Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR PRODUCING
INK INTENSITY MODULATED INK JET PRINTING
Field of the Invention
This invention relates to ink jet printing and more particularly to a method
of
printing and an apparatus for providing images having color levels of varying
intensity,
especially for printing on transparencies used to produce high quality medical
images
such as X-ray, ultrasound, nuclear medicine, magnetic resonance, computed
tomography, positron emission tomography, and angiography.
Background of the Invention
Prior drop-on-demand ink jet printers typically employ one or more inks of a
single intensity. Images are formed on a recording medium by ejecting drops of
ink
from an ink jet head onto the medium. Color ink jet printers typically use
four
subtractive primary colors of ink: cyan, magenta, yellow and black. Non-
primary
colors are produced by printing dots of different subtractive primary colors
on top of
one another. Modulation of the intensity of color c>f the printed image,
hereinafter
referred to as gray scale printing, is typically achieved by one of two
methods: (1)
modulating the diameter or size of each ink dot while leaving the number of
dots within
a specific area of the image unchanged; or (2) varying the number of dots
printed in a
specific area without changing the diameter of each individual dot.
Modulation of ink dot size entails controlling the volume of each drop of ink
ejected by the ink jet head. The larger the dot size, the darker the color
intensity of the
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printed image. Methods for modulating the volume of ink drops ejected from an
ink
jet print head are known in the art. For example, U.S. Patent No. 3,946,398
describes
a drop-on-demand ink jet print head that ejects ink drops ofvariable size in
response to
pressure pulses developed in an ink pressure chamber by a piezoceramic
transducer
(PZT). Ink drop volume is modulated by varying the amount of electrical
waveform
energy applied to the PZT for the generation of each pressure pulse. However,
varying the ink drop volume causes variation in the ink drop ejection velocity
resulting
in drop landing position errors.
U.S. Patent No. 4,393,384 describes a method for independently controlling
both the drop volume and ejection velocity. In order to provide dots small
enough for
low intensity images, a very small ink jet orifice is required. Such an ink
jet print head
is difficult to manufacture and clogs easily.
Other approaches have employed a method for controlling the drop volume
size and the drop ejection velocity by means of an electric field which
accelerates the
ink drops in inverse proportion to their volume, thereby reducing the effect
of
variations in ejection velocity. In addition, the electric field enables
formation of an ink
drop smaller than the orifice diameter. However, use of the electric field
increases the
complexity and cost of the printer.
U.S. Patent No. 5,495,270, issued February 27, 1996 and assigned to the
assignee of the present application, discloses an ink jet printer which
produces ink
drops of differing volumes having substantially the same ejection velocity by
providing
multiple PZT drive waveforms. The number of different ink drop sizes and
therefore
the number of gray scale levels which can be produced using this technique is
very
limited. In addition, the technology required to implement this method is
quite
complex.
In single ink dot size printing, the printer provides drops of one size which
are large enough to provide adequate "solid fill" printing for a given
resolution. Color
intensity is manipulated by a process referred to as "dithering" in which the
perceived
intensity of an array of dots is modulated by selectively printing or not
printing
individual dots within an array thereby varying the number of dots in the
specific area.
For example, if a 50 percent average intensity is desired, half of the dots in
the array
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are printed. Multiple dither pattern dot densities are possible to provide a
wide range
of intensity levels. For a two-by-two dot array, five intensity level patterns
are
possible. An eight-by-eight dot array can produce 65 different intensity
levels. Usable
gradations of color in an image are thus achieved by distributing a myriad of
appropriately dithered arrays across the recording medium in a predetermined
arrangement.
However, with dithering there is a trade-offbetween the number of possible
intensity levels and the size of the dot array required to achieve those
levels.
Increasing the size of the dither cell leads to loss of spatial accuracy due
to the lower
resolution of the dither patterns. This in turn results in printed images
having a grainy
appearance.
The Canon FP-510 printer employs ink drops of varying sizes to produce an
image of varying color intensity. The Canon FP-S 10 also uses three different
densities
of liquid, water soluble cyan and magenta ink (thick, medium and light) to
provide up
to 64 color gradations. In addition to using liquid ink, the Canon FP-510 can
be used
only with specially coated roll paper, thereby limiting the versatility of the
machine.
In medical diagnostic imaging there is the need for creating images of
substantial contrast between the imaged and non-imaged areas and to highlight
the
differences between different levels of gray obtained when using solid or
phase change
ink. There still remains the necessity, while using inks of varying intensity
to achieve
multiple gray scale levels, for long shelf life, and resistance to light.
There thus continues to be a need in the art for a simple, inexpensive and
easy-to-use ink jet printer and a method of printing which provides high-
resolution
gray scale printing, especially in medical diagnostic imaging applications on
transparency films, without sacrificing performance and versatility of use.
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SUMMARY OF TIC NTION
An aspect of the present invention is to provide a gray scale ink jet printing
method and apparatus that provides high quality images.
Another aspect of the present invention is to provide a gray scale ink jet
printing method and apparatus that produces high quality images having a large
number of different color intensities without the grainy appearance associated
with
dithering.
A further aspect of the present invention is to provide a high resolution gray
scale ink jet printing method and apparatus which employs conventional ink jet
print
heads, thereby allowing the use of existing print head technologies.
Yet another aspect of the present invention is to provide such a method and
apparatus which can be used to form images on any standard recording medium.
Still another aspect of the present invention is to provide a high resolution
gray scale ink jet printer and method of printing using phase change ink
compositions
that include black coloring agents in thermally stable black colorant systems
in
conjunction with a clear ink without any coloring agents to provide contrast
and
highlighting to the imaged areas.
It is a feature of the present invention that the ratio of the dyes comprising
the colorant system when incorporated into inks can be adjusted to yield an
absorbance
spectrum comparable to the absorbance spectrum on silver halide films between
about
380 nanometers and about 630 nanometers.
It is another feature of the present invention that the image produced from
the phase change inks incorporating the black colorant systems and the clear
ink
duplicate the silver halide black color perceived by the human eye when
observed in
the environment in which the medical images are normally viewed on a
fluorescent
lightbox.
It is another feature of the present invention that the image produced from
the phase change inks incorporating black colorant systems and the clear ink
produce
the desired optical density in the final imaged non-silver halide-containing
transparency
film for use in medical diagnostic imaging applications.
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It is an advantage of the present invention that phase change inks produced
from the
combining of a process or composite black colorant, such as dye, and another
colorant,
such as dye, with a phase change ink base and a clear phase change ink can be
used in
an ink jet imaging system that is environmentally friendly and a relatively
low cost
alternative imaging system to the chemical wet processing system using silver
halide
photographic film currently employed in medical diagnostic imaging.
It is another advantage of the present invention that the phase change inks
employing the compatible black colorant systems manifest no precipitates or
print head
ink jet orifice clogging when used in an ink jet printer.
It is another advantage of the present invention that the black colorant
systems
are compatible in phase change inks when used in an ink jet printer in medical
diagnostic imaging applications.
It is a further advantage of the present invention that the black colorant
systems
axe stationary and do not migrate over time in the imaged areas.
It is still a further advantage of the present invention that none of the dyes
in the
black colorant systems bloom; that is no dye crystallises and migrates to the
surface
manifesting itself as a dust-like powder on the surface of the priinted image.
In accordance with one aspect of the present invention there is provided a
method for generating a printed image having variable color intensities
comprising the
steps of: a) mixing a black colored phase change ink with a clear ink base in
a plurality
of ratios, wherein the ratios are selected to form desired gray scale level
black inks; b)
forming solid ingots of the gray scale level black inks; c) forming solid
ingots of the
clear ink base; d) placing the solid ingots of the gray scale level black inks
and the solid
ingots of the clear ink base in a plurality of ink reservoirs fluidically
coupled to a drop-
on-demand phase change ink jet printer print head; e) melting the solid ingots
of gray
scale level black inks and the solid ingots of the clear ink base in the ink
reservoirs and
feeding the resulting gray scale level black inks and the clear ink base to
the print head;
and f) ejecting the drops of the gray scale level black inks and the clear ink
base from
the print head onto a recording medium at a plurality of locations to generate
the printed
image.
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In accordance with another aspect of the present invention there is provided a
drop-on-demand ink jet printer for generating a ,printed image having variable
color
intensities comprising: a) a first ink reservoir for holding a clear phase
change ink base;
b) a plurality of reservoirs for holding a corresponding plurality of colored
phase change
inks, each colored phase change ink having a different gray scale level, the
colored
phase change inks having specific ratios of coloring agents to the clear phase
change ink
base wherein the ratios are selected to form the different gray shale levels;
and c) means
for transfernng the clear phase change ink base and the colored phase change
inks of
different gray scale levels to a print head for ejecting drops of the clear
phase change
ink base and the colored phase change inks of different gray scale levels onto
a
recording medium at a plurality of locations to generate the printed image.
These and other aspects, features, and advantages are achieved according to
the
present invention by printing with different intensity black gray scale phase
change
inks and a clear phase change ink base, thereby producing multiple black gray
scale
levels and a contrasting clear area. The formulation of the black gray scale
phase
change inks can either be performed prior to placement of the black phase
change inks
in the printer, or can take place within the printer to produce different
levels of color
intensity during the printing process. The black colorant systenns used in the
present
invention combine a black coloring agent such as a dye having, a low
absorbance
region with at least a second coloring agent such as a dye having a high
absorbance
region corresponding to the low absorbance region of the blacl': coloring
agent to
produce inks that are useful in ink jet medical diagnostic imaging
applications to create
images with black colored regions in the human visible response spectrum of
from
about 380 to about 670 nanometers. These images are comparable to medical
Sa
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diagnostic images produced using traditional black silver halide photographic
film
. when viewed using a fluorescent light source typically used by radiologists.
BRIEF DESCRIPTION OF TIC DRAWINGS
These and other aspects, features and advantages will become apparent
upon consideration of the following detailed disclosure of the invention,
especially
when it is taken in conjunction with the accompanying drawings wherein:
Figure 1 is a schematic of a four level gray scale ink jet printer of the
present
invention.
Figure 2A is an isometric view of a mixing jet of the present invention.
Figure 2B is a cross-sectional view of a piezoelectric driver of the present
invention.
Figure 3 is a fragmentary, isometric view of a mixing chamber of the present
invention.
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DETAILED DESCRIPTION OF THE PREFEIZRFD EMBOD NT
As used herein, the following terms will be understood to mean the following:
A compatible black colorant system means at least one coloring agent that is
black in color and which is chemically and physically compatible (e.g. non-
reactive and
soluble) with the phase change ink base and the coloring agents or colorants
themselves. It is to be understood that the black coloring agent used in the
compatible
black colorant system can be a process black (a single colorant) or a
composite black
(a blend of colorants). Lightfast means the colorant system is resistant to
fading upon
exposure to light. Thermally stable means the colorant system will not
discolor, readily
oxidize or otherwise react at operating temperatures of the ink jet printing
system.
Low absorbance region and high absorbance region mean the absorbance of
light in the low absorbance region in the human visible response spectrum is
less than
about 80% of the absorbance of light in the high absorbance region of the
human
visible response spectrum for colorants used in the present invention. This is
reflected
in the black dye spectrum which has a low absorbance region from about 425 to
about
525 nanometers (nm) and has high absorbance regions from about 350 to about
400
nm and from about 550 to about 630 nm. It shall be noted that the human
visible
response is only significant from about 400 to about 670 nm.
Additionally, compatibility preferably includes colorants that are non-
blooming and tinctorially strong. Non-blooming means that no colorant will
crystallize
and migrate to the surface manifesting itself by a dust-like powder on the
surface of the
printed image. Non-migrating means that one colorant, such as a dye, will not
migrate
over time within the imaged areas, for example, from a dark area to a clear or
light
area. Tinctorially strong means a colorant that produces strong absorbance per
unit
weight or a very deep (optically dense) color from a minimum amount of
colorant.
Colorant or coloring agent will be understood to preferably include dyes, but
could as
well include appropriate pigments, colored isocyanate-derived urethane waxes,
polymeric colorants and their derivatives, and colored isocyanate-derived
mixed
urea/urethane resins.
The phase change inks of the present invention are composed of two parts,
namely, a colorant system portion and a phase change ink carrier or base
portion,
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except where clear ink is employed that uses only an uncolored phase change
ink carrier
or base portion.
The gray scale printing method and apparatus of the present invention employ
phase change inks. 'These inks are in the solid phase at ambient temperature
but exist in
the liquid phase at the elevated operating temperature of an ink jet printer.
In a typical
phase change ink jet printer, solid ingots of phase change ink are placed in
individual
reservoirs. Once the printer is switched on, the ink is heated to .above its
melting
temperature and is maintained in the stand-by phase at approximately 100
°C. When the
printer enters the ready phase, the ink is heated to approximately 120 "C and
passed to
the ink jet head, which is maintained at approximately 140 °C.
Phase change inks offer several advantages over liquid, water-soluble inks.
First,
they are easy to store and to handle at room temperature. Second, the problem
of nozzle
clogging due to ink evaporation is largely eliminated, leading to improved
reliability of
the printer. In addition, the ink drops solidify immediately upon contact with
the
recording medium, thereby preventing migration of ink along the medium and
improving image quality.
Preferred phase change inks for use in the present invention have high
flexibility
and high melting points, most preferably about 80 °C, thereby improving
the durability
of the images formed from the inks. In addition, the preferred phase change
inks
demonstrate low melt viscosity, resulting in increased efficiency of the
jetting process.
Phase change ink bases suitable for use in the present invention include those
described
in U.S. Patent Nos. 4,889,560 and 5,084,099. Other phase change ink bases are
known
in the art and may be usefully employed with the present invention.
In a first embodiment of the present invention, ingots of phase change ink
having different gray scale levels may be prepared by first heating a colored
phase
change ink base above its melting temperature. The molten colored ink is then
mixed
with a clear ink base containing no colorants and allowed to cool to room
temperature to
form a solid ingot of gray scale ink. By varying the ratio of colored ink base
to clear ink
base, different levels of color intensity are obtained. The preferred ratio of
colored ink
base to clear ink base depends on many parameters, such as dye conditions
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including, for example dye tinctorial strength, drop mass and the kind of ink
base used.
For example, ratios of 1:4, 1:8, 1:16, 1:32 and 1:64 colored ink base to clear
ink base
may be used. The resulting ingots of gray scale phase change ink are then
employed in
a standard phase change ink jet printer, such as a Tektronix Phaser~ 300 or
Phaser~
350, to produce high resolution images.
High quality monochrome images may be formed according to this method
by heating a black phase change ink base to its melting temperature and then
diluting
the ink with a clear ink base, thereby producing inks of different shades of
black. The
resulting ingots of black phase change inks are employed in a standard phase
change
ink jet printer to form high resolution monochrome images. Ingots of clear
phase
change ink are employed with the ingots of black phase change inks in this
method.
The use of the clear phase change ink accomplishes complete area coverage with
ink
and leaves no unprinted areas without ink. The use of the clear phase change
ink helps
contain the monochrome image formed by the multiple levels of black gray scale
ink,
prevents dot gain caused by spreading of the black gray scale ink dots,
provides
contrast and highlights the imaged areas. This technique is particularly
useful in
medical imaging where a computer generated monochrome image can be printed
directly onto a standard recording medium, such as transparency film or
alternatively
paper, thereby forming a high quality image which is both convenient to view
and easy
to handle.
The percentage of black colorant system to the phase change ink base is
determined by the sufficient amount of black colorant system necessary to
achieve the
desired absorbance. The percentage of black colorant system to the ink base is
from
about 0.1 to about 7 parts per hundred parts by weight (.1%-7%) and more
preferably
is from about 0.2 to about 4 parts per hundred parts by weight (.2%-4%).
The colorant portion of the black inks used in the present invention
preferably is made up of two or more dyes. One of those dyes is a black dye,
such as
Color Index (C.L) Solvent Black 45. Other suitable dyes can include C.I.
Solvent
Black dyes 22, 27, 28, 29 and 35. The most preferred is C.I. Solvent Black 45.
However, any black dye may be acceptable that has the combination of
properties of
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(1) solubility in the phase change ink base portion, (2) thermal stability,
and (3)
sufficiently lightfastness to be useful for medical imaging applications.
The other coiorants of the colorant system of the present invention are
primarily chosen because they provide increased absorbance in the deficient
low
absorbance region of the visible spectrum of the black colorants (i.e. at
about 425 to
about 525 nm for C.I. Solvent Black 45). Furthermore, these other colorants
should
also possess sufl'lcient solubility in the phase change ink base portion;
thermal stability,
compatibility with the black colorant, non-migrating and lightfastness to be
of utility in
medical imaging applications. Furthermore, it is preferred that this
additional colorant
or colorants be environmentally safe and non-toxic, have Toxic Substance
Control Act
(TSCA) registration, be non-blooming, be tinctorially strong, and be
commercially
available. Two particular dyes, C.I. Disperse Orange 47 and C.I. Solvent
Orange 60,
are preferred as colorants.
When C.I. Disperse Orange 47 and C.I: Solvent Black 45 are used in
combination, it has been found that the parts by weight ratio of C.I. Disperse
Orange
47 to C.I. Solvent Black 45 is preferably from about 5 parts to about 10 parts
of
orange dye per 100 parts of black dye, more preferably, about 7 parts to about
8.5
parts of orange dye per 100 parts of black dye. It is believed that the ratios
of the
other suitable dyes would be adjusted dependent upon their individual
tinctorial
strengths.
The resulting absorbance of the colorant system in the phase change ink
should be approximately equal throughout the visible spectrum from about 380
nm to
about 630 nm (i.e. the absorbance in any one region will be not less than 80
percent of
the absorbance in any other region). The functional approach is to balance out
the
absorbance between the high absorbance and low absorbance regions. This
produces a
colorant system where the individual dye absorbances of the Solvent Black 45
and the
C.I. Disperse Orange 47 are combined, resulting in a substantially balanced
absorbance
across the portion of the visible spectrum to which humans respond.
Furthermore, the
inks used in the present invention should possess all of the above recited
desired
properties of the colorants. Where pigments are employed as the colorant, a
dispersant
or surfactant may be used to prevent settling or aggregation of the pigments.
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In a preferred case, the phase change ink base compositions
employed with the particular black inks of desired optical density comprise a
tetra-amide and a functional mono-amide compound and a modifying agent which
includes a tackifier, a plasticizer, and an antioxidant. The preferred
compositional
ranges of these phase change ink base composition are as follows: from about
10 to
about 50 and most preferably from about 15 to about 30 percent by weight of a
tetra-amide compound, from about 30 to about 80 and most preferably from about
40
to about 55 percent by weight of a mono-amide compound, from about 0 to about
40
and most preferably about 15 to about 35 weight percent of a tackifier, from
about 0
to about 30 and most preferably about 4 to about 10 percent by weight of a
plasticizer
and about 0 to about 2 and most preferably .OS to about 1 percent by weight of
an
antioxidant. These phase change ink bases are described in further detail in
U.S.
Patent No. 5,372,852, issued December 13, 1994 and assigned to the assignee of
the
present invention.
In operation the black gray scale inks and the clear phase change base ink
utilized in the process and system of the instant invention are preferably
initially in solid
form and are then changed to a molten state by the application of heat energy
to raise
the temperature from about 85°C to about 150°C. Temperatures
above this range will
cause degradation or chemical breakdown of the ink over time. The molten inks
are
then applied in raster fashion from the ink jets in the print head to the
exposed surface
of the liquid layer forming the intermediate transfer surface, where they are
cooled to
an intermediate temperature and solidify to a malleable state in which they
are
transferred to the final receiving surface via a contact transfer by entering
the nip
between the pressure and fusing roller and the liquid layer forming the
intermediate
transfer surface on the support surface or dnum. This intermediate temperature
where
the solidified ink is maintained in its malleable state is between about
30°C to about
80°C.
Once the solid malleable ink image enters the nip, it is deformed to its final
image conformation and adheres or is fixed to the final receiving substrate
either by the
pressure exerted against the ink image on the final receiving substrate by the
pressure
and fusing roller alone, or by the combination of the pressure and heat
supplied by an
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appropriate heating apparatus. An additional heating apparatus could
optionally be
employed to supply heat to facilitate the process at this point. The pressure
exerted on
the ink image is between about 10 to about 2000 pounds per square inch (psi)
and
more preferably between about 200 to about 1000 psi. The pressure must be
sufficient
to have the ink image adhere to the final receiving substrate and be
suffciently
deformed to ensure that light is transmitted through the ink image
rectilinearly or
without significant deviation in its path from the inlet to the outlet in
those instances
when the final receiving substrate is a transparency. Once adhered to the
final
receiving substrate, the ink image is cooled to an ambient temperature of
about 20° to
about ZS°C. The ink forming the image must be ductile, or be able to
yield or
experience plastic deformation without fracture when kept above the glass
transition
temperature. Below the glass transition temperature the ink is brittle. The
temperature of the ink image in the ductile state is between about -
10°C and to about
the melting point, or less than about 85°C. The indirect printing
process described
herein is described in greater detail in U.S. Patent No. 5,389,958 issued
February 14,
1995 and assigned to the assignee of the present invention.
Another important property of phase change inks is viscosity. The viscosity
of the molten ink must be matched to the requirements of the ink jet print
head. For
purposes of this invention, the viscosity of the phase change ink is measured
on a
Bohlin Model CS-50 Rheometer utilizing a cup and bob geometry. It is preferred
that
the viscosity of the phase change ink composition of the present invention, at
about
140°C, is from about 10 to about 16 centipoise (cPs), and more
preferably about 12 to
about 14 cPs.
The viscosity of the preferred phase change ink composition can be adjusted
by adding either more mono-amide or tetra-amide compound. Adding more mono-
amide compound will reduce the viscosity, while adding more tetra-amide
compound
will increase the viscosity.
The final receiving substrate for use with the ink of the present invention
can
be a variety of media including permeable or impermeable, transparent, semi-
transparent or opaque substrates. Where paper is used, the amount of ink
deposited by
the printer to achieve the same apparent optical density will be approximately
half of
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the amount deposited on a transparent substrate, such as polyester film
transparencies.
This is because light passes through the ink on paper twice in reflective
mode, both
going away from and returning toward the eye. In contrast, with a transparency
that is
viewed in the transmittance mode, light passes through once going toward the
eye.
The greater dynamic range in the optical density for transparencies compared
with
reflection prints makes transparencies the preferred medium for medical
diagnostic
imaging providing distinguishably discernable useful gray levels. Paper has a
limited
maximum optical density range achievable in reflective mode viewing which does
not
permit sufficient levels of black to be achieved to be reliably useful in
diagnostic
applications. However, transparencies are the preferred medium for diagnostic
imaging because they are capable of a greater range of optical density
compared with
reflection prints.
One preferred embodiment of the present invention permits multiple gray
levels to be obtained by using inks with four different concentrations of
colorant
systems individually and mixed by overlapping printing. In this embodiment a
clear ink
using only the base without any of the black colorant system is used in
combination
with inks having three different percentages by weight of black dye;
specifically about
0.41 percent by weight black dye, about 1.18 percent by weight black dye and
about
3.15 percent by weight black dye. These dye percentages give inks of low,
medium
and high optical density black ink, respectively. All of the black inks
include the same
ratio of orange dye to black dye to obtain a more uniform absorbance across
the visible
spectrum. In this embodiment, C.I. Disperse Orange 47 dye and C.I. Solvent
Black 45
dye are used together. They are used in the same ratio for all inks,
preferably the ratio
of C.I. Disperse Orange 47 dye to C.I. Solvent Black 45 dye is from about .070
to
about .085 parts of orange to one part of black. This constant ratio of orange
dye to
black dye simulates the black color obtained in x-ray films using silver
halide film for
medical imaging. The composite black colorant system of the present invention
can be
employed whereby individual colorant components can be adjusted to give an
absorbance spectrum comparable to that of an image on silver halide film.
Preparation
of the three level black ink system, not including the clear ink, will have
inks of
different overall intensities, yet the individual colorant components will
have a constant
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ratio to each other in each of the three inks. The different levels of
colorants in the
inks used herein allow the generation of multiple levels of optical density. A
clear ink
base without any black or orange dye is used in medical imaging applications
to obtain
the dynamic range in optical densities with low, medium and high optical
density inks.
In a second embodiment of the present invention, mixing of colored phase
change inks with a clear ink base to provide gray scale levels is performed
"on the fly"
within a phase change ink jet printer. Figure 1 is a schematic illustration of
a four level
gray scale ink jet printer of the present invention. Ingots of three different
gray scale
level of colors of black phase change ink, namely low, medium, high and black,
together with a clear ink base are placed in the printer with each color being
placed in a
separate conventional ink reservoir 10. The ingots are heated to above the
melting
point of the inks using standard techniques, and the molten ink is pumped to
mixing
chambers 12, where black colored ink is mixed with clear ink base to produce
multiple
gray scale levels. Each mixing chamber 12 is dedicated to producing one level
of gray
scale ink.
Different gray scale levels of ink are produced by varying the ratio of
colored ink to clear ink base. For example, a 1:7 ratio of black ink to clear
ink drops
will give one gray scale level of black while a 1:32 ratio will give a lighter
gray scale
level of black.
From mixing chambers 12, gray scale level inks pass to print head 14 where
ink dots are ejected from banks of image jets 16 onto a recording medium. Each
bank
of ink jets is preferably dedicated to one specific gray scale level of ink.
An ink jet
print head suitable for use with the present invention is disclosed in U.S.
Patent No.
5,087,930, assigned to the assignee of the present application. Other print
head
designs are well known in the art and may be usefully employed with the
present
invention.
While the embodiment of the present invention illustrated in Figure 1
produces three gray scale levels of each black ink, it will be apparent to one
of skill in
the art that more or fewer mixing chambers can be employed to produce more or
fewer
gray scale levels. Similarly, fewer black colors may be placed in the printer
to provide
an image having a reduced range of grayscale levels .
Cfi Jaeger et al 14 Dkt No. 5895 US 1
CA 02245374 1998-08-18
Molten ink is pumped from reservoir 10 to mixing chamber 12 by means of
a mixing jet. As shown in Figure 2A, each mixing jet comprises an inlet
channel 18, a
pressure chamber 20, an outlet channel 22 with an orifice 24. Ink from
reservoir 10
flows through inlet channel 18 and into pressure chamber 20. Ink leaves
pressure
chamber 20 by way of outlet channel 22 to orifice 24, from which ink drops are
ejected.
Pressure chamber 20 is operated by an electromechanical transducer
mechanism, such as a piezoelectric driver, as shown in Figure 2B. Ink pressure
chamber 20 is bound on one side by a flexible diaphragm 28. An
electromechanical
transducer 30, such as a PZT, is secured to diaphragm 28 and overlays pressure
chamber 20. In a conventional manner, transducer 30 has metal film layers 32
to
which an electronic transducer driver 34 is electrically connected. Transducer
30 is
typically operated in its bending mode such that when a voltage is applied
across metal
film layers 32, transducer 30 attempts to change ifs dimensions. However,
because it
is rigidly attached to the diaphragm, transducer 30 bends, deforming diaphragm
28 and
thereby displacing ink in pressure chamber 20, causing the outward flow of ink
through
outlet channel 22 to orifice 24. While this embodiment of the present
invention has
been described with reference to a specific pumping mechanism, other pumping
mechanisms which may be usefully employed in this invention are well known in
the
art. Such pumping mechanisms include electromagnetic actuators, electrostatic
ink jets
or methods employing mechanical valves.
A mixing chamber of the present invention is illustrated in Figure 3. Two
mixing jets eject drops of ink from orifices 24 in an orifice plate 36 across
an air gap 38
onto a mixing plate 40. One jet ejects colored ink while the other ejects
clear ink base,
ZS thereby preventing the inks from diffusing back into ink reservoirs 10. The
ink drops
collect against mixing plate 40 and run into a secondary mixing chamber 42.
The ink is
thereby mixed at mixing plate 40 and in secondary mixing chamber 42. The mixed
ink
then passes through an aperture 44 to a standard ink jet print head (not
shown). The
ratio of colored ink to clear ink base is controlled by varying the frequency
of the drive
wavefonm applied to the PZT. This is easily achieved using software well known
in
the art.
CW Jaeger et al 15 ~kt No. 5895 US 1
CA 02245374 1998-08-18
To ensure efficient mixing of the colored ink and clear ink base, the drops
ejected by the mixing jets are of a small volume, preferably in the range of
about 100 to
about 10,000 p1, more preferably in the range of about S00 to about 5,000 p1
and most
preferably in the range of about 1,000 to about 2,000 p1. To avoid pooling of
the inks
on mixing plate 40 and in secondary mixing chamber 42, secondary mixing
chamber 42
preferably has a small volume. In a preferred embodiment, secondary mixing
chamber
42 is about 0.508 cm deep and about 0.127 cm long, and narrows from a width of
about 0.508 cm at the mixing plate end to about 0.127 cm at the outlet end.
The present invention is further illustrated by the following examples in
which Example 1 describes the production of a high quality monochrome image
using
the first embodiment of the invention and Example 2 describes the design and
testing
of a mixer jet suitable for use in a second embodiment of the invention.
Examples 3-6
show the use of a clear ink base and varying black dye loading to create
multiple levels
of black gray scale inks and Example 7 shows printing with a clear ink base
and
multiple levels of black gray scale inks to produce diagnostic quality images
on
polyethylene film.
A high resolution monochrome image was formed according to the first
embodiment of the present invention as follows.
A standard black phase change ink base commercially available from
Tektronix, Inc. of Wilsonville, Oregon was heated to approximately 135
°C and mixed
with a clear ink base in the ratios of 1:4, 1:16 and 1:64 black ink base to
clear ink base
to produce three different shades of gray ink. The mixed inks were poured into
molds
and allowed to cool to room temperature. The resulting ingots of gray scale
inks,
together with an ingot of 100% full strength black phase change ink, were
placed in a
Tektronix Phaser 300 ink jet printer. A high quality monochrome print
requiring no
gamma correction was produced employing these gray scale inks.
CV1 Jaeger et al 16 Dkt No. 5895 US 1
CA 02245374 1998-08-18
EXAMPLE 2
A mixing jet for use with clear and black gray scale inks of the present
invention was designed as follows.
The necessary flow rate for each mixing chamber 12 is determined by the
number of image jets which must be supplied, the repetition rate of the image
jets, the
size of the image drops ,and the repetition rate of the mixing jets. The
maximum mass
flow rate for each chamber would be a full page fill of a single gray scale
color.
Assuming that each mixing chamber supplies 16 image jets on a print head
running in a
1 page per 2 minutes printing mode, generating 200 p1 drops, the maximum
required
flow is calculated as follows:
V~ (B.Sin)(llin)(300dpi)z(200x10''2~(1000cm')=1.68cm3
I
This in turn gives the following mass flow rate for each chamber:
m = (1.68cm3)(0~)( 1 ) = 11.9
cm3 2min s
This rate is approximately 9 times greater than the flow rate produce by
standard
image jets. For example, the image jets employed in a conventional print head
typically
have a flow rate of 1.4 mg/s. Using a one dimensional lumped parameter model,
it was
calculated that, in order to achieve the maximum required flow rate, a PZT
drive with
a diameter of 0.635cm (0.250 in) that displaced 11,000 p1 with a nominal
ground to
peak voltage of 60 volts would be required.
Using current jet design tools well known in the art, it was predicted that a
mixing jet of the dimensions shown in Table 1 would produce 2200 p1 drops at 2
kHz
to give a mass flow rate of 3.8 mg/sec.
TABLE 1
All dimensions in cm
Feature Length Width Height Cross Section
Inlet channel 1.27 0.0254 0.0254 Circular
Pressure chamber 0.0254 0.635 0.635 Circular
Outlet channel 0.216 0.0635 0.0254 Rectangular
Orifice 0.01524 0.01524 0.01524 Circular
CW Jaeger et al 1 7 Dkt No. 5895 US 1
CA 02245374 1998-08-18
A mixing jet of these dimensions was constructed and found to produce
1400 p1 drops at 1 kHz resulting in a mass flow rate of 1.2 mg/sec. This mass
flow
rate can be increased by modifying the mixing jet design to gain larger drops
at a faster
repetition rate or by increasing the number of mixing jets per mixing chamber.
Mixing jets of this design are employed to transfer clear ink base and a
colored ink from conventional reservoirs to at least two, preferably four,
mixing
chambers, where the inks are mixed in the ratios of from about 1:1 to about
1:64
colored ink to clear ink base. The gray scale inks thus formed are passed to a
standard
ink jet print head and used to form high quality images of variable color
intensities.
CW Jaeger et al 18 Dkt No. 5895 US 1
CA 02245374 1998-08-18
EXAMPLE 3
A plasticized (722 grams) and molten stearyl stearamide2 (3746 grams, and an
antioxidant3 (16.00 grams) were added (in that order) to a pre-heated
110°C stainless
steel container. The components were then mixed with a propeller mixer and a
rosin
ester resin4 ( 1781.92 grams) was slowly added to the mixture over 20 minutes,
maintaining a mixture temperature of at least 100°C. A dimer acid-based
tetra-amides
(1509.84 grams) was then added to the mixture over 15 minutes, while also
maintaining a minimum mixture temperature of 100°C. The blend was
allowed to mix
for 1 hour until all the tetra-amide had dissolved. At this point, an orange
dye6 (16.08
grams) and a black dye' (208.01 grams) were added and allowed to mix for
approximately 2 hours. The ink was then passed through a 2.0 micron filter
(Pall Filter
P/N PFYlU2-20ZJ, S/N 416) under approximately 5 psi of nitrogen pressure.
A sample of this product was tested for spectral strength. It was found to
have
2.60% black dye and 0.197% orange dye in the filtered product. The viscosity
of the
ink was found to be 12.89 centipoise at 140°C measured with a Bohlin
Model CS-50
Rheometer using a cup and bob geometry. The ratio of absorbance at the 475
nanometer region to the 580 nanometer region for this ink was 0.978:1. Dynamic
mechanical analyses (DMA) were used on a Rheometrics Solids Analyzer (RSA In
manufactured by Rheometrics, Inc. of Piscataway, N.J. using a dual cantilever
beam
geometry to determine the following physical properties: glass transition
temperature
(T~ = 10.8°C; storage modulus E'=2.5 x 109 dynes/cmz at 25°C and
1.5 x 109
dynes/cm2 at 50°C; the integral of log tan b was 25.4 from about -
40°C to about 40°C.
The ink displayed a phase change transition of about 90°C by the
technique of
differential scanning calorimetry (DSC) using a TA Instrument DSC 2910
Modulated
DSC.
t SANTiCIZER 278, phthalate ester plasticizer manufactured by Monsanto Polymer
Products Co. of
St Louis, MO.
= IS;EMAMIDE S-180, stearyl stearamide manufactured by Witco Chemical Company
of Memphis,
'TN.
3 NAUGARD 445, antioxidant manufactured by Uniroyal Chemical Company of
Middleberg, CT.
~ KE-100, glycerol ester of hydrogenated abietic (rosin) acid manufactured by
Arakawa
Chemical Industries Inc. of Osaka, Japan
s UhIIREZ 2970, manufactured by Union Camp Corporation of Wayne, N.J.
6 DISPERSE ORANGE 47 dye, commercially available from Keystone Aniline
Corporation of
Chicago,1L.
' SOLVENT BLACK 45 dye, commercially available from Clariant Corporation of
Charlotte, N.C.
CW Jaeger et al 19 Dkt No. 5895 US 1
CA 02245374 1998-08-18
EXAMPLE 4
A plasticizerl (217.5 grams) and molten stearyl stearamidez (1382.9 grams),
and an
antioxidant3 (5.4 grams) were added (in that order) to a pre-heated
110°C stainless
steel container. The components were then mixed with a propeller mixer and a
rosin
ester resin; (579.3 grams) was slowly added to the mixture over 20 minutes,
maintaining a mixture temperature of at least 100°C. A dimer acid-based
tetra-amides
(516.5 grams) was then added to the mixture over 15 minutes, while also
maintaining a
minimum mixture temperature of 100°C. The blend was allowed to mix for
1 hour
until all the tetra-amide had dissolved. At this point, an orange dye6 (6.8
grams) and a
black dye' (88.4 grams) were added and allowed to mix for approximately 2
hours.
The ink was then passed through a 2.0 micron filter (Pall Filter P/N PFYlU2-
20ZJ,
S/N 416) under approximately 5 psi of nitrogen pressure.
A sample of this product was tested for spectral strength. It was found to
have 3.081% black dye and 0.227% orange dye in the filtered product. The ratio
by
weight of the orange dye to the black dye was 0.074 to 1Ø The viscosity of
the ink
was found to be 12.88 centipoise at 140°C measured with a Bohlin Model
CS-50
Rheometer using a cup and bob geometry. The ratio of absorbance at the 475
nanometer region to the 580 nanometer region for this ink was 0.970:1. Dynamic
mechanical analyses (DMA) were used on a Rheometrics Solids Analyzer (RSA II)
manufactured by Rheometrics, Inc. of Piscataway, N.J. using a dual cantilever
beam
geometry to determine the following physical properties: glass transition
temperature
(TJ = 10.8°C; storage modulus E'=2.3 x 109 dynes/cm2 at 25°C and
1.4 x 109
dynes/cm2 at 50°C; the integral of log tan b was 25.2 from about -
40°C to about 40°C.
The ink displayed a phase change transition of about 90°C by the
technique of
differential scanning calorimetry (DSC) using a TA Instrument DSC 2910
Modulated
DSC.
1 SANTICIZER 278, phthalate ester plasticizer manufactured by Monsanto Polymer
Products Co. of
St. Louis, MO.
= KEMAMIDE S-180, stearyl stearamide manufactured by Witco Chemical Company of
Memphis,
TN.
3 NAUGARD 445, antioxidant manufactured by Uniroyal Chemical Company of
Middleberg, C'T.
~ KE-100, glycerol ester of hydrogenated abietic (rosin) acid manufactured by
Arakawa Chemical
Industries Inc. of Osaka, Japan
s UNtREZ 2970, manufactured by Union Camp Corporation of Wayne, N.1.
6 DISPERSE ORANGE 47 dye, commercially available from Keystone Aniline
Corporation of
Chicago, IL.
' SOLVENT BLACK 45 dye, commercially available from Clariant Corporation of
Charlotte, N.C.
CA 02245374 1998-08-18
EXAMPLE 5
A plasticized (226.8 grams) and molten stearyl stearamide2 (1229.7 grams), and
an
antioxidant' (5.4 grams) were added (in that order) to a pre-heated
110°C stainless
steel container. The components were then mixed with a propeller mixer and a
rosin
ester resin4 (668.6 grams) was slowly added to the mixture over 20 minutes,
maintaining a mixture temperature of at least 100°C. A dimer acid-based
tetra-amides
(567.8 grams) was then added to the mixture over 15 minutes, while also
maintaining a
minimum mixture temperature of 100°C. The blend was allowed to mix for
1 hour
until all the tetra-amide had dissolved. At this point, an orange dye6 (2.5
grams) and a
black dye' (33.0 grams) were added and allowed. to mix for approximately 2
hours.
The ink was then passed through a 2.0 micron filter (Pall Filter P/N PFYlU2-
2021,
S/N 416) under approximately 5 psi of nitrogen pressure.
A sample of this product was tested for spectral strength. It was found to
have 1.21% black dye and 0.086% orange dye in the filtered product. The ratio
by
weight of the orange dye to the black dye was 0.071 to 1Ø The viscosity of
the ink
was found to be 12.78 centipoise at 140°C measured in a Bohlin Model CS-
50
Rheometer using a cup and bob geometry. The ratio of absorbance at the 475
nanometer region to the 580 nanometer region for this ink was 0.957:1. Dynamic
mechanical analyses (DMA)were used on a Rheometrics Solids Analyzer (RSA II)
manufactured by Rheometrics, Inc. of Piscataway, N.1. using a dual cantilever
beam
geometry to determine the following physical properties: glass transition
temperature
(T~ = 9.0°C; storage modulus E'=2.3 x 109 dynes/cm2 at 25°C and
1.2 x 109
dynes/cm2 at 50°C; the integral of log tan b was 27.6 from about -
40°C to about 40°C.
The ink displayed a phase change transition of about 92°C by the
technique of
differential scanning calorimetry (DSC) using a TA Instrument DSC 2910
Modulated
DSC.
1 SANTICIZER 278, phthalate ester plasticizer manufactured by Monsanto Polymer
Products Co. of
St. Louis, MO.
2 KEMAMiDE S-180, stearyl stearamide manufactured by Witco Chemical Company of
Memphis,
TN.
3 NAUGARD 445, antioxidant manufactured by Uniroyal Chemical Company of
Middleberg, C'T.
4 KE-100, glycerol ester of hydrogenated abietic (rosin) acid manufactured by
Arakawa Chemical
Industries Inc. of Osaka, Japan
s UNIREZ 2970, manufactured by Union Camp Corporation of Wayne, N.J.
6 DISPERSE ORANGE 47 dye, commercially available from Keystone Aniline
Corporation of
Chicago, IL.
' SOLVENT BLACK 45 dye, commercially available from Clariant Corporation of
Charlotte, N.C.
21
CA 02245374 1998-08-18
EXAMPLE 6
A plasticized (212.5 grams) and molten stearyl stearamide2 (1180.2 grams), and
an
antioxidant3 (5.4 grams) were added (in that order) to a pre-heated
110°C stainless
steel container. The components were then mixed with a propeller mixer and
rosin
ester resin4 (689.0 grams) was slowly added to the mixture over 20 minutes,
maintaining a mixture temperature of at least 100°C. A dimer acid-based
tetra-amides
(614.8 grams) was then added to the mixture over 15 minutes, while also
maintaining
a minimum mixture temperature of 100°C. The blend was allowed to mix
for 1 hour
until all the tetra-amide had dissolved. At this point, an orange dye6 (0.9
grams) and a
black dye' (11.1 grams) were added and allowed to mix for approximately 2
hours.
The ink was then passed through a 2.0 micron filter (Pall Filter PIN PFYlU2-
20ZJ,
SIN 416) under approximately 5 psi of nitrogen pressure.
A sample of this product was tested for spectral strength. It was found to
have 0.42% black dye and 0.032% orange dye in the filtered product. The ratio
by
weight of the orange dye to the black dye was 0.076 to 1Ø The viscosity of
the ink
was found to be 12.83 centipoise at 140°C measured with a Bohlin Model
CS-SO
Rheometer using a cup and bob geometry. The ratio of absorbance at the 4?5
nanometer region to the 580 nanometer region for this ink was 0.983:1. Dynamic
mechanical analyses (DMA) were used on a Rheometrics Solids Analyzer (RSA II)
manufactured by Rheometrics, Inc. of Piscataway, N.J. using a dual cantilever
beam
geometry to determine the following physical properties: glass transition
temperature
(T J = 9.5°C; storage modulus E'=2.3 x 109 dynes/cm2 at 25°C and
1.2 x 109
dynes/cmz at 50°C; the integral of log tan b was 27.7 from about -
40°C to about
40°C. The ink displayed a phase change transition of about 93°C
by the technique of
differential scanning calorimetry (DSC) using a TA Instrument DSC 2910
Modulated
DSC.
t SANTICIZER 278, phthalate ester plasticizer manufactured by Monsanto Polymer
Products Co. of
St. Louis, MO.
2 KEMAMIDE S-180, stearyl stearamide manufactured by Witco Chemical Company of
Memphis,
TN.
3 NAUGARD 445, antioxidant manufactured by Uniroyal Chemical Company of
Middleberg, CT.
4 KE-100, glycerol ester of hydrogenated abietic (rosin) acid manufactured by
Arakawa Chemical
Industries Inc. of Osaka, Japan
s 2970, manufactured by Union Camp Corporation of Wayne, N.J.
6 DISPERSE ORANGE 47 dye, commercially available from Keystone Aniline
Corporation of
Chicago, IL.
SOLVENT BLACK 45 dye, commercially available from Ctariant Corporation of
Charlotte, N.C.
CA 02245374 1998-08-18
EXAMPLE 7
A clear ink unshaded with any colorant system was prepared according to the
following procedure and used to obtain the dynamic range in optical densities
when
employed in an ink jet printer with black shaded low, medium, and high optical
density
inks. A plasticizer' (207.9 grams) and molten stearyl stearamide2 (1169.7
grams), and
an antioxidant3 (5.4 grams) were added (in that order) to a pre-heated
110°C stainless
steel container. The components were then mixed with a propeller mixer and a
rosin
ester resin4 (711.0 grams) was slowly added to the mixture over 20 minutes,
maintaining a mixture temperature of at least 100°C. A dimer acid-based
tetra-amides
(605.8 grams) was then added to the mixture over 15 minutes, while also
maintaining
a minimum mixture temperature of 100°C. The blend was allowed to mix
for 1 hour
until all the tetra-amide had dissolved. The clear ink was then passed through
a 2.0
micron filter (Pall Filter P/N PFYlU2-20ZJ, S/N 416) under approximately 5 psi
of
nitrogen pressure.
The viscosity of the clear ink was found to be 12.79 centipoise at
140°C measured
with a Bohlin Model CS-50 Rheometer CS-50 using a cup and bob geometry.
Dynamic mechanical analyses (DMA) were used on a Rheometrics Solids Analyzer
(RSA II) manufactured by Rheometrics, Inc. of Piscataway, N.J. using a dual
cantilever beam geometry to determine the following physical properties: glass
transition temperature (T~ = 11.1°C; storage modulus E'=2.1 x 109
dynes/cm2 at
25°C and 1.1 x 109 dynes/cm2 at 50°C; the integral of log tan b
was 27.0 from about -
40°C to about 40°C. The ink displayed a phase change transition
of about 94°C by the
technique of differential scanning calorimetry (DSC) using a TA Instrument DSC
2910
Modulated DSC.
t SANTICIZER 278, phthalate ester plasticizer manufactured by Monsanto Polymer
Products Co. of
St. Louis, MO.
Z KEMAMIDE S-180, stearyl stearamide manufactured by Witco Chemical Company of
Memphis,
TN.
3 NAUGARD 445, antioxidant manufactured by Uniroyal Chemical Company of
Middleberg, CT.
~ KE-100, glycerol ester of hydrogenated abietic (rosin) acid manufactured by
Arakawa Chemical
Industries. Inc. of Osaka, Japan
s UhIIREZ 2970, manufactured by Union Camp Corporation of Wayne, N.J.
CA 02245374 1998-08-18
The following procedures were used to obtain the visible absorbance spectra of
the
ink samples in Examples 3-7 and for determining the dye content of those
samples.
A solution of the orange shaded black ink was prepared by weighing about
0.16211
grams of the ink of Example 3 into a 250 mL volumetric flask. The ink was
dissolved
in n-butanol. When the ink was completely dissolved, the volumetric flask was
filled to
volume with n-butano;. The solution was thoroughly mixed. The absorbance
spectrum of the sample was measured against a reference cell containing the
solvent, n-
butanol, in a dual beam Perkin-Elmer Lambda 2S UV-Visible Spectrometer
scanning
from 350 nm to 750 nm. The absorbances at 580 nm and 475 nm were used to
calculate the actual amounts of the two dyes incorporated into the ink after
filtering.
Determination of Black Dye Content in Inks Containine the Black Colorant
$~rstem
In the visible absorbance spectrum of the ink of Example 3, the absorbance at
580
nm is 0.5104 for 0.16211 grams of the ink sample in 250.0 mL of n-butanol. The
spectral strength was 787 mL A/gram (where A = absorbance). A commercially
available black ink for the Phaser~ 340 and 350 color printers containing
2.344% C.I.
Solvent Black 45 dye has a spectral strength of 710 mL A/gram. Therefore the
ink of
Example 3 contains 787/710 X 2.344%, or 2.60% black dye.
I2~termination of.Oran~e Die Content in Inks Containin~the Black Colorant
System
The absorbance at 580 nm in the visible spectrum of the ink in Example 3 is
0.5104,
and is due entirely to the black dye. No portion of the orange dye absorbs in
this
region of the spectrum. The ink containing only black dye has an absorbance at
4?5
nm that is 64.82% of its 580 nm absorbance. Therefore the absorbance at 475 nm
in
the spectrum attributable to the black dye is 0.5104 times 0.6482 or 0.3308.
Since the
absorbance in the visible spectrum of the ink of Example 3 is actually 0.4991,
the
additional absorbance is due entirely to the amount of orange dye that is
present, or
0.4991-0.3308 = 0.1683. The orange dye was determined from using the
CW Jaeger et al 24 Dkt No. 5895 US 1
CA 02245374 1998-08-18
aforementioned spectrometer to have an absorbance of 0.527 for every 1 mg of
dye in
250 mL of n-butanol. Therefore, the amount of the orange dye in the black
colorant
system must be 0.1683/0.527 = 0.319 mg. A sample size of 162.11 mg of the ink
of
Example 3 was used to generate the visible spectrum. Therefore the orange
content of
the sample of the ink of Example 3 is 0.319 mg divided by 162.11 mg or 0.197%
orange dye in the black ink. The ratio of orange to black dyes is 0.197 to
2.60 or
0.076 to 1.00.
Thermal Stabilit~Testing
An ink the same as described in Example 3 above was heated for 408 hours in a
glass beaker with a simulated print head reservoir in an oven at about
145°C. The
spectral strength (milliliters Absorbance per gram) decreased from about 771
to 645
or alternatively, the ink lost about 16.3% of its initial dye strength. This
compares very
favorably with actual operating conditions where it can be expected that the
ink would
be subjected to the elevated operating temperature in the print head of about
140° C
for at most and routinely less than about 8 hours.
Com tp~ ibility Testing
The black and orange dyes from Examples 3-6 were found to be mutually
compatible when used in a Tektronix Phaser~ 350 printer with a modified print
head
in which the cyan, yellow, magenta and black colors were replaced by the
clear, low,
medium and high optical density inks of Examples 7, 6, 5 and 4, respectively.
No
clogging of any of the orifices of the ink jet print head was observed, even
with
multiple purging/wiping cycles in the printer or even with extended dwell time
of the
test inks in the printers.
No reaction occurred among these inks and no precipitates were formed in the
inks on or around the print head surface during multiple normal purging cycles
while
the printer was in operation.
CW Jaeger et al 25 Dkt No. 5895 US 1
CA 02245374 1998-08-18
Adhesion Durability Testing
Samples of the inks in Examples 3-7 and a commercially available black ink
used in a Tektronix Phaser~ 350 color printer were tested for adhesion
durability on
transparent films or substrates routinely used for fluorescent lightbox
viewing in
medical diagnoses as follows. The first set of data is for a sample that was
imaged
twice, first with the ink of Example 3 and then with the ink of Example 5 to
achieve
125% coverage of the imaged area. The remaining samples were imaged just once
with the indicated ink of high, medium, low and clear optical density, and
with
commercially available black ink to compare adhesion to the transparent film
substrate.
A small test fixture that holds tautly a 1.9" square imaged sample of a 100
solid fill phase change ink on a transparency final receiving substrate was
utilized for
each test. A round approximately'/z inch diameter and approximately 1/4 inch
raised
plastic head mounted on a flat metal spring impacts the media or non-imaged
side of
the sample centered vertically and just above the midpoint. The hammer is
driven by a
3-S inch long, 7/16 inch wide and about 0.0035 inch tick metal spring that is
cocked
back about 1 inch using a trigger and release method. The sample is secured by
two
upright poles on either side that clamp the sample along the entire length of
each side
by sandwiching the sample between the upright and another piece of bracket.
The
amount of ink remaining on the imaged transparency substrate after impact is
determined by use of a software image analysis program and a flat bed scanner
that
first scans a selected area (a 1.46 x 1.09" rectangle) of the hammer impacted
image at a
resolution of 439 dots per inch and then analyzes the scanned area. The
software
program then calculates the percentage of ink that has been removed from the
scanned
rectangular area which permits an interpolation to be done to provide the
percentage
of ink remaining on the transparency substrate as shown in Table 2.
Gouee Durability Testing
Durability testing for gouging of solid fill phase change ink imaged
transparency substrates using samples of the inks and printing method for the
samples
described above for adhesion durability testing was performed as follows. A
variable
weight gouge test fixture was employed which is composed of three arms with
CSi Jaeger et al 26 Dkt No. 5895 US 1
CA 02245374 1998-08-18
weighted gouge fingers and a metal plate to which a print sample is secured.
The
metal plate moves the imaged print beneath the gouge fingers.
A print with a 100% solid fill image (at least 10" long and wide enough for up
to six interlaced scratch passes of the gouge fingers, each pass about 2
inches in width)
on transparency substrate was secured to the metal moveable plate so the gouge
was
along the length of the substrate on the ink image side. The three gouge
fingers have a
net weight of 924, 660, and 396 crams, respectively, during the first gouge.
Each
gouge finger is 0.5" wide by 1.245" long with a point of contact curve
equivalent to a
0.995" diameter disc. The disc is free of any ink particulate prior to all
gouging. The
gouge fingers are gently lowered at one end of the imaged portion of the
substrate so
that the gouge finger edges make a contact angle of approximately 75°
along the
leading edge of the gouge and approximately 15° along the trailing edge
(i.e. the image
was pulled against the gouge fingers, not pushed). The moveable metal plate
was
advanced for 9ti/32 inches at a speed of 0.450.05 inches/second. A second
gouge
was performed on the transparencies on the same print samples with the three
gouge
fingers containing a net weight of 1188, 1056, and 792 grams, respectively.
The sum of the areas of the resulting six gouges for each transparency media
are measured in mm= using the flat bed scanner and imaging analysis software
system
described above with respect to adhesion durability testing. The area with ink
removed is shown in Table 2.
TABLE 2
Example ExampleE.cample E.~campleExamplePhaser~
4 5 6 7 350
3/5 High IntermediateLow Clear printer
High/InterOpticalOptical Optical black
ink
125.o DensityDensity Density
fill
Adhesion
Durabilin~% 99.85 99.87 99.86 100.00 100.00 96.56
(Higher
is
Better)
Gouge mmZ 2481.42 2.106.782243.97 2232.62 - 3433.02
Resistance
(L,ower
is
Better)
zz
CA 02245374 2002-07-31
'the results show that the black shaded inks in Examples 3-b and the clear ink
in
Example 7 provide better adhesion durability on transparency media than the
current
commercially available black Tektronix Phaser~ 350 ink and the twice imaged or
over-
printed sample, and that the black shaded inks in Examples 4-6 also display
better
gouge resistance.
Having illustrated and described the principles of our invention in a
preferred
embodiment thereof, it should be readily apparent to those skilled in the art
that the
invention can be modified in arrangement and detail without departing from
such
principles. For example, the ink base or corner composition to form the ink
composition
of the present invention can be a low viscosity semicrystalline or crystalline
amide wax,
an ester wax, a polyethylene wax, a microcrystalline wax or a p~~raffin in
combination
with a hydrocarbon or resin based amorphous material, or an oligomer, or low
molecular
weight polymer or copolymer, or a tackifier, or a plasticizer and combinations
thereof.
In addition, the phase change ink base or carrier composition can comprise
isocyanate-
derived urethane resins, isocyanate-derived urethane/urea mixed resins,
isocyanate-
derived urethane waxes, and combinations thereof as disclosed in co-pending
U.S. Patent
Application Serial Nos. 08/672,815 entitled "Phase Change Ink Formulation
Using
Urethane and Urethane/Urea Isocyanate Derived Resins," filed June 28, 1996 and
08/907,805, entitled "Phase Change Ink Formulation Using an Isocyanate-Derived
Wax
and a Clear Ink Corner Base," filed August 8, 1997, both assigned to the
assignee of the
present invention. The combination of the ink carrier or base composition and
the
compatible black colorant system can be used with either a direca printing or
an indirect
transfer or offset printing printer. Also the phase change inks employing the
colorant
system of the present invention can be used in conjunction with an adhesion
promoting
coating that is applied to the transparent substrate prior to imaging. It
should be noted
that the present invention may be usefully employed in combination with
various prior
art techniques for obtaining variations in color intensity, including
dithering and
variation of ink drop size to provide enhanced gray scale image resolution and
quality.
Although the present invention has been described in terms of specific
embodiments,
changes and modifications can be carried out without departing from the scope
of the
invention which is intended to be limited only by the scope of the appended
claims.
28
