Reversible temperature-induced multistage color-changing microcapsule and preparation method thereof

Abstract

The invention relates to a reversible temperature-induced multistage color-changing microcapsule which comprises a core material and a shell material wrapping the core material, the core material is a reversible thermochromic core material; the shell material is a colored layer formed by uniformly dispersing a water-soluble dye in a shell material matrix; the microcapsule is obtained by adding a water-soluble dye solution into a core material solution for emulsification and then adding the prepolymer of the shell material matrix; the core material solution comprises a non-ionic emulsifier, the water-soluble dye solution comprises an anionic emulsifier, and the water-soluble dye is an anionic dye or a non-ionic dyestuff. Through the microcapsule structure design, the reversible temperature-dependent multi-stage color-changing microcapsule with the average particle size being smaller than 1 micron is obtained, and the reversible temperature-dependent multi-stage color-changing microcapsule has the advantages that the reversible temperature-dependent multi-stage color-changing microcapsule is prepared; and meanwhile, a good color development effect of the reversible temperature-induced multi-stage color-changing microcapsule is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of thermochromic technology, and in particular to a reversible thermochromic multi-stage color-changing microcapsule and a preparation method thereof. Background Art

[0002] Thermochromic materials are a special type of functional materials whose color changes with temperature. They have the ability to monitor temperature changes in real time, and therefore have important application potential in many fields. There are many types of thermochromic materials, which are divided into organic, inorganic and liquid crystal types according to the performance of the materials. Among them, inorganic thermochromic materials have a high color change temperature, complex preparation process and toxicity, high cost and low sensitivity, which limits the application of inorganic thermochromic materials. Liquid crystal thermochromic materials have high color change sensitivity, but poor stability, especially sensitive to chemical substances, and are easily affected by the external environment, causing degradation or failure, resulting in unstable color change effect, so they are limited in application. There are many types of organic thermochromic materials, such as triarylmethane, fluorane, spiropyran, triarylmethanephthalide, etc. This material has the advantages of a wide color change temperature range, high color change sensitivity and low cost. It is the hot spot and focus of current thermochromic material research and has been widely used in temperature display, medical and health, advertising, printing ink and other fields. Organic thermochromic materials can usually be divided into reversible and irreversible materials according to whether the color returns to its original color when the temperature is lowered. In addition, according to the color change mechanism, it can also be subdivided into molecular ring opening and closing, pH value change, electron gain and loss transfer, etc. Among them, the thermochromic material of the electron gain and loss transfer mechanism type is usually composed of three substances: a leucochromic agent (electron donor), a developer (electron acceptor) and a solvent. By absorbing or radiating a certain wavelength of light during the electron transfer process, the macroscopic color change is achieved. In this process, the leucochromic agent determines the color of the substance, the developer determines the depth of the color, and the solvent determines the color change temperature of the material. Usually, the redox potential of the thermochromic material and the developer is close. Temperature changes will cause different degrees of change in the redox potential of the two, resulting in changes in the molecular structure. These changes cause the gain and loss of electrons, resulting in a reversible thermochromic phenomenon. Since thermochromic materials are exposed to the external environment, they are easily affected by the surrounding environmental conditions, causing degradation or denaturation of the active ingredients and thus losing the ability to respond to heat. Therefore, microencapsulation technology is needed to encapsulate the color-changing materials to isolate them from the external environment in order to achieve the purpose of protecting the color-changing materials.

[0003] The existing technical solutions are limited to achieving the color change from colored to colored by adding oil-soluble dyes to the color-changing core material, and the oil-soluble dyes used occupy the volume of the core material, so that the space occupied by the color-changing component is reduced, and the color development effect is not obvious. Secondly, since the shell will weaken the color development effect of the core material to a certain extent, if a better color development effect is required, more dyes and color-changing core materials need to be added, but this will inevitably make the size of the microcapsules larger. Patent CN115888572A uses water-soluble dyes, and the prepared microcapsules include three layers: the inner core (color-changing core material), the oil droplet attachment layer (acidic water-soluble dye) and the melamine resin shell layer. The added water-soluble dye makes the microcapsules show the dye color at high temperature, thereby realizing the change from colored to colored, and the average particle size of the microcapsules is 2-5μm. However, since the added dye is attached to the periphery of the oil droplet alone, and the shell will block the color of the core material, the color development effect is poor. At the same time, since the added dye is coated in the core, it will occupy the volume of the core material, causing the size of the microcapsules to become larger. However, the existing thermochromic microcapsules have the problem of too large particle size, and are not suitable for the melt spinning of ultrafine (microcapsule particle size less than 1 μm) and intelligent color-changing ES fibers.

[0004] Therefore, how to simultaneously obtain thermochromic materials with good color rendering effect and small particle size, especially particle size less than 1 μm, is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a reversible thermochromic multi-stage color-changing microcapsule and a preparation method thereof. Through the microcapsule structure design of the present invention, a reversible thermochromic multi-stage color-changing microcapsule with an average particle size of less than 1 μm is obtained, while ensuring the good color rendering effect of the reversible thermochromic multi-stage color-changing microcapsule.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] A reversible thermochromic multi-stage color-changing microcapsule comprises a core material and a shell material wrapping the core material; the core material is a reversible thermochromic core material; the shell material is a colored layer in which a water-soluble dye is uniformly dispersed in a shell material matrix; the microcapsule is obtained by adding a water-soluble dye solution to a core material solution for emulsification and then adding a prepolymer of the shell material matrix; the core material solution comprises a nonionic emulsifier, the water-soluble dye solution comprises an anionic emulsifier, and the water-soluble dye is an anionic dye or a nonionic dye.

[0008] Furthermore, the average particle size of the microcapsules is less than 1 μm.

[0009] Furthermore, the average particle size of the microcapsules is 0.2 μm-0.7 μm.

[0010] Furthermore, the core material is a ternary color-changing core material.

[0011] Furthermore, the leucochromic agent in the ternary color-changing core material is preferably crystal violet lactone, thermosensitive red, thermosensitive black or a combination thereof.

[0012] Furthermore, the color developer in the ternary color-changing core material is preferably bisphenol A, and the solvent is preferably tetradecanol.

[0013] Furthermore, the mass ratio of the leucochrome agent, the developer and the solvent in the ternary color-changing core material is 1-5:2-10:50-80, preferably 1:3:60.

[0014] Furthermore, the shell material matrix is ​​melamine resin, and the shell material displays the color of the water-soluble dye.

[0015] Specifically, the mass of the core material is 1.3-1.5 times, preferably 1.4 times, that of the shell material matrix.

[0016] Furthermore, the nonionic emulsifier is Span 80.

[0017] Furthermore, the anionic emulsifier is styrene maleic anhydride copolymer.

[0018] Furthermore, the mass ratio of the nonionic emulsifier to the anionic emulsifier is 2-4:6-8, preferably 3:7. The total mass of the nonionic emulsifier and the anionic emulsifier accounts for 5-20% of the core material.

[0019] Furthermore, the water-soluble dye is direct red, alkaline yellow or a combination thereof.

[0020] Specifically, the mass of the water-soluble dye is 0.6-5% of the core material.

[0021] The present invention also provides a method for preparing reversible temperature-induced multi-stage color-changing microcapsules, comprising the following steps:

[0022] 1) adding the water-soluble dye solution to the core material solution for emulsification;

[0023] 2) adding the prepolymer of the shell material matrix, mixing evenly, and adjusting the pH; and obtaining the reversible temperature-induced multi-stage color-changing microcapsules after stirring, centrifuging, washing, and drying.

[0024] Furthermore, in the step 1), the core material solution is obtained by fully mixing a leuco agent, a developer and a solvent, adding the nonionic emulsifier, and stirring evenly; the water-soluble dye solution is formed by mixing and dissolving the anionic emulsifier and the water-soluble dye in water.

[0025] Furthermore, in the step 1), high-speed shear emulsification is adopted, and the rotation speed is 8000-22000 r / min, preferably 8000 r / min.

[0026] Furthermore, the prepolymer is prepared by conventional methods in the art, such as when the shell material matrix is ​​melamine resin, 2-6 parts of melamine, 3-9 parts of formaldehyde solution and 20-60 parts of water are added to a three-necked flask, the pH is adjusted to 8-9, and stirred for 30-50 minutes to obtain.

[0027] Furthermore, in the step 2), the pH is adjusted to 5-6.

[0028] Furthermore, in the step 2), washing is performed with water.

[0029] Beneficial effects:

[0030] 1. The present invention obtains reversible temperature-induced multi-stage color-changing microcapsules with an average particle size of less than 1 μm, especially 0.2 μm-0.7 μm, through microcapsule structure design, while ensuring the good color development effect of the reversible temperature-induced multi-stage color-changing microcapsules, overcoming the technical problems in the prior art such as the dye occupying the core material volume resulting in poor color change effect and large microcapsule size, and can be applied to the melt spinning molding of ultrafine (microcapsule particle size less than 1 μm) and intelligent color-changing ES fibers, and has excellent application prospects.

[0031] 2. The present invention adds a water-soluble dye solution to the core material solution for emulsification, and combines specific nonionic emulsifiers and anionic emulsifiers so that when the water-in-water emulsion is emulsified, the water-soluble dye is evenly dispersed around the oil droplets. The anionic emulsifier used in the present invention has a hydrophobic end facing the surface of the oil droplets and a hydrophilic end facing the water phase with a negative charge. The dye used in the present invention is negatively charged and nonionic, and will not gather around the oil droplets alone, but will be evenly dispersed around the oil droplets with the subsequently added shell material prepolymer. The actual microcapsule is a two-layer structure, wherein the core material of the microcapsule plays a thermochromic function, and the shell material of the microcapsule is the color of the dye. On the one hand, the shell material has the color of the dye. In addition to protecting the core material, it also has the function of coloring, so that the microcapsule shows the color of the dye at high temperature (the core material is colorless at high temperature), and shows the mixed color of the dye and the color-developing core material at low temperature, realizing the change of the microcapsule from colored to colored, solving the problem of single color change of the microcapsule; on the other hand, the water-soluble dye does not occupy the space of the core of the microcapsule, so that the prepared microcapsule is smaller in size. In addition, the shell layer of the microcapsule prepared by this method is the color of the dye, which avoids the weakening effect of the melamine resin shell layer on the color of the core material and shows a better coloring effect.

[0032] 3. The present invention not only obtains microcapsules with a smaller average particle size, but also obtains the technical effects of rich color changes and high color difference, with the color difference value reaching 22.06-57.31. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic comparison diagram of the color development of microcapsules added with oil-soluble dyes (a1) in the prior art and added with water-soluble dyes (a2) in the present invention;

[0034] Figure 2 The DSC temperature increase (a1) and temperature decrease (a2) measurement results of the temperature-induced multi-stage color-changing microcapsules in Example 1 of the present invention are shown;

[0035] Figure 3 The SEM image (a1) and particle size distribution diagram (a2) of the temperature-induced multi-stage color-changing microcapsules in Example 1 of the present invention;

[0036] Figure 4 The actual pictures of the temperature-induced multi-stage color-changing microcapsules in Example 1 of the present invention at different temperatures (-5°C (a1), 30°C (a2), 50°C (a3));

[0037] Figure 5 The SEM image (a1) and particle size distribution diagram (a2) of the temperature-induced multi-stage color-changing microcapsules in Example 2 of the present invention;

[0038] Figure 6 The actual pictures of the temperature-induced multi-stage color-changing microcapsules in Example 2 of the present invention at different temperatures (-5°C (a1), 5°C (a2), 15°C (a3), 40°C (a4), 50°C (a5));

[0039] Figure 7 The SEM image (a1) and particle size distribution diagram (a2) of the temperature-induced multi-stage color-changing microcapsules in Example 3 of the present invention;

[0040] Figure 8 The actual pictures of the temperature-induced multi-stage color-changing microcapsules in Example 3 of the present invention at different temperatures (-5°C (a1), 5°C (a2), 15°C (a3), 30°C (a4), 40°C (a5), 50°C (a6));

[0041] Fig. 9 The SEM image (a1) and particle size distribution diagram (a2) of the temperature-induced multi-stage color-changing microcapsules in Example 4 of the present invention;

[0042] Fig.10 The actual pictures of the temperature-induced multi-stage color-changing microcapsules in Example 4 of the present invention at different temperatures (-5°C (a1), 30°C (a2), 50°C (a3));

[0043] Fig.11 The SEM image (a1) and particle size distribution diagram (a2) of the temperature-induced multi-stage color-changing microcapsules in Example 5 of the present invention;

[0044] Fig.12 The actual pictures of the temperature-induced multi-stage color-changing microcapsules in Example 5 of the present invention at different temperatures (-5°C (a1), 5°C (a2), 15°C (a3), 30°C (a4), 40°C (a5), 50°C (a6)); DETAILED DESCRIPTION

[0045] The technical solution provided by the present invention is more clearly described below in conjunction with the embodiments and drawings, but the scope of protection claimed by the present invention is not limited to the following embodiments.

[0046] Example 1

[0047] (1) Preparation of ternary color-changing core material

[0048] Weigh 0.0775g of crystal violet lactone, 0.235g of bisphenol A and 4.68g of tetradecanol, first put the tetradecanol into a beaker, and heat it in a 70℃ water bath to melt; after it is completely melted, add crystal violet lactone and bisphenol A respectively; then heat the water bath to 90℃, and stir continuously while heating to accelerate melting and fully mix the three components; keep warm and stir for 1h, then add 0.075g of Span 80 to the core material, and stir evenly to obtain a ternary color-changing compound.

[0049] (2) Preparation of SMA / dye / aqueous solution

[0050] 0.875 g of 20% by mass styrene maleic anhydride copolymer (SMA) and 0.03 g of direct red (water-soluble) were added to 150 g of deionized water and dissolved at 60°C.

[0051] (3) Preparation of prepolymer

[0052] 2.2 g of melamine, 3.68 g of 37% formaldehyde solution and 22.2 g of deionized water were added into a three-necked flask, the pH was adjusted to 9 with aqueous ammonia, and the mixture was stirred in a water bath at 80° C. for 40 minutes to obtain a prepolymer.

[0053] (4) Add the above SMA / dye / water solution to the ternary color-changing compound, emulsify for 5 minutes at 8000r / min using a high-speed shearing machine to form a white emulsion, and stir at 70°C. Add the above-prepared prepolymer dropwise to the above white emulsion using a syringe pump, stir for 40 minutes, and after the two are evenly mixed, adjust the pH to 6 with 10% citric acid. Stir for 3 hours, centrifuge, wash with deionized water, and dry at 60°C to obtain a reversible multi-stage thermochromic microcapsule powder that changes from pink purple to red. The average particle size of the microcapsules is 0.399μm, and the color difference value reaches 35.79.

[0054] Example 2

[0055] The only difference from Example 1 is that alkaline tender yellow (water-soluble) is used to replace direct red (water-soluble) in Example 1. A blue-green to yellow-green reversible multi-stage thermochromic microcapsule powder is obtained. The average particle size of the microcapsules is 0.6 μm, and the color difference value reaches 44.4.

[0056] Example 3

[0057] The only difference from Example 2 is that the crystal violet lactone in Example 2 is replaced by thermosensitive red. An orange-yellow-to-yellow reversible multi-stage thermochromic microcapsule powder is obtained. The average particle size of the microcapsules is 0.5 μm, and the color difference value reaches 38.54.

[0058] Example 4

[0059] The only difference from Example 1 is that the crystal violet lactone in Example 1 is replaced by thermosensitive black. The brown-red to red reversible multi-stage thermochromic microcapsule powder has an average particle size of 0.34 μm and a color difference value of 22.06.

[0060] Example 5

[0061] The only difference from Example 2 is that the crystal violet lactone in Example 2 is replaced by thermosensitive black. A reversible multi-stage thermochromic microcapsule powder that changes from black to yellow is obtained. The average particle size of the microcapsules is 0.29 μm, and the color difference value reaches 57.31.

[0062] Test results:

[0063] like Figure 1 As shown, by adding different dyes during the preparation of microcapsules, colored to colored thermochromic microcapsules can be obtained. After adding oil-soluble dyes, the microcapsules show a mixed color of the color-changing core material and the dye at low temperatures, but the space of the color-changing core material is occupied by the oil-soluble dye, resulting in an increase in the volume of the microcapsules, and the shell material will weaken the color of the core material, making the color development effect relatively poor. The added water-soluble dye does not occupy the volume of the microcapsule core, making the microcapsule size smaller, and the dye can color the shell material. The microcapsules show a mixed color of the shell and the core material at low temperatures. Therefore, the shell layer has the dual functions of color development and protection of the core material.

[0064] Figure 2 This is the DSC measurement result diagram of the temperature-induced multi-stage color-changing microcapsules in Example 1. The melting enthalpies of tetradecanol and the temperature-induced multi-stage color-changing microcapsules are 220.1 J / g and 102.6 J / g, respectively, and the crystallization enthalpies are 219.8 J / g and 94.62 J / g, respectively, indicating that the microcapsules have a high energy storage value.

[0065] Figure 3 The SEM image and particle size distribution diagram of the thermochromic multi-stage color-changing microcapsules in Example 1. The prepared microcapsules have a complete spherical structure, the microcapsules are well dispersed, and the average particle size of the microcapsules is about 0.399 μm.

[0066] Figure 4 The actual pictures of the pink-purple-to-red microcapsules in Example 1 at different temperatures show that the microcapsules have a significant color change effect with temperature.

[0067] Figure 5 The SEM image and particle size distribution diagram of the thermochromic multi-stage color-changing microcapsules of Example 2. The prepared microcapsules have a complete spherical structure, the microcapsules are well dispersed, and the average particle size of the microcapsules is about 0.6 μm.

[0068] Figure 6 The actual pictures of the blue-green to yellow-green microcapsules in Example 2 at different temperatures show that the microcapsules have a significant color change effect with temperature.

[0069] Figure 7 The SEM image and particle size distribution diagram of the temperature-induced multi-stage color-changing microcapsules in Example 3. The prepared microcapsules have a complete spherical structure, the microcapsules are well dispersed, and the average particle size of the microcapsules is about 0.5 μm.

[0070] Figure 8 The actual pictures of the orange-yellow to yellow microcapsules in Example 3 at different temperatures show that the microcapsules have a significant color change effect with temperature.

[0071] Fig. 9 The SEM image and particle size distribution diagram of the temperature-induced multi-stage color-changing microcapsules in Example 4. The prepared microcapsules have a complete spherical structure, the microcapsules are well dispersed, and the average particle size of the microcapsules is about 0.34 μm.

[0072] Fig.10 The actual pictures of the brown-red to red microcapsules in Example 4 at different temperatures show that the microcapsules have a significant color change effect with temperature.

[0073] Fig.11 The SEM image and particle size distribution diagram of the thermochromic multi-stage color-changing microcapsules of Example 5. The prepared microcapsules have a complete spherical structure, the microcapsules are well dispersed, and the average particle size of the microcapsules is about 0.29 μm.

[0074] Fig.12 The actual pictures of the black-to-yellow microcapsules in Example 5 at different temperatures show that the microcapsules have a significant color change effect with temperature.

[0075] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A reversible thermochromic multi-stage color-changing microcapsule, characterized in that: It comprises a core material and a shell material wrapping the core material; the core material is a reversible thermochromic core material; the shell material is a colored layer in which a water-soluble dye is uniformly dispersed in a shell material matrix; the microcapsule is obtained by adding a water-soluble dye solution to a core material solution for emulsification and then adding a prepolymer of the shell material matrix; the core material solution comprises a nonionic emulsifier, the water-soluble dye solution comprises an anionic emulsifier, and the water-soluble dye is an anionic dye or a nonionic dye.

2. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The average particle size of the microcapsules is less than 1 μm.

3. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The core material is a ternary color-changing core material.

4. The reversible thermochromic multi-stage color-changing microcapsule according to claim 3, characterized in that: The leucochromic agent in the ternary color-changing core material is crystal violet lactone, thermosensitive red, thermosensitive black or a combination thereof.

5. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The shell material matrix is ​​melamine resin, and the shell material displays the color of the water-soluble dye.

6. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The nonionic emulsifier is Span 80.

7. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The anionic emulsifier is styrene maleic anhydride copolymer.

8. The reversible thermochromic multi-stage color-changing microcapsule according to claim 1, characterized in that: The water-soluble dye is direct red, alkaline yellow or a combination thereof.

9. The method for preparing the reversible thermochromic multi-stage color-changing microcapsules according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1) adding the water-soluble dye solution to the core material solution for emulsification; 2) adding the prepolymer of the shell material matrix, mixing evenly, and adjusting the pH; and obtaining the reversible temperature-induced multi-stage color-changing microcapsules after stirring, centrifuging, washing, and drying.

10. The preparation method according to claim 9, characterized in that: In the step 1), the core material solution is obtained by fully mixing a leuco agent, a developer and a solvent, adding the nonionic emulsifier, and stirring evenly; the water-soluble dye solution is formed by mixing and dissolving the anionic emulsifier and the water-soluble dye in water.

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