
not used as a component of the grind. Incorporation of shear
unstable latexes in the grind can result in coagulation of the
latex, yielding a lumpy paint with no, or little, film-forming
capability. Consequently, paints are generally prepared by adding
the latex polymer in the letdown. However, the some paints
formulated in accordance with various embodiments of the invention
contain latex polymers that are generally shear stable. Therefore,
the latex paints can be prepared by incorporating some or all of
the latex polymer into the grind. Preferably, at least some of the
latex polymer is put in the grind.
[0060] Two examples of possible forms of the process are described
below. Again, one of skill in the art will recognize variants that
may be utilized in performing the novel process described herein.
The following examples are presented to exemplify embodiments of
the invention. All numerical values are approximate. When numerical
ranges are given, it should be understood that embodiments outside
the stated ranges may still fall within the scope of the invention.
Specific details described in each example should not be construed
as necessary features of the invention.
Example No. 1
[0061] In this example, 535.0 kg of aluminum phosphate was
prepared. The wet product was dried in a "turbo-dryer" and
presented characteristics of hollow particles with 15% humidity and
P:Al (phosphorus:aluminum) ratio of 1:1.50.
[0062] 940.0 kg of fertilizer phosphoric acid containing 55.0% of
P.sub.2O.sub.5 was prepared. In the initial preparation phase, the
acid discoloration was carried out, which lasted approximately
thirty minutes, at a temperature of 85.degree. C. For this phase, a
solution with 8.70 kg of hydrogen peroxide containing around 50% of
H.sub.2O.sub.2 was added to the acid. Then, the acid was diluted
with 975.0 kg of process water, cooled to a temperature of
40.degree. C. and then stored at the concentration of 27.0% of
P.sub.2O.sub.5.
[0063] The aluminum source employed in this application was a
commercial aluminum sulfate solution containing 28% of
Al.sub.2O.sub.3. The solution was filtered and diluted with process
water. Specifically, 884.30 kg of aluminum sulfate solution and
1,776.31 kg of process water was combined to create a solution of
approximately 9.30% Al.sub.2O.sub.3.
[0064] This particular experiment used as a neutralizing reagent a
diluted solution of commercial sodium hydroxide containing 20.0% of
NaOH. Specifically, 974.0 kg of sodium hydroxide solution with 50%
of NaOH and 1,461.0 kg of process water were mixed. The final
mixture was cooled to 40.degree. C.
[0065] The three reagents were mixed simultaneously, for
approximately 30 minutes, in a reactor with 7,500 liters. During
the addition of the reagents in the reactor, the mixture
temperature was kept in the 40.degree. C. to 45.degree. C. range,
the pH was controlled to stay in a range of 4.0 to 4.5. At the end
of the addition of reagents, the mixture was kept sloshing for
approximately 15 minutes. The pH at this point was controlled at
approximately 5.0 with the addition of a sodium hydroxide solution
containing 5.0% of NaOH. The resulting suspension was approximately
7,000 kg with a density of 1.15 g/cm.sup.3, presented 6.5% of
solids, which represent around 455.0 kg of precipitate.
[0066] Then, the suspension was filtered in a press-filter
resulting in 1,300 kg of wet cake and 5,700 kg of filtrate. The
filtrate consisted primarily of a sodium sulfate solution
(Na.sub.2SO.sub.4). The cake consisted of approximately 35% solids.
The cake was washed, directly in the press filter, with 3,860
liters of process water, at room temperature, being kept at a
washing ratio of approximately 8.5 cm.sup.3 of the washing solution
per ton of dry cake. The filtrate generated in the washing of the
cake was stored for optional future use or for effluent treatment.
The cake extracted from the filter, around 1,300 kg, was then
transferred to a disperser (of approximately 1,000 liters) through
a peristaltic pump. The dispersed solution, containing
approximately 35% of solids, had a density of 1.33 g/cm.sup.3 and
viscosity of 17,400 cP.
[0067] The dispersed aluminum phosphate suspension, with
approximately 35% of solids, was then pumped to a turbo-drier. The
product was heated, through a hot air stream, at a temperature of
135.degree. C. Approximately 535.0 kg of aluminum orthophosphate
with 15% of humidity was produced. The final product was micronized
and its granulometry was kept below the 400 mesh. The final
analysis of the dry product presented the following results: the
phosphorus content in the product was approximately 15.0%; the
aluminum content was approximately 8.7%; the pH was approximately
7.0; the water content was approximately 15%; specific density of
2.20 g/cm.sup.3, and average diameter of particles from 5 to 10
um.
Example No. 2
[0068] From the results of Example No. 1, around 200 kg of dried
and micronized aluminum phosphate was used. The sample was used for
the manufacturing of a home paint sample. Initially, 900 liters of
opaque white acrylic paint was prepared. Such paint was applied and
the performance was evaluated in comparison with one of a
commercially available paint. The basic composition of the paint
based on an original formulation containing around 18% of titanium
dioxide was as follows: aluminum phosphate was approximately
14.20%; titanium oxide was approximately 8.34%; kaolin was
approximately 7.10%; algamatolite was approximately 10.36%;
diatomite was approximately 0.84%; acrylic resin was approximately
12.25%, and PVC was approximately 47.45%. The characteristics of
the paint prepared with aluminum phosphate, after the application
of it in painting, was the as follows: a) wet coverage similar to
the reference paint coverage; b) dry coverage was better than the
coverage with the reference paint; and c) resistance tests after
six months of home painting provided excellent results. Finally, it
was seen that the opaque acrylic paint soluble in water with
aluminum phosphate, prepared in Example No. 2, kept all the
characteristics of commercially available paints with yield of 50
m.sup.2/3.6 liters on the surface prepared with filler.
[0069] Typical chemical composition data of the aluminum phosphate
product is in Table 1. These results demonstrate that the invention
described herein is a hydrous, non-crystalline and neutral aluminum
phosphate made out of nanosized particles. In addition, the average
aggregate, and swollen, particle size (in the slurry) is in the
200-1500 nm range, as determined by dynamic light scattering. More
preferably, the average aggregate, and swollen, particle size (in
the slurry) is in the 400-700 nm range. Individual particle sizes,
however, may have a radius as small as 5 to 80 nm, as determined by
electron microscopy. More preferably, the individual particle sizes
may have a radius as small as 10 to 40 nm.
TABLE-US-00001 TABLE 1 Chemical Compositions of Various Grades of
Novel Product As Determined by X-Ray Fluorescence Using Fundamental
Parameters Grade P Al S Si Fe Ca 1 1 0.8 nil 0.067 0.0006 0.0005 2
1 0.82 nil 0.049 0.0005 0.0014 3 1 0.769 0.026 0.058 0.0007 0.0012
4 1 1.26 0.54 0.04 0.019 nil
[0070] As mentioned, a basic titanium dioxide water-based paint is
made out of a suitable latex dispersion and pigment particles. The
latex particles are responsible for making a coalesced film filled
with the pigmented particles, and are responsible for the film
hiding power. Many additives are also used, such as: inorganic
fillers, which decrease the requirements of resin and pigment;
coalescing agents that improve resin film formation; dispersants
and rheological modifiers, that prevent pigment and filler caking
and thus improve the paint shelf-life together with the rheological
paint properties.
[0071] In a typical paint dry film, the pigment and filler
particles are dispersed in the resin film. The hiding power is
largely dependent on the particle refractive indices and sizes. As
mentioned titanium dioxide is currently the standard white pigment
because of its large refractive index and of the absence of light
absorption in the visible region. A dry film of a paint formulated
with the novel aluminum phosphate in some embodiments has several
differences from the typical paint dry film. First, the film with
the aluminum phosphate is not just a resin film. It is rather
formed by enmeshed resin and aluminum phosphate. It is thus a
nanocomposite film that combines two interpenetrating phases with
different properties to achieve synergistic benefits, concerning
film mechanical properties and resistance to water and to other
aggressive agents. Second, good film hiding power is obtained at
lower titanium dioxide contents, because the film contains a large
amount of closed pores that scatter light. Moreover, if a titanium
dioxide particle is adjacent to one of these voids, it will scatter
much more than if it is fully surrounded by resin, due to the
larger refractive index gradient. This creates a synergism between
the novel aluminum phosphate and titanium dioxide, as far as the
hiding power is concerned.
[0072] In tests comparing a standard paint dry film to a film with
aluminum phosphate, a standard market formulation of a semi-matt
acrylic paint was chosen and titanium dioxide was progressively
replaced by the novel aluminum phosphate product described herein.
Water content and other paint components were adjusted as required.
Several of the modifications in the formula in this embodiment are
related to a decreased use of thickener/rheology modifier,
dispersant, acrylic resin and coalescing agent. Table 2 describes
an example of one of the formulas used in this experiment, together
with the corresponding formula for the novel aluminum
phosphate.
TABLE-US-00002 TABLE 2 A standard paint formula currently used in
the market and the corresponding formula using the aluminum
phosphate. The amounts are given in grams. Standard Formula
prepared Formula using novel slurry Water 839.79 361.86
Propyleneglycol 30.00 30.00 Thickener/rheology modifier 84.00 4.50
Antifoaming agent 0.60 1.17 Sodium tetrapyrophosfate 0.87 9.00
Anti-oxidant 0.87 0.90 Dispersant 20.94 11.00 Ammine 5.00 AFE
anionic 7.86 7.86 Bactericide 4.50 4.50 Fungicide 4.50 4.50
Ammonium hydroxide 25% 7.11 15.00 Titanium dioxide 534.00 267.00
Kaolin #325 169.50 169.50 CaCO.sub.3 nat. Micronized 161.28 161.28
Dolomite #325 300.00 300.00 Aluminium silicate #1000 60.18 60.18
Aluminum phosphate slurry 763.00 0.35 Acrylic resin 735.00 591.00
Antifoaming/mineral spirit 9.00 6.00 Coalescing agent 60.00 43.47
Total (grams) 3030.00 2816.72
[0073] In the formula above, a replacement of 50% TiO.sub.2 (on a
weight basis) was achieved, keeping the opacity and whiteness
conditions of the dry film. In addition, the other properties of
the novel product as a rheological modifier and also as a film
structuring agent were explored. Comparison between the two
formulas above shows that the pigments made according to
embodiments of the invention will lead to additional cost reduction
beyond that derived from the replacement of titanium dioxide
pigment. Moreover, such gains may be obtained while producing a
better performance in the applied paint film.
[0074] It can be observed from the foregoing description of
different embodiments of the invention that the novel product and
process differs from existing aluminum phosphates or polyphosphates
in several aspects. For example, as its stoichiometry is not
definite, various formulations of the invention can be prepared by
changing the fabrication process and thus the final product
composition. Because the invention is made under controlled pH
levels, it is nearly neutral thus avoiding environmental and
toxicological problems.
[0075] In addition, the invention may also be free from corrosion
problems associated with some aluminum phosphates found in the
market and used in the transformation of iron oxides into iron
phosphate. In addition, the non-stoichiometry together with the
relative non-crystallinity (both in slurry and powder form) and the
carefully controlled water content of the dry powder allow for easy
swelling control that is beneficial for its performance. The
nanosized particles are easily dispersed and they are stable
towards settling, which allow uniform paint dispersions. Also, the
nanoparticles can be strongly compatible with latex particles, by
the mechanisms of capillary adhesion (in the dispersion drying
stage) followed by ion-cluster mediated electrostatic adhesion (in
the dry film)--bicontinuous networks may be formed, in many cases.
Finally, the novel product is also strongly compatible with many
other particulate solids commonly used as paint fillers, such as
the various silicates, carbonates and oxides found in formulated
water-based dispersions, which may contribute to the cohesion and
strength of the paint dry film.
[0076] Thus, the invention described herein uses a different raw
material that offers alternate benefits, making the process more
economical and offering surprising results. Disclosed herein are
the purification, discoloration, and purification of a phosphoric
acid, broadly available in the fertilizer industry. Phosphoric acid
is generally available at a price which is a fraction of the price
of the phosphates or metaphosphates previously used. As the
phosphoric is the raw material that typically has the highest price
used in the manufacturing of aluminum phosphates pigment
manufacturing, the use of an acid degree allows an important
reduction in the manufacturing costs of aluminum phosphates. Such a
process makes the broad adoption of these pigments feasible. In
addition, certain features of the invention described herein
present new ways to use the aluminum phosphates, such as in
dispersion or in wet powder. These new methods allow important
technological gains. For example, the novel methods and products
prevent problems of particle aggregation, which damage the
performance of the pigment and reduce its coverage power. In
addition, the novel method and product eliminate problems of
particles dispersion in latex particles used in the manufacturing
of paints based on water, facilitating the usage processes of
aluminum phosphate in home paints. Further, the novel processes and
products do not require exhaustive drying steps of the phosphate,
which increase the complexity and cost of manufacturing.
[0077] Another beneficial aspect of the novel process described
herein is that it may be considered a "green chemistry"
zero-effluent product, in that it is made under mild temperature
and pressure conditions that do not create any environmental
problems during the fabrication process. Due to its chemical
nature, the residues created by the described novel process may be
safely discarded in the environment as a fertilizer component. It
is produced as slurry as well as a dry powder. In both cases it is
easily dispersed in water, forming stable dispersions that have
stable Theological properties.
[0078] As demonstrated above, embodiments of the invention provide
a novel method of making amorphous aluminum phosphate. While the
invention has been described with respect to a limited number of
embodiments, the specific features of one embodiment should not be
attributed to other embodiments of the invention. No single
embodiment is representative of all aspects of the invention. In
some embodiments, the compositions or methods may include numerous
compounds or steps not mentioned herein. In other embodiments, the
compositions or methods do not include, or are substantially free
of, any compounds or steps not enumerated herein. Variations and
modifications from the described embodiments exist. The method of
making the resins is described as comprising a number of acts or
steps. These steps or acts may be practiced in any sequence or
order unless otherwise indicated. Finally, any number disclosed
herein should be construed to mean approximate, regardless of
whether the word "about" or "approximately" is used in describing
the number. The appended claims intend to cover all those
modifications and variations as falling within the scope of the
invention.
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