U.S. patent application number 11/933469 was filed with the patent office on 2008-12-11 for nanosized particles of monoazo laked pigment with tunable properties.
This patent application is currently assigned to XEROX CORPORATION. Invention is credited to C. Geoffrey ALLEN, Rina CARLINI, Sandra J. GARDNER.
Application Number | 20080302275 11/933469 |
Document ID | / |
Family ID | 40094674 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302275 |
Kind Code |
A1 |
ALLEN; C. Geoffrey ; et
al. |
December 11, 2008 |
NANOSIZED PARTICLES OF MONOAZO LAKED PIGMENT WITH TUNABLE
PROPERTIES
Abstract
A nanoscale pigment particle composition includes an organic
monoazo laked pigment including at least one functional moiety, and
a sterically bulky stabilizer compound including at least one
functional group, wherein the functional moiety on the pigment
associates non-covalently with the functional group of the
stabilizer; and the nanoscale pigment particles have an average
particle size of from about 10 nm to about 500 nm and have tunable
coloristic properties that depend on both particle composition and
average particle size.
Inventors: |
ALLEN; C. Geoffrey;
(Waterdown, CA) ; CARLINI; Rina; (Oakville,
CA) ; GARDNER; Sandra J.; (Oakville, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC.
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
XEROX CORPORATION
Norwalk
CT
|
Family ID: |
40094674 |
Appl. No.: |
11/933469 |
Filed: |
November 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11759913 |
Jun 7, 2007 |
|
|
|
11933469 |
|
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Current U.S.
Class: |
106/402 |
Current CPC
Class: |
C09D 11/101 20130101;
C09D 11/322 20130101; C09D 7/41 20180101; C09D 11/34 20130101; C09D
11/36 20130101; C09B 67/0013 20130101; C09D 11/037 20130101; C09B
67/0009 20130101; B82Y 30/00 20130101; C09B 67/0005 20130101; C09B
63/005 20130101 |
Class at
Publication: |
106/402 |
International
Class: |
C09B 63/00 20060101
C09B063/00 |
Claims
1. A nanoscale pigment particle composition, comprising: an organic
monoazo laked pigment having at least one functional moiety, and a
sterically bulky stabilizer compound having at least one functional
group, wherein the functional moiety on the pigment associates
non-covalently with the functional group of the stabilizer; and the
nanoscale pigment particles have an average particle size of from
about 10 nm to about 500 nm and have coloristic properties that are
changeable in accordance with both particle composition and average
particle size.
2. The composition of claim 1, wherein the nanoscale pigment
particles have an average particle diameter, as derived from
transmission electron microscopy imaging, of less than about 200
nm.
3. The composition of claim 1, wherein the nanoscale pigment
particles have an average particle size (d.sub.50 or Z-average), as
derived by dynamic light scattering analysis methods, of less than
about 250 nm.
4. The composition of claim 1, wherein the nanoscale pigment
particles have an average particle size, as derived by transmission
electron microscopy imaging, of from about 25 nm to about 150
nm.
5. The composition of claim 1, wherein the nanoscale pigment
particles have a geometric standard deviation, as derived by
dynamic light scattering analysis methods, of from about 1.1 about
1.8.
6. The composition of claim 1, wherein the nanoscale pigment
particles have a shape selected from the group consisting of rods,
platelets, needles, prisms, ellipsoids, and nearly spherical, and
have an aspect ratio (length:width) of from about 1:1 to about
5:1.
7. The composition of claim 1, wherein the coloristic properties
are measured when the nanoscale pigment particles are dispersed in
a polymer binder.
8. The composition of claim 1, wherein the coloristic properties
are directly correlated with variable average particle size, as
derived by dynamic light scattering analysis methods.
9. The composition of claim 1, wherein the coloristic properties
are selected from the group consisting of L*, a*, b*, chroma C*,
hue angle, normalized Light Scatter Index (NLSI), and combinations
thereof.
10. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a hue angle, as derived from a 2-dimensional b*
a* color gamut space, ranging from about 345.degree. to about
0.degree..
11. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a hue angle measured on a 2-dimensional b* a*
color gamut space of from about 345.degree. to about
355.degree..
12. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a NLSI value, determined as a degree of spectral
absorbance due to particle light scattering in a near-infrared
spectral region between 700-900 nm, ranging from about 0.1 to about
3.0.
13. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a NLSI value of from about 0.1 to about 1.5.
14. The composition of claim 1, wherein the nanoscale pigment
particles have enhanced chroma as compared to a similar organic
monoazo laked pigment not having the sterically bulky stabilizer
compound and not having nanoscale-sized particles.
15. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a hue angle, as derived from a 2-dimensional b*
a* color gamut space, ranging from about 345.degree. to about
0.degree. and a NLSI value, calculated from spectral absorbance in
the near-infrared spectral region between 700-900 nm, ranging of
from about 0.1 to about 3.0.
16. The composition of claim 1, wherein the nanoscale pigment
particles exhibit a hue angle, as derived from a 2-dimensional b*
a* color gamut space, ranging from about 345.degree. to about
355.degree., and a NLSI value, calculated from spectral absorbance
in the near-infrared spectral region between 700-900 nm, ranging
from about 0.1 to about 1.0.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/759,913 to Rina Carlini et al. filed Jun.
7, 2007, the entire disclosure of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] This disclosure is generally directed to nanoscale pigment
particle compositions, and methods for producing such nanoscale
pigment particle compositions, as well as to uses of such
compositions, for example, in ink compositions. More specifically,
this disclosure is directed to organic mono-azo laked nanoscale
pigments with tunable properties such as particle size, coloristic
properties, and properties as pigmented liquid dispersions. Such
particles are useful, for example, as nanoscopic colorants for such
compositions as inks, toners and the like.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0003] Disclosed in commonly assigned U.S. patent application Ser.
No. 11/759,913 to Rina Carlini et al. filed Jun. 7, 2007, is a
nanoscale pigment particle composition, comprising: an organic
monoazo laked pigment including at least one functional moiety, and
a sterically bulky stabilizer compound including at least one
functional group, wherein the functional moiety associates
non-covalently with the functional group; and the presence of the
associated stabilizer limits the extent of particle growth and
aggregation, to afford nanoscale-sized pigment particles. Also
disclosed is a process for preparing nanoscale-sized monoazo laked
pigment particles, comprising: preparing a first reaction mixture
comprising: (a) a diazonium salt including at least one functional
moiety as a first precursor to the laked pigment and (b) a liquid
medium containing diazotizing agents generated in situ from nitrous
acid derivatives; and preparing a second reaction mixture
comprising: (a) a coupling agent including at least one functional
moiety as a second precursor to the laked pigment and (b) a
sterically bulky stabilizer compound having one or more functional
groups that associate non-covalently with the coupling agent; and
(c) a liquid medium combining the first reaction mixture into the
second reaction mixture to form a third mixture and effecting a
direct coupling reaction which forms a monoazo laked pigment
composition wherein the functional moiety associates non-covalently
with the functional group and having nanoscale particle size.
Further disclosed is a process for preparing nanoscale monoazo
laked pigment particles, comprising: providing a monoazo precursor
dye to the monoazo laked pigment that includes at least one
functional moiety; subjecting the monoazo precursor dye to an ion
exchange reaction with a cation salt in the presence of a
sterically bulky stabilizer compound having one or more functional
groups; and precipitating the monoazo laked pigment as nanoscale
particles, wherein the functional moiety of the pigment associates
non-covalently with the functional group of the stabilizer and
having nanoscale particle size.
[0004] Disclosed in commonly assigned U.S. patent application Ser.
No. 11/759,906 to Maria Birau et al. filed Jun. 7, 2007, is a
nanoscale pigment particle composition, comprising: a quinacridone
pigment including at least one functional moiety, and a sterically
bulky stabilizer compound including at least one functional group,
wherein the functional moiety of the pigment associates
non-covalently with the functional group of the stabilizer; and the
presence of the associated stabilizer limits the extent of particle
growth and aggregation, to afford nanoscale-sized particles. Also
disclosed is a process for preparing nanoscale quinacridone pigment
particles, comprising: preparing a first solution comprising: (a) a
crude quinacridone pigment or pigment precursor including at least
one functional moiety and (b) a liquid medium; preparing a second
solution comprising: (a) a sterically bulky stabilizer compound
having one or more functional groups that associate non-covalently
with the pigment functional moiety, and (b) a liquid medium;
combining the first solution into the second solution to form a
third reaction mixture which forms a quinacridone pigment
composition of nanoscale particle size and wherein the functional
moiety of the pigment associates non-covalently with the functional
group of the stabilizer. Still further is disclosed a process for
preparing nanoscale quinacridone pigment particles, comprising:
preparing a first solution comprising a quinacridone pigment
including at least one functional moiety in an acid; preparing a
second solution comprising an liquid medium and a sterically bulky
stabilizer compound having one or more functional groups that
associate non-covalently with the functional moiety of the pigment;
treating the second solution with the first solution to precipitate
quinacridone pigment of nanoscale particle size, wherein the
functional moiety of the pigment associates non-covalently with the
functional group of the stabilizer.
[0005] The entire disclosure of the above-mentioned application is
totally incorporated herein by reference.
BACKGROUND
[0006] Pigments are a class of colorants useful in a variety of
applications such as, for example, paints, plastics and inks,
including inkjet printing inks. Dyes have typically been the
colorants of choice for inkjet printing inks because they are
readily soluble colorants which enable jetting of the ink. Dyes
have also offered superior and brilliant color quality with an
expansive color gamut for inks, when compared with conventional
pigments. However, since dyes are molecularly dissolved in the ink
vehicle, they are often susceptible to unwanted interactions that
lead to poor ink performance, for example photooxidation from light
(will lead to poor lightfastness), dye diffusion from the ink into
paper or other substrates (will lead to poor image quality and
showthrough), and the ability for the dye to leach into another
solvent that makes contact with the image (will lead to poor
water/solventfastness). In certain situations, pigments are the
better alternative as colorants for inkjet printing inks since they
are insoluble and cannot be molecularly dissolved within the ink
matrix, and therefore do not experience colorant diffusion.
Pigments can also be significantly less expensive than dyes, and so
are attractive colorants for use in all printing inks.
[0007] Key challenges with using pigments for inkjet inks are their
large particle sizes and wide particle size distribution, the
combination of which can pose critical problems with reliable
jetting of the ink (i.e. inkjet nozzles are easily blocked).
Pigments are rarely obtained in the form of single crystal
particles, but rather as large aggregates of crystals and with wide
distribution of aggregate sizes. The color characteristics of the
pigment aggregate can vary widely depending on the aggregate size
and crystal morphology. Thus, an ideal colorant that is widely
applicable in, for example, inks and toners, is one that possesses
the best properties of both dyes and pigments, namely: 1) superior
coloristic properties (large color gamut, brilliance, hues, vivid
color); 2) color stability and durability (thermal, light, chemical
and air-stable colorants); 3) minimal or no colorant migration; 4)
processable colorants (easy to disperse and stabilize in a matrix);
and 5) inexpensive material cost. Thus, there is a need addressed
by embodiments of the present invention, for small, nano-sized
pigment particles that possess some or all of the aforementioned
properties, in order to minimize or avoid the problems associated
with using conventional larger-sized pigment particles in inks and
toners. The present nanosized pigment particles are useful in for
example paints, coatings and inks (e.g., inkjet printing inks) and
other compositions where pigments can be used such as plastics,
optoelectronic imaging components, photographic components and
cosmetics among others.
[0008] Whether formulated for office printing or for production
printing, printing inks and toners are expected to produce images
that are robust and durable under stress conditions, such as
exposure to abrasive or sharp objects or actions that produce a
crease defect in the image (such as folding or scratching the
imaged paper). For example, in a typical design of a piezoelectric
ink jet device, the image is applied by jetting appropriately
colored inks during four to six rotations (incremental movements)
of a substrate (an image receiving member or intermediate transfer
member) with respect to the ink jetting head, i.e., there is a
small translation of the printhead with respect to the substrate in
between each rotation. This approach simplifies the printhead
design, and the small movements ensure good droplet registration.
At the jet operating temperature, droplets of liquid ink are
ejected from the printing device and, when the ink droplets contact
the surface of the recording substrate, either directly or via an
intermediate heated transfer belt or drum, they quickly solidify to
form a predetermined pattern of solidified ink drops. Inkjet
printing inks comprised of pigments should have appropriate
viscosity characteristics under various shear forces, so as to
enable reliable jetting of the pigmented ink. There is a need to
nano-sized pigments having suitable dispersion and viscosity
properties to enable optimum jetting performance and ultimately,
printhead reliability.
[0009] The following documents provide background information:
[0010] Hideki Maeta et al., "New Synthetic Method of Organic
Pigment Nano Particle by Micro Reactor System," in an abstract
available on the internet at
http://aiche.confex.com/aiche/s06/preliminaryprogram/abstract.sub.--40072-
.htm, describes a new synthetic method of an organic pigment nano
particle was realized by micro reactor. A flowing solution of an
organic pigment, which dissolved in an alkaline aqueous organic
solvent, mixed with a precipitation medium in a micro channel. Two
types of micro reactor can be applied efficiently on this build-up
procedure without blockage of the channel. The clear dispersion was
extremely stable and had narrow size distribution, which were the
features, difficult to realize by the conventional pulverizing
method (breakdown procedure). These results proved the
effectiveness of this process on micro reactor system.
[0011] U.S. Patent Application Publication No. 2005/0109240
describes a method of producing a fine particle of an organic
pigment, containing the steps of: flowing a solution of an organic
pigment dissolved in an alkaline or acidic aqueous medium, through
a channel which provides a laminar flow; and changing a pH of the
solution in the course of the laminar flow.
[0012] WO 2006/132443 A1 describes a method of producing organic
pigment fine particles by allowing two or more solutions, at least
one of which is an organic pigment solution in which an organic
pigment is dissolved, to flow through a microchannel, the organic
pigment solution flows through the microchannel in a non-laminar
state. Accordingly, the contact area of solutions per unit time can
be increased and the length of diffusion mixing can be shortened,
and thus instantaneous mixing of solutions becomes possible. As a
result, nanometer-scale monodisperse organic pigment fine particles
can be produced in a stable manner.
[0013] U.S. Patent Application Publication No. 2003/0199608
discloses a functional material comprising fine coloring particles
having an average primary particle diameter of 1 to 50 nm in a
dried state, and having a BET specific surface area value of 30 to
500 m.sup.2/g and a light transmittance of not less than 80%. The
functional material composed of fine coloring particles, exhibits
not only an excellent transparency but also a high tinting strength
and a clear hue.
[0014] WO 2006/011467 discloses a pigment, which is used, for
example, in color image display devices and can form a blue pixel
capable of providing a high level of bright saturation,
particularly a refined pigment, which has bright hue and is
excellent in pigment properties such as lightfastness, solvent
resistance and heat resistance, and a process for producing the
same, a pigment dispersion using the pigment, and an ink for a
color filter. The pigment is a subphthalocyanine pigment that is
prepared by converting subphthalocyanine of the specified formula,
to a pigment, has diffraction peaks at least at diffraction angles
(2.theta.) 7.0.degree., 12.3.degree., 20.4.degree. and 23.4.degree.
in X-ray diffraction and an average particle diameter of 120 to 20
nm.
[0015] U.S. Patent Application Publication No. 2006/0063873
discloses a process for preparing nano water paint comprising the
steps of: A. modifying the chemical property on the surface of nano
particles by hydroxylation for forming hydroxyl groups at high
density on the surface of the nano particles; B. forming
self-assembly monolayers of low surface energy compounds on the
nano particles by substituting the self-assembly monolayers for the
hydroxyl groups on the nano particles for disintegrating the
clusters of nano particles and for forming the self-assembly
monolayers homogeneously on the surface of the nano particles; and
C. blending or mixing the nano particles having self-assembly
monolayers formed thereon with organic paint to form nano water
paint.
[0016] WO 2006/005536 discloses a method for producing
nanoparticles, in particular, pigment particles. Said method
consists of the following steps: (i) a raw substance is passed into
the gas phase, (ii) particles are produced by cooling or reacting
the gaseous raw substance and (iii) an electrical charge is applied
to the particles during the production of the particles in step
(ii), in a device for producing nanoparticles. The disclosure
further relates to a device for producing nanoparticles, comprising
a supply line, which is used to transport the gas flow into the
device, a particle producing and charging area in order to produce
and charge nanoparticles at essentially the same time, and an
evacuation line which is used to transport the charged
nanoparticles from the particle producing and charging area.
[0017] Japanese Patent Application Publication No. JP 2005238342 A2
discloses irradiating ultrashort pulsed laser to organic bulk
crystals dispersed in poor solvents to induce ablation by nonlinear
absorption for crushing the crystals and recovering the resulting
dispersions of scattered particles. The particles with average size
approximately 10 nm are obtained without dispersants or grinding
agents for contamination prevention and are suitable for pigments,
pharmaceuticals, etc.
[0018] U.S. Pat. No. 6,837,918 discloses a process and apparatus
that collects pigment nanoparticles by forming a vapor of a pigment
that is solid at room temperature, the vapor of the pigment being
provided in an inert gaseous carrying medium. At least some of the
pigment is solidified within the gaseous stream. The gaseous stream
and pigment material is moved in a gaseous carrying environment
into or through a dry mechanical pumping system. While the
particles are within the dry mechanical pumping system or after the
nanoparticles have moved through the dry pumping system, the
pigment material and nanoparticles are contacted with an inert
liquid collecting medium.
[0019] U.S. Pat. No. 6,537,364 discloses a process for the fine
division of pigments which comprises dissolving coarsely
crystalline crude pigments in a solvent and precipitating them with
a liquid precipitation medium by spraying the pigment solution and
the precipitation medium through nozzles to a point of conjoint
collision in a reactor chamber enclosed by a housing in a microjet
reactor, a gas or an evaporating liquid being passed into the
reactor chamber through an opening in the housing for the purpose
of maintaining a gas atmosphere in the reactor chamber, and the
resulting pigment suspension and the gas or the evaporated liquid
being removed from the reactor through a further opening in the
housing by means of overpressure on the gas entry side or
underpressure on the product and gas exit side.
[0020] U.S. Pat. No. 5,679,138 discloses a process for making ink
jet inks, comprising the steps of: (A) providing an organic pigment
dispersion containing a pigment, a carrier for the pigment and a
dispersant; (B) mixing the pigment dispersion with rigid milling
media having an average particle size less than 100 .mu.m; (C)
introducing the mixture of step (B) into a high speed mill; (D)
milling the mixture from step (C) until a pigment particle size
distribution is obtained wherein 90% by weight of the pigment
particles have a size less than 100 nanometers (nm); (E) separating
the milling media from the mixture milled in step (D); and (F)
diluting the mixture from step (E) to obtain an ink jet ink having
a pigment concentration suitable for ink jet printers.
[0021] Japanese Patent Application Publications Nos. JP 2007023168
and JP 2007023169 discloses providing a pigment dispersion compound
excellent in dispersibility and flowability used for the color
filter which has high contrast and weatherability. The solution of
the organic material, for example, the organic pigment, dissolved
in a good solvent under the existence of alkali soluble binder (A)
which has an acidic group, and a poor solvent which makes the phase
change to the solvent are mixed. The pigment nanoparticles
dispersed compound re-decentralized in the organic solvent
containing the alkali soluble binder (B) which concentrates the
organic pigment nanoparticles which formed the organic pigment as
the particles of particle size less than 1 .mu.m, and further has
the acidic group.
[0022] Kazuyuki Hayashi et al., "Uniformed nano-downsizing of
organic pigments through core-shell structuring," Journal of
Materials Chemistry, 17(6), 527-530 (2007) discloses that
mechanical dry milling of organic pigments in the presence of
mono-dispersed silica nanoparticles gave core-shell hybrid pigments
with uniform size and shape reflecting those of the inorganic
particles, in striking contrast to conventional milling as a
breakdown process, which results in limited size reduction and wide
size distribution.
[0023] U.S. Patent Application Publication No. 2007/0012221
describes a method of producing an organic pigment dispersion
liquid, which has the steps of: providing an alkaline or acidic
solution with an organic pigment dissolved therein and an aqueous
medium, wherein a polymerizable compound is contained in at least
one of the organic pigment solution and the aqueous medium; mixing
the organic pigment solution and the aqueous medium; and thereby
forming the pigment as fine particles; then polymerizing the
polymerizable compound to form a polymer immobile from the pigment
fine particles.
[0024] K. Balakrishnan et al., "Effect of Side-Chain Substituents
on Self-Assembly of Perylene Diimide Molecules: Morphology
Control," J. Am. Chem. Soc., vol. 128, p. 7390-98 (2006) describes
the use of covalently-linked aliphatic side-chain substituents that
were functionalized onto perylene diimide molecules so as to
modulate the self-assembly of molecules and generate distinct
nanoparticle morphologies (nano-belts to nano-spheres), which in
turn impacted the electronic properties of the material. The
side-chain substituents studied were linear dodecyl chain, and a
long branched nonyldecyl chain, the latter substituent leading to
the more compact, spherical nanoparticle.
[0025] The appropriate components and process aspects of each of
the foregoing may be selected for the present disclosure in
embodiments thereof, and the entire disclosure of the
above-mentioned references are totally incorporated herein by
reference.
SUMMARY
[0026] The present disclosure addresses these and other needs, by
providing nanoscale pigment particle compositions, and methods for
producing such nanoscale pigment particle compositions.
[0027] In an embodiment, the present disclosure provides a
nanoscale pigment particle composition, comprising:
[0028] an organic monoazo laked pigment including at least one
functional moiety, and
[0029] a sterically bulky stabilizer compound including at least
one functional group,
[0030] wherein the functional moiety of the pigment associates
non-covalently with the functional group of the stabilizer; and
[0031] the nanoscale pigment particles have an average particle
size ranging from about 10 nm to about 500 nm and have tunable
coloristic properties. For example, when dispersed in a colorless,
transparent polymer binder for making thin film coatings, the
nanoscale particles of monoazo laked pigments exhibit coloristic
properties that are correlated and tunable with average pigment
particle size as well as the composition of the pigment with
associated stabilizer.
[0032] In another embodiment, the present disclosure provides
processes for preparing nanoscale-sized monoazo laked pigment
particles, comprising:
[0033] providing an organic pigment precursor to a monoazo laked
pigment that contains at least one functional moiety,
[0034] providing a sterically bulky stabilizer compound that
contains at least one functional group, and
[0035] carrying out a chemical reaction to form a monoazo laked
pigment composition, whereby the functional moiety found on the
pigment precursor is incorporated within the monoazo laked pigment
and non-covalently associated with the functional group of the
stabilizer, so as to allow the formation of nanoscale-sized pigment
particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 shows a b* a* Gamut for pigmented coatings prepared
with example PR57:1 pigments (Magenta Optical Density=1.5).
[0037] FIG. 2 shows a relationship between hue angle and normalized
light scatter index (NLSI) for pigmented coatings on Mylar film,
prepared according to embodiments (Magenta Optical
Density=1.5).
[0038] FIG. 3 shows a relationship between hue angle of pigmented
coatings and Z-average particle size prepared with example PR57:1
pigments (Magenta Optical Density=1.5).
[0039] FIG. 4 shows a relationship between normalized light scatter
index of pigmented coatings and Z-average particle size prepared
with example PR57:1 pigments (Magenta Optical Density=1.5).
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0040] Embodiments of the present disclosure provide nanoscale
pigment particle compositions, and methods for producing such
nanoscale pigment particle compositions. The nanoscale pigment
particle compositions generally comprise an organic monoazo laked
pigment including at least one functional moiety that associates
non-covalently with a functional group from a sterically bulky
stabilizer compound. The presence of the associated stabilizer
limits the extent of particle growth and aggregation, to afford
nanoscale particles. The nanoscale pigment particles have an
average particle size of from about 10 nm to about 500 nm and have
coloristic properties that are that are correlated and tunable with
average pigment particle size as well as the composition of the
pigment and associated stabilizer.
[0041] Organic monoazo "laked" pigments are the insoluble metal
salt colorants of monoazo colorants which can include monoazo dyes
or pigments, and in certain geographic regions these pigments have
been referred to as either "toners" or "lakes". The process of ion
complexation with a metal salt, or "laking" process, provides
decreased solubility of the non-ionic monoazo pigment, which can
enhance the migration resistance and thermal stability properties
of a monoazo pigment, and thereby enable the applications of such
pigments for robust performance, such as colorizing plastics and
heat-stable paints for outdoor use. Formula 1 depicts a general
representation of monoazo laked pigments, which are ionic compounds
that are structurally comprised of a diazo group (denoted G.sub.d)
and a nucleophilic coupling group (denoted as G.sub.c) that are
linked together with one azo (N.dbd.N) functional group, and a
cation (M.sup.n+) which is typically a metal salt. Either or both
of the groups G.sub.d and G.sub.c can contain one or more ionic
functional moieties (denoted as FM), such as sulfonate or
carboxylate anions or the like.
##STR00001##
[0042] As an example, the organic monoazo laked pigment PR 57:1
("PR" refers to Pigment Red) has two functional moieties of two
different types, a sulfonate anion group (SO.sub.3.sup.-) and
carboxylate anion group (CO.sub.2.sup.-) and a metal counter-cation
M.sup.n+ that is chosen from Group 2 alkaline earth metals such as
Ca.sup.2+. Other monoazo laked pigment compositions also exist that
have a counter-cattion chosen from either Group 2 alkaline earth
metals (Be, Mg, Ca, Sr, Ba,), Group 3 metals (_B, Al, Ga), Group 1
alkali metals (Li, Na, K, Cs), the transition metals such as Cr,
Mn, Fe, Ni, Cu, Zn, or others non-metallic cations such as ammonium
(NR.sub.4.sup.+), phosphonium (PR.sub.4.sup.+) wherein R-group can
be H or alkyl group having from about 1 to about 12 carbons.
Further, the azo group in the compounds can generally assume one or
more tautomeric forms, such as the "azo" tautomer form which has
the (N.dbd.N) linkage, and the "hydrazone" tautomer form which has
the (C.dbd.N--NH--) linkage that is stabilized by an intramolecular
hydrogen bond, where the hydrazone tautomer is known to be the
preferred structural form for PR 57:1.
##STR00002##
It is understood that formula (1) is understood to denote both such
tautomer forms. Due to the structural nature of monoazo laked
pigments being ionic salts, it is possible to have compounds that
associate non-covalently with the pigment, such as organic or
inorganic ionic compounds that can associate with the metal cation
through ionic or coordination-type bonding. Such ionic compounds
are included in a group of compounds which herein are referred to
as "stabilizers", and that function to reduce the surface tension
of the pigment particle and neutralize attractive forces between
two or more pigment particles or structures, thereby stabilizing
the chemical and physical structure of the pigment. The term
"complementary" as used in "complementary functional moiety" of the
stabilizer indicates that the complementary functional moiety is
capable of noncovalent chemical bonding with the functional moiety
of the organic pigment and/or the functional moiety of a pigment
precursor.
[0043] The term "precursor" as used in "precursor to the organic
pigment" can be any chemical substance that is an advanced
intermediate in the total synthesis of a compound (such as the
organic pigment). In embodiments, the organic pigment and the
precursor to the organic pigment may or may not have the same
functional moiety. In embodiments, the precursor to the organic
pigment may or may not be a colored compound. In still other
embodiments, the precursor and the organic pigment can have
different functional moieties. In embodiments, where the organic
pigment and the precursor have a structural feature or
characteristic in common, the phrase "organic pigment/pigment
precursor" is used for convenience rather than repeating the same
discussion for each of the organic pigment and the pigment
precursor.
[0044] The functional moiety (denoted as FM) of the organic
pigment/precursor can be any suitable moiety capable of
non-covalent bonding with the complementary functional group of the
stabilizer. Illustrative functional moieties of the organic
pigment/precursor include (but are not limited to) the following:
sulfonate/sulfonic acid, (thio)carboxylate/(thio)carboxylic acid,
phosphonate/phosphonic acid, ammonium and substituted ammonium
salts, phosphonium and substituted phosphonium salts, substituted
carbonium salts, substituted arylium salts, alkyl/aryl
(thio)carboxylate esters, thiol esters, primary or secondary
amides, primary or secondary amines, hydroxyl, ketone, aldehyde,
oxime, hydroxylamino, enamines (or Schiff base), porphyrins,
(phthalo)cyanines, urethane or carbamate, substituted ureas,
guanidines and guanidinium salts, pyridine and pyridinium salts,
imidazolium and (benz)imidazolium salts, (benz)imidazolones,
pyrrolo, pyrimidine and pyrimidinium salts, pyridinone, piperidine
and piperidinium salts, piperazine and piperazinium salts,
triazolo, tetraazolo, oxazole, oxazolines and oxazolinium salts,
indoles, indenones, and the like.
[0045] Pigment precursors for making monoazo laked nanopigments
consist of a substituted aniline precursor (denoted as "DC" in
Table 1) which forms the diazo group G.sub.d of Formula (1), a
nucleophilic or basic coupling compound (denoted as "CC" in Tables
2-6) which leads to the coupling group G.sub.c of Formula (1), and
a cation salt which is preferably a metal (denoted as "M" as shown
in Formula (1)). Representative examples of the aniline precursor
of laked monoazo pigments that have the functional moiety capable
of non-covalent bonding with a complementary functional group on
the stabilizer, include (but are not limited to) the following
structures (with the functional moiety "FM" denoted, if
applicable).
[0046] In an embodiment, the substituted aniline precursor (DC)
which leads to the diazonium group can be of the formula (2):
##STR00003##
where R.sub.1, R.sub.2, and R.sub.3 independently represent H, a
straight or branched alkyl group of from about 1 to about 10 carbon
atoms (such as methyl, ethyl, propyl, butyl, and the like), halogen
(such as Cl, Br, I), NH.sub.2, NO.sub.2, CO.sub.2H,
CH.sub.2CH.sub.3, and the like; and functional moiety FM represents
SO.sub.3H, --C(.dbd.O)--NH-Aryl-SO.sub.3.sup.- where the aryl group
can be unsubstituted or substituted with either halogens (such as
Cl, Br, I, F) or alkyl groups having from about 1 to about 10
carbons (such as methyl, ethyl, propyl, butyl and the like)
CO.sub.2H, halogen (such as Cl, Br, I), NH.sub.2,
--C(.dbd.O)--NH.sub.2, and the like. The substituted aniline
precursor (DC) can be also be Tobias Acid, of the formula (3):
##STR00004##
Specific examples of types of aniline precursors (DC) that are used
to make the diazo group G.sub.d in the monoazo laked pigments
include those of Table 1:
TABLE-US-00001 TABLE 1 ##STR00005## Pre- cursor to Functional Group
Moiety G.sub.d FM R.sub.1 R.sub.2 R.sub.3 DC1 SO.sub.3H CH.sub.3 H
NH.sub.2 DC2 SO.sub.3H CH.sub.3 Cl NH.sub.2 DC3 SO.sub.3H Cl
CH.sub.3 NH.sub.2 DC4 SO.sub.3H Cl CO.sub.2H NH.sub.2 DC5 SO.sub.3H
Cl CH.sub.2CH.sub.3 NH.sub.2 DC6 SO.sub.3H Cl Cl NH.sub.2 DC7
SO.sub.3H H NH.sub.2 H DC8 SO.sub.3H H NH.sub.2 CH.sub.3 DC9
SO.sub.3H NH.sub.2 H Cl DC10 SO.sub.3H H H NH.sub.2 DC11 SO.sub.3H
H NH.sub.2 H DC12 SO.sub.3H NO.sub.2 NH.sub.2 H DC13 ##STR00006##
NH.sub.2 CH.sub.3 H DC14 CO.sub.2H H H NH.sub.2 DC15 Cl H H
NH.sub.2 DC16 NH.sub.2 CH.sub.3 H H DC17 NH.sub.2 H CH.sub.3 H DC18
##STR00007## NH.sub.2 CH.sub.3 H DC19 ##STR00008## H NH.sub.2 H
DC20 NH.sub.2 H H H DC21 ##STR00009##
[0047] In an embodiment, the coupling group G.sub.c of Formula (1)
can include .beta.-naphthol and derivatives of Formula (4),
naphthalene sulfonic acid derivatives of Formulas (5) and (6),
pyrazolone derivatives of Formula (7), acetoacetic arylide
derivatives of Formula (8), and the like. In formulas (4)-(8), the
asterisk "*" denotes the point of coupling or attachment to the
monoazo (N.dbd.N) linkage.
##STR00010##
where FM represents H, CO.sub.2H, SO.sub.3H,
--C(.dbd.O)--NH-Aryl-SO.sub.3.sup.- where the aryl group can be
unsubstituted or substituted with either halogens (such as Cl, Br,
I, F) or alkyl groups having from about 1 to about 10 carbons (such
as methyl, ethyl, propyl, butyl and the like) CO.sub.2H, halogen
(such as Cl, Br, I), NH.sub.2, --C(.dbd.O)--NH.sub.2, substituted
benzamides such as:
##STR00011##
wherein groups R.sub.2' R.sub.3', R.sub.4' and R.sub.5' can
independently be H, alkyl groups having from about 1 to 10 carbons
(such as methyl, ethyl, propyl, butyl, and the like), alkoxyl
groups (such as OCH.sub.3, OCH.sub.2CH.sub.3, and the like),
hydroxyl or halogen (such as Cl, Br, I, F) or nitro NO.sub.2; or
benzimidazolone amides such as:
##STR00012##
and the like.
##STR00013##
where FM represents preferably SO.sub.3H, but also can represent
CO.sub.2H, --C(.dbd.O)--NH-Aryl-SO.sub.3.sup.- where the aryl group
can be unsubstituted or substituted with either halogens (such as
Cl, Br, I, F) or alkyl groups having from about 1 to about 10
carbons (such as methyl, ethyl, propyl, butyl and the like)
CO.sub.2H, halogen (such as Cl, Br, I), NH.sub.2,
--C(.dbd.O)--NH.sub.2 groups R.sub.3 and R.sub.4 independently
represent H, SO.sub.3H, and the like.
##STR00014##
where FM represents preferably SO.sub.3H, but also can represent
CO.sub.2H, --C(.dbd.O)--NH-Aryl-SO.sub.3.sup.- where the aryl group
can be unsubstituted or substituted with either halogens (such as
Cl, Br, I, F) or alkyl groups having from about 1 to about 10
carbons (such as methyl, ethyl, propyl, butyl and the like)
CO.sub.2H, halogen (such as Cl, Br, I), NH.sub.2,
--C(.dbd.O)--NH.sub.2; R.sub.1, R.sub.2, R.sub.3 and R.sub.4
independently represent H, SO.sub.3H, --C(.dbd.O)--NH-Phenyl, and
the like.
##STR00015##
where G represents CO.sub.2H, straight or branched alkyl such as
having from 1 to about 10 carbons atoms (such as methyl, ethyl,
propyl, butyl, or the like), and the like; and R.sub.1', R.sub.2',
R.sub.3' and R.sub.4' independently represent H, halogen (such as
Cl, Br, I), SO.sub.3H, nitro (NO.sub.2) or alkoxyl group such as
OCH.sub.3 or OCH.sub.2CH.sub.3 and the like.
##STR00016##
where R.sub.1' represents a straight or branched alkyl group
having, for example, from 1 to about 10 carbon atoms (such as
methyl, ethyl, propyl, butyl, and the like); R.sub.2' represents a
benzimidazolone group:
##STR00017##
or a substituted aryl group
##STR00018##
where each of R.sub.a, R.sub.b, and R.sub.c independently
represents H, a straight or branched alkyl group having, for
example, from 1 to about 10 carbon atoms (such as methyl, ethyl,
propyl, butyl, and the like), alkoxyl groups such as OCH.sub.3 or
OCH.sub.2CH.sub.3 and the like, halogen (such as Cl, Br, I), nitro
NO.sub.2, and the like.
[0048] Representative examples of the nucleophilic coupling
component as a precursor of lakes monoazo pigments which have the
functional moiety that is capable of non-covalent bonding with a
complementary functional group on the stabilizer, include (but are
not limited to) the following structures shown in Tables 2-6 (with
the functional moiety "FM" denoted, if applicable):
TABLE-US-00002 TABLE 2 ##STR00019## Precursor to Class of
Functional group Coupling Moiety G.sub.c Component FM CC1
.beta.-Naphthol H CC2 .beta.-oxynaphthoic acid CO.sub.2H ("BONA")
CC3 Naphthol ASderivatives ##STR00020## CC6 Benzimidazolone
##STR00021##
TABLE-US-00003 TABLE 3 ##STR00022## Precursor to Class of group
Coupling G.sub.c Component FM R.sub.3 R.sub.4 CC4a Naphthalene
Sulfonic SO.sub.3H H H Acid derivatives CC4b Naphthalene Sulfonic
SO.sub.3H SO.sub.3H H Acid derivatives
TABLE-US-00004 TABLE 4 ##STR00023## Precursor to Class of group
Coupling G.sub.c Component FM R.sub.1 R.sub.2 R.sub.3 R.sub.4 CC5
Naphthalene SulfonicAcid derivatives SO.sub.3H ##STR00024## H H
SO.sub.3H
TABLE-US-00005 TABLE 5 ##STR00025## Precursor to Class of group
Coupling G.sub.c Component G R.sub.1' R.sub.2' R.sub.3' R.sub.4'
CC7 Pyrazolone deriv. CO.sub.2H H H SO.sub.3H H CC8 Pyrazolone
deriv. CH.sub.3 H H SO.sub.3H H CC9 Pyrazolone deriv. CH.sub.3 H
SO.sub.3H H H CC10 Pyrazolone deriv. CH.sub.3 Cl H SO.sub.3H Cl
TABLE-US-00006 TABLE 6 ##STR00026## Precursor to Class of group
Coupling G.sub.c Component R.sub.1' R.sub.2' R.sub.a R.sub.b
R.sub.c CC11 Acetoacetic arylide CH.sub.3 ##STR00027## H H H CC12
Acetoacetic arylide CH.sub.3 ##STR00028## CH.sub.3 H H CC13
Acetoacetic arylide CH.sub.3 ##STR00029## Cl H H CC14 Acetoacetic
arylide CH.sub.3 ##STR00030## H OCH.sub.3 H CC15
Acetoaceticbenzimidazolone CH.sub.3 ##STR00031## -- -- --
[0049] The organic pigment, and in some embodiments, the organic
pigment precursor, also generally includes a counterion as part of
the overall structure. Such counterions can be, for example, any
suitable counterion including those that are well known in the art.
Such counterions can be, for example, cations or anions of either
metals or non-metals that include N, P, S and the like, or
carbon-based cations or anions. Examples of suitable cations
include ions of Ba, Ca, Cu, Mg, Sr, Li, Na, K, Cs, Mn, Cu, Cr, Fe,
Ti, Ni, Co, Zn, V, B, Al, Ga, and other metal ions, as well as
ammonium and phosphonium cations, mono-, di-, tri-, and
tetra-substituted ammonium and phosphonium cations, where the
substitutents can be aliphatic alkyl groups, such as methyl, ethyl,
butyl, stearyl and the like, as well as aryl groups such as phenyl
or benzyl and the like.
[0050] Representative examples of monoazo laked pigments comprised
from a selection of substituted aniline precursor (denoted DC)
which can also include Tobias Acid, nucleophilic coupling component
(denoted as CC) and metal salts (denoted as M) to provide the
counter-cation M.sup.n+ of the formula (1) are listed in Table 7,
and other laked pigment structures may arise from other
combinations of DC and CC and metal cation salt (M) that are not
shown in Table 7.
TABLE-US-00007 TABLE 7 ##STR00032## Color Color Index Index G.sub.d
G.sub.c Metal # (C.I.) (C.I.) Name Laked Pigment Class precursor
precursor Salt M 15500:1 Red 50:1 .beta.-Naphthol Lakes DC14 CC1
1/2 Ba 15510:1 Orange 17 .beta.-Naphthol Lakes DC7 CC1 Ba 15510:2
Orange 17:1 .beta.-Naphthol Lakes DC7 CC1 2/3 Al 15525 Red 68
.beta.-Naphthol Lakes DC4 CC1 2 Ca 15580 Red 51 .beta.-Naphthol
Lakes DC8 CC1 Ba 15585 Red 53 .beta.-Naphthol Lakes DC3 CC1 2 Na
15585:1 Red 53:1 .beta.-Naphthol Lakes DC3 CC1 Ba 15585:3 Red 53:3
.beta.-Naphthol Lakes DC3 CC1 Sr 15602 Orange 46 .beta.-Naphthol
Lakes DC5 CC1 Ba 15630 Red 49 .beta.-Naphthol Lakes DC21 CC1 2 Na
15630:1 Red 49:1 .beta.-Naphthol Lakes DC21 CC1 Ba 15630:2 Red 49:2
.beta.-Naphthol Lakes DC21 CC1 Ca 15630:3 Red 49:3 .beta.-Naphthol
Lakes DC21 CC1 Sr 15800 Red 64 .beta.-oxynaphthoic acid (BONA)
Lakes DC20 CC2 1/2 Ba 15800:1 Red 64:1 .beta.-oxynaphthoic acid
(BONA) Lakes DC20 CC2 1/2 Ca 15800:2 Brown 5 .beta.-oxynaphthoic
acid (BONA) Lakes DC20 CC2 1/2 Cu 15825:2 Red 58:2
.beta.-oxynaphthoic acid (BONA) Lakes DC9 CC2 Ca 15825:4 Red 58:4
.beta.-oxynaphthoic acid (BONA) Lakes DC9 CC2 Mn 15850:1 Red 57:1
.beta.-oxynaphthoic acid (BONA) Lakes DC1 CC2 Ca 15860:1 Red 52:1
.beta.-oxynaphthoic acid (BONA) Lakes DC3 CC2 Ca 15860:2 Red 52:2
.beta.-oxynaphthoic acid (BONA) Lakes DC3 CC2 Mn 15865:1 Red 48:1
.beta.-oxynaphthoic acid (BONA) Lakes DC2 CC2 Ba 15865:2 Red 48:2
.beta.-oxynaphthoic acid (BONA) Lakes DC2 CC2 Ca 15865:3 Red 48:3
.beta.-oxynaphthoic acid (BONA) Lakes DC2 CC2 Sr 15865:4 Red 48:4
.beta.-oxynaphthoic acid (BONA) Lakes DC2 CC2 Mn 15865:5 Red 48:5
.beta.-oxynaphthoic acid (BONA) Lakes DC2 CC2 Mg 15867 Red 200
.beta.-oxynaphthoic acid (BONA) Lakes DC5 CC2 Ca 15880:1 Red 63:1
.beta.-oxynaphthoic acid (BONA) Lakes DC21 CC2 Ca 15880:2 Red 63:2
.beta.-oxynaphthoic acid (BONA) Lakes DC21 CC2 Mn 15892 Red 151
Naphthol AS Lakes DC10 CC3 Ba (R.sub.2' = H, R.sub.4' = SO.sub.3H)
15910 Red 243 Naphthol AS Lakes DC2 CC3 1/2 Ba (R.sub.2' =
OCH.sub.3, R.sub.4' = H) 15915 Red 247 Naphthol AS Lakes DC13 CC3
Ca (R.sub.2' = H, R.sub.4' = OCH.sub.3) 15985:1 Yellow 104
Naphthalene Sulfonic Acid Lakes DC7 CC4a 2/3 Al 15990 Orange 19
Naphthalene Sulfonic Acid Lakes DC15 CC4a 1/2 Ba 16105 Red 60
Naphthalene Sulfonic Acid Lakes DC14 CC4b 3/2 Ba 18000:1 Red 66
Naphthalene Sulfonic Acid Lakes DC16 CC5 1/2 Ba, Na
[0051] The complementary functional group of the stabilizer can be
one or more of any suitable moiety capable of non-covalent bonding
with the functional moiety of the stabilizer. Illustrative
complementary functional groups on the stabilizer include the
following: sulfonate/sulfonic acid,
(thio)carboxylate/(thio)carboxylic acid, phosphonate/phosphonic
acid, ammonium and substituted ammonium salts, phosphonium and
substituted phosphonium salts, substituted carbonium salts,
substituted arylium salts, alkyl/aryl (thio)carboxylate esters,
thiol esters, primary or secondary amides, primary or secondary
amines, hydroxyl, ketone, aldehyde, oxime, hydroxylamino, enamines
(or Schiff base), porphyrins, (phthalo)cyanines, urethane or
carbamate, substituted ureas, guanidines and guanidinium salts,
pyridine and pyridinium salts, imidazolium and (benz)imidazolium
salts, (benz)imidazolones, pyrrolo, pyrimidine and pyrimidinium
salts, pyridinone, piperidine and piperidinium salts, piperazine
and piperazinium salts, triazolo, tetraazolo, oxazole, oxazolines
and oxazolinium salts, indoles, indenones, and the like.
[0052] The stabilizer can be any compound that has the function of
limiting the extent of pigment particle or molecular self-assembly
so as to produce predominantly nanoscale-sized pigment particles.
The stabilizer compound should have a hydrocarbon moiety that
provides sufficient steric bulk to enable the function of the
stabilizer to regulate pigment particle size. The hydrocarbon
moiety in embodiments is predominantly aliphatic, but in other
embodiments can also incorporate aromatic groups, and generally
contains at least 6 carbon atoms, such as at least 12 carbons or at
least 16 carbons, and not more than about 100 carbons, but the
actual number of carbons can be outside of these ranges. The
hydrocarbon moiety can be either linear, cyclic or branched, and in
embodiments is desirably branched, and may or may not contain
cyclic moieties such as cycloalkyl rings or aromatic rings. The
aliphatic branches are long with at least 2 carbons in each branch,
such as at least 6 carbons in each branch, and not more than about
100 carbons.
[0053] It is understood that the term "steric bulk" is a relative
term, based on comparison with the size of the pigment or pigment
precursor to which it becomes non-covalently associated. In
embodiments, the phrase "steric bulk" refers to the situation when
the hydrocarbon moiety of the stabilizer compound that is
coordinated to the pigment/precursor surface, occupies a
3-dimensional spatial volume that effectively prevents the approach
or association of other chemical entities (e.g. colorant molecules,
primary pigment particles or small pigment aggregate) toward the
pigment/precursor surface. Thus, the stabilizer should have its
hydrocarbon moiety large enough so that as several stabilizer
molecules become non-covalently associated with the chemical entity
(pigment or precursor), the stabilizer molecules act as surface
barrier agents for the primary pigment particles and effectively
encapsulates them, and thereby limits the growth of the pigment
particles and affording only nanoparticles of the pigment. For
example, for the pigment precursor Lithol Rubine and for the
organic pigment Pigment Red 57:1, the following illustrative groups
on a stabilizer are considered to have adequate "steric bulk" so as
to enable the stabilizer to limit the extent of pigment
self-assembly or aggregation and mainly produce pigment nano-sized
particles:
##STR00033##
Representative examples of stabilizer compounds that have both the
functional group that non-covalently associates with the pigment
and the sterically bulky hydrocarbon moiety, include (but are not
limited to) the following compounds:
##STR00034##
[0054] Z=H; Metal cations such as Na, K, Li, Ca, Ba, Sr, Mg, Mn,
Al, Cu, B, and others; [0055] Organic cations such as
NH.sub.4.sup.+, NR.sub.4.sup.+, PR.sub.4.sup.+, and others
##STR00035##
[0056] Z=H; Metal cations such as Na, K, Li, Ca, Ba, Sr, Mg, Mn,
Al, Cu, B, and others; [0057] Organic cations such as
NH.sub.4.sup.+, NR.sub.4.sup.+, PR.sub.4.sup.+, and others [0058]
and methylene units (m+n)>1
##STR00036##
[0059] Z=H; Metal cations such as Na, K, Li, Ca, Ba, Sr, Mg, Mn,
Al, Cu, B, and others; [0060] Organic cations such as
NH.sub.4.sup.+, NR.sub.4.sup.+, PR.sub.4.sup.+, and others [0061]
and methylene units (m+n)>1 [0062] per branch
##STR00037##
[0063] Z=H; Metal cations such as Na, K, Li, Ca, Ba, Sr, Mg, Mn,
Al, Cu, B, and others; [0064] Organic cations such as
NH.sub.4.sup.+, NR.sub.4.sup.+, PR.sub.4.sup.+, and others [0065]
and methylene units m.gtoreq.1 [0066] and for iso-stearic acid,
n.ltoreq.1 wherein m and n denotes the number of repeated methylene
units, and where m can range between 1 and 50, and n can range
between 1 and 5, however the values can also be outside these
ranges.
[0067] In additional embodiments, other stabilizer compounds having
different structures than those described previously may be used in
addition to sterically bulky stabilizer compounds, to function as
surface active agents (or surfactants) that either prevent or limit
the degree of pigment particle aggregation. Representative examples
of such surface active agents include, but are not limited to,
rosin natural products such as abietic acid, dehydroabietic acid,
pimaric acid, rosin soaps (such as the sodium salt of the rosin
acids), hydrogenated derivatives of rosins and their alkyl ester
derivatives made from glycerol or pentaerythritol or other such
hydrocarbon alcohols, acrylic-based polymers such as poly(acrylic
acid), poly(methyl methacrylate), styrene-based copolymers such as
poly(styrene sodio-sulfonate) and poly(styrene)-co-poly(alkyl
(meth)acrylate), copolymers of .alpha.-olefins such as
1-hexadecene, 1-octadecene, 1-eicosene, 1-triacontene and the like,
copolymers of 4-vinyl pyridine, vinyl imidazole, and vinyl
pyrrolidinone, polyester copolymers, polyamide copolymers,
copolymers of acetals and acetates, such as the copolymer
poly(vinylbutyral)-co-(vinyl alcohol)-co-(vinyl acetate).
[0068] The types of non-covalent chemical bonding that can occur
between the functional moiety of the precursor/pigment and the
complementary functional group of the stabilizer are, for example,
van der Waals' forces, ionic or coordination bonding, hydrogen
bonding, and/or aromatic pi-stacking bonding. In embodiments, the
non-covalent bonding is predominately ionic bonding, but can
include hydrogen bonding and aromatic pi-stacking bonding as
additional or alternative types of non-covalent bonding between the
functional moieties of the stabilizer compounds and the
precursor/pigment.
[0069] The "average" pigment particle size, which is typically
represented by Z-average, which is defined as an intensity mean
which is derived from the cumulants analysis of an intensity signal
obtained from dynamic light scattering method, and also by
d.sub.50, which is defined as the median particle size value at the
50th percentile of the particle size distribution, wherein 50% of
the particles in the distribution are greater than the d.sub.50
particle size value and the other 50% of the particles in the
distribution are less than the d.sub.50 value. Average particle
size can be measured by methods that use light scattering
technology to infer particle size, such as by dynamic light
scattering (DLS). The term "particle diameter" as used herein
refers to the length of the pigment particle at the longest
dimension (in the case of acicular shaped particles) as derived
from images of the particles generated by Transmission Electron
Microscopy (TEM). The term "nano-sized", "nanoscale", "nanoscopic",
or "nano-sized pigment particles" refers to for instance, an
average particle size, d.sub.50, or Z-average, or an average
particle diameter of less than about 150 nm, such as of about 1 nm
to about 100 nm, or about 10 nm to about 80 nm. Typically, the
distribution of a population of particle sizes is expressed by a
width parameter or the polydispersity index (PDI), such as can be
derived by DLS technique, and also by geometric standard deviation
(GSD) which is a dimensionless number that typically estimates a
population's dispersion of a given attribute (for instance,
particle size) about the median value of the population and is
derived from the exponentiated value of the standard deviation of
the log-transformed values. If the geometric mean (or median) of a
set of numbers {A.sub.1, A.sub.2, . . . , A.sub.n} is denoted as
.mu..sub.g, then the geometric standard deviation is calculated
as:
.sigma. g = exp i = 1 n ( ln A i - ln .mu. g ) 2 n ##EQU00001##
[0070] The method of making nano-sized particles of the monoazo
laked pigments such as those listed in Table 7 is a process that
involves at least one or more reaction steps. A diazotization
reaction is a key reaction step for synthesis of the monoazo laked
pigment, whereby a suitably substituted aniline precursor (denoted
as diazo component DC) such as those listed in Table 1, and
Formulas (2) and (3), is either directly or indirectly converted
first to a diazonium salt using standard procedures, such as that
which includes treatment with an effective diazotizing agent such
as nitrous acid HNO.sub.2 (which is generated in situ by mixing
sodium nitrite with dilute protic acid solution such as
hydrochloric acid), or nitrosyl sulfuric acid (NSA), which is
commercially available or can be prepared by mixing sodium nitrite
in concentrated sulfuric acid. Initially, it may be necessary to
first dissolve the precursor substituted aniline in alkaline
solution (such as aqueous potassium hydroxide solution, or ammonia
water) followed by treatment with the diazotizing agent and acid
solution, so as to generate the diazonium salt. The diazotization
procedure is typically carried out at cold temperatures so as to
keep the diazonium salt stable, and the resulting reaction mixture
will comprise mainly the diazonium salt either dissolved or
suspended as a precipitate in acidic medium. If desired and
effective, an aqueous solution of the metal salt (M.sup.n+) can be
optionally added that will define the specific composition of the
desired monoazo laked pigment product, such as those listed in
Table 7. A second solution or suspension is prepared by dissolving
or suspending the nucleophilic coupling component (denoted as CC,
such as those shown in Tables 2-6, and Formulas (4)-(8)) mainly
into water, which may optionally contain another liquid such as an
organic solvent (for example, iso-propanol, tetrahydrofuran,
methanol, or other), and either acids or bases to render the
coupling component into solution or a fine suspension and aid
reaction with the diazonium salt solution, and additionally any
buffers or surface active agents including the sterically bulky
stabilizer compounds such as those described previously.
[0071] The reaction mixture containing the dissolved or suspended
diazonium salt is then transferred into the solution or suspension
of the desired nucleophilic coupling component, and the temperature
of the mixture can range from about 10.degree. C. to about
75.degree. C., in order to produce a solid colorant material
suspended as a precipitate in an aqueous slurry.
[0072] The solid colorant material may be the desired monoazo laked
pigment product formed as nano-sized particles, or it may be an
advanced synthetic intermediate for making the monoazo laked
pigment product. In the case of the latter, a two-step process is
required for preparing the nano-sized particles of monoazo laked
pigment, whereby the second step involves rendering the advanced
synthetic intermediate of the first step above (the pigment
precursor) into homogeneous liquid solution by treatment with
either strong acid or alkaline base, then treating this solution
with one or more surface active agents in addition to the
sterically bulky stabilizer compounds, as described previously,
followed lastly by treatment with the required metal salt solution
to provide the desired laked monoazopigment composition as a solid
precipitate, said metal salt solution effectively functioning as a
pigment precipitating agent. There are several chemical as well as
physical processing factors can affect the final particle size and
distribution of the monoazo laked pigment nanoparticles, including
stoichiometries of the DC and CC starting reactants, metal salt,
surface active agents, and stabilizer compounds, the concentrations
of chemical species in the liquid medium, pH of liquid medium,
temperature, addition rate, order of addition, agitation rate,
post-reaction treatments such as heating, isolation and washing of
particles, and drying conditions.
[0073] In embodiments is disclosed a two-step method of making
nano-sized monoazo laked red pigments, for example Pigment Red
57:1, wherein the advanced pigment precursor Lithol Rubine is first
synthesized as a potassium salt and is a water-soluble orange dye.
The first step involves the diazotization of
2-amino-5-methyl-benzenesulfonic acid (DC1 in Table 1) by first
dissolving the DC in dilute aqueous potassium hydroxide solution
(0.5 mol/L) and cooling to a temperature anywhere in the range of
about -5.degree. C. to about 5.degree. C., and then treating the
solution with an aqueous solution of sodium nitrite (20 wt %),
following with slow addition of concentrated hydrochloric acid at a
rate that maintains the internal reaction temperature between
-5.degree. C. and +5.degree. C. The resulting suspension that forms
is stirred for additional time so as to ensure completeness of
diazotization, and then the suspension is carefully transferred to
a second solution containing 3-hydroxy-2-naphthoic acid dissolved
in dilute alkaline solution (0.5 mol/L potassium hydroxide), using
vigorous agitation as the colorant product is produced in the
aqueous slurry. After stirring for additional time of at least 1
hour at room temperature, the colorant product (Lithol
Rubine-potassium salt) is isolated by filtration as an orange
dyestuff and washed with deionized water to remove excess salt
by-products.
[0074] The second step of the process involves redispersing the
orange Lithol Rubine-potassium salt dyestuff in deionized water to
a concentration that can range from about 0.5 wt % to about 20 wt
%, such as from about 1.5 wt % to about 10 wt % or from about 3.5
wt % to about 8 wt %, but the concentrations can also be outside of
these ranges. The colorant solids in the slurry is then dissolved
completely into liquid solution by treatment with aqueous alkaline
base, such as sodium hydroxide or potassium hydroxide or ammonium
hydroxide solution, until the pH level is high, such as above pH
8.0 or above pH 9.0 or above pH 10.0. To this alkaline solution of
dissolved Lithol Rubine colorant can be optionally added a surface
active agent as described previously, in particular embodiments
surface active agent such as rosin soaps, delivered as an aqueous
solution in the amount ranging from 0.1 wt % to 20 wt % based on
colorant solids, such as in an amount ranging from 0.5 wt % to
about 10 wt %, or in an amount ranging from 1.0 wt % to about 8.0
wt % based on colorant solids, but the amount used can also be
outside of these ranges.
[0075] In embodiments, the preparation of ultrafine and nanosized
particles of the monoazo laked Pigment Red 57:1 was only enabled by
the additional use of a sterically bulky stabilizer compound having
a functional group that could non-covalently bond to the
complementary functional moiety of the pigment as well as branched
aliphatic functional groups that could provide steric bulk to the
pigment particle surface. In embodiments, particularly suitable
sterically bulky stabilizer compounds are branched hydrocarbons
with either carboxylate or sulfonate functional groups, compounds
such as di[2-ethylhexyl]-3-sulfosuccinate sodium or sodium
2-hexyldecanoate, and the like. The stabilizer compound is
introduced as a solution or suspension in a liquid that is
predominantly aqueous but may optionally contain a water-miscible
organic solvent such as THF, iso-propanol, NMP, Dowanol and the
like, to aid dissolution of the stabilizer compound, in an amount
relative to colorant moles ranging from about 5 mole-percent to
about 100 mole-percent, such as from about 20 mole-percent to about
80 mole-percent, or from about 30 mole-percent to about 70
mole-percent, but the concentrations used can also be outside these
ranges and in large excess relative to moles of colorant.
[0076] Lastly, the metal cation salt is added to transform the
pigment precursor (Lithol Rubine-potassium salt in embodiments)
into the desired monoazo laked pigment (Pigment Red 57:1 in
embodiments), precipitated as nano-sized pigment particles. The
aqueous solution of metal salt (calcium chloride in embodiments)
with concentration ranging anywhere from 0.1 mol/L to about 2
mol/L, is slowly added dropwise in nearly stoichiometric quantities
such as amounts ranging from 1.0 molar equivalents relative to
about 2.0 molar equivalents, or from 1.1 to about 1.5 molar
equivalents, or from 1.2 to about 1.4 molar equivalents relative to
moles of colorant, however the amounts used can also be outside of
these ranges and in large excess.
[0077] The type of metal salt can have an impact on the extent of
forming nano-sized pigment particles of monoazo laked pigments, in
particular the type of ligand that is coordinated to the metal
cation and the relative ease with which it is displaced by a
competing ligand from either the pigment functional moiety or the
complementary functional moiety of the stabilizer compound, or
both. In embodiments for monoazo laked Pigment Red 57:1, the
nano-sized particles are formed using calcium (II) salts with
ligands such as chloride, sulfate, acetate, and hydroxide; however
a particularly desirable metal salt is calcium chloride for fastest
reactivity.
[0078] The rates of addition of metal salt solution can also vary.
For example, the slower the rate of addition, the more controlled
is the rate of pigment crystal formation and particle aggregation,
and therefore the smaller in size the pigment particles become.
[0079] Also important is the agitation rate and mixing pattern as
the pigment formation/precipitation step is occurring. The higher
the agitation rate and the more dynamic or complex is the mixing
pattern (i.e. with baffles to prevent dead mixing zones), the
smaller is the average particle diameter and the more narrow is the
particle size distribution, as observable by Transmission Electron
Microscopy (TEM) imaging. Agitation can be made more effective by
using high-shear mixers such as homogenizers, attritors, our even
the use of ultrasonic probes.
[0080] Temperature during the pigment precipitation step using the
metal salt solution is also important. In embodiments, lower
temperatures are desired, such as from about 10.degree. C. to about
50.degree. C., or from about 15.degree. C. to about 30.degree. C.,
but the temperature can also be outside of these ranges.
[0081] In embodiments, the slurry of pigment nanoparticles is not
treated nor processed any further, such as performing additional
heating which is often practiced by pigment manufacturers, but
instead is isolated by vacuum filtration or centrifugal separation
processes. The pigment solids can be washed copiously with
deionized water to remove excess salts or additives that are not
tightly associated or bonded with the pigment particle surface. The
pigment solids can be dried by freeze-drying under high vacuum, or
alternatively, they can be pre-rinsed with a water-miscible solvent
such as isopropanol or acetonitrile to remove excess water and then
vacuum-oven dried. The resulting nano-size pigment particles are
generally non-aggregated and of high quality, which when imaged by
TEM (Transmission Electron Microscopy), exhibit primary pigment
particles and small aggregates ranging in diameters from about 10
nm to about 300 nm, and predominantly from about 50 nm to about 150
nm. (Here, it is noted that average particle size d.sub.50 or
Z-average, and GSD particle size distributions are measured by
Dynamic Light Scattering, an optical measurement technique that
estimates the hydrodynamic radius of non-spherical pigment
particles gyrating and translating in a liquid dispersion via
Brownian motion, by measuring the intensity of the incident light
scattered from the moving particles. As such, the d.sub.50 or the
Z-average particle size metric obtained by DLS technique is always
a larger number than the actual particle diameters observed by TEM
imaging.)
[0082] Characterization of the chemical composition of washed and
dried nano-sized pigment particles are performed by NMR
spectroscopy and elemental analysis. In embodiments, the
composition of the monoazo laked pigment Red 57:1 indicated that
the nano-sized particles prepared by the methods described above,
particularly when using di[2-ethylhexyl]-3-sulfosuccinate sodium as
the sterically bulky stabilizer, retained at least 80% of the
sterically bulky stabilizer that was loaded into the process of
making the nanoparticles, even after copious washing with deionized
water to remove excess salts. Solid state .sup.1H- and .sup.13C-NMR
spectroscopic analyses indicated that the steric stabilizer
compound was associated non-covalently with the pigment as a
calcium salt, and the chemical structure of the pigment adopted the
hydrazone tautomer form, as shown in Figure below.
##STR00038##
[0083] Pigment particles of monoazo laked pigments such as PR 57:1
that have smaller particle sizes could also be prepared by the
above two-step method in the absence of using sterically bulky
stabilizers and with the use of surface active agents alone (for
example, only rosin-type surface agents), depending on the
concentrations and process conditions employed, but the pigment
product did not predominantly exhibit nano-sized particles nor did
the particles exhibit regular morphologies. In the absence of using
the sterically bulky stabilizer compound, the two-step method
described above typically produced rod-like particle aggregates,
ranging in average particle diameter from 200-700 nm and with wide
particle distribution, and such particles were difficult to
disperse into a polymer coating matrix and generally gave poor
coloristic properties. In embodiments, the combined use of a
suitable sterically bulky stabilizer compound, such as branched
alkanesulfonates or alkylcarboxylates, with a minor amount of
suitable surface active agent such as derivatives of rosin-type
surfactants, using either of the synthesis methods described
previously would afford the smallest fine pigment particles having
nanometer-scale diameters, more narrow particle size distribution,
and low aspect ratio. Various combinations of these compounds, in
addition to variations with process parameters such as
stoichiometry of reactants, concentration, addition rate,
temperature, agitation rate, reaction time, and post-reaction
product recovery processes, enables the formation of pigment
particles with tunable average particle size (d.sub.50 or
Z-average) from nanoscale sizes (about 1 to about 100 nm) to
mesoscale sizes (about 100 to about 500 nm) or larger.
[0084] The advantages of this process include the ability to tune
particle size and composition for the intended end-use application
of the monoazo laked pigment, such as for use in toners and inks
and coatings, which for example include phase-change, gel-based and
radiation-curable inks, solid and non-polar liquid inks,
solvent-based inks and aqueous inks and ink dispersions. For the
end-use application in piezoelectric inkjet printing, nano-sized
particles are advantageous to ensure reliable inkjet printing and
prevent blockage of jets due to pigment particle agglomeration. In
addition, nano-sized pigment particles are advantageous for
offering enhanced color properties in printed images, since in
embodiments the color properties of nano-sized particles of monoazo
laked pigment Red 57:1 were tunable with particle size. It was
observed that as average particle size was decreased to the
nanometer-scale, the hue angles were shifted from yellowish-red
hues to bluish-red hues by an amount ranging from about 5 to about
35.degree. in the color gamut space.
[0085] In embodiments, the nanosized pigment particles that were
obtained for monoazo laked pigments can range in average particle
size, d.sub.50 or Z-average, or the average particle diameter, from
about 10 nm to about 250 nm or about 500 nm, such as from about 25
nm to about 175 nm, or from about 50 nm to about 150 nm, as
measured by either dynamic light scattering method or from TEM
images. The pigment average particle size can accordingly be tuned
by the above method, to provide compositions with desired average
particle sizes. For example, within the broad suitable size range
of about 1 nm to about 500 nm or larger, the pigment composition
can be provided to have an average particle size that is generally
in the nanoscale size range (about 1 to about 100 nm) or generally
in the mesoscale size range (about 100 to about 500 nm) or larger.
In embodiments, the pigment composition can be provided to have an
average particle size in the ranges of from about 10 nm to about 50
nm, about 50 nm to about 100 nm, about 100 nm to about 150 nm, or
about 150 nm to about 300 nm. For example, in embodiments, the
pigment composition can be provided to have an average particle
size of about 50 nm to about 12550 nm. In embodiments, the particle
size distributions can range such that the geometric standard
deviation can range from about 1.1 to about 1.9, or from about 1.2
to about 1.7, as measured by dynamic light scattering method. The
shape of the nanosized pigment particles can be one or more of
several morphologies, including rods, platelets, needles, prisms or
nearly spherical, and the aspect ratio of the nanosize pigment
particles can range from about 1:1 to about 10:1, such as having
aspect ratio between about 1:1 and about 5:1; however the actual
metric can lie outside of these ranges.
[0086] In addition, nanosized pigment particles are advantageous
for offering enhanced color properties in printed images, since in
embodiments the color properties of nanosized particles of monoazo
laked pigment Red 57:1 were tunable with particle size. In
embodiments is disclosed the coloristic properties (hue angle, a*,
b*, and NLSI as measure of specular reflectivity) of nanosized
pigment particles, particularly of monoazo laked red pigment, that
are directly correlated and tunable with the average pigment
particle size, measured by either Dynamic Light Scattering or
electron microscopy imaging techniques, as well as pigment
composition with the non-covalently associated stabilizer, the
latter which enables the control of particle size during pigment
synthesis, and also enables enhanced dispersability within certain
polymer binders for coating or other applications. For example, as
average particle size was decreased to nanometer-scale, the hue
angles were shifted from yellowish-red hues to bluish-red hues by
an amount ranging from about 5 to about 35.degree. in the color
gamut space. The color of the nanosized pigment particles have the
same general hue as is found with larger pigment particles.
However, in embodiments, is disclosed coloristic properties of thin
coatings of the nano-sized pigment particles of red monoazo laked
pigments dispersed in a polymer binder (such as of poly(vinyl
butyral-co-vinyl alcohol-co-vinyl acetate)), that exhibited a
significant shift to lower hue angle and lower b* values that
revealed more bluish magenta hues, and having either no change or a
small enhancement of a* value. In embodiments, any suitable polymer
can be used to effect both good pigment dispersion and to act as a
pigment binder to allow a good film forming quality about the
substrate. In other embodiments, it is advantageous when assessing
coloristic properties of pigments, as they are dispersed in
coatings, for example, that the polymer used to disperse a pigment
is transparent to visible light, either chemically or by way of not
scattering light owing to the polymer being more amorphous than
crystalline, not be prone to fluorescence, and does not discolor
during a dispersion making process or during the drying process
after it has been coated on a substrate.
[0087] In embodiments, the hue angles of the coatings dispersed
with the nanosized particles of monoazo laked pigment such as
Pigment Red 57:1 measured in the range from about 345.degree. to
about 5.degree. on the 2-dimensional b* a* color gamut space, as
compared with hue angles ranging from about 0.degree. to about
20.degree. for similarly prepared polymer coatings dispersed with
conventional larger sized particles of Pigment Red 57:1. The
coatings dispersed with the nanosized particles of monoazo laked
pigment can accordingly exhibit hue angles of from about
345.degree. to about 5.degree., such as from about 345.degree. to
about 0.degree., or from about 345.degree. to about 350.degree. or
to about 355.degree., on the 2-dimensional b* a* color gamut
space.
[0088] Additionally, the specular reflectivity of the coatings of
the nanosized monoazo laked red pigment was significantly enhanced
from coatings produced with conventional larger sized pigment
particles, which is an indicator of having very small particles
being well-dispersed within the coating. Specular reflectivity was
quantified as the degree of light scattering for the pigmented
coating, a property that is dependent on the size and shape
distributions of the pigment particles and their relative
dispersability within the coating binder. The Normalized Light
Scatter Index (NLSI) was quantified by measuring the spectral
absorbance of the coating, using a Shimadzu UV-160
spectrophotometer, in a region where there is no absorbance from
the chromogen of the monoazo laked pigment, but only absorbance due
to light scattered from large aggregates and/or agglomerated
pigment particles dispersed in the coating binder. The light
scattering absorbance data is then normalized to a lambda-max
optical density of 1.5, resulting in the NLSI value, in order to
directly compare the light scattering indices of several pigmented
coatings. The lower is the NLSI value, the smaller is the pigment
particle size within the dispersed coating matrix. In embodiments,
the NLSI value of the nanosized monoazo laked red pigments can
range from about 0.1 to about 3.0, such as from about 0.1 to about
1.0. In comparison, the NLSI values observed with similarly
prepared coatings containing conventional larger sized monoazo
laked red pigments range anywhere from about 3.0 to about 75 (which
indicates a very poorly dispersed coating).
[0089] The formed nanoscale pigment particle compositions can be
used, for example, as coloring agents in a variety of compositions,
such as in liquid (aqueous or non-aqueous) ink vehicles, including
inks used in conventional pens, markers, and the like, liquid ink
jet ink compositions, solid or phase change ink compositions, and
the like. For example, the colored nanoparticles can be formulated
into a variety of ink vehicles, including "low energy" solid inks
with melt temperatures of about 60 to about 130.degree. C., and
solvent-based liquid inks or radiation-curable such as UV-curable
liquid inks comprised of alkyloxylated monomers, and even aqueous
inks.
[0090] In addition to ink compositions, the nanoscale-sized pigment
composition can be used in a variety of other applications, where
it is desired to provide a specific color to the composition. For
example, the nanoscale-sized pigment composition can also be used
in the same manner as conventional pigments in such uses as
colorants for paints, resins, lenses, filters, printing inks, and
the like according to applications thereof. By way of example only,
the nanoscale-sized pigment composition of embodiments can be used
for toner compositions, which include polymer particles and
nanoscale pigment particles, along with other optional additives,
that are formed into toner particles and optionally treated with
internal or external additives such as flow aids, charge control
agents, charge-enhancing agents, filler particles,
radiation-curable agents or particles, surface release agents, and
the like.
[0091] An example is set forth herein below and is illustrative of
different compositions and conditions that can be utilized in
practicing the disclosure. All proportions are by weight unless
otherwise indicated. It will be apparent, however, that the
disclosure can be practiced with many types of compositions and can
have many different uses in accordance with the disclosure above
and as pointed out hereinafter.
EXAMPLES
Examples of Monoazo Laked Red Pigment Compositions and Methods of
Making in Various Particle Sizes
Comparative Example 1
Synthesis of Pigment Red 57:1 Particles Using a Two-Step Method
[0092] Step 1: Diazotization and Coupling: Into a 500 mL round
bottom flask equipped with a mechanical stirrer, thermometer, and
addition funnel was dissolved 2-amino-5-methylbenzenesulfonic acid
(8.82 g) into 0.5M KOH aqueous solution (97.0 mL). The resulting
brown solution was cooled to 0.degree. C. A 20 wt % aqueous
solution of sodium nitrite (NaNO.sub.2; 3.28 g dissolved into 25 mL
water) was added slowly to the first solution while maintaining the
temperature below 3.degree. C. To the red-brown homogeneous mixture
was added dropwise concentrated HCl (10M, 14.15 mL) over 1 hour,
maintaining the internal temperature below 2.degree. C. The mixture
formed a pale brown suspension, and following complete addition of
conc. HCl, the suspension was stirred an additional 30 min.
[0093] In a separate 2-L resin kettle was dissolved
3-hydroxy-2-naphthoic acid (8.86 g) into an aqueous solution of KOH
(8.72 g) in water (100 mL). An additional 250 mL of water was
added, and the light-brown solution was then cooled to 15.degree.
C. while stirring vigorously. The cold suspension of the diazonium
salt suspension was then added slowly to the coupling solution
while mixing vigorously. The color changed initially to a dark red
solution, and ultimately to a yellowish-red (orange) slurry of
precipitated dyestuff. The mixture was stirred for 2 hours while
warming up to room temp, then filtered and diluted with about 500
mL of deionized water to produce an orange aqueous slurry of Lithol
Rubine-Potassium salt dye (a synthetic precursor of Pigment Red
57:1) having solids content of about 1.6 wt %.
[0094] Step 2: Laking Step to Produce Pigment Red 57:1
Particles
[0095] Into a 500 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 126 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor from above having about 1.6% wt
solids content. The pH of the slurry was adjusted to at least 9.0
or higher by addition of 0.5 M KOH solution, after which the
dyestuff was fully dissolved. An aqueous solution of calcium
chloride dihydrate (0.5 M solution, 13 mL) was added dropwise to
the slurry while stirring vigorously. A red precipitate formed
immediately, and after addition was completed, the slurry was
stirred for an additional 1 hour. The red slurry was then heated to
about 75.degree. C. for 20 min, then cooled to room temp. The
slurry was filtered under high vacuum through a 1.2 .mu.m acrylic
polymer membrane, then reslurried twice with 200 mL portions of
deionized water. The pH and conductivity of the filtrates after
each filtration were measured and recorded, with the final wash
filtrate having nearly neutral pH of 6.2 and conductivity of about
13.5 .mu.S/cm, indicating low residual salts. The red pigment
filtercake was reslurried into about 200 mL of DIW and freeze-dried
for 48 hours, to afford a red colored powder (1.95 grams). TEM
microscopy revealed long rod-like particles and aggregates, with
particle diameters ranging from about 200 nm to about 700 nm, and
large aspect ratios ranging from about 4:1 to about 10:1.
Example 1
Synthesis of Nano-Sized Particles of Pigment Red 57:1 by a Two-Step
Method
[0096] Step 1: Diazotization and Coupling: Into a 500 mL round
bottom flask equipped with a mechanical stirrer, thermometer, and
addition funnel was dissolved 2-amino-5-methylbenzenesulfonic acid
(8.82 g) into 0.5M KOH aqueous solution (97.0 mL). The resulting
brown solution was cooled to 0.degree. C. A 20 wt % aqueous
solution of sodium nitrite (NaNO.sub.2; 3.28 g dissolved into 25 mL
water) was added slowly to the first solution while maintaining the
temperature below 3.degree. C. To the red-brown homogeneous mixture
was added dropwise concentrated HCl (10M, 14.15 mL) over 1 hour,
maintaining the internal temperature below 2.degree. C. The mixture
formed a pale brown suspension, and following complete addition of
conc. HCl, the suspension was stirred an additional 30 min.
[0097] In a separate 2-L resin kettle was dissolved
3-hydroxy-2-naphthoic acid (8.86 g) into an aqueous solution of KOH
(8.72 g) in water (100 mL). An additional 250 mL of water was
added, and the light-brown solution was then cooled to 15.degree.
C. while stirring vigorously. The cold suspension of the diazonium
salt suspension was then added slowly to the coupling solution
while mixing vigorously. The color changed immediately to a dark
red solution, and ultimately to a yellowish-red (orange) slurry of
precipitated dyestuff. The mixture was stirred for 2 hours while
warming up to room temp, then filtered and reslurried with about
500 mL of deionized water to produce an orange aqueous slurry of
Lithol Rubine-Potassium salt dye having solids content of about 1.6
wt %.
[0098] Step 2: Laking Step to Produce Pigment Red 57:1
Particles:
[0099] Into a 500 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 126 g of aqueous slurry of Lithol
Rubine-Potassium salt dye from above (Example 1, Step 1) having
about 1.6% wt solids content. The pH of the slurry was adjusted to
at least 9.0 or higher by addition of 0.5 M KOH solution, after
which the dyestuff was fully dissolved. An aqueous solution 5 wt %
Dresinate X (4.0 mL) was added, followed by a solution containing
sodium dioctyl sulfosuccinate (0.96 g) dissolved in 100 mL of 90:10
deionized water/THF mixture. No visible change was observed. An
aqueous solution of calcium chloride dihydrate (0.5 M solution, 13
mL) was added dropwise to the slurry while stirring vigorously. A
red precipitate formed immediately, and after complete addition of
the calcium chloride solution, the slurry was stirred for an
additional 1 hour. The red slurry was then heated to about
75.degree. C. for 20 min, then cooled to room temp. The slurry was
filtered under high vacuum through a 0.45 .mu.m Nylon membrane
cloth, then reslurried twice with 75 mL portions of DIW. The pH and
conductivity of the final wash filtrate was 7.4 and about 110
.mu.S/cm, respectively, indicating that residual acids and salt
by-products were removed. The red pigment filtercake was reslurried
in about 250 mL of DIW and freeze-dried for 48 hours to afford a
dark red colored powder (2.65 grams). Transmission electron
microscopy images of the powder revealed platelet-like particles
with particle diameters ranging from 30-150 nm, and aspect ratios
that were less than 3:1. .sup.1H-NMR spectroscopy analysis (300
MHz, DMSO-d.sub.6) of the pigment indicated that the pigment
adopted the hydrazone tautomer form, and that the dioctyl
sulfosuccinate stabilizer compound was present at approximately 40
mol % (representing about 80% remaining of actual loading) and was
associated with a calcium cation (determined by ICP
spectroscopy).
Example 2
Synthesis of Nano-Sized Particles of Pigment Red 57:1 by a Two-Step
Method
[0100] The procedure of Step 1 of Example 1 above was
reproduced.
[0101] Step 2: Laking
[0102] Into a 500 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 126 g of aqueous slurry of Lithol
Rubine-Potassium salt dye from above (Example 1) having about 1.6%
wt solids content. The pH of the slurry was adjusted to at least
9.0 or higher by addition of 0.5 M KOH solution, after which the
dyestuff was fully dissolved. An aqueous solution 5 wt % Dresinate
X (4.0 mL) was added, followed by a solution containing sodium
dioctyl sulfosuccinate (0.96 g) dissolved in 100 mL of 90:10
deionized water/THF mixture. No visible change was observed. An
aqueous solution of calcium chloride dihydrate (0.5 M solution, 13
mL) was added dropwise to the slurry while stirring vigorously. A
red precipitate formed immediately, and after complete addition of
the calcium chloride solution, the slurry was stirred for an
additional 1 hour. The red slurry was then heated to about
75.degree. C. for 20 min, then cooled to room temp. The slurry was
filtered under high vacuum through a 0.45 .mu.m Nylon membrane
cloth, then reslurried twice with 75 mL portions of DIW. The pH and
conductivity of the final wash filtrate was 7.15 and about 155
.mu.S/cm, respectively. The red pigment filtercake was reslurried
in about 250 mL of DIW and freeze-dried for 48 hours to afford a
dark red-colored powder (2.62 grams). Transmission electron
microscopy images of the powder revealed platelet-like particles
with particle diameters ranging from 50-175 nm, and aspect ratios
equal to or less than 3:1
Example 3
Synthesis of Nano-Sized Particles of Pigment Red 57:1 by a Two-Step
Method
[0103] Step 1: Diazotization and Coupling: Into a 500 mL round
bottom flask equipped with a mechanical stirrer, thermometer, and
addition funnel was dissolved 2-amino-5-methylbenzenesulfonic acid
(12.15 g) into 0.5M KOH aqueous solution (135 mL). The resulting
brown solution was cooled to 0.degree. C. A 20 wt % aqueous
solution of sodium nitrite (NaNO.sub.2; 4.52 g dissolved into 30 mL
water) was added slowly to the first solution while maintaining the
temperature below -2.degree. C. Concentrated HCl (10M, 19.5 mL) was
then slowly added dropwise over 1 hour while maintaining the
internal temperature below 0.degree. C. The mixture formed a pale
brown suspension and following complete addition of conc. HCl, the
suspension was stirred an additional 30 min.
[0104] In a separate 2-L resin kettle was dissolved
3-hydroxy-2-naphthoic acid (12.2 g) into an aqueous solution of KOH
(12.0 g) in water (130 mL). An additional 370 mL of water was
added, and the pale brown solution was then cooled to about
15.degree. C. while stirring. The cold suspension of the diazonium
salt solution was then added slowly to the coupling solution while
mixing vigorously. The color change was immediate to dark black-red
solution, and ultimately to a yellowish-red (orange) slurry of
precipitated dyestuff. The mixture was stirred for at least 2 hours
while warming up to room temp, then filtered and reslurried with
about 600 mL of deionized water to produce an orange-colored slurry
of Lithol Rubine-Potassium salt dye having solids content of about
3.75%-wt.
[0105] Step 2: Laking Step to Produced Nano-Sized Particles of
Pigment Red 57:1
[0106] Into a 1-L resin kettle equipped with mechanical stirrer and
condenser was charged 265 g of aqueous slurry of Lithol
Rubine-Potassium salt dye prepared from Step 1 of Example 2 above,
having approximately 3.75%-wt solids content). The pH of the slurry
was adjusted to at least 9.0 or higher by addition of 0.5 M KOH
solution, after which the dyestuff was fully dissolved. An aqueous
solution 5 wt % Dresinate X (20.0 mL) was added while stirring,
followed by a solution containing sodium dioctyl sulfosuccinate
(4.8 g) dissolved in 220 mL of 90:10 deionized water/THF mixture
was slowly added to the mixture with stirring. An aqueous solution
of calcium chloride dihydrate (0.5 M solution, 65 mL) was added
dropwise to the slurry while stirring vigorously. A red precipitate
formed immediately, and after complete addition of the calcium
chloride solution, the slurry was stirred for an additional 1 hour.
The red slurry was then heated to about 60.degree. C. for 30 min,
then cooled immediately in a cold water bath. The slurry was
filtered under high vacuum through a 0.8 micron Versapor membrane
cloth (obtained from PALL Corp.), then reslurried twice with about
750 mL portions of DIW, and filtered once more. The pH and
conductivity of the final wash filtrate was 7.5 and about 208
.mu.S/cm, respectively. The red pigment filtercake was reslurried
in about 600 mL of deionized water and freeze-dried for 48 hours,
to afford a dark red-colored powder (12.75 grams). Transmission
electron microscopy images of the powder revealed predominantly
platelet-like particles with particle diameters ranging from 50-150
nm, and aspect ratios that were equal to or less than about 3:1
Example 4
Preparation of Nano-Sized Particles of Pigment Red 57:1 Using the
Two-Step Method
[0107] Into a 250 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 10 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor prepared as in Step 1 of
Example 3, except that the solids concentration in the aqueous
slurry was about 10.0 wt %. The pH of the slurry was adjusted to at
least 9.0 or higher by addition of 0.5 M KOH solution, after which
the dyestuff was fully dissolved. An aqueous solution 5 wt %
Dresinate X (1.0 mL) was added, followed by a 0.05 mol/L solution
(34.5 mL) containing sodium dioctyl sulfosuccinate dissolved in
90:10 deionized water/THF. No visible change was observed. An
aqueous solution of calcium chloride dihydrate (1.0 M solution,
2.15 mL) was added dropwise by syringe pump to the slurry while
stirring vigorously. A red precipitate formed immediately, and then
the slurry was stirred at room temperature for an additional 30
min. The red slurry was then filtered under high vacuum through a
0.8 .mu.m Versapor membrane cloth (obtained from PALL Corp.), then
reslurried twice with 50 mL portions of deionized water and
filtered each time after reslurrying. The pH and conductivity of
the final wash filtrate was 7.5 and about 135 .mu.S/cm,
respectively, indicating that residual acids and salt by-products
were removed. The red pigment filtercake was reslurried in about 30
mL of deionized water and freeze-dried for 48 hours to afford a
dark red colored powder (1.32 grams). Transmission electron
microscopy images of the powder revealed very small platelet-like
particles with particle diameters ranging from 50 to 175 nm, and
aspect ratios were equal to or less than about 3:1. Dynamic Light
Scattering analysis measured an average particle size, d.sub.50, of
189 nm and GSD of 1.54 (Z-average particle size of 176 nm;
polydispersity index, PDI, of 0.143). .sup.1H-NMR spectroscopy
analysis (300 MHz, DMSO-d.sub.6) of the material indicated that the
pigment adopted the hydrazone tautomer form, and that the dioctyl
sulfosuccinate stabilizer compound was present at a level ranging
from approximately 50-75 mol %.
Example 5
Preparation of Small Particles of Pigment Red 57:1 Using the
Two-Step Method
[0108] Into a 500 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 126 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor (prepared as in Step 1 of
Example 1) having about 1.6% wt solids content. The pH of the
slurry was adjusted to at least 9.0 or higher by addition of 0.5 M
KOH solution, after which the dyestuff was fully dissolved. An
aqueous solution 5 wt % Dresinate X (4.0 mL) was added, followed by
a solution containing sodium dioctyl sulfosuccinate (1.92 g)
dissolved in 100 mL of 90:10 deionized water/THF mixture. No
visible change was observed. An aqueous solution of calcium
chloride dihydrate (0.5 M solution, 13 mL) was added dropwise to
the slurry while stirring vigorously. A red precipitate formed
immediately, and after complete addition of the calcium chloride
solution, the slurry was stirred for an additional 1 hour. The red
slurry was then heated to about 75.degree. C. for 20 min, then
cooled to room temp. The slurry was filtered under high vacuum
through a 0.45 .mu.m Nylon membrane cloth, then reslurried twice
with 75 mL portions of DIW. The pH and conductivity of the final
wash filtrate was 7.75 and conductivity of about 500 .mu.S/cm. The
red pigment filtercake was reslurried in about 250 mL of DIW and
freeze-dried for 48 hours to afford a dark red-colored powder (2.73
grams). Transmission electron microscopy images of the powder
showed a distribution of particle sizes, with diameter ranging from
50 to 400 nm and having particle morphologies that were
predominantly platelets.
Example 6
Preparation of Small Particles of Pigment Red 57:1 Using a Two-Step
Method
[0109] The sterically bulky stabilizer compound used was potassium
salt of 2-hexyldecanoic acid, prepared by treatment of
2-hexyldecanoic acid with potassium hydroxide dissolved in THF,
after which the THF solvent was removed. Into a 500-mL round-bottom
flask equipped with condenser and mechanical stirrer was charged
126 g of aqueous slurry of Lithol Rubine-Potassium salt (prepared
as in Step 1 of Example 1) having about 1.6% wt solids content. The
pH of the slurry was adjusted to at least 9.0 or higher by addition
of 0.5 M KOH solution, after which the dyestuff was fully
dissolved. An aqueous solution 5 wt % Dresinate X (4.0 mL) was
added, followed by a solution containing potassium 2-hexyldecanoate
(1.28 g) dissolved in 100 mL of 80:20 deionized water/THF mixture,
added dropwise while stirring vigorously. An aqueous solution of
calcium chloride dihydrate (0.5 M solution, 13 mL) was added to the
slurry while stirring vigorously causing a bluish-red pigment
precipitate to form. The slurry was stirred for 1 hour, heated to
about 75.degree. C. for 20 min, then cooled to room temperature.
The slurry was filtered under high vacuum through a 0.8 .mu.m Nylon
membrane cloth, then reslurried once with 150 mL of DIW and
filtered again. The pH and conductivity of the final wash filtrate
was pH 8.38 and conductivity of about 63 .mu.S/cm. The red pigment
57:1 filtercake was reslurried into about 150 mL of DIW and
freeze-dried for 48 hours to afford a red powder (2.95 grams). TEM
micrograph images showed a distribution of particle sizes, with
diameters ranging from 50 to about 400 nm and having particle
morphologies that included platelets as well as rods.
Example 7
Preparation of Pigment Red 57:1 Particles Using the Two-Step
Method
[0110] Into a 250 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 25 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor prepared as in Step 1 of
Example 3, except that the solids concentration in the aqueous
slurry was about 4.0 wt %. The pH of the slurry was adjusted to at
least 9.0 or higher by addition of 0.5 M KOH solution, after which
the dyestuff was fully dissolved. An aqueous solution of 5 wt %
Dresinate X (1.0 mL) was added, followed by a 0.05 mol/L solution
(11 mL) containing sodium dioctyl sulfosuccinate dissolved in 90:10
deionized water/THF. No visible change was observed. An aqueous
solution of calcium chloride dihydrate (0.5 M solution, 6.5 mL) was
added dropwise by syringe pump to the slurry while stirring
vigorously. A red precipitate formed immediately, and then the
slurry was stirred at room temperature for an additional 30 min.
The red slurry was then filtered under high vacuum through a 0.8
.mu.m Versapor membrane cloth (obtained from PALL Corp.), then
reslurried twice with 50 mL portions of deionized water and
filtered each time after reslurrying. The pH and conductivity of
the final wash filtrate was 6.7 and about 22.5 .mu.S/cm,
respectively, indicating that residual acids and salt by-products
were removed. The red pigment filtercake was reslurried in about 30
mL of deionized water and freeze-dried for 48 hours to afford a
dark red colored powder (0.92 grams). Transmission electron
microscopy images of the powder revealed irregular rod-like
particles with particle diameters ranging from 100-600 nm with the
majority of particles less than about 300 nm, and aspect ratios of
greater than about 4:1. Dynamic Light Scattering analysis measured
an average particle size, d.sub.50, of 259 nm and GSD of 1.60
(Z-average particle size of 224 nm; polydispersity index, PDI, of
0.145).
Example 8
Preparation of Pigment Red 57:1 Particles Using the Two-Step
Method
[0111] Into a 250 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 25 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor prepared as in Step 1 of
Example 3, except that the solids concentration in the aqueous
slurry was about 4.0 wt %. The pH of the slurry was adjusted to at
least 9.0 or higher by addition of 0.5 M KOH solution, after which
the dyestuff was fully dissolved. An aqueous solution of 5 wt %
Dresinate X (4.0 mL) was added, followed by a 0.25 mol/L solution
(2 mL) containing sodium dioctyl sulfosuccinate dissolved in 90:10
deionized water/THF. No visible change was observed. An aqueous
solution of calcium chloride dihydrate (1.0 M solution, 2 mL) was
added dropwise by syringe pump to the slurry while stirring
vigorously. A red precipitate formed immediately, and then the
slurry was stirred at room temperature for an additional 30 min.
The red slurry was then filtered under high vacuum through a 0.8
.mu.m Versapor membrane cloth (obtained from PALL Corp.), then
reslurried twice with 50 mL portions of deionized water and
filtered each time after reslurrying. The pH and conductivity of
the final wash filtrate was 6.9 and about 75.4 .mu.S/cm,
respectively, indicating that residual acids and salt by-products
were removed. The red pigment filtercake was reslurried in about 30
mL of deionized water and freeze-dried for 48 hours to afford a
dark red colored powder (0.70 grams). Transmission electron
microscopy images of the powder revealed large rod-like particles
with particle diameters ranging from 180-900 nm with the majority
of particles less than about 400 nm, and aspect ratios of greater
than about 4:1. Dynamic Light Scattering analysis measured an
average particle size, d.sub.50, of 269 nm and GSD of 1.64
(Z-average particle size of 252 nm; polydispersity index, PDI, of
0.185).
Example 9
Preparation of Pigment Red 57:1 Particles Using the Two-Step
Method
[0112] Into a 250 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 25 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor prepared as in Step 1 of
Example 3, except that the solids concentration in the aqueous
slurry was about 4.0 wt %. The pH of the slurry was adjusted to at
least 9.0 or higher by addition of 0.5 M KOH solution, after which
the dyestuff was fully dissolved. An aqueous solution of 5 wt %
Dresinate X (4.0 mL) was added, followed by a 0.05 mol/L solution
(34.5 mL) containing sodium dioctyl sulfosuccinate dissolved in
90:10 deionized water/THF. No visible change was observed. An
aqueous solution of calcium chloride dihydrate (1.0 M solution, 2
mL) was added dropwise by syringe pump to the slurry while stirring
vigorously. A red precipitate formed immediately, and then the
slurry was stirred at room temperature for an additional 30 min.
The red slurry was then filtered under high vacuum through a 0.8
.mu.m Versapor membrane cloth (obtained from PALL Corp.), then
reslurried twice with 50 mL portions of deionized water and
filtered each time after reslurrying. The pH and conductivity of
the final wash filtrate was 6.8 and about 77 .mu.S/cm,
respectively, indicating that residual acids and salt by-products
were removed. The red pigment filtercake was reslurried in about 30
mL of deionized water and freeze-dried for 48 hours to afford a
dark red colored powder (0.62 grams). Transmission electron
microscopy images of the powder revealed platelets as well as
rod-like particles with particle diameters ranging from 100-400 nm
with the majority of particles less than about 250 nm, and aspect
ratios of less than about 4:1. Dynamic Light Scattering analysis
measured an average particle size, d.sub.50, of 235 nm and GSD of
1.61 (Z-average particle size of 224 nm; polydispersity index, PDI,
of 0.152).
Example 10
Preparation of Small Particles of Pigment Red 57:1 Using the
Two-Step Method
[0113] Into a 250 mL round bottom flask equipped with mechanical
stirrer and condenser was charged 10 g of aqueous slurry of Lithol
Rubine-Potassium salt dye precursor prepared as in Step 1 of
Example 3, except that the solids concentration in the aqueous
slurry was about 10.0 wt %. The pH of the slurry was adjusted to at
least 9.0 or higher by addition of 0.5 M KOH solution, after which
the dyestuff was fully dissolved. An aqueous solution of 5 wt %
Dresinate X (4.0 mL) was added, followed by a 0.05 mol/L solution
(11 mL) containing sodium dioctyl sulfosuccinate dissolved in 90:10
deionized water/THF. No visible change was observed. An aqueous
solution of calcium chloride dihydrate (1.0 M solution, 3.25 mL)
was added dropwise by syringe pump to the slurry while stirring
vigorously. A red precipitate formed immediately, and then the
slurry was stirred at room temperature for an additional 30 min.
The red slurry was then filtered under high vacuum through a 0.8
.mu.m Versapor membrane cloth (obtained from PALL Corp.), then
reslurried twice with 50 mL portions of deionized water and
filtered each time after reslurrying. The pH and conductivity of
the final wash filtrate was 7.5 and about 42.7 .mu.S/cm,
respectively, indicating that residual acids and salt by-products
were removed. The red pigment filtercake was reslurried in about 30
mL of deionized water and freeze-dried for 48 hours to afford a
dark red colored powder (0.61 grams). Transmission electron
microscopy images of the powder revealed platelets as well as
rod-like particles with particle diameters ranging from 75 nm to
about 300 nm with the majority of particles less than about 200 nm,
and aspect ratios of less than about 3:1. Dynamic Light Scattering
analysis measured an average particle size, d.sub.50, of 209 nm and
GSD of 1.57 (Z-average particle size of 193 nm; polydispersity
index, PDI, of 0.148).
Examples of Liquid Dispersions Containing Monoazo Laked Pigment
Particles (Including Nano-Sized Particles) and Their Coloristic
Properties
Example 11
Method for Preparation of Liquid Dispersions and of Polymer
Coatings
[0114] A series of liquid, non-aqueous dispersions were prepared
using a polymeric dispersant and the nano-sized PR 57:1 pigments
from Examples 1, 2, 3, 4, 5 and 6; the larger-sized pigment
particles prepared as described in the Comparative Example 1; as
well as two commercial sources of PR 57:1 obtained from Clariant
(lot #L7B01) and Aakash. Coatings on clear Mylar film were prepared
from these liquid dispersions, and evaluated in the following
manner: Into a 30 mL amber bottle was added 0.22 g of pigment,
0.094 g polyvinylbutyral (B30HH obtained from Hoescht), 7.13 g
n-butyl acetate (glass-distilled grade, obtained from Caledon
Laboratories) and 70.0 g of 1/8' stainless steel shot (Grade 25
440C obtained from Hoover Precision Products). The bottles were
transferred to a jar mill and were allowed to gently mill for 4
days at 100 RPM. Two draw-down coatings were obtained for each
dispersion using an 8-path gap on clear Mylar film such that the
wet thicknesses for each coating comprised of PR 57:1 pigment
sample were 0.5 and 1 mil. The air-dried coatings on clear Mylar
film were then dried in a horizontal forced-air oven at 100.degree.
C. for 20 minutes.
Example 12
Measurement of Pigment Particle Size by Dynamic Light
Scattering
[0115] The measurements of various example PR57:1 pigments'
particle sizes were performed on a Malvern ZetaSizer HT at
25.degree. C. Each of the pigment dispersions prepared in Example 8
were diluted in a solution of polyvinylbutyral (B30HH obtained from
Hoescht) in n-butyl acetate (glass-distilled grade, obtained from
Caledon Laboratories) and sonicated at low power for 1 minute. For
each determination of particle size and distribution, 3 replicates
of 12 runs were performed wherein the repeatability of particle
size data was realized for each sample. The particle size data for
the diluted samples that were prepared in Example 8 can be found in
Table 10.
Example 13
Evaluation of Coatings Prepared from Liquid Pigment Dispersions
[0116] The coatings on clear Mylar film prepared as described in
Example 11 were assessed for coloristic and light scattering
properties in the following manner: The UV/VIS/NIR transmittance
spectra of each coating were obtained using a Shimadzu UV160
spectrophotometer, and the results showed dramatically reduced
light scattering and remarkable specular reflectivity for the
nano-sized PR57:1 pigment samples described herein, compared with
the spectra of coatings prepared with commercial PR57:1 pigment
samples obtained from Clariant and Aakash. The degree of light
scattering in a coating is dependent on both the size and shape
distributions of the pigment particles and their relative
dispersability within the coating matrix, and the Normalized Light
Scatter Index (NLSI) method was developed to be a measure of this
characteristic for the pigmented coatings. NLSI is quantified by
first measuring the spectral absorbance of the coating in a region
where there is no absorbance from the chromogen of the monoazo
laked pigment (for PR57:1, a suitable region is 700-900 nm), but
only absorbance due to light scattered from large aggregates and/or
agglomerated pigment particles dispersed in the coating binder. The
Normalized Light Scatter Index (NLSI) is then obtained by
normalizing each of the samples' light scattering indices (from 700
to 900 nm) to a lambda-max optical density=1.5. In this way, the
degree of light scattering for each pigmented coating could be
compared directly against each other. The lower the NLSI value, the
smaller the inferred particle size of the dispersed pigment in the
coating. A relationship between decreasing average particle size
and decreasing NLSI value was found to exist with the coatings
prepared from the example pigments shown in Table 8. In particular,
the nano-sized monoazo laked pigment PR57:1 of Example 3 had by far
the lowest degree of light scattering, with an NLSI value of 0.3.
The coloristic properties of the Mylar coatings were determined
using an X-RITE 938 spectrodensitometer. L* a* b* and optical
density (O.D.) values were obtained for each of the samples, and
the L* a* b* were normalized to an optical density of 1.5, and used
to calculate the hue angle and chroma (C*), as listed in Table
8.
TABLE-US-00008 TABLE 8 Normalized Light Scatter Indices (NLSI),
Coloristic properties normalized to O.D. = 1.5, Particle size
ranges and Dispersion stabilities of example PR57:1 pigments
Clariant Aakash Comparative Example Metric PR57:1 PR57:1 Example 1
1 2 3 4 5 6 7 8 9 10 L*.sup.a 47.9 48.0 44.8 50.8 50.6 51.7 53.0
49.9 49.6 50.1 49.0 50.8 52.0 a*.sup.a 71.1 71.2 71.5 76.5 77.2
79.4 78.8 76.7 73.6 76.4 74.7 77.2 77.7 b*.sup.a 8.7 17.5 34.8
-16.4 -17.4 -18.8 -15.0 -18.9 1.4 -2.4 6.1 -5.8 -12.5 Hue Angle
(.degree.).sup.a 6.6 13.8 28.1 347.9 347.1 346.6 349.2 346.1 0.9
358.3 4.6 355.8 350.9 C*.sup.a 72.6 73.4 78.1 78.6 77.5 81.3 80.5
78.9 73.9 78.2 76.7 78.9 79.9 Particle Size ~50 to ~50 to ~200 to
~30 to ~50 to ~50 to ~50 to ~50 to ~50 to ~100 to ~180 to ~100 to
~75 to Diameter Range.sup.b ~400 ~400 ~700 ~150 ~175 ~150 ~175 ~400
~400 ~600; ~900; ~400; ~300; (nm) most most most most <300
<400 <250 <200 nm nm nm nm Normalized Light 5.5 9.9 74.1
0.3 1.3 1.0 0.7 0.9 4.8 1.8 2.2 1.5 0.4 Scatter Index.sup.a
Dispersion 2 days 2 days <1 day 6 3 3 3 6 2 3 3 3 3 Stability
months months months months months months months months months
months In Table 8, .sup.adenotes that the various coloristic and
light scatter index metrics were normalized to optical density of
1.5, and, .sup.bdenotes that the particle size diameter was
determined by Transmission Electron Microscopy.
[0117] For the data in Table 9, the various coloristic properties,
normalized light scatter indices, of the example pigments as they
were dispersed and coated onto Clear Mylar.RTM. and the dispersion
stabilities found in Table 8 have been organized into various
ranges by way of the following:
a) .sup.1L*, where A denotes 49.ltoreq.L*.ltoreq.54, B denotes
L*>54, C denotes L*<49, b) .sup.2a*, where A denotes
a*.gtoreq.78, B denotes 75.ltoreq.a*<78, C denotes a*<75, c)
.sup.3b*, where A denotes b*.ltoreq.-18, B denotes
-10.ltoreq.b*<-18, C denotes -2.ltoreq.b*<-10, D denotes
6.ltoreq.b*<-2, E denotes b*>6, d) .sup.4NLSI, where A
denotes NLSI.ltoreq.1, B denotes 1<NLSI.ltoreq.2, C denotes
NLSI>2, and e) .sup.5Dispersion Stability at Room Temperature,
where A denotes stability .gtoreq.3 months, B denotes stability
.gtoreq.1 week but <3 months, C denotes stability <1
week.
[0118] From table 9, it is clear that a variety of coloristic
properties can be realized by adjusting the synthetic process of
nano-sized PR57:1 to suit pigment compositions having relatively
smaller particle sizes, relatively larger particle sizes or a
combination of particle sizes to suit the needs of a particular
application. For example, it may useful in a particular
application, such as in ink formulations, to have the ability to
tune the coloristic properties of an ink, a magenta ink, for
example, without using excessive energy to grind down the pigment
particles. The ability to control various properties of nano-sized
PR57:1, such as hue angle, as determined from its synthesis and
work-up history, is beneficial to the environment as lower energy
consumption would be required to process a dispersion or ink for a
given application, such as for coatings or ink jet inks, such as
piezo inkjet inks.
TABLE-US-00009 TABLE 9 Ranged and Normalized Scatter Indices
(NLSI), Coloristic and Dispersion Stability Properties of example
PR57:1 pigments, normalized to O.D. = 1.5 Clariant Aakash
Comparative Example Metric PR57:1 PR57:1 Example 1 1 2 3 4 5 6 7 8
9 10 L*.sup.1 C C C A A A A A A A A A A a*.sup.2 C C C B B A A B C
B C B B b*.sup.3 E E E B B A B A D C E C B Normalized Light C C C A
B A A A C B C B A Scatter Index.sup.4 Dispersion C C C A A A A A A
A A A A Stability.sup.5
Example 14
b*a* Coloristic Properties of Coatings prepared from Liquid Pigment
Dispersions
[0119] The graphs in FIGS. 1 and 2 visually illustrate the
significant shifts in b* a* gamut observed with coatings prepared
with the nano-sized PR57:1 pigments from Examples 1, 2, 3, 4 and 5,
in addition to the extended C* chroma for the nano-sized pigment
examples. Furthermore, the graph in FIG. 1 shows a clear
blue-shifting of hue that directly corresponds to decreasing
particle size/particle diameters of the example PR57:1 pigments, a
relationship which is also inferred from the Normalized Light
Scatter Index (NLSI) values of Table 8. (Note: For ease of
generating the graph, the b* vertical axis shows "negative" hue
angles, which represent the number of degrees <360 degrees.) The
light scattering and coloristic data accumulated provide evidence
for the ability to tune color properties and specular reflectivity
of pigmented coatings with tunable particle size of
surface-enhanced fine particles of monoazo laked red pigments, in
particular Pigment Red 57:1. This is achieved by using the methods
of making such nano-sized pigments of PR57:1 as described herein,
in particular using the two-step process which uses sterically
bulky stabilizer compounds to limit particle aggregation and
thereby limit particle size as well as enhance dispersion and color
characteristics of the nano-sized pigment particles. Furthermore,
the ability to easily tune color properties of such monoazo laked
pigments provides a means to control the color quality so that
inexpensive azo laked pigments like PR57:1 can be used to obtain
magenta color that are normally exhibited by higher cost red
pigments, such as the quinacridone-type Pigment Red 122 and Pigment
Red 202.
[0120] It can be seen from the data in FIG. 2 that there is a
semi-logarithmic correlation between hue angle and Normalized Light
Scatter Index (NLSI) of the example PR57:1 pigments, normalized to
an optical density of 1.5. The relatively greater degree of
blue-shifting of hue for some example pigments, especially those
made in Examples 1, 2, 3, 4, and 5 occurred with correspondingly
lower NLSI values. As well, red-shifting of hue for some example
pigments occurred with correspondingly higher NLSI values.
Furthermore, the direct correlation between hue angle of example
pigments coated onto clear Mylar.RTM. (normalized to O.D.=1.5) and
of particle size (prepared and measured as Z-average as disclosed
in Example 9) as seen in FIG. 3 clearly indicate a range of hue
angles (colors) suitable for various applications, such as inks or
coatings. Thus various properties of example PR57:1 pigments can be
easily, including pigment particle size and dispersed pigment hue,
by adjusting certain aspects of the PR57:1 composition and method
of making, including, for example, reactant loading and
stoichiometry, reactants rate of addition and concentration,
stirring speed, temperature and various pigment work up variances,
including types and volumes of pigment washes.
[0121] FIG. 4 shows the nearly linear correlation between NLSI and
Z-average particle size indicating that the particle size
distributions in the dispersions made with example PR57:1 pigments
were retained in the coatings, after evaporation of n-butyl acetate
by oven drying, as inferred by the NLSI data.
[0122] It will be appreciated that various of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Also that various presently unforeseen or
unanticipated alternatives, modifications, variations or
improvements therein may be subsequently made by those skilled in
the art which are also intended to be encompassed by the following
claims.
* * * * *
References