Note: Descriptions are shown in the official language in which they were submitted.
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REVERSIBLE THERMOCHROMIC AND PHOTOCHROMIC INK PENS AND
MARKERS
RELATED APPLICATIONS
[0001] This application claims benefit of priority to U.S.
Provisional Patent
Application Serial No. 61/584,398 filed January 9, 2012 and U.S. Provisional
Patent
Application Serial No. 61/732,120 filed November 30, 2012, the disclosures of
which are
incorporated herein by reference.
BACKGROUND
[0002] Ink is a liquid or paste that contains pigments or dyes and is
used to
color a surface to produce an image, text, or design. Ink is used for drawing
or writing
with a pen, brush, or quill. Thicker inks, in paste form, are used extensively
in letterpress
and lithographic printing. Conventional inks contain solvents, pigments, dyes,
resins,
lubricants, solubilizers, surfactants, particulate matter, fluorescers, and
other materials.
These materials control flow and thickness of the ink, and the appearance of
the ink when
dry.
[0003] Ink colorants include pigments and dyes. Pigment inks are used
more
frequently than dyes because they are more color-fast. Even so, pigments are
often more
expensive, less consistent in color, and have less of a color range than dyes.
Pigments are
solid, opaque particles suspended in ink to provide color. Pigment molecules
typically
link together in crystalline structures that are from 0.1-2 p m in size and
usually comprise
5-30 percent of the ink volume. Qualities such as hue, saturation, and
lightness vary
depending on the source and type of pigment.
[0004] Dye-based inks may have better color development than do
pigment-
based inks, as they can produce more color density per unit of mass. However,
because
dyes are dissolved in the liquid phase, they have a tendency to soak into
paper, making
the ink less efficient and potentially allowing the ink to bleed at the edges
of an image.
To circumvent this problem, dye-based inks are made with solvents that dry
rapidly or are
used with quick-drying methods of printing, such as blowing hot air on the
fresh print.
[0005] Chemicals that change color over a range of temperatures are
known as
thermochromic systems. Thermochromic chemicals can be manufactured to have a
color
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change that is reversible or irreversible. U.S. Patent No. 5,591,255, entitled
"Thermochromic Ink Formulations, Nail Lacquer and Methods of Use", issued
January 7,
1997 to Small et al., discloses methods of producing thermochromic coating
formulations
without ingredients known to be harmful to thermochromic inks. The use of
distilled
water as a fountain solution for off-set printing using thermochromic ink is
also disclosed.
[0006] Thermochromic systems use colorants that are either liquid
crystals or
leuco dyes. Liquid crystals are used less frequently than leuco dyes because
they are very
difficult to work with and require highly specialized printing and handling
techniques.
Thermochromic pigments are a system of interacting parts. Leuco dyes act as
colorants,
while weak organic acids act as color developers. Solvents or waxes variably
interact
with the leuco dyes according to the temperature of the system. As is known in
the art,
thermochromic systems are microencapsulated in a protective coating to protect
the
contents from undesired effects from the environment. Each microcapsule is
self-
contained, having all of the components of the entire system that are required
for the color
change. The components of the system interact with one another differently at
different
temperatures. Generally, the system is ordered and colored below a temperature
corresponding to the full color point. The system becomes increasingly
unordered and
starts to lose its color at a temperature corresponding to an activation
temperature.
[0007] Below the activation temperature, the system is usually
colored.
Above the activation temperature the system is usually clear or lightly
colored. The
activation temperature corresponds to a range of temperatures at which the
transition is
taking place between the full color point and the clearing point. Generally,
the activation
temperature is the temperature at which the human eye can perceive that the
system is
starting to lose color, or alternatively, starting to gain color. Presently,
thermochromic
systems are designed to have activation temperatures over a broad range, from
about -20
C to about 80 C or more. With heating, the system becomes increasingly
unordered and
continues to lose color until it reaches a level of disorder at a temperature
corresponding
to a clearing point. At the clearing point, the system lacks any recognizable
color.
[0008] In this manner, thermochromic pigments change from a specific
color
to clear upon the application of thermal energy or heat in a thermally-driven
cycle
exhibiting well-known hysteresis behavior. Thermochromic pigments come in a
variety
of colors. When applied to a substrate, such as paper, the pigment exhibits
the color of the
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dye at the core of the microcapsules. In one example, when heat is applied
generally in
the range of 30 to 32 C, the ink changes from the color of the pigment to
clear. When the
substrate is allowed to return to a temperature under approximately 30 C, the
ink returns
to the original color of the pigment.
[0009] U.S. Patent No. 5,785,746, entitled "Preparation Method for
Shear-
Thinning Water-Based Ball-Point Pen Inks Compositions and Ball-Point Pens
Employing
the Same", issued July 28, 1998 to Kito et al., discloses reversible
thermochromic
microcapsular pigment mixed in an ink composition. The microcapsules have
concavities
to moderate stress resulting from an external force during use in a ball-point
pen.
[0010] U.S. Patent No. 5,805,245, entitled "Multilayered Dispersed
Thermochromic Liquid Crystal", issued September 8, 1998 to Davis, discloses a
thermochromic substance, applied to inert films in stacked layers with a non-
invasive
barrier between each thermochromic substance. The thermochromic substance in
each
layer responds in a different temperature range so that as the temperature
changes, each
layer repeats a similar sequence of colors. The substrate is a water-based
acrylic
copolymer formulation coated or permeated with a black pigment. A transparent
inert
film or non-invasive barrier serves as a protective coating for the
thermochromic film and
as a support for the next layer of the thermochromic substance.
[0011] Specific thermochromic coating formulations are known in the
art.
See, for example, United States Patents 4,720,301, 5,219,625 5,558,700,
5,591,255,
5,997,849, 6,139,779, 6,494,950 and 7,494,537, all of which are expressly
incorporated
herein by reference. These thermochromic coatings are known to use various
components
in their formulations, and are generally reversible in their color change.
Thermochromic;
pigments for use in these coatings are commercially available in various
colors, with
various activation temperatures, clearing points and full color points.
Thermochromic
coatings may be printed by offset litho, dry offset, letterpress, gravure,
flexo and screen
processes, amongst others.
[0012] Ink pens have previously been developed that have
thermochromic
inks which can be activated by frictional heat into a colorless state. The
colored form of
the thermochromic ink cannot be regained without considerable difficulty. For
example,
reversing the thermochromic transition from colorless to color has previously
required
difficult and burdensome conditions, such as cooling the thermochromic ink to
a
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temperature of about below the freezing point of water. In addition to being
very difficult
to regain or reverse the thermochromic transition, previous colored to
colorless transitions
do not allow for a color to color and/or black to color transitions.
SUMMARY
[0013] Presented herein are improved and novel reversible
thermochromic and
photochromic ink compositions useful in pens and markers. Gel-ink and ball-ink
pens
disclosed herein use thermochromic and photochromic ink compositions, such as
thermochromic ink that transitions from one color to another color, and/or
from color to
colorless.
[0014] In one embodiment, the thermochromic ink compositions
disclosed
herein are activated at about body temperature.
[0015] In one embodiment, the thermochromic ink compositions
disclosed
herein are activated at about room temperature or higher than room
temperature.
[0016] In one embodiment, the present disclosure relates to
compositions for
reversible thermochromic and photochromic inks useful in shear-thinning ball-
point pens,
and a ball-point or gel-ink pen making use of the ink composition. The markers
and pens
using the ink compositions disclosed have eliminated the difficulties involved
in
conventional ball-point pen thermochromic and photochromic inks by providing
thermochromic ink compositions that allow for reversible thermochromic and
photochromic transitions from color to color, black to color and novel color
to colorless
transitions. The pens disclosed herein can give a smooth writing touch.
[0017] A reversible thermochromic composition may contain, by way of
example, a reversible thermochromic pigment in an amount from I% to 50% by
weight of
the ink. The reversible thermochromic pigment is susceptible to a temperature-
modulated
change of color between a first state and a second state along a thermally
activated
hysteresis loop. A non-thermochromic pigment is also provided. This may be,
for
example, a dye or photochromic material. The non-thermochromic pigment is of a
different color from the reversible thermochromic pigment when the reversible
thermochromic pigment is in a colored state, such that the non-thermochromic
pigment
and the reversible thermochromic pigment together present a first color when
the
reversible thermochromic pigment is in the first state and together present a
second color
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when the reversible thermochromic pigment is in the second state. These
pigments are
mixed for substantially homogenous distribution in a vehicle as the balance of
the
composition. This vehicle may be formulated to present an ink for use in a
ball point pen,
a gel pen or a marker.
[0018] In one aspect, a thermochromic ink formulation shifts color,
either
reversibly or irreversibly, from one color to another color upon the
application of heat to
the ink or to the substrate on which the ink resides. The thermochromic ink
formulation
preferably includes one or more thermochromic pigments in combination with a
non-
thermochromic pigment.
[0019] The ink may be formulated as a gel ink, a pen ink having less
viscosity
than the gel ink, or as a marker ink.
[0020] The ink may be formulated such that themochromic microcapsules
are
mixed with a microencapsulated photochromic dye as the non-thermochromic
colorant. .
DETAILED DESCRIPTION
[0021] A thermochromic ink formulation shifts from one color to
another
color upon the application of heat, either to the ink or to the substrate on
which the ink
has been applied. The thermochromic ink formulation preferably includes at
least one
thermochromic pigment in combination with a non-thermochromic colorant, such
as a
conventional pigment or dye. The non-thermochromic colorant may be any type of
conventional colorant known to the art.
[0022] In some embodiments, the ink is formulated as a gel ink,
substituting
the colorants described herein for the colorants of a conventional gel ink. In
other
embodiments, the ink is formulated as a pen ink, substituting the colorants
described
herein for the colorants of a conventional pen ink. In other embodiments, the
formulation
is used in a marker, substituting the colorants described herein for the
colorants of a
conventional marker.
[0023] The thermochromic ink formulation includes at least two
components,
such that after creating an image on a substrate, e.g., paper, and upon the
application of a
certain amount of thermal energy, the image changes from one color to another
color. The
thermochromic ink formulation may include, for example, thermochromic
microcapsules
and a conventional pigment that differs in color from the developed color of
the
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thermochromic pigment. The color of the thermochromic ink formulation may be
the
dominant, or visible, color as the ink is applied to the substrate. However,
upon the
application of thermal energy to the ink image, the thermochromic ink shifts
from colored
to clear, thereby allowing the non-dominant color of the non-thermochromic
component
to become visible.
[0024] In another example, a thermochromic pigment and a non-
thermochromic pigment may be combined in relative proportions so that the
combined
color pigments create a different color altogether when the thermochromic
color is
developed, and a second color when the thermochromic color is not developed.
For
example, the developed color of the thermochromic pigment may be blue, while
the color
of the non-thermochromic pigment may be yellow so that, when blended, they
create a
green color. Then, upon the application of thermal energy, the color of the
thermochromic
pigment goes to clear, thus allowing the yellow of the non-thermochromic
pigment to
dominate as the only visible color. The result is that the color of the image
goes from
green to yellow when heated. The image returns to the "blended" green color
when the
image is allowed to cool past the color developing temperature. The blending
of a color-
changing thermochromic ink with a static color ink provides essentially
limitless potential
for the image.
[0025] Thermochromic pigments for use in formulations of the present
disclosure are available commercially from a number of different manufacturers
or
suppliers. Manufacturers of thermochromic inks include, but are not limited
to, Color
Change Corporation (Streamwood, Illinois, US), LCR Hallcrest (Glenview,
Illinois, US),
Gem'innov (Gemenos, France), ISCA Limited (Newport, Wales, UK), B&H Colour
Change (London, England, UK), Thermographics Measurements Limited (Flintshire,
UK), Fujian Mecode Chemical Industry Company (Quanzhou, Fujian, China), and
Matsui
Color (Gardena, California, US). Distributors of thermochromic slurries
include, but are
not limited to, QCR Solutions Corporation (Port St. Lucie, Florida, US), Woo
Jeong Ind.
Inc. (Seoul, South Korea), HW Sands Corp. (Jupiter, Florida, US), Devine
Chemicals
(Consett, England, UK), Chemical Plus (Bangkok, Thailand), and PMC Chemicals
Limited (Altrincham, England, UK).
[0026] In a preferred embodiment, a thermochromic ink formulation
includes
thermochromic microcapsules in the thermochromic slurry that are spherical or
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substantially spherical in shape and exhibit a tight particle size
distribution in order to
achieve a homogeneous dispersion in the thermochromic ink formulation. The
thermochromic microcapsules are preferably all small or substantially all
small and are
more preferably all or substantially all under three micrometers in diameter.
The
thermochromic slurry preferably does not include flat or hemispherical
microcapsules or
microcapsules with surface concavities or other irregularities.
[0027] In a method of preparing a thermochromic ink formulation, a
thermochromic ink formulation is used as the pigment in a conventional gel ink
or a pen
ink. The viscosity of the combination may be adjusted by adding compatible
solvent to or
removing solvent from the combination to achieve the thermochromic ink
formulation.
The viscosity of the thermochromic ink formulation is preferably adjusted to a
predetermined value dependent upon the application for which the thermochromic
ink
formulation is to be used.
[0028] In some embodiments, the thermochromic ink formulation
includes
one or more additives, which may include, but is not limited to, one or more
of a
fluorescent additive, an optical brightener, and an infrared (IR) additive. In
a non-limiting
embodiment, the additive is used to provide a covert or an over security
benefit to a
substrate to which the thermochromic ink formulation is applied.
[0029] A non-thermochromic colorant is preferably mixed with a
thermochromic pigment in a ratio in the range of 1:1 to 3:1 by weight. The non-
thermochromic colorant is more preferably mixed with the thermochromic pigment
in a
ratio in the range of 1.5:1 to 2.5:1 by weight. In some embodiments, the non-
thermochromic colorant is mixed with the thermochromic pigment in a ratio in
the range
of 1.9:1 to 2.1:1 by weight. In one embodiment of the present invention, a non-
thermochromic colorant is mixed with a thermochromic pigment in a 2:1 ratio by
weight.
[0030] In some embodiments, the ink is a gel fluorescent ink. In some
embodiments, the color of the thermochromic pigment and the color of the non-
thermochromic colorant are contrasting or complementary and create a blend
color in the
thermochromic ink formulation below a critical temperature, although any
combination of
colors may be used within the spirit of the present invention.
[0031] In other embodiments, a thermochromic ink formulation includes
more
than one thermochromic pigment such that at least two temperature-dependent
color
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changes of the thermochromic ink formulation occur. The thermochromic pigments
preferably have different critical temperatures such that, in the case of a
thermochromic
ink formulation with two thermochromic pigments, at a first temperature below
the
critical temperatures of both thermochromic pigments, the formulation has a
first color,
which is the sum of colors of the first thermochromic pigment, the second
thermochromic
pigment, and the non-thermochromic colorant. At a temperature above the
critical
temperature of the first thermochromic pigment but below the critical
temperature of the
second thermochromic pigment, the formulation has a second color different
from the
first color, which is the sum of colors of the second thermochromic pigment
and the non-
thermochromic colorant. At a temperature above the critical temperatures of
the first
thermochromic pigment and the second thermochromic pigment, the formulation
has a
third color different from the first and second colors, which is the color of
the non-
thermochromic colorant. Any number of thermochromic pigments may be combined
in
this manner.
[0032] In a non-limiting example, the thermochromic ink is blue, the
non-
thermochromic pigment is fluorescent pink, the thermochromic pigment is purple
below a
critical temperature, and the thermochromic ink formulation is pink above the
critical
temperature. In some embodiments, the process is reversible, with the
thermochromic
pigment returning to a purple color upon cooling below the critical
temperature. In other
embodiments, the color change is irreversible. The reversibility of the color
change
depends on the hysteresis of the color change. The reversibility of the color
change is
preferably selected based on the specific application for the thermochromic
ink.
[0033] In the case of a thermochromic ink formulation where the color
changes are reversible, the thermochromic ink formulation may be used as a
visual
temperature range indicator, especially when multiple thermochromic pigments
are used
in the formulation to indicate multiple temperature thresholds. In the case of
such a
thermochromic ink formulation where the color changes are irreversible, the
thermochromic ink formulation may be used as a visual indicator of the maximum
temperature range to which the thermochromic ink formulation has been exposed.
[0034] The critical temperature is also preferably selected based on
the
specific application for the thermochromic ink. In some embodiments, the
critical
temperature is below room temperature. In other embodiments, the critical
temperature is
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above room temperature but below human body temperature such that the color
change is
triggered by human touch. In some embodiments, the critical temperature is
between 25
and 37 C. In some embodiments, the critical temperature is about 31 C. In
yet other
embodiments, the critical temperature is above human body temperature such
that another
heat source is required to bring the ink to the critical temperature.
[0035] In a non-limiting example, a thermochromic pen ink formulation
or a
thermochromic gel ink formulation of the present invention is converted to a
thermochromic marker ink formulation of the present invention by adding about
10% of
water by volume to the thermochromic pen ink formulation or thermochromic gel
ink
formulation.
[0036] In some embodiments, a gel pen of the present invention
includes a
thermochromic gel ink formulation of the present invention. In some
embodiments, the
gel pen includes an about 8-mm ball tip. In some embodiments, the ball tip is
at least 8
mm in diameter. An 8-mm diameter ball tip allows the passage of the
thermochromic
particles without damaging the particles for some thermochromic gel ink
formulations of
the present invention.
[0037] In some embodiments, a marker of the present invention
includes a
marker ink composition of the present invention. In some embodiments, the
marker is a
mechanical valve-type marker, also known as a paint marker, with a porous-type
felt tip.
[0038] Accordingly, it is to be understood that the embodiments of
the
invention herein described are merely illustrative of the application of the
principles of
the invention. Reference herein to details of the illustrated embodiments is
not intended to
limit the scope of the claims, which themselves recite those features regarded
as essential
to the invention.
Overview of Thermochromic Pigments
[0039] Reversible thermochromic and photochromic ink pens disclosed
herein
contain thermochromic systems that are prepared by combining a color forming
molecule
or molecules such as leuco dyes that are capable of extended conjugation by
proton gain
or electron donation; a color developer or developers that donate a proton or
accept an
electron; and a single solvent, or a blend of co-solvents. The solvent or
blend of co-
solvents are chosen based on melting point and establish the thermochromic
temperature
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range of the system. These formulations are then microencapsulated within a
polymeric
shell.
[0040] These microcapsules encapsulate a thermochromic system mixed
with
a solvent. The thermochromic system has a material property of a thermally
conditional
hysteresis window that presents a thermal separation. Thermochromic
encapsulated dyes
undergo a color change over a specific temperature range. By way of example, a
dye may
change from a particular color at low temperature to colorless at a high
temperature, such
as red at 21 C and colorless at above 33 C. The color change temperature is
controllable, such that the color change can take place at different
temperatures. In one
example, the color change may occur at a temperature just below a person's
external body
temperature so that a color change occurs in response to a human touch or may
transition
at about room temperature. For example, the ideal temperature of color change
may
range from 12 C to 15 C, 21 C to 27 C, 23 C to 27 C, 27 C to 33 C.
Custom
thermochromic pigments and inks with specified colors and transition
temperature ranges
may be formulated and produced on commercial order from such companies as
Chromatic Technologies, Inc. of Colorado Springs, Colorado.
[0041] Several types of ingredients are traditionally added to ink
formulations.
The combination of all the ingredients in an ink, other than the pigment, is
called the
vehicle. The vehicle carries the pigment to the substrate and binds the
pigment to the
substrate. The correct combination of vehicle ingredients will result in the
wetting of an
ink. This wetting means that the vehicle forms an absorbed film around the
pigment
particles. The main ingredient in an ink is the binder. This may be a resin,
lacquer or
varnish or some other polymer. The binder characteristics vary depending on
the type of
printing that is being done and the desired final product. The second main
ingredient is
the colorant itself, for example, as described above. The remaining
ingredients are added
to enhance the color and printing characteristics of the binder and the
colorant. These
remaining ingredients may include reducers (solvents), waxes, surfactant,
thickeners,
driers, and/or UV inhibitors.
Definitions
[0042] Activation temperature - The temperature above which the ink
has
almost achieved its final clear or light color end point. The color starts to
fade at
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approximately 4 C below the activation temperature and will be in between
colors within
the activation temperature range.
[0043] Ball-point pen - As referred to herein, ball-point pens and
gel-ink pens
are interchangeable embodiments of pen means using reversible thermochromic
and
photochromic ink compositions of the present disclosure. A ball-point pen may
also be
referred to as a marker. A ball-point pen may also be referred to as a writing
instrument.
[0044] Clearing point - The temperature at which the color of a
thermochromic system is diminished to a minimal amount and appears to lose no
further
color density upon further heating.
[0045] Full color point - The temperature at which a thermochromic
system
has achieved maximum color density upon cooling and appears to gain no further
color
density if cooled to a lower temperature.
[0046] A gel ink, as used herein, refers to a fluid composition
including a
pigment suspended in a based gel. Gel inks typically have a higher viscosity
than pen
inks and can have a higher concentration of pigment. Gel inks are available in
a wide
variety of colors, including, but not limited to, pastel colors, bright
colors, metallic colors,
glittery colors, and opalescent colors. The pigments in a gel ink are
generally not in a
dissolved state.
[0047] Gel-ink pen - As referred to herein, ball-point pens and gel-
ink pens
are interchangeable embodiments of pen means using reversible thermochromic
and
photochromic ink compositions of the present disclosure. A gel-ink pen may
also be
referred to as a marker. A gel-ink pen may also be referred to as a writing
instrument.
[0048] Hysteresis - The difference in the temperature profile of a
thermo
chromic system when heated from the system when cooled.
[0049] Hysteresis window - The temperature difference in terms of
degrees
that a thermochromic system is shifted as measured between the derivative plot
of chroma
of a spectrophotometer reading between the cooling curve and the heating
curve.
[0050] A marker, as used herein, refers to any writing instrument
with a
porous tip or felt tip made of a fibrous material for delivering ink.
A pen, as used herein, refers to any non-marker, ink-based writing instrument
including,
but not limited to, ball-point pens, roller-ball pens, and fountain pens.
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[0051] A pen ink, as used herein, refers to a fluid or gel
composition including
a pigment and a carrier or vehicle in which the pigment is suspended. In some
embodiments, the vehicle is water. In other embodiments, the solvent is a non-
aqueous
solvent, such as an organic solvent such as alcohol. Photochromic ink - A
mixture of
dyes, solvents, and additives (encapsulated or non-encapsulated) that can
undergo
reversible color change in response to exposure to light of various
wavelengths.
[0052] Thermochromic system - A mixture of dyes, developers,
solvents, and
additives (encapsulated or non-encapsulated) that can undergo reversible color
change in
response to temperature changes.
[0053] Thermochromic ink ¨ An ink that contains a pigment formed of a
mixture of dyes, developers, solvents, and additives that are encapsulated and
can
undergo reversible color change in response to temperature changes. The color
change is
based upon the action of micrpoencapsulated leuco dyes and developers, which
are
referred to herein as thermochromic pigments. Thermochromic pigments may be
sold as
dry powders or in water-based slurries of encapsulated dye.
[0054] Leuco dye - A leuco dye is a dye whose molecules can acquire
two
forms, one of which is colorless.
Thermochromic Inks
[0055] Thermochromic inks useful in ball-point pens and gel-ink pens
contain
microcapsules, which encapsulate a thermochromic system mixed with a solvent.
The
thermochromic system has a material property of a thermally conditional
hysteresis
window that presents a thermal separation. These inks may be improved
according to the
instrumentalities described herein by using a co-solvent that is combined with
the
thermochromic system and selected from the group consisting of derivatives of
mysristic
acid, derivatives of behenyl acid, derivatives of palmytic acid and
combinations thereof.
This material may be provided in an effective amount to reduce the thermal
separation in
the overall ink to a level less than eighty percent of separation that would
otherwise occur
if the material were not added. This effective amount may range, for example
from the
12% to 15% by weight of the composition.
[0056] The thermochromic system may contain, for example, at least
one
chromatic organic compound and co-solvents.
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[0057] One example of a thermochromic system includes a leuco dye
having a
lactone ring structure and a phenolic developer. Within the encapsulated
thermochromic
systems, complexes form between the dye and the weak acid developer that allow
the
lactone ring structure of the leuco dye to be opened. The nature of the
complex is such
that the hydroxyl groups of the phenolic developer interact with the open
lactone ring
structure forming a supra-molecular structure that orders the dyes and
developers such
that a color is formed. Color forms from this supra-molecular structure
because the dye
molecule in the ring open structure is cationic in nature and the molecule has
extended
conjugation allowing absorption in the visible spectrum thus producing a
colored species.
The color that is perceived by the eye is what visible light is not absorbed
by the complex.
The nature of the dye/developer complex depends on the molar ratio of dye and
developer. The stability of the colored complex is determined by the affinity
of the
solvent for itself, the developer or the dye/developer complex. In a solid
state, below the
full color point, the dye/developer complex is stable. In the molten state,
the solvent
destabilizes the dye/developer complex and the equilibrium is more favorably
shifted
towards a developer/solvent complex. This happens at temperatures above the
full color
point because the dye/developer complex is disrupted and the extended
conjugation of the
7E cloud electrons that allow for the absorption of visible light are
destroyed.
[0058] The melting and crystallization profile of the solvent system
determines the nature of the thermochromic system. The full color point of the
system
occurs when the maximum amount of dye is developed. In a crystallized solvent
state,
the dye/developer complex is favored where the dye and developer exist in a
unique
crystallized structure, often intercalating with one another to create an
extended
conjugated 7E system. In the molten state, the solvent(s), in excess, have
enough kinetic
energy to disrupt the stability of the dye/developer complex, and the
thermochromic
system becomes decolorized.
[0059] The addition of a co-solvent with a significantly higher
melting point
than the other dramatically changes the melting properties of both the
solvents. By
mixing two solvents that have certain properties, a blend can be achieved that
possesses a
eutectic melting point. The melting point of a eutectic blend is lower than
the melting
point of either of the co-solvents alone and the melting point is sharper,
occurring over a
smaller range of temperatures. The degree of the destabilization of the
dye/developer
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complex can be determined by the choice of solvents. By creating unique
eutectic blends,
both the clearing point and the full color point can be altered
simultaneously. The degree
of hysteresis is then shifted in both directions simultaneously as the
sharpness of the
melting point is increased.
[0060] Temperature changes in thermochromic systems are associated
with
color changes. If this change is plotted on a graph having axes of temperature
and color,
the curves do not align and are offset between the heating cycle and the
cooling cycle.
The entire color versus temperature curve has the form of a loop. Such a
result shows
that the color of a thermochromic system does not depend only on temperature,
but also
on the thermal history, i.e. whether the particular color was reached during
heating or
during cooling. This phenomenon is generally referred to as a hysteresis cycle
and
specifically referred to herein as color hysteresis or the hysteresis window.
Decreasing
the width of this hysteresis window to approximately zero would allow for a
single value
for the full color point and a single value for the clearing point. This would
allow for a
reliable color transition to be observed regardless of whether the system is
being heated or
cooled. Nonetheless, the concept decreasing separation across the hysteresis
window is
elusive in practice. Thus, it is an object of the present disclosure to
provide
thermochromic systems with a reduced hysteresis window achieved by shifting
both the
full color point and the clearing point such as in memory inks, for example.
[0061] It is also an object of this disclosure to provide
formulations of
extended hysteresis windows in ink formulations.
Leuco Dyes
[0062] Leuco dyes most commonly used as color formers in
thermochromic
systems of the present disclosure include, but are not limited to, generally;
spirolactones,
fluorans, spiropyrans, and fulgides; and more specifically; diphenylmethane
phthalide
derivatives, phenylindolylphthalide derivatives, indolylphthalide derivatives,
diphenylmethane azaphthalide derivatives, phenylindolylazaphthalide
derivatives, fluoran
derivatives, styrynoquinoline derivatives, and diaza-rhodamine lactone
derivatives which
can include: 3,3-bis(p-dimethylaminopheny1)-6-dimethylaminophthalide; 3-(4-
diethylaminopheny1)-3-(1-ethyl-2-methylindol-3-y1) phthalide; 3,3-bis(1-n-
buty1-2-
methylindo1-3-yflphthalide; 3,3-bis(2-ethoxy-4-diethylaminopheny1)-4-
azaphthalide; 3-
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[2-ethoxy-4-(N-ethylanilino)phenyl[-3-(1-ethyl-2-methylindol-3-y1)-4-
azaphthalide; 3,6-
dimethoxyfluoran; 3,6-di-n-butoxyfluoran; 2-methyl-6-(N-ethyl-N-p-
tolylamino)fluoran;
3-chloro-6-cyclohexylaminofluoran; 2-methyl-6-cyclohexylaminofluoran; 2-(2-
chloroanilino)-6-di-n-butylamino fluoran; 2-(3-trifluoromethylanilino)-6-
diethylaminofluoran; 2-(N-methylanilino)-6-(N-ethyl-N-p-tolylamino) fluoran,
1,3-
dimethy1-6-diethylaminofluoran; 2-chloro-3-methy1-6-diethylamino fluoran; 2-
anilino-3-
methy1-6-diethylaminofluoran; 2-anilino-3-methyl-6-di-n-butylamino fluoran; 2-
xylidino-
3-methy1-6-diethylaminofluoran; 1,2-benzo-6-diethylaminofluoran; 1,2-benzo-6-
(N-ethyl-
N-isobutylamino)fluoran,1,2-benzo-6-(N-ethyl-N-isoamylamino)fluoran; 2-(3-
methoxy-4-
dodecoxystyryl)quinoline; spiro[5H-(1) benzopyrano(2,3-d)pyrimidine-
5,1(3'H)isobenzofuran[-3'-one; 2-(diethylamino)-8-(diethylamino)-4-methyl-
spiro[5H-
(1)benzopyrano(2,3-d)pyrimidine-5,P(3'H)isobenzofuran[-3'-one; 2-(di-n-
butylamino)-8-
(di-n-butylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-
5,1(3'H)isobenzofuran[-3'-one; 2-(di-n-butylamino)-8-(diethylamino)-4-methyl-
spiro[5H-
(1)benzopyrano(2,3-d)pyrimidine-5,1(3'H)isobenzofuran[-3'-one; 2-(di-n-
butylamino)-
8(N-ethyl-N-isoamylamino)-4-methyl-spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-
5,1(3'H)isobenzofuran[-3'-one; and 2-(di-n-butylamino)-8-(di-n-butylamino)-4-
phenyl
and trisubstitutecl pyridines.
Developers
[0063] Weak acids that can be used as color developers act as proton
donors,
changing the dye molecule between its leuco form and its protonated colored
form;
stronger acids make the change irreversible. Examples of developers used in
the present
disclosure include but are not limited to: bisphenol A; bisphenol F;
tetrabromobisphenol
A; 1'-methylenedi-2-naphthol; 1,1,1-tris(4-hydroxyphenyl)ethane; 1,1-bis(3-
cyclohexy1-
4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-
bis(4-hydroxyphenyl)cyclohexane; 1,3-bis[2-(4-hydroxypheny1)-2-propyl[benzene;
1-
naphthol; 2-naphthol; 2,2 bis(2-hydroxy-5-biphenylyl)propane; 2,2-bis(3-
cyclohexy1-4-
hydroxy)propane; 2,2-bis(3-sec-buty1-4-hydroxyphenyl)propane; 2,2-bis(4-
hydroxy-3-
isopropylphenyl)propane; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-bis(4-
hydroxyphenyl)propane; 2,3,4-trihydroxydiphenylmethane; 4,4' -(1,3-
Dimethylbutylidene)diphenol; 4,4' -(2-Ethylidene)diphenol; 4,4' -(2-
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hydroxybenzylidene)bis(2,3,6-trimethylphenol); 4,4'-biphenol; 4,4'-
dihydroxydiphenyl
ether; 4,4'-dihydroxydiphenylmethane; 4,4'-methylidenebis(2-methylphenol); 4-
(1,1,3,3-
tetramethylbutyl)phenol; 4-phenylphenol; 4-tert-butylphenol; 9,9-bis(4-
hydroxyphenyl)fluorine; 4,4'-(ethane-1,1-diy1)diphenol; alpha,alpha'-bis(4-
hydroxypheny1)-1,4-diisopropylbenzene; alpha,alpha,alpha'-tris(4-
hydroxypheny1)-1-
ethy1-4-isopropylbenzene; benzyl 4-hydroxybenzoate; bis(4-
hydroxyphenyl)sulfide;
bis(4-hydroxyphenyl)sulfone; propyl 4-hydroxybenzoate; methyl 4-
hydroxybenzoate;
resorcinol; 4-tert-butyl-catechol; 4-tert-butyl-benzoic acid; 1,f-methylenedi-
2-naphthol
1,1,1-tris(4-hydroxyphenyl)ethane; 1,1-bis(3-cyclohexy1-4-
hydroxyphenyl)cyclohexane; 1,1-
bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-bis(4-hydroxyphenyl)cyclohexane;
1,3-
bis112-(4-hydroxypheny0-2-propyllbenzene; 1- naphthol 2,2'-biphenol; 2,2-
bis(2-
hydroxy-5-biphenylyl)propane; 2,2-bis(3-cyclohexy1-4-hydroxyphenyl)propane;
2,2-
bis(3-sec-buty1-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-
isopropylphenyl)propane;
2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-bis(4-hydroxyphenyl)propane;
2,3,4-
trihydroxydiphenylmethane; 2- naphthol; 4,4'-(1,3-dimethylbutylidene)diphenol;
4,4'-(2-
ethylhexylidene)dipheno14,4'-(2-hydroxybenzylidene)bis(2,3,6-trimethylphenol);
4,4'-
biphenol; 4,4'-dihydroxydiphenyl ether; 4,4'-dihydroxydiphenylmethane; 4,4'-
ethylidenebisphenol; 4,4'-methylenebis(2-methylphenol); 4-(1,1,3,3-
tetramethylbutyl)phenol; 4-phenylphenol; 4-tert-butylphenol; 9,9-bis(4-
hydroxyphenyl)fluorine; alpha,alpha'-bis(4-hydroxypheny0-1,4-
diisopropylbenzene;
a,a,a-tris(4-hydroxypheny1)-1-ethyl-4-isopropylbenzene; benzyl 4-
hydroxybenzoate;
bis(4-hydroxyphenyl) sulfidem; bis(4-hydroxyphenyl) sulfone methyl 4-
hydroxybenzoate; resorcinol; tetrabromobisphenol A; 3,5-di-tertbutyl-salicylic
acid; zinc
3,5-di-tertbutylsalicylate; 3-phenyl-salicylic acid; 5-tertbutyl-salicylic
acid; 5-n-octyl-
salicylic acid; 2,2'-biphenol; 4,4'-di-tertbuty1-2,2'-biphenol; 4,4'-di-n-
alky1-2,2'-
biphenol; and 4,4'-di-halo-2,2'-biphenol, wherein the halo is chloro, fluoro,
bromo, or
iodo.
Solvents
[0064] The best solvents to use within the thermochromic system are
those
that have low reactivity, have a relatively large molecular weight (i.e. over
100), and
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which are relatively non-polar. Very low molecular weight aldehydes, ketones,
diols and
aromatic compounds should not be used as solvents within the thermochromic
system.
[0065] Thermochromic inks disclosed herein use a co-solvent that is
combined with the thermochromic system and selected from the group consisting
of
derivatives of mysristic acid, derivatives of behenyl acid, derivatives of
palmytic acid and
combinations thereof. This material may be provided in an effective amount to
reduce
the thermal separation in the overall ink to a level less than eighty percent
of separation
that would otherwise occur if the material were not added. This effective
amount may
range, for example from the 12% to 15% by weight of the composition.
[0066] The addition of a co-solvent with a significantly higher
melting point
than the other dramatically changes the melting properties of both the
solvents. By
mixing two solvents that have certain properties, a blend can be achieved that
possesses a
eutectic melting point. The melting point of a eutectic blend is lower than
the melting
point of either of the co-solvents alone and the melting point is sharper,
occurring over a
smaller range of temperatures. The degree of the destabilization of the
dye/developer
complex can be determined by the choice of solvents. By creating unique
eutectic blends,
both the clearing point and the full color point can be altered
simultaneously. The degree
of hysteresis is then shifted in both directions simultaneously as the
sharpness of the
melting point is increased. Copending application no. 13/363,070 filed January
31, 2012
discloses thermochromic systems with controlled hysteresis, and is hereby
incorporated
by reference to the same extent as though fully replicated herein. According
to the
instrumentalities described therein, the microencapsulate pigments may be
formulated to
have color transition temperatures across a hysteresis window of less than
five degrees
centigrade or more than 60 or 80 degrees centigrade.
[0067] Properties of at least one of the co-solvents used in the
present
disclosure include having a long fatty tail of between 12 and 24 carbons and
possessing a
melting point that is about 70 C to about 200 C greater than the co-solvent
partner. The
co-solvents are preferably also completely miscible at any ratio.
[0068] Solvents and/or co-solvents used in thermochromic generally
may
include, but are not limited to, sulfides, ethers, ketones, esters, alcohols,
and acid amides.
These solvents can be used alone or in mixtures of 2 or more. Examples of the
sulfides
include: di-n-octyl sulfide; di-n-nonyl sulfide; di-n-decyl sulfide; di-n-
dodecyl sulfide; di-
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n-tetradecyl sulfide; di-n-hexadecyl sulfide; di-n-octadecyl sulfide; octyl
dodecyl sulfide;
diphenyl sulfide; dibenzyl sulfide; ditolyl sulfide; diethylphenyl sulfide;
dinaphthyl
sulfide; 4,4'-dichlorodiphenyl sulfide; and 2,4,5,4'tetrachlorodiphenyl
sulfide. Examples
of the ethers include: aliphatic ethers having 10 or more carbon atoms, such
as dipentyl
ether, dihexyl ether, diheptyl ether, dioctyl ether, dinonyl ether, didecyl
ether, diundecyl
ether, didodecyl ether, ditridecyl ether, ditetradecyl ether, dipentadecyl
ether, dihexadecyl
ether, dioctadecyl ether, decanediol dimethyl ether, undecanediol dimethyl
ether,
dodecanediol dimethyl ether, tridecanediol dimethyl ether, decanediol diethyl
ether, and
undecanediol diethyl ether; alicyclic ethers such as s-trioxane; and aromatic
ethers such as
phenylether, benzyl phenyl ether, dibenzyl ether, di-p-tolyl ether, 1-
methoxynaphthalene,
and 3,4,5trimethoxytoluene.
[0069] Examples of ketone solvents include: aliphatic ketones having
10 or
more carbon atoms, such as 2-decanone, 3-decanone, 4-decanone, 2-undecanone, 3-
undecanone, 4-undecanone, 5-undecanone, 6-undecanone, 2-dodecanone, 3-
dodecanone,
4-dodecanone, 5-dodecanone, 2-tridecanone, 3-tridecanone, 2-tetradecanone, 2-
pentadecanone, 8-pentadecanone, 2-hexadecanone, 3-hexadecanone, 9-
heptadecanone, 2-
pentadecanone, 2-octadecanone, 2-nonadecanone, 10-nonadecanone, 2-eicosanone,
11-
eicosanone, 2-heneicosanone, 2-docosanone, laurone, and stearone; aryl alkyl
ketones
having 12 to 24 carbon atoms, such as n-octadecanophenone, n-
heptadecanophenone, n-
hexadecanophenone, n-pentadecanophenone, n-tetradecanophenone, 4-n-
dodecaacetophenone, n-tridecanophenone, 4-n-undecanoacetophenone, n-
laurophenone,
4-n-decanoacetophenone, n-undecanophenone, 4-n-nonylacetophenone, n-
decanophenone, 4-n-octylacetophenone, n-nonanophenone, 4-n-heptylacetophenone,
n-
octanophenone, 4-n-hexylacetophenone, 4-n-cyclohexylacetophenone, 4-tert-
butylpropiophenone, n-heptaphenone, 4-n-pentylacetophenone, cyclohexyl phenyl
ketone, benzyl n-butyl ketone, 4-n-butylacetophenone, n-hexanophenone, 4-
isobutylacetophenone, 1-acetonaphthone, 2-acetonaphthone, and cyclopentyl
phenyl
ketone; aryl aryl ketones such as benzophenone, benzyl phenyl ketone, and
dibenzyl
ketone; and alicyclic ketones such as cyclooctanone, cyclododecanone,
cyclopentadecanone, and 4-tert-butylcyclohexanone, ethyl caprylate, octyl
caprylate,
stearyl caprylate, myristyl caprate, stearyl caprate, docosyl caprate, 2-
ethylhexyl laurate,
n-decyl laurate, 3-methylbutyl myristate, cetyl myristate, isopropyl
palmitate, neopentyl
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palmitate, nonyl palmitate, cyclohexyl palmitate, n-butyl stearate, 2-
methylbutyl stearate,
stearyl behenate 3,5,5-trimethylhexyl stearate, n-undecyl stearate, pentadecyl
stearate,
stearyl stearate, cyclohexylmethyl stearate, isopropyl behenate, hexyl
behenate, lauryl
behenate, behenyl behenate, cetyl benzoate, stearyl p-tert-butylbenzoate,
dimyristyl
phthalate, distearyl phthalate, dimyristyl oxalate, dicetyl oxalate, dicetyl
malonate,
dilauryl succinate, dilauryl glutarate, diundecyl adipate, dilauryl azelate,
di-n-nonyl
sebacate, 1,18-dineopentyloctadecylmethylenedicarboxylate, ethylene glycol
dimyristate,
propylene glycol dilaurate, propylene glycol distearate, hexylene glycol
dipalmitate, 1,5-
pentanediol dimyristate, 1,2,6-hexanetriol trimyristate, 1,4-cyclohexanediol
didecanoate,
1,4-cyclohexanedimethanol dimyristate, xylene glycol dicaprate, and xylene
glycol
distearate.
[0070] Ester solvents can be selected from esters of a saturated
fatty acid with
a branched aliphatic alcohol, esters of an unsaturated fatty acid or a
saturated fatty acid
having one or more branches or sub stituents with an aliphatic alcohol having
one or more
branches or 16 or more carbon atoms, cetyl butyrate, stearyl butyrate, and
behenyl
butyrate including 2-ethylhexyl butyrate, 2-ethylhexyl behenate, 2-ethylhexyl
myristate,
2-ethylhexyl caprate, 3,5,5-trimethylhexyl laurate, 3,5,5-trimethylhexyl
palmitate, 3,5,5-
trimethylhexyl stearate, 2-methylbutyl caproate, 2-methylbutyl caprylate, 2-
methylbutyl
caprate, 1-ethylpropyl palmitate, 1-ethylpropyl stearate, 1-ethylpropyl
behenate, 1-
ethylhexyl laurate, 1-ethylhexyl myristate, 1-ethylhexyl palmitate, 2-
methylpentyl
caproate, 2-methylpentyl caprylate, 2-methylpentyl caprate, 2-methylpentyl
laurate, 2-
methylbutyl stearate, 2-methylbutyl stearate, 3-methylbutyl stearate, 2-
methylheptyl
stearate, 2-methylbutyl behenate, 3-methylbutyl behenate, 1-methylheptyl
stearate, 1-
methylheptyl behenate, 1-ethylpentyl caproate, 1-ethylpentyl palmitate, 1-
methylpropyl
stearate, 1-methyloctyl stearate, 1-methylhexyl stearate, 1,1dimethylpropyl
laurate, 1-
methylpentyl caprate, 2-methylhexyl palmitate, 2-methylhexyl stearate, 2-
methylhexyl
behenate, 3,7-dimethyloctyl laurate, 3,7-dimethyloctyl myristate, 3,7-
dimethyloctyl
palmitate, 3,7-dimethyloctyl stearate, 3,7-dimethyloctyl behenate, stearyl
oleate, behenyl
oleate, stearyl linoleate, behenyl linoleate, 3,7-dimethyloctyl erucate,
stearyl erucate,
isostearyl erucate, cetyl isostearate, stearyl isostearate, 2-methylpentyl 12-
hydroxystearate, 2-ethylhexyl 18-bromostearate, isostearyl 2-ketomyristate, 2-
ethylhexy1-
2-fluoromyristate, cetyl butyrate, stearyl butyrate, and behenyl butyrate.
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[0071] Examples of the alcohol solvents include monohydric aliphatic
saturated alcohols such as decyl alcohol, undecyl alcohol, dodecyl alcohol,
tridecyl
alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl
alcohol,
octadecyl alcohol, eicosyl alcohol, behenyl alcohol and docosyl alcohol;
aliphatic
unsaturated alcohols such as allyl alcohol and oleyl alcohol, alicyclic
alcohols such as
cyclopentanol, cyclohexanol, cyclooctanol, cyclododecanol, and 4-tert-
butylcyclohexanol; aromatic alcohols such as 4-methylbenzyl alcohol and
benzhydrol;
and polyhydric alcohols such as polyethylene glycol. Examples of the acid
amides
include acetamide, propionamide, butyramide, capronamide, caprylamide, capric
amide,
lauramide, myristamide, palmitamide, stearamide, behenamide, oleamide,
erucamide,
benzamide, capronanilide, caprylanilide, capric anilide, lauranilide,
myristanilide,
palmitanilide, stearanilide, behenanilide, oleanilide, erucanilide, N-
methylcapronamide,
N-methylcaprylamide, N-methyl (capric amide), N-methyllauramide, N-
methylmyristamide, N-methylpalmitamide, N-methylstearamide, N-
methylbehenamide,
N-methyloleamide, N-methylerucamide, N-ethyllauramide, N-ethylmyristamide, N-
ethylpalmitamide, N-ethylstearamide, N-ethyloleamide, N-butyllauramide, N-
butylmyristamide, N-butylpalmitamide, N-butylstearamide, N-butyloleamide, N-
octyllauramide, N-octylmyristamide, N-octylpalmitamide, N-octylstearamide, N-
octyloleamide, N-dodecyllauramide, N-dodecylmyristamide, N-dodecylpalmitamide,
N-
dodecylstearamide, N-dodecyloleamide, dilauroylamine, dimyristoylamine,
dipalmitoylamine, distearoylamine, dioleoylamine, trilauroylamine,
trimyristoylamine,
tripalmitoylamine, tristearoylamine, trioleoylamine, succinamide, adipamide,
glutaramide, malonamide, azelamide, maleamide, N-methylsuccinamide, N-
methyladip
amide, N-methylglutaramide, N-methylmalonamide, N-methylazelamide, N-
ethylsuccinamide, N-ethyladipamide, N-ethylglutaramide, N-ethylmalonamide, N-
ethylazelamide, N-butylsuccinamide, N-butyladipamide, N-butylglutaramide, N-
butylmalonamide, N-octyladipamide, and N-dodecyladipamide.
[0072] Among these solvents, it has been discovered that certain
solvents have
the effect of reducing the hysteresis window. The solvent may be material
combined with
the thermochromic system, for example, to reduce thermal separation across the
hysteresis window to a level demonstrating 80%, 70%, 50%, 40%, 30% or less of
the
thermal separation that would exist if the co-solvent were not present. The co-
solvent is
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selected from the group consisting of derivatives of mysristic acid,
derivatives of behenyl
acid, derivatives of palmytic acid and combinations thereof. Generally, these
materials
include myristates, palmitates, behenates, together with myristyl, stearyl,
and behenyl
materials and certain alcohols. In one aspect, these materials are preferably
solvents and
co-solvents from the group including isopropyl myristate, isopropyl palmitate,
methyl
palmitate, methyl stearate, myristyl myristate, cetyl alcohol, stearyl
alcohol, behenyl
alcohol, stearyl behenate, and stearamide. These co-solvents are added to the
encapsulated thermochromic system in an amount that, for example, ranges from
9% to
18% by weight of the thermochromic system as encapsulated, i.e., excluding the
weight
of the capsule. This range is more preferably from about 12% to about 15% by
weight.
Light Stabilizers
[0073] Thermochromic inks containing leuco dyes are available for all
major
ink types such as water-based, ultraviolet cured and epoxy. The properties of
these inks
differ from process inks. For example, most thermochromic inks contain the
thermochromic systems as microcapsules, which are not inert and insoluble as
are
ordinary process pigments. The size of the microcapsules containing the
thermochromic
systems ranges typically between 3-5 um which is more than 10-times larger
than regular
pigment particles found in most inks. The post-print functionality of
thermochromic inks
can be adversely affected by ultraviolet light, temperatures in excess of 140
C and
aggressive solvents. The lifetime of these inks is sometimes very limited
because of the
degradation caused by exposure to ultraviolet light from sunlight.
[0074] In other instances, additives used to fortify the encapsulated
thermochromic systems by imparting a resistance to degradation by ultraviolet
light by
have a dual functionality of also reducing the width of separation over the
hysteresis
window. Light stabilizers are additives which prevent degradation of a product
due to
exposure to ultraviolet radiation. Examples of light stabilizers used in
thermochromic
systems of the present disclosure and which may also influence the hysteresis
window
include but are not limited to: avobenzone, bisdisulizole disodium ,
diethylaminohydroxybenzoyl hexyl benzoate, Ecamsule, methyl anthranilate, 4-
aminobenzoic acid, Cinoxate, ethylhexyl triazone, homosalate, 4-
methylbenzylidene
camphor, octyl methoxycinnamate, octyl salicylate, Padimate 0,
phenylbenzimidazole
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sulfonic acid, polysilicone-15, trolamine salicylate, bemotrizinol,
benzophenones 1-12,
dioxybenzone, drometrizole trisiloxane, iscotrizinol, octocrylene, oxybenzone,
sulisobenzone , bisoctrizole, titanium dioxide and zinc oxide.
[0075] Careful preparation of encapsulated reversible thermochromic
material
enhances coating stability in the presence of low molecular weight polar
solvents that are
known to adversely affect thermochromic behavior. One skilled in the art of
microencapsulation can utilize well-known processes to enhance the stability
of the
microcapsule. For example, it is understood that increasing the cross linking
density will
reduce the permeability of the capsule wall, and so also reduces the
deleterious effects of
low molecular weight solvents. It is also commonly understood that, under
certain
conditions, weak acids with a pKa greater than about 2 may catalyze
microcapsule wall
polymerization and increase the resulting cross linking density. It is
presently the case
that using formic acid as a catalyst enhances solvent stability of blue
thermochromic
microcapsules in the presence of low molecular weight ketones, diols, and
aldehydes at
room temperature. Further, it is well understood that increasing the diameter
of the
thermochromic microcapsule can result in enhanced solvent stability.
[0076] The selection of material for use as the non-polar solvent for
the
thermochromic dye and color developer that is encapsulated within the
thermochromic
pigment determines the temperature at which color change is observed. For
example,
changing the solvent from a single component to a two component solvent system
can
shift the temperature at which full color is perceived almost 7 C from just
under 19 C to
12 C. The present disclosure shows how to apply this knowledge in preparing
resin-
based vehicle coatings for use in can and coil coatings with full color
temperatures, i.e.,
the temperature at which maximum color intensity is observed, as low as -5 C
and as
high as 65 C. No adverse effects on the physical properties of the resulting
coating were
observed as the full color temperature was changed over the above range by the
use of
different straight chain alkyl esters, alcohols, ketones or amides.
[0077] Thermochromic materials including encapsulated thermochromic
systems with a variety of color properties may be purchased on commercial
order from
such companies as Chromatic Technologies, Inc., of Colorado Springs, Colorado.
[0078] Control over observed color intensity is demonstrated in
several ways,
generally by providing increased amounts of pigment. For a typical coating,
material
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thickness ranges from 1 mg/in2 to 6 mg/in2. Very intense color is observed for
coatings
with thickness greater than about 3 mg/in2. Increasing thermochromic pigment
solids can
also result in a more intense observed color even when coating thickness is
decreased.
However, dried film properties such as flexibility and toughness may be
compromised if
too much thermochromic pigment is incorporated. The optimal range of
thermochromic
pigment solids is within 5 to 40% by weight of the coating.
Vehicle
[0079] Physical properties of the finished coating can be
significantly affected
by the selection of resin to be used. When no resin is used in formulating a
reversible
thermochromic coating, a matte finish is achieved that is able to be formed
into can ends,
tabs, caps and/or other closures. While this result may be desired, the
inclusion of a low
viscosity, relatively low molecular weight resin, monomer, oligomer, polymer,
or
combination thereof, can enhance gloss and affect other physical film
properties such as
hardness, flexibility and chemical resistance. The resin is designed to
supplement the total
solids deposited on the substrate, thus impacting the physical properties of
the dried film.
Any resin material, monomer, oligomer, polymer, or combination thereof that
can be
polymerized into the commercially available can and coil coating material is
suitable for
inclusion in the formulation of the current reversible thermochromic can and
coil coating.
Acceptable classes of resins include, but are not limited to polyester,
urethane, acrylic
acid and acrylate, or other types of resin systems with suitably high solids
content.
Encapsulation Process
[0080] Nearly all thermochromic systems require encapsulation for
protection.
As is known in the art, the most common process for encapsulation is
interfacial
polymerization. During interfacial polymerization the internal phase (material
inside the
capsule), external phase (wall material of the capsule) and water are combined
through
high-speed mixing. By controlling all the temperature, pH, concentrations, and
mixing
speed precisely, the external phase will surround the internal phase droplet
while
crosslinking with itself. Usually the capsules are between 3-5 p m or smaller.
Such small
sizes of capsules are referred to as microcapsules and the thermochromic
system within
the microcapsules are microencapsulated. Microencapsulation allows
thermochromic
systems to be used in wide range of materials and products. The size of the
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microcapsules requires some adjustments to suit particular printing and
manufacturing
processes.
[0081] The size distribution of microcapsules can range from as much
as
0.2p m to 100 p m. Further example techniques of physical microencapsulation
include
but are not limited to pan coating, air suspension coating, centrifugal
extrusion, vibration
nozzle, and spray drying. Examples of chemical microencapsulation techniques
include
but are not limited to interfacial polymerization, in-situ polymerization, and
matrix
polymerization. Example polymers used in the preferred chemical
microencapsulation
include but are not limited to polyester, polyurethane, polyureas, urea-
formaldehyde,
epoxy, melamine-formaldehyde, polyethylene, polyisocyanates, polystyrene,
polyamides,
and polysilanes.
[0082] The capsule isolates the thermochromic system from the
environment,
but the barrier that the capsule provides is itself soluble to certain
solvents. Therefore, the
microcapsule constituents interact with the environment to some extent. The
solubility
parameter describes how much a material will swell in the presence of
different solvents.
This swelling will directly impact the characteristics of the reaction
potential within the
capsule, as well as potentially making the capsule more permeable, both of
which will
likely adversely affect the thermochromic system. Solvents in which the
microcapsules
are exposed to are chosen so as not to destroy, or affect, the thermochromic
system
within.
[0083] The capsule is hard, thermally stable and relatively
impermeable. The
infiltration of compounds through the capsule are stopped or slowed to the
point that the
characteristics of the dye are not affected. The pollution of the
thermochromic system
within the capsule by solvents from the environment affects the shelf life of
the
thermochromic system. Therefore, the formulation of the applied thermochromic
system,
as an ink for example, should be carefully considered.
[0084] In an embodiment of the present disclosure, capsules are made
from
urea formaldehyde. One technique used to produce the encapsulated
thermochromic
systems is to combine water, dye, oil, and urea formaldehyde and mix to create
a very
fine emulsification. Because of the properties of the compounds, the oil and
dye end up
on the inside of the capsule and the water ends up on the outside, with the
urea
formaldehyde making up the capsule itself. The capsule can then be thermo-set,
similar
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to other resins, such as formica. The thermo-set substance is very hard and
will not break
down, even at temperatures higher than the encapsulated thermochromic system
is
designed to be exposed to. The urea formaldehyde capsule is almost entirely
insoluble in
most solvents, but it is permeable to certain solvents that might destroy the
ability of the
thermochromic system to color and decolorize throughout a temperature range.
[0085] The extent to which capsules will react with their environment
is
influenced by the pH of the surrounding medium, the permeability of the
capsule, the
polarity and reactivity of compounds in the medium, and the solubility of the
capsule.
Preferred media used in formulating encapsulated thermochromic system are
engineered
to reduce the reactivity between that medium and the capsules to a low enough
level that
the reactivity will not influence the characteristics of the dye for an
extended period of
time.
[0086] Highly polar solvent molecules, with the exception of water,
often
interact more with the leuco dye than with the capsule shell and other non-
polar
molecules of the thermochromic system. Therefore, polar solvents that are able
to cross
the capsule barrier should, in general, be eliminated from the medium within
which the
encapsulated thermochromic system is formulated.
[0087] Aqueous media that the encapsulated thermochromic systems are
placed within should have a narrow pH range from about 6.5 to about 7.5. When
an
encapsulated thermochromic system is added to a formulation that has a pH
outside this
range, often the thermochromic properties of the system are destroyed. This is
an
irreversible effect.
[0088] One aspect of the present disclosure is for a method of
improving the
formulations of the thermochromic system by removing any aldehydes, ketones,
and diols
and replacing them with solvents which do not adversely affect the
thermochromic
system. Solvents having a large molecular weight (i.e. greater than 100)
generally are
compatible with the thermochromic systems. The acid content of the system is
preferably
adjusted to an acid number below 20 or preferably adjusted to be neutral,
about 6.5 - 7.5.
Implementing these solvent parameters for use in the thermochromic system will
preserve
the reversible coloration ability of the leuco dyes.
[0089] Formulations for thermochromic systems are engineered with all
the
considerations previously mentioned. The examples below describe a
thermochromic
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system with excellent color density, low residual color, narrow temperature
ranges
between full color and clearing point, and a narrow hysteresis window. The
full color
point and the clearing point are determined by visual inspection of the
thermochromic
system at a range of temperatures. The difference in temperature between the
maxima of
color change during the cooling cycle and the heating cycle is used to
calculate hysteresis.
Adjusting the Acid Content
[0090] Water-based inks are pH adjusted prior to addition of
thermochromic
pigment. As mentioned above, the pH should be neutral unless observation
indicates that
a different pH is required. To achieve the correct pH, one uses a good proton
donor or
acceptor, depending on whether the pH is to be adjusted up or down. To lower
the pH,
sulfuric acid is used, to raise it, the best proton acceptor so far is KOH.
These two
chemicals are very effective and do not seem to impart undesirable
characteristics to the
medium. The most effective pH is about 7.0, however, some tolerance has been
noted
between 6.0 and 8Ø A pH below 6.0 and above 8.0 has almost always
immediately
destroyed the pigment.
[0091] The acid value is defined as the number of milligrams of a 0.1
N KOH
solution required to neutralize the alkali reactive groups in 1 gram of
material under the
conditions of ASTM Test Method D-1639-70. It is not yet fully understood how
non-
aqueous substances containing acid affect the thermochromic, but high acid
number
substances have inactivated the thermochromic pigments. Generally, the lower
the acid
number the better. To date ink formulations with an acid value below 20 and
not
including the harmful solvents described above have worked well. Some higher
acid
value formulations may be possible but generally it is best to use vehicle
ingredients with
low acid numbers or to adjust the acid value by adding an alkali substance.
The greatest
benefit of a neutral or low acid value vehicle will be increased shelf life.
Buffers have
been used historically in offset ink formulations to minimize the effects of
the fountain
solution on pigment particles. This is one possible solution to the potential
acidity
problem of the varnishes. One ingredient often used as a buffer is cream of
tartar. A
dispersion of cream of tartar and linseed oil can be incorporated into the
ink. The net
effect is that the pigments in the ink are protected from the acidic fountain
solution.
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Ink Formulations
[0092] The encapsulated thermochromic systems of the present
disclosure
may be referred to as pigments. In order to add normal pigment to ink, dye, or
lacquer,
the pigment itself is ground into the base. This disperses the pigment
throughout the
base. The addition of more pigment intensifies the color. Since the pigment
often has a
very intense color, it is sometimes acceptable for only about 10% of the final
ink to be
made up of normal pigments.
[0093] A base for an ink formulation using encapsulated thermochromic
systems of the present disclosure may be developed using off the shelf
ingredients. The
ink will incorporate, where possible, and be compatible with different ink
types and
solvents with molecular weights larger than 100 while avoiding aldehydes,
diols, ketones,
and, in general, aromatic compounds. Important considerations with respect to
the
ingredients within the ink vehicle are the reactivity of the ingredients with
the
encapsulated thermochromic system.
[0094] Unwanted interactions between media and the encapsulated
thermochromic systems can occur between compounds found in ink formulations.
The
long alkyl chains of many of the compounds found in ink vehicles may have
reactive
portions that can fit through the pores of the capsule and interact with the
inner phase and
denature it through this interaction. Since the behavior of the thermochromic
system is
related to the shape and the location of its molecules at given temperatures,
disrupting
these structures could have a large impact on the characteristics of the
thermochromic
system. Even molecules that cannot fit through the capsule pores may have
reactive
portions that could protrude into the capsule and thereby influence the color
transition of
the thermochromic system within the capsule. Therefore, mineral spirits,
ketones, diols,
and aldehydes are preferably minimized in any medium in which the encapsulated
are
also preferably avoided. If these compounds are substantially reduced or
eliminated the
thermochromic systems will perform better and have a longer shelf life.
[0095] Another important step in using the encapsulated thermochromic
systems of the present disclosure in ink formulations is to adjust the pH or
lower the acid
value of the ink base before the thermochromic system is added. This can be
done by
ensuring that each individual component of the base is at the correct pH or
acid value or
by simply adding a proton donor or proton acceptor to the base itself prior to
adding the
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thermochromic system. The appropriate specific pH is generally neutral, or
7Ø The pH
will vary between 6.0 and 8.0 depending on the ink type and the color and
batch of the
thermochromic system.
[0096] Once a slurry and the base have been properly prepared, they
are
combined. The method of stirring should be low speed with non-metal stir
blades. Other
additives may be incorporated to keep the thermochromic system suspended. The
ink
should be stored at room temperature.
[0097] Most thermochromic pigments undergo a color change from a
specific
color to colorless. Therefore, layers of background colors can be provided
under
thermochromic layers that will only be seen when the thermochromic pigment
changes to
colorless. If an undercoat of yellow is applied to the substrate and then a
layer containing
blue thermochromic pigment is applied the color will appear to change from
green to
yellow, when what is really happening is that the blue is changing to
colorless.
[0098] The substrates that the thermochromic inks are printed upon
are
preferably neutral in pH, and should not impart any chemicals to the capsule
that will
have a deleterious effect on it.
[0099] Thermochromic inks or coatings contain, in combination, a
vehicle and
a pigment including thermochromic microcapsules. The thermochromic
microcapsules
are preferably present in an amount ranging from I% to 50% of the ink by
weight on a
sliding scale relative to other pigments. The vehicle contains a solvent that
is preferably
present in an amount ranging from 25% to 75% by weight of the coating.
[0100] The aqueous pigment slurries have particle sizes less than 5
microns
and when drawn-down on ink test paper and dried, the pigment coating shows
reversible
thermochromic properties when cooled to the solidification point of the fatty
ester,
alcohol, amide, or a blend designed to obtain a specific temperature for full
color
formation. Such pigments can be designed to have a range of temperature for
transition
from full absorption temperature (full absorption color or UVA absorption
point) to no
color or no UVA absorption temperature (clearing point) of 2-7 C. The
pigments are
very useful for manufacture of ink, coating, and injected molded plastic
products by spray
drying prior to formulation into inks or coating compositions or extrusion
into
thermoplastic polymers to produce pellet concentrates for manufacture of
injection
molded thermochromic plastic products such as cups, cup lids, jars, straws,
stirrers,
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container sleeves, shrink wrap labels. For example, thermochromic compositions
were
identified that permit generation of high quality saturated photographic
quality yellow
color that is very useful to formulate new orange, red, and green colors by
mixing with
magenta and/or cyan thermochromic pigments or by initial co-encapsulation of
the yellow
leuco dye with magenta and/or cyan leuco dyes and appropriate color developers
during
the pigment manufacture. Alternatively leuco pigments were identified that can
change
from absorption mainly in the region from 280 to 350 nm to absorption mainly
from 350
to 400 nm. In an embodiment, this leuco dye can be used in a photochromic gel
ink pen as
disclosed above.
Ball-Point Pens
[0101] Ball-point pens employing the thermochromic inks disclosed
herein
may be used in a conventional ball-point pen mechanism or marker.
[0102] The thermochromic inks disclosed herein are endowed with
thixotropic
properties. The thermochromic inks disclosed herein have a high viscosity when
left to
stand without application of shear stress and is stably held in the ball-point
pen
mechanism, and only the ink around the ball becomes low viscous at the time of
writing
because of the high shear force attributable to the ball that rotates at a
high speed, so that
the ink smoothly passes through a gap between the ball and a ball holder by
capillary
action and is transferred to the paper surface. The ink transferred to the
paper surface or
the like is released from shear force and hence again brought into a highly
viscous state,
not causing the feathering in writing.
[0103] The thermochromic ink compositions disclosed herein satisfies
properties suited for ball-point pen inks, can be free from line splitting,
blurs and
blobbing in writing, has stable viscosity characteristics with time, and
satisfies practical
performances as water-based ball-point pen inks containing various colorants.
As the
colorants, pigments and dyes of various types can be used, and hence ball-
point pens
having a variety in color tones can be provided. Also, in the system where the
thermochromic microcapsular pigment material is used as the colorant,
convenient ball-
point pens that can give thermochromic written images can be provided,
promising the
spread of new uses. Such applicable uses and advantages attributable thereto
will be
exemplified below.
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[0104] In an embodiment, confidential images such as letters and
pictures that
cause metachromatism at temperature lower than the room temperature can be
formed on
post cards, Christmas cards, greeting cards and so forth. Thus, the images may
be made to
come into sight when cooled, so as to be applicable to magical use, or images
that can
alternately change from color (A) to color (B) may be formed so that the
metachromatism
may be caused by body temperature, hand temperature, or other heat source.
[0105] In another embodiment, thermochromic inks disclosed herein are
capable of forming color only when it is cold, e.g., at a metachromatic
temperature of 10
C., or a thermochromic pigment material having hysteresis characteristics in a
wide
temperature range, images that cannot be read at room temperature can be
recorded, using
the ball-point pen of the present disclosure as a confidential pen. Thus, the
pen can be
used to write memos or the like that must be made confidential.
[0106] In another embodiment, pens using the thermochromic inks
disclosed
herein can be used for learning in school or the like, e.g., for questions,
tests, drills, blank
maps and English translations, where necessary answers or remarks are written
and the
written information is erased by heating so that again the problems or the
like can be
engaged in the state completely reset to have neither answers nor memos.
[0107] In another embodiment, pens using the thermochromic inks
disclosed
herein can be used for temperature indication as if it functions as a
thermometer. A set of
thermochromic ink ball-point pens having different metachromatic temperature
may be
provided so that various images are formed to make them function as
temperature
detectors. Thus, the ink composition of the present invention can be used in
not only toys
and stationery but also in a variety of industrial fields, e.g., can be
conveniently used in
temperature control of reaction tanks, temperature control of processing
steps, indication
for suitable temperature control of low-temperature circulation food, display
for
preventing overheat due to short of electric code outlets.
[0108] In another embodiment, the thermochromic inks disclosed herein
can
be used in articles of clothing, illustrations or pictures may be drawn on
casual wear such
as T-shirts with a 30 C-metachromatic thermochromic ink ball-point pen so
that users
themselves can design T-shirts capable of causing metachromatism utilizing a
temperature difference between the outdoors and the room in the summer season.
This
can also be applied to gloves, shoes, hats or caps, ski wear and swimming
suits.
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[0109] In another embodiment, pens using the thermochromic inks
disclosed
herein can be used for preventing forgery, genuine things and imitations can
be
discriminated by cooling or heating. For example, some information may be
handwritten
with the ball-point pen of the present disclosure in tickets, merchandize
bonds, coupon
tickets and so forth on a scale of private concerns or small lots. This can
effectively
prevent forgery.
[0110] In another embodiment, pens using the thermochromic inks
disclosed
herein can be used in combination with usual non-metachromatic ink ball-point
pens so
that the state of changes can be in more variety.
[0111] The present disclosure provides thermochromic inks for use in
a shear-
thinning ball-point pen. In an embodiment, the thermochromic ink compositions
have a
viscosity within the range of from about 25 mPas to about 160 mPas and a shear
thinning
index adjusted within the range of from about 0.1 to about 0.6.
[0112] The non-limiting embodiments that follow teach by way of
example
and should not be construed as unduly limiting the scope of this disclosure.
[0113] In one aspect, a reversible thermochromic ink for use in pens
contains
a reversible thermochromic pigment in an amount from 1% to 40% by weight of
the
coating, and a vehicle forming the balance of the coating. The vehicle
including a resin
selected from the group consisting of polyester, urethane, acrylic acid and
acrylate resins,
and combinations thereof.
[0114] Commercially available thermochromic pigments may be readily
obtained in a variety of colors demonstrating color transition temperatures
from about 5
C and up to about 65 C. A range of color formulations may be made by mixing
the
pigment to include one or more of the following reversible thermochromic
colors: yellow,
magenta, cyan, and black. These may be further mixed to include other dyes or
solid
pigments that are non-thermochromic in nature. The pigment may change from a
colorless state to a colored state upon cooling to the reactive temperature,
or to a colored
state upon heating to the reactive temperature. It is preferred that the
microcapsules are
formed of urea formaldehyde or melamine formaldehyde that is acid catalyzed to
enhance
the inherent stability in polar, low molecular weight solvents having a
molecular weight
of about less than 100 g/mol.
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Thermochromic Inks Used in Pens
[0115] In an embodiment, thermochromic inks of the present disclosure
contain microencapsulated leuco dye, developer, and solvent with the
appropriate
solvency and melting point to achieve the temperature activated color change.
In an
embodiment, the base colorant is a permanently colored pigment or dye that is
suspended
in the ink formulation, or soluble in the ink formulation.
[0116] In an embodiment, the shear thinning ink may be formulated
using a
film forming compound such as ethylene maleic anhydride or an equivalent
substitute
fully hydrolyzed in water and adjusted to the desired thixotropic behavior
with xanthan
gum. The film forming properties of the ink could be achieved using many
resins/vehicles
such as ethylene maleic anhydride, styrene acrylonitrile polymers, acrylic
emulsions, or
urethane emulsions for example. The rheology to achieve the viscosity and
shear thinning
ability could be controlled by surfactants and agents such as xanthan gum and
hydroxyl
ethyl cellulose as well as a number of others.
[0117] In an embodiment, the temperature between full color
development
and clearing point activation can be engineered with a mixture of alkyl esters
such as
methyl palmitate, methyl stearate, isopropyl palmitate, stearyl behenate, and
behenyl
alcohol to produce the following color to color effects, for example: a full
color
development between 23 C and 27 C and color clearing between 27 C and 33 C
for
easily activated reversible thermochromic color to color options.
[0118] In an embodiment, ball-point pen and gel-ink pens disclosed
herein use
thermochromic inks that transition from one color to another color, or from
color to
colorless, when activated at about body temperature or at about room
temperature.
[0119] Strong color to color transition and color to colorless
examples are as
follows:
Purple to pink Blue thermochromic + pink/red base color
Green to yellow Blue thermochromic + yellow base color
Orange to yellow Red thermochromic + yellow base color
Burgundy to blue Red thermochromic + blue base color
Brown to green Red thermochromic + green base color
Green to blue Yellow thermochromic + blue base color
Orange to pink Yellow thermochromic + pink/red base color
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Blue to colorless Blue thermochromic + white/ clear base color
Black to colorless Black thermochromic + white/ clear base
color
[0120] The above embodiments of color to color options are achieved by
mixing different ratios of thermochromic microcapsules with standard colored
bases, as
described herein. The base colorants may be pigments or dyes that are
compatible in the
ink formulation.
[0121] The color to color transitions sometimes lack high contrast between
the
color developed state and the base color. In order to increase contrast, black
to color
transition inks are herein disclosed.
[0122] In an embodiment, black to color transitions use blue/cyan,
red/magenta, yellow, and black thermochromics with red/magenta, blue/cyan,
yellow, and
white base colorants. Examples of thermochromic inks having black to color
transition
are as follows:
Black to blue Thermochromic magenta,
black, yellow + blue base
Black to yellow Thermochromic magenta, black, blue +
yellow base
Black to red/pink Thermochromic blue, yellow, black + pink/magenta
base
Black to orange Thermochromic blue, black + pink
and yellow base
Black to green Thermochromic magenta, black + blue and yellow base
Black to violet Thermochromic yellow, black + blue and pink base
Black to brown Thermochromic blue, black + pink,
yellow, blue base
[0123] By mixing different ratios of thermochromic pigments with standard
colored bases, a neutral black to almost any colored base is possible. These
black to color
transitions can be used to create black and white images that will change to
colored states
when heat activated.
Photochromic Ink Pens
[0124] In an embodiment, photochromic microcapsules can also be
formulated by encapsulating photochromic dyes in resins, monomers, and
polymers using
standard encapsulating techniques to achieve a particle size between 300 nm
and 5
microns. For example, in situ or interfacial polymerization using melamine
resin, epoxy
resin, or urea-formaldehyde may be used to encapsulate hydrophobic, water
immiscible
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internal phase materials in which the dye is dissolved. Antioxidants, hindered
amine light
stabilizers, and UV absorbers may be used either alone or in combination with
each other
to enhance the UV stability of the system. The internal phase solvent may be
maintained
as a liquid, or polymerized to a solid within the microcapsule.
[0125] The microencapsulated photochromic systems then can be
formulated
into a water-based shear thinning gel ink for use in roller ball pens. Inks
can be produced
that are virtually invisible under normal fluorescent or incandescent lighting
indoors, but
which will develop vibrant colors under UV light such as natural sunlight. By
mixing
colored bases with the photochromic inks, color to color development is also
possible.
The shear thinning properties and film forming properties of the ink can be
achieved
using many resins/vehicles such as ethylene maleic anhydride, styrene
acrylonitrile
polymers, acrylic emulsions, or urethane emulsions for example.
[0126] The rheological manipulations to achieve the viscosity and
shear
thinning of the photochromic inks can be controlled by surfactants and agents
such as
xanthan gum, hydroxyl ethyl cellulose and various other agents well known in
the art.
The end result is a gel ink that flows from a roller ball pen smoothly so as
to form a
uniform ink line without starving or blobbing.
[0127] Embodiments of photochromic inks useful in pens include:
Colorless to Blue Microencapsulated blue + Clear gel base
Yellow to Green Microencapsulated blue + Yellow base color + Clear
gel base
Colorless to Red Microencapsulated red + Clear gel base
Blue to Purple Microencapsulated red + Blue base color + Clear
gel base
EXAMPLES
[0128] Black to Green Temperature Memory Ink
[0129] A thermochromic ink composition, commercially available from
Chromatic Technologies Inc., with full color between 12 C and 15 C and color
clearing
between 21 C and 27 C for a color to color option was made so that the color
of the
thermochromic portion of the ink was maintained up to room temperature, but
easily
activated by body temperature to a clearing point to reveal the base color.
[0130] The thermochromic ink was a composition consisting of a
thermochromic blue dye with a magenta leuco dye, and a developer to achieve a
reversible thermochromic system with a full color development around 12 C and
a
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clearing temperature of 25 C. Magenta thermochromic capsules were
incorporated into
a water-based shear thinning gel ink with a neon blue pigmented gel ink and a
neon
yellow pigmented gel ink.
[0131] The shear thinning thermochromic ink was formulated using a
film
forming compound such as ethylene maleic anhydride fully hydrolyzed in water
and
adjusted to the desired thixotropic behavior with xanthan gum.
[0132] The result was an aqueous ink that appeared black when cooled
to a
temperature below 12 C and remained black until heated to a temperature above
25 C
when it changed to a bright green color.
[0133] The thermochromic reversible color changing ink was injected
into a
standard 0.7 mm to 1.0 mm tip gel ink pen for transfer to a paper substrate.
[0134] In an embodiment, a drawing or written image could then be
made that
will appear black at room temperature. In an embodiment, the colored image may
easily
be activated to the bright orange by gentle rubbing and the black color can
only be
regained by cooling to a temperature around 12 C for a few minutes.
[0135] The color to color options are achieved by mixing different
ratios of
thermochromic microcapsules with standard colored bases. The base colorants
may be
pigments or dyes that are compatible in the ink formulation. These color to
color options
are artistically pleasing, but are somewhat limited as far as high contrast
between the
color developed state and the base color. Thermochromic pigments are
commercially
available from Chromatic Technologies Inc. in Colorado Springs, CO.
[0136] In order to achieve a maximum color effect for artistic
reasons, neutral
charcoal/ black to color options are proposed. In one example that shows the
mixing of
colors, these thermochromic pigments:
blue/cyan, red/magenta, yellow, and black may be mixed with the following base
colorants ( pigments or dyes):
red/magenta, blue/cyan, yellow, and white.
Moreover, any neutral black to color option is achievable.
[0137] This is achieved by mixing different ratios of thermochromic
pigments
with standard colored bases. It is possible to achieve a neutral black to
almost any
colored base is possible. This allows full dramatic effect to such an extent
that the user
can create a black and white image that will change to the colored state when
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activated. For example, picture a natural setting of a tree on a hillside. The
trunk of the
tree will be black to brown, the leaves of the tree will be black to green,
the sun will be
black to orange and black to yellow, the grass on the hillside will be black
to green, and
clouds will be black to blue. By selectively choosing the black to color
option, any scene
can be depicted that will transition from the neutral black sketch to a fully
colored sketch
as it is heated.
[0138] The thermochromic component of the invention is a
microencapsulated
leuco dye, developer, and solvent with the appropriate solvency and melting
point to
achieve the temperature activated color change.
[0139] The base colorant is a permanently colored pigment or dye that
is
suspended in the ink formulation, or soluble in the ink formulation.
[0140] The temperature between full color development and clearing
point
activation can easily be engineered with a variety of internal phase solvents
as described
in a number of patents to achieve microencapsulated pigments with color
development
between -10C and 65C.
Example of Black to Orange
[0141] A microencapsulated pigment with an internal phase engineered
with a
blue leuco dye and a phenolic developer to achieve a reversible thermochromic
system
with a full color development between 23C and 27C and a clearing temperature
between
28C and 31C (available from Chromatic Technologies, Inc.)
[0142] The red thermochromic capsules are incorporated into a water-
based
shear thinning gel ink with a neon pink pigmented gel ink and a neon yellow
pigmented
gel ink.
[0143] The shear thinning ink may be formulated using a film forming
compound such as ethylene maleic anhydride fully hydrolyzed in water and
adjusted to
the desired thixotropic behavior with xanthan gum. The film forming properties
of the ink
could be achieved using many resins/vehicles such as ethylene maleic
anhydride, styrene
acrylonitrile polymers, acrylic emulsions, or urethane emulsions for example.
The
rheology to achieve the viscosity and shear thinning ability could be
controlled by
surfactants and agents such as xanthan gum and hydroxyl ethyl cellulose as
well as a
number of others.
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[0144] A thermochromic ink composition, commercially available from
Chromatic Technologies Inc., consisting of a thermochromic blue with a blue
leuco dye
and a developer to achieve a reversible thermochromic system with a full color
development around 27 C and a clearing temperature of 32 C was produced. The
blue
thermochromic microcapsules were incorporated into a water-based shear
thinning gel ink
with a neon pink pigmented gel ink and a neon yellow pigmented gel ink.
[0145] The resulting thermochromic ink appeared black when below 27 C
and gradually changed to a bright orange when heated to a temperature above 32
C.
[0146] The thermochromic reversible color changing ink was injected
into a
standard 0.7 mm to 1.0 mm tip gel ink pen for transfer to a paper substrate.
BLACK TO ORANGE COLOR CHANGING THERMOCHROMIC
PEN/MARKER FORMULATION:
Component Amount (g) wt %
Ethylene maleic anhydride solution ( 10-20% ) 10-20 6.7-10
Xanthan gum solution ( 0.25%) 10-20 6.7-10
Blue microcapsule slurry ( 40-50% capsule solids) 30-40 26.7-30
Black microcapsule slurry ( 40-50% capsule solids) 10-20 6.7-10
Pigmented yellow gel ink ( 20-30% pigment solids) 20-25 16.7-20
Pigmented pink gel ink (20-30% pigment solids) 20-25 16.7-20
Water-based anti-foaming surfactant 0.5-1.0 0.25-0.5
[0147] The result is an ink that will appear black when below 27 C
and
gradually change to a bright orange when heated to a temperature above 31 C.
[0148] The thermochromic reversible color changing ink is injected
into a
standard .7 mm to 1.0 mm tip gel ink pen for transfer to a paper substrate. As
non-
limiting examples the ink formulated can be for a ball point pen or a fibrous
tip marker
type writing instrument.
[0149] A nonlimiting example of a Purple to pink Temperature Memory
Ink:
[0150] Full color between 12 C and 15 C and color clearing between 21
C
and 27 C for a color to color option so that the color of the thermochromic
portion of the
ink is maintained up to room temperature, but easily activated by body
temperature to a
clearing point to reveal the base color. A microencapsulated pigment
engineered to have
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a wide hysteresis effect using a magenta dye and a phenolic developer to
achieve a
reversible thermochromic system with a full color development between 12-13 C
and a
clearing temperature between 23-25 C.
[0151] The blue thermochromic capsules are incorporated into a water-
based
shear thinning gel ink with a neon pink pigmented gel ink.
[0152] The shear thinning ink is formulated using a film forming
compound
such as ethylene maleic anhydride fully hydrolyzed in water and adjusted to
the desired
thixotropic behavior with xanthan gum.
[0153] The result is an aqueous ink that will appear purple when
cooled to a
temperature below 12C and will remain purple until heated to a temperature
above 23-
25 C, where it will then change to a bright pink color.
[0154] The thermochromic reversible color changing ink is injected
into a
standard .7 mm to 1.0 mm (or larger) tip gel ink pen for transfer to a paper
substrate.
[0155] A drawing or written image can be made that will appear purple
at
room temperature ( 20-23C). The colored image may easily be activated to the
bright pink
by gentle rubbing or heating. The purple color can only be regained by cooling
to a
temperature around 12 C for a few seconds achievable by placing the printed
image in a
refrigerator set at normal conditions.
Photochromic Gel Ink Pen
[0156] Photochromic microcapsules can also be formulated by
encapsulating
photochromic dyes in resins, monomers, and polymers using standard
encapsulating
techniques to achieve microcapsules suitable for use as a pigment in a gel
ink. For
example, in situ or interfacial polymerization using melamine resin, epoxy
resin, or urea-
formaldehyde may be used to encapsulate hydrophobic, water immiscible internal
phase
materials in which the dye is dissolved. Antioxidants, hindered amine light
stabilizers,
and UV absorbers may be used either alone or in combination with each other to
enhance
the UV stability of the system. The internal phase solvent may be maintained
as a liquid,
or polymerized to a solid within the microcapsule. The microencapsulated
photochromic
systems then can be formulated into a water-based shear thinning gel ink for
use in roller
ball pens. Inks can be produced that are virtually invisible under normal
fluorescent or
incandescent lighting indoors, but which will develop vibrant colors under UV
light such
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as natural sunlight. By mixing colored bases with the photochromic inks, color
to color
development is also possible. The shear thinning properties and film forming
properties
of the ink could be achieved using many resins/vehicles such as ethylene
maleic
anhydride, styrene acrylonitrile polymers, acrylic emulsions, or urethane
emulsions for
example. The rheology to achieve the viscosity and shear thinning ability
could be
controlled by surfactants and agents such as xanthan gum and hydroxyl ethyl
cellulose
and a number of others. The end result would be a gel ink that would flow from
a roller
ball pen smoothly so as to form a uniform ink line without starving or
blobbing.
Clear Base Gel
[0157] The nonlimiting example that follows shows one embodiment for
a
clear base gel incorporating the instrumentalities described above. The clear
gel base can
be formulated as follows:
Component Amount (g) wt %
Ethylene maleic anhydride solution ( 10-20% ) 40-50 40-50
Xanthan gum solution ( 0.25%) 40-50 40-50
Anti-foaming surfactant 0.25-0.50 0.25-
0.50
[0158] This may be mixed with pigment as follows. The amount of the
pigment is added to suit the eye.
Colorless to Blue: Microencapsulated blue + Clear gel base
Yellow to Green: Microencapsulated blue + Yellow base color + Clear
gel base
Colorless to Red: Microencapsulated red + Clear gel base
Blue to Purple: Microencapsulated red + Blue base color + Clear
gel base
[0159] In general
50-98% gel base is blended with 1-50% photochromic dye
or microencapsulate photochromic dye, and 1-50% of a colored dye. Preferably,
60-95%
mixed with 5-40% photochromic dye or microencapsulated dye, and 1-10% of a
colored
dye.
[0160] An example photochromic yellow to green pen/marker ink is:
90% gel base
5% photochromic microencapsulated pigment
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% Tartrazine dye
[0161] Additional temperature profiles with various degrees of color
memory
may be achieved with other internal phase materials such as tetradecanol,
dodecyl
decanoate,and decanophenone, where the color may be fully developed at a lower
temperatures and maintained until some higher clearing point temperature.
[0162] The foregoing disclosure teaches by way of example, and not by
limitation. Those skilled in the art will appreciate that what is claimed may
be subjected
to9insubstatial change with9ut departing form the scope and spirit of the
invention.
Accordingly. the inventors hereby state their intention to rely upon the
doctrine of
Equivalents, in order to protect their rights in the invention.
