U.S. patent number 3,999,946 [Application Number 05/660,562] was granted by the patent office on 1976-12-28 for time-temperature history indicators.
This patent grant is currently assigned to Allied Chemical Corporation. Invention is credited to Ray H. Baughman, Gordhanbhai N. Patel, Anthony F. Preziosi.
United States Patent |
3,999,946 |
Patel , et al. |
December 28, 1976 |
Time-temperature history indicators
Abstract
Compositions containing at least two conjugated acetylene groups
(-C.tbd.C-C.tbd.C-) are suitable as integral time-temperature
history indicators. These compositions exhibit sequences of
irreversible color changes at combinations of times and
temperatures specific to each composition. Thus, when supported on
the surface of a product or on a substrate affixed to a product,
they are useful for indicating whether a perishable (e.g.,
foodstuff, pharmaceutical, chemical, etc.) has been exposed to an
undesirable time-temperature history that results in substantial
degradation of the perishable or whether a product has been exposed
to a desirable time-temperature history during processing (e.g.,
the sterilization of a foodstuff or biomedical material).
Inventors: |
Patel; Gordhanbhai N. (Morris
Plains, NJ), Preziosi; Anthony F. (Ledgewood, NJ),
Baughman; Ray H. (Morris Plains, NJ) |
Assignee: |
Allied Chemical Corporation
(Morris Township, NJ)
|
Family
ID: |
24650030 |
Appl.
No.: |
05/660,562 |
Filed: |
February 23, 1976 |
Current U.S.
Class: |
422/400; 252/962;
436/2; 426/88 |
Current CPC
Class: |
G01N
31/229 (20130101); G01N 33/02 (20130101); Y10S
252/962 (20130101) |
Current International
Class: |
G01N
33/02 (20060101); G01N 31/22 (20060101); G01N
031/22 () |
Field of
Search: |
;23/253TP ;426/87,88
;73/356 ;116/114AM |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Reese; Robert M.
Attorney, Agent or Firm: Collins; David W. Polin; Ernest
A.
Claims
What is claimed is:
1. A process which comprises applying to a perishable product an
integral time-temperature history indicator comprising at least one
acetylenic compound having at least two conjugated acetylene groups
per molecule.
2. The process of claim 1 in which the acetylenic compound is
deposited on a substrate affixed to the product.
3. The process of claim 1 in which the acetylenic compound is
deposited on the product.
4. The process of claim 1 in which the acetylenic compound is
applied from a solution of the acetylenic compound in a solvent and
the solvent is evaporated from the solution.
5. The process of claim 1 in which the thermal reactivity of the
acetylenic compound is increased by low temperature exposure to
actinic radiation.
6. The process of claim 1 in which the acetylenic compound is
selected from the group consisting of diynes, triynes, tetraynes
and hexaynes.
7. The process of claim 1 in which the acetylenic compound contains
at least one substituent selected from the group consisting of
alkyl, aryl, sulfonate, urethane, acid and alcohol derivatives.
8. The process of claim 1 in which a UV filter is incorporated in
the indicator.
9. The process of claim 1 which further comprises deactivating an
integral time-temperature thermal history indicator comprising at
least one acetylenic compound having at least two conjugated
acetylene groups per molecule.
10. The process of claim 9 which comprises inducing a phase change
from an active phase to a substantially inactive phase.
11. The process of claim 10 in which the phase change is induced by
applying a mechanical stress.
12. The process of claim 10 in which the acetylenic compound is
rapidly heated to a temperature above its melting point.
13. The process of claim 9 in which unreacted acetylenic compound
is extracted by a solvent.
14. The process of claim 9 in which unreacted acetylenic compound
is removed by sublimation.
15. The process of claim 9 in which unreacted acetylenic compound
is deactivated by donor-acceptor complex formation.
16. The process of claim 9 in which unreacted acetylenic compound
is deactivated by a chemical reaction which eliminates the
conjugated acetylene groups.
17. A perishable product having applied thereto an integral
time-temperature history indicator comprising at least one
acetylenic compound having at least two conjugated acetylene groups
per molecule.
18. The product of claim 17 in which the acetylenic compound is
selected from the group consisting of diynes, triynes, tetraynes
and hexaynes.
19. The product of claim 17 in which the acetylenic compound
contains at least one substituent selected from the group
consisting of alkyl, aryl, sulfonate, urethane, acid and alcohol
derivatives.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to visual, irreversible time-temperature
history indicators useful for indicating whether perishables, such
as foodstuffs, pharmaceuticals, chemicals, photographic films and
the like, have experienced undesirable time-temperature histories
which result in substantial degradation or whether products have
been exposed to desirable time-temperature histories during
processing.
2. Description of the Prior Art
The need to know whether a product has been exposed either to an
undesirable time-temperature history which results in substantial
degradation or to a correct time-temperature history required
during processing is self-evident. This applies, for example, to
frozen foods, pharmaceuticals or photographic films which may be
exposed to undesirable high temperatures for significant time
periods during storage and distribution. This also applies to
canned goods and biomedical materials, which must be held at high
temperatures for a specific time period in an autoclave to
guarantee sterilization.
A number of patents have issued disclosing indicators useful, for
example, in detecting whether frozen foods have been exposed either
to time-temperature combinations or to a particular temperature
which results in substantial degradation. U.S. Pat. No. 2,553,369,
issued May 15, 1951 to S. Hoffman, discloses a time-temperature
indicator comprising a combination of hydrated potassium triiodide,
a soluble starch and a diastase. At temperatures above freezing,
the diastase (which is a starch-digesting enzyme) hydrolyzes the
starch, thereby altering the blue color initially rendered to the
starch by the potassium triiodide.
U.S. Pat. No. 2,892,798, issued June 30, 1959 to D. L. Dobbs et
al., discloses an irreversible temperature indicator for frozen
foods comprising an aqueous solution of mercuric and cuprous iodide
colloidally dispersed in a liquid phase comprising an alkali metal
iodide. Upon exposure to thawing temperatures, a color change
occurs.
U.S. Pat. No. 3,545,400, issued Dec. 8, 1970 to V. L. Smith,
discloses a freeze and thaw indicator which is activated by rupture
of a dye-filled container upon freezing. Upon thawing, the released
dye flows onto an absorbent pad, thereby providing the positive
indicator response.
U.S. Pat. No. 3,768,976, issued Oct. 30, 1973 to K. H. Hu et al.,
discloses a process for constructing a time-temperature history
indicator. The operation of this indicator depends upon the rate of
permeation of oxygen through a polymer envelope containing an
aqueous solution of a redox red dye. Upon oxidation, the red dye
turns colorless, providing the warning signal that the perishable
has been exposed to too high a temperature for too long a time
period.
U.S. Pat. No. 3,844,718, issued Oct. 29, 1974 to H. Cohen,
discloses a defrost indicator which is activated by the contact of
water or water vapor with a water-soluble ink supported on a
hygroscopic substrate.
Indicators have also been disclosed for high temperature
applications; see, for example, U.S. Pat. No. 1,668,767, issued May
8, 1928 to J. Hansen et al., which discloses a process for
indicating whether cans filled with food have been exposed to
sufficiently high cooking temperatures. The process comprises
marking the cans with a colored substance which changes color at
212.degree. F. The coloring substance is an organic color such as
erythrocine in a binder, such as shellac, and a solvent, such as
grain alcohol.
U.S. Pat. No. 3,078,182, issued Feb. 19, 1963 to J. W. Crone, Jr.,
et al., discloses a color-changing pressuresensitive adhesive
indicator tape for indicating whether sterilization of packages has
occurred. The indicator comprises a mixture of a halogen-containing
binder resin and a heat sensitive heteropolymolybdate pigment.
The foregoing references are representative of many patents in this
area. A drawback of many of the indicators in the prior art is,
however, that they are useful only over very limited temperature
ranges, such as within a few degrees of the freezing point of
water, or that they are bulky or expensive, or that they depend on
diffusion or on complex reaction mechanisms for their operation.
Furthermore, most of these indicators do not provide a direct
measure of time-temperature history. This is most important, since
both proper product processing and degradation of perishables often
depend on the time exposure to particular temperatures. For
example, food exposed for a period of time at one temperature may
degrade to the same extent as if exposed for a shorter period of
time at a higher temperature. Similarly, high temperature
processing for a short period of time may achieve the same effect
as lower temperature processing for a longer period of time. Thus,
the time-temperature history to which an article has been exposed
is often more critical than whether it has been exposed to a
particular undesirable degradation temperature or to a desirable
processing temperature. Indicator materials are consequently
required which match the time-temperature degradation
characteristics of a wide range of perishables and the
time-temperature characteristics of a wide range of production
processes.
Accordingly, it is often desirable that a time-temperature
indicator should undergo a series of readily detectable changes
corresponding to the progressive development of time-temperature
history. Thus, the indicator should preferably be used to denote
the integral, or sum total, of thermal exposure (time and
temperature), rather than merely that a particular temperature has
been exceeded. Many of the indicators disclosed in the prior art
are not capable of denoting integral time-temperature behavior.
Finally, many of the indicators disclosed in the prior art are not
conveniently activated or deactivated. If the indicator cannot be
conveniently activated, preusage storage of the active indicator
can become a problem. Only if time-temperature history development
can be conveniently halted, is it possible to obtain permanent
indicator responses at various points in the storage and
distribution of a perishable or the processing of a product.
There are many materials that evidence an irreversible color change
upon exposure to temperature. For example, polyacetylenes having at
least two conjugated acetylene groups have been disclosed in U.S.
Pat. No. 3,822,134, issued July 2, 1974 to A. A. Rasch et al., for
use as vacuum-deposited radiation-sensitive elements. Some of these
radiation sensitive elements evidence an irreversible color change
upon exposure to temperature. However, such a color change, by
itself, is insufficient to suggest its use as a practical
time-temperature history indicator, since the color change may
simply indicate that a particular temperature has been exceeded,
without an indication either of the length of time that temperature
has been exceeded or of the time averaged exposure at higher
temperatures. Further, in order to construct a readily readable
indicator, a sharp color change which occurs in a narrow time
interval for each of a range of exposure temperatures is
required.
Practical indicators accumulate a time-temperature history in
integrated form as a single reading. Desirably, such indicators
should parallel the reaction of the particular perishable product
to which they are attached to changes in temperatures over periods
of time.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a process of
applying to a perishable product an integral time-temperature
history indicator comprising at least one acetylenic compound
having at least two conjugated acetylene groups (-C.tbd.C-C.tbd.C-)
per molecule. Further, there is provided a perishable product
having attached thereto an integral time-temperature history
indicator comprising at least one acetylenic compound having at
least two conjugated acetylene groups per molecule.
Such acetylenic compounds accumulate a time-temperature history in
integrated form as a single reading. Depending upon the particular
application, acetylenic compounds can be selected that parallel the
response of the perishable product to which they are attached to
changes in temperatures over periods of time. The time-temperature
history indicator composition is either deposited on the surface of
the perishable product (self-supported) or deposited on a substrate
affixed to the perishable product and is conveniently applied by
melt, vapor, or solution crystallization. The term "applied to"
employed in the appended claims is intended to include both of the
aforesaid deposition procedures. The indicator response results
from a series of relatively abrupt color changes which occur upon
the progressive development of time-temperature history.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a representation of color changes obtained for a
time-temperature history indicator (comprising
2,4-hexadiyne-1,6-diol-bisphenylurethane deposited on filter paper
by the evaporation of the solvent, p-dioxane, from an absorbed
solution) after exposure at the times and temperatures denoted;
and
FIG. 2 is a plot, on coordinates of time in hrs and temperature in
.degree. C and .degree. F, depicting isochromatic responses of a
time-temperature history indicator (comprising
2,4-hexadiyne-1,6diol-bis-p-toluene sulfonate deposited on filter
paper by evaporation of the solvent, ethyl acetate, from an
absorbed solution) exposed to various time-temperature
combinations.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, there is provided a process of
applying to a perishable product an integral time-temperature
history indicator comprising at least one acetylenic compound
having at least two conjugated acetylene groups (-C.tbd.C-C.tbd.C-)
per molecule. Further, there is provided a perishable product
having attached thereto an integral time-temperature history
indicator comprising at least one acetylenic compound having at
least two conjugated acetylene groups per molecule. Such acetylenic
compounds accumulate a visual and irreversible time-temperature
history in integrated form as a single reading. Particular
acetylenic compounds can be matched to particular perishable
products to parallel the response of the product to changes in
temperatures over periods of time. As used herein, the term
"perishable product" refers to package frozen foods, dairy
products, meat, pharmaceuticals, photographic film, canned goods
and the like. The processes monitored by the acetylenic
compositions include undesirable degradation and desirable
processing of these products.
The acetylenic compound may be monomeric or polymeric, cyclic or
acyclic, so long as it contains at least two conjugated acetylene
groups. Examples of suitable acetylenic compounds include diynes,
triynes, tetraynes and hexaynes. In the simplest case monomers are
of the form R-C.tbd.C-C.tbd.C-R, where R is a substituent group,
while polymers are of the form (-C.tbd.C-C.tbd.C-R-).sub.n, where n
has a high value. Examples of R groups include alkyl, aryl,
benzoates, sulfonates, urethanes, acids, alcohols and the like.
These indicator materials include homopolymers and copolymers
containing (-C.tbd.C-).sub.m functionalities (where m is equal to
or greater than 2) either in the backbone, or side groups or both.
Preferred acetylenic compounds include diynes, triynes, tetraynes
and hexaynes. Preferred derivatives include mono and bis
sulfonates, mono and bis urethanes, mono and bis acids and mono and
bis alcohols of acetylenic compounds. Such preferred compounds and
derivatives are most useful as time-temperature history indicators
over the times and temperatures likely to be experienced by
commercial perishable products. Examples of acetylenic compounds
useful as indicator compositions in the practice of the invention
include:
A. SULFONATES
1. p-CH.sub.3 -CH.sub.6 H.sub.4 SO.sub.3 CH.sub.2
-C.tbd.C-C.tbd.C-CH.sub.2 SO.sub.3 C.sub.6 H.sub.4 -p-CH.sub.3
2,4-hexadiyne-1,6-diol-bis-p-toluene sulfonate
2. p-CH.sub.3 -C.sub.6 H.sub.4 SO.sub.3 CH.sub.2
-C.tbd.C-C.tbd.C-(CH.sub.2).sub.2 -C.tbd.CH
2,4,8-nonatriyne-1-ol-p-toluene sulfonate
3. [p-CH.sub.3 -C.sub.6 H.sub.4 SO.sub.3 CH.sub.2
C.tbd.C-C.tbd.C-(CH.sub.2).sub.2 -C.tbd.C-].sub.2
2,4,8,10,14,16-octadecahexayne-1,18-diol-bis-p-toluene
sulfonate
B. URETHANES
1. c.sub.6 h.sub.5 nhococh.sub.2 -c.tbd.c-c.tbd.c-ch.sub.2
oconhc.sub.6 h.sub.5 2,4-hexadiyne-1,6-diol-bisphenylurethane
2. C.sub.2 H.sub.5 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-CH.sub.2
OCONHC.sub.2 H.sub.5 2,4-hexadiyne-1,6-diol-bisethylurethane
3. C.sub.4 H.sub.9 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-CH.sub.2
OCONHC.sub.4 H.sub.9 2,4-hexadiyne-1,6-diol-bis-n-butylurethane
4. C.sub.6 H.sub.5 (CH.sub.2).sub.2 C.tbd.C-C.tbd.C-CH.sub.2
OCONHC.sub.2 H.sub.5 7-phenyl-2,4-heptadiyne-1-ol-ethylurethane
5. C.sub.2 H.sub.5 NHOCO(CH.sub.2).sub.2
-C.tbd.C-C.tbd.C-(CH.sub.2).sub.2 OCONHC.sub.2 H.sub.5
3,5-octadiyne-1,8-diol-bisethylurethane
6. CH.sub.3 NHOCO(CH.sub.2).sub.4 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.4
OCONHCH.sub.3 5,7-dodecadiyne-1,12-diol-bismethylurethane
7. C.sub.6 H.sub.5 NHOCO(CH.sub.2).sub.4
-C.tbd.C-C.tbd.C-(CH.sub.2).sub.4 OCONHC.sub.6 H.sub.5
5,7-dodecadiyne-1,12-diol-bisphenylurethane
8. CH.sub.3 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.CH 2,4,8-nonatriyne-1-ol-methylurethane
9. C.sub.2 H.sub.5 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.CH 2,4,8-nonatriyne-1-ol-ethylurethane
10. C.sub.2 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-C.tbd.C-C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.2 H.sub.5
2,4,6,8-decatetrayne-1,10-diol-bisethylurethane
11. CH.sub.3 NHOCO-C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.C-C.tbd.C-OCONHCH.sub.3
2,4,8,10-dodecatetrayne-1,12-diol-bismethylurethane
12. C.sub.2 H.sub.5 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.2 H.sub.5
2,4,8,10-dodecatetrayne-1,12-diol-bisethylurethane
13. C.sub.6 H.sub.5 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.6 H.sub.5
2,4,8,10-dodecatetrayne-1,12-diol-bisphenylurethane
14. [CH.sub.3 NHOCOCH.sub.2 -C.tbd.C-C.tbd.C-(CH.sub.2).sub.2
-C.tbd.C-].sub.2
2,4,8,10,14,16-octadecahexayne-1,18-diol-bismethylurethane
15. [C.sub.2 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-C.tbd.C-(CH.sub.2).sub.2 -C.tbd.C-].sub.2
2,4,8,10,14,16-octadecahexayne-1,18-diol-bisethylurethane
16. [C.sub.6 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-C.tbd.C-(CH.sub.2).sub.2 -C.tbd.C-].sub.2
2,4,8,10,14,16-octadecahexayne-1,18-diol-bisphenylurethane
C. OTHER
1. hooc(ch.sub.2).sub.8 c.tbd.c-c.tbd.c-ch.sub.2 oh
10,12-tetradecadiynoic acid-14-ol
Similarly suitable for the practice of the invention are cyclic
compositions such as ##STR1## where R is --CO(CH.sub.2).sub.3 CO--,
--CO(CH.sub.2).sub.4 CO--, --(CH.sub.2).sub.3 --, --CH.sub.2
CH=CHCH.sub.2 -- (cis or trans), --CH.sub.2 C=CCH.sub.2 -- or
--CH.sub.2 (m-C.sub.6 H.sub.4)CH.sub.2 --.
All acetylenic compounds (monomeric or polymeric) containing at
least two conjugated acetylene groups which polymerize in the solid
state when thermally annealed are useful in the practice of the
invention. The color changes which give rise to the thermal
response of the indicator usually correspond to addition reactions
which transform one or more of the conjugated acetylenic
functionalities in an acetylenic compound or in a mixture thereof
to fully conjugated chains of the type (=C-(C.tbd.C).sub.r
-C=).sub.q, where q corresponds to the number of mutually reacting
acetylenic functionalities, which is dependent upon reaction
conditions, and where r is 1 or larger. The intense coloration of
the polymerized materials results from the fully conjugated
chains.
The acetylenic compounds may be prepared by known methods. For
example, the mono- and bis-urethane derivatives may be prepared by
reacting the corresponding diyne-ol or diyne-diol with an
isocyanate having the formula RNCO. Examples of R include C.sub.6
H.sub.5 (CH.sub.2).sub.r --, CH.sub.3 (CH.sub.2).sub.r --, and
C.sub.10 H.sub.7 (CH.sub.2).sub.r --, where r is an integer,
typically from 0 to 11. Thus, for example,
2,4-hexadiyne-1-ol-methylurethane may be prepared by reacting
1-hydroxy-2,4-hexadiyne with methylisocyanate, and
3,5-octadiyne-1,8-diol-bis-.alpha.-naphthylurethane may be prepared
by reacting 3,5-octadiyne-1,8-diol with .alpha.-naphthyl
isocyanate. A catalyst may be added to the reaction mixture to
increase the reaction rate to produce the desired acetylenic
compound. Conventional tin catalysts (e.g.,
dibutyl-tin-di-2-ethylhexoate) and tertiary amines (e.g., triethyl
amine) may be used as catalysts. The reaction mixture may also be
warmed, as for example, to about 45.degree. to 55.degree. C to
speed up the reaction, which is usually moderately exothermic. Such
heating, however, is not required. The desired diyne-ol or
diyne-diol may also be prepared by conventional methods. Thus, for
example, 4,6-decadiyne-1,10-diol may be prepared by the oxidative
coupling of the corresponding alkyne, i.e. 4-pentyne-1-ol.
Following preparation of the desired acetylenic compound, it must
be crystallized from an appropriate solvent, from the melt, or from
the vapor, so as to provide an active phase. Suitable solvents
include, for example, alkyl esters of monocarboxyl acids, alkyl
alcohols, paraffins, olefins, benzene, alkylated benzenes, ethers,
ketones, petroleum ether, halogenated hydrocarbons and water.
Particularly useful crystallizing solvents are 1,2-dimethoxyethane,
petroleum ether, acetone, chloroform, benzene, methanol, ethanol,
xylene, ethylacetate and water. Crystallization may, for example,
be effected by room temperature evaporation of solutions containing
from 0.0001 to 0.5 parts by weight of monomer per part by weight of
solvent or solvent blend. Alternatively, other conventional
crystallization procedures may be used, such as sublimation, mixing
of solvent and non-solvent, or cooling a saturated solution to a
sufficiently low temperature (usually above about -30.degree. F)
such that the required crystallization occurs.
It is important to select the proper solvent for crystallization,
since some solvents result in a more active indicator material and
other solvents result in a less active indicator material. A more
active indicator material changes color at a lower temperature in a
shorter period of time than a less active indicator material. For
example, the compound [C.sub.6 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-].sub.2, when crystallized from a 20% solution in
p-dioxane, becomes deep blue after 3 hr at 60.degree. C and
transforms from deep blue to dark red after 9 hr at this
temperature. By comparison, the same compound, when crystallized
from a 20% solution in bromoform, turns a light pink after 16 hr at
70.degree. C. Similarly, different phases with various reactivities
may be obtained by variations in melt crystallization or vapor
deposition conditions.
For obtaining acetylenic compounds of the invention with highest
thermal reactivities, several approaches may be followed.
Composition reactivities tend to increase substantially with
increasing values of n in the functionality (--C.tbd.C-).sub.n.
Similarly, decreasing the size and number of unreactive
functionalities in the composition tends to increase reactivity, as
does increasing ring strain in compositions having cyclic
structures. Alternatively, extremely high reactivity indicator
compositions can be obtained by low temperature exposure of
acetylenic compounds to actinic radiation (such as .gamma.-rays,
electron beams, ultraviolet radiation and X-rays). This processing
introduces reactive centers which propagate as a function of
time-temperature history, thereby producing color changes.
The thermal reactivity of certain acetylenic compounds can be
dramatically increased by low temperature exposure to actinic
radiation, such as Co.sup.60 .gamma.-ray radiation. For example,
the initially colorless compound [C.sub.6 H.sub.5
NHOCO(CH.sub.2).sub.4 -C.tbd.C-].sub.2, when crystallized from a
cooled, saturated ethyl acetate solution and exposed at
-196.degree. C to 50 Mrad of Co.sup.60 .gamma.-rays at a dosage of
1 Mrad/hr, is tan colored immediately after irradiation and
irreversibly turns reddish bronze within 5 to 10 min after removal
from that temperature to ambient temperature.
For certain compounds, the reactivity of similarly
irradiation-activated material is so high that substantial
reaction, along with the associated color changes, occurs in less
than 2 days at liquid nitrogen temperature (-196.degree. C). This
behavior has been observed for the initially colorless phase of
[C.sub.2 H.sub.5 NHOCO(CH.sub.2).sub.3 -C.tbd.C-].sub.2 obtained by
crystallization from ethyl acetate. This composition, when
activated with 50 Mrad of .gamma.-rays, turns deep blue within 50
hr at -196.degree. C.
The thermal reactivity of acetylenic compounds of the invention can
also be increased by adding a suitable conventional initiator.
Examples of conventional initiators include alkyl peroxides such as
dicumyl peroxide, azo compounds such 2-t-butylazo-2-cyano propane,
diacyl peroxides such as benzoyl peroxide, hydroperoxides such as
cumene hydro peroxide, ketone peroxides such as cyclohexanone
peroxide and peroxyesters such as t-butyl peroxyacetate. The
thermal reactivity can be decreased by adding a suitable
conventional inhibitor. Examples include quinones such as
benzoquinone, and aromatic nitro-compounds such as m-nitrobenzene
and 2,4-dinitrochlorobenzene.
The time-temperature history indicator is prepared by depositing an
acetylenic compound or a mixture of acetylenic compounds on a
substrate which is affixed to the perishable product.
Alternatively, the perishable product itself may serve as the
substrate. The substrate may be porous or nonporous. Typical
examples include paper, cardboard, wood, glass, ceramics, plastics
and metals.
Both the range of color change and the composition reactivity can
be varied by codeposition of different acetylenic compounds (at
least one of which contains at least two conjugated acetylene
groups) or by the codeposition of one or more acetylenic compounds
which contain at least two conjugated acetylene groups with one or
more compounds which have similar molecular shape and polarity as
the acetylenic compound, but which do not contain reactive
acetylenic functionalities. Such codepositions can be from the
vapor, melt or solution phases.
The acetylenic compounds are conveniently deposited from a
solution, allowing the solvent to evaporate. While in solution,
they are usually relatively inactive and will not change color,
regardless of time or temperature. Once deposited as a solid on the
substrate, however, they are then responsive to time-temperature
exposures. Some compounds evidence color changes in a specified
time period at comparatively low temperatures while others evidence
comparable color changes in a similar time period only at
comparatively high temperatures. In general, the acetylenic
compounds within the scope of the invention evidence color changes
within the range of -180.degree. to +250.degree. C for time periods
of practical interest. Selection of both compound and solvent
govern the actual time-temperature history indicating behavior.
The acetylenic compounds of the invention are also generally
substantially inactive in the molten state and in the vapor state.
Deposition on a substrate by melt solidification or vapor
deposition results in an active phase that is responsive to
time-temperature exposures.
In some cases, the acetylenic compounds are sensitive to exposure
to short wavelength UV or UV-visible radiation. To construct an
indicator material from such compounds, it may be desirable to
incorporate a filter material with the indicator to eliminate
undesirable photo-induced reactions. The UV reactivity evident for
certain acetylenic compounds is substantially eliminated by
protecting such compounds from exposure with a UV-absorbing film
over the acetylenic compound. Conventional UV stabilizers are also
useful for this purpose. Examples of UV stabilizers include
benzophenones such as 2-hydroxy-4-methoxy benzophenone,
benzotrazoles such as 2-(2'-hydroxy-5'-methylphenyl) benzotriazole,
substituted acrylates such as ethyl-2-cyano-3,3-diphenyl acrylate
and aryl esters such as phenyl salicylate.
The integral time-temperature history indicators in accordance with
the invention are useful in a number of applications. For example,
when affixed to containers of perishables, the indicators can be
used to indicate whether the perishables have been exposed to
thermal conditions which result in appreciable degradation.
Likewise, indicators can be attached to individual cans to indicate
whether canned goods have experienced desirable sterilization
conditions. As another example, the indicator compositions can be
dispersed in the polymeric insulation used for electrical wiring.
Color changes of the composite insulator composition would then
indicate that long term overheating is occurring which could lead
to insulation breakdown or to combustion of surrounding
materials.
To deactivate an indicator composition, a phase change from a
highly active phase to a substantially inactive phase may be
induced either by changing temperature above a critical limit,
which is dependent upon composition, or by applying a mechanical
stress.
Since the acetylenic compounds are usually inactive when molten,
the indicator can be deactivated by heating to some temperature
above the melting point of the unpolymerized material. In such a
case, the heating step should be done rapidly, at a rate dependent
upon the reactivity of the indicator composition, so that
significant thermal reaction does not occur during the deactivation
step.
Similarly, certain symmetrical acetylenic compounds with paraffinic
sidegroups crystallize from the melt as thermally inactive phases.
Upon cooling such a phase to a temperature T.sub.c which is between
-50.degree. and 25.degree. C, depending upon composition, a
reversible phase transformation occurs to a thermally active phase.
Consequently, the existence of this reversible phase transformation
can be utilized to either activate or deactivate the indicator
response.
The fact that many acetylenic compounds form phases in which
non-acetylenic molecules enter interstitially or substitationally
is useful in either activating or deactivating indicator response.
For example, formation of donor-acceptor complexes between
acetylenic compounds with donor sidegroups, such as aromatic
groups, and acceptors, such as tetracyanoethylene or
tetracyanoquinodimethane, is usually observed to transform a highly
active to an inactive phase, although the addition of such
materials in amounts substantially less than equimolar can increase
phase reactivity. The decrease in reactivity results from the
formation of the donor-acceptor complex, which forces the
conjugated acetylene functionalities so far apart that neighboring
acetylenic groups cannot thermally react. Consequently, indicator
response can be either activated by disrupting donor-acceptor
interactions, e.g., via heat or mechanical stress, or deactivated
by forming such a complex, e.g., by exposure of the acetylenic
compound to vapors or to a solution containing a complexing
agent.
The stress-induced phase transformation of certain of these
indicators may be utilized to "freeze" information so that further
exposure to temperature no longer produces a color change. For
example, the symmetrical benzoate of 2,4-hexadiyne-1,6-diol
(R-C.tbd.C-C.tbd.C-R, where R is --CH.sub.2 OCOC.sub.6 H.sub.5) is
obtained as Phase I crystals by crystallizing a 1.3 to 23.8 wt%
solution at 5.degree. C in methanol. On the other hand,
crystallization at the same temperature from diethyl ether solution
results in either phase I or phase II crystals, depending upon
concentration (about 12.3 wt% solution for the former and 17.4 to
29.6 wt% solution for the latter). Phase II crystals are thermally
inactive, while phase I crystals have a low thermal reactivity
usable for high temperature, long time period indicator
applications (e.g., several years at temperatures above room
temperature and below the melting temperature of 74.8.degree. to
75.8.degree. C.). Application of mechanical stress, as by striking,
causes a phase transformation from the active phase I to the
inactive phase II.
Further, the composition 2,4-hexadiyne-1,6-diol-bisphenyl urethane,
represented by the formula C.sub.6 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.6 H.sub.5, when crystallized
from p-dioxane undergoes a stress-induced phase transformation to
an inactive phase. Thus, a convenient tear-off indicator can be
fabricated, which is stamped with code numbers at various points in
the storage and distribution of perishables, for eventual
evaluation of product handling procedures. The indicator regions
under each stamp will be deactivated at the time of stamping,
thereby providing permanent records on one indicator of the state
of the perishable at various points from manufacture to eventual
consumer purchase.
The indicator also can be deactivated by any process which removes
the unreacted indicator composition, such as by sublimation or by
solvent extraction. Further, a composition, such as bromine
solution or vapor, which preferentially reacts with the unreacted
acetylenic compounds, thereby eliminating the reactive conjugated
acetylene groups employed in the indicator, is also used to
deactivate the indicator.
For example, indicator tabs are deactivated by solvent extraction
of unreacted indicator material, since the reaction product is
typically insoluble in most conventional solvents. This is
conveniently done using an indicator construction analogous to that
used for instant photographic film development, whereby pulling a
tab exposes the indicator composition to a solvent, which
immobilizes the indicator response. A similar tab-like construction
is also used to initiate indicator activity. In this case, pulling
a tab exposes an inactive solution of an indicator composition to
the atmosphere, permitting solvent evaporation and thereby forming
the active indicator phase. In order to obtain the widest possible
range of indicator response in one device, the indicator can
consist of a mixture of different indicator compositions, each of
which undergoes a series of color changes during thermal history
development. Alternatively, the indicator can consist of adjacent
strips containing different acetylenic compositions with different
activities. A device which directly reads in terms of the
equivalent storage time at a reference temperature can be
constructed from such an array, via the propagation of a particular
color change across members in the array.
In particular instances, it may be convenient to apply the
indicator composition in the form of a printed message, which will
not be readable on the chosen background until the color
development corresponding to a specified thermal treatment is
obtained.
EXAMPLES
In the examples below, the time-temperature histories of particular
acetylenic compounds of the invention were observed by the
following procedure. Squares of No. 42 Whitman filter paper were
saturated with a solution of the respective compositions in an
appropriate solvent (usually a B 20% by weight solution). Following
solvent evaporation, each square was exposed to a particular
temperature for a particular period of time.
EXAMPLE 1
A 20% solution of 2,4-hexadiyne-1,6-diol-bisphenylurethane, as
represented by the formula C.sub.6 H.sub.5 NHOCOCH.sub.2
-C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.6 H.sub.5, in p-dioxane was
sprayed onto 1.5 .times. 1.5 inch squares of filter paper and the
solvent was evaporated. The indicators thus obtained were annealed
at -20.degree., 0.degree., 23.degree., 40.degree., 50.degree., and
60.degree. C in the dark for various time periods. With the
exception of those filter papers stored at -20.degree. and
0.degree. C, the filter papers were removed from their respective
temperature environment at different times and stored at
-20.degree. C. At the completion of the experiment, the papers were
mounted on a white paper background and photographed at 0.degree.
C. The following results were observed:
At -20.degree. C, there was little development of color.
At 0.degree. C, a light pale blue color developed very slowly.
At 23.degree. C, a blue color developed and intensified, but did
not change to a red color even after 40 days.
At 40.degree. C, a blue color developed, intensified and changed to
red after about 67 hr. The red color then intensified slightly with
time.
At 50.degree. C, a blue color developed rapidly and then changed to
red after about 22 hr. The red color then intensified slightly with
time.
At 60.degree. C, a blue color developed very rapidly and then
changed to red after about 8 hr. The red color then intensified
slightly with time.
These color changes are schematically depicted in FIG. 1, which
shows the colors developed by the squares of filter paper at the
time and temperatures indicated. The relative spacing of lines is
used to indicate intensity.
EXAMPLE 2
A 20% solution of 2,4-hexadiyne-1,6-diol-bis-p-toluene sulfonate,
as represented by the formula p-CH.sub.3 -C.sub.6 H.sub.4 SO.sub.3
CH.sub.2 -C.tbd.C-C.tbd.C-CH.sub.2 SO.sub.3 C.sub.6 H.sub.4
-p-CH.sub.3, in ethyl acetate was sprayed onto filter paper and the
solvent was evaporated as in Example 1. The following results were
observed:
At -20.degree. C, no development of color occurred, even after 5
months.
At 23.degree. C, a red color developed slowly, but did not change
to a green-gold color even after 40 days.
At 40.degree. C, a red color developed, intensified and changed to
green-gold after about 250 hr.
At 50.degree. C, a red color developed rapidly and intensified with
time and changed to green-gold after about 85 hr.
At 60.degree. C, a red color developed and intensified rapidly and
changed to green-gold after about 32 hr.
At 70.degree. C, a red color developed and intensified very rapidly
and changed to green-gold after about 11 hr.
These color changes are graphically depicted in FIG. 2, which is a
plot depicting isochromatic responses as a function of time and
temperature.
EXAMPLE 3
Polymers of the type
where m is 2, 3 or 4 and n is large, corresponding to a high
polymer, were formed by addition reactions between hexamethylene
diisocyanate and the respective diol.
These polymers strongly adhered to glass and to metal surfaces
after solvent or melt deposition on these surfaces. For m = 2, the
initial color was a light pink. For m = 3 or 4, the initial color
was a light blue. The polymers were exposed to 135.degree. C in the
dark and rapidly cooled to room temperature for examination. For m
= 2, the color turned red-purple after 2 hr. For m = 3, the color
turned blue-purple after 2 hr. For m = 4, the color turned light
brown after 2 hr.
EXAMPLE 4
The following materials, deposited onto white filter paper as in
Example 1 from solution in the solvents tabulated below, were
tested at temperatures of -26.degree., 8.degree., 24.degree. and
50.degree. C. Color development was determined periodically by
matching the indicator color to a Munsell Photometer chart
(available from Munsell Color Co., Inc.) with the results listed in
Table I below:
TABLE I
__________________________________________________________________________
Munsell Color Temperature, .degree. C Code -26.degree. -8.degree.
24.degree. 50.degree.
__________________________________________________________________________
##STR2## (in methanol) 5RP3/6 25 d 5RP4/12 336 hr 5RP5/10 25 d 168
hr 5RP6/10 72 hr 6 hr 5RP7/8 79 d 48 hr 3 hr 5RP8/6 336 hr 22 hr 1
hr 5RP9/2 72 hr 3 hr 30 min ##STR3## (in acetone) 5RP3/6 336 hr
5RP4/12 25 d 72 hr 5RP5/10 168 hr 22 hr 5RP6/10 79 d 30 hr 6 hr
5RP7/8 25 d -- 3 hr 5RP8/6 72 hr 22 hr 1 hr 5RP9/2 336 hr 22 hr 1
hr 30 min
__________________________________________________________________________
Green colored filter paper was also employed, with similar results
obtained, except that the initial color was green. Green colored
filter paper is useful because of the conventional association of
green and red with "proceed" and "stop," respectively. With respect
to perishables, such colors might be chosen to indicate whether to
proceed with usage or to stop usage because of degradation.
EXAMPLE 5
Employing a Cadiot-Chodkiewicz-type reaction, 3-bromopropyne-1-ol
was reacted with 1,5-hexadiyne to give two products,
2,4,8-nonatriyne-1-ol (I) and 2,4,8,10-dodecatetrayne-1,12-diol
(II), which were separated by use of appropriate solvents.
Oxidative coupling of (I) gave
2,4,8,10,14,16-octadecahexayne-1,18-diol (III).
Urethanes (--NHOCO-) of (I), (II) and (III) were obtained by
addition-type reactions with the appropriate isocyanates. Benzoates
(C.sub.6 H.sub.5 OCO--) and p-toluene sulfonates (p-CH.sub.3
-C.sub.6 H.sub.4 SO.sub.3 --) were formed by employing a
Schotten-Bauman-type reaction; the former reaction used pyridine
and the latter, potassium hydroxide.
The following materials in powder form were tested at the times and
temperatures indicated with the results listed in Table II
below:
TABLE II
__________________________________________________________________________
Color change after: Composition, Color as Formed 16 hr at
25.degree. C indicated time periods and Crystallization Solvent in
day light at 5.degree. C in the
__________________________________________________________________________
dark ##STR4## none; pink little change (1 mo); (white) (CH.sub.3
OH/H.sub.2 O) (4 mo) light pink (4 mo) ##STR5## none; light little
change (1 mo) (white) (CH.sub.3 OH/H.sub.2 O) pink (4 mo) very
light pink (4 mo) ##STR6## none none (1 mo) (white) (CH.sub.3 OH)
##STR7## " little change (1 mo.) (white) (pet. ether,
60.degree.-110.degree. C) ##STR8## " " (white) (CH.sub.3 OH)
##STR9## red-purple red-purple (16 hr) (red) (acetone/pet. ether,
60.degree.-110.degree. C) (1) ##STR10## none; light none (2 wk);
very (white) (acetone/pet. ether, 60.degree.-110.degree. C) red (4
mo) light pink (4 mo) ##STR11## red-purple light pink (2 wk) (light
pink) (acetone/CH.sub.3 OH) ##STR12## none none (2 wk) (white)
(acetone/CH.sub.3 OH) ##STR13## none none (2 wk) (light tan) (ethyl
acetate/CH.sub.3 OH) ##STR14## blue-red blue-red (16 hr) (red)
(acetone/pet. ether, 60.degree.-110.degree. C) (2) ##STR15## medium
pink light pink (2 wk) (white) (acetone/pet. ether,
60.degree.-110.degree. C) ##STR16## light pink rose-red (2 wk)
(white) (acetone) ##STR17## none none (2 wk) (white)
(acetone/CH.sub.3 OH) ##STR18## red red (16 hr) (tan)
(ethylacetate/pet. ether, 60.degree.-110.degree. C)
__________________________________________________________________________
(1) turns very light red at 100.degree. C after 10 min turns light
red at 115.degree. C after 10 min turns red-purple at 125.degree. C
after 15 min (2) turns light purple at 100.degree. C after 10 min
turns medium purple at 115.degree. C after 10 min turns dark purple
at 125.degree. C after 10 min
EXAMPLE 6
Diacetylenes of the form [R-C.tbd.C-].sub.2 were prepared by a
conventional reaction of the corresponding diol and isocyanate.
Solutions of the various diacetylenes were prepared in a variety of
solvents and deposited as in Example 1 on white filter paper.
Following drying, the color at various times t and temperatures T
was noted. Those results are tabulated below in Table III. The
as-formed compositions, before thermal history development, were
colorless.
TABLE III
__________________________________________________________________________
R Solvent Concentration T, .degree. C t, hr Color
__________________________________________________________________________
C.sub.2 H.sub.5 NHOCOCH.sub.2 methanol 20% 25 960 light pink 40 960
pink 50 960 metallic copper 60 288 " 70 75 " carbon 20% 25 16
colorless tetrachloride 70 16 light blue-pink bromoform 20% 25 16
colorless 70 16 light blue-pink dichloromethane 20% 25 16 colorless
70 16 light blue-pink n-C.sub.4 H.sub.9 NHOCOCH.sub.2 bromoform 20%
25 16 light blue 70 16 red carbon 20% 25 16 light blue
tetrachloride 70 16 red isopropyl 20% 25 16 light blue ether 70 16
red dichloromethane 20% 25 16 light blue 70 16 red C.sub.6 H.sub.5
NHOCOCH.sub.2 p-dioxane 20% 25 115 blue 40 67 red 50 22 " 60 8 "
bromoform 20% 25 16 colorless 70 16 very light pink
p-CH.sub.3C.sub.6 H.sub.4 SO.sub.3 CH.sub.2 acetone 0.5% 40 68
light red 50 68 dark red 60 68 metallic gold 70 68 " ethylacetate
20% 23 960 red 40 250 metallic gold 50 85 " 60 32 " 70 11 "
chloroform 10% 70 3 pink 70 16 red bromoform 10% 70 3 pink 70 16
gold acetone 5% 70 3 pink 70 16 gold carbon 5% 70 3 pink
tetrachloride 70 16 gold dimethyl 5% 70 3 colorless formamide 70 16
colorless C.sub.2 H.sub.5 NHOCO(CH.sub.2).sub.2 acetone 5% 70 16
very light pink 2% 120 0.2 light red ethylacetate 2% 120 0.2 light
red p-dioxane 2% 120 0.2 light red tetrahydro- 2% 120 0.2 light red
furan acetone/ 2% 120 0.2 light red ethylacetate dichloromethane
20% 25 16 colorless 70 16 very light pink bromoform 20% 25 16
colorless 70 16 very light pink CH.sub.3 NHOCO(CH.sub.2).sub.4
tetrahydro- 2% 120 0.5 violet furane p-dioxane 2% 120 0.5 violet
glyme 2% 120 0.2 violet
__________________________________________________________________________
EXAMPLE 7
Sodium amide at low temperature in an ammonia media was reacted
with 1,4-dichlorobutyne, then with p-formaldehyde. Extraction with
diethyl ether gave 2,4-pentadiyne-1-ol.
Oxidative coupling gave 2,4,6,8-decatetrazne-1,10-diol. After
recrystallization from chloroform, this compound was reacted with
ethyl isocyanate to give the desired urethane, [C.sub.2 H.sub.5
NHOCOCH.sub.2 C.tbd.C-C.tbd.C-].sub.2.
One inch squares of Whitman No. 42 filter paper were soaked in a 1%
solution of the urethane in acetone and dried in the dark. The
indicator sheets were then annealed in the dark at temperatures of
-26.degree., -8.degree., 24.degree. and 50.degree. C. Color
development was determined periodically by matching the indicator
color to a Munsell Photometer Chart, with results as listed in
Table IV below:
TABLE IV ______________________________________ Munsell Color
Temperature, .degree. C Code -26.degree. -8.degree. 24.degree.
50.degree. ______________________________________ 5Y4/4 28 d 72 hr
N2/ -- 2.5 hr 5B3/4 84 d 72 hr 2 hr 5PB3/8 -- 21 hr 50 min 5PB4/10
-- 5 hr 40 min 5B4/6 49 d 4 hr 30 min 5B5/6 28 d 3 hr 20 min 5B6/6
-- 2 hr 10 min 5B7/6 104 d -- 1.5 hr -- 5B8/4 60 d 72 hr 20 min --
5B9/2 40 d 24 hr -- -- ______________________________________
EXAMPLE 8
The following experiments were performed to demonstrate that the
thermal reactivity of certain acetylenic compounds can be
dramatically increased by low temperature .gamma.-ray irradiation.
The initially colorless compounds were sealed in vacuum and
irradiated at liquid nitrogen temperature with 50 Mrad of Co.sup.60
.gamma.-rays at 1 Mrad/hr. After irradiation, the color of the
samples was noted before and 5 to 10 min after the samples were
removed from the liquid nitrogen.
The compound [C.sub.6 H.sub.5 NHOCO(CH.sub.2).sub.4
-C.tbd.C-].sub.2, which was crystallized by cooling a saturated
ethyl acetate solution, was tan colored immediately after
irradiation, but turned reddish bronze within 5 to 10 min after
removal from the liquid nitrogen.
The compound C.sub.6 H.sub.5 (CH.sub.2).sub.2
C.tbd.C-C.tbd.C-CH.sub.2 OCONHC.sub.2 H.sub.5,
which was crystallized by cooling a saturated petroleum ether
(60.degree.-110.degree. C fraction) solution, was light tan
immediately after irradiation, but turned metallic gold within 5 to
10 min after removal from the liquid nitrogen. In both cases, the
observed color change was irreversible.
* * * * *