DE102014104901B3 - Temperature indicator for detecting the exceeding of an upper temperature threshold within a cooling chain - Google Patents

Abstract

A temperature indicator for detecting the transgression of an upper temperature threshold within a refrigeration chain, comprising a temperature-memory polymer and a graphic element formed at least in section thereon, the graphic element remaining in a first state as long as an ambient temperature of the indicator exceeds the upper temperature threshold is not reached, and changes to a second state as soon as the ambient temperature reaches or exceeds the temperature threshold, and remains in the second state even if the ambient temperature falls below the upper temperature threshold again, with machine readability of the graphical element in the first state and in the first state second state and one of the two states allows machine readability.

Description

 The invention is in the field of time-temperature indicators and relates to the detection of temperature peaks in temperature profiles, in particular in cold chains.

 The quality of refrigerated goods, in particular those of certain foods, medical and chemical products, depends significantly on the maintenance of the temperatures in the cold chain during transport or storage. In order to detect any loss of quality not visible from the outside, temperature profiles, in particular interruptions of the cold chain, are documented by means of technical devices. Known and comparatively robust solutions of so-called time-temperature indicators are based on a temperature total detection. For example, a UV-activatable indicator dye from the OnVu label used in Europe and North America fades when heated, indicating an interruption of the cold chain. The indicator may be printed directly on food packaging in the form of a blue print or with an adhesive label (see www.bizerbaopenworld.com/media/en/pdf/iv307.pdf), but it is not intended to detect short term temperature peaks.

In US 2012/0 326 878 A1 there is described an apparatus for detecting the reaching and / or exceeding of at least one temperature threshold comprising a component which changes shape and / or size when exposed to a particular temperature. US Pat. No. 6,382,125 B1 teaches a temperature control material and method based thereon that relies on the use of a leuco dye. In EP 1 560 009 A1 There will be described a temperature indicating screen device using an information recording thin film. In WO 2004/050 507 A1 there is described a packaging for storing goods in an unspoiled condition and a method for producing such a packaging, wherein a bar code comprises a contrast agent which prevents it from being read when a specific temperature is exceeded. In WO 2007/012132 A1 a temperature-time indicator based on colored waxes of different melting temperatures is described.

 A corresponding indicator, also called TTI / time temperature indicator, should be environmentally friendly and resource-saving and allow maximum functionality. In particular, excesses of discrete temperature threshold values should be detectable, since relevant processes which reduce the quality of a product can be bound to exceed certain temperature values.

 Against this background, according to claim 1, a temperature indicator, according to claim 6, a manufacturing method for such, according to claim 11 whose use, according to claim 12, a commodity comprising such and according to claim 14, a device proposed. Other embodiments, modifications and improvements will become apparent from the following description and the appended claims.

 According to a first embodiment, a temperature indicator is proposed for detecting the exceeding of an upper temperature threshold within a cooling chain. The temperature indicator comprises a temperature-memory polymer and a graphic element formed at least in sections on the surface of the temperature-memory polymer. The graphic element remains in a first state as long as an ambient temperature of the indicator does not reach the upper temperature threshold. It changes to a second state as soon as the ambient temperature reaches and / or exceeds the temperature threshold. It then remains permanently in the second state, even if the ambient temperature drops again below the upper temperature threshold. A machine readability of the graphic element in the first state differs from the machine readability of the same graphical element in the second state. One of the two machine readabilities enables automatic detection of information carried by or associated with the graphical element. In other words, in one of the two states the information is readable, not in the other.

 Advantages consist in the fact that the exceeding of the threshold temperature on the change of the readability is recognizable.

 According to a further embodiment, a characteristic geometric feature, in particular a length of the temperature indicator, differs in the first state and in the second state.

 Advantages result from the obvious, visible to the unaided eye display of a threshold temperature during the previous transport and / or storage of a provided with the temperature indicator goods.

According to a further embodiment of the temperature indicator, the graphical element is selected from a symbol, a logo, a letter of a number or a code, in particular a QR code, a DataMatrix code, an Aztec code or a barcode.

 Advantages result from the high information density of the markings achievable with the help of such codes.

 According to a further embodiment of the temperature indicator, the temperature-memory polymer is selected from the group of semicrystalline elastomers and is in particular a poly (ester urethane) or a poly [ethylene-ran- (vinyl acetate)] copolymer having crystallizable segments of polyethylene.

 A benefit of poly (ester urethanes) is the commercial availability of semi-finished products comprising these polymers.

 According to another embodiment, a temperature indicator is proposed whose upper temperature threshold is selected between -40 ° C and +40 ° C, in particular between 0 ° C and +20 ° C. Such temperature thresholds correspond to thresholds of particular practical relevance to the food trade.

According to a further embodiment, a production method for a temperature indicator according to one of the preceding embodiments is proposed, which comprises the following steps:
(1) introducing a graphic element into the colored surface of a temperature-memory polymer; (2) cutting a label; (3) setting a switching temperature of the temperature-memory polymer, (4) providing the temperature indicator with a fastener.

 Advantages result from the simplicity of the manufacturing process and the consequently comparatively low cost of a label comprising the temperature indicator.

 According to a further embodiment, the setting of the switching temperature in the production method (a) comprises an at least partial heating of the polymer with temperature memory to the switching temperature; (b) deforming the temperature-memory polymer by means of a load application such that the applied graphic element loses machine readability; (c) relieving the deformed polymer with temperature memory while maintaining the switching temperature; (d) cooling the unloaded polymer with temperature memory to a temperature below the switching temperature.

 A key advantage of these process steps is again the simplicity and consequently robustness of the manufacturing process. Only simple aids are needed: For example, a heating medium, possibly in the form of an enclosed tempered space (chamber) and a clamping device. A significant advantage over known methods of programming a polymer with temperature memory is that the stretched at the switching temperature indicator is cooled in the load-free state. On the other hand, known processes require cooling under continuous mechanical stress. This saves a process step and significantly speeds up the production of corresponding indicators. This results in significantly lower unit cost of the label, including the temperature indicator.

 According to a further embodiment, the step of "introducing the graphic element" comprises treating the surface of the temperature-memory polymer and is selected from: dyeing, printing (for example by screen printing) or coating; Laser engraving; Casting and / or embossing.

 Advantageously, such a machine-readable mark with sufficient contrast, comprising one or more graphic elements can be generated.

 According to a further embodiment, the "programming" method step comprises the loading with a tensile and / or compressive force of the temperature-memory polymer provided at least in sections with a graphic element on a surface.

 Process engineering and cost advantages in turn result from the simplicity and robustness of the process step.

According to a further embodiment, the step of "providing with a fastening means" comprises applying an adhesive, attaching a wire, a string, a thread, a cable or a band.

 Advantages arise from the wide availability of these fasteners for goods and goods of different sizes and shapes.

 According to a further embodiment, it is proposed to use the temperature indicator described for the monitoring of storage conditions of a perishable goods during a transport process, comprising a reloading, repackaging and / or a change of a means of transport used for the transport process.

 Such steps are typical of modern logistics processes, especially in cross-border goods traffic. Typically, at least one change between a ship transport and a transport by rail or road. If used packaging units, such as containers or storage rooms are cooled, so are caused by waiting interim interruptions of a cold chain can not be excluded. The proposed time-temperature indicator helps to exclude potentially harmful effects and to ensure the quality of a perishable good to the end user.

 Accordingly, there is further proposed a frozen food comprising a temperature indicator according to any of the embodiments described above.

 Advantages of such marked goods are obvious and have already been touched on.

 In particular, it is proposed for this purpose that foods comprising an animal protein are labeled with time-temperature indicators of the type described.

 Protein-rich goods such as fish, meat and derived foods require extra careful monitoring because of their perishability. The temperature-time indicator facilitates reliable monitoring and detection of cold chain interruptions.

 According to a further embodiment, a device is proposed which is adapted for the automatic detection of the information displayed by time-temperature indicators. The apparatus typically comprises a transport unit for transporting transport units (goods) and a scanner unit. The transport unit is therefore adapted to transport the goods in question, may for example comprise a conveyor belt, a running device or a guide device. It ensures a directed movement of the goods equipped with the time-temperature indicator past the scanner unit. The at least one scanner unit is set up so that information readable by a graphical element of the temperature indicator can be reliably detected.

 According to a further embodiment, the device comprises a sorting unit, in particular a separating unit for separating out such pieces, which comprise a temperature indicator with a non-readable graphic element. By sorting out such potentially corrupted goods, even if they are unaltered by external inspection, the health of consumers and the reputation of the merchant can be protected. The first is always, the latter in times of high competitive pressure (see various "rotten" scandals) particularly desirable.

 The described embodiments can be combined with each other as desired.

 With the proposed embodiments, an information carrier in the form of a label is proposed as a time-temperature indicator comprising a polymer with temperature memory. The adaptation of the indicator to the respective threshold temperature via a thermo-mechanical programming of the polymer with temperature memory. It therefore requires only a minimum of effort and allows maximum functionality of the indicator.

The thermo-mechanically programmed temperature memory polymer undergoes a significant and initially irreversible shape change at a discrete temperature, typically within a very narrow temperature range. The so-called shape change temperature is by the before at exactly this switching temperature (the temperature of the desired threshold) made adjustable thermo-mechanical programming. Exceeding the temperature threshold triggers the temperature memory effect and is indicated by an associated pronounced change in the shape of the indicator. For example, the temperature triggered (triggered) can switch a graphical element contained in the surface of the temperature-memory polymer from an unreadable to a readable state, or vice versa. Already checking for machine readability of this element then reveals whether the indicator or the product physically in communication with it has been heated above a threshold temperature. The parallel use of multiple indicator elements, which can change shape at different temperature thresholds and thus document discrete temperature peaks, is feasible.

 To produce the proposed time-temperature indicator, an information carrier is produced from a polymer with temperature memory. This information carrier may have the form of a label which can be equipped with a fastening means. For example, the tag has a machine-readable digital code.

 The information carrier is brought to the later desired switching temperature. This switching temperature corresponds for example to a maximum permissible limit temperature in the cold chain, the achievement of which is to be displayed. At this temperature, the temperature-memory polymer is now deformed mechanically (for example, in the pulling direction) and, unlike the programming methods customary in the specialist literature, subsequently relieved again. The polymer is thereby programmed a residual strain, whereby the information is distorted and machine readable. This temporary shape remains stable as long as the polymer is stored at a temperature below the switching temperature. In exactly this state, the information carrier, comprising the polymer with temperature memory as an indicator in the cold chain is used. Only when the set switching temperature is exceeded again, there is an irreversible shape recovery, eg. A strain change. By restoring the original shape as much as possible, the information is again readable by machine and thus indicates that the limit temperature in the cold chain has been exceeded.

 Thus, switching temperatures of information carriers, which are composed of the same polymer with temperature memory, according to the method described herein in a wide temperature range between -40 and 40 ° C with an accuracy of +/- 2.5 ° C can be set. The thermo-mechanical parameters are chosen so that not only a strong change in shape takes place at the switching temperature, but in addition, for example, an equalization of a code. This equalization is so pronounced that the equalized pattern can be machine read while the distorted pattern of the programmed time-temperature indicator is unreadable.

According to a practical embodiment, samples of material from Desmopan DP 2795A SMP (Bayer MaterialScience AG) were used, which were in the form of 2 mm injection molded plates. The hard segment of this block copolymer comprises 4,4'-methylenediphenyl diisocyanate (MDI) with a 1,4-butanediol (BD) chain extender. Poly (1,4-butylene adipate) (PBA) with an average molecular weight M _w of 3500 g mol ^-1 represents the soft segment. According to further embodiments, structurally related PEUs were investigated, which differed mainly in the MW of the shift weights (1500-10.000 g / mole)

Differential Scanning Calorimetry (DSC) measurements were taken with an EXSTAR DSC7020 (Seiko Instruments Inc., Japan). The sample mass was about 5 mg. First, the DSC samples were cooled to -90 ° C and held at this temperature for 5 minutes. After heating to 90 ° C, was cooled again to -90 ° C. In each case heating or cooling rates of 10 ° C min ^{-1 were} chosen.

A dynamic mechanical analysis (DMA) was performed on a Netzsch DMA 242 test rig, which was operated in a single-beam bending test. In this case, material samples of a size of 5 mm × 2 mm × 2 mm were used. Temperature ramps from -100 to 80 ° C were run at a heating rate of 1 ° C min ^-1 . In parallel, the elastic modulus E 'and the loss modulus E "were determined. Since the DMA results proved to be extremely sensitive to the thermal history of the PEU (eg storage conditions), the samples were first annealed for 10 minutes at 60 ° C and stored at 23 ° C (50% humidity) for at least one week before their visco-elastic properties were examined.

Thermo-mechanical measurements (except in the case of information carriers with QR codes) were made with an electromechanical test system (Zwick / Roell Z005) equipped with a Thermal chamber (Zwick / Roell) and a thermostat (Eurotherm 2261e). Test results were documented and evaluated with the test software testXpert ^® II (V 3.31). Dumbbell-shaped tension rods of type 5B (EN ISO 527-2: 1996) were punched from PEU plates. Samples with an initial measuring length of 10 mm were clamped with pneumatic test clamps at a clamping pressure of 5 bar. A 100N load cell was used to determine the force. The stress σ was obtained by dividing the force by the starting cross-sectional area of the sample. During the measurements, the course of the strain ε was determined directly from the path change of the crosshead.

For programming (adjustment of the temperature threshold), a PEU sample was deformed at a deformation rate of 30 mm min ^-1 up to a maximum strain value ε _m of 100% at a deformation temperature T _d between -20 ° C and 40 ° C. Young's modulus E was determined from the initial increase in the stress-strain curve as the ratio of stress to strain. In the following two programming routes for polymers with temperature memory are described. With route 1 a conventional programming approach was pursued, ie programming according to route 1 is often found in the specialist literature. The approach to Route 2 was completely different. Here, a completely new sequence of single steps was combined in a new programming strategy. After 5 minutes, the sample was cooled to the relief temperature T _u = -20 ° C and relieved (Route 1, T _d > T _u ) or directly (without cooling) relieved at T _d before the sample was recooled to -20 ° C C (route 2, T _d = T _u ). In both cases a relief rate of 10% min ^{-1 was} chosen.

The strain fixation ratio R _f and the total strain recovery ratio R _{r, dead} represent significant parameters for the ability of the materials for shape fixation and shape recovery. They are derived following equations 1 and 2:

The programmed strain ε _u , which describes the elongation after setting (programming) the temporary shape, was determined at -20 ° C. The thermal response was recorded during heating from -20 to 80 ° C both load-free and under constant held strain. The measurements were carried out at uniform heating and cooling rates of 3 and -3 ° C min ^-1 , respectively. In order to detect the stretch recoverability, the strain was recorded at 80 ° C after the triggering of the temperature memory effect ε _p . The switching temperature T _sw was defined as the temperature at which half of the strain reduction ε _u - ε _{p was} reached. In order to precisely determine the switching temperature T _sw , the tangents of the return curves in the strain temperature test protocols and the temperatures at their intersections at the beginning and end of the heating process were defined as T _{sw, on} and T _{sw, off} . For cases in which the stress recovery behavior was measured under constant elongation, the temperature values were determined at which respective maxima of the restoring tension σ _{max were} determined. These temperature values were defined as the stress _recovery temperature T _{σ, max} . For more accurate characterization, tangents were applied to the voltage recovery curves in the voltage-temperature test protocols. The temperatures that coincided with the intersections of the tangents at the beginning of the stress build-up and at the end of the stress relaxation were defined as on and offset stress recovery temperatures T _{σ, on} and T _{σ, off} .

At 80 ° C, the samples were relieved at a rate of 10% min ^-1 before being finally finally cooled to 23 ° C without stress.

Tensile tests were taken at T _d = -30, -40, -50 and -60 ° C, with the above-mentioned rates of deformation observed. This was not about the programming of the temperature memory effect (TGE programming), but about tensile tests, from which the mechanical properties were determined at lower temperatures.

To obtain indicator samples with superficially introduced QR code, PEU samples were surface-colored and laser-engraved. A specially developed test specimen has the in 1 shown shape and dimensions.

 The QR codes were generated using a software freely accessible via the Internet address "http://goQR.me", selecting the error correction level "M" (error correction level "M"). The data matrix codes were generated via the software available from the Internet address http://www.barcode-generator.org.

The deformation and recovery of QR code carriers was performed using a thermo-mechanical test stand (MTS Insight 10) equipped with a thermal chamber (Thermcraft) and a thermostat (Eurotherm 2404). First, the QR code carrier was clamped with a clamping distance a ₀ = 13.5 mm in the pneumatic clamps of the device at a contact pressure of 5.6 bar. A 250 N load cell was used to determine the force. To program the temperature memory effect, the QR code carrier, ie, a time-temperature indicator, was used 1 , held for 10 min at a temperature T _d = 0 ° C, 10 ° C or 20 ° C, before it with a deformation rate of 30 mm min ^-1 to a maximum elongation Δa / a ₀ to 150% (T _d = 0 ° C), 155% (T _d = 10 ° C) or 165% (T _d = 20 ° C) of the initial length was stretched. After 5 minutes, the QR code carrier was relieved and cooled to -20 ° C. A holding step of 5 min at this temperature marked the end of thermo-mechanical programming. Subsequently, the temperature memory effect was triggered by heating the sample to 80 ° C. Parallel to the reshaping of the QR code carrier, the machine readability of the QR code was checked regularly.

As a machine scanner (scanner) was a Samsung Galaxy S I9000 with Android ^TM operating system version 2.3.3, which was equipped with a 1.4 GHz processor and 5.0 megapixel camera (2560 × 1920 pixels) with auto focus function. The software used was the barcode scanner (version 3.6) of the ZXing "zebra crossing" team. This was downloaded for free as a software application ("App") from the Android Market ™ (open source). Likewise, other combinations of a suitable camera or scanner with customized control or image recognition software may be used to machine-read the representation.

 The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. The elements of the drawings are relative to one another and not necessarily to scale. Like reference numerals designate corresponding parts accordingly.

1 schematically shows the contours of the test specimen used in expansion tests with inverse QR code;

2 shows by means of DSC and DMA certain thermal and mechanical properties of PEU;

3 shows stress-strain curves of PEU at different temperatures;

4 shows temperature memory properties of PEU during heating after programming via Route 1 under stress-free conditions (strain-related temperature memory properties, upper part of a-figure) and under constant held strains (voltage-related temperature memory properties, lower part of a-figure), including the evolution of T _sw and T _{σ, max} with T _d (b);

5 shows strain-related temperature-memory properties of PEU during heating after programming via Route 2 under stress-free conditions (strain-related temperature memory properties, upper part of a-figure) and under constant strain (voltage-related temperature memory properties, lower part of a-image), including the evolution of T _sw and T _{σ, max} with T _d (b);

6 Temperature memory properties of PEU at T _d = 10 ° C with deformations of 50, 100, 150, 200, 250, 300, 350 and 400% and subsequent discharge

7 Temperature memory properties of PEU at T _d = 40 ° C with deformations of 50, 100, 150, 200, 250, 300, 350 and 400% and subsequent discharge.

8th shows voltage-related temperature memory characteristics of PEU after programming via Route 1 under conditions of a constant held clamping distance during heating;

9 shows the temperature memory behavior when heating up three QR code carriers, with preset switching temperature via Route 2;

10 shows the behavior of PEU samples in Route 1 during cooling after stress at different deformation temperatures T _d s. The formation of stress σ (solid line) and temperature T (dashed line) over time t. The minimum stress σ _min is indicated by black arrows;

11 shows the load / unload behavior of PEU at different deformation temperatures T _d s;

12 shows the dependence of the width of the temperature-memory transition region .DELTA.T represented by the difference of T _{sw, on} - T _{sw, off} and T _{σ, on} - T _{σ, off,} as a function of the programming on the deformation temperature T _d.

In particular shows 1 a test piece, which carries an inverse, by laser engraving unilaterally introduced inverse QR code. The specified numerical values correspond to millimeters, the clamping distance in the thermo-mechanical testing system was 13.5 mm.

2 shows the results of the measurements from the described DSC and DMA measurements. In particular shows 2 the behavior of the soft segments of the PEU. It shows 2a ) - the first heating and cooling according to DSC and 2 B ) determined by DMA temperature dependence of E 'and tan δ. The calorimetric properties of PEU were characterized by a PBA melt transition between 33 and 54 ° C, a spread of the PBA crystallization transition of 14 to -20 ° C and a PBA glass transition at -45 ° C (see. 2a ). Typical of physically cross-linked PEUs [Chen S, Hu J, Liu Y, Liem H, Zhu Y and Meng Q 2007 Effect of molecular weight on shape memory behavior in polyurethane films Polym Int 56 1128-1134; Chen S, Hu J, Liu Y, Liem H, Zhu Y, and Liu Y 2007 Effect of SSL and HSC on PHA-based PHP-based Polymorph Polym Phys Physic 45 444-454; Bothe M, Emmerling F and Pretsch T 2013 Poly (ester urethane) with varying polyester chain length: Polymorphism and shape memory behavior Macromol Chem Phys 214 2683-2693], a melt transition in the DMA follows the glass transition. This results from the two-stage waste in the storage module. The peak of the value tan (δ), which is frequently used to determine the glass transition temperature T _g of polymers, was -35 ° C. (cf. 2 B ).

To elucidate the influence of programming on the temperature memory behavior of PEU, two scenarios were investigated. In the first, the sample was subjected to tensile stress at the deformation temperature T _d before being cooled to -20 ° C under constant strain, and then released. This temperature corresponded to the DSC offset of the crystallization temperature of PBA. For example, a rather conventional experimental strategy was pursued with the selection of a T _d above the discharge temperature T _u (T _d > T _u , route 1) [Xie T 2011 Recent advances in polymer shape memory polymer 52 4985-5000; Kratz K, Madbouly SA, Wagermaier W and Lendlein A 2011 Temperature-Memory Polymer Networks with Crystallizable Controlling Units Adv Mater 23 4058-4062; Kratz K, Voigt U and Lendlein A 2012 Temperature-Memory Effect of Copolyesterurethane and Their Application Potential in Minimally Invasive Medical Technologies Adv Func Mater 22 3057-3065]. In the other case, uniaxial stretching and unloading were carried out at identical temperatures (T _d = T _u , route 2). Programming was then completed by cooling the sample to -20 ° C. Irrespective of the selected programming route, in both cases a maximum tensile strain ε _m of 100% was applied at T _d (cf. 3 ). Here, at a strain rate of 300% min ^-1, Young's moduli are 1341 MPa (-60 ° C), 1145 MPa (-50 ° C), 746 MPa (-40 ° C), 483 MPa (-30 ° C), 282 MPa (-20 ° C), 217 MPa (-10 ° C), 156 MPa (0 ° C), 144 MPa (10 ° C), 116 MPa (20 ° C), 103 MPa (30 ° C) and 43 MPa (40 ° C).

The stress-strain curves clearly show the influence of moduli of elasticity, Young's moduli and yield stresses due to stepwise consolidation of the PBA switching segment on cooling due to the increasing crystallinity of PBA (the crystallites act as filler) and the concomitant increasing density of physical crosslinks. Tensile tests at -30, -40, -50 and -60 ° C showed continuously increasing modulus of elasticity, Young's moduli and yield strengths (see relevant curves in 3 ). Below the PBA glass transition, vitrification of the PBA and the accompanying brittleness only allowed tensile testing at very low stress.

After programming, the samples were heated to 80 ° C without load or with constant elongation (cf. 4 and 5 ).

According to the route 1 thermo-mechanical protocols, the strain and stress resets set in the early stages of heating ( 4a ). In addition, a pronounced shape recovery was noted ( 4a , upper part). As can be seen, the switching temperatures T _{sw increased} with a gradually increasing deformation temperature. Accordingly, maximum restraining stresses σ _max s for continuously increasing temperatures T _{σ, max} s were determined under constant elongations (cf. 4a , lower part). Over the entire temperature range investigated, a nearly linear relationship between T _sw / T _d and T _{σ, max} / T _{d was} confirmed (cf. 4b ). This impressively confirms the temperature-memory behavior of PEU. In this respect PEU fulfills the basic requirements for a polymer with temperature-memory properties (T _d ≈ T _sw ≈ T _{σ, max} ). However, it should not be concealed that the mean T _sw of T _d deviated by 4 ° C and of T _{σ, max} by 9 ° C.

The heating of the programmed according to Route 2 samples gave a slightly different, but also characteristic image of the strain and voltage provisions (see. 5 ). Again a temperature-memory behavior could be confirmed (cf. 5a ), which is characterized by an almost linear increase of T _sw and T _{σ, max} with T _d (cf. 5b ).

In contrast to the samples programmed according to route 1, one of the most notable aspects is an increase with T _{d of} the onset reset temperatures T _{sw, on} and T _{σ, on} , which mark the onset of strain relaxation and stress increase. Both temperatures differed from T _d on average by 7 ° C and 2 ° C, respectively. In other words, a programming of the onset temperature memory could be achieved.

For a better overview, all relevant thermo-mechanical characteristics are summarized in Table 1. Tab. 1

As described above, according to both Route 1 and Route 2, a maximum tensile strain ε _m of 100% was applied at each T _d indicated. However, significantly higher strains according to Route 2 can be programmed into the materials. The temperature memory properties determined are shown in the 6 and 7 shown. For T _d = 10 ° C ( 6 ) and 40 ° C ( 7 ) were Deformations of 50, 100, 150, 200, 250, 300, 350 and 400% applied. Thereafter, the sample was relieved. The 6a respectively. 7a show the corresponding stress-strain diagrams. In addition, the sample was cooled to -20 ° C. The strain-temperature diagrams recorded in the subsequent heating of the samples at 70 ° C are in 6b , respectively. 7b shown. From the restoring behavior it becomes clear that in addition to temperature memory properties, above all the respective onset values in the return curves for the different strains could be programmed.

The thermal history of the samples (before loading) was identical for routes 1 and 2. This ensured that the morphology of PBA in the PEU samples was identical before deformation. The main difference between Route 1 and Route 2 was that no voltage reduction was allowed in Route 1 until PBA crystallization was complete by cooling to -20 ° C. During cooling, the tension initially dropped, mainly due to the crystallization of PBA, before a final increase in stress occurred (cf. 10 ).

It is believed that the latter is due to the limited molecular mobility in amorphous regions of PBA due to the presence of crystallites. An elongation kept constant during cooling gave good elongation fixations (evidenced by R _f ) and comparatively higher maximum restoring stresses in the subsequent heating (see Table 1). In this case, the fixed strain ε _{u increased} with increasing T _d (cf. 4a , upper part), since the PBA phase had an increase in the proportion of crystallizable polymer chains. Taking into account the elongation of the sample by relieving according to Route 2, was a decrease in the elasticity with lower T _d s visible (see FIG. 11 ).

 In addition to the aspect of the crystallinity of polymers used here, reference is made to in situ wide-angle X-ray diffractometry (WAXS). With this method, the crystallization and melting behavior of switching segments can be investigated. From the WAXS data for the PEUs described here, it is clear that the switching segment prior to deformation is in a polymorphic mixture consisting of a thermo-dynamically stable α-phase (a = 6.777 Å, b = 7.905 Å, c = 14.42 Å, β = 135.6 °) and a metastable β-phase (a = 5.06 Å, b = 7.35 Å, c = 14.67 Å). In the course of the WAXS investigations, it was found that a crystalline fraction in PEUs between 10 and 20%, in particular between 13 and 15%, enables the detection of pronounced temperature-memory properties.

Basically, the polymer chains present in a rubbery state at T _d in Route 2 determine the elongation after release. It seems reasonable to assume that crystalline constituents increasingly counteract an entropy-elastic recovery of the samples at low temperatures, whereby ε _u noticeably increases (cf. 5a , upper part). Furthermore, it became clear that PBA chains, which should crystallize on cooling, do not hinder the stability in elongation on cooling. In any case, the stretch in Route 2 was already fixed at T _d . This could also be demonstrated in further Route 2 experiments for T _d = 30 and 40 ° C, in which not cooled to -20 ° C, but only to 23 ° C by opening the temperature chamber and the associated air exchange with the environment has been.

Another facet of thermo-responsiveness is the width of the observed temperature-memory transition. According to Route 1, this was between 60 and 75 ° C, and unfavorably extended over much of the temperature range studied. In contrast, in the samples treated according to route 2, it steadily decreased with increasing T _d s from about 70 to 10 ° C. (cf. 12 ). Thermal response in Route 1 was determined by the temperature stability of those PBA crystallites which formed under constant elongation on cooling. In contrast, after programming with Route 2, primary melting of PBA crystallites already present in the material prior to deformation and therefore having thermal stability of T ≥ T _d occurred.

Notably, the programming route had no effect on the recoverability of the strain. The total recovery ratio R _{r, tot} was always between 86 and 90% (see Table 1). However, the maximum reset voltages in Route 1 were higher because the entropy-driven reset was also blocked during programming by the PBA units that crystallized during cooling.

In order to complete the thermo-mechanical investigations on test bars, the programming route 1 was extended to temperatures below the glass transition of PBA. Again the same strains were applied as before but the samples were now cooled to -70 ° C before being heated to 80 ° C at constant strain (cf. 8th ).

During the early phase of heating, a compressive force developed. Exactly at the time of approaching the glass transition, the onset of a contraction was detectable. Usually, a change in the coefficient of thermal expansion from positive to negative can be observed when stretched elastomers are heated under constant tension to a temperature above their T _g [Lendlein A and Kelch S 2002 Shape-Memory Polymers Angew Chem Int Ed 41 2034-2057]. Continued heating in turn allowed the temperature memory effects to be detected. It has been observed, as well as above for Route 1 that the maximum reset voltage with higher T _d s was smaller. This seems logical, considering that the tensile loads also decreased with increasing temperature. The last step was the programming of temperature memory properties using the example of QR code carriers. Route 2 was selected for this. Subsequently, the thermoresponsiveness was investigated (cf. 9 ). In the 9 the information release temperatures are marked with an asterisk. The vertical distance between the two clamps Δa / a ₀ is indicated in the white highlighted boxes.

As stated, tensile strains Δa / a ₀ of 150% (T _d = 0 ° C), 155% (T _d = 10 ° C) and 165% (T _d = 20 ° C) were prior to relief and cooling, respectively. 20 ° C made. As a result of the programming, the QR code carriers could be stabilized with strains close to 90%. During heating, the QR codes could be changed from an unreadable state to one at 0 ° C (T _d = 0 ° C), 10 ° C (T _d = 10 ° C) and 20 ° C (T _d = 20 ° C) readable state can be switched.

The most noticeable thing was that programmed deformations of the QR code could be equalized at comparable strains of around 85%, which made it readable again. It is noteworthy that the individual forms in each state of in 9 conditions were stable. In addition, preliminary results of the stability studies showed that Route 2 programmed QR code carriers stored for four weeks at 0 ° C held the temperature memory characteristics as described above.

 As proposed, a monitoring, display and control of undesirable temperature exceedings of products is achieved, which must be subject to use of a continuous cooling.

 With the aid of the method proposed here, a machine-readable code can be transferred from a temporarily unreadable to a machine-readable state. Typical of the proposed solution is the permanent and indestructible connection between the temperature-memory polymer and the information that undergoes complete complete thermo-mechanical pretreatment (programming).

 The machine readability of the code also enables automation and remote verification of the condition in the cold chain, e.g. B. by means of a scanner.

In addition, the programming differs for setting the switching temperature and change in shape: As in the publication WO2009095434 A1 As shown, the polymer is heated to the predetermined programming temperature where it is forced into a new mold and cooled while maintaining mold constraint below the mold fixing temperature. However, according to the method proposed here, the programming of the time-temperature indicator takes place in only three steps. These consist of setting the programming temperature, applying a deformation and then relieving. So it does not have to be cooled under load as before. As a result, an energy-intensive process step is saved and the production of corresponding indicators can be significantly accelerated. In contrast to previously known solutions, it is not a tearing of crystallites, but a melting, which causes the temperature memory effect. When setting the trigger temperature, therefore, the morphology of the switching segments of the polymers used before the deformation below the offset melting temperature of the switching segments is crucial. The programming is done according to route 2 by deforming the material and then relieving it again. Deformation and relief take place directly at the deformation temperature. As a result of this new path, the step of cooling down to a lower temperature is eliminated, especially if one wants to program the temperature memory effect (TGE) above 23 ° C. This step is not necessary if you want to program the temperature-memory effect above 23 ° C. Otherwise, the polymer (or the label) must of course be cooled at least to the deformation temperature in the course of programming under constant load. The WO2009095434 A1 documents this step very precisely, and basically does not make any reference to machine-readable codes.

 The results represent a further development of the functionality of information carriers. Basically, the switching temperature of a polymer with temperature memory, in particular an information carrier comprising such an innovative authenticity feature. Control over the functionality of such a label requires a wide pool of thermo-mechanical functionalization repertoire.

 Information carriers with temperature memory can be used as smart sensor / actuator pairs in cold chains. No elaborate synthesis variation is necessary to set the desired switching temperature, but only a simple adaptation of the programming procedure. Monitoring can be carried out with information carriers, scanning and decoding devices directly on the marked product (goods). Thus, the labels for both the producer and for intermediaries and end users as a seal of quality for checking the quality of the goods makes sense.

 In a particularly effective manner, parts of a cold chain or an entire cold chain can be monitored or controlled by means of scans that take place during the goods already being handled.

 While specific embodiments have been illustrated and described herein, it is within the scope of the present invention to properly modify the illustrated embodiments without departing from the scope of the present invention. The following claims are a first, non-binding attempt to broadly define the invention.

Claims (15)

 Temperature indicator for detecting the transgression of an upper temperature threshold value within a cooling chain, comprising a polymer with a temperature memory and a graphic element formed at least in sections on its surface, wherein the graphical element remains in a first state as long as an ambient temperature of the indicator does not reach the upper temperature threshold, and changes to a second state as soon as the ambient temperature reaches or exceeds the temperature threshold, and remains in the second state even if the ambient temperature drops again the upper temperature threshold drops, wherein machine readability of the graphical element differs in the first state and the second state and one of the two states enables machine readability.  The temperature indicator of claim 1, wherein the temperature indicator in the first state differs from the temperature indicator in the second state by a length of an edge of the indicator  Temperature indicator according to claim 1 or 2, wherein the graphical element is selected from a symbol, a logo, a letter of a number or a code, a one-, two- or three-dimensional code, a barcode, a QR code, a DataMatrix code or an Aztec code, whereby in the case of 3D codes another dimension for coding the information is added.  Temperature indicator according to claim 1 to 3, wherein the temperature-memory polymer is selected from the group of semicrystalline elastomers and a poly (ester urethane) or a poly [ethylene-ran- (vinyl acetate)] copolymer having crystallizable segments of polyethylene.  Temperature indicator according to one of the preceding claims, wherein the upper temperature threshold is between -40 ° C and +40 ° C or between 0 ° C and +20 ° C.  A manufacturing method of a temperature indicator according to any one of claims 1 to 5, comprising: - introducing a graphic element into the surface of a temperature-memory polymer; - cutting a label; - Set a switching temperature of the polymer with temperature memory; - Provide the temperature indicator with a fastener. The manufacturing method of a temperature indicator according to claim 6, wherein the setting of the switching temperature comprises: - at least partially heating the temperature-memory polymer to the switching temperature; Deforming the temperature-memory polymer such that the applied graphic element loses machine readability; Relieving the deformed polymer with temperature memory at the switching temperature; Cooling the unloaded polymer with temperature memory to a temperature below the switching temperature.  The manufacturing method of claim 7, wherein the incorporation of the graphic element comprises treating the surface of the temperature-memory polymer selected from: dyeing; printing; Printing by screen printing; coating; Laser engraving; Casting and / or embossing.  The manufacturing method according to claim 6 to 8, wherein the setting comprises stretching and / or compressing.  The manufacturing method according to any one of claims 6 to 9, wherein the mistake comprises applying an adhesive, attaching a wire, a string, a thread, a cable or a ribbon.  Use of a temperature indicator according to one of claims 1 to 5 for monitoring storage conditions during a transport process, comprising a reloading, repackaging and / or a change of a means of transport used for the transport process.  Frozen goods, comprising a temperature indicator according to one of claims 1 to 5.  The frozen article of claim 12, wherein the article is a food comprising an animal protein.  An apparatus comprising a transport unit and a scanner unit, the transport unit being adapted to transport a commodity comprising a temperature indicator according to any one of claims 1 to 5, past the scanner unit, the scanner unit being arranged to detect one of the graphical element of the temperature indicator readable information.  The apparatus of claim 14, further comprising a reject unit for rejecting a commodity, comprising a temperature indicator having a non-readable graphic element.

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