Thermal measuring and testing – Temperature measurement – Composite temperature-related paramenter
Reexamination Certificate
1999-04-30
2003-02-11
Martin, David (Department: 2841)
Thermal measuring and testing
Temperature measurement
Composite temperature-related paramenter
C376S104000, C376S106000, C116S206000, C347S221000, C503S201000
Reexamination Certificate
active
06517239
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the field of time-temperature indicators (TTIs). TTIs are colorimetric labels which respond to cumulative exposure to time and temperature. TTIs provide a visual indicator that gradually changes with time, typically faster at elevated temperatures and slower at colder temperatures.
TTIs are attached to perishable products at the time of production to monitor the cumulative time/temperature exposure. TTIs are used for monitoring time and temperature exposure of a wide variety of items including perishables in-transit, consumer packages, and medical perishables. TTIs are typically more reliable in monitoring the remaining shelf life of a perishable product than expiration dates such as “sell-by” or “use-by” dates. Expiration dates assume a certain temperature history, and temperature histories that vary from this assumption result in either the sale of a spoiled product or the premature disposal of a good product. In contrast, TTIs respond directly to the temperature history of the product.
TTIs are commonly attached to shipping boxes for use by commercial distributors in the distribution of food and pharmaceuticals. The most common use is to ensure the integrity of the cold chain up to the supermarket.
Prepared TTIs have the disadvantage in that they must be stored at low temperatures or protected from actinic radiation prior to use. This requirement greatly increases the cost of production of TTIs and introduces an element of uncertainty as to the reliability of the indicators. Therefore, there is a need for TTI labels that can be activated at the site of application, thereby obviating a need for protection of the labels prior to use.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a thermal transfer medium which is suitable for use in a thermal transfer printing apparatus and which contains at least one indicator compound within a thermal transfer layer of the thermal transfer medium which is convertible from an inactive state to an active state by the application of heat. The indicator compound may be transferred to a recording medium with a portion of the thermal transfer layer and converted from an inactive state to an active state by the application of heat in the thermal transfer printing apparatus, thereby forming a time-temperature indicator. The terms “time-temperature indicator’ and “TTI’, as used herein, refer to any calorimetric label which responds to an exposure element in a manner that indicates the degree of exposure to that element. Exposure elements include, for example, time, air, visible light, temperature, actinic radiation, and atomic radiation.
Also in accordance with this invention, a method of generating a time-temperature indicator (TTI) is provided as well as the time-temperature indicators produced. The method entails providing a thermal transfer medium suitable for use in a thermal transfer printing apparatus, wherein a thermal transfer layer of said medium contains at least one indicator compound. The method also entails heating the thermal transfer medium in the thermal transfer printing apparatus to a temperature sufficient to transfer the thermal transfer layer of the medium to a receiving substrate and convert the indicator compound within the thermal transfer layer from an inactive state to an active state. Once in the active state, the indicator compounds serve to monitor the exposure of the time-temperature indicator to various exposure elements.
A thermal transfer medium, which contains an inactive form of an indicator compound within a thermal transfer layer, can be manufactured, stored and shipped under normal conditions without resort to refrigerated and light-protected environments. The indicator compound can then be activated when desired through processing in a thermal transfer printing apparatus to generate a time-temperature indicator.
Indicator Compounds
Indicator compounds that are contemplated as part of this invention are any compounds which exhibit detectable changes in response to an exposure element, which may be converted from an inactive state to an active state through the application of heat from the print head of a thermal transfer printing apparatus and which can be incorporated in a thermal transfer layer of a thermal transfer medium and transferred to a receiving substrate. Preferred compounds are kinetic indicator compounds which provide a change in color (typically darken) from a chemical reaction in response to the exposure elements of interest such as the integrated time-temperature exposure of a product or article. The use of kinetic indicator compounds which respond to visible light, air, actinic radiation or atomic radiation and the TTIs prepared therewith, are also considered a part of this invention.
A preferred temperature range for integrated TTIs responding to both time and temperature, or for TTIs, which respond primarily to temperature will depend on their intended use. Where the TTI is to detect thawing, a range from about 0° C. and above is preferred. Where the TTI is to detect freezing, a range of about 0° C. and below is preferred. Manipulation of the response to different temperatures can be accomplished through the selection of indicator compounds and additives known in the art.
Preferred wavelength and intensity ranges for TTIs, which respond primarily to actinic radiation, will also depend on the intended use of the TTI. For example, where the TTI is intended to detect the exposure of film to harmful radiation, the TTI may be responsive to x-rays, UV light and visible light. Manipulation of the response to radiation at different wave lengths and intensities can be accomplished through the selection of indicator compounds and additives known in the art.
It is contemplated that activation of indicator compounds by processing of a thermal transfer medium in a thermal transfer printing apparatus may occur by various mechanisms including, for example, the following: melt recrystallization of the compounds to transform inactive compounds into active compounds, the application of heat to combine more than one indicator compound wherein the combination of the indicator compounds (such as from separate thermal transfer layers) results in the activation of the compounds, the activation of an initiator compound which catalyzes the polymerization of the indicator compounds. A preferred method of activation is by melt recrystallization. As another example, two different indicator compounds may be present in encapsulated form within the thermal transfer layer, wherein the compounds are able to mix and polymerize only after the application of heat has released the encapsulated forms. As a further example, substantially inactive compounds may be converted to substantially active compounds through heat activation of an initiator compound. For example, peroxides, which thermally decompose into free radicals, may be employed as an initiator compound to convert substantially inactive compounds into substantially active compounds.
Preferred temperature ranges for conversion of the indicator compounds from the inactive state to the active include those typically applied to a thermal transfer medium by the print head of a thermal transfer printing apparatus. For example, the temperature is preferably between 50° C. and 300° C., more preferably between 75° C. and 250° C.
Particularly preferred compounds that are contemplated as part of this invention are acetylenic compounds having at least two conjugated acetylene groups (—C≡C—C≡C—) per molecule. The manufacture and use of acetylenic compounds as time-temperature indicators are described in the following U.S. Patents, all of which are hereby incorporated by reference: U.S. Pat. No. 3,999,946 (Patel et al.); U.S. Pat. No. 4,220,747 (Preziosi et al.); U.S. Pat. No. 4,189,399 (Patel); U.S. Pat. No. 4,228,126 (Patel et al.); U.S. Pat. No. 4,208,186 (Patel); U.S. Pat. No. 4,235,108 (Patel); U.S. Pat. No. 4,276,190 (Patel); U.S. Pat. No. 4,298,348 (Ivory); U.S. Pat. No. 4,339,240
Rosenbaum John C.
Roth Joseph D.
Goodwin Jeanne-Marguerite
Martin David
Millen White Zelano & Branigan PC
NCR Corproation
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