Thermally responsive microcapsules, methods of making the same, and liquid epoxy encapsulants

Abstract

This application discloses a thermoresponsive microcapsule, its preparation method, and a liquid epoxy molding compound. The thermoresponsive microcapsule comprises a core material and a shell material covering the core material. The shell material is polymerized from an isocyanate compound, a thermoresponsive crosslinking agent, and an amine compound. The thermoresponsive functional groups in the thermoresponsive crosslinking agent are introduced into the shell material. By utilizing the thermally ruptured characteristics of these functional groups, the rupture of the shell material is temperature-controlled, thereby achieving temperature-controlled release of the core material. This thermoresponsive core-shell structure can be used to encapsulate accelerators, other water-insoluble compounds, or other highly reactive compounds, thus being compatible with various systems and application scenarios to achieve temperature-controlled triggering.

Description

Technical Field

[0001] This application relates to the field of microcapsule technology, specifically to a thermoresponsive microcapsule and its preparation method, and a liquid epoxy molding compound. Background Technology

[0002] Currently, the main methods for preparing core-shell microcapsules include interfacial polymerization, in-situ polymerization, and infusion methods. Among these, interfacial polymerization is one of the most classic and widely used methods. Some related technologies use isocyanate compounds and amine compounds (such as ethylenediamine and diethylenetriamine) to form polyurea shell walls, which are then used to encapsulate water-immiscible materials, including pesticides, fungicides, water treatment agents, and preservatives, to prepare controlled-release capsules. Other related technologies involve mixing phase change materials and modifiers in a specific ratio, heating and stirring to prepare an oil phase, then adding it to an aqueous solution containing an emulsifier. An emulsion is prepared by stirring and emulsifying, and the mixture is slowly cooled while maintaining dispersion conditions to form solid microspheres. Subsequently, toluene diisocyanate (TDI) and polyethylene polyamine are added sequentially to the surface of the microspheres for polymerization, forming polyurea microcapsules encapsulating phase change materials. Other related technologies propose a simpler method for preparing polyurea microcapsules. Specifically, a mixed solution of diisocyanate compound and phase change material is used as the oil phase, and an aqueous solution containing polyamine and stabilizer is used as the aqueous phase. The oil phase is added through a needle into a pipe carrying a flowing aqueous phase for interfacial polymerization. After the reaction, solid and liquid are separated, and after washing, polyurea microcapsules coated with phase change material are obtained.

[0003] However, the urea bonds (-NH-CO-NH-) formed by the reaction of isocyanates with amines are very stable chemical bonds. Both the C=O double bond and the CN bond have high bond energies, giving the urea bonds very high thermal stability. Their decomposition mainly occurs at high temperatures, typically above 150°C. If this component is used to design microcapsule structures, the temperature of the microcapsule structure usually needs to be controlled to rise above 150°C to effectively release the core material encapsulated within the polyurea shell. This does not match the temperature window required for some low- and medium-temperature applications below 150°C. Summary of the Invention

[0004] This application provides a thermoresponsive microcapsule and its preparation method, as well as a liquid epoxy molding compound, aiming to solve the problem that polyurea microcapsules need to be at high temperatures to effectively release the core material.

[0005] This application provides a thermoresponsive microcapsule, comprising a core material and a shell material covering the core material, wherein the shell material is polymerized from an isocyanate compound, a thermoresponsive crosslinking agent, and an amine compound.

[0006] Optionally, in some embodiments of this application, the core material includes an accelerator.

[0007] Optionally, in some embodiments of this application, the promoter is an imidazole compound.

[0008] Optionally, in some embodiments of this application, the imidazole compounds include at least one selected from 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-aminoethyl-2-methylimidazole, 1-(2-hydroxy-3-phenoxypropyl)-2-methylimidazole, and 1-(2-hydroxy-3-phenoxypropyl)-2-ethyl-4-methylimidazole.

[0009] Optionally, in some embodiments of this application, the shell material is polymerized from a composition comprising (5-30) parts of the isocyanate compound, (0.1-5) parts of the thermoresponsive crosslinking agent, and (5-30) parts of the amine compound, by weight.

[0010] Optionally, in some embodiments of this application, the thermally responsive microcapsules comprise (5 to 90) parts of the core material by weight.

[0011] Optionally, in some embodiments of this application, the thermoresponsive crosslinking agent includes at least one of an azo compound and a peroxide.

[0012] Optionally, in some embodiments of this application, the azo compound includes at least one of a monofunctional azo compound and a difunctional azo compound.

[0013] Optionally, in some embodiments of this application, the structural formula of the difunctional azo compound is shown in formula (I): Equation (Ⅰ); In formula (Ⅰ), R1 and R2 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

[0014] Optionally, in some embodiments of this application, the peroxide comprises a difunctional peroxide, the structural formula of which is shown in formula (II): Equation (II); In formula (II), R3 and R4 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

[0015] Optionally, in some embodiments of this application, the isocyanate compound includes at least one selected from aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, aliphatic triisocyanates, and polyisocyanates; and / or, The amine compounds include at least one of aliphatic amines, alicyclic amines, and aromatic amines; and / or, The molar ratio of the isocyanate compound to the amine compound is 1:(1.1~2).

[0016] Accordingly, this application also provides a method for preparing thermoresponsive microcapsules, comprising: The core material, isocyanate compound, thermally responsive crosslinking agent and organic solvent are mixed to obtain an oil phase mixture; The emulsifier and water are mixed to obtain an aqueous mixture; Amine compounds are mixed with water to obtain a wall-forming reaction solution; The oil phase mixture and the aqueous phase mixture are mixed to obtain a water-oil mixture; The temperature of the water-oil mixture is lowered to below 10°C, and the water-oil mixture is stirred and emulsified to obtain an oil-in-water emulsion. The wall-forming reaction solution was added dropwise to the oil-in-water emulsion under stirring conditions to obtain the reaction solution; The reaction solution is controlled to undergo a polymerization reaction to obtain thermally responsive microcapsules.

[0017] Optionally, in some embodiments of this application, the isocyanate compound is (5~30) parts, the core material is (5~90) parts, the thermally responsive crosslinking agent is (0.1~5) parts, the organic solvent is (50~400) parts, the amine compound is (5~30) parts, the emulsifier is (0.1~10) parts, and the water is (400~1000) parts.

[0018] Optionally, in some embodiments of this application, the stirring rate of the emulsification process is 500 rpm to 20000 rpm, and the emulsification time is 1 min to 30 min; and / or, During the dropwise addition process, the temperature of the oil-in-water emulsion is controlled to not exceed 15°C, and the dropwise addition time of the wall-forming reaction solution is 10 min to 60 min; and / or, The polymerization reaction temperature is -10℃ to 50℃, and the polymerization reaction duration is 30 min to 72 h.

[0019] Optionally, in some embodiments of this application, the organic solvent includes at least one selected from hydrocarbon solvents, ketone solvents, ester solvents, and alcohol solvents; and / or, The emulsifier includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, Tween-80, and polyvinyl alcohol.

[0020] In addition, this application also provides a liquid epoxy molding compound, comprising: liquid epoxy resin, curing agent, and the above-mentioned thermoresponsive microcapsules or thermoresponsive microcapsules prepared by the above-mentioned method, wherein the core material includes an accelerator.

[0021] Optionally, in some embodiments of this application, the content of the thermoresponsive microcapsules in the liquid epoxy molding compound is 0.1wt%~1.5wt%; and / or, In the liquid epoxy molding compound, the content of the liquid epoxy resin is 10wt%~20wt%; and / or, In the liquid epoxy molding compound, the content of the curing agent is 5wt%~15wt%.

[0022] Optionally, in some embodiments of this application, the liquid epoxy resin includes at least one of monoepoxy compounds and polyepoxy compounds. Optionally, the liquid epoxy resin includes the polyepoxy compounds, which include at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, cresol phenolic varnish, 3,4-epoxycyclohexylmethyl methacrylate, 3,4-epoxycyclohexylformate-3',4'-epoxycyclohexylmethyl ester, 3,4-epoxycyclohexene methyl-3,4-epoxycyclohexenoester, 4-vinyl-1-cyclohexene diepoxide, aminophenol type epoxy resin, and naphthalene-based epoxy resin.

[0023] Optionally, in some embodiments of this application, the curing agent includes at least one selected from diethyltoluenediamine, dimethylthiotoluenediamine, 4,4'-diaminodiphenyl sulfone, 4-ethylaniline, diethyltoluenediamine, 2-ethylaniline, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, trimethylhexanediamine, m-phenylenediamine, m-phenylenediamine, methyltetrahydrophthalic anhydride, modified methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, methylnadic anhydride, and dodecenylsuccinic anhydride.

[0024] Optionally, in some embodiments of this application, the liquid epoxy molding compound further includes filler in a content of 70wt% to 90wt%, wherein the filler is an inorganic filler, and the inorganic filler includes at least one of silicon dioxide, alumina, silicon nitride, boron nitride, aluminum nitride and silicon carbide.

[0025] Optionally, in some embodiments of this application, the liquid epoxy molding compound further includes a modifier at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a stress-relieving agent at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a diluent at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a colorant at a content of 0.1wt% to 1wt%; and / or, The liquid epoxy molding compound also includes a defoamer at a content of 0.01wt% to 0.5wt%.

[0026] The shell of the thermoresponsive microcapsule provided in this application is polymerized from isocyanate compounds, thermoresponsive crosslinking agents, and amine compounds. Thermoresponsive functional groups from the crosslinking agent are introduced into the shell. By utilizing the thermally rupture characteristics of these functional groups, the rupture of the shell is temperature-controlled, thereby achieving temperature-controlled release of the core material. This thermoresponsive core-shell structure can be used to encapsulate accelerators, other water-insoluble compounds, or other highly reactive compounds, thus being compatible with various systems and application scenarios to achieve temperature-controlled triggering. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of the thermally responsive microcapsule provided in an exemplary embodiment of this application; Figure 2 This is a schematic diagram of an organic polymer network in a thermoresponsive microcapsule provided by an exemplary embodiment of this application; Figure 3 This is a schematic diagram illustrating the reaction between toluene diisocyanate and ethylenediamine according to an exemplary embodiment of this application; Figure 4 This is a schematic diagram illustrating the reaction between toluene diisocyanate and azodicyanovalerate provided in an exemplary embodiment of this application; Figure 5 This is a TEM image of the thermoresponsive microcapsule C-1 obtained in Example 1 of this application. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] This application provides a thermoresponsive microcapsule and its preparation method, as well as a liquid epoxy molding compound. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in a range format; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that a range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0031] Firstly, please see Figure 1 This application provides a thermoresponsive microcapsule 10. The thermoresponsive microcapsule 10 includes a core material 1 and a shell material 2 covering the core material 1. The shell material 2 is polymerized from an isocyanate compound, a thermoresponsive crosslinking agent, and an amine compound.

[0032] It is understood that the thermoresponsive microcapsule 10 has a core-shell structure, wherein the core material 1 is the core and the shell material 2 is the outer shell, and the shell material 2 encapsulates the core material 1 inside. The shell material 2 is an organic polymer polymerized from isocyanate compounds, thermoresponsive crosslinking agents and amine compounds.

[0033] Isocyanates are a class of organic compounds containing isocyanate groups (-NCO) in their molecules. Based on the number of isocyanate groups, isocyanates can be classified into monoisocyanates, diisocyanates, and polyisocyanates. Optionally, isocyanates contain at least two isocyanate groups.

[0034] Amines are an important class of nitrogen-containing organic compounds. They are derivatives of ammonia (NH3), in which one or more hydrogen atoms in the ammonia molecule are replaced by a hydrocarbon group (R). Amine molecules contain an amino group (-NH2 or -NHR). Optionally, amines contain at least two amino groups.

[0035] The isocyanate group in isocyanate compounds can react with the amino group in amine compounds to form urethane bonds or urea bonds. In other words, the organic polymer forming shell material 2 has urethane bonds and / or urea bonds.

[0036] The structural formula of the urea bond is shown below: , The urea bond functional groups on the surface of the thermoresponsive microcapsule 10 can be detected by Fourier transform infrared spectroscopy (FT-IR). The urea bonds have a 1630 cm⁻¹ diameter. -1 ~1680cm -1 The infrared characteristic absorption band.

[0037] The structural formula of the carbamate bond is shown below: , The urethane functional groups on the surface of the thermoresponsive microcapsule 10 can also be detected by FT-IR, and the urethane bonds have a 1730 cm⁻¹ diameter. -1 ~1755cm -1 The infrared characteristic absorption band.

[0038] Thermally responsive crosslinking agents are crosslinking agents containing thermally responsive functional groups. These functional groups can break down upon heating. For example, the thermally responsive functional groups are azo bonds or peroxide bonds. Thermally responsive crosslinking agents participate in polymerization reactions together with isocyanate compounds and amine compounds, thus introducing the thermally responsive functional groups of the crosslinking agent into the resulting organic polymer.

[0039] For example, see Figure 2 A thermoresponsive functional group B (e.g., an azo bond) is introduced into an organic polymer network A (e.g., a polyurea network). When the thermoresponsive functional group B is broken by heat, the organic polymer network A ruptures, thereby forming voids in the shell material 2. The core material 1 inside the shell material 2 can then leak out through these voids. It is understandable that the thermal stability of the shell material 2 decreases after the thermoresponsive functional group is introduced into it.

[0040] To more clearly illustrate the polymerization reaction between isocyanate compounds, thermoresponsive crosslinking agents, and amine compounds, the following example uses toluene diisocyanate (TDI) as the isocyanate compound, ethylenediamine as the amine compound, and azodicyanovalerate (ACPA) as the thermoresponsive crosslinking agent. Please refer to [link to relevant documentation]. Figure 3 Toluene diisocyanate undergoes a polymerization reaction with ethylenediamine to form the main organic polymer network; please refer to [link to relevant documentation]. Figure 4 Toluene diisocyanate can also undergo polymerization with azodicyanovalerate to introduce azo compounds into the organic polymer network chain.

[0041] The shell material 2 of the thermoresponsive microcapsule 10 provided in this application embodiment is polymerized from isocyanate compound, thermoresponsive crosslinking agent and amine compound. In this way, thermoresponsive functional groups in the thermoresponsive crosslinking agent are introduced into the shell material 2. By utilizing the characteristic of the thermoresponsive functional groups to break when heated, the rupture of the shell material 2 is temperature controlled, thereby realizing the release of the temperature-controlled core material 1.

[0042] This thermally responsive core-shell structure can be used to coat promoters, other water-insoluble compounds, or other highly active compounds, thus being compatible with a variety of systems and application scenarios to achieve temperature-controlled triggering.

[0043] Liquid molding compound (LMC) is a key material in electronic packaging used to protect the reliability of chips and their electronic components under humid and thermal conditions. Its composition typically includes epoxy resin, inorganic fillers, curing agents, and other additives. During the curing process, a three-dimensional network structure is formed through the cross-linking reaction between the epoxy groups and the curing agent, resulting in excellent electrical insulation, high mechanical strength, and outstanding chemical corrosion resistance. This effectively protects the chip from adverse effects such as external humidity, corrosion, and mechanical damage.

[0044] In recent years, with the widespread adoption of advanced packaging integration architectures such as fan-out wafer-level packaging and 2.5D / 3D, the number of heterogeneous interfaces within the package has increased significantly, and heat-sensitive components are becoming more densely packed. This poses a severe challenge to the curing characteristics of low-temperature ceramic capacitors (LMCs). High-temperature curing processes can lead to a mismatch in the coefficients of thermal expansion between different materials, resulting in significant residual stress and affecting their performance and reliability. More and more heat-sensitive components cannot withstand prolonged high-temperature environments. Furthermore, reducing thermal energy consumption is essential to meet the demands of green manufacturing. Therefore, developing LMC systems suitable for medium- and low-temperature curing (e.g., 80℃~120℃) while also possessing good process applicability and storage stability has become an urgent need in the field of electronic packaging materials.

[0045] The main problem with existing low-temperature curing processes for LMC is the difficulty in balancing accelerator reactivity and storage stability. Latent accelerators have good room temperature stability, but often require higher temperatures to trigger the reaction, making them unsuitable for low-temperature curing systems. High-activity low-temperature accelerators, on the other hand, react at room temperature, which is inconvenient for actual production, transportation, and storage. Therefore, balancing the room temperature stability and low-temperature reactivity of accelerators during LMC curing is a current research challenge. To address the difficulty in balancing accelerator reactivity and storage stability in the low-temperature curing process of liquid epoxy molding compounds, this application proposes a microencapsulation technique to encapsulate highly reactive compounds (such as accelerators) as an improvement.

[0046] In some embodiments of this application, the core material 1 includes an accelerator.

[0047] Epoxy resin-anhydride systems require high curing temperatures, so accelerators are typically added to accelerate the curing reaction. Commonly used accelerators, such as imidazole compounds, catalyze the ring-opening of the anhydride in the system by donating lone pairs of electrons from the nitrogen atoms on the ring. This releases nucleophilic sites, which then attack the epoxy groups in the epoxy resin, initiating a cross-linking polymerization reaction. However, different accelerators have varying reactivity. Selecting a suitable accelerator while balancing production and storage stability, and ensuring compatibility with medium- and low-temperature curing processes, has always been a challenge in the industry.

[0048] This is because epoxy resin systems using only anhydride curing agents typically require high curing temperatures. Small amounts of accelerators are usually added to lower the curing temperature and accelerate the curing rate. However, the matching of accelerators is crucial. Latent accelerators are highly stable at room temperature, but also have high activation temperatures for the reaction. Room temperature accelerators already have high reactivity at room temperature, thus limiting their suitability for room temperature production and storage.

[0049] This application embodiment designs a core-shell microcapsule structure with a shell containing thermoresponsive functional groups, encapsulating a highly active accelerator as the core material to ensure stability during room temperature production and storage. When the temperature is raised to a set level, the thermoresponsive functional groups in the shell 2 break down, causing the organic polymer network to rupture and form voids. The highly active accelerator encapsulated in the shell 2 is released and transferred to the epoxy resin system, immediately catalyzing the system to cure and crosslink. In other words, by designing a thermoresponsive microcapsule structure, the release of the highly active accelerator is temperature-controlled.

[0050] Therefore, based on the design of the polyurea shell wall, this application introduces thermoresponsive functional groups into the hybrid polyurea network, providing a new approach for temperature-controlled sustained-release of highly active compounds. Furthermore, using this thermoresponsive microcapsule structure to encapsulate highly active promoters achieves high stability at room temperature and rapid release of the core material under medium- and low-temperature conditions, thereby precisely triggering the crosslinking reaction between the epoxy resin and the curing agent. This design can construct an LMC system with controllable reaction characteristics, providing a new solution for the advanced packaging industry.

[0051] In some embodiments of this application, the accelerator is an imidazole compound. Imidazole compounds are a very important class of accelerators in epoxy resin curing technology, typically achieving curing at 60°C to 150°C (i.e., achieving medium-temperature curing), and in particular, significantly reducing the curing temperature of anhydride or dicyandiamide systems. Optionally, the imidazole compound includes at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecanylimidazole, 2-phenylimidazole, 1-aminoethyl-2-methylimidazole, 1-(2-hydroxy-3-phenoxypropyl)-2-methylimidazole, and 1-(2-hydroxy-3-phenoxypropyl)-2-ethyl-4-methylimidazole.

[0052] In some embodiments of this application, the shell material 2 is polymerized from a composition comprising (5-30) parts of isocyanate compound, (0.1-5) parts of thermoresponsive crosslinking agent, and (5-30) parts of amine compound, by weight. The isocyanate compound, thermoresponsive crosslinking agent, and amine compound are all used as polymerization raw materials for the shell material 2. The isocyanate compound and amine compound are used to polymerize and form the main organic polymer network of the shell material 2, while the thermoresponsive crosslinking agent is mainly used to introduce thermoresponsive functional groups into the organic polymer network. Therefore, the amount of thermoresponsive crosslinking agent is generally no higher than the amount of isocyanate compound, nor higher than the amount of amine compound, thereby ensuring the stability and mechanical strength of the shell material 2. As an example, the amount of isocyanate compound used is 5 parts, 10 parts, 15 parts, 20 parts, 25 parts or 30 parts by mass, the amount of thermally responsive crosslinking agent used is 0.1 parts, 1 part, 2 parts, 3 parts, 4 parts or 5 parts, and the amount of amine compound used is 5 parts, 10 parts, 15 parts, 20 parts, 25 parts or 30 parts.

[0053] Furthermore, the thermoresponsive microcapsule 10 comprises (5~90) parts of core material 1 by weight. By simultaneously controlling the amount of polymer raw material in the shell material 2 and the amount of core material 1, it can be ensured that the formed shell material 2 effectively encapsulates the core material 1. As an example, the mass parts of core material 1 in the thermoresponsive microcapsule 10 are 5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 parts.

[0054] In some embodiments of this application, the thermoresponsive crosslinking agent includes at least one of an azo compound and a peroxide. When the thermoresponsive crosslinking agent is an azo compound, the azo bonds of the azo compound are introduced as thermoresponsive functional groups into the organic polymer network of the shell material 2; when the thermoresponsive crosslinking agent is a peroxide, the peroxide bonds of the peroxide are introduced as thermoresponsive functional groups into the organic polymer network of the shell material 2, thereby achieving temperature-controlled cracking of the shell material 2.

[0055] In some embodiments of this application, the azo compound includes at least one of a monofunctional azo compound and a difunctional azo compound.

[0056] When the thermally responsive crosslinking agent used is an azo compound, the azo bond in this type of compound will break at the target temperature, generating two carbon-centered free radicals and releasing nitrogen gas. The generated free radicals can attack the polymer backbone and reduce the crosslinking density. The nitrogen gas generated by decomposition can provide additional shell-breaking pressure from the inside, further improving the efficiency of releasing core material 1 (e.g., accelerator) at the target temperature. The above mechanisms work synergistically to achieve shell breaking of microcapsules at the target temperature, thereby releasing core material 1.

[0057] A difunctional azo compound contains two independent, chemically reactive functional groups linked together by an azo bond (-N=N-). A monofunctional azo compound contains only one functional group.

[0058] In some embodiments of this application, the structural formula of the difunctional azo compound is shown in formula (Ⅰ): Equation (Ⅰ); In formula (Ⅰ), R1 and R2 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

[0059] The thermal decomposition temperature of the aforementioned difunctional azo compounds is 50℃~120℃, which can be well matched with the low-temperature curing process of LMC.

[0060] R1 and R2 can be the same or different. For example, both R1 and R2 may be carboxyl groups (-COOH); or both R1 and R2 may be hydroxyl groups (-OH); or both R1 and R2 may be amino groups; or R1 may be carboxyl and R2 may be hydroxyl; or R1 may be hydroxyl and R2 may be amino; or R1 may be hydroxyl and R2 may be amino. The amino group can be a primary amine (-NH2), a secondary amine (-NRH), or a ketimine-protected amino group.

[0061] Optionally, the difunctional azo compound includes at least one of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobiscyanopentanoic acid (ACPA), 4,4-diaminoazobenzeneazo, and diisopropylimidazoline.

[0062] In some embodiments of this application, the peroxide includes a difunctional peroxide, the structural formula of which is shown in formula (II): Equation (II); In formula (II), R3 and R4 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

[0063] The thermal decomposition temperature of the aforementioned difunctional peroxide is 80℃~150℃, which can be well matched with the low-temperature curing process of LMC.

[0064] R3 and R4 can be the same or different. For example, both R3 and R4 are carboxyl groups (-COOH); or both R3 and R4 are hydroxyl groups (-OH); or both R3 and R4 are amino groups; or R3 is a carboxyl group and R4 is a hydroxyl group; or R3 is a hydroxyl group and R4 is an amino group; or R3 is a hydroxyl group and R4 is an amino group.

[0065] In some embodiments of this application, the isocyanate compound includes at least one selected from aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, aliphatic triisocyanates, and polyisocyanates. Aliphatic diisocyanates include at least one selected from ethylene diisocyanate, propylene diisocyanate, butyl diisocyanate, and trimethylhexamethylene diisocyanate. Alicyclic diisocyanates include at least one selected from 4,4-cycloethylmethane diisocyanate, norbornane diisocyanate, and 1,4-diisocyanocyclohexane. Aromatic diisocyanates include at least one selected from toluene diisocyanate, 4,4-diphenylmethane diisocyanate, xylene diisocyanate, and 1,5-naphthalene diisocyanate. Aliphatic triisocyanates include at least one selected from 1,6,11-undecane triisocyanate, 1,8-diisocyanato-4-isocyanate-methyloctane, and 1,3,6-triisocyanate-methylethane. Polyisocyanates include at least one of polymethylene polyphenyl polyisocyanates, carbamate-type p-isocyanates, and urethane-type polyisocyanates.

[0066] In some embodiments of this application, the amine compounds include at least one of aliphatic amine compounds, alicyclic amine compounds, and aromatic amine compounds. The aliphatic amine compounds include at least one of small molecule amine compounds and polymeric amine compounds; wherein the small molecule amine compounds include at least one of methylamine, ethylamine, propylamine, butylamine, ethylenediamine, diethylenetriamine, hexamethylenediamine, 2-hydroxyethylethylenediamine, and tetraethylenepentamine; and the polymeric amine compounds include at least one of polyetheramine, polyethyleneimine, and polyallylamine. The alicyclic amine compounds include at least one of cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, and isophorone diamine. The aromatic amine compounds include at least one of aniline, toluidine, benzylamine, naphthylamine, m-phenylenediamine, and diaminodiphenyl sulfone.

[0067] In some embodiments of this application, the molar ratio of the isocyanate compound to the amine compound is 1:(1.1~2). The amount of the amine compound is greater than the amount of the isocyanate compound. For example, the molar ratio of the isocyanate compound to the amine compound is 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2.0.

[0068] Secondly, embodiments of this application also provide a method for preparing thermoresponsive microcapsules, comprising: S1. Mix the core material, isocyanate compound, thermally responsive crosslinking agent and organic solvent to obtain an oil phase mixture; S2. Mix the emulsifier and water to obtain an aqueous mixture; S3. Mix the amine compound with water to obtain the wall-forming reaction solution; S4. Mix the oil phase mixture and the water phase mixture to obtain a water-oil mixture; S5. Reduce the temperature of the water-oil mixture to below 10°C, and then stir and emulsify the water-oil mixture to obtain an oil-in-water emulsion. S6. Under stirring conditions, the wall-forming reaction liquid is added dropwise to the oil-in-water emulsion to obtain the reaction liquid; S7. Control the reaction solution to carry out the polymerization reaction to obtain thermally responsive microcapsules.

[0069] This application describes the preparation of thermoresponsive microcapsules with a core-shell structure using interfacial polymerization. By introducing a thermoresponsive crosslinking agent, a dense hybrid organic polymer shell is endowed with thermoresponsive functional groups. When the temperature reaches a critical value, the chemical bonds in the thermoresponsive functional groups break upon heating, causing the organic polymer network to disintegrate and releasing the core material encapsulated within the shell.

[0070] The preparation of microcapsules mainly utilizes emulsification technology, in which a mixed solution including accelerators, thermally responsive crosslinking agents, and isocyanate compounds is uniformly dispersed in an aqueous solution of mixed amine compounds, and interfacial polymerization is carried out by stirring and emulsification.

[0071] The above-described method for preparing thermoresponsive microcapsules is used to prepare the thermoresponsive microcapsules provided in the first aspect. The raw materials, such as the core material, isocyanate compound, thermoresponsive crosslinking agent, and amine compound, used in the preparation are the same as those described in the first aspect, and will not be repeated here.

[0072] In some embodiments of this application, the organic solvent includes at least one selected from hydrocarbon solvents, ketone solvents, ester solvents, and alcohol solvents. Hydrocarbon solvents include at least one selected from benzene, toluene, xylene, cyclohexane, and petroleum ether. Ketone solvents include at least one selected from acetone, methyl ethyl ketone, and methyl isobutyl ketone. Ester solvents include at least one selected from ethyl acetate, n-butyl acetate, and propylene glycol monomethyl ether acetate. Alcohol solvents include at least one selected from methanol, isopropanol, n-butanol, and butylcarbitol.

[0073] In some embodiments of this application, the emulsifier includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, Tween-80, and polyvinyl alcohol.

[0074] In some embodiments of this application, by weight, the isocyanate compound is (5-30) parts, the core material is (5-90) parts, the azo compound is (0.1-5) parts, the organic solvent is (50-400) parts, the amine compound is (5-30) parts, the emulsifier is (0.1-10) parts, and the water is (400-1000) parts. As an example, in the preparation of the thermoresponsive microcapsules, by weight, the amount of isocyanate compound used is 5, 10, 15, 20, 25, or 30 parts; the amount of core material used is 5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 parts; the amount of azo compound used is 0.1, 1, 2, 3, 4, or 5 parts; and the amount of organic solvent used is... 50 parts, 100 parts, 150 parts, 200 parts, 250 parts, 300 parts, 350 parts or 400 parts; amine compounds in amounts of 5 parts, 10 parts, 15 parts, 20 parts, 25 parts or 30 parts; emulsifiers in amounts of 0.1 parts, 1 part, 2 parts, 4 parts, 6 parts, 8 parts or 10 parts; and water in amounts of 400 parts, 500 parts, 600 parts, 700 parts, 800 parts, 900 parts or 1000 parts.

[0075] In some embodiments of this application, the stirring rate of the stirring emulsification process is 500 rpm to 20000 rpm, and the emulsification time is 1 min to 30 min. Optionally, the stirring emulsification process involves high-speed shearing and emulsification using a high-speed homogenizer or stirrer to obtain an oil-in-water (O / W) emulsion. As examples, the stirring rate is 500 rpm, 1000 rpm, 5000 rpm, 10000 rpm, 15000 rpm, or 20000 rpm, and the emulsification time is 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. Here, rpm refers to revolutions per minute.

[0076] In some embodiments of this application, the temperature of the oil-in-water emulsion is controlled to not exceed 15°C during the dropwise addition process, and the dropwise addition time of the wall-forming reaction solution is 10 min to 60 min. During the dropwise addition process, the oil-in-water emulsion is stirred using a mechanical stirring device while the wall-forming reaction solution is slowly added dropwise to the oil-in-water emulsion. As examples, the dropwise addition time is 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min.

[0077] In some embodiments of this application, the polymerization temperature is -10℃ to 50℃, and the polymerization duration is 30 min to 72 h. After the wall liquid is added dropwise, the reaction solution is subjected to polymerization at a set temperature. During the reaction, the isocyanate peak in the reaction solution is detected by infrared spectroscopy. The reaction ends when the isocyanate peak disappears, resulting in microcapsules coated with a core material (e.g., an accelerator). The polymerization temperature is -10℃ to 50℃, optionally 10℃ to 40℃. As examples, the polymerization temperature is -10℃, 0℃, 10℃, 20℃, 30℃, 40℃, or 50℃. The polymerization duration is 30 min to 72 h, optionally 30 min to 24 h. As examples, the polymerization duration is 30 min, 1 h, 6 h, 12 h, 24 h, 36 h, 48 h, 60 h, or 72 h.

[0078] This application also provides a liquid epoxy molding compound, which includes: liquid epoxy resin, curing agent, and the above-mentioned thermoresponsive microcapsules or thermoresponsive microcapsules prepared by the above-mentioned method, wherein the core material includes an accelerator.

[0079] Thermoresponsive microcapsules are introduced into the formulation of liquid epoxy molding compounds. Due to this temperature-controlled release core-shell structure, the stability of the highly active accelerator is effectively protected during production, processing, and storage at room temperature. However, when the temperature is heated to the critical value of the thermoresponsive valence bonds, the 'weaknesses' on these shell materials are triggered, causing the covalent bonds to break, forming voids, and releasing the core material inside the shell. That is, the highly active accelerator encapsulated in the shell is released and transferred to the liquid epoxy molding compound formulation system, immediately catalyzing the curing and cross-linking of the formulation system, ultimately enabling the liquid epoxy molding compound to achieve a rapid, medium-to-low temperature curing effect.

[0080] The thermoresponsive microcapsules described above, or the thermoresponsive microcapsules prepared by the above method, are used in liquid epoxy molding compounds and exhibit rapid medium-to-low temperature curing. The medium-to-low temperature range is 60℃ to 90℃. For example, any one or any two of 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, and 90℃.

[0081] This application embodiment utilizes thermoresponsive microcapsules containing accelerators as the core material in liquid epoxy molding compounds, effectively reducing the curing temperature of epoxy resin and curing agents (especially anhydride systems). The encapsulated accelerators have high reactivity and, upon release, can rapidly catalyze the curing reaction, improving curing efficiency and achieving rapid curing at medium to low temperatures. Furthermore, the core-shell structure of the thermoresponsive microcapsules ensures the stability of the highly active components within the shell material during the production, processing, and storage of the liquid epoxy molding compound.

[0082] In some embodiments of this application, the content of thermoresponsive microcapsules in the liquid epoxy molding compound is 0.1wt% to 1.5wt%. As examples, the content of thermoresponsive microcapsules is 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, or 1.5wt%.

[0083] In some embodiments of this application, the liquid epoxy molding compound contains 10wt% to 20wt% of liquid epoxy resin. As examples, the content of liquid epoxy resin is 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%.

[0084] In some embodiments of this application, the content of the curing agent in the liquid epoxy molding compound is 5wt% to 15wt%. As examples, the content of the curing agent is 5wt%, 7wt%, 9wt%, 11wt%, 13wt%, or 15wt%.

[0085] In some embodiments of this application, the curing agent is liquid at room temperature and includes at least one of diethyltoluenediamine, dimethylthiotoluenediamine, 4,4'-diaminodiphenyl sulfone, 4-ethylaniline, diethyltoluenediamine, 2-ethylaniline, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, trimethylhexanediamine, m-phenylenediamine, m-phenylenediamine, methyltetrahydrophthalic anhydride, modified methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, methylnadic anhydride, and dodecenylsuccinic anhydride.

[0086] In some embodiments of this application, the liquid epoxy resin includes at least one of monoepoxy compounds and polyepoxy compounds. Optionally, the liquid epoxy resin includes monoepoxy compounds and polyepoxy compounds, or the liquid epoxy resin includes multiple polyepoxy compounds. As examples, the polyepoxy compounds include at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, cresol phenolic varnish, 3,4-epoxycyclohexylmethyl methacrylate, 3,4-epoxycyclohexylformate-3',4'-epoxycyclohexylmethyl ester, 3,4-epoxycyclohexene methyl-3,4-epoxycyclohexene ester, 4-vinyl-1-cyclohexene diepoxide, aminophenol type epoxy resin, and naphthalene-based epoxy resin.

[0087] In some embodiments of this application, the liquid epoxy molding compound further includes filler in a content of 70wt% to 90wt%. In this case, the filler constitutes the majority of the liquid epoxy molding compound, and increasing the filler content can improve the mechanical strength of the liquid epoxy molding compound after curing.

[0088] In some embodiments of this application, the filler is an inorganic filler, including at least one selected from silicon dioxide, alumina, silicon nitride, boron nitride, aluminum nitride, and silicon carbide. Optionally, the inorganic filler includes spherical silicon dioxide with an average particle size of 1 μm to 30 μm. As an example, the average particle size of the spherical silicon dioxide is 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm.

[0089] In some embodiments of this application, the liquid epoxy molding compound further includes a modifier in an amount of 0.1 wt% to 5 wt%. As an example, the modifier content in the liquid epoxy molding compound is 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Optionally, the modifier includes an alkoxysilane compound. The alkoxysilane compound includes at least one selected from the following: alkoxysilane compounds having a primary amino group, alkoxysilane compounds having a secondary amino group, alkoxysilane compounds having a tertiary amino group, alkoxysilane compounds having an epoxy group, alkoxysilane compounds having a mercapto group, alkoxysilane compounds having an alkyl group, alkoxysilane compounds having a urea group, and alkoxysilane compounds having a vinyl group.

[0090] In some embodiments of this application, the liquid epoxy molding compound further includes a stress-relieving agent in a content of 0.1 wt% to 5 wt%. As an example, the stress-relieving agent content in the liquid epoxy molding compound is 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Optionally, the stress-relieving agent includes at least one of the following: polysiloxane-structured epoxy-modified silicone oil, liquid silicone rubber, organosilicon-modified epoxy resin, polyether elastomer, polyurethane, styrene-butadiene copolymer, and their derivatives. Further, the stress-relieving agent is selected from at least one of acrylonitrile-butadiene-styrene copolymer, epoxy-terminated styrene-butadiene-styrene block copolymer, epoxidized styrene-butadiene-styrene block copolymer, styrene-butadiene rubber, carboxyl-terminated liquid nitrile butadiene rubber (CTBN), and hydroxyl-terminated liquid nitrile butadiene rubber (HTBN).

[0091] In some embodiments of this application, the liquid epoxy molding compound further includes a diluent in an amount of 0.1 wt% to 5 wt%. As an example, the diluent content in the liquid epoxy molding compound is 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%. Optionally, the diluent includes at least one of polypropylene glycol diglycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, tolyl glycidyl ether, p-sec-butylphenyl glycidyl ether, allyl glycidyl ether, glycidyl methacrylate, glycidyl acrylate, or 1-vinyl-3,4-epoxycyclohexane, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerol triglycidyl ether.

[0092] In some embodiments of this application, the liquid epoxy molding compound further includes a colorant in a content of 0.1wt% to 1wt%. As an example, the colorant content in the liquid epoxy molding compound is 0.1wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, or 1wt%. As an example, the colorant is carbon black.

[0093] In some embodiments of this application, the liquid epoxy molding compound further includes a defoamer at a content of 0.01wt% to 0.5wt%. As an example, the defoamer content in the liquid epoxy molding compound is 0.01wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, or 0.5wt%. As an example, the defoamer is an acrylic copolymer.

[0094] In some embodiments of this application, the preparation method of liquid epoxy molding compound includes: S21. The liquid epoxy resin is stirred and mixed with stress-relieving agent, diluent, colorant and defoamer to obtain the first mixture; S22. Add the curing agent and filler to the first mixture, continue to add the thermally responsive microcapsules, stir, and obtain the liquid molding compound.

[0095] In step S21, the stirring speed is 800 rpm to 1800 rpm, and the stirring time is 1 min to 6 min. In step S22, the filler is added in multiple batches (e.g., three batches), with each addition requiring a stirring speed of 800 rpm to 1800 rpm and a stirring time of 1 min to 6 min. In step S22, after adding the thermoresponsive microcapsules, the stirring speed is 1200 rpm to 2000 rpm, and the stirring time is 1 min to 4 min.

[0096] Preparation Example 1 This preparation example provides a thermoresponsive microcapsule, and the preparation process of the thermoresponsive microcapsule is as follows: S1. In a dry beaker, weigh 5.0 g of toluene diisocyanate (TDI), 0.3 g of azodicyanovalerate (ACPA), and 10.0 g of 2-ethyl-4-methylimidazolium. Add 80 ml of ethyl acetate and heat at 30 °C with thorough stirring to completely dissolve or uniformly disperse the above components, obtaining the oil phase.

[0097] S2. In a three-necked flask, take 500 ml of deionized water to prepare a 2 wt% polyvinyl alcohol solution to prepare the aqueous phase.

[0098] S3. Dissolve 2.5g of ethylenediamine in 200ml of deionized water and stir well to obtain the wall-forming reaction solution.

[0099] S4. Place an ice bath device and slowly add the oil phase to the aqueous phase using a syringe. Keep the temperature of the water-oil mixture below 10°C and emulsify for 5 minutes under high-speed shear at 8000 rpm to prepare a stable oil-in-water emulsion.

[0100] S5. Then switch to a mechanical stirrer, set the speed to 500 rpm, and slowly add the wall-forming reaction solution, keeping the emulsion temperature below 15°C during the dropwise addition. After the wall solution has been added in 30 minutes, remove the ice bath. Then, react at room temperature for 2 hours, then raise the temperature to 40°C and continue the reaction for 2 hours.

[0101] S6. After the reaction is complete, cool to room temperature and wash the system three times each with ethyl acetate and deionized water to remove unreacted monomers and emulsifiers. Then, dry the solid in a vacuum drying oven at 25°C for 24 hours.

[0102] Preparation Example 2 This preparation example provides a thermoresponsive microcapsule, and the preparation process of the thermoresponsive microcapsule is as follows: S1. In a dry beaker, weigh 5.0 g of toluene diisocyanate (TDI), 0.3 g of ACPA, and 5 g of 2-ethyl-4-methylimidazole. Add 80 ml of ethyl acetate and heat at 30 °C with stirring until the components are completely dissolved or uniformly dispersed to obtain the oil phase.

[0103] S2. In a three-necked flask, take 500 ml of deionized water to prepare a 2 wt% polyvinyl alcohol solution to prepare the aqueous phase.

[0104] S3. Dissolve 2.5g of ethylenediamine in 200ml of deionized water and stir well to obtain the wall-forming reaction solution.

[0105] S4. Place an ice bath device and slowly add the oil phase to the aqueous phase using a syringe. Keep the temperature of the water-oil mixture below 10°C and emulsify for 5 minutes under high-speed shear at 8000 rpm to prepare a stable oil-in-water emulsion.

[0106] S5. Then switch to a mechanical stirrer, set the speed to 500 rpm, and slowly add the wall-forming reaction solution, keeping the emulsion temperature below 15°C during the dropwise addition. After the wall solution has been added in 30 minutes, remove the ice bath. Then, react at room temperature for 2 hours. Subsequently, raise the temperature to 40°C and continue the reaction for 2 hours.

[0107] S6. After the reaction is complete, cool to room temperature and wash the system three times each with ethyl acetate and deionized water to remove unreacted monomers and emulsifiers. Then, dry the solid in a vacuum drying oven at 25°C for 24 hours.

[0108] Preparation Example 3 This preparation example provides a thermoresponsive microcapsule, and the preparation process of the thermoresponsive microcapsule is as follows: S1. In a dry beaker, weigh 5.0 g of toluene diisocyanate (TDI), 0.1 g of ACPA, and 10.0 g of 2-ethyl-4-methylimidazole. Add 80 ml of ethyl acetate and heat at 30 °C with thorough stirring to completely dissolve or uniformly disperse the above components, obtaining the oil phase.

[0109] S2. In a three-necked flask, take 500 ml of deionized water to prepare a 2 wt% polyvinyl alcohol solution to prepare the aqueous phase.

[0110] S3. Dissolve 2.5g of ethylenediamine in 200ml of deionized water and stir well to obtain the wall-forming reaction solution.

[0111] S4. Place an ice bath device and slowly add the oil phase to the aqueous phase using a syringe. Keep the temperature of the water-oil mixture below 10°C and emulsify for 5 minutes under high-speed shear at 8000 rpm to prepare a stable oil-in-water emulsion.

[0112] S5. Then switch to a mechanical stirrer, set the speed to 500 rpm, and slowly add the wall-forming reaction solution, keeping the emulsion temperature below 15°C during the dropwise addition. After the wall solution has been added in 30 minutes, remove the ice bath. Then, react at room temperature for 2 hours. Subsequently, raise the temperature to 40°C and continue the reaction for 2 hours.

[0113] S6. After the reaction is complete, cool to room temperature and wash the system three times each with ethyl acetate and deionized water to remove unreacted monomers and emulsifiers. Then, dry the solid in a vacuum drying oven at 25°C for 24 hours.

[0114] Preparation Example 4 This preparation example provides a thermoresponsive microcapsule. The preparation process of the thermoresponsive microcapsule is described in Preparation Example 3, except that the amount of ACPA used in S1 is 0.5g.

[0115] Examples 1-4 This embodiment provides a liquid epoxy molding compound. Please refer to Table 1. The preparation process of this liquid epoxy molding compound is as follows: Bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin - 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, stress absorber terminal carboxyl liquid nitrile rubber (CTBN), diluent polypropylene glycol diglycidyl ether, colorant carbon black, and acrylic defoamer were mixed uniformly at 1500 rpm for 5 min. Then, the curing agent methyl hexahydrophthalic anhydride and silica filler were added to the above mixture in three batches, with each addition of filler being stirred at 1500 rpm for 5 min. Finally, referring to Table 2, the thermoresponsive microencapsulated accelerators (C-1, C-2, C-3, C-4) were added to the mixture and stirred at 1800 rpm for 3 min to obtain the liquid epoxy molding compound.

[0116] Table 1

[0117] Table 2

[0118] Comparative Example 1 Bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin - 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, stress absorber terminal carboxyl liquid nitrile rubber (CTBN), diluent polypropylene glycol diglycidyl ether, colorant carbon black, and acrylic defoamer are mixed evenly at 1500 rpm for 5 min. Then, the curing agent methyl hexahydrophthalic anhydride and silica filler are added to the above mixture in three batches, and the mixture is stirred at 1500 rpm for 5 min after each addition of filler to obtain liquid epoxy molding compound.

[0119] Comparative Example 2 Bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin - 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, stress absorber terminal carboxyl liquid nitrile rubber (CTBN), diluent polypropylene glycol diglycidyl ether, colorant carbon black, and acrylic defoamer were mixed evenly at 1500 rpm for 5 min. Then, the curing agent methyl hexahydrophthalic anhydride and silica filler were added to the above mixture in three batches, with each addition of filler being stirred at 1500 rpm for 5 min. Finally, the common accelerator imidazole accelerator was added to the mixture, and the mixture was stirred at 1800 rpm for 3 min to obtain liquid epoxy molding compound.

[0120] Performance testing The prepared microcapsules were subjected to the following performance tests, and the test methods were as follows: 1. Transmission electron microscopy (TEM): The size and structure of the thermoresponsive microcapsules prepared in Example 1 were observed, and the results are as follows: Figure 5 As shown. From Figure 5 As can be seen, the diameter of the thermoresponsive microcapsules is approximately 157.27 nm, and the microcapsules are nearly spherical in shape with a distinct core-shell structure. Figure 5 The dark area in the center of the circular area corresponds to the core material, and the light area surrounding the dark area corresponds to the shell material.

[0121] 2. Differential Scanning Calorimetry (DSC): This method was used to determine the microcapsule breakage temperature and the exothermic curing peak of the released core material. For each measurement, the sample was placed in an aluminum standard dish. The test temperature range was from room temperature to 220°C. The temperature characteristic curve was generated by heating to the set endpoint at a rate of 5°C / min, followed by cooling to the initial temperature at a rate of 5°C / min. The test results are recorded in Table 3.

[0122] Table 3

[0123] Results analysis: As can be seen from the test results in Table 3, the quality of ACPA differs between Examples 1, 3, and 4. This difference affects the efficiency of the release promoter. The results show that the higher the ACPA content, the earlier the DSC inflection point.

[0124] As can be seen from Example 1 compared to Example 2, the content of the core material is directly related to the curing efficiency of LMC. The higher the content of the core material, the earlier the curing temperature is.

[0125] Comparative Example 1, without the addition of an accelerator, showed that the DSC onset temperature was 118°C. Without the presence of an accelerator, the curing temperature of the epoxy resin-anhydride system was higher.

[0126] Comparative Example 2, with the addition of a common accelerator, had an initial temperature of 50°C. Without the protection of a core-shell structure, the curing reaction started at a lower temperature.

[0127] The foregoing has provided a detailed description of a thermoresponsive microcapsule and its preparation method, as well as a liquid epoxy molding compound, provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A thermoresponsive microcapsule, characterized in that, It includes a core material and a shell material covering the core material, the shell material being polymerized from isocyanate compounds, thermally responsive crosslinking agents, and amine compounds.

2. The thermoresponsive microcapsule according to claim 1, characterized in that, The core material includes an accelerator.

3. The thermoresponsive microcapsule according to claim 2, characterized in that, The accelerator is an imidazole compound.

4. The thermoresponsive microcapsule according to claim 3, characterized in that, The imidazole compounds include at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-aminoethyl-2-methylimidazole, 1-(2-hydroxy-3-phenoxypropyl)-2-methylimidazole, and 1-(2-hydroxy-3-phenoxypropyl)-2-ethyl-4-methylimidazole.

5. The thermoresponsive microcapsule according to any one of claims 1 to 4, characterized in that, The thermoresponsive crosslinking agent includes at least one of azo compounds and peroxides.

6. The thermoresponsive microcapsule according to claim 5, characterized in that, The azo compound includes at least one of monofunctional azo compounds and difunctional azo compounds.

7. The thermoresponsive microcapsule according to claim 6, characterized in that, The structural formula of the difunctional azo compound is shown in formula (Ⅰ): Equation (Ⅰ); In formula (Ⅰ), R1 and R2 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

8. The thermoresponsive microcapsule according to claim 5, characterized in that, The peroxide includes a difunctional peroxide, the structural formula of which is shown in formula (II): Equation (II); In formula (II), R3 and R4 are each independently selected from one of the carboxyl, hydroxyl and amino groups.

9. The thermoresponsive microcapsule according to any one of claims 1 to 4, characterized in that, The shell material, by weight, is polymerized from a component comprising (5-30) parts of the isocyanate compound, (0.1-5) parts of the thermoresponsive crosslinking agent, and (5-30) parts of the amine compound.

10. The thermoresponsive microcapsule according to claim 9, characterized in that, The thermally responsive microcapsules comprise (5 to 90) parts of the core material by weight.

11. The thermoresponsive microcapsule according to any one of claims 1 to 4, characterized in that, The isocyanate compound includes at least one selected from aliphatic diisocyanates, alicyclic diisocyanates, aromatic diisocyanates, aliphatic triisocyanates, and polyisocyanates; and / or, The amine compounds include at least one of aliphatic amines, alicyclic amines, and aromatic amines; and / or, The molar ratio of the isocyanate compound to the amine compound is 1:(1.1~2).

12. The method for preparing thermoresponsive microcapsules according to any one of claims 1 to 11, characterized in that, include: The core material, isocyanate compound, thermally responsive crosslinking agent and organic solvent are mixed to obtain an oil phase mixture; The emulsifier and water are mixed to obtain an aqueous mixture; Amine compounds are mixed with water to obtain a wall-forming reaction solution; The oil phase mixture and the aqueous phase mixture are mixed to obtain a water-oil mixture; The temperature of the water-oil mixture is lowered to below 10°C, and the water-oil mixture is stirred and emulsified to obtain an oil-in-water emulsion. The wall-forming reaction solution was added dropwise to the oil-in-water emulsion under stirring conditions to obtain the reaction solution; The reaction solution is controlled to undergo a polymerization reaction to obtain thermally responsive microcapsules.

13. The method for preparing thermoresponsive microcapsules according to claim 12, characterized in that, By mass fractions, the isocyanate compound comprises (5-30) parts, the core material comprises (5-90) parts, the thermally responsive crosslinking agent comprises (0.1-5) parts, the organic solvent comprises (50-400) parts, the amine compound comprises (5-30) parts, the emulsifier comprises (0.1-10) parts, and the water comprises (400-1000) parts.

14. The method for preparing thermoresponsive microcapsules according to claim 12, characterized in that, The stirring rate for the emulsification process is 500 rpm to 20000 rpm, and the emulsification time is 1 min to 30 min; and / or, During the dropwise addition process, the temperature of the oil-in-water emulsion is controlled to not exceed 15°C, and the dropwise addition time of the wall-forming reaction solution is 10 min to 60 min; and / or, The polymerization reaction temperature is -10℃ to 50℃, and the polymerization reaction duration is 30 min to 72 h.

15. The method for preparing thermoresponsive microcapsules according to claim 12, characterized in that, The organic solvent includes at least one of hydrocarbon solvents, ketone solvents, ester solvents, and alcohol solvents; and / or, The emulsifier includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, Tween-80, and polyvinyl alcohol.

16. A liquid epoxy molding compound, characterized in that, The invention includes: liquid epoxy resin, curing agent, and thermoresponsive microcapsules prepared by the method of preparing thermoresponsive microcapsules as described in any one of claims 1 to 11 or as described in any one of claims 12 to 15, wherein the core material includes an accelerator.

17. The liquid epoxy molding compound according to claim 16, characterized in that, In the liquid epoxy molding compound, the content of the thermoresponsive microcapsules is 0.1wt%~1.5wt%; and / or, In the liquid epoxy molding compound, the content of the liquid epoxy resin is 10wt%~20wt%; and / or, In the liquid epoxy molding compound, the content of the curing agent is 5wt%~15wt%.

18. The liquid epoxy molding compound according to claim 16, characterized in that, The liquid epoxy resin comprises at least one of monoepoxy compounds and polyepoxy compounds. Optionally, the liquid epoxy resin comprises the polyepoxy compound, which includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, cresol phenolic varnish, 3,4-epoxycyclohexylmethyl methacrylate, 3,4-epoxycyclohexylformate-3',4'-epoxycyclohexylmethyl ester, 3,4-epoxycyclohexene methyl-3,4-epoxycyclohexene ester, 4-vinyl-1-cyclohexene diepoxide, aminophenol type epoxy resin, and naphthalene-based epoxy resin; and / or The curing agent includes at least one of diethyltoluenediamine, dimethylthiotoluenediamine, 4,4'-diaminodiphenyl sulfone, 4-ethylaniline, diethyltoluenediamine, 2-ethylaniline, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, trimethylhexanediamine, m-phenylenediamine, m-phenylenediamine, methyltetrahydrophthalic anhydride, modified methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, methylnadic anhydride, and dodecenylsuccinic anhydride.

19. The liquid epoxy molding compound according to any one of claims 16 to 18, characterized in that, The liquid epoxy molding compound also includes filler in a content of 70wt% to 90wt%, wherein the filler is an inorganic filler, and the inorganic filler includes at least one of silicon dioxide, alumina, silicon nitride, boron nitride, aluminum nitride and silicon carbide.

20. The liquid epoxy molding compound according to any one of claims 16 to 18, characterized in that, The liquid epoxy molding compound further includes a modifier at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a stress-relieving agent at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a diluent at a content of 0.1wt% to 5wt%; and / or, The liquid epoxy molding compound further includes a colorant at a content of 0.1wt% to 1wt%; and / or, The liquid epoxy molding compound also includes a defoamer at a content of 0.01wt% to 0.5wt%.

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