Note: Descriptions are shown in the official language in which they were submitted.
CA 02198287 2003-07-08
BLEED ALLEVIATED AQUEOUS PIGMENT
DISPERSION-BASED INK-JET INK COMPOSITIONS
TECHNICAL FIELD
The present invention relates to ink compositions employed in ink jet printing
and, more particularly, to the reduction of bleed and improvement of dry time
of
aqueous pigment dispersion-based ink-jet ink compositions.
2~9~287
2
BACKGROUND ART
Ink jet printing is a non-impact printing process in which droplets of ink are
deposited on print media, such as paper, transparency film, or textiles. Low
cost and
high quality of the output, combined with relatively noise-free operation,
have made
ink jet printers a popular alternative to other types of printers used with
computers.
Essentially, ink jet printing involves the ejection of fine droplets of ink
onto print me-
dia in response to electrical signals generated by a microprocessor.
There are two basic means currently available for achieving ink droplet
ejection
in ink jet printing: thermally and piezoelectrically. In thermal ink jet
printing, the en-
ergy for drop ejection is generated by electrically-heated resistor elements,
which heat
up rapidly in response to electrical signals from a microprocessor to create a
vapor
bubble, resulting in the expulsion of ink through nozzles associated with the
resistor
elements. In piezoelectric ink jet printing, the ink droplets are ejected due
to the vibra-
tions of piezoelectric crystals, again, in response to electrical signals
generated by the
microprocessor. The ejection of ink droplets in a particular order forms
alphanumeric
characters, area fills, and other patterns on the print medium.
Ink jet inks are mostly available as dye-based compositions. However, a very
limited number of pigment-based inks are also available. Indeed, only two
black pig
2 0 ment-based inks are commercially available at the present time; no color
pigment-based
inks are commercially available. Perhaps the most desirable property that
pigments of
fer is their superior lightfastness. However, pigments have not found
extensive use in
ink jet ink compositions partly due to their natural tendency to agglomerate
in aqueous
(hydrophilic) media. Pigment particles tend to agglomerate because their outer
surfaces
2 5 create natural forces of attraction between the particles. The
agglomeration of pigment
particles can result in poor print quality, due to defects such as those
deriving from
print density variation and mottling, and poor reliability. Typically, water-
soluble dis-
persing agents are used to deagglomerate pigment particles in aqueous
solutions.
While the agglomeration problems associated with pigments have been ad
3 0 dressed, difficulties in unheated bleed control constitute another problem
area for
aqueous pigment dispersion based inks, albeit one shared with aqueous dye-
based inks.
Pigment-based inks formulated as dispersions in aqueous media exhibit bleed
when
Case 10961301
298287
3
printed adjacent to other aqueous ink compositions, whether dye-based or
pigment-
based. The term "bleed", as used herein, is defined to be the invasion of one
color into
another, as evidenced by a ragged border therebetween. Bleed occurs as colors
mix
both on the surface of the paper substrate as well as within the substrate
itself. Bleed is
particularly problematic in ink jet color printing, given that aqueous yellow,
cyan, and
magenta ink compositions are printed in various proportions and combinations
adja-
cent to one another and to black ink. To achieve superior print quality, it is
necessary
to have borders between colors that are bleed-free.
Various solutions to the problem of black to color and color to color bleed
have been proffered. Some solutions involve changing the ink environment to
reduce
bleed. For instance, heated platens and other heat sources, along with
specially-
formulated paper, have been employed to reduce bleed. However, heated platens
add
cost to the printer, and specially formulated paper is more expensive than
"plain" pa-
per. Thus, using external paraphernalia to reduce bleed in ink jet color
printing is gen-
erally not cost effective. Another commonly-employed method for reducing bleed
in-
volves the use Qf bleed control algorithms in ink jet printers to provide
borders be-
tween colors that are clean and free from the invasion of one color into
another; how-
ever, such algorithms slow down the printer.
Other proposed solutions to the problem of bleed involve changing the com-
2 0 position of an ink jet ink. For example, surfactants have been effectively
used to reduce
bleed in dye-based ink formulations; see, e.g., U.S. Patent No. 5,106,416
entitled
"Bleed Alleviation Using Zwitterionic Surfactants and Cationic Dyes", issued
to John
Moffatt et al; U. S. Patent No. 5,116,409 entitled "Bleed Alleviation in Ink-
Jet Inks",
issued to John Moffatt; and U.S. Patent No. 5,133,803 entitled "High Molecular
2 5 Weight Colloids Which Control Bleed", issued to John Moffatt, all assigned
to the
same assignee as the present application. However, surfactants increase the
penetration
rate of the ink into the paper, which may also result in the reduction of edge
acuity.
Other solutions specific to dye-based ink compositions, disclosed in patents
assigned to
the present assignee, are found in U. S. Patent No. 5,198,023, entitled
"Cationic Dyes
3 0 with Added Multi-Valent Cations to Reduce Bleed in Thermal Ink-Jet Inks",
issued to
John Stoffel, and U.S. Patent No. 5,181,045, entitled "Bleed Alleviation Using
pH-
Case 10961301
- 21y~28T
4
Sensitive Dyes", issued to James Shields et al, both assigned to the same
assignee as
the present application.
While the problem of black to color and color to color bleed has been the sub
ject of much study, none of the above-described solutions are applicable to
pigment
s based ink compositions, save for the use of heated platens and specially-
formulated
paper, which generally are not cost effective. For example, surfactants, if
added in con-
centrations similar to those used in dye-based formulations to achieve bleed
control,
would destabilize pigment dispersions made with water-soluble dispersing
agents. This
is because the dispersing agents, themselves being surface active compounds,
would be
competitively displaced by the added surfactants that compete to attach to the
pigment
surface.
Related U.S. Patent 5,565,022, entitled "Bleed-Alleviated, Waterfast, Pig-
ment-Based Ink-Jet Ink Compositions" and assigned to the same assignee as the
pres-
ent application, is directed to bleed control of solvent-dispersed pigment-
based ink jet
ink compositions. More specifically, bleed control for such inks is achieved
by dispers-
ing the pigment in a water-insoluble organic compound kept in solution in the
form of
a microemulsion. The microemulsion is an isotropic solution of water, a water-
insoluble organic compound, and an amphiphile, there being sufficient
amphiphile to
solubilize the water-insoluble compound in water. The pigment is dispersed in
the wa-
2 0 ter-insoluble portion of the microemulsion by such means as a hydrophobic
dispersing
agent, an encapsulant, or by surface modification. Thus, the water-insoluble
organic
compound serves as a primary solvent for the pigment particles and the water
serves as
a continuous phase for the microemulsion droplets of organic compound, having
been
formed with the addition of an amphiphile. Again, however, this solution to
bleed is
not directed to aqueous pigment dispersion-based ink jet inks, but rather is
specifically
directed to solvent-dispersed pigment-based inks.
Therefore, while bleed control has been achieved by adjusting the compositions
of dye-based and solvent-dispersed pigment-based ink jet ink compositions, the
bleed
experienced with aqueous pigment dispersion-based ink jet ink compositions
remains
3 0 largely unchecked, save for the use of printer paraphernalia such as
heated platens,
specially-formulated paper, and bleed control algorithms.
Case 10961301
2198287
s
In addition to desiring bleed control in ink jet ink formulations, it is also
uni-
versally desired to develop ink formulations with improved dry times in ink
jet printing
in order to gain in throughput. Ink jet printers are presently incapable of
matching the
level of throughput generated by laser printers, due in large part to the
relatively slow
dry time of ink jet inks as well as to printer slow-down deriving from the
resident
bleed-control algorithms in the printer. The solutions used to effect bleed
control de-
scribed above also typically improve dry times, these two attributes being
closely as-
sociated with one another.
Accordingly, a need exists for aqueous pigment dispersion-based inks for use
in
ink jet printing that evidence reduced bleed and dry rapidly upon impact with
the print
medium. However, the print quality of the ink composition must not be
sacrificed to
achieve faster dry times.
DISCLOSURE OF INVENTION
In accordance with the invention, an aqueous pigment dispersion-based ink jet
ink composition is provided which employs pigment particles dispersed in the
aqueous
phase of a microemulsion. Specifically, the pigment-based ink jet ink
composition of
the present invention comprises:
2 0 (a) at least one aqueous pigment dispersion; and
(b) a microemulsion comprising:
(i) at least one water-insoluble organic compound,
(ii) at least one hydrotropic amphiphile, and
(iii) water, wherein the hydrotropic amphiphile is present in an amount
2 5 sufficient to solubilize the organic compound.
Any aqueous pigment dispersion suitable for use in ink jet printing may
benefit
in the practice of the invention, so long as it remains compatible with the
remaining
components in the ink jet ink composition. The microemulsion comprising a
water-
insoluble organic compound, a hydrotropic amphiphile, and water is a
thermodynami-
3 0 tally-stable isotropic solution in which the interfacial tension between
the water and
the water-insoluble organic compound has been minimized by the amphiphile.
Case 10961301
21 X8287
6
A method of reducing bleed in ink jet printing is also provided which involves
providing the above described aqueous pigment dispersion-based ink and
printing the
same onto a print medium. Since typical color ink jet printers employ an ink
set having
three color inks and a single black ink, it is contemplated that any or all of
the four inks
may be formulated according to the present invention to achieve high quality
printing
with reduced bleed. Preferably all four inks in a set of ink jet inks would be
formulated
in accordance with the invention, such that the print quality optimally
benefits from
improved dry time, bleed control, and uniformity of coverage and thickness.
The present aqueous pigment dispersion-based ink jet ink composition and
method of reducing bleed may be used with a variety of ink jet printers such
as con-
tinuous, piezoelectric drop-on-demand printers and thermal or bubble jet drop-
on-
demand printers. Printing may be done on a variety of media; examples include
paper,
textiles, and transparencies. The reduction of bleed and dry-time improvement
in aque-
ous pigment dispersion-based inks achieved in the practice of the invention
enable ink-
jet printers to effect high print qualities in a cost-effective manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are ternary phase diagrams showing the composition regions of
2 0 the microemulsion-based vehicle component of ink jet ink compositions made
in ac-
cordance with the invention, the microemulsion component having a particular
combi-
nation of a water-insoluble organic compound, a hydrotropic amphiphile, and
water.
2 5 BEST MODES FOR CARRYING OUT THE INVENTION
In the practice of the invention, the bleed alleviation and fast dry times are
ex-
hibited by the aqueous pigment dispersion-based inks by employing a
microemulsion as
the ink vehicle. More specifically, the microemulsion comprises (i) at least
one water-
3 0 insoluble organic compound; (ii) at least one hydrotropic amphiphile; and
(iii) water.
Case 10961301
2198281
The hydrotropic amphiphile is present in an amount that completely solubilizes
the or-
ganic compound, thereby resulting in a clear, stable microemulsion.
All concentrations herein are in weight percent, unless otherwise indicated.
The
purity of all components is that employed in normal commercial practice for
ink jet
inks.
A wide variety of organic and inorganic pigments, either alone or in combina-
tion, may be benefited in the practice of the invention, since it is
contemplated that any
pigment or combination thereof may be benefited in the practice of the
invention. The
term "pigment" as used herein means a water insoluble colorant. In practice,
pigment
particles are deagglomerated or dispersed in aqueous media to achieve greater
uni-
formity in print quality of the ink. Any means for dispersing the pigment
particles that
is compatible with the remaining ink components may be employed in the
practice of
the invention. Examples of suitable dispersing means include hydrophilic
pigment dis-
persing agents and the modification of the pigment surface to achieve
compatibility
with an aqueous solution. Any hydrophilic dispersing agent that is compatible
with the
pigment may be employed in the practice of the invention. Examples of classes
of
polymeric dispersing agents commonly used to disperse pigment particles in
aqueous
media include random, block, and branched-type polymers. The polymer may be
ani-
onic, cationic, or nonionic in nature.
2 0 It is contemplated that a commercially-available concentrated aqueous
pigment
dispersion is employed in the practice of the invention. Examples of such
pigment dis-
persions include Hostafine Yellow and Hostafine Green, which are available
from
Hoechst; and Fuji BBL Red and Fuji BBL Magenta, which are available from Fuji
Pigment Co., Japan. It is noted that the water present in such commercially-
available
2 5 concentrated aqueous pigment dispersions forms part of the microemulsion-
based ink.
The particle size of the pigments is an important consideration in ink jet
print-
ing, since the pigment particles must be sufficiently small to permit free
flow of the ink
through the ink jet printing devices. For example, the ejecting nozzles of
thermal ink-
jet office printers typically have diameters on the order of about 10 to 60
pm. The par-
3 0 ticle size of the pigments is also an important consideration in achieving
stability of the
pigment dispersion as well as color strength and gloss. Given these
considerations, the
Case 10961301
2198287
s
range of useful particle size is about 0.005 to 15 p,m. Preferably, the
pigment particle
size should range from about 0.005 to 5 pm and, more preferably, from about
0.005 to
1 pm. Most preferably, the pigment particle size ranges from about 0.005 to
0.3 p.m.
However, in non-office applications, larger pigment particle sizes may be
employed.
The pigment may represent up to about 20 wt% of the ink composition, but
should generally range from about 0.1 to 10 wt%. Preferably, the pigment
represents
about 0.1 to 8 wt% of the ink composition.
In accordance with the invention, the aqueous pigment dispersion is taken in a
microemulsion-based vehicle to achieve bleed control and fast drying in the
resulting
ink jet ink formulation. Microemulsions are defined as thermodynamically
stable iso
tropic "solutions" of water, oil, and amphiphile and are used to solubilize
water-
insoluble compounds. In the practice of the invention, the microemulsion
comprises
water, at least one water-insoluble organic compound, and at least one
hydrotropic
amphiphile. Within the microemulsion composition, the function of the
amphiphile is to
lower the interfacial tension between water and the water insoluble organic
compound,
thereby forming a stable system.
Examples of water-insoluble organic compounds that may be suitably employed
in the practice of the invention include, but are not limited to, water-
insoluble mono-
or polyglycol ethers; water-insoluble mono- or polyglycol phenyl ethers; water-
2 0 insoluble alcohols; water-insoluble mono- or polyglycol esters; water-
insoluble ter-
penes; water-insoluble phenols; water-insoluble aldehydes and ketones; and wa-
ter-insoluble hydrocarbons. In general, any water-insoluble organic compound,
or
combination thereof, may be employed in the practice of the invention so long
as it
may be solubilized by a hydrotropic amphiphile and so long as it is compatible
with the
2 5 other components in the ink jet ink composition. Specific examples of
water-insoluble
organic compounds that are preferably employed in the practice of the
invention in-
clude, but are not limited to: ( 1 ) ethylene, propylene, polyethylene, and
polypropylene
glycol phenyl ethers; (2) ethylene, propylene, polyethylene, and polypropylene
glycol
esters such as acrylates; and (3) benzyl alcohol. Additionally, specific
examples of
3 0 preferably-employed hydrocarbons include toluene, xylenes, naphthalene,
and phenan-
threne. Further examples of the water-insoluble organic compounds include al-
Case 10961301
~1~8~87
9
pha-terpineol, citronellat, hydroxy citronellal, cyclohexyl methanol, cyclohex-
anone and its alkyl (C1 to C$) derivatives, cyclohexanol and its alkyl (CI to
Cs)
derivatives, cyclopentanone and its allryl (C1 to C8) derivatives,
cyclopentanot
and its alkyl (C, to Cs) derivatives, eugenol, 1-heptanol, n-hexanol, 2-
hexanol, n-
pentanol, cinnamyl atcohol, cinnamaldehyde, m-cresol, 3-phenyl-1-propanol, and
salicylaldehyde. Mono- and diethylene glycol phenyl ether, mono- and
dipropylene
glycol phenyl ether, and benzyl alcohol are most preferably employed in the
practice of
the invention.
The water-insoluble organic component may range in concentration from about
1 to 70 wt% of the ink jet ink composition. Preferably, the water-insoluble
organic
component ranges from about 1 to 20 wt% of the ink jet ink composition.
In addition to providing the microemulsion with an oil component, the water-
insoluble organic component serves as a co-solvent in the present ink jet ink
composi-
tions such as commonly employed in ink jet printing. More particularly, when
the pen
of the ink jet printer idles and is exposed to the atmosphere, the water in
the ink vehi-
cle evaporates. The presence of this co-solvent in the ink vehicle prevents
crust forma-
tion and nozzle clogging. Hence, the vapor pressure of the organic compound
should
be su~ciently low in comparison to that of water that it does not evaporate
during the
normal operation of ink jet printing. It is noted that an advantage to
increasing the
2 0 concentration of the water-insoluble organic component in the present ink
jet ink com-
positions is a reduction in paper cockle, which derives from the attendant
decrease in
the water content of the ink.
The hydrotropic amphiphile employed in the practice of the invention may be
any hydrotropic amphiphile that yields a microemulsion with the water-
insoluble or
2 5 ganic compound and water. Suitable hydrotropic amphiphiles, like other
surfactants in
general, solubilize the water-insoluble organic compound in water by breaking
the
compound into very small droplets and maintaining these droplets in a
microemulsion.
However, unlike other classes of surfactants, hydrotropic amphiphiles do not
compete
with the hydrophilic dispersing agent (also a surface active compound) for the
pigment
3 0 surface, which might destabilize the pigment dispersion. Further,
hydrotropic am-
phiphiles do not result in the precipitous drop in surface tension associated
with the use
of other surfactants, such that the reduction in surface tension for inks
employing hy-
Case 10961301
- 218287
to
drotropic amphiphiles in the practice of the invention is curbed in
comparison. In con-
trast, the steep drop in surface tension caused by the incorporation of other
surfactants
into ink jet inks is known to cause puddles on the nozzle plates of the
printhead,
thereby negatively affecting drop ejection characteristics. Moreover, these
other sur-
factants increase the penetration rate of the ink into the paper to such a
degree that
edge acuity may be affected. Thus, hydrotropic amphiphiles serve to solubilize
the
water-insoluble organic compound without risking ( 1 ) destabilization of the
pigment
dispersion; (2) puddling on the nozzle plate; or (3) loss of edge acuity.
The proper amount of hydrotropic amphiphile in the microemulsion is that
amount that solubilizes the water-insoluble organic compound. It is noted that
a mix-
ture of hydrotropic amphiphiles may be employed in the practice of the
invention. The
determination of a given hydrotropic amphiphile and its concentration is
considered not
to constitute undue experimentation in view of the teachings of this
invention.
The hydrotropic amphiphile may be anionic, cationic, or non-ionic in nature.
Examples of anionic hydrotropic amphiphiles suitably employed in the practice
of the
invention include, but are not limited to, salts of: benzoic acid, salicylic
acid, ben-
zene sulfonic acid, benzene disulfonic acid, toluene sulfonic acid, xylene
sulfonic
acid, cumene sulfonic acid, cymene sulfonic acid, cinnamic acid, octane
sulfonic
acid, hexane sulfonic acid, butane sulfonic acid, and decane sulfonic acid.
The
2 0 cation associated with these salts may be Na+, K+, Li+, or NH4+.
Examples of cationic hydrotropic amphiphiles suitably employed in the practice
of the invention include, but are not limited to, p-amino benzoic acid
hydrochloride,
procaine hydrochloride, caffeine, and salts of: alkylpyridium, alkyltrimethyl
am-
monium, benzyltrialkyl (C1 to C4) ammonium, and phenyltrimethyl ammonium
2 5 cations. The anions associated with these salts may be any of the halides,
particu-
lady CI-.
Examples of non-ionic hydrotropic amphiphiles suitably employed in the prac-
tice of the invention include, but are not limited to, resorcinol and
pyrogallol.
Optionally, a co-surfactant may be added to the present ink jet ink composi-
3 0 tions. Examples of suitably-employed co-surfactants include, but are not
limited to,
lactams such as 2-pyrrolidone; glycols; diols; glycol esters; mono- and di-
glycol ethers,
Case 10961301
218287
11
including ethylene glycol monobutyl ether, diethylene glycol ethers,
diethylene glycol
mono ethyl, butyl, hexyl ethers, propylene glycol ether, dipropylene glycol
ether, and
triethylene glycol ether; mid-chain alcohols such as butyl alcohol, pentyl
alcohol, and
homologous alcohols; and acetylenic polyethylene oxides. Preferably, if a co-
surfactant
is employed, the co-surfactant comprises a mid-chain alcohol or a diol, having
from 3
to 8 carbon atoms. The co-surfactant may represent up to 10 wt% of the ink
composi-
tion, either serving as a separate component or as a partial replacement for
the hydrot-
ropic amphiphile.
The amount of hydrotropic amphiphile appropriately employed in a particular
microemulsion may be determined in at least two ways, namely by an abbreviated
method or a more systematic method. In the abbreviated method, one must first
com-
bine the water-insoluble organic compounds) and water in a ratio that reflects
the de-
sired final composition of the microemulsion for the ink jet ink composition.
The re-
sulting two-phase liquid is thereafter titrated with the selected hydrotropic
am-
phiphile(s) until a clear solution is obtained, representing the
solubilization of the or-
ganic compound such that a single-phase solution is achieved. About 1 % excess
hy-
drotropic amphiphile may optionally be added to ensure a stable solution.
Thus, the
appropriate relational concentrations of the water-insoluble organic
compound(s),
water, and hydrotropic amphiphile(s) are determined through the above-
described ti-
2 0 tration process.
In the event one chooses to determine the appropriate amount of hydrotropic
amphiphile(s) in a more systematic approach, the first step involves the
construction of
a phase diagram to represent the combination of the water-insoluble organic
compound
and water. More specifically, a phase diagram is constructed by combining
water and
2 5 the water-insoluble organic compounds) in various proportions, titrating
each mixture
against the hydrotropic amphiphile(s) until a clear, single-phase region is
determined
within the phase diagram. By further titrating beyond the clear point, other
regions of
mufti-phase or semi-solid compositions can be determined. These results, when
plotted
on a conventional triangular plot, represent a ternary phase diagram. For
example,
3 0 FIG. 1 depicts such a ternary phase diagram for a microemulsion comprising
propylene
glycol phenyl ether, sodium xylene sulfonate, and water, wherein Area A
represents a
Case 10961301
CA 02198287 2003-07-08
12
milky region having two phases, Area B represents a single-phase isotropic
region, and
Area C represents a semi-solid region. The single-phase isotropic region (Area
B of
FIG. 1 ) indicates compositions of organic compound(s), water, and hydrotropic
amphiphile(s) that are most suitable for use in an ink jet ink composition.
Thus, one
may select any composition from this single-phase region in the practice of
the
invention, provided the composition meets any other criteria for the
particular ink jet ink
composition. In another example, FIG. 2 depicts such a ternary phase diagram
for a
micro-emulsion comprising benzyl alcohol, sodium xylene sulfonate, and water,
where
Area B again represents the single phase isotropic region.
Similar results are obtained in the following ternary systems: (1) water-
sodium
salicylate-ethylene glycol phenyl ether; (2) water-sodium salicylate-propylene
glycol
phenyl ether; (3) water-sodium benzoate-ethylene glycol phenyl ether; (4)
water-sodium
benzoate-propylene glycol phenyl ether; (5) water-sodium xylene sulfonate-
ethylene
glycol phenyl ether; (6) water-pyrogallol-benzyl alcohol; and (7) water-sodium
xylene
1 S sulfonate-benzyl alcohol.
It should be noted that compositions within Area A may be employed in those
applications not requiring a long shelf life, such as textile printing.
Likewise, use of a
heated print cartridge could permit compositions within Area C to be employed.
Consistent with the requirements for this invention, various types of
additives
may be employed in the ink to optimize the properties of the ink composition
for
specific applications. For example, as is well known to those skilled in the
art, one or
more biocides, fungicides, and/or slimicides (microbial agents) may be used in
the ink
composition as is commonly practiced in the art. Examples of suitably employed
microbial agents include, but are not limited to, NUOSEPT* (Nudex, Inc.),
UCARCDE* (Union Carbide), VANCIDE* (RT Vanderbilt Co.), and PROXEL* (ICI
America). Additionally, sequestering agents such as EDTA may be included to
eliminate deleterious effects of heavy metal impurities, and buffer solutions
may be used
to control the pH of the ink. Other known additives such as viscosity
modifiers and
other acrylic or non-acrylic polymers may be added to improve various
properties of the
ink compositions as desired.
*trade-marks
219887
13
To formulate the ink jet ink composition, water, hydrotropic amphiphile(s),
and
the water-insoluble organic compound are first combined. This mixture is then
"let
down" into the pigment dispersion concentrate at a slow flow rate while
agitating the
pigment dispersion. Any additional additives may also be added to the mixture.
The
mixture is then homogenized, such as by stirnng, shaking, or other means of
agitation,
to form the microemulsion-based ink. Attempts to formulate the microemulsion
by
merely adding all of the ingredients together could result in flocculating the
pigment
dispersion.
Aqueous pigment dispersion-based ink compositions formulated in accordance
with the invention are bleed alleviated and will exhibit fast dry times and
good print
qualities. The examples given below demonstrate just that.
EXAMPLES
An ink jet ink composition was prepared consisting of 3 wt% Hostafine Yellow
as a colorant (commercially available from Hoescht); 10 wt% propylene glycol
phenyl
ether; 13 wt% sodium xylene sulfonate; and the balance water, with the
concentrations
of the vehicle components having been determined by constructing the phase
diagram
depicted in FIG. 1. More specifically, the phase diagram depicted in FIG. 1
was con-
2 0 structed by combining propylene glycol phenyl ether and water in various
proportions
and then titrating each mixture against sodium xylene sulfonate until a clear,
single-
phase region was determined. Thus, Area A of FIG. 1 represents the various
combina-
tions of propylene glycol phenyl ether, sodium xylene sulfonate, and water
than yielded
a two-phase region evidenced by a milky appearance. Area B of FIG. 1
represents the
2 5 various combinations of propylene glycol phenyl ether, sodium xylene
sulfonate, and
water that yielded a clear, single-phase region. Area C of FIG. 1 was defined
by fi~rther
titrating the mixtures of propylene glycol phenyl ether and water with sodium
xylene
sulfonate beyond the clear point until a semi-solid phase region was defined.
The sin-
gle-phase isotropic region of FIG. 1 indicates compositions of propylene
glycol phenyl
3 0 ether, sodium xylene sulfonate, and water that may be suitably employed in
the practice
Case 10961301
219287
14
of the invention. The compositions indicated by Areas A and C represent ink
vehicles
outside of the scope of the invention.
The ink jet ink composition of this example falls within the single-phase iso-
tropic region of Area B in FIG. 1. More specifically, the vehicle of this ink
composition
contained, as a percentage of total ink vehicle, about 10 wt% propylene glycol
phenyl
ether, about 13 wt% sodium xylene sulfonate, and the balance water. Point D on
FIG.
1 indicates that the vehicle of this example ink composition indeed falls
within the clear
single-phase region Area B of the ternary phase diagram.
The ink jet ink composition of this example was printed on plain paper using a
45 picoliter drop volume pen at a 300 dpi resolution. The ink dried
instantaneously
upon impact with plain paper. In comparison, it is known that ink jet ink
compositions
having a water-soluble co-solvent, such as 2-pyrrolidone, exhibit finite,
readily-
measurable dry times and lack bleed control when printed on plain paper (see,
e.g.,
U.S. Patent No. 4,963,189 entitled "Waterfast Ink Formulations with a Novel
Series of
Anionic Dyes Containing Two or More Carboxyl Groups", issued to Suraj
Hindagolla
et al and assigned to the same assignee as the present application).
Furthermore, when
the ink of the above example was printed next to another ink of identical
vehicle, but
with a different colorant, namely Hostafine Green, it was bleed alleviated.
2 0 Thus, it is has been demonstrated that ink jet ink compositions made in
accor-
dance with the invention are bleed alleviated and exhibit fast dry times upon
printing by
an ink jet printer.
INDUSTRIAL APPLICABILITY
The present ink jet ink compositions and method for controlling bleed and re-
ducing dry time in ink jet printing as disclosed herein are expected to find
commercial
use in ink jet printing.
Thus, there has been disclosed an aqueous pigment dispersion-based ink jet ink
composition as well as a method of controlling bleed and reducing dry time in
ink jet
Case 10961301
218287
IS
printing. It will be readily apparent to those skilled in the art that various
changes and
modifications of an obvious nature may be made without departing from the
spirit of
the invention, and all such changes and modifications are considered to fall
within the
scope of the invention as defined by the appended claims.
Case 10961301
