Ink cartridges having ink compositions with pigmented particles and methods for their manufacture and use

Ink cartridges containing ink compositions containing nanometer scale pigment particles are produced by preparing a pigment solution including a solubilized pigment-Lewis acid complex and an aprotic solvent system, separating the pigment from the pigment solution to form pigmented particles either by precipitating pigment nanoparticles or by dyeing colloidal particles with the solubilized pigment-Lewis acid complex, concentrating the pigmented particles, then dispersing the pigmented particles in a formulating solvent to form an ink composition, and finally introducing the ink composition into an ink cartridge. The ink compositions are particularly suitable for use in ink jet ink cartridges.

FIELD OF THE INVENTION 
This invention is generally directed to ink compositions having ultrafine 
molecularly dispersed pigments, and the preparation and use of such ink 
compositions in ink cartridges. More specifically, the present invention 
is directed to ink cartridges having ink jet ink compositions wherein the 
ink jet ink compositions are prepared by processes wherein pigmented 
particles are provided by Lewis acid pigment solubilization and either 
subsequent precipitation of pigment nanoparticles or subsequent dyeing of 
colloidal particles with pigment from a solubilized pigment/Lewis acid 
complex. 
BACKGROUND 
Ink jet printing is a non-impact method for recording information in 
response to an electronic signal, such as that generated by a computer. In 
the printer, the electronic signal produces droplets of ink that are 
deposited on a substrate such as paper. Ink jet printers have found broad 
commercial acceptance due to their rapid printing speeds, relatively quiet 
operation, graphic capability and low cost. 
The printed image produced by an ink jet printer, as in most printing 
processes, consists of discrete dots of at least one ink composition. Both 
dyes and pigments have been used in ink compositions for ink jet printers. 
While satisfactory for many applications, conventional dye based inks are 
not well-suited for recording high quality images since the dye tends to 
wick in the paper fibers, causing the dots to have a feathered edge. Thus, 
the dots do not have the sharp boundaries needed to produce a high 
resolution image unless special paper is used. Also, the dyes tend to 
smear after the printing operation due to their high water solubility. 
Limitations of dye based inks are particularly apparent when it is desired 
to record a high quality, multi-colored image. Color selection is limited 
in that many of the readily available dyes lack color fastness (i.e., the 
dye tends to fade upon exposure to ultraviolet light) or do not have 
enough solubility to give the desired chroma. Moreover, the tendency of 
the printed dots to wick, or bleed together, is an aggravated problem 
because the printing of a high quality image depends on the formation of 
small, sharply defined dots of each printing color. While some of the 
problems associated with dye based inks may be overcome or alleviated to 
some extent by using special substrates, such as coated paper, there is a 
need for improved inks for ink jet printing. 
Inks compositions comprising pigment dispersions have been suggested in an 
attempt to avoid the foregoing deficiencies of dye based inks. For 
example, U.S. Pat. No. 5,085,698 discloses pigmented aqueous inks for ink 
jet printers, comprising an aqueous carrier medium and particles of 
pigment stabilized by a block copolymer. U.S. Pat. No. 5,106,417 discloses 
ink compositions suitable for drop-on-demand ink jet printing containing 
specified selected amounts of a solid pigment preparation, a water-soluble 
organic solvent, a humectant and water. U.S. Pat. No. 5,160,372 discloses 
an ink for ink jet printers which comprises an aqueous carrier medium, 
pigment dispersion or dye and an amide diol or ester diol cosolvent 
penetrant. U.S. Pat. No. 5,169,436 discloses ink, jet ink compositions 
comprising an aqueous carrier medium, a colorant and a sulfoxide or 
sulfone penetrant. U.S. Pat. No. 5,224,987 discloses ink compositions for 
ink jet printers comprising an aqueous carrier medium, pigment dispersion 
or dye and a selected amide or lactam penetrant. U.S. Pat. No. 5,229,786 
discloses a recording liquid including a pigment, a water-soluble resin, a 
water-soluble organic solvent and water, such that the recording liquid is 
used in an ink-jet recording method. 
It has been found, however, that ink compositions comprising pigment 
particles can have relatively poor storage stability, particularly when 
the pigment particles are relatively large. Large pigment particles are 
also known to cause clogging problems for ink ejecting devices, such as 
ink jet nozzles, of ink cartridges. Moreover, color strength and gloss 
provided by large pigment particles are inferior to those provided by 
small pigment particles. 
Thus, there has been a desire to produce and use in ink cartridges ink 
compositions comprising relatively small pigment particles. Conventional 
means of minimizing the size of pigment particles in inks include 
attrition and/or grinding steps. For example, U.S. Pat. No. 5,085,698 
discloses that a deflocculating (i.e., dispersing) 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. 
According to this patent, pigment particles of 0.005 to 15 microns (5 to 
15,000 nm) can be produced by such conventional methods. Unfortunately, 
such conventional methods of producing small pigment particles require a 
large expenditure of energy. 
Processes of preparing small pigment particles using Lewis acid 
solubilization are disclosed in U.S. Pat. No. 5,405,724, where pigment 
particles are used as photoconductors in a photoreceptor, and in U.S. Pat. 
No. 5,449,582, where pigment particles are prepared for use in fabricating 
solution coated photosensitive pigment layers, and photo- and 
opto-electronic devices. Neither of these patent suggests ink compositions 
formed by either the precipitation of pigmented particles or the dyeing of 
colloidal particles with a solubilized pigment/Lewis acid solution. 
All references cited herein are incorporated herein by reference in their 
entireties. 
SUMMARY OF THE INVENTION 
The invention provides a simple method of efficiently and cost-effectively 
producing ink cartridges, or ink applicators, comprising ink compositions, 
the method comprising solubilizing pigments in a polar aprotic solvent 
through the use of Lewis acids to provide a pigment solution comprising 
solubilized pigment-Lewis acid complexes, mixing the pigment solution with 
a pigment separator to separate the pigment from the solubilized 
pigment/Lewis acid complex in the form of pigmented particles, 
concentrating the pigmented particles, then dispersing the pigmented 
particles to form the ink composition, and finally introducing the ink 
composition into the ink cartridge. Thus, the inventive method provides 
ink cartridges having ink compositions comprising small pigment particles. 
The ink compositions according to the invention have good stability, do not 
clog ink spraying devices and have excellent color properties. 
Furthermore, according to the invention, thermal ink jet and acoustic 
drop-on-demand inks can be prepared. The method of preparing ink 
compositions is substantially more efficient than conventional methods of 
preparing pigment based ink compositions, which have relied on energy and 
time inefficient means of solubilizing pigment particles, such as 
mechanical grinding of pigments. The inventive method does not appear to 
be limited to use with any particular type of pigment, but rather appears 
generally applicable to all color pigments. 
Ink compositions according to the invention can be used with a variety of 
ink applicators, such as ink cartridges, and are particularly adapted for 
use in printing applications involving, for example, ink jet printers. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The pigment solubilization process of the invention solubilizes a pigment 
or mixture of pigments using at least one Lewis acid and at least one 
solvent. The pigment solubilization process of the invention is analogous 
in embodiments to the solubilization of heterocyclic ladder and rigid rod 
polymers by Lewis acids as described, for example, by Jenekhe in U.S. Pat. 
Nos. 4,945,156 and 4,963,616 and by Jenekhe and Johnson in Macromolecules, 
23, 4419 (1990) and references cited therein, particularly references 16 
to 24 of the Macromolecules reference. 
The solubilization processing of pigments in accordance with the invention 
can be comprised of a one or more step process that provides a complexed 
pigment solution comprised of pigment, a Lewis acid, and a polar aprotic 
solvent. In a one-step process, pigment complex formation and 
solubilization take place simultaneously or concurrently. In a two-step 
process, the first step comprises forming a solid pigment-metalloid 
complex resulting from any suitable complexation reaction, and the second 
step comprises solubilization of the solid complex in a suitable organic 
solvent. A related two-step process is described in U.S. Pat. No. 
4,963,616 at column 10, line 4. The resulting solutions obtained from 
either the one-step or two-step solubilization process contain soluble 
pigment complexes. 
Pigment molecules with electron-rich or electron-donating heteroatoms or 
pi-electrons readily coordinate with Lewis acid molecules to form 
pigment-metal complexes that are particularly soluble in polar aprotic 
solvents. Thus, although the invention is generally applicable to all 
pigments, pigments such as quinacridones, phthalocyanines, azo and 
polyazo, squarylium, cyanine pigments, and the like, that are rich in 
pi-electrons or electron donating heteroatoms, for example, nitrogen, 
sulfur, oxygen and other Group VA and Group VIA chemical elements in the 
periodic table, and that are capable of coordinating with certain electron 
acceptors such as Lewis acids, are particularly suitable for use in the 
invention. In particular, suitable pigments according to the invention can 
be selected from the group consisting of metal phtalocyanines, metal-free 
phthalocyanines, oligomeric phthalocyanines, quinacridones, benzimidazole 
perylenes, perylene tetracarboxyl diimides, substituted 
2,4-diamino-triazines, squaraines, polynuclear aromatic quinones, 
thiopyrylium compounds and mixtures thereof. 
Lewis acids generally are electron acceptors which can combine with a donor 
molecule or ion by forming a coordinated chemical bond with two electrons 
from the donor molecule or ion. Other suitable complexing agents include 
nitrosyl salts, NO.sup.+ A.sup.-, where A is BF.sub.4, HSO.sub.4, 
PF.sub.6, SbCl.sub.6, AsF.sub.6, and the like. The Lewis acids or other 
complexing agents selected should preferably be soluble in polar aprotic 
solvents and dissolve, react with or controllably decompose in, protic 
solvents. In particular, suitable Lewis acids according to the invention 
include AlCl.sub.3, GaCl.sub.3, FeCl.sub.3, InCl.sub.3, SnCl.sub.4, 
BF.sub.3, ZnCl.sub.2, TiCl.sub.4, SbCl.sub.3, SbCl.sub.5, CuCl.sub.2, 
SbF.sub.5, VCl.sub.4, TaCl.sub.5, ZrCl.sub.4, AsF.sub.3, and the like, and 
mixtures thereof. The Lewis acid trifluoroacetic acid may also be used. 
Preferably, the Lewis acid is aluminum chloride, AlCl.sub.3. 
An aprotic solvent system can be used for the preparation of the pigment 
complex solution of the invention. The aprotic solvent system can comprise 
a polar aprotic solvent or a mixture of polar aprotic solvents. The use of 
a mixture of about two to about ten solvents can modify the solubilization 
and primary particle size behaviors of the resultant ultrafine pigment 
particles. The aggregation behavior of the solubilized pigment may also be 
influenced by the choice of solvent or solvents used in the solubilization 
process. A suitable polar aprotic solvent, in embodiments of the 
invention, can be selected from the group consisting of nitromethane, 
nitroethane, 1-nitropropane, 1,2-dichloroethane, methylene chloride, 
benzene, toluene, and the like, and mixtures thereof. Additional useful 
solvents are disclosed, for example, in U.S. Pat. No. 4,963,616 at column 
8, line 54. Any amount of solvent is suitable so long as the pigment 
solubilization of the present invention is achieved. In a preferred 
embodiment according to the invention, a polar aprotic solvent system is a 
mixture of at least one organic solvent and at least one nitro organic 
solvent selected from the group consisting of methylene chloride, 
chloroform, trichloroethane, 1,2-dichloroethane, nitroalkanes or 
nitroalkenes having 1 to 6 carbon atoms, benzene and toluene. 
Lewis acid complexed pigment solutions may optionally contain a mixture of 
two to about ten solubilized pigments for the purpose of preparing a 
predispersion of ultrafine particulate sized mixed pigments. The 
predispersion is subsequently formulated into an ink composition according 
to the invention. 
A suitable pigment weight percent in a pigment-complex solution is from 
about 0.005 to about 20 percent, and preferably from about 1 to about 10 
percent. The molar ratio of Lewis acid or Lewis acid molecule mixture to 
pigment molecules is preferably equal to, or greater than, the number of 
electron donating elements present in the pigment molecule. In 
embodiments, the molar ratio of Lewis acid to pigment used in forming 
Lewis acid-pigment complex solutions ranges from about 1:1 to about 20:1. 
Following preparation of a pigment solution comprising a solubilized 
pigment-Lewis acid complex and a polar aprotic solvent, the pigment 
solution is mixed with a pigment separator to separate the pigment from 
the pigment/Lewis acid complex. In embodiments, the pigment separator is a 
precipitating solution, and the step of mixing the precipitating solution 
and the pigment solution forms a heterogeneous mixture comprising 
precipitated pigment particles and polar aprotic solvent containing 
dissolved Lewis acids. The solubilized pigment complex can be precipitated 
directly and rapidly into a precipitating solution comprising a protic 
solvent such as water, or a non-aqueous solvent with the agency of 
external cooling to control exothermicity which is not the situation in 
conventional acid pasting processing. 
In embodiments, the ultrafine pigmented particles are precipitated from 
solution by the controlled addition of a precipitating solution comprising 
a protic solvent. The protic solvent can be a non-solvent or diluent for 
the aprotic organic solvent used to dissolve the Lewis acid pigment 
complex. The precipitating solution can contain water, methanol, ethanol, 
isopropanol, acetic acid and mixtures thereof, in admixture with, for 
example, formamide, acetone, acetonitrile, dimethyl formamide, N-methyl-2 
pyrrolidone and mixtures thereof. Preferably, the precipitating solution 
can contain protic solvents such as water or methanol, or a mixture 
thereof. 
In embodiments, the precipitating solution can contain pigment dispersants. 
Preferably, the dispersant is a polymeric dispersant. In addition to, or 
in place of, a polymeric dispersant, surfactant compounds may be used as 
dispersants. These may be anionic, cationic, nonionic or amphoteric. A 
detailed list of non-polymeric as well as some polymer 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. 
A random sampling and X-ray diffraction analysis of molecularly dispersed 
pigments prepared by the method of the present invention indicated that no 
particulate or crystalline bodies greater than about 5 to about 10 nm were 
detectable. In embodiments, the average primary particle size of the 
ultrafine pigmented particles was less than about 3 nm to about 5 nm as 
measured by X-ray diffraction, these particle sizes being smaller than by 
about two times the sizes obtained by conventional pigmented particle 
preparation methodologies. The precipitated pigmented particles range in 
size from about 2 nm to about 10 nm. Preferably, the precipitated 
pigmented particles range in size from about 2 nm to about 5 nm. 
In other embodiments of the invention, the step of mixing a pigment 
separator with the pigment solution uses colloidal particles as the 
pigment separator. The colloidal particles are mixed with the pigment 
solution and dyed with the pigment from the solubilized pigment/Lewis acid 
complex in the pigment solution. The step of dyeing the colloidal 
particles in the pigment solution results in a heterogeneous mixture 
comprising pigmented particles. The colloidal particles serve as carriers 
or supports for the pigment nanoparticles which result from the colloidal 
particle dyeing process. 
In the practice of the invention, it important that the colloidal particles 
possess pores of sufficient size to permit penetration by the pigment 
solution during the colloidal particle dyeing process. In embodiments, 
swelling of the colloidal particles during immersion in, for example, 
pigment solution, produces pores of sufficient size to practice the 
invention. 
Both organic and inorganic colloidal particles can be used in embodiments 
as the carrier particles for the molecular pigment. The particles should 
be white or light in color or transparent. In addition, the preferred 
colloidal particles are not soluble in the pigment solution containing the 
solubilized pigment/Lewis acid complex and aprotic solvent. Organic 
colloidal particles can be selected from latex particles of polystyrene, 
polyacrylates, polyvinyl acetate, polymethacrylates and the corresponding 
copolymers and crosslinked polymers. The surface group of the organic 
colloidal particles can be sulfates, carboxylates or hydroxy groups. 
Inorganic particles can be selected from metal oxides such as silica, 
alumina, tin oxide, and titanium oxide. Inorganic particles can also be 
selected from cadmium selenide and cadmium sulfide. Inorganic particles 
can also be silica-cadmium sulfide particles, such as those disclosed in 
J. Am. Chem. Soc., 1994, 116, 6739-6744. This article is incorporated 
herein by reference. 
The colloidal particles have a particle size of between about 50 nanometers 
and about 5.0 microns. Preferably, the colloidal particles have a particle 
size of between about 100 nanometers and about 1.0 micron. 
Following the mixing of a pigment separator with the pigment solution to 
form a heterogeneous mixture comprising pigmented particles, the pigmented 
particles are concentrated to form a concentration of pigmented particles. 
In embodiments, the step of concentrating the pigmented particles involves 
first dialyzing the heterogeneous mixture containing pigmented particles 
to separate and concentrate the pigmented particles. Preferably, the 
separated pigmented particles are essentially free of the Lewis acid. 
Lewis acid can be removed from the concentration of separated pigmented 
particles by washing with protic solvents as described below. The 
separated pigmented particles are then dispersed by dilution with at least 
one formulating solvent to form an ink composition. 
In other embodiments, the step of concentrating the pigmented particles 
involves first isolating the pigmented particles in a concentration of 
pigmented particles known as a "pigmented wet cake" (alternatively, "water 
wet presscake"). The pigmented particle isolation is accomplished by 
separating solvent from the pigmented particles of the heterogeneous 
mixture by means such as centrifugation, filtration, sedimentation or 
evaporation. In wet cake form, the pigmented particles are not aggregated 
to the extent that they are in dry form. Thus, pigmented particles in wet 
cake form do not require as much deaggregation in the process of preparing 
ink as do pigmented particles in dry form. A pigment wet cake has a very 
long shelf life as long as it is kept wet. 
According to the invention, preferably the concentration of pigmented 
particles in the pigmented wet cake and in the dialyzed concentration of 
pigmented particles, described above, is essentially free of Lewis acids. 
Lewis acids can be removed from the pigmented wet cake by washing the 
pigmented wet cake with the protic solvents that can comprise the 
precipitating solution. These protic solvents effectively neutralize the 
Lewis acid, by decomposing, dissolving and subsequently selectively 
removing substantial amounts of the Lewis acid component from the 
pigmented particles. Extensive washing of pigmented wet cake, made 
according to the present invention, resulted in pigmented wet cake in 
which only trace amounts of Lewis acid species were measurable by energy 
dispersive X-ray analysis and related spectroscopic means. When the 
pigmented wet cake is not washed and neutralized prior to being dispersed 
in aqueous and organic solvents to form ink compositions, the level of 
residual Lewis acid species or ions in the ink formulations is 
considerably higher. 
To form an ink composition, the concentration of pigmented particles in the 
pigmented wet cake are dispersed in a formulating solvent. A pigmented wet 
cake prepared according to the invention can be flushed into any liquid 
solvent to form "instant" fine pigment dispersions and ink compositions. 
In general, the formulating solvent according to the present invention can 
be any organic based liquid media or solvent, or any aqueous based liquid 
media or solvent, which does not hinder the dispersion of pigment 
particles mixed in it. In embodiments, the formulating solvent can be 
water, ethylene glycol, and mixtures thereof. In preferred embodiments, 
the formulating solvent contains at least one pigment dispersant. 
In embodiments of the invention, surfactants can be added to the 
formulating solvent. Surfactants can alter surface tension as well as 
maximize penetration. Surfactants that improve the stability of the ink 
compositions of the present invention can be non-ionic, cationic, anionic 
or amphoteric surfactants. Nonionic surfactants include those polyethylene 
oxide compounds and polymers and polypropylene oxide compounds and 
polymers, such as polyethylene 400 distearate and copolymers of 
polyethylene oxide and polypropylene oxide. Examples of cationic 
surfactants include stearyl ammonium chloride and cetyltrimetylammonium 
bromide. Examples of anionic surfactant include sodium stearate and sodium 
lauryl sulfate. Examples of amphoteric surfactants include oleyl 
amino-oleate and Miranol CM. Additional surfactants are disclosed in 
"Surfactant Science Series", M. J. Schick and F. M. Fowkes, editors, 
volumes 1-25, published by Marcel Dekker, Inc., of New York, the contents 
of which are incorporated herein by reference. 
The ink compositions prepared according to the invention may contain 
various known additives, including biocides to inhibit the growth of 
microorganisms, and sequestering agents such as EDTA to eliminate 
deleterious effects of heavy metal impurities. Other known additives, such 
as humectants, viscosity modifiers and other acrylic or non-acrylic 
polymers may also be added to improve various properties of the ink 
compositions. 
After dispersing the concentration of pigmented particles in a formulating 
solvent to form an ink composition, the ink composition is introduced into 
an ink cartridge or applicator to complete a method of manufacture of an 
ink cartridge according to the invention. The ink cartridge or applicator 
comprises a reservoir to contain the ink composition, and a means for 
removing the ink composition during a printing process. The means for 
removing the ink composition can be an ink ejecting or spraying device, 
such as an ink jet nozzle. 
Another method of manufacture of an ink cartridge according to the 
invention comprises introducing the ink composition of the invention into 
an applicator such as the ink supply system of U.S. Pat. No. 5,420,625. 
This reference is incorporated herein in its entirety. 
According to the invention, an ink cartridge is provided. The ink cartridge 
is manufactured according to the methods described above. 
According to the invention, a method of printing is provided. In the method 
of printing, the ink cartridge of the invention is used to print. In 
embodiments, the method of printing involves ejecting or spraying an ink 
composition comprising pigmented particles from the ink cartridge. In 
preferred embodiments, the method of printing is carried out using ink jet 
printers.

EXAMPLES 
The invention will be illustrated in more detail with reference to the 
following Examples, but it should be understood that the present invention 
is not deemed to be limited thereto. 
Example 1 
Solubilized pigment/aluminum chloride complex solutions are prepared by 
stirring a mixture of a pigment, aluminum chloride (AlCl.sub.3) and 
nitromethane or a mixed solvent of nitromethane or methylene chloride. The 
solutions are capped in 20 ml vials in a glove box under nitrogen 
atmosphere for 12 to 16 hours at room temperature. A set of pigment 
solutions with certain compositions is summarized in Table 1. The molar 
ratio of the pigment to AlCl.sub.3 is 1:6 in all situations. These 
solutions have about 2 weight percent of pigment and are easily passed 
through 0.45 micrometer filters. 
TABLE 1 
______________________________________ 
pigments & 
reagents soln. 1 soln. 2 soln. 3 
soln. 4 
soln. 5 
soln. 6 
______________________________________ 
TiOPc 0.26 -- -- -- -- -- 
VOPc -- 0.26 -- -- -- -- 
PV Fast Blue 
-- -- 0.29 -- -- -- 
(grams) 
Permanent 
-- -- -- 0.30 -- -- 
Yellow 
(grams) 
Hostaperm 
-- -- -- -- 0.17 -- 
Pink E 
(grams) 
benzimidazole 
-- -- -- -- -- 0.26 
perylene 
(grams) 
AlCl.sub.3 (grams) 
0.39 0.39 0.39 0.39 0.39 0.39 
nitromethane 
8 8 10 10 10 8 
(mL) 
methylene 
2 2 -- -- -- 2 
chloride 
(mL) 
______________________________________ 
Example 2 
Solution 5 of Table 1 is poured into a homogenizing (8000 rpm) aqueous 
surfactant solution (40 ml) comprising 2 wt % polyethylene glycol (MW 
10,000-25,000). Homogenization is continued for 1 minute. The resulting 
mixture is centrifuged at 5000 rpm for 15 minutes. The aqueous layer is 
decanted to give a pigment wet cake. To this is added ethylene glycol to 
give an ink with a total weight of 5 grams. 
Example 3 
Solution 5 of Table 1 is poured into a homogenizing (8000 rpm) aqueous 
surfactant solution (40 ml) comprising 2 wt % polyethylene glycol (MW 
10,000-25,000). Homogenization is continued for 1 minute. The resulting 
mixture is centrifuged at 5000 rpm for 15 minutes. The aqueous layer is 
decanted to give a pigment wet cake. To this is added ethylene 
glycol/ethanol (70/30 wt ratio) to give an ink with total weight of 5 
grams. 
Example 4 
The following procedure is performed under nitrogen atmosphere. Into 
solution 4 of Table 1 is added dried titanium oxide particles (1 gram) in 
nitromethane (5 ml). The resulting mixture is stirred at room temperature 
for 8 hours and then centrifuged. The solution is decanted and 
nitromethane (10 ml) is added. The resulting mixture is stirred for 2 
hours and then centrifuged. The solution is decanted to give a wet cake of 
colored titanium dioxide. To this is added ethylene glycol to give an ink 
with a total weight of 8 grams. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.