A kind of cationic modified melamine resin thermochromic microcapsule and preparation method thereof
By using cationically modified melamine resin prepolymer and anionic emulsifier in the preparation of color-changing microcapsules, the double electron layer is formed, which solves the problems of high empty packing rate and low shell density, and significantly improves the microstructure The wear resistance and particle size uniformity of the capsule.
Patent Information
- Application Number
- CN202310578515.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-05-22
- Publication Date
- 2024-12-06
- Estimated Expiration
- 2043-05-22
AI Technical Summary
The existing color-changing microcapsules are prone to empty packs during the preparation process and the shell material is low in density.
Using cationically modified melamine resin prepolymers, a double-electron layer is formed through electrostatic action with anionic cationic emulsifier, which enhances the density of the shell material, and reduces free melamine through specific process steps such as adjusting pH and heating conditions. The resin prepolymer forms stable microcapsules.
Color-distorted microcapsules with low empty packing rate and high shell density are achieved, and the wear resistance and particle size uniformity of the microcapsules are improved.
Smart Images
Figure CN116554855B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of color-changing materials, and in particular to a cationic modified melamine resin thermochromic microcapsule and a preparation method thereof. Background Art
[0002] Thermochromic materials refer to materials whose colors change when they sense changes in the temperature of the external environment. The color change is accompanied by changes in their physical or chemical structure. The change in the material structure causes a change in its spectral properties, thus showing a change in macroscopic color. As a type of intelligent material with thermal memory function, thermochromic materials have been widely used in various fields such as anti-counterfeiting, temperature indication, textiles and daily life.
[0003] Compared with single compounds with thermochromic properties, organic thermochromic materials are easy to obtain and inexpensive. There are many types of organic substances that can be used as cryptanthogens, color developers and phase change materials, and they have received widespread attention. Organic thermochromic materials have reversible color change properties from colored to colorless, but they are easily affected by the external environment. Therefore, researchers use the protective effect of microcapsules to encapsulate organic thermochromic materials and apply them to the substrate after microencapsulation, which not only expands the application range of thermochromic materials, but also enhances the convenience of using thermochromic materials. When organic thermochromic materials are made into microcapsules, the commonly used shell material is melamine resin. For example, patent CN102477290A discloses a thermochromic material microcapsule and a preparation method thereof. The core material of the microcapsule is a thermochromic compound composed of a coloring agent, a color developer and a solvent, and the wall material is a melamine resin prepolymer. During the polymerization process of melamine resin prepolymer, there are still a lot of free prepolymers in the water phase, and the entire reaction system shows the characteristics of increased viscosity and shear thinning, which leads to the problems of bimodal distribution of particle size, easy generation of empty bags and reduced density of shell material in color-changing microcapsules with melamine resin prepolymer as shell material.
[0004] Based on the above analysis, it is very important to provide a color-changing microcapsule with low empty package rate and high shell material density. Summary of the invention
[0005] The embodiment of the present application provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, so as to solve the problem that the existing color-changing microcapsules in the related art are prone to produce empty capsules and low density of the shell material during the preparation process.
[0006] The present application provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, comprising the following steps:
[0007] Step S101, mixing melamine, formaldehyde and a cationic modifier, adding an alkaline solution to adjust the pH value to 8.3-8.6, heating to react, and obtaining a colorless, clear and transparent cationic modified melamine resin prepolymer;
[0008] Step S102, mixing and melting the leuco dye, the developer and the phase change material to obtain a core material solution;
[0009] Step S103, adding an acid solution to the anionic emulsifier to adjust the pH value to 4-5, heating, and then adding the core material solution to the anionic emulsifier for emulsification for 5-15 minutes to obtain a thermochromic core material emulsion;
[0010] Step S104, adding the cationic modified melamine resin prepolymer to the thermochromic core material emulsion, heating and stirring, adding an acid solution to adjust the pH value to 4-5, heating again, and then cooling to room temperature to obtain a thermochromic microcapsule emulsion;
[0011] Step S105, adding deionized water to the thermochromic microcapsule emulsion for dilution, and then drying to obtain the thermochromic microcapsule powder.
[0012] In some embodiments, the cationic modifier is a mixture of one or more of choline chloride, betaine, and polyquaternium-10.
[0013] In some embodiments, the alkaline solution is a mixture of one or more of sodium carbonate, triethanolamine, and sodium hydroxide.
[0014] In some embodiments, the acid solution is a mixture of one or more of citric acid, acetic acid, and sulfuric acid.
[0015] In some embodiments, the leuco dye is crystal violet lactone or chlorophyll-5.
[0016] In some embodiments, the developer is a mixture of one or more of bisphenol A, bisphenol AF, bisphenol S, methyl gallate, and propyl gallate.
[0017] In some embodiments, the phase change material is a mixture of one or more of n-dodecanol, n-tetradecanol, n-hexadecanol, and n-octadecyl alcohol.
[0018] In some embodiments, the molar ratio of melamine to formaldehyde is 1:3-1:4, and the molar ratio of melamine to cationic modifier is 1:0.03-1:0.08.
[0019] In some embodiments, the weight ratio of the cationic modified melamine resin prepolymer to the core material solution is 1:1-1:4.
[0020] In some embodiments, in step S101, the heating temperature is 75-85°C.
[0021] In some embodiments, in step S102, the melting temperature is 125-135°C.
[0022] In some embodiments, in step S103, the heating temperature is 70-80°C.
[0023] In some embodiments, in step S104, the heating temperature is 70-80°C, and the re-heating temperature is 85-95°C.
[0024] In some embodiments, in step S105, the drying temperature is 80-90°C.
[0025] In a second aspect, the present application further provides a cationic modified melamine resin thermochromic microcapsule, wherein the wall material of the microcapsule is a cationic modified melamine resin, and the core material is a leuco dye, a developer and a phase change material.
[0026] In some embodiments, the cationic modified melamine resin is prepared from melamine, formaldehyde and a cationic modifier.
[0027] In some embodiments, the molar ratio of the leuco dye to the developer is 1:3-1:6.
[0028] In some embodiments, the mass of the phase change material is 80%-90% of the total mass of the core material.
[0029] The beneficial effects brought about by the technical solution provided by the present application include: the preparation method provided by the present application first utilizes melamine and formaldehyde to undergo a nucleophilic addition reaction under weakly alkaline conditions to form a water-soluble melamine resin prepolymer, and then the hydroxymethyl group of the cationic modifier dehydrates and condenses with the hydroxymethyl group of the prepolymer to form a cationic modified melamine resin prepolymer containing both positive and negative charges. After the cationic modified melamine resin prepolymer is added to the reaction system, on the one hand, the electrostatic effect between anions and cations greatly enhances the adsorption capacity of the anionic emulsifier for the cationic modified melamine resin prepolymer, and reduces the free melamine resin prepolymer in the aqueous phase. On the other hand, a double electron layer formed by the emulsifier and the cationic modifier is formed on the surface of the microcapsule shell material, which hinders the formation of transient molecular bridges. Therefore, the viscosity of the entire reaction system is stable and has no obvious change before and after the addition of the cationic modified melamine resin prepolymer, and the obtained microcapsule product has no obvious empty bags, and the shell material is more dense and uniform, and the wear resistance is significantly better than that of microcapsules that have not been cationically modified. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.
[0031] Figure 1This is a schematic diagram of the reaction process for preparing a cationic modified melamine resin prepolymer in Example 1 of the present application;
[0032] Figure 2 This is a SEM image of the thermochromic microcapsule prepared in Example 1 of the present application;
[0033] Figure 3 This is a SEM image of the thermochromic microcapsules prepared in Comparative Example 1 of the present application. Implementation
[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.
[0035] The embodiment of the present application provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, which can solve the problem in the prior art that the color-changing microcapsules are prone to produce empty capsules and low density of the shell material during the preparation process. Example
[0036] Example 1 provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, comprising the following steps:
[0037] (1) Add 30 g of melamine, 60 g of formaldehyde aqueous solution (37%), and 1.7 g of choline chloride into a three-necked flask, add triethanolamine dropwise until the pH is 8.5, heat in a water bath to 85°C, keep warm and stir for 1.5 hours, then discharge the material to obtain a colorless, clear and transparent cationic modified melamine resin prepolymer;
[0038] (2) Preparation of core material solution: 70 g of octadecyl alcohol, 3 g of crystal violet lactone, and 8 g of bisphenol AF were placed in a beaker, stirred and heated to 130°C to melt, to obtain a core material solution;
[0039] (3) Preparation of thermochromic core material emulsion: Take 150 g of SMA (5%) emulsifier, add citric acid (10%) until the pH is 4.5, heat to 75 °C, add the core material solution and emulsify on an emulsifier for 15 min to obtain a thermochromic core material emulsion;
[0040] (4) Preparation of thermochromic microcapsule emulsion: 50 g of cationic modified melamine resin prepolymer was added to the thermochromic core material emulsion, and the mixture was kept in a water bath at 75 °C for 1 h. Then, citric acid (10%) was added dropwise until the pH value was 4.5. The system was heated to 95 °C and kept in temperature for 2 h, then cooled to room temperature and discharged to obtain the thermochromic microcapsule emulsion.
[0041] (5) Preparation of thermochromic microcapsule powder: The thermochromic microcapsule emulsion was diluted with deionized water, spray-dried, and the outlet air temperature was controlled at 90°C to obtain a thermochromic microcapsule powder. The particle size D of the thermochromic microcapsule powder was 90 About 5 microns.
[0042] The reaction process of melamine, formaldehyde and choline chloride in Example 1 is shown in Figure 1 ,from Figure 1 It can be seen that the prepared cationic modified melamine resin prepolymer contains both positive and negative charges.
[0043] The SEM image of the thermochromic microcapsules prepared in Example 1 is shown in Figure 2 ,from Figure 2 It can be seen that the shell material of the prepared thermochromic microcapsule is dense.
[0044] The thermochromic microcapsules prepared in Example 1 are royal blue at room temperature, begin to fade at 38° C., and completely fade to white at 40° C.
[0045] Comparative Example 1:
[0046] Comparative Example 1 provides a method for preparing melamine-formaldehyde resin thermochromic microcapsules, comprising the following steps:
[0047] (1) Add 30 g of melamine and 60 g of formaldehyde aqueous solution (37%) into a three-necked flask, add triethanolamine dropwise until the pH is 8.5, heat in a water bath to 85°C, keep warm and stir for 1.5 hours, then discharge the material to obtain a melamine-formaldehyde prepolymer;
[0048] (2) Preparation of core material solution: 70 g of octadecyl alcohol, 3 g of crystal violet lactone, and 8 g of bisphenol AF were placed in a beaker, stirred and heated to 130°C to melt, to obtain a core material solution;
[0049] (3) Preparation of thermochromic core material emulsion: Take 150 g of SMA (5%) emulsifier, add citric acid (10%) until the pH is 4.5, heat to 75 °C, add the core material solution and emulsify on an emulsifier for 15 min to obtain a thermochromic core material emulsion;
[0050] (4) Preparation of thermochromic microcapsule emulsion: 50 g of melamine-formaldehyde prepolymer was added to the thermochromic core material emulsion, and the mixture was kept in a water bath at 75 °C for 1 h. Then, citric acid (10%) was added dropwise until the pH value was 4.5. The system was heated to 95 °C and kept in temperature for 2 h, and then cooled to room temperature to obtain the thermochromic microcapsule emulsion.
[0051] (5) Preparation of thermochromic microcapsule powder: The thermochromic microcapsule emulsion was diluted with deionized water, spray-dried, and the outlet air temperature was controlled at 90°C to obtain thermochromic microcapsule powder.
[0052] The SEM image of the thermochromic microcapsules prepared in Comparative Example 1 is shown in Figure 3 ,from Figure 3 It can be seen that the particle size distribution of the thermochromic microcapsules prepared in Comparative Example 1 is uneven, there are empty capsules, and the shell material deposition is not dense. This is because after the addition of melamine-formaldehyde prepolymer, the viscosity of the reaction system increases significantly, resulting in an increase in bubbles.
[0053] The thermochromic microcapsules prepared in Comparative Example 1 are royal blue at room temperature, begin to fade at 38° C., and completely fade to white at 40° C.
[0054] The wear resistance test of the thermochromic microcapsules prepared in Example 1 and Comparative Example 1 was carried out. The results showed that under the same temperature and pressure conditions, the microcapsules prepared in Example 1 exhibited better wear resistance. Example
[0055] Example 2 provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, comprising the following steps:
[0056] (1) Preparation of cationic modified melamine resin prepolymer: 30 g melamine, 60 g formaldehyde aqueous solution (37%), and 1.6 g betaine were added into a three-necked flask, and sodium hydroxide aqueous solution (10%) was added dropwise until the pH value was 8.5. The mixture was heated to 80°C in a water bath, stirred for 1.5 h, and then discharged to obtain a colorless, clear, and transparent cationic modified melamine resin prepolymer.
[0057] (2) Preparation of core material solution: 65 g of hexadecanol, 2 g of crystal violet lactone, and 6 g of bisphenol AF were placed in a beaker, stirred and heated to 135°C to melt, to obtain a core material solution;
[0058] (3) Preparation of thermochromic core material emulsion: Take 130 g of SMA (5%) emulsifier, add citric acid (10%) until the pH is 4.5, heat to 75 °C, add the core material solution and emulsify on an emulsifier for 15 min to obtain a thermochromic core material emulsion;
[0059] (4) Preparation of thermochromic microcapsule emulsion: 46 g of cationic modified melamine resin prepolymer was added to the thermochromic core material emulsion, and the mixture was kept in a water bath at 70 °C for 1 h. Then, citric acid (10%) was added dropwise until the pH value was 4.5. The system was heated to 95 °C and kept in temperature for 2 h, then cooled to room temperature and discharged to obtain a thermochromic microcapsule emulsion.
[0060] (5) Preparation of thermochromic microcapsule powder: The thermochromic microcapsule emulsion was diluted with deionized water, spray-dried, and the outlet air temperature was controlled at 80°C to obtain thermochromic microcapsule powder.
[0061] The thermochromic microcapsules prepared in Example 2 are blue at room temperature, begin to fade at 28°C, and completely fade to white at 31°C. Example
[0062] Example 3 provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, comprising the following steps:
[0063] (1) Preparation of cationic modified melamine resin prepolymer: 30 g melamine, 60 g formaldehyde aqueous solution (37%), and 2.0 g choline chloride were added into a three-necked flask, and sodium hydroxide aqueous solution (10%) was added dropwise until the pH value reached 8.5. The mixture was heated to 85°C in a water bath, stirred for 1.5 h, and then discharged to obtain a colorless, clear, and transparent cationic modified melamine resin prepolymer.
[0064] (2) Preparation of core material solution: 75 g of octadecyl alcohol, 3 g of green pigment-5, and 5.5 g of bisphenol AF are placed in a beaker, stirred and heated to 130°C to melt, and a core material solution is obtained;
[0065] (3) Preparation of thermochromic core material emulsion: Take 150 g SDBS (5%) emulsifier, add citric acid (10%) until the pH is 4.5, heat to 75 °C, add the core material solution and emulsify on an emulsifier for 15 min to obtain a thermochromic core material emulsion;
[0066] (4) Preparation of thermochromic microcapsule emulsion: 55 g of cationic modified melamine resin prepolymer was added to the thermochromic core material emulsion, and the mixture was kept in a water bath at 75 °C for 1 h. Then, citric acid (10%) was added dropwise until the pH value was 4.5. The system was heated to 90 °C and kept in temperature for 2 h, then cooled to room temperature and discharged to obtain a thermochromic microcapsule emulsion.
[0067] (5) Preparation of thermochromic microcapsule powder: The thermochromic microcapsule emulsion was diluted with deionized water, spray-dried, and the outlet air temperature was controlled at 90°C to obtain thermochromic microcapsule powder.
[0068] The thermochromic microcapsules prepared in Example 3 are green at room temperature, begin to fade at 38° C., and completely fade to light green at 41° C. Example
[0069] Example 4 provides a method for preparing a cation-modified melamine resin thermochromic microcapsule, comprising the following steps:
[0070] (1) Preparation of cationic modified melamine resin prepolymer: 30 g melamine, 60 g formaldehyde aqueous solution (37%), and 2.0 g betaine were added into a three-necked flask, and sodium hydroxide aqueous solution (10%) was added dropwise until the pH value reached 8.5. The mixture was heated to 75°C in a water bath, stirred for 1.5 h, and then discharged to obtain a colorless, clear, and transparent cationic modified melamine resin prepolymer.
[0071] (2) Preparation of core material solution: 25 g of octadecyl alcohol, 45 g of hexadecanol, 3 g of green pigment-5, and 5.5 g of bisphenol AF were placed in a beaker, stirred and heated to 125°C to melt, and a core material solution was obtained;
[0072] (3) Preparation of thermochromic core material emulsion: Take 150 g of SMA (7%) emulsifier, add acetic acid (10%) until the pH is 4.5, heat to 70 °C, add the core material solution and emulsify on an emulsifier for 15 min to obtain a thermochromic core material emulsion;
[0073] (4) Preparation of thermochromic microcapsule emulsion: 55 g of cationic modified melamine resin prepolymer was added to the thermochromic core material emulsion, and the mixture was kept in a water bath at 75 °C for 1 h. Acetic acid (10%) was added dropwise until the pH value was 4.5. The system was heated to 85 °C and kept in temperature for 2 h, then cooled to room temperature and discharged to obtain a thermochromic microcapsule emulsion.
[0074] (5) Preparation of thermochromic microcapsule powder: Add an equal volume of sodium bicarbonate aqueous solution (10%) to the thermochromic microcapsule emulsion, stir until there are no obvious bubbles, filter on qualitative filter paper, and wash with an equal volume of deionized water. The obtained wet cake is dried in an oven at 90°C for 10 h and sieved on a 400-mesh sieve to obtain thermochromic microcapsule powder.
[0075] The thermochromic microcapsules prepared in Example 4 are green at room temperature, begin to fade at 30°C, and completely fade to light green at 33°C.
[0076] In the description of this specification, the description with reference to the terms "one embodiment / method", "some embodiments / methods", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments / methods or examples. In addition, those skilled in the art may combine and combine the different embodiments / methods or examples described in this specification and the features of the different embodiments / methods or examples, unless they are contradictory.
[0077] It should be noted that, in the present application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements. In the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically stipulated.
[0078] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.
Claims
1. A method for preparing a cation-modified melamine resin thermochromic microcapsule, characterized in that: The following steps are involved: S101, mixing melamine, formaldehyde and a cationic modifier, adding an alkaline solution to adjust the pH value to 8.3-8.6, heating for reaction, and obtaining a cationic modified melamine resin prepolymer; S102, mixing and melting the leuco dye, the developer and the phase change material to obtain a core material solution; S103, adding an acid solution to the anionic emulsifier to adjust the pH value to 4-5, heating, and then adding the core material solution to the anionic emulsifier for emulsification to obtain a thermochromic core material emulsion; S104, adding a cationic modified melamine resin prepolymer to the thermochromic core material emulsion, heating and stirring, adding an acid solution to adjust the pH value to 4-5, heating again, and then cooling to room temperature to obtain a thermochromic microcapsule emulsion; S105, adding deionized water to the thermochromic microcapsule emulsion to dilute it, and then drying it to obtain a thermochromic microcapsule powder; Among them, the cationic modifier is a mixture of one or more of choline chloride, betaine, and polyquaternium-10; the leuco dye is crystal violet lactone or green pigment-5; the developer is a mixture of one or more of bisphenol A, bisphenol AF, bisphenol S, methyl gallate, and propyl gallate; the phase change material is a mixture of one or more of n-dodecanol, n-tetradecanol, n-hexadecanol, and n-octadecyl alcohol; the anionic emulsifier is styrene-maleic anhydride or sodium dodecylbenzene sulfonate.
2. The method for preparing the cation-modified melamine resin thermochromic microcapsules according to claim 1, characterized in that: The alkaline solution is a mixture of one or more of sodium carbonate, triethanolamine and sodium hydroxide; the acid solution is a mixture of one or more of citric acid, acetic acid and sulfuric acid.
3. The method for preparing the cation-modified melamine resin thermochromic microcapsules according to claim 1, characterized in that: The molar ratio of melamine to formaldehyde is 1:3-1:4, the molar ratio of melamine to cationic modifier is 1:0.03-1:0.08; the weight ratio of cationic modified melamine resin prepolymer to core material solution is 1:1-1:
4.
4. The method for preparing the cation-modified melamine resin thermochromic microcapsules according to claim 1, characterized in that: The molar ratio of the leuco dye to the developer is 1:3-1:6; the mass of the phase change material is 80%-90% of the total mass of the core material.
5. The method for preparing the cation-modified melamine resin thermochromic microcapsules according to claim 1, characterized in that: In step S101, the heating temperature is 75-85°C; in step S102, the melting temperature is 125-135°C; in step S103, the heating temperature is 70-80°C; in step S104, the heating temperature is 70-80°C, and the reheating temperature is 85-95°C; in step S105, the drying temperature is 80-90°C.
6. The cationic modified melamine resin thermochromic microcapsules prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The wall material of the microcapsule is a cationic modified melamine resin, and the core material is a leuco dye, a developer and a phase change material.