U.S. patent application number 13/537704 was filed with the patent office on 2014-01-02 for pigment-based inkjet inks.
The applicant listed for this patent is Thomas B. Brust, Brian P. Cleary, Dale E. DeCann, Yongcai Wang. Invention is credited to Thomas B. Brust, Brian P. Cleary, Dale E. DeCann, Yongcai Wang.
Application Number | 20140000477 13/537704 |
Document ID | / |
Family ID | 49776804 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140000477 |
Kind Code |
A1 |
Brust; Thomas B. ; et
al. |
January 2, 2014 |
PIGMENT-BASED INKJET INKS
Abstract
An inkjet ink composition comprising: (a) water; (b) dispersed
pigment particles; and (c) at least one humectant; wherein the
pigment particles are present from about 4.5% by mass to about 10%
by mass, and the pigment particles have a mass weighted mean
Stoke's diameter of from about 35 nm to about 70 nm wherein the
Stoke's diameter is determined by differential centrifugal
sedimentation of the particles through a fluid in a disc
centrifuge. The present invention employs specified sedimentation
particle sizing criteria for selection of appropriate pigment
particle sizes at high pigment concentrations to obtain improved
ink performance. Further embodiments of the invention also
demonstrate that the criticality of humectant types and levels
employed in an ink can also become much more important at high
pigment loading in order to obtain desired performance.
Inventors: |
Brust; Thomas B.; (Webster,
NY) ; Wang; Yongcai; (Rochester, NY) ; Cleary;
Brian P.; (Webster, NY) ; DeCann; Dale E.;
(Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brust; Thomas B.
Wang; Yongcai
Cleary; Brian P.
DeCann; Dale E. |
Webster
Rochester
Webster
Rochester |
NY
NY
NY
NY |
US
US
US
US |
|
|
Family ID: |
49776804 |
Appl. No.: |
13/537704 |
Filed: |
June 29, 2012 |
Current U.S.
Class: |
106/31.65 ;
524/104; 524/106; 977/773 |
Current CPC
Class: |
C09D 11/322 20130101;
C09D 11/38 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
106/31.65 ;
524/104; 524/106; 977/773 |
International
Class: |
C09D 11/10 20060101
C09D011/10; C09D 11/02 20060101 C09D011/02 |
Claims
1. An inkjet ink composition comprising; (a) water, (b) dispersed
pigment particles, and (c) at least one humectant, wherein the
pigment particles are present from about 4.5% by mass to about 10%
by mass, and the pigment particles have a mass weighted mean
Stoke's diameter of from about 35 nm to about 70 nm.
2. The ink composition of claim 1, wherein the pigment particles
are dispersed with a polymeric dispersant.
3. The ink composition of claim 2, further comprising at least one
water-dispersible polymer binder.
4. The ink composition of claim 3, wherein the at least one
humectant comprises at least one pyrrolidinone compound.
5. The ink composition of claim 3, wherein the at least one
humectant comprises 1-(2-hydroxyethyl)-2-pyrrolidinone,
2-pyrrolidinone, imidazolidone or glycerol, or a combination of any
two or more thereof.
6. The ink composition of claim 5, wherein the sum of the amounts
of 1-(2-hydroxyethyl)-2-pyrrolidinone, 2-pyrrolidinone and
imidazolidone is greater than 50 weight % of the total humectant
concentration of the ink composition.
7. The ink composition of claim 6, wherein the amount of
1-(2-hydroxyethyl)-2-pyrrolidinone is at least 10 weight % of the
total humectant concentration, the amount of imidazolidone is less
than 41% of the total humectant concentration, the amount of
glycerol is less than 25 weight % of the total humectant
concentration, and the amount of 2-pyrrolidinone is less than 25
weight % of the total humectant concentration.
8. The ink composition of claim 7, further comprising a 1,2
alkanediol.
9. The ink composition of claim 8, wherein the 1,2-alkanediol is
selected from 1,2-pentanediol and 1,2-hexanediol.
10. The ink composition of claim 7, comprising imidazolidone
present at greater than 0.1 weight percent.
11. The ink composition of claim 10, wherein the imidazolidone is
present at less than 13 weight percent.
12. The ink composition of claim 7, wherein the at least one
humectant further comprises triethylene glycol.
13. The ink composition of claim 7, wherein the polymeric
dispersant for the pigment particles comprises a hydrophobic
monomer having a carbon chain length of greater than or equal to 12
carbons.
14. The ink composition of claim 7, wherein the at least one
water-dispersible binder is a polyurethane having an acid number
between about 50 and 150 and molecular weight less than about
150,000.
15. The ink composition of claim 6 wherein the at least one
humectant comprises at least 1-(2-hydroxyethyl)-2-pyrrolidinone,
and wherein imidazolidone, if present, is present in an amount less
than about 7 weight %, wherein the sum of the amounts of
1-(2-hydroxyethyl)-2-pyrrolidinone and imidazolidone is greater
than or equal to 9 weight %, wherein the sum of the amounts of
1-(2-hydroxyethyl)-2-pyrrolidinone and imidazolidone is greater
than 50% of the total humectant concentration, and wherein the
amounts of 2-pyrrolidinone and glycerol, if present, are each less
than 25% of the total humectant concentration.
16. The ink composition of claim 15 wherein the total humectant
content is from about 12 weight % to about 24 weight %.
17. The ink composition of claim 16, comprising 2-pyrrolidinone at
from 0 to less than 4 weight %.
18. The ink composition of claim 17, comprising 2-pyrrolidinone at
less than 2 weight %.
19. The ink composition of claim 1, wherein the pigment particles
are present at from about 4.5% by mass to about 7.5% by mass.
20. The ink composition of claim 1, wherein the pigment particles
have a mass weighted mean Stoke's diameter of from about 39.0 nm to
about 57.0 nm
21.-23. (canceled)
24. The ink composition of claim 1, wherein the pigment particles
are magenta pigment particles.
25. (canceled)
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to the field of
pigment-based inks for inkjet printing, and in particular to inks
with high pigment loading and specific pigment particle size
distributions for improved reliability and redispersibility of
pigment-based inkjet inks.
BACKGROUND OF THE INVENTION
[0002] Inkjet printing is a non-impact method for producing printed
images by the deposition of ink droplets in a pixel-by-pixel manner
to an image-recording element in response to digital signals. There
are various methods that may be utilized to control the deposition
of ink droplets on the image-recording element to yield the desired
printed image. In one process, known as drop-on-demand inkjet,
individual droplets are projected as needed onto the
image-recording element to form the desired printed image. Common
methods of controlling the ejection of ink droplets in
drop-on-demand printing include thermal bubble formation (thermal
inkjet (TIJ)) and piezoelectric transducers. In another process
known as continuous inkjet (CIJ), a continuous stream of droplets
is generated and expelled in an image-wise manner onto the surface
of the image-recording element, while non-imaged droplets are
deflected, caught and recycled to an ink sump. Inkjet printers have
found broad applications across markets ranging from desktop
document and photographic-quality imaging, to short run printing
and industrial labeling.
[0003] Ink compositions containing colorants used in inkjet
printers can be classified as either pigment-based, in which the
colorant exists as pigment particles suspended in the ink
composition, or as dye-based, in which the colorant exists as a
fully solvated dye species that consists of one or more dye
molecules. Pigments are highly desirable since they are far more
resistant to fading than dyes. However, pigment inks can have
inferior durability after printing, especially under conditions
where abrasive forces have been applied to the printed image and
especially at short time intervals from immediately after printing
to several minutes while the inks are drying.
[0004] Pigment inks can be difficult to jet through ink jet print
heads having small nozzle diameters especially by the thermal ink
jet printing process. In recent years, thermal ink jet printers
have moved to higher jetting frequencies and smaller nozzle
diameters to provide faster printing speeds with higher image
quality. Thermal ink jet printers are now capable of printing (in
drop volumes of 3 picoliters or less) at jetting frequencies in
excess of 10 kHz and the need for higher frequency firing is a
highly desirable feature. However, this high frequency firing often
comes at the cost of variability in the firing velocity, which
leads to poor image quality in the final printed image. In
addition, the demands of current thermal ink jet printing require
that the nozzles fire reliably for a large number of firings during
the life-time of a printer. As an example, a typical ink jet nozzle
may be required to fire in excess of 5.times.10.sup.7, and up to as
many as 1.times.10.sup.9, individual firing events without
malfunctioning or ceasing to fire altogether.
[0005] Another problem for drop-on-demand inkjet printing devices,
especially those using pigment inks, is the recovery of a nozzle
that has not been fired for a period of time such that the ink in
the chamber has begun to dry out. This can occur during the time
required to print a document if only certain inks are required for
that document and the remaining inks remain idle. This phenomenon
is typically referred to in the art as latency. Most ink jet
printers will fire idle nozzles at specified intervals to maintain
the reliable firing of all the jets. Unfortunately, pigment inks,
and in particular pigment inks with high loads of pigment and
polymers designed for high image quality and durability on the
broadest range of media, can still show poor reliability even with
reasonable idle-jet maintenance routines. If an ink requires
excessive amounts of maintenance firing, this can also reduce the
number of pages that can be printed from an ink tank, thereby
reducing the efficiency of the tank and increasing the cost of
printing.
[0006] Additional reliability problems can occur in situations
where the printhead is left idle or uncapped for long periods of
time and then is actuated again to eject ink. In some instances the
idle printhead nozzles can partially clog or crust with ink
components thereby degrading the ability of the printhead to eject
properly. For example, the ink can be misdirected from the
partially clogged nozzles or the drop velocity can be greatly
diminished. In some instances, the nozzle will become permanently
clogged and in other instances a lengthy and costly maintenance
operation may be required to recover the nozzle back to a usable
state of operation.
[0007] An important attribute for pigment-based inks, especially
those with high loading of pigments and polymers is the ability of
fresh ink to redissolve and redisperse ink that has dried in or
around the nozzles. An ink that easily redissolves will readily
recover even if the print head is allowed to dry, and will
generally be more reliable during normal operation and latency
conditions. The ability of an ink to redissolve is easily tested by
allowing a specific amount of ink to dry out under specified
conditions and then observe if that ink redissolves into a
specified amount of fresh ink. An ideal ink will quickly redissolve
all of the dried ink without forming visible particles or chunks.
An ink with poor redissolution properties will not dissolve the
dried ink or at best will only break it up into large chunks or
particles that still may clog a print head nozzle.
[0008] Pigment-based inks formulated with polymeric dispersants and
binders can be difficult to jet through inkjet printheads having
small nozzle diameters especially by the thermal inkjet printing
process. This is especially true of pigment-based inks, which are
formulated with humectants or penetrants that lower dynamic surface
tension.
[0009] Ink jet inks employing pigment dispersions that also include
pyrrolidinone compounds to improve the jetting reliability are
disclosed in Brust et al., US2009/0170986, Yatake, U.S. Pat. No.
7,981,947, and Saito et al., U.S. Pat. No. 8,013,035. The use of
pigment levels in inkjet inks up to 10 wt % is generally described
in the prior art, although use of pigment concentrations of 4 wt %
and less are frequently employed to avoid printer reliability
problems.
PROBLEM TO BE SOLVED BY THE INVENTION
[0010] Pigment-based inks can provide high optical density on plain
office papers. The compositions of plain office papers, however,
can vary, especially the low-cost light-weight papers widely used
for normal office operation, and can produce a wide range of
optical densities with some papers having very low and non-uniform
ink adsorption on the paper fibers resulting in low optical density
and poor image quality. The formulation of pigment-based inks with
relatively high loading of pigments can improve the optical density
on most plain papers, but the high level of pigment and any
associated polymer dispersants and binders can cause a wide variety
of reliability problems that are related to the tendency of high
solids inks to have very high viscosity as they begin to dry out
and more importantly, poor redissolution properties once they have
dried.
[0011] Although the use of pigment-based inks with high pigment
loads have found use in inkjet printers there remains the need to
provide pigmented inkjet inks that are simultaneously capable of
providing high optical density and image quality on plain papers
without degrading the jetting reliability of the printer. It is
therefore an object of this invention to provide an inkjet ink, and
an ink set including two or more colored inks for inkjet printing,
wherein the inks contain a high loading of pigment particles which
jet from a thermal inkjet printhead at high frequency and with low
velocity variability, and which provide reliable jetting and print
head recovery as expected from good redissolution properties. It is
a further objective of the present invention that the pigmented ink
compositions containing the high loading of pigment particles
provide excellent image quality on the various compositions of
plain office papers. It is a further object of the invention to
provide inks which remain stable over time and are free of
precipitated components. It is also an object of embodiments of
this invention to provide for improved paper curl performance.
SUMMARY OF THE INVENTION
[0012] In accordance with one embodiment, the invention is directed
towards an inkjet ink composition comprising;
[0013] (a) water,
[0014] (b) dispersed pigment particles, and
[0015] (c) at least one humectant,
[0016] wherein the pigment particles are present from about 4.5% by
mass to about 10% by mass, and the pigment particles have a mass
weighted mean Stoke's diameter of from about 35 nm to about 70 nm
wherein the Stoke's diameter is determined by differential
centrifugal sedimentation of the particles through a fluid in a
disc centrifuge.
[0017] The prior art typically relies on dynamic light scattering
to characterize the particle size of pigments employed therein.
This characterization can be highly dependent on the composition
and particle morphology leading to very large discrepancies with
actual performance of an ink relative to the characterized mean
particle size and size distribution. In particular, it has been
found that the criticality of a specific range of particle sizes
with regard to ink reliability and redispersibility when high
pigment levels are employed in an ink can be masked if only light
scattering methods are used. The present invention improves on the
prior art by employing specified sedimentation particle sizing
criteria for selection of appropriate pigment particle sizes at
high pigment concentrations to obtain improved ink performance.
Further embodiments of the invention also demonstrate that the
criticality of humectant types and levels employed in an ink can
also become much more important at high pigment loading in order to
obtain desired performance. The prior art does not teach these
critical relationships for high pigment load inks.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The inkjet inks of the present invention are aqueous-based
inks. By aqueous-based it is meant that the ink comprises mainly
water as the carrier medium for the remaining ink components. In a
preferred embodiment, the inks of the present invention comprise at
least about 50 weight percent water. Pigment-based inks are defined
as inks containing at least a dispersion of water-insoluble pigment
particles. Dye-based inks are defined as inks containing at least a
colored dye, which is soluble in the aqueous carrier. Colorless
inks are defined as inks, which are substantially free of colorants
such as dyes or pigments and as such, are not intended to
contribute to color formation in the image forming process.
[0019] An ink set is defined as a set of two or more inks. The ink
sets may contain inks of different colors, for example, cyan,
magenta, yellow, red, green, blue, orange, violet or black. In one
embodiment, a carbon black pigmented ink is used in an ink set
comprising at least three inks having separately, a cyan, a magenta
and a yellow colorant. Further useful ink sets also include, in
addition to the cyan, magenta and yellow inks, complimentary
colorants such as red, blue, violet, orange or green inks. In
addition, the ink set may comprise light and dark colored inks, for
example, light cyan and light magenta inks commonly used in the ink
sets of wide format printers. It is possible to include one or more
inks that comprise a mixture of different colorants in the ink set.
An example of this is a carbon black pigment mixed with one or more
colored pigments or a combination of different colored pigments or
dyes in the same ink. An ink set may also include one or more
colored inks in combination with one or more colorless inks. An ink
set may also include at least one or more pigment-based inks in
combination with additional inks that are dye-based ink.
[0020] The pigment-based inks of the present invention comprise
pigment particles dispersed in the aqueous carrier. The pigment
particles that are useful in the invention may be prepared by any
method known in the art of inkjet printing. Useful methods commonly
involve two steps: (a) a dispersing or milling step to break up the
pigments to primary particles, where primary particle is defined as
the smallest identifiable subdivision in a particulate system, and
(b) a dilution step in which the pigment dispersion from step (a)
is diluted with the remaining ink components to give a working
strength ink.
[0021] The milling step (a) is carried out using any type of
grinding mill such as a media mill, a ball mill, a two-roll mill, a
three-roll mill, a bead mill, and air-jet mill, an attritor, or a
liquid interaction chamber. In the milling step (a), pigments are
optionally suspended in a medium that is typically the same as or
similar to the medium used to dilute the pigment dispersion in step
(b). Inert milling media are optionally present in the milling step
(a) in order to facilitate breakup of the pigments to primary
particles. Inert milling media include such materials as polymeric
beads, glasses, ceramics, metals and plastics as described, for
example, in U.S. Pat. No. 5,891,231. Milling media are removed from
either the pigment dispersion obtained in step (a) or from the ink
composition obtained in step (b).
[0022] A dispersant is optionally present in the milling step (a)
in order to facilitate breakup of the pigments into primary
particles. For the pigment dispersion obtained in step (a) or the
ink composition obtained in step (b), a dispersant is optionally
present in order to maintain particle stability and prevent
settling. Dispersants may be added to the pigment dispersion prior
to, or during the milling step (a), and include surfactants and
soaps such as the potassium or sodium salt of oleoyl methyl taurate
(commonly referred to as OMT) and polymers such as homopolymers and
copolymers; anionic, cationic or nonionic polymers; or random,
block, branched or graft polymers. Polymeric dispersants useful in
the milling operation include random and block copolymers having
hydrophilic and hydrophobic portions; see for example, U.S. Pat.
No. 4,597,794; U.S. Pat. No. 5,085,698; U.S. Pat. No. 5,519,085;
U.S. Pat. Nos. 5,272,201; 5,172,133; U.S. Pat. No. 6,043,297 and WO
2004/111140A1; and graft copolymers; see for example, U.S. Pat. No.
5,231,131; U.S. Pat. No. 6,087,416; U.S. Pat. No. 5,719,204; or
U.S. Pat. No. 5,714,538.
[0023] Typically, these polymeric resins are copolymers made from
hydrophobic and hydrophilic monomers. In this case, the copolymers
are designed to act as dispersants for the pigment by virtue of the
arrangement and proportions of hydrophobic and hydrophilic
monomers. The pigment particles are colloidally stabilized by the
dispersant and are referred to as a polymer dispersed pigment
dispersion.
[0024] The size of pigment particles can be characterized by
several different methods including dynamic light scattering,
direct sizing by electron microscopy, or by sedimentation
techniques such as the disc centrifuge method. In the present
invention, a disc centrifuge technique is used to measure the
particle size distribution of the pigment particles. The principle
of the method is based on the size dependence of the rate of
sedimentation of particles in a fluid when a centrifugal force is
applied. In general, the measurement is based on the time the
particles take to sediment from the top of the fluid in a disc
centrifuge device to a light source near the bottom of the rotor of
the device. This sedimentation time is converted to particle
diameters through Stokes' Law, where the calculated Stoke's
diameter (also referred to as the equivalent sedimentation speed
diameter) is defined as the diameter of a spherical particle of the
same constitution and sedimentation speed of the tested particle.
For the disc centrifuge method, Stoke's law is modified to account
for the variation in g-force with distance from the center of
rotation. The modified Stoke's law equation is:
D={(18.eta.
ln(R.sub.f/R.sub.0))/((.rho..sub.p-.rho..sub.f).omega..sup.2t}.sup.0.5
where D is the calculated Stoke's particle diameter (cm)
[0025] .eta. is the fluid viscosity (poise)
[0026] R.sub.f is the final radius of rotation (cm)
[0027] R.sub.0 is the initial radius of rotation (cm)
[0028] .rho..sub.p is the particle density (g/ml)
[0029] .rho..sub.f is the fluid density (g/ml)
[0030] .omega. is the rotational velocity (radians/sec) and
[0031] t is the time required to sediment from R.sub.0 to R.sub.f
(sec).
Sedimentation rates increase as the square of the particle
diameter, so particles that differ in size by a small amount settle
at significantly different rates. The absorption signal of the
particles as they pass by the detector is related to the frequency
of the particle size distribution. Based on the separation of
particles, a particle size distribution is directly measured based
on the modified Stoke's law equation.
[0032] The pigment dispersions employed in the invention have a
mean Stoke's particle diameter of from about 35 nm to about 70 nm,
preferably greater than 39.0 and less than about 70.0 nm, more
preferably greater than 39.0 and less than about 57.0 nm, as
measured using a disc centrifuge method. The coefficient of
variation of the pigment particle size distribution (standard
deviation of particle size divided by mean particle size) is
preferably less than about 0.45, more preferably less than 0.40,
and most preferably less than 0.35 as measured using a disc
centrifuge method.
[0033] Dispersants can be non-polymeric molecules such as
surfactants or soaps like the potassium or sodium salt of oleoyl
methyl taurate (commonly referred to as OMT). The pigment
dispersing agent can also be a polymer or copolymer with a wide
range of monomer compositions that include both hydrophobic and
hydrophilic functionality. The polymeric dispersant (copolymer) for
the pigment is not limited in the arrangement of the monomers
comprising the copolymer. The arrangement of monomers may be
totally random, or they may be arranged in blocks such as AB or ABA
wherein, A is the hydrophobic monomer and B is the hydrophilic
monomer. In addition, the polymer may take the form of a random
terpolymer or an ABC tri-block wherein, at least one of the A, B
and C blocks is chosen to be the hydrophilic monomer and the
remaining blocks are hydrophobic blocks dissimilar from one
another.
[0034] Especially useful copolymer dispersants are those where the
hydrophobic monomer is selected from benzyl methacrylate or
acrylate, or from methacrylic or acrylic acid esters containing an
aliphatic chain having twelve or more carbons, which aliphatic
chains may be linear or branched. Examples of methacrylic and
acrylic acid esters having twelve or more carbons include; lauryl
acrylate, lauryl methacrylate, tridecyl acrylate, tridecyl
methacrylate, tetradecyl acrylate, tetradecyl methacrylate, cetyl
acrylate, iso-cetyl acrylate, stearyl methacrylate, iso-stearyl
methacrylate, stearyl acrylate, stearyl methacrylate,
decyltetradecyl acrylate, decyltetradecyl methacrylate, and the
like. Preferably the methacrylate or acrylate monomer is stearyl or
lauryl methacrylate or acrylate. The hydrophobic portion of the
polymer may be prepared from one or more of the hydrophobic
monomers.
[0035] Preferred copolymer dispersants are those where the
hydrophilic monomer is selected from carboxylated monomers.
Preferred polymeric dispersants are copolymers prepared from at
least one hydrophilic monomer that is an acrylic acid or
methacrylic acid monomer, or combinations thereof. Preferably, the
hydrophilic monomer is methacrylic acid.
[0036] Typically, the weight average molecular weight of the
copolymer dispersant has an upper limit such that it is less than
about 50,000 Daltons. Desirably the weight average molecular weight
of the copolymer is less than about 25,000 Daltons; more preferably
it is less than 15,000 and most preferably less than 10,000
Daltons. The molecular weight of the copolymer has a weight average
molecular weight lower limit such that it is greater than about 500
Daltons.
[0037] In one preferred embodiment the copolymer dispersants are
those wherein the hydrophobic monomer is benzyl methacrylate and is
present from 50 weight percent to 80 weight percent relative to the
total weight of the polymeric dispersant and the hydrophilic
monomer is methacrylic acid.
[0038] In a second preferred embodiment the copolymer dispersants
comprises a hydrophobic monomer having a carbon chain length of
greater than or equal to 12 carbons present in an amount of at
least 10% by weight of the total copolymer, and more preferably
greater than 20% by weight, an optional additional hydrophobic
monomer comprising an aromatic group, and the hydrophilic monomer
is methacrylic acid. For example, the additional aromatic group
containing monomer may be benzyl acrylate or benzyl methacrylate. A
preferred additional monomer is benzyl methacrylate.
[0039] The total amount of hydrophobic monomers, comprising the
monomer having a chain with greater than or equal to 12 carbons and
optionally, monomer containing an aromatic group, are present in
the polymer in an amount of 20 to 95% by weight of the total
polymer. The hydrophobic aromatic-group containing monomer may be
present in an amount from about 0 to 85% by weight of the total
polymer, more preferably from about 0 to 60%, and most preferably
from about 0 to 50%. A particularly preferred embodiment is a
terpolymer of benzyl methacrylate, stearyl methacrylate and
methacrylic acid.
[0040] Particularly useful polymeric pigment dispersants are
further described in U.S. Application Numbers 2006/0012654 and
2007/0043144, the disclosures of which are incorporated herein by
reference.
[0041] Encapsulating type polymeric dispersants and polymeric
dispersed pigments thereof can also be used in the invention.
Specific examples are described in U.S. Pat. No. 6,723,785, U.S.
Pat. No. 6,852,777, and US Pat. App. Pub. Nos. 2004/0132942 A1,
2005/0020731 A1, 2005/00951 A1, 2005/0075416 A1, 2005/0124726 A1,
2004/007749 A1, and 2005/0124728 A1, the disclosures of which are
incorporated by reference. Encapsulating type polymeric dispersants
can be especially useful because of their high dispersion stability
on keeping and low degree of interaction with ink components.
Composite colorant particles having a colorant phase and a polymer
phase are also useful in aqueous pigment-based inks of the
invention. Composite colorant particles are formed by polymerizing
monomers in the presence of pigments; see for example, US
2003/0199614 A1; US 2003/0203988 A1; or US 2004/0127639.
Microencapsulated-type pigment particles are also useful and
consist of pigment particles coated with a resin film; see for
example U.S. Pat. No. 6,074,467.
[0042] Pigments suitable for use in the invention include, but are
not limited to, azo pigments, monoazo pigments, disazo pigments,
azo pigment lakes, .beta.-Naphthol pigments, Naphthol AS pigments,
benzimidazolone pigments, disazo condensation pigments, metal
complex pigments, isoindolinone and isoindoline pigments,
polycyclic pigments, phthalocyanine pigments, quinacridone
pigments, perylene and perinone pigments, thioindigo pigments,
anthrapyrimidone pigments, flavanthrone pigments, anthanthrone
pigments, dioxazine pigments, triarylcarbonium pigments,
quinophthalone pigments, diketopyrrolo pyrrole pigments, titanium
oxide, iron oxide, and carbon black.
[0043] Typical examples of pigments that may be used include Color
Index (C. I.) Pigment Yellow 1, 2, 3, 5, 6, 10, 12, 13, 14, 16, 17,
62, 65, 73, 74, 75, 81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100,
101, 104, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120, 121,
123, 124, 126, 127, 128, 129, 130, 133, 136, 138, 139, 147, 148,
150, 151, 152, 153, 154, 155, 165, 166, 167, 168, 169, 170, 171,
172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185,
187, 188, 190, 191, 192, 193, 194; C. I. Pigment Red 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32,
38, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 49:3, 50:1, 51, 52:1, 52:2,
53:1, 57:1, 60:1, 63:1, 66, 67, 68, 81, 95, 112, 114, 119, 122,
136, 144, 146, 147, 148, 149, 150, 151, 164, 166, 168, 169, 170,
171, 172, 175, 176, 177, 178, 179, 181, 184, 185, 187, 188, 190,
192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216,
220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252,
253, 254, 255, 256, 258, 261, 264; C.I. Pigment Blue 1, 2, 9, 10,
14, 15:1, 15:2, 15:3, 15:4, 15:6, 15, 16, 18, 19, 24:1, 25, 56, 60,
61, 62, 63, 64, 66, bridged aluminum phthalocyanine pigments; C.I.
Pigment Black 1, 7, 20, 31, 32; C. I. Pigment Orange 1, 2, 5, 6,
13, 15, 16, 17, 17:1, 19, 22, 24, 31, 34, 36, 38, 40, 43, 44, 46,
48, 49, 51, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69; C.I. Pigment
Green 1, 2, 4, 7, 8, 10, 36, 45; C.I. Pigment Violet 1, 2, 3, 5:1,
13, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50; or C.I. Pigment
Brown 1, 5, 22, 23, 25, 38, 41, 42.
[0044] The pigment particles of the present invention are
preferably dispersed by a dispersant in an amount sufficient to
provide stability in the aqueous suspension and subsequent ink. The
amount of dispersant relative to pigment is a function of the
desired particle size and related surface area of the fine particle
dispersion. The ratio of pigment to dispersant can range from about
10:1 to about 1:1, and more preferably from about 5:1 to about 2:1.
It is understood that the amount of polymer and relative ratios of
the monomer constituents can be varied to achieve the desired
particle stability and ink firing performance for a given pigment,
as it is known that pigments can vary in composition and affinity
for the dispersant.
[0045] The inks of the invention may also optionally comprise
self-dispersing pigments that are dispersible without the use of a
dispersant. Pigments of this type are those that have been
subjected to a surface treatment such as oxidation/reduction,
acid/base treatment, or functionalization through coupling
chemistry. The surface treatment can render the surface of the
pigment with anionic, cationic or non-ionic groups. Examples of
self-dispersing type pigments include, but are not limited to,
Cab-O-Jet.RTM. 200 and Cab-O-Jet.RTM. 300 (Cabot Corp.) and
Bonjet.RTM. Black CW-1, CW-2, and CW-3 (Orient Chemical Industries,
Ltd.).
[0046] Dyes suitable for use in the invention include, but are not
limited to, those commonly used in the art of inkjet printing. For
aqueous-based ink compositions, such dyes include water-soluble
reactive dyes, direct dyes, anionic dyes, cationic dyes, acid dyes,
food dyes, metal-complex dyes, phthalocyanine dyes, anthraquinone
dyes, anthrapyridone dyes, azo dyes, rhodamine dyes, solvent dyes
and the like. Specific examples of dyes usable in the present
invention are as follows; yellow dyes including: C.I. Acid Yellow
1, 3, 11, 17, 19, 23, 25, 29, 36, 38, 40, 42, 44, 49, 59, 61, 70,
72, 75, 76, 78, 79, 98, 99, 110, 111, 127, 131, 135, 142, 162, 164,
and 165; C.I. Direct Yellow 1, 8, 11, 12, 24, 26, 27, 33, 39, 44,
50, 58, 85, 86, 87, 88, 89, 98, 110, 132, 142, and 144; C.I.
Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18,
22, 23, 24, 25, 26, 27, 37, and 42; and C.I. Food Yellow 3 and 4;
magenta dyes including: C.I. Acid Red 1, 6, 8, 9, 13, 14, 18, 26,
27, 32, 35, 37, 42, 51, 52, 57, 75, 77, 80, 82, 85, 87, 88, 89, 92,
94, 97, 106, 111, 114, 115, 117, 118, 119, 129, 130, 131, 133, 134,
138, 143, 145, 154, 155, 158, 168, 180, 183, 184, 186, 194, 198,
209, 211, 215, 219, 249, 252, 254, 262, 265, 274, 282, 289, 303,
317, 320, 321, and 322; C.I. Direct Red 1, 2, 4, 9, 11, 13, 17, 20,
23, 24, 28, 31, 33, 37, 39, 44, 46, 62, 63, 75, 79, 80, 81, 83, 84,
89, 95, 99, 113, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229,
230, and 231; C.I. Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13,
15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36,
37, 38, 39, 40, 41, 42, 43, 45, 46, 49, 50, 58, 59, 63, and 64; and
C.I. Food Red 7, 9, and 14; cyan dyes including; C.I. Acid Blue 1,
7, 9, 15, 22, 23, 25, 27, 29, 40, 41, 43, 45, 54, 59, 60, 62, 72,
74, 78, 80, 82, 83, 90, 92, 93, 100, 102, 103, 104, 112, 113, 117,
120, 126, 127, 129, 130, 131, 138, 140, 142, 143, 151, 154, 158,
161, 166, 167, 168, 170, 171, 182, 183, 184, 187, 192, 199, 203,
204, 205, 229, 234, 236, and 249; C.I. Direct Blue 1, 2, 6, 15, 22,
25, 41, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 120, 123,
158, 160, 163, 165, 168, 192, 193, 194, 195, 196, 199, 200, 201,
202, 203, 207, 225, 226, 236, 237, 246, 248, and 249; C.I. Reactive
Blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25,
26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40, 41, 43, 44, and 46;
and C. I. Food Blue 1 and 2; black dyes including: C.I. Acid Black
1, 2, 7, 24, 26, 29, 31, 48, 50, 51, 52, 58, 60, 62, 63, 64, 67,
72, 76, 77, 94, 107, 108, 109, 110, 112, 115, 118, 119, 121, 122,
131, 132, 139, 140, 155, 156, 157, 158, 159, and 191; C.I. Direct
Black 17, 19, 22, 32, 39, 51, 56, 62, 71, 74, 75, 77, 94, 105, 106,
107, 108, 112, 113, 117, 118, 132, 133, 146, 154, and 168; C.I.
Reactive Black 1, 3, 4, 5, 6, 8, 9, 10, 12, 13, 14, 31, and 18; and
C.I. Food Black 2, CAS No. 224628-70-0 sold as JPD Magenta EK-1
Liquid from Nippon Kayaku Kabushiki Kaisha; CAS No. 153204-88-7
sold as Intrajet.RTM. Magenta KRP from Crompton and Knowles Colors;
the metal azo dyes disclosed in U.S. Pat. Nos. 5,997,622 and
6,001,161.
[0047] Also useful in the invention are polymeric dyes or
loaded-dye/latex particles. Examples of polymeric dyes are
described in U.S. Pat. No. 6,457,822 B1 and references therein.
Examples of loaded-dye/latex particles are described in U.S. Pat.
No. 6,431,700 B1; US 2004/0186199 A1; US 2004/0186198 A1; US
2004/0068029 A1; US 2003/0119984 A1; and US 2003/0119938 A1.
[0048] The pigments used in the ink compositions of the invention
can be present at high pigment loads, generally greater than 4.5%
by weight, preferably 4.5 to 10% by weight, and more preferably
from 4.5 to 7.5% by weight.
[0049] In a specific embodiment, ink compositions of the present
invention further comprise, as water-miscible organic solvents, at
least one pyrrolidinone compound and optionally an alternative
cyclic amide such as imidazolidinone as well as other optional
water miscible humectants and solvents such as glycerol, and
1,2-alkanediols having from four to eight carbon atoms. The
pyrrolidinone compounds are effective as humectants that improve
the reliability of the system by allowing dried ink to readily
redissolove or redisperse in contact with fresh ink. Pyrrolidinone
compounds such as 1-(2-hydroxyethyl)-2-pyrrolidinone can have the
added advantage of reducing the tendency of office papers to curl
when large regions of the paper are printed. Other cyclic amides
such as imidazolidinone can be added with the pyrrolidinone
compounds to further enhance the redispersability of the ink while
still providing good humectant and plain paper curl properties.
[0050] Glycerol is also an effective humectant for pigment-based
inks and provides stable vapor bubble formation in a thermal inkjet
printhead. Glycerol is a desirable ingredient in a thermal inkjet
ink since it aids in maintaining the heater surface which leads to
long term printhead lifetimes. The low volatility of glycerol will
cause it to remain in the dried ink for a long period of time where
it can plasticize the polymers in the dried ink and thereby improve
the ability of fresh ink to redissolve the dried ink. Inks
formulated with some glycerol as a humectant can show good latency
performance and print head recovery. Inks of the present invention
in certain embodiments comprise glycerol at levels from about 0.5%
to about 5%, more preferably from about 1% to about 4%, and most
preferably from about 1% to 3% based on the total components of the
ink.
[0051] Inks in certain embodiments of the present invention may
further comprise at least one 1,2-alkanediol having from four to
eight carbon atoms. Examples of 1,2-alkanediols useful in the
present invention include, 1,2-butanediol, 1,2-pentanediol,
1,2-hexanediol, and 1,2-octanediol. Preferred diols for use in the
present invention are 1,2-pentanediol and 1,2-hexanediol. The
1,2-alkanediols can preferably be present in the ink composition at
levels from about 1% to about 5% by weight and more preferably from
about 2% to about 4%. 1,2-alkanediols are known in the art of
inkjet printing as penetrants or dynamic surface tension reducing
agents. The presence of such diols can provide favorable
interactions between the inks and the receiver elements, however,
they can also severely degrade the latency performance of inks
formulated with polyhydric alcohol humectants commonly used in
inkjet inks, such as glycerol. For example, the addition of a
1,2-alkanediol to a glycerol based ink can reduce the latency wait
times by an order of magnitude compared to inks containing no
1,2-alkanediol.
[0052] The redissolution performance of inks comprising glycerol
and 1,2-alkanediols can be significantly improved in accordance
with the invention by the additional presence of a pyrrolidinone
compound and optionally an alternative cyclic amide such as
imidazolidone. Preferred pyrrolidinone compounds include,
2-pyrrolidinone, 1-(2-hydroxyethyl)-2-pyrrolidinone, and
1-methyl-2-pyrrolidinone. The pyrrolidinone may be used alone or as
a mixture of two or more such compounds. A particularly preferred
pyrrolidinone is a 1-(2-hydroxyethyl)-2-pyrrolidinone. Ink
compositions of the present invention can also include a
combination of glycerol, a 1,2-alkanediol having from four to eight
carbon atoms, a pyrrolidinone compound and a substituted urea
compound such as imidazolidinone.
[0053] In certain embodiments of the invention, at least one cyclic
amide compound such as a pyrrolidinone or imidazolidone compound is
present in the ink composition at levels from about 6% to about
25%, more preferably from about 8% to about 20% based on the total
components in the ink. In a preferred embodiment of the present
invention the combination of all pyrrolidinone compounds and
optionally imidazolidone comprise greater than 50%, more preferably
greater than about 55% by weight, based on the sum total of all
humectants including the 1,2-alkanediol. In the preferred
embodiment it is desirable that the imidazolidone be present at
less than 41% of the total humectants in the ink to avoid the
formation of crystals in the dried ink deposits.
[0054] In addition to the pyrrolidinone compounds and the optional
imidazolidone, glycerol, and 1,2-alkanediol, ink compositions
useful in the invention can also comprise additional humectants.
Representative examples of additional humectants which may be
employed in the present invention include; (1) triols, such as;
1,2,6-hexanetriol, 2-ethyl-2-hydroxymethyl-propane diol,
trimethylolpropane, alkoxlated triols, alkoxylated
pentaerythritols, saccharides and sugar alcohols, (2) diols, such
as ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, polyalkylene glycols having four or more alkylene
oxide groups, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol,
1,7-hexanediol, 2-ethyl-1,3-hexanediol,
2,2,4-trimethyl-1,3-pentanediol, 1,8-octanediol; and thioglycol, or
a mixture thereof. Typical aqueous-based ink compositions useful in
the invention may contain 2-30 weight percent total humectant(s),
more preferably from about 6-25% humectant, most preferably from
about 12-24% humectant.
[0055] The ink compositions of the present may also include, in
addition to the above humectants, additional other water miscible
co-solvent or penetrants. Representative examples of other
co-solvents useful in the aqueous-based ink compositions include
(1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl
alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,
t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and
tetrahydrofurfuryl alcohol; (2) lower mono- and di-alkyl ethers
derived from the polyhydric alcohols; such as, ethylene glycol
monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol
monoethyl ether acetate, diethylene glycol monomethyl ether, and
diethylene glycol monobutyl ether; and (3) sulfur-containing
compounds such as 2,2'-thiodiethanol, dimethyl sulfoxide and
tetramethylene sulfone.
[0056] In a preferred embodiment, the inks of the present invention
comprise from about 8% to about 30% of total organic solvent,
wherein total organic solvent is defined as the summation of
glycerol, the cyclic amide compounds such as the pyrrolidinone
compounds and imidazolidone, 1,2-alkanediol and additional
humectant or penetrants. Preferably, the total organic solvent
content in the ink compositions is between about 10% and about 25%.
Inks having excellent redissolution performance can be realized
when the total organic solvent condition is within the defined
ranges.
[0057] In a specific embodiment of the invention, at least one
humectant employed in the ink composition may comprise
1-(2-hydroxyethyl)-2-pyrrolidinone, 2-pyrrolidinone, imidazolidone
or glycerol, or a combination of any two or more thereof. In such
embodiment, the sum of the amounts of
1-(2-hydroxyethyl)-2-pyrrolidinone, 2-pyrrolidinone and
imidazolidone is preferably greater than 50 weight % of the total
humectant concentration of the ink composition. Further, the amount
of 1-(2-hydroxyethyl)-2-pyrrolidinone is preferably at least 10
weight % of the total humectant concentration, the amount of
imidazolidone is preferably less than 41% of the total humectant
concentration, the amount of glycerol is preferably less than 25
weight % of the total humectant concentration, and the amount of
2-pyrrolidinone is preferably less than 25 weight % of the total
humectant concentration. Ink compositions in accordance with such
embodiment may further preferably comprise a 1,2-alkanediol such as
1,2-pentanediol and 1,2-hexanediol. Imidazolidone may preferably be
present at greater than 0.1 weight percent to less than 13 weight
percent, and the ink composition may further comprises triethylene
glycol as an additional humectant.
[0058] In a further specific embodiment of the invention, the at
least one humectant comprises at least
1-(2-hydroxyethyl)-2-pyrrolidinone, and imidazolidone, if present,
is present in an amount less than about 7 weight %, and the sum of
the amounts of 1-(2-hydroxyethyl)-2-pyrrolidinone and imidazolidone
is greater than or equal to 9 weight %, the sum of the amounts of
1-(2-hydroxyethyl)-2-pyrrolidinone and imidazolidone is greater
than 50% of the total humectant concentration, and the amounts of
2-pyrrolidinone and glycerol, if present, are each less than 25% of
the total humectant concentration. In such embodiment, the total
humectant content is preferably from about 12 weight % to about 24
weight %, and 2-pyrrolidinone is preferably present at from 0 to
less than 4 weight %, more preferably less than 2 weight %.
[0059] Ink compositions in certain embodiments of the present
invention further comprise at least one water-dispersible binder,
preferably a water-dispersible polyurethane compound. By
water-dispersible it is meant to include individual polymer
molecules or colloidal assemblies of polymer molecules, which are
stably dispersed in the ink without the need for a dispersing
agent. Water dispersible polyurethanes employed in the present
invention may have the general formula of (I)
##STR00001##
wherein R.sub.1 in the structure (I) above is the central portion
of the monomer unit that is the polymerization product of a
diisocyanate; R.sub.2 represents the central portion of a unit that
is the polymerization product of at least one type of polyol or,
optionally, a polyamine; R.sub.3 is the central portion of a unit
containing an acid group; and X and Y can be the same or different
and are --O-- or --N-- atom.
[0060] R.sub.1 is preferably a hydrocarbon group having a valence
of two, more preferably containing a substituted or unsubstituted
alicyclic, aliphatic, or aromatic group, preferably represented by
one or more of the following structures:
##STR00002##
[0061] R.sub.2 preferably represents a soft segment comprising a
prepolymer having ester, carbonate, or ether linkages.
[0062] The soft segment is introduced into the polyurethane
backbone by using the prepolymer with both ends terminated with a
hydroxyl (diol) or an amino (diamine) group. The prepolymer having
terminal hydroxyl groups is known as polyols, and that having
terminal amine groups is known as polyamine. Polyols useful for the
practice of the invention include a) a polyester polyol obtained
by, for example, esterification of a dicarboxylic acid with a diol;
or ring opening reaction of a lactone (e.g. .epsilon.-caprolactone)
and a diol, b) a polycarbonate polyol obtained, for example, by
reacting a diols with diaryl carbonates or phosgene; and, a
polyether diol, c) a polyether polyol as a condensation product of,
for example, ethylene glycol, propylene glycol, or tetramethylene
glycol. Preferably the polyols have a molecular weight above about
300 and below about 3000. Polyamines useful for the practice of the
invention include those sold tradename JEFFAMINE.RTM. D, ED, and M
series from HUNTSMAN. Another more preferred polyether diamine is a
polytetrahydrofuran bis(3-aminopropyl) terminated having a
molecular weight of about 1,000.
[0063] R.sub.2 may further or alternatively represent one or more
soft segment having siloxane groups such as described, e.g., in
U.S. Patent Application Pub. No. 2010/0055322. In such an
embodiment, R.sub.2 may represent a segment derived from a
polysiloxane group-containing prepolymer, and in a specific
embodiment a polydimethyl siloxane (PDMS) group-containing
prepolymer. The polysiloxane segment may be introduced into the
polyurethane by using the prepolymer with both ends terminated with
a hydroxyl (diol) or an amino (diamine) group. The prepolymer
having terminal hydroxyl groups may be, e.g., a silanol or carbinol
terminated polydimethyl siloxane, and that having terminal amine
groups may be, e.g., an aminoalkyl terminated polydimethyl
siloxane. The resulting polyurethanes are referred to as siloxane
group functionalized, since they contain siloxane groups as part of
the polymer composition.
[0064] R.sub.3 is preferably the central portion of a monomeric
unit containing a phosphoric acid, carboxylic acid or sulfonic acid
group, most preferably being carboxylic acids, such as
2,2'-bis(hydroxymethyl)propionic acid,
2,2'-bis(hydroxymethyl)butyric acid, hydroxyethylether of
4,4'-bis(4-hydroxyphenyl)valeric acid. These materials may be
prepared by any of the well known techniques in art of polyurethane
manufacture, for example, processes disclosed in U.S. Pat. No.
4,335,029 Dadi, et al. assignee Witco Chemical Corporation (New
York, N.Y.) and in Aqueous Polyurethane Dispersions B. K. Kim,
Colloid & Polymer Science, Vol. 274, No. 7 (1996)
599-611.COPYRGT. Steinopff Verlag 1996.
[0065] Preferred polyurethanes for use in this invention have a
sufficient amount of acid groups in the molecule to have an acid
number from about 50 to about 150, more preferably 60 to 130 and
most preferably 70 to 120 wherein, the acid number is defined as
the milligrams of potassium hydroxide required to neutralize one
gram of polymer. The acid number of the polymer may be calculated
by the formula given in the following equation: Acid number=[(moles
of acid monomer)*(56 grams/mole)*(1000)/(total grams of monomers)]
where moles of acid monomer is the total moles of all acid group
containing monomers that comprise the polymer, 56 is the formula
weight for potassium hydroxide, and total grams of monomers is the
summation of the weight of all the monomers, in grams, comprising
the target polymer.
[0066] Polyurethane dispersions useful for the practice of the
invention can be prepared by preparing a prepolymer having a
relatively low molecular weight and a small excess of isocyanate
groups and chain-extending with a chain extender the prepolymers
into a high molecular weight polyurethane during the dispersion
process. Such processes have been disclosed in, for example, U.S.
Pat. No. 4,335,029 by Dadi, et al. assigned to Witco Chemical
Corporation (New York, N.Y.); in "Aqueous Polyurethane Dispersions"
by B. K. Kim, Colloid & Polymer Science, Vol. 274, No. 7 (1996)
599-611.COPYRGT. Steinopff Verlag 1996; and in "Polyurethane
Dispersion Process)" by Mania et al. Paint and Coating Industry,
Jan 200, Page 30.
[0067] Preferred diamine chain extenders for the practice of the
invention include ethylene diamine, diethylene triamine, propylene
diamine, butylene diamine, hexamethylene diamine, cyclohexylene
diamine, phenylene diamine, tolylene diamine, xylylene diamine,
3,3'-dinitrobenzidene, ethylene methylenebis(2-chloroaniline),
3,3'-dichloro-4,4'-biphenyl diamine. 2,6-diaminopyridine,
4,4'-diamino diphenylmethane, adducts of diethylene triamine with
acrylate or its hydrolyzed products, hydrazine, and substituted
hydrazines.
[0068] The polyurethane dispersions useful for the practice of this
invention can also be prepared without involving the
chain-extension step during the dispersion step. In the process the
chemical reaction for forming urethane or urea linkages is
completed prior to the dispersion step.
[0069] Polyurethanes used in the invention preferably have a
minimum weight average molecular weight of at least 8,000.
Preferably, the polyurethane has a maximum weight average molecular
weight of 150,000. More preferably, the molecular weight of
polyurethane is between about 10,000 and 100,000, and most
preferably between about 15,000 and 50,000. Polyurethane
dispersions useful for the practice of this invention preferably
have a mean particle size of less than 100 nm and more preferably
less than 50 nm.
[0070] The acid groups on the polyurethanes and the acrylic polymer
dispersants when employed are at least partially neutralized
(converted into salts) using organic or inorganic bases, preferably
monovalent inorganic bases, and most preferably aqueous alkaline
metal hydroxides, selected from; potassium hydroxide, sodium
hydroxide, rubidium hydroxide or lithium hydroxide. In a preferred
embodiment, at least 50 percent of the available acid groups on the
polymer are converted into salts using monovalent inorganic base,
more preferably at least 70% and most preferably at least 85% of
the available acid groups are converted. From a manufacturing
perspective, preferably less than 100% of the acid groups are
neutralized as this can lead to lack of control of the pH of the
inks. Monovalent inorganic bases are highly preferred over organic
bases such as amines as the neutralizing agents for the acrylic and
polyurethane polymers since inks containing polymers neutralized
with organic amines show very poor jetting performance in a thermal
inkjet printhead.
[0071] Surfactants may be added to adjust the surface tension of
the ink to an appropriate level. In a particular embodiment,
relative dynamic and static surface tensions of various pigment
based inks and colorless protective ink of an ink set may be
controlled as described in U.S. Patent Application Pub. No.
2008/0207805, the disclosure of which is incorporated by reference
herein, to control intercolor bleed between the inks. In
particular, where cyan, magenta, yellow, black and colorless inks
are employed, the surface tensions of the inks may have the
relationships wherein (i) the dynamic surface tension at 10
milliseconds surface age for all inks of the ink set is greater
than or equal to 35 mN/m, (ii) the static surface tensions of the
yellow ink and of the colorless protective ink are at least 2.0
mN/m lower than the static surface tensions of the cyan, magenta
and black inks of the ink set, and (iii) the static surface tension
of the colorless protective ink is at least 1.0 mN/m lower than the
static surface tension of the yellow ink.
[0072] The surfactants may be anionic, cationic, amphoteric or
nonionic and used at levels of 0.01 to 5% of the ink composition.
Examples of suitable nonionic surfactants include, linear or
secondary alcohol ethoxylates (such as the Tergitol.RTM. 15-S and
Tergitol.RTM. TMN series available from Union Carbide and the
Brij.RTM. series from Uniquema), ethoxylated alkyl phenols (such as
the Triton.RTM. series from Union Carbide), fluoro surfactants
(such as the Zonyls.RTM. from DuPont; and the Fluorads.RTM. from
3M), fatty acid ethoxylates, fatty amide ethoxylates, ethoxylated
and propoxylated block copolymers (such as the Pluronic.RTM. and
Tetronic.RTM. series from BASF, ethoxylated and propoxylated
silicone based surfactants (such as the Silwet.RTM. series from CK
Witco), alkyl polyglycosides (such as the Glucopons.RTM. from
Cognis) and acetylenic polyethylene oxide surfactants (such as the
Surfynols from Air Products).
[0073] Examples of anionic surfactants include; carboxylated (such
as ether carboxylates and sulfosuccinates), sulfated (such as
sodium dodecyl sulfate), sulfonated (such as dodecyl benzene
sulfonate, alpha olefin sulfonates, alkyl diphenyl oxide
disulfonates, fatty acid taurates and alkyl naphthalene
sulfonates), phosphated (such as phosphated esters of alkyl and
aryl alcohols, including the Strodex.RTM. series from Dexter
Chemical), phosphonated and amine oxide surfactants and anionic
fluorinated surfactants. Examples of amphoteric surfactants
include; betaines, sultaines, and aminopropionates. Examples of
cationic surfactants include; quaternary ammonium compounds,
cationic amine oxides, ethoxylated fatty amines and imidazoline
surfactants. Additional examples are of the above surfactants are
described in "McCutcheon's Emulsifiers and Detergents: 1995, North
American Editor".
[0074] A biocide (0.01-1.0% by weight) may also be added to prevent
unwanted microbial growth which may occur in the ink over time. A
preferred biocide for the inks employed in the present invention is
Proxel.RTM. GXL (Zeneca Colours Co.) at a concentration of
0.05-0.1% by weight or/and Kordek.RTM. (Rohm and Haas Co.) at a
concentration of 0.05-0.1% by weight (based on 100% active
ingredient. Additional additives which may optionally be present in
an inkjet ink composition include thickeners, conductivity
enhancing agents, anti-kogation agents, drying agents, waterfast
agents, dye solubilizers, chelating agents, binders, light
stabilizers, viscosifiers, buffering agents, anti-mold agents,
anti-curl agents, stabilizers and defoamers.
[0075] The pH of the aqueous ink compositions of the invention may
be adjusted by the addition of organic or inorganic acids or bases.
Inorganic bases are preferred, however small amounts of organic
bases, such as triethanolamine, may be used to adjust the pH of the
ink. Useful inks may have a preferred pH of from about 4 to 10,
depending upon the type of pigment being used. Preferably, the pH
of the present ink is from 6 to 9, more preferably from 7.5 to
8.5.
[0076] The inks of the present invention can be printed through an
inkjet printhead capable of achieving firing frequencies of at
least 12 kHz with a near nozzle velocity of at least 10
meters/second. Any of the known printhead designs in the art of
inkjet printing may be used which are capable of achieving these
high speed firing frequencies. Preferably, the inkjet printer is
equipped with a thermal inkjet printhead. Particularly preferred
printhead designs are disclosed in United States Patent Application
Pub. Nos. 2006/0103691 and 2008/0136867, the disclosures of which
are incorporated by reference herein.
[0077] Inks of the present invention may be applied to a
photoglossy or plain paper receiver. The two types of receivers are
distinguished from one another in that the photoglossy receiver is
manufactured with a coated layer above the underlying paper
support. Examples of plain papers include: Kodak bright white
inkjet paper, Hewlett Packard Color inkjet paper, Xerox Extra
Bright white inkjet paper, Georgia-Pacific inkjet Paper Catalog
Number 999013, Staples inkjet paper International Paper Great White
MultiUse 20 Paper, Xerox Premium Multipurpose Paper, Hammermill
Copy plus or ForeMP paper, and Hewlett Packard Multipurpose paper.
The plain papers may include papers that have been treated with
multivalent salts during or after manufacture of the paper.
[0078] Inks of the present invention can be printed as digital
images having photographic quality if a suitable recording medium,
such as glossy inkjet paper, is used. Photoglossy receivers may be
further categorized as being a swellable media (having a non-porous
polymer coating) or a microporous media, although hybrid designs
are also well known. The microporous media are typically comprised
of water-absorbing fine particles or powders mixed with a polymeric
hydrophilic binder to form a microporous structured coating. The
hydrophilic particles or powders are typically polycrystalline
inorganic materials such as boehmite alumina, porous and non-porous
silicas (for example Sylojet or Ludox particles) or amorphous
inorganic materials such as aluminum silicates or silica
dispersions. Microporous photoglossy media are preferred due to
their relatively quick drying capabilities and improved
water-fastness and smudge resistance compared to swellable media.
The design of the both plain paper and photoglossy media vary
widely depending on materials and paper manufacturing processes and
should not be construed to limit the scope of the present
invention.
Examples
[0079] The following examples illustrate, but do not limit, the
utility of the present invention.
Pigment Dispersions
[0080] Aqueous pigment dispersions were prepared using a high speed
mill equipped with polymeric milling media having a diameter of 50
microns. The type of mixing blade, the rotational speed of the
mixer, milling time, the ratio of milling media to pigment, and the
ratio of pigment to dispersant were varied to produce different
pigment particle size distributions. Table I shows the pigment and
dispersant type, and the resulting mean Stoke's diameter particle
size and size coefficient of variation as determined by the disc
centrifuge method.
Particle Size Measurement by Disc Centrifuge
[0081] A CPS disc centrifuge model DC18000 (supplied from CPS
Instruments Inc, 7349 SE Seagate Lane, Stuart, Fla., 34997, USA)
was used to make the measurements. A pigment dispersion sample was
injected into the instrument and the disc spun at 16,000 rpm.
Sucrose solutions of 2 to 10% were used to create a density
gradient necessary for stable sedimentation. It may take
approximately 2 hours to sediment the smallest particles
(approximately 10 nm). A Stoke's diameter particle size
distribution is calculated from the sedimentation time using 1.49 g
cm.sup.-3 to be the density of the magenta pigment particles. From
the measured distribution, Stoke's diameter particle size and width
parameters are calculated based on the modified Stoke's law
equation.
Typical Polymerically Dispersed Pigment Example
[0082] M-1: A dispersion of magenta pigment Clarient E02 (solid
solution of PR122 and PV19) dispersed with an acrylic copolymer A
made from a monomer composition of 37 wt % benzyl methacrylate, 30
wt % n-octadecylmethacrylate, and 33 wt % methacrylic acid, having
a weight average molecular weight of 8000 to 10000 as determined by
the Size Exclusion Chromatography neutralized with potassium
hydroxide (degree of neutralization of about 90%). The dispersion
was prepared using a high tip speed on the mixing blade with the
resulting mean Stoke's diameter particle size of 33.7 nm and a
coefficient of variation of 0.356 as measured by disc
centrifuge.
Typical Small-Molecule Dispersed Pigment Example
[0083] M-30: A dispersion of magenta pigment Sun Quindo (solid
solution of PR202 and PV19) dispersed with the potassium salt of
oleoyl methyl taurate (KOMT). The dispersion was prepared using a
high tip speed on the mixing blade with the resulting mean Stoke's
diameter particle size of 28.2 nm and a coefficient of variation of
0.425 as measured by disc centrifuge.
Polyurethane Dispersions Used in the Ink Examples
[0084] The polyurethane dispersion shown in the ink examples below
typically has a particle size in the range from about 10 to about
40 nanometers in diameter. These sizes may change depending on the
specific aqueous environment of the ink formulations. Unless
otherwise stated, the polyurethanes dispersions are prepared by
carrying out the polymerization reaction in either tetrahydrofuran
(THF) or ethyl acetate using isophorone diisocyanate,
2,2-bis(hydroxymethyl)propionic acid, and a polyol or polyamine,
neutralizing the resultant polymer with aqueous potassium hydroxide
solution, diluting with additional deionized water if necessary,
and removing volatile solvent by vacuum evaporation or
stripping.
[0085] Polyurethane PU-1: A 100 acid number polyurethane made with
isophorone diisocyanate, 2,2-bis(hydroxymethyl)proprionic acid, and
a 2000 Mw polytetrahydrofuran polyol where 95% of the acid groups
are neutralized with potassium hydroxide. The weight average
molecular weight of PU-1 is about 20,000.
[0086] Polyurethane PU-2: A 76 acid number polyurethane made with
isophorone diisocyanate and a combination of poly(hexamethylene
carbonate)diol and 2,2-bis(hydroxymethyl)proprionic acid where 100%
of the acid groups are neutralized with potassium hydroxide. The
weight average molecular weight is about 25,000.
Magenta Ink for Polymerically Dispersed Pigment Evaluation in Table
I, II, and III
[0087] Into an approximately 250 ml high density polyethylene
bottle with magnetic stirring, the following components were added
in order as: high purity water, 2 wt % of glycerol, 7 wt % of
1-(2-hydroxyethyl)-2-pyrrolidinone, 6 wt % of 2-imidazolidone (from
a 35% solution in water), 3 wt % of 1,2-hexanediol, 0.5 wt % of
Surfynol 465 surfactant, 1 to 2 wt % of polyurethane PU-1 (from an
approximately 25 wt % aqueous solution), 0.02 wt % of the biocide
Kordek MLX, and 5% of the magenta pigment from the magenta pigment
dispersion generally described above and listed in Table I. The
resulting 240 g of ink were stirred for at least an hour and
filtered with a 1.0 um disk filter.
Magenta Ink for Non-Polymeric Surfactant Dispersed Pigment
Evaluation
[0088] Into an approximately 250 ml high density polyethylene
bottle with magnetic stirring, the following components were added
in order: high purity water, 13 wt % of glycerol, 3 wt % of
1,2-pentanediol, 0.75 wt % of Surfynol 465 surfactant, 1.2 wt % of
polyurethane PU-2 (from an approximately 25% aqueous solution),
0.9% of an acrylic copolymer prepared from 67 wt % benzyl
methacrylate and 33% methacrylic acid with about 85% of the acid
groups neutralized with potassium hydroxide, 0.02 wt % of the
biocide Kordek MLX, and 4.5% of the magenta pigment from the
magenta pigment dispersions M-30 or M-31 listed in Table I. The
resulting 240 g of ink were stirred for at least an hour and
filtered with a 1.0 um disk filter.
Evaluation of Redissolution
[0089] Redissolution is evaluated by allowing 5.0 g of ink to dry
in a flat-bottom dish for 18 hrs at 60 C. The state of the dry ink
is noted, especially if crystals have formed. An ideal ink dries to
a glassy appearance. After the ink dried ink is removed from the
oven and allowed to cool to room temperature, 2.5 g of fresh ink is
added and agitated every 15 to 30 minutes for 4 hrs. The degree of
dissolution of the dried ink by the fresh ink is rated as
follows:
[0090] 1--indicates complete dissolution with no significant
particles
[0091] 2--some particles or a few small soft chunks may be
present
[0092] 3--significant soft and moveable chunks are present
[0093] 4--a large amount of swollen often gel-like ink remains
[0094] 5--the dried ink show little sign of swelling or
dissolving
Intermediate ratings are possible by interpolating or averaging
multiple measurements.
Evaluation of Plain Paper Curl
[0095] Curl is evaluated by printing on a plain paper substrate
(STAPLES Copy Paper 30% recycled) a large rectangular patch of ink
asymmetrically printed relative to the major axis of the paper such
that it would cause severe curl on one side of the paper. The
printed papers are left on a solid surface under normal room
temperature and humidity conditions for 24 hrs and then the degree
of curl is judged. Inks that cause the print to roll, especially
those forming a tube are judged poor. Prints from inks that remain
nearly flat or show modest bowing are judged acceptable or
good.
Evaluation of Gloss
[0096] Gloss is evaluated by printing an area on a glossy photo
media substrate (KODAK Ultra Premium Photo Paper--High Gloss) with
the ink composition and measuring the 60-degree gloss of the
printed image area on a BYK Gardner Gloss Meter.
TABLE-US-00001 TABLE I Disc Centrifuge Particle size Results,
Redissolution, and Gloss Results Mean Stoke's Standard Coefficient
wt % diameter particle Deviation of Variation Pigment Polyurethane
Magenta Ink Average Ink Dispersion Dispersing agent Size (nm) (nm)
(SD/Mean) loading wt % level Redissolution 60 deg gloss Comp-1 M-1
Acrylic copolymer A 33.7 12 0.356 5 2 4.4 85.55 Comp-2 M-2 Acrylic
copolymer A 31.3 11.5 0.367 5 2 4.4 85.45 Ink-1 M-3 Acrylic
copolymer A 38.8 13.5 0.348 5 2 2.5 85.35 Ink-2 M-4 Acrylic
copolymer A 36.4 15.5 0.426 5 2 2.6 85.6 Ink-3 M-5 Acrylic
copolymer A 36.8 14.5 0.394 5 2 2 85.1 Ink-4 M-6 Acrylic copolymer
A 42.4 14.5 0.342 5 2 1.5 85.95 Ink-5 M-7 Acrylic copolymer A 43.5
14.5 0.333 5 2 1.3 90 Ink-6 M-8 Acrylic copolymer A 49.95 16 0.320
5 2 1 89.8 Ink-7 M-9 Acrylic copolymer A 43.5 14.5 0.333 5 2 1.3
87.85 Ink-8 M-10 Acrylic copolymer A 45 15 0.333 5 2 1 89.8 Ink-9
M-11 Acrylic copolymer A 45 15 0.333 5 2 1.6 86.3 Ink-10 M-12
Acrylic copolymer A 49.96 16 0.320 5 2 1.8 93.6 Ink-11 M-13 Acrylic
copolymer A 52 14.5 0.279 5 2 1.5 94.2 Comp-3 M-14 Acrylic
copolymer A 78.5 32.7 0.417 5 2 1.5 81.9 Comp-4 M-15 Acrylic
copolymer A 74.45 31.14 0.418 5 2 1.5 79.4 Comp-5 M-19 Acrylic
copolymer A 31.4 14 0.446 5 2 4.5 Ink-12 M-20 Acrylic copolymer A
36.5 14.5 0.397 5 2 2.3 Ink-13 M-21 Acrylic copolymer A 36.5 14
0.384 5 2 2.5 Ink-14 M-22 Acrylic copolymer A 47.4 14.5 0.306 5 2
1.7 Ink-15 M-23 Acrylic copolymer A 41.4 13 0.314 5 2 2.0 Comp-6
M-25 Acrylic copolymer A 29.33 13.9 0.474 5 2 4 Ink-16 M-26 Acrylic
copolymer A 56.97 22.45 0.394 5 2 1 Ink-17 M-27 Acrylic copolymer A
50.7 15.5 0.306 5 2 1 Ink-18 M-28 Acrylic copolymer A 49.87 15.5
0.311 5 2 1 Comp-7 M-29 Acrylic copolymer A 29.95 13.5 0.451 5 2 5
Comp-8 M-24 Acrylic copolymer A 29.5 12 0.407 5 2 4 Ink-19 M-10
Acrylic copolymer A 45 15 0.333 5.5 2 1.4 Ink-20 M-10 Acrylic
copolymer A 45 15 0.333 6 1 1 Ink-21 M-10 Acrylic copolymer A 45 15
0.333 6.5 1 1.8 Ink-22 M-10 Acrylic copolymer A 45 15 0.333 7 1 1.8
Comp-9 M-30 KOMT 28.23 12 0.425 4.5 2 4 Ink-23 M-31 KOMT 36.05 15.5
0.43 4.5 2 2.4
TABLE-US-00002 TABLE II Comparison of Disc Centrifuge Results with
Dynamic Light Scattering Results Disc Centrifuge Disc Disc Mean
Stoke's Centrifuge Centrifuge Dynamic Dynamic Dynamic Dynamic
Dynamic diameter Standard Coefficient Light Light Light Light Light
Magenta Ink particle Size Deviation of Variation Scattering
Scattering Scattering Scattering Scattering Ink Dispersion
Redissolution (nm) (nm) (SD/Mean) V10 V50 V90 V90 - V10 (V90 -
V10)/V50 Comp-2 M-2 4.4 31.3 11.5 0.367 11.04 16.03 75.2 64.16 4.00
Comp-1 M-1 4.4 33.7 12 0.356 11.69 17.06 95.2 83.51 4.90 Ink-2 M-4
2.6 36.4 15.5 0.426 12.06 20.8 98.4 86.34 4.15 Ink-3 M-5 2 36.8
14.5 0.394 11.96 17.71 90.3 78.34 4.42 Ink-1 M-3 2.5 38.8 13.5
0.348 12.63 23.2 100.7 88.07 3.80 Ink-4 M-6 1.5 42.4 14.5 0.342
11.99 19.56 104.8 92.81 4.74 Ink-5 M-7 1.3 43.5 14.5 0.333 13.71
27.21 113 99.29 3.65 Ink-7 M-9 1.3 43.5 14.5 0.333 11.92 18.76
104.4 92.48 4.93 Ink-8 M-10 1 45 15 0.333 12.92 23.38 111.1 98.18
4.20 Ink-9 M-11 1.6 45 15 0.333 12.75 28.95 118.2 105.45 3.64 Ink-6
M-8 1 49.95 16 0.320 14.13 41.4 104.8 90.67 2.19 Ink-10 M-12 1.8
49.96 16 0.320 12.64 27.42 113.2 100.56 3.67
TABLE-US-00003 TABLE III Redissolution and plain paper density as a
function of pigment loading Disc Centrifuge Mean Disc Stoke's
Centrifuge Density on diameter Coefficient of Density Staples
particle Variation Pigment level on Kodak 30% Ink Dispersion Size
(nm) (SD/Mean) wt % redissolution Ultimate Recycled Comp-10 M-1
33.7 0.36 5.0 4.5 1.30 1.01 Ink-24 M-10 45.0 0.33 5 1 1.33 0.97
Comp-11 M-14 78.5 0.42 5 1 1.36 0.97 Comp-12 M-1 33.7 0.36 4.5 2.5
1.29 0.97 Ink-25 M-10 45.0 0.33 4.5 1.3 1.32 0.96 Comp-13 M-14 78.5
0.42 4.5 1 1.32 0.96 Comp-14 M-1 33.7 0.36 4 2.1 1.26 0.94 Comp-15
M-10 45.0 0.33 4 1 1.29 0.95 Comp-16 M-14 78.5 0.42 4 1 1.31 0.93
Comp-17 M-1 33.7 0.36 3 1 1.21 0.91 Comp-18 M-10 45.0 0.33 3 1 1.22
0.93 Comp-19 M-14 78.5 0.42 3 1 1.17 0.89
Table I shows that inks containing at least 4.5 wt % pigment made
from pigment dispersions with a mean Stoke's diameter particle size
greater than 35 nm have acceptable redissolution performance (with
a preferred rating of about 2.5 or less). Inks made from
dispersions with mean Stoke's diameter pigment size greater than 70
nm have an unacceptable gloss level of below 85 when printed on
photo print media.
[0097] Table II shows that the sizing measurements determined by
dynamic light scattering do not correlate with the Stoke's diameter
particle sizing results from the disc centrifuge method, and would
therefore not have shown the desired relationship between the
redissolution results and the Stoke's diameter particle size and
size distribution as determined by the disc centrifuge method.
[0098] Table III shows that as the pigment loading is reduced below
5% the density formed on both treated and untreated plain paper
drops although the redissolution improves for all of the
dispersions regardless of particle size. This shows that inks
prepared with levels of pigment less than about 4.5% would not show
poor redissolution performance from a dispersion outside the
inventive size range.
[0099] Although Stoke's diameter particle size of the pigment
dispersion is shown to be critical in Tables I-III, it has further
been found that humectant selection can further impact the desired
results, even when particle size is as desired for good
redissolution at high pigment concentrations. Further Examples were
prepared as described in Tables IV-V, with varying humectant
compositions and concentrations, where Glyc is glycerol; 2-Pyr is
2-pyrrolidinone; HEP is 1-(2-hydroxyethyl)-2-pyrrolidinone; TEG is
triethylene glycol; 1,2-HD is 1,2-hexanediol; and 2-Im is
2-imidazolidinone.
Ink Preparation for Magenta Inks Described in Table IV and V
[0100] Into an approximately 250 ml high density polyethylene
bottle with magnetic stirring, the following components were added
in order at levels specified in Tables IV and V unless otherwise
stated: high purity water, glycerol,
1-(2-hydroxyethyl)-2-pyrrolidinone, 2-pyrrolidinone, imidazolidone,
triethylene glycol, 1,2-hexanediol, 0.5 wt % of Surfynol 465
surfactant, 2 wt % of polyurethane PU-1 (from an approximately 25
wt % aqueous solution), 0.02 wt % of the biocide Kordek MLX, and 5%
of the magenta pigment dispersion M-1. The resulting 240 g of ink
were stirred for at least an hour and filtered with a 1.0 um disk
filter.
TABLE-US-00004 TABLE IV Humectant variations and crystallization,
redissolution, and curl results wt % % HEP + 2-lm + % 2-lm of %
glyc of glyc as % wt % wt % wt % wt % 2- wt % 1,2- 2-pyr of total
total total of HEP + Redis- Ink dispersion Glyc HEP 2-Pyr lm TEG HD
humectant humectant humectant 2-lm Crystals solution curl Comp-20
M-1 2 11 0 2 0 3 72 11 11 15 none 4.0 good Comp-21 M-1 2 9 0 4 0 3
72 22 11 15 none 3.7 good Comp-22 M-1 2 7 0 6 0 3 72 33 11 15 none
3.8 good Comp-23 M-1 2 5 0 8 0 3 72 44 11 15 yes 1.0 good Comp-24
M-1 2 3 0 10 0 3 72 56 11 15 yes 1.7 good Ink-26 M-9 2 5 0 8 0 3 72
44 11 15 yes 1.0 good Ink-27 M-9 2 3 0 10 0 3 72 56 11 15 yes 1.0
good Ink-28 M-9 2 0 5 8 0 3 72 44 11 25 yes 1.0 poor Ink-29 M-9 2 0
7 6 0 3 72 33 11 33 slight 1.3 poor Ink-30 M-9 2 0 9 4 0 3 72 22 11
50 none 1.2 poor Ink-31 M-9 2 9 4 0 0 3 72 0 11 22 none 1.7 poor
Ink-32 M-9 2 7 6 0 0 3 72 0 11 29 none 1.6 poor Ink-33 M-9 2 5 8 0
0 3 72 0 11 40 none 1.4 poor Ink-34 M-9 4 3 0 6 0 3 56 38 25 44
none 4.1 good Ink-35 M-9 5 6 0 4 0 3 56 22 28 50 none 3.5 good
Ink-36 M-9 2 3 0 6 4 3 50 33 11 22 none 3.0 good Ink-37 M-9 2 5 0 4
4 3 50 22 11 22 none 3.3 good Ink-38 M-9 2 5 0 4 4 3 50 22 11 22
none 2.6 good Ink-39 M-9 2 7 0 2 4 3 50 11 11 22 none 3.5 good
Ink-40 M-9 2 8 0 1 4 3 50 6 11 22 none 2.8 good Ink-41 M-9 2 4 0 4
5 3 44 22 11 25 none 3.3 good Ink-42 M-9 2 5 0 3 5 3 44 17 11 25
none 3.3 good Ink-43 M-9 2 6 0 2 5 3 44 11 11 25 none 2.8 good
Ink-44 M-9 2 7 0 1 5 3 44 6 11 25 none 2.9 good Ink-45 M-9 2 1 0 6
6 3 39 33 11 29 none 4.0 good Ink-46 M-9 2 3 0 4 6 3 39 22 11 29
none 4.1 good
TABLE-US-00005 TABLE V Humectant variations and crystallization,
redissolution, and curl results wt % % HEP + 2-lm + % 2-lm of %
glyc of glyc as % dis- wt % wt % wt % wt % wt % 1,2- 2-pyr of total
total total of HEP + Ink persion Glyc HEP 2-Pyr 2-lm TEG HD
humectant humectant humectant 2-lm Crystals Redissolution curl
Ink-47 M-9 2 11 0 2 0 3 72 11 11 15 none 1.8 good Ink-48 M-9 2 9 0
4 0 3 72 22 11 15 none 1.3 good Ink-49 M-9 2 7 0 6 0 3 72 33 11 15
none 1.0 good Ink-50 M-9 2 8 0 4 1 3 67 22 11 17 none 1.0 good
Ink-51 M-9 2 7 0 5 1 3 67 28 11 17 none 1.0 good Ink-52 M-9 2 6 0 6
1 3 67 33 11 17 none 1.0 good Ink-53 M-9 0 7 0 4 4 3 61 22 0 0 none
1.3 good Ink-54 M-9 1 7 0 4 3 3 61 22 6 9 none 1.5 good Ink-55 M-9
2 7 0 4 2 3 61 22 11 18 none 1.0 good Ink-56 M-9 2 7 0 4 2 3 61 22
11 18 none 1.0 good Ink-57 M-9 3 7 0 4 1 3 61 22 17 27 none 1.3
good Ink-58 M-9 4 7 0 4 0 3 61 22 22 36 none 1.5 good Ink-59 M-9 2
6 0 5 2 3 61 28 11 18 none 1.0 good Ink-60 M-9 2 5 0 6 2 3 61 33 11
18 none 1.3 good Ink-61 M-9 4 5 0 6 0 3 61 33 22 36 none 1.4 good
Ink-62 M-9 2 10 0 0 3 3 56 0 11 20 none 2.3 good Ink-63 M-9 2 9 0 1
3 3 56 6 11 20 none 2.0 good Ink-64 M-9 2 8 0 2 3 3 56 11 11 20
none 1.7 good Ink-65 M-9 2 7 0 3 3 3 56 17 11 20 none 2.0 good
Ink-66 M-9 0 6 0 4 5 3 56 22 0 0 none 1.3 good Ink-67 M-9 1 6 0 4 4
3 56 22 6 10 none 1.0 good Ink-68 M-9 2 6 0 4 3 3 56 22 11 20 none
1.3 good Ink-69 M-9 3 6 0 4 2 3 56 22 17 30 none 2.0 good Ink-70
M-9 4 6 0 4 1 3 56 22 22 40 none 2.4 good Ink-71 M-9 2 6 0 4 3 3 56
22 11 20 none 1.3 good Ink-72 M-9 2 5 0 5 3 3 56 28 11 20 none 1.5
good Ink-73 M-9 2 4 0 6 3 3 56 33 11 20 none 1.0 good Ink-74 M-9 2
3 0 6 2 3 56 38 13 22 none 1.8 good Ink-75 M-9 0 3 0 6 4 3 56 38 0
0 slight 1.2 good Ink-76 M-10 2 7 0 6 0 0 87 40 13 15 none 1 good
Ink-77* M-10 2 7 0 6 0 3 72 33 11 15 none 1.5 good *Ink-77 does not
contain any urethane polymer.
[0101] Table IV lists the ink formulations that show that
dispersions that do not meet the inventive requirements with regard
to particle size will show poor redissolution even if preferred
humectant concentration formulation requirements are met
(Comparatives 20-22). Comparatives 23 and 24 show that good
redissolution performance can be obtained with a poor dispersion,
but it requires a relatively high level (e.g., 8 wt % or more) of
imidazolidone such that the ink crystallizes during dry-down. Inks
26 and 27 are further examples which demonstrate crystallization,
in this case with an inventive pigment dispersion but without
preferred humectant concentrations. Inks 28 through 33 show that
good redissolution can be obtained with 2-pyrrolidonone replacing
HEP or imidazolidone, but the curl performance is poor with
excessive levels of this humectant (e.g., at 4 wt % and higher).
Inks 34 and 35 show that poor redissolution may also result if the
glycerol level is too high. The remaining Inks 36-46 show that poor
redissolution may also result when the combined level of HEP and
optionally imidazolidone is less than or equal to 50% of the total
humectants.
[0102] Table V lists ink formulations with the inventive pigment
dispersion particle size and concentration and preferred humectant
concentrations and shows that good redissolution performance (e.g.,
rating of about 2.5 or less) consistently results when the combined
level of HEP and optionally imidazolidone is greater than 50% of
the total humectants level and the optional imidazolidone is less
than 41% of the total humectants and glycerol is also optional with
a level less than 25% of the total humectants. Inks 76 and 77 show
that 1,2-hexanediol and polyurethane are also optional, and good
redissolution can also be obtained without these components in the
formulation.
[0103] Tables IV and V thus demonstrate the desired ink performance
obtained for ink compositions in accordance with preferred
humectant concentration embodiments of the present invention.
[0104] The invention has been described with reference to preferred
embodiments. However, it will be appreciated that variations and
modifications can be effected by a person of ordinary skill in the
art without departing from the scope of the invention.
* * * * *