U.S. patent application number 13/082254 was filed with the patent office on 2011-10-13 for thermochromic indicator materials with controlled reversibility.
This patent application is currently assigned to The Board of Governors for Higher Education, State of Rhode Island and Providence Plantations. Invention is credited to William B. Euler, Brett Lucht, Yu Wang.
Application Number | 20110248224 13/082254 |
Document ID | / |
Family ID | 30000873 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110248224 |
Kind Code |
A1 |
Lucht; Brett ; et
al. |
October 13, 2011 |
THERMOCHROMIC INDICATOR MATERIALS WITH CONTROLLED REVERSIBILITY
Abstract
A thermal indicator material which comprises a plurality of
polythiophenes having a second low temperature color and a high
temperature color. The polythiophenes are structured and arranged
to exhibit a color change from the second low temperature color to
the high temperature color when the thermal indicator material is
exposed to a temperature that meets or exceeds a predetermined
temperature and to exhibit a color change from the high temperature
color to a first low temperature color when the thermal indicator
material is exposed to a decline in temperature from a temperature
that meets or exceeds the predetermined temperature to a
temperature of within the range of between about 5 to 20.degree. C.
below the pre-determined temperature that occurs in a time period
of greater than 2.0 seconds.
Inventors: |
Lucht; Brett; (Wakefield,
RI) ; Euler; William B.; (Narragansett, RI) ;
Wang; Yu; (Worcester, MA) |
Assignee: |
The Board of Governors for Higher
Education, State of Rhode Island and Providence Plantations
|
Family ID: |
30000873 |
Appl. No.: |
13/082254 |
Filed: |
April 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12405027 |
Mar 16, 2009 |
7943063 |
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13082254 |
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11024326 |
Dec 28, 2004 |
7517475 |
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12405027 |
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Current U.S.
Class: |
252/583 ;
549/59 |
Current CPC
Class: |
G01K 11/16 20130101 |
Class at
Publication: |
252/583 ;
549/59 |
International
Class: |
G02F 1/17 20060101
G02F001/17; C09D 5/26 20060101 C09D005/26; C09D 11/00 20060101
C09D011/00; C07D 409/14 20060101 C07D409/14 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The U.S. Government has a paid-up license in this invention
and, the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
of FY01-PS10 awarded by USDOT.
Claims
1. A method for producing a thermal indicator material comprising:
providing a plurality of compounds having the following structure:
##STR00006## wherein: R.sub.1-R.sub.6=a hydrogen, substituted or
unsubstituted alkyl radical, substituted or unsubstituted alkoxy
radical, substituted or unsubstituted thioalkyl radical,
substituted or unsubstituted trialkylsilyl radical, substituted or
unsubstituted acyl radical, substituted or unsubstituted ester
radical, substituted or unsubstituted amine radical, substituted or
unsubstituted amide radical, substituted or unsubstituted
heteroaryl or substituted or unsubstituted aryl radical; n is
between 1 and 1000; m is between 0 and 1000; l is between 1 and
1000; and the compounds having a first low temperature color;
heating the compounds to a temperature of or above a pre-determined
temperature to form heated compounds; and cooling the heated
compounds to a temperature within a range of between about
0.degree. C. and 30.degree. C. in a time period of less than 2.0
seconds to form cooled compounds, the cooled compounds exhibiting a
second low temperature color and exhibiting a color change from the
second low temperature color to the first low temperature color
when the compounds are exposed to a temperature that meets or
exceeds the pre-determined temperature and then cooled to a
temperature within the range of between about 5 to 20.degree. C.
below the pre-determined temperature in a time period of greater
than 2.0 seconds.
2. The method of claim 1 wherein the heating step comprises heating
the compound for a time period within the range of between about
5.0 seconds to 1000 seconds.
3. The method of claim 1 which further comprises admixing the
cooled compounds with a carrier medium.
4. The method of claim 3 wherein the cooled compounds are present
in the thermal indicator material in an amount of about 0.05 to
about 25.0% by weight based on the total weight of the thermal
indicator material.
5. The method of claim 1 wherein the pre-determined temperature is
in the range of between about -30 to 150.degree. C.
6. The method of claim 5 wherein the pre-determined temperature is
85.degree. C., the first low temperature color is burgundy, and the
second low temperature is orange.
7. The method of claim 3 wherein the carrier medium is selected
from the group consisting of polyurethanes; elastomers including
polysiloxanes and polydienes; polyacrylates, poly(ethylene
terephthalate)s (PET), polysytrenes, polyolefins including
polyethylenes (HDPE and LDPE) and polypropylene, polycarbonates,
polyacrylics, polyacrylic acids, polyacrylamides, polymethacrylics,
polyvinyl ethers, polyvinyl halides, poly(vinyl nitrile)s polyvinyl
esters, polyesters, polysulfones, polysulfonamides, polyamides,
polyimines, polyimides, and carbohydrates.
8. The method of claim 3 wherein the carrier medium is an ink
formulation.
9. The method of claim 3 wherein the ink formulation comprises
oils, resins, pigment extenders and additives.
10. A thermal indicator material comprising: a plurality of
compounds having the following structure: ##STR00007## wherein:
R.sub.1-R.sub.6=a hydrogen, substituted or unsubstituted alkyl
radical, substituted or unsubstituted alkoxy radical, substituted
or unsubstituted thioalkyl radical, substituted or unsubstituted
trialkylsilyl radical, substituted or unsubstituted acyl radical,
substituted or unsubstituted ester radical, substituted or
unsubstituted amine radical, substituted or unsubstituted amide
radical, or substituted or unsubstituted aryl radical; n is between
1 and 1000; m is between 0 and 1000; l is between 1 and 1000; the
compounds having a first low temperature color and a second low
temperature color; and the compounds are structured and arranged to
exhibit a color change from the second low temperature color to the
first low temperature color when the thermal indicator material is
exposed to a temperature that meets or exceeds a pre-determined
temperature and then cooled to a temperature of within the range of
between about 0.degree. C. to 30.degree. C. in a time period of
greater than 2.0 seconds.
11. The thermal indicator material of claim 10 which further
comprises a carrier medium.
12. The thermal indicator material of claim 11 wherein the
compounds are present in the thermal indicator material in an
amount of about 0.05 to about 25.0% by weight based on the total
weight of the thermal indicator material.
13. The thermal indicator material of claim 10 wherein the
pre-determined temperature is in the range of between about -30 to
150.degree. C.
14. The thermal indicator material of claim 10 wherein the
pre-determined temperature is 85.degree. C. and the first low
temperature color is burgundy, and the second low temperature color
is orange.
15. The thermal indicator material of claim 11 wherein the carrier
medium is selected from the group consisting of polyurethanes;
elastomers including polysiloxanes and polydienes; polyacrylates,
poly(ethylene terephthalate)s (PET), polysytrenes, polyolefins
including polyethylenes (HDPE and LDPE) and polypropylene,
polycarbonates, polyacrylics, polyacrylic acids, polyacrylamides,
polymethacrylics, polyvinyl ethers, polyvinyl halides, poly(vinyl
nitrile)s polyvinyl esters, polyesters, polysulfones,
polysulfonamides, polyamides, polyimines, polyimides, and
carbohydrates.
16. The thermal indicator material of claim 11 wherein the carrier
medium is an ink formulation.
17. The thermal indicator material of claim 11 wherein the ink
formulation comprises oils, resins, pigment extenders and
additives.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 12/405,027, filed Mar. 16, 2009, which
is a continuation of U.S. patent application Ser. No. 11/024,326,
filed Dec. 28, 2004, and issued as U.S. Pat. No. 7,517,475, issued
Apr. 14, 2009. U.S. patent application Ser. No. 11/024,326, filed
Dec. 28, 2004, claims the benefit of U.S. Provisional Application
Ser. No. 60/392,452 filed Jun. 28, 2002, and International Patent
Application Serial No. PCT/US2003/020537 filed Jun. 30, 2003, all
applications of which are hereby incorporated by reference in their
entireties. U.S. patent application Ser. No. 11/024,326 filed Dec.
28, 2004 is related to International Patent Application Serial No.
PCT/US02/22079, filed Jan. 10, 2002 and U.S. patent application
Ser. No. 09/758,075, filed Jan. 10, 2001 now U.S. Pat. No.
6,706,218, both applications of which are hereby incorporated by
reference in their entireties.
FIELD OF THE INVENTION
[0003] The invention relates to thermo chromic indicator materials
comprised of polythiophenes.
DESCRIPTION OF RELEVANT ART
[0004] Polythiophenes are known for their electrically conductive
properties. One technique used to study polythiophenes is to
analyze associated color changes when the temperature of the
polythiophene is varied. Color changes provide insight into the
electro-conductive properties of the polymer. There are numerous
patent and literature citations which describe this work.
[0005] In many instances it is clearly desirable to know when an
object or article reaches or has exceeded a specific temperature
simply by viewing the object and noting that at least a portion of
the object has exhibited a color change. Viewing includes visual
observation by an individual or detection of color change by a
sensor, which sensor would output a signal to be detected in any
suitable manner.
[0006] For example, the useful life of many products can become
comprised if exposed to temperatures above a pre-determined
temperature. Accordingly, a need exists for a thermal indicator
that exhibits a controlled color change indicative of when such
products, e.g., food and protective fire suits, have been exposed
to the pre-determined temperature. The present invention addresses
this need.
BRIEF SUMMARY OF THE INVENTION
[0007] Broadly, the invention comprises a thermal indicator
material comprised of temperature sensitive polymers that exhibit a
visually detectable color change at a proscribed temperature within
the range of between about -30 to 150.degree. C. The visual
detection can include visual observation by an individual or
detection of the exhibited color change by a sensor, which sensor
would output a signal to be detected in any suitable manner. The
temperature of the color change (hereinafter referred to as the
thermo chromic transition) can be adjusted by synthetically
modifying the thermo chromic polymers. Upon heating a sample of the
thermal indicator material to a high temperature within the range
of between about 130.degree. C. and 160.degree. C., preferably
140.degree. C., followed by rapid cooling, the sample will maintain
a new color at low temperatures within the range of between about
0.degree. C. and 30.degree. C., preferably 20.degree. C. When the
sample is reheated above the thermo chromic transition and allowed
to cool slowly, the sample reverts to the original low temperature
color. This controlled reversible thermochromic transition results
from the heating of the sample to a high temperature followed by
the rapid cooling of the sample. The temperature sensitive
polymers, when used as pigments to mark an item, can indicate
whether the marked item has met or exceeded a pre-determined
temperature at any time after marking. Items coated with the
polymers show no detectable loss of the mark after more than one
year of storage below the thermo chromic transition temperature.
The thermo chromic polymers can be dispersed in commercial plastics
(polyurethane, polystyrene, polyethylene, etc.) at low
concentrations and retain the controlled reversibility. The
temperature sensitive polymers can also be used as a pigment for
inks.
[0008] The thermochromic polymers are generally of the
structure:
##STR00001##
wherein R.sub.1-R.sub.6=a hydrogen, substituted or unsubstituted
alkyl radical, substituted or unsubstituted alkoxy radical,
substituted or unsubstituted aryl radical, substituted or
unsubstituted thioalkyl radical, substituted or unsubstituted
trialkylsilyl radical, substituted or unsubstituted acyl radical,
substituted or unsubstituted ester radical, substituted or
unsubstituted amine radical, substituted or unsubstituted amide
radical, substituted or unsubstituted heteroaryl or substituted or
unsubstituted aryl radical
[0009] n is between 1 and 1000,
[0010] m is between a and 1000, and
[0011] 1 is between 1 and 1000.
[0012] Compound I has reversible color changes upon temperature
variation. The temperature of the color change and the
reversibility is dependent upon the structure of the polymer or the
oligomer. The mechanism for the thermo chromic transition is based
on a two-step process. At low temperature the polymer has the
conjugated repeat units (responsible for color) in a planar
conformation and the substituents of the polythiophene chain are
ordered into a lattice. As the temperature is raised, the side
chain lattice melts and the resulting disorder allows the main
chain repeat units to twist away from planarity as shown below in
Scheme 1:
##STR00002## ##STR00003##
[0013] The twisting of the polythiophene units increases the band
gap which results in a blue shift of the optical absorption as
shown in Scheme 2:
##STR00004##
[0014] Polythiophenes with long sidechains are believed to have
sharp thermochromic transitions due to the two-phase morphology.
The melting of the sidechains causes a zipper effect, which results
in a sharp thermo chromic transition. When polythiophenes with long
side-chains films are rapidly cooled the side chain lattice freezes
before the main chain twists back to a planar conformation. Since
the main-chain is locked in a staggered conformation the color of
the material has a shorter wavelength absorption than
polythiophenes that are cooled slowly allowing the main-chain
thiophene units to become planar.
[0015] In one aspect, the invention comprises a method for
producing a thermal indicator material which comprises a plurality
of compounds having the following structure:
##STR00005##
[0016] wherein R.sub.1-R.sub.6 is a hydrogen, substituted or
unsubstituted alkyl radical, substituted or unsubstituted alkoxy
radical, substituted or unsubstituted aryl radical, substituted or
unsubstituted thioalkyl radical, substituted or unsubstituted
trialkylsilyl radical, substituted or unsubstituted acyl radical,
substituted or unsubstituted ester radical, substituted or
unsubstituted amine radical, substituted or unsubstituted amide
radical, substituted or unsubstituted heteroaryl or substituted or
unsubstituted aryl radical, n is between 1 and 1000, m is between 0
and 1000, and l is between 1 and 1000. The compounds have a first
low temperature color and are structured to exhibit a high
temperature color when the compound is exposed to temperatures
above a pre-determined temperature. The compounds are heated to a
temperature within the range of between about 130.degree. C. and
160.degree. C., preferably 140.degree. C. to form heated compounds.
The heated compounds are cooled within a time period of less than
2.0 seconds, preferably 0.1 seconds, to a temperature within the
range of between about 0.degree. C. and 30.degree. C., preferably
20.degree. C., to form cooled compounds. The cooled compounds
exhibit a second low temperature color and exhibit a color change
from the second low temperature color to the high temperature color
when the thermal indicator material is exposed to a temperature
that meets or exceeds the pre-determined temperature and exhibit a
color change from the high temperature color to the first low
temperature color when the thermal indicator material is exposed to
a decline in temperature from a temperature that meets or exceeds
the predetermined temperature to a temperature within the range of
about 5 to 20.degree. C. below the pre-determined temperature, the
decline in temperature occurring in a time period of greater than
2.0 seconds, preferably 20 seconds. The compounds can be heated for
a time period within the range of between about 5 seconds to 1000
seconds, preferably 40 seconds. The predetermined temperature range
of the compounds can be in the range of between about -30 to
150.degree. C., preferably 65 to 100.degree. C.
[0017] In another aspect of the invention, the method further
comprises admixing the cooled compounds with a carrier medium. The
cooled compounds can be present in the thermal indicator material
in an amount of about 0.05 to about 25.0%, preferably 5.0% by
weight based on the total weight of the thermal indicator
material.
[0018] In yet another aspect of the invention, the pre-determined
temperature can be 85.degree. C., the first low temperature color
is burgundy, the high temperature color is yellow and the second
low temperature color is orange.
[0019] In another aspect of the invention, R.sub.1 and R.sub.4 are
C.sub.20-C.sub.50 alkyls or substituted alkyls, and R.sub.2,
R.sub.3, R.sub.5 and R.sub.6 are H, n is 0.8, m is 0.2, and 1 is,
between 15 and 100.
[0020] In yet another aspect of the invention, the carrier medium
comprises an ink formulation.
[0021] In yet another aspect, the thermal indicator material
produced by the method will exhibit a color change from the high
temperature color to the second low temperature color when the
thermal indicator material is exposed to a decline in temperature
from a temperature that meets or exceeds the pre-determined
temperature to a temperature within the range of between about 20
to 50.degree. C. below the pre-determined temperature that occurs
in a time period of less than 2 seconds.
[0022] The invention also comprises the thermal indicator materials
produced by the method as well as the thermal indicator materials
admixed with a carrier material.
[0023] As used herein, the terms low temperature color means the
color the polythiophenes will exhibit below the pre-determined
temperature and when the color change has either been completed or
commenced. The term high temperature color means the color the
polythiophenes will exhibit above the pre-determined temperature
and when the color change has been either completed or
commenced.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0024] FIG. 1 depicts polythiophene films of the invention on paper
at: (a) room temperature; (b) above the thermo chromic temperature;
(c) thermally marked with Sargent key; and (d) thermally marked
with a circle;
[0025] FIG. 2 is a graph depicting the reflectance spectra of
thermo chromic indicator materials of the invention below the
thermo chromic transition before marking, above the thermo chromic
transition, and below the thermo chromic transition after
marking;
[0026] FIG. 3 depicts polythiophene films of the invention on paper
thermally marked with a circle; and
[0027] FIG. 4 depicts polythiophene films of the invention on paper
thermally marked with a circle.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0028] Referring to FIG. 1, a photograph depicting polythiophene
films on paper at: (a) room temperature; (b) above the thermo
chromic temperature; (c) thermally marked with Sargent key; and (d)
thermally marked with a circle is shown. The films are comprised of
a polythiophene wherein R.sub.1 and R.sub.4 are
--(CH.sub.2).sub.21CH.sub.3, R.sub.2, R.sub.3, R.sub.5 and R.sub.6
are H, n is 0.8, m is 0.2, and l is between 25 and 50. The films in
FIG. 1 were spin coated from THF solutions of the polythiophene
onto paper. After spin coating, the films were heated with a heat
gun to between 120 and 150.degree. C. and then were allowed to
slowly cool (>2 seconds) to room temperature to remove any
residual solvent. This provided the burgundy film shown in FIG. 1
a. Heating the film a second time to between 120 and 150.degree. C.
causes the film to change in color from burgundy to yellow as shown
in FIG. 1b. After heating films to between 120 and 150.degree. C.
the films can be rapidly cooled (0.1 seconds) by pressing a metal
key onto the surface of the film. Rapid cooling to low temperature,
0 to 30.degree. C., allows the generation of an orange mark in the
form of a key. The remainder of the film, which cooled slowly,
returns to the original low temperature color, burgundy (FIG. 1c).
If the film is maintained at temperatures below the thermo chromic
transition of the polythiophene film (85.degree. C.) the mark will
be retained for more than a year. However, if the film is heated
above 85.degree. C. the mark will disappear. After heating films to
between 120 and 150.degree. C. the films can be rapidly cooled by
pressing metal fuse onto the film. Rapid cooling to low
temperature, 0 to 30.degree. C., allows the generation of an orange
mark in the form of a circle (FIG. 1d).
[0029] Referring to FIG. 2, a graph depicting the reflectance
spectra of thermo chromic indicator materials of the invention
below the thermo chromic transition before marking, above the
thermo chromic transition, and below the thermo chromic transition
after marking. The films are comprised of a polythiophene wherein
R1 and R4 are --(CH2b CH3, R2, R3, Rs and R6 are H, n is 0.8, m is
0.2, and l is between 25 and 50.
[0030] Referring to FIG. 3, a photograph depicting polythiophene
films on paper thermally marked with a circle. The films are
comprised of a polythiophene wherein R.sub.1 and R.sub.4 are
--(CH.sub.2).sub.21CH.sub.3, R.sub.2, R.sub.3, R.sub.5 and R.sub.6
are H, n is 0.8, m is 0.2, and l is between 25 and 50. The films in
FIG. 3 were spin coated from THF solutions of the polythiophene
onto paper. After spin coating, the films were heated with a heat
gun to between 120 and 150.degree. C. and then were allowed to
slowly cool (>2 seconds) to room temperature to remove any
residual solvent. The low 20 temperature films are red. After
heating films to between 120 and 150.degree. C. the films can be
rapidly cooled (0.1 second) by pressing a metal fuse onto the
surface of the film. Rapid cooling to low temperature, 0 to
30.degree. C., allows the generation of an orange mark in the form
of a circle. The remainder of the film, which cooled slowly,
returns to the original low temperature color, red (FIG. 3). If the
film is maintained at temperatures below the thermo chromic
transition of the polythiophene film (75.degree. C.) the mark will
be retained for more than a year.
[0031] Referring to FIG. 4, a photograph depicting polythiophene
films on paper thermally marked with a circle. The films are
comprised of a polythiophene wherein R.sub.1 and R.sub.4 are
--(CH.sub.2).sub.21CH.sub.3, R.sub.2, R.sub.3, R.sub.5 and R.sub.6
are H, n is >0.95, m is <0.05, and 1 is between 25 and 50.
The films in FIG. 4 were spin coated from THF solutions of the
polythiophene onto paper. After spin coating, the films were heated
with a heat gun to between 120 and 150.degree. C. and then were
allowed to slowly cool (>2 seconds) to room temperature to
remove any residual solvent. The low temperature films are purple.
After heating films to between 120 and 150.degree. C. the films can
be rapidly cooled (0.1 seconds) by pressing a metal fuse onto the
surface of the film. Rapid cooling to low temperature, 0 to
30.degree. C., allows the generation of a red mark in the form of a
circle. The remainder of the film, which cooled over more than 2
seconds, returns to the original low temperature color, purple
(FIG. 4). If the film is maintained at temperatures below the
thermo chromic transition of the polythiophene film (95.degree. C.)
the mark will be retained for more than a year.
[0032] The synthesis of compound(s) I is known in the art. In the
synthesis of compound(s) I to exhibit the color change at the
pre-determined temperature, e.g., for the series of
poly(3-alkylthiophene)s, there is roughly an inverse correlation
with the length of the n-alkane substituent and the temperature of
the thermo chromic transition for both the regiorandom
(R.sub.1=alkyl, R.sub.4=alkyl, n.about.0.8, m.about.2, 1=40-80,
R.sub.2,R.sub.3,R.sub.5,R.sub.6.dbd.H) and regioregular
(R.sub.1=alkyl, n=40-80, m=0, R.sub.2,R.sub.5,R.sub.6.dbd.H),
poly(3-n-alkylthiophene)s. For regiorandom polymers longer
substituents such as n-hexadecyl have lower temperature thermo
chromic transitions (81.degree. C.) than shorter chain substituents
such as n-octyl (130.degree. C.). The regioregular polymers have
higher thermo chromic transitions than the regiorandom polymers but
the same inverse correlation with chainlength is observed. The
n-hexadecyl and n-octyl have thermo chromic transition centered
around 125 and 175.degree. C. The thermo chromic transition
temperatures are dependent upon the molecular weight of the
polymer. Lower molecular weight polymers have lower thermo chromic
transition temperatures while higher molecular weight polymers have
higher thermo chromic transition temperatures.
[0033] In one embodiment, the invention includes the use of
compound I as pure compounds or admixed with paints including
polyurethanes, polysiloxanes, polyacrylates, and other related
polymer-based paints and coatings with about 0.5% polymer based
pigment with retention of the thermo chromic behavior. The thermo
chromic polymer-based pigments can be incorporated via injection
molding or extrusion into many commercially important plastics such
as poly(ethylene terephthalate) (PET), polysytrene, polyethylene
(HDPE and LDPE), other polyolefins, polydienes, polycarbonates,
polyacrylics, polyacrylic acids, polyacrylamides, polymethacrylics,
polyvinyl ethers, polyvinyl halides, poly(vinyl nitrile)s poly
vinyl esters, polyesters, polysulfones, polysulfonamides,
polyamides, polyimines, polyimides, carbohydrates, and polymer
mixtures and copolymers. The plastics retain a visually retrievable
thermo chromic response with pigment loadings of about 0.5%
polymer-based pigment.
[0034] In yet another embodiment of the invention, polythiophenes
exhibiting controlled thermo chromic transitions are dispersed in
commercially available printable ink formulations, e.g. oil with
resins, pigment extenders and other additives, to form thermal
indicator ink systems. The polythiophenes are present in the
thermal indicator ink in an amount of 1.0-25% by weight based on
the total weight of the thermal indicator ink, preferably 7.0 to
14% weight. The ink can be printed using conventional methods such
as ink-jet and letter press. Examples of ink formulations that
polythiophene can be dispersed in can include combinations of
resins such as cellulose, nitrocellulose with co-binders including
polyamides, polyester amides, alkyd, epoxy acrylates, amine
acrylates, polyurethanes, and polyvinyl butyral (UNI-REZ, UNI-JET,
BECKOSOL, EPOTUF), suitable oils such as napthenic petroleum oils
and vegetable oils, e.g. soy bean oil, and suitable pigment
extenders and additives that can include organic acids and esters
of organic acids such as malic acid and organic solvents such as
1,5-pentanediol, diethylene glycol, along with other alcohols and
related compounds (VERTEC, SYLFAT, UNIKYD, and ICM, DY-SOLVE lines
of additives.).
[0035] In yet another embodiment the invention, the thermal
indicator ink is printed on at least a portion of a suitable
substrate, e.g. a portion of paper, plastic, or ceramic
food/beverage containers, a portion of packaging materials for
foods and goods, labels, a portion of labels, stickers, etc., using
conventional printing methods. The polythiophenes dispersed in the
ink system can be in particulate form and have diameters in the
range of between about 0.01-0.1 microns thereby rendering the
system suitable for fine printing.
[0036] In another embodiment of the invention, the thermal
indicator material is applied to an article, e.g., a portion of
paper, plastic or ceramic food/beverage containers, as a coating on
an area of the article, or the entire article, which will be
visible during the expected use of the article. The coating can be
applied by any technique known in the art, such as by brush,
roller, spraying, etc. Accordingly, the coatings typically have a
thickness of 0.1 to 1000 microns. The thermal indicator material
can also be absorbed on a surface or both absorbed and adsorbed on
a surface.
[0037] Suitable carrier mediums to be admixed with the
polythiophenes exhibiting controlled reversible thermo chromic
transitions can include polyurethanes; elastomers including
polysiloxanes and polydienes; polyacrylates, poly(ethylene
terephthalate)s (PET), polysytrenes, polyolefins including
polyethylenes (HDPE and LDPE) and polypropylene, polycarbonates,
polyacrylics, polyacrylic acids, polyacrylamides, polymethacrylics,
polyvinyl ethers, polyvinyl halides, poly(vinyl nitrile)s polyvinyl
esters, polyesters, polysofones, polysulfonamides, polyamides,
polyimines, polyimides, and carbohydrates.
[0038] The invention will further be described with reference to
following non-limiting examples.
Example I
[0039] The thermal indicator material comprising the polythiophenes
exhibiting controlled thermo chromic transitions can be prepared
via a two step process. Thin films or powders of polythiophenes can
be heated above the thermochromic transition, typically
120-150.degree. C., with a heat gun, oven, or hot plate. The
samples are typically heated over a short period of time (5-20
seconds), but slower heating rates are appropriate also, e.g.,
greater than at least 20 seconds, preferably 20 to 1000 seconds.
The heated films or powders are then rapidly removed from the heat,
e.g., within a time period of about 0 to 10 seconds, preferably
less than 2 seconds and cooled via contact with a thermally
conductive material such as a metal plate. The metal plate can be
at room temperature or below room temperature as long as it is at
least 20.degree. C. below the thermo chromic transition
temperature. The contact with the low temperature thermally
conductive surface rapidly cools the polythiophenes from at or
above the thermo chromic transition to within 5 to 20.degree. below
the thermochromic transition within a time period less than 2
seconds, preferably 0.1 seconds, resulting in the production of the
second low temperature colored material.
[0040] The polythiophene films in FIG. 1 have a thermo chromic
transition of 85.degree. C. The films in FIG. 1 were spin coated
from THF solutions of the polythiophene onto paper. After spin
coating, the films were heated with a heat gun to between 120 and
150.degree. C. and then were allowed to slowly cool (>2 seconds)
to room temperature to remove any residual solvent. This provided
the burgundy film shown in FIG. 1a. Heating the film a second time
to between 120 and 150.degree. C. for 5 seconds causes the film to
change in color from burgundy to yellow as shown in FIG. 1 b. After
heating films to between 120 and 150.degree. C. the films can be
rapidly cooled by pressing a metal key onto the surface of the
film. Cooling to low temperature, 0 to 30.degree. C. in 0.1
seconds, allows the generation of an orange mark in the form of a
key. The remainder of the film, which cooled slowly, returns to the
original low temperature color, burgundy (FIG. 1c). If the film is
maintained at temperatures below the thermo chromic transition of
the polythiophene film (85.degree. C.) the mark will be retained
for more than a year. However, if the film is heated above
85.degree. C. the mark will disappear. After heating films to
between 120 and 150.degree. C. the films can be rapidly cooled by
pressing metal fuse onto the film. Rapid cooling to low
temperature, 0 to 30.degree. C., allows the generation of an orange
mark in the form of a circle.
[0041] The polythiophene films in FIG. 3 have a thermo chromic
transition of 75.degree. C. The films in FIG. 3 were spin coated
from THF solutions of the polythiophene onto paper. After spin
coating, the films were heated with a heat gun to between 120 and
150.degree. C. and then were allowed to slowly cool (>2 seconds)
to room temperature to remove any residual solvent. The low
temperature films are red. After heating films to between 120 and
150.degree. C. for 5 seconds the films can be rapidly cooled by
pressing a metal fuse onto the surface of the film. Cooling to low
temperature, 0 to 30.degree. C., in 0.1 seconds allows the
generation of an orange mark in the form of a circle. The remainder
of the film, which cooled slowly, returns to the original low
temperature color, red (See FIG. 3). If the film is maintained at
temperatures below the thermo chromic transition of the
polythiophene film (75.degree. C.) the mark will be retained for
more than a year.
[0042] The polythiophene films in FIG. 4 have a thermo chromic
transition of 95.degree. C. The films in FIG. 4 were spin coated
from THF solutions of the polythiophene onto paper. After spin
coating, the films were heated with a heat gun to between 120 and
150.degree. C. and then were allowed to slowly cool to room
temperature to remove any residual solvent. The low temperature
films are purple. After heating films to between 120 and
150.degree. C. for 5 seconds the films can be rapidly cooled by
pressing a metal fuse onto the surface of the film. Cooling to low
temperature, 0 to 30.degree. C., in 0.1 seconds allows the
generation of a red mark in the form of a circle. The remainder of
the film, which cooled slowly, returns to the original low
temperature color, purple (See FIG. 4). If the film is maintained
at temperatures below the thermo chromic transition of the
polythiophene film (95.degree. C.) the mark will be retained for
more than a year.
[0043] The foregoing description has been limited to a specific
embodiment of the invention. It will be apparent, however, that
variations and modifications can be made to the invention, with the
attainment of some or all of the advantages of the invention.
Therefore, it is the object of the appended claims to cover all
such variations and modifications as come within the true spirit
and scope of the invention.
* * * * *