CA1185157A - Thermally-activated time-temperature indicator - Google Patents
Thermally-activated time-temperature indicatorInfo
- Publication number
- CA1185157A CA1185157A CA000413990A CA413990A CA1185157A CA 1185157 A CA1185157 A CA 1185157A CA 000413990 A CA000413990 A CA 000413990A CA 413990 A CA413990 A CA 413990A CA 1185157 A CA1185157 A CA 1185157A
- Authority
- CA
- Canada
- Prior art keywords
- article
- colored
- solvent
- stratum
- temperature range
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K3/00—Thermometers giving results other than momentary value of temperature
- G01K3/02—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values
- G01K3/04—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values in respect of time
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S252/00—Compositions
- Y10S252/962—Temperature or thermal history
Abstract
Abstract Device which visually indicates exposure to a temperature within a predetermined range for a predeter-mined length of time. The device may be used in the fast food industry to make certain that all food sold has been recently prepared. An opaque microporous sheet has a colored stratum on the back and a transparent fusible coating on the face. The coating is a solid solution of amorphous rubbery polymer in crystallizable solvent which, upon melting, gradually penetrates and transparentizes the microporous layer, rendering the colored stratum visible.
Description
THERMALLY-ACTIV~TED TIME-TEMPE~T~RE INDICATOR
Background of -the Invention ~ _ _ . _ . .
This invention relates to time-temperature indicators and is particularly concerned with devices which indicate exposure time above a -threshold temperature.
For at least the past forty years there has been a desire for a simple means -to determine whether an article's exposure to a temperature at or above a predeter-mined threshold has exceeded a predetermined ~ime limit.
Such information is of interest, for example, in deter-mininc3 whether ~rozen foods have thawed, and much of the prior art has been concerned with this problem. One threshold tempera~ure indicating device, operatin~ sub-stantially independent of time, is shown in U,S. Patents No. 2,269,035, where a colored paper is provided with an opaque coating of a powdered sharp-melting compound dispersed in a polymeric carrier. Exposure to a temperature above the melting point fuses the compound, rendering it transparent and permitting the colored backing ~0 to be seen. O-ther devices, taking bo-th time and temperature into account, have been based on the fact that a low-melting solid will, upon melting, wick along a porous substrate such as Eilter paper, cardboard, etc., at a predictable rate, the distance of travel thus being directly related to the time the substance was in liquid form. Illustrative devices incorporating this general principle are shown in ~.S. Patents No. 3,414,~15,
Background of -the Invention ~ _ _ . _ . .
This invention relates to time-temperature indicators and is particularly concerned with devices which indicate exposure time above a -threshold temperature.
For at least the past forty years there has been a desire for a simple means -to determine whether an article's exposure to a temperature at or above a predeter-mined threshold has exceeded a predetermined ~ime limit.
Such information is of interest, for example, in deter-mininc3 whether ~rozen foods have thawed, and much of the prior art has been concerned with this problem. One threshold tempera~ure indicating device, operatin~ sub-stantially independent of time, is shown in U,S. Patents No. 2,269,035, where a colored paper is provided with an opaque coating of a powdered sharp-melting compound dispersed in a polymeric carrier. Exposure to a temperature above the melting point fuses the compound, rendering it transparent and permitting the colored backing ~0 to be seen. O-ther devices, taking bo-th time and temperature into account, have been based on the fact that a low-melting solid will, upon melting, wick along a porous substrate such as Eilter paper, cardboard, etc., at a predictable rate, the distance of travel thus being directly related to the time the substance was in liquid form. Illustrative devices incorporating this general principle are shown in ~.S. Patents No. 3,414,~15,
2,560,537, 2,782,749, 3,113,774, and 3,24~,303.
Another time-temperature indicatinc3 device, shown in ~.S. Patent No. 3,065,083, is a two-compartment envelope containing a colorless indicator dye separated from a solid fatty acid by a fat-soluble isobutylene:
styrene barrier film. When the envelope is heated -to a su~ficiently hi~Jh temperature, the acid melts, slowly dissolves the film, and reacts with the indica-tor dye, causing a color change.
~' In more recent times, modern -technology has imposed new requirements for time-temperature indica-ting devices. For example, the so-cal:Led "East food" chains, which specialize in the mass production oE specific food items, pride themselves on making certain that the food is served while it is still fresh. Thus, a freshly prepared hamburger sandwich is placed in a heated holding area, and, unless it is sold within 10 minutes, it is thrown away. It is difficult for a busy worker to remember when each sandwich has been placed in the holdiny area, and there thus exists a desire for an inexpensive means to indicate visually the aging o~ each individual sandwich~
It is believed that none of the time-temperature indicators of the prior art is suitable Eor the use described in the preceding paragraph, all such prior art devices being more complicated and expensive than -the use will permit, unsuitable for the temperature range involved, lacking in customer appeal, incapable of reactin~ within a brief but finite time span, etc.
Brief Statement of the Invention The present inven-tion provides a simple, reli ablel and inexpensive way to determine when a permissible time within a predetermined temperature range has been exceeded. Articles oE the invention are particularly adapted for use in the fast food industry, where they can be readily attached to a wrapper to indicate whether an individual food product has exceeded the brief permissible time between preparation and serving.
The invention thus comprises an article ~or irreversibly displaying visual evidence of exposure within a predetermined temperature range for at least a predeter-mined length of time. The article comprises in combination a. an opaque open cell microporous diffusely light-reflective layer having first and second surfaces and being formed o-E components which will not melt at the upper end of the predetermined temperature range, ~5~
b. a colored stratum firmly joined to the first surface of the microporous layer, and c. overlying, but not appreciably penetrating, at least a portion oE the second surEace of the microporous layer, a substantially transparent coating of a composition comprising a solid solution of (1) an amorphous rubbery polymer having a glass transition temperature below the lower end oE
the predetermined temperature range, dissolved in (2) a crys-tallizable solvent Eor the rubbery polymer, the solvent having a melting point below the lower end predetermined temperature range.
~he solvent:polymer ratio is selected to control viscosity and thus assure penetration of the en-tire depth oE the microporous layer by the composition at the explration oE
the predetermined length oE time in the temperature range.
2Q For convenience in attaching articles of the type just described to products whose time-temperature history is to be monitored, it is desirable to provide, over at least a portion of the surEace opposite that on which the transparent coating is applied, a normally tac]cy and 25 pressure-sensitive adhesive, thereby obtaining a form oE
pressure-sensitive adhesive tape. In such cons-tructions, the solid solution functions as a low adhesion backsize, enablin~ the tape to be wound convolutely upon itselE about a core and subse~uently unwound without adhesive transEer;
30 a typical force to unwind such a roll oE tape is about 20 g/cm width.
In a typical use, a product oE the type just described is adhered to the exterior surface of the wrapping of a Ereshly prepared hamburger, which is then 35 placed in a heated holding area having a temperature of 145F. + ~F. (approximately 63C~ ~ 3C.). ~elow 60C~
the crystalli~abLe solvent melts, "activating" the composi-tion, so that within the 60-66C. temperature range, -the amorphous polymer:crystallizable solvent composition is a viscous liquid solution which gradually penet-rates the microporous layer. Since the refractive index oE the 5 composition is essentially the same as that of the solid component in the microporous layer, the microporous layer gradually becomes transparent. When the composition has penetrated substantially the entire depth of the micro-porous layer, the resulting transparency reveals the 10 underlying colored stratum, indicatiny that the permissible time of retention for the hamburger has expired. The product may be sold any time before such visual indication has taken place but not thereafter.
Opaque microporous layers, suitable Eor use in the practice oE ~he invention, are known to the art. In this regard, attention is directed to applicant's U.S~
Patent No. 4,299,880 which discloses a preEe~red structure in which the microvoid-containing layer consists essen-tially of particles held in pseudo-sintered juxtaposition 20 by a thermoseL binder. ~ther opaque microporous layers include, e.g., those shown in U.S. Patents No. ~,299,991,
Another time-temperature indicatinc3 device, shown in ~.S. Patent No. 3,065,083, is a two-compartment envelope containing a colorless indicator dye separated from a solid fatty acid by a fat-soluble isobutylene:
styrene barrier film. When the envelope is heated -to a su~ficiently hi~Jh temperature, the acid melts, slowly dissolves the film, and reacts with the indica-tor dye, causing a color change.
~' In more recent times, modern -technology has imposed new requirements for time-temperature indica-ting devices. For example, the so-cal:Led "East food" chains, which specialize in the mass production oE specific food items, pride themselves on making certain that the food is served while it is still fresh. Thus, a freshly prepared hamburger sandwich is placed in a heated holding area, and, unless it is sold within 10 minutes, it is thrown away. It is difficult for a busy worker to remember when each sandwich has been placed in the holdiny area, and there thus exists a desire for an inexpensive means to indicate visually the aging o~ each individual sandwich~
It is believed that none of the time-temperature indicators of the prior art is suitable Eor the use described in the preceding paragraph, all such prior art devices being more complicated and expensive than -the use will permit, unsuitable for the temperature range involved, lacking in customer appeal, incapable of reactin~ within a brief but finite time span, etc.
Brief Statement of the Invention The present inven-tion provides a simple, reli ablel and inexpensive way to determine when a permissible time within a predetermined temperature range has been exceeded. Articles oE the invention are particularly adapted for use in the fast food industry, where they can be readily attached to a wrapper to indicate whether an individual food product has exceeded the brief permissible time between preparation and serving.
The invention thus comprises an article ~or irreversibly displaying visual evidence of exposure within a predetermined temperature range for at least a predeter-mined length of time. The article comprises in combination a. an opaque open cell microporous diffusely light-reflective layer having first and second surfaces and being formed o-E components which will not melt at the upper end of the predetermined temperature range, ~5~
b. a colored stratum firmly joined to the first surface of the microporous layer, and c. overlying, but not appreciably penetrating, at least a portion oE the second surEace of the microporous layer, a substantially transparent coating of a composition comprising a solid solution of (1) an amorphous rubbery polymer having a glass transition temperature below the lower end oE
the predetermined temperature range, dissolved in (2) a crys-tallizable solvent Eor the rubbery polymer, the solvent having a melting point below the lower end predetermined temperature range.
~he solvent:polymer ratio is selected to control viscosity and thus assure penetration of the en-tire depth oE the microporous layer by the composition at the explration oE
the predetermined length oE time in the temperature range.
2Q For convenience in attaching articles of the type just described to products whose time-temperature history is to be monitored, it is desirable to provide, over at least a portion of the surEace opposite that on which the transparent coating is applied, a normally tac]cy and 25 pressure-sensitive adhesive, thereby obtaining a form oE
pressure-sensitive adhesive tape. In such cons-tructions, the solid solution functions as a low adhesion backsize, enablin~ the tape to be wound convolutely upon itselE about a core and subse~uently unwound without adhesive transEer;
30 a typical force to unwind such a roll oE tape is about 20 g/cm width.
In a typical use, a product oE the type just described is adhered to the exterior surface of the wrapping of a Ereshly prepared hamburger, which is then 35 placed in a heated holding area having a temperature of 145F. + ~F. (approximately 63C~ ~ 3C.). ~elow 60C~
the crystalli~abLe solvent melts, "activating" the composi-tion, so that within the 60-66C. temperature range, -the amorphous polymer:crystallizable solvent composition is a viscous liquid solution which gradually penet-rates the microporous layer. Since the refractive index oE the 5 composition is essentially the same as that of the solid component in the microporous layer, the microporous layer gradually becomes transparent. When the composition has penetrated substantially the entire depth of the micro-porous layer, the resulting transparency reveals the 10 underlying colored stratum, indicatiny that the permissible time of retention for the hamburger has expired. The product may be sold any time before such visual indication has taken place but not thereafter.
Opaque microporous layers, suitable Eor use in the practice oE ~he invention, are known to the art. In this regard, attention is directed to applicant's U.S~
Patent No. 4,299,880 which discloses a preEe~red structure in which the microvoid-containing layer consists essen-tially of particles held in pseudo-sintered juxtaposition 20 by a thermoseL binder. ~ther opaque microporous layers include, e.g., those shown in U.S. Patents No. ~,299,991,
3,031,328, and 3,508~344; in some circumstances, certain Eilter paper may also be employed. The prior art describes providing a rnicroporous layer with a colored support stratum and the subsequent application oE a liquid having a refractive index closely approximating that of the solid components in the microporous layer, thereby transparen-tizing the microporous layer and rendering the colored support stratum visible. No such art, however, suggests the application of a composition which is a nOn-pelletratLng solid tha-t is meltable to a liquid penetrating state, let alone a solid composition in which an amorphous polymer is dissolved in a crystalline solvent.
Detailed Description Understanding of the invention will be further enhanced by reEerring to the following illustrative bu-t D ;~
non-limiting examples, in which all pa-rts are by weight unless otherwise specifiedO
In each of Examples 1-6 below, a microvoid-fonning composition was prepared by mixing 18.12 parts toluene~ 3062 parts diisobutylketone, 1.11 parts cellulose acetate butyrate (Eas-tman CAB 500-1), 7025 parts methyl isobutyl ketone, 10.00 parts of a 60~ solution of hydroxy functional acrylic resin (~-lenkel Co. "G Cure 868 RX-60'l), 58.00 parts 5-micrometer silica (Pennsylvania Sand Glass Corporation "Min-U-Sil"); and 1.90 parts oE a 75~ SOlutiO
of 1,6-hexamethylene diisocyanate in 1:1 xylene:2-e-thoxy acetate (Mobay "Desmodur" N-75). This composition was then coated onto the surface of black 60-micrometer greaseproof paper and allowed to dry and cure at room temperature Eor 10 days; the drie~d layer was Inicroporous and approximately 12.7 micrometers thick.
A varnish was applied to the surEa e of the microvoid, coating in a pattern of 2.5-millimeter wide diagonal lines spaced about 6.4 millimeters apart. The transparenti~lng effect resulted in an initial pattern of black lines on a white background, evaporation oE the solvent causing the lines to appear dark grayO The varnish formed a Eilm, sealiny the pores and thus preventing subsequent penetration by the liquified fusible layerO
A ~Eamily of fusible compositions was prepared by blending various ratios of polyisobutylene having a glass transition temperature of about -65C. and a number average molecular weight in the rany~ of 81,000-99,000 ("Vistanex"
L-100) and paraffin wax ("Shellwax" loo! havinq a melting 30 point of 125F. (roughly 50Co) and dissolving in toluene to form a 25% solids solution. Each such solution was knife coated onto a release liner using a 125-micrometer slot and dried at about 93C. The mol-ten coa-ting was then chilled to solidify it and form a solid solution oE the polyisobutylene and paraEfin wax. The solid c~ating was then placed in contact with the surface of the stripe-coated microporous layer and laminated thereto by passing -the layers between squeeze rolls (one rubber~ one steel), both internally heated to a temperature of about 52C., a pressure of about 485 N/cm width, and a rate of abou-t 2 m/min, the exact conditions being varied controllably to ensure good bonding of the Eusible coatin~ to the microporous layer with negligible penetra-tion.
Examples 7-11 below were prepared in the same manner as Examples L-6 except Eor tne microvoid-Eorrning layer and the composition used in printing the lines. The microvoid-forming layer was made by blending 77.39 par-ts -toluene, 11.18 parts diisobutylketone, 22037 parts methy]isobutylketorle, 44.47 parts of a 60% solution of hydroxy-functional acrylic resin (Henkel Co. "G-Cure 868 RX-60"), 0.9 part di(dioctylpyrophosphate) ethylene titanate, 466 parts 0.5-15 micrc~eter calcium carbonate (Sylacauga Calcium Produc-ts "Microwhite" 25), and 7.9 parts oE a 75% solution oE ],6-hexal~ethylene diisccyanate. The dried thickness of the microvoid layer was 25 micrometers.
Stripes were printed using a lacquer containing a small amount of carbon black.
Strips (about 2.5 cm x 12.7 cm) of the produc-t of each example were now hung in a circulating air oven main-tained at specified temperatures ~ 1F. (-~ 006C.) and observed through a transparent door until the initially white surface became lndistinguishable from the gray stripes, indicating tha-t the coating composition had penetrated the microvoids, transparentizing the layer and making the underlying bla~k greaseproof paper v:Lsible.
Continued exposure to the oven temperatui-e caused Eurther darkerling, so that widc black stripes were visible bc~tween the narrow printed dark gray stripes. Results are summarlzed below:
~ ~ ~ 5 ~
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o ~ I ~ U~ I I I I I I I I
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tn ~ ~9 a~ O
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~r U ~ ~ ~D ~ O O
.
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. ~ ~ I~ I ~ i ~ I I I I I I I I
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.,~
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~ ~ l '1' . ~l ~., O O
a) o ,, a~ ~ 0 ,~ ~ r~ o o o o~
~ ~1 O ~ ~ ~ ~ ~ l_ .,. O O l-- O O O . . . ~ .
~ ~ ~ ~ 1-- 1~ ~ U~ O ~ ~ O C~ 1--Q ~ " ...... ~ r o~
O ~ o o ~ o o O .. .0 .. .. .. ..
~ ~ r~ ~r u~ o c~ o o o O ~ ~ ~ c~ o ~, _l O
Q~ ~
~ o ~1 X O
It is apparen-t that the length of time required to change color at a given temperature is dependent on the polyiso~
butylene.paraffin ratio. It also appears that the presence o~ the polylsobutylene may reduce the eEfect oE
temperature above the threshold value on rate of color change. The tabulated values should be considered typical, but they are subject to change with variation in the type and thickness of microvoid layer, the molecular weight of the polyisobutylene, and the melting point of the crystalline solvent. For the system shown, however, a 105 polyisobutylene:paraffin ratio is considered desirable for displaying an exposure to a temperature of 60C. -~ 2 for about lO minutesO
Example l2 A time-temperature indicating article similar to that in Example 2 was prepared. The microvoid-forminy composition was obtained by blending 58.80 parts toluene, 5.15 parts vinyl toluene:butadiene (Goodyear "Pliolite"
VT), 5.15 parts diphenyl phthalate, and 30.90 parts reagent grade powdered magnesium carbonate. The product was coated on ~reaseproof paper and dried as in Example 2, after which the thickness of the microvoid layer was found to be approximately 50 micrometers. A fusible composition was then coated over the microvoid layer as in Example 2, except that the isobutylene:paraffin wax ratio was 23.4:76.6. When placed in an air circulating oven main-tained at 100C., the article clisplayed a color change at 4 minutes.
Example 13 A time-temperature indicating article similar to that of Example 8 was prepared. The colored stratuml how-ever, was a 127-micrometer black greaseproof and waterproof Eilmq Additionally, the microvoid-forming composition was prepared by blending 0.91 part sodium alginate, 90.83 parts 35 water, and 8.26 parts powdered (0.04 micrometer equivalent spherical diameter) calcium carbonate (HM Royal "Homocal"
D~. After coating and dryin~ as in the preceding examples, the thickness of the resul~ant rnicrovoid layer was found to be approximately 23 microme-ters. Samples of the resultant 5 product, when placed in an air circulating oven maintained at 100C., displayed color change at 8 minutes.
Example 14 A time-temperature indicating article similar to that of Example 3 was prepared. The microvoid-forminy composition was prepared by blending 57.19 parts "Min-U-Sil" silica, 2.97 parts of a 65~ solution of oil-free reactive alkyd resin (Ashland Chemica:ls Co.
"Aroplaz'l 6022-R-C5), 1.28 parts mixed aromatic solvents (boiling point c./50C.), 0.37 part methyl heptyl ]cetone, 1.72 parts "Desmodur" N-75 diisocyanate solution, 27.90 parts xylene 6.86 parts ethylene glycol monobutyl ether, 0.57 part ~-glycidoxypropyl trimethoxysilane7 and 1.14 parts CAB 500-1 cellulose acetate butyrate. After coating and drying as in the preceding examples, ~he thickness oE
the microvoid layer was found to be approximately 28 micro-meters. A 21:79 polyisobutylene:paraffin wax composi-tion of the type previously described was coated over the microvoid layer as described in preceding examples. When placed in a 145F. (approximately 65C.) circula-ting air oven, color change occurrecl at 8 minutes.
Example 15 A time-temperature indicating aL-,icle, substan-tially the same as those of Examples 7-11 was prepared, except that the fusible layer was Eormed from a 20080 cis-polybutadiene:paraEfin blend. Rates of color change at various temperatures are shown below:
Temperature F 115 130 145 160 ~C 46.1 54.4 62~8 71O1 Time to Change Color, Minutes >360 9 5 3 3~
-:LO-Examples 16-l9 ~ ime-temperature indicating articles, substan-tially -the same as those of Examples 7-11 except that a higher melting paraffin was used in the fusible layer, were prepared. The paraEEin ("Shellwax" 200) had a melting point of 141E. (60.6C.) L When subjected to -the test previously described, no color change occurred at 130Fo (54.4~C.) or less. Rate of color change at 160F.
(68.2C.) is shown below.
Polyisobutylene:Time, Minutes, to ExampleParaffin RatioShow Full Color Chan~e Control0;100 0.1 1617.7$:82.22 6.0 1718.60:~1.40 6.5 1819.50:80.50 7.0 1920.50:79.50 7.5 Example 20 A s~lution was prepared by dissolving, in 300 parts toluene, 15.1 parts of polyisobutylene (Tg of -60C., molecular weight in the range of 64,000-81,000, commercially available as "Vistanex" 80) and 84.9 parts of paraffin wax (melting point 52C.). The solution was kn.ife-coated on a silicone release liner and the solvent evaporated. The dried fusible composition was then laminated to one side of a sheet oE 180-micrometer loose texture Eilter p~per ("Whatman" 4), usin(J the same ~enera:L
procedure as in Example 1.
Into a 25% solids solution oE 95.5:~.5 is-~octyl acrylate:acrylic acid copolymer pressure-sensitive adhesive in 70:30 heptane:isopropanol was mixed sufficient finely divided carbon black to constitute 14~ of the to-tal solids. The resultant black adhesive solution was kniEe-coated (125-micrometer slot) onto a si:licone-coated release liner and the solvent evaporated. The dried black adhesive layer was then laminated to the other side of ~he filter paper.
The product could be wound convolutely on itselE
in roll form and unwound without adhesive transfer, the fusible layer functioning as a low adhesion backsize. The black adhesive layer not only enabled the produc-t to be conveniently mounted in a desired location but also pro-vided the colored stratum necessary for the visual deter-mination oE time-temperature exposure. The initially white appearance of the Eace side o the product of this example became black after exposure to 1~5YO ( about 630CD ) temperature for 10 minutes.
Example 21 Example 7 was repeated, omitting the reference stripes and substltuting for the composition used to prepare the fusible layer a 19~ solids toluene solution of a 15:~5 natural rubber:stearic acid (melting point 69-70C.) blend. The resulting product had an imaging time of 5 minutes at 165~. (about 74Co ) 7 While the foregoing description sets forth illustrative examples of the invention, the discussion has not been exhaustive, and numerous modifications will occur to those ordinarily skilled in the art. To illustrate, the amorphous polymer and crystalline solvent may be milled together and e~truded directly onto the surface o-c the microporous layer, greatly simplifying the manufacturing process.
Similarly, it will be recognized that time-temperature indicatinq devices ~or any o~ numerous desired temperature ranges can be prepared by judicious selection of type and molecular weight of amorphous polymers type ancl melting point of crystalline solvents, amorphous polymer:crystalline solvent ratios, type and thickness of microporous layers, etc.
In order to maintain a fairly constant time ~or color change to occur throughout the predetermined tempera-3~ ture range, it is important that the glass transition tem-perature (Tg) of the amorphous polymer be less than the r~
lower end of the temperature range. Desirably, -the Tg should be substantially lower, e.g., 50C. or more below the lower end of the range.
Example 22 A construction indentical to that described in Example 10 was prepared except that the printed lines were formed using a solution of 61.24~ methyl isobutyl ke-tone, 0.01% Oil Blue A dye, 2.75~ oleophobic fluorochemical [C~l7~o2N(cH3)c2H4ocH2cH(cH2cl)o2ccH2cH2]27 and 36~ of a l0 dark gray Elexographic printing ink (consolidated FA-14889). The lines were a dark gray but did not physically block the pore openings oE the microvoid layer as in other examples. The oleophoblc nature of the lines did, ho~ever, prevent penetratiGn of liquefied Eusible 15 layer. (It is important that the liquefied fusible material no-t penetrate the printed lines; if it does penetrate the lines, the lines become darker, making it hard to determine the end point.) The ~ollowing trade names, used hereinabove, are 20 believed to be registered trade marks: "Aroplaz", "Desmodur", "Homocal", "Microwhite", "Min-U-Sil", "Pliolite", "Shellwax", "Vistanex", and "Whatman".
Detailed Description Understanding of the invention will be further enhanced by reEerring to the following illustrative bu-t D ;~
non-limiting examples, in which all pa-rts are by weight unless otherwise specifiedO
In each of Examples 1-6 below, a microvoid-fonning composition was prepared by mixing 18.12 parts toluene~ 3062 parts diisobutylketone, 1.11 parts cellulose acetate butyrate (Eas-tman CAB 500-1), 7025 parts methyl isobutyl ketone, 10.00 parts of a 60~ solution of hydroxy functional acrylic resin (~-lenkel Co. "G Cure 868 RX-60'l), 58.00 parts 5-micrometer silica (Pennsylvania Sand Glass Corporation "Min-U-Sil"); and 1.90 parts oE a 75~ SOlutiO
of 1,6-hexamethylene diisocyanate in 1:1 xylene:2-e-thoxy acetate (Mobay "Desmodur" N-75). This composition was then coated onto the surface of black 60-micrometer greaseproof paper and allowed to dry and cure at room temperature Eor 10 days; the drie~d layer was Inicroporous and approximately 12.7 micrometers thick.
A varnish was applied to the surEa e of the microvoid, coating in a pattern of 2.5-millimeter wide diagonal lines spaced about 6.4 millimeters apart. The transparenti~lng effect resulted in an initial pattern of black lines on a white background, evaporation oE the solvent causing the lines to appear dark grayO The varnish formed a Eilm, sealiny the pores and thus preventing subsequent penetration by the liquified fusible layerO
A ~Eamily of fusible compositions was prepared by blending various ratios of polyisobutylene having a glass transition temperature of about -65C. and a number average molecular weight in the rany~ of 81,000-99,000 ("Vistanex"
L-100) and paraffin wax ("Shellwax" loo! havinq a melting 30 point of 125F. (roughly 50Co) and dissolving in toluene to form a 25% solids solution. Each such solution was knife coated onto a release liner using a 125-micrometer slot and dried at about 93C. The mol-ten coa-ting was then chilled to solidify it and form a solid solution oE the polyisobutylene and paraEfin wax. The solid c~ating was then placed in contact with the surface of the stripe-coated microporous layer and laminated thereto by passing -the layers between squeeze rolls (one rubber~ one steel), both internally heated to a temperature of about 52C., a pressure of about 485 N/cm width, and a rate of abou-t 2 m/min, the exact conditions being varied controllably to ensure good bonding of the Eusible coatin~ to the microporous layer with negligible penetra-tion.
Examples 7-11 below were prepared in the same manner as Examples L-6 except Eor tne microvoid-Eorrning layer and the composition used in printing the lines. The microvoid-forming layer was made by blending 77.39 par-ts -toluene, 11.18 parts diisobutylketone, 22037 parts methy]isobutylketorle, 44.47 parts of a 60% solution of hydroxy-functional acrylic resin (Henkel Co. "G-Cure 868 RX-60"), 0.9 part di(dioctylpyrophosphate) ethylene titanate, 466 parts 0.5-15 micrc~eter calcium carbonate (Sylacauga Calcium Produc-ts "Microwhite" 25), and 7.9 parts oE a 75% solution oE ],6-hexal~ethylene diisccyanate. The dried thickness of the microvoid layer was 25 micrometers.
Stripes were printed using a lacquer containing a small amount of carbon black.
Strips (about 2.5 cm x 12.7 cm) of the produc-t of each example were now hung in a circulating air oven main-tained at specified temperatures ~ 1F. (-~ 006C.) and observed through a transparent door until the initially white surface became lndistinguishable from the gray stripes, indicating tha-t the coating composition had penetrated the microvoids, transparentizing the layer and making the underlying bla~k greaseproof paper v:Lsible.
Continued exposure to the oven temperatui-e caused Eurther darkerling, so that widc black stripes were visible bc~tween the narrow printed dark gray stripes. Results are summarlzed below:
~ ~ ~ 5 ~
~ --7--o I ~ I I I I I I I 1,, ~ ~ l l l l l l l l l l l o "~ I I ~o I ~ I I I I ~ I ~ I
o ~ I ~ U~ I I I I I I I I
o I I ~ a~ ~ i I I I I I I I
~ ~ I C~
v ~ r~
~1 ~
~J Lf) ' I a~ I ~D I I I I I I I I
n ~ I I o~ I I I I I I I I
tn ~ ~9 a~ O
~ ~ n I I ~ I
.Y U
,, . o ~ ~r o o o ~ o ~1 0 ~r o ~r ,~ u~ . ~1 ~r o ~D
~r U ~ ~ ~D ~ O O
.
~ o O ~ o . .
o o I ~, I
a~ a ,~ ~ ~ ~
.~. .~ . I ~ I ~ I
. ~ ~ I~ I ~ i ~ I I I I I I I I
u~ ~
m .,, ~ ~ ~1 O I I U~ I I I I I I I I
.,~
E~
~ ~ I ~ I
u~
~ ~ l '1' . ~l ~., O O
a) o ,, a~ ~ 0 ,~ ~ r~ o o o o~
~ ~1 O ~ ~ ~ ~ ~ l_ .,. O O l-- O O O . . . ~ .
~ ~ ~ ~ 1-- 1~ ~ U~ O ~ ~ O C~ 1--Q ~ " ...... ~ r o~
O ~ o o ~ o o O .. .0 .. .. .. ..
~ ~ r~ ~r u~ o c~ o o o O ~ ~ ~ c~ o ~, _l O
Q~ ~
~ o ~1 X O
It is apparen-t that the length of time required to change color at a given temperature is dependent on the polyiso~
butylene.paraffin ratio. It also appears that the presence o~ the polylsobutylene may reduce the eEfect oE
temperature above the threshold value on rate of color change. The tabulated values should be considered typical, but they are subject to change with variation in the type and thickness of microvoid layer, the molecular weight of the polyisobutylene, and the melting point of the crystalline solvent. For the system shown, however, a 105 polyisobutylene:paraffin ratio is considered desirable for displaying an exposure to a temperature of 60C. -~ 2 for about lO minutesO
Example l2 A time-temperature indicating article similar to that in Example 2 was prepared. The microvoid-forminy composition was obtained by blending 58.80 parts toluene, 5.15 parts vinyl toluene:butadiene (Goodyear "Pliolite"
VT), 5.15 parts diphenyl phthalate, and 30.90 parts reagent grade powdered magnesium carbonate. The product was coated on ~reaseproof paper and dried as in Example 2, after which the thickness of the microvoid layer was found to be approximately 50 micrometers. A fusible composition was then coated over the microvoid layer as in Example 2, except that the isobutylene:paraffin wax ratio was 23.4:76.6. When placed in an air circulating oven main-tained at 100C., the article clisplayed a color change at 4 minutes.
Example 13 A time-temperature indicating article similar to that of Example 8 was prepared. The colored stratuml how-ever, was a 127-micrometer black greaseproof and waterproof Eilmq Additionally, the microvoid-forming composition was prepared by blending 0.91 part sodium alginate, 90.83 parts 35 water, and 8.26 parts powdered (0.04 micrometer equivalent spherical diameter) calcium carbonate (HM Royal "Homocal"
D~. After coating and dryin~ as in the preceding examples, the thickness of the resul~ant rnicrovoid layer was found to be approximately 23 microme-ters. Samples of the resultant 5 product, when placed in an air circulating oven maintained at 100C., displayed color change at 8 minutes.
Example 14 A time-temperature indicating article similar to that of Example 3 was prepared. The microvoid-forminy composition was prepared by blending 57.19 parts "Min-U-Sil" silica, 2.97 parts of a 65~ solution of oil-free reactive alkyd resin (Ashland Chemica:ls Co.
"Aroplaz'l 6022-R-C5), 1.28 parts mixed aromatic solvents (boiling point c./50C.), 0.37 part methyl heptyl ]cetone, 1.72 parts "Desmodur" N-75 diisocyanate solution, 27.90 parts xylene 6.86 parts ethylene glycol monobutyl ether, 0.57 part ~-glycidoxypropyl trimethoxysilane7 and 1.14 parts CAB 500-1 cellulose acetate butyrate. After coating and drying as in the preceding examples, ~he thickness oE
the microvoid layer was found to be approximately 28 micro-meters. A 21:79 polyisobutylene:paraffin wax composi-tion of the type previously described was coated over the microvoid layer as described in preceding examples. When placed in a 145F. (approximately 65C.) circula-ting air oven, color change occurrecl at 8 minutes.
Example 15 A time-temperature indicating aL-,icle, substan-tially the same as those of Examples 7-11 was prepared, except that the fusible layer was Eormed from a 20080 cis-polybutadiene:paraEfin blend. Rates of color change at various temperatures are shown below:
Temperature F 115 130 145 160 ~C 46.1 54.4 62~8 71O1 Time to Change Color, Minutes >360 9 5 3 3~
-:LO-Examples 16-l9 ~ ime-temperature indicating articles, substan-tially -the same as those of Examples 7-11 except that a higher melting paraffin was used in the fusible layer, were prepared. The paraEEin ("Shellwax" 200) had a melting point of 141E. (60.6C.) L When subjected to -the test previously described, no color change occurred at 130Fo (54.4~C.) or less. Rate of color change at 160F.
(68.2C.) is shown below.
Polyisobutylene:Time, Minutes, to ExampleParaffin RatioShow Full Color Chan~e Control0;100 0.1 1617.7$:82.22 6.0 1718.60:~1.40 6.5 1819.50:80.50 7.0 1920.50:79.50 7.5 Example 20 A s~lution was prepared by dissolving, in 300 parts toluene, 15.1 parts of polyisobutylene (Tg of -60C., molecular weight in the range of 64,000-81,000, commercially available as "Vistanex" 80) and 84.9 parts of paraffin wax (melting point 52C.). The solution was kn.ife-coated on a silicone release liner and the solvent evaporated. The dried fusible composition was then laminated to one side of a sheet oE 180-micrometer loose texture Eilter p~per ("Whatman" 4), usin(J the same ~enera:L
procedure as in Example 1.
Into a 25% solids solution oE 95.5:~.5 is-~octyl acrylate:acrylic acid copolymer pressure-sensitive adhesive in 70:30 heptane:isopropanol was mixed sufficient finely divided carbon black to constitute 14~ of the to-tal solids. The resultant black adhesive solution was kniEe-coated (125-micrometer slot) onto a si:licone-coated release liner and the solvent evaporated. The dried black adhesive layer was then laminated to the other side of ~he filter paper.
The product could be wound convolutely on itselE
in roll form and unwound without adhesive transfer, the fusible layer functioning as a low adhesion backsize. The black adhesive layer not only enabled the produc-t to be conveniently mounted in a desired location but also pro-vided the colored stratum necessary for the visual deter-mination oE time-temperature exposure. The initially white appearance of the Eace side o the product of this example became black after exposure to 1~5YO ( about 630CD ) temperature for 10 minutes.
Example 21 Example 7 was repeated, omitting the reference stripes and substltuting for the composition used to prepare the fusible layer a 19~ solids toluene solution of a 15:~5 natural rubber:stearic acid (melting point 69-70C.) blend. The resulting product had an imaging time of 5 minutes at 165~. (about 74Co ) 7 While the foregoing description sets forth illustrative examples of the invention, the discussion has not been exhaustive, and numerous modifications will occur to those ordinarily skilled in the art. To illustrate, the amorphous polymer and crystalline solvent may be milled together and e~truded directly onto the surface o-c the microporous layer, greatly simplifying the manufacturing process.
Similarly, it will be recognized that time-temperature indicatinq devices ~or any o~ numerous desired temperature ranges can be prepared by judicious selection of type and molecular weight of amorphous polymers type ancl melting point of crystalline solvents, amorphous polymer:crystalline solvent ratios, type and thickness of microporous layers, etc.
In order to maintain a fairly constant time ~or color change to occur throughout the predetermined tempera-3~ ture range, it is important that the glass transition tem-perature (Tg) of the amorphous polymer be less than the r~
lower end of the temperature range. Desirably, -the Tg should be substantially lower, e.g., 50C. or more below the lower end of the range.
Example 22 A construction indentical to that described in Example 10 was prepared except that the printed lines were formed using a solution of 61.24~ methyl isobutyl ke-tone, 0.01% Oil Blue A dye, 2.75~ oleophobic fluorochemical [C~l7~o2N(cH3)c2H4ocH2cH(cH2cl)o2ccH2cH2]27 and 36~ of a l0 dark gray Elexographic printing ink (consolidated FA-14889). The lines were a dark gray but did not physically block the pore openings oE the microvoid layer as in other examples. The oleophoblc nature of the lines did, ho~ever, prevent penetratiGn of liquefied Eusible 15 layer. (It is important that the liquefied fusible material no-t penetrate the printed lines; if it does penetrate the lines, the lines become darker, making it hard to determine the end point.) The ~ollowing trade names, used hereinabove, are 20 believed to be registered trade marks: "Aroplaz", "Desmodur", "Homocal", "Microwhite", "Min-U-Sil", "Pliolite", "Shellwax", "Vistanex", and "Whatman".
Claims (10)
1. An article for irreversibly displaying visual evidence of exposure within a predetermined temperature range for at least a predetermined length of time, comprising in combination:
a. an opaque open cell microporous diffusely light-reflective layer having first and second surfaces and being formed of components which will not melt at the upper end of said predetermined temperature range, b. a colored stratum firmly joined to the first surface of said microporous layer, and c. overlying, but not appreciably penetrating, at least a portion of the second surface of said microporous layer, a substantially transparent coating of a compo-sition comprising a solid solution of (1) an amorphous rubbery polymer having a glass transition temperature below the lower end of said predetermined temperature range, dissolved in (2) a crystallizable solvent for said rubbery polymer, said solvent having a melting point below the lower end of said predetermined temperature range, the solvent:polymer ratio being selected to control viscosity and assure penetration of the entire depth of said microporous layer by said composition at the expiration of said predetermined length of time in said temperature range to thereby make the colored stratum visible.
a. an opaque open cell microporous diffusely light-reflective layer having first and second surfaces and being formed of components which will not melt at the upper end of said predetermined temperature range, b. a colored stratum firmly joined to the first surface of said microporous layer, and c. overlying, but not appreciably penetrating, at least a portion of the second surface of said microporous layer, a substantially transparent coating of a compo-sition comprising a solid solution of (1) an amorphous rubbery polymer having a glass transition temperature below the lower end of said predetermined temperature range, dissolved in (2) a crystallizable solvent for said rubbery polymer, said solvent having a melting point below the lower end of said predetermined temperature range, the solvent:polymer ratio being selected to control viscosity and assure penetration of the entire depth of said microporous layer by said composition at the expiration of said predetermined length of time in said temperature range to thereby make the colored stratum visible.
2. The article of claim 1 wherein the amorphous polymer is polyisobutylene and the crystalline solvent is paraffin wax.
3. The article of claim 2 wherein the paraffin wax has a melting point of about 50°C.
4. The article of claim 3 wherein the amorphous polymer:crystalline solvent weight ratio is about 1:5.
5. The article of claim 1 or 2 wherein at least one reference mark, of generally the same color as the colored spectrum, is visible at the second surface of the microporous layer.
6. The article of claim 1 or 2 wherein the colored stratum is an opaque sheet.
7. The article of claim 1 or 2 wherein the colored stratum is an opaque sheet and normally tacky and pressure-sensitive adhesive covers the exposed surface of the colored stratum.
8. The article of claim 1 or 2 wherein the colored stratum is a normally tacky and pressure-sensitive adhesive.
9. The article of claim 1 or 2 wherein normally tacky and pressure-sensitive adhesive covers the exposed surface of the colored stratum and the article is in elongate strip form wound convolutely upon itself about a core to form a roll of tape.
10. The article of claim 1 or 2 wherein the colored stratum is a normally tacky and pressure-sensitive adhesive and the article is in strip form wound convolutely upon itself about a core to form a roll of tape.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/321,372 US4428321A (en) | 1981-11-16 | 1981-11-16 | Thermally-activated time-temperature indicator |
US321,372 | 1981-11-16 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1185157A true CA1185157A (en) | 1985-04-09 |
Family
ID=23250345
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000413990A Expired CA1185157A (en) | 1981-11-16 | 1982-10-22 | Thermally-activated time-temperature indicator |
Country Status (7)
Country | Link |
---|---|
US (1) | US4428321A (en) |
EP (1) | EP0093764B1 (en) |
JP (1) | JPS58501920A (en) |
AU (2) | AU1011782A (en) |
CA (1) | CA1185157A (en) |
DE (1) | DE3269863D1 (en) |
WO (1) | WO1983001834A1 (en) |
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-
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- 1982-10-20 JP JP82503543A patent/JPS58501920A/en active Pending
- 1982-10-20 WO PCT/US1982/001490 patent/WO1983001834A1/en active IP Right Grant
- 1982-10-20 EP EP82903549A patent/EP0093764B1/en not_active Expired
- 1982-10-20 AU AU1011782A patent/AU1011782A/en active Pending
- 1982-10-20 AU AU10117/83A patent/AU566175B2/en not_active Ceased
- 1982-10-22 CA CA000413990A patent/CA1185157A/en not_active Expired
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Also Published As
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EP0093764A1 (en) | 1983-11-16 |
DE3269863D1 (en) | 1986-04-17 |
AU1011782A (en) | 1983-06-01 |
EP0093764B1 (en) | 1986-03-12 |
US4428321A (en) | 1984-01-31 |
JPS58501920A (en) | 1983-11-10 |
WO1983001834A1 (en) | 1983-05-26 |
AU566175B2 (en) | 1987-10-08 |
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