Multi-color-gamut multi-stage controllable thermochromic microcapsule mixture and preparation method thereof

Abstract

The invention relates to the technical field of thermochromic materials, in particular to a mixture of multi-color-gamut and multi-stage controllable thermochromic microcapsules and a preparation method of the mixture, and the mixture of the thermochromic microcapsules comprises at least two thermochromic microcapsules; each thermochromic microcapsule comprises a core material and a wall material, the core material comprises a color developing agent, a leuco agent and a thermal response carrier, the melting points of the thermal response carriers of the thermochromic microcapsules are different, and the unresponsive colors of the thermochromic microcapsules have obvious chromatic aberration. The thermochromic microcapsules with different thermal reaction carrier melting points are synergistically matched, so that a mixed color which is not responded by the thermochromic microcapsules is displayed at low temperature; as the temperature rises, the thermochromic microcapsules change color in sequence from low to high according to the melting point of the thermal reaction carrier, so that clear switching of the color along with the temperature change is realized, and the requirement of multi-section temperature indication is accurately met; and multiple color gamuts can be flexibly allocated, diversified color requirements are met, and the application boundary is greatly widened.

Description

Technical Field

[0001] This invention relates to the technical field of thermochromic materials, specifically to a mixture of multi-color gamut, multi-stage controllable thermochromic microcapsules and its preparation method. Background Technology

[0002] Thermochromic microcapsules, as functional materials exhibiting temperature-responsive color changes, have demonstrated significant application value in numerous technological fields such as smart indicators, anti-counterfeiting labels, and textile decoration. Compared to other thermochromic materials, thermochromic microcapsules effectively protect the core thermosensitive material through their wall material, not only extending the material's lifespan but also preventing adverse chemical reactions between the thermosensitive material and external media, thus ensuring the stability of its color-changing performance and significantly improving safety in use. Furthermore, the micron-sized particle morphology of thermochromic microcapsules gives them excellent dispersibility and processing adaptability in various carrier media such as inks, coatings, and polymer matrices, greatly facilitating industrial production. These advantages make thermochromic microcapsules the most industrially promising and application-flexible thermochromic material system currently available.

[0003] However, existing thermochromic microcapsule technology still has significant technical shortcomings in achieving multi-stage color-changing functionality. The vast majority of thermochromic microcapsule products on the market can only achieve color changes at a single temperature point. This simple two-stage temperature-sensing color change cannot meet the refined requirements of modern industry and the market for multi-level temperature monitoring. A few multi-stage thermochromic microcapsules exhibit chaotic color-changing stages, poor color superposition effects, and narrow color-changing ranges, making it impossible to accurately achieve color gradient changes across multiple temperature ranges and failing to meet the needs of multi-level temperature indication in complex application scenarios.

[0004] Therefore, developing a thermochromic microcapsule with flexible temperature control and multi-stage color-changing function has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] One of the objectives of this invention is to provide a mixture of multi-color gamut, multi-stage controllable thermochromic microcapsules that can achieve multi-color gamut, multi-segment temperature indication, and flexibly adjust the color change range to achieve flexible adjustment of the color change temperature.

[0006] The second objective of this invention is to provide a method for preparing a mixture of multi-color gamut, multi-stage controllable thermochromic microcapsules, which can enhance the stability and cycle life of the prepared microcapsules, extend their service life, and make the microcapsules biocompatible, thus meeting the requirements for use in food and pharmaceuticals.

[0007] One of the solutions adopted to achieve the objective of this invention is: a mixture of multi-color gamut, multi-stage controllable thermochromic microcapsules, comprising at least two types of thermochromic microcapsules; each of the thermochromic microcapsules comprises a core material and a wall material, wherein the core material comprises a color developer, a leuco agent and a thermally responsive carrier, the thermally responsive carriers of each of the thermochromic microcapsules have different melting points, and there is a significant color difference between the non-responsive colors of each of the thermochromic microcapsules.

[0008] Preferably, the core material of at least one thermochromic microcapsule further comprises a pigment. When the ambient temperature changes from low to high, the mixture of microcapsules sequentially exhibits multi-stage color development at different temperature ranges. The multi-stage color development includes at least: a non-responsive color of low-melting-point thermochromic microcapsules, a pigment color and a mixed color of a non-responsive color of high-melting-point thermochromic microcapsules, a pigment color and a mixed color of a non-responsive color of high-melting-point thermochromic microcapsules, and a pigment color.

[0009] Preferably, the core material of the thermochromic microcapsule with the lowest melting point of the thermally responsive carrier contains a pigment.

[0010] Preferably, the pigment is an oil-soluble pigment, including at least one of red, yellow, green, and blue pigments.

[0011] Preferably, the leucoant of each thermochromic microcapsule is independently selected from at least one of crystal violet lactone, 6''-(diethylamino)-1',2-benzofuran, 3-diethylamino-7-chlorofluorane, thermoblack, and thermogreen, and they are different; the thermal response carrier of each thermochromic microcapsule is independently selected from at least one of decaol, dodecanol, tetradecyl alcohol, hexadecyl alcohol, and octadecyl alcohol, and they are different; the color-developing agent of each thermochromic microcapsule is independently selected from at least one of bisphenol A, bisphenol AF, lauryl gallate, and bisphenol S, and they may be the same or different; the wall material of each thermochromic microcapsule includes gum arabic, gelatin, and chitosan, and the mass ratio of the three is 1:0.8-1.2:0.05-0.2.

[0012] Preferably, in the thermally responsive carrier, the melting point of decaol is 6-8℃, the melting point of dodecaol is 24-26℃, the melting point of tetradecaol is 35-40℃, the melting point of hexadecylol is 48-50℃, and the melting point of octadecylol is 57-59℃. The thermochromic microcapsules change color at the melting point of the thermally responsive carrier, and the color change range of the mixture is 5-60℃.

[0013] Preferably, within the temperature range of 20-60℃, the thermal response carrier can be precisely selected to match the required color change temperature.

[0014] Preferably, the leucoant contains crystal violet lactone in a blue system, 6''-(diethylamino)-1',2-benzofuran in a red system, 3-diethylamino-7-chlorofluorane in a yellow system, thermosensitive black in a black system, and thermosensitive green in a green system; when combined with oil-soluble pigments, it can be flexibly formulated to produce multiple color gamuts such as red, yellow, blue, and green.

[0015] Preferably, the multi-color gamut controllable thermochromic microcapsules are of two types, wherein the mass ratio of low-melting-point thermochromic microcapsules to high-melting-point thermochromic microcapsules is 1:0.8-1.2.

[0016] Preferably, the particle size of each thermochromic microcapsule is 20-100 μm.

[0017] The second objective of this invention is achieved by the following method: a method for preparing a mixture of multi-color-gamut, multi-stage controllable thermochromic microcapsules, characterized by comprising the following steps: preparing each thermochromic capsule separately and mixing them according to a certain mass ratio; The preparation of the thermochromic microcapsules includes the following steps: (1) Dissolve and mix the core material raw materials completely to form a core material solution; (2) Prepare a solution of gum arabic of a certain concentration; (3) Add the core material solution from step (1) to the gum arabic solution from step (2) to emulsify and form an oil-water emulsion system; (4) Add gelatin solution to the oil-water emulsion system in step (3), mix evenly, adjust the pH value of the system to 3.6-4.0, stir to carry out the coagulation reaction, and obtain the preliminary microcapsules encapsulating the core material; (5) After cooling the preliminary microcapsules in step (4), add chitosan solution to perform physical cross-linking; (6) Cool the system after physical cross-linking in step (5) to 8-12℃, add cross-linking agent, adjust pH to 5.5-7.5, and carry out chemical cross-linking; (7) The chemically cross-linked system in step (6) is filtered, washed and dried to obtain thermochromic microcapsules; In step (1), the core material raw materials include leuco colorant, color developer, and thermally responsive carrier, or leuco colorant, color developer, pigment and thermally responsive carrier.

[0018] Preferably, a stable structure is achieved by using a dual process of "physical cross-linking of chitosan + chemical cross-linking of glutaraldehyde," which enhances the cycle stability of the microcapsules and extends their service life. By using food-grade gum arabic and gelatin as a base, combined with chitosan to form a composite wall material, and by optimizing the post-processing to control the cross-linking agent residue within a safe threshold, the biocompatibility of the microcapsules is significantly improved, ensuring that they can meet the usage requirements of food / pharmaceutical contact scenarios.

[0019] Preferred, In step (1), the mass percentage of the leucoant is 0.5-2%, the mass percentage of the color developer is 1%-4%, the mass percentage of the thermally responsive carrier is 80%-95%, and the mass percentage of the pigment is 0.5%-2%. In step (2), the concentration of the gum arabic solution is 1.0 wt%-4.0 wt%. In step (3), the mass ratio of the core material to gum arabic is 1-8:1, and the emulsification temperature is 43-47℃; In step (4), the mass fraction of the gelatin solution is 1.0wt%-4.0wt%, and the volume ratio of the gelatin solution to the gum arabic solution is 1:0.8-1.2; In step (5), the concentration of the chitosan solution is 0.5-1.5 wt%, and the amount of chitosan added is 5%-20% of the mass of gum arabic. In step (6), the crosslinking agent includes at least one of glutaraldehyde, tannic acid, genipin, transglutaminase, citric acid, and vanillin.

[0020] Compared with the prior art, the present invention has the following advantages: This invention utilizes the synergistic combination of thermochromic microcapsules with different melting points of the thermal reaction carriers to display a mixed color that the thermochromic microcapsules do not respond to at low temperatures. As the temperature increases, the thermochromic microcapsules change color sequentially according to the melting point of the thermal reaction carriers from low to high, thereby achieving a clear switching of color with temperature changes and accurately meeting the needs of multi-segment temperature indication.

[0021] This invention is based on a thermochromic achromic composite system composed of a leuco and a developer, which can be flexibly formulated to produce multiple color gamuts such as red, yellow, blue, and green, to meet diverse color needs such as food indication and intelligent decoration, and greatly expand the application boundaries. Attached Figure Description

[0022] Figure 1 This is a diagram showing the color change effect of the microcapsule mixture in Example 1 of this experiment; Figure 2 The image shows a scanning electron microscope (SEM) image of the microcapsule mixture in Example 1 of this invention, where the scale bar for a is 100 μm and the scale bar for b is 10 μm. Figure 3 This is a cyclic stability diagram of the microcapsule mixture in Example 1 of the present invention; Figure 4 The image shows a scanning electron microscope image of the microcapsule mixture in Example 1 of the present invention after 200 cycles, where the scale bar of a is 100 μm and the scale bar of b is 10 μm. Figure 5This is a diagram showing the color change effect of the microcapsule mixture in Example 2 of this experiment; Figure 6 The particle size values ​​of microcapsules with different concentrations of gum arabic (GA), gelatin (GE), and different amounts of chitosan (CS) added on the basis of 3wt% gelatin and gum arabic are shown in this invention. Figure 7 This is a potential change diagram during the preparation process of the microcapsules of the present invention; Figure 8 The infrared spectra of each component of microcapsule A in Example 1 of this invention are shown below. Figure 9 Infrared spectra of microcapsules containing different concentrations of gelatin and gum arabic in this invention; Figure 10 Infrared spectra of microcapsules with different concentrations of chitosan added in this invention; Figure 11 The DSC endothermic graphs are for tetradecanol, thermochromic complex, microcapsules containing only tetradecanol, and microcapsules containing thermochromic complex in Example 1 of this invention. Figure 12 The above are DSC endothermic diagrams of the thermochromic complex and microcapsules with different concentrations of gelatin and gum arabic in Example 1 of this invention. Figure 13 The above are DSC endothermic diagrams of the thermochromic complex in Example 1 of this invention and microcapsules with different concentrations of chitosan added on the basis of 3wt% gelatin and gum arabic. Figure 14 The DSC exothermic diagrams are of tetradecyl alcohol, thermochromic complex, microcapsules containing only tetradecyl alcohol, and microcapsules containing thermochromic complex in Example 1 of the present invention. Figure 15 The above are DSC exothermic diagrams of the thermochromic complex and microcapsules with different concentrations of gelatin and gum arabic in Example 1 of this invention. Figure 16 The above are DSC exothermic diagrams of the thermochromic complex in Example 1 of the present invention and microcapsules with different concentrations of chitosan added on the basis of 3wt% gelatin and gum arabic. Figure 17 The encapsulation efficiency of gelatin and gum arabic microcapsules of different concentrations, calculated based on the phase transition enthalpy of the microcapsules and thermochromic complex in the DSC in Example 1 of this invention.

[0023] Figure 18 This refers to the encapsulation efficiency of microcapsules with different concentrations of chitosan added, calculated based on the phase transition enthalpy of the microcapsules and thermochromic complex in the DSC in Example 1 of the present invention, on the basis of 3wt% gelatin and gum arabic. Detailed Implementation

[0024] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0025] Example 1 The preparation of thermochromic microcapsules A includes the following steps: A1. Weigh 0.062g of crystal violet lactone, 0.16g of bisphenol A, and 3.716g of tetradecyl alcohol. Add 0.062g of solvent yellow pigment and place in a constant temperature water bath at 75℃. Stir at 500rpm for 30min until all raw materials are completely dissolved to form a uniform yellow core material solution.

[0026] A2. Weigh 1.5g of gum arabic powder, add 50ml of deionized water, stir at 500rpm for 10min at 45℃, and then let stand for 30min to allow swelling treatment to prepare a 3% gum arabic solution.

[0027] A3. Slowly add the yellow core material solution prepared in step A1 to the gum arabic solution prepared in step A2, and use a high-speed disperser to emulsify it at 15,000 rpm for 15 minutes to form a stable oil-water emulsion.

[0028] A4. Add 1.5g of gelatin to 50ml of deionized water and let it swell at 60℃ for 30min to obtain a gelatin solution. Add 50ml of 3% gelatin solution to the oil-water emulsion obtained in step A3, stir evenly, slowly adjust the pH of the system to 3.8 with 0.1mol / L dilute hydrochloric acid, and maintain stirring at 1000rpm for 1h until pale yellow particles are observed in the system.

[0029] A5. Dissolve 0.075g of chitosan in 0.5ml of 1% acetic acid and add 7ml of deionized water to prepare a chitosan solution. Cool the system formed in step A4 to room temperature at a rate of 2℃ / min, add 7.5ml of 1% chitosan solution, and stir at 500rpm for 30min.

[0030] A6. Cool the system after step A5 to 10℃, dilute 1.6ml of 50% glutaraldehyde solution with 50ml of deionized water, and add it dropwise to the system at a rate of 1 drop / second. After the addition is complete, adjust the pH of the system to 6 with 0.1mol / L sodium hydroxide solution, and stir for 4h at a constant temperature of 10℃ and a speed of 500rpm.

[0031] A7. The system after step A6 is filtered, washed three times with deionized water, and then freeze-dried to obtain thermochromic microcapsules A.

[0032] The preparation of thermochromic microcapsules B includes the following steps: B. Replace the crystal violet lactone in the core material of step A1 with 6''-(diethylamino)-1',2-benzofuran, and replace tetradecyl alcohol with hexadecyl alcohol. Do not add pigments. According to steps A1 to A7, thermochromic microcapsules B can be prepared.

[0033] The preparation of the three-stage color-changing microcapsule mixture includes the following steps: The thermochromic microcapsules A and B prepared in the previous step were mixed at a mass ratio of 1:1 and stirred evenly to obtain a mixture of three-stage thermochromic microcapsules.

[0034] Figure 1 The figure shows the color-changing effect of the microcapsule mixture in this embodiment. As can be seen from the figure, the three-stage color-changing microcapsule mixture is a dark gray mixture of "blue + red + yellow" at 25°C, a green mixture of "red + yellow" at 40°C, and a pure yellow at 60°C. It can achieve three-stage color switching of "room temperature - medium temperature - high temperature" and is suitable for multi-temperature indication scenarios.

[0035] Figure 2 The image shown is a scanning electron microscope image of the microcapsule mixture in this embodiment. As can be seen from the image, the microcapsules are regular spherical and have a stable structure.

[0036] Figure 3 The figure shows the cyclic stability of the microcapsule mixture in this embodiment. According to GB / T 3979-2008 "Methods for Measuring the Color of Objects" and relevant national standards for packaging materials such as GB / T 13022-2003, the visual identification threshold for color difference (ΔEab) needs to be defined in conjunction with the application scenario. When ΔEab ≤ 1.0, the human eye cannot distinguish color differences under normal conditions. When ΔEab is in the range of 1.0-2.0, careful comparison under the same light source and background is required to detect very slight color differences. When ΔEab is in the range of 2.0-3.0, only experienced observers can detect slight differences. In the industrial packaging field, ≤3.0 is often used as the acceptable threshold, considered as having no obvious visual color difference. When ΔEab > 3.0, ordinary observers can intuitively see significant color changes. As can be seen from the figure, the color difference of the microcapsule mixture remains within 3 within 200 cycles. The color difference between the microcapsule mixture after cycling and the microcapsule mixture before cycling is very small, and the color similarity between the two is high, making it difficult to visually perceive the difference.

[0037] Figure 4 The image shown is a scanning electron microscope (SEM) image of the microcapsule mixture after 200 cycles in this embodiment. As can be seen from the image, the microcapsules are regularly spherical in shape, and... Figure 1 The differences are minimal; the microcapsule mixture exhibits a stable structure, good cycle stability, and a long service life.

[0038] Example 2 The only difference from Example 1 is that in this example, the core material of thermochromic microcapsules A is replaced with thermosensitive green, bisphenol AF, and dodecanol; the core material of thermochromic microcapsules B is replaced with 6''-(diethylamino)-1',2-benzofuran, bisphenol A, and tetradecyl alcohol. Thermochromic microcapsules A and B are mixed at a mass ratio of 1:1 and stirred until homogeneous to obtain a three-stage thermochromic microcapsule mixture.

[0039] Figure 5 The figure shown is a color-changing effect diagram of the microcapsule mixture in this embodiment. As can be seen from the figure, the three-stage color-changing microcapsule mixture is a "red + green" mixture that turns purple at 15°C, red at 30°C, and colorless at 50°C. It can achieve three-stage color switching of "room temperature - medium temperature - high temperature" and is suitable for multi-temperature indication scenarios.

[0040] The scanning electron microscope (SEM) images, cyclic stability diagrams, and SEM images after 200 cycles in this embodiment are similar to those in Embodiment 1.

[0041] Example 3 The only difference from Example 1 is that in this example, thermochromic microcapsules A and B are mixed at a mass ratio of 1:1.2 and stirred evenly to obtain a mixture of three-stage thermochromic microcapsules.

[0042] The three-stage color-changing microcapsule mixture is a dark gray mixture of "blue + red + yellow" at 25°C, a green mixture of "red + yellow" at 40°C, and a pure yellow at 60°C. It can achieve three-stage color switching of "room temperature - medium temperature - high temperature" and is suitable for multi-temperature indication scenarios.

[0043] The color-changing effect diagram, scanning electron microscope image, cycle stability diagram, and scanning electron microscope image after 200 cycles in this embodiment are similar to those in Embodiment 1.

[0044] Example 4 The only difference from Example 1 is that in this example, the masses of gum arabic, gelatin, and chitosan used in thermochromic microcapsules A and B are 0.5g, 0.5g, and 0.075g, respectively. Thermochromic microcapsules A and B are mixed at a mass ratio of 1:1 and stirred until homogeneous to obtain a three-stage color-changing microcapsule mixture.

[0045] The three-stage color-changing microcapsule mixture is a dark gray mixture of blue, red, and yellow at 25°C, a green mixture of red and yellow at 40°C, and a pure yellow at 60°C. It can switch between three stages of color: room temperature, medium temperature, and high temperature, making it suitable for multi-temperature indication scenarios. The color-changing effect diagram, scanning electron microscope image, cycle stability diagram, and scanning electron microscope image after 200 cycles in this embodiment are similar to those in Embodiment 1.

[0046] Example 5 The only difference from Example 1 is that in this example, the masses of gum arabic, gelatin, and chitosan used in thermochromic microcapsules A and B are 1.5g, 1.5g, and 0.15g, respectively. Thermochromic microcapsules A and B are mixed at a mass ratio of 1:1 and stirred until homogeneous to obtain a three-stage color-changing microcapsule mixture.

[0047] The three-stage color-changing microcapsule mixture is a dark gray mixture of blue, red, and yellow at 25°C, a green mixture of red and yellow at 40°C, and a pure yellow at 60°C. It can switch between three stages of color: room temperature, medium temperature, and high temperature, making it suitable for multi-temperature indication scenarios. The color-changing effect diagram, scanning electron microscope image, cycle stability diagram, and scanning electron microscope image after 200 cycles in this embodiment are similar to those in Embodiment 1.

[0048] Figure 6 The figure shows the particle size values ​​of microcapsules with different concentrations of gum arabic (GA), gelatin (GE), and different amounts of chitosan (CS) added to a 3wt% gelatin or gum arabic base. As can be seen from the figure, the particle size of the microcapsules increases with the increase of the concentration of gelatin and gum arabic. However, the particle size decreases slightly after the addition of chitosan due to its cross-linking and tightening effect. When the amount of chitosan is further increased to 15%, the particle size increases accordingly, reaching close to 80 μm when the amount of chitosan is 20%. This indicates that the microcapsules are most stable when the amount of chitosan added is 5%-10% due to the cross-linking and tightening effect.

[0049] Figure 7 The diagram shows the potential changes during the microcapsule preparation process. It can be seen that the microcapsule preparation process relies on the attraction between positive and negative charges. Gum arabic is negatively charged, while gelatin is positively charged at around pH 3.8, and the positive and negative charges attract each other. Subsequent addition of different concentrations of chitosan showed that the charges were essentially neutralized at a concentration of 5%-10%, demonstrating the cross-linking effect of chitosan. At this concentration, the system was most stable, while the stability was slightly lower at 15%-20% chitosan.

[0050] Figure 8 The image shows the infrared spectra of each component of microcapsule A in Example 1; Figure 9 The image shows the infrared spectra of microcapsules containing gelatin and gum arabic at different concentrations. Figure 10 The image shows the infrared spectra of microcapsules with different concentrations of chitosan added to a 3wt% gelatin and gum arabic base; combined with... Figure 8-10 It can be seen that gelatin, gum arabic, and chitosan do not undergo a chemical reaction but rather physical cross-linking. A chemical cross-linking reaction occurs after the addition of a cross-linking agent.

[0051] Figure 11 The figure shows differential scanning calorimetry (DSC) endothermic graphs of tetradecyl alcohol, thermochromic complex, microcapsules containing only tetradecyl alcohol, and microcapsules containing thermochromic complex in Example 1. Figure 12 The figure shows the DSC endothermic diagrams of the thermochromic complex and microcapsules with different concentrations of gelatin and gum arabic in Example 1. Figure 13 The figure shows the DSC endothermic diagrams of the thermochromic complex in Example 1 and microcapsules with different concentrations of chitosan added on the basis of 3wt% gelatin and gum arabic. It can be seen that in the microcapsules, tetradecanol in the core material has a decisive effect on the color change temperature, and under the wall material composed of gelatin, gum arabic, chitosan and other materials, the color change temperature will not be significantly changed. The thermal response carrier can be flexibly adjusted to make the microcapsules have different color change temperatures to meet the requirements of various temperature conditions.

[0052] Figure 14 The image shows DSC exothermic diagrams of tetradecyl alcohol, thermochromic complex, microcapsules containing only tetradecyl alcohol, and microcapsules containing thermochromic complex in Example 1. Figure 15 The image shows the DSC exothermic diagrams of the thermochromic complex and microcapsules with different concentrations of gelatin and gum arabic in Example 1. Figure 16 The figure shows the DSC exothermic diagrams of the thermochromic complex in Example 1 and microcapsules with different concentrations of chitosan added to a 3wt% gelatin and gum arabic base; combined with Figure 11-13 It can be seen that the microcapsules release heat when cooling down and absorb heat when heating up. The tetradecanol in the core material has a decisive effect on the color change temperature, and the color change of the microcapsules during cooling and heating is reversible.

[0053] Figure 17 The figure shows the encapsulation efficiency of gelatin and gum arabic microcapsules of different concentrations, calculated based on the phase transition enthalpy of the microcapsules and thermochromic complex in the DSC in Example 1. Figure 18 Ecs represents the encapsulation efficiency of microcapsules with different concentrations of chitosan added on a base of 3wt% gelatin and gum arabic, calculated in Example 1 based on the phase change enthalpy of the microcapsules and thermochromic complex in the DSC. The encapsulation efficiency, i.e. the proportion of core material effectively encapsulated, is calculated by multiplying the ratio of the measured phase change enthalpy of the microcapsule to the theoretical phase change enthalpy of the pure core material (TCM) by 100%. Een is the encapsulation efficiency calculated from the melting enthalpy during the heating process of the microcapsule, and Ecs is the encapsulation efficiency calculated from the crystallization enthalpy during the cooling process of the microcapsule.

[0054] It can be seen that as the concentration of gelatin and gum arabic increases, the encapsulation efficiency gradually decreases. Excessive wall material concentration leads to a sharp increase in the viscosity of the gelatin aqueous phase and an imbalance in the charge between gelatin and gum arabic, resulting in poor dispersion of the core material, defects in the shell, and dilution of the core, ultimately reducing the proportion of effectively encapsulated cores. Adding chitosan increases the encapsulation efficiency. Chitosan can regulate the charge balance of the gelatin-gum arabic system, enhance the density and stability of the shell, reduce uneven dispersion and leakage of the core material, and thus improve the encapsulation efficiency. However, excessive addition can lead to charge imbalance and a decrease in encapsulation efficiency. With gelatin and gum arabic concentrations of 1.0wt%-4.0wt% and chitosan additions of 5%-20%, the encapsulation efficiency of the microcapsules is high. The microcapsule core material is effectively encapsulated within the wall material, exhibiting good biocompatibility and ensuring compliance with the requirements for use in food / pharmaceutical contact scenarios.

[0055] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A mixture of multi-gamut, multi-stage controllable thermochromic microcapsules, characterized in that, Includes at least two types of thermochromic microcapsules; Each of the thermochromic microcapsules includes a core material and a wall material. The core material includes a color developer, a leuco agent, and a thermally responsive carrier. The thermally responsive carriers of each thermochromic microcapsule have different melting points, and there is a significant color difference between the non-responsive colors of each thermochromic microcapsule.

2. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 1, characterized in that, At least one of the thermochromic microcapsules also contains a pigment in its core material. When the ambient temperature changes from low to high, the mixture of microcapsules sequentially exhibits multi-stage color development at different temperature ranges. The multi-stage color development includes at least: a non-responsive color of low-melting-point thermochromic microcapsules, a pigment color and a mixed color of a non-responsive color of high-melting-point thermochromic microcapsules, a pigment color and a mixed color of a non-responsive color of high-melting-point thermochromic microcapsules, and a pigment color.

3. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 2, characterized in that, The core material of thermochromic microcapsules, which have the lowest melting point among thermally responsive carriers, contains pigments.

4. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 2, characterized in that, The pigment is an oil-soluble pigment, including at least one of red, yellow, green, and blue pigments.

5. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 1, characterized in that, The leucoant of each thermochromic microcapsule is independently selected from at least one of crystal violet lactone, 6''-(diethylamino)-1',2-benzofuran, 3-diethylamino-7-chlorofluorane, thermoblack, and thermogreen, and they are different; the thermal response carrier of each thermochromic microcapsule is independently selected from at least one of decaol, dodecanol, tetradecyl alcohol, hexadecyl alcohol, and octadecyl alcohol, and they are different; the color-developing agent of each thermochromic microcapsule is independently selected from at least one of bisphenol A, bisphenol AF, lauryl gallate, and bisphenol S, and they may be the same or different; the wall material of each thermochromic microcapsule includes gum arabic, gelatin, and chitosan, with a mass ratio of 1:0.8-1.2:0.05-0.

2.

6. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 1, characterized in that, The color change range of the mixture is 5-60℃.

7. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 1, characterized in that, The multi-gamut controllable thermochromic microcapsules are of two types, wherein the mass ratio of low-melting-point thermochromic microcapsules to high-melting-point thermochromic microcapsules is 1:0.8-1.

2.

8. The mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 1, characterized in that, The particle size of each thermochromic microcapsule is 20-100 μm.

9. A method for preparing a mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to any one of claims 1-8, characterized in that, Includes the following steps: Each thermochromic capsule was prepared separately and then mixed in a certain mass ratio to obtain the final product. The preparation of the thermochromic microcapsules includes the following steps: (1) Dissolve and mix the core material raw materials completely to form a core material solution; (2) Prepare a solution of gum arabic of a certain concentration; (3) Add the core material solution from step (1) to the gum arabic solution from step (2) to emulsify and form an oil-water emulsion system; (4) Add gelatin solution to the oil-water emulsion system in step (3), mix evenly, adjust the pH value of the system to 3.6-4.0, stir to carry out the coagulation reaction, and obtain the preliminary microcapsules encapsulating the core material; (5) After cooling the preliminary microcapsules in step (4), add chitosan solution to perform physical cross-linking; (6) Cool the system after physical cross-linking in step (5) to 8-12℃, add cross-linking agent, adjust pH to 5.5-7.5, and carry out chemical cross-linking; (7) The chemically cross-linked system in step (6) is filtered, washed and dried to obtain thermochromic microcapsules; In step (1), the core material raw materials include leuco colorant, color developer, and thermally responsive carrier, or leuco colorant, color developer, pigment and thermally responsive carrier.

10. The method for preparing a mixture of multi-gamut, multi-stage controllable thermochromic microcapsules according to claim 9, characterized in that, In step (1), the mass percentage of the leucoant is 0.5-2%, the mass percentage of the color developer is 1%-4%, the mass percentage of the thermally responsive carrier is 80%-95%, and the mass percentage of the pigment is 0.5%-2%. In step (2), the concentration of the gum arabic solution is 1.0 wt%-4.0 wt%. In step (3), the mass ratio of the core material to gum arabic is 1-8:1, and the emulsification temperature is 43-47℃; In step (4), the mass fraction of the gelatin solution is 1.0wt%-4.0wt%, and the volume ratio of the gelatin solution to the gum arabic solution is 1:0.8-1.2; In step (5), the concentration of the chitosan solution is 0.5-1.5 wt%, and the amount of chitosan added is 5%-20% of the mass of gum arabic. In step (6), the crosslinking agent includes at least one of glutaraldehyde, tannic acid, genipin, transglutaminase, citric acid, and vanillin.

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