A high-stability thermochromic microsphere ink composition and a preparation method thereof

Abstract

This invention discloses a highly stable thermosensitive color-changing microsphere ink composition and its preparation method. The composition comprises 10-30 parts of thermosensitive color-changing microspheres, 20-40 parts of binder resin, 0.5-3 parts of intramolecular synergistic stabilizer, 0.5-2 parts of additives, and the balance being a dispersion medium. The thermosensitive color-changing microspheres have a core-shell structure, with the shell containing silane-modified photothermal conversion nanomaterials and the outer surface covalently grafted with temperature-responsive polymers. This invention constructs a complete chain system of active thermal stress management, dynamic interface buffering, and molecular-level synergistic protection, fundamentally solving the problem of ink functional degradation caused by dynamic thermo-mechanical coupling stress, significantly improving the ink's cycle stability, weather resistance, and storage stability, and is suitable for fields such as intelligent anti-counterfeiting and temperature-sensing labeling.

Description

Technical Field

[0001] This invention relates to the fields of intelligent functional materials and special printing technology, specifically to a highly stable thermosensitive color-changing microsphere ink composition and its preparation method. Background Technology

[0002] Thermochromic ink is a type of intelligent printing material that can reversibly change color with changes in ambient temperature. Its core function relies on core-shell thermochromic microcapsules. The wall material forms physical isolation and protection for the internal thermochromic core material, thereby ensuring the reversibility and cycle stability of the color-changing function. With its visible temperature response characteristics, it has been widely used in food cold chain traceability, high-end product anti-counterfeiting, and industrial equipment temperature monitoring.

[0003] Currently, industry improvements to thermochromic inks mainly focus on three main directions: First, enhancing the static mechanical strength of microcapsules by doping with rigid nanofillers and increasing the cross-linking degree of the wall material, thereby reducing the breakage rate of microspheres due to high shear forces during ink preparation; second, statically modifying the surface of microspheres with silane coupling agents and epoxy monomers to improve the interfacial compatibility between microspheres and ink binders; and third, physically compounding UV absorbers, antioxidants, and other additives into the ink system to delay the photo-oxidative and thermo-oxidative aging of the resin and microsphere wall material.

[0004] Among them, reference document 1 (publication number CN114854236A, title: A thermosensitive color-changing microcapsule water-based ink and its preparation method, publication date March 11, 2022) is the closest prior art. It discloses a thermosensitive color-changing microcapsule ink with nano-silica doped and reinforced melamine resin wall material and surface modified with glycidyl methacrylate, representing the current mainstream technical route of "passive reinforcement and static protection" in the industry. Although this solution can improve the static mechanical strength and room temperature dispersibility of microspheres to a certain extent, it still does not break out of the logic of fragmented improvement and cannot fundamentally solve the functional failure problem of thermosensitive color-changing ink throughout its entire life cycle.

[0005] Current industry solutions generally fail to fully grasp that the core bottleneck in the functional failure of thermochromic inks lies in the continuous accumulation and release of dynamic thermo-mechanical coupling stress: the thermochromic core material undergoes solid-liquid phase change and volume expansion and contraction with temperature changes, which will form local heat accumulation and uneven internal stress inside the microspheres. At the same time, the difference in thermal expansion coefficients between the microspheres and the binder resin will generate continuous shear stress at the interface during temperature cycling. The dynamic stress formed by the coupling of the two will gradually cause the initiation of microcracks in the wall material and interface debonding, eventually leading to core material leakage and irreversible decay of the color-changing function. Furthermore, the degradation of material performance caused by environmental aging will further weaken the system's ability to resist dynamic stress and accelerate the failure process.

[0006] Currently, several separate technical solutions have been disclosed, outlining relevant improvements: Reference document 2 (Publication No. CN110204578A, Title: A Photothermal Conversion Microcapsule and its Preparation Method, Publication Date: September 6, 2019) discloses the use of copper sulfide nanosheets in a microcapsule system to achieve photothermal conversion and temperature field control. The technical problem it addresses is the photothermal response efficiency of the microcapsule, but it does not address internal thermal stress relief; Reference document 3 (Publication No. CN109529964A, Title: A Thermosensitive Microcapsule and its Preparation Method, Publication Date: September 6, 2019) discloses... On March 29, a paper disclosed a method of grafting poly-N-isopropylacrylamide onto the surface of thermosensitive microcapsules to improve interfacial compatibility. The technical problem it solves is the dispersibility of microspheres, but it does not involve interfacial shear stress buffering. Prior art document 4 (publication number CN102558447A, title: An intramolecular composite light stabilizer, publication date July 11, 2012) disclosed a hindered phenol-benzotriazole integrated intramolecular synergistic stabilizer for anti-aging of polymer materials. The technical problem it solves is the photo-oxidative aging of polymer materials, but it does not involve synergistic cooperation with the microsphere structure protection.

[0007] The aforementioned existing technologies are all fragmented improvements in a single dimension. No existing technology teaches how to combine these three techniques, nor does it recognize that combining them can form a complete stress protection system, producing unexpected synergistic effects. Therefore, they cannot fundamentally solve the problem of progressive failure caused by dynamic thermo-mechanical coupling stress. To date, the industry has not yet developed a systematic solution addressing the nature of this failure, which has become a core technological bottleneck restricting the long-term stability and application expansion of thermochromic inks. Summary of the Invention

[0008] In view of this, the present invention proposes a thermosensitive color-changing microsphere ink composition and its preparation method. Starting from the failure root cause of dynamic thermo-mechanical coupling stress, it constructs a closed-loop system of "internal active thermal stress management - interface dynamic stress buffering - system molecular-level synergistic protection", which completely solves the core defects of the fragmented improvement of the existing technology.

[0009] The technical solution of this invention is implemented as follows:

[0010] This invention provides a thermochromic microsphere ink composition, comprising the following components in parts by weight: 10-30 parts thermochromic microspheres, 20-40 parts binder resin, 0.5-3 parts intramolecular synergistic stabilizer, 0.5-2 parts additives, and a dispersion medium to bring the total mass of the composition to the balance of 100 parts; the thermochromic microspheres have a core-shell structure, with a core material being a thermochromic core material, and a shell material being a polymer wall material and photothermal conversion nanomaterials uniformly dispersed in the wall material; the photothermal conversion nanomaterials are copper sulfide nanosheets modified with 3-aminopropyltriethoxysilane, and cesium tungsten bronze nanowires. One of the following is less, and its mass accounts for 5%-25% of the total dry weight of the shell; the outer surface of the thermosensitive color-changing microspheres is covalently grafted with a temperature-responsive polymer; the temperature-responsive polymer is a homopolymer of poly(N-isopropylacrylamide), or a random copolymer formed by poly(N-isopropylacrylamide) and a comonomer; the comonomer is any hydrophilic monomer among acrylamide and N-vinylpyrrolidone, or any hydrophobic monomer among butyl methacrylate and methyl methacrylate; the critical dissolution temperature of the temperature-responsive polymer is lower than or equal to the color-changing temperature of the thermosensitive color-changing core material, and the temperature difference between the two is 0-5℃.

[0011] In some embodiments, the intramolecular synergistic stabilizer is 2-(2H-benzotriazol-2-yl)-4-tert-butyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenol.

[0012] Existing technologies that physically mix UV absorbers and antioxidants often suffer from inconsistent migration rates, localized enrichment, or precipitation within resin systems due to differences in molecular structure and polarity, leading to the failure of the synergistic effect of UV protection and free radical scavenging. The intramolecular synergistic stabilizer selected in this invention covalently fixes the benzotriazole UV-absorbing group and the hindered phenolic free radical scavenging group within the same molecule. This ensures that the two functional groups are always spatially and temporally synchronized within the system. The UV-absorbing group absorbs UV energy at the source, preventing the breakage of chemical bonds between the resin and the wall material, while the adjacent hindered phenolic group simultaneously captures a small amount of generated free radicals, blocking the aging chain reaction and achieving full molecular chain protection for the ink system. Simultaneously, by delaying material aging and degradation, it ensures the long-term stability of the microsphere structure and stress control function, forming a synergistic protection with the two core technical features mentioned above.

[0013] In some embodiments, the polymer wall material is any one of melamine resin, urea-formaldehyde resin, polyurethane, and gelatin-gum arabic composite.

[0014] The aforementioned polymer wall materials are all mature systems in the field of thermosensitive color-changing microcapsules, possessing excellent film-forming properties, barrier properties, and processability. They can form good interfacial bonds with modified photothermal conversion nanomaterials, are suitable for in-situ polymerization or composite condensation preparation processes, and ensure the integrity and functional stability of the microsphere structure.

[0015] In some embodiments, the thermosensitive color-changing core material is any one of a leuco dye-developer-solvent organic system or a vanadium dioxide inorganic system.

[0016] The organic system of leuco dyes has the characteristics of sensitive color change, large color difference and wide range of color selection; the inorganic system of vanadium dioxide has the advantages of good weather resistance and long service life. The solution of this invention can be adapted to both of the two mainstream thermo-sensitive color-changing systems at the same time, which greatly expands the applicable scenarios of inks.

[0017] In some embodiments, the binder resin is any one of waterborne polyurethane resin, waterborne acrylic resin, nitrocellulose liquid, and two-component epoxy resin; the additive is at least one of leveling agent, defoamer, and polymeric dispersant; and the dispersion medium is any one or a mixture of two or more of deionized water, anhydrous ethanol, and ethyl acetate.

[0018] Different types of binder resins and dispersion media can be adapted to mainstream printing processes such as flexographic printing, gravure printing, and screen printing, as well as different printing substrates such as plastics, paper, metals, and glass; various additives can synergistically improve the rheological properties and printability of inks, ensuring the industrial application value of inks.

[0019] In some embodiments, the present invention also provides a method for preparing the above-mentioned thermochromic microsphere ink composition, comprising the following steps: (1) Preparation of thermosensitive color-changing microspheres: ①Preparation of thermosensitive color-changing core material: Heat and melt the raw materials of thermosensitive color-changing core material to obtain a homogeneous oil phase, and keep it at the temperature for later use; ② Preparation of the aqueous phase containing photothermal conversion nanomaterials: Polymer monomers and emulsifiers are added to deionized water, the pH value is adjusted and the mixture is heated to react, resulting in a polymer prepolymer solution; the photothermal conversion nanomaterials modified with 3-aminopropyltriethoxysilane are ultrasonically dispersed in deionized water to obtain a nano-dispersion; the nano-dispersion is added to the prepolymer solution and stirred evenly to obtain the aqueous phase; ③ In-situ polymerization preparation of composite wall material microspheres: The heat-insulated oil phase is added dropwise to the aqueous phase, and high-speed shear emulsification is performed to obtain an O / W type fine emulsion. The in-situ polymerization reaction is completed by constant temperature stirring to obtain a core-shell structured composite wall material microsphere suspension. After washing and drying, microsphere powder is obtained. ④ Surface initiator modification: The composite wall material microsphere powder was dispersed in anhydrous toluene, 3-(2-bromoisobutyryloxy)propyltrimethoxysilane was added, and the reaction was carried out at a constant temperature under nitrogen protection. After washing, microspheres with surface covalently grafted initiators were obtained. ⑤ Grafted temperature-responsive polymer: Microspheres with surface-grafted initiators were dispersed in a methanol / water mixed solvent, and a temperature-sensitive monomer and pentamethyldiethylenetriamine ligand were added. After three cycles of freezing-vacuuming-nitrogen purging to remove oxygen, cuprous bromide catalyst was added, and the reaction was carried out at a constant temperature under nitrogen protection. After washing and drying, temperature-sensitive color-changing microspheres were obtained. In the reaction system, the molar ratio of temperature-sensitive monomer, initiator grafted on the surface of microspheres, cuprous bromide catalyst, and pentamethyldiethylenetriamine ligand was 100:1:1:2. (2) Low-damage dispersion formulation of ink: The binder resin, intramolecular synergistic stabilizer and additives are dispersed in the dispersion medium and dispersed at high speed to obtain a uniform base material; under low-speed stirring at 300-500 rpm, the thermosensitive color-changing microspheres obtained in step (1) are added to the base material, mixed evenly and filtered to obtain the target ink composition.

[0020] In-situ polymerization can achieve uniform doping of photothermal conversion nanomaterials in the wall material matrix, avoiding stress concentration caused by nanomaterial agglomeration and ensuring the uniformity of thermal management function; surface-initiated atom transfer radical polymerization technology can achieve precise control of polymer grafting density and chain length, ensuring the stability of temperature-sensitive response and stress buffering function, and covalent grafting can prevent polymer detachment during storage and use, ensuring long-term interfacial buffering function; low-speed stirring and dispersion process can avoid damage to the core-shell structure of microspheres by high shear force, ensuring the structural integrity of microspheres in ink preparation process, and ultimately achieving stable presentation of the core function of ink composition.

[0021] In some embodiments, in step (1) ③, the reaction temperature of in-situ polymerization is 60-65℃ and the reaction time is 2.5-3.5h; in step (1) ⑤, the reaction temperature of surface-initiated atom transfer radical polymerization is 25-35℃ and the reaction time is 5-8h.

[0022] The above process parameters are the optimal range verified by a large number of experiments. They can ensure that the polymer prepolymer is uniformly cross-linked and forms a film on the oil phase surface, while avoiding problems such as loose wall material structure and core material leakage caused by excessively fast reaction. They also take into account the density and formability of the wall material. The polymerization reaction parameters can ensure that the reaction is stable and controllable, avoid excessively wide polymer molecular weight distribution caused by explosive polymerization, and precisely control the polymer grafting density and critical dissolution temperature within the target range.

[0023] In some embodiments, in step (1) ⑤, the critical dissolution temperature of the polymer is controlled by adjusting the molar ratio of N-isopropylacrylamide to the comonomer in the thermosensitive monomer, so that it is lower than or equal to the color change temperature of the thermosensitive color-changing core material, and the temperature difference between the two is 0-5℃.

[0024] The phase transition temperature range of the thermosensitive color-changing core material is precisely the range where the difference in thermal expansion between the microspheres and the binder resin is greatest, and the interfacial shear stress is most concentrated. This invention, by precisely defining the critical dissolution temperature, ensures that the phase transition behavior of the polymer is triggered synchronously with the phase transition process of the core material. When the temperature rises to the range where the core material is about to undergo a phase transition, the polymer simultaneously undergoes a hydrophobic phase transition and rapidly shrinks, instantaneously forming a deformable buffer free volume at the microsphere interface. This adaptively absorbs the interfacial shear stress caused by the change in the core material's phase transition volume and the difference in thermal expansion of the resin. This reverses the thermosensitive shrinkage behavior that needs to be avoided in traditional solutions, using it as the core mechanism for interfacial stress buffering, completely solving the defect that static modification cannot cope with dynamic interfacial stress.

[0025] This invention has the following outstanding substantive features and significant progress compared to the prior art: This invention completely overturns the fragmented improvement approach of traditional thermochromic inks, which focuses on "passive enhancement and static protection." For the first time, it addresses the core issue of ink failure—dynamic thermo-mechanical coupling stress—by constructing a closed-loop system encompassing "internal active thermal stress management, interface dynamic stress buffering, and system-level molecular-level synergistic protection." It eliminates the root cause of internal thermal stress in microspheres through photothermal conversion nanomaterials, adaptively buffers interfacial shear stress during temperature cycling using temperature-responsive polymers, and achieves synchronous aging protection across the entire system through intramolecular synergistic stabilizers. These three elements are not simply a superposition of technical effects, but rather create an unexpected synergistic effect: active thermal management reduces internal stress by over 80% at the source, dynamic interface buffering eliminates residual stress and interfacial shear stress, and intramolecular synergistic protection ensures the long-term stability of the first two functions. The combination of these three elements fundamentally solves the problem of irreversible functional degradation caused by dynamic stress accumulation and environmental aging throughout the entire lifecycle of thermochromic inks, from processing and storage to use. The technical solution of this invention is compatible with mainstream thermochromic systems, printing processes and application scenarios. The preparation process is highly controllable and has a good foundation for industrial mass production, breaking through the application bottleneck of existing technologies. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] I. General Basic Instructions 1. Common Raw Materials and Reagents: All raw materials used in the examples and comparative examples in this section are industrial grade / analytical grade and can be obtained through conventional commercial channels. Specific information is as follows: Thermosensitive color-changing raw materials: crystal violet lactone, bisphenol A, octadecanol, hexadecyl alcohol, vanadium dioxide (VO2) nanoparticles (average particle size 50nm); Wall material raw materials: melamine, formaldehyde solution (37wt%), urea, waterborne polyurethane prepolymer (NCO content 5%, solid content 40%), gelatin, gum arabic, glutaraldehyde crosslinking agent; Nanomaterials: copper sulfide nanosheets (average particle size 50nm), cesium tungsten bronze nanowires (diameter 20nm, length 500nm), hydrophilic nano-silica (average particle size 50nm). All nanomaterials were surface modified with 3-aminopropyltriethoxysilane (KH550) before use. Polymerization raw materials: N-isopropylacrylamide (NIPAM), acrylamide (Am), N-vinylpyrrolidone (NVP), butyl methacrylate (BMA), methyl methacrylate (MMA), 3-(2-bromoisobutyryloxy)propyltrimethoxysilane (BIBTS), pentamethyldiethylenetriamine (PMDETA), cuprous bromide; Ink raw materials: Intramolecular synergistic stabilizer (2-(2H-benzotriazole-2-yl)-4-tert-butyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenol), waterborne polyurethane resin, waterborne acrylic resin, nitrocellulose liquid, two-component epoxy resin E-51, fatty amine curing agent, leveling agent, defoamer, polymeric dispersant; Solvents: deionized water, anhydrous toluene, anhydrous ethanol, methanol, ethyl acetate.

[0028] 2. General-purpose instruments and equipment: high-speed shear emulsifier, constant temperature magnetic stirring reactor, vacuum drying oven, ultrasonic disperser, nitrogen glove box, X-ray photoelectron spectrometer (XPS), surface area and pore size analyzer (BET), gel permeation chromatography (GPC), atomic force microscope, infrared thermal imager, scanning electron microscope, colorimeter, universal tensile testing machine, constant temperature oven, micro-area Raman spectrometer.

[0029] 3. Core Parameter Testing Methods Critical dissolution temperature (LCST) test: Using a UV-Vis spectrophotometer, the change in transmittance of the polymer aqueous solution at a wavelength of 500 nm was tested during the heating process. The temperature at which the transmittance drops to 50% is the critical dissolution temperature. The heating rate is 1℃ / min. Thermosensitive color-changing core material color-changing temperature test: A colorimeter is used in conjunction with a programmable temperature control table. The temperature at which the color difference ΔE of the test sample changes abruptly during the heating process is the color-changing temperature. The heating rate is 1℃ / min. Calculation of total dry weight of shell layer: calculated as the sum of the theoretical dry weight of the polymer monomer after complete cross-linking and curing and the mass of photothermal conversion nanomaterials fed into the shell layer. Actual measurement of internal thermal stress of microspheres: The temperature field distribution inside the microspheres was measured using a micro-area Raman spectrometer, and the actual thermal stress value was calculated using thermoelastic mechanics formulas.

[0030] 4. General Performance Testing Methods All tests were conducted under standard conditions of 25℃ and 50% relative humidity. Each sample was tested in triplicate, and the average value was taken. (1) Microsphere structural integrity test: The ink composition to be tested was uniformly coated on a PET substrate and dried to make a standard strip with a thickness of 25 μm. The strip was placed in a tensile testing machine with programmable temperature control and the temperature was changed at a rate of 5 °C / min between 25 °C and 50 °C. 0.5% cyclic tensile strain was applied to each temperature plateau and the cycle frequency was 1 time / min. A total of 1000 cycles were accumulated. After the cycle, the total number of microspheres and the number of broken microspheres in 10 random fields of view were observed with a scanning electron microscope. The microsphere breakage rate was calculated as follows: breakage rate = number of broken microspheres / total number of microspheres × 100%. The smaller the value, the better the microsphere structural stability.

[0031] (2) Color change performance stability test: Use a colorimeter to test the color parameters of the ink sample before and after the above-mentioned cyclic temperature-stretch test at the core material color change temperature, and calculate the color difference ΔE before and after the cycle. The smaller the value, the better the color change performance is maintained.

[0032] (3) Temperature homogenization performance test: Take an equal amount of microsphere powder to be tested and press it into a disc with a thickness of 1 mm and a diameter of 10 mm; use a laser point heat source with a wavelength of 808 nm, a power of 1 W and a spot diameter of 1 mm to locally heat the center of the disc. After 10 seconds, use an infrared thermal imager to record the temperature difference between the heated center point and the edge (4 mm away from the center). The smaller the value, the better the temperature homogenization effect and the stronger the thermal management capability.

[0033] (4) Interface buffering performance test: A temperature-controlled atomic force microscope was used with a silicon probe with an elastic modulus of 0.4 N / m and the test was conducted in tapping mode. The microspheres to be tested were fixed on the steel sample stage with a small amount of epoxy resin glue. After stabilizing for 30 minutes at each temperature point, the test was conducted. The surface elastic modulus of the microspheres was tested at 25℃ (below the critical dissolution temperature of the polymer) and 40℃ (above the critical dissolution temperature of the polymer). Five different sites were tested for each sample and the average value was taken. The modulus change rate at the two temperatures was calculated. The larger the value, the more obvious the polymer phase change response and the stronger the interface buffering capacity.

[0034] (5) Aging resistance test: The ink sample was placed in an 85℃ constant temperature oven for a heat aging test for 500 hours. The color change response time of the sample from 25℃ to the core material color change temperature was tested before and after aging. The color change performance retention rate was calculated by the ratio of the response time after aging to that before aging. The closer the value is to 100%, the better the aging resistance performance.

[0035] (6) Storage stability test: The ink composition to be tested is sealed and placed in an environment of 25°C for 60 days. Every 5 days, observe and record whether precipitation or stratification occurs in the system. Record the time when soft precipitation or hard precipitation occurs. No precipitation is the best grade.

[0036] 5. Scope of application of general process parameters (1) In the surface initiator modification step, the amount of BIBTS used is 3%-8% of the mass of the microsphere powder, and the optimal amount is 5%; (2) In the in-situ polymerization step, the parameter range of high-speed shear emulsification is 8000-12000 rpm, and the emulsification time is 3-8 minutes. The optimal parameters are 10000 rpm and 5 minutes. (3) In the gelatin-gum arabic composite coagulation system, the amount of glutaraldehyde crosslinking agent is 1%-3% of the dry weight of the wall material, and the optimal amount is 2%.

[0037] II. Preparation of Examples All embodiments strictly follow the single variable principle. Except for the explicitly marked adjustment variables, the other raw materials, operating steps, and environmental parameters are completely consistent with those in Embodiment 1, fully covering all the technical features of the claims.

[0038] Example 1: Core Optimal Example Step 1: Preparation of thermosensitive color-changing core material: Weigh 1.0g crystal violet lactone, 2.5g bisphenol A, and 12.0g octadecyl alcohol, place them in a sealed glass container, heat to 60℃ and stir at a constant temperature for 30 minutes until all materials are completely melted and mixed evenly to obtain a transparent and uniform oil phase. Maintain the temperature at 60℃ throughout the process for later use. The measured color-changing temperature of this core material is 31℃.

[0039] Step 2: Aqueous phase preparation of photothermal conversion nanomaterials: Weigh 5.0g melamine, 15.0g 37% formaldehyde solution, and 2.0g polyvinyl alcohol (PVA-1788), add to 120g deionized water, stir evenly, adjust the pH of the system to 8.5 with triethanolamine, heat to 60℃ and stir for 20 minutes to obtain a clear and transparent melamine resin prepolymer solution; Weigh 1.36g of copper sulfide nanosheets modified with KH550, add to 20g deionized water, and ultrasonically disperse at 300W power for 30 minutes, with the ultrasonic mode being 2 seconds on and 3 seconds off, to obtain a uniform nano-dispersion; Slowly add the nano-dispersion to the prepolymer solution, and stir at 60℃ for 10 minutes to obtain a uniform aqueous phase, in which copper sulfide nanosheets account for 12% of the total dry weight of the shell.

[0040] Step 3: In-situ polymerization to prepare composite wall material microspheres: The oil phase from Step 1, which was kept at a constant temperature, was slowly added dropwise to the aqueous phase from Step 2 at 60°C. After the addition was complete, the mixture was sheared at 10,000 rpm for 5 minutes to obtain a uniform O / W type fine emulsion. The emulsion was transferred to a three-necked flask equipped with a reflux condenser and stirred at 300 rpm throughout the process. The reaction was carried out at a constant temperature of 60°C for 3 hours to complete the in-situ polymerization and obtain a suspension of composite wall material microspheres. After the suspension was cooled to room temperature, it was filtered and washed three times each with deionized water and anhydrous ethanol. The mixture was then vacuum dried at 40°C for 12 hours to obtain composite wall material microsphere powder.

[0041] Step 4: Initiator modification of microsphere surface: Weigh 2.0g of microsphere powder obtained in Step 3, add it to 50mL of anhydrous toluene, sonicate for 15 minutes, purge with nitrogen for 30 minutes to remove oxygen, add 0.1g of BIBTS (5% of the mass of microspheres), and stir at 80℃ for 12 hours under nitrogen protection. After the reaction is completed, magnetically separate the microspheres, wash them three times each with anhydrous toluene and anhydrous ethanol to remove unreacted initiator, and obtain microspheres with covalently grafted initiator on the surface.

[0042] Step 5: Grafting temperature-responsive polymer onto microsphere surface: Weigh 2.0 g of microspheres with the surface-grafted initiator obtained in Step 4, add to 50 mL of a methanol / water mixture (1:1 volume ratio), ultrasonically disperse for 15 minutes, add 5.0 g of NIPAM monomer and 0.1 mL of PMDETA ligand, stir evenly, and then deoxygenate through three cycles of freezing-vacuuming-nitrogen purging; weigh 0.05 g of cuprous bromide catalyst in a nitrogen glove box, quickly add to the deoxygenated system, seal, and stir at 30 °C for 6 hours; the molar ratio of monomer / initiator / catalyst / ligand in the reaction system is 100:1:1:2; after the reaction, terminate the reaction by exposure to air, wash three times each with deionized water and anhydrous ethanol to remove unreacted monomer and catalyst, and vacuum dry at 40 °C for 12 hours to obtain temperature-sensitive color-changing microspheres; the polymer grafting density was measured to be 0.8 chains / nm.2 The critical melting temperature is 30℃, which is 1℃ lower than the color change temperature of the core material.

[0043] Step 6: Preparation of ink composition: Weigh 35 parts of waterborne polyurethane resin and 41 parts of deionized water based on a total mass of 100 parts. After stirring evenly, add 1.5 parts of intramolecular synergistic stabilizer, 1.0 part of leveling agent, 0.5 parts of defoamer, and 1.0 part of polymeric dispersant. Disperse at high speed of 2000 rpm for 20 minutes to obtain a uniform ink base. Under low speed stirring of 400 rpm, slowly add 20 parts of the thermosensitive color-changing microspheres obtained in Step 5 to the base and continue stirring for 30 minutes until evenly dispersed. Filter through a 200-mesh filter to obtain the target thermosensitive color-changing microsphere ink composition.

[0044] Example 2: Verification of the lower limit of photothermal material addition amount The only difference from Example 1 is that the amount of copper sulfide nanosheets added in step 2 is adjusted to 5% of the total dry weight of the shell layer; all other aspects are completely the same.

[0045] Example 3 Verification of the upper limit of photothermal material addition The only difference from Example 1 is that the amount of copper sulfide nanosheets added in step 2 is adjusted to account for 25% of the total dry weight of the shell layer; all other aspects are completely the same.

[0046] Example 4: Verification of the lower limit of polymer grafting density The only difference from Example 1 is that the amount of NIPAM monomer added in step 5 was adjusted to 0.5g, the reaction time was adjusted to 2 hours, and the measured polymer grafting density was 0.1 chains / nm. 2 The rest of the content is completely identical.

[0047] Example 5: Verification of the Upper Limit of Polymer Grafting Density The only difference from Example 1 is that the amount of NIPAM monomer added in step 5 was adjusted to 12.0 g, the reaction time was adjusted to 10 hours, and the measured polymer grafting density was 2.0 chains / nm. 2 The rest of the content is completely identical.

[0048] Example 6: Verification of the Upper Limit of the Difference Between LCST and Core Material Color Change Temperature The only difference from Example 1 is that in step 5, NIPAM and Am comonomers (mass ratio 9:1) were used, and the measured critical melting temperature of the polymer was 31°C, which is 0°C different from the color change temperature of the core material. All other contents are completely the same.

[0049] Example 7 Boundary Verification of LCST and Core Material Color Change Temperature Difference The only difference from Example 1 is that in step 5, NIPAM and BMA comonomers (mass ratio 95:5) were used, and the measured critical melting temperature of the polymer was 26°C, which is 5°C different from the color change temperature of the core material. All other contents are completely the same.

[0050] Example 8: Core Group Allocation Ratio Lower Limit Verification The only difference from Example 1 is that the ink formula in step 6 is adjusted to 10 parts of thermosensitive color-changing microspheres, 20 parts of binder resin, 0.5 parts of intramolecular synergistic stabilizer, 0.5 parts of additives, and the balance of deionized water. All other contents are completely the same.

[0051] Example 9: Verification of the Upper Limit of Core Group Allocation Ratio The only difference from Example 1 is that the ink formula in step 6 is adjusted to 30 parts of thermosensitive color-changing microspheres, 40 parts of binder resin, 3 parts of intramolecular synergistic stabilizer, 2 parts of additives, and the balance of deionized water. All other contents are completely the same.

[0052] Example 10: Validation of a Photothermal Material Alternative (Cesium Tungsten Bronze Nanowires) The only difference from Example 1 is that in step 2, copper sulfide nanosheets are replaced with cesium tungsten bronze nanowires of equal mass; otherwise, they are completely identical.

[0053] Example 11 Validation of the hydrophilic comonomer Am alternative The only difference from Example 1 is that NIPAM and Am comonomers (mass ratio 9:1) are used in step 5; all other aspects are exactly the same.

[0054] Example 12 Validation of the hydrophilic comonomer NVP alternative The only difference from Example 1 is that in step 5, NIPAM and NVP comonomers (mass ratio 9:1) were used, and the measured critical melting temperature of the polymer was 30°C. All other contents are completely the same.

[0055] Example 13 Validation of an alternative to the hydrophobic comonomer MMA The only difference from Example 1 is that in step 5, NIPAM and MMA comonomers (mass ratio 95:5) were used, and the measured critical melting temperature of the polymer was 27°C. All other contents are completely the same.

[0056] Example 14: Validation of Alternative Wall Material Systems (Urea-Formaldehyde Resin) The only difference from Example 1 is that in step 2, urea and formaldehyde solutions in an equimolar ratio are used instead of melamine and formaldehyde prepolymer, the pH is adjusted to 4.0, the in-situ polymerization reaction temperature is adjusted to 55°C, and the reaction time is 3 hours. All other contents are completely the same.

[0057] Example 15: Validation of Alternative Wall Material Systems (Polyurethane) The only difference from Example 1 is that in step 2, an equimolar ratio of aqueous polyurethane prepolymer is used instead of melamine and formaldehyde prepolymer, and 0.1% of dibutyltin dilaurate catalyst is added. The in-situ polymerization reaction temperature is 70°C and the reaction time is 4 hours. All other contents are completely the same.

[0058] Example 16: Validation of Alternative Wall Material Systems (Gelatin-Gum Arabinate Complex) Step 1: Preparation of thermosensitive color-changing core material: completely consistent with Step 1 of Example 1.

[0059] Step 2: Aqueous phase preparation of photothermal conversion nanomaterials: Weigh 5.0g of gelatin and 5.0g of gum arabic, add to 120g of deionized water at 40℃, stir until completely dissolved, adjust the pH of the system to 4.0 with 10wt% acetic acid solution to obtain a composite coagulated prepolymer solution; Weigh 1.36g of copper sulfide nanosheets modified with KH550, add to 20g of deionized water and ultrasonically disperse evenly to obtain a nano-dispersion; Slowly add the nano-dispersion to the prepolymer solution, stir at 40℃ for 10 minutes to obtain a homogeneous aqueous phase, with copper sulfide nanosheets accounting for 12% of the total dry weight of the shell.

[0060] Step 3: Preparation of composite wall material microspheres by composite coagulation method: The heat-insulated oil phase is slowly added dropwise to the aqueous phase at 40℃. After the addition is completed, high-speed shearing emulsification is performed at 8000 rpm for 5 minutes to obtain an O / W type fine emulsion. Composite coagulation is completed by stirring at 40℃ for 30 minutes. Then, the temperature is lowered to 10℃ in an ice bath, and glutaraldehyde crosslinking agent accounting for 2% of the dry weight of the wall material is added. The mixture is cured at a constant temperature for 2 hours to obtain a composite wall material microsphere suspension. After washing and drying, microsphere powder is obtained.

[0061] Steps 4-6: Completely consistent with steps 4-6 of Example 1.

[0062] Example 17: Verification of an Alternative Solution for Inorganic Thermosensitive Color-Changing Core Material The only difference from Example 1 is that in step 1, the thermosensitive color-changing core material is replaced with VO2 nanoparticles. 10g of VO2 nanoparticles are weighed and dispersed in 12g of paraffin wax, and melt-mixed at 60°C to obtain the oil phase. The measured color-changing temperature of the core material is 68°C. In step 5, NIPAM and Am copolymer monomers (mass ratio 7:3) are used. The measured critical dissolution temperature of the polymer is 66°C, which is 2°C lower than the color-changing temperature of the core material. All other contents are completely the same.

[0063] Example 18: Full Validation of Resin Alternatives for Binders This embodiment includes 4 sets of parallel samples, and the only difference from Embodiment 1 is: Parallel Sample 1: In step 6, waterborne acrylic resin was used to replace waterborne polyurethane resin of equal mass, the dispersion medium was still deionized water, and the other process parameters remained unchanged. Parallel Sample 2: In step 6, the aqueous polyurethane resin was replaced with an equal mass of nitrocellulose solution, and the dispersion medium was changed to a 1:1 volume ratio of ethanol / ethyl acetate mixed solvent, while the other process parameters remained unchanged. Parallel Sample 3: In step 6, the waterborne polyurethane resin was replaced with an equal mass of two-component epoxy resin E-51 and aliphatic amine curing agent (mass ratio 2:1), the dispersion medium was changed to ethyl acetate, and the other process parameters remained unchanged. The rest of the content is completely consistent with Example 1.

[0064] Example 19 Boundary Verification of In-situ Polymerization Process Parameters This embodiment includes two sets of parallel samples, and the only difference from Embodiment 1 is: Parallel Sample 1: The in-situ polymerization reaction was carried out using a parameter combination of 60℃ / 2.5h; Parallel sample 2: The in-situ polymerization reaction was carried out using the parameter combination of 65℃ / 3.5h; The rest of the content is completely consistent with Example 1.

[0065] Example 20: Boundary Validation of Polymerization Reaction Parameters This embodiment includes two sets of parallel samples, and the only difference from Embodiment 1 is: Parallel Sample 1: Surface-initiated atom transfer radical polymerization was performed using a parameter combination of 25℃ / 8h; Parallel Sample 2: Surface-initiated atom transfer radical polymerization was performed using a parameter combination of 35℃ / 5h; The rest of the content is completely consistent with Example 1.

[0066] Example 21: Verification of Hybrid Photothermal Material Scheme The only difference from Example 1 is that in step 2, copper sulfide nanosheets and cesium tungsten bronze nanowires of equal mass (mass ratio 1:1) are used instead of single copper sulfide nanosheets. The total amount added still accounts for 12% of the total dry weight of the shell. All other contents are completely the same.

[0067] III. Comparative Example Preparation All comparative examples use Example 1 as the control benchmark, strictly adhere to the single variable principle, accurately address the core questions raised in the inventive step examination, and comprehensively cover the single feature solutions of the prior art.

[0068] Comparative Example 1: The closest complete reproduction scheme to the prior art (CN114854236A) Step 1: Preparation of thermosensitive color-changing core material: completely consistent with Step 1 of Example 1.

[0069] Step 2: Preparation of nano-reinforced aqueous phase: Weigh 5.0g melamine, 15.0g 37wt% formaldehyde solution, and 2.0g PVA-1788, add them to 120g deionized water, adjust the pH to 8.5, and stir at 60℃ to obtain melamine resin prepolymer solution; Weigh 1.36g unmodified nano silica, disperse it ultrasonically, and add it to the prepolymer solution to obtain the aqueous phase.

[0070] Step 3: In-situ polymerization to prepare microspheres: This is completely consistent with step 3 of Example 1.

[0071] Step 4: Conventional surface modification: The microsphere powder was redispersed in deionized water, 0.3 g glycidyl methacrylate was added, and the mixture was stirred at 60°C for 0.5 hours. After washing and drying, the modified microspheres were obtained.

[0072] Step 5 Ink Preparation: Weigh 35 parts of waterborne polyurethane resin and 41 parts of deionized water based on a total mass of 100 parts. After stirring evenly, add 0.8 parts of UV-326, 0.7 parts of antioxidant BHT, 1.0 part of leveling agent, 0.5 parts of defoamer, and 1.0 part of polymeric dispersant. Disperse at high speed to obtain the base material. Add 20 parts of modified microspheres under low speed stirring. After stirring evenly, filter to obtain the comparative ink composition.

[0073] Comparative Example 2: Single-factor missing - No active thermal management function Design objective: To verify the necessity of photothermal conversion nanomaterials. The only difference from Example 1 is that copper sulfide nanosheets are not added in step 2, and the rest are completely the same.

[0074] Comparative Example 3: Single-factor missing data - No dynamic interface buffering function Design objective: To verify the necessity of temperature-responsive polymers. The only difference from Example 1 is that steps 4 and 5 are not performed, and the microspheres obtained in step 3 are used directly for ink formulation. All other aspects are completely identical.

[0075] Comparative Example 4: Single-factor loss - lack of intramolecular synergistic protective function Design objective: To verify the necessity of intramolecular synergistic stabilizers. The only difference from Example 1 is that in step 6, a physical mixture of 0.8 parts UV-326 and 0.7 parts antioxidant BHT is used instead of the intramolecular synergistic stabilizer. All other aspects are completely identical.

[0076] Comparative Example 5: Pair Combinations - Active Thermal Management + Dynamic Interface Buffer Design objective: To verify the technical effect of the two-to-one combination. The only difference from Example 1 is that in step 6, the intramolecular synergistic stabilizer is replaced by a physical mixture of 0.8 parts UV-326 and 0.7 parts antioxidant BHT. All other contents are completely the same.

[0077] Comparative Example 6: Pair Combinations - Active Thermal Management + Intramolecular Synergistic Protection Design objective: To verify the technical effect of pairwise combinations. The only difference from Example 1 is that steps 4 and 5 are not performed. The microspheres obtained in step 3 are directly used for ink preparation. All other contents are completely the same.

[0078] Comparative Example 7: Pairwise Combinations - Dynamic Interface Buffer + Intramolecular Synergistic Protection Design objective: To verify the technical effect of pairwise combinations. The only difference from Example 1 is that copper sulfide nanosheets are not added in step 2, and the rest are completely the same.

[0079] Comparative Example 8: Conventional Material Replacement - Nano-silica Replacement of Photothermal Materials Design objective: To verify that the performance improvement comes from the photothermal management function rather than rigidity enhancement. The only difference from Example 1 is that in step 2, nano-silica with the same particle size and the same modification process as the copper sulfide nanosheets is used to replace the copper sulfide nanosheets by the same mass. All other contents are completely the same.

[0080] Comparative Example 9: Out-of-range parameter - LCST difference exceeds 5°C Design purpose: To verify the necessity of the parameter range. The only difference from Example 1 is that the critical dissolution temperature of the polymer in step 5 is adjusted to 25°C, which is 6°C lower than the color change temperature of the core material. All other contents are completely the same.

[0081] Comparative Example 10: Out-of-range parameter - Photothermal material addition amount below the lower limit Design purpose: To verify the necessity of the parameter range. The only difference from Example 1 is that the amount of copper sulfide nanosheets added in step 2 is adjusted to 3% of the total dry weight of the shell. All other contents are completely the same.

[0082] Comparative Example 11: Single Feature of Prior Art - Photothermal Material Using Only Comparative Document 2 Design objective: To verify that a single existing technical feature cannot achieve the effect of the present invention. The only difference from Comparative Example 1 is that modified copper sulfide nanosheets of equal mass are used instead of nano-silica. All other contents are completely consistent with Comparative Example 1.

[0083] Comparative Example 12: Single Feature of Prior Art - Using Only the Temperature-Sensitive Polymer Brush from Comparative Document 3 Design purpose: To verify that a single existing technical feature cannot achieve the effect of the present invention. The only difference from Comparative Example 1 is that steps 4 and 5 of Example 1 are used instead of GMA surface modification. All other contents are completely consistent with Comparative Example 1.

[0084] Comparative Example 13: Single Feature of Prior Art - Intramolecular Stabilizer Using Only Reference Document 4 Design objective: To verify that a single existing technical feature cannot achieve the effect of the present invention. The only difference from Comparative Example 1 is that the physical mixture of UV-326 and BHT is replaced with an equal mass of the intramolecular synergistic stabilizer of the present invention. All other contents are completely consistent with Comparative Example 1.

[0085] IV. Performance Test Result Statistics Table

[0086] V. Results Analysis The results of the above embodiments show that the technical solution of the present invention can stably achieve excellent comprehensive performance within the raw material composition, ratio range, and process parameter range defined in the claims. After 1000 cycles of temperature-stretching, the microsphere breakage rate is controlled within 5.2%, the color difference ΔE before and after cycling does not exceed 1.1, and the color change performance retention rate after 500 hours of heat aging is higher than 85%. At the same time, it has excellent storage stability, which fully verifies the universality of the technical solution of the present invention and the rationality and necessity of the parameter boundaries defined in the claims.

[0087] Compared with Comparative Example 1, which is closest to the prior art, the microsphere structure stability, color change performance retention rate, and long-term aging resistance of the present invention are all improved by orders of magnitude, completely solving the problem of progressive failure due to dynamic thermo-mechanical coupling stress that the prior art cannot handle. Comparative Examples 2-4, which lack single factors, and Comparative Examples 5-7, which combine two features, all show significantly inferior overall performance compared to the complete solution of the present invention; Comparative Examples 11-13, which only use a single feature of the prior art, show no essential difference in performance from the closest prior art, and are far inferior to the complete solution of the present invention. The above results directly prove that photothermal conversion nanomaterials, surface-grafted temperature-responsive polymers, and intramolecular synergistic stabilizers are the necessary technical features to achieve the purpose of the invention, and they form an unexpected synergistic effect: in comparative examples 2-4 where a single factor is missing, the microsphere breakage rate increases to 21.5%, 18.3%, and 4.1%, respectively; in comparative examples 5-7 where the two are combined, the performance can only achieve optimization in a single dimension; while in Example 1 where the three are combined, an extremely low breakage rate of 3.2%, an extremely small color difference of 0.8%, and a high aging retention rate of 92.5% are achieved simultaneously. The performance improvement far exceeds the expectations of those skilled in the art for the simple superposition of the individual effects of the three features, and is not a conventional combination of existing technical means.

[0088] The performance of Comparative Example 8, which uses conventional nanomaterials as substitutes, and Comparative Examples 9-10, which use parameters outside the range, both showed significant deterioration, further proving that the performance improvement of this invention comes from a specific technical concept, rather than a simple adjustment of conventional technical means in the field; the thermal stress reduction data measured by micro-area Raman spectroscopy directly verifies the authenticity of the core principle of this invention, rather than the theoretical effect derived by simulation.

[0089] In summary, the technical solution of this invention breaks through the bottleneck of the existing technology of "passive enhancement and static protection", has outstanding substantive features and significant progress, fully realizes the preset invention purpose, and meets all the legal requirements for invention patent authorization.

Claims

1. A thermosensitive color-changing microsphere ink composition, characterized in that, It consists of the following components in parts by weight: Thermochromic microspheres: 10-30 parts; Binding resin: 20-40 parts; Intramolecular synergistic stabilizer: 0.5-3 parts; Additives: 0.5-2 parts; Dispersion medium: Make up the total mass of the composition to the remainder of 100 parts. The thermosensitive color-changing microspheres have a core-shell structure, with a core of thermosensitive color-changing core material and a shell of polymer wall material and photothermal conversion nanomaterials uniformly dispersed in the wall material. The photothermal conversion nanomaterials are at least one of copper sulfide nanosheets modified with 3-aminopropyltriethoxysilane and cesium tungsten bronze nanowires, accounting for 5%-25% of the total dry weight of the shell. The total dry weight of the shell refers to the sum of the theoretical dry weight of the polymer wall material after complete curing and the mass of the photothermal conversion nanomaterials. The outer surface of the thermosensitive color-changing microspheres is covalently grafted with a temperature-responsive polymer; the temperature-responsive polymer is a homopolymer of poly(N-isopropylacrylamide) or a random copolymer of poly(N-isopropylacrylamide) and a comonomer; the comonomer is any hydrophilic monomer of acrylamide or N-vinylpyrrolidone, or any hydrophobic monomer of butyl methacrylate or methyl methacrylate; the critical dissolution temperature of the temperature-responsive polymer is lower than or equal to the color-changing temperature of the thermosensitive color-changing core material, and the temperature difference between the two is 0-5℃.

2. The ink composition according to claim 1, characterized in that, The intramolecular synergistic stabilizer is 2-(2H-benzotriazol-2-yl)-4-tert-butyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenol.

3. The ink composition according to claim 1, characterized in that, The polymer wall material is any one of melamine resin, urea-formaldehyde resin, polyurethane, or gelatin-gum arabic composite.

4. The ink composition according to claim 1, characterized in that, The thermosensitive color-changing core material can be any one of the following: a leuco dye-developer-solvent organic system or a vanadium dioxide inorganic system.

5. The ink composition according to claim 1, characterized in that, The binder resin is any one of waterborne polyurethane resin, waterborne acrylic resin, nitrocellulose liquid, and two-component epoxy resin.

6. The ink composition according to claim 1, characterized in that, The additive is at least one of leveling agent, defoamer, and polymeric dispersant; the dispersion medium is any one or a mixture of two or more of deionized water, anhydrous ethanol, and ethyl acetate.

7. A method for preparing the thermosensitive color-changing microsphere ink composition according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of thermosensitive color-changing microspheres: ①Preparation of thermosensitive color-changing core material: Heat and melt the raw materials of thermosensitive color-changing core material to obtain a homogeneous oil phase, and keep it at the temperature for later use; ② Preparation of the aqueous phase containing photothermal conversion nanomaterials: Polymer monomers and emulsifiers are added to deionized water, the pH value is adjusted and the mixture is heated to react, resulting in a polymer prepolymer solution; the photothermal conversion nanomaterials modified with 3-aminopropyltriethoxysilane are ultrasonically dispersed in deionized water to obtain a nano-dispersion; the nano-dispersion is added to the prepolymer solution and stirred evenly to obtain the aqueous phase; ③ In-situ polymerization preparation of composite wall material microspheres: The heat-insulated oil phase is added dropwise to the aqueous phase, and high-speed shear emulsification is performed to obtain an O / W type fine emulsion. The in-situ polymerization reaction is completed by constant temperature stirring to obtain a core-shell structured composite wall material microsphere suspension. After washing and drying, microsphere powder is obtained. ④ Surface initiator modification: The composite wall material microsphere powder was dispersed in anhydrous toluene, 3-(2-bromoisobutyryloxy)propyltrimethoxysilane was added, and the reaction was carried out at a constant temperature under nitrogen protection. After washing, microspheres with surface covalently grafted initiators were obtained. ⑤ Grafted temperature-responsive polymer: Microspheres with surface-grafted initiators were dispersed in a methanol / water mixed solvent, and a temperature-sensitive monomer and pentamethyldiethylenetriamine ligand were added. After three cycles of freezing-vacuuming-nitrogen purging to remove oxygen, cuprous bromide catalyst was added, and the reaction was carried out at a constant temperature under nitrogen protection. After washing and drying, temperature-sensitive color-changing microspheres were obtained. In the reaction system, the molar ratio of temperature-sensitive monomer, initiator grafted on the surface of microspheres, cuprous bromide catalyst, and pentamethyldiethylenetriamine ligand was 100:1:1:

2. (2) Low-damage dispersion formulation of ink: The binder resin, intramolecular synergistic stabilizer and additives are dispersed in the dispersion medium and dispersed at high speed to obtain a uniform base material; under low-speed stirring at 300-500 rpm, the thermosensitive color-changing microspheres obtained in step (1) are added to the base material, mixed evenly and filtered to obtain the target ink composition.

8. The preparation method according to claim 7, characterized in that, In step (1) ③, the reaction temperature of in-situ polymerization is 60-65℃ and the reaction time is 2.5-3.5h.

9. The preparation method according to claim 7, characterized in that, In step (1) ⑤, the reaction temperature for surface-initiated atom transfer radical polymerization is 25-35℃, and the reaction time is 5-8h.

10. The preparation method according to claim 7, characterized in that, In step (1) ⑤, the critical dissolution temperature of the polymer is controlled by adjusting the molar ratio of N-isopropylacrylamide to the comonomer in the thermosensitive monomer, so that it is lower than or equal to the color change temperature of the thermosensitive color-changing core material, and the temperature difference between the two is 0-5℃.

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