Activatable time-temp. indicator system

Activated time-temperature indicator system

BACKGROUND OF THE INVENTION The present invention relates to an indicator system that can respond at a certain rate of thermal change to produce a visually distinguishable indication when the cumulative heat exposure of the relevant product has exceeded a predetermined temperature accumulation. More specifically, the present invention relates to a system that is affixed to a heat-sensitive perishable product unit and activated when the unit is put into commercial use to begin monitoring the cumulative exposure of the unit to harmful temperatures. This system can produce a visually distinguishable color that marks the end of the safe storage period of the product when the allowable time-temperature accumulation is exceeded. In a preferred embodiment, the indicator system of the present invention includes the use of a direct thermal label paper and an additional element, which is attached to the label to react with it and induce a time- and temperature-dependent color change , This change can be used to monitor the cumulative environmental temperature exposure of marked perishable products.

Temperature-sensitive indicators capable of monitoring the color or color change of perishable items are generally known, and their use for this purpose is increasing. This indicator is used to generate a signal when the perishable item with the indicator reaches a point of quality loss or unsafe conditions due to excessive temperature exposure. After that, the product should not be used again or the product should be carefully checked before use. Ensure qualified quality. An indicator system with such properties is important for ensuring the quality and safety of perishable foods, drugs, chemicals, and other such sensitive items.

In the case of perishable foods, modern packaging techniques are used to try to extend the shelf life of meat, poultry, and fish. For example, plastic films with different gas permeability and barrier properties are used to maintain the gas mixture in the package to reduce the propagation of aerobic spoilage organisms. However, the food microorganisms contained in this type of packaging allow anaerobic pathogens to grow in this altered atmosphere and under suitable temperature conditions without sensory signs of spoilage. Therefore, food exposed to a variety of possible temperatures will produce lethal pathogen concentrations without providing a detectable signal of spoilage. Therefore, if the product is consumed, it can lead to serious health consequences. Therefore, for consumers, a safety feature is an indicator system related to perishable products. The purpose is to provide a visual indication that can warn that the product has been exposed to more than the qualified time and temperature, that is, the critical "time-temperature accumulation" visual indication .

Regarding highly perishable foods, such as meat, poultry, and fish, the indicator system is best placed on each unit of the merchandise sold for continuous monitoring from packaging to use. Otherwise, it is impossible to indicate the unknown temperature history that the packaged product has been subjected to, such as during transportation and circulation or caused by intermittent customer handling or removal from the cold storage room, which will cause a significant deterioration in quality and endanger health.

In order to be most effective, an indicator system should be formulated and used to provide visual indications, such as color changes accompanying the occurrence of spoilage conditions in related perishable products. For this purpose, the indicator system should preferably have a visual change speed consistent with the deterioration speed of the relevant product. Although such ideal performance is not easy to obtain due to countless conditions that affect product spoilage, it should be possible to operate the indicator at least during the period that is only related to the product. In other words, an effective indicator system should not sensitively respond to or record the temperature gradient that it is exposed to during the time between manufacture and the final application of the perishable product. Only in this way can the indicator system reliably monitor the complete thermal history of the relevant perishable products at different stages in the entire product storage and circulation.

In the early attempts to meet the requirements for independent response in the time-temperature indicator system, such as freeze/thaw monitors and shelf life markers, labels, marking devices, etc. indicator products are immediately related to actinic properties once they are made. The temperature is separated, for example by freezing or at least cooling to an inactive temperature. For example, widely used labels containing diacetylene monomer inks that record irreversible color generation as a function of ambient temperature changes during polymerization need to be stored at temperatures below the threshold for significant color polymerization from the time they are manufactured. Such a stopgap is effective as long as storage and handling conditions are carefully monitored. However, these indicator system products themselves are randomly affected by human behavior, just like the perishable products to be protected, so the required reliability is also compromised. However, the equipment and resource costs caused by trying to ensure the required storage conditions, although occasionally insignificant, sometimes exceed the initial cost of the indicator product.

Therefore, in addition to the basic requirements of reproducibility and manufacturing economy, an acceptable indicator system must avoid the following situations in an economical and "fail-safe" manner: triggering its own temperature response and reducing its response to a certain final The ability of perishable products related to it to record the true time-temperature accumulation. The most reliable way to avoid is to formulate or construct a certain indicator system so that it is in an inactive state that can only be activated when it is connected to the product unit that needs to be monitored. The present invention provides such an economical, reliable and activatable time-temperature indicator system.

Many activatable time-temperature indicator systems have been proposed before, but none of them can provide a convenient and economical way to prevent the premature initiation of potential temperature-sensitive indicator reactions. For example, in most systems containing labels to be affixed to perishable products, the potential co-reactant components, such as the precursors of the room temperature color reaction, are placed next to each other in the form of a continuous layer or a dispersed mixture. However, the reactive isolation is still maintained through additional intervening layers, encapsulation membranes, etc. However, such isolation method requires additional raw materials and manufacturing operation costs. Moreover, these indicator products are still sensitive to accidental premature activation due to the close proximity of the potential reactants, for example, when the fracturable separation capsule is subjected to misoperation or the latent photosensitive co-reactant undergoes sudden light exposure. Chemical exposure, or beyond other acceptable storage conditions.

Another aspect that causes the limited acceptability of the current activatable indicator system is that the cost of materials and manufacturing operations is too high. This is because the indicator and activation composition or activation method are required to be separately formulated and separated together with the separation method. Assemble into the final indicator system product. Therefore, from the standpoint of economic acceptability alone, it is best to use the minimum amount of effective and low-cost components and raw materials for the time-temperature indicator industrial products.

For this purpose, the present invention utilizes ready-made common or commercial materials as visually responsive co-reactant elements, such as thermal printing label products, which contain a composition, for example, a mixture of potentially reactive color-forming precursors, which is low in It has inherent resistance to activation under abnormal ambient temperature conditions. The present invention also includes an additional, economical activator product element that must be combined with the visually responsive label product when it is finally applied to the perishable product that needs to be monitored. In this way, the present invention not only eliminates the potential danger of premature activation of the indicator, but also greatly reduces the dedicated time-temperature by introducing existing readily available universal visual response products, such as temperature-responsive thermal recording product labels, as the main component. The cost of the indicator system.

Thermally responsive marking or printing products, especially direct thermal label products, are now widely circulated and used. Because of their simple response to heat-marked labels, these clean, non-staining products help quickly replace labels and printing equipment that require refilling ink and color ribbons. Therefore, thermal printing devices are almost universally used in point-of-sale labeling equipment, such as weighing scales and dispensing devices used to sell perishable food and other commodities. It is precisely in combination with the thermal recording label products used in these occasions that the embodiment of the time-temperature indicator activating element product of the present invention finds a special application.

In a preferred embodiment, the present invention takes the form of a label with a paper or film substrate. The substrate is provided with a coating containing a first or primary composition that is thermally responsive and produces significant Visual changes, such as darkening or strengthening of colors. This embodiment also includes a second composition, which is spontaneously generated or carried on a second substrate, which can activate or accelerate the environmental thermal response of the first composition when it is in contact with the label coating. From the beginning of this activation, usually when the label and the perishable product unit are connected by self-adhesion or other common methods, the thermally responsive composition of the combined system inevitably changes with time and temperature at a rate that changes with the ambient temperature. The critical accumulation direction carries out the color reaction, and the accumulated amount of time and temperature reaches the predetermined color density deepening level, and the indicator will indicate that the relevant perishable product has reached the end of the effective period of use.

The preferred first composition label may be a self-adhesive thermal recording label, which is generally distributed by weighing stations in supermarkets, delicatessens, fast food commercial centers, meat, fish and poultry processing plants, etc. It usually contains a primary color "Direct thermal paper" form of high temperature printing composition. Other products that incorporate thermal recording compositions, such as fax and thermal imaging papers and films, represent an additional source of component components for the first composition of the invention.

The second active element component preferably takes the form of a self-adhesive label or a label comprising a substrate and an adhesive composition, the latter additionally comprising an activating component, which, for example, when applied to a direct thermal label coating, In combination with the first composition, for example, the color forming reaction can be carried out in a lower temperature range than the thermal record response requirements designed for label products. The lower temperature range is generally above the safe storage temperature of perishable products. Within this range, the product is likely to spoil and deteriorate. In a modified embodiment, the activating co-reactant component can be prevented from prematurely acting on the first color-forming composition by using an isolation method encapsulated in a rupturable capsule, or it can also include a component that requires exposure to actinic radiation Only photosensitive compound. Alternatively, the active composition can be directly adhered to the first composition coating in the form of, for example, a fluid or a sheet when marked at the point of sale and applied to the product unit.

In another embodiment of the present invention, the active label composition may include a co-reactant as an active component. When combined with one or more reactant components in the first high-temperature printing composition, the co-reactant can form The second color-forming composition, which can perform color-forming reaction at its own thermal reaction speed in a relatively low medium ambient temperature range, and this temperature range represents the risk of spoilage of food or perishable products. The medium spoilage temperature range can vary with the corporate environment, for example, due to the differences in fish, meat and poultry in the supermarket environment, various activation element labels can automatically be within different environmental temperature response ranges and different critical time-temperature accumulations The first label composition is activated within the amount. The operators choice or weighing workstation computer will determine the appropriate activator label based on the perishable product category.

The obvious visual end point of the critical time-temperature cumulant can adopt any convenient or direct form according to the predetermined occasion, in which it can be clearly observed. That is to say, the activator can be applied to the first label composition in a clear shape or design, for example, it can generate or obscure a barcode that the supermarket equipment will respond to, or show a gradient matching color density or color for the benefit of customers. Color warning message.

Direct thermal paper and other similar products containing the first high-temperature color-forming printing composition are widely known and are commercially available from many industrial sources. Each of these products is ubiquitously used in fax machines, price/weight labeling machines in supermarkets and food processing plants, point-of-sale credit card readers, etc. They generally contain a substrate coated with a mixture of co-reactant materials. When exposed to high temperatures exceeding 60°C, the co-reactant material can produce a visually distinguishable mark or color. These sheet products generally include paper, polymer film, foil and other substrates coated with a co-reactant compound or material composition, which are combined at a predetermined temperature to form a generally irreversible reaction with the background of the unreacted composition. High-contrast colors.

Thermally responsive color-forming co-reactant compositions are well known in the art. Typically these compositions are pH-sensitive conjugates, containing an azo dye precursor, a co-reactant coupling compound, and a basic reaction initiator, or a colorless or off-white dye and a proton-donating substance such as an acid, when specified It will form a contrast dye color together with temperature. The color-forming reaction of these compositions to the heat may be directly caused by the inherent thermodynamics of the color-forming reaction, or may be due to activation of a thermally labile co-reactant or thermally initiated release of the co-reactant from the meltable matrix or encapsulated protective membrane.

Representatives of many color-forming compositions and dyes, acid co-reactants, and adhesive matrix components that are known in the art and which do not constitute an essential part of the present invention themselves but are useful in the practice of the present invention are: color Precursors, such as furan, lactone, 2-benzo[c]furanone or triarylmethane dyes, such as crystal violet lactone, 3,N-cyclohexyl-β-methyl-amino-6-methyl-7 -Anilinofuran or 3-pyrolidino-6-methyl-7-anilinefuran, acid generating co-reactants such as p-benzyl hydroxybenzoate, bisphenol A, phenol condensation products, low-melting organic acids or esters, and Cellulose and mono- and co-polymeric binder materials such as vinyl acetate, ethanol, pyrrolidone, acrylate or acrylamide. A detailed list of these known components and compositions can be found in published materials, for example in the patent documents of Iwata et al., US 4,370,370; Glanz, US 4,535,347; Arbree et al., US 4,591,887; Kang, US 4,898,849; Smith et al., US 5,071,821; Kawakami et al., US 5,288,688; and Hoffmann et al., US 5,354,724; each document is incorporated herein by reference.

Figure 5 schematically depicts the plan view (a)-(b) gradually formed by the accumulation of colors over time in the activation area of the label of a thermally printed product. This product will eventually obscure the barcode to indicate that the product has passed its shelf life. Figure 6 schematically depicts the plan view (a)-(b) of the color gradually formed in the selective activation area of the thermal printing product label. This product will eventually become darker at any time-temperature accumulation to indicate that the product has passed the shelf life Information; Figure 7 graphically depicts the effect of the activator composition and temperature on the color forming rate in the embodiment of the present invention; and Figure 8 graphically depicts the increased activator composition on the color forming rate in the embodiment of the present invention Impact.

Detailed Description of the Invention As shown in Figure 1, a preferred first element of the time-temperature indicator of the present invention is selected from a large number of widely used commercial direct thermal printing products, especially self-adhesive label products 10, which include thermal The substrate 11 such as paper and film of the reaction color-forming layer 13. The bottom surface of the substrate 11 is coated with a pressure-sensitive or low-temperature heat-activatable adhesive layer 15. When the aforementioned adhesive composition is used, the adhesive layer 15 has a debonding sheet or film 17 that can be easily separated. The film 17 can be It is removed to allow the adhesion layer 15 to adhere to the perishable product exposed to the time-temperature accumulation to be monitored. As a measure to protect the reactive composition layer 13 from physical damage or contamination such as oil or solvent, an optional barrier layer 19 is often included.

In ordinary use, the upper surface of the label, that is, on the layer 19, is selectively printed with a thermal label at a high temperature above 60°C as specified by the label manufacturer to affect the selective reaction of the composition layer 13 to form a color Marking, indicating the weight, price, barcode recognition, etc. of the product unit. The resulting printed label is then removed from the supply roll, usually automatically in a weighing device, for adhesion to the product unit via an adhesive layer. The labeled product unit is then either returned to a safe storage environment, such as a food freezer, or delivered to the customer who needs it.

Such a direct thermal label product applies a second activator element, as shown in FIG. 2 20, to the thermally responsive composition layer 13, or brings it into close contact in the presence of the protective layer 19, and Introduced into the time-temperature indicator system according to the present invention. A preferred embodiment of the activator 20 is in the form of a small sheet or label, containing a transparent film such as polyester, polycarbonate, polyolefin or similar materials commonly used in the coating field as the substrate 21, which has an adhesive composition The layer 25, the sheet can be adhered to the outer surface of the direct thermal printing label 10 through the layer 25, especially preferably in the above label printing procedure. If a pressure sensitive adhesive is used, the activator element 20 will generally contain a removable protective layer 27 coated with a debonding agent.

According to the present invention, the composition of the adhesion layer 25 includes an activating component or activating composition 26, which can initiate a direct thermal color-forming reaction when it comes into contact with at least one of the first co-reactants in the direct thermal composition 13. In the first embodiment, the activating component itself is a co-reactant, which when combined with the first co-reactant of the direct thermal composition will produce a color-forming composition, which produces a visually obvious color change Preferably, the rate of change in the medium ambient temperature range is close to the degradation rate of the relevant perishable products. For example, the activating component co-reactant may include an acid or leuco dye that will form a reaction pair with the complementary component of the direct thermal composition.

Alternatively, in the second embodiment, the activation component or composition 26 will create an environment or condition under which the co-reactant component of the first direct thermal reaction will be in a moderate environment Reaction within the temperature range. In this embodiment, the activating component can dissolve at least one of the generally thermally unstable co-reactants of the first thermal recording reaction, thereby enabling the reaction to proceed in an intermediate temperature range. As a variation, the activating component can dissolve or act on intermediate components, such as an isolation matrix or encapsulation formation containing layer 13, to cause the release of the first co-reactant and allow the reaction to proceed in the mid-temperature range.

The effect of the activation element can be seen in the assembly 30 shown in FIG. 3, in which the adhesive activation composition layer 25 of the activation sheet directly adheres to the first direct thermal composition layer 13. The variation of the embodiment can also be seen, where the direct thermal label product may also not have the optional protective upper layer 19, and the activation sheet also includes an element layer 33 in the form of an overprint mask. 33 has an open central area 35, which can be passed through 35. See the color composition layer 13 below. This mask can be used to provide a reference for monitoring the color process, which will be described in more detail below. It can also be seen that the activated label binder is adhered to the surface of the packaging material 39 via the label adhesive layer 15, which wraps a perishable product unit that needs to be monitored.

When the activated sheet is applied to the product label, the activated component of the composition 25 combines with one or more adjacent components in the layer 13 to produce the activated area 37 of the first thermal recording composition. Therefore, this area performs a prescribed color reaction within a medium temperature range. For direct thermal printing labels, this temperature range is much lower than the threshold of 60°C, and is reasonably compatible with the temperature at which the perishable products under monitoring are prone to decay. The range is comparable. In this way, the activation label can meet the purpose of the time-temperature indicator system to respond to changes in ambient temperature exceeding a certain temperature range. This temperature range is helpful for the safe storage of perishable products and ultimately by displaying a predetermined level of color. Deepen the density to indicate that the safe hourly temperature accumulation has been exceeded, thereby doubting the safety and quality of the relevant perishable product unit.

The response of the activation label system of FIG. 3 can be seen in FIG. 4, where, in the activation stage (a), the combination 30 includes a disc-shaped activation sheet 20, which includes a mask 33 printed with ordinary ink. The selected color density matches the expected color density formed during a predetermined critical time-temperature accumulation period. At this stage, the normal low-density color of the unreacted direct thermal color-forming composition can be seen through the mask window 43. With the passage of time, the exposure of perishable products to changing temperatures accumulates to meet the critical time-temperature accumulation of the activated label, which can visually reflect the color density of the label composition 45, as in stage (b), it reaches the mask The color density of 33 indicates the end of the product shelf life. Further exposure of the product to another cumulative amount of time-temperature will cause the window signal density 47, such as in stage (c), to far exceed the threshold 33, reminding the user that the quality of the product may have been severely degraded.

An application change of the time-temperature indicator system can be seen in Figure 5. For example, in the activation stage (a), the direct thermal composition layer 13 of the synthetic label 30 has been thermally printed with labels indicating weight, price, etc. 53, including product category bar code 55. An activated sheet containing the transparent sheet layer 21 has been adhered to the label composition layer 13 in a position such that the activated area 37 and the barcode 55 of the layer 13 composition expand together. Once the shelf life of the relevant perishable product expires, that is, at the critical point in stage (b)-when the temperature accumulation is reached, the color density of the reaction color-forming composition area 57 becomes blurred, or the barcode 55 is changed to make it sufficient for the computer system in the market Recorded as product failure or unsafe.

Figure 6 describes a similar use of this indicator, which meets customer requirements. Therefore, in the activation stage (a), the label system 30 printed with the direct heat label 63 generally related to the product has already adhered the activation sheet to the color composition layer 13, and the transparent support film 21 of the activation sheet has an adhesive combination The layer 25 has a low color density activator component, which is printed in the form of an identifiable label or information 65 during the process of manufacturing the sheet. After the critical time-temperature cumulative amount has been reached, such as in stage (b), the activated zone of the composition layer 13 is directly heated to obtain a higher color density 69 that has reacted, which has sufficient contrast with the background adhesion composition 25 , To remind consumers of dangerous product conditions.

From the foregoing description, those skilled in the art can clearly see that the predetermined value of the critical time-temperature cumulant of a particular indicator system will depend on two basic factors. The first is the time factor, which is determined by the total The reactant determines the speed of the color reaction; the second is the temperature factor, that is, the influence of the random environmental temperature on the reaction speed. For example, a certain white dye/acid co-reactant pair can form a distinguishing color dye at a nearly negligible rate at about 0°C, but at a moderately high temperature, such as about 24°C and room temperature, after only a few hours or more than about 60°C. The bright density is immediately obtained at the direct thermal printing temperature of °C. Therefore, the color forming speed will change with the increase of the ambient temperature throughout the predetermined operating range, so that after a period of time determined by the cumulative temperature effect, that is, the "critical time-temperature cumulative amount", a preselected The color density of the bright end point.

Therefore, in preparing the indicator system according to the present invention, two parameters, the operating temperature range and the color deepening speed within this range, must be considered. Based on these considerations, one of the main and new advantages of the present invention is that it provides a method for establishing a set of known and precise initiation time data to operate the indicator system, that is, independent activation of color reaction, and When the product just leaves the strictly controlled acceptable ambient temperature, the new activation system is applied to the method of monitoring the perishable product. Based on the established basic data, the system composition deployer can concentrate on selecting the appropriate known co-reactant materials and compositions, which will ensure the color deepening rate consistent with the target perishable product deterioration rate.

To prepare indicator systems containing special color-forming compositions, for example, the selection of the first and activating co-reactant components is entirely under the control of the system manufacturer, but the indicator system is formulated based on experience based on prior art methods. Compositions requiring reaction speed. Such speed can be determined by the color-forming reaction itself or by adding different types or concentrations of composition additives, such as co-reactant solubilizers with different melting points. Therefore, the specific composition indicator system embodiment may include, in the first element layer 13 (FIG. 3), about 5% by weight of crystal violet lactone dispersed in an acrylic adhesive, and a second activator The element layer 25 contains about 4.5% by weight of benzyl-4-hydroxybenzoate in a similar adhesive material, and a sufficient amount of phthalate plasticizer is added to make the composition of the resulting layer 25 It has self-adhesive properties to adhere to layer 13. The resulting activated zone 37 of the combined indicator system will become the desired end-point dye after a few hours of ambient temperature changes. The degree of reaction of the color precursor/activator combination and the critical time-temperature cumulative amount can be changed as required by changing the concentration of the co-reactant component or the coating thickness or viscoelasticity. Any similar dedicated composition indicator system can be easily derived from existing technology through ordinary tests.

Another important advantage of the present invention is that it can economically introduce the main known direct thermal marking products into an effective time-temperature indicator system. In this particular embodiment of the present invention, one or more co-reactant components in the first high temperature direct thermal imaging or color forming reaction composition in the label product are combined with the activating component of the activator sheet element used Used to reduce the activation temperature range of the first imaging reaction, or to generate a second color reaction that is active in the middle temperature range to provide the required visual change, indicating the expiration of the predetermined critical time-temperature accumulation. For example, the active label composition of layer 25 may simply include a solvent and high boiling point organic components, such as isophorone, hexanediol, etc., to soften the matrix of the label composition layer 13 and make the first composition co-reactant The components can be blended at lower temperatures. As a variant embodiment, the activator label composition may contain additional or different types of co-reactants to increase the speed of the first reaction in the medium ambient temperature or to constitute another color reaction to increase the visual density of the indicator response.

The activator element composition of the embodiment of the present invention may further include an activator component capable of simultaneously using the activator element and the direct thermal label product containing the protective layer element 19 (FIG. 1 ). Although such a composition containing a protective layer element can reduce the instantaneous influence of external oil, moisture or solvent materials on the first direct thermal label component, the activation composition in layer 25 can be conveniently formulated to contain barriers that can counteract barriers or other The solvent or penetrant affected by the protection mode is to activate the color reaction. These additives can include long-lasting high-boiling solvents or wetting agents, which can effectively overcome the temporary protection provided by barrier layers and the like, and can activate potential color-forming reactions. As an extreme method, physical abrasives or penetrating devices may be considered.

Although the foregoing points of the embodiments of the present invention have generally regarded the new activation element as comprising a composition layer coated on a supporting substrate, in fact, the coating of the activation component or the co-reactant can also be coated with a fluid or Laminated method to achieve. For example, a clear ink containing an active co-reactant component can be applied to the position of the activation sheet 21 (FIG. 5) to achieve the same effect as the obscuring barcode 55 when the predetermined critical time-temperature accumulation ends.

Based on the foregoing discussion of the embodiments of the present invention, the following examples will provide those skilled in the art with further guidance for effective formulation and manufacture of the present invention. In order to simplify the ranking evaluation of the composition and to consider the expected advantages of combining the present invention with commercial direct thermal imaging products, most of these embodiments use representative direct thermal products such as thermal recording fax paper (AccuFux brand, PM Company, Cincinnati, OH) and direct thermal label (Nashua brand, Nashua Company, Nashua, NH). The preparation and testing of the samples in these examples used common coating technology, methods and equipment. Unless otherwise stated, the proportions of the compositions are expressed on the basis of weight.

The first embodiment of the present invention including the activated sheet product 20 (FIG. 2) of Example I includes including an acidic co-reactant 26 used as a white dye in the adhesive layer composition 25, containing a typical direct thermal label product. The preparation method of the activator composition includes: a certain amount of polyacrylic acid pressure-sensitive adhesive composition (Gelva 2497, Solutia, St. Louis, Mo) dissolved in a commercial organic solvent and a sufficient amount of 30% p-toluenesulfonic acid The solution of monohydrate (PTSAM) dissolved in ethyl acetate is mixed, and there is about 2.8% PTSAM in the resulting mixture. The mixture is then diluted with a medium volatile organic coating carrier solvent to provide a convenient coating viscosity and coated on the 0.05mm polyester film 21 with a common Meyer bar device to obtain a flow coating of about 0.05-0.07mm thick , And air-dried at room temperature of about 24°C to obtain an adhesion layer of about 0.04 mm. A piece of ordinary silicon-coated debonding paper 27 is attached to the adhesive layer for subsequent processing.

The prepared activator sheet material is cut into a number of sheets 20 of suitable size for testing. After removing the layer 27, such a sheet was adhered to the reactive surface of a piece of AccuFax thermal recording facsimile paper to form a sample of a common activated time-temperature indicator system as described in 30 in FIG. 3. The activated sample is kept at a constant temperature, or is subjected to varying measurement temperatures in a common laboratory oven or refrigeration equipment cycle.

After activation, the X-Rite 404 portable reflection densitometer was used to measure the optical density of the color change in the activated area under the sample label in the cyano mode at selected times. In addition, sample labels with different concentrations of activated acid PTSAM in layer 25 are prepared and tested in the same way. The test results obtained at room temperature of about 24°C are shown in Table I: the optical density changes with time after the system is activated. From this test variation, a achieved optical density can be selected as an indicator of the critical time-temperature cumulant end point. The degradation speed of perishable products is similar to the color deepening speed in the activated label system.

Example II The activated samples prepared according to Example I were tested for changes in optical density during storage at room temperature and 5°C. The results shown in Table II show the effect of temperature changes on the reaction speed of the activation indicator system. This effect is illustrated in Figure 7, where the activator of the present invention is used to track the extent of the slow time-temperature accumulation of perishable products exposed to it. In Figure 7, the listed PTSAM concentrations of 0, 2.8, 5.8, and 7.5% are represented by lines 71, 73, 75, and 77, respectively.

Example III The test sample prepared according to Example I was used to activate another type of direct thermal product, namely Nashua NT7433. As shown in the results in Table III, this tag has lower reactivity to a given activator reagent, mostly due to the presence of the barrier layer.

Example IV prepares the activator label as in Example III, using an activator composition containing 4% PTSAM and different amounts of additional humectant component hexylene glycol (HG). The resulting label was used to activate Nashua NT7433 direct thermal label paper, and the results are shown in Table IV. Among these results, the barrier layer penetration and fluid reaction medium improvement effect imparted by the additive component is obvious, and is illustrated in a graph in FIG. 8.

Example V AccuFax paper was activated with an activator label sample prepared according to the method of Example IV and containing 4% PTSAM and 7.7% HG. The response speed of the obtained activation indicator system under refrigeration (4°C) and room temperature (24°C) is shown in Table V, and the temperature can similarly affect the food spoilage speed.

Example VI prepared the activator label according to the method of Example I, except that bisphenol A, a weak acid activator component, was used instead of PTSAM. The effect of these labels on AccuFax paper (50°C) as an indicator system is shown in Table VI.

Example VII The activator label sample was prepared according to the method of Example VI, and at the same time, about 10% of the high boiling point organic solvent isophorone (boiling point 214°C) was added, and then applied to the activated AccuFax paper. This additional solvent component retains part of the activation composition, while increasing the fluidity of the color forming reaction medium, and results in a higher indicator system response rate, as shown in Table VII.

Example VIII A number of activator label samples were prepared according to the method of Example I, using ester, benzyl-4-hydroxybenzoate (B4HB) as the activator acid. This component is introduced into the Gelva 2497 adhesion matrix of many different activator compositions as a 35% solution in different solvents at a rate of about 5%, because only a small amount of these solvents are left in the final activator combination Therefore, the response speed of the activation indicator system using AccuFax paper at 50°C is very similar, see Table VIII.

Example IX The activator label was prepared according to the method of Example VIII, and the concentration of B4HB in the methanol solvent was different. The influence of the change of activator concentration at 24°C on the deepening density of AccuFax paper is shown in Table IX. Similar results were obtained with Nashua NT7433 paper.

Example X The activator label with improved stability was prepared according to the method of Example I, and the photoacid compound 2-nitrobenzaldehyde was used as the activator component. This component provides the additional benefit of further ensuring precise activation time data beyond the data generally established by the application of activation tags to co-reactant tags. This embodiment improves the erratic activation conditions by requiring the label composition to be exposed to actinic radiation, such as strong ultraviolet light. This exposure is to generate acidic components and affect the activation of the system. The influence of different solvents on the introduction of photoacid was checked by the method of Example VIII, and the results are shown in Table X. Similar enhancement of activation requires the use of activated microencapsulated high-boiling solvents dispersed in the activator label matrix. In such an embodiment, the attached activation label needs to be pressurized to activate the indicator system.

Example XI An activator label was prepared according to the method of Example I, using a commercial water-dispersible polyacrylic acid pressure-sensitive adhesive composition Kiwo D185 (KIWO, Seabrook, TX) instead of the Gelva adhesive composition dissolved in an organic solvent. In addition, the activator acid PTSAM is replaced with trichloroacetic acid (TCA). The efficiency of the activator label applied to AccuFax paper at 24°C is shown in Table XI.

Example XIII An activator label was prepared according to the method of Example XI, using a special co-reactant color-forming composition containing a commercial irreversible thermochromic ink (CTI Dynacolor, Chromatic Technologies). The preparation method of the first color forming system component sheet layer is to use a doctor bar device to coat the ink on a universal printing paper sheet and dry it at room temperature. An activator label containing about 5% trichloroacetic acid was applied to the resulting coreactant sheet and the rate of color density deepening of the activation system was measured at 24°C. The results are shown in Table XII.

Example XIII The activator label was prepared according to the method of Example I, using 4.2% trichloroacetic acid (TCA) instead of PTSAM. Label samples were also prepared in which the activator composition contained 4.2% trichloroacetic acid in the Gelva 2497 matrix and 2.5% additional decanol (DOH-MP, 6.4°C). Attach the activator label to the sheet of the special co-reactant CTI Dynacolor ink composition, and immediately measure the optical density of the obtained activation system sample, and then measure it after refrigerating at 2°C for about 16 hours. At this time, no sample exhibits color density. Significant growth. The sample was then transferred to a room temperature of about 24°C, and the increase in color density within a few hours was measured. In the results shown in Table XIII, the effect of DOH flow agent on accelerating color formation is obvious.

In a variation of this example, an activator label containing n-decanoic acid (NDA-MP 31°C) was prepared and applied to AccuFax paper. During storage at a room temperature of 24°C, the activator composition has to be separated from the color-forming paper composition due to its stable crystalline properties, and the paper hardly exhibits an increase in color density after several hours. The activated sample was then moved to an environment of about 37°C, and it produced a significant color density within a few minutes, which was basically the same as the density achieved by AccuFax paper at the specified printing temperature of about 60°C. Such an activator variant therefore has a dual function: it initiates a time-temperature accumulation reaction in a predetermined intermediate temperature range, and at the same time it can give an indication signal, even if a temporary temperature change exceeds a pre-designed threshold temperature limit. Before or after that, it is proved that there is no exposure to this threshold, which is immediately destructive to the availability of the product that needs to be monitored, just like with a certain antibiotic or vaccine.

Example XIV Many direct thermal label papers contain a barrier layer on top of the color precursor composition layer to prevent physical damage or penetration by oils, solvents, etc. If you want to use a commercial direct thermal label as a component of the activatable hour-temperature indicator system of the present invention, you must consider the influence of such a barrier layer. Activator label using Gelva 2497 adhesive composition containing hexylene glycol wetting agent and 5% activator acid co-reactant, and the results related to barrier layer (Nashua NT5726) and non-barrier layer (Nashua NT8821) paper Table XIV.

Based on the foregoing description and examples, it can be expected that other embodiments and modifications of the present invention are obvious to skilled artisans, and these embodiments and changes are intended to be included in the scope of the present invention, as in the appended claims. As described in the book.