Ink jet printing ink composition with detectable label material

An ink jet printing ink composition is disclosed for use with an ink jet printing apparatus comprising a printhead, an ink delivery system adapted to provide the ink to the printhead, and a sensor associated with the ink delivery system adapted to produce a signal which is characteristic of the concentration of a label material in a printing ink, where said signal is used to indicate the appropriateness of using a particular printing ink. The ink composition comprises a carrier, a colorant, and a predetermined concentration of a distinct label material, the weight ratio of the label material to the colorant being less than 1. The label material may be easily detected by a sensor associated with the ink delivery system.

CROSS REFERENCE TO RELATED APPLICATIONS 
Reference is made to commonly assigned U.S. patent application Ser. No. 
08/846,923 INK DELIVERY SYSTEM AND PROCESS FOR INK JET PRINTING APATUS 
filed in the name of Xin Wen concurrently herewith. 
FIELD OF THE INVENTION 
This invention relates generally to the field of digitally controlled ink 
transfer printing systems, and more particularly to ink jet printing ink 
compositions. 
BACKGROUND OF THE INVENTION 
Ink jet printing has become recognized as a prominent contender in the 
digitally controlled, electronic printing arena because, e.g., of its 
non-impact, low-noise characteristics, its use of plain paper and its 
avoidance of toner transfers and fixing. Ink jet printing mechanisms can 
be categorized as either continuous ink jet or drop-on-demand ink jet. 
U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a 
drop-on-demand ink jet printer which applies a high voltage to a 
piezoelectric crystal, causing the crystal to bend, applying pressure on 
an ink reservoir and jetting drops on demand. Other types of piezoelectric 
drop-on-demand printers utilize piezoelectric crystals in push mode, shear 
mode, and squeeze mode. Piezoelectric drop-on-demand printers have 
achieved commercial success at image resolutions up to 720 dpi for home 
and office printers. 
Great Britain Patent No. 2,007,162, which issued to Endo et al. in 1979, 
discloses an electrothermal drop-on-demand ink jet printer which applies a 
power pulse to an electrothermal heater which is in thermal contact with 
water based ink in a nozzle. A small quantity of ink rapidly evaporates, 
forming a bubble which cause drops of ink to be ejected from small 
apertures along the edge of the heater substrate. This technology is known 
as Bubblejet.TM. (trademark of Canon K.K. of Japan). 
U.S. Pat. No. 4,490,728, which issued to Vaught et al. in 1982, discloses 
an electrothermal drop ejection system which also operates by bubble 
formation to eject drops in a direction normal to the plane of the heater 
substrate. As used herein, the term "thermal ink jet" is used to refer to 
both this system and system commonly known as Bubblejet.TM.. 
Thermal ink jet printing typically requires a heater energy of 
approximately 20 .mu.J over a period of approximately 2 .mu.sec to heat 
the ink to a temperature between 280.degree. C. and 400.degree. C. to 
cause rapid, homogeneous formation of a bubble. The rapid bubble formation 
provides the momentum for drop ejection. The collapse of the bubble causes 
a tremendous pressure pulse on the thin film heater materials due to the 
implosion of the bubble. 
U.S. Pat. No. 4,275,290, which issued to Cielo et al., discloses a liquid 
ink printing system in which ink is supplied to a reservoir at a 
predetermined pressure and retained in orifices by surface tension until 
the surface tension is reduced by heat from an electrically energized 
resistive heater, which causes ink to issue from the orifice and to 
thereby contact a paper receiver. This system requires that the ink be 
designed so as to exhibit a change, preferably large, in surface tension 
with temperature. The paper receiver must also be in close proximity to 
the orifice in order to separate the drop from the orifice. 
U.S. Pat. No. 4,166,277, which also issued to Cielo et al., discloses a 
related liquid ink printing system in which ink is supplied to a reservoir 
at a predetermined pressure and retained in orifices by surface tension. 
The surface tension is overcome by the electrostatic force produced by a 
voltage applied to one or more electrodes which lie in an array above the 
ink orifices, causing ink to be ejected from selected orifices and to 
contact a paper receiver. The extent of ejection is claimed to be very 
small in the above Cielo patents, as opposed to an "ink jet", contact with 
the paper being the primary means of printing an ink drop. 
In U.S. Pat. No. 4,751,531, which issued to Saito, a heater is located 
below the meniscus of ink contained between two opposing walls. The heater 
causes, in conjunction with an electrostatic field applied by an electrode 
located near the heater, the ejection of an ink drop. There are a 
plurality of heater/electrode pairs, but there is no orifice array. The 
force on the ink causing drop ejection is produced by the electric field, 
but this force is alone insufficient to cause drop ejection. That is, the 
heat from the heater is also required to reduce either the viscous drag 
and/or the surface tension of the ink in the vicinity of the heater before 
the electric field force is sufficient to cause drop ejection. The use of 
an electrostatic force alone requires high voltages. 
Commonly assigned U.S. patent application Ser. No. 08/750,438 entitled A 
LIQUID INK PRINTING APATUS AND SYSTEM filed in the name of Kia 
Silverbrook on Dec. 3, 1996, discloses a liquid printing system that 
affords significant improvements toward overcoming prior art problems 
associated with drop size and placement accuracy, attainable printing 
speeds, power usage, durability, thermal stresses, other printer 
performance characteristics, manufacturability, and characteristics of 
useful inks. Silverbrook provides a drop-on-demand printing mechanism 
wherein the means of selecting drops to be printed produces a difference 
in position between selected drops and drops which are not selected, but 
which is insufficient to cause the ink drops to overcome the ink surface 
tension and separate from the body of ink, and wherein an additional means 
is provided to cause separation of said selected drops from said body of 
ink. Several drop separation techniques are disclosed by Silverbrook to 
ensure that the selected drops form dots on the printing medium. The drop 
separation means discriminates between selected drops and un-selected 
drops to ensure that unselected drops do not form dots on the printing 
medium. 
Ink jet printers as described above can comprise several systems: print 
heads that can utilize one of the above described printing methods, ink 
delivery system that supply ink to the printhead, printhead transport 
systems that transport the printhead across the page, receiver transport 
systems that move receiver medium across the printhead for printing, image 
data process and transfer systems that provide digital signals to the 
printhead, printhead service stations that cleans the printhead, and the 
mechanical encasements and frames that support all the above systems. 
The ink delivery system in an ink jet printer may exist in several forms. 
In most page-size ink jet printers, the ink usage is relatively low. The 
ink is stored in a small cartridge that is attached to, or built in one 
unit with, the printhead. Examples of the ink cartridges are disclosed in 
U.S. Pat. Nos. 5,541,632 and 5,557,310. In large format ink jet printers, 
the ink usage per print is usually high. Auxiliary ink reservoirs are 
required to store large volumes of ink fluid that are connected to the ink 
cartridges near the print heads. Examples of auxiliary ink reservoirs are 
disclosed in European Patents EP 0 745 481 A2 and EP 0 745 482 A2. The 
level of the ink residual quantity in a reservoir may be monitored either 
electrically or optically. U.S. Pat. No. 5,250,957, for example, discloses 
an ink detector that senses ink by measuring the electric resistance in 
the ink. 
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. The use of a particular ink desirably results in physical 
properties compatible with the specific range of ejecting conditions 
associated with a particular printing device, i.e., driving voltages and 
pulse widths for thermal ink jet printing devices, driving frequencies of 
the piezo element for either a drop-on-demand device or a continuous 
device, and the shape and size of the nozzle. 
One problem associated with ink jet printing lies in the variabilities in 
the physical properties and the chemical compositions of various 
commercial ink jet inks. As discussed above, the various types of ink jet 
printers require use of inks which possess distinct critical physical 
properties in order to function effectively during printing. Also, for 
color printing, combinations of inks comprising specific cyan, magenta and 
yellow colorants are generally required to provide accurate, visibly 
pleasing reproductions of the overall color gamut. Mismatching the wrong 
types of inks to a printer and receiver medium can compromise the ideal 
performance of the ink jet printers. For example, print density and color 
balance can be adversely affected by variations in the physical properties 
or chemical composition of the ink. These adverse effects can occur within 
a print, between prints of a given printer, and/or between prints from 
different printers. Print failures such as in-jet nozzle plugging can also 
occur as a result of the above described variabilities. Verification of 
the use of the desired type of ink jet ink with a particular ink jet 
printer is complicated by the fact that almost all ink jet inks comprise 
visually similar cyan, magenta, yellow or black formulations, which are 
not easily distinguishable prior to use. 
DISCLOSURE OF THE INVENTION 
It is an object of the present invention to overcome to the previously 
described difficulties. 
It is another object of the present invention to provide printing inks 
which easily allow for monitoring ink colorant concentrations for reducing 
variabilities in color gamut and print densities. 
It is another object of the present invention to provide printing inks 
which easily allow for detecting ink type during ink refillinging 
processes and before printing operations so that the ink matches the 
printer and the receiver media for achieving the best print image 
qualities and printer performance. 
In accordance with one embodiment of the present invention, an ink jet 
printing ink composition is disclosed for use with an ink jet printing 
apparatus comprising a printhead, an ink delivery system adapted to 
provide the ink to the printhead, and a sensor associated with the ink 
delivery system adapted to produce a signal which is characteristic of the 
concentration of a label material in a printing ink, where said signal is 
used to indicate the appropriateness of using a particular printing ink. 
The ink composition comprises a carrier, a colorant, and a predetermined 
concentration of a label material, the weight ratio of the label material 
to the colorant being less than 1. The label material may be easily 
detected by a sensor associated with the ink delivery system. 
According to various preferred embodiments of the present invention, the 
label material may comprise a static or electromagnetic field generating 
material, a magnetizable material, a fluorescent photon emitting material, 
a material which substantially changes the dielectric properties of the 
ink composition, or a material which absorbs in the ultraviolet, visible, 
or infrared regions of the electromagnetic spectrum which exhibits 
absorption characteristics distinct from those of the colorants used in 
the inks. 
The invention, and its objects and advantages, will become more apparent in 
the detailed description of the preferred embodiments presented below.

DETAILED DESCRIPTION OF THE INVENTION 
The present description will be directed in part to elements forming part 
of, or cooperating more directly with, apparatus which may be used with 
ink compositions in accordance with the present invention. It is to be 
understood that elements not specifically shown or described may take 
various forms well known to those skilled in the art. 
Ink compositions in accordance with the present invention may be used with 
printers which comprise an ink delivery system which includes an ink 
reservoir and an ink flow channel between the ink reservoir and the 
printhead. The sensor in such ink delivery system may be positioned to 
sense the concentration of the label material in the ink in the flow 
channel or in the ink reservoir. 
Ink compositions in accordance with the present invention may be used in a 
process for ink refilling comprising the steps of detecting the presence 
of a label material in ink and rejecting inks that do not contain the 
label material or least a predetermined concentration of the label 
material, or that do not contain the label material within a predetermined 
concentration range. 
Details of the work flow algorithms for the ink refilling process and the 
printing preparation process which may be used with ink compositions in 
accordance with the present invention are disclosed in commonly assigned 
and concurrently filed U.S. patent application Ser. No. 08/846,923, now 
abandoned, cross-referenced above, the disclosure of which is incorporated 
by reference herein in its entirety. 
FIGURE 1 illustrates a preferred embodiment of an ink delivery system 
comprising a label material sensor which may be used with ink compositions 
in accordance with preferred embodiments of the present invention. 
Microcontroller 24 is connected to a computer 72, a Read Only Memory (ROM) 
74 a Random Access Memory (RAM) 76, and ink pressure regulator 26 that 
regulates the ink pressure in ink reservoirs 28. Microcontroller 24 is 
also connected to four ink sensors 78-81 that detect predetermined 
characteristics of the inks in the ink reservoirs 82-85, respectively. 
Microcontroller 24 is also connected to four ink sensors 86-89 that detect 
characteristics of the inks in ink connection tubes 90-93. Microcontroller 
24 is further connected to the holder of the ink cartridge (not shown) for 
detecting the presence of the ink cartridge. The ink jet printer can 
utilize multiple print heads 94-97, with each printhead connected to one 
ink reservoir. The ink types include black, yellow, magenta, and cyan 
colors and can also include several inks within each color. For example, 
labels "magenta1" and "magenta2" in FIGURE 1 can represent magenta inks at 
different colorant concentrations. 
Sensors 78-81 and 86-89 are designed to be used in combination with inks in 
accordance with the invention, so as to be able to detect the existence 
and the concentration of a label material in the ink. The term "label 
material" refers herein to an ink ingredient that is added to the ink and 
is detectable by sensors 78-81 and 86-89 in the ink delivery system, which 
sensors produce a signal which is characteristic of the concentration of 
the label material in the ink. The concentration of the label material is 
predetermined by the ink manufacturer, and is used as a signature for the 
ink being used. The ratio of the label concentration to the concentration 
of the colorant is held as constant in the ink The label material 
preferably is not required to perform any other functions in the printhead 
or on the receiver media. In other words, the ink can preferably print 
images with desired qualities in the absence of the label materials. Use 
of inks in accordance with the invention comprising distinct label 
materials allow for easily detecting ink type during ink refillinging 
processes and before printing operations to assure that the ink matches 
the printer and the receiver media for achieving the best print image 
qualities and printer performance, as well as monitoring ink colorant 
concentrations for reducing variabilities in color gamut and print 
densities. 
Printing ink compositions in accordance with the invention comprise a 
carrier, a colorant and a label material. The present invention is 
generally applicable to many kinds of inks: pigmented inks, dye based 
inks, inks formed in aqueous solutions or organic solvents. Properties and 
examples of pigmented and dye inks can be found in "Dye Versus Pigment: 
The Truth" by P. Gregory, p276 "Recent Progress in Ink Jet Technologies", 
published by Society for Imaging Science and Technology. 
The inks of the present invention may be used in black only, or in color 
printers, such as three- or four-color ink jet printers, e.g., printers 
which contain print cartridges capable of printing cyan, magenta, and 
yellow (CMY three-color printers), or cyan, magenta, yellow, and black 
(CMYK four-color printers). Suitable cyan, magenta, yellow and black 
pigments for use as ink colorants are disclosed, e.g., in copending, 
commonly assigned U.S. Ser. No. 08/699,877 of Sanfilli et al. A useful 
3-color ink set comprises pigment red 122, pigment yellow 74, and 
bis(phthalocyanylalumino)tetraphenyldisiloxane. A useful 4-color pigmented 
ink set comprises pigment black 7, pigment red 122, pigment yellow 74, and 
bis(phthalocyanylalumino)tetraphenyldisiloxane. Inks may also be made from 
suitable dye compounds colorants as is well known in the art, such as 
described, e.g., in U.S. Pat. Nos. 4,239,544, 4,269,627, and 5,565,022. 
The process of preparing inks from pigment colorants commonly involves two 
steps: (a) a dispersing or milling step to break up the pigment to the 
primary particle, and (b) dilution step in which the dispersed pigment 
concentrate is diluted with a carrier and other addenda to a working 
strength ink. In the milling step, the pigment is usually suspended in a 
carrier (typically the same carrier as that in the finished ink) along 
with rigid, inert milling media. Mechanical energy is supplied to this 
pigment dispersion, and the collisions between the milling media and the 
pigment cause the pigment to deaggregate into its primary particles. A 
dispersant or stabilizer, or both, is commonly added to the pigment 
dispersion to facilitate the deaggregation of the raw pigment, to maintain 
colloidal particle stability, and to retard particle reagglomeration and 
settling. 
There are many different types of materials which may be used as milling 
media, such as glasses, ceramics, metals, and plastics. In a useful 
embodiment, the grinding media can comprise particles, preferably 
substantially spherical in shape, e.g., beads, consisting essentially of a 
polymeric resin. 
In general, polymeric resins suitable for use as milling media are 
chemically and physically inert, substantially free of metals, solvent and 
monomers, and of sufficient hardness and friability to enable them to 
avoid being chipped or crushed during milling. Suitable polymeric resins 
include crosslinked polystyrenes, such as polystyrene crosslinked with 
divinylbenzene, styrene copolymers, polyacrylates such as poly(methyl 
methylacrylate), polycarbonates, polyacetals, such as DELRIN.TM., vinyl 
chloride polymers and copolymers, polyurethanes, polyamides, 
poly(tetrafluoroethylenes), e.g., TEFLON.TM., and other fluoropolymers, 
high density polyethylenes, polypropylenes, cellulose ethers and esters 
such as cellulose acetate, poly(hydroxyethylmethacrylate), 
poly(hydroxyethyl acrylate), silicone containing polymers such as 
polysiloxanes and the like. The polymer can be biodegradable. Exemplary 
biodegradable polymers include poly(lactides), poly(glycolids) copolymers 
of lactides and glycolide, polyanhydrides, poly(imino carbonates), 
poly(N-acylhydroxyproline) esters, poly(N-palmitoyl hydroxyprolino) 
esters, ethylene-vinyl acetate copolymers, poly(orthoesters), 
poly(caprolactones), and poly(phosphazenes). The polymeric resin can have 
a density from 0.9 to 3.0 g/cm.sup.3. Higher density resins are especially 
useful inasmuch as it is believed that these provide more efficient 
particle size reduction. Especially useful are crosslinked or 
uncrosslinked polymeric media based on styrene. 
Milling can take place in any suitable grinding mill. Suitable mills 
include an airjet mill, a roller mill, a ball mill, an attritor mill and a 
bead mill. A high speed mill is particularly useful. 
By high speed mill we mean milling devices capable of accelerating milling 
media to velocities greater than about 5 meters per second. The mill can 
contain a rotating shaft with one or more impellers. In such a mill the 
velocity imparted to the media is approximately equal to the peripheral 
velocity of the impeller, which is the product of the impeller revolutions 
per minute, .pi., and the impeller diameter. Sufficient milling media 
velocity is achieved, for example, in Cowles-type saw tooth impeller 
having a diameter of 40 mm when operated at 9,000 rpm. Useful proportions 
of the milling media, the pigment, the liquid dispersion medium and 
dispersant can vary within wide limits and depends, for example, upon the 
particular material selected and the size and density of the milling media 
etc. The process can be carried out in a continuous or batch mode. 
In an exemplary batch milling process, a slurry of &lt;100 .mu.m milling 
media, liquid, pigment and dispersant is prepared using simple mixing. 
This slurry may be milled in conventional high energy batch milling 
processes such as high speed attritor mills, vibratory mills, ball mills, 
etc. This slurry is milled for a predetermined length of time to allow 
comminution of the active material to a minimum particle size. After 
milling is complete, the dispersion of active material is separated from 
the grinding media by a simple sieving or filtration. 
In an exemplary continuous media recirculating milling process, a slurry of 
&lt;100 .mu.m milling media, liquid, pigment and dispersant may be 
continuously recirculated from a holding vessel through a conventional 
media mill which has a media separator screen adjusted to &gt;100 .mu.m to 
allow free passage of the media throughout the circuit. After milling is 
complete, the dispersion of active material is separated from the grinding 
media by simple sieving or filtration. 
With either of the above modes the useful amounts and ratios of the 
ingredients of the mill grind will vary widely depending upon the specific 
materials and the intended applications. The contents of the milling 
mixture comprise the mill grind and the milling media. The mill grind 
comprises pigment, dispersant and a liquid carrier such as water. For 
aqueous ink jet inks, the pigment is usually present in the mill grind at 
1 to 50 weight %, excluding the milling media. The weight ratio of pigment 
to dispersant is 20:1 to 1:2. The high speed mill is a high agitation 
device, such as those manufactured by Morehouse-Cowles, Hockmeyer et al. 
The dispersant is another important ingredient in the mill grind. Useful 
dispersants for aqueous ink jet inks include sodium dodecyl sulfate, 
acrylic and styrene-acrylic copolymers, such as those disclosed in U.S. 
Pat. Nos. 5,085,698 and 5,172,133, and sulfonated polyesters and 
styrenics, such as those disclosed in U.S. Pat. No. 4,597,794. Other 
patents referred to above in connection with pigment availability also 
disclose a wide variety of useful dispersants. The dispersant used in the 
examples is sodium N-methyl-N-oleoyl taurate (OMT). 
The milling time can vary widely and depends upon the pigment, mechanical 
means and residence conditions selected, the initial and desired final 
particle size, etc. For aqueous mill grinds using the useful pigments, 
dispersants, and milling media described above, milling times will 
typically range from 1 to 100 hours. The milled pigment concentrate is 
preferably separated from the milling media by filtration. 
The carrier medium of the printing ink compositions of the invention may be 
either an aqueous or organic solvent based solution, and preferably 
comprises water or a mixture of water and at least one water miscible 
co-solvent. Selection of a suitable mixture depends on requirements of the 
specific application, such as desired surface tension and viscosity, the 
selected pigment or dye colorant, drying time of the ink jet ink, and the 
type of paper onto which the ink will be printed. Representative examples 
of water-miscible co-solvents that may be selected include (1) alcohols, 
such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl 
alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl 
alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones or 
ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; 
(3) ethers, such as tetrahydrofuran and dioxane; (4) esters, 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 
thioglycol; (6) lower alkyl mono- or di-ethers derived from alkylene 
glycols, such as ethylene glycol mono-methyl (or -ethyl) ether, diethylene 
glycol mono-methyl (or -ethyl) ether, propylene glycol mono-methyl (or 
-ethyl) ether, triethylene glycol mono-methyl (or -ethyl) ether and 
diethylene glycol dimethyl (or -ethyl) 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. 
The label material of the ink compositions of the invention can be any 
material which can be easily detected in a printing ink by a respective 
sensor. In one example, the label material can comprise dielectric 
properties that are different from those of the inks. The change in the 
dielectric properties in the ink comprising this label material can be 
detected by a sensor which generates an electromagnetic field. In another 
example, the label material absorbs in the ultraviolet, visible, or 
infrared wavelengths with absorption characteristics distinctly different 
from that provided by the main colorant in the inks. The presence and 
concentration of these label materials can be detected by measuring the 
absorption spectrum of the label materials. In yet another example, the 
label material can emit fluorescent photons at specific wavelengths when 
the label material is illuminated by the certain photons. The detection of 
these fluorescent photons with an appropriate sensor again can be used for 
sensing the label material in the ink. In preferred embodiments of the 
invention, the label material comprises a static or electromagnetic field 
generating material (e.g., ferromagnetic materials such as .gamma.-ferric 
oxides, cobalt-.gamma.-ferric oxides, magnetite, cobalt-magnetite, barrium 
ferrite, strontium ferrite, or other magnetic metal alloys) or a 
magnetizable material (e.g., a paramagnetic material). While printing inks 
have been previously proposed which may comprise substantial levels of 
components such as infrared absorbing or magnetic materials (which types 
of materials may function as label materials in accordance with the 
invention) in order to provide a printed image with corresponding 
properties, the instant invention is distinguished in that the label 
material is used at a relatively low concentration relative to the ink 
colorant, as it is not required to provide a function in the resulting 
printed image. 
Label materials in inks in accordance with the invention are desirably 
easily detectable with conventional sensors and capable of providing 
distinct signals unique to a particular printing ink composition. Various 
magnetic sensors, e.g., can be used to detect the presence and 
concentration of magnetic label material in inks in accordance with 
preferred embodiments of the invention. For example, sensors are known 
wherein an internal resistance changes as a function of the magnetic field 
strength experienced by the sensor. This is an indication of the 
concentration of magnetic label material in the ink. The resistance of the 
magnetic sensors varies as a function of the magnetic field strength. 
Details of the detection circuits for the magnetic resistance sensors are 
disclosed in U.S. Pat. Nos. 4,845,456 and 5,483,162. One type of magnetic 
resistance sensors is the thin-film magnetoresistance sensor. This type of 
sensor is described in U.S. Pat. Nos. 5,225,951, 5274,520 and 5,351,158. 
Hall-effect magnetic sensors, as disclosed in U.S. Pat. No. 4,931,719, can 
also be used for the purpose of the present invention. 
In general it is desirable to make a pigmented ink jet ink in the form of a 
concentrated mill grind, which is subsequently diluted to the appropriate 
concentration for use in the ink jet printing system. This technique 
permits preparation of a greater quantity of pigmented ink from the 
equipment. If the mill grind was made in a solvent, it is diluted with 
water and optionally other solvents to the appropriate concentration. If 
it was made in water, it is diluted with either additional water or water 
miscible solvents to the desired concentration. By dilution, the ink is 
adjusted to the desired viscosity, color, hue, saturation density, and 
print area coverage for the particular application. 
Colorants may typically be used in ink jet printing ink compositions at 
concentrations up to approximately 30% by weight, but will generally be in 
the range of approximately 0.1 to 10% (more commonly 1-5%) for dyes and 
approximately 0.1 to 15% (more commonly 1-10%) for organic pigments, 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 colorant than with comparable inks 
employing organic pigments or dyes, and may be as high as approximately 
75% in come cases. 
The concentration of label material in the ink compositions of the 
invention is less than that of the colorant. In order to minimize any 
effect of the label material on the resulting color and physical 
performance characteristics of the printing ink, weight ratios of label 
material to colorant of less than or equal to 0.5, and more preferably 
less than or equal to 0.1 are suggested, as well as absolute 
concentrations of less than 5%, more preferably less than 1%, and most 
preferably less than 0.1% label material by weight of the total ink 
composition. In order to provide a good signal to noise response from a 
corresponding sensor, weight ratios of label material to colorant of at 
least 10.sup.-6, more preferably at least 10.sup.-4 and even more 
preferably 10.sup.-2 are suggested, with absolute concentrations of at 
least 0.1 part per million, preferably at least 0.001% and more preferably 
at least 0.01% label material by weight of the total ink composition. Use 
of a distinct label materials at such relatively minor concentrations as a 
signature for the ink being used allows for easily detecting ink type 
without substantially changing ink color and performance. 
The amount of carrier medium is generally in the range of approximately 70 
to 99 weight %, preferably approximately 90 to 99 weight %, based on the 
total weight of the ink. A mixture of water and a polyhydric alcohol, such 
as diethylene glycol, is useful as an aqueous carrier medium. In the case 
of a mixture of water and diethylene glycol, the aqueous carrier medium 
usually contains from about 30% water/70% diethylene glycol to about 95% 
water/5% diethylene glycol. Useful ratios are approximately 60% water/40% 
diethylene glycol to about 95% water/5% diethylene glycol. Percentages are 
based on the total weight of the aqueous carrier medium. 
Block copolymers may be used as dispersants for colorants, especially for 
milled pigments. Preferably, such dispersants are added in a concentration 
of 0.2 to 5 weight percent if not already included in a mill grind. 
Included are block copolymer of ethylene oxide and propylene oxide having 
a structure selected from the following: 
##STR1## 
having a number average molecular weight of 4000 to 15,000 and the ratio 
of n/m of 5 to 10; 
##STR2## 
having a number average molecular weight of 4000 to 9000 and a ratio of 
n/m of 8 to 15. 
##STR3## 
having a number average molecular weight of 5,000 to 40,000 and a ratio of 
n/m of 5 to 10; and 
##STR4## 
having a number average molecular weight of 8,000 to 20,000 and a ratio of 
n/m of 8 to 15. The structure may be either linear triblock (ABA or BAB) 
morphology in which A represents polyethylene oxide and B the 
polypropylene oxide. Useful block copolymers also include branched 
tetrafunctional type copolymers derived from the sequential addition of 
propylene oxide and ethylene oxide to ethylenediamine. 
Solid block copolymers (A), (B), (C) and (D), having the defined molecular 
weights, and the blocks of polyethylene oxide and polypropylene oxide are 
commercially available from BASF Corporation under the name Pluronic.RTM. 
and Tetronic.RTM. surfactants. Block copolymer concentration in the inks 
is most useful from 0.2 to 5 weight percent, based on the total weight of 
the ink composition. Concentration below 0.2 weight percent have limited 
effectiveness, while at concentrations higher than 5% image quality may 
deteriorate. 
Examples of useful block copolymers, together with their respective 
Pluronic.RTM. trade designations, number average molecular weights, number 
of each block copolymer units and their relative ratios in the block 
copolymer are presented below. Examples of ABA block copolymers are: 
______________________________________ 
Pluronic .RTM. 
Designation MW Each n m n/m 
______________________________________ 
F38 4k 40 10 8 
F68 8k 80 20 8 
F108 14K 140 40 7 
______________________________________ 
Examples of BAB block copolymers are: 
______________________________________ 
Pluronic .RTM. 
Designation MW Each n m n/m 
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10R8 5K 90 15 6 
17R8 7K 135 23 6 
25R8 9K 160 30 6 
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Branched block copolymers are available under the tradename TETRONIC from 
BASF Corporation. Tradename designations falling within the structures (C) 
and (D) are TETRONIC 707, 1107 and 1508. 
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 Pigmented ink jet inks suitable for use with ink jet printing 
systems generally should have a surface tension in the range of about 20 
dynes/cm to about 60 dynes/cm and, more preferably, in the range 30 
dynes/cm to about 50 dynes/cm. Control of surface tensions in aqueous inks 
is accomplished by additions of small amounts of surfactants. The level of 
surfactants to be used can be determined through simple trial and error 
experiments. Anionic and cationic surfactants may be selected from those 
disclosed in U.S. Pat. Nos. 5,324,349; 4,156,616 and 5,279,654 as well as 
many other surfactants known in the ink jet ink art. Commercial 
surfactants include the Surfynols.RTM. from Air Products; the Zonyls.RTM. 
from DuPont and the Fluorads.RTM. from 3M. 
Acceptable viscosities are generally no greater than 20 centipoise, and 
preferably in the range of about 1.0 to about 10.0, preferably 1.0 to 5.0 
centipoise at room temperature. 
Additional ingredients may also be added to the ink jet inks of the 
invention. A humectant, or co-solvent, is commonly added to ink jet inks 
to help prevent the ink from drying out or crusting in the orifices of the 
printhead. A penetrant may also be optionally added to help the ink 
penetrate the receiving substrate, especially when the substrate is a 
highly sized paper. A biocide, such as Proxel.RTM. GXL from Zeneca Colours 
may be added at a concentration of 0.05-0.5 weight percent to prevent 
unwanted microbial growth which may occur in the ink over time. Additional 
additives which may optionally be present in ink jet inks include 
thickeners, pH adjusters, buffers, conductivity enhancing agents, 
anti-kogation agents, drying agents, and defoamers. 
Ink jet printing inks are most advantageously used in conjunction with ink 
jet paper or transparent media optimized for the ink jet printer and the 
specific desired application. Photographic quality inkjet paper, such as 
that manufactured and sold by the Eastman Kodak Company, may be 
particularly useful, as the optical density and color gamut are typically 
enhanced when inks are deposited on this type of paper. However, the inks 
compositions of the invention will also be useful for printing on a 
variety of transparent and opaque films, and even on so-called plain 
papers. 
The formulations of primary inks, label materials and inks comprising label 
material can be better understood by the following examples. 
Primary Ink Formula 
In the present invention, the term primary ink refers to the inks that can 
be used by the prior art ink jet printing apparatus for ink jet printing 
in the absence of any label material. The primary ink used in the 
following examples of the present invention was black in color and was 
based on pigment black 7, Black Pearls 880 obtained from Cabot Corp., and 
was prepared as follows. First, the following ingredients were added to a 
1-liter, water-cooled milling vessel: 
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300 g polymeric beads, 50 micron mean diameter (milling media) 
200 g de-ionized water 
16 g N-methyl-N-oleoyl taurate (OMT, dispersant) 
40 g pigment black 7 (Black Pearls 880, Cabot Corp.). 
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The mixture was milled for 4 hr at 700 rpm using a Cowles-type dispersing 
blade (40 mm diameter). The mill grind was separated from the grinding 
media by passing through 15-micron filter. The mill grand is then diluted 
to a working strength ink with the following composition: 
2.25 wt % Pigment Black 
2.5 wt % diethylene glycol 
2.5 wt % glycerol 
de-ionized water to 100 wt %. 
Details of the preparation process including other colored inks are 
disclosed in the commonly assigned co-pending U.S. patent application Ser. 
No. 08/699,877 by Santilli et al. 
Magnetic Label Material A Dispersion 
The Magnetic Label Material A comprise a finely divided concentrate of a 
magnetic material made by milling 20 parts of Co-surface-treated 
.gamma.-iron oxide powder supplied by Toda Kogyo under the trade 
designation CSF 4085V2 and 20 parts of a 50 wt % solution of the 
dispersion Syn Fac 8337 (solid by Milliken Chemical) in 70 parts deionized 
water in a small media mill. The sample was milled for 1-1.5 hours until 
the average particle size was down to 0.25 microns. Details of the milling 
procedure including the dispersant in the milling are disclosed in 
commonly assigned U.S. Pat. No. 5,457,012 by Nair and Oltean. 
Magnetic Label Material B Dispersion 
Magnetic Label Material B is a dilute aqueous magnetic ink dispersion 
prepared by letdown of a small quantity of a concentrated aqueous magnetic 
dispersion. The concentrated magnetic dispersion was milled with a 
starting composition as follows: 
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Magnetic particle 
Toda CSF 4085V2 
600 g 
Deionized water 723 g 
Dispersant Dequest 2006 12 g 
Total 1335 g 
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The mill was filled with water, the Dequest 2006 was added to the mill, 
then the Toda CSF 4085V2 magnetic powder was added slowly to the mill 
while agitating the slurry contained in the mill funnel that is waiting to 
be circulated through the mill chamber. The mill contained 250 ml small 
media mill loaded with 1.3 mm steel media at 85 vol % of the mill chamber. 
The milling process lasted for 3 hours at about 3700 rpm and 65 F. 
Details of the Magnetic Label Material B can be found in commonly assigned 
U.S. Pat. No. 5,520,954 by Oltean et al. 
Magnetic Label Material C Dispersion 
The Magnetic Label Material C is a Cobalt-.gamma.-Ferric Oxide 
(Co-.gamma.-Fe.sub.2 O.sub.3) hydrosol that is available from Nissan 
Chemical Industries, LTD., under sample number F-2. The hydrosol is 
dispersed in water and has a dark brown color. It has a specific gravity 
of 1.196 g/cc at 25 C., pH 9.31 stabilized by KOH, and viscosity of 45.8 
c.p. at 25 C. The mean particle size is estimated to be 21.2 nanometers as 
measured by specific surface area using gas absorption technique. 
Magnetic Label Material D Dispersion 
The Magnetic Label Material D is the same as that of Magnetic Label 
Material C, except a different concentration is used as indicated in Table 
I below. 
Magnetic Label Material E Dispersion 
This label material is a cobalt magnetite hydrosol (Co-Fe.sub.3 O.sub.4) 
that is available from Nissan Chemical Industries, LTD., under sample 
number F-3. The hydrosol is dispersed in water and has a black clear 
color. It has a specific gravity of 1.204 g/cc at 25 C., pH 9.10 
stabilized by KOH, and viscosity of 79.2 c.p. at 25 C. The particle size 
is estimated to be 23.8 nanometers as measured by specific surface area 
using gas absorption technique. 
Final Ink Composition 
The final inks comprising magnetic label materials are obtained by mixing 
the magnetic label material dispersions prepared by each of the Magnetic 
Label Material Formula A, B, C, D or E to the primary ink, which are 
summarized in Table 1 to provide the indicated label:colorant weight 
ratios. The workable concentration range of the magnetic label material in 
the final ink is 0.1 part per million to 5 wt %. The most preferred ratio 
of label material to colorant in the final ink is from 1:10 to 1:100. 
TABLE I 
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Summary of Inks Comprising Magnetic Label Materials 
Mag- Mag- 
netic Coer- Specific netic 
Label sive Magnetic Label Color of 
Colorant: 
Mater- 
Force Moment Concen- Magnetic 
Label 
ial (Oe) (emu/g) tration Label weight ratio 
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A 830 72 0.11 wt % 
Brown 20.5 
B 830 72 0.14 wt % 
Brown 16.1 
C 695 63.1 0.15 wt % 
Brown 15 
D 695 63.1 0.05 wt % 
Brown 45 
E 830 72 0.10 wt % 
Black 22.5 
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The final inks comprising the magnetic label materials were tested in an 
ink jet printing apparatus involving the following steps. First an ink 
solution was filled into an ink reservoir. The ink was then drawn into the 
connect tubes that connect the ink reservoir and the ink jet print head. 
An Hall-effect magnetic detector was used to detect the magnetic label 
material in the connection tube. When the detector was away of any 
magnetic materials, the detector outputted no signal. When the detector 
was brought to close vicinity of the ink connect tubing or the ink 
reservoir, an electric voltage was generated in the sensor. The magnitude 
of the voltage signal increased with the strength of the magnetic field it 
detected, which corresponds to the concentration of the magnetic label 
material in the ink. The concentration of the colorant in the inks may be 
determined from the voltage signal based on the label:colorant ratios 
listed in Table I. 
The magnetic materials described in the above examples are non-limiting 
examples of types of label materials which may be used in the ink 
compositions of the invention. It will be readily understood by the 
artisan that many other signal generating label materials may 
alternatively be used in inks which are detectable by their respective 
sensors as described above. The important feature is that a distinct label 
material is used in an otherwise functional printing ink to provide a 
signal which is readily detectable to identify the ink being used in an 
ink jet printer. 
While the above examples demonstrate the invention with the use of a black 
or brown label material in combination with a black pigmented ink, 
magnetic particles and other types of label materials can exist in many 
other colors, and can be used to match the color of the inks in accordance 
with the present invention in order to minimize any effect of the label 
material on the resulting final ink color. Details of preparation of 
colored magnetic particles, e.g., are disclosed in U.S. Pat. No. 
5,506,079. 
In accordance with various embodiments of the invention, color ink jet ink 
sets comprising cyan, magenta, and yellow (and further optionally black) 
inks may be prepared with different concentrations of a label material so 
that the inks may be readily differentiated from each other when used with 
an ink delivery system employing an appropriate sensor. Alternatively, all 
inks of a set may employ a label material at the same concentration to 
identify them as belonging to the same set. However, if desired, only one 
or two (or three) of the inks of a set may comprise the label material. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.