TEMPERATURE INDICATING DEVICE

Abstract: A critical temperature indicating device is provided. It includes a microporous membrane, an indicating composition containing less than about 10 wt.% water, and means for containing the microporous membrane and the indicating composition. The indicating composition includes: a primary organic component comprising at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30 DEG C above the critical temperature; a modifying component comprising at least one compound that has a freezing point below the critical temperature; and a wetting component comprising at least one compound that has a freezing point below the critical temperature and is capable of spontaneously wetting out the microporous membrane at about the critical temperature.

Description: TEMPERATURE INDICATING DEVICE Field of the Invention This invention relates to critical temperature indicating devices More particularly, it relates to a critical temperature indicating device comprising an indicating composition that provides an irreversible visual signal to the user that a product has been exposed to a predetermined temperature Background of the Invention Blood, emulsions, pharmaceuticals, beverages, and other items are often chilled in order that they may be preserved for later use If exposed to too low a temperature, however, the characteristics of these items may change so that they are undesirable for later use In fact, many of these items may be rendered completely useless if exposed to too low a temperature, such as the freezing point of water It is, therefore, desirable to provide an indicating device that will accurately show whether or not the item is exposed to a temperature below a critical value It is also typically desirable for the device to provide its indication relatively rapidly and that the indication be irreversible so that the user will be alerted to a previously attained cπtical temperature, even if that condition is not maintained Critical temperature indicating devices are known that utilize the expansion characteristic of water to break a frangible ampule That is, once the indicating device is exposed to a temperature below the freezing point of water, the volume increases as the water in the ampule changes to ice, thereby causing the ampule to break After the ice is formed and the surrounding temperature returned to a point about the melting point ofthe ice, the resultant water is absorbed by a pad, thus providing an indication that the device had gone through a freeze stage and back through a thaw stage Such indicating devices are not always accurate due to the super-cooling effect of water Under some conditions, water may be cooled to as low as -16°C without freezing This problem has been partially overcome by the addition of nucleating agents to the water to enhance ice formation Water-based indicating devices are also known that utilize a microporous layer water, and a second liquid that can wet out the microporous layer upon solidification ofthe water See, U S Patent No 4,846,095 (Emslander) The micropores of the microporous layer cause scatteπng of transmitted light, causing the microporous layer to appear opaque When the voids are filled with a liquid having substantially the same index of refraction as the material ofthe microporous layer, the filled voids do not significantly scatter transmitted light, thus rendering the microporous layer transmissive to visible light The opacity ofthe microporous layer masks a visible indicator, which can be seen after the indicator is activated (i e after the second liquid enters the voids of the microporous layer) Emslander also discloses that a seeding agent or a salt can be added to the aqueous mixture to slightly modify the indicating temperature Emslander further discloses that two nonaqueous compounds (ethanolamine and n-butanol), one of which solidifies and one of which wets out the microporous layer, can be used in the indicating devices containing a microporous layer Other temperature indicating devices are known that include organic compounds in a capillary tube or bulb attached to a capillary tube See, for example, U S Patent Nos 4,457,252 and 4,457,253 These indicating devices utilize the volume reduction characteristics of organic compounds as they undergo a change from the liquid state to the solid state Two organic liquids are separated by a porous plug and/or a separating liquid that is immiscible with the two organic liquids One ofthe organic liquids is colored and has a freezing point that is higher than that ofthe other (colorless) organic liquid At the cπtical temperature, the colorless organic liquid solidifies and the colored liquid is drawn mto that portion ofthe capillary tube or bulb containing the colorless, solidified organic liquid, thereby providing a visual indication that the first compound solidified Even with these nonaqueous indicating devices, there is a need for additional indicating devices, particularly those that are responsive relatively rapidly and reproducibly within a relatively narrow temperature range Furthermore, there is a need for additional indicating devices that are capable of being readily modified to a wide range of cπtical temperatures Summary of he Invention The present invention provides a device for indicating if an object is exposed to a critical temperature; the indicating device comprising: (a) a microporous membrane; (b) an indicating composition containing less than about 10 wt-% water; the composition comprising: (i) a major amount of a primary organic component comprising at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 0°C above the critical temperature; (ii) a modifying component comprising at least one compound that has a freezing point below the critical temperature; and (iii) a wetting component comprising at least one compound that has a freezing point below the critical temperature and is capable of spontaneously wetting out the microporous membrane at about the critical temperature, and (c) means for containing the microporous membrane and the indicating composition; wherein the primary organic component, modifying component, and wetting component are miscible liquids above the critical temperature, and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the critical temperature, but does wet it out at about the critical temperature upon solidification of a portion ofthe composition. The present invention also provides a device for indicating if an object is exposed to a critical temperature; the indicating device comprising: (a) a microporous membrane; (b) an indicating composition containing less than about 1 wt-% water; the composition comprising: (i) at least about 50 wt-%) of a primary organic component comprising at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, (u) no greater than about 40 wt-% of a modifying component compπsing at least one compound that has a freezing point below the cπtical temperature, and (m) no greater than about 20 wt-% of a wetting component compπsing at least one compound that has a freezing point below the cπtical temperature and is capable of spontaneously wetting out the microporous membrane at about the critical temperature, and (c) means for containing the microporous membrane and the indicating composition, wherein the pπmary organic component, modifying component, and wetting component are miscible liquids above the cntical temperature, and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, but does spontaneously wet it out at about the critical temperature upon solidification of a portion ofthe composition A further embodiment ofthe present invention is a device for indicating if an object is exposed to a cπtical temperature, the indicating device compπsing (a) a microporous membrane compπsing a polyolefin, (b) an indicating composition containing less than about 1 wt-% water, the composition comprising (i) at least about 50 wt-% of a primary organic component compπsing at least one polyfunctional alcohol that has a freezing point above the cπtical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, (n) no greater than about 40 wt-% of a modifying component compπsing at least one polyfunctional alcohol that has a freezing point below the cπtical temperature, and (in) no greater than about 20 wt-%> of a wetting component compnsing at least one compound selected from the group consisting of alcohols, ketones, ethers, alkanes, alkenes, amines, and combinations thereof, wherein the compound has a freezing point below the critical temperature and is capable of spontaneously wetting out the microporous membrane at about the critical temperature, and (c) means for containing the microporous membrane and the indicating composition and retarding transmission of water vapor into the indicating composition, wherein the primary organic component, modifying component, and wetting component are miscible liquids above the critical temperature, and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, but does spontaneously wet it out at about the critical temperature upon solidification of a portion ofthe composition In this application, "activated" refers to the condition of the indicating device wherein the microporous membrane has been "wetted out" thereby providing an irreversible indication (e.g., a message or a colored composition) that the device has been exposed to the critical temperature for which it was designed, "critical temperature" refers to the temperature at, or below which, the object being monitored is damaged such that it is undesirable for later use, at this temperature, a portion of the indicating composition solidifies sufficiently to change the surface tension of the indicating composition and cause wetting out of the pores of the microporous membrane, "microporous membrane" refers to a polymeric material having a void volume (i.e., the total amount of space not occupied by polymer) ranging from about 20%) to about 90%) which is characterized by having open porosity (i.e , external pores or pores open to the surface of the membrane) with interconnected channels, "miscible liquids" refers to a combination of two or more liquids that form a clear solution upon viewing by the unaided eye, "response time" refers to the time required for the indicating device of the present invention to be activated at the critical temperature for which it is designed, "surface energy" refers to the critical wetting tension (γ c ) of a solid, which is equal to the surface tension of a liquid that would yield a zero contact angle when placed in contact with the solid (i e , when the liquid completely wets out the solid), "surface tension" refers to the force acting on the surface of a liquid tending to minimize the area ofthe surface and is equal to the free energy per unit surface area, and "spontaneous wet out" refers to entry of a portion ofthe liquid indicating composition into the pores ofthe microporous membrane in the absence of a pressure gradient across the membrane; the portion ofthe liquid indicating composition that enters the pores ofthe microporous membrane includes at least the wetting component, but it also may include the modifying component and/or nonsolidified primary component Brief Description of the Drawings Figure 1 is a sectional view of one embodiment ofthe indicating device of this invention Figure 2 is a sectional view of a second embodiment ofthe indicating device of this invention Figure 3 is a sectional view of a third embodiment ofthe indicating device of this invention Figure 4 is a sectional view of the embodiment of Figure 3 adhered to an object being monitored Detailed Description The present invention provides a device for indicating whether an object has been exposed to a critical temperature (i e., a predetermined temperature below which the object should not be exposed) The indicating device includes a microporous membrane, an indicating composition containing less than about 10 percent by weight (wt-%)) water, based on the total weight ofthe indicating composition, and means for containing the microporous membrane and the indicating composition, and preferably, retarding the transmission of water vapor into the indicating composition Preferably, the indicating composition contains less than about 1 wt-%> water Typically, indicating devices containing less than about 10 wt-% water are not sub j ect to the problems associated with super-cooling They tend to be relatively rapidly responsive For example, preferred indicating devices of the present invention have a response time of no greater than about 60 minutes (more preferably, no greater than about 45 minutes, and most preferably no greater than about 30 minutes) They also tend to be more precise and reproducible within a relatively narrow temperature range For example, indicating devices of the present invention are preferably capable of being activated within ±2°C ofthe cπtical temperature of the object being monitored using the test method descnbed herein which generally involves a cooling rate of about 1°C per 30 minutes The indicating composition can be a solution a dispersion, a gel (l e , a high viscosity solution or dispersion) or the like It includes at least three components a first organic component (I e , the pπmary organic component) that includes at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the desired cπtical temperature of the object (e g , pharmaceutical substance, plant mateπal, microorganism etc ) being monitored, a second component (I e , the modifying component) that includes at least one compound that has a freezing point below the critical temperature (I e , it is a liquid at the cπtical temperature and is used to modify the temperature at which the indicating device is activated), and a third component (I e , the wetting component) that includes at least one compound that has a freezing point below the cπtical temperature and is capable of spontaneously wetting out the microporous membrane at the cπtical temperature The pnmarv organic component, modifying component, and wetting component are miscible liquids above the cπtical temperature They are present in a ratio such that the indicating composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C (preferably, at least about 45°C, and more preferably, at least about 60°C) above the cπtical temperature, but does spontaneously wet it out at about the cπtical temperature upon solidification of a portion of the composition At about the cπtical temperature, at least the pπmary organic component solidifies out of the indicating composition, although either or both the wetting component and the modifying component may also solidify with the pnmary organic component While not being bound by theory, it is believed that this results in an increase in concentration of the wetting component in the nonsolidified (I e , remaining liquid) portion ofthe indicating composition, which causes spontaneous wet out ofthe microporous membrane at about the cntical temperature It will be understood by one of skill in the art that the microporous membrane may be wet out by a mixture ofthe wetting component and other nonsolidified components ofthe indicating composition, however, at least the wetting component will wet out the microporous membrane An indicating composition that includes a modifying component provides advantage over an indicating composition that includes only a pπmary component that solidifies and a wetting component Such indicating compositions that include the modifying component provide indicating devices that are capable of being readily modified to a wide range ot cπtical temperatures Furthermore, the temperature at which the indicating device is activated can be precisely adjusted by adjusting the relative amounts ofthe primary organic component, the modifying component, and the wetting component This provides a greater number of temperatures generally over a broader temperature range to which a combination of any three components can be tailored, as well as a precise adjustment ofthe temperature Thus, the temperature at which the primary organic component solidifies can be modified through the use ofthe modifying component The pure form ofthe pπmary organic component (or pure torms of the individual compounds ofthe pπmary organic component if more than one compound is used) has a freezing point above (preferably, at least about 5°C above) the critical temperature for which the indicating device is designed The pure form ofthe modifying component (or pure forms ofthe individual compounds ofthe modifying component if more than one compound is used) has a freezing point below (preferably, at least about 5°C below) the cπtical temperature for which the indicating device is designed The modifying component may cocrystallize with the pπmary organic component or may simply depress its freezing point Thus, the temperature at which the pπmary organic component solidifies (1 e , its freezing temperature) when pure is higher than the temperature at which solidification occurs in the indicating composition Upon the temperature dropping to or below the critical temperature, a portion ofthe indicating composition solidifies, the concentration ofthe wetting component in the indicating composition increases, thereby causing the spontaneous wet out ofthe microporous membrane This is what is believed to occur when the indicating device is "activated " As stated above, at least the wetting component enters the pores ofthe microporous membrane, although a mixture ofthe wetting component and other nonsolidified components of the indicating composition may also enter the pores ofthe microporous membrane with the wetting component This wetting out ofthe microporous membrane can cause the membrane to become generally transparent (l e , to transmit visible light), or at least translucent Thus, as in U S Patent No 4,846,095 (Emslander), the device is a visual indicator in that the membrane is initially opaque and becomes transparent, or at least translucent when it is wetted out Under normal conditions of use (1 e , temperatures of about 0- 60°C without a pressure gradient across the membrane), the membrane will stay generally transparent or translucent If colorant, such as a dye or pigment, is present, however, the membrane will not necessarily become transparent or even translucent Rather, the colorant can be carried into the pores ofthe membrane and thereby change the color ofthe membrane This change in opacity and/or color indicates that the temperature has dropped to, or below, the cπtical temperature to be indicated The indicating device ofthe present invention can be in a vanety of configurations That is, means for containing the indicating composition and microporous membrane can be in the form of a pouch, a blister pack, etc The container is formed from one or more materials that can be shaped and sealed to form a reservoir to hold the indicating composition and microporous membrane These mateπals are preferably barπer materials for holding out moisture and environmental gases Bamer mateπals are typically used when one or more of the components ofthe indicating composition is hygroscopic Referπng now to Figure 1, the temperature indicating device 10 includes two layers 12 and 13 of barπer mateπal, each of which is bonded to a microporous membrane 14 and 15, thereby forming reservoir 16 between microporous membranes 14 and 15 The microporous membranes may be bonded to the barrier layers about their penphery, or across the entire membrane That is, microporous membrane 14, for example, can be bonded to barrier layer 12 about the periphery ofthe membrane Alternatively, the entire surface ofthe membrane can be bonded to the barrier layer Barrier layers 12 and 13 are preferably bonded to microporous membranes 14 and 15 by heat sealing, although an adhesive or alternative means of bonding could be used Reservoir 16 contains the indicating composition It is believed that once the indicating device is exposed to the critical temperature for which it is designed, at least the primary organic component solidifies (which may cocrystallize with either the modifying component or the wetting component or both) and the concentration ofthe wetting component increases in the liquid phase to a point where this nonsolidified portion ofthe indicating composition (at least the wetting component) spontaneously wets out the microporous membrane If the indicating composition includes a colorant, the indicating composition becomes visible as a result ofthe microporous membrane losing its opacity and/or as a result ofthe colorant entering the pores ofthe microporous membrane The indicating device shown in Figure 1 can be in a variety of shapes, such as a rectangular, square, or circular flat pouch One surface ofthe indicating device can have a layer of adhesive disposed thereon for attaching to a surface ofthe object to be monitored In such embodiments, there may only be one microporous membrane That is, the reservoir 16 would be formed between a barrier layer and a layer of microporous membrane on one side and simply a barrier layer on the other side When in position on the object to be monitored, the side ofthe indicating device with only the barrier layer would be closest to the object to be monitored The reservoir can also be formed by a washer (i e , a flat ring) made of a nonporous material, such as a thermoplastic, thermoset, or metallic material This washer is adhered to a layer of a barrier material on one side, and a second layer of a barrier material with a microporous membrane adhered thereto is adhered to the other side ofthe washer The reservoir is thereby formed for placement ofthe indicating composition A layer of adhesive on a release liner could also be a temporary barrier, thereby eliminating the need for a barrier layer at least on one side ofthe indicating device Once the release liner is removed, the adhesive could be placed against a glass container, or some other object, that could act as a barrier. Alternatively, if the adhesive is sufficiently hydrophobic (e.g., a rubber-based adhesive), it may serve as a barrier even when place on a porous substrate. The barrier material not only provides the container for the indicating composition and microporous membrane, but it can provide a barrier to retard the evaporation ofthe components ofthe indicating composition and it acts to seal out water and water vapor, which may adversely affect the reproducibility and precision of the indicating device. The barrier material is typically at least partially transmissive to visible light so that the visible indicator may be seen therethrough once the indicating device has been activated. If the barrier material is attached to a surface ofthe object being monitored and is therefore on the "backside" of the indicating device, however, it does not need to be transmissive to visible light. Thus, an indicating device can include more than one type of barrier material, as long as at least a portion ofthe barrier material is at least partially transmissive to visible light. Referring now to Figure 2, the temperature indicating device 20 includes a thermoformed barrier material 22 and a microporous membrane 24 bonded thereto, and backing 28 bonded to the periphery ofthe thermoformed barrier material 22, thereby forming reservoir 26 for the indicating composition. Thermoformed barrier material 22 is preferably bonded to microporous membrane 24 using a layer of adhesive (not shown) about the periphery ofthe membrane, although other means of bonding can be used (e.g., thermal and ultrasonic welding). Generally, if the entire surface of microporous membrane 24 were bonded to thermoformed barrier material 22, this would not necessarily prevent it from being wetted out. In this embodiment, backing 28 is not transmissive to visible light, although it could be if desired. In fact, backing 28 could be made ofthe same material as thermoformed barrier material 22, although it is generally preferred that the backing 28 be made of a metallic foil, plastic, or a laminate that has a sufficiently low water vapor transmission rate and that prevents the transmission of visible light. The backing 28 can be coated with a heat sealable material such that it can be thermally bonded to the thermoformed barrier material 22, although an adhesive could be used. Again referring to Figure 2, the backing 28 can bear an image (e g , "REJECT" or "FROZEN 7 ') thereon that cannot be seen through microporous membrane 24 prior to the indicating device being activated Once activated, however, the image could be seen through the thermoformed barrier material 22 and the microporous membrane 24 Alternatively, the indicating composition could include a colorant that would be seen upon wetting out ofthe microporous membrane, or the indicating composition could be colorless and backing 28 could be colored Referring now to Figure 3, the temperature indicating device 30 includes a layer 32 of barrier material, thermoformed barrier material 33, and microporous membrane 34 The microporous membrane 34 is bonded to the barrier material 32, preferably by heat sealing, although an adhesive layer or other means of sealing could be used The baπier material 32 is bonded to thermoformed barrier material 33, thereby forming reservoir 36 for the indicating composition Alternatively, the microporous membrane 34 can be fused between the barrier material 32 and the thermoformed barrier material 33 depending on the materials used Thermoformed barrier material 33 is backed with an adhesive layer 38 forming hollow space 39 Adhesive layer 38 is used to attach the indicating device to the surface of the object to be monitored Thus, barπer mateπal 32 is at least partially transmissive to visible light because that is the portion of the indicating device through which a person would look Generally, the indicating composition in this embodiment would include a colorant, such that it would become visible as a result ofthe microporous membrane losing its opacity and/or as a result ofthe colorant entering the pores ofthe microporous membrane Referring now to Figure 4, the temperature indicating device 40 includes a layer 42 of barrier material, thermoformed barrier material 43, and microporous membrane 44 The microporous membrane 44 is bonded to the barrier material 42, preferably by heat sealing, although an adhesive layer or other means of sealing could be used The barrier material 42 is bonded to thermoformed barrier material 43, thereby forming reservoir 46 for the indicating composition Alternatively, the microporous membrane 44 can be fused between the barrier material 42 and the thermoformed barrier material 43 depending on the materials used. Indicating device 40 is positioned against container 47 and held in place by extensions 48 and 49 of thermoformed bamer mateπal 43 Alternatively, or additionally, indicating device 40 can be held in place by adhesive positioned between the surfaces ofthe indicating device and the container that are in contact Polymeπc microporous membranes (depicted as, for example, 14 and 15 in Figure 1) may be made from polyolefins such as polypropylene and polyethylene, polysulfones, polytetrafluoroethylene (PTFE), polyamide, polyester, cellulose acetate and other cellulose derivatives, and the like, as well as from combinations of these polymers Preferred microporous membranes include polyolefins such as polyethylene or polypropylene Microporous membranes may be produced by solvent casting of polymers, or by a phase separation processes, for example The surface energy ofthe membranes can be modified by corona treating, flame treating, or by adding a surface active agent, for example Suitable microporous membranes have a void volume of about 20-90%, more preferably about 40-85% Preferably, the structure is characteπzed by having open porosity with interconnected channels An example of a material that is suitable for use as the microporous membrane is described in U S Patent No 4,726,989 (Mrozinski) This microporous membrane includes a multiplicity of spaced, randomly dispersed, nonuniformly shaped, equiaxed (I e , approximately equal dimensions in all directions) particles of a crystallizable thermoplastic polymer (e g , a polyolefin such as polypropylene) coated with a compound with which the thermoplastic polymer is miscible These particles are separated from one another to provide a network of interconnected micropores, yet they are connected to one another by fibrils ofthe thermoplastic polymer Furthermore, these particles include a nucleating agent in the inteπor ofthe particles They are made by a phase separation process and are often referred to as thermally induced phase separation membranes (I e , "TIPS" membranes) Such membranes are commercially available from Minnesota Mining and Manufacturing Company of St Paul, MN Commercially available microporous membranes include a particle-filled polyethylene commercially available under the trade designation "EXXAIRE FILM" from Exxon Chemical Co of Florida, TX, and polypropylene membranes commercially avaiiable under the trade designation "AKZO" from Akzona of Germany or "CELGARD" from Hoechst Celanese of Sommerville, NJ Also available are particle- filled microporous membranes available under the trade designation "EXEPORE" from Mitsubishi Chemical of Yokohama, Japan The micropores ofthe microporous membrane cause scattering of incident light, causing the microporous membrane to appear opaque When the voids are substantially filled with a liquid having substantially the same index of refraction as the matenal ofthe microporous membrane, the substantially filled voids result in a dramatic decrease in scattering, thus rendeπng the microporous layer transmissive to visible light If however the indicating composition of the present invention includes a colorant, the wetting compound does not have to have substantially the same index of refraction, rather, it merely needs to be able to wet out the microporous membrane Even if the temperature exceeds the critical temperature for which the indicating device was designed, after it has been activated (yet is still within a reasonable temperature of about 0-60°C and there is no pressure gradient across the membrane), the wetting compound is generally unable to leave the pores, thereby rendering their microporous membrane generally ineversibly transparent, translucent, or with colorant therein Prefened barrier matenals provide a barrier to water vapor, environmental gases, etc , such that they do not contaminate the indicating composition in the device Preferably, the barrier material has a water vapor transmission rate (WVTR) of less than about 1 gram/meter 2 in 24 hours, as measured according to American Society for Testing Mateπals (ASTM) Test Method F- 1249-90 on a MOCON Permatran at 38°C and 90%) relative humidity More preferably, it has a WVTR of less than about 0 5 gram/meter 2 in 24 hours, and most preferably, less than about 0 1 gram/meter 2 in 24 hours It is desirable to keep water vapor (and water) out ofthe indicating composition (except for the small amount that may be used as a modifying compound) to ensure reproducibihty, precision, and relatively short response times Typically, the bamer mateπal is at least partially transmissive to visible light, although it can be completely opaque Suitable barrier materials (depicted as, for example, 12 and 13 in Figure 1) include polymeric films, metallized polymeπc films, metallic foils, and laminates compnsing films and foils As stated above, when used on both sides ofthe construction, at least one ofthe layers of bamer matenal is at least partially transmissive to visible light, so that the change in the opacity of the membrane is visible when the cπtical temperature is reached The prefened bamer mateπals are such polymeric films as fluoropolymers, polyolefins such as polyethylene, polyesters halogenated polyolefins such as polyvinyl chloπde, metallized polyesters, and metallic foils such as aluminum Suitable commercially available barπer materials include laminated mateπals One such laminate is a polymeric laminate commercially available under the product designation "MLL-B-22191 , Type 1, Class 2" from Georgia Packaging, Inc of Columbus, GA This material has a WVTR of 0 34 g/m 2 /24 hours and includes a layer of a thermoplastic fluoropolvmer having high moisture barrier properties commerciallv available under the trade designation "ACLAR" from Allied Signal of Momstown, NJ It also includes two layers of low density polyethylene (PE) and a layer of polyethylene terephthalate (PET) Specifically, this material includes a layer of 0 015 mm "ACLAR RX 160" (WVTR = 0 42 g/m 2 /24 hours), a layer of 0 012 mm polyethylene terephthalate (PET), and a layer of 0 064 mm low density polvethylene (LDPE) Between the layer of "ACLAR RX160" and the layer of PET is a layer of 0 017 mm LDPE, which acts as an adhesive to bond these two films together Other suitable polymeric laminates include one formed from a layer of 0 19 mm polyvinyl chloπde (PVC), 0 051 mm PE, 0 015 mm "ACLAR RX 160 " and 0 051 mm PE, which is available under the product designation "VPA 760," and one formed from a layer of 0 19 mm PVC, 0 051 mm LDPE, 0 015 mm "ACLAR RX160," and 0 051 mm LDPE, which is available under the product designation "VPA 790," both of which are available from TekniPlex, Inc of Somerville, NJ Prefened barπer mateπals may be thermoplastic and thus thermoformable Thermoforming is used to produce a desired profile for the barπer mateπal, as depicted, for example, in Figures 2, 3, and 4 Thermoforming is earned out by techniques well known to those in the art Typically, the material is positioned on a heated, shaped platen and pressed or vacuum formed into a desired shape The thermoformable matenal is used in making blister packages For example, such shaped mateπals are particularly useful for protecting gelatin capsules for the pharmaceutical industry Examples of thermoformable materials include polyvinyl chloπdes, polystyrenes, polycarbonates, cellulosics, and the like Prefened thermoformable bamer matenals are laminated "ACLAR" materials, which are commercially available from Tek Plex, Inc of Somerville, NJ One such matenal includes a layer of 0 038 mm "ACLAR 22A" (WVTR = 0 34 g/m 2 /24 hours), a layer of 0 051 mm low densιt polyethylene, and a layer 0 19 mm polyvinyl chloπde Another such matenal includes a layer of 0 023 mm "ACLAR SupRx900" (WVTR = 0 26 g/m 2 /24 hours) and a laver of 0 19 mm polyvmyl chloπde Other laminated mateπals can be made to desired specifications In addition to being thermoformable, these mateπals are heat sealable Other mateπals that can be used as the barπer matenal include metallic foils and other materials that are capable of being cold formed For example, aluminum foil (e g , about 7 5-75 micrometers thick) can be formed into a desired shape and used as the barner material If desired, the metallic foil can be coated with a heat sealabie coating Such coating materials are commercially available Examples include vinylic and acrylic heat seal coatings available under the product designations "4506" and "4514" from Lawson Mardon of Arlington Heights, IL Although barrier materials having WVTR values of less than about 1 g/m 2 /24 hours are prefened, this is not a requirement Materials that are permeable to water vapor and/or environmental gases can be used to form the containment means, however, such materials are not suitable for highly hygroscopic indicating compositions Thus, a wide variety of materials can be used to form the barπer mateπal Examples include a polyester copolymer available under the trade designation "SCOTCHPAK 146" from Minnesota Mining and Manufacturing Company of St Paul, MN as well as other "SCOTCHPAK" stπppable lid films The bamer material may have an image applied thereto, which will be masked when the pores ofthe microporous membrane are not wetted out (l e , when the microporous membrane appears opaque), but will be visible when the pores ofthe microporous membrane are wetted out (thus appearing transparent or translucent) For example, the image can be a printed message on at least one major surface The pnnted layer is typically formed from an appropriate printing ink and/or embossed directly into the mateπal In such embodiments, this layer of barπer mateπal is refened to as a backing (see Figure 2), and the bamer material is opaque Preferably, the bamer material (e g , the backing) is a metallic foil such as aluminum foil Thus, the metallic foil may have paper adhered to one surface to allow placement ofthe text or graphics To prepare the indicating device shown in Figure 1 , a laminate is formed compπsing a first microporous membrane adhered to a first bamer layer It may be adhered with adhesive or by heat sealing about the outer penphery Two pieces of this laminate are then placed m a facing relationship such that the microporous membrane sides face each other and sealed about the outer peπphery This creates a reservoir for the indicating composition Alternatively, the microporous membrane is adhered to a first bamer layer and used with at least one other bamer layer to form a receptacle For example, the membrane is heat sealed to a first transparent bamer layer, and then this construction is heat sealed to a second barrier layer, such as heat sealed aluminum foil The reservoir is formed by the microporous membrane and the second bamer layer The indicating composition contains less than about 10 wt-%> water Preferably, it contains less than about 1 wt-%) water Compositions with less than about 10 wt-% water, and particularly with less than about 1 wt-%, provide indicating devices with good precision and reproducibility For example, they will preferably be reproducibly activated within about ±2°C, and more preferably within about ± I °C, of the desired cπtical temperature, using the test method descnbed in the examples section, which generally involves a cooling rate of 1°C/ 30 minutes Compositions with less than about 10 wt-%> water provide indicating devices with relatively short response times For example, the indicating devices ofthe present invention preferably respond m no greater than about 60 minutes, more preferably, in no greater than about 45 minutes, and most preferably, in no greater than about 30 minutes Furthermore, they make it possible to indicate at temperatures other than 0°C The pnmary organic component includes compounds that do not wet out the microporous membrane under normal use and/or transportation conditions Typically, suitable compounds for use in the pπmary orgamc component do not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the critical temperature Preferred such compounds do not spontaneously wet it out at a temperature at least about 45°C (and more preferably, at least about 60°C) above the critical temperature The wetting component includes compounds that do spontaneously wet out the microporous membrane at about the critical temperature In its initial state (i e , prior to being activated), the indicating composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the critical temperature for which the indicating device is designed It is believed that at or below about the desired critical temperature (i e., the temperature to be avoided), a sufficient amount ofthe primary organic component solidifies, causing the concentration of the wetting component to increase, allowing the remaining liquid portion (i e , the nonsolidified portion) ofthe indicating composition (at least the wetting component) to wet out the pores ofthe microporous membrane by reducing the surface tension ofthe indicating composition When the nonsolidified portion ofthe indicating composition (i e , the wetting component or a mixture ofthe wetting component and other components of the indicating composition) enters the pores ofthe microporous membrane, the membrane becomes at least partially transmissive to visible light If a colorant (i e , a pigment or dye) is present, the color will be apparent when the membrane becomes transparent If a soluble colorant is in the indicating composition, the colorant can be carried into the pores ofthe microporous membrane The microporous membrane then changes from opaque (white) to the color ofthe colorant (e g , dye) When a colorant is used, it is preferably soluble in the indicating composition within the temperature range over which the indicating device is to be used The colorant, typically in the form of a pigment or dye, can penetrate the pores ofthe microporous membrane once the temperature has dropped to about the critical temperature It can also remain in the pores even if the indicating device is exposed to elevated temperatures within normal use and transportation conditions The color imparted to the device by the colorant should be easily seen by the unaided eye Preferably, the colorant is generally safe for human contact, such as a food-grade dye Preferred dyes are commercially available under the product designations "ERIOGLAUCINE" (blue CI 42090), "ERITHROSIN B" (red CI 45430), "TARTRAZINE" (yellow CI 19140), and "FAST GREEN FCF"(green CI 42053) from Aldrich Chemical Co of Milwaukee, WI The colorant is added in an amount sufficient to color the indicating composition and make the color change apparent to the unaided eye when the indicating device has been exposed to the critical temperature Typically, this ranges from about 0 01 wt-% to about 0 5 wt-%, based on the weight ofthe indicating composition It is preferred to use small amounts of colorant because they may affect the freezing point ofthe solution and because they are expensive The primary organic component includes at least one organic compound that does not enter the pores ofthe microporous membrane when in the pure state at least in the absence of a pressure gradient across the membrane at a temperature at least about 30°C above the critical temperature for which the indicating device is designed Prefened such compounds do not spontaneously wet it out at a temperature at least about 45°C (and more preferably, at least about 60°C) above the critical temperature Such compounds have a generally high dipole moment resulting in a generally high surface tension Preferably, the surface tension is greater than about 30 dynes/cm, more preferably, greater than about 35 dynes/cm, and most preferably, greater than about 40 dynes/cm, as measured using ASTM Test Method Dl 331-89, Method A, at 23 °C for materials that are liquid at this temperature For materials that are solids at this temperature, the surface tension is measured at 5°C above the freezing point The surface tension of the primary organic component is greater than the surface energy of the microporous membrane chosen For example, for a microporous membrane made of polypropylene, the surface energy is about 30 dynes/cm Thus, suitable compounds for the primary organic component have a surface tension greater than about 30 dynes/cm when the microporous membrane is polypropylene Preferably, compounds used in the primary organic component have a viscosity greater than about 10 centipoise, more preferably, greater than about 30 centipoise, and most preferably, greater than about 50 centipoise, measured at 23°C for materials that are liquid at this temperature For materials that are solids at this temperature, the viscosity is measured at 5°C above the freezing point (i e , melting point) The freezing point ofthe compounds suitable for use in the primary organic component is above (preferably, at least about 5°C above, more preferably, at least about 10°C above, and most preferably, at least about 15°C above) the desired critical temperature. Generally, the freezing point of such compounds are no more than about 60°C above the desired critical temperature Suitable compounds include polyfunctional alcohols such as 1,3 -propanediol, ethylene glycol, di(ethylene glycol), glycerol, tripropylene glycol, as well as polyethoxylated derivatives of these glycols, and polyethylene glycol Other suitable compounds include very polar esters and amides, for example Preferably, the primary organic component comprises at least one polyfunctional alcohol The modifying component includes at least one compound that has a freezing point below (preferably, at least about 5°C below, more preferably, at least about 10°C below, and most preferably, at least about 15°C below) the desired critical temperature. Generally, the freezing point of such compounds are no more than about 60°C below the desired critical temperature Preferably, such compounds do not spontaneously enter the pores ofthe microporous membrane when in a pure state in the absence of a pressure gradient across the membrane at a temperature at least about 30°C above the critical temperature (although when mixed with the wetting component, the modifying component may contribute to the wet out ofthe membrane) More preferably, compounds suitable for use in the modifying component do not spontaneously wet out the microporous membrane at a temperature at least about 45°C (and most preferably, at least about 60°C) above the critical temperature Preferred compounds suitable for use in the modifying component have a generally high dipole moment resulting in a generally high surface tension. Preferably, the surface tension is greater than about 30 dynes/cm, more preferably, greater than about 35 dynes/cm, and most preferably, greater than about 40 dynes/cm, as measured using ASTM Test Method D1331-89, Method A, at 23°C for materials that are liquid at this temperature For materials that are solids at this temperature, the surface tension is measured at 5°C above the freezing point The surface tension ofthe prefeπed modifying component is greater than the surface energy ofthe microporous membrane chosen. For example, for a microporous membrane made of polypropylene, the surface energy is about 30 dynes/cm. Thus, suitable compounds for the modifying component have a surface tension greater than about 30 dynes/cm when the microporous membrane is polypropylene. Preferably, compounds used in the modifying component have a viscosity greater than about 10 centipoise, more preferably, greater than about 30 centipoise, and most preferably, greater than about 50 centipoise, measured at 23°C for materials that are liquid at this temperature. For materials that are solids at this temperature, the viscosity is measured at 5°C above the freezing point Suitable compounds include polyfunctional alcohols such as 1,3-butanediol, 1,4-butanediol, 2, 3 -butanediol, 1,3- propanediol, triethanol amine, ethylene glycol, di(ethylene glycol), triethylene glycol, propylene glycol, glycerol. tripropylene glycol, as well as polyethoxylated derivatives of these glycols, polyethylene glycol, and block copolymers of ethylene glycol and propylene glycol Other suitable compounds include very polar esters and amides, for example Preferably, the modifying component comprises at least one polyfunctional alcohol The wetting component includes at least one organic compound that is capable of wetting out the pores ofthe microporous membrane when in the pure state at about the critical temperature in the absence of a pressure gradient across the membrane Such compounds have characteristics such as a generally low viscosity and a generally low surface tension Preferably, the viscosity is less than about 50 centipoise, more preferably, iess than about 25 centipoise, and most preferably, less than about 10 centipoise, at 23°C for materials that are liquid at this temperature For materials that are solids at this temperature, the viscosity is measured at 5°C above the freezing point For effective wet out, the surface tension ofthe wetting component is iess than the surface energy ofthe microporous membrane chosen Preferably, the surface tension of compounds used in the wetting component is less than about 30 dynes/cm, more preferably, less than about 27 dynes/cm at 23°C for materials that are liquid at this temperature. For materials that are solids at this temperature, the surface tension is measured at 5°C above the freezing point. Suitable wetting compounds include alcohols, ketones, ethers, halogenated or nonhalogenated alkanes, halogenated or nonhalogenated alkenes, amines, and combinations thereof Preferably, the wetting compounds include propylene glycols having a weight average molecular weight of less than about 2000, (d-C 8 )alcohols (e g , methanol, ethanol, propanol, and butanol), (C -C 8 )ketones (e g , acetone, 2-butanone), (C 2 -C 8 )ethers, (C5-C. 8 )alkanes (e g , heptane), halogenated (C 5 -Cι 8 )alkanes (e g , trichloroethane), (C 5 -Cιg)alkenes, halogenated (C<rCι 8 )alkenes, and (Cι-Cg)amιnes (e g , ethylamine and diethylamme) When selecting the compounds to be used in the primary organic component, the modifying component, and the wetting component, the following parameters are typically considered First, the freezing point ofthe pπmary organic component (whether one pπmary organic compound or a mixture of such compounds is used) should be at a higher temperature than the critical indicating temperature Second, an amount ofthe wetting component (whether one wetting compound or a mixture of such compounds is used) is used to ensure wetting ofthe microporous membrane at about the critical indicating temperature, but not at useful temperatures greater than the cnticai indicating temperature Third, the freezing point ofthe modifying component (whether one modifying compound or a mixture of such compounds is used) should be at a lower temperature than the critical indicating temperature Fourth, an amount of the modifying component (whether one modifying compound or a mixture of such compounds is used) is used to adjust the indicating temperature of the device to the cπtical indicating temperature for the desired application In practice, the order of addition of these components does not matter Typically, at least about 50 wt-% ofthe primary organic component is used in an indicating composition Preferably, at least about 70 wt-% (more preferably, at least about 80 wt-%>) and no greater than about 98 wt-%> ofthe indicating composition is the pnmary organic component Typically, at least about 1 wt-% ofthe wetting component is used in an indicating composition Preferably, at least about 3 wt-% and no greater than about 20 wt-%> (more preferably, no greater than about 15 wt-%>, and most preferably, no greater than about 10 wt-%>) ofthe indicating composition is the wetting component Typically, at least about 1 wt-% ofthe modifying component is used in an indicating composition Preferably, at least about 10 wt-% and no greater than about 40 wt-% (more preferably, no greater than about 30 wt-%) ofthe indicating composition is the modifying component If water is used in the modifying component , no greater than about 10 wt-% of water is used In prefened indicating compositions, there is less than about 1 wt-% water (whether intentionally added or through absorption by hygroscopic components ofthe composition) All weight percents are based on a percentage ofthe weight ofthe total indicating composition The desired ratio of these components depends upon the desired critical temperature Furthermore, the ratio of any three components can be varied to obtain a wide variety of critical temperatures This can be readily determined by a minor amount of experimentation For example, for an indicating device that activates at the critical temperature of -0 5°C, the indicating composition includes about 81 wt-% 1,4- butanediol (pnmary organic component), about 14 wt-% propylene glycol (modifying component), and about 5 wt-% isopropanol (wetting component) For an indicating device that activates at the critical temperature of 3 0°C, the indicating composition includes about 85 wt-% 1,4-butanediol, about 10 wt-% propylene glycol, and about 5 wt-%) isopropanol For an indicating device that activates at the cπtical temperature of -5 0°C, the indicating composition includes about 75 wt-% 1 ,4-butanediol, about 20 wt-%) propylene giycol, and about 5 wt-% isopropanol Other materials (preferably, those which are soluble in the indicating composition) can be added to control the freezing point and/or alter the viscosity of the solution For example, immobilizing agents can be added to control the rate of diffusion and/or build viscosity Immobilizing agents such as thickeners and viscosifiers can be added to increase the viscosity ofthe indicating composition, and even form a gel A gel is desirable because it would be easier to dispense into a pouch ofthe device and it would leak less if there were a failure in the pouch seal Examples of such thickeners and viscosifiers include modified celluloses, starches, proteins, polymers prepared from ethylenically unsaturated monomers such as acrylates, acrylamides, vinyl pyrrolidine, vinyl acetate, acrylonitrile, styrene, and the like, polyurethanes, fumed silicas (such as that available under the trade designations "AEROSIL" from Degussa AG of Frankfort, Germany or "Cab-O-Sil M5" from Cabot Corp of Tuscosa, IL), and clays Other immobilizing agents include immobilizing matnces such as fibrous materials made from woven or nonwoven natural or synthetic matenals, such as Kraft blotter papers (such as that available under the trade designation "VERIGOD" blotting paper available from James River Corp of Richmond, VA), sponges, or flocked porous materials, and polypropylene nonwoven material (such as that available under the trade designation "THINSULATE" from Minnesota Mining and Manufacturing Company of St Paul, MN), air laid web such as paper towels, and nonwoven hydrophilic materials (such as filter paper available from Whatman of Maidstone, England) Nucleating agents can also be added (although it is envisioned that they are not necessary) to prevent super-cooling and improve reproducibility Examples of such nucleating agents include Agl, silica, fumed silica, ground glass, or other materials having a high surface area with a rough topology The indicating devices ofthe present invention are relatively easy to make Generally, the only precaution that needs to be taken is to ensure that the indicating composition does not include any significant amount of water absorbed from the atmosphere Standard handling techniques for this are known to one of skill in the art Once the indicating composition is prepared, it is placed in the desired container, typically via pipette or microsyringe Preferably it is filled in a way which eliminates air bubbles, although this is not a requirement The container is sealed together completely, and the device is ready for use. As discussed above, the container can be in a variety of shapes and sizes, as shown in Figures 1-4 The only requirement is that as the indicating composition and microporous membrane should be in contact prior to activation Thus, the indicating device can include separate compartments to avoid activation during shipping from the point of manufacture to the point of use For example, the indicating composition can be encased in a rupturable container, which is impermeable to the indicating composition A preferred rupturable container is formed of polymeric material, and can be sealed by means of heat or adhesive Prior to using the indicating device, the rupturable container should be broken, typically by hand pressure, so the indicating composition and microporous membrane come in contact. When adhesive is used to bond various components together or to affix the indicating device to a substrate, the adhesives are preferably pressure-sensitive adhesives, such as, for example, silicone-based adhesives, e g., polysiloxanes, acrylic- based adhesives, e g., isooctyl acrylate/acrylic acid copolymers, rubber-based adhesives, e.g., styrene-isoprene-styrene block copolymers, styrene-butadiene-styrene block copolymers, and nitrile rubbers, e.g , acrylonitrile-butadiene, and mixtures of these Pressure-sensitive adhesives are well-known to one of ordinary skill in the art Also useful are foam adhesives and double sided tapes (such as "9579" tape or "409" carpet tape, which are commercially available from Minnesota Mining and Manufacturing Company of St Paul, MN) Also useful are curable adhesives such as epoxies, silicones, cyanoacrylates, and the like Hot melt and curable hot melt adhesives are also suitable It is important when selecting and adhesive to ensure that the composition does not solubilize or soften the adhesive resulting in bond failure The indicating device may be attached to a product via adhesive For example, it can be adhered to the top, bottom or side of a vial, can, jar, carton, or box It can be customized with graphics and have a visible window on either front or back ofthe container to allow for inspection For example, a word, phrase, or graphic could be imprinted in the inner side ofthe indicating device, such as on the microporous membrane, which would be obscured by the opacity of the membrane Upon reaching the critical temperature, the membrane would become transparent (or at least translucent) making the word, phrase, or graphic visible Alternatively, when colorant is incoφorated into the device, there is a change in color in the microporous film which indicates the critical temperature has been reached A word, phrase, or message could be imprinted on the membrane such that it is visible prior to activation Upon activation, if the indicating composition contains a colorant ofthe same color as the printed message, the message would disappear The indicating device is useful when used as an indicator for flash frozen foods (such as poultry), paints, water-based adhesives, dairy products, plants, pharmaceuticals or water-based chemicals It can be used to indicate when the product is exposed to undesirably low temperatures. It is useful as an indicator on food products, for instances where it is important that the temperature remain cold but not so cold that the product freezes, such as fresh poultry or frozen meat It is also useful on pharmaceuticals and medicines, where the temperature should remain about +5°C For example, at 5°C, vaccines are stable for up to one year, if exposed to temperatures of about 0°C, the reliability of the vaccines is questionable Objects and advantages of this invention are further illustrated by the following examples, but the particular mateπals and amounts thereof recited in these examples as well as other conditions and details, should not be construed to unduly limit this invention All materials are commercially available except where stated or otherwise made apparent Examples Determination of Indicating Temperature To test for indicating temperatures, devices of the present invention were prepared and then tested at desired temperatures in a water bath The devices were conditioned by holding for one hour in a desiccator pnor to the test To determine the temperature at which the composition results in penetration ofthe pores of the membrane to render it transparent, a water bath (commercially available as NESLAB RTE- 1 1 1 from Neslab Instruments of Newington, NH) controllable to temperatures + 0 1°C, was used The temperature was set at a desired testing temperature and equilibrated for 30 minutes pnor to testing a sample The samples were placed on clips and completely immersed into the bath They were held for 30 minutes in the bath, and then examined to see if any changes in the transparency of the microporous membrane had occurred If the device had not been activated, the temperature was reduced 1 °C and held for 30 minutes This procedure was repeated until activation occuπed A minimum of three samples were tested and averaged Typically, five samples were used The membrane in the indicating device changes from opaque to transparent at the cπtical temperature, or if a dye is present, the membrane may change color to that of the dye Wet Out Test To determine the utility of the components in the indicating composition, tests were caπied out using microporous membrane available as an "oil-out" polypropylene microporous membrane from Minnesota Mining and Manufacturing Company of St Paul, MN to determine wetting and non-wetting characteristics The tests were carried out at room temperature Test 1 A section of microporous membrane was cut into 2 5 cm squares The membrane was placed on a bench top A 0 33 ml sample ofthe component was deposited via microsyringe onto the membrane If the microporous membrane became transparent in 5-10 minutes, the component was considered to be a wetting component If the membrane did not become transparent in this time interval, the component was considered a primary organic component or a modifying component For components that are solids at room temperature (22-25°C), exactly the same procedure was carried out, except that the component was warmed up until it was liquid and then tested with the liquid and membrane maintained at a temperature just above the freezing point (i e , melting point) Test 2 If the component was observed to wet out the membrane, the component was placed into an indicating device prepared as described in Example 1, below The effect ofthe component was readiiy observed by seeing the changes in the membrane, which was covered by a transparent barπer layer If the microporous membrane became transparent in 5- 10 minutes, the component was considered to be a wetting component If the membrane did not become transparent in this time interval, the component was considered a primary organic component or a modifying component For components which were solids at room temperature (22° - 25°C), exactly the same procedure was carried out, except that the component was warmed up until it was liquid and then deposited into the reservoir in the indicating device, which was also held at this elevated temperature Test 3 If the component passed both Tests 1 and 2 (I e , it wetted out the membrane), it was used as a wetting component in an indicating composition Several suitable indicating solutions are shown in Table 2. Indicating compositions were made up and deposited via microsyringe into the device prepared as described in Example 1 To test the critical temperature ofthe device, it was placed in a freezer at a temperature of -15°C It was checked at 30 minute intervals to see if the indicating de¬ composition had wet out the microporous membrane (thus rendering it transparent), and if it was solid rather than liquid. Example 1 This example illustrates the preparation of a device of this invention wherein a receptacle is formed between two layers of microporous film This construction is similar to that depicted in Figure 1 1) Adhering the microporous membrane to a barrier layer A piece of microporous polypropylene membrane, commercially available as "oil-out" microporous membrane from Minnesota Mining and Manufacturing Company of St Paul, MN, was cut to about 2.5 cm by about 305 cm A piece of barrier layer material, available under the trade designation "MIL SPEC B22191, Type 1, Class 2" from Georgia Packaging Inc of Columbus, GA, which consisted of a layer of 0 015 mm "ACLAR R 160", a layer of 0 018 mm low density polyethylene, a layer of 0 012 mm polyethylene terephthalate, and a layer of 0 064 mm low density polyethylene, was cut to about 2 8 cm by about 33 cm The microporous membrane was placed on the lower jaw of a laboratory heat sealer (commercially available under the trade designation Sentinel Heat Sealer from Sentinel Corp of Hyannis, MA) The bamer film was positioned on top ofthe microporous membrane such that the membrane was about 0 63 cm from the edge of the barrier film The sealer was activated, the settings were 121 1°C ± 2 8°C, 0 28 MPa, 2 seconds dwell time 2) Preparing a pouch The heat sealer was adjusted to a higher temperature, 221 1°C ± 2 8°C, 0.28 MPa, 2 seconds dwell time Two pieces, prepared as described in step 1 , were placed together with the membrane side (depicted as layers 14 and 15 in Figure 1 ) in a face to face relation The barrier layer formed the outside ofthe pouch (depicted as layers 12 and 13 in Figure 1) This was heat sealed to form a strip about 0 63 cm wide, thus forming the base of the pouch This strip was cut into about 3 8 cm by about 3 8 cm squares Two edges of each square were heat sealed together, leaving one edge open The ends of this open section were heat sealed about 0 63 cm in from each edge to yield about a 2 5 cm section along the center section of one edge of each pouch which was not sealed 3) Filling the pouch Using the same heat settings from step 2), the pouch was filled with the desired indicating composition by using about 0 3 cm 1 of desired indicating mixture, care being taken to remove all air bubbles from the pouch The top ofthe pouch was heat sealed, as in step 2) The device was then ready for testing (as described above) or for placement on a container by use of a pressure sensitive adhesive (commercially available under product number 467 from Minnesota Mining and Manufacturing Company of St Paul, MN) 4) Indicating Compositions The following indicating compositions were prepared by combining the compounds in Table 1 in the weight percentages indicated Each ofthe components, some of which are very hygroscopic, was stored in a sealed container with molecular sieve under an atmosphere of nitrogen All compositions were prepared in air and then purged with nitrogen Each of composition included 0 1 gram Euroglaucine dye from Aldrich Chemical Co of Milwaukee, WI 1 ,4-Butanediol (99% pure, 0 35% water), 1,2-propanediol (99%> pure), triethylene glycol (99% pure), and diethylene glycol (99% pure) were obtained from Aldrich Chemical Co of Milwaukee, WI, isopropanol (reagent grade, 99 7% pure) was obtained from EM Science of Gibbstown, NJ, glycerol (99 5%> pure, 0 5%> water) was obtained from Mallinckrodt Baker, Inc of St Louis, MO, ethylene glycol (99 991 ) pure, 0 009%) water) and methyl ethyl ketone (99 7% pure, 0 02% water) was obtained from JT Baker Inc of Phillipsburg, NJ The critical temperature for each is an average of 10 trials The error for each is less than about 1°C Table 1 Critical Temperature -4.8°C -3.2°C -2.0°C 3.4°C 1.6°C -0.4°C 2°C 2°C 4°C 2°C 1 ,4-butanedιol 75 85 80 80 87.5 81 85 90 87 90 (primary component) 1,2-propanedιol 20 6 14 8 (modifying component) isopropanol 5 5 5 5 5 5 5 (wetting component) methanol 5 (wetting component) glycerol 10 (modifying component) triethylene glycol 5 (modifying component) diethylene glycol 7 5 (modifying component) ethylene giycol 10 5 5 (modifying component) methyl ethyl ketone 5 5 (wetting component) Example 2 This example illustrates the preparation of a device as depicted in Figure 2 A barrier material (depicted as 28 in Figure 2) is a laminate of a layer of polyethylene terephthalate (PE), a layer of low density polyethylene (LDPE), a layer of aluminum foil, another layer of low density polyethylene (LDPE), and a layer of 0.064 mm linear low density polyethylene (LLDPE), which is commercially available under the trade designation "BN 48" from Georgia Packaging Inc. of Columbus, GA In this construction, the LLDPE side ofthe laminate faces the inside ofthe device and the PET side is on the outside A second barrier material (depicted as 22 in Figure 2) is a thermoformed laminate of a layer of 0 19 mm polyvinyl chloride (PVC), a layer of 0 051 mm LDPE, a layer of 0 015 mm "ACLAR RxlόO" fluoropolymer, and a layer 0 051 mm LDPE, which is commercially under the trade designation "VPA 760" from Tekni Plex Inc of Somerville, NJ. In this construction, the LDPE side of the laminate faces the inside of the device and the PVC side is on the outside The microporous polypropylene membrane (depicted as 24 in Figure 2) descnbed in Example 1 was cut into a 1 cm diameter disc and heat sealed under the conditions descnbed in Example 1 around the periphery to the bottom ofthe reservoir formed by the second barner material The desired indicating composition was then placed in the reservoir and the first barrier material was heat sealed to the second bamer matenal across the top Example 3 This example demonstrates the effect of a thickener on the indicating composition and the device Three indicating compositions were prepared, each having a different thickener concentration, and the time to wet out the membrane was recorded The indicating composition included 81% 1 4-butanedιol, 14% 1,2- propanediol, and 5% isopropyl alcohol To this was added 0 1 gram of Enoglaucine dye This indicating composition has a cntical indicating temperature of -0 4°C To 100 grams of this dye-containing composition was added 3 75 grams, 2 5 grams, or 1 25 grams, respectively, of fumed silica, which is commercially available under the trade designation "Cab-O-Sil Ml 5" from Cabot Corp Of Tuscosa, IL These mixtures were placed in individual jars purged with nitrogen, sealed, and placed on a shaker overnight to agitate the compositions An indicating device was prepared as described in Example 1 To each of 5 such devices for each concentration of silica, 0 3 ml ofthe thickened indicating composition was added The indicating devices were placed in a constant temperature bath at -2°C The 3 75 wt-% silica sample was activated in 1 hour, the 2 5 wt-% silica sample was activated in 45 minutes, the 1 25 wt-%> silica sample was activated in 30 minutes as did a control sample that contained no silica Example 4 This example illustrates the lower level of wetting component and modifying component needed for activation Indicating devices as described in Example 1 were used Five samples of each composition were tested at -3 °C for 30 minutes Each of the following compositions included 0 1 gram Euroglaucine dye For a composition containing 98%> 1,4-butanediol, 1%> 1,2-propanedιol, and 1%> isopropanol, none ofthe samples were activated For a composition containing 97% 1 ,4-butanediol, 2% 1,2- propanediol, and 1% isopropanol, two ofthe five samples were activated For a composition containing 97% 1,4-butanediol, 1% 1,2-propanediol, and 2% isopropanol, five ofthe five samples were activated For a composition containing 98%) 1,4- butanediol, 1% propylene glycoi, and 1% isopropanol, five of five the samples were activated Thus, indicating compositions containing as little as 1%. wetting component and 1% modifying component can produce effective indicating devices Example 5 This example illustrates that a three component system can provide indicating devices that activate at a wide variety of temperatures over a relatively broad temperature range Indicating devices as described in Example 1 were used Ten samples of each composition were tested Each ofthe following compositions included 0 1 gram Euroglaucine dye Samples were placed in a low temperature bath at a temperature above the cπtical temperature and the temperature was lowered by 1°C increments every 30 minutes The temperature at which each ofthe samples activated was recorded For any one composition, the critical temperature recorded in Table 2, below, was an average of ten samples Table 2 1,4-Butanediol 1,2-Propane Isopropyl Temp. (°C) Standard Glycol Alcohol Deviation 89.0 6 0 5 0 4 5 0 5 87 0 8 0 5 0 4 0 0 0 85 0 10 0 5 0 3 0 0 0 83 0 12 0 5 0 2 0 0 3 81.0 14 0 5 0 -0 4 0 5 80 0 15 0 5 0 -1.1 0 3 79 0 16 0 5 0 -1.8 0 4 75 0 20 0 5 0 -4 8 0 4 Although the invention has been described with respect to specific prefened embodiments, it should be appreciated that other embodiments utilizing the concept of the present invention are possible without departing from the scope ofthe invention The invention, for example, is not intended to be limited to the specific adhesive articles discloses in the preferred embodiments The invention is not intended to be limited to the preferred embodiments described herein, but rather the invention is defined by the claims and equivalents thereof

Claims: CLAIMS: 1 A device for indicating if an object is exposed to a critical temperature, the indicating device compnsing (a) a microporous membrane, (b) an indicating composition containing less than about 10 wt-% water, the composition comprising (0 a major amount of a pnmary organic component compnsing at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the critical temperature, (n) a modifying component compnsing at least one compound that has i freezing point below the critical temperature, and (in) a wetting component comprising at least one compound that has a freezing point below the critical temperature and is capable of spontaneously wettin out the microporous membrane at about the cπtical temperature, and (c) means for containing the microporous membrane and the indicating cΛomIllpj oUsMitUioUnlI, wherein the primary organic component, modifying component, and wetting component are miscible liquids above the cπtical temperature, and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, but does wet it out at about the critical temperature upon solidification of a portion ofthe composition 2 The indicating device of claim 1 wherein the containing means compπses a baπier mateπal that retards the transmission of water vapor into the indicating composition 3 The indicating device of claim 1 which has a response time of no greater than about 60 minutes 4 The indicating device of claim 3 which has a response time of no greater than about 30 minutes. 5 The indicating device of claim 1 which is capable of being activated within about ± 2°C of the critical temperature ofthe object being monitored 6 The indicating device of claim 1 wherein the primary organic component is a mixture of two organic compounds 7 The indicating device of claim 1 wherein the pπmary organic component, modifying component, and wetting component are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 45°C above the critical temperature 8 The indicating device of claim 7 wherein the microporous membrane comprises a material selected from the group consisting of polyolefin, poiysulfone, polytetrafluoroethylene, polyamide, polyester, cellulose derivatives, and combinations thereof 9 The indicating device of claim 8 wherein the microporous membrane comprises a polyolefin. 10 The indicating device of claim 1 wherein the modifying component comprises water in an amount of less than about 1 wt-%> based on the total weight ofthe indicating composition 1 1 The indicating device of claim 1 wherein the indicating composition further includes a colorant 12 The indicating device of claim 1 wherein the primary organic component comprises a polyfunctional alcohol 13 The indicating device of claim 12 wherein the modifying component comprises a polyfunctional alcohol 14 The indicating device of claim 12 wherein the wetting component comprises a (Cι-C 8 )alcohol 15 The indicating device of claim 1 wherein the wetting component has a viscosity of less than about 50 Centipoise at 23 °C 16 The indicating device of claim 1 wherein the wetting component comprises a compound selected from the group consisting of propylene glycol having a weight average molecular of less than about 2000, (Cι-C 8 )alcohol, (C -C 8 )ketone, (C 2 - C 8 )ether, (C 5 -C 18 )alkane, halogenated (C 5 -C. 8 )alkane, (C 5 -C. 8 )alkene, halogenated (C;-Cι 8 )alkene, (C t -C 8 )amιne, and combinations thereof 17 A device for indicating if an object is exposed to a cπtical temperature, the indicating device comprising (a) a microporous membrane, (b) an indicating composition containing less than about 1 wt-% water, the composition comprising (i) at least about 50 wt-% of a primary organic component comprising at least one compound that has a freezing point above the critical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the critical temperature, (ii) no greater than about 40 wt-%> of a modifying component comprising at least one compound that has a freezing point below the critical temperature, and (iii) no greater than about 20 wt-%> of a wetting component comprising at least one compound that has a freezing point below the critical temperature and is capable of spontaneously wetting out the microporous membrane at about the cπtical temperature, and (c) means for containing the microporous membrane and the indicating composition, wherein the pnmary organic component, modifying component, and wetting component are miscible liquids above the critical temperature, and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature, but does spontaneously wet it out at about the critical temperature upon solidification of a portion ofthe composition 18 The indicating device of claim 17 which has a response time of no greater than about 30 minutes 19 The indicating device of claim 18 which is capable of being activated withm about ± 1°C ofthe critical temperature ofthe object being monitored 20 The indicating device of claim 17 wherein the means for containing the microporous membrane and indicating composition compπses a barπer material selected from the group consisting of a fluoropolymer, polyolefin, polyester, halogenated polyolefin, metallized polyester, metallic foil, and combinations thereof 21 The indicating device of claim 17 wherein the means for containing the microporous membrane and indicating composition comprises a thermoformable barπer mateπal 22 The indicating device of claim 17 wherein the indicating composition is contained in a reservoir formed by a nonporous washer 23 The indicating device of claim 17 wherein the pπmary organic component compπses a polyfunctional alcohol 24 The indicating device of claim 23 wherein the primary organic component comprises a compound selected from the group consisting of 1,3 -butanediol, 1,4- butanediol, 2,3-butanediol, 1,3-propanediol, and triethanol amine, ethylene glycol, di(ethylene glycol), glycerol, tripropylene glycol, polyethoxylated derivatives of these glycols, polyethylene glycol, block copolymers of ethylene glycol and propylene glycol, and combinations thereof 25 The indicating device of claim 23 wherein the modifying component comprises a polyfunctional alcohol 26 The indicating device of claim 25 wherein the modifying component comprises a compound selected from the group consisting of 1,3-propanediol, ethylene glycol, di(ethylene glycol), triethylene glycol, propylene glycol, glycerol, tripropylene glycol, polyethoxylated derivatives of these glycols, polyethylene glycol, and combinations thereof 27 The indicating device of claim 17 wherein the wetting component comprises a compound selected from the group consisting of (C C 8 )alcohol, (C -C 8 )ketone, (C?- C 8 )ether, (C 5 -Cι 8 )alkane, halogenated (C 5 -Cι 8 )alkane, (C 5 -Cι 8 )alkene, halogenated (C 5 -Cι 8 )alkene, (Cι-C 8 )amιne, and combinations thereof 28 The indicating device of claim 17 wherein the indicating composition further includes an immobilizing agent 29 A device for indicating if an object is exposed to a cπtical temperature, the indicating device comprising (a) a microporous membrane comprising a polyolefin, (b) an indicating composition containing less than about 1 wt-%> water, the composition comprising (l) at least about 50 wt-% of a pnmary organic component compπsing at least one polyfunctional alcohol that has a freezing point above the cπtical temperature and does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cntical temperature, (n) no greater than about 40 wt-%) of a modifying component compπsing at least one polyfunctional alcohol that has a freezing point below the cπtical temperature, and (in) no greater than about 20 wt-% of a wetting component comprising at least one compound selected from the group consisting of alcohols, ketones, ethers, alkanes, alkenes, amines, and combinations thereof, wherein the compound has a freezing point below the critical temperature and is capable of spontaneously wetting out the microporous membrane at about the critical temperature, and (c) means for containing the microporous membrane and the indicating composition and retarding the transmission of water vapor into the indicating composition, wherein the pnmary organic component, modifying component, and wetting component are miscible liquids above the cπtical temperature and are present in a ratio such that the composition does not spontaneously wet out the microporous membrane at a temperature at least about 30°C above the cπtical temperature but does spontaneously wet it out at about the critical temperature upon solidification of a portion of the composition 30 The indicating device of claim 29 which has a response time of no greater than about 60 minutes and is capable of being activated within about ± 2°C of the cntical temperature ofthe object being monitored

Inventors: BIRKHOLZ RUSSELL D, PEREYRA RODGER J, SCHOLZ MATTHEW T, BIRKHOLZ, RUSSELL, D., PEREYRA, RODGER, J., SCHOLZ, MATTHEW, T.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: G01K11
IPC codes: G01K11