Composite microcapsule color-changing pigment and preparation method thereof

Abstract

The present application relates to the technical field of pigment preparation, in particular to a kind of composite microcapsule color-changing pigment and its preparation method, the pigment is composed of intelligent microcapsule, water-based acrylic resin, film-forming aid and thickening agent according to specific proportion.Intelligent microcapsule adopts multi-compartment structure, core is thermochromic microcapsule, surface is fixed by chemical bonding multiple perfume release sub-capsules with different thermal response threshold, realize selective fragrance release based on temperature gradient.Thermochromic composite is composed of crystal violet lactone, bisphenol A and specific solvent, ensure excellent thermochromic performance.The design realizes the multifunctional integration of pigment, has temperature response color change and phased fragrance release, is widely used in intelligent coating and sensory material field, has significant innovation and practical value.

Description

Technical Field

[0001] This invention relates to the field of pigment preparation technology, specifically to a composite microcapsule color-changing pigment and its preparation method. Background Technology

[0002] Thermochromic materials, due to their significant color changes with temperature variations, are widely used in temperature indication, smart materials, and temperature control devices, becoming an important direction in functional materials research. However, existing thermochromic materials generally suffer from problems such as insufficient stability, limited response sensitivity, high preparation costs, and poor environmental adaptability, which seriously restrict their widespread promotion and practical application. In particular, crystal violet lactone (CVL), as a typical organic thermochromic material, although possessing obvious thermo-induced phase change characteristics, its performance is easily affected by external factors such as pH value, light, and humidity, resulting in unstable color-changing effects and insufficient durability.

[0003] Microencapsulation technology is widely used due to its ability to effectively protect core active substances from external environmental influences, especially showing promising applications in encapsulating thermochromic materials. For example, existing research has achieved multicolor photochromic microcapsules with strong photoresponsiveness and excellent thermal stability by encapsulating organic photochromic materials with polymers such as polyurethane; other technologies have combined thermochromic materials with water-soluble dyes and phase change materials to prepare multifunctional microcapsules with rich chromatograms and reversible color changes. However, traditional microcapsules are mostly single-function carriers and usually only respond to a single stimulus, limiting their potential for achieving multi-stimulus and multifunctional responses in the field of smart materials.

[0004] Therefore, developing novel composite microcapsule thermochromic materials with multi-stimulus response and stable performance has become the key to improving the application performance and expanding the application range of thermochromic materials. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a composite microcapsule color-changing pigment and its preparation method. The pigment is composed of intelligent microcapsules, water-based acrylic resin, film-forming aids, and thickeners in a specific ratio. The intelligent microcapsules employ a multi-compartment structure, with a thermochromic microcapsule at the core. Multiple fragrance-releasing subcapsules with different thermal response thresholds are chemically bonded to the surface, achieving selective fragrance release based on a temperature gradient. The thermochromic composite is composed of crystal violet lactone, bisphenol A, and a specific solvent, ensuring excellent thermochromic performance. This design achieves multifunctional integration of the pigment, combining temperature-responsive color changing and staged fragrance release, making it widely applicable in the fields of intelligent coatings and sensory materials, and possessing significant innovation and practical value.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A composite microcapsule color-changing pigment comprises the following components by weight: 30-50 parts intelligent microcapsules, 40-60 parts water-based acrylic resin, 2-3 parts film-forming aid, and 0.5-1 part thickener;

[0008] The smart microcapsule has a multi-compartment structure, including a thermochromic microcapsule as the core, and at least one fragrance-releasing subcapsule that is chemically bonded to the surface of the thermochromic microcapsule.

[0009] The core material of the thermochromic microcapsule contains a thermochromic complex, the core material of the fragrance-releasing subcapsule contains a fragrance, and the wall materials of different fragrance-releasing subcapsules have different thermal response thresholds to achieve selective fragrance release based on temperature gradient.

[0010] Preferably, the thermochromic complex is composed of an electron donor, an electron acceptor, and a solvent in a mass ratio of (0.08-0.1):(0.4-0.5):(3-6); the electron donor is crystal violet lactone, the electron acceptor is bisphenol A, and the solvent is one or more of tetradecanol and hexadecyl alcohol.

[0011] Preferably, the wall material of the thermochromic microcapsule is a polyacrylate-styrene copolymer resin; the chemical bonding is a covalent bond formed between the imidazole ring on the surface of the thermochromic microcapsule wall material and the reactive groups on the surface of the fragrance release capsule wall material.

[0012] Preferably, the fragrance-releasing capsules include low-temperature fragrance-releasing capsules, medium-temperature fragrance-releasing capsules, and high-temperature fragrance-releasing capsules;

[0013] The wall material of the low-temperature fragrance-releasing capsule is a gelatin-gum arabic composite, its core material is menthol, and the trigger release temperature is 25-34℃.

[0014] The wall material of the medium-temperature releasing lavender capsule is ethyl cellulose, its core material is lavender oil, and its trigger release temperature is 35-45℃.

[0015] The wall material of the high-temperature fragrance-releasing capsule is polystyrene-acrylic acid copolymer, its core material is citral, and the trigger release temperature is above 46°C.

[0016] Preferably, the particle size range of the thermochromic microcapsules is 1-20 μm, and the particle size range of the fragrance release subcapsules is 100-800 nm.

[0017] Preferably, the smart microcapsule is prepared by the following steps:

[0018] S11. Using the thermochromic composite as the core material, the thermochromic microcapsules are encapsulated with polyacrylate-styrene copolymer resin as the wall material by interfacial polymerization to obtain thermochromic microcapsules.

[0019] S12. Using fragrance as the core material, the fragrance is coated by one of the following methods: complex coagulation, solvent evaporation, or interfacial polymerization. During the coating process, chemical modification is used to add groups that can react with the functional groups on the surface of the thermochromic microcapsule wall material to obtain fragrance release subcapsule.

[0020] S13. Mix the thermochromic microcapsules obtained in step S11 with the fragrance release capsules obtained in step S12, and stir and react at 20-60℃ for 4-12 hours to fix the fragrance release capsules on the surface of the thermochromic microcapsules through chemical bonding. After washing and drying, the smart microcapsules are obtained.

[0021] Preferably, in step S11, the reaction conditions for the interfacial polymerization method are: the pH value of the aqueous phase is adjusted to 4-5, the reaction temperature is 55-65℃, the stirring speed is 1000-1200 rpm, and the reaction time is 1.5-2 h.

[0022] Preferably, in step S12, when the fragrance releasing subcapsule includes a low-temperature fragrance releasing subcapsule, the low-temperature fragrance releasing subcapsule is prepared by a complex coagulation method;

[0023] When the fragrance-releasing capsules include intermediate-temperature fragrance-releasing capsules, the intermediate-temperature fragrance-releasing capsules are prepared by solvent evaporation.

[0024] When the fragrance-releasing subcapsule includes a high-temperature fragrance-releasing subcapsule, the high-temperature fragrance-releasing subcapsule is prepared by interfacial polymerization.

[0025] The specific method of the chemical modification is as follows:

[0026] When using the complex coagulation method, glutaraldehyde is added to the wall material at a rate of 1.5%-2.0% of the wall material's weight, and sodium chloroacetate is added for carboxymethylation modification at a rate of 2%-4% of the wall material's weight. The carboxymethylation reaction conditions are a temperature of 50-60℃, a time of 2-3 hours, and a pH of 10-11. Subsequently, under ice bath conditions at 0-5℃, thionyl chloride is added at a rate of 1.2-1.5 times the molar amount of carboxymethyl groups to carry out a chlorination reaction, ultimately generating chloroalkane side chains on the surface of the wall material.

[0027] When using the solvent evaporation method, 1-chlorododecane is incorporated into the organic phase of the wall material at an addition amount of 5%-10% of the total weight of the wall material. The emulsification process is carried out under high-speed shear at 8000-12000 rpm for 15-25 minutes. During the solvent evaporation stage, the temperature is controlled at 35-40℃, the stirring speed is 250-350 rpm, and the evaporation time is 4-6 hours. Through blending and emulsification, the chloroalkyl groups are stably exposed on the surface of the subcapsule.

[0028] When using interfacial polymerization, 4-chloromethylstyrene is added to the oil phase at an amount of 0.5%-5% of the wall material monomer weight. The chloroalkyl groups are embedded into the wall material polymer chain through the polymerization reaction. The polymerization reaction temperature is maintained at 70-80℃, the reaction time is 4-6h, the pH value of the system is adjusted to 8-9, and the stirring speed is controlled at 800-1200 rpm.

[0029] Preferably, in step S13, the mass ratio of the thermochromic microcapsule to the fragrance-releasing subcapsule is 1:2-6.

[0030] A method for preparing a composite microcapsule color-changing pigment, comprising the following steps:

[0031] S1. Add the smart microcapsules to the water-based acrylic resin according to the mass ratio, and stir at 200-300 rpm for 15-20 min;

[0032] S2. Add thickener and film-forming aid in sequence according to the mass parts, stir at 200-300 rpm for 20-30 min, degas under vacuum of 0-5 MPa for 20-30 min, and remove agglomerates through a 400-mesh sieve to obtain the composite microcapsule color-changing pigment.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention achieves an organic combination of thermochromic function and selective fragrance release by constructing intelligent microcapsules with a multi-compartment structure, significantly enhancing the multifunctionality and response complexity of the composite microcapsule thermochromic pigment. The thermochromic microcapsules use crystal violet lactone as an electron donor and bisphenol A as an electron acceptor, combined with a specific ratio of tetradecanol or hexadecyl alcohol solvent, to form a stable thermochromic complex. This complex can induce color changes through phase transitions in its molecular structure within a certain temperature range, exhibiting high sensitivity and controllable thermal response characteristics. Polyacrylate-styrene copolymer resin, used as the wall material, not only provides excellent mechanical protection for the thermochromic microcapsules but also forms a strong chemical bond between the imidazole rings on the wall material and the reactive groups on the fragrance-releasing subcapsule wall material through covalent bonds, thus ensuring structural stability and functional synergy. The fragrance-releasing subcapsule uses gelatin-gum arabic composite, ethyl cellulose, and polystyrene-acrylic acid copolymer as wall materials with different thermal response thresholds, containing fragrances such as menthol, lavender oil, and citral. It can sequentially release different fragrances according to the ambient temperature gradient, achieving a multi-stage, controllable fragrance release function. The optimized microcapsule particle size design ensures uniform pigment dispersion and efficient heat conduction, effectively improving temperature response speed and the precision of release control.

[0035] In the preparation process, the rational selection and combination of interfacial polymerization, complex coagulation, and solvent evaporation methods enable the efficient formation of various microcapsules. Furthermore, chemical modification introduces active groups that react with the functional groups on the surface of the thermochromic microcapsules, ensuring the stable bonding and functional synergy of the two types of microcapsules. The overall design principle, based on a multi-cavity structure, achieves independent encapsulation of the load and multimodal response, breaking the limitations of traditional single-stimulus color-changing materials. It not only exhibits rich chromatographic changes in temperature-triggered color changes but also achieves graded fragrance release under temperature gradients, greatly enriching the material's sensory performance and application potential. This composite microcapsule color-changing pigment possesses excellent thermal response sensitivity, structural stability, and multifunctional integration capabilities, making it suitable for the field of smart materials and effectively promoting the development of thermochromic technology towards multifunctionality and intelligence. Attached Figure Description

[0036] Figure 1 This is a flow chart of the preparation process of the composite microcapsule color-changing pigment described in this invention;

[0037] Figure 2 This is a flowchart illustrating the preparation process of the intelligent microcapsules described in this invention.

[0038] Figure 3 This is a SEM image of the smart microcapsule prepared in Example 1 of the present invention. Detailed Implementation

[0039] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. 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.

[0040] Please see Figure 1-3 The present invention provides a technical solution:

[0041] Example 1

[0042] This embodiment provides a formulation for a composite microcapsule color-changing pigment, comprising the following components by weight (one part by weight is defined as 100g):

[0043]

[0044] The waterborne acrylic resin is designated as Soluryl R-20B.

[0045] The film-forming aid is diethylene glycol monomethyl ether;

[0046] The thickener is carboxymethyl cellulose;

[0047] The smart microcapsule described in this embodiment has a multi-compartment structure, including a thermochromic microcapsule as the core, and three fragrance-releasing subcapsules that are chemically bonded to the surface of the thermochromic microcapsule.

[0048] The core material of the thermochromic microcapsule contains a thermochromic complex, the core material of the fragrance-releasing subcapsule contains a fragrance, and the wall materials of different fragrance-releasing subcapsules have different thermal response thresholds to achieve selective fragrance release based on temperature gradient.

[0049] The thermochromic compound is composed of crystal violet lactone, bisphenol A, and tetradecyl alcohol in a mass ratio of 0.1:0.5:6;

[0050] The fragrance-releasing capsules include low-temperature fragrance-releasing capsules, medium-temperature fragrance-releasing capsules, and high-temperature fragrance-releasing capsules;

[0051] The intelligent microcapsule is prepared through the following steps:

[0052] S11. Using the thermochromic composite as the core material, the thermochromic microcapsules are encapsulated with polyacrylate-styrene copolymer resin as the wall material by interfacial polymerization to obtain thermochromic microcapsules.

[0053] S12. Using fragrance as the core material, the fragrance is coated by one of the following methods: complex coagulation, solvent evaporation, or interfacial polymerization. During the coating process, chemical modification is used to add groups that can react with the functional groups on the surface of the thermochromic microcapsule wall material to obtain fragrance release subcapsule.

[0054] S13. The thermochromic microcapsules obtained in step S11 are mixed with the fragrance release capsules obtained in step S12, and stirred at 25°C for 8 hours to fix the fragrance release capsules on the surface of the thermochromic microcapsules through chemical bonding. After washing and drying, the smart microcapsules are obtained.

[0055] The thermochromic microcapsule emulsion is prepared by interfacial polymerization, specifically including the following steps:

[0056] 1. Emulsification: The oil phase (a mixture of core and wall material monomers, crosslinking agent, and initiator) is added to the aqueous phase (a 0.5% sodium dodecyl sulfate aqueous solution) under slow stirring (200 rpm), with a water-to-oil phase volume ratio of 4:1. Subsequently, emulsification is performed for 25 min using a high-speed shear emulsifier at 8000 rpm to form a stable oil-in-water (O / W) emulsion.

[0057] The core material is a thermochromic composite, which is made by melting and mixing crystal violet lactone (0.1 parts), bisphenol A (0.5 parts), and tetradecyl alcohol (6 parts) at 60°C in a mass ratio of 0.1:0.5:6.

[0058] The wall material monomer is a mixture of methyl methacrylate and styrene in a molar ratio of 1:2, with a total amount of 10 parts.

[0059] The crosslinking agent is 0.05 parts of ethylene glycol dimethacrylate;

[0060] The initiator is 0.01 parts azobisisobutyronitrile;

[0061] 2. Interfacial Polymerization: The emulsion was transferred to a reactor equipped with a reflux condenser and a nitrogen inlet pipe. Under nitrogen protection, the temperature was slowly increased to 55°C. The pH of the system was adjusted to 5 using citric acid solution and sodium hydroxide solution. Under these conditions, the reaction was carried out with constant temperature stirring at 1000 rpm for 1.5 hours, allowing the monomers to polymerize at the oil-water interface to form a dense polyacrylate-styrene copolymer resin wall material.

[0062] 3. Post-processing: After the reaction was completed, the emulsion was cooled to room temperature. The microcapsule solids were collected by centrifugation (5000 rpm, 10 min) and washed three times with deionized water and anhydrous ethanol to thoroughly remove unreacted monomers, emulsifiers and other impurities. The resulting thermochromic microcapsules were redispersed in deionized water for later use.

[0063] The low-temperature fragrance-releasing capsules are prepared by complex coagulation, specifically including the following steps:

[0064] 1. Complex Agglomeration Encapsulation: Dissolve 1 part gelatin and 1 part gum arabic separately in warm water at 40°C to form 5% solutions. Add 1 part menthol to the gelatin solution while stirring, and after initial emulsification, mix with the gum arabic solution. Adjust the pH of the mixture to 4.5 with dilute acetic acid, and react for 2 hours at 50°C and 500 rpm, forming microcapsules through complex agglomeration.

[0065] 2. Chemical Modification: 0.08 parts of sodium chloroacetate were added to the system, and the reaction was carried out at 60℃ and pH 10 (adjusted with NaOH solution) for 2 hours to introduce carboxyl groups onto the wall material molecular chain. The system was then cooled to an ice bath at 4℃. Thionyl chloride (1.2 times the molar amount of carboxymethyl) was slowly added, and the reaction was stirred at this low temperature for 2 hours to convert the carboxyl groups into chloroalkane groups. 0.04 parts of glutaraldehyde were added for cross-linking and curing. After the reaction was completed, the product was filtered, washed, and dried to obtain low-temperature fragrance-releasing capsules with chloroalkane groups on the surface.

[0066] The medium-temperature fragrance-releasing capsules are prepared by solvent evaporation method, specifically including the following steps:

[0067] 1. Emulsion Preparation: 1 part lavender oil, 2 parts ethyl cellulose, and 0.2 parts 1-chlorododecane (a chemically modified monomer) were dissolved together in dichloromethane to form an organic phase. This organic phase was then added dropwise to an aqueous phase containing polyvinyl alcohol (0.5% concentration) with stirring, at a volume ratio of 5:1. Emulsification was carried out at a high-speed shear rate of 12000 rpm for 25 min to form a stable O / W emulsion.

[0068] 2. Solvent Evaporation and Encapsulation: The emulsion was transferred to a reactor and evaporated for 4 hours under slow stirring at 35°C and 350 rpm to ensure complete evaporation of the organic solvent. Ethyl cellulose precipitated and deposited on the surface of the core material droplets to form the capsule wall. During this process, the chloroalkyl groups in 1-chlorododecane were exposed on the surface of the subcapsule. The microcapsules were collected by filtration, washed with water, and dried to obtain medium-temperature fragrance-releasing subcapsule.

[0069] The high-temperature fragrance-releasing capsules are prepared by interfacial polymerization, specifically including the following steps:

[0070] 1. Emulsification: The oil phase (a mixture of core and wall material monomers, chemically modified monomers, crosslinking agents, and initiators) is mixed with the aqueous phase (a 0.5% sodium dodecyl sulfate aqueous solution) at a volume ratio of 4:1. Emulsification is carried out at 8000 rpm for 20 minutes to form a uniform O / W emulsion.

[0071] The core material is citral, and the dosage is 1 part.

[0072] The wall material monomer is a mixture of methyl methacrylate and styrene in a molar ratio of 1:2, with a total amount of 3 parts;

[0073] The functional monomer is 4-chloromethylstyrene, and the dosage is 0.1 parts;

[0074] The crosslinking agent is divinylbenzene, and the amount used is 0.05 parts;

[0075] The initiator is 0.01 parts azobisisobutyronitrile;

[0076] 2. Interfacial Polymerization and Group Intercalation: The emulsion was placed in a reactor and heated to 70°C under nitrogen protection. The pH of the system was adjusted to 9, and the reaction was carried out for 4 hours with stirring at 1200 rpm. During this period, monomers in the oil phase (including 4-chloromethylstyrene) underwent a copolymerization reaction at the droplet interface to form a polystyrene-acrylic acid copolymer wall material, with chloroalkyl groups directly intercalated into the polymer chain. After the reaction was completed, the product was collected, cooled, washed, and dried to obtain high-temperature fragrance-releasing capsules.

[0077] In the preparation process of the intelligent microcapsule, in step S13, the mass ratio of the thermochromic microcapsule to the fragrance-releasing subcapsule is 1:4; the mass ratio of the low-temperature fragrance-releasing subcapsule, the medium-temperature fragrance-releasing subcapsule, and the high-temperature fragrance-releasing subcapsule is 1:1:1.

[0078] This embodiment also provides a method for preparing composite microcapsule color-changing pigments, including the following steps:

[0079] S1. Add the smart microcapsules to the water-based acrylic resin according to the mass fraction, and stir at 300 rpm for 20 min;

[0080] S2. Thickener and film-forming aid are added sequentially according to the mass fraction. After stirring at 200 rpm for 20 min, the mixture is degassed under a vacuum of 5 MPa for 30 min, and agglomerates are removed by passing it through a 400-mesh sieve to obtain the composite microcapsule color-changing pigment.

[0081] Example 2: Example 2 differs from Example 1 in that the fragrance-releasing capsules in Example 2 include low-temperature fragrance-releasing capsules and medium-temperature fragrance-releasing capsules, and the use of high-temperature fragrance-releasing capsules is omitted. The remaining steps are exactly the same as in Example 2 and Example 1.

[0082] Example 3: Example 3 differs from Example 1 in that the fragrance-releasing capsules in Example 3 include medium-temperature fragrance-releasing capsules and high-temperature fragrance-releasing capsules, and the use of low-temperature fragrance-releasing capsules is omitted. The remaining steps are exactly the same as in Example 3 and Example 1.

[0083] Example 4: Example 4 differs from Example 1 in that, in Example 4, the fragrance releasing capsules only include low-temperature fragrance releasing capsules, and the use of medium-temperature and high-temperature fragrance releasing capsules is omitted. The remaining steps are exactly the same as in Example 4 and Example 1.

[0084] Example 5: Example 5 differs from Example 1 in that, in Example 5, the fragrance releasing capsules only include medium-temperature fragrance releasing capsules, and the use of low-temperature and high-temperature fragrance releasing capsules is omitted. The remaining steps are exactly the same as in Example 5 and Example 1.

[0085] Example 6: Example 6 differs from Example 1 in that, in Example 6, the fragrance releasing capsules only include high-temperature fragrance releasing capsules, and the use of low-temperature and medium-temperature fragrance releasing capsules is omitted. The remaining steps are exactly the same as in Example 6 and Example 1.

[0086] Comparative Example

[0087] Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that the chemical modification treatment of the low-temperature fragrance-releasing capsule, the medium-temperature fragrance-releasing capsule, and the high-temperature fragrance-releasing capsule was eliminated in Comparative Example 1, thereby eliminating the chemical bonding between the fragrance-releasing capsule and the thermochromic capsule. In Comparative Example 1, the smart microcapsules were prepared by simple physical-mechanical mixing. The remaining steps were exactly the same as those in Comparative Example 1 and Example 1.

[0088] Comparative Example 2: The only difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the low-temperature fragrance-releasing capsules, medium-temperature fragrance-releasing capsules, and high-temperature fragrance-releasing capsules are all prepared by interfacial polymerization, and the wall material is polystyrene-acrylic acid copolymer. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0089] Performance testing

[0090] SEM image of the smart microcapsule obtained in Example 1, as shown below. Figure 3 As shown in the figure, the microcapsules are generally regular spherical or nearly spherical in shape, with complete morphology and smooth surface. The particle size is distributed within a relatively concentrated range. Based on the comparison with the scale, the particle size is estimated to be mainly between several micrometers and tens of micrometers, which is consistent with the target particle size range set in the technical solution.

[0091] Importantly, at high magnification, individual smart microcapsules exhibit a clear "core-satellite" multi-compartment structure. The larger spherical core in the image is identifiable as the thermochromic microcapsule serving as the core. Furthermore, smaller granular substructures are observed attached to the core surface via distinct connection points; these are likely fragrance-releasing subcapsules fixed by chemical bonding. This structure directly demonstrates that the fabrication process successfully achieved effective fixation of subcapsules on the surface of the core microcapsule, rather than simple physical mixing, confirming the successful construction of the multi-compartment structure.

[0092] Furthermore, to scientifically evaluate the technological superiority of the composite microcapsule color-changing pigments (Examples 1-6) compared to traditional simplified methods (Comparative Examples 1-2), we designed and implemented a systematic test plan. The tests focused on four core performance dimensions: thermochromic performance, the gradient and precision of fragrance release, the stability of the microstructure, and the final synergistic response of vision and olfaction. All tests were conducted under identical environmental conditions to ensure the comparability of results, as detailed below:

[0093] Thermochromic performance test: The phase transition temperature range of the sample was determined using a differential scanning calorimeter (DSC), and the color change was measured using a colorimeter under programmed temperature control conditions (20°C to 70°C, heating rate 2°C / min). A color difference value ΔE>40 was used as the standard for significant color change.

[0094] Fragrance release gradient test: The concentration of volatile organic compounds in stationary samples was monitored in real time during the programmed temperature rise (25°C to 60°C) using gas chromatography-mass spectrometry (GC-MS). By analyzing the characteristic ion peak areas of specific fragrances, a curve was plotted to show the release rate as a function of temperature, in order to determine the trigger release temperature and release peak value.

[0095] Structural stability test (subcapsule retention rate): The prepared smart microcapsules were dispersed in deionized water and centrifuged at 5000 rpm for 30 minutes. The microstructure of the samples before and after centrifugation was observed by scanning electron microscopy (SEM), and the number of subcapsules still attached to the surface of the thermochromic microcapsules by chemical bonding was counted using image analysis software. The retention rate was calculated (retention rate = number of subcapsules after centrifugation / number of subcapsules before centrifugation × 100%).

[0096] Synergistic responsiveness test: The sample is coated onto a glass slide and placed on a hot stage equipped with a high-definition camera and a miniature odor sensor array. While the temperature is programmed to rise, the color change of the sample (visual signal) and the electrical signal response of the odor sensor to a specific fragrance (olfactory signal) are recorded simultaneously, and the temporal correlation between the two signals is analyzed.

[0097] The relevant test results are shown below:

[0098]

[0099] As can be seen from the above, Example 1 (full-function design) has significant advantages in technical performance compared to the comparative example. The fundamental reason for this is the ingenious "nuclear-satellite" multi-compartment structure design and the robust chemical bonding strategy.

[0100] First, regarding thermochromic performance, all examples exhibited a broad (31-58°C) and significant (ΔE>40) color change range. This is attributed to the reliable reversible electron transfer mechanism of the crystal violet lactone / bisphenol A / tetradecyl alcohol system in the core thermochromic microcapsules, and the effective protection of the polyacrylate-styrene copolymer resin wall material. In contrast, Comparative Example 1, due to its simple physical mixing, resulted in mutual interference between functional units, leading to a weak and ambiguous color change response. Comparative Example 2, because all subcapsules used a single polystyrene-acrylic wall material, had similar thermodynamic properties that limited the response of the thermochromic composite to a narrow temperature window.

[0101] The most crucial advantage lies in the gradient and precision of fragrance release. Example 1 successfully achieved selective and sequential release of three fragrances under a continuous temperature gradient. This is because the three fragrance-releasing subcapsules utilize wall materials with distinct thermodynamic properties: the gelatin-gum arabic complex releases menthol at low temperatures due to the softening of the gel network; ethyl cellulose undergoes a glass transition in the mid-temperature range, releasing lavender oil; and the polystyrene-acrylic acid copolymer melts and releases citral at higher temperatures. This differentiated design based on the intrinsic thermal response threshold of the wall material is the physical basis for achieving precise controlled release. In contrast, Comparative Example 1, lacking chemical bonding, relies solely on weak physical adsorption between the subcapsules and the core thermochromic microcapsules. This physical hybrid structure is easily damaged under external stress, causing subcapsules to detach from the core surface or be unevenly distributed. This unstable structure cannot ensure that the release threshold of the subcapsules corresponds precisely to the color change behavior of the core: the subcapsules release fragrance prematurely or delayed due to displacement or aggregation, and subcapsules with different thresholds are prone to interfering with each other, ultimately causing the fragrance release to lose its gradient and exhibit a mixed or unordered response; in contrast, due to the uniformity of the wall material, all fragrances can only be released simultaneously in large quantities within a narrow range close to the glass transition temperature of the polymer, resulting in mixed fragrances and completely losing the function of sequential release.

[0102] Regarding structural stability, Example 1 demonstrated a subcapsule retention rate exceeding 95%, proving that its multi-chamber structure, constructed through chemical bonding (covalent bonds formed between imidazole rings and chloroalkane groups), possesses excellent mechanical stability and effectively resists centrifugal shear forces. In contrast, Comparative Example 1, relying solely on physical adsorption, exhibited an extremely fragile structure, with most subcapsules detaching under centrifugal force. While Comparative Example 2 also attempted bonding, its uniform wall material structure resulted in uneven distribution or low efficiency of bonding sites. Although its stability was better than physical mixing, it still fell short of the differentiated and precise design of the examples.

[0103] In summary, the experimental data fully demonstrate that the composite microcapsule color-changing pigment provided by this invention, through its multi-compartment structure, differentiated wall materials, and chemical bonding strategy, has successfully achieved precise synergy between color-changing and sequential fragrance release functions under temperature gradients, and possesses excellent structural stability, demonstrating significant technical advantages.

[0104] 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 variations 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 composite microcapsule color-changing pigment, characterized in that, The product comprises the following components by weight: 30-50 parts intelligent microcapsules, 40-60 parts water-based acrylic resin, 2-3 parts film-forming aid, and 0.5-1 part thickener; The smart microcapsule has a multi-compartment structure, including a thermochromic microcapsule as the core, and at least one fragrance-releasing subcapsule that is chemically bonded to the surface of the thermochromic microcapsule. The core material of the thermochromic microcapsule contains a thermochromic complex, the core material of the fragrance-releasing subcapsule contains a fragrance, and the wall materials of different fragrance-releasing subcapsules have different thermal response thresholds to achieve selective fragrance release based on temperature gradient. The fragrance-releasing capsules include low-temperature fragrance-releasing capsules, medium-temperature fragrance-releasing capsules, and high-temperature fragrance-releasing capsules; The wall material of the low-temperature fragrance-releasing capsule is a gelatin-gum arabic composite, its core material is menthol, and the trigger release temperature is 25-34℃. The wall material of the medium-temperature releasing lavender capsule is ethyl cellulose, its core material is lavender oil, and its trigger release temperature is 35-45℃. The wall material of the high-temperature fragrance-releasing capsule is polystyrene-acrylic acid copolymer, its core material is citral, and the trigger release temperature is above 46°C. The intelligent microcapsule is prepared through the following steps: S11. Using the thermochromic composite as the core material, the thermochromic microcapsules are encapsulated with polyacrylate-styrene copolymer resin as the wall material by interfacial polymerization to obtain thermochromic microcapsules. S12. Using fragrance as the core material, the fragrance is coated by one of the following methods: complex coagulation, solvent evaporation, or interfacial polymerization. During the coating process, chemical modification is used to add groups that can react with the functional groups on the surface of the thermochromic microcapsule wall material to obtain fragrance release subcapsule. S13. Mix the thermochromic microcapsules obtained in step S11 with the fragrance release capsules obtained in step S12, and stir and react at 20-60℃ for 4-12 hours to fix the fragrance release capsules on the surface of the thermochromic microcapsules through chemical bonding. After washing and drying, the smart microcapsules are obtained. In step S12, when the fragrance-releasing sub-capsule includes a low-temperature fragrance-releasing sub-capsule, the low-temperature fragrance-releasing sub-capsule is prepared by a complex coagulation method; When the fragrance-releasing capsules include intermediate-temperature fragrance-releasing capsules, the intermediate-temperature fragrance-releasing capsules are prepared by solvent evaporation. When the fragrance-releasing subcapsule includes a high-temperature fragrance-releasing subcapsule, the high-temperature fragrance-releasing subcapsule is prepared by interfacial polymerization. The specific method of the chemical modification is as follows: When using the complex coagulation method, glutaraldehyde is added to the wall material at a rate of 1.5%-2.0% of the wall material's weight, and sodium chloroacetate is added for carboxymethylation modification at a rate of 2%-4% of the wall material's weight. The carboxymethylation reaction conditions are a temperature of 50-60℃, a time of 2-3 hours, and a pH of 10-11. Subsequently, under ice bath conditions at 0-5℃, thionyl chloride is added at a rate of 1.2-1.5 times the molar amount of carboxymethyl groups to carry out a chlorination reaction, ultimately generating chloroalkane side chains on the surface of the wall material. When using the solvent evaporation method, 1-chlorododecane is incorporated into the organic phase of the wall material at an addition amount of 5%-10% of the total weight of the wall material. The emulsification process is carried out under high-speed shear at 8000-12000 rpm for 15-25 minutes. During the solvent evaporation stage, the temperature is controlled at 35-40℃, the stirring speed is 250-350 rpm, and the evaporation time is 4-6 hours. Through blending and emulsification, the chloroalkyl groups are stably exposed on the surface of the subcapsule. When using interfacial polymerization, 4-chloromethylstyrene is added to the oil phase at an amount of 0.5%-5% of the wall material monomer weight. The chloroalkyl groups are embedded into the wall material polymer chain through the polymerization reaction. The polymerization reaction temperature is maintained at 70-80℃, the reaction time is 4-6h, the pH value of the system is adjusted to 8-9, and the stirring speed is controlled at 800-1200 rpm.

2. The composite microcapsule color-changing pigment according to claim 1, characterized in that, The thermochromic complex is composed of an electron donor, an electron acceptor, and a solvent in a mass ratio of (0.08-0.1):(0.4-0.5):(3-6); the electron donor is crystal violet lactone, the electron acceptor is bisphenol A, and the solvent is one or more of tetradecanol and hexadecyl alcohol.

3. The composite microcapsule color-changing pigment according to claim 1, characterized in that, The wall material of the thermochromic microcapsule is a polyacrylate-styrene copolymer resin; the chemical bonding is a covalent bond formed between the imidazole ring on the surface of the thermochromic microcapsule wall material and the reactive groups on the surface of the fragrance release capsule wall material.

4. The composite microcapsule color-changing pigment according to claim 1, characterized in that, The thermochromic microcapsules have a particle size range of 1-20 μm, and the fragrance-releasing subcapsules have a particle size range of 100-800 nm.

5. The composite microcapsule color-changing pigment according to claim 1, characterized in that, In step S11, the reaction conditions for the interfacial polymerization method are as follows: the pH value of the aqueous phase is adjusted to 4-5, the reaction temperature is 55-65℃, the stirring speed is 1000-1200rpm, and the reaction time is 1.5-2 h.

6. The composite microcapsule color-changing pigment according to claim 1, characterized in that, In step S13, the mass ratio of the thermochromic microcapsule to the fragrance-releasing subcapsule is 1:2-6.

7. A method for preparing a composite microcapsule color-changing pigment, used to prepare the composite microcapsule color-changing pigment according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Add the smart microcapsules to the water-based acrylic resin according to the mass ratio, and stir at 200-300 rpm for 15-20 min; S2. Add thickener and film-forming aid in sequence according to the mass parts, stir at 200-300 rpm for 20-30 min, degas under vacuum of 0-5 MPa for 20-30 min, and remove agglomerates through a 400-mesh sieve to obtain the composite microcapsule color-changing pigment.

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