Field of the Invention

The invention is from the field of detection of temperature changes on the basis of chemical and physical changes in substances. Its application falls within the graphics technology, namely in the realization of so-called smart labels which are an integral part of a smart packaging.

Description of the Problem

Smart packaging that enables dynamic storage and display of various information on a packed product, has introduced a variety of solutions from the field of printed electronics. They normally require power supply and special devices for reading the written information, such as smart phones having adequate software. These options are an advantage for certain data and for certain participants in this process. However, a strong risk of overlooking the relevant information in every circumstance can occur, even without additional equipment and for all participants. The temperature and particularly the temperature history of items belong to this type of information. The temperature must be clearly visible and recognizable to everyone in all circumstances. Such indication should be implemented by one of the methods for packaging preparation, preferably by methods of graphics technology.

Prior Art

The problem of indication of temperature and temperature history does not have known solutions that would meet the requirements of smart packaging and could be implemented by using methods of modern graphics technology.

The idea is closest to the sterilization indicator of the company 3M. It is the indicator of the 5 ^th grade used to control success of steam sterilization (3M™ Comply™ Thermalog™) Steam Chemical Integrator 2134MM). Such an indicator is characterized by a line movement achieved within the required time at a defined temperature (for example, 10 minutes at 121°C or 2 minutes at 134°C. This solution significantly differs from the object of this invention by the activation temperature which limits the conditions for the preparation of the indicator and requires the use of different materials. Therefore, the assembly used by 3M Comply Thermalog is not suitable for indicating temperatures that are below room temperature. The above mentioned version also fails to meet the requirements for smart labels.

An interesting solution is MonitorMark™ of the company 3M (J ™ MonitorMark™ Time Temperature Indicators). This is an indicator used for monitoring the temperature and time of the entire supply/delivery chain. It is characterized by a line movement achieved within the required time at a defined temperature. Recommended application is within protective packaging and not directly on a packaged product. The indicator is limited to a rectangular shape. Given the fact that the indicator is relatively thick and not flexible, it cannot be applied on a packaging and does not meet the conditions for a smart label.

The proposed solution is also different from the Safe-T-Vue temperature indicator, which is used only to indicate the exceeded temperature but not to record the exposure time above the activation temperature (http ://wil liam labs . com/products/safe-t- vue/) . These indicators also fail to meet the requirements for smart labels.

In the field of patent protection several solutions to temperature indication are known. We will concentrate on the patents which address time-temperature effects (TTI-time-temperature indicators) and especially the way, how their activation is carried out. TTI-indication is described by way of (i) two-component/two-part systems, or (ii) special barriers.

Two-component systems consist of two elements that, while applied, are joined on an item normally one on top of another, such that a bottom part is applied first and the upper part is applied on top of the bottom part. When the elements are applied, a protective layer is removed from each one of them. When both elements are joined, this simultaneously means activation of the indicator. These solutions carry out indication through increased transparency or by means of colour change. Transparency can for instance be increased by an identical refractive index of a mobile material and a porous layer (WO 03/025530 Al Time-temperature integrating indicator), or by a viscoelastic substance and a micro structured layer having a well-defined morphology (WO 99/56098: Time-temperature integrating indicator device with barrier material). In variants of two-part indicators with a change in colours either indirect thermochromism is applied, where an activator component developer is present in one part and a temperature sensitive reactant with a colorant in a second part (WO 01/64430 Al : Activatable time- temperature indicator system), or temperature-dependent transition of a colorant (together with the substrate substance) from a layer in one part of the indictor to another part, which parts are in direct contact when merged (EP 2728328 Al : Time-temperature indicator and monitoring method for monitoring quality state of thermally sensitive article). Quantitative detection of a change in colour is carried out by means of a colorant free reference indicator. In a similar variant of a two-component temperature indicator any number of layers can be applied, said layers regulating actuation of the indicator and extending detection time (EP 0484578 Al : Multifunctional time-temperature indicator).

(ii) Solutions with barriers solve a problem of two-component solutions by using barriers that prevent activation of indication before an indicator is applied onto an item and provide for a controlled activation of recording temperature changes, once the indicator has been applied. The simplest example is a removable oxygen-impermeable layer which covers a substrate with a coating of a thermally sensitive material, the colour of which develops at a certain temperature in the presence of oxygen (EP 0231499 Al : Activatable time-temperature indicator). Other variants have an active substance reservoir separated from the environment by a barrier; once the barrier is opened, the active substance propagates into the environment of the reservoir. Controlled propagation and detection are carried out with increased transparency of empty micro structured parts of a second reservoir, into which the active fluid flows (US 2003/0214997 Al : Time or time-temperature indicating articles). The barrier is opened by being pushed and the migration process into the micro structured part of the indicator is only efficient if the air outlet from the empty parts of the micro structure is opened simultaneously. Another way of detection makes use of a change in colour. In such a variant a reservoir contains a material that liquefies at a certain temperature and is separated by a barrier from an adsorption layer, on which indicator dye is applied. Once the barrier is ultrasonically destroyed or thermally degraded, the active material from the reservoir can flow to the adsorption layer, where coloration occurs. The path length of the active material depends on the temperature and the pathway time (WO 91 109287: Time- temperature indicator).

The described versions of indicators have drawbacks that are explained herein below and are solved by the present invention in a very elegant way.

Two-component TTI variants mean that two separate elements are available that are joined on an item. Such a variant presents an additional complication at application onto packaging. Since joining of both components also means beginning of indication, this can make preparation of packaging more difficult. The products which are subject to a temperature-controlled chain must be packaged immediately after a two-component indicator is applied. This may prove unfavourable in many instances. Moreover, two-component variants call for relatively thick indicators in several instances (EP 0484578 Al).

The beginning of TTI recording is best monitored by barriers that allow beginning of recording only when we want (when the product has been completely packed). Implementation of barriers in the described patents may require complicated structures (EP 0231499 Al) or even discharge of superfluous air (EP 0231499 Al). Activation by ultrasound or increased temperature can also pose a problem and is less practical (WO 91 109287).

Solution to the problem

The temperature indicator of the invention, hereinafter the indicator, is completely feasible by a combination of methods used in graphics technology. All manufacturing methods fall within the scope of graphics technology by making use of lamination, cutting and various printing techniques. An important solution is also a precise realization of a reservoir for an indicator material that allows for precise dosage of same, thus ensuring reproducibility of all variants of the indicator.

The indicator solves a problem of time-temperature indicators - TTI, i. e. indication of temperature fluctuations and recording of time, in which the pre-set activation temperature has been exceeded; where the activation temperature is below room temperature. This indication indirectly provides the user the information on the safety and quality of the product (for example animal food) where such an indicator is used. The indicator records the temperature fluctuations above the activation temperature even if the ambient temperature of the surroundings or the article decreases below the mentioned temperature or in the case when the fluctuations above it repeat again. In the case of such fluctuations we obtain an indication of the total duration of the exceedances of the activation temperature, as each fluctuation above the temperature increases the total effect of the indications. The described effect is possible up to the maximum time interval, called the maximum cumulative time of indication. The indication is unique, determined by a clearly visible colour change that cannot be deleted or otherwise abused. The indicator of the invention is therefore a self-sufficient indicator which does not require any power and the recorded information is readable in all circumstances of visual and/or video detection.

The implementation of the indicator allows the use of flexible substrates, while the product is thin and flexible. Before being activated, the indicator should be cooled in a horizontal position to several °C below the activation temperature; afterwards it can be in a vertical position as well. When activated, the indicator can be already present on the article, so the packaging can be completely prepared separately from product packing and the indicator is activated only when the packed product has entered a cold chain. Activation is initiated once a pull-out tab is removed.

This means that the conditions for smart label and its use in smart packaging of different shapes are met. The assembly of the indicator of the invention is suitable for implementation in the context of graphics technology with customized procedures, which fall within the scope of smart labels (for example vignettes) and security printing.

Description of the figures

Figure 1 : Assembly of embodiment 1 of the indicator.

Figure 2: Assembly of embodiment 2 of the indicator.

Figure 3: Cross-section of embodiments 1 and 2 of the indicator.

Figure 4: Thermal properties of indicator materials #1, #2 and #3.

Figure 5: Path length of indicator materials #1, #2 and #3 by absorption layers from materials A, B and C as a function of temperature of the indicator.

Figure 6: Path length of indicator materials #1, #2 and #3 by absorbing materials A, B, C, as a function of time, measured at room temperature.

Description of the invention

The object of the invention is a temperature indicator for irreversible recording of exceeding temperature which is below the room temperature, wherein said indicator is completely feasible with methods of graphics technology used for production of smart labels and within security printing. The temperature indicator is designed to control transport and/or storage of products or substances whose physical, chemical and/or biological properties significantly depend on temperature and time of exceeding the highest permitted temperature, where said temperature is below room temperature. Said temperature is a typical temperature of the indicator and is called the activation temperature. This is also a control temperature for items or conditions, which are controlled by the temperature indicator of the invention or the prescribed temperature, at which products need to be maintained according to legislation or manufacturer's regulations.

The temperature indicator is shown in Figures 1 and 2 and consists of: a carrier substrate 1 with a conical groove la, a first adhesive layer 2, an indicator material 3, a separation ribbon 4, a second adhesive layer 5, a pull-out tab 6, a third adhesive layer 7, a protective layer 8, an absorption layer 9, and a self-adhesive film 10 with a transparent portion 10a.

The carrier substrate 1, the pull-out tab 6, the protective layer 8 and the self-adhesive film 10 with the transparent portion 10a are formed of a thermoplastic polymer flexible foil such as PET, PI, PVC, PS, PC, PMMA, wherein the foil to be used for the self-adhesive film 10 is printable on at least one side. The thickness of the foil which constitutes the carrier substrate allows formation of a conical groove l a and is preferably 0.5 mm, the thickness of the foil for the pull- out tab 6 is preferably between 0.1 and 0.25 mm, the thickness of the foil for the protective layer 8 is preferably between 0.1 and 0.25 mm, the thickness of the foil for the self-adhesive film 10 is preferably between 0.1 and 0.3 mm. The selected materials and their thicknesses allow fabrication of a temperature indicator with a combination of methods used for the fabrication of smart labels and in security printing such as: lamination, cutting, application of adhesive layers by coating, and various printing techniques.

The conical groove la is formed in the carrier substrate 1 on its upper surface along the edge. The conical groove la is formed by known methods of micro transformation of a surface, for instance by micro milling or by using a lamination plate with conical protrusions of a required dimension. Such fabrication method of the conical groove la, which is a reservoir for the indicator material 3, provides for a precise and reproducible fabrication of a reservoir, while its shape ensures optimal discharge in case of exceeded activation temperature and consequently maximum exploitation of the indicator. Preparation of the conical groove la by modern graphics technology makes it possible to form the conical groove la with reproducible dimensions, wherewith precise dosing of the indicator material 3 is ascertained, for instance with spray nozzles directly on the printing line.

A transfer glue or a liquid glue is used for the adhesive layers 2, 5 and 7, which glue is applied by printing such as screen printing, flexo, offset, and dried by an adequate method, e. g. heat, UV. The first adhesive layer 2 is applied in an adequate thickness on the surface of the entire upper side of the carrier substrate 1 with the exception of the groove 1 a and the surface covered by the absorption layer 9. The second adhesive layer 5 is applied only on the surface of the perforated portion of the separation ribbon 4. It is herewith ascertained that upon activation of the indicator, i. e. when the pull-out tab 6 is pulled out, the separation ribbon 4 is removed only on the spot corresponding to the position of the conical groove la with the indicator material 3. The third adhesive layer 7 is applied onto part of the upper surface of the pull-out tab 6 and equals the surface of the polymer foil of the protective layer 8.

For the indicator material 3 a health-friendly organic solvent could be used or a substance which changes the aggregate state from solid to liquid within the required temperature range, and a conventional dye or a coloured material. Another option is to use thermochromic composites consisting of a dye, a developer and a suitable solvent. The melting point of the applied indicator material determines the activation temperature of the indicator, at which the indicator material starts propagating across the absorption layer 9. The activation temperature of the indicator material is determined by a thermal analysis. The indicator material 3 is applied into the entire volume of the conical groove 1 a in liquid state, for instance with nozzles arranged on a printing line.

The separation ribbon 4 prevents the expansion of the indicator material 3 prior to activation and is preferably an aluminium ribbon perforated up to 1 mm outwards from the edge of the site of the groove 1 a. The ribbon can also be made from another material that allows fabrication of a perforation and efficient tearing along said perforation when the ribbon is being pulled out. The thickness of the separation ribbon is preferably between 0.02 and 0.2 mm. The offset of the perforation from the edge of the site of the groove allows activation of the indicator and prevents the propagation of the indicator material in undesired directions. The absorption layer 9 is made from a paper or synthetic material, for instance a chromatographic paper or filter paper of adequate grades, e. g. Whatman 1 , 5, 589/3, 589/1, 674, 615.

The self-adhesive film 10 with the transparent portion 10a is identical in shape and surface to the carrier substrate 1 , wherein the surface of the transparent portion 10a is identical in shape and surface to the absorption layer 9. The transparent portion 10a of the self-adhesive film 10 is not imprinted, while the imprint can be present anywhere else.

A cross-section of the indicator is shown in Figure 3. The indicator can be of any shape but at least one of the dimensions of the indicator should at least equal the length of the absorption path on the absorption layer 9 which is defined in each case with respect to the selected indicator material 3 and the selected absorption layer 9. Adequate shapes are for instance circle, ellipse, any polygon or any other free shape. In this case, the external edges of the carrier substrate 1, the adhesive layer 2 and the self-adhesive film 10 are identical to the desired shape of the indicator, while the external edges of the separation ribbon 4, the adhesive layer 7 and the protective layer 8 can be adequately adapted to the edges of the selected shape.

The shape and dimensions of the absorption layer 9 and of the transparent portion 10a depend on the length of the absorption path which is determined in each case as a function of the selected indicator material 3. In fact, the length must at least equal the length of the absorption path which is determined on the basis of the selected indicator material 3 and the selected absorption layer 9.

Prior to use, i.e. before the activation of the indicator it is necessary to cool it for at least some °C below the prescribed temperature - it should be put for at least 1 hour in the horizontal position so that the carrier substrate 1 is on the bottom. In such conditions, the indicator material 3 changes the aggregate state to solid and only insignificantly adheres to the separation ribbon 4. While the indicator is cooled, its bottom side must be on the bottom otherwise the indicator material 3 adheres to the separation ribbon 4 and when the pull-out tab 6 is pulled out, the latter pulls out some indicator material 3 as well and this impacts the quantitative effect of indication - the time, in which the indicator is active can get considerably reduced. The indicator so cooled is attached to an item in the cold chain, for instance a packaging, and activated by pulling the pull- out tab 6 for activation; the perforated portion of the separation ribbon 4 and the protective layer 8 are removed together with adhesive layers 5 and 7. After extraction the indicator should be stroked by hand on the spots where the layers have been pulled out, so that the self-adhesive film 10 also fixes to the separation ribbon 4 on pull-out sites. This ensures avoiding any loss of indicator material 3 during liquefaction, which assures quantitative proper functioning of the indicator.

The colour change is caused by rise or by fall in temperature in the vicinity of the indicator, which causes a change in physical appearance of the indicator material 3, preferably the aggregate state of the indicator material 3 changes from solid to liquid, and its path through the absorption layer 9. The propagation speed and the path length of the indicator material 3 on the absorption layer 9 may vary by the indicator material 3 type or with its rheological properties and by the properties of the absorption layer 9 such as hydrophilicity/hydrophobicity, porosity, size and distribution of pores, roughness and grammage.

The indicator materials 3 are prepared according to the desired activation temperature which is lower than the temperature used in the preparation of the indicator, and with a different colour response, even a response that can be detected through surveillance cameras, while the latter can operate also outside of the visible light spectre. The indicator allows implementation of various graphic designs which also allow transmission of functional (instructions, explanations) and commercial information.

Prior to fabrication of the indicator in a production line, the indicator material 3 needs to be selected or prepared with respect to the desired activation temperature and with respect to final use, in particular to possible non-tolerance to toxicity and specific optical requirements for detecting colour change. The selected absorption layer 9 must be compatible with the indicator material 3 and must provide for adequate absorption, stability and functionality of the same.

Each functional requirement of the indicator material is subject to basic testing of thermal properties of the indicator material 3 and the length of the absorption path of the indicator material 3 across the absorption layer 9 as a function of temperature and time.

Figures 4, 5 and 6 show the results of testing properties of various temperature indicators, made with three indicator materials 3, namely the composites #1 , #2 and #3 and with three different absorption materials A, B, C. Figure 4 shows thermal properties of indicator materials #1, #2 and #3. Materials #1 and #2 practically have identical activation temperature yet a different solidification temperature. Material #3 has a somewhat higher activation temperature and solidification temperature than the remaining two materials and needs a somewhat smaller temperature flux (energy) for activation than the other two.

Figure 5 shows the path lengths of absorbed indicator materials #1, #2 and #3 by absorption layers from material A, B and C as a function of the indicator temperature. The embodiments are valid for detecting a response of an indicator that was activated at 5°C and then transferred to room temperature and as a result exposed to heating up to room temperature. The example shows co-dependence in response of the indicator and the indicator and absorption materials.

Figure 6 shows the path lengths of indicator materials #1, #2 and #3 by absorption materials A, B, C as a function of the time measured at room temperature. The embodiments are valid for a response of an indicator that is taken from a cool room (in this case < 0°C) and exposed to room temperature.

The layers, of which the temperature indicator consists, allow that an appropriate amount of indicator material is applied on the substrate material and can be activated with a specific procedure, wherein the indicator material irreversibly propagates across the absorption layer and causes a clearly visible change on the surface of the indicator. The indicator is covered by a protection film which could contain printed instructions and any commercial messages, except on the place of the absorption layer where it should remain transparent. None of the indicator layers must affect the chemical and physical properties of the indicator material. All layers, of which the indicator is comprised, must be resistant to conditions, to which the indicator is exposed: low temperatures, increased humidity, light.

The assembly and the selected materials for the indicator allow mass-production in printing technology at a temperature of the production line. This means that temperature control of the production line of the indicator is not required. The indicator can be produced anywhere with adequate graphics technology and applied on an adequate spot on the packaging. Completely produced packaging is delivered in any temperature conditions to a packing site. Before packed, the packaging with the applied indicator is cooled in a horizontal position, such that the carrier substrate 1 of the indicator is on the bottom. Once the indicator is cooled, the packaging is assembled, for instance to a box, and filled with a product. The indicator is activated when the packed product exits the packaging place in the cool chain. When activated, the cooled indicator can be in any position within the packaging. The described mode of application of the temperature indicator makes it possible to prepare the packaging completely independently on product packing and can therefore be prepared anywhere.

The indicator enables recording of time, in which the temperature of the item, on which the indicator was applied, was above its activation temperature which is below room temperature. The indication of exceeded said temperature is unique, simple, and irreversible and cannot be erases. The indicator also enables additive indication of exceeded time, in which the allowed temperature was exceeded, if this time is reasonably long (cumulative indicating time). If the active material is a thermochromic composite, the indicator has a further property since it indicates with a colour change whether the current temperature is below or above the activation temperature also after the time exceeds the cumulative indicating time.

The precision of temperature indicator for the cold chain is ± 3°C. By indicating the actual temperature of items in the cold chain, it is necessary to take into account also thermal conductivity of packaging materials. Apart from that, regulations concerning the maintenance of products and allowed exceeded temperature/deviation of the temperature for a certain period of time need to be taken into account as well.

The proposed invention solves the described problem and has typical advantages over the prior patents in this field by:

(a) implementation - allows use of a flexible substrate, while the product is thin and flexible;

(b) preparation is customized to graphics technology and can be combined with procedures of lamination, cutting and printing;

(c) precise formation of a reservoir for the indicator material provides for precise dosing of this material and this allows fabrication of indicators with maximal possible repeatability of operation;

(d) prior to activation, the temperature indicator must be cooled in horizontal position to several °C below activation temperature and can be positioned afterwards in any position, even vertical; (e) upon activation, the temperature indicator can already be present on the item or packaging and activation is done by pulling out the pull-out tab. This means that the packaging can be completely produced separately from product packing and the indicator can be activated only when the packed product is within the temperature controlled environment;

(f) target activation temperature is below the temperature, at which the production of the indicator takes place on the production line. Closest existing related patents indicate heating of the articles above room temperature (or similarly, above their production temperature) their implementation is significantly more expensive than ours and does not meet the basic requirements for smart labels;

(g) the temperature indicator allows indication of exceeded cumulative time even after the first excess of the activation temperature and cooling below it;

(h) possibility to use recyclable and harmless materials. The invention is illustrated by but not limited to embodiments. Embodiments

Embodiment 1 is shown in Figure 1 and Figure 3. The indicator consists of ten layers as follows:

A carrier substrate 1 with a conical groove la is formed of a polycarbonate foil of a thickness of 0.5 mm and dimensions: length 7 cm, width 2 cm. The conical groove la is formed by a micro milling cutter, wherein the diameter of the groove is 1 cm and the depth of the groove is 0.3 mm. The conical groove la is formed on the upper surface of the carrier substrate 1 , 0.5 cm from its left edge, 0.5 cm from its bottom edge, and 0.5 cm from its top edge.

An adhesive layer 2 is a layer of liquid glue which is applied at a thickness of 0.03 mm onto a surface of the entire upper side of the carrier substrate 1 except on the site of the conical groove la and the surface covered by an absorption layer 9 by flexo printing and oxidatively dried. An indicator material 3 is a thermochromic composite based on the leuco dye crystal violet lactone (CVL) applied into the total volume of the conical groove la in liquid form by nozzles arranged in the printing line.

A separation ribbon 4 is an aluminium ribbon of a length of 2 cm, width 2 cm, thickness of 0.023 mm and is perforated 1 mm outside the edge of the conical groove 1 a and applied at the left side of the carrier substrate 1.

An adhesive layer 5 is a layer of liquid glue applied in a thickness of 0.03 mm on the upper surface of the separation ribbon 4 only on the surface of the conical groove la by flexo printing and oxidatively dried.

A pull-out tab 6 is made from a PET fiol of a thickness of 0.15 mm and dimensions: width 1 cm, length 4 cm. The right side of the pull-out tab 6 is positioned in a way to completely cover the surface of the adhesive layer 5 1.5 cm from the left edge of the carrier substrate 1, 0.5 cm from its bottom edge, 0.5 cm from its top edge.

An adhesive layer 7 is a layer of liquid glue applied at a thickness of 0.03 mm and with dimensions: width 1 cm, length 1.5 cm, onto the upper surface of the pull-out tab 6 to its right side by flexo printing and oxidatively dried.

A protective layer 8 is made from a PET foil of a thickness of 0.1 mm of dimensions: width 2 cm and length 1.5 cm. It is applied at the beginning of the left side of the carrier substrate 1, such that it completely covers the surface of the adhesive layer 7.

An absorption layer 9 is made from a cellulose chromatography paper No. 232-674-9 (Macherey-Nagel GmbH & Co. KG) and having dimensions: width 0.5 cm and length 5 cm. It is applied 1 cm from the left edge of the earner substrate 1 , 7.5 mm from its top edge (1), and 7.5 mm from its bottom edge.

A self-adhesive film 10 with a transparent portion 10a is made from a transparent polycarbonate foil of a thickness of 0.15 mm, one-side printable. The dimensions of the self-adhesive film 10 are identical to the dimensions of the carrier substrate 1. The transparent portion 10a of the self-adhesive film 10 is located 2 cm from the left edge of the carrier substrate 1 , 8 mm from the bottom of the carrier substrate 1 , 8 mm from the top edge of the carrier substrate 1 , a length of 4 cm.

No printing is allowed on the transparent portion but it can be elsewhere. Embodiment 2 is shown in Figure 2 and Figure 3.

The indicator consists of identical layers and in the same way as in Embodiment 1. The shape of the absorption layer 9 and of the transparent portion 10a of the self-adhesive film 10 is changed and so is the material, from which the absorption layer 9 is made.

The absorption layer 9 is made from a filter paper Whatman of grade 1 and has a shape of an equilateral triangle with a basis of 1 cm and a height of 5 cm. The shape of the transparent portion 10a of the self-adhesive film 10 is adapted to the shape of the absorption layer 9.