A thermochromic microcapsule coated with a silica hybrid modified epoxy resin wall material and a preparation method thereof

Abstract

The present invention relates to thermochromic microcapsules coated with a silica hybrid-modified epoxy resin wall material. The microcapsules are composed of a silica hybrid-modified epoxy resin wall material, which is a coating layer obtained by in-situ hybridization of a silicon-sourced epoxy resin with a polyamine curing agent, and a core material comprising a thermochromic material, a color developer, and a temperature-regulating solvent. The microcapsules are prepared quickly and simply, and the resulting thermochromic microcapsules have excellent thermal stability and are completely free of health-damaging aldehydes. The microcapsule wall material has high density and excellent mechanical properties, maintaining the integrity and elasticity of the capsule under external impact. Furthermore, the capsule wall has excellent light transmittance, resulting in a more vibrant color for the microcapsules.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a thermochromic microcapsule coated with a silica hybrid modified epoxy resin wall material and a preparation method thereof. Background Art

[0002] Materials that change color when the temperature rises or falls below a certain temperature range are called thermochromic materials. Continuous color change with temperature is called continuous thermochromism, while discontinuous thermochromism occurs only at a specific temperature. Reversible thermochromism occurs when the temperature rises or falls, while irreversible thermochromism occurs only once. Since Houston observed the thermochromism of inorganic substances such as CuI in 1871, research on thermochromism has been ongoing. Compounds with thermochromic properties have expanded from simple metals, metal oxides, complex salts, and complexes to various organic compounds, liquid crystals, polymers, and biomacromolecules. As early as 1926, it was reported that colorless 2-β-naphthylspiropyran appears blue when melted and returns to a colorless state after cooling. Since then, people have synthesized a series of thermochromic organic compounds and found that these organic thermochromic materials have the characteristics of being diverse, rich in colors, and bright in color. Therefore, this type of compound has become a research hotspot for thermochromic materials.

[0003] Thermochromic microcapsules are coated with this thermochromic material. When the ambient temperature reaches a certain value, the core material inside the thermochromic microcapsules reacts, and the pigment particles change their original color. The principle is that the core material is composed of a thermochromic material, a color developer, and a temperature-regulating solvent. When the temperature changes, the temperature-regulating solvent changes its solid-liquid state, allowing the color developer and thermochromic material to combine with each other, resulting in changes in material structure, proton gain and loss between molecules, or electron transfer equilibrium reactions in organic molecules. The core material changes color. By adjusting the raw material formula of the temperature-regulating solvent and changing the melting point of the entire core material, the thermochromic microcapsules can be made to change color at different temperature points.

[0004] A microcapsule is a miniature container with a polymer or inorganic wall. Through microcapsule granulation technology, solids, liquids or gases can be embedded and sealed into a solid microcapsule, and the thermochromic core material is coated in the microcapsule so that it will not be lost or inactivated due to extreme environments such as scratching, squeezing, long-term high temperature or long-term exposure during use. This type of microcapsule is collectively called thermochromic microcapsule. Since thermochromic microcapsules are often used in surface coatings, spun fibers, anti-counterfeiting labels and other products, the scratch and extrusion resistance and temperature resistance of their wall materials are particularly important. When preparing traditional thermochromic microcapsules, melamine-formaldehyde resins and urea-formaldehyde resins are usually used as wall materials. Although these low-cost resins can provide excellent mechanical properties to protect the microcapsules from rupture and failure due to external factors, they will produce a large amount of aldehydes that are harmful to health. In an environment above 150°C, they will rapidly age and decompose, thus losing their original function. The thermochromic core material will frequently undergo solid-liquid phase transitions as the ambient temperature changes. Once the wall material is damaged or ruptured, the thermochromic core material will quickly disappear, and the microcapsules will lose their function.

[0005] Chinese patent application CN111604014A discloses a method for preparing color-changing microcapsules that can be used in textile applications and color-changing microcapsules. Monomers containing carbon-carbon double bonds are selected and polymerized at the oil-water interface under the action of a free radical initiator to form a capsule wall. Although this type of substance has good coating properties, its wall material is formed by the addition polymerization of unsaturated bonds, has a low glass transition temperature (Tg), and has poor mechanical properties. Long-term exposure to the natural environment will cause rapid aging and decomposition, making it difficult to use in surface coatings, melt spinning, or outer packaging materials.

[0006] Chinese patent application CN104877065A discloses an organic reversible thermochromic microcapsule with a long lifespan and large color difference and a preparation method. Acrylate monomers or acrylate epoxy resins are selected to synthesize polyacrylate or epoxy resin capsule walls. Although these substances can provide good mechanical properties at room temperature, due to their low glass transition temperature (Tg), the capsule walls will soften, stick, or even break when the temperature exceeds 120°C, reducing their protective ability when used in the high temperature process of melt spinning.

[0007] Chinese Patent Application 114130321A discloses a double-layer wall material-coated photosensitive microcapsule and a preparation method thereof. A layer of silica wall material is deposited on a polyurea-polyurethane wall material to enhance the rigidity and temperature resistance of the microcapsule. However, during preparation, the two wall materials rely solely on hydrogen bonds for adsorption, deposition, and mutual bonding. The bonding force between the two is weak, and there is a possibility of the two wall materials falling off, which restricts the complementarity between the two materials. Summary of the Invention

[0008] The purpose of the present invention is to address the deficiencies in the prior art and provide a thermochromic microcapsule coated with a silica hybrid-modified epoxy resin wall material and a preparation method thereof, so as to provide excellent mechanical properties and heat resistance under the premise of ensuring that the microcapsule core material can fully play its role. KH560 is used as a silicon source to form an epoxy resin by in-situ hybridization modification of the wall material, thereby overcoming the shortcomings of the silica wall material prepared by the sol-gel method alone, that is, the insufficient density, and the shortcomings of the wall material prepared by the in-situ polymerization method, that is, the high rigidity and poor toughness, and improving the temperature resistance of the epoxy resin and the overall rigidity of the microcapsule.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] The first aspect of the present invention provides a thermochromic microcapsule coated with a silica hybrid modified epoxy resin wall material, which is composed of a silica hybrid modified epoxy resin wall material and a core material. The silica hybrid modified epoxy resin wall material is a coating layer obtained by in-situ hybrid modification of the epoxy resin by a silicon source under the conditions of a polyamine curing agent. The core material includes a thermochromic material, a color developer and a temperature regulating solvent. The weight ratio of the wall material to the core material is 1:5 to 1:2.

[0011] Specifically, the silicon source is KH560, which can be hydrolyzed under acidic conditions and then polymerized under alkaline conditions to form a silica sol-gel with epoxy groups.

[0012] Preferably, the epoxy resin is a bisphenol A epoxy resin. Epoxy resins with bisphenol A groups can reduce the reaction consumption with phenolic developers.

[0013] Specifically, the core material is formed by melting and blending a thermochromic material, a color developer and a temperature-adjusting solvent under high temperature conditions.

[0014] Specifically, the thermochromic material is one or more of spiropyran color-changing polymers, fluorane color-changing polymers, phenothiazine color-changing polymers, Schiff base color-changing polymers, dianthrone color-changing polymers, triarylmethane color-changing polymers, α-naphthoquinone derivative color-changing polymers and organic compound color-changing polymers, accounting for 2 to 10% of the total weight of the core material.

[0015] Specifically, the developer is one or more of phenols, carboxylic acids, benzotriazoles and halogenated alcohols, accounting for 10-20% of the total weight of the core material.

[0016] Specifically, the temperature-adjusting solvent is one or more of fatty alcohol, fatty alkane, fatty acid and diphenyl carbonate, accounting for 75-85% of the total weight of the core material.

[0017] Specifically, the formation process of the silica hybrid modified epoxy resin wall material is as follows: the silicon source is hydrolyzed into silica sol under acidic conditions of pH ≤ 5.0, and then polymerized under alkaline conditions of pH ≥ 9.0 to form a sol-gel with epoxy groups, which is then ring-opened under the action of a polyamine curing agent and cross-linked with the epoxy resin to form the silica hybrid modified epoxy resin wall material.

[0018] Taking KH560 as the silicon source, bisphenol A epoxy resin as the epoxy resin, and ethylenediamine as the polyamine curing agent as an example, KH560 is hydrolyzed into a sol under acidic conditions of pH ≤ 5.0, and then polymerized to form a sol-gel under alkaline conditions of pH ≥ 9.0. After ring opening under the action of ethylenediamine, it cross-links with the epoxy resin to form a silica hybrid modified epoxy resin wall material.

[0019] The reaction equation is as follows:

[0020]

[0021] R is a portion with an epoxy group.

[0022] A second aspect of the present invention provides a method for preparing thermochromic microcapsules coated with a silica hybrid modified epoxy resin wall material, comprising the following steps:

[0023] 1) Heat the temperature-adjusting solvent, developer and thermochromic material to 120-150°C, so that the thermochromic material and developer are fully and evenly dissolved in the temperature-adjusting solvent. When the temperature of the mixed core material is kept above 120°C, add epoxy resin and KH560;

[0024] 2) adding the oil phase solution obtained in step 1) to an aqueous solution containing an emulsifier at 70-75° C. and stirring at high speed to form an oil-in-water (O / W) emulsion, maintaining the temperature at 70-75° C. and continuing stirring, adjusting the pH of the emulsion to ≤ 5.0 to allow KH560 to fully hydrolyze at the interface of the emulsion droplets to form a sol-gel layer, reacting for 1-1.5 hours, then adjusting the pH to ≥ 9.0 with a polyamine curing agent, and simultaneously raising the temperature to 80-85° C. and reacting for 2-3 hours to allow the sol-gel to form a coating layer;

[0025] 3) stirring the emulsion obtained in step 2) at 70-75° C. for 18-24 hours;

[0026] 4) cooling the emulsion obtained in step 3), filtering and washing it, and drying it to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

[0027] Preferably, the emulsifier is one or more of polyvinyl alcohol, styrene-maleic anhydride block polymer, and hexadecyltrimethylammonium bromide, accounting for 5% of the total weight of the aqueous solution.

[0028] Preferably, sulfuric acid, acrylic acid or citric acid is used to adjust the pH of the emulsion.

[0029] Compared with the prior art, the present invention has the following outstanding effects:

[0030] The present invention's thermochromic microcapsules coated with a silica-modified epoxy resin wall material are quick and easy to prepare, have excellent thermal stability, are completely free of health-damaging aldehydes, and feature high wall density, preventing core material leakage even at temperatures exceeding 200°C. Furthermore, the microcapsules exhibit excellent mechanical properties, maintaining their integrity and elasticity under external impact, protecting the core material and isolating it from the external environment. Furthermore, the capsule wall exhibits excellent light transmittance, allowing the color of the color-changing core material to be more intuitively displayed on the outside of the microcapsule, resulting in a more vibrant color. Existing thermochromic microcapsules, on the other hand, produce large amounts of health-damaging aldehydes and rapidly age and decompose in temperatures exceeding 150°C, losing their original function. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a detailed photograph of the thermochromic microcapsules coated with the silica hybrid modified epoxy resin wall material prepared in Example 1 observed using a scanning electron microscope (SEM). DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0033] Example 1

[0034] Weigh 0.5 g of crystal violet lactone, 8.5 g of bisphenol-A, 30 g of dodecanol, and 11 g of tetradecanol, mix them evenly, stir and heat to 150°C to completely melt all components to a clear and transparent state, then add 3 g of KH560 and 7 g of bisphenol A epoxy resin (E51) and fully dissolve and stir evenly.

[0035] The above oil phase solution was added to a 70°C emulsifier aqueous solution containing 7g of polyvinyl alcohol, 1g of hexadecyltrimethylammonium bromide, and 132g of deionized water, and stirred at high speed to form an oil-in-water (O / W) emulsion. A 0.1mol / L sulfuric acid solution was slowly added dropwise to the emulsion until the pH value reached 3.5. The solution was kept at 70°C and stirred continuously to allow KH560 to form a sol layer on the interface of the emulsion droplets and react with the epoxy resin for ring-opening for 1.5 hours. The pH value was then adjusted to 11.0 with an ethylenediamine solution, and the temperature was raised to 85°C for reaction for 2 hours to cross-link the epoxy resin and the siloxane to form a molding.

[0036] The emulsion was cooled to 70° C. and stirred for 24 hours, then cooled, filtered, washed, and dried to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

[0037] Scanning electron microscopy (SEM) confirmed that the appearance of the thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material was a complete microcapsule monodisperse state. The details of the double-layer silica-coated thermochromic microcapsules prepared in Example 1 were observed by scanning electron microscopy (SEM), as shown in FIG. Figure 1 shown.

[0038] Example 2

[0039] Weigh 4.5 g of 2-phenylamino-3-methyl-6-dibutylaminofluoran, 4.5 g of bisphenol-AF, 6 g of tetradecanol, and 30 g of hexadecanol, mix well, stir, and heat to 150°C to completely dissolve all components until they become clear and transparent. Then, add 4 g of KH560, 3 g of bisphenol A epoxy resin (E55), and 5 g of bisphenol A epoxy resin (E51), and dissolve them thoroughly with stirring.

[0040] The above oil phase solution was added to a 75°C emulsifier aqueous solution containing 5g of polystyrene-maleic anhydride block copolymer, 2g of hexadecyltrimethylammonium bromide, and 135g of deionized water, and stirred at high speed to form an oil-in-water (O / W) emulsion. A 0.1mol / L sulfuric acid solution was slowly added dropwise to the emulsion until the pH value reached 4.0. The solution was kept at 75°C and stirred continuously to allow KH560 to form a sol layer on the interface of the emulsion droplets and react with the epoxy resin for ring-opening for 1.5 hours. The pH value was then adjusted to 11.5 with a diethylenetriamine solution, and the temperature was raised to 85°C for reaction for 2 hours to crosslink the epoxy resin and the siloxane to form a molding.

[0041] The emulsion was cooled to 70° C. and stirred for 24 hours, then cooled, filtered, washed, and dried to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

[0042] Example 3

[0043] Weigh 2 g of 2'-chloro-6'-diethylaminofluoran, 8 g of bisphenol-AF, 20 g of dodecanol, and 30 g of tetradecanol, mix them evenly, stir, and heat to 150°C to completely melt all components until they become clear and transparent. Then add 2 g of KH560, 7 g of bisphenol A epoxy resin (E55), and 6 g of bisphenol A epoxy resin (E44), and dissolve them thoroughly and stir evenly.

[0044] The above oil phase solution was added to a 70°C emulsifier aqueous solution containing 6g of polyvinyl alcohol, 1g of hexadecyltrimethylammonium bromide, and 135g of deionized water, and stirred at high speed to form an oil-in-water (O / W) emulsion. A 0.1mol / L sulfuric acid solution was slowly added dropwise to the emulsion until the pH value reached 4.0. The solution was heated to 72°C and stirred continuously to allow KH560 to form a sol layer on the interface of the emulsion droplets and react with the epoxy resin for ring-opening for 1 hour. The pH value was then adjusted to 11.5 with a diethylenetriamine solution, and the solution was heated to 82°C and reacted for 2.5 hours to crosslink the epoxy resin and the siloxane to form a molding product.

[0045] The emulsion was cooled to 75° C. and stirred for 24 hours, then cooled, filtered, washed, and dried to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

[0046] Example 4

[0047] Weigh 1.0 g of crystal violet lactone, 9.0 g of bisphenol-A, 30 g of hexadecane, and 20 g of diphenyl carbonate, mix them evenly, stir and heat to 120°C to completely melt all components to a clear and transparent state, then add 4 g of KH560, 5 g of bisphenol A epoxy resin (E55) and 6 g of bisphenol A epoxy resin (E44) to fully dissolve and stir evenly.

[0048] The above oil phase solution was added to a 72°C emulsifier aqueous solution containing 5g of polyvinyl alcohol, 1.8g of hexadecyltrimethylammonium bromide, and 135g of deionized water, and stirred at high speed to form an oil-in-water (O / W) emulsion. A 0.1mol / L sulfuric acid solution was slowly added dropwise to the emulsion until the pH value reached 3.0. The solution was kept at 72°C and stirred continuously to allow KH560 to form a sol layer on the interface of the emulsion droplets and react with the epoxy resin for ring-opening for 1.5 hours. The pH value was then adjusted to 10.5 with a tetraethylenepentamine solution, and the temperature was raised to 80°C for reaction for 3 hours to cross-link the epoxy resin and the siloxane to form a molding.

[0049] The emulsion was cooled to 72° C. and stirred for 24 hours, then cooled, filtered, washed, and dried to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

Claims

1. A thermochromic microcapsule coated with a silica hybrid modified epoxy resin wall material, characterized in that: The invention comprises a silica hybrid modified epoxy resin wall material and a core material, wherein the silica hybrid modified epoxy resin wall material is a coating layer obtained by in-situ hybrid modification of epoxy resin with a silicon source under the condition of a polyamine curing agent, and the core material comprises a thermochromic material, a color developer and a temperature regulating solvent, and the weight ratio of the wall material to the core material is 1:5 to 1:2; the silicon source is KH560, which can be hydrolyzed under acidic conditions and then polymerized under alkaline conditions to form a silica sol-gel with epoxy groups; the formation process of the silica hybrid modified epoxy resin wall material is specifically as follows: KH560 is hydrolyzed to a sol under acidic conditions of pH ≤ 5.0, and then polymerized under alkaline conditions of pH ≥ 9.0 to form a sol-gel with epoxy groups, which is then ring-opened under the action of a polyamine curing agent and then cross-linked with the epoxy resin to form the silica hybrid modified epoxy resin wall material.

2. The thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 1, characterized in that: The epoxy resin is bisphenol A epoxy resin.

3. The thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 1, characterized in that: The core material is formed by melting and blending a thermochromic material, a color developer and a temperature regulating solvent under high temperature conditions.

4. The thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 3, characterized in that: The thermochromic material is one or more of spiropyran color-changing polymers, fluorane color-changing polymers, phenothiazine color-changing polymers, Schiff base color-changing polymers, dianthrone color-changing polymers, triarylmethane color-changing polymers, α-naphthoquinone derivative color-changing polymers and organic compound color-changing polymers.

5. The thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 3, characterized in that: The developer is one or more of phenols, carboxylic acids, benzotriazoles and halogenated alcohols.

6. The thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 3, characterized in that: The temperature regulating solvent is one or more of fatty alcohol, fatty alkane, fatty acid and diphenyl carbonate.

7. A method for preparing thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to any one of claims 1 to 6, characterized in that: The steps include: 1) Heat the temperature-adjusting solvent, developer and thermochromic material to 120-150°C, so that the thermochromic material and developer are fully and evenly dissolved in the temperature-adjusting solvent. When the temperature of the mixed core material is kept above 120°C, add epoxy resin and KH560; 2) adding the oil phase solution obtained in step 1) to an aqueous solution containing an emulsifier at 70-75° C. and stirring at high speed to form an oil-in-water (O / W) emulsion, maintaining the temperature at 70-75° C. and continuing stirring, adjusting the pH of the emulsion to ≤ 5.0 to allow KH560 to fully hydrolyze at the interface of the emulsion droplets to form a sol-gel layer, reacting for 1-1.5 hours, then adjusting the pH to ≥ 9.0 with a polyamine curing agent, and simultaneously raising the temperature to 80-85° C. and reacting for 2-3 hours to allow the sol-gel to form a coating layer; 3) stirring the emulsion obtained in step 2) at 70-75° C. for 18-24 hours; The emulsion obtained in step 3) is cooled, filtered, washed, and dried to obtain thermochromic microcapsule powder coated with silica hybrid modified epoxy resin wall material.

8. The method for preparing thermochromic microcapsules coated with silica hybrid modified epoxy resin wall material according to claim 7, characterized in that: The emulsifier is one or more of polyvinyl alcohol, styrene-maleic anhydride block polymer, and hexadecyltrimethylammonium bromide.

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