Polymeric dispersants for pigmented inks

The invention relates to polymeric dispersants used in formulating aqueous ink compositions, as well as inks containing those dispersants. The dispersants are graft copolymers comprising a hydrophilic polymeric segment, a hydrophobic polymeric segment incorporating a hydrolytically-stable siloxyl substituent, and a stabilizing segment, such as a reactive surfactant macromer, a protective colloid macromer, or a non-siloxyl hydrophobic monomer. The inks made with these dispersants show excellent stability, print characteristics, water-fastness, optical density, and in-use maintenance characteristics.

This invention is related to copending application Ser. No. 08/667,269, 
entitled "Pigmented Inks With Polymeric Dispersants". 
TECHNICAL FIELD 
This invention relates to dispersants used in pigmented ink formulations 
for ink jet printers. 
BACKGROUND OF THE INVENTION 
Ink jet printing is accomplished by ejecting ink from a nozzle toward paper 
or another print medium. The ink is driven from the nozzle toward the 
medium in a variety of ways. For example, in electrostatic printing, the 
ink is driven by an electrostatic field. Another ink jet printing 
procedure, known as squeeze tube, employs a piezo-electric element in the 
ink nozzle. Electrically-caused distortions of the piezo-electric element 
pump the ink through the nozzle and toward the print medium. In still 
another ink jet printing procedure, known as thermal or bubble ink jet 
printing, the ink is driven from the nozzle toward the print medium by the 
formation of an expanding vapor phase bubble in the nozzle. These various 
printing methods are described in "Output Hard Copy Devices," edited by 
Durbeck and Sherr, Academic Press, 1988 (see particularly chapter 13, 
entitled "Ink Jet Printing"). 
Ink compositions for use in ink jet printers generally comprise deionized 
water, a water soluble or water miscible organic solvent, and a colorant. 
Frequently, the colorant is a soluble dye. Unfortunately, inks comprising 
soluble dyes can exhibit many problems, such as poor water-fastness, poor 
light-fastness, clogging of the jetting channels as a result of solvent 
evaporation and changes in the dye's solubility, dye crystallization, ink 
bleeding and leathering on the printed page, poor thermal stability, 
chemical instability, and ease of oxidation. Many of these problems can be 
minimized by replacing the soluble dyes used in ink formulations with 
insoluble pigments. In general, pigments have superior properties when 
compared to dyes, including good water-fastness, good light-fastness, 
thermal stability, oxidative stability, and compatibility with both 
coated/treated and plain papers. 
In pigmented ink compositions, the insoluble pigment is generally 
stabilized in a dispersion by a polymeric component. Generally speaking, 
most pigment inks stabilized by polymers in aqueous media are based on an 
electrostatic stabilizing mechanism in which the hydrophobic group in the 
dispersant acts as an anchor adsorbed on the pigment particle surface 
through acid-base, electron donor/acceptor, Van der Waals forces, or 
physical absorption. In this type of system, the hydrophilic group in the 
dispersant is extended into the aqueous medium to keep the dispersant 
soluble and to set up an electrosteric layer to prevent aggregation of the 
particles. This results in a competition in the dispersing process between 
the pigment particle and the polymer, the polymer and the solvent, and the 
pigment particle and the solvent. In order to form a stable polymeric 
dispersion, several factors need to be considered. First, the polymer must 
be firmly anchored to the particle surface to withstand shear force and 
the competition of other ingredients. This requires a careful match of the 
polarity of the particle surface and the hydrophobic group in the 
dispersant. Second, there is a need to adjust the identity, length and 
weight of the hydrophobic group in the dispersant to fully cover the 
particle, otherwise, the adsorbed polymer will act as a flocculent. Third, 
an electrosteric layer with requisite thickness around the particle to 
repulse aggregation is needed. This intricate balancing becomes even more 
complex when the dispersion is used in inks, since it is common to add 
cosolvents, surfactants, defoamers, biocides and other additives to the 
pigmented ink to optimize its print quality, dry time and maintenance 
characteristics. These additives may compete with the anchor group in the 
dispersant to adsorb on the particle surface. Their existence may also 
lower the solubility of the polymer in the media especially at higher 
temperatures, thereby destabilizing the dispersion system. Destabilization 
of pigment dispersions in inks can result in flocculation of the pigment 
in the nozzle of the ink jet printer which can eventually adversely impact 
the printing process. Most prior art pigment dispersions will irreversibly 
clog the nozzle of ink jet printers when left standing in the atmosphere 
for an extended period of time (e.g., 6 hours). The result of these 
interrelated and competing forces is that it has been extremely difficult 
to formulate a polymeric dispersant for pigmented ink jet inks which 
simultaneously provides excellent stability, excellent water-fastness for 
the inks, minimized printer clogging, and excellent print density. 
U.S. Pat. No. 5,085,698, Ma, et al., issued Feb. 4, 1992, discloses an ink 
composition comprising pigment, an aqueous medium, and an acrylic/acrylate 
block copolymer as a stabilizing agent. See also, U.S. Pat. No. 5,221,334, 
Ma, et al., issued Jun. 22, 1993. 
U.S. Pat. No. 5,302,197, Wickramanayke, et al., issued Apr. 12, 1994, 
describes aqueous ink jet compositions comprising a pigment dispersion 
(pigment together with a conventional dispersing agent), an aqueous 
carrier medium, and a cosolvent mixture which includes a polyol/alkylene 
oxide condensate and a cyclic amide derivative. The polymeric dispersants 
utilized in these compositions are preferably block polymers containing 
hydrophobic and hydrophilic segments. 
U.S. Pat. No. 4,597,794, Ohta, et al., issued Jul. 1, 1986, describes ink 
used in an ink jet recording process which contains polymeric dispersing 
agents including both hydrophilic and hydrophobic portions. Preferred 
polymeric dispersants contain N- methylol acrylamide or N-methylol 
methacrylamide portions. 
U.S. Pat. No. 4,469,840, Alberts, et al., issued Sep. 4, 1984, discloses 
graft polymers which are used to treat textiles. These polymers comprise 
diorganopolysiloxane components, surfactant and/or water-soluble polyether 
components, and polymerized units of vinyl compounds which form bridges 
between the first two components. 
U.S. Pat. No. 4,778,862, Woo, et al., issued Oct. 18, 1988, describes the 
synthesis of copolymers of acrylic resins, silicone resins, and 
fluorinated alcohols, used as binders in paint compositions. 
U.S. Pat. No. 5,310,778, Schor, et al., issued May 10, 1994, describes a 
process for preparing ink jet inks wherein a two roll mill is charged with 
pigment and polymeric dispersant, the components are milled to obtain a 
mixture, which is then dispersed in an aqueous carrier. Polymeric 
dispersants disclosed as being useful in the process include graft or 
block polymers containing both hydrophobic and hydrophilic groups. 
U.S. Pat. No. 5,418,277, Ma, et al., issued May 23, 1995, describes aqueous 
pigment inks which include a fluorinated block copolymer prepared from a 
fluorinated oxazoline or oxazine. 
U.S. patent application Ser. No. 08/360,200, Beach, et al., filed Dec. 21, 
1994, describes stabilizers used for pigmented inks. These stabilizers are 
graft polymers which contain a carboxylic acid-containing hydrophilic 
polymeric backbone to which is grafted a hydrophobic group, oligomer or 
polymer connected by the reaction of the carboxylic acid group on the 
backbone with the functional group on the hydrophobe. Examples of such 
stabilizers include aliphatic or alkyl aryl amines condensed with 
polyacrylic acid, amine-terminated acrylic esters condensed with 
polyacrylic acid, amine-terminated polyoxyalkylene polymers condensed with 
polyacrylic acid, and amine polymer backbones condensed with 
acid-containing hydrophobic segments. 
U.S. patent application Ser. No. 08/360,199, Beach, et al, filed Dec. 21, 
1994, describes aqueous ink compositions for ink jet printers which 
comprise an aqueous carrier, an insoluble pigment, and a block or graft 
copolymer comprising a hydrophilic polymeric segment and a hydrophobic 
polymeric segment having a hydrolytically stable siloxyl substituent. 
It is to be noted that none of these references describe or suggest the 
graft copolymers of the present invention, which contain a hydrophilic 
polymeric segment, a hydrophobic polymeric segment incorporating a 
hydrolytically stable siloxyl substituent, and a stabilizing segment. 
These copolymers, when used as dispersants in pigment ink compositions, 
provide outstanding benefits in terms of composition stability, 
water-fastness, optical density, and printer maintenance characteristics. 
SUMMARY OF THE INVENTION 
The present invention relates to graft copolymers, useful as dispersants in 
ink jet ink compositions, having a molecular weight of from about 1,500 to 
about 20,000, comprising: 
(a) a hydrophilic polymeric segment; 
(b) a hydrophobic polymeric segment, having a molecular weight of from 
about 400 to about 3,000, which incorporates a hydrolytically stable 
siloxyl substituent; and 
(c) a stabilizing segment having a molecular weight of from about 200 to 
about 2,000, preferably selected from the group consisting of reactive 
surfactant macromers, protective colloid macromers and non-siloxyl 
hydrophobic monomers. 
The present invention also relates to aqueous ink compositions which 
include those polymeric dispersants. Specifically, these compositions for 
use in ink jet printers comprise from about 0.5% to about 10% of an 
insoluble pigment, from about 0.25% to about 10% of the polymeric 
dispersant described above, and an aqueous carrier. 
All percentages and ratios, used herein, are "by weight" unless otherwise 
specified. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to polymeric dispersants used to stabilize 
aqueous pigment ink compositions, as well as pigment ink compositions 
containing those dispersants. The polymers of the present invention have a 
molecular weight of from about 1,500 to about 20,000, preferably from 
about 2,000 to about 10,000, most preferably about 2,500 to about 5,000. 
The polymers function to stabilize the pigment dispersion in the aqueous 
ink composition. The polymers also assist in the redispersion of the 
pigment after drying out of the nozzle during printer shutdown. Finally, 
the polymers provide for inks having good water-fastness and excellent 
print quality and optical density characteristics. 
The polymers of the present invention are graft copolymers comprising three 
distinct segments: a hydrophilic polymeric segment, a hydrophobic segment 
which incorporates a hydrolytically stable siloxy substituent, and a 
stabilizing segment. Each of these segments will be described in detail 
below. 
The hydrophilic portion of the polymer helps control polymer solubility in 
the ink composition. Generally, the hydrophilic segment will include 
acidic functional groups, such as carboxylic or sulfonic acid groups. 
Suitable hydrophilic polymers will be known to those skilled in the art. 
Preferred hydrophilic segments contain carboxyl substituents. Preferably, 
the hydrophilic segment is an acrylic or methacrylic polymer or a 
copolymer thereof. In an alternative embodiment, the hydrophilic segment 
can comprise an acrylic copolymer, such as a copolymer of acrylic acid 
with another monomer, such as styrene, which does not interfere with the 
hydrophilic character of the segment. Hydrophilic segments which may be 
used in the present invention are disclosed in U.S. Pat. No. 5,219,945, 
Dicker, et al., issued Jun. 15, 1993; U.S. Pat. No. 5,085,698, Ma, et al., 
issued Feb. 4, 1992; and U.S. Pat. No. 5,221,334, Ma, et al., issued Jun. 
22, 1993, all of which are incorporated herein by reference. The 
hydrophilic segment comprises from about 20% to about 80% of the entire 
polymeric dispersant. The hydrophilic segment itself must be long enough 
such that it acts to provide a stabilizing function to the dispersant. 
The hydrophobic polymeric segment comprises a polymer or copolymer 
containing a hydrolyrically stable linear or branched siloxyl substituent. 
This segment functions as the anchor to adsorb the dispersant onto the 
pigment particle surface. A siloxyl substituent (an oligomeric siloxane) 
has the formula: 
##STR1## 
wherein n is from about 1 to about 50, preferably from about 2 to about 
16, R.sub.1 to R.sub.5 are independently alkyl or aryl, preferably lower 
alkyl (C.sub.1 -C.sub.6), phenyl or benzyl, and may optionally be 
substituted with a variety of non-interfering substituents. For branched 
siloxy substituents, R.sub.4 and/or R.sub.5 are siloxyl substituents. 
Suitably, the siloxyl substituent will be terminated with a lower alkyl 
group. In this formula, R.sub.1 and R.sub.3 -R.sub.5 are preferably 
methyl, i.e., the siloxyl substituent is a dimethyl polysiloxane; and 
R.sub.2 is preferably butyl. Acryloyl or methacryloyl-terminated 
polydialkylsiloxane macromers are preferred hydrophobic polymeric 
segments. The siloxyl substituent is hydrolytically stable in that it does 
not react with water under neutral conditions. 
A preferred linear or branched substituent has the formula: 
##STR2## 
wherein n is from about 2 to about 16, and each R is independently benzyl, 
siloxyl, or lower alkyl (C.sub.1 -C.sub.6, preferably C.sub.1 -C.sub.4). 
In this formula, R.sub.1 and R.sub.3 -R.sub.7 are preferably methyl, 
R.sub.2 is preferably butyl, and R.sub.8 is preferably a methacryl 
oxypropyl group. 
In a preferred embodiment, the hydrophobic segment is an acrylate or 
methacrylate ester (oxo or thio), or an amide polymer having a siloxyl 
substituent (e.g., an oligomeric siloxane grafted to a polyacrylate or 
polymethacrylate). Other suitable hydrophobic copolymers having a siloxyl 
substituent will be known to those skilled in the art. The hydrophobic 
segment has a molecular weight of from about 400 to about 3,000, 
preferably from about 400 to about 2,000, more preferably from about 800 
to about 1,200, most preferably about 900. 
The third segment of the copolymer, referred to herein as the stabilizing 
segment, also acts to help bind the dispersant to the pigment particles as 
well as to enhance the stabilizing efficacy of the entire polymer. The 
stabilizing segment is preferably selected from either a reactive 
surfactant or a protective colloid macromer material or a non-siloxyl 
hydrophobic monomer. This segment has a molecular weight of from about 200 
to about 2,000, preferably from about 200 to about 1,000. The stabilizing 
segment must include a moiety which enables it to polymerize into the 
remainder of the polymer. Preferred stabilizing segments accomplish that 
through the inclusion of an acrylic group. Reactive surfactants contain 
both hydrophobic and hydrophilic moieties and not only function as 
surfactants in the conventional manner but also tend to effectively 
uniformly coat insoluble particles in a dispersion. These materials can 
have the properties of nonionic or anionic surfactants. Protective 
colloids are reactive polymers derived from cellulose (methyl cellulose, 
hydroxymethyl cellulose, and hydroxyethyl cellulose), polyvinyl alcohols 
and polyglycols. These products can provide the protective qualities of 
methyl cellulose, hydroxyethyl cellulose, or polyglycols without the 
attendant disadvantages of these products, such as water sensitivity and 
poor compatibility with certain compounding formulations. Non-siloxyl 
hydrophobic monomers may be derived from long chain aliphatic groups, long 
chain alcohols, and alkyl aryl alcohols. Examples of such materials would 
include stearyl or lauryl acrylate or methacrylate or nonyl phenol 
acrylate or methacrylate. 
Materials which can be used as stabilizing segments are commercially 
available, for example, from Monomer-Polymer & Dajac Laboratories, Inc., 
Feasterville, Pa., and Aldrich Chemical, Milwaukee, Wis. Examples of such 
reactive surfactants include nonylphenoxy poly(ethyleneoxy)--acrylate 
(containing from 1 to about 40 moles of ethylene oxide), nonylphenoxy 
poly(ethyleneoxy)--methacrylate (containing from 1 to about 40 moles of 
ethylene oxide), nonylphenoxy poly(ethyleneoxy)--crotonate (containing 
from about 5 to about 40 moles of ethylene oxide), bis-nonylphenoxy 
poly(ethyleneoxy)!--fumarate (containing from about 5 to about 40 moles of 
ethylene oxide), phenoxypoly(ethyleneoxy) acrylate (containing from about 
5 to about 40 moles of ethylene oxide), perfluoroheptoxypoly (propyloxy) 
acrylate, perfluoroheptoxypoly (propyloxy) methacrylate, sorbitol 
acrylate, sorbitol methacrylate, allyl methoxy triethylene glycol ether, 
monosodium ethylsulfonate monododecyl maleate, sodium allyl sulfonate, 
sodium methallyl sulfonate, 3-sulfopropyl acrylate, and vinyl sulfonate. 
Examples of protective colloid materials include hydroxyethylcellulose 
acrylate, hydroxyethylcellulose methacrylate, methoxypoly(ethyleneoxy) 
acrylate (containing from about 5 to about 40 moles of ethylene oxide), 
methoxypoly(ethyleneoxy) methacrylate (containing from about 5 to about 40 
moles of ethylene oxide), methylcellulose acrylate, methylcellulose 
methacrylate, methylcellulose crotonate, stearyloxypoly(ethyleneoxy) 
acrylate (containing from 1 to about 40 moles of ethylene oxide), and 
stearyloxypoly(ethyleneoxy) methacrylate (containing from about 10 to 
about 40 moles of ethylene oxide). Mixtures of these materials may be 
used. 
Preferred stabilizing segments which may be used in the polymers of the 
present invention include stearyl acrylate, stearyl methacrylate, lauryl 
acrylate, lauryl methacrylate, nonylphenol acrylate, nonylphenol 
methacrylate, nonylphenoxy poly(ethyleneoxy).sub.n methacrylate, wherein n 
is from 1 to about 40, preferably from 6 to about 15; nonylphenoxy 
poly(ethyleneoxy).sub.n acrylate, wherein n is from 1 to about 40, 
preferably from about 6 to about 15; methoxypoly(ethyleneoxy).sub.n 
methacrylate, wherein n is from about 5 to about 40, preferably from about 
5 to about 15; methoxypoly(ethyleneoxy).sub.n acrylate, wherein n is from 
about 5 to about 40, preferably from about 5 to about 15; 
stearyloxypoly(ethyleneoxy).sub.n methacrylate, wherein n is from about 1 
to about 20; stearyloxypoly(ethyleneoxy).sub.n acrylate, wherein n is from 
about 1 to about 20; perfluoro or highly fluorinated C.sub.1 -C.sub.18 
alkyl methacrylate; perfluoro or highly fluorinated C.sub.1 -C.sub.18 
alkyl acrylate (such as trihydroperfluoro undecyl methacrylate and 
trihydroperfluoro undecyl acrylate); poly(propylene glycol) methyl ether 
methacrylate; poly(propylene glycol) methyl ether acrylate; poly(propylene 
glycol) 4-nonylphenol ether methacrylate; poly(propylene glycol) 
4-nonylphenol ether acrylate; methacryloxy-trimethylsiloxy-terminated 
polyethylene oxide, and acryloxy-trimethylsiloxy-terminated polyethylene 
oxide. Particularly preferred stabilizing segments include stearyl 
methacrylate (having a molecular weight of about 325), stearyl acrylate, 
lauryl methacrylate, lauryl acrylate, nonylphenoxy PEG-10 methacrylate, 
trimethylsiloxy-terminated PEG 4-5 methacrylate, PPG-4-nonylphenol 
acrylate, and trihydroperfluoro undecyl methacrylate. Stearyl methacrylate 
is particularly preferred. Mixtures may be used. 
The graft copolymers of the present invention can be made by standard 
synthetic techniques such as those described in Steven's Polymer 
Chemistry, An Introduction, Oxford University Press (1990), the disclosure 
of which is incorporated herein by reference. Free radical polymerization 
is the preferred method of synthesis. Such a free radical polymerization 
reaction utilizes initiators and chain transfer agents to control the 
polymer molecular weight. Any conventional free radical initiator and 
chain transfer agent materials known in the art may be used in the present 
invention as long as they are compatible with the reactants being 
utilized. Preferred free radical initiators are of the azo-type or 
peroxide-type (preferably the azo-type) and preferred chain transfer 
agents include C.sub.4 to C.sub.18 (preferably C.sub.12 to C.sub.16) 
alkylthiol groups. Particularly preferred is n-C.sub.12 thiol. 
The molecular weight of the dispersant polymer is from about 1,500 to about 
20,000, preferably from about 2,000 to about 10,000. It is preferred that 
the ratio in the polymeric dispersant be from about 10 to about 100 
hydrophilic monomers to 1 siloxane hydrophobic macromer, preferably from 
about 15 to about 50 hydrophilic monomers to about 1 siloxane hydrophobic 
macromer. The ratio of siloxane hydrophobic macromer to stabilizing 
monomer/macromer is from about 1 to about 2 siloxane hydrophobic macromer 
to from about 1 to about 5 stabilizing monomer/macromer segments 
(preferably about 1:1). 
A particularly preferred polymeric dispersant of the present invention is 
one having the following structural formula 
##STR3## 
wherein x is from about 5 to about 100, preferably from about 15 to about 
50; y is from about 1 to about 2, most preferably about 1; z is from about 
1 to about 5, preferably from about 1 to about 2, most preferably about 1; 
a is from about 3 to about 45, preferably from about 3 to about 24, most 
preferably about 9; b is from about 3 to about 29, preferably from about 5 
to about 17, most preferably from about 15 to about 17; c is from about 2 
to about 8, preferably about 3; and d is from 0 to about 7, preferably 
about 3. 
The aqueous ink compositions of the present invention comprise from about 
0.5% to about 10% of an insoluble pigment, from about 0.25% to about 10%, 
preferably from about 0.5% to about 5%, of the polymeric dispersant 
discussed above, and an aqueous carrier. 
A wide variety of organic and inorganic pigments, alone or in combination, 
may be selected for use in the aqueous inks of the present invention. The 
key selection criteria for the pigment is that they must be dispersable in 
the aqueous medium. The term "pigment", as used herein, means an insoluble 
colorant. The pigment particles are sufficiently small to permit free flow 
of the ink through the ink jet printing device, especially at the ejecting 
nozzles that usually have a diameter ranging from about 10 microns to 50 
microns. The particle size also has an influence on pigment dispersion 
stability, which is critical throughout the life of the ink. It is also 
desirable to use small particles for maximum color strength and gloss. The 
range of useful particle size is from approximately 0.05 micron to 
approximately 15 microns. Preferably, the pigment particle size should 
range from about 0.05 micron to about 5 microns and, most preferably, from 
about 0.05 micron to about 1 micron. Useful pigments are described in U.S. 
Pat. No. 5,085,698, Ma, et al., issued Feb. 4, 1992, incorporated herein 
by reference. 
The selected pigment may be used in dry or wet form. For example, pigments 
are usually manufactured in aqueous media and the resulting pigment is 
obtained as water wet presscake. In presscake form, the pigment is not 
agglomerated to the extent that it is in dry form. Thus, pigments in water 
wet presscake form do not require as much deflocculation in the process of 
preparing the inks as do dry pigments. 
Fine particles of metal or metal oxides may also be used to practice the 
invention. For example, metal and metal oxides are suitable for the 
preparation of magnetic ink jet inks. Fine particle size oxides, such as 
silica, alumina, titania, and the like, may also be used. Furthermore, 
freely divided metal particles, such as copper, iron, steel, aluminum and 
alloys, may be selected for appropriate applications. 
Pigments suitable for use in the present invention include, for example, 
azo pigments, such as azo lakes, insoluble azo pigments, condensed azo 
pigments and chelate azo pigments, polycyclic pigments, perylene pigments, 
anthraquinone pigments, quinacridone pigments, dioxazine pigments, 
thioindigo pigments, isoindolinone pigments, quinophthalone pigments, and 
dry lakes. Useful organic pigments include nitro pigments, nitroso 
pigments, aniline black and daylight fluorescent pigments. Preferred 
pigments include titanium oxide, iron oxide, and carbon black. Examples of 
commercially available pigments which may be used in the present invention 
include the following: Heliogen.RTM. Blue L 6901F (BASF), Heliogen.RTM. 
Blue NBD 7010 (BASF), Heliogen.RTM. Blue K 7090 (BASF), Heucophthal.RTM. 
Blue G XBT-583D (Heubach), Irgalite.RTM. Rubine 4BL (Ciba-Geigy), 
Quindo.RTM. Magenta (Mobay), Indofast.RTM. Brilliant Scarlet (Mobay), 
Hostaperm.RTM. Scarlet GO (Hoechst), Permanent Rubine F6B (Hoechst), 
Monastral.RTM. Scarlet (Ciba-Geigy), Raven.RTM. 1170 (Col. Chem.), Special 
Black 4A (Degussa), Black FW18 (Degussa), Sterling.RTM. NS Black (Cabot), 
Sterling.RTM. NSX 76 (Cabot), Monarch.RTM. 880 (Cabot), Tipure.RTM. R-101 
(DuPont), Mogul L (Cabot), BK 8200 (Paul Uhlich), Heliogen.RTM. Green K 
8683 (BASF), Heliogen.RTM. Green L 9140 (BASF), Monastral.RTM. Red B 
(Ciba-Geigy), Monastral.RTM. Violet R (Ciba-Geigy), Hostaperm.RTM. Orange 
GR (Hoechst), Paliogen.RTM. Orange (BASF), L75-2377 Yellow (Sun Chem.), 
L74-1357 Yellow (Sun Chem.), Hostaperm.RTM. Yellow H4G (Hoechst), 
Irgazin.RTM. Yellow 5GT (Ciba-Geigy), Permanent Yellow G3R-01 (Hoechst), 
Novoperm.RTM. Yellow FGL (Hoechst), Chromophthal.RTM. Yellow 3G 
(Ciba-Geigy), Hansa Yellow X (Hoechst), Dalamar.RTM. Yellow YT-858-D 
(Heubach), and Hansa Brilliant Yellow 5GX-02 (Hoechst). 
The amount of pigment used in the inks may vary depending on their 
structure, but generally the pigments are used in a range of from about 
0.5% to about 10%, preferably from about 2 to about 6%, by weight of the 
ink composition. The pigment to dispersant (weight) ratio is preferably 
about 3:1, but may vary from about 1:1 to about 6:1. 
The third component of the ink composition of the present invention is the 
aqueous carrier medium which is generally present at from about 80% to 
about 99% of the composition. The aqueous carrier medium comprises water 
(preferably deionized water) and, preferably, at least one water soluble 
organic solvent. Selection of a suitable carrier mixture depends on the 
requirements of the specific application involved, such as desired surface 
tension and viscosity, the selected pigment, the desired drying time of 
the ink, and the type of paper onto which the ink will be printed. 
Representative examples of water soluble organic solvents that may be 
selected include (1) alcohols, such as methyl alcohol, ethyl alcohol, 
n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, 
t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and 
tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols, such as acetone, 
methyl ethyl ketone and diacetone alcohol; (3) ethers, such as 
tetrahydrofuran and dioxane; (4) ethers, such as ethyl acetate, ethyl 
lactate, ethylene carbonate and propylene carbonate; (5) polyhydric 
alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, 
propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 
2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thiodiglycol; (6) lower 
alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene 
glycol monomethyl (or monoethyl) ether, diethylene glycol monomethyl (or 
monoethyl) ether, propylene glycol monomethyl (or monoethyl) ether, 
triethylene glycol monomethyl (or monoethyl) ether and diethylene glycol 
dimethyl (or diethyl) ether; (7) nitrogen-containing cyclic compounds, 
such as pyrrolidone, N-methyl-2-pyrrolidone, and 
1,3-dimethyl-2-imidazolidinone; and (8) sulfur-containing compounds, such 
as dimethyl sulfoxide and tetramethylene sulfone. Other useful organic 
solvents include lactones and lactams. 
Preferred water soluble organic solvents include polyhydric alcohols, such 
as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 
1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol; 
diols, such as butanediol, pentanediol, hexanediol and homologous diols; 
glycol ethers, such as propylene glycol laureate; glycerol; polyalkyl 
glycols, such as polyethylene glycol; and lower alkyl ethers of polyhydric 
alcohols, such as ethylene glycol monomethyl or monoethyl ether, 
diethylene glycol methyl or ethyl ether, and triethylene glycol monomethyl 
or monoethyl ether. Particularly preferred organic solvents include 
ethylene glycol, diethylene glycol, and tetraethylene glycol. 
Mixtures of these solvents may be used in the present invention. A 
particularly preferred organic solvent for use in the present invention is 
1,3-propanediol or 1,4-butanediol which may be used either alone or in 
combination with other organic solvents particularly (1) polypropylene 
glycols and mixed polyethylene polypropylene glycols having molecular 
weights of from about 200 to about 600 (polyethylene glycol 200-600 is 
particularly preferred); or (2) polyol/alkylene oxide condensates having 
the formula 
##STR4## 
wherein X is hydrogen or methyl, R is H, CH.sub.3, C.sub.2 H.sub.5, 
C.sub.3 H.sub.7, C.sub.4 H.sub.9, or CH.sub.2 O (CH.sub.2 CH.sub.2 
O).sub.e HX; b is 0 or 1; a+d+f (c+e)=about 2 to about 100; and f is from 
about 1 to about 6. An example of such a polyol/alkylene oxide condensate 
is Liponic EG-1, commercially available from Lipo Chemicals Co., Paterson, 
N.J., wherein R=H, b=O, f=1, X=H and a+d+f (c+e)=26. 
In the instance where the aqueous carrier medium contains a mixture of 
water and organic solvent, that mixture usually contains from about 25% 
water/75% organic solvent to about 95% water/5% organic solvent. The 
preferred ratios range from approximately 50% water/50% organic solvent to 
approximately 95% water/5% organic solvent. Percentages are based on the 
total weight of the aqueous carrier medium, not the entire composition. 
The ink compositions of the present invention are manufactured using 
procedures well known in the art, such as those described in U.S. Pat. No. 
5,085,698, Ma, et al., issued Feb. 4, 1992, incorporated herein by 
reference. The ink is preferably prepared by mixing the pigment, 
dispersant and deionized water together in an attritor to form a 
concentrate. The pigment concentrate is ground until the appropriate 
particle size is obtained. The concentrate is then diluted with water and 
the appropriate formulation components added to give the desired ink. 
Optionally, surfactants may be added to modify the surface tension of the 
ink and to control the penetration of the ink into the paper. Suitable 
surfactants include nonionic, amphoteric and ionic surfactants. Other 
additives, such as biocides, humectants, chelating agents, and viscosity 
modifiers, may be added to the ink composition at their art-established 
levels.

The following examples are detailed descriptions of methods of preparation 
and use of the polymeric dispersants and the ink compositions of the 
present invention. The detailed descriptions fall within the scope of, and 
serve to exemplify, the more general description set forth above. The 
examples are presented for illustrative purposes only, and are not 
intended as a restriction on the scope of the invention. 
EXAMPLE 1 
A polymeric dispersant of the present invention is made as follows. 
A solution of methacrylic acid 22.8 g (265 mmol), 
monomethacryloxypropyl-terminated polydimethylsiloxane (PDMS-MA) 7.84 g 
(8.7 mmol, MW 900), nonylphenol PEG-10 methacrylate 6.33 g (8.7 mmol), 
dodecanethiol 2.06 g (9.9 mmol), dimethyl 2,2'-azobisisobutyrate (V-601) 
0.64 g (2.84 mmol) and isopropyl alcohol 100 mL is degassed with argon 
(done by repeated partial evacuation followed by argon backfill using a 
Firestone Valve) and then heated to 70.degree. C. for 16 hours. The 
mixture is allowed to cool to room temperature and then added slowly to 
rapidly stirred hexane 1.0 L. The resulting solid is isolated by vacuum 
filtration and dried in vacuum overnight at 80.degree. C. The yield of the 
reaction varies from 85% to 90%. The co-polymer is characterized by proton 
NMR and GPC. 
The co-polymer dispersant stock solution is prepared as follows: A 400 mL 
beaker containing 40 g of DI water is set on a hot plate with a magnetic 
stirrer. The co-polymer, 12 g, is added to the beaker while stirring, then 
18 g of 20% KOH is added to the system. The mixture is heated to 
50.degree. C. for 2 hours. The pH is adjusted to 7.5 by addition of 20% 
KOH. Then DI water is added to bring the total weight to 100 g. 
______________________________________ 
Preparation A 
Components Amount 
______________________________________ 
Carbon Black (Degussa Corp., Special Black 4A) 
27.0 g 
MAA-co-PDMS-co-Nonylphenol-PEG-10-MA stock solution 
75.0 g 
DI Water 52.4 g 
Ethylene glycol 25.6 g 
______________________________________ 
______________________________________ 
Preparation B 
Components Amount 
______________________________________ 
Carbon Black (Degussa Corp., FW18) 
20.3 g 
MAA-co-PDMS-co-Nonylphenol-PEG-10-MA 
67.5 g 
DI Water 92.2 g 
______________________________________ 
Preparations A and B are made as follows. The components are premixed by 
mechanical stirring until there are no visible lumps. The mixture is 
dispersed by an attrition process using a Szegvari attritor model 01 std 
with 10-12 mesh zirconium silicate shot at a speed of 700 rpm. The 
attrition process is typically performed for a minimum of one hour, 
however, longer times at controlled temperature can also be used. The 
carbon black dispersion mix is removed from the attritor and let down, by 
the addition of DI water, to a final premix percent solids of 17.5%. 
Ink A. 
An ink is prepared by mixing the concentrated premix dispersion Preparation 
A with ethylene glycol and DI water. The biocide Proxel.RTM. GXL 
commercially available from Zeneca, is also added. The formulation is 
given below: 
______________________________________ 
Components Amount 
______________________________________ 
Premix Dispersion Preparation A 
38.0 g 
Ethylene Glycol 19.5 g 
DI Water 75.0 g 
Proxel .RTM. GXL 0.27 g 
______________________________________ 
The final pH of the ink is adjusted to 8.0 by the addition of 20% KOH. The 
ink is filtered through a series of filters with the final filter being 
1.2 microns. The median particle size determined by Leeds and Northrop 
Microtrac UPA 150 measurement is about 190 nm. 
Ink B 
An ink composition is prepared, using the same procedure as for Ink A, 
above, except that MAA-co-PDMS-co-Trimethylsiloxy-terminated PEG (4-5) 
Methacrylate is used as the dispersant. 
Ink C 
An ink composition is prepared, using the same procedure as for Ink A, 
above, except that MAA-co-PDMS-co-Stearyl Methacrylate is used as the 
dispersant. 
Ink D 
An ink composition is prepared, using the same procedure as for Ink A 
above, except that MAA-co-PDMS-co-PPG-4-Nonylphenol acrylate is used as 
the dispersant. 
Ink E 
An ink is prepared by mixing the concentrated premix dispersion Preparation 
B with diethylene glycol, tetraethylene glycol and DI water. 
______________________________________ 
Components Amount 
______________________________________ 
Premix Dispersion Preparation B 
83.3 g 
Diethylene Glycol 15.0 g 
Tetraethylene Glycol 
5.0 g 
DI Water 96.3 g 
Proxel .RTM. GXL 0.4 g 
______________________________________ 
The final pH of the ink is adjusted to 8.0 by the addition of 20% KOH. The 
ink is filtered through a series of filters with the final filter being 
1.2 microns. The median particle size is about 140 nm. 
Ink F 
An ink composition is prepared, using the same procedure as for Ink E, 
above, except that MAA-Co-PDMS-Co-Trimethylsiloxy-terminated PEG 4-5 
methacrylate is used as dispersant. 
Ink G 
An ink composition is prepared, using the same procedure as for Ink E, 
above, except that MAA-co-PDMS-co-Stearyl Methacrylate is used as 
dispersant. 
Ink H 
An ink composition is prepared, using the same procedure as for Ink E, 
above, except that MAA-Co-PDMS-Co-PPG-4-Nonylphenol acrylate is used as 
dispersant. 
Print testing of ink 
The inks described above are print tested using an IBM Model IJ4076 
printer, manufactured by Lexmark International. The print samples are 
generated on IBM Multisystem bond paper and are tested using the following 
procedures: 
Optical density: measured by a Macbeth densitometer. All inks show a good 
optical density. 
Water-fastness: Print samples are soaked in DI water for 5 minutes. After 
drying, the optical density of the samples are measured and compared to 
the presoaked optical density. The optical densities of the soaked samples 
are 99-100% of the presoaked optical densities. 
Maintenance testing: Capping stations of a Lexmark 4076 printhead are 
disabled to leave the printhead uncapped when the printer is not printing. 
The printer is left in standby mode for 6 hours at ambient condition. The 
printer is then activated and run for 6750 heater fires for each of the 56 
nozzles of the printhead. The recovery of the nozzles of the printhead are 
observed to see if any remain clogged. These tests show recovery for all 
56 nozzles in the printhead when the inks of the present invention are 
used. 
Stability testing: The inks are placed in an oven at 60.degree. C. to 
examine their stability. Change in the particle size is monitored weekly 
for 5 weeks. Little, if any, change in particle size is seen. 
Dry time test: The inks of the present invention show good dry times which 
are, in fact, less than similar inks which use a dispersant which does not 
include the stabilizing segment. 
EXAMPLE 2 
A second polymeric dispersant of the present invention is made as follows. 
A solution of methacrylic acid 22.8 g (265 mmol), 
monomethacryloxypropyl-terminated polydimethylsiloxane (PDMS-MA) 7.84 g 
(8.7 mmol, MW 900), stearyl methacrylate 2.95 g (8.7 mmol), dodecanethiol 
2.06 g (9.9 mmol), dimethyl 2,2'-azobisisobutyrate 0.64 g (2.84 mmol) and 
isopropyl alcohol 100 mL is degassed with argon (done by repeated partial 
evacuation followed by argon backfill using a Firestone Valve) then heated 
to 70.degree. C. for 16 hours. The mixture is allowed to cool to room 
temperature and then added slowly to rapidly stirred hexane 1.0 L. The 
resulting solid is isolated by vacuum filtration and dried in vacuum 
overnight at 80.degree. C. The yield of the reaction is about 85%. The 
co-polymer is characterized by proton NMR and GPC. 
This polymeric dispersant is formulated into a pigment ink composition as 
described in the present application. The ink composition shows excellent 
stability, print characteristics, water-fastness, optical density, and 
in-use printer maintenance characteristics.