Nitrogen-containing organic cosolvents for aqueous ink jet inks

Aqueous ink jet ink compositions comprising an aqueous carrier medium, a colorant, such as a pigment dispersion or dye, and a nitrogen-containing organic cosolvent having a solubility in water of at least 4.5 % at 25.degree. C., exhibit freedom from plug formation and excellent storage stability.

FIELD OF THE INVENTION 
This invention relates to aqueous inks for ink jet printers. More 
particularly, this invention relates to aqueous ink jet inks comprising 
selected nitrogen-containing cosolvents that impart resistance to nozzle 
plug formation and improved ink stability. 
BACKGROUND OF THE INVENTION 
Ink jet printing is a non-impact method that produces droplets of ink that 
are deposited on a substrate such as paper or transparent film in response 
to an electronic digital signal. Thermal or bubble jet drop-on-demand ink 
jet printers have found broad application as output devices for personal 
computers in the office and the home. 
Thermal ink jet printers use a plurality of nozzles each containing a 
resistor element to fire ink droplets toward the print substrate. Nozzle 
openings are typically about 25-50 micrometers in diameter. These small 
openings are easily plugged by precipitating, crystallizing or 
flocculating materials or by particulate foreign matter. The nozzle 
openings are exposed to the atmosphere, thereby rendering the ink subject 
to evaporation or reaction with oxygen or carbon dioxide with the 
potential to produce particulate, non-dispersed material causing formation 
of a plug in the nozzle openings. In dye-based inks, evaporation can cause 
crystallization or precipitation of the dye or solid additives, commonly 
referred to as "crusting." In pigment-based inks this evaporation can 
cause precipitation of the dispersant, flocculation of the pigment 
dispersion, and precipitation of solid additives. 
Accordingly, a critical requirement for an ink jet ink is the ability to 
remain fluid upon exposure to air, so called "decap" conditions. This 
allows a pen to function after a period of non-use ("long-term decap") or 
during operation of infrequently utilized nozzles ("short-term decap"). A 
major concern with all ink jet printers is pluggage of nozzles during 
operation and between operations. Decap time is a measure of the interval 
of time that a nozzle can remain exposed to air and continue to print. 
Initial evaporation generally causes an increase in viscosity which affects 
the ability of the nozzle to fire a drop of ink since ink jet pens are 
designed to operate within specific viscosity ranges. The inception of 
pluggage may cause distortion of the image, which may appear as a drop of 
ink which is displaced from its intended position or a splitting of the 
drop into two or more droplets displaced from the intended target 
position. In addition, "streamers" or "banners" may appear as artifacts 
attached to the right side of the alphanumeric characters. On some 
occasions the drop may reach its intended position but at a lower drop 
volume producing a lower optical density image. Ultimately the plugged 
nozzle will fail to fire and no image will be generated. 
In a decap test, a series of successive drops are fired at predetermined 
and increasing time intervals. For example, if the time interval between 
firings is set at five minutes, then the printings will take place after 
intervals of 5 minutes, then 10 minutes, then 15 minutes, etc. The 
interval of time needed to cause failure of the first, fifth and 
thirty-second consecutively printed drops are recorded. The first drop 
failure interval is important because it is the critical measure of the 
reliability of the system without the need for engineering or software 
cures for printing failure. In addition, it affects the productivity or 
printing rate because programmed routines must be used to clear the 
pluggage, so-called "spitting" and these routines interrupt the actual 
printing chore. The thirty-second drop decap time determines the period of 
time that a nozzle can remain uncapped and recover after 32 non-printing 
firings. 
Several methods of addressing the crusting problems are known in the art. 
For example, most ink jet printers are designed to prevent excessive 
evaporation of solvent from pen nozzles by seating the pen cartridge in an 
air tight chamber when not in use. These devices become ineffective with 
continued printer use because dried ink deposits at the rubber seals and 
the system loses its air-tight condition. Also, it is possible to shut 
down a printer inadvertently and prematurely, thereby not allowing the 
printer routine to place the pen nozzles in the air-tight capping chamber. 
Another device to combat pluggage is a elastomeric wiper that removes solid 
formed at the surface of the nozzle. This device is often ineffective 
because the depth or hardness of the plug resists mechanical removal. 
Another pluggage fix is the use of forced air or vacuum suction to clear 
the nozzle. These devices are often ineffective and add considerable 
expense to the cost of the printer. 
A second critical requirement for inks where the colorant is a pigment is 
for the pigment dispersion to remain stable throughout the life of the ink 
jet cartridge. Many cosolvents that impart long decap or rapid penetration 
are incompatible with the pigment dispersion and therefore cannot be used. 
Therefore a need exists for aqueous ink jet inks with good dispersion 
stability and high resistance to plug formation. 
SUMMARY OF THE INVENTION 
In accordance with this invention, there is provided an aqueous ink jet ink 
composition consisting essentially of: 
(a) an aqueous carrier medium; 
(b) a colorant selected from the group consisting of a pigment dispersion 
and a dye; and 
(c) an organic cosolvent having a solubility in water of at least 4.5% a 
25.degree. C., and which is selected from the group consisting of: 
1) alkyl amides having the general structure: 
##STR1## 
wherein R=--H or --CH.sub.3, 
R'=--C.sub.3 H.sub.8 or --C(CH.sub.3).sub.2, when R=--H, and 
R'=--C.sub.2 H.sub.5, when R=--CH.sub.3 ; 
2) cyclic amides having the general structure: 
##STR2## 
wherein R=--H or --CH.sub.3 ; 
3) cyclic diamides having the general structure: 
##STR3## 
wherein R=--H or --CH.sub.3 ; 
4) alkyl diamides having the general structure: 
##STR4## 
wherein R=--H or --CH.sub.3 ; 
5) alkyl diol diamides having the general structure: 
##STR5## 
wherein R=--H, --CH.sub.3 or --C.sub.2 H.sub.5 ; 
6) hydroxyamides having the general structure: 
##STR6## 
wherein a=1-6, 
b=2-4, 
x=0-3, 
y=0-3, 
x+y=1-6, 
n=+1 or -1, 
a.gtoreq.x, 
b.gtoreq.y; 
7) hydroxyalkyl ureas having the general structure: 
##STR7## 
wherein a=1-7, 
n=+1 or -1, 
R is selected from the group consisting of --CH.sub.2 CHOHCH.sub.2 OH and 
--CH.sub.2 CH.sub.2 OH, and 
R' is selected from the group consisting of --CH.sub.2 CH.sub.2 OH and --H; 
and 
8) mixtures thereof.

DETAILED DESCRIPTION OF THE INVENTION 
The ink jet ink compositions of this invention are particularly suited for 
use in ink jet printers in general, and thermal ink jet printers in 
particular. The ink jet ink compositions encompasses both pigment and dye 
colorant inks. The inks may be adapted to the requirements of a particular 
ink jet printer to provide a balance of light stability, smear resistance, 
viscosity, surface tension, optical density, low toxicity, high material 
compatibility and drying rate. The organic cosolvents of this invention 
are stable to oxygen and are especially resistant to hydrolysis in aqueous 
inks when formulated near a neutral pH. 
AQUEOUS CARRIER MEDIUM 
The aqueous carrier medium comprises water (preferably deionized water) or 
a mixture of water and at least one water soluble organic solvent other 
than the selected nitrogen-containing solvent. Representative examples of 
water-soluble organic solvents are disclosed in U.S. Pat. No. 5,085,698, 
the disclosure of which is incorporated herein by reference. Selection of 
a suitable mixture of water and water soluble organic solvent depends upon 
the requirements of the specific application, such as desired surface 
tension and viscosity, the selected colorant, drying time of the ink, and 
the type of substrate onto which the ink will be printed. 
A mixture of a water soluble organic solvent having at least 1 hydroxyl 
group (diethylene glycol, triethylene glycol, butyl carbitol, etc.) and 
deionized water is preferred as the aqueous carrier medium. The aqueous 
carrier medium usually contains from about 5% to about 95% water, with the 
remainder (i.e., 95% to about 5%) being the water soluble organic solvent. 
The preferred ratios are approximately 60% to about 95% water, based on 
the total weight of the aqueous carrier medium. Most preferably, the 
aqueous vehicle comprises about 90% water and the balance a glycol ether 
such as butyl carbitol. Higher concentrations of glycols may result in 
poor print quality. Lower concentrations will lead to drying out of the 
printhead or "crusting" of the ink. The aqueous carrier medium is present 
in the range of approximately 65 to 99.8%, preferably approximately 85 to 
98.5%, based on the total weight of the ink. 
When a mixture of water and organic solvent is used, the aqueous carrier 
medium usually contains between 30% and 95%, preferably 60% to 95%, water 
based on the total weight of the aqueous carrier medium plus organic 
cosolvent. The amount of aqueous carrier medium plus organic cosolvent is 
in the range of approximately 70 to 99.8%, preferably approximately 94 to 
99.8%, based on the total weight of the ink when an organic pigment is 
selected; approximately 25 to 99.8%, preferably approximately 70 to 99.8% 
when an inorganic pigment is selected; and 80 to 99.8% when a dye is 
selected. 
COLORANTS 
The colorants useful in the present invention may be a pigment dispersion 
or a dye. The term pigment dispersion, as is known in the art and as used 
herein, refers to a mixture of a pigment and a dispersing agent. 
Preferably, the dispersing agent is a polymeric dispersant compound. 
Dyes which are commonly used in aqueous ink jet inks, such as for example 
Acid, Direct, Food and Reactive dyes, are suitable colorants for the ink 
compositions of the present invention. 
In the preferred embodiment of the present invention, the colorant is a 
pigment dispersion. In addition to, or in place of the preferred polymeric 
dispersant compounds, surfactant compounds may be used as dispersants. 
These may be anionic, cationic, nonionic, or amphoteric surfactants. A 
detailed list of non-polymeric as well as some polymeric dispersants are 
listed in the section on dispersants, pages 110-129, 1990 McCutcheon's 
Functional Materials, North American Edition, Manufacturing Confection 
Publishing Co., Glen Rock, N.J., 07452, the disclosure of which is 
incorporated herein by reference. 
Polymeric dispersants suitable for practicing the invention include AB, BAB 
or ABC block copolymers. In the AB or BAB block copolymers, the A segment 
is a hydrophobic (i.e., water insoluble) homopolymer or copolymer which 
serves to link with the pigment and the B block is a hydrophilic (i.e., 
water soluble) homopolymer or copolymer, or salts thereof, and serves to 
disperse the pigment in the aqueous medium. Such polymeric dispersants and 
the synthesis thereof are disclosed in the aforementioned U.S. Pat. No. 
5,085,698. 
Preferred AB block polymers are: methyl methacrylate//methyl 
methacrylate/methacrylic acid(10//5/7.5), 2-ethylhexyl 
methacrylate//2-ethylhexyl methacrylate/methacrylic acid(5//5/10), n-butyl 
methacrylate//n-butyl methacrylate/methacrylic acid (10//5/10), n-butyl 
methacrylate//methacrylic acid(10//10), ethylhexyl methacrylate//methyl 
methacrylate/methacrylic acid (5//10/10), n-butyl 
methacrylate//2-hydroxyethyl methacrylate/methacrylic acid(5//10/10), 
n-butyl methacrylate//2-hydroxyethyl methacrylate/methacrylic acid 
(15//7.5/3), methyl methacrylate//ethylhexyl methacrylate/methacrylic acid 
(5//5/10), and butyl methacrylate//butyl methacrylate/dimethylaminoethyl 
methacrylate(5//5/10). 
Preferred BAB block polymers are: n-butyl methacrylate/methacrylic 
acid//n-butyl methacrylate//n-butyl methacrylate/methacrylic acid 
(5/10//10//5/10), methyl methacrylate/methacrylic acid//methyl 
methacrylate//methyl methacrylate/methacrylic acid (5/7.5//10//5/7.5). The 
double slash indicates a separation between blocks and a single slash 
indicates a random copolymer. The values in parenthesis represent the 
degree of polymerization of each monomer. 
ABC triblock copolymers that can be used to advantage in the present 
invention comprise a hydrophilic A block, a B block which is capable of 
binding to the pigment, and a hydrophilic or hydrophobic C block. Suitable 
ABC block copolymers and their method of synthesis are disclosed in 
Assignee's copending U.S. application Ser. Nos. 07/838,181, filed Feb. 20, 
1992 and 07/838,165, filed Feb. 20, 1992, the disclosures of which are 
incorporated herein by reference. Preferred ABC triblock polymers include 
poly(methacrylic acid//2-phenethyl methacrylate//ethoxytriethylene glycol 
methacrylate) (13//10//4); poly(methacrylic acid//2-phenethyl 
methacrylate/dimethylaminoethyl methacrylate ethoxytriethylene glycol 
methacrylate) (13//8/2//4); poly(methacrylic acid//benzyl 
methacrylate//ethoxytriethylene glycol methacrylate) (13//10//4); poly 
(methacrylic acid//2-phenethyl methacrylate//methoxypolyethylene glycol 
400 methacrylate) (13//10//4); poly(dimethylaminoethyl methacrylate/methyl 
methacrylate//2-phenethyl methacrylate//ethoxytriethylene glycol 
methacrylate) (7.5/5//10//4). 
To solubilize the polymers into the aqueous medium, it may be necessary to 
neutralize the acid or amino groups contained in the polymer. Neutralizing 
agents for the acid groups include organic bases; alcohol amines; 
pyridine; ammonium hydroxide; tetraalkylammonium salts; alkali metals such 
as lithium, sodium and potassium, and the like. Neutralizing agents for 
the amino groups include organic acids such as acetic, formic and oxalyic; 
halogens such as chloride, fluoride and bromide; inorganic acids such as 
sulfuric and nitric; and the like.. 
Although random copolymers can be used as dispersing agents, they are not 
as effective in stabilizing pigment dispersions as the block polymers, and 
therefore are not preferred. 
The acrylic block polymer is present in the range of approximately 0.1 to 
30% by weight of the total ink composition, preferably in the range of 
approximately 0.1% to 8% by weight of the total ink composition. If the 
amount of polymer becomes too high, the ink color density will be 
unacceptable and it will become difficult to maintain desired ink 
viscosity. Dispersion stability of the pigment particles is adversely 
affected if insufficient acrylic block copolymer is present. 
Useful pigments for the dispersion comprise a wide variety of organic and 
inorganic pigments, alone or in combination. 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 10 micron to 50 micron. The particle size also has an influence on 
the pigment dispersion stability, which is critical throughout the life of 
the ink. Brownian motion of minute particles will help prevent the 
particles from settling. It is also desirable to use small particles for 
maximum color strength. The range of useful particle size is approximately 
0.005 micron to 15 micron. Preferably, the pigment particle size should 
range from 0.005 to 5 micron and most preferably, from 0.01 to 0.3 micron. 
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 
aggregated to the extent that it is in dry form. Thus, pigments in water 
wet presscake form do not require as much deaggregation in the process of 
preparing the inks from dry pigments. Representative commercial dry and 
presscake pigments that may be used in practicing the invention are 
disclosed in the aforementioned U.S. Pat. No. 5,085,698. 
Fine particles of metal or metal oxides also may 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, also may be selected. Furthermore, 
finely divided metal particles, such as copper, iron, steel, aluminum and 
alloys, may be selected for appropriate applications. 
In the case of organic pigments, the ink may contain up to approximately 
30% pigment by weight, but will generally be in the range of approximately 
0.1 to 15%, preferably approximately 0.1 to 8%, by weight of the total ink 
composition for most thermal ink jet printing applications. If an 
inorganic pigment is selected, the ink will tend to contain higher weight 
percentages of pigment than with comparable inks employing organic 
pigment, and may be as high as approximately 75% in some cases, because 
inorganic pigments generally have higher specific gravities than organic 
pigments. 
Up to 20% of dye may be present, based on the total weight of the ink. 
COSOLVENTS 
The organic cosolvents of the present invention have a solubility in water 
of at least 4.5% (4.5 parts cosolvent in 100 parts of water) at 25.degree. 
C. and are selected from the group consisting of: 
1) alkyl amides having the general structure: 
##STR8## 
wherein R=--H or --CH.sub.3, 
R'=--C.sub.3 H.sub.8 or --C(CH.sub.3).sub.2, when R=--H, and 
R'=--C.sub.2 H.sub.5, when R=--CH.sub.3. 
An example of amides fitting this formula include is isobutyramide. 
2) cyclic amides having the general structure: 
##STR9## 
wherein R=--H or --CH.sub.3. 
Examples of amides fitting this formula include: 
1-pyrrolidinecarboxaldehyde and N-acetylpyrrolidine. 
3) cyclic diamides having the general structure: 
##STR10## 
wherein R=--H or --CH.sub.3. 
Examples of amides fitting this formula include: 
1,4-piperazinedicarboxaldehyde and N,N'-diacetylpiperazine. 
4) alkyl diamides having the general structure: 
##STR11## 
wherein R=--H or --CH.sub.3. 
Examples of amides fitting this formula include: N,N'-ethylene bisformamide 
and N,N'-ethylene bisacetamide. 
5) alkyl diol diamides having the general structure: 
##STR12## 
wherein R=--H, --CH.sub.3, or --C.sub.2 H.sub.5. 
Examples of amides fitting this formula include: tartaric acid diamide, 
N-methyltartaric acid diamide, N,N-dimethyltartaric acid diamide, 
N,N'-dimethyltartaric acid diamide, N,N,N',N'-tetramethyltartaric acid 
diamide, N,N,N',N'-tetraethyltartaric acid diamide and the like. 
6) Hydroxyamides having the general structure: 
##STR13## 
wherein a=1-6, 
b=2-4, 
x=0-3, 
y=0-3, 
x+y=1-6, 
n=+1 or -1, 
a.gtoreq.x, and 
b.gtoreq.y. 
When n=+1, the group is acyclic. When n=-1, the group is cyclic, e.g. 
cyclopentyl, cyclohexyl. The total number of hydroxyl groups is x+y. 
Preferably a=1-4, b=2-3 and y=1. Also preferred are compounds where x=2 
and y=1-2. 
Examples of hydroxyamides of this structure are 
N-(2-hydroxyethyl)acetamide, N-(2-hydroxyethyl)butanamide, 
N-(2-hydroxyethyl)methyl-propanamide, DL-Panthenol and various isomers of 
N-(2-hydroxyethyl)hexanamide and the like. 
7) Hydroxyalkylureas having the general structure: 
##STR14## 
wherein a=1-7, 
x=+1 or -1, 
R is selected from the group consisting of: --CH.sub.2 CHOHCH.sub.2 OH and 
--CH.sub.2 CH.sub.2 OH, and 
R' is selected from the group consisting of: --CH.sub.2 CH.sub.2 OH and 
--H. 
Examples of hydroxyalkylureas of this structure are 
3-N-(N'-methylureido)-1,2-propanediol, 
3-N-(N'-ethylureido)-1,2-propanediol, 
3-N-(N'-1'-propylureido)-1,2-propanediol, 
3-N-(N'-2'-propylureido)-1,2-propanediol, 
3-N-(N'-1'-n-butylureido)-1,2-propanediol, 
3-N-(N'-2'-butylureido)-1,2-propanediol, 
3-N-(N'-isobutylureido)-1,2-propanediol, 
3-N-(N'-tertbutylureido)-1,2-propanediol, the various pentyl isomers of 
3-N-(N'-pentylureido)-1,2-propanediol, the various hexyl isomers of 
3-N-(N'-hexylureido)-1,2-propanediol, 
3-N-(N'-cyclopentylureido)-1,2-propanediol, 
3-N-(N'-cyclohexylureido)-1,2-propanediol, 
3-N-(N'-cycloheptylureido)-1,2-propanediol, 
N-(N'-methylureido)-N,N-bis(ethanol-2), 
3-N-(N'-ethylureido)-N,N-bis(ethanol-2), 
3-N-(N'-1'-propylureido)-N,N-bis(ethanol-3-N-(N'-2'-propylureido)-N,N-bis( 
ethanol-2), 3-N-(N'-1'-n-butylureido)-N,N-bis(ethanol-2), 
3-N-(N'-2'-butylureido)-N,N-bis(ethanol-2), 
3-N-(N'-isobutylureido)-N,N-bis(ethanol-2), 
3-N-(N'-tertbutylureido)-N,N-bis(ethanol-2), the various pentyl isomers of 
3-N-(N'-pentylureido)-N,N-bis(ethanol-2), the various hexyl isomers of 
3-N-(N'-hexylureido)-N,N-bis(ethanol-2), 
3-N-(N'-cyclopentylureido-N,N-bis(ethanol-2), 
3-N-(N'-cyclohexylureido)-N,N-bis(ethanol-2), 
3-N-(N'-cycloheptylureido)-N,N-bis(ethanol-2), 
N-(N'-methylureido)-N-ethanol-2, 3-N-(N'-ethylureido)-N-ethanol-2, 
3-N-(N'-1'-propylureido)-N-ethanol-2, 
3-N-(N'-2'-propylureido)-N-ethanol-2, 3-N-(N'-1'-n-butylureido)-N-ethanol- 
2, 3-N-(N'-2'-butylureido)-N-ethanol-2, 
3-N-(N'-isobutylsdureido)-N-ethanol-2, 
3-N-(N'-tertbutylureido)-N-ethanol-2, the various pentyl isomers of 
3-N-(N'-pentylureido)-N-ethanol-2, the various hexyl isomers of 
3-N-(N'-hexylureido)-N-ethanol-2, 3-N-(N'-cyclopentylureido)-N-ethanol-2, 
3-N-(N'-cyclohexylureido)-N-ethanol-2 and 
3-N-(N'-cycloheptylureido)-N-ethanol-2, for example. 
8) Mixtures of these compounds have also been found to be useful in this 
invention. 
The compounds of this invention have unique and surprising properties 
relative to their nearest homologues. For example, formamide and acetamide 
are known in the literature as cosolvents for aqueous ink jet inks. These 
compounds, however, pose serious toxicological problems; acetamide is a 
carcinogen and formamide is a developmental toxin. Furthermore, formamide, 
1-formylpiperidine, N-(2-hydroxyethyl)formamide and 
N,N'-diacetyl-1,3-propanediamine are not effective pluggage inhibitors and 
diacetamide imparts non-printability and dispersion instability to an ink. 
Compounds of this invention such as isobutyramide, N,N'-ethylene 
bisacetamide, amides derived from N-(2-hydroxyethyl)acetamide and 
N-(2-hydroxyethyl)butanamide and 1-pyrrolidinecarboxaldehyde, are less 
hazardous and produce more stable inks with better decap properties. 
As little as 1% organic cosolvent may have some effect on decap 
performance, but about 3-10% is a useful range. Higher concentrations may 
be used to maximize pluggage resistance most preferably up to 15%, less 
preferably to 55%, and least preferably to 70%, but this increased 
pluggage resistance must be balanced against increased drying rate of the 
ink. 
The nitrogen-containing cosolvents may be chosen for specific inks on the 
basis of a need for certain physical properties such as boiling point, 
melting point or drying rate with a specific set of ingredients. Mixtures 
of selected organic cosolvents may also be used to optimize and balance 
various ink properties. It should also be pointed out that the performance 
of the organic cosolvents is dependant upon their purity, as impurities 
can cause or retard plug formation. Therefore the source of the organic 
cosolvents may be important. Specific sources of cosolvents used in the 
Examples are indicated in Table 1. 
OTHER INGREDIENTS 
The ink may contain other ingredients. For example, the surfactants 
mentioned above may be used to alter surface tension as well as maximize 
penetration. However, they may also destabilize the pigment dispersion for 
pigmented inks. The choice of a specific surfactant is also highly 
dependent on the type of media substrate to be printed. It is expected 
that one skilled in the art can select the appropriate surfactant for the 
specific substrate to be used in printing. In aqueous inks, the 
surfactants may be present in the amount of 0.01-5% and preferably 0.2-2%, 
based on the total weight of the ink. 
Biocides may be used in the ink compositions to inhibit growth of 
microorganisms. Dowicides.RTM. (Dow Chemical, Midland, Mich.), 
Nuosept.RTM. (Huls America, Inc., Piscataway, N.J.), Omidines.RTM. (Olin 
Corp., Cheshire, Conn.), Nopcocides.RTM. (Henkel Corp., Ambler, Pa.), 
Troysans.RTM. (Troy Chemical Corp., Newark, N.J.) and sodium benzoate are 
examples of such biocides. 
In addition, sequestering agents such as EDTA may also be included to 
eliminate deleterious effects of heavy metal impurities. 
Other known additives, such as humectants, viscosity modifiers and other 
acrylic or non-acrylic polymers made also be added to improve various 
properties of the ink compositions. 
INK PREATION 
The ink compositions of the present invention are prepared in the same 
manner as other ink jet ink compositions. If a pigment dispersion is used 
as the colorant, the dispersion is prepared by premixing the selected 
pigment(s) and dispersant in water. The dispersion step may be 
accomplished in a horizontal mini mill, a ball mill, an attritor, or by 
passing the mixture through a plurality of nozzles within a liquid jet 
interaction chamber at a liquid pressure of at least 1000 psi to produce a 
uniform dispersion of the pigment particles in the aqueous carrier medium. 
Amide cosolvents as well as other cosolvents may be present during the 
dispersion step. 
If a dye is used as the colorant, there is no dispersant present and no 
need for pigment deaggregation. The dye-based ink is prepared in a well 
agitated vessel rather than in dispersing equipment. 
It is generally desirable to make the ink jet inks in concentrated form, 
which is subsequently diluted with a suitable liquid to the appropriate 
concentration for use in the ink jet printing system. By dilution, the ink 
is adjusted to the desired viscosity, color, hue, saturation density, and 
print area coverage for the particular application. 
Jet velocity, separation length of the droplets, drop size, and stream 
stability are greatly affected by the surface tension and the viscosity of 
the ink. Ink jet inks suitable for use with ink jet printing systems 
should have a surface tension in the range of about 20 dyne/cm to about 70 
dyne/cm and, more preferably, in the range 30 dyne/cm to about 70 dyne/cm 
at 20.degree. C. Acceptable viscosities are no greater than 20 cP, and 
preferably in the range of about 1.0 cP to about 10.0 cP at 20.degree. C. 
The ink has physical properties compatible with a wide range of ejecting 
conditions, i.e., driving voltage and pulse width for thermal ink jet 
printing devices, driving frequency of the piezo element for either a 
drop-on-demand device or a continuous device, and the shape and size of 
the nozzle. They may be used with a variety of ink jet printers such as 
continuous, piezoelectric drop-on-demand and thermal or bubble jet 
drop-on-demand, and are particularly adapted for use in thermal ink jet 
printers. The inks have excellent storage stability for a long period and 
do not clog in an ink jet apparatus. Fixing the ink on the media 
substrate, such as, paper, fabric, film, etc., can be carried out rapidly 
and accurately. 
The printed ink images have clear color tones, high density, excellent 
water resistance and lightfastness. Furthermore, the ink does not corrode 
parts of the ink jet printing device it comes in contact with, and it is 
essentially odorless. 
The following examples further illustrate, but do not limit, the invention. 
The parts and percentages are by weight unless otherwise noted. 
EXAMPLES 
A pigmented ink composition was prepared and used with the organic 
cosolvents of the invention and other known cosolvents for comparison. 
Preparation of Polymeric Dispersant 
A block copolymer of n-butyl methacrylate and methacrylic acid was prepared 
by adding 3750 grams of tetrahydrofuran and 7.4 grams of p-xylene to a 
12-liter flask equipped with a mechanical stirrer, thermometer, nitrogen 
inlet, drying tube outlet and addition funnels. Feed I, which consisted of 
3.0 ml of a 1.0 M solution of tetrabutyl ammonium m-chlorobenzoate 
catalyst in acetonitrile, was started at 0 minutes and added over 150 
minutes and 291.1 gm (1.25 mol) of an initiator, 
1,1-bis(trimethylsiloxy-2-methyl propene, was injected. Feed II, which 
consisted of 1976 gm (12.5 mol) trimethylsilyl methacrylate, was started 
at 0 minutes and added over 35 minutes. One hundred eighty minutes after 
Feed II was completed (over 99% of the monomers had reacted), Feed III, 
which consisted of 1772 gm (12.5 mol) butyl methacrylate, was started and 
added over 30 minutes. 
At 400 minutes, 780 grams of dry methanol were added to the above solution 
and distillation commenced. During the first stage of distillation, 1300.0 
grams of material with a boiling point below 55.degree. C. were removed 
from the flask. The theoretical amount of methoxytrimethylsilane, having a 
boiling point of 54.degree. C., to be removed was 1144.0 grams. 
Distillation continued during the second stage while the boiling point 
increased to 76.degree. C. 5100 grams of isopropanol were added during the 
second stage of distillation. A total of 7427 grams of solvent were 
removed. 
The resultant resin solution contained 55.8% solids and had a 
neutralization equivalent of 4.65 milliequivalents of potassium hydroxide 
per gram of solids. The resin was neutralized by adding to a 1000 ml 
cylindrical polyethylene bottle: 
200.0 grams dispersant solution 
174.4 grams 15% potassium hydroxide 
137.6 grams deionized water 
The mixture was tumbled on a roller mill for 3-4 hours and then 
magnetically stirred for 16-20 hours to give a slightly cloudy solution. 
Preparation of Pigment Dispersion 
The following materials were added to a 1 liter beaker: 
78.3 grams deionized water 
66.7 grams neutralized polymeric dispersant solution 
3.0 grams 15% potassium hydroxide 
The solution was mechanically stirred while 20.0 grams of carbon black 
pigment, FW 18 (Degussa Corp., Ridgefield Park, N.J. 07660) were added 
slowly while stirring was continued for 30 minutes. The mixture was then 
added to a Mini Motormill 100 (Eiger Machinery Inc., Bensenville, Ill.) 
with another 32 grams of deionized water as a rinse. The contents were 
milled at 3500 rpm for one hour. The yield was 190.8 grams. The pH was 
7.6. The particle size was 138 nm as determined by a Brookhaven BI-90 
Particle Analyser (Brookhaven Instruments Corp., Holtsville, N.Y.). 
Preparation of Hydroxyalkylamides and Hydroxyalkylureas 
All chemical reactants were obtained from Aldrich Chemical Company, 
Milwaukee, Wis. 
2',4'-dihydroxy-3',3'-dimethylbutanamido-N-ethanol-2 was prepared by adding 
DL-Pantolactone (6.51 g, 0.50 mol) to a clear homogeneous solution of 
ethanolamine (3.05 g, 0.50 mol) in tetrahydrofuran (30 ml). The reaction 
mixture was refluxed 16 hours, cooled, and concentrated in vacuum to give 
a viscous oil. The residue was titrated with ether to produce a white 
powder (8.8 g, 92%); mp=95.degree.-96.degree. C. 
Hydroxyalkylureas were prepared by reacting the appropriate amine with the 
appropriate isocyanate. These preparations are illustrated by the 
preparation of 3-N-(tert-butylureido)-1,2-propanediol as follows: 
A suspension of 3-amino-1,2-propanediol (9.11 g, 0.10 mol) in 
tetrahydrofuran (30 ml) was heated to 60.degree. C. to give a fairly clear 
solution. The heating was discontinued and tert-butylisocyanate (9.91 g, 
0.10 mol) was added dropwise to maintain a gentle reflux. The reaction was 
stirred overnight at 60.degree. C. and was vacuum distilled to dryness. 
The residue was triturated with ethyl ether to produce a white powder 
(11.72 g, 66%); mp =76.degree.-78.degree. C. Likewise, cyclohexyl 
isocyanate, ethanolamine and diethanolamine were appropriately reacted to 
give the desired hydroxyalkylurea. 
Preparation of Inks 
Using the 22.5 grams of pigment dispersion from the above procedures, a 
series of aqueous inks were prepared by combining 2.6 grams diethylene 
glycol (Aldrich Chemical Co. Inc., Milwaukee, Wis.), 0.5 grams Silwet.RTM. 
L-77 (Union Carbide Corp., Danbury, Conn.) 37.2 grams deionized water and 
2.6 grams of a cosolvent identified in Table 1 with magnetic stirring over 
a period of 10-15 minutes. 
TABLE 1 
______________________________________ 
Control Cosolvent And Selected 
Cosolvent Identification and Source 
Comparative 
Cosolvents 
Source Name 
______________________________________ 
Control # 
1 Formamide B 
2 Acetamide B 
3 1-Formylpiperidine A 
4 4-Formylmorpholine A 
5 Diacetamide A 
6 N,N'-Diacetyl-1,3-propanediamine 
C 
7 Caprolactam A 
8 N-(2-Hydroxyethyl)formamide 
E 
9 N,N-Bis(2-hydroxyethyl)formamide 
A 
10 N,N-Bis(2-hydroxyethyl)acetamide 
E 
11 N,N-Bis(2-hydroxyethyl)hexanamide 
E 
Example # 
1 Isobutyramide D 
2 1-Pyrrolidinecarboxaldehyde 
A 
3 1,4-Piperazinedicarboxaldehyde 
A 
4 N,N'-Ethylene-bisacetamide 
C 
5 N,N,N',N'-Tetramethyl-L-tartaric 
B 
acid diamide 
6 N-(2-hydroxyethyl)acetamide 
E 
7 N-(2-hydroxyethyl)butanamide 
E 
8 N-(2-hydroxypropyl-1)pentanamide 
E 
9 2',4'-dihydroxy-3',3'- F 
dimethylbutanamido-N-ethanol-2 
10 D-Panthenol or 2',4'-dihydroxy- 
B 
3',3'-dimethylbutanamido)-N-propanol-3 
11 N-(tert-butyl)-ureido-N'-3- 
F 
propanediol-(1,2) 
12 N-(tert-butyl)-N'-(2-hydroxyethyl)urea 
F 
13 N-(cyclohexyl)-N'-(2-hydroxyethyl)urea 
F 
14 N-cyclohexyl-N',N'-bis(2-hydroxyethyl)- 
F 
urea 
______________________________________ 
A. Aldrich Chemical Co. Milwaukee WI 53233 
B. Fluka Chemical Corp. Ronkonkoma NY 11779 
C. Pfaltz and Bauer, Waterbury, CT 06708 
D. Eastman Kodak Co., Rochester, NY 14650 
E. Dixon Chemicals, Sherwood Park, Alberta T8C 1G9 Canada 
F. From above procedures. 
TABLE 2 
______________________________________ 
Decap Times 
Decap times were obtained on a Hewlett Packard Deskjet 
printer that had been altered so that the ink cartridge 
would not be vacuum suctioned nor spit into a spittoon. 
The last time interval that the particular drop did not 
fail is recorded. 
1st Drop 32nd Drop 
Sample seconds minutes 
______________________________________ 
Control # 
1 60 1.5 
2 CARCINOGEN 
3 30 1.5 
4 50 1.4 
5 POOR PRINTER 
6 40 1.5 
7 HIGHLY TOXIC 
8 40 0.6 
9 40 1.6 
10 65 3.0 
11 70 2.0 
Example # 
1 115 3.8 
2 75 180-360 
3 85 180-360 
4 75 30-60 
5 70 540-720 
6 70 360-540 
7 70 &gt;720* 
8 55 540-720 
9 50 120-240 
10 45 &gt;900* 
11 55 &gt;720* 
12 50 26 
13 30 5-10 
14 50 960-1080 
______________________________________ 
*Test terminated at indicated time interval without a 32nd drop failure. 
TABLE 3 
______________________________________ 
Dispersion Stability 
Dispersion stability was obtained by subjecting 15 
grams of ink to four temperature cycles, each consisting of 
4 hours at -20.degree. C. and 4 hours at 60.degree. C. Particle sizes 
were measured on a Brookhaven BI-90 (Brookhaven 
Instruments Corp., Holtsville, NY 11742) 
before and after cycling. 
Change in Particle Size, 
Sample delta nanometers 
______________________________________ 
Control # 
1 4 
2 CARCINOGEN 
3 9 
4 -2 
5 POOR PRINTER 276 
6 8 
7 HIGHLY TOXIC 
8 5 
9 12 
10 26 
11 34 
Example # 
1 3 
2 9 
3 13 
4 3 
5 3 
6 10 
7 2 
8 7 
9 5 
10 1 
11 3 
12 2 
13 -1 
14 8 
______________________________________