Temperature change anti-counterfeiting printing coating

Abstract

The invention relates to the technical field of anti-counterfeit printing materials, and discloses a temperature change anti-counterfeit printing coating which comprises a bearing substrate, a functional layer group and a protective surface layer which are sequentially arranged from bottom to top, the bearing substrate is made of a material adaptive to a target application scene, and the material comprises any one of plastic, paper and metal; the functional layer group at least comprises a temperature change core layer, the temperature change core layer contains at least one thermochromic component, the thermochromic component is selected from a nano modified microencapsulated pigment, and the color change temperature precision of the temperature change core layer is less than or equal to + / -0.3 DEG C. According to the invention, environmental thermal disturbance is resisted in a targeted manner through differentiated structural design, namely, the cavity of the heat insulation layer in the eight-layer structural scheme and the heat insulation sheet work together, so that interference of external temperature fluctuation on the temperature change core layer can be isolated, and the response time is shortened by more than or equal to 50%; according to the five-layer structure scheme, the photothermal conversion efficiency is optimized through 8% of graphene / CNTs composite filler, and rapid conduction and uniform distribution of heat are achieved.

Description

Technical Field

[0001] This invention relates to the field of anti-counterfeiting printing materials technology, specifically to an integrated thermochromic anti-counterfeiting printing coating. Background Technology

[0002] Temperature-sensitive anti-counterfeiting printing coatings are widely used in anti-counterfeiting traceability, temperature monitoring, and other fields. The market demand for wide temperature range coverage (-10℃ to 70℃) and high-precision response (±0.3℃ level) is increasingly urgent. However, existing technologies have consistently failed to simultaneously meet these two core requirements, with the main bottlenecks concentrated in two areas: Firstly, environmental thermal disturbances cause response delays, making accuracy difficult to control. Existing coatings lack structural design optimization for wide-temperature-range thermal interference. External temperature fluctuations can cause lag in internal temperature transfer within the coating, amplifying color-changing errors. For example, the thermochromic microcapsule coating for double-layer silica wall materials disclosed in CN114525124A, due to the lack of dedicated heat insulation and anti-interference components, exhibits a temperature response delay of over 3 seconds in a wide temperature range test from -10℃ to 70℃, with color-changing accuracy only controllable within ±2.2℃, far below the required ±0.3℃.

[0003] Secondly, the mismatch in the thermal expansion coefficients of the multilayer materials leads to microcapsule rupture and failure. The core of thermochromic coatings is the thermochromic microcapsule, but in existing technologies, the thermal expansion coefficients of the various functional layers lack coordinated design. Uneven thermal expansion and contraction under wide temperature cycling causes stress concentration between layers, damaging the microcapsule structure. For example, in the thermochromic microcapsule coating disclosed in CN104910714A, the difference in thermal expansion coefficients between the substrate, adhesive, and thermochromic layer exceeds 1.5 × 10⁻⁻⁻⁶. 5 After 500 cycles in the temperature range of -10℃ to 60℃, the microcapsule rupture rate reached over 30%, the color change accuracy decreased to ±2.5℃, and it could not maintain long-term stability.

[0004] Therefore, developing a wide-temperature-range, high-precision temperature-changing anti-counterfeiting printing coating that can resist environmental thermal disturbances and solve the problem of thermal expansion matching of multi-layer materials has become a technical challenge that the industry urgently needs to solve. Summary of the Invention

[0005] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a thermochromic anti-counterfeiting printing coating and its preparation method, aiming to solve the problems of poor weather resistance, insufficient temperature accuracy, and limited functionality of existing thermochromic coatings, and to achieve the anti-counterfeiting requirements of precise temperature response, long-term stability, and multi-process adaptability.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a thermochromic anti-counterfeiting printing coating, comprising a carrier substrate (1), a functional layer group, and a protective surface layer arranged sequentially from bottom to top; the carrier substrate (1) is a material adapted to the target application scenario, including any one of plastic, paper, and metal; the functional layer group includes at least a thermochromic core layer, the thermochromic core layer contains at least one thermochromic component, the thermochromic component is selected from nano-modified microencapsulated pigments, and the color-changing temperature accuracy of the thermochromic core layer is ≤ ±0.3℃, and the temperature-induced color-changing response time is ≤ 1s; the thermochromic... The core layer can also selectively incorporate one or more of the following components: heat insulation, photothermal conversion, or phase change synergistic components, to adapt to the response requirements of different scenarios. The protective surface layer is a coating structure with wear resistance and weather resistance, with a thickness of 2-8 μm, and is cured by UV or thermosetting. The raw materials for preparing the coating contain environmentally friendly solvents and no heavy metal additives, achieving a VOC content of ≤50g / L and a heavy metal content of ≤100ppm. It is compatible with screen printing, flexographic printing, or gravure printing processes, has an outdoor application life of ≥4 years, a temperature resistance cycle of ≥1000 times, and an adhesion rating of 0 in the cross-cut test.

[0007] Preferably, the functional layer group includes, from bottom to top, a release layer (2), a first ink layer (3), a heat insulation layer (4) containing heat insulation components, an adhesive layer (5), a temperature-sensitive core layer (6), and a second ink layer (7); the protective surface layer is a waterproof layer (8); the heat insulation layer (4) has a cavity (9) and a heat insulation sheet (10) inside; the lower surface of the waterproof layer (8) and the upper surface of the temperature-sensitive core layer (6) are both provided with grooves (11), and the grooves (11) are filled with temperature-sensitive materials. Color paint; the temperature-changing core layer (6) contains at least two types of color-changing temperature threshold temperature-sensitive color-changing paints selected from -10℃, 0℃, 30℃, 40℃, 50℃, 60℃, and 70℃, covering the color-changing range from -10℃ to 70℃ through a combination of multiple thresholds; the cavity (9) of the heat insulation layer (4) works synergistically with the heat insulation sheet (10) to shorten the coating response time by ≥50%; the double-layer groove (11) structure, compared with the single-layer groove, can increase the color difference ΔE before and after color change by ≥15%.

[0008] Preferably, the functional layer group includes, from bottom to top, a base layer (12), a photothermal conversion layer (13) containing photothermal conversion components, and a temperature-changing core layer (6); the protective surface layer is a protective layer (15); the base layer (12) is a modified epoxy resin with a solid content of 40%, with a coating thickness of 3-5 μm, and is cured at 120℃ for 5 min; the photothermal conversion layer (13) contains 6%-10% graphene / CNTs composite filler and acrylic resin carrier, with a thickness of 5-8 μm, and when the graphene / CNTs composite filler content is 8%, the coating temperature rise response time reaches the optimal inflection point of 0.8s; the temperature-changing core layer (6) is a polyurea wall material microcapsule composite system with a thickness of 5-7 μm; the protective layer (15) contains 5% nano SiO2 and polyurethane resin, with a thickness of 2-3 μm, and is cured by 800 mJ / cm² UV irradiation.

[0009] Preferably, the color change temperature accuracy of the temperature-changing core layer (6) is ±0.3℃, the color change response time meets the requirements of heating up and color change ≤1s, cooling down and color change ≤3s, and the color difference before and after color change ΔE≥30; if the cavity (9) of the heat insulation layer (4) is removed, the heating response time of the coating is extended to ≥3.5s, and the temperature accuracy is reduced to ±2.5℃.

[0010] Preferably, the microcapsules in the temperature-changing core layer (6) contain inorganic phase change materials, electron transfer organic dyes and color developers. The inorganic phase change materials include CaCl2·6H2O and organic esters, with a phase change enthalpy > 300 J·g⁻¹, and the difference between the phase change temperature of the inorganic phase change materials and the color change temperature of the electron transfer organic dyes is ≤ 2℃. When the content of graphene / CNTs composite filler is less than 8%, the coating heating response time is ≥ 1.5s.

[0011] Preferably, the raw materials for preparing the coating include thermochromic pigments, binders, additives and solvents; the compatibility between the binder and the substrate (1) is as follows: the plastic substrate corresponds to acrylic resin, the paper substrate corresponds to polyurethane resin, and the metal substrate corresponds to waterborne epoxy resin; the additives include polycarboxylate dispersants, nano-silica wear-resistant agents and thickeners corresponding to the printing process.

[0012] Preferably, the raw materials for preparing the coating include nano-modified microencapsulated pigments, acrylic resin carriers, modified epoxy resins, graphene / CNTs composite fillers, polycarboxylate dispersants, nano-silica wear-resistant agents, and bio-based solvents.

[0013] Preferably, the thermochromic pigment accounts for no more than 40% of the total mass of the coating, and the solvent is a citrate-based biodegradable solvent; the coating simultaneously satisfies the requirements of VOC content ≤ 50 g / L and temperature resistance cycle ≥ 1000 times, wherein the temperature resistance cycle reaches 1200 times when the VOC content is 45 g / L, and the temperature resistance cycle reaches 1000 times when the VOC content is 48 g / L.

[0014] Preferably, the coating is compatible with screen printing, flexographic printing or gravure printing processes, with corresponding process viscosities of 10000-15000cps, 3000-5000cps and 500-3000cps respectively, and the coating drying temperature is 5-10℃ lower than the color change temperature of thermochromic pigments; the coating has an outdoor application life of ≥5 years, a temperature resistance cycle of ≥1000 times, and a surface hardness of Shore D ≥60.

[0015] Preferably, the coating has a color-changing temperature accuracy of ±0.3℃, a temperature-increase color-changing response time of ≤0.8s, an outdoor application life of ≥4 years, a temperature resistance cycle of ≥1200 times, and a surface hardness of Shore D ≥58.

[0016] (III) Beneficial Effects Compared with existing technologies, the temperature-sensitive anti-counterfeiting printing coating provided by this invention precisely overcomes the core bottleneck of existing technologies in achieving high precision over a wide temperature range, while also possessing multiple functions and environmentally friendly long-lasting characteristics. The specific beneficial effects are as follows: 1. Wide temperature range and high-precision response, completely solving the problem of thermal disturbance interference: This invention specifically resists environmental thermal disturbance through differentiated structural design—the cavity of the insulation layer and the insulation sheet in the eight-layer structure work together to isolate the interference of external temperature fluctuations on the temperature-changing core layer, reducing the response time by ≥50%; the five-layer structure optimizes photothermal conversion efficiency through 8% graphene / CNTs composite filler, achieving rapid heat conduction and uniform distribution. Both schemes achieve full temperature range coverage from -10℃ to 70℃, with a color-changing temperature accuracy of ±0.3℃, far exceeding the accuracy level of existing technologies of ±2.2℃ to ±2.5℃; the heating color-changing response time is ≤1s (five-layer structure ≤0.8s), and the cooling color-changing time is ≤3s. Combined with the double-layer groove structure, the color difference ΔE is ≥30, resulting in clear visual recognition and perfectly meeting the dual requirements of wide temperature range and high precision in multiple scenarios such as cold chain, industry, and anti-counterfeiting.

[0017] 2. Interlayer Synergistic Adaptation to Solve Microcapsule Rupture Failure: This invention achieves synergistic matching of the thermal expansion coefficients of multilayer materials through raw material selection and structural design. Combined with the high-strength encapsulation characteristics of polyurea wall material microcapsules, it effectively disperses interlayer stress under wide temperature range cycling, preventing microcapsule rupture. Testing shows that the coating withstands ≥1000 temperature cycles (≥1200 cycles for a five-layer structure), far superior to the performance of existing technologies where the microcapsule rupture rate exceeds 30% after 500 cycles. Simultaneously, the temperature difference between the inorganic phase change material and the color-changing dye in the temperature-changing core layer is ≤2℃, achieving a synergistic response between phase change heat absorption / release and temperature-changing color development, further improving performance stability over a wide temperature range. Outdoor application life is ≥4 years (≥5 years for an eight-layer structure), surface hardness is ≥Shore D58, and adhesion reaches grade 0 in the cross-cut adhesion test, resisting external erosion such as friction and temperature-changing cycling.

[0018] 3. High functional integration, adaptable to diverse application scenarios: This invention covers all seven temperature thresholds: -10℃, 0℃, 30℃, 40℃, 50℃, 60℃, and 70℃, supporting multiple threshold combinations. By adding 1%–3% spiropyran photocrosslinking agents, it achieves irreversible color change at 60℃, forming a dual mode of "reversible monitoring + irreversible anti-counterfeiting," resulting in a high anti-counterfeiting threshold and making it difficult to replicate. Simultaneously, the eight-layer structure provides both heat insulation and waterproofing, while the five-layer structure integrates photothermal conversion and phase change synergistic characteristics, allowing for integration with smart technologies such as the Internet of Things and blockchain, adapting to diverse needs in fields such as food cold chain, luxury goods anti-counterfeiting, and industrial equipment monitoring.

[0019] 4. Environmentally friendly and compliant with processes, facilitating large-scale applications: Utilizing citrate-based biodegradable solvents and free of heavy metal additives, it achieves VOC content ≤50g / L and heavy metal content ≤100ppm. It overcomes the bottleneck of existing technologies' "contradiction between environmental protection and long-term effectiveness," maintaining ≥1000 temperature cycle resistance under low VOC conditions. The coating is compatible with screen printing, flexographic printing, or gravure printing processes, with precise viscosity matching to corresponding processes. The drying temperature avoids the discoloration temperature range, without affecting core performance, which is conducive to industrial-scale production and reduces application costs. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the first structure of the present invention; Figure 2 This is a schematic diagram of the second structure of the present invention.

[0021] In the diagram: 1. Supporting substrate; 2. Release layer; 3. First ink layer; 4. Heat insulation layer; 5. Adhesive layer; 6. Temperature-changing core layer; 7. Second ink layer; 8. Waterproof layer; 9. Cavity; 10. Heat insulation sheet; 11. Groove; 12. Base adhesive layer; 13. Photothermal conversion layer; 15. Protective layer. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1: Temperature-sensitive anti-counterfeiting printing coating for food cold chain packaging (eight-layer structure, covering 30℃ and 40℃) Coating structure The substrate (1) is made of food-grade plastic film. The functional layer group includes, from bottom to top, a release layer (2), a first ink layer (3), a heat insulation layer (4) containing a cavity (9) and a heat insulation sheet (10), a water-based epoxy resin adhesive layer (5), a temperature-changing core layer (6), and a second ink layer (7). The protective surface layer is a waterproof layer (8). The grooves (11) of the waterproof layer (8) and the temperature-changing core layer (6) are filled with thermochromic paint. The temperature-changing core layer (6) contains 30℃ reversible thermochromic paint and 40℃ reversible thermochromic paint, covering the medium and low temperature monitoring range.

[0024] Raw material ratio (by mass percentage) 30% nano-modified thermochromic pigment (15% for 30℃ type and 15% for 40℃ type), 25% waterborne epoxy resin, 3% polycarboxylate dispersant, 2% nano silica abrasion resistant agent, 1% cellulose thickener, and 39% citrate ester bio-based solvent.

[0025] Preparation process (1) Vacuum premixing: Add polymer carrier, thermochromic pigment and dispersant to vacuum mixing tank, evacuate to 0.08MPa, and stir at 25℃ and 1200rpm for 60min; (2) Addition of functional components: Reduce the rotation speed to 1000 rpm, add the binder and UV absorber in 3 batches, with an interval of 5 min between each batch, and stir at 30℃ for 30 min; (3) Viscosity adjustment: The target process is screen printing. First, add 50% solvent and stir at 1100 rpm for 10 min. Then add the remaining solvent and stir at 700 rpm for 5 min to adjust the viscosity to 12000 cps. (4) Filtration and purification: Filtration is carried out using a 200-mesh nylon screen under a pressure of 0.1 MPa; (5) Layered printing: Each layer is printed sequentially by screen printing process. The temperature-changing core layer (6) is printed with a pressure of 0.2MPa. The heat insulation layer (4) is formed into a cavity (9) by molding process and the heat insulation sheet (10) is embedded. The waterproof layer (8) is cured by 800mJ / cm² UV. The overall drying temperature is 55℃ (5℃ lower than the minimum color change temperature) and the drying time is 15min.

[0026] Performance testing Color change temperature accuracy ±0.3℃, 30℃ heating response time 0.8s, cooling and recoloring time 2.2s, 40℃ heating response time 0.7s, cooling and recoloring time 2.5s, color difference ΔE=32, outdoor life 6 years, VOC content 45g / L, heavy metal content ≤80ppm, meets food contact safety standards, can accurately monitor temperature fluctuations in the 30℃ (exceeding normal temperature limit) and 40℃ (high temperature risk) range during cold chain transportation.

[0027] Example 2: Temperature-sensitive printing coating for anti-counterfeiting of luxury goods (eight-layer structure, covering 30℃ and 60℃ (irreversible)) Coating structure The substrate (1) is made of high-grade paper substrate, and the functional layer group and protective surface structure are the same as in Example 1; the temperature-changing core layer (6) contains 30℃ reversible color-changing thermochromic paint and 60℃ irreversible color-changing system (with 2% spiropyran photocrosslinking agent added) to achieve the dual functions of "room temperature identification + high temperature permanent anti-counterfeiting".

[0028] Raw material ratio (by mass percentage) 35% of nano-modified thermochromic pigment (20% of 30℃ type and 15% of 60℃ type), 2% of spiropyran photocrosslinking agent, 22% of polyurethane resin, 2% of polycarboxylate dispersant, 3% of nano-silica wear-resistant agent, 1% of polyurethane thickener, and 37% of citrate ester bio-based solvent.

[0029] Preparation process For flexographic printing, the viscosity is adjusted to 4000 cps, the drying temperature is 70℃ (the color change temperature is 10℃ below 60℃), and other parameters are the same as in Example 1.

[0030] Performance testing Color-changing temperature accuracy ±0.2℃, 30℃ heating response time 0.6s, cooling and color restoration time 2.0s, 60℃ heating response time 0.9s, color is permanently fixed after reaching 60℃ and does not revert after cooling; cycle life 1200 times, surface hardness 2H, abrasion resistance ≥800 times, VOC content 42g / L, heavy metal content ≤75ppm, high anti-counterfeiting threshold, difficult to replicate.

[0031] Example 3: Temperature-changing anti-counterfeiting printing coating for industrial ambient temperature equipment monitoring (five-layer structure, covering 50℃) Coating structure The supporting substrate (1) is a thin metal plate. The functional layer group includes, from bottom to top, a base adhesive layer (12), a photothermal conversion layer (13) (with 8% graphene / CNTs composite filler content), a thermochromic core layer (6), and a protective surface layer (15). The thermochromic core layer (6) is a polyurea wall material microcapsule composite system. The inorganic phase change material inside the microcapsule has a phase change temperature of 48℃, which corresponds to a dye color change temperature of 50℃ (difference ≤ 2℃).

[0032] Raw material ratio (by mass percentage) 38% nano-modified thermochromic pigment (50℃ type), 20% acrylic resin, 8% graphene / CNTs composite filler, 2% polycarboxylate dispersant, 3% nano silica wear-resistant agent, and 29% citrate ester bio-based solvent.

[0033] Preparation process (1) Vacuum premixing: Add acrylic resin carrier, nano-modified microencapsulated pigment and polycarboxylate dispersant to a vacuum mixing tank, evacuate to 0.08MPa, and stir at 28℃ and 1400rpm for 45min; (2) Addition of functional components: Reduce the rotation speed to 1100 rpm, add modified epoxy resin, graphene / CNTs composite filler and ultraviolet absorber in 4 batches, with an interval of 8 min between each batch, and stir at 32℃ for 25 min. (3) Viscosity adjustment: The target process is gravure printing. First, add 60% solvent and stir at 1150 rpm for 9 min. Then add the remaining solvent and stir at 750 rpm for 4 min to adjust the viscosity to 2000 cps. (4) Filtration and purification: Filtration is carried out using a 200-mesh nylon screen under a pressure of 0.15 MPa; (5) Layered printing: Print the base layer (12) (cured at 120℃ for 5 min), photothermal conversion layer (13), temperature-changing core layer (6), and protective layer (15) in sequence. The thickness of each layer is within the specified range. The drying temperature is 65℃ (the color change temperature is 15℃ below 50℃).

[0034] Performance testing Color change temperature accuracy ±0.3℃, heating response time 0.7s, cooling and recoloring time 2.8s, color difference ΔE=31, temperature resistance cycle count 1300 times, photothermal conversion efficiency ≥85%, surface hardness Shore D59, adhesion reaches cross-cut test level 0, VOC content 46g / L, can accurately monitor the operating status of industrial equipment at 50℃ (safe critical temperature).

[0035] Example 4: Temperature-sensitive anti-counterfeiting printing coating for low-temperature cold chain monitoring (eight-layer structure, covering -10℃ and 0℃) Coating structure The substrate (1) is made of low-temperature resistant plastic film, and the functional layer group and protective surface structure are the same as in Example 1; the temperature-changing core layer (6) contains -10℃ reversible color-changing thermochromic paint and 0℃ reversible color-changing thermochromic paint, which is suitable for the cold chain monitoring scenario of frozen food.

[0036] Raw material ratio (by mass percentage) 32% nano-modified thermochromic pigment (18% -10℃ type and 14% 0℃ type), 24% waterborne epoxy resin, 3% polycarboxylate dispersant, 2% nano silica abrasion resistant agent, 1% cellulose thickener, and 38% citrate ester bio-based solvent.

[0037] Preparation process The target process is gravure printing, with the viscosity adjusted to 800 cps and the drying temperature set at -5℃ (the color change temperature is 5℃ below -10℃, so a low-temperature drying process is used). Other parameters are the same as in Example 1.

[0038] Performance testing Color change temperature accuracy ±0.3℃, -10℃ heating response time 0.9s, cooling and color recovery time 3.0s, 0℃ heating response time 0.8s, cooling and color recovery time 2.7s, color difference ΔE=29, low temperature cycle resistance ≥1500 times, outdoor life 5 years, VOC content 47g / L, can accurately monitor the temperature change of frozen food at -10℃ (freezing critical) and 0℃ (thawing risk).

[0039] Example 5: Temperature-sensitive anti-counterfeiting printing coating for monitoring high-temperature industrial equipment (five-layer structure, covering 60℃ and 70℃) Coating structure The supporting substrate (1) is made of high temperature resistant metal sheet, and the functional layer group and protective surface structure are the same as in Example 3; the temperature change core layer (6) contains 60℃ reversible color-changing thermochromic paint and 70℃ reversible color-changing thermochromic paint, and the phase change temperature of the inorganic phase change material in the microcapsule is 58℃ (2℃ difference from the 60℃ color change temperature) and 68℃ (2℃ difference from the 70℃ color change temperature).

[0040] Raw material ratio (by mass percentage) The composition includes 39% nano-modified thermochromic pigment (20% for 60℃ type and 19% for 70℃ type), 19% acrylic resin, 8% graphene / CNTs composite filler, 2% polycarboxylate dispersant, 3% nano silica wear-resistant agent, and 29% citrate ester bio-based solvent.

[0041] Preparation process The drying temperature is 80℃ (the color change temperature is 20℃ below 60℃), and other parameters are the same as in Example 3.

[0042] Performance testing Color change temperature accuracy ±0.3℃, 60℃ heating response time 0.6s, cooling and color recovery time 2.5s, 70℃ heating response time 0.5s, cooling and color recovery time 2.9s, color difference ΔE=33, temperature resistance cycle 1400 times, surface hardness Shore D60, suitable for temperature monitoring in the 60℃~70℃ range of industrial kilns, high-temperature pipelines, etc.

[0043] Example 6: Multifunctional composite anti-counterfeiting thermochromic printing coating (eight-layer structure, covering -10℃, 40℃, 60℃ (irreversible), 70℃) Coating structure The substrate (1) is made of composite paper substrate, and the functional layer group and protective surface structure are the same as in Example 1; the temperature-changing core layer (6) contains four temperature-changing components: -10℃ reversible, 40℃ reversible, 60℃ irreversible (with 3% spiropyran photocrosslinking agent added), and 70℃ reversible, to achieve full temperature range monitoring and multiple anti-counterfeiting measures.

[0044] Raw material ratio (by mass percentage) 36% of nano-modified thermochromic pigments (8% of -10℃ type, 10% of 40℃ type, 10% of 60℃ type, and 8% of 70℃ type), 3% of spiropyran photocrosslinking agent, 20% of polyurethane resin, 2% of polycarboxylate dispersant, 3% of nano-silica wear-resistant agent, 1% of polyurethane thickener, and 35% of citrate ester bio-based solvent.

[0045] Preparation process For flexographic printing, the viscosity is adjusted to 4500 cps, the drying temperature is 75℃ (the color change temperature is 5℃ below 60℃), and other parameters are the same as in Example 1.

[0046] Performance testing Color-changing temperature accuracy ±0.3℃, heating response time of -10℃ is 1.0s and cooling recovery time is 3.0s, heating response time of 40℃ is 0.7s and cooling recovery time is 2.3s, heating response time of 60℃ is 0.9s (irreversible), heating response time of 70℃ is 0.6s and cooling recovery time is 2.8s, color difference ΔE≥30, temperature resistance cycle count is 1200 times, VOC content is 43g / L, suitable for high-end pharmaceuticals, precision electronics and other scenarios requiring full-temperature monitoring and anti-counterfeiting.

[0047] Comparative Experiment To verify the superiority of the technical solution of the present invention, the following comparative examples are provided: Comparative Example A (no insulation layer cavity): The formula and process of Example 1 were used, except that the cavity (9) of the insulation layer (4) was removed, and the rest of the structure and parameters remained unchanged. Performance test results: 30℃ heating response time 3.5s, 40℃ heating response time 3.2s, color change temperature accuracy ±2.5℃, color difference ΔE=26, and temperature resistance cycle count 850 times.

[0048] Comparative Example B (without spiropyran crosslinking agent): The formulation and process of Example 2 were used, except that the spiropyran photocrosslinking agent was removed, while the remaining structure and parameters remained unchanged. Performance test results: After color change at 60℃, the initial color could be restored by cooling. There was no irreversible anti-counterfeiting function. After 50 cycles of use, the color change accuracy decreased to ±1.2℃.

[0049] Comparative Example C (Graphene / CNTs content 5%): The formulation and process of Example 3 were used, except that the content of graphene / CNTs composite filler in the photothermal conversion layer (13) was changed to 5%, while the rest of the structure and parameters remained unchanged. Performance test results: The response time to 50℃ heating was 1.5s, and the photothermal conversion efficiency was 68%, which was significantly lower than 0.7s and 85% in Example 3.

[0050] This invention achieves full temperature range coverage from -10℃ to 70℃ and high-precision response of ±0.3℃ through differentiated layer structure design, thermochromic component combination and introduction of spiropyran crosslinking agent. It also has reversible / irreversible multiple color-changing modes, which can meet the needs of food, luxury goods, industry, medicine and other fields. It is environmentally friendly and has long-term stability, and has broad market application prospects.

[0051] Explanation of the irreversible mechanism The irreversible color-changing function described in this invention is achieved by adding 1%–3% of spiropyran-based photocrosslinking agents: spiropyran compounds contain spirocyclic structures in their molecular structure. When triggered at 60°C, the spirocyclic structure breaks and undergoes a photocrosslinking reaction, irreversibly transforming the molecule from an open-ring to a closed-ring. Simultaneously, the crosslinked molecules form stable chemical bonds with the thermochromic pigment components in the thermochromic core layer, resulting in a permanent fixation of the color of the coating at temperatures of 60°C and above. After cooling, the color cannot be restored to its initial state, thus achieving an irreversible anti-counterfeiting label function.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A thermochromic anti-counterfeiting printing coating, characterized in that, It includes, from bottom to top, a supporting base (1), a functional layer group and a protective surface layer; The supporting substrate (1) is made of a material adapted to the target application scenario, including any one of plastic, paper, and metal; The functional layer group includes at least a thermochromic core layer, which contains at least one thermochromic component. The thermochromic component is selected from nano-modified microencapsulated pigments, and the color-changing temperature accuracy of the thermochromic core layer is ≤ ±0.3℃, and the temperature-induced color-changing response time is ≤1s. The thermochromic core layer may also selectively include one or more of the following: heat insulation component, photothermal conversion component, or phase change synergistic component, to adapt to the response requirements of different scenarios. The protective surface layer is a coating structure with wear-resistant and weather-resistant functions, with a thickness of 2-8μm, and is formed by UV curing or thermosetting. The coating is prepared using environmentally friendly solvents and additives free of heavy metals, achieving a VOC content of ≤50g / L and a heavy metal content of ≤100ppm. It is compatible with screen printing, flexographic printing, or gravure printing processes, has an outdoor application life of ≥4 years, a temperature resistance cycle of ≥1000 times, and an adhesion rating of 0 in the cross-cut test.

2. The thermochromic anti-counterfeiting printing coating according to claim 1, characterized in that, The functional layer group includes, from bottom to top, a release layer (2), a first ink layer (3), a heat insulation layer (4) containing heat insulation components, an adhesive layer (5), a temperature-changing core layer (6), and a second ink layer (7); the protective surface layer is a waterproof layer (8); The heat insulation layer (4) is provided with a cavity (9) and a heat insulation sheet (10). The lower surface of the waterproof layer (8) and the upper surface of the temperature-changing core layer (6) are both provided with grooves (11). The grooves (11) are filled with temperature-sensitive color-changing paint. The temperature-sensitive core layer (6) contains at least two types of color-changing temperature threshold temperature-sensitive color-changing paints selected from -10℃, 0℃, 30℃, 40℃, 50℃, 60℃, and 70℃, and covers the color-changing range from -10℃ to 70℃ through a combination of multiple thresholds. The cavity (9) of the heat insulation layer (4) works in conjunction with the heat insulation sheet (10) to shorten the coating response time by ≥50%; the double-layer groove (11) structure can increase the color difference ΔE before and after color change by ≥15% compared with the single-layer groove.

3. The thermochromic anti-counterfeiting printing coating according to claim 1, characterized in that, The functional layer group includes, from bottom to top, a base adhesive layer (12), a photothermal conversion layer (13) containing photothermal conversion components, and a temperature-changing core layer (6); the protective surface layer is a protective layer (15). The base layer (12) is a modified epoxy resin with a solid content of 40%, with a coating thickness of 3-5 μm, and is cured at 120°C for 5 min. The photothermal conversion layer (13) contains 6%-10% graphene / CNTs composite filler and acrylic resin carrier, with a thickness of 5-8μm. When the content of graphene / CNTs composite filler is 8%, the coating heating response time reaches the optimal inflection point of 0.8s. The temperature-changing core layer (6) is a polyurea wall material microcapsule composite system with a thickness of 5-7 μm; The protective layer (15) contains 5% nano-SiO2 and polyurethane resin, with a thickness of 2-3 μm, and is cured by UV irradiation of 800 mJ / cm².

4. The thermochromic anti-counterfeiting printing coating according to claim 2, characterized in that, The color change temperature accuracy of the temperature-changing core layer (6) is ±0.3℃, the color change response time meets the requirements of heating up and color change ≤1s, cooling down and color change ≤3s, and the color difference before and after color change ΔE≥30; if the cavity (9) of the heat insulation layer (4) is removed, the heating response time of the coating is extended to ≥3.5s, and the temperature accuracy is reduced to ±2.5℃.

5. The thermochromic anti-counterfeiting printing coating according to claim 3, characterized in that, The microcapsules in the temperature-changing core layer (6) contain inorganic phase change materials, electron transfer organic dyes and color developers. The inorganic phase change materials include CaCl2·6H2O and organic esters, with a phase change enthalpy > 300 J·g⁻¹, and the difference between the phase change temperature of the inorganic phase change materials and the color change temperature of the electron transfer organic dyes is ≤ 2℃. When the content of graphene / CNTs composite filler is less than 8%, the coating heating response time is ≥ 1.5s.

6. The thermochromic anti-counterfeiting printing coating according to claim 2, characterized in that, The raw materials for preparing the coating include thermochromic pigments, binders, additives and solvents; the compatibility between the binder and the substrate (1) is as follows: the plastic substrate corresponds to acrylic resin, the paper substrate corresponds to polyurethane resin, and the metal substrate corresponds to waterborne epoxy resin; the additives include polycarboxylate dispersants, nano-silica wear-resistant agents and thickeners corresponding to the printing process.

7. The thermochromic anti-counterfeiting printing coating according to claim 3, characterized in that, The raw materials for preparing the coating include nano-modified microencapsulated pigments, acrylic resin carriers, modified epoxy resins, graphene / CNTs composite fillers, polycarboxylate dispersants, nano-silica wear-resistant agents, and bio-based solvents.

8. The thermochromic anti-counterfeiting printing coating according to claim 2 or 6, characterized in that, The thermochromic pigment accounts for no more than 40% of the total mass of the coating, and the solvent is a citrate-based biodegradable solvent. The coating simultaneously meets the requirements of VOC content ≤ 50 g / L and temperature resistance cycle ≥ 1000 times, wherein the temperature resistance cycle reaches 1200 times when the VOC content is 45 g / L and 1000 times when the VOC content is 48 g / L.

9. The thermochromic anti-counterfeiting printing coating according to claim 2, characterized in that, The coating is compatible with screen printing, flexographic printing or gravure printing processes, with corresponding process viscosities of 10000-15000cps, 3000-5000cps and 500-3000cps respectively. The coating drying temperature is 5-10℃ lower than the color change temperature of thermochromic pigments. The coating has an outdoor application life of ≥5 years, a temperature resistance cycle of ≥1000 times, and a surface hardness of Shore D ≥60.

10. The thermochromic anti-counterfeiting printing coating according to claim 3 or 5, characterized in that, The coating has a color-changing temperature accuracy of ±0.3℃, a temperature-increase color-changing response time of ≤0.8s, an outdoor application life of ≥4 years, a temperature resistance cycle of ≥1200 times, and a surface hardness of Shore D ≥58.

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