Precise heat-sensitive label based on carrier-dye weak binding system and preparation process thereof

Abstract

This application discloses a precision thermal tag based on a carrier-dye weakly bound system and its preparation process, belonging to the field of thermal recording materials technology. The thermal tag includes a substrate layer, a thermally sensitive functional layer, and a protective layer. The thermally sensitive functional layer comprises a porous carrier material and a weakly bound color-changing system loaded thereon. This system consists of a non-covalent weakly bound complex formed by a thermally sensitive dye and a color-developing agent through hydrogen bonds, van der Waals forces, and / or stacking interactions, which dissociates upon heating and undergoes a color-developing reaction. This application effectively suppresses pre-reaction at room temperature and improves storage stability through the synergistic effect of the weakly bound system and the porous carrier, and allows for precise control of the color-changing temperature window (within 2°C), making it suitable for high-precision monitoring scenarios such as vaccine cold chains. This application also discloses the preparation process of the thermal tag. This application has advantages such as precise response, good stability, and strong adaptability.

Description

Technical Field

[0001] This application relates to the field of thermal recording materials technology, specifically to a precision thermal label based on a carrier-dye weakly bound system and its preparation process. Background Technology

[0002] Thermal recording materials are a class of functional materials that utilize the principle of thermochromic color change to record information. They are widely used in logistics labels, anti-counterfeiting labels, food packaging, and pharmaceutical cold chain monitoring. Thermal labels typically combine colorless or light-colored electron-donating leuco dyes with electron-accepting color developers to form a thermal coating. Under the heating action of a thermal head or laser, the two react chemically to reveal the color, thus recording patterns or text.

[0003] Existing thermal label technologies mainly include direct thermal printing labels, reversible thermal recording labels, and time-temperature indicator labels. For example, current thermal labels typically involve coating a substrate such as paper, synthetic paper, film, or plastic with a coating solution containing leuco dyes and developers, then heating the substrate to melt and mix the two components, resulting in a color reaction. In recent years, in the field of reversible thermal recording media, patented technologies have utilized the color reaction between electron-donating and electron-accepting coloring compounds to control thermal energy, achieving image formation and reversible erasure. Furthermore, thermal dyes based on microencapsulation technology have been extensively studied, such as using polymer microcapsules to encapsulate organic thermal dyes, developers, and decolorizing agents to improve system stability and the controllability of color-changing temperatures. Regarding time-temperature indicators, there are thermal labels that utilize the color change caused by the adsorption of volatile dyes after volatilization by an adsorption material layer, as well as temperature-time labels based on diffusion principles.

[0004] However, existing thermal label technology still has the following shortcomings: First, in traditional thermal systems, dyes and color developers have a certain degree of contact and pre-reaction at room temperature, resulting in a darker label background color and poor storage stability, especially in humid and hot environments where premature coloring or uneven color change is likely to occur; Second, the color change response accuracy of existing thermal labels needs to be improved, and the color change temperature window is relatively wide, making it difficult to meet the needs of application scenarios that are highly sensitive to temperature changes (such as vaccine cold chain, high-end food logistics, etc.); Third, some thermal labels use a strong chemical bonding system, which cannot achieve a gradual response once a color change reaction occurs, resulting in insufficient flexibility; Fourth, existing preparation processes still have room for improvement in terms of dispersion uniformity, coating adhesion, and adaptability to large-scale production.

[0005] Therefore, how to design a thermal label that is accurate in response, stable, easy to prepare, and can be mass-produced has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This application provides a precision thermosensitive label based on a carrier-dye weak binding system and its preparation process. By constructing a weak binding system between the dye and the color developer, and combining it with a carrier material with a porous / multi-channel structure, the precise and controllable release of the dye on the carrier and thermochromic effects can be achieved, which can effectively solve the problems in the background technology.

[0007] To achieve the above objectives, this application provides the following technical solution: A precision thermosensitive label based on a carrier-dye weakly bound system comprises a base layer, a thermosensitive functional layer, and a protective layer stacked sequentially. The thermosensitive functional layer includes a porous carrier material and a weakly bound color-changing system loaded on the porous carrier material. The weakly bound color-changing system includes a thermosensitive dye and a color developer. The thermosensitive dye and the color developer form a non-covalent weak bond through hydrogen bonds, van der Waals forces, and / or stacking interactions, and undergo dissociation and contact color-changing reactions under heating conditions. The weakly bound color-changing system is dispersed in the pores and / or surface channels of the porous carrier material. The base layer provides support, and the protective layer covers the thermosensitive functional layer to provide protection. This technical solution achieves uniform dye loading and precise, controllable thermochromic response on the carrier by constructing a weakly bound system combined with a porous carrier structure.

[0008] Furthermore, in the weakly bound color-changing system, the dissociation temperature of the non-covalent weak bond between the thermosensitive dye and the color developer can be controlled by adjusting the molecular structure of the dye, the type of substituents in the color developer, and / or the solvent environment. Through these settings, the color-changing initiation temperature and response sensitivity of the thermosensitive label can be flexibly set according to the needs of different application scenarios. The color-changing temperature window can be precisely controlled within 2℃, significantly improving response accuracy.

[0009] Furthermore, the thermosensitive dye is selected from one or more of the following: fluorane dyes, phthalide dyes, phenothiazine dyes, or spiropyran dyes; the color developer is selected from one or more of the following: phenolic compounds, sulfonylurea compounds, aromatic carboxylic acid compounds, or inorganic acid compounds; the molar ratio of the thermosensitive dye to the color developer is 1:0.5 to 1:5. Through the above settings, the ratio of dye to color developer can be optimized according to the reactivity and color change temperature requirements of different color development systems, thereby improving the stability and color development efficiency of weakly bound systems.

[0010] Furthermore, the porous support material is selected from one or more of porous silica, mesoporous molecular sieves, metal-organic framework materials, porous polymers, or natural porous minerals. The pore size of the porous support material is 2 nm to 500 nm, and the porosity is 30% to 85%. Through the above configuration, the porous support material provides abundant specific surface area and channel structure, which is beneficial for the uniform loading and stable fixation of the weakly bound color-changing system on the support. At the same time, the pore structure provides spatial channels for the diffusion and release of dye under heating conditions, thereby achieving precise and controllable thermochromic changes.

[0011] Furthermore, the thermosensitive functional layer also includes a sensitizer with a melting point of 60℃ to 180℃; the mass ratio of the sensitizer to the thermosensitive dye is 1:1 to 1:10. Through this configuration, the sensitizer melts first upon heating, promoting the dissociation and interdiffusion of the dye and color developer in the weakly bound system, reducing the response threshold of the thermosensitive label, and improving color development sensitivity and uniformity.

[0012] Furthermore, the weakly bound color-changing system is encapsulated in a polymer wall material in the form of microcapsules. The microcapsules have a particle size of 0.5 μm to 15 μm, and the microcapsule wall material is selected from one or more of polyurethane resin, urea-formaldehyde resin, melamine resin, or polyester resin. Through this configuration, microencapsulation of the weakly bound color-changing system effectively isolates it from external environmental interference (such as moisture, oxygen, acidic or alkaline substances), improving the storage stability and weather resistance of the thermal label. Simultaneously, the thermal sensitivity or melting characteristics of the wall material enable precise triggering and release of the dye and color developer upon heating.

[0013] Furthermore, the weakly bound color-changing system is dispersed within the microcapsules in a solvent carrier. The solvent carrier has a boiling point of 100℃ to 300℃ and is selected from one or more of higher fatty acid esters, vegetable oil-based solvents, or synthetic esters. Through this configuration, the solvent carrier maintains a stable liquid environment at room temperature, which facilitates the formation of stable non-covalent weak bonds between the dye and the color developer within the microcapsules. When heated to a predetermined temperature, the solvent carrier releases the dye due to thermal expansion or changes in the local microenvironment, achieving precise thermochromic changes.

[0014] Furthermore, the base layer is one of paper substrate, polymer film, or non-woven fabric, and the thickness of the base layer is 20 μm to 200 μm; the protective layer is a transparent polymer coating selected from one or more of acrylic resins, polyurethane resins, or silicone resins, and the thickness of the protective layer is 1 μm to 10 μm. Through the above configuration, the base layer provides sufficient mechanical strength to support the label structure, while the protective layer effectively blocks external physical scratches and environmental factors from affecting the heat-sensitive functional layer, extending the label's lifespan and ensuring the visibility of the color development effect.

[0015] Furthermore, a base coating layer is provided between the substrate layer and the thermosensitive functional layer. The base coating layer comprises a white pigment and a binder, wherein the white pigment is selected from one or more of titanium dioxide, calcium carbonate, or kaolin. Through the above arrangement, the base coating layer can smooth out surface defects of the substrate layer and improve the contrast and visual clarity of the thermosensitive color image.

[0016] Furthermore, the thermosensitive functional layer also includes a thermodynamic response modifier, which is selected from one or more of paraffin wax, polyethylene wax, or fatty acid amides, and has a melting point of 40℃ to 200℃. Through the above configuration, the thermodynamic response modifier regulates the local heat conduction and heat distribution within the thermosensitive functional layer through a phase change process, achieving precise control of the color change response curve, ensuring that the thermosensitive label maintains a consistent color development threshold and color depth under different heating rates.

[0017] Compared with the prior art, the beneficial effects of this application are: 1. This application constructs a weak binding system between the thermosensitive dye and the color developer, formed by hydrogen bonds, van der Waals forces, and / or stacking interactions, to pre-bind the dye and color developer onto a porous carrier. This effectively suppresses the pre-reaction and dark background color problems caused by direct contact between the dye and color developer at room temperature in traditional thermosensitive labels, significantly improving the storage stability and white paper preservation of thermosensitive labels. The shelf life under humid and hot conditions can be extended by more than 30% compared to traditional labels.

[0018] 2. This application utilizes the pore and channel structure of porous carrier materials to confine the loading of weakly bound color-changing systems. Combined with the adjustable design of the weak binding dissociation temperature between the thermosensitive dye and the color developer (achieved through molecular structure modification, substituent adjustment, or solvent environment optimization), the color-changing temperature window of the thermosensitive tag is precisely controllable, achieving a color-changing initiation temperature accuracy within 2℃, meeting the application requirements of high-precision monitoring scenarios such as vaccine cold chain and biological product transportation.

[0019] 3. This application uses microencapsulation technology to encapsulate the weakly bound color-changing system in a polymer wall material. Combined with the environmental regulation effect of the solvent carrier, the isolation and protection effect and the sensitivity of the thermal response of the weakly bound system are further improved. At the same time, through the synergistic effect of sensitizers and thermal response modifiers, the adaptability of thermal tags in terms of color-changing temperature, response rate and usage environment is broadened, which has good versatility and potential for large-scale application. Attached Figure Description

[0020] Figure 1 This is a structural schematic diagram of an embodiment of this application.

[0021] In the figure: 1. Base layer; 2. Undercoat layer; 3. Thermosensitive functional layer; 31. Porous carrier material; 32. Weakly bonded color-changing system; 321. Microcapsule; 4. Protective layer. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In the description of this application, any descriptions of orientation, such as up, down, front, back, left, right, etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are merely for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. When a feature is referred to as being set, fixed, or connected to another feature, it can be directly set, fixed, or connected to the other feature, or it can be indirectly set, fixed, or connected to the other feature.

[0024] Please see Figure 1 This application provides the following technical solutions: Example 1 A precision thermal label based on a carrier-dye weak binding system includes a base layer 1, a thermal functional layer 3, and a protective layer 4 stacked sequentially.

[0025] The base layer 1 is a paper substrate with a thickness of 100 μm. The thermosensitive functional layer 3 includes a porous carrier material 31 and a weakly bound color-changing system 32 loaded on the porous carrier material 31. The porous carrier material 31 is mesoporous silica with a pore size of 5 nm to 50 nm and a porosity of 65%. The weakly bound color-changing system 32 includes a thermosensitive dye and a color developer. The thermosensitive dye is crystal violet lactone (CVL), and the color developer is bisphenol A (BPA). The thermosensitive dye and the color developer form a non-covalent weak bond through intermolecular hydrogen bonding. The molar ratio of the thermosensitive dye to the color developer is 1:2. The weakly bound color-changing system 32 is encapsulated in a polyurethane resin wall material in the form of microcapsules 321. The particle size of the microcapsules 321 is 2 μm to 8 μm. The microcapsules 321 also contain a solvent carrier (higher fatty acid methyl ester, boiling point 180 °C) and a sensitizer (dimethyl terephthalate, melting point 140 °C, mass ratio to thermosensitive dye 1:3). The above-mentioned microencapsulated weakly bound color-changing system 32 is uniformly loaded into a mesoporous silica carrier by impregnation, and then coated onto the substrate layer 1 to form a thermosensitive functional layer 3. The protective layer 4 is an acrylic transparent polymer coating with a thickness of 5 μm, covering the thermosensitive functional layer 3.

[0026] In use, the aforementioned thermal label is affixed to the surface of the item to be monitored, and then heated and recorded using a thermal printer or thermoforming equipment. At room temperature, the thermal dye and the developer form a stable, weakly bound complex through hydrogen bonding, without any color development reaction. When the thermal label is heated by a heat source, the heat is first absorbed by the sensitizer, causing it to melt. Subsequently, the internal temperature of the thermal functional layer rises, the microcapsule wall material softens upon heating, and releases the internal weakly bound color-changing system. Simultaneously, the solvent carrier expands upon heating, disrupting the weak hydrogen bonds between the dye and the developer, allowing for effective contact and electron transfer, thereby triggering a color development reaction and forming a clear recorded image on the surface of the thermal label. By adjusting the molecular structure of the thermal dye or the type of substituents in the developer, the dissociation temperature of the weak bond can be precisely adjusted, allowing the color-changing initiation temperature of the thermal label to be flexibly set within the range of 40℃ to 180℃, and the color-changing temperature window can be controlled within 2℃.

[0027] Example 2 The difference from Example 1 is that: the porous carrier material 31 is a metal-organic framework material MOF-5 (pore size approximately 10 nm, porosity 45%), the thermosensitive dye in the weakly bound color-changing system 32 is a fluorane dye (2-chloro-6-(diethylamino)fluorane), the color developer is dodecyl gallate, the molar ratio of the thermosensitive dye to the color developer is 1:1, and the weak binding is a combination of stacking and van der Waals forces. The substrate layer 1 is a polyethylene terephthalate (PET) film with a thickness of 75 μm. A base layer 2 is also disposed between the substrate layer 1 and the thermosensitive functional layer 3, the base layer 2 containing titanium dioxide pigment and polyvinyl alcohol binder. The preparation process of this example is the same as that of Example 1.

[0028] Example 3 The difference from Example 1 is that the weakly-bound color-changing system 32 is not microencapsulated. Instead, the thermosensitive dye and the developer are directly loaded into the pores of the porous carrier material 31 by the solvent blending method, and a complex is formed by weak hydrogen bonding between the dye and the developer. The preparation process of the thermosensitive label in this example is more simplified and is suitable for application scenarios that are cost-sensitive and have a relatively mild use environment.

[0029] It should be noted that the component ratios and process parameters involved in this example can be adjusted according to the actual application scenario. The pore diameter of the porous carrier material is preferably 10 nm to 100 nm, and the porosity is preferably 50% to 75% to obtain the best dye loading and desorption and release performance. The selection of the microcapsule wall material can be based on the target color-changing temperature and the use environment: polyester resin can be selected for low-temperature scenarios (60 °C); polyurethane resin can be selected for medium-temperature scenarios (60 °C to 120 °C); urea-formaldehyde resin or melamine resin can be selected for high-temperature scenarios (120 °C). The control switch group and the core chip of the thermosensitive printing device can select the control module supporting the commercially available thermosensitive print head, and the specific model can be configured according to actual needs. The color display control and printing process of the thermosensitive label adopt the thermosensitive printing method commonly used in the prior art.

[0030] Although the embodiments of the present application have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A precision thermal label based on a carrier-dye weakly binding system, characterized in that: It includes a base layer (1), a thermal functional layer (3), and a protective layer (4) stacked in sequence. The thermosensitive functional layer (3) includes a porous carrier material (31) and a weakly bonded color-changing system (32) loaded on the porous carrier material (31). The weakly bound color-changing system (32) includes a thermosensitive dye and a color developer. The thermosensitive dye and the color developer form a non-covalent weak bond through hydrogen bonds, van der Waals forces and / or stacking effects, and undergo dissociation and contact color development reactions under heating conditions. The weakly bonded color-changing system (32) is dispersed in the pores and / or surface channels of the porous carrier material (31).

2. The precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: In the weakly bound color-changing system (32), the dissociation temperature of the non-covalent weak bond between the thermosensitive dye and the color developer is controlled by adjusting the molecular structure of the dye, the type of substituent in the color developer, and / or the solvent environment.

3. The precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: The thermosensitive dye is selected from one or more of fluorane dyes, phthalide dyes, phenothiazine dyes, or spiropyran dyes; the color developer is selected from one or more of phenolic compounds, sulfonylurea compounds, aromatic carboxylic acid compounds, or inorganic acid compounds; the molar ratio of the thermosensitive dye to the color developer is 1:0.5 to 1:

5.

4. A precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: The porous carrier material (31) is selected from one or more of porous silica, mesoporous molecular sieve, metal-organic framework material, porous polymer or natural porous mineral, and the pore size of the porous carrier material (31) is 2nm to 500nm and the porosity is 30% to 85%.

5. A precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: The thermosensitive functional layer (3) also contains a sensitizer, the melting point of which is 60℃~180℃; the mass ratio of the sensitizer to the thermosensitive dye is 1:1~1:

10.

6. A precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: The weakly bonded color-changing system (32) is encapsulated in a polymer wall material in the form of microcapsules (321). The particle size of the microcapsules (321) is 0.5m to 15m, and the microcapsule wall material is selected from one or more of polyurethane resin, urea-formaldehyde resin, melamine resin or polyester resin.

7. A precision thermal label based on a carrier-dye weakly binding system according to claim 6, characterized in that: The weakly bound color-changing system (32) is dispersed in a solvent carrier within a microcapsule (321), wherein the solvent carrier has a boiling point of 100°C to 300°C and is selected from one or more of higher fatty acid esters, vegetable oil-based solvents, or synthetic esters.

8. A precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: The base layer (1) is one of paper substrate, polymer film or non-woven fabric, and the thickness of the base layer (1) is 20 μm to 200 μm; the protective layer (4) is a transparent polymer coating selected from one or more of acrylate resin, polyurethane resin or silicone resin, and the thickness of the protective layer (4) is 1 μm to 10 μm.

9. A precision thermal label based on a carrier-dye weakly binding system according to claim 1, characterized in that: A base layer (2) is also provided between the base layer (1) and the thermosensitive functional layer (3). The base layer (2) contains a white pigment and a binder. The white pigment is selected from one or more of titanium dioxide, calcium carbonate, or kaolin.

10. A process for preparing a precision thermal label based on a carrier-dye weakly binding system, characterized in that, Includes the following steps: Step 1: Preparation of a weakly bound color-changing system (32): The thermosensitive dye and the color developer are mixed in a molar ratio of 1:0.5 to 1:5, and a non-covalent weakly bound complex is formed in a solvent through hydrogen bonding, van der Waals forces and / or stacking effects; Optionally, the complex is mixed with a sensitizer and a solvent carrier and then encapsulated in a polymer wall material using a microencapsulation process to obtain a weakly bound color-changing system in the form of microcapsules (321); Step 2, Loading: The weakly bonded color-changing system (32) obtained in Step 1 is impregnated or sprayed into the pores and / or surface channels of the porous carrier material (31), and after drying, a heat-sensitive functional layer material loaded with the weakly bonded color-changing system (32) is formed. Step 3: Coating and molding: The heat-sensitive functional layer material obtained in step 2 is coated on the substrate layer (1) to form the heat-sensitive functional layer (3); optionally, a primer layer (2) is first coated between the substrate layer (1) and the heat-sensitive functional layer (3). Step 4: Apply or attach a transparent polymer protective layer (4) over the thermal functional layer (3), and obtain the precision thermal label after drying and curing.

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