U.S. patent application number 13/737728 was filed with the patent office on 2013-07-11 for reversible thermochromic and photochromic ink pens and markers.
This patent application is currently assigned to Chromatic Technologies Inc.. The applicant listed for this patent is Chromatic Technologies Inc.. Invention is credited to Terrill Scott Clayton, Timothy J. Owen.
Application Number | 20130177703 13/737728 |
Document ID | / |
Family ID | 47604204 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130177703 |
Kind Code |
A1 |
Clayton; Terrill Scott ; et
al. |
July 11, 2013 |
REVERSIBLE THERMOCHROMIC AND PHOTOCHROMIC INK PENS AND MARKERS
Abstract
Reversible thermochromic and photochromic ink compositions and
markers, pens or writing instruments that use them are herein
disclosed.
Inventors: |
Clayton; Terrill Scott;
(Colorado Springs, CO) ; Owen; Timothy J.;
(Colorado Springs, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chromatic Technologies Inc.; |
Colorado Springs |
CO |
US |
|
|
Assignee: |
Chromatic Technologies Inc.
Colorado Springs
CO
|
Family ID: |
47604204 |
Appl. No.: |
13/737728 |
Filed: |
January 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61584398 |
Jan 9, 2012 |
|
|
|
61732120 |
Nov 30, 2012 |
|
|
|
Current U.S.
Class: |
427/145 ;
106/31.6; 427/331 |
Current CPC
Class: |
C09D 11/50 20130101;
C09D 13/00 20130101; B41M 5/305 20130101; B41M 5/287 20130101; C09D
11/17 20130101; C09D 11/18 20130101; C09D 5/26 20130101; C09D 11/16
20130101 |
Class at
Publication: |
427/145 ;
106/31.6; 427/331 |
International
Class: |
C09D 11/16 20060101
C09D011/16 |
Claims
1. A reversible thermochromic composition, said reversible
thermochromic ink composition comprising, a reversible
thermochromic pigment in an amount from 1% to 50% by weight of the
ink, the reversible thermochromic pigment being susceptible to a
temperature-modulated change of color between a first state and a
second state along a hysteresis loop; a non-thermochromic colorant
of a different color from the reversible thermochromic pigment when
the reversible thermochromic colorant is in a colored state, such
that the non-thermochromic colorant 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 when the reversible thermochromic pigment is
in the second state; and a vehicle forming the balance of the
composition.
2. The composition of claim 1, wherein the first state is a colored
state and the second state is substantially clear.
3. The composition of claim 1 where in the composition is
formulated for use in a ball point pen.
4. The composition of claim 1 wherein the composition is formulated
for use in a gel pen.
5. The composition of claim 1 wherein the composition is formulated
for use in a marker.
6. The composition of claim 1 wherein the composition is formulated
for use in a paint.
7. The composition of claim 1 wherein the composition is formulated
for use in a crayon.
8. The composition of claim 1 wherein the thermochromic pigment is
formulated to have a hysteresis window extending across a range
greater than 60.degree. C.
9. The composition of claim 1 wherein the thermochromic pigment is
formulated to have a hysteresis window extending across a range
greater than 80.degree. C.
10. The composition of claim 1 wherein the ink is formulated to
change color in consequence of heating from black to a color other
than black.
11. The composition of claim 1 wherein the ink is formulated to
change color in consequence of heating from one color to a
different color.
12. In a ball-point pen or marker, the improvement comprising the
composition of claim 1 used as an ink
13. In a ball-point pen or marker, the improvement comprising the
composition of claim 11 used as an ink
14. The composition of claim 1 wherein the non-thermochromic
colorant is a microencapsulated photochromic dye.
15. A method of using the composition of claim 1, wherein the
composition is applied by a writing instrument to paper, clothing,
cardboard or other surfaces and then subjected to a color change by
the action of temperature change.
16. A method of reversibly highlighting using the composition of
claim 1, comprising applying the ink to a surface at a first
temperature; and changing the temperature of said surface to a
second temperature whereby said ink becomes colorless.
Description
RELATED APPLICATIONS
[0001] This application claims benefit of priority to U.S.
Provisional Patent Application Ser. No. 61/584,398 filed Jan. 9,
2012 and U.S. Provisional Patent Application Ser. No. 61/732,120
filed Nov. 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 .mu.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 change that is reversible or
irreversible. U.S. Pat. No. 5,591,255, entitled "Thermochromic Ink
Formulations, Nail Lacquer and Methods of Use", issued Jan. 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.degree. C. to about 80.degree. 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 dye at the core of the microcapsules. In one example,
when heat is applied generally in the range of 30 to 32.degree. 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.degree. C., the ink returns to the original color of the
pigment.
[0009] U.S. Pat. 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 Jul. 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. Pat. No. 5,805,245, entitled "Multilayered Dispersed
Thermochromic Liquid Crystal", issued Sep. 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, U.S. Pat. Nos. 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 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 1%
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 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 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, Ill., US), LCR Hallcrest (Glenview, Ill.,
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, Calif., US). Distributors of thermochromic slurries
include, but are not limited to, QCR Solutions Corporation (Port
St. Lucie, Fla., US), Woo Jeong Ind. Inc. (Seoul, South Korea), HW
Sands Corp. (Jupiter, Fla., 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 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 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 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.degree. C. In some
embodiments, the critical temperature is about 31.degree. 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.
[0039] Overview of Thermochromic Pigments
[0040] 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 range
of the system. These formulations are then microencapsulated within
a polymeric shell.
[0041] 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.degree. C. and colorless at
above 33.degree. 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.degree. C. to
15.degree. C., 21.degree. C. to 27.degree. C., 23.degree. C. to
27.degree. C., 27.degree. C. to 33.degree. 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,
Colo.
[0042] 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.
[0043] Definitions
[0044] 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 approximately 4.degree. C. below the
activation temperature and will be in between colors within the
activation temperature range.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] Hysteresis--The difference in the temperature profile of a
thermo chromic system when heated from the system when cooled.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] Leuco dye--A leuco dye is a dye whose molecules can acquire
two forms, one of which is colorless.
[0057] Thermochromic Inks
[0058] 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.
[0059] The thermochromic system may contain, for example, at least
one chromatic organic compound and co-solvents.
[0060] 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 .pi. cloud electrons that allow for
the absorption of visible light are destroyed.
[0061] 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 .pi. 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.
[0062] 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.
[0063] 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.
[0064] It is also an object of this disclosure to provide
formulations of extended hysteresis windows in ink
formulations.
[0065] Leuco Dyes
[0066] 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-dimethylaminophenyl)-6-dimethylaminophthalide;
3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl) phthalide;
3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide;
3,3-bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide;
3-[2-ethoxy-4-(N-ethylanilino)phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-az-
aphthalide; 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-dimethyl-6-diethylaminofluoran;
2-chloro-3-methyl-6-diethylaminofluoran;
2-anilino-3-methyl-6-diethylaminofluoran;
2-anilino-3-methyl-6-di-n-butylamino fluoran;
2-xylidino-3-methyl-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-5,1'(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)benzop-
yrano(2,3-d)pyrimidine-5,1'(3'H)isobenzofuran]-3'-one; and
2-(di-n-butylamino)-8-(di-n-butylamino)-4-phenyl and trisubstituted
pyridines.
[0067] Developers
[0068] 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-cyclohexyl-4-hydroxyphenyl)cyclohexane;
1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;
1,1-bis(4-hydroxyphenyl)cyclohexane;
1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene; 1-naphthol;
2-naphthol; 2,2 bis(2-hydroxy-5-biphenylyl)propane;
2,2-bis(3-cyclohexyl-4-hydroxy)propane;
2,2-bis(3-sec-butyl-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-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-diyl)diphenol;
alpha,alpha'-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene;
alpha,alpha,alpha'-tris(4-hydroxyphenyl)-1-ethyl-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-cyclohexyl-4-hydroxyphenyl)cyclohexane;
1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;
1,1-bis(4-hydroxyphenyl)cyclohexane;
1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene; 1- naphthol
2,2'-biphenol; 2,2- bis(2-hydroxy-5-biphenylyl)propane;
2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane;
2,2-bis(3-sec-butyl-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)diphenol
4,4'-(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-hydroxyphenyl)-1,4-diisopropylbenzene;
.alpha.,.alpha.,.alpha.-tris(4-hydroxyphenyl)-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-tertbutyl-2,2'-biphenol;
4,4'-di-n-alkyl-2,2'-biphenol; and 4,4'-di-halo-2,2'-biphenol,
wherein the halo is chloro, fluoro, bromo, or iodo.
[0069] Solvents
[0070] 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 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.
[0071] 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.
[0072] 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
Ser. No. 13/363,070 filed Jan. 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.
[0073] 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.degree. C. to about 200.degree. C. greater than the co-solvent
partner. The co-solvents are preferably also completely miscible at
any ratio.
[0074] 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-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.
[0075] 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 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.
[0076] 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 substituents 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-ethylhexyl-2-fluoromyristate, cetyl butyrate, stearyl butyrate,
and behenyl butyrate.
[0077] 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.
[0078] 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 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.
[0079] Light Stabilizers
[0080] 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 .mu.m 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.degree. 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.
[0081] 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 O, phenylbenzimidazole sulfonic acid,
polysilicone-15, trolamine salicylate, bemotrizinol, benzophenones
1-12, dioxybenzone, drometrizole trisiloxane, iscotrizinol,
octocrylene, oxybenzone, sulisobenzone , bisoctrizole, titanium
dioxide and zinc oxide.
[0082] 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.
[0083] 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.degree.
C. from just under 19.degree. C. to 12.degree. 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.degree. C. and as high as
65.degree. 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.
[0084] 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, Colo.
[0085] Control over observed color intensity is demonstrated in
several ways, generally by providing increased amounts of pigment.
For a typical coating, material 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.
[0086] Vehicle
[0087] 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.
[0088] Encapsulation Process
[0089] 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
.mu.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 microcapsules requires some adjustments to suit
particular printing and manufacturing processes.
[0090] The size distribution of microcapsules can range from as
much as 0.2 .mu.m to 100 .mu.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.
[0091] 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.
[0092] 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.
[0093] 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 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] Formulations for thermochromic systems are engineered with
all the considerations previously mentioned. The examples below
describe a thermochromic 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.
[0099] Adjusting the Acid Content
[0100] 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 8.0. A pH below 6.0 and above 8.0 has
almost always immediately destroyed the pigment.
[0101] 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.
[0102] Ink Formulations
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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 thermochromic system. The
appropriate specific pH is generally neutral, or 7.0. The pH will
vary between 6.0 and 8.0 depending on the ink type and the color
and batch of the thermochromic system.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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 1% 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.
[0111] 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.degree. 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, 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.
[0112] Ball-Point Pens
[0113] Ball-point pens employing the thermochromic inks disclosed
herein may be used in a conventional ball-point pen mechanism or
marker.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] 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.degree. 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.
[0118] 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.
[0119] 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.
[0120] 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.degree. 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.
[0121] 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.
[0122] 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.
[0123] 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.
[0124] The non-limiting embodiments that follow teach by way of
example and should not be construed as unduly limiting the scope of
this disclosure.
[0125] 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.
[0126] Commercially available thermochromic pigments may be readily
obtained in a variety of colors demonstrating color transition
temperatures from about 5.degree. C. and up to about 65.degree. 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.
[0127] Thermochromic Inks Used in Pens
[0128] 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.
[0129] 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.
[0130] 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.degree. C. and 27.degree. C. and color
clearing between 27.degree. C. and 33.degree. C. for easily
activated reversible thermochromic color to color options.
[0131] 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.
[0132] Strong color to color transition and color to colorless
examples are as follows:
TABLE-US-00001 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 Blue to colorless Blue thermochromic + white/clear base
color Black to colorless Black thermochromic + white/clear base
color
[0133] 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.
[0134] 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.
[0135] 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:
TABLE-US-00002 Black to blue Thermochromic magenta, + blue base
black, yellow Black to yellow Thermochromic magenta, + yellow base
black, blue Black to red/ Thermochromic blue, + pink/magenta base
pink yellow, black Black to orange Thermochromic blue, black + pink
and yellow base Black to green Thermochromic magenta, + blue and
black yellow base Black to violet Thermochromic yellow, black +
blue and pink base Black to brown Thermochromic blue, black + pink,
yellow, blue base
[0136] 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.
[0137] Photochromic Ink Pens
[0138] 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 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.
[0139] 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.
[0140] 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.
[0141] Embodiments of photochromic inks useful in pens include:
TABLE-US-00003 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
[0142] Black to Green Temperature Memory Ink
[0143] A thermochromic ink composition, commercially available from
Chromatic Technologies Inc., with full color between 12.degree. C.
and 15.degree. C. and color clearing between 21.degree. C. and
27.degree. 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.
[0144] 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.degree. C. and a clearing temperature of
25.degree. 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.
[0145] 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.
[0146] The result was an aqueous ink that appeared black when
cooled to a temperature below 12.degree. C. and remained black
until heated to a temperature above 25.degree. C. when it changed
to a bright green color.
[0147] 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.
[0148] 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.degree. C. for a few minutes.
[0149] 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, Colo.
[0150] 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:
[0151] blue/cyan, red/magenta, yellow, and black may be mixed with
the following base colorants (pigments or dyes): [0152]
red/magenta, blue/cyan, yellow, and white. [0153] Moreover, any
neutral black to color option is achievable.
[0154] 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
heat 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.
[0155] 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.
[0156] The base colorant is a permanently colored pigment or dye
that is suspended in the ink formulation, or soluble in the ink
formulation.
[0157] 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.
[0158] Example of Black to Orange
[0159] 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 23 C and 27 C and a clearing temperature
between 28 C and 31 C (available from Chromatic Technologies,
Inc.)
[0160] 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.
[0161] 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.
[0162] 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.degree. C. and a clearing temperature of 32.degree. 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.
[0163] 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.
[0164] 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
TABLE-US-00004 [0165] Amount Component (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
[0166] The result is an ink that will appear black when below
27.degree. C. and gradually change to a bright orange when heated
to a temperature above 31.degree. C.
[0167] The thermochromic reversible color changing ink is injected
into a standard 0.7 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.
[0168] A nonlimiting example of a Purple to pink Temperature Memory
Ink:
[0169] Full color between 12.degree. C. and 15.degree. C. and color
clearing between 21.degree. C. and 27.degree. 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 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.degree. C. and a clearing temperature between
23-25.degree. C.
[0170] The blue thermochromic capsules are incorporated into a
water-based shear thinning gel ink with a neon pink pigmented gel
ink.
[0171] 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.
[0172] The result is an aqueous ink that will appear purple when
cooled to a temperature below 12 C and will remain purple until
heated to a temperature above 23-25.degree. C., where it will then
change to a bright pink color.
[0173] The thermochromic reversible color changing ink is injected
into a standard 0.7 mm to 1.0 mm (or larger) tip gel ink pen for
transfer to a paper substrate.
[0174] A drawing or written image can be made that will appear
purple at room temperature (20-23 C). 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.degree. C. for a few seconds achievable by placing the
printed image in a refrigerator set at normal conditions.
[0175] Photochromic Gel Ink Pen
[0176] 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 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.
[0177] Clear Base Gel
[0178] 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:
TABLE-US-00005 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
[0179] This may be mixed with pigment as follows. The amount of the
pigment is added to suit the eye.
TABLE-US-00006 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
[0180] 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.
[0181] An example photochromic yellow to green pen/marker ink
is:
[0182] 90% gel base
[0183] 5% photochromic microencapsulated pigment
[0184] 5% Tartrazine dye
[0185] 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.
[0186] 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.
* * * * *