WO2018224000A1

WO2018224000A1 - A system for quality monitoring of temperature sensitive product and method for manufacturing thereof

Info

Publication number: WO2018224000A1
Application number: PCT/CN2018/090232
Authority: WO
Inventors: Noel Peter Bengzon Tan; Cathy Kwan Wing CHEU; Missy Minsi HE; Wei Li; Jonathan Christianto; Yeuk Tin Lau; Xin Shi
Original assignee: Nano And Advanced Materials Institute Limited
Priority date: 2017-06-07
Filing date: 2018-06-07
Publication date: 2018-12-13

Abstract

A time-temperature indicator (TTI) system for temperature sensitive products and methods for manufacturing thereof. In one embodiment, an activatable TTI system is provided, comprising a multilayer assembly made of at least three functional membrane layers comprising a variable-thickness layer, a time-dependent permeability membrane layer and an indicator layer, where said variable-thickness layer has a variable thickness along the surface in contact with incoming air; said time-dependent permeability membrane has pores for ceasing further air flow into the system when it is saturated with water from the incoming air; and said indicator layer contains indicating dye which changes in color shading according to ambient temperature. In another embodiment, a TTI system which is free from activation or preconditioning is provided, comprising an indicator strip, a sealing strip, a reservoir of reactant, and a driver, which are assembled on a substrate attached to or on the products. An indicating dye contained in the indicator strip is reactive to the reactant from the reservoir and the reactant is released according to the ambient temperature change over time, in order to indicate the change in ambient temperature by the change in the indicating dye color.

Description

A SYSTEM FOR QUALITY MONITORING OF TEMPERATURE SENSITIVE PRODUCT AND METHOD FOR MANUFACTURING THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patent application serial number 62/603,637 filed on 7 June 2017, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

The present invention relates to a system that gives and records optically visible color indications of temperature exposure of products. Particularly, the products referred herein are products that are temperature-sensitive in nature such as frozen food products. The present system comprises a time-temperature indicator (TTI) device that creates a response reflecting that of the device’s reaction which provides indirectly the quality of the monitored product. The present invention also relates to a combination comprising said TTI device and the storage or enclosure thereof. A method for manufacturing said system is also provided.

BACKGROUND

The following references described herein are incorporated by reference in their entirety:

[1] Taoukis, P.S., Labuza, T.P. Applicability of time-temperature indicators as shelf-life monitors of food products. 1989 Journal of Food Science 54 (4) , 793-78.

[2] Karel, M., Lund, D.B. Physical principles of Food Preservation, 2 ^nd edition. Marcel Drekker, New York 2003.

[3] Suppakul, P. Chapter 38 Intelligent Packaging. Handbook of Frozen Food Processing and Packaging. Da-Wen Sun. CRC Press 2011. Pages 837-860. DOI: 10.1201/b11204-46.

[4] Deng, Z., Ying, X., Shui, X. Time-temperature indicator and monitoring method for monitoring quality state of thermally sensitive article. US 9618398B2. April 11, 2017.

[5] Spevacek, J.A. Time-temperature integrating indicator. US 6614728B2. September 2, 2003.

[6]Prusik, T., Arnold, R.M., Fields, S.C. Time-temperature indicator device and method of manufacture. US 6042263. March 28, 2000.

[7] Patel, G.N., Preziosi, A.F., Baughman, R.H. Time-temperature history indicators. US 399946. December 28, 1976.

Time-Temperature Indicators (TTIs) are devices used to monitor and record temperature cumulatively. Such devices indirectly indicate the influence of temperature history on food quality and safety during transport and storage. With the use of TTI's, food quality and safety are monitored through recorded temperature, indicating whether products have been exposed above or below a reference or critical temperature. Deviation from a reference temperature creates warning for potential spoilage or denaturation of food commodities.

Food quality and safety go hand in hand as a priority for food manufacturers, and in many monitoring and controlling agencies that transport products straight to consumer tables. A precise definition of a Time-Temperature Indicator was given by Tauukis and Labuza [1] which states that TTIs are simple, cost-effective and user-friendly devices to monitor, record and cumulatively indicate the overall influence of temperature history on the food product quality from the point of manufacture up to the consumer. Control of temperature during transport and storage is an important condition due to its effect on the growth of microorganisms, metabolic activities and other chemical, sensorial and nutritional reactions [2] . While food traceability is now a legal requirement in EU markets [3] , existing TTIs have challenges to fully answer the need to ensure the safety of food products during delivery and storage. These challenges include limited temperature range, limited working time, temperature history recording problems, potential adulteration of the product itself, limited scalability and cost effectiveness. In addition, many commercial TTIs only function as triggers for products that have been exposed to a reference temperature (e.g., critical temperature, etc. ) indicating whether the thermally-sensitive product has failed or deteriorated. There have been patents relating to Time Temperature Indicators, classified as diffusion-based, enzyme-based, polymer-based, bacteria-based and photochromic-based TTIs; however, commercially available TTIs are typically polymer-, enzyme-and diffusion-based types.

For example, a commercial TTI such as 3M MONITOR MARK ^TM is based on diffusion of a dye on a string and the temperature range and response time depends on the type of dyes. This type of TTI works on a single designated temperature ranging from 15℃ to 30℃, with 24 hours to the two-week run-out window. It also needs to be preconditioned at a certain temperature for 2 hours before it is used. A 12-hour monitor of a single temperature can be obtained by TIMESTRIP ^TMPLUS TTI, which needs manual activation by pressing a button. However, this fails to indicate the exact temperature above the threshold temperature. The same function can be performed by Delta Trak WARMMARK ^TM, in which a single designated temperature is monitored for 48 hours. It can be activated by folding up and stripping to activate the TTI. But then again it does not indicate the exact temperature above the threshold temperature. Another polymer-based commercial TTI is the VITSAB ^TM (e.g. Vitsab L5-8 Smart labels) that can monitor temperatures within the standard refrigerator, and freezer ranges with up to 2-6 months of storage temperature depending on the exact temperature to monitor. Single-use commercial TTIs such as ONVU ^TM and TOPCRYO ^TM can also be used for several days for single temperature monitoring. But then they do not offer a record of temperature history.

A newly-patented TTI created by Deng et al. [4] uses a volatile dye attached to an adsorbing material and sealed in one package. The volatile dye absorbs heat and volatilizes. The evaporated dye is absorbed by the adsorbing material while the original dye lightens its color. The volatilization was created as a product of heat absorption. Thus, volatilization amount in the dye is proportional to the thermal history of the monitored product. Another related patent in this field of TTI is from Spevacek [5] , wherein an amorphous viscous material is exposed to a pre-determined temperature migrating into a porous matrix. Such action monitors the cumulative time-temperature exposure of a monitored product for a short period at a certain temperature. In 2000, Prusik et al. [6] invented a composite label or TTI device that uses a wicking strip containing a heat-fusible substance. The heat-fusible strip melts and flows through the wicking strip when exposed above a pre-determined temperature. Patel et al. [7] were able to use temperature-sensitive acetylenic compounds (e.g., comprising 2, 4-hexadiyne-1, 6-diol-bisphenylurethane with p-dioxane) that can achieve color changes at different temperatures at different time intervals.

With those above-mentioned commercialized and patented TTIs, there are still areas to improve especially on the broad temperature range application of TTI and cost-effective use of materials.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides at least two configurations of TTI systems. The first configuration is a TTI system which is a fluid-free system (e.g., enzyme-free, bacteria-free, etc. ) because fluids can adulterate or contaminate the products attached thereto or thereon. The first configuration of the present system comprises layers of polymeric membranes for different compositions and functions. In the first configuration, there are at least three types of functional layers of polymeric membranes comprising a variable-thickness layer, a time-dependent permeability membrane layer and an indicator layer. Said variable-thickness layer communicates with the time-dependent permeability membrane layer and is configured to selectively permit delivery of a reactant to the time-dependent permeability membrane layer. In one embodiment, the reactant is oxygen. To serves as an air-flow controller, the variable-thickness layer has variable thickness on a surface distal to the time-dependent permeability membrane layer such that there is a thickness difference between a thickness in a first portion and a thickness in a second portion on said surface of the variable-thickness layer, and etc., in order to control the rate of oxygen flowing through the time-dependent permeability membrane layer and reaching the indicator layer. Said time-dependent permeability membrane layer is a porous layer having pores that are configured to close upon absorption of water and communicates with the indicator layer such that the oxygen ceases to reach the indicator layer when substantially all the pores in the time-dependent permeability membrane react with the water from the incoming air. Said indicator layer contains an indicating material which is reactive to the reactant flowing through the time-dependent permeability membrane. In one embodiment, said indicating material is a dye. After certain amount of oxygen reaching the indicator layer, the dye gives different grades of shading of a color which indicates different temperatures to which the products so attached are exposed. The different grades of shading of the color in the indicator layer is due to the oxidation reaction between the dye and the oxygen flowing therethrough, and the oxidation rate is dependent on the temperature change of the environment where the attached products are exposed. The dye in said dye/polymer matrix layer is only exposed to air when the present system, which is initially under vacuum, is opened. The grade of shading of the color given by the dye in the indicator layer is then compared with a reference color in order to indicate the temperature of the environment where the attached products are exposed. In another embodiment, the first configuration of the present system further comprises at least three other membrane layers including a substrate and/or protection layers of the at least three functional layers described herein.

A method for manufacturing the first configuration of the present system is also provided, comprising syntheses of the at least three functional layers, i.e., said variable-thickness membrane, time-dependent permeability membrane, and indicator layers, layer-by-layer preparation of the multilayer membrane assembly of the present system, sealing of the multilayer membrane assembly, and packaging the sealed multilayer membrane assembly with the products attached thereto or thereon. A reference color indicator for comparison with the change in color shading from the dye/polymer matrix layer can also be included in the package of the present system.

A second configuration of the present invention is a TTI system comprising an indicator strip including an indicating material that changes its indicating property upon exposure to a reactant, an exposure amount of the reactant being directly related to an ambient temperature to which the time-temperature recorder is subjected; a sealing strip for sealing the indicator strip following exposure to the reactant; a reservoir of the reactant; and a driver to transport the indicator strip past the reservoir of reactant for exposure to the reactant and to transport the indicator strip into contact with the sealing strip such that an indicating material property change is preserved by the sealing strip and that no further reactant contacts the indicator strip. In one embodiment, said indicating material is a dye. The reactant can be a liquid having a variation in vapor pressure within the range of operating temperature. Said indicator strip is an adhesive sealing strip. Said indicator strip and sealing strip are each formed into rolls. The second configuration of the present system further comprises drive rollers connected to the driver to transport the indicator strip past the reactant reservoir. The second configuration of the present system additionally comprises a take-up roller to receive a sealed indicator strip. Said indicator strip is pH-sensitive which reacts with the reactant from the reactant reservoir such that the color of the dye in the indicator strip is changed due to the pH change. The release rate of the reactant from the reservoir is proportional to the change in ambient temperature to which the products attached thereto or thereon are exposed. The take-up roller serves to receive the indicator strip which is sealed such that the color change due to the acid or base released from the reservoir can be preserved for a sufficiently longer time during the whole monitoring process. Since the length of indicator strip, and the rotational speed of the drive rollers and take-up roller are adjustable, it is able to record for an arbitrary length of time, e.g., within 30 days, and has a shelf-life of at least two years. In addition, the present system is easy-to-handle, for no activation or preconditioning is required before use. The mechanical parts therein could be reusable; the indicator strip is replaceable; and the acid or base in the reservoir is refillable when needed, which provides a more cost-effective way for temperature monitoring.

The present invention further provides a method for manufacturing the system in the second configuration. Said method comprises preparing the indicator strip and assembling said sealing strip, reservoir, and driver onto a substrate to form an assembly. In one embodiment, the assembly may also include a layer under the substrate to absorb or the substrate may be filled with a chemical to react with any excessive reactant from said reservoir.

Both the first and second configurations of the present system can work at a wide temperature range. In one embodiment, the working temperature ranges from about -15℃ to about 50℃.

The present invention will be described in more detail as to how each of the components in each of the configurations is synthesized or prepared and how each of the configurations is used in monitoring, recording and indicating quality of the products that the present system is attached thereto or thereon.

This Summary is intended to provide an overview of the present invention and is not intended to provide an exclusive or exhaustive explanation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described in more detail hereinafter with reference to the drawings, in which:

Figure 1 is a schematic diagram showing the major functional components of the multilayered structure of the first embodiment (first configuration) and the direction on the flow of oxygen indicated by solid arrows, which is sourced from the incoming air.

Figure 2 demonstrates the arrangement of the multilayered structure of the first embodiment (first configuration) including other layers additional to the three major functional layers.

Figure 3 is a picture showing the internal part of the first embodiment (first configuration) and the packaging template with individual pockets fitting each multilayer component.

Figure 4 is the design of the seven successive-day configuration of the first embodiment (first configuration) with a dimension of 18.5 cm x 4.5 cm.

Figure 5 shows correlation between time and temperature of the first embodiment (first configuration) in (a) 6 successive-day period and (b) 30 successive-day period.

Figure 6 is a product layout of the first embodiment (first configuration) with specific dimensions for 7-successive day (upper panel) and 30-successive day (lower panel) configurations, respectively.

Figure 7 is a series of pictures and SEM image showing how the surface membrane is synthesized in the first embodiment (first configuration) : (a) PVDF-HFP solution cast on a glass substrate above the film applicator; (b) film applicator is used to spread the PVDF-HFP solution throughout the glass substrate surface to create a membrane; (c) pore-making roller used to make pores in the surface membrane; (d) an SEM image showing the pores produced on the surface membrane using the pore-making roller device as shown in (c) .

Figure 8 is a series of picture and SEM images showing the morphology and porosity of the synthesized protection membrane in the first embodiment (first configuration) : (a) bright-field image of the Na-alginate/PVA protection membrane; (b) SEM image of protection membrane at x2,000 magnification; (c) SEM image of protection membrane at x6, 500 magnification; (d) another SEM image of protection membrane at x6, 500 magnification.

Figure 9 is a schematic diagram illustrating a method of producing the protection membrane (i.e., Na-Alginate membrane) in the first embodiment (first configuration) , which includes cross-linking and salt-leaching processes.

Figure 10 is a demonstration of the closing of pores on the protection membrane in the first embodiment (first configuration) (a) before and (b) after adding PVP molecules and exposed for 24 hours: bright-field images and their corresponding SEM images are shown on left and right panels, respectively.

Figure 11 is a schematic diagram illustrating how the dye/polymer membrane in the first embodiment (first configuration) is synthesized.

Figure 12 is a table showing the visible change in color grading (upper panel) and change in color code standard in terms of L, a, and b parameters (lower panel) of the first embodiment (first configuration) over different exposed temperatures.

Figure 13 is a standardized color reference card designed for visual color grade matching for use in the first embodiment (first configuration) .

Figure 14 is a graph showing the air permeability in a protection membrane over time according to the first embodiment (first configuration) of the present invention.

Figure 15 is a schematic diagram of the second embodiment (second configuration) from (a) top and side views and (b) perspective view: A: transparent adhesive tape with tailor-made pH paper; B: transparent sealing tape; C: cylinder, driven by battery device; D: turning wheels; E: container filling with ammonia solution; F: substrate filled with boric acid or salicylic acid, to absorb excess ammonia.

Figure 16 is a 24-hour design of the second embodiment (second configuration) with a time-temperature graph correlation.

Figure 17 is an illustration of preparation method of the tailor-made pH paper roll in the second embodiment (second configuration) .

Figure 18 is the standardized color card used in color grade matching for the second embodiment (second configuration) .

Figure 19 is an illustration of gas permeability results of transparent adhesive tape and the white adhesive tape in the second embodiment (second configuration) .

DETAILED DESCRIPTION OF THE INVENTION

The present invention is not to be limited in scope by any of the following descriptions. The following examples or embodiments are presented for exemplification only.

References in the specification to “one embodiment” , “an embodiment” , “an example embodiment” , etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a concentration range of “about 0.1%to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt. %to about 5 wt. %, but also the individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1%to 0.5%, 1.1%to 2.2%, and 3.3%to 4.4%) within the indicated range.

In this document, the terms “a” or “an” are used to include one or more than one and the term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In the methods of preparation described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E, and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated.

Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

Definitions

The singular forms “a, ” , “an” and “the” can include plural referents unless the context clearly dictates otherwise.

The term "about" can allow for a degree of variability in a value or range, for example, within 10%, or within 5%of a stated value or of a stated limit of a range.

The term "independently selected from" refers to referenced groups being the same, different, or a mixture thereof, unless the context clearly indicates otherwise. Thus, under this definition, the phrase "X1, X2, and X3 are independently selected from noble gases" would include the scenario where, for example, X1, X2, and X3 are all the same, where X1, X2, and X3 are all different, where X1 and X2 are the same but X3 is different, and other analogous permutations.

Description

Embodiment 1: First Configuration

For the first configuration, the new TTI device system includes at least three components. These include a variable-thickness surface layer, a time-dependent permeability membrane layer ( “protection membrane” ) and indicator layer ( “dye/polymer membrane” ) . The development of each component includes material selection and optimization of its synthetic routes. Second is the examination of each layer regarding its corresponding intended functions. The third is the integration of the components into one system forming the device and modifying them by inserting other optional components or membranes for a packaged TTI.

An illustrative example of how these three components are arranged in the first configuration is shown in Figure 1. In Figure 1, the variable-thickness surface membrane has a thickness gradient from the cross-sectional view of the multilayered structure that increases from one end to the other, such that the thickness gradient is proportional to the flow rate of oxygen from the incoming air over time when the device is exposed to the air. In other words, the degree and gradient of thickness of the surface membrane are variable according to the desired duration of monitoring of the oxygen flow, the oxygen flow rate, and/or the cumulative volume of the oxygen flow over time of monitoring. The surface membrane in the first configuration can therefore be virtually partitioned in terms of the successive day of monitoring due to the feature of the thickness gradient on said surface membrane which is proportional to the oxygen flow rate.

Surface membrane materials can be selected from poly (methyl methacrylate) PMMA, poly (vinyl pyrrolidone) PVP, poly (vinyl alcohol) PVA, poly (vinylidene fluoride) PVDF and poly (vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP. Each of these polymeric materials has unique properties and advantages. Among these choices, PVDF-HFP is chosen in some examples because of its ideal properties for a surface membrane (i.e., film forming, transparent, porous, moisture resistant, and chemical resistant) . In those examples, three types of synthetic routes are performed in the synthesis of PVDF-HFP film as surface membrane, including phase inversion method, salt leaching method and casting through the use of the film applicator. Example 1 will describe the casting method accompanied by Figures 7a and b.

Under the surface membrane, the time-dependent permeability membrane is positioned. In one embodiment, this protection membrane may include pores is positioned above the indicator layer which may comprise a dye/polymer matrix membrane having a dye indicator detecting the presence of oxygen. The protection membrane is polymeric network with pores to allow certain volume of oxygen to pass through until all pores substantially react with water coming from the air flowing therethrough. At that point, the porous network is “closed” and no more air can flow through the protection membrane to reach the dye/polymer matrix membrane. Thus, once the time-dependent permeability membrane is “closed” the indicator layer beneath that portion of the membrane will no longer react with oxygen. In this manner, only a limited period of time will be recorded such as successive 24-hour periods along the length of the TTI.

Thus, in operation, the variable-thickness layer controls the exposure of the time-dependent permeability membrane to air. That is, the thickness is selected so that successive sections of the variable-thickness layer permit air to penetrate to the time-dependent permeability membrane for successive periods of time such as successive 24-hour periods. When the time-dependent permeability membrane makes contact with air, it gradually closes during its 24-hour period of exposure as moisture closes the pores. As a result, the indicator layer below each section of the time-dependent permeability membrane only records the temperature (based on the amount of exposure to air which is directly proportional to the air temperature) for a single time period (such as a 24-hour time period or any other period of time selected based on thicknesses and porosity levels) . In this manner, successive time periods of exposure accurately depict the color change for each period.

Protection membrane materials can be selected from several material sources such as polyurethane PU, poly (acrylonitrile) PAN, poly (vinyl alcohol) PVA, poly (methyl methacrylate) PMMA, Sodium-alginate or Na-Alginate, Polyurethane/PVDF, and poly (vinylpyrrolidone) PVP. Each of these polymeric materials has unique properties and advantages. Criteria for the protection membrane include porosity and ability to crosslink. The ability to crosslink is responsible for the “closing mechanism” of the protection membrane. Such a mechanism is important to ensure locking of the protection membrane’s pores and thus to prevent entry of oxygen towards the indicator layer (dye/polymer membrane) . Among these choices, sodium alginate with PVA or Na-Alginate as referred hereinafter is chosen in some examples because of their ideal properties for a protection membrane. Example 2 will describe the synthesis of sodium alginate by a wet chemical method accompanied by Figure 9. In those examples, a hygroscopic material is used to assist in closure of the protection membrane film. More specifically, poly (vinylpyrrolidone) or PVP is used as an agent to close the film once exposed to water vapor. PVP is known to be used as a binder in many pharmaceutical tablets. An example of adding PVP into Na-alginate composite film is illustrated in Figure 10, which is a direct method of applying PVP powder on the surface of the ready-made Na-alginate film. In that example, PVP white powder (around 1 g) was spread on top of the dried sodium alginate film in 16 mL/12”diameter on a petri dish (Figure 10a) and left for PVP to react with water vapor at ambient temperature. To further give evidence on the closing of the protection membrane, a permeability study on the protection membrane is also performed. This test attests to the closing of the protection membrane as permeability of air on the membrane decreases significantly over 24 hours. Thus, it is demonstrated that the protection membrane can fully close its pores after 24 hours (Figure 10b) . Example 3 displays this behavior of the protection membrane with air permeability.

Other material for the protection membrane include poly (vinyldifluoride) -polyurethane or referred here as PVDF-PU. Synthetic routes of making this type of protection membrane include catalytic and non-catalytic route of PU, salt leaching method of PU, etc. However, irregular-shaped pores are produced in the preceeding methods while the films are too soft and easily torn apart. Thus, these cannot be used practically as protection membranes. In contrast, electrospinning methods may be used in the synthesis of the PU in DMF, Toluene, THF-DMF , PAN in DMF, and PMMA in DMF as protection membranes.

Electrospinning uses a voltage difference between a polymer solution and a substrate to produce a nanofiber, resulting in a porous film structure. It can produce a porous and transparent film. This method uses variables in solution, process and ambient properites of electrospinning. However, based on the results, such method can have limitations on some parameters such as distance to substrate and voltage usage.

Indicator layer that include dye/polymer membrane materials can be selected from different composites of inorganic materals with different polymers as matrices. Characteristics of this membrane include high stability and good film-forming attributes. The dyes include cadmium sulfide (CdS) , copper (II) oxide (Cu ₂O) , catechol, ferrous sulfate, methylene blue/riboflavin. Polymer matrices used are epoxy, PVA, and chitosan. Among the dyes, methylene blue was selected as the dye and PVA as the polymer matrix; in other embodiments, glycerol was included in the mixture (Figure 11) .

The dye, methylene blue, from its reduced state (i.e., Leuco Methylene blue, colorless) gives off different shades or tones of blue from light to dark upon exposure to oxygen from the air. The oxidation reaction is depicted below. To reduce the original methylene blue from blue to colorless, LED light was used to expose the dye/polymer composite before oxidation.

The relationship between time and temperature based on different types of TTI (i.e. 6 or 30 successive days) can be further explained. For example, using a 6-day TTI (Figure 5a) , its correlation of time to temperature can be summarized as:

Day 0 –Day 1: The refrigerated food was shipped from the factory to the supermarket by a refrigerated truck, which equipped a cooling chamber of -10 ℃.

Day 1 –Day 3: When truck arrived, the refrigerated food was moved into the cool house below -15℃ for storage.

Day 3 –Day 5.5: The refrigerated food was placed in the refrigerated counter of 0 ℃ for sale.

Day 5.5 –Day 6: A customer bought this refrigerated food and stored it in the refrigerator of -5 ℃.

For a 30-day TTI (Figure 5b) , its correlation of time to temperature can be summarized as:

Day 0 –Day 4: The frozen good was stored under the temperature of -10 ℃ in the warehouse of the plant.

Day 4 –Day 11: The frozen good was transported to neighboring county by a refrigerated truck. Because the cooling system was out of control, the frozen good was exposed to 30 ℃.

Day 11–Day 16: When the driver was trying to fix the cooling system, the temperature dropped to -10 ℃ gradually.

Day 16 –Day 30: Once the cooling system was fixed, the transportation continued with the frozen good kept under -5℃ on the truck. Finally, the frozen good arrived at the destination on Day 30.

Color standardization of the dye/polymer membrane was obtained by first activating the TTI with the light emitting diode (LED) light. When the color of the TTI changes to colorless, the TTI is ready to use. Carefully rip open the package and expose the TTI to air at a specified temperature (i.e., -15 ℃, -10 ℃, 0 ℃, 3.1 ℃, 22 ℃, 30 ℃, 40 ℃ &50 ℃) . After 24 hours later, the final color of TTI was converted by the use of a spectrophotometer (CM-2500d, KONICA MINOLTA) into color code (based on L*a*b*color system) . After summarizing the test results, the color card (Figure 12) , which shows the final color of TTI at different temperatures, is prepared. Comparing the colors of used TTI with the color card, the user can tell the temperature history of a monitored product through the TTI.

After material selection and process optimization were fixed, integration process was developed. Integration process includes: 1) Plasma treatment of the surface membrane on both sides at appropriate settings (i.e. medium for 10 minutes) ; 2) Cut all the three major component membranes and other polymeric membranes (i.e., with appropriate sizes based on the design, See Figure 6) . Other membranes include an adhesive substrate, porous polypropylene, and porous low density poly (ethylene) . Integrate all six layers carefully based on Figure 2; 3) Separately make the packaging template cover with the stripping mechanism at the back part of the TTI device; 4) Vacuum seal the integrated multi-layers with the LDPE cover in the oxygen-free chamber; 5) Check for leaks, quality, and integrity of the vacuum sealed TTI configuration.

Figure 3 depicts the multilayered structure when it is inserted into each pocket of the packaging template, subject to vacuum and sealed. The outside packaging or the template of the TTI can be a tailor-made or any commercially available composite such as poly (ethylene) -polyamide (nylon) (PE-PA) . This type of package has two faces. One is a front face and the other with a pulling mechanism face is at the back. The front face comes in direct contact with the substrate side of the as-prepared multilayered structure while the other side comes in contact with the surface membrane.

Figure 4 shows a seven successive multilayer-component which is designed in an 18.5 cm by 4.5 cm dimension. This device is first activated by the use of LED light. Activation means to make ready the product before its utilization. Activation by LED light transforms the blue dye in the dye/polymer membrane to colorless. This color change is a result of the reduction of methylene blue, which is blue in color to leuco methylene blue, which is colorless. In another example of this TTI device is a 6 successive-day and 30 successive-day designed with multilayer-component as seen in Figure 5a and b respectively. This has the same mechanism as the previous 7-day, wherein activation by LED light is performed prior to its use. A detailed product layout of the TTI device is given in Figure 6.

Figure 7 shows how the porous surface membrane made of PVDF-HFP is synthesized, which is through a solution preparation of 20%PVDF-HFP, casting on a glass plate, and drying on a film applicator. PET, on the other hand, was made from the commercially available source of a series of thickness. Pores of the surface membrane were created by the use of a pore-making roller. Other surface membranes that are appropriate for the same function of this TTI device include poly (methylmethacrylate) PMMA, poly (vinyl pyrrolidone) PVP, and poly (vinyl alcohol) PVA.

Figure 8 shows how the porous protection membrane or composite made of sodium alginic acid salt (Na-Alginate) , poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) is synthesized. Other protection membrane materials that are appropriate for the same function of this TTI device include polyurethane (PU) , polyacrylonitrile (PAN) , poly (vinyl alcohol) (PVA) , poly (methylmethcrylater) (PMMA) , Polyurethane/PVDF, and poly (vinylpyrrolidone) (PVP) . In Figure 8, the protection membrane was prepared by the salt-leaching process from a 2%Na-Alginate/5%PVA (by weight) solution in water with 0.3M of Calcium chloride as the cross-linker. The prepared solution was first dried in an oven at 70℃ for 2.5 hours and cooled to ambient temperature, immerse in 0.3M Calcium chloride solution, wash with distilled water, and dry with nitrogen gas (Figure 9) . PVP powder was scattered on the surface of the as-prepared protection membrane. The closing of the protection membrane layer is achieved through the moisture sensitive PVP on top of the Na-Alginate membrane. Such closing of the protection membrane is evident after a 24-hour exposure PVP on the surface of the Na-Alginate protection membrane with air (Figure 10) .

The dye/polymer matrix membrane layer is composed of poly (vinyl alcohol) (PVA) , glycerol and Methylene Blue. It was prepared by first preparing a mixture of 10 w. t. %PVA (99+%hydrolysed) solution, 5%w. t. %glycerol solution and 0.0276M Methylene Blue solution. The mixture was cast on a petri dish (17cm x 7cm x 1cm) and dried (Figure 11) . The dye/polymer membrane shows different shades of color blue (i.e., from light to dark) depending on its environment temperature. The showing of color in the dye/polymer membrane is a product of the oxidation reaction of the leuco methylene blue, which is colorless to methylene blue. The dye/polymer tested at different temperature shows different shades of blue and thus standardized to be used as a guide for color-temperature correlation (Figure 12) .

To facilitate the correlation of the TTI color tones to temperature, a standard color card was established for this purpose. Color standardization of the dye/polymer membrane was further discussed in the description of the invention. An example of the standardized color card is shown in Figure 13.

The first configuration has a shelf-life of two years. The “shelf-life” described herein means that this TTI product can be used for at least two years after it was vacuum sealed. After two years, the TTI is still functional and aesthetically preserved. The shelf-life test was carried out in a simulated environmental chamber with a cyclic process of changing temperature and humidity. Example 6 will illustrate the result of the test in more detail.

Embodiment 2: Second Configuration

Another aspect of a TTI system is depicted in Figure 15. The TTI includes an indicator strip including an indicating material that changes its indicating property upon exposure to a reactant, an exposure amount of the reactant being directly related to an ambient temperature to which the time-temperature recorder is subjected. A sealing strip seals the indicator strip following exposure to the reactant. A reservoir of the reactant is provided. A driver transports the indicator strip past the reservoir of reactant for exposure to the reactant and to transport the indicator strip into contact with the sealing strip such that an indicating material property change is preserved by the sealing strip and that no further reactant contacts the indicator strip.

For the second configuration, the new TTI device system comes in three phases. First is the preparation of the tailor-made indicator layer, such as a pH paper. Second is the integration of major components into one system. The third is the examination of whole device regarding its corresponding intended function.

Figure 15 shows an example of the second configuration, which includes a reservoir E with acid /alkali, two rolls of adhesive strips A and B, one of them accompanying the tailor-made pH paper, and electrical/mechanical drive components.

The pH indicators used in the preparation of pH paper were chosen from litmus, Congo red, phenol red, thymol blue, cobalt chloride, methyl red, bromothymol blue and phenolphthalein. Among the choices, a combination of thymol blue, methyl red, bromothymol blue and phenolphthalein was selected based on the ideal properties for the pH paper used in TTI (i.e., the color change when exposed to an alkaline, such as ammonia, pH value range, discoloration after use) . Staining method was performed in the synthesis of the acidified pH paper and Example 4 describes the steps of preparation. (Figure 17) .

The tailor-made pH paper may be a combination of acidified pH paper and a transparent adhesive substrate. The transparent adhesive substrate may be selected from any commercially available polymers, including biaxially-oriented polypropylene, a variant of polypropylene (PP) , with adhesive thereon. This transparent adhesive substrate, which has low gas permeability, serves not only as the adhesive substrate of pH paper, it also protects the pH paper from the external influence such as humidity, acidic or basic gases. The acidified pH paper is prepared by the staining process. First of all, phenolphthalein, bromothymol blue and thymol blue dissolved in ethanol is mixed with a methyl red solution. A white paper strip in any required length is immersed into the resulting solution. The stained paper is spread on a petri dish and allowed to air dry. The dried strip is acidified with a H ₃PO ₄ solution and allowed to air dry again. The pH paper strip is affixed to an adhesive substrate (Figure 17) . For storage, the pH paper roll/adhesive substrate may be be sealed into an aluminum foil bag for storage. The pH paper roll is installed into the TTI device of Figure 15 before its utilization.

The desired functions of transparent adhesive polymer are used as an adhesive substrate of pH paper and for protecting the pH paper from the external influence such as humidity, acidic or basic gases. Therefore, gas permeability is the measuring parameter. Two commercial adhesive materials were tested using a gas permeability machine. According to the test result illustrated in Example 5, the transparent adhesive substrate having a relatively low gas permeability was selected.

The electrical/mechanical components in the second configuration include a gear motor (speed reduction motor) to drive a cylinder C as shown in Figure 15a. This gear motor has an operating voltage of 12V. The gear motor was fixed under the cylinder C. The two rolls of adhesive materials A and B were mounted on bearings.

The integration process includes: 1) fixing the gear motor under the cylinder C. 2) two rolls of adhesive material A and B are mounted on bearings. 3) place a reactant reservoir outlet in the middle of the two adhesive rolls. The reactant reservoir outlet in the form of a thin tube was used to deliver a reactant, ammonia from reservoir E to react with the pH paper on adhesive material A. The reactant reservoir E may be filled with 28%ammonia solution and checked for any potential leakage before use. The entire device may be powered by a 12V battery (optionally, a power supply for converting alternating current from a building supply to direct current may be employed) . As shown in Figure 15b, the dimension of the second configuration can be 20cm (W) × 20cm (D) × 95cm (H) . After all the components are integrated, the TTI may be sealed in an aluminum foil bag (not shown in Figure 15) , to protect the device from ambient conditions, including basic gases and humidity.

In practice, the assembled TTI may be placed on the top of or near the monitored product. Switching on the motor begins the temperature monitoring. The reservoir E is exposed to ambient temperature, and according to the change in ambient temperature, the ammonia inside the container will pass through the thin tube and react with the pH paper. Since higher temperatures will accelerate the evaporation of ammonia, a greater amount of ammonia reacts with the pH paper, resulting in color change to yellow or even green. Thus the color change of the pH paper is directly proportional to the ambient temperature. The result of color change will be sealed with the lamination by adhesive material. According to the rotation speed of the device, and the color change result, the temperature history will be recorded. The temperature for a given time period may be determined by comparing the color of the pH paper to the provided color card (which correlate color and ambient temperature) .

In order to meet various requirements in different cold chain systems, the second configuration has flexible monitoring time periods, from several minutes to 30 days. According to the specific monitoring time, the pH paper roll of corresponding length is assembled into the TTI device. Moreover, the resolution of TTI is determined by rotational speed of the cylinder C. The faster the cylinder rotates, the longer the time period each segment of pH paper represents. The actual color change is compared with a standardized color reference card as shown in Figure 18.

After all the components are assembled, examination of whole device regarding its corresponding intended function is conducted. Color standardization of the tailor-made pH paper was obtained by exposing the TTI to different specified temperatures (i.e., -15 ℃, 5 ℃, 25 ℃, 50 ℃) . The color change of the pH paper was recorded by a camera. After summarizing the test results, the color card (Figure 18) was prepared. By comparing the colors of exposed pH paper with the color card, the user can tell the temperature history of the monitored product.

The relationship between time and temperature based on the color changing of TTI may be further explained. For example, using a 24-hour TTI (Figure 16) , its correlation of time to temperature can be summarized as:

0 hr. –3 hr.: The frozen good was stored under the temperature of -15 ℃ in the warehouse.

3 hr. –4hr.: Because the cooling system was out of control, temperature rose to 30 ℃.

4 hr. –5.5 hr.: When the worker noticed the abnormal situation, he reset the system and set the temperature as -15℃, thus the temperature dropped to -15 ℃ gradually.

8.5 hr. –12 hr.: The temperature rose to 25 ℃, when the worker kept the door open and moved other products into the warehouse .

12 hr. –13.5 hr.: After the worker finished the job and locked the door, the temperature went back to -15℃.

13.5 hr. –24 hr.: The temperature remained consistent at -15℃ during this time period.

The shelf-life test was conducted in an accelerated humidity and temperature KOMEG environmental chamber. Humidity and temperature cycles are summarized in Example 6. Tested samples were taken out from the environmental chamber for observation after two weeks. Samples that survived aesthetically and functionally are determined to be usable up to two years from manufacture.

The following examples which may be accompanied with drawings will illustrate the present invention in more detail. The present invention is not limited to the examples given herein.

Example 1

For the first configuration, casting by Film applicator method for PVDF-HFP surface membrane is depicted in Figure 7a and b.

Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) (20 g) was dissolved in N, N-dimethylformamide (DMF) (180 g) at 50℃ to give a 20%PVDF-HFP solution. PVDF-HFP solution in DMF (20 mL) was added on a glass plate (190 mm x 190 mm x 2 mm) and spread on the glass plate evenly by an adjustable film applicator with the height of the gap of 3.5 mm.The glass plate with the spread PVDF-HFP solution was dried at 70℃ for 3 hours on a tilted platform with an angle of 0.4°. Pores of the surface membrane were made by a pore making roller.

Example 2

For the first configuration, a mixture of 5%wt. of Na-alginate/PVA (40/60) was prepared in D. I. water by mixing 4 g of Na-alginate granules and 6 g PVA powder in a beaker. The mixture was then diluted to 200 mL D.I. water, stirred thoroughly and then heated at 60℃ until totally dissolved. An appropriate volume of the liquid mixture was cast on a 12 cm diameter glass petri dish and further heated at 70℃ for 2.5 hours, and then cooled to room temperature until a dried film is formed. The dried film was immersed on the petri dish with calcium chloride solution (0.3M) for at least 20 minutes. The film was then peeled off from the glass petri dish and washed with deionized water. The film was rinsed and immersed with deionized water alternately every two hours for several hours. Excess water was removed from the film and the film was further dried by patting with dry tissue and finally with nitrogen gas.

Example 3

It is observed from Figure 14 that the air permeability decreases from high-value permeability significantly after 24 hours to almost near zero. This attests to the closing of the protection membrane after 24 hours’exposure to air.

Example 4

For the second configuration, 1wt%thymol blue solution, 1wt%bromothymol blue solution and 1wt%phenolphthalein solution were dissolved in 95%ethanol and mixed with 1wt%methyl red solution (volume ratio: 1: 1: 1: 1) to obtain an indicating dye. A white paper strip in any required length was immersed into the indicating dye. The paper strip after immersing into the indicating dye was laid on a petri dish and allowed to air dry. The dried strip was then acidified with a H ₃PO ₄ solution and air dried again to obtain an acidic pH paper strip. The acidic pH paper strip was then adhered to an adhesive substrate such as adhesive tape (Figure 17) and then the pH paper roll would be sealed into the aluminum foil bag for storage. The storage bag was opened and the pH paper roll was put in the appropriate place of TTI device before its utilization.

Example 5

Gas transmission rate (GTR) is one of the gas permeability parameters for the second configuration. For the pH paper to react with the basic solution or gas, additional protection is required to ensure the pH paper can perform the desired function. The adhesive substrate with lower gas permeability would have better performance in preventing the exposed pH paper from contacting further gas or humid air which may influence the pH paper, causing further color change. Therefore, transparent adhesive tape with relatively low gas permeability [GTR = 913 cm ³ / (m ² ·24h ·0.1MPa) ] is used in the TTI device, comparing with white adhesive tape [GTR = 8822 cm ³ / (m ² ·24h ·0.1MPa) ] . (Figure 19)

Example 6

Table 1 summarizes the cyclic change of relative humidity from 30%, 60%and 90%at different temperatures and time intervals used in the shelf-life test of the TTI device for both the first and second configurations.

Table 1:

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The present invention provides a time-temperature indicator (TTI) that is applicable in delivery service, logistic, and storage industries of products for which quality is sensitive to temperature change. The present system is easy to use, with long shelf-life, and the components therein are mostly reusable or replaceable, such that the manufacturing and operation costs are low.

Claims

A time-temperature recorder comprising:

an indicator strip including an indicating material that changes its indicating property upon exposure to a reactant, an exposure amount of the reactant being directly related to an ambient temperature to which the time-temperature recorder is subjected;

a sealing strip for sealing the indicator strip following exposure to the reactant;

a reservoir of the reactant;

a driver to transport the indicator strip past the reservoir of reactant for exposure to the reactant and to transport the indicator strip into contact with the sealing strip such that an indicating material property change is preserved by the sealing strip and that no further reactant contacts the indicator strip.
The time-temperature recorder of claim 1, wherein the indicating material is a dye.
The time-temperature recorder of claim 2, wherein the dye has a pH-dependent color change and is selected from litmus, Congo red, phenol red, thymol blue, cobalt chloride, methyl red, bromothymol blue, phenolphthalein, or mixtures thereof.
The time-temperature recorder of claim 2 wherein the dye is able to detect the presence of a chemical by a color change.
The time-temperature recorder of claim 1, wherein the reactant is a substance having a variation in vapor pressure within the range of operating temperature.
The time-temperature recorder of claim 5, wherein the reactant is an acid or base.
The time-temperature recorder of claim 1, wherein the sealing strip is an adhesive sealing strip.
The time-temperature recorder of claim 1, wherein the indicator strip and the sealing strip are each formed into rolls.
The time-temperature recorder of claim 7, further comprising drive rollers to transport the indicator strip past the reactant reservoir.
The time-temperature recorder of claim 8, further comprising a take-up roller to receive a sealed indicator strip.
A multilayer time-temperature recorder comprising:

an indicator layer including an indicating material that changes its indicating property upon exposure to a reactant, an exposure amount of the reactant being directly related to an ambient temperature to which the time-temperature recorder is subjected;

a time-dependent permeability membrane layer communicating with the indicator layer, the time-dependent permeability layer selectively permitting the reactant to reach the indicator layer for a selected period of time, followed by blocking the reactant from reaching the indicator layer;

a variable-thickness layer communicating with the time-dependent permeability membrane layer, the variable-thickness layer being configured to selectively permit delivery of the reactant to the time-dependent permeability membrane layer, the variable thickness layer having a first thickness in a first portion such that the reactant reaches a first region of the time-dependent permeability membrane during a first time period and having a second thickness in a second portion thicker than the first thickness such that the reactant reaches a second region of the time-dependent permeability membrane during a second period of time, the second period of time being after the first period of time.
The multilayer time-temperature recorder of claim 11, wherein the reactant is a component of air.
The multilayer time-temperature recorder of claim 11, wherein the indicating material is a dye.
The multilayer time-temperature recorder of claim 13, wherein the dye changes color upon reaction with the component of air, the hue of the color being related to the amount of that component reacted with the dye.
The multilayer time-temperature recorder of claim 13, wherein the dye is selected from an oxygen indicating dye such as cadmium sulfide, copper (II) oxide, catechol, ferrous sulfate, or methylene blue.
The multilayer time-temperature recorder of claim 11, wherein the time-dependent permeability layer is a porous layer wherein pores in the porous layer are configured to close upon absorption of water.
The multilayer time-temperature recorder of claim 16, wherein the time-dependent permeability layer is selected from polyurethane, poly (acrylonitrile) , poly (vinyl alcohol) , poly (methyl methacrylate) , sodium alginate, polyurethane/PVDF, or poly (vinylpyrrolidone) .
The multilayer time-temperature recorder of claim 110, wherein the variable-thickness layer is selected from poly (methyl methacrylate) , poly (vinyl pyrrolidone) , poly (vinyl alcohol) , poly (vinylidene fluoride) , or poly (vinylidene fluoride-co-hexafluoropropylene) .