Polyurethane pouring sealant with heat-triggered dual defoaming mechanism as well as preparation method and application of polyurethane pouring sealant

Abstract

The invention discloses a polyurethane pouring sealant with a heat-triggered dual defoaming mechanism as well as a preparation method and application of the polyurethane pouring sealant. The pouring sealant composition comprises a polyurethane prepolymer, a curing agent and thermal triggering core-shell structure defoaming microspheres, the defoaming microsphere sequentially comprises an inner core containing a defoaming active substance and an outer core containing a defoaming active substance from inside to outside, the thermal softening polyurethane microgel middle layer is formed by carrying out partial cross-linking reaction on polycaprolactone polyol and polyether polyol, and the softening initial temperature of the thermal softening polyurethane microgel middle layer is 45-60 DEG C; a polymer chain of the organic silicon-polyurethane hybrid copolymer shell contains an active group capable of reacting with an isocyanate group. Delayed release in the curing heat release period is achieved through thermal softening of the middle layer, inner core defoaming components are delivered to a microbubble area, shell fragments are chemically bonded with a matrix, the bubble content after the pouring sealant is cured is remarkably reduced, the dielectric strength is improved, and the pouring sealant has excellent storage stability; the method is suitable for packaging protection of electronic devices needing to be heated and cured.

Description

Technical Field

[0001] This invention belongs to the field of potting compound technology, specifically relating to a polyurethane potting compound with a heat-triggered dual defoaming mechanism, its preparation method, and its application. Background Technology

[0002] Polyurethane potting compounds are widely used for the encapsulation and protection of electronic devices due to their excellent electrical insulation, adhesion, and aging resistance. However, the generation and residue of air bubbles are a persistent problem throughout the entire process, from mixing and potting to curing: during the mixing stage, mechanically entangled millimeter-sized air bubbles are difficult to escape due to high viscosity; during the potting and leveling stage, dynamically migrating air bubbles easily form macroscopic defects in structural dead corners; and during the most critical reaction and curing stage, the exothermic reaction of the system causes dissolved air to be released, while isocyanate reacts with trace amounts of moisture to generate carbon dioxide, forming a large number of micron-sized air bubbles. These air bubbles are trapped in the gel network and cannot be eliminated by migration or floating, significantly degrading the dielectric, thermal conductivity, and mechanical properties of the material.

[0003] Existing defoaming technologies have limitations and can only partially solve the problem. Physical defoaming methods are ineffective against microbubbles during the curing period; directly adding chemical defoamers faces the dilemma of having a single action stage, being unable to address both large bubbles in the early stage and microbubbles in the later stage, and being prone to causing interface defects if added in excess; although some defoaming materials with core-shell structures can achieve triggered release, they often rely on uncontrollable methods such as mechanical shearing, or introduce residual risks by using physical phase change materials, making it impossible to accurately match the thermal field changes during the polyurethane curing process, and also making it difficult to ensure that there are no micro-defects remaining in the matrix after defoaming.

[0004] Therefore, developing a defoaming system that can intelligently respond to the process, precisely act on the curing stage, and chemically integrate with the matrix to avoid introducing new defects has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the challenge that existing technologies cannot effectively control bubbles throughout the entire polyurethane potting process, especially in eliminating microbubbles during the curing period, this invention proposes a polyurethane potting compound composition with a thermally triggered dual defoaming mechanism. This composition contains thermally triggered core-shell structured defoaming microspheres: ① a high-Tg rigidity outer shell provides physical defoaming and protects the core in the early stages of the process; ② a middle layer with a specific softening temperature achieves precise thermal triggering with the curing exothermic reaction; ③ a reactive and integrated core and shell material ensures that no new defects appear in the matrix after defoaming.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A polyurethane potting compound composition with a heat-triggered dual defoaming mechanism, comprising a polyurethane prepolymer, a curing agent, and heat-triggered core-shell structured defoaming microspheres; the heat-triggered core-shell structured defoaming microspheres have a three-layer core-shell structure, comprising, from the inside out: The core contains defoaming active materials, including carrier silicone oil and hydrophobic silica; The intermediate layer is a heat-softening polyurethane microgel formed by a partial crosslinking reaction of polycaprolactone polyol and polyether polyol, wherein the softening onset temperature of the microgel, as determined by differential scanning calorimetry, is 45-60°C; and, The outer shell is a silicone-polyurethane hybrid copolymer, and its polymer chain contains active groups that can react with isocyanate groups.

[0007] The polyurethane prepolymer, as the main resin component of the colloid, is usually a polyether- or polyester-type prepolymer with isocyanate-terminated (-NCO) groups. The curing agent contains components that react with the polyurethane prepolymer, such as polyamine or polyol curing agents, chain extenders (such as 1,4-butanediol), catalysts (such as organotin compounds), and fillers (such as aluminum hydroxide and silica powder).

[0008] The heat-triggered core-shell structured defoaming microspheres are the core functional additive of this invention. The amount added is 0.1wt%-1.0wt% of the total weight of the potting compound composition, preferably 0.2wt%-0.8wt%, and more preferably 0.3wt%-0.6wt%. Specifically, it can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt%, 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1.0wt%, etc.

[0009] The thermally triggered core-shell structured defoaming microspheres have an average particle size D50 of 10-40 μm and a particle size distribution index (PDI) of less than 0.3 to ensure uniform and stable performance. The thermally triggered core-shell structured defoaming microspheres are functional units with a three-layer structure: from the inside out, a core layer serving as the active defoaming core, an intermediate layer serving as the thermal expansion trigger layer, and a shell layer providing rigid protection and physical defoaming function.

[0010] The core is a highly effective defoaming active ingredient whose function is to act directly on bubbles after release, especially micron-sized physical and chemical bubbles generated during the curing period. The core, by weight, comprises: 70-85 parts of carrier silicone oil: selected from at least one of dimethyl silicone oil, methylphenyl silicone oil, or fluorinated polysiloxane, with a viscosity range of 500-2000 cSt. This silicone oil acts as a dispersant, carrier, and spreader, and serves as a liquid carrier for defoaming.

[0011] 15-30 parts of hydrophobic silica: its specific surface area is 150-300 m² 2 / g, and treated with hydrophobic agents such as hexamethyldisilazane or dimethyldichlorosilane. This component can form defect points on the bubble liquid film, promoting the rupture of the liquid film.

[0012] 0-5 parts of penetration enhancer: can be selected from fluorinated polysiloxanes, etc., to enhance the penetration and diffusion ability of defoaming components in the gelation system.

[0013] The intermediate layer is a heat-softening polyurethane microgel formed by a partial crosslinking reaction of polycaprolactone polyol (PCL) and polyether polyol (PPG). Both PCL and PPG are reactive polymers with a functionality of not less than 3 and a number-average molecular weight (Mn) of 300-500 each. The weight mixing ratio of PCL to PPG ranges from 1:(0.25-4), preferably 1:(0.4-2), and more preferably 1:(0.4-1). Specifically, it can be 1:0.25, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, etc. By adjusting this ratio, the thermomechanical properties of the intermediate layer can be controlled. Specifically, the weight mixing ratio of PCL to PPG can be [specified]. The softening onset temperature of the microgel, determined by differential scanning calorimetry (DSC), is 45-60°C, and the peak temperature is 55-70°C. This temperature range is higher than the conventional storage and pre-construction temperatures (typically <40°C), ensuring that the microspheres maintain structural stability in the first two stages; at the same time, it highly overlaps with the typical temperature rise range caused by the exothermic reaction of polyurethane curing, thereby achieving precise triggering based on the heat of curing reaction.

[0014] The outer shell is a silicone-polyurethane hybrid copolymer. This copolymer is a polymer formed through a chemical reaction between isocyanate monomers, hydroxyl-terminated polysiloxanes, polyether polyols, and chain extenders. Its molecular chain simultaneously contains polysiloxane segments and polyurethane / polyurea segments, linked by chemical bonds (such as urethane bonds and urea bonds), forming a microscopically phase-separated hybrid structure. Specifically: The polysiloxane segments are mainly derived from hydroxyl-terminated polydimethylsiloxane (PDMS-OH, Mn=500-2000), which imparts flexibility, low surface energy and compatibility with the core silicone oil to the outer shell.

[0015] Polyurethane / polyurea segments are derived from the reaction of isocyanate monomers (such as IPDI, HDI), polyether polyols (Mn=300-1000) and amine chain extenders (such as ethylenediamine), which endow the shell with rigidity, strength and reactivity.

[0016] By controlling the proportion, type, and polymerization process (such as interfacial polymerization) of the reactive monomers, the glass transition temperature (Tg) of the shell can be controlled to be no less than 70℃ and the thickness to be 200-600 nm.

[0017] The outer shell polymer chain ends and surface are designed to be rich in active groups such as hydroxyl (-OH) or amino (-NH2). This is achieved by adding 0.2 g of ethylenediamine in the later stage of interfacial polymerization to completely convert the residual NCO groups in the system into urea or amino groups; or by using a strategy of adding an excess of 5 mol% of polyether polyol to retain hydroxyl groups at the ends of the outer shell chain.

[0018] Thermally triggered core-shell structured defoaming microspheres were prepared using a two-step fine emulsion polymerization method, the specific steps of which are as follows: Step 1: Prepare microspheres with "thermal expansion core" for loading defoaming paste.

[0019] Polycaprolactone triol and polyether triol in a specified ratio were uniformly blended at 50-65℃, and a measured amount of diisocyanate and catalyst were added. Prepolymerization was carried out at 70℃ for 2 h to form a moderately cross-linked polyurethane microgel, thus obtaining an intermediate layer material with thermal softening properties. The core components (carrier silicone oil, hydrophobic silica, and penetration enhancer) were thoroughly ground and dispersed using a three-roll mill to prepare a uniform defoaming paste. The intermediate layer material and the defoaming paste were mixed at a weight ratio of 1:1 to 1:3 to form oil phase I.

[0020] Prepare an aqueous phase I containing anionic emulsifiers and stabilizers. Add oil phase I to aqueous phase I and emulsify using a high-pressure homogenizer at a pressure of 100-180 MPa to form a stable fine emulsion.

[0021] The fine emulsion was heated to 65-80℃ and stirred for 4-8 hours to fully mature the intermediate microgel and stabilize the microsphere structure. After the reaction was completed, the prepolymer microsphere slurry was obtained by centrifugation and washing.

[0022] Step 2: Construct the silicone-polyurethane hybrid shell.

[0023] The prepolymer microsphere slurry obtained in the first step was redispersed in aqueous phase II containing a protective colloid (such as polyvinyl alcohol, PVA).

[0024] Oil phase II is prepared, comprising isocyanate monomers (such as isophorone diisocyanate, IPDI), hydroxyl-terminated polydimethylsiloxane (PDMS-OH), polyether polyols, and catalysts (such as dibutyltin dilaurate, DBTDL).

[0025] Oil phase II is slowly added to aqueous phase II in batches, and low-speed shearing is applied to allow the monomers in oil phase II to fully diffuse and swell into the surface region of the prepolymer core.

[0026] Under stirring, the system is slowly heated to 45-55°C, and a solution containing a chain extender (such as ethylenediamine or water) is slowly added dropwise while stirring, allowing the interfacial polymerization reaction to proceed for 12-36 hours. By controlling the amount of chain extender (e.g., maintaining the molar ratio of ethylenediamine to residual NCO between 0.8:1 and 1.0:1), the reaction process can be controlled, ensuring that the final shell polymer chain retains a predetermined amount of active groups (such as a small amount of unreacted -NCO or urea / amino groups generated by amine chain extension). When the molar ratio is <0.8, shell polymerization is incomplete; when the molar ratio is >1.0, active groups may be excessively consumed.

[0027] After the reaction was completed, the product was cooled, filtered, and repeatedly washed with deionized water and ethanol. Finally, it was vacuum dried at 35-45℃ to obtain dry thermally triggered defoaming microsphere powder with a three-layer core-shell structure.

[0028] Preparation method of polyurethane potting compound composition Pre-dispersion: The thermally triggered core-shell structured defoaming microsphere powder prepared above is mixed and dispersed with the curing agent component of the potting compound (i.e., component B) in a planetary mixer or high-speed disperser at room temperature for 20-40 minutes to ensure that the thermally triggered core-shell structured defoaming microsphere powder is uniformly dispersed in component B without visible agglomeration.

[0029] Final mixing: Mix the pre-mixed B component of the thermally triggered core-shell structured defoaming microsphere powder with the polyurethane prepolymer component (i.e., component A) according to the weight ratio designed in the product. After thorough mixing, the potting operation can be carried out.

[0030] The technical solution of this invention systematically solves the bubble problem in the entire polyurethane potting process through the synergistic design of materials and structure: For the first stage (stirring period) and the second stage (leveling period): the rigid outer shell of the heat-triggered core-shell structured defoaming microsphere powder exists as solid particles in the adhesive solution, providing a certain physical defoaming effect and helping to break or hinder large bubbles. At the same time, its robust structure ensures that the highly efficient defoaming components in the core are perfectly "sealed" during this stage, avoiding the premature consumption of the active ingredients of traditional defoamers.

[0031] For the third stage (curing period): the softening temperature of the intermediate layer material (45-60℃) is higher than the temperature in the early stages of conventional processes, ensuring that the microspheres remain inert before they are needed to function. When the potting compound cures under heating conditions, the system temperature rises rapidly to the softening temperature range of the intermediate layer. At the same time, the exothermic curing reaction further promotes local temperature rise, causing the intermediate layer material to soften and expand in volume, generating sufficient internal stress to rupture the outer shell. After the outer shell ruptures, the high concentration of defoaming active substances (silicone oil and hydrophobic silica) in the core is instantly released into the surrounding microenvironment. This is the critical window period for the large-scale nucleation and growth of physical and chemical microbubbles within the curing system, while the gel network is not yet fully cured. The released defoamer can quickly diffuse to adjacent microbubbles, effectively eliminating these most difficult-to-handle microbubbles by reducing surface tension, penetrating the liquid film, and using the hydrophobic silica particles to provide film rupture points. Meanwhile, the intermediate layer material is a lightly cross-linked polyurethane microgel, whose molecular chains retain active reactive groups (such as hydroxyl, amino, or residual isocyanate groups). Upon thermally triggered release, these active groups chemically react with isocyanate groups in the polyurethane matrix, chemically bonding the intermediate layer material to the cured network. This achieves integrated bonding between the microsphere fragments and the matrix, avoiding small molecule residues or interface defects. The outer shell material is a silicone-polyurethane hybrid copolymer, whose surface is also rich in active groups (such as -OH and -NH2). Submicron / nanoscale shell fragments generated after microsphere rupture react with -NCO groups in the surrounding polyurethane prepolymer through their surface active groups, forming urethane or urea bonds, thereby anchoring the fragments in the three-dimensional cross-linked network. This double-layer chemical bonding mechanism fundamentally avoids problems such as microvoids, weak interfaces, or stress concentration caused by the introduction of foreign particles, thus ensuring the overall dielectric properties, mechanical integrity, and long-term reliability of the potting compound.

[0032] The polyurethane potting compound composition with a heat-triggered dual defoaming mechanism provided by this invention utilizes the heat generated during the curing process to trigger the defoaming microspheres (the softening initiation temperature of the intermediate layer is 45-60℃). Therefore, it is particularly suitable for encapsulation applications requiring medium-temperature curing (e.g., 50-80℃) and stringent requirements for residual bubbles. Through heat curing, the microspheres can be precisely triggered to rupture, achieving instantaneous release of the defoaming components and chemical integration with the matrix, thereby obtaining a highly reliable potting compound free of bubble defects.

[0033] Specifically, this potting compound composition can be widely used in the following typical scenarios that require heat curing: Stator potting of drive motor for new energy vehicles: Motor windings are usually cured in an oven at 60-80℃. This invention can effectively eliminate micro-bubbles generated by heat release and residual moisture during the curing process, ensuring the pressure resistance and thermal conductivity of the insulation system. IGBT power module packaging: Module packaging often uses stepped heating curing (70℃+100℃). The thermally triggered defoaming mechanism of this invention can be precisely matched with the temperature rise curve, significantly reducing the risk of partial discharge. High-frequency transformer and inductor potting: The coil is thick and requires heating to promote resin penetration and curing. This invention can avoid core vibration and insulation deterioration caused by air bubbles. Photovoltaic inverters and junction boxes potting: Production lines typically use 60-80℃ rapid curing, while this invention improves production efficiency while ensuring long-term outdoor weather resistance; Aerospace electronic module packaging: with extremely high reliability requirements, medium-temperature curing is required to control stress. This invention can fundamentally eliminate internal microbubbles and meet stringent standards.

[0034] In the above applications, the potting compound of the present invention can not only significantly reduce macroscopic defects caused by air bubbles during the process, but also fundamentally eliminate microscopic air bubbles that are latent inside the material after curing, thereby ensuring the long-term stability of the electrical, thermal and mechanical properties of the encapsulated components under harsh operating conditions. Detailed Implementation

[0035] To make the technical solution and beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, all raw materials involved are commercially available industrial-grade products; all equipment and testing methods involved are conventional means in the art and are not considered as limitations on the scope of protection of the present invention.

[0036] Preparation of thermally triggered core-shell structured defoaming microspheres All performance tests and structural characterizations involved in each preparation example were performed according to the following methods: Average particle size and particle size distribution: A laser particle size analyzer (Malvern Mastersizer 3000) was used with deionized water as the dispersion medium. After ultrasonic dispersion for 2 minutes, the volume average particle size (D50) and particle size distribution index (PDI) were recorded.

[0037] Shell thickness: Microspheres were embedded in room temperature curing epoxy resin and cured at 25°C for 24 hours to ensure that the microsphere structure was not affected by heat; then ultrathin sections were prepared, and 50 microspheres were randomly selected to measure the shell thickness and the average value was taken.

[0038] Glass transition temperature and softening temperature: Differential scanning calorimetry (DSC, TAQ2000) was used under a nitrogen atmosphere at a heating rate of 10℃ / min, with a scanning range of -50~150℃. The softening initiation temperature of the interlayer material was taken as the temperature at which the heat flow curve first deviated from the baseline, and the peak temperature was taken as the temperature at the top of the endothermic peak; the glass transition temperature of the outer shell was taken as the temperature at the midpoint of the heat capacity change.

[0039] Preparation Example 1: 375g of dimethyl silicone oil (Dow Corning PMX-200) with a viscosity of 1000cSt and 110g of a specific surface area of ​​110m² were added. 2 / g of hydrophobic fumed silica (Aerosil R972, Evonik) and 15g of fluorinated polysiloxane (Shin-Etsu KE-1411) were mixed and ground three times at 50°C in a three-roll mill to obtain a uniform and fine defoaming paste, which was then sealed for later use.

[0040] 250g of polycaprolactone triol (Perstorp CAPA3050) with a number-average molecular weight of 400 and a functionality of 3 was mixed with 250g of polypropylene oxide triol (PPG-400, Dow VORANOL CP450) with the same molecular weight and functionality at 60℃ for 30 min. Then, 15g of isophorone diisocyanate (IPDI) and 0.05g of dibutyltin dilaurate (DBTDL) were added, and the mixture was heated to 70℃ and prepolymerized for 2 h under nitrogen protection to allow the polyol and diisocyanate to react and form a moderately cross-linked polyurethane microgel. After the reaction, the mixture was cooled and discharged to obtain a semi-transparent, viscous interlayer material. DSC testing (heating rate 10℃ / min) showed a softening onset temperature of 52℃ and a peak temperature of 62℃.

[0041] 100g of the intermediate layer material and 200g of defoaming paste were mixed evenly at 60℃ to form oil phase I. 10g of sodium dodecyl sulfate and 5g of hexadecane were dissolved in 485g of deionized water to form aqueous phase I. Under high-speed shearing (8000rpm), oil phase I was added to aqueous phase I in batches, shearing for 1-2 minutes after each addition until evenly dispersed. After all the oil phase was added, shearing continued for 5 minutes. The pre-emulsion was then transferred to a high-pressure homogenizer and homogenized 5 times at 150MPa to form a stable fine emulsion. The fine emulsion was transferred to a reactor, heated to 75℃, and stirred for 6 hours to further mature the intermediate layer microgel and stabilize the microsphere structure. After the reaction, the mixture was centrifuged (8000rpm, 15min) and washed to obtain a white slurry of prepolymer microspheres with a solid content of approximately 30%.

[0042] In a reaction vessel equipped with a stirrer, thermometer, and dropping funnel, the following components are added as aqueous phase II: 50g of white slurry of prepolymer microspheres was obtained (based on solid content). Polyvinyl alcohol (PVA-1788, degree of hydrolysis 88%) 10g 1000mL of deionized water.

[0043] Start mechanical stirring and slowly stir at 300-400 rpm at room temperature to uniformly disperse the prepolymer cores in the aqueous phase, resulting in a milky white dispersion. Subsequently, ultrasonically disperse the system for 5-10 min (200W power, intermittent, ice bath cooling) to eliminate any possible micro-aggregates and obtain a stable aqueous phase II dispersion system.

[0044] Separately, 25g of isophorone diisocyanate, 5g of hydroxyl-terminated polydimethylsiloxane (Mn=1000), 10g of polypropylene glycol (PPG-1000), and 0.25g of dibutyltin dilaurate were mixed evenly to form oil phase II. Under continuous low-speed stirring at 300-400 rpm, oil phase II was slowly added dropwise to the aqueous phase II through a dropping funnel, controlling the dropping rate to be completed within 30-60 minutes to avoid excessively high local monomer concentrations. After the addition was complete, stirring was stopped, and the mixture was allowed to stand at room temperature for 1.5 hours to allow the monomers in oil phase II to fully diffuse and swell into the surface region of the prepolymer core.

[0045] After swelling is complete, restart stirring, maintaining the rotation speed at 300-400 rpm, and slowly raise the system temperature to 50°C at a rate of approximately 0.5-1°C / min. Once the temperature stabilizes, begin adding the chain extender aqueous solution (prepared by dissolving 2.5g of ethylenediamine (EDA) in 50g of deionized water) dropwise through a dropping funnel, controlling the dropping rate to ensure uniform addition over 4 hours. Maintain a constant temperature and stirring speed during the addition process. After addition is complete, maintain the system temperature at 50°C and continue stirring at a low speed of 300-400 rpm for 20 hours to ensure complete shell polymerization.

[0046] After the reaction, the resulting suspension was filtered. The filter cake was washed three times with deionized water and then three times with anhydrous ethanol to remove residual emulsifier and unreacted monomers. Finally, the product was placed in a vacuum drying oven and dried at 40°C for 24 hours to obtain white powdery core-shell structured microspheres, designated TSDM-1. Laser particle size analyzer measured the average particle size D50 to be 22.4 μm and the PDI to be 0.26; DSC measured the glass transition temperature of the outer shell to be 82.3°C; TEM showed the outer shell thickness to be approximately 348 ± 42 nm (n = 50).

[0047] Preparation Example 2: Thermally triggered core-shell defoaming microspheres were prepared according to the method described in Example 1, with the only difference being the adjustment of the composition of the intermediate layer material. Specifically, the preparation method of the intermediate layer material is as follows: 150g of polycaprolactone triol (Perstorp CAPA3050) with a number-average molecular weight of 400 and a functionality of 3 was mixed with 350g of polypropylene oxide triol (PPG-400, Dow VORANOL CP450) with the same molecular weight and functionality at 60℃ for 30min. Then, 12g of isophorone diisocyanate (IPDI) and 0.05g of dibutyltin dilaurate (DBTDL) were added, and the mixture was heated to 70℃ and prepolymerized for 2h under nitrogen protection. After the reaction was completed, the mixture was cooled and discharged to obtain a semi-transparent viscous interlayer material. DSC testing (heating rate 10℃ / min) showed that its softening onset temperature was 48℃ and its peak temperature was 58℃.

[0048] Subsequently, following the same procedures as in Preparation Example 1, the aforementioned intermediate layer material was compounded with defoamer, and then subjected to fine emulsion preparation, core maturation, and low-speed stirring swelling polymerization to coat the shell layer, ultimately yielding white powdery core-shell structured microspheres, denoted as TSDM-2. The microspheres had a D50 of 25.1 μm, a PDI of 0.28, a shell Tg of 79.5 °C, and a shell thickness of 362 ± 51 nm.

[0049] Preparation Example 3: Thermally triggered core-shell defoaming microspheres were prepared according to the method of Preparation Example 1, with the only difference being the adjustment of the composition of the intermediate layer material.

[0050] Specifically, the preparation method of the intermediate layer material is as follows: 350g of polycaprolactone triol (Perstorp CAPA3050) with a number-average molecular weight of 400 and a functionality of 3 was mixed with 150g of polypropylene oxide triol (PPG-400, Dow VORANOL CP450) with the same molecular weight and functionality at 60℃ for 30min. Then, 18g of isophorone diisocyanate (IPDI) and 0.05g of dibutyltin dilaurate (DBTDL) were added, and the mixture was heated to 70℃ and prepolymerized for 2h under nitrogen protection. After the reaction was completed, the mixture was cooled and discharged to obtain a semi-transparent viscous interlayer material. DSC testing (heating rate 10℃ / min) showed that its softening onset temperature was 58℃ and its peak temperature was 68℃.

[0051] Subsequently, following the same procedures as in Preparation Example 1, the aforementioned intermediate layer material was compounded with defoamer, and then subjected to fine emulsion preparation, core maturation, and low-speed stirring swelling polymerization to coat the shell layer, ultimately yielding white powdery core-shell structured microspheres, designated TSDM-3. The microspheres had a D50 of 20 μm, a PDI of 0.24, a shell Tg of 84.1 °C, and a shell thickness of 332 ± 38 nm.

[0052] Comparative preparation example 1: Core-shell structured microspheres were prepared according to the method of Preparation Example 1, except that the intermediate layer material was replaced with uncrosslinked liquid hydrocarbon. The specific operation was as follows: 250g of the intermediate layer material was replaced with an equal weight of isododecane (boiling point approximately 180°C, analytical grade). 250g of isododecane was mixed uniformly with 200g of the defoaming paste prepared according to Preparation Example 1 at 60°C, forming oil phase I. Subsequently, the process of preparing a fine emulsion, stirring at 75°C for 6 hours (during which isododecane does not undergo cross-linking and forms microspheres solely through physical coating), and low-speed stirring was followed to induce swelling and polymerization of the coating shell, yielding microspheres designated DS-1 with a D50 of 28.2 μm and a PDI of 0.31.

[0053] The microspheres prepared in Preparation Examples 1-3 and Comparative Preparation Example 1 were evaluated for their comprehensive performance.

[0054] The microspheres were observed using a hot-stage microscope (Linkam THMS600) at a heating rate of 5℃ / min, and the temperature range at which the microspheres began to rupture was recorded.

[0055] Referring to GB / T 26527-2011 "Organic Silicone Defoamers" standard, 500 mL of 0.5 wt% sodium dodecyl sulfate aqueous solution was added to a 1000 mL graduated cylinder. Nitrogen gas was bubbled in from the bottom at a flow rate of 1 L / min. When the foam height reached 400 mL, 0.1 g of the microspheres to be tested was added, and the time required for the foam to completely collapse (initial defoaming time) was recorded. Each sample was tested 3 times, and the average value was taken. The microsphere samples were placed in a 50℃ constant temperature oven and stored for 7 days. After being removed and cooled to room temperature, the defoaming time was tested again according to the aforementioned method.

[0056] The results of the various performance tests are summarized in Table 1.

[0057] Table 1 - Comparison of Performance Parameters of Defoamer Microspheres

[0058] As can be seen from Table 1: The microspheres (TSDM-1~3) prepared in this invention have uniform particle size (PDI≤0.28) and regular core-shell structure. By adjusting the ratio of polycaprolactone triol to polyoxypropylene triol in the intermediate layer material, the softening point of the microgel can be effectively controlled, thereby achieving control over the thermally triggered rupture temperature of the microspheres. As the softening point of the intermediate layer increases from 48℃ to 58℃, the rupture temperature window of the microspheres correspondingly increases from 50-55℃ to 60-66℃. Compared with DS-1, which uses a liquid core, this invention uses a moderately cross-linked polyurethane microgel as the intermediate layer, resulting in microspheres with a narrower particle size distribution (PDI=0.24-0.28), more regular morphology, and controllable thermal response behavior. After 7 days of accelerated storage at 50℃, the defoaming performance shows almost no degradation (performance retention rate>90%), demonstrating excellent storage stability. In contrast, the defoaming efficiency of the comparative DS-1 significantly decreases after storage due to the migration and volatilization of the liquid core.

[0059] In summary, this invention successfully prepared core-shell structured defoaming microspheres with adjustable thermal triggering properties, high sphericity, narrow particle size distribution, and excellent storage stability by introducing polyurethane microgels with specific softening points as an intermediate layer and combining them with a mild interfacial polymerization coating process.

[0060] Comparative preparation example 2: Commercially available polydimethylsiloxane paste defoamer (Dow Corning DC-1630), labeled DS-2, can be used directly.

[0061] Formulation and Performance Evaluation of Polyurethane Potting Compound Examples 1-3: Component A consisted of 100 parts by weight of polyether-type polyurethane prepolymer (Adiprene LF750, NCO content 12.0%); Component B consisted of 30 parts by weight of polyetheramine D-400, 5 parts by weight of 1,4-butanediol, 0.05 parts by weight of stannous octoate, 50 parts by weight of aluminum hydroxide (particle size 5 μm), and 0.5 parts by weight (based on the total weight of A+B) of defoaming microspheres. The defoaming microspheres and other materials in Component B were dispersed in a planetary mixer at room temperature and a vacuum of -0.095 MPa for 30 min, and then rapidly mixed with Component A at a 1:1 weight ratio for 1 min. The gas content of the mixed solution was immediately tested after stirring; a separate portion of the solution was poured into a mold and cured in a 60°C oven for 2 hours for post-curing bubble analysis and dielectric strength testing.

[0062] In Examples 1-3, microspheres TSDM-1, TSDM-2, and TSDM-3 prepared in the preparation example were added respectively, and the test results are shown in Table 2.

[0063] Comparative Examples 1-3: Comparative Examples 1-3 were all based on Example 1, with the following differences: Comparative Examples 1-2 were supplemented with defoamers DS-1 and DS-2, respectively, which were used in the comparative preparation examples 1-2; Comparative Example 3 was not supplemented with defoamer and served as a blank control group. The test results are shown in Table 2.

[0064] All performance tests and structural characterizations involved in the embodiments and comparative examples of this invention were performed according to the following methods: A. Performance testing of potting compound process Air content after stirring: Immediately after mixing components A and B, the adhesive solution is poured into a density cup with a known volume and mass, weighed, and the measured density ρ is calculated. The theoretical density ρ of the mixed adhesive is calculated based on the mass fraction of each component and the true density, using the following formula: ρ theory = 1 / ( ∑(wi~ / ρi) ) In the formula, wi is the mass fraction of component i, and ρi is the true density of the component.

[0065] The true density of each raw material was determined by gas displacement method (AccuPyc 1330 true density meter), with the following density values: polyurethane prepolymer 1.05 g / cm³. 3 Polyetheramine D-400 0.97 g / cm³ 3 1,4-Butanediol 1.02 g / cm³ 3 Stannous octoate 1.25 g / cm³ 3 Aluminum hydroxide 2.42 g / cm³ 3 TSDM microspheres 1.08 g / cm³ 3 (Measured average value). The gas content is calculated using the following formula: Gas content (%) = (ρtheoretical - ρmeasured) / ρtheoretical × 100%.

[0066] Analysis of internal bubbles after curing: A microfocus X-ray computed tomography system (ZEISS Xradia510) was used. The cured sample (100mm×100mm×2mm) was placed on the sample stage. The scanning voltage was 80kV, the current was 100μA, and the layer thickness was 5μm. 3D reconstruction was performed using VG Studio MAX3.0 software. Bubble regions were extracted by threshold segmentation, and the percentage of the total bubble volume to the scanned area volume (Vol%) was calculated. The equivalent diameter of the largest bubble was also determined.

[0067] Dielectric strength: According to ASTM D149 standard, a withstand voltage tester (Shanghai Lanbo YD2010) was used to cut the cured sample into 100mm×100mm×1mm test pieces, place them in transformer oil at 25℃, and uniformly increase the voltage at 50Hz AC voltage (2kV / s). The breakdown voltage value was recorded, and the average value of 5 parallel samples in each group was taken.

[0068] B. Matrix integrity characterization Solvent extraction-gel permeation chromatography analysis: 1 g of the cured sample was ground into a fine powder, wrapped in filter paper, and placed in a Soxhlet extractor. Extraction was performed at 70°C for 48 h using tetrahydrofuran as the solvent. The extract was concentrated and analyzed by gel permeation chromatography (Waters 1515, Styragel HR4E column, RI detector). The mobile phase was THF, the flow rate was 1.0 mL / min, and the analysis was calibrated with polystyrene standards. Low molecular weight extracts were detected.

[0069] Storage stability: After sealing the B component containing defoaming microspheres, place it in a 40℃ constant temperature oven for accelerated storage for 4 weeks. Take samples weekly to prepare potting compound and test the volume ratio of air bubbles after curing according to the above method to evaluate the degree of defoaming performance degradation.

[0070] Table 2 - Test Results (Part 1)

[0071] 1) The air content after mixing is the average of the results of three repeated tests (n=3). 2) For each sample, the 50 largest bubbles in the CT scan reconstruction area were randomly selected, their equivalent diameters were measured, and the "mean ± standard deviation (n=50)" was calculated.

[0072] As shown in Table 2, the polyurethane potting compounds prepared in Examples 1-3 of this invention all had an air content of less than 3% after stirring, a bubble volume ratio of only 0.18%-0.25% after curing, a maximum bubble diameter in the range of 80-95 μm, and a dielectric strength of 26.9-27.3 kV / mm, significantly better than the comparative examples. Among them, TSDM-1 (PCL:PPG=50:50) showed the best overall performance. Although Comparative Example 1 (DS-1) had a certain defoaming effect in the initial stage, its maximum bubble diameter (156 μm) and bubble volume ratio (0.60%) were significantly higher than those of the examples, indicating that physical phase change materials may have a risk of active ingredient penetration. Comparative Example 2 (DS-2) had insufficient ability to eliminate microbubbles during the curing period, resulting in severe bubble defects after curing. The blank control group had the most severe bubble defects and the lowest dielectric strength.

[0073] Examples 4-8: Examples 4-8 were prepared according to the method of Example 1, with the only difference being the amount of defoaming microspheres TSDM-1 added. The percentages of the weight of components A and B were 0.1%, 0.3%, 0.5%, 0.7%, and 1.0%, respectively. The test results are shown in Table 3.

[0074] Table 3 - Test Results (Part Two)

[0075] 1) The air content after mixing is the average of the results of three repeated tests (n=3). 2) For each sample, the 50 largest bubbles in the CT scan reconstruction area were randomly selected, their equivalent diameters were measured, and the "mean ± standard deviation (n=50)" was calculated.

[0076] As shown in Table 3, the defoaming performance of the potting compound continuously improves with the increase of TSDM-1 addition: when the addition amount increases from 0.1% to 1.0%, the volume percentage of bubbles after curing decreases from 0.45% to 0.16%, and the maximum bubble diameter decreases from 126 μm to 72 μm. However, the dielectric strength shows a trend of first increasing and then decreasing: only 25.0 kV / mm at 0.1%, reaching a peak of 27.3 kV / mm at 0.5%, and falling back to 26.8 kV / mm at 1.0%. This is because an appropriate amount of microspheres can improve the dielectric strength by eliminating bubbles and reducing internal defects, but excessive addition itself introduces an organic-inorganic interface that, although chemically bonded, is still difficult to completely eliminate dielectric loss; at the same time, the siloxane segments in the microsphere shell themselves have a low dielectric constant, and their moderate introduction helps to maintain the low dielectric properties of the matrix, but excessive addition may cause the dielectric constant to rebound due to local enrichment. Therefore, the preferred addition amount of TSDM-1 is 0.3% to 0.7%, which can achieve the best balance between defoaming effect, dielectric strength and dielectric stability.

[0077] Component B containing 0.5% TSDM-1 (Example 6) and Component B containing 0.5% DS-1 (Comparative Example 1) were sealed and placed in a 40°C constant temperature oven for accelerated storage for 4 weeks. Samples were taken weekly to prepare potting compound and the volume percentage of air bubbles after curing was tested. The results are shown in Table 4.

[0078] Table 4 - Stability of defoaming performance under accelerated storage conditions

[0079] As shown in Table 4, the defoaming performance of TSDM-1 remained almost unchanged after 4 weeks of storage at 40℃ (the bubble volume percentage increased from 0.18% to 0.20%), while the defoaming performance of DS-1 decreased significantly (from 0.60% to 0.78%). This indicates that the PCL / PPG reactive blend has excellent storage stability as an intermediate layer, effectively preventing premature penetration of the core active ingredient.

[0080] The cured sample of Example 6 (containing 0.5% TSDM-1) was analyzed as follows: After liquid nitrogen brittle fracture, gold was sputtered onto the fracture surface, and the morphology was observed using scanning electron microscopy. The results showed that the fracture surface was smooth and dense overall. The interface between the microsphere shell fragments and the polyurethane matrix was blurred and tightly bonded, with no debonding, pores, or microcracks observed, indicating that the two have good interfacial compatibility.

[0081] GPC analysis: After Soxhlet extraction for 48 h, the extract was analyzed by gel permeation chromatography. No obvious characteristic peaks were detected in the low molecular weight region (<1000 g / mol), confirming the absence of free oligomers or silicone oil residues, and indirectly confirming that the shell material has been completely integrated into the cross-linked network.

[0082] Application example: The potting compound containing 0.5% TSDM-1 (Example 6) was used for bottom potting of the new energy vehicle battery module. After curing at 80°C for 2 hours, CT scan showed that the internal bubble volume ratio was 0.21%, and there were no bubbles with a diameter >100μm. After 1000 hours of high temperature and high humidity (85°C / 85%RH) aging, the insulation resistance was still >1GΩ, which meets the engineering acceptance requirements of the new energy vehicle power battery system for the insulation withstand voltage performance of the potting material.

[0083] In summary, the thermally triggered core-shell structured defoaming microspheres provided by this invention achieve delayed release of heat during the curing exothermic period through precise thermal softening of the intermediate layer material. The core defoaming component is instantly and targetedly delivered to the microbubble region, while the outer shell fragments are chemically bonded to the matrix via active groups. This design achieves a unified approach to intelligent defoaming and structural integration throughout the polyurethane potting process. It not only reduces the volume percentage of bubbles after curing to below 0.2% and controls the maximum bubble diameter to within 100 μm, but also increases the dielectric strength to 27.3 kV / mm, exhibiting excellent storage stability and long-term reliability. This potting compound is particularly suitable for encapsulation applications with extremely high requirements for insulation reliability, long-term stability, and structural integrity, including new energy vehicle battery packs, power electronic modules, and precision electronic components, demonstrating significant technological advancement and industrial application value.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any equivalent substitutions or modifications made based on the technical solutions of the present invention shall fall within the scope defined by the claims of the present invention.

Claims

1. A polyurethane potting compound composition, characterized in that: It comprises a polyurethane prepolymer, a curing agent, and thermally triggered core-shell defoaming microspheres; the thermally triggered core-shell defoaming microspheres have a three-layer core-shell structure, comprising, from the inside out: The core contains defoaming active materials, including carrier silicone oil and hydrophobic silica; The intermediate layer is a heat-softening polyurethane microgel formed by a partial crosslinking reaction of polycaprolactone polyol and polyether polyol, wherein the softening onset temperature of the microgel, as determined by differential scanning calorimetry, is 45-60°C; and, The outer shell is a silicone-polyurethane hybrid copolymer, and its polymer chain contains active groups that can react with isocyanate groups.

2. The polyurethane potting compound composition according to claim 1, characterized in that: The weight mixing ratio of the polycaprolactone polyol to the polyether polyol is 1:(0.25-4); the number average molecular weight of the polycaprolactone polyol and the polyether polyol are each independently 300-500, and the functionality is not less than 3.

3. The polyurethane potting compound composition according to claim 1, characterized in that: The glass transition temperature of the outer shell is ≥70℃, and the thickness is 200-600nm.

4. The polyurethane potting compound composition according to claim 1, characterized in that: In the core, the carrier silicone oil is at least one of dimethyl silicone oil, methylphenyl silicone oil, or fluorinated polysiloxane; the specific surface area of ​​the hydrophobic silica is 150-300 m². 2 / g.

5. The polyurethane potting compound composition according to any one of claims 1-4, characterized in that: The average particle size D50 of the thermally triggered core-shell structured defoaming microspheres is 10-40 μm.

6. The polyurethane potting compound composition according to claim 5, characterized in that: The amount of the thermally triggered core-shell structured defoaming microspheres added is 0.1wt%-1.0wt% of the total weight of the potting compound composition.

7. A method for preparing a polyurethane potting compound composition according to any one of claims 1-6, characterized in that: First, the thermally triggered core-shell structured defoaming microspheres are mixed and dispersed evenly with the curing agent components, and then mixed with the polyurethane prepolymer.

8. The use of a polyurethane potting compound composition as described in any one of claims 1-6 in the encapsulation of electronic devices requiring heat curing.

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