PROCESS FOR MONITORING INCREMENTAL ENVIRONMENTAL EXPOSURES OF PRODUCTS THAT UNDERGO PROGRESSIVE QUALITY CHANGES IN RESPONSE TO ENVIRONMENT STIMULI

Abstract: A new process is disclosed for successively measuring the environmental exposure of environmental indicating devices. Environmental indicating devices that may be mea­ sured by the new process include devices that have at least one variable region of reflectivity and at least one non-­ variable region of reflectivity. Upon exposure to chemical, radiation or time-temperature stimuli, the reflectivity of the variable region relative to the reflectivity of the non-variable region is correlated to an incremental change in the en­ vironmental exposure of an indicator device based upon a preestablished relationship between the relative reflectivity and the incremental change in the environmental exposure of the device. The incremental change in the environmental exposure of the indicating device is then correlated to a remaining shelf-life or extent of processing value for a product that undergoes progressive quality changes upon exposure to environmental stimuli. Other information such as the identity of a product and/or of a material comprising the variable region of reflectivity may be read and deter­ mined by the correlation process.

Description: DESCRIPTION PROCESS FOR MONITORING INCREMENTAL ENVIRONMENTAL EXPOSURES OF PRODUCTS THAT UNDERGO PROGRESSIVE QUALITY CHANGES IN RESPONSE TO ENVIRONMENTAL STIMULI BACKGROUND OF THE INVENTION The process of this invention relates to a new method for measuring the incremental environmental exposure of environmental indicating devices that are employed to monitor the environmental exposure of products that undergo progressive quality changes in response to environmental stimuli. Chemical, radiation, humidity, temperature, and cumulative time-temperature exposures may be monitored by the process of this invention. Acetylenic compounds having at least two conjugated triple bonds are preferably employed as environmental indicating materials by the novel process. However, the process of this invention may employ materials other than acetylenic compounds as environmental indicating materials. U.S. Patent No. 3,999,946 (Patel et al.) discloses acetylenic compounds having at least two conjugated acetylene moieties that polyermize and undergo irreversible color changes upon exposure to time-temperature stimuli, and which are useful as time-temperature history indicators. Patel el al. teach that the extent of polymerization (i.e., time-temperature exposure) may be determined by visual color matching. In the process of this invention, the amount of light that is reflected by the indicating material is measured to obtain a reflectance value. Once the reflectance value has been obtained, the reflectance value is correlated with a predetermined reflectance shelf-life relationship to derive the remaining shelflife of the product being monitored. Most importantly, the process may be repeatedly performed in an automated fashion. Thus, more accurate remaining shelf-life information may be obtained, human error is eliminated, and the process of determining the remaining shelf-life of a large number of items may be rapidly and easily accomplished. BRIEF DESCRIPTION OF THE INVENTION This invention relates to a novel process for measuring the incremental environmental exposure of an environmental indicator device wherein said process comprises the steps: a. measuring the reflectivity at specified wavelengths of at least one variable region of said indicator device, said variable region comprising an acetylenic compound having at least two conjugated acetylenic moieties which in response to environmental conditions undergoes incremental degrees of polymerization as said environmental exposure continues with resultant incremental changes in reflectivity accompanying said incremental degrees of polymerization at said specified wavelength; b. measuring the reflectivity at said selected wavelengths of at least one non-variable region of said indicator device, said non-variable region being unaffected by said environmental exposure; ; c. determining the reflectivity of said variable region relative to that of at least one non-variable region; and d. correlating said reflectivity of step (c) to an incremental change in the environmental exposure of said device based upon a pre-established relationship between said reflectivity of step (c) and the incre mental change in the environmental exposure of said device; and correlating said incremental change in the environmental exposure to a remaining shelf-life or extent of processing value for a product that undergoes progressive quality changes upon exposure to environmental stimuli. BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates an environmental indicator device that may be measured by the process of this invention. The device includes a variable region 1 of reflectivity that comprises an acetylenic compound and four non-variable regions 2, 3, 4 and 5 of reflectivity. Figures 2, 3 and 4 illustrate an environmental indicator device having a darkened variable region 1, in addition to non-variable regions 2, 3, 4 and 5, due to the exposure of the device to temperature over increasing periods of time. Figure 5 illustrates an environmental indicator device having a product identification means 6 and an acetylenic compound identification means 7. Figure 6 illustrates two general types of curves that are obtained when percent reflectance is plotted vs. time. Curve type II is obtained for acetylenic compounds that gradually polymerize. Curve type I is obtained for acetylenic compounds that polymerize by autocatalytic reaction kinetics. Figure 7 is a graph of percent reflectance at 500C and 250C vs. time for 4,6,8-tetradecatriyn-14-monomethyl urethane. Figure 8 is an environmental indicator device that may be measured by the process of this invention. The device includes a variable region 8 of reflectivity that comprises an acetylenic compound and four non-variable regions 9, 10,11 and 12 of reflectivity. Figure 9 is a graph of reflectance values at 600C and 40"C vs. time for 2,4-hexadiyne-1,6-diol-bis-p- toluene sulfonate. Figure 10 is an Arrhenius-type plot showing the number of days vs. temperature ( F) for an epoxy prepreg to degrade to unacceptable quality (i.e., loss of tack). Arrhenius-type plots showing the number of days vs. temperature (CF) for acetylenic indicators (i.e., full life and pretreated indicators) to reach their endpoint are also shown by Figure 10. DETAILED DESCRIPTION OF INVENTION This invention relates to a novel process for measuring the environmental exposure of an environmental exposure indicating device. In the context of this invention, the term environmental exposure includes radiation exposure, chemical exposure, temperature exposure, humidity exposure, and cumulative timetemperature exposure. Devices that measure these exposures may be employed for the determination of the remaining useful life of a variety of products, wherein the useful life of said products is directly related to the environmental exposure of the products. The process of this invention is capable of automatically determining minute degrees of environmental exposure. More particularly, environmental exposure and the accompanying remaining useful life or extent of processing of a product may be measured incrementally and automatically. Environmental indicating devices that may be measured by the process of this invention include devices that have at least one non-variable region of reflectivity and at least one variable region of reflectivity that undergoes reflectivity changes upon exposure to environmental stimuli. The reflectivity change of the variable region may occur via numerous means. For example, the variable region may undergo reflectivity changes upon response to environmental exposure due to an intrinsic thermally induced chemical reaction or a thermally induced mixing, such as solvent mixing, of two components. However, in the preferred embodiments of the invention, the variable region of reflectivity simply comprises an indicating material which undergoes incremental reflectivity changes upon exposure to environmental stimuli. Acetylenic compounds having at least two conjugated triple bonds (hereinafter referred to as acetylenic compounds), are especially preferred for use as indicating materials in the process of this invention. Other indicating materials that undergo reflectivity changes (e.g. increases or decreases in reflectivity) upon exposure to environmental stimuli are disclosed in Photochromism (Glenn H. Brown, editor, Techniques of Chemistry Vol. III, John Wiley & Sons, 1971), incorporated herein by reference. Illustrative generic examples of indicating materials disclosed in this book include spiropyrans, triarylmethane dyes, polymethine dyes, azo compounds, azomethine compounds, alkali metal salts, alkaline earth solids, and alkali metal azides. Examples of these generic classes of compounds include: 5,7-dichloro-6-nitro-BIPS (BIPS = 1',3',3'-tri-methylspiro-[2H-l-benzopyran-2,2' indoline), 6-chloro-8-nitro BIPS, 7-nitro BIPS, Malachite Green, Crystal Violet, Pararosaniline, 4dimethylaminoazobenzene, 4-nitroazobenzene, azobenzene, 1,2-naphthoquinone-2-diphenylhydrazone, sodium chloride, potassium chloride, potassium bromide, La doped CaF2, Ce doped CaF2, Gd doped CaF2, KN3, and NaN3. Spiropyrans are preferred in many embodiments of this invention. Many of these materials can be incorporated into a film and printed in an essentially colorless form. Upon exposure to light of the appropriate wavelengths, the spiropyran becomes highly colored. This colored state will fade back to its original color or near its original color as a function of time and temperature. Thus, once activated the reflectance will increase. The thermal fade time can be adjusted from seconds to years at room temperature depending upon the spiropyran and the solvent/coating system employed. The process of this invention employs reflectance or reflectivity measurements of indicator devices in order to determine the extent of environmental exposure. Reflectance or reflectivity is measured as the amount of light at selected wavelengths as determined by an appropriate detector after said light has impinged upon a surface. A perfectly reflective material has a reflectance equal to one. An absorbing material has a decreased reflectance that approaches zero for high absorbances. The variable materials employed as environmental indicators in this application have a reflectance between zero and one. Percent reflectance or percent reflectivity is equal to one hundred times the reflectivity. The process of this invention includes two primary steps. The first primary step includes several substeps or operations. In the first step of the process, an indicator device having regions of reflectivity as described is read with a suitable reflectance scanner in order to obtain a reflectance measurement. The reflectance measurement may be obtained in a single operation such as by moving the indicator device by a reflectance scanner having a light source and photo cells in a fixed position, by moving a hand-held scanner over the reflecting areas of the indicator device, or by conventional moving beam scanners. In deriving the reflectance measurement, the scanner emits a beam of light. As each region is subjected to the beam of light, a certain amount of light is reflected by each region. The amount of reflected light for each region is determined by a detector, and this information is used to determine the difference between the respective amounts of reflected light from the variable and nonvariable regions of the device. The relative reflectance of the environmentally exposed indicator device is measured in this manner. The second primary step of the process involves correlating the relative reflectance measurement obtained by the first primary step of the process with reflectance data that has been previously established to represent the remaining useful shelf-life of the product being monitored in order to determine the useful shelf life of the product. In simpler terms, the second primary step of the process determines the useful life of the product being monitored by matching the relative reflectance value of the first step of the process with a predetermined reflectance-remaining shelf-life relationship. Due to obvious economical and practical considerations, the second step of the process should be con- ducted automatically via conventional computer techniques. It should be appreciated, however, that the efficient use of an automated computer system to match the reflectance measurement with a predetermined reflectance-remaining shelf-life relationship will require that the environmental indicator labels contain a product identification means and/or an indicating material identification means. These requirements may be necessary in order for the reflectance of the product being monitored to be correlated with the proper predetermined reflectance-useful shelf-life relationship for the particular product being monitored. Suitable identification means for the products being monitored and for the indicating material include any image, symbol, letter, numeral, code system or similar means that may be automatically read by an optical scanner. An optical scanner simply consists of a light source capable of illuminating a surface, a detector to sense the amount of reflected light, and a means to output the signal from the optical detector. Conventional bar code identification procedures are preferred for identification purposes in many embodiments of this invention when an automated computer system is employed to correlate reflectance with a predetermined reflectanceremaining shelf-life relationship. In the especially preferred embodiments of this invention, acetylenic compounds are employed as environmental indicating materials. Acetylenic compounds incrementally or gradually undergo reflectivity changes, usually via a polymerization mechanism that results in the development of color, upon exposure to environmental stimuli. In the preferred embodiments of the invention, polymerization of the acetylenic compound is accompanied by a simultaneous incremental development of color absorbing light in the 300 nm to 850 nm spectral region. Many acetylenic compounds having at least two conjugated triple bonds that are useful as environmental indicating materials have been previously disclosed and are well known to those skilled in the art. More specifically, acetylenic compounds which are useful as environmental indicating materials are disclosed in United States Patent Nos. 3,999,946; 4,215,208; 4,125,534; 4,189,399; 4,235,108; 4,258,352; 4,278,561; 4,228,126; 4,339,240; 4,276,190; and copending application Serial No. 208,227, filed March 19, 1980, incorporated herein by reference. Any acetylenic composition having at least two conjugated acetylenic groups (-CC-CC-) that undergoes a gradual color change exhibited by decreased reflectivity at some wavelength may be employed in the preferred practice of this invention. Preferred acetylenic monomers include those of the formula R1-C=C-C=C-R2 wherein R1 and R2 are the same or different and may include one or more moieties selected from the group consisting of alkyl, alkyoxy, aryl, carbonyl, benzoate, urethane, sulfoflate, alcohol or acid moieties. Acetylenic compounds which are particularly preferred in many embodiments of this invention contain an alkoxycarbonylalkylene moiety or a sulfonate moiety. Particularly preferred acetylenic compounds that contain these moieties include 2,4-hexadiyne-1,6-diol-bis-p-toluene sulfonate (hereinafter referred to as PTS), 5,7 dodecadiyn-1,12-bis-butoxyearbonylmethylene urethane (hereinafter referred to as 4BCMU), and 4,6,8-tetradecatriyn-14-monomethyl urethane (hereinafter referred to as 3R4M). It is believed that acetylenic compounds that contain urea moieties may be a preferred class of compounds for use in the process of this invention. Acetylenic compounds that contain urea moieties are the invention of A. F. Preziosi and T. Prusik. Such compounds are of the general formula [RNHCONH(CH2)nC=C]2 wherein R is an ester containing moiety, a substituted aryl moiety, or an alkyl moiety with n being an integer from 1 to 9. The urea containing compounds may be synthesized via conventional procedures in accordance with the following general scheme: EMI9.1 <tb> H2N-tCH2) <SEP> -C <SEP> CH <SEP> + <SEP> RNCO <SEP> tetrahydrofuran <SEP> + <tb> <SEP> O <SEP> n <tb> <SEP> RNHCNH(CH2)n-C- < H <SEP> CuCl/N,N,N <SEP> ,N <SEP> -tetramethylethylened <SEP> iamine <tb> RNHCNH0(CH2n <SEP> O2 <tb> [RNHCNH(CH2)n-C--C32 <tb> wherein R and n are as described above. Illustrative acetylenic compounds that contain urea moieties believed to be useful for the process of this invention include 2,4-hexadiyn-1,6-bis(ethylurea); 2,4-hexadiyn-1,6 bis(propylurea), 2,4-hexadiyn-1,6-bis(butylurea); and 2,4-hexadiyn-1,6-bis(octadecylurea). Environmental indicator devices that are preferred in the process of this invention comprise a substrate having at least one non-variable region of reflectivity and at least one variable region of reflectivity that includes the acetylenic compound. As previously described and as is evident from the patents relating to acetylenic compounds incorporated herein by reference, acetylenic compounds develop color usually by polymerization upon exposure to various environmental stimuli. Thus, upon exposure to environmental stimuli, the variable region of reflectance will reflect decreasing amounts of light which in turn will result in decreased reflectance. If only one non-variable region of reflectivity is employed, the acetylenic compound will cover a geometric area similar to the non-variable region. If two non-variable regions of reflectivity are employed, however, the variable region may be located between two reference bars, stripes, etc. Alternatively, a double non-variable region indicator may be constructed by employing a variable acetylenic containing region comprising a bar, stripe or other suitable form and one non-variable region comprising a colored bar, stripe, etc., wherein a second non-variable region comprises the remainder of the substrate. However, in many preferred embodiments of the invention, the environmental indicators employ four non-variable regions of reflectivity and one variable region of reflectivity in the form of a label which may be applied to a product. In this preferred embodiment, the variable region comprises an acetylenic compound in bar or stripe form, etc., with two non-variable regions of reflectivity having different reflectivities being located on each side of the variable region. Figure 1 illustrates this preferred type of indicator device which may be employed in the process of this invention. As the cumulative effects of time and temperature cause the variable region to gradually polymerize, the variable region will reflect decreasing amounts of light at the analyzing wavelength, thus resulting in a decreasing reflectance value. This phenomenon (i.e., decreasing reflectance of the variable region) is illustrated by Figures 2, 3 and 4 which illustrate a deeper and deeper colored variable region. In many preferred embodiments of the invention, the labels include a bar code product identification means 6 and a bar code acetylenic compound identification means 7 as is illustrated by Figure 5. It should be appreciated that the above-described indicator devices are preferred devices for this invention and that indicator devices may be constructed in other manners. All that is required for the process of this invention is that the indicator devices have at least one variable region of reflectivity and a nonvariable region of reflectivity. Using these criteria, one may design any shape or form of indicator device that is desired for a particular product. Also, it will be appreciated that some of the indicating materials that are useful for this invention may undergo reflectivity changes upon exposure to visible or ultraviolet radiation. In order to prevent such changes from occurring, the indicator devices may contain any one of a number of protective radiation absorbers known to those skilled in the art. Environmental indicator devices having at least one variable region of reflectivity and at least one nonvariable region of reflectivity comprising an acetylenic compound are also included in this invention. In many preferred embodiments of this invention, the indicator devices include a product identification means. In many especially preferred embodiments of this invention, the indicator devices include an acetylenic composition identification means. Identification means that are preferred include any image or symbol that can be read by an automatic scanner, with conventional bar codes being especially preferred. It will also be appreciated that a simple yes-no device capable of indicating the expiration of shelflife based upon an established reflectance-shelf-life correlation is part of this invention. In this case, a computer could decide if a relative reflectance value of the variable region has reached a threshold value which has previously been established to represent the end of useful shelf-life for a particular product. If this value has been reached, the device would not be read by the system and the product could be discarded. Substrates that may be employed for constructing devices that may be employed in the process of this invention include paper, paperboard, fiberboard, cardboard, Kindura , Mylar , polyethylene, polypropylene, polyacrylate polymers and copolymers, cellulose ethers, cellulose esters, mixed esters or other similar materials. Other exemplary examples of materials that may be employed as substrates for the environmental indicator labels include synthetic resins and plastics as described in U.S. Patent No. 3,501,302, col. 19, lines 14-51, herein incorporated by reference. Additionally, it should be appreciated that containers for various products may also serve as a substrate upon which the environmental indicator labels are constructed. For the preferred devices which employ acetylenic compounds as indicating materials, the variable region of the devices may be applied to the substrate in various fashions. For example, an ink solution comprising an acetylenic compound and solvent may be sprayed onto the substrate in order to deposit the acetylenic compound onto the desired area of the substrate. The solution should include the acetylenic compound in an amount comprising about 1% to about 60% and preferably about 10% to about 30% by weight. This method, in effect, employs an acetylenic monomer as a dye (i.e., monomer soluble in the ink vehicle). This method is more particularly described in U.S. Patent No. 4,189,399 where acetone, with lacquer added as a binder, is employed to dissolve the acetylenic compound. Upon spray coating of a substrate, followed by evaporation of the acetone, an active indicator is printed. Of course, this ink system could be printed by more conventional methods such as flexographic, screen, gravure, letterpress, ink-jet printing, or the like. Solvents that may be employed for forming the above-described ink solutions depend somewhat upon the nature of the particular acetylenic compound. More particularly, polar solvents and moderately polar solvents are preferably employed for symmetrical monomers. Representative solvents for symmetrical monomers include acetic acid, propanoic acid, heptanoic acid, nonanoic acid, hydroxy acetone, 1,1,3,3-tetramethylurea, triethanolamine, n-decylamine, sec-phenethyl alcohol, ethyl ester of cinnamic acid, triacetal glycerol, diethyl sebacate, decyl ester of decanoic acid, mono-ethyl ester of succinic acid, dimethyl sulfoxide, p-xylene, and mixtures of ortho, meta, and para xylene. Additionally, water is a suitable solvent for alkali metal salt systems. Moderately polar and non-polar solvents are more amenable to unsymmetrical acetylenic monomers. Representative examples of moderately polar and non-polar solvents which may be utilized in forming the solutions include p-xylene, 4-chlorotoluene, 2-chloro- p-xylene, 3-methyl biphenyl, dodecane, tetradecane, l-hexadecene, l-heptadecene, l-pentadecyne, 10-methyl stearic acid, ethyloctyl-ether, 3,3-dimethyl-2-butanol, cycloheptanol, 4-methyl-cyclohexanol, l0-undecen-l-ol, and triethylene glycol. Another method for applying the acetylenic compound to the indicator devices involves initially grinding the acetylenic compound into fine particles and forming a suspension of the particles in a suitable binder-solvent system. Suitable binders for forming these suspensions include natural and synthetic plastics, resins, waxes, colloids, gels, and the like including gelatin and other similar binders described in U.S. Patent No. 3,501,302 at col. 20, lines 13-43 incorporated herein by reference. The suspension comprising the binder and the acetylenic compound may then be applied to the desired area of the label by spraying, screen printing, gravure, letterset, or other conventional printing means. This method of applying the acetylenic compound to the substrate employs the active acetylenic material as a pigment in a conventional ink. This method is more particularly described by U.S. Patent No. 3,501,297 herein incorporated by reference. It should be appreciated that another method for applying the acetylenic compound to the substrate indicator device is in the form of an ink via conventional printing techniques. Inks may be formed by dissolving about to 1 to 60 parts by weight of an acetylenic compound in 99 to 40 parts of a conventional colorless ink. Printing techniques that may be employed to print acetylenic inks on the desired area of the indicator labels include gravure, screen, flexographic, letterpress, offset, ink-jet or other conventional printing means. It should be appreciated that solutions comprising a solvent and an environmental indicating material may be applied to a substrate in the form of conventional microencapsules. As stated above, the process of this invention may be employed to monitor radiation, chemical, humidity, temperature, and cumulative time-temperature exposures. However, at present, it is believed that the process is most useful for monitoring time-temperature exposures of environmental indicating devices that are in some manner attached to products which experience progressive quality changes as they are subjected to certain temperatures over certain periods of time. Thus, in many preferred embodiments of this invention, cumulative time-temperature indicating devices are monitored. In order to practice the preferred process of this invention, however, certain information must have been previously ascertained. More particularly, the following information should have been obtained: 1) the timetemperature quality change characteristics of the product that is to be monitored; 2) an acetylenic compound having polymerization characteristics (i.e., color change) in a time-temperature range similar to that of the quality change characteristics of the product to be monitored; 3) an electro-optical system that emits and detects changes of reflected light which may be absorbed by the acetylenic compound chosen; and 4) reflectivity values of the acetylenic compound (deposited with the method of choice on a substrate) that have been correlated with time-temperature exposure. One method for determining the time-temperature quality change characteristics of the product being monitored is isothermal testing. Isothermal testing employs at least two, and preferably more than two, temperature controlled chambers. Samples of the product to be monitored are stored at various temperatures and product quality of each sample is monitored as a function of time at that temperature to determine the cumulative effects of time and temperature on product quality. Isothermal testing will yield the time at which the product will have degraded to an unacceptable quality at that temperature. For example, the time as a function of temperature required for an epoxy prepreg (Hercules Corporation product No. 3501-6/AS) to lose tack is shown in Table A. Tack is defined as the ability of a substance to adhere to a substrate or the ability of a substance to adhere to itself. TABLE A* Time Temperature (days) (OF) (OC) 0.3 160 71.1 2.0 120 48.9 3.8 104 40.0 29.0 74 23.5 29.0 78 25.5 *These data were obtained from a research report filed with the United States Government by Z. N. Sanjana of the Westinghouse Corp. Research and Development Center in accordance with U.S. Government Contract No. N00019-78-C-0600. The research report is a public document and may be obtained from the Department of the Navy. The epoxy prepreg and many other products, including perishables such as vaccines, foodstuffs, etc., are believed, and some have been shown, to degrade via Arrhenius or near Arrhenius type kinetics over a certain temperature range. The equation that describes this relationship at two temperatures is: tL In E AT = a (1) ln (t ) = 1.9872 TH TL wherein tL is the time to reach the end of the shelflife at some temperature TL ( K); wherein tH is the time to reach the end of the shelf-life at some temperature TH (OR); wherein AT = TH-TL where TL < TH; and wherein Ea is the activation energy (cal/mole). The described relationship assumes that the time required to reach the endpoint (i.e., end of shelf life and accompanying unacceptable product quality) is inversely proportional to the rate of degradation. Once the time-temperature quality change requirements are known, one may then examine available literature in order to determine the acetylenic compounds that polymerize and change color over the time-temperature range that is similar to the degradation time-temperature range of the product being monitored. U.S. Patent Nos. 3,999,946; 4,189,399; 4,339,240 and 4,215,208 are particularly useful sources of information in this respect. For example, for the epoxy prepreg discussed above, one would desire an acetylenic compound that polymerizes and develops color over a time-temperature range that is similar to the data in Table A above. A compound should be selected that does not undergo a complete color development sooner than the time required for the product to reach unacceptable quality according to the data in Table A. However, the compound could undergo complete color development over a longer time period and still be useful. This is because the process of this invention can determine incremental color changes of the indicating compound as a function of time and temperature. Thus, all that is required is that the acetylenic compound chosen should not undergo a complete color change prior to the end of the useful shelf-life of the product being monitored. Also, if desired, an indicating material that undergoes complete color development over a longer time-temperature period may be pre-treated by thermal annealing or other means so that complete color development by the indicating material will correspond exactly to the end of the shelf-life of the product to be monitored. In order to select an acetylenic compound that would be suitable for monitoring a time-temperature range that is similar to the degradation data in Table A above, one might consult U.S. Patent No. 3,999,946. Example 7 of this patent teaches that 2,4,6,8-decate trayn-l ,10-bis-ethylurethane, [C2H5NHOCOCH2C=C-C=C+2, rapidly develops a blue color in 2.5 hours at 500C. This complete color development is too fast for the compound to be of any value as an indicator material for a product that has the degradation data reported in Table A. Compound 1 [(C2H5NHOCOCH2CiC+2] in Example 6 of U.S. Patent No. 3,999,946, undergoes a color change to a light pink after 960 hours at 400C. This compound changes color too slowly, at least for practical purposes, for the data in Table A. Example 2 of U.S. Patent No. 3,999,946 teaches that 2,4-hexadiyne-1,6- diol-bis-p-toluene sulfonate (i.e., PTS) undergoes a complete color development in 0.46 days at 70 C, 1.3 days at 600C and 3.5 days at 400C. These complete color changes are longer than the times listed in Table A for unacceptable degradation at the same temperature. However, the correlation is sufficiently close, and incremental color change measurements of the indicating material may be determined. Thus, PTS is a candidate indicating material for the epoxy prepreg. After a suitable acetylenic compound has been selected for use in the process, an electro-optical scanner capable of measuring reflectance may be selected. Bar code scanning technology is preferred for the practice of this invention. Thus, any conventional bar code scanner that operates with light in the appropriate wavelength region is suitable. It should be appreciated, however, that the process of this invention is not limited to bar code technology, and other electro-optical hardware such as densitometers may also be employed in the practice of this invention. The preferred acetylenic compositions for this invention polymerize to blue, red or black upon being subjected to various time-temperature exposures. These preferred compositions are described in more detail above. Blue polymers absorb light at wavelengths below about 650 nm. Red polymers absorb light below about 580 nm. The He-Ne laser scanner operates at 633 nm. The Intermec 1240 and 1241 (Intermec Corporation product Nos. 1240 and 1241) scanner wands operate with a 630 nm LED. The He-Ne laser scanner and the Intermec scanners are ideally suited for blue-colored polymers or red polymers that turn black/metallic. An incandescent lamp with an appropriate filter could be used for polymers of any color. Lasers using gases such as argon, krypton, argon-krypton or helium-cadmium may be used for either red or blue colored polymers. Dye lasers may also be employed for either color polymers. These electrooptical systems or other similar electro-optical system employing an appropriate light source and detector are suitable for the process of this invention. The major criterion one considers when choosing an electro-optical system is whether the particular instrument emits light that will be absorbed by the polymers that have been employed as an indicating material. If the polymer will absorb some or all of the light emitted based upon its extent of polymerization, the electro-optical system or instrument is a candidate for the practice of this invention. Of course, the electro-optical system must include a detector that will detect the amount of reflected light. It should be appreciated that the reflectance of the indicator device may be measured at different wavelengths. This extends the range of conditions that may be monitored by the environmental exposure indicator devices. This principle is illustrated by Example 3. Once the progressive quality change characteristics of the product to be monitored are known and a suitable acetylenic compound and electro-optical system have been selected for use in the process of this invention, the effects of time-temperature on the reflectance of the acetylenic compound, as employed in an environmental indicating device, may then be ascertained. In order to obtain this information, one may perform experiments similar to those which were performed on the epoxy prepreg composition to determine the epoxy prepreg degradation characteristics, except in this instance, the experiments are performed on the indicating device. Indicating devices may be stored at several temperatures, periodically withdrawn, and the reflectance of each device may be measured as described in Example 4 of this application. In following these procedures, at least two general types of curves (see Figure 6) will be generated depending upon the nature of the polymerization of the acetylenic composition, the color of the polymer and the wavelength that is being monitored. Curve type II in Figure 6 is discussed in Example 4. Curve type I will be employed at this point to continue the discussion of the epoxy prepreg application which has been discussed above. It should be appreciated that Curve type I discussed herein should not limit in any manner the scope of this application. It is being employed for convenience, since a significant amount of our work has been conducted with the compound from which this curve has been generated (i.e., PTS). Curve type I was generated by preparing indicators in accordance with Example 4 of this application, using PTS as the active acetylenic composition. The indicators were stored at 600C and 400C. The indicators were periodically withdrawn and reflectance measurements were taken. As may be seen in Figure 9, the shapes of reflectance curves for PTS at 600C and 400C are the same. Thus, storage of an indicator at 400C for 120 hours is equivalent to storage of an indicator at 600C for 13.6 hours. This amounts to dividing the time at 400C by about 8.8 to correspond to the time at 600C with Ea = 22.5 kcal/mole according to equation (1). This also means that storage at 400C for 60 hours followed by storage at 600C for 6.8 hours is equivalent to storage at 400C for 120 hours or storage at 600C for 13.6 hours. Support for these statements may be derived from Figure 9, which is part of Example 4. The same shape of curve should be followed at all temperatures. However, the time axis will depend on the activation energy which may be derived from equation 1. This ultimately means that a single reflectance value yields an average cumulative time-temperature exposure value for the indicator. Therefore, a reflectance value can be correlated with the storage time at a given temperature to determine the remaining shelf life of the product. This correlation is illustrated by Examples 5 and 6. Using conventional computer techniques, an equation can be derived that correlates reflectance and remaining shelflife. It should be appreciated that non-Arrhenius kinetics and simple empirical correlations may also be employed to perform this function. These same procedures may be easily followed by those skilled in the art in order to derive a reflectance time-temperature relationship for acetylenic compounds that are being considered for employment in the practice of this invention. The process of this invention is particularly suitable for monitoring the remaining shelf-life of a variety of products that undergo degradation in response to environmental stimuli. For example, a more exact measure of the remaining useful life of perishables such as food products and pharmaceuticals may be obtained by employing the process of this invention. Other examples of products that may be monitored by the new process include materials or components that are to be employed or incorporated in some fashion into another product wherein said materials or components are subjected to environmental stimuli prior to their employment or incorporation into the final product. In cases of this nature, the process of this invention could alert one to the fact that the materials or components are defective and should not be employed. It will be appreciated that the process of this invention can be of invaluable assistance to various entities in monitoring the remaining shelf-life or quality of various materials or products that the entity sells, manufactures, or employs in the manufacture of another article. This is especially true when computer technology is employed to correlate the information obtained by an automatic scanner and to store the information obtained concerning the remaining shelf-life that remains for particular products or a certain class of products. For example, grocery retailers could employ the process of this invention in automated fashion to obtain a daily record of the remaining shelf life of any product they sell that degrades in response to environmental stimuli. With respect to food products, including frozen food products, if the automated version of the process of this invention were employed at each step of the distribution chain (i.e., producer, shipper, wholesaler, retailer, etc.), one could monitor the remaining useful life of food products at each step of the distribution chain. Therefore, one within the distribution chain could speed up transit of certain items if necessary. Also, if a significant number of items were negligently exposed to conditions that resulted in spoilage of a number of items, computer analyses of the data collected at each step could identify the point(s) in the distribution chain where abuse occurred. EXAMPLE 1 An ink was formed by mixing 1 gram of a solid acetylenic monomer, 4BCMU, with 10 grams of Aquaset Screen Printing Ink Extender Base WIT 800 RM (Advance). The mixture was heated to dissolve the 4BCMU, and then cooled to cause the acetylenic compound to crystallize as fine particles. The ink was used to print the variable region as in Figure 1. The black stripes were printed using Hunt Speedball Jet Black Flat Finish Screen Process Ink No. 4803. Bond paper was used as the substrate. The indicator was irradiated for various times at a distance of 8.25 cm from the surface. The W source used to cause the polymerization was a low pressure mercury lamp (Oriel Model 6047). The signal from the wand (Intermec 1402) was sent through an amplifier (Skan-a-matic) to a TechLab I computer (Tec Mar, Inc.) where the data was processed as described in Example 5. The results are shown in Table I. TABLE I PERCENT REFLECTANCE UV DURATION (SECONDS) 97 0 80 2 75 4 68 6 63 8 51 16 37 40 33 150 EXAMPLE 2 Two labels were prepared by screen printing white and blue as reference colors on a 5 mil mylar sheet. 3R4M, an acetylenic time-temperature indicating compound, was sprayed onto paper substrates, and the paper substrates with 3R4M thereon were positioned between the two reference colors on each label in order to prepare indicator label 5. The indicator labels so prepared were stored at 500C or 250C for differing amounts of time in order to cause a different color change to occur in each acetylene containing substrate due to different time-temperature exposures. The reflectance value of each label at the various time-temperature exposures was measured with a MacBeth Densitometer using the blue filter of the densitometer. The reflectance readings were obtained by passing the measuring module of the densitometer over the three-colored labels in one motion. The densitometer readings were recorded for each of the printed surfaces. The reflectance data obtained is reported in Table II. The readout of a Macbeth Densitometer is in density units where density is defined as the negative logarithm of the reflectance. TABLE II Indicator T Time Tet. 0C Reflectance (%) 1 0 50 83.2 1 3 hr. 50 min. 50 45.7 1 7 hr. 5 min. 50 33.1 1 24 hr. 5 min. 50 25.7 1 30 hr. 5 min. 50 24.5 2 0 25 83.2 2 3 hr. 50 min. 25 81.3 2 7 hr. 5 min. 25 74.1 2 24 hr. 5 min. 25 66.1 2 30 hr. 5 min. 25 61.7 2 150 hr. 20 min. 25 39.8 2 772 hr. 25 16.0 The data in Table II demonstrate that indicators stored at 500C obtain decreased reflectance values more rapidly than indicators stored at 250C. The decreased reflectance values result from additional color development due to a higher degree of polymerization. Thus, decreased reflectance is directly related to the degree of polymerization which is a function of time and temperature. The data reported in Table II is graphically illustrated in Figure 7. In Figure 7, the time required to reach a reflectance value of 46% for indicators stored at each temperature (i.e., 250C and 500C) was used to normalize the time axis of the graph in accordance with equation 1 (with Ea = 25 kcal/mole). As Figure 7 illustrates, the general curve type II of Figure 6 is obtained at 250C and 500C. This indicates that a cumulative exposure of 4 hours at 500C is equivalent to 4.4 days at 250C. A reflectivity reading of 46% was arbitrarily chosen as the endpoint because it is on the steep portion of the curve and one can accurately monitor this cumulative time-temperature effect. EXAMPLE 3 The indicators stored at 500C in Example 4 were scanned using the red and yellow filters of the MacBeth Densitometer. The reflectance values obtained using the red and yellow filters are reported in Table III, along with the reflectance values obtained from the same samples using the blue filter of the densitometer. TABLE III Reflectance (%) Indicator Time Blue Red Yellow 1 0 83.2 85.1 81.3 2 3 hr. 50 min. 45.7 60.3 77.6 3 7 hr. 5 min. 33.1 46.8 66.1 4 24 hr. 5 min. 25.7 36.3 56.2 5 30 hr. 5 min. 24.5 35.5 6 150 hr. 20 min. 15.5 23.4 41.7 7 772 hr. 6.8 10.5 22.4 The data reported in Table III demonstrate that switching from the blue to red filter almost doubles the effective lifetime of the indicator when 46% is employed as the endpoint. Similarly, the above data demonstrate that employing the yellow filter of the densitometer yields a 25 fold increase in the lifetime of the indicator. EXAMPLE 4 PTS (25g) was ball milled for 16 hours with Ethocell Standard-45 (3g) and n-butanol (72mL). The resultant finely pulverized suspension was mixed with an equal weight of 128 (W/V) Ethocell Standard-45 n-butanol solution. An indicator label as is illustrated by Figure 8 was screen printed on Scott Offset White Paper with Hunt Speedball Jet Black Flat Finish Screen Process Ink No. 4803 as the reference color on a paper background. A second reference strip was the white paper background. A variable strip was screen printed with the PTS ink described above. The indicators were stored at either 40"C or 600C in a temperature controlled compartment for varying lengths of time. Upon removal of the indicators from the temperature controlled compartment, each indicator was scanned with an Intermec 1401 scanning wand. A signal was forwarded through an amplifier (Signal Control Module T22050, Skan-a-matic Corp.) and into a multichannel analyzer signal processor. The signal was processed by averaging the White (W) and Black (B) values and the values of the acetylenic com pound (AC) as R = AC - B . This value was used to deter W-B mine the reflectance of the diacetylene compound relative to the white and black reference colors. These data are presented in Figure 9. EXAMPLE 5 Figure 10 illustrates a plot of the time required for a graphite-impregnated composite material (Hercules Corp. product No. 3501-61A5) to lose tack. The graph also illustrates the time required for PTS, an acetylenic time-temperature composition, to reach its endpoint. Seven time-temperature labels were prepared by printing the diacetylene indicator compound on a label using flexographic printing techniques, followed by the application of a pressure sensitive optically-clear lamination over the entire printed surface. This printed tab was then placed onto an indicator card having white and black stripes used for optical triggering and electro-optical reference points. As is illustrated by Figure 10, the graphite composite material has a shelf-life that is only about 60% of the lifetime (i.e., endpoint) of the indicator. Therefore, the time-temperature indicator labels were annealed for 10.5 hours at 600C in order to render the endpoint of the indicator equivalent to the useful shelf life of the graphite composite material. Each time-temperature indicator was then subjected to a temperature of 600C for a specific period of time, and then each indicator was read by an automatic scanner in order to determine relative reflectance for each indicator. In this example, an Intermec 1401 scanning wand was employed. This wand has a peak response at 630 nm which is optimum for many diacetylene compounds. The output of the wand was digitized in a multichannel analyzer as in Example 4. The signal was processed by averaging the white (W) and black (B) reference values and the values of the acetylenic compound (AC). The reflectance given as AC-B was used for subsequent W-B calculations. This value was used because of the necessity of determining a relative reflectance value between the diacetylenic compound and the reference colors. This relative reflectance was independent of scan angle and optical integrity of the scanning system. The data obtained from this example are illustrated in Table IV below. TABLE rv Remaining Indicator Temp. Time R* Life (%) 1 60 OC 40.5 min. 69 95 2 600C 2 hr. 45 min. 64 80 3 600C 5 hr. 24 min. 58 60 4 600C 8 hr. 6 min. 47 40 5 600C 10 hr. 13 min. 30 20 6 600C 13 hr. 30 min. 12 0 *Percent reflectance EXAMPLE 6 An indicator label similar in format to the indicator illustrated by Figure 5 was printed on pressure sensitive paper label stock. PTS was employed as the acetylenic indicating material. A line printer (Printronix Model 300) was used to print two interleaved two-of-five bar codes, one for product identification and one for acetylenic indicator indentification. A scanning wand (Intermec Product No. 1241) with a Tech Lab I (Tec Mar) were utilized to scan the product identification bar code, acetylenic indicator identification bar code and the variable region of reflectivity of the indicator label. The system read the two bar codes and determined a relative reflectivity value of 68 percent for the variable region of the indicator label. Using the predetermined shelf-life - reflectance relationship from Example 5, a computer program automatically correlated this reflectance value to represent a remaining shelf-life of 93 percent for an epoxy prepreg product. EXAMPLE 7 Chromadye-2 (a spiropyran purchased from Chroma Chemicals, Inc., Dayton, Ohio) was dissolved in xylenes (0.5g/20 ml). 2.4 grams of Ethocell 45 were added to this solution and mixed with heating until the solution was clear. This ink was screen printed on transparent yellow acetate sheets (approx. 5 ml thick). Several pieces of this coating were cut and fabricated as indicators (similar to Fig. 1) with the yellow barrier protecting the spiropyran coating. The indicators were activated using 30 seconds of long wavelength W irradiation from a Model WSL-25 mineralight lamp (Ultraviolet Products, Inc. San Gabriel, California) at a distance of 1 cm to produce a colored state. A white background paper was positioned behind the indicator and fastened with tape. Reflectance readings were taken after irradiation and the indicators were then stored at several temperatures and the reflectance was monitored. The signal was detected as in Example 1 and the results are listed in Table V. (All initial reflectance values were approximately 10%.) Table V Temp. 240C Temp. ¯ 40C Temp. - -200C Time (Mins) 96R Time (Hrs) %R Time (Hrs) 26 4 37 18.5 49 90 31 6 38 23.8 56 162 40 8 51 45.5 69 305 45 12 57 22 74 57 It should be appreciated that the increased reflectance values of this example can be analyzed and correlated in a manner analagous to Examples 5 and 6.

Claims: Claims: 1. A process for measuring the incremental environmental exposure of an indicator device which comprises the steps: a. measuring the reflectivity at specified wavelengths of at least one variable region of said indicator device, said variable region comprising an acetylenic compound having at least two conjugated acetylenic moieties which in response to environmental conditions undergoes incremental degrees of polymerization as said environmental exposure continues, with resultant incremental changes in reflectivity accompanying said incremental degrees of polymerization at said specified wavelengths; b. measuring the reflectivity at said selected wavelengths of at least one non-variable region of said indicator device, said non-variable region being unaffected by said environmental exposure; ; c. determining the reflectivity of said variable region relative to that of at least one non-variable region; and d. correlating said reflectivity of step c to an incremental change in the environmental exposure of said device based upon a pre-established relationship between said reflectivity of step c and the incremental change in the environmental exposure of said device; and correlating said incremental change in the environmental exposure to a remaining shelf-life or extent of processing value for a product that undergoes progressive quality changes upon exposure to environmental stimuli. 2. A process in accordance with claim 1 wherein said wavelength is about 300 nm to about 850 nm. 3. A process in accordance with claim 1 or 2 wherein said process includes determining the identity of a product by electro-optically scanning a product identification means of said indicator device and correlating said identity and said reflectivity of step c of claim 1 with said pre-established relationship and said useful shelf life value of step d of claim 1. 4. A process in accordance with claim 3 wherein said process includes determining the identity of said acetylenic compound by electro-optically scanning an acetylenic compound identification means of said indicator device and correlating said identity of said acetylenic compound and said reflectivity of step c of claim 1 with said pre-established relationship and said useful shelf life value of step d of claim 1. 5. A process in accordance with claim 4 wherein said product identification means and said acetylenic composition identification means may be the same or different and are selected from the group consisting of bar codes, letters, numerals, or combinations thereof. 6. A process in accordance with any previous claim wherein said environmental exposure is time-temperature exposure. 7. A process in accordance with any previous claim wherein said indicator device includes one variable region of reflectivity and four non-variable regions of reflectivity, with two non-variable regions of differing reflectivities being located adjacent to one side of said variable region and two non-variable regions of reflectivity being located adjacent to another side of said variable region. 8. An environmental indicating device wherein said device includes at least one region of variable reflectivity and at least one region of non-variable reflectivity, with said variable region comprising an acetylenic composition having at least two conjugated acetylenic moieties. 9. A device in accordance with claim 8 that includes a product identification means. 10. A device in accordance with claim 8 or 9 that includes an acetylenic composition identification means. 11. A product that undergoes progressive quality changes in response to environmental exposure having attached thereto the device of claim 8 or 9 or 10. 12. A product in accordance with claim 11 that undergoes progressive quality changes in response to time-temperature exposure. 13. A process for measuring the incremental environmental exposure of an indicator device which comprises the steps: a. measuring the reflectivity at specified wavelengths of at least one variable region of said indicator device, wherein said variable region undergoes incremental reflectivity changes upon exposure to environmental stimuli; b. measuring the reflectivity at said selected wavelengths of at least one non-variable region of said indicator device, said non-variable region being unaffected by said environmental exposure; c. determining the reflectivity of said variable region relative to that of at least one non-variable region; and d. correlating said reflectivity of step c to an incremental change in the environmental exposure of said device based upon a pre-established relationship between said reflectivity of step c and the incremental change in the environmental exposure of said device; and correlating said incremental change in the environmental exposure to a remaining shelf-life or extent of processing value for a product that undergoes progressive quality changes upon exposure to environmental stimuli. 14. A process in accordance with claim 13 wherein said process includes determining the identity of a product by electro-optically scanning a product identification means of said indicator device and correlating said identity and said reflectivity of step c of claim 13 with said pre-established relationship and said remaining shelf-life or extent of processing value of step d of claim 13. 15. A process in accordance with claim 14 wherein said variable region of reflectivity comprises an indicating material which undergoes reflectivity changes upon exposure to environmental stimuli, and wherein said process includes determining the identity of said indicating material by electro-optically scanning an indicator material identification means of said indicator device and correlating said identity of said indicating material and said reflectivity of step c of claim 13 with said pre-established relationship and said remaining shelf-life value of step d of claim 13. 16. A process in accordance with claim 15 wherein said product identification means and said indicating material identification means may be the same or different and are selected from the group consisting of bar codes, letters, numerals, or combinations thereof.

Inventors: BAUGHMAN, RAY HENRY, CHANCE, RONALD RICHARD, ECKHARDT, HELMUT, FIELDS, STEPHEN CARL, GRABINER, FREDERICK ROBERT, PRUSIK, THADDEUS
Applicants: LIFELINES TECHNOLOGY INC.
Application year: 1984
Main classification: G01D1
IPC codes: G01N21, C09K3, G01K3, G01N17, G01N31, G01N33