Note: Descriptions are shown in the official language in which they were submitted.
CA 02386091 2002-05-29
This is a divisional application of co-pending"
applicatiori 2,201,397, filed.September 29, 1995.
THERMfJCHROMIC INK FORMULATIONS, NAIL LACQUER AND
METHODS OF USE
FIELD OF THE INVENTION
The invention pertains to the filed of thermochromic dye formulations. More
particularly, the invention pertains to thermochromic dye formulations for
inks used in
lithographic, flexographic or rotogravure printing techniques or thermochromic
dye
formulations for laquers.
BACKGROUND OF THE INVENTION
Thermochromic and photochromic encapsulated dyes were developed a, number of
years ago, and primarily incorporated into plastic or textile colorants for
wide commercial
applications (e.g. the "mood ring" and thermochromic dyed clothing).
Thermochromic
dyes go through a color change over a specific temperature range. The dyes
currently
available change at from a particular color at low temperature to colorless at
a high
temperature (e.g. red at 85 Fahrenheit and colorless at above 90
Fahrenheit). The color
change temperature can be controlled, such that the color-change can take
place at different
temperatures (e.g. just below a person's external body temperature so that a
color change
occurs in response to a human touch). The thermochromic dye manufactures are
able to
manipulate the critical temperature for the color change.
The variability in the dyes is a result of the process used in their
manufacture. One
technique used to produce the thermochromic
CA 02386091 2002-05-29
2
encapsulated dye is to combine water, dye, oil, and melamine formaldehyde
and shake 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 melamine formaldehyde making up
the capsule itself. The encapsulation, melamine formaldehyde, is a thermo
set resin similar to formica. The substance is very hard and will not break
down at high temperature. It is almost entirely insoluble in most solvents,
but it is permeable.
This idea is important to success with respect to product development
using this material. A key factor is exposure. In other words, what the
encapsulated dye "sees" is of the utniost iniportance, and will be a
determining factor in the extent of deterioration in the color change
characteristics of the material. It is this effect that has heretofore
prevented
the incorporation of thermochromic dyes in many types of ink and lacquer
products.
Over the years, discoveries have been made in microencapsulation
techniques, as well as in tlierniochromic chemistry, that have broadened the
potential application of these materials. Most thermochromic dyes consist
of an internal phase of "liquid phase" which changes color when it reaches a
certain temperature, and the external or 'solid phase' which protects the
internal phase. Originally, the product had a size of 5 to 15 microns, could
only change color at one temperature, and would deteriorate quickly in the
sun. The size of tlie capsule has decreased, (0.5 to 5.0 microns), and
ingredients have been added to the liquid phase that greatly improved color
fastness and allow one to adjust the temperature at which the color change
takes place. These improvements niake it possible to incorporate the
thermochromic into ink vehictes, and to print them using different methods.
The problem is that, even though these niaterials have been greatly
improved, they are still very sensitive to external changes in environment.
In order to overcoine the shortcomings of tlie product as it now
stands, we began our research by closely exantining the chemical and
mechanical aspects of the ink manufacturing, thermochromic chemistry, and
printing methods relevant to our problem. Since the surface of the capsules
is very different compared to ttie surface of traditional pigments, the
interface of the vehicle and the capsule surface were the main point of
CA 02386091 2002-05-29
- _3
focus. There are several types of ingredients that are traditionally added to
an ink
formulation. 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. It can be a resin,
lacquer or varnish
or some other polymer. Its characteristics may vary depending on the type of
printing
being done and the desired final product. The second main ingredient is the
colorant itself.
The remaining ingredients are added to enhance the color and printing
characteristics of the binder and the colorant. These might include reducers
(solvents), waxes, surfactant,
thickeners, driers, and/or UV inhibitors.
Those involved with attempting to solve this problem in the past have taken a
traditional ink-making approach to finding a solution. To our knowledge the
manufactures
of the thermochromic capsules have left the problem of creating the ink
product to ink
chemists. Ink chemists that we have spoken with have treated the thermochromic
capsules
as though they were normal pigments. Their resulting ink would not flow on the
rollers,
and would not change colors, if there was any color at all on the printed
paper. The
conclusions drawn from such an approach is that the rollers are crushing the
thermochromic capsule. This hypothesis is false we have studied the process by
which it is
manufactured and the chemicals used in that process. We then studied its
behavior in
several varied environments.
U.S. Patent no. 4,421,560 entitled "Thermochromic Materials" granted to Kito
et al. and U.S. Patent no. 4,425,161 entitled "Thermochromic Materials"
granted
to Shibahashi et al. both state that thermochromic inks can be made with
"conventional
additive used to improve conventional printing inks." Furthermore, U.S. Patent
no.
4,421,560 states that the inks can include many solvents and compounds that
the applicants
have discovered destroy the color change characteristics of thermochromic
pigment
currently commercially available. (e.g. alcohols, -ketone, amino resin,
petroleum solvents,
etc.) These patents fail to teach that many of the solvents and compounds
commonly used
CA 02386091 2002-05-29
4
to make printing ityks are harmful to the thermochromic dye and therefore fail
to teach the
necessary principles to create a thermochromic printing ink that works.
Thermochromic screen inks have been sold previously by Liasion Printing, Inc.,
and
these inks were all of neutral pH inherently or the pH was adjusted to be
neutral, however,
the harmful solvents were not removed and these inks only had a shelf life of
about 6
weeks.
The patents referred to above also state that it is possible to use the
thermochromic dyes in inks for lithographic printing but provide no
instructions for how to use the inks.
Lithography depends upon the separation of oil and water. The oil is the ink
and the water
is the fountain solution. The fountain solution is acidic to minimize the
emulsification of
ink. The higher the pH the more scumming occurs; i.e. the movement of ink into
areas of
the image that are supposed to be free of ink. The acid and other components
in fountain
solutions destroy the color change characteristics of the thermochomic
pigments.
U.S. Patent Number 4,920,991 teaches a thermochromic artificial nail that has
a
thermochromic layer embedded in acrylic-resin. This means that a customer must
purchase
premade artificial nails with the desired color-change characteristics. The
user can not
apply the thermochromic layer herself and experiment with different background
colors.
SUMMARY OF THE INVENTION .
The present invention provides-4nk formulations and a method of correcting
formulations that normally destroy the color change properties of
thermochromic dyes such
that the thermochromic dye can be added to the formulations or corrected
formulation and
nlaintain its color change properties. The present invention also provides
lithographic,
fl.exographic or rotogravure printing techniques for thermochromic inks. The
present
invention also provides formulations for thermochromic nail lacquers.
The present invention comprises a series of discoveries related to the
problems
associated with the printing of microencapsulated thermochromic
CA 02386091 2002-05-29
dyes, including the ink vehicle into which tliey are incorporated, the
printing
process and the printing substrate.
The present invention includes formulations that can be used to create
inks including thermochromic material. The inks tliemselves avoid many of
5 the standard solvents and materials in inks that have been discovered to be
harmful to thermochromic pigments. The acid content of the ink vehicles
has also been reduced as much as possible.
These inks can be used with traditional offset presses and plates,
however, a novel method of using these presses is taught in this application.
To print with these inks in an offset press, all harmful solvents must be
cleaned from the press as well as any residual standard printing ink. The
press should be run with a fountain solution tliat is does not harm
thermochromic pigment (eg. distilled water). Traditionally, all lithography
(offset printing) uses fountain solution to enhance the separation of the oil
(ink) and "water" (fountain solution). Fountain solutions are very expensive
and hazardous to the environment. Heretofore, it was unknown that high
definition lithography could be accomplished using distilled water as a
fountain solution. Therefore, this technology is a major step forward in the
ari of lilliography in general, as well as a specific development of a method
of printing with thermochromic inks for the first time.
One aspect of the present invention is the discovery of a method of
correcting these formulations to allow the addition of thermochromic dyes.
The method comprises making a series of adjustments to the formulations
prior to adding thermocliromic dye. Certain solvents and other compounds
destroy the dye, therefore any aldehydes, ketones, and diols should be
removed from the formulation_and if needed they should be replaced with
solvents which do not adversely effect the thermochrornic pigment.
Solvents having a large molecular weight (i.e. greater than 100) generally
are compatible with the thermochromic pigments. Secondly, the acid
content of the formulation must be adjusted low (i.e. acid number below 20)
or adjusted to be neutral (i.e. 6.5-7.5 pH). These two adjustments will
allow the thermochroniic dyes to be added to the forniulation without a loss
of its color change properties.
CA 02386091 2007-08-16 SECTION 8 CORRECTION
SEE CERTIFICATE
CORRECTION- ARTICLE 8
VOIR CERTIFICAT
5a
Thus, in accordance with one aspect of the invention, there is provided a
document
with a pattern camouflage comprising said following:
a) at least a portion of said document printed with a color changing ink that
is
permanently reversible between colorless and colored in response to
temperature or light;
b) at least a portion of said document printed with a non color changing ink
such
that a pattern is camouflaged when said color changing ink is colored and a
pattern is
revealed when said color changing ink turns colorless.
In accordance with a further aspect of the invention, there is provided a ldt
for
creating a document with a pattern camouflage comprising said following:
a) a color changing ink that is permanently reversible between colorless and
colored in response to temperature or light;
b) a non color changing ink that is color matched to said color changing ink
such
that when said color changing ink has a color it is close enough in color to
said non color
changing ink that it is difficult for a human observer to detect a color
differential between
said inks on said a printed with said inks.
In accordance with yet a further aspect of the invention, there is provided a
method
of camouflaging a pattern on a document comprising the steps of
a) selecting a color changing ink that is permanently reversible between
colorless
and colored in response to temperature or light;
b) selecting a non color changing ink that is color matched to said color
changing
ink such that when said color changing ink has a color it is close enough in
color to said
non color changing ink that it is difficult for a human observer to detect a
color differential
between said inks on said a printed with said inks;
c) printing a document using said color matched color changing ink and said
non
color changing ink such that a pattern is camouflaged when said color changing
ink is
colored and a pattern is revealed when said color changing ink turns
colorless.
CA 02386091 2002-05-29
6 -
BR.iEF DESCRIPTION OF TIIE DRAWING
Figure 1 shows a representational view of a three layer system for
nail polish that includes a thermochromic layer.
DESCRIPTION OF TIiE PREFERRED EMBODIMENT
Thermochromic dyes can be purchased from any one of a number of
suppliers. The present invention was developed using dyes purchased from
the following suppliers: Pilot Inc. and Davis Liquid Crystal Inc.. The
other reagents described herein are standard and can be purchased from
most chemical supply companies
The following detailed description inciudes a general discussion of
the problems associated with thermochrornic dye formulations. The
principles of reactivity, pH, permeability, polarity, and reactivity are
important to understanding this technology. Also taught fully herein are
new formulations using thermochromic dyes made according to the general
principles. Printing inks for lithographic, flexographic and rotogravure
process are taught with specific examples for each. Also taught herein is a
thermochromic nail lacquer.
General Pri_ncioles
Reactivity is very diffcult to explain because it is itself often
ambiguous. It is, however, the cornerstone of an understanding of these
materials. The extent to which molecules will react with each other is
influenced by the pH of the sw rounding medium, the pertneability of the
capsule, the polarity of all conipounds involved, the solubility of the
capsule
and the reactivity of the compounds. The goal of tinding an appropriate
medium for the thermochromic capsules, is to reduce the reactivity between
that medium and the capsules to zero, or at least to a low enough level that
the reactivity will not influence the characteristics of the dye for an
extended
period of time.
Water has a neutral pH. The therrnochroniic dye is often sold in a
slurry of encapsulated dye in a water base. It happens that tiie pH of this
CA 02386091 2002-05-29
7 slurry is neutral: All aqueous media, therefore, that the dye is placed in
must be at a neutral pH (+/- 0.5). This variability is caused by the
reactivity of certain solutions at a given pH. Therefore, some empirical
work may be needed to determine what pH in this range is best, but when
the thermochromic dye is added to a formulation that has a pH outside this
range, the color change properties are almost always Iost. This is an
irreversible effect and therefore, it is iniportant to adjust the pH prior to
adding the thermochromic dye.
As previously mentioned, the capsule haspores in it. The rate at 10 which
substances move through the capsule into the core, is described in
terms of permeability. The more permeable a partition, the more quickly
something will move through it. At this point it should be stated that all of
these principles are related to one another in integral ways. They must be
considered in relationship to one another in order to be effective in solving
the problems we are discussing.
In simple terms, polarity is defined by the uneven distribution of the
outer electrons within a given molecule. The riiore uneven this distribution
is, the more polar the niolecule is said to be. By the sarne token, non-polar
molecules have a relatively even distribution of electrons throughout ihe
molecule. In general, highly polar molecules will react more with the dye
and capsule than non-polar molecules. (There are exceptions to this rule.
Fortunately, the only serious exception is water, which is highly polar but
obviously does not have an adverse effect on the dye.)
Solubility, is how easily something dissolves in the presence of a
given solvent. If something (like salt) is highly soluble in water, for
instance, then water will dissolve it completely if enough water is present.
Temperature is usually directly proportional to solubility. (as temperature
increases, solubility will increase.) This is iinportant because the capsule
itself, though very hard, is soluble to an extent. This solubility is
characterized by wliat is known as the "solubitity paranieter". This
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 making the capsule more
permeable, both of which adversely affect the niaterial. Solvents must
therefore be chosen with great care.
CA 02386091 2002-05-29
8
The goal is to minimize the interactions between the dye and its
surroundings. The capsule is the major part of this. The capsule is hard,
non-polar, thermally very stable (it won't melt), and relatively impermeable.
The infiltration of compounds through the capsule must be stopped or
slowed to the point that the characteristics of the dye are not effected.
Shelf-life is an issue and must be considered in the context of the above
principles. Almost any solvent will penetrate the capsule given enough
time. The question that each person using this technology will need to ask
themselves is: What is an acceptable shelf-life for the product we are
developing and will our formulation give us the desired result?
We already know that the capsules and the dye they contain will not
react with water. Why not? It is a highly polar, small molecule. Why
doesn't it destroy the dye's properties? The fact that it does not react with
the capsule or the dye gives us several hints about the material. The most
important principle to learn from this is that there must be certain
combinations of characteristics present for a substance to effect the dye.
Melamine formaldehyde is not soluble in water. The water is not
absorbed by it, so the capsules is impermeable to water. Water has a
greater affinity for itself than it has for most other substances. Using the
above principles and the knowledge that we have of water outlined above,
we can deduce many things that will help us in creating inks, dyes, and
other media that are essentially unreactive with the capsule or dye.
SQlvents
There are three types of solvents to avoid when working with this
material. There are four clakes of solvents known as aldehydes, ketones,
diols and aromatic compounds that should not be used when developing
products. No ink will work with these types of solvents in them. There are
obviously other solvents that will not work, but one must try them before
you will know for sure.
Therefore the first step in creating a thermochroniic dye formulation
of the present invention is to remove any harniful solvents from the
formulation. If needed non-harmful solvents can be used to replace the
solvents that have been removed. The best solvents to use will be those that
CA 02386091 2002-05-29
9
have low reactivity, are large molecular weight (i.e. over 100), and which are
relatively
non-polar. One solvent that fit.c. this category is cyclohexane. It has low
toxicity and works well.
Adjystirlg the Acid Content
The second step is the most effective and most straight forward. All water-
base inks that
are used must he pH adjusted prior to addition of thermochromic pigment. As
mentioned above,
the pH should he neutral unless (ihcervation indicates that a'different pH is
required. To achieve
;r=,a.
~
''df~ the correct pH, one must use a good proton donor or acceptor, depending
on whether the pH
must he adjusted up or down. To lower the pH. HC1 is used, to raise it, the
hest proton acceptor
so far is KOH. These twt) chemicals are very effective and do not seem to
impart undesirable
characteristics tti the medium. (in other words. K+ and Cl- do not seem to
harm the
thermochrnmic pigment.) Use pH paper to determine the pH. Remember not to add
pigment
before the pH and all ather characteristics frr that matter are correct in the
ink itself. The most
effective pH has been 7Ø however. some tolerance has been noted between 6.0
and B.O. A pH
below 6.0 and above 8.0 has almost always immediately destroyed the pigment.
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 I gram of material under the
conditions of ASTM Test
Method D-1639-70. it is not yet fully understr-od how non-aqueous substances
containing acid
effect the therme+chromic, but high acid number substances have inactivated
the thermachromic
pigments. Generalty. the lower the acid number the better. To date ink
formulations with an
acid value below 20 and nnt including the harmful solvents described above
have worked well.
Some higher acid value formulations may he possible but generally it is best
to use vehicle
i4p
ingredients with low acid numbers or to adjust the acid value by adding an
alkali substance. The
greatest henefit iif a nentr:d (ir low acid value vehicle will he increased
shelf life.
Buffers have been uced historically in inks to minimize the effects of the
fountain solution
on pigment particles. This is one possible solution to the i+citential acidity
problem of the
varnishes. One ingredient (iftrn uced as a hufrer is cream of tartar. A
dispersion of cream of
tartar and linseed oil
CA 02386091 2002-05-29
-
can be incorpora'led into the ink. The net effect is (hat the pigments in the
ink are protected from the acidic fountain solution.
Mixing
5 The thermochroniic inks are sold in two ways: 1) as a dry powder
and 2) in a water based slurry. Mixing systems have been developed for
both slurry and powder that will allow for consistent and well dispersed
pigment.
10 DWggtechniaue
The aqueous slurry can be used to make solvent based ink
formulations by drying of the slurry first.
In traditional ink manufacturiiig, there is a technique known as
flushing. Many traditional pigments corne in slurry forrn, similar to that of
the thermochromic capsules. 'Flushing" in traditional manufaeturing,
means to press most of the water out of the slurry to form what is called a
press cake which is then "flushed" into a mixing varnish. The press cake is
about 25-40% solids. Because of the hydrophobic properties of the pigment
and the varnish, the pigment is mixed into the varnish and away from the
water. The water separates from the varnish and is left behind. Flushing
with the thermochromic capsules does not work. All of the water stays in
the varnish rather than separating. We believe it does this because of the
waters attraction to the surface of the capsule.
The thermochromic encapsulated dye is purchased in slurry form
from Davis. This slurry is placed in a forced nir dryer, where the
temperature is maintained at between 100 and 150 degrees F. When the
slurry reaches the "stiff clay" stage, at about 80% to 95% solids, the slurry
is removed and incorporated into a varnish. The varnish is mixed until
smooth and the remaining ingredients are than added to this niixture. This
mixture is then put over the mill between one and fifteen times, making the
final product. We have tried to mix our inks with a "press cake" which has
80 to 95 percent solids so that the water does not alter the properties of the
ink too severely.
~ __
CA 02386091 2002-05-29
11
We have 'found that using this mixing technique, we can achieve good
dispersion and much improved color intensity over using the dried
thermochromic capsules. Not only is it difficult to get the dried capsules to
disperse appropriately, but the drying process used by the manufacturer
apparently destroys between 10% and 30% of the colorant.
By using an ink mill, on low pressure (0.0 to 100.0 psi), an
acceptable grind can be achieved without further dainage to the
thermochromic capsule. Several passes (1 to 15) may be necessary to
disperse the thermochromic colorant sufficiently, but the fewer passes on the
10 mill the better in terms of daniage to the material. The number of passes
on
the mill can be reduced by niore vigorous pre-mixing.
j, jltra=nd Techniaue
If the ink requires powder to make it, there may be a problem with
dispersion because, in the drying process, the capsules form aggregates that
are very difficult to break up. Over stirring or the wrong type of stirring
will damage or denature the dye.
The technique that has been developed to solve this problem is
simple, effective and inexpensive. The first step is to add the powder to an
appropriate solvent. For the nail lacquer, the solvent used for this step is
the same as the same solvent used in the lacquer itself, Butylacetate. With
the rest of the inks, either cycloliexane or other aromatic compounds can be
used. The solids content of this mixture should be about the same as for the
water base slurry of 50% solids. Once the solvent and the powder are
combined, the container with the mixture is subrnerged in an ultrasound
bath. The vibration breaks up-the aggregates and also conditions the capsule
for its addition to the rest of the medium.
General Procedures for Mixing Formulations
For the applications discussed herein, the teclinique is essentially that
of adding pignient to different media to attain a desired result; that of
mimicking the visual appearance of normal pigments while trying to add the
dimension of thermal activity to its properties.
CA 02386091 2002-05-29
12 _
In order:to add normal pigment to ink, dye, or lacquer, the pigment
itself is ground into the base. This disperses Ihe pigment throughout the
base. Since the pigment is usually a solid crystal with a diameter no larger
than 1.0 microns this grinding is not difficult to do. The eye cannot see
particles that size, so the pigment will give the base a solid color. The
addition of more pigment simply intensiCes the color. Since the pigment
has a very intense color only about 10% of the final ink is made up of
normal pigments. Also, the normal pigment itself is relatively impervious
to the effects of solvent and pH.
Others have used thermochromic dyes, however, these attempts have
focused simply on the addition of thermochromic capsules to an ink base at
random and observing whether or not the capsules maintain their original
color-changing properties. There are Plastisol and water-based UV inks that
are now on the market that cliange color with temperature. The reason
these have been successful, is because the inks do not contain any chemicals
or chemical properties that will adversely effect the capsule or dye. No one
realized why it was possible to use tliermochromic pigments in solvent based
inks and to use them with a traditionaI offset press until the present
invention.
In general, the present invention teaches the following procedure for
making formulations with thermochroniic dyes. If in slurry form, and is
intended for addition to a water base ink, the water is removed to give
slurry between 80% and 95% solids. This is then mixed with an
appropriate ink vehicle and milled.
A base for an ink is developed using off the shelf ingredients. The
ink will incorporate, where possible, and conipatible with the ink types,
solvents with molecular weig'h'ts larger than 100 and avoid all aldehydes,
diols, and ketones, and aromatic conipounds. Selection of the ingredients is
critical. The important considerations with respect to the ingredients within
the ink vehicle deal with the reactivity of these ingredients with the
thermochromic capsule and its contents.
One possible explanation for deterioration, is tliat there may be a
breakdown of the capsule by molecules contained in the ink vehicle. This
would allow deleterious compounds that would otherwise be kept out to
subsequently enter the capsule and alter the chemistry of the liquid phase.
CA 02386091 2002-05-29
13
This phenomenon would depend on the reactivity of the particular molecule
in the vehicle. We have carefu{ly chosen varnishes, reducers, extenders,
and driers with low reactivity in order to minitnize their influence on the
capsule. These additives will also extend the life of the product over time.
Another explanation for the breakdown may lie in cross-capsule
interactions between vehicle molecules and the liquid phase. Due to the
long-chain nature of the compounds found in ink vehicles, there may be
reactive portions of the molecules that can fit through the pores of the
capsule and interact with the liquid phase and d'enature it through this
interaction. Since the behavior of ttu thermochromic is related to its shape
and the location of its electrons at given temperatures, a minor impact due
to outside molecules, could have a large impact on the characteristics of the
liquid phase. Molecules that cannot fit through the capsule pores, may have
reactive portions that could protrude into the capsule and thereby influence
the liquid phase.
Ketones, Diols, atid Aldeliydes must be niininiized, as well as most
mineral spirits, excluding cyclohexane and other chemically similar
compounds. Ammonia, and other highly reactive compounds must also be
avoided. The lower the amounts of these compounds, the better the
performance of the thermochromic and the longer the shelf life of the
product.
One very important step is to adjust the pH or lower the acid value of
the ink base before the pigment 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 pigment. The appropriate specific pH is generally neutral, or
7Ø The pH will vary between 6.0 and 8.0 depending on the ink type and
the color and batch of the pigment.
Once the slurry and the base have been properly prepared, they are
combined. The method of stirring should be low speed with non-metal stir
blades. An ink mill may be used so long as the mill pressure is set low
enough to avoid harniing the microcapsules. Otlier additives may be
incorporated to keep the pigrnent suspended. The ink should be stored at
room temperature.
CA 02386091 2002-05-29
14
Most thermochromic dyes undergo a color change from a speciric
color to colorless (i.e. clear). Therefore, layers of background colors can
be provided under thermochromic layers that will only be seen when the
thermochromic layer changes to colorless. Tf an undercoat of yellow is
applied to the substrate and then a layer containing blue thermochromic dye
is applied the color will appear to change frotn green to yellow, when what
is really happening is that the blue is changing to colorless.
The Substrate
One issue that rnust also be addressed at this stage is the chemical
characteristics of the material printed on. This area of focus has essentially
one component. It must be remembered that whatever surface or substrate
one prints to. that substrate must have the swnie characteristics that the ink
base has. That is, all substrates should be neutral in pH, and must not
impart any chemicals to the capsule that will have a deleterious effect on it.
The greatest concern is with paper. Many types of paper produced today
have relatively low pH and could impact (lie capsule. Low pH could cause
serious deterioration in a matter of weeks. If quality control is to be
maintained, this aspect of the chemistry should be taken into consideration.
Use neutral paper whenever possible.
Specific Formulations
Examples of specific formulations of thermochromic dye
formulations are provided below using the principles and techniques taught
above. -
An aqueous slurry of thermochromic pigment containing
approximately 50% pigment solids is dried in an oven at 100-150_ degrees
F to achieve a solids concentration of 80% - 95 % by weight of
thermochromic pigment. Solid levels below 80% introduce excess water
into finished ink forniuiations and make it difficult to properly disperse the
pigment in the ink vehicle, and generally solids concentrations above 90%
are preferable. Solids greater than 95% result in strong agglomeration of
the pigment particles and make dispersion difticult, however, drying to
solids concentrations up to 98 % has worked. The consistency of the dried
pigment slurry will vary between that of wet clay and nearly dry kernels and
CA 02386091 2002-05-29
flakes. This material is then comb'ined with a grinding/mixing varnish
formulated for the dispersion of dry pigment or presscake, which typically is
high in tack and viscosity, may contain a significant proportion of aikyd
resin, and have an acid value not to exceed 15.
5 ExamF1~1
The dried pigment slurry is added to the vehicle under mechanical
agitation in an amount to achieve a weight/weight ration of 1 part of
pigment solids to I part of vehicle. Agitation piay be provided by various
types of mixers, however, the finat viscosity of the mix will be quite high,
10 and the flow properties of the dispersion may be poor, therefore, a dual
axial, planetary, or turntable-type niixer is recommended. Care must be
taken to ensure that the thermochroniic pigment particles are not ruptured
during the dispersion. A three-roller ink mill may also be used for making
the dispersion, but the rollers must be set in a loose manner, so as not to
15 rupture the pigment particle. Agitation is continued until a smooth glossy
dispersion is obtained. The grind rating of the finished dispersion, as .
determined on a NPIRI Grind Gauge, should be a minimum of 3. This mix
will be referred to below as Offset Ink Base. The acid value of the vehicle
used in this ink should not exceed 40.
Exaninle I-A
Offset Ink Base is combined with other ink components to produce a
Quick-Set lithographic ink as follows: (the acid value of the vehicles used
should not exceed 15.)
Ingredient iVeight %
Offset Ink Base 75.0
Quick Set Gel Vehicle 12.5
Quick Set Free F1oiv vehicle 7.5
12% Cobalt Drier 1.0
6% Manganese Drier 1.0
Ink Oil (IBP 510 deg. F.) 3.0
TOTAL 100.0
CA 02386091 2002-05-29
16
Example 1-B
To the ink described in I-A, a finely divided microcrystalline wax,
polyethylene wax, Fisher-Tropsch wax, either alone or in combination with
a finely divided polytetrafluorethylene polymer, is added to the ink to
improve the dry rub resistance of the dried ink film. Additions of dry wax
may be made from 0.5 % to 3.0 9b . Additions of compounded waxes may be
from 1.5 % to 10%, depending on the wax compound used should not
exceed 15.
Example I -C
Offset Ink Base is combined with other ink coniponents to produce a
hard drying, high solids ink as follows:
Ingredient Weight %
Offset Ink Base 75.0
Iiigh-solids Gel Vehicle 10.0
High-solids Free Flow Veliicle 10.0
1296 Cobalt Drier 1.0
6% Manganese Drier 1.0
Litho Varnish 3.0
TOTAL 100.0
Examnfe 1-D
The ink described in 1-C, where wax is added to improve the rub
resistance of the dry ink film in the same manner described in 1-B.
Exam lR e 1_E
Offset Ink Base is combined with other ink components to produce an
ink suitable for printing business forms and newsprint as follows:
CA 02386091 2002-05-29
17 Ingredient ~Yejglit 96
Offset Ink Base 75.0
Mineral Oil Forms Gel Vehicle 10.0
Mineral Oil Forms Free Flow Vehicle 10.0
Mineral Oil 5.0
TOTAL 100.0
The vehicles in this type of ink formulatidn would be primarily
hydrocarbon resins dissolved in mineral oil. The acid value of such vehicles
generally does not exceed 5, but no instance should it be greater than 15
Example 1-
Soya oil-based vehicles are substituted for the niineral oil-based
vehicles in i-E to produce soya-based fornis and newsprint ink.
Examlile i-G
Offset ink Base is combined with other ink components to produce a
heat-set ink as follows:
Itlg!'editiD~ might %
Offset Ink Base 73.0
Iieat Set Gel Vehicle 10.0
IIeat Set Free Flow Vehicle 10.0
Ink Oil (IBP 470 deg. F) 5.0
TOTAL 100.0
The acid value of the vehicles used in this ink should not exceed 15.
Example 1-H
To the ink described in 1-G, wax, as described in 1-B, is added to
improve the rub resistance of the dry ink film
CA 02386091 2002-05-29
_ .. . = . ~~
EXAhiPLE 2
A metal deccirating ink is made by dispersing tlie dried pigment slurry, as
described in Example I. with an oil-free polyester resin vehicle, as follows:
ingredient Weisht k
Dried Pignient Sturry 37.5
Single Coniponent Oil-Free Polyester 37.5
Vehicle
These two components are mixed mechanically, as in Example l, until a fine
dispersion is achieved. To tliis dispersion is added
Single Component Oil-Free Polyester 20
Vehicle
Polyglycol Solvent 5=0
TOTAL 100.0
Exam2le 2-A
Wax, as described in 1-B, is added to the ink in Example 2 to improve the rub
and abrasion resistance of the dry ink film.
x m & 3
i:~,';x=':'r;K -
An aqueotrs ink for flexographic and-gravure applications is made by
dispersing
the aqueous therrnoclirornic pigment slurry, as supplied, before drying, into
a neutralized
acrylic or moditied -acrylic cc-lloiclat dispersion resin, by adding a
volatile base, strch as
amrnonitrrn hydroxide, to neutrali7e xnd therefore solubili7e, the resin, as
follows
Tngredient Weight %
Colloidal Dispersion Resin (40% Solids) 40.0
Piginent Slurry 50.0
Water 9.0 .
CA 02386091 2002-05-29
-19 _
Defoamer 1 .0 -
Anunonium Hydroxide to neutrality
The colloidal acrylic resin used in this formulation should have a maximum
acid
value of 80. The amount of base added should not exceed that needed to
neutralize the
resin.
There are many possible vehicles and resins in the market that will work in
these
formulations. Also, many variations of each individual formula are possible,
and probable
necessary, to adjust color, color strength, and the working properties of each
type of ink.
The formulations presented above are meant to be typical, not absolute.
Nail Lacquer
As with inks, pigments are ground into lacquer. One main aspect of nail
lacquer is
that many shades are necessary. These different shades are attained by
combining different
pigments into the same lacquer. By using the different pigments in different
ratios,
thousands of colors and shades can be realized.
The chemistry of nail lacquer is straight forward. There is no impact on the
normal
pigments, i.e. not thermochromic, by anything within the lacquer from a
chemical stand
point. The three common ingredients in almost all nail lacquers are
butylacetate,
ethylacetate, and nitrocellulose. Some type of alcohol or aldehyde are also
often used in
smaller quantities. Again, the pigment size is small enough that it can not be
detected by
the human eye. When the lacquer itse,}f dries, it is clear. It is only the
pigment that adds
opacity and color.
U.S. Patent No. 4,920,991 teaches a thermochromic artificial nail. This
process is
very similar to that used to make mugs and other plastic products. There is no
attempt to
incorporate thermochromics into an actual lacquer that can be applied to the
nail.
As with inks the idea is to develop a nail lacquer that is similar'to the non-
thermochromic product in all respects, except that ours changes color with
changes in
temperature.
CA 02386091 2002-05-29
There were four main obstacles in the creation of this product. The
first was finding a forniulation of a lacquer that wotild accommodate the
thermochromic capsules without destroying them. Using the principles
described above this formulation was developed.
5 All diols, aldehydes and ketones are exciuded from the formulation.
Depending on the specifications of the lacquer producer,. the amount of
ethylacetate is reduced as much as possible. Any other substances that may
harm the capsule are also excluded.
The lacquer must also be maintained at a neutral pH. This can be
10 done by ensuring that all of the respective components of the lacquer are
neutral, or by adjusting the pH once all of the ingredients, minus the
thermochromic slurry, have been mixed together.
The second obstacle was that of dispersion. Once the lacquer
formuiation was perfected, the pigment was added, in the powder form, to
15 the lacquer. The capsules were clumping together in large aggregates once
they were added to the lacquer. This gave the lacquer a grainy look. To
overcome this, cyclohexane was added to the powder and then the slurry
was placed in an ultrasound bath, to disperse the capsules before adding
them to the lacquer or the dried slurry form of the pigment was used as in
20 the ink formulations. This gave a stnoother look to the lacqtzer when
applied to the nail.
The next problem was that of color. Thermocliromic dyes go from a
color to no color. In order to get conibinations of two different colors
required some sort of mixture of regular pigment with the thermochromic
pigment. The problem with this was that if the thermochromic pigment is
simply added directly to a cot-dred lacquer it will greatly diminish the
visible
color change characteristics. This problem is solved by layering the
pigments. A base color is applied to the nail and then a thermochromic
layer is applied on top of the base color. Clear lacquer is used as a base.
The thermochromic pigment is incorporated to make ttie thermochromic
lacquer. By putting down a base colt af a regular pigmented lacquer, and
then a thermochromic layer over that, the desired result was achieved. For
instance, if a red base layer is put down with a blue thermochromic layer
over the base layer, the result is a purple color in the cold and a red
colored
nail as it's temperature increases above a certain point. This lechnique was
CA 02386091 2002-05-29
21
a real breakthrough because now we had the ability to create hundreds of
different color combinations.
Our final problem was that of shine. The look of the nail was still
rough. Since the capsules can be as much as 5 times tlie size of regular
pigment, the finish is "bumpy", giving it the rough look. The aggregates
discussed earlier made the problem even worse, so part of the problem was
solved by the dispersion technique already mentioned. It was still not at the
level of quality that we needed, however. The problem was overcome by
adding one additional layer of clear top coat. 10 The final product is
produced using a three layer technique illustrated
in figure 1. A base coat of regular pigmented lacquer 1 is applied, then a
middle thermochromic layer is applied 2 and a thin, clear top coat 3. The
middle layer being the one that requires the special chemical and dispersion
adjustments.
Printing Process
The press must first have all residual standard ink removed from it
using traditional cleaning solvents. This will nxan at least two good
cleanings depending on the amount of ink in the press.
All of the cleaning solvent must be removed from the press using
cyclohexane or other appropriate solvent. The press sliould be completely
dry before the thermochromic ink is added to the press.
The fountain solution must also be removed from the fountain, rollers
and the plate being used if there is any solution on them. This should be
done with tap water to clean the components of solution, and then rinsed
with distilled water.
NEW FOUNTAIN SOLUTION
DISTILLED WATER should be used instead of a regular fountain
solution. If normal solution is used, the chernicals in the solution and the
acidity of the solution will destroy the color change characteristics of the
therniochroniic. TO OUR KNOWLEDGE, THE USE OF DISTILLED
~: :
CA 02386091 2002-05-29
22
WATER AS A FOUNTAIN SOLUTION, IIAS NEVER BEEN DONE
BEFORE IN OFF-SET PRINTING.
In order for regular inks to perform correctly in a lithographic
process, the fountain solution must include a variety of compounds that are
harmful to the ink. These compounds prevents scumining and
emulsification of the water with the ink while running the press. (see
Chemistry of the Graphic Arts) Other fountain solution additives enhance
the performance of the ink. The special properties of our ink, allow it to be
printed with distilled water in place of the fountain solution.
The explanation for why our ink works when printed with distilled
water has to do with the properties of the thermochromic colorant being
used, as well as the water that is included in our ink by virtue of the ink
manufacturing process and low acid value of the vehicle. The
thermochromic capsule is a melamine formaldeiiyde. This substance has
both hydrophobic as well as hydrophilic properties, making its interaction
with the ink vehicle unique.
Gum Arabic is applied to the portions of the printing plate that are
not intended to receive ink. Often a small amount of gum arabic is added to
the fountain solution. Gum arabic is a relatively high molecular weight and
is not known to be detrimental to the thermochromic pigment. It is possible
that a small amount could be added to distilled water when printing with the
thermochromic inks. However, using distilled water as the fountain solution
is known to work extremely well and is the current preferred embodiment
and best mode of practicing the invention.
Heating
We have found in our experinientation that heating the press under
certain conditions will intprove the tlow characteristics of the ink. By
simply raising the teniperature of the ink to above 90 degrees Fahrenheit
will have the desired effect. This higher teinperature can be achieved by
putting heating tape on the ink fountain and using a forced air heater for the
other rollers. Heating is not always necessary, and eventually we believe
CA 02386091 2002-05-29
23 .
that no heating will be required, but right now it is the considered the best
mode of
practicing the invention.
Other solvents
We have found cyclohexane to be effective for the purposes of dispersion of
the dry thermochromic powder, or for the cleaningiof the press in preparation
for
printing the thermochromic ink. There are however several other possi'ble
options
for cleaning or as reducers witbin the ink itself that will also be effective.
We
have isolated a few that work well, but many others exist. We have already
discussed the classes of solvents that are deleterious.
Pattern Camouflage
One of the benefits of the thermochromic lithographic ink technology is that
hidden images can be printed in documents printed with a combination of non-
thermochromic and thermochromic images. The hidden image appears when the
lithographic ink undergoes a color change. This is one of the more important
aspects of the marketability aspects of the inks for toys, advertising and
security
issnes. If the thermochromic aad non-thermochromic inks overlap prob1ems in
shading occur, tberefore, the in~ -are color and texture matched and laid down
in
a non-overlapping pattern but next to each other such that the original image
appears uniform. As the thermochromic ink undergoes a color change the hidden
image appears. 1le pattern of the image can be modified to be distracttng to
the
user to prevent noticing subtle changes in pattern without a color-change.
CA 02386091 2002-05-29
24
Aocordingly; it is to be understood that the embodiments of the invention
herein described are merely iUustrabive of the application of the principles
of the
invention. Referencx herein to detsils of the illustrated embodiments are not
intended to limit the scope of the claims, which themselves recite those
features
regarded as essential to the invention.
