Microcapsule type latent curing accelerator prepared by taking modified graphene as stabilizer through Pickering emulsion method
The microcapsule-type latent curing accelerator prepared by modified graphene solves the problems of insufficient storage stability and poor release controllability in the existing technology, achieves high stability and rapid responsiveness of the epoxy resin curing system, and is suitable for high-end manufacturing fields.
Patent Information
- Application Number
- CN202510937368.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-08
- Publication Date
- 2025-10-03
AI Technical Summary
Existing microcapsule-type latent curing accelerators have insufficient storage stability at room temperature, delayed trigger responsiveness, and poor controllability of accelerator release, which cannot meet the large-scale application needs in high-end fields.
Modified graphene was used as a stabilizer, and a microcapsule-type latent curing accelerator was prepared by the Pickering emulsion method. Modified graphene oxide was used to form a stable emulsion at the oil-water interface, which was then coated with accelerators such as TPP to form an organic-inorganic hybrid structure, thereby improving storage stability and release controllability.
It significantly enhances the room temperature storage stability and high temperature curing activity of the epoxy resin curing system, improves the thermal stability and glass transition temperature, and achieves rapid and effective release and uniform triggering of the accelerator.
Smart Images
Figure CN120737313A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of latent curing accelerators, and in particular to a microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer. Background Art
[0002] Epoxy resin curing systems are widely used in high-end manufacturing applications such as electronic packaging, composite prepregs, and one-component adhesives due to their excellent mechanical properties, bonding performance, and chemical stability. However, traditional curing agents (such as amines and imidazoles) suffer from poor storage stability and limited process applicability, making them difficult to meet the stringent requirements of modern industry for ease of operation and performance stability. Against this backdrop, latent curing agents have emerged. By remaining inert at room temperature and only cross-linking with epoxy resin when triggered by specific external conditions (such as heat, light, pressure, or humidity), these latent curing agents significantly extend the shelf life of the curing system and expand its process applicability.
[0003] In the field of electronic packaging, anhydride curing agents have become the mainstream choice due to the excellent thermal and dielectric properties of their cured products. However, the lack of active hydrogen in the anhydride molecular structure prevents direct reaction with epoxy groups, resulting in a curing process that requires high temperatures (typically ≥150°C) and long periods of time (several to tens of hours). To reduce curing energy consumption and shorten the process cycle, curing accelerators such as triphenylphosphine (TPP) have been widely introduced into anhydride / epoxy resin systems. TPP catalyzes the ring opening of the anhydride through the nucleophilicity of the lone pair electrons of the phosphorus atom, significantly reducing the curing temperature to 80-120°C. However, the activity of TPP is easily affected by environmental factors, and it must be weighed and added on-site before curing, making it difficult to premix directly into epoxy resin coatings, limiting its convenience in actual industrial production.
[0004] To address these issues, microencapsulation technology has been introduced into the preparation of latent curing accelerators. This technology encapsulates accelerators such as TPP at the micrometer level using a membrane material, creating a core-shell encapsulated latent curing accelerator. At room temperature, the capsule membrane effectively isolates the accelerator from the epoxy resin, preventing premature crosslinking. Under specific triggering conditions (such as heating), the capsule membrane ruptures, releasing the accelerator and initiating the curing reaction. However, existing encapsulated latent curing accelerators still have significant drawbacks: Insufficient storage stability at room temperature: Conventional capsule membrane materials (such as polyurea and polyurethane) are sensitive to moisture, temperature, or mechanical stress. As a result, epoxy resin coatings containing such capsules undergo significant crosslinking within one month of storage at room temperature, making them unable to meet long-term storage requirements. Trigger response hysteresis: Some capsule membranes need to be ruptured at higher temperatures or for a longer time, resulting in a narrower curing process window; Poor controllability of accelerator release: After the capsule ruptures, the accelerator release rate is difficult to precisely control, which can easily lead to local uneven curing or stress concentration problems.
[0005] These drawbacks severely restrict the large-scale application of microencapsulated latent curing accelerators in high-end fields such as electronic packaging and aerospace. Therefore, developing a microencapsulated latent curing accelerator that combines ultra-long room-temperature storage stability, rapid trigger responsiveness, and controlled accelerator release has become a key challenge in epoxy resin curing technology.
[0006] The present invention aims to break through the limitations of existing technologies by innovating the design and preparation process of capsule membrane materials, and to provide a latent curing accelerator solution for epoxy resin curing systems that combines high performance and high stability. Summary of the Invention
[0007] A problem with the prior art is that encapsulated latent curing accelerators lack room-temperature storage stability. They release their properties within one month of storage at room temperature, causing significant crosslinking in the resin curing system. To address this technical problem, the present invention provides a microcapsule-based latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer. The preparation method comprises the following steps: (1) Graphene oxide reacts with diethanolamine-adipic acid condensation polymer to form an amide bond to obtain modified graphene oxide; (2) uniformly dispersing the modified graphene oxide in deionized water to obtain an aqueous phase; (3) Mix TPP, St, MEMA, cross-linking agent and initiator to obtain an oil phase; (4) Add the oil phase to the water phase at a volume ratio of 1:4 and homogenize and emulsify to obtain a stable O / W Pickering emulsion; (5) The Pickering emulsion is transferred to a reactor. After deoxygenation, St and MEMA are subjected to a heating copolymerization reaction under the protection of nitrogen or inert gas. After the reaction is completed, it is cooled to room temperature and solid-liquid separation is performed to obtain a solid product. The obtained solid product is washed with hydrochloric acid, ammonia water, and deionized water in sequence, and then freeze-dried to obtain a microcapsule-type latent curing accelerator.
[0008] Preferably, the graphene oxide is graphene oxide obtained by a modified Hummer's method.
[0009] Preferably, the diethanolamine-adipic acid polycondensate is a product obtained by amidation polycondensation reaction of diethanolamine and adipic acid.
[0010] Preferably, the molar ratio between diethanolamine and adipic acid is 1:1.
[0011] Preferably, the mass percentage of the modified graphene oxide in the aqueous phase is 0.24%.
[0012] Preferably, the amount ratio of TPP to St, MEMA, crosslinking agent and initiator in the oil phase is 2.0 g:8.0 mL:2.0 mL:0.3 g:0.2 g.
[0013] Preferably, the cross-linking agent is DVB.
[0014] Preferably, the initiator is AIBN.
[0015] Preferably, the steps of homogenizing and emulsifying are as follows: Premix at no less than 5000 rpm for at least 1 min, then increase the speed to no less than 16000 rpm and mix for at least 15 min, keeping the temperature in an ice bath at ≤25°C throughout the process.
[0016] The present invention has the following beneficial effects: Microencapsulated curing accelerators impart significantly enhanced room-temperature storage stability and comparable high-temperature curing activity to epoxy curing systems. As the temperature rises, the encapsulated accelerator is rapidly and efficiently released, triggering the chain motion of the polymer microcapsules. Furthermore, due to the organic-inorganic hybrid nature, the addition of microcapsules increases the glass transition temperature and thermal stability of epoxy thermoset resins. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1 : SEM image of the microcapsule type latent curing accelerator obtained in Example 1 of the present invention.
[0018] Figure 2 : TGA curves of the microcapsule latent curing accelerators obtained in Examples 1-3 of the present invention.
[0019] Figure 3 : DSC curve of the microcapsule type latent curing accelerator obtained in Example 1 of the present invention.
[0020] Figure 4 : TPP standard working curve used in the present invention.
[0021] Figure 5 : Comparison of the flow properties of the E51 / MHHPA / TPP system (comparative application 5) and the E51 / MHHPA / microcapsule system (application 2) after storage for different days. DETAILED DESCRIPTION
[0022] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.
[0023] The graphene oxide used in the present invention is prepared according to the following steps (modified Hummer's method): Pour 230 mL of 98% concentrated sulfuric acid into a three-necked flask and pre-cool it in an ice-water bath. Then, weigh 10 g of natural graphite powder and stir for 30 minutes, maintaining the temperature below 5°C. Then, weigh 30 g of KMnO₄ and add it in batches, keeping the temperature below 20°C. Remove the ice bath, raise the temperature to 35°C, and stir for 24 hours until the reaction turns dark green. Stop stirring, slowly add deionized water, raise the temperature to 95°C, maintain the temperature for 30 minutes, and then slowly add 50 mL of 30% hydrogen peroxide solution until the reaction mixture turns bright yellow. Cool the reaction mixture to room temperature, wash with water, centrifuge, and freeze-dry to obtain graphene oxide powder, designated as GO powder.
[0024] Example 1
[0025] The preparation method of microcapsule latent curing accelerator is as follows: (1) Add 12.5 g of diethanolamine and 18 g of adipic acid into a three-necked flask and stir the mixture at 110 °C under vacuum (pressure of 0.1 MPa) for 2 hours to obtain a diethanolamine-adipic acid polycondensate.
[0026] (2) Weigh 0.06 g of GO powder and prepare 50.0 g of GO aqueous suspension with a mass concentration of 0.12%; (3) Weigh 0.05 g of diethanolamine-adipic acid condensation polymer and prepare 0.5 g of a 10% aqueous solution of the condensation polymer; (4) The GO aqueous suspension and the condensation polymer aqueous solution were mixed uniformly to obtain a dispersion, and then the dispersion was centrifuged at 10,000 rpm for 15 minutes. The supernatant was discarded, and the solid precipitate was collected and freeze-dried for 48 hours to obtain modified graphene oxide powder, which was recorded as modified GO powder; (5) Weigh 2.0 g of TPP, 8.0 mL of styrene (St), 2.0 mL of methoxyethyl methacrylate (MEMA), 0.3 g of divinylbenzene (DVB), and 0.2 g of azobisisobutyronitrile (AIBN), mix them, and ultrasonicate for 10 minutes to obtain an oil phase; (6) The modified GO powder was evenly dispersed in 40 mL of deionized water to obtain a modified GO suspension with a mass concentration of 0.24 wt%, and ultrasonicated in an ice bath for 30 min to obtain an aqueous phase; (7) According to the volume ratio of oil phase to water phase of 1:4, the oil phase was slowly poured into the water phase, pre-stirred at 500 rpm for 5 minutes, and homogenized and emulsified using a high-speed disperser. Pre-mixed at 5000 rpm for 1 minute, and then the speed was increased to 16000 rpm and homogenized for 15 minutes. The temperature of the homogenization and emulsification was controlled in an ice bath at <25 °C throughout the process, and finally a Pickering emulsion was obtained; (8) The Pickering emulsion was transferred to a dry neck flask, and a condenser, a mechanical stirring paddle (the blade was 1 cm from the bottom of the flask), and a nitrogen inlet tube were installed. Nitrogen was bubbled at a constant flow rate (0.5 L / min) for 30 minutes to completely eliminate the oxygen in the system. Then, the St and MEMA copolymerization reaction was initiated in an oil bath at 70 °C under nitrogen protection for 8 hours (mechanical stirring at 300 rpm). After the reaction was completed, the mixture was cooled to room temperature and centrifuged (5000 rpm, 5 minutes) to collect the microcapsule precipitate. (9) The obtained microcapsule precipitate was washed three times with a 1 mol / L hydrochloric acid solution, then washed once with a 1 mol / L ammonia solution, and finally washed three times with deionized water. After freeze-drying for 24 hours, a white microcapsule powder was obtained, i.e., a microcapsule-type latent curing accelerator. The embedding efficiency of the obtained microcapsule-type latent curing accelerator was 32.65 wt%. The SEM image of the microcapsule-type latent curing accelerator obtained in Example 1 is shown in the attached manual. Figure 1 As shown in the image, the microcapsules are relatively regular spherical with a particle size of approximately 20 μm. The surface is also relatively rough, due to the large number of modified GO particles adhering to the microcapsule surface, forming an organic-inorganic hybrid surface. During the polymerization process, the modified GO acts as a particle emulsifier, stabilizing the oil-water interface. Therefore, it adheres to the microcapsule surface after polymerization.
[0027] The DSC curve of the microcapsule latent curing accelerator obtained in Example 1 of the present invention is shown in the attached specification. Figure 3 As shown, the images show that the Tg of the hybrid microcapsules containing TPP is about 90°C.
[0028] Example 2 is the same as Example 1, except that the mechanical stirring speed in step (8) of Example 2 is 200 rpm. The embedding efficiency of the microcapsule-type latent curing accelerator obtained in Example 2 is 19.61 wt%.
[0029] Example 3 is the same as Example 1, except that the mechanical stirring speed in step (8) of Example 3 is 400 rpm. The embedding efficiency of the microcapsule-type latent curing accelerator obtained in Example 3 is 28.74 wt%.
[0030] The TGA curves of the microcapsule latent curing accelerators obtained in Examples 1-3 of the present invention are shown in the attached specification. Figure 2The images show that the thermal decomposition of the microcapsules can be divided into two stages: the first stage, at 200-300°C, is caused by the decomposition of the TPP core material encapsulating the microcapsules. The second stage, at 350-450°C, is attributed to the decomposition of the microcapsule shell, which is composed of polymers of styrene and divinylbenzene. This indicates that the prepared microcapsules can protect the encapsulated TPP, thereby improving thermal stability.
[0031] The microcapsule embedding efficiency obtained by the present invention is calculated by the standard working curve of TPP as shown in the attached manual. Figure 4 As shown. With anhydrous ethanol as a blank control, the standard solution of TPP was diluted to 25 mg / mL, 12 mg / mL, 6 mg / mL, and 3 mg / mL, respectively, and the absorbance value was measured at the maximum absorption wavelength. The standard working curve was drawn by the correspondence between the absorption intensity and the concentration of the TPP solution. Weigh 0.5 g of microcapsule sample, wash it thoroughly with 50 mL of anhydrous ethanol, filter it, and dilute the filtrate to 100 mL with anhydrous ethanol. The absorbance of the solution was measured at the maximum absorption wavelength, and the content of TPP adsorbed on the surface of the microcapsule was calculated using the standard curve. Take 0.5 g of microcapsules, dissolve them in 1 mL of deionized water, add excess anhydrous sodium sulfate to remove moisture, extract TPP with anhydrous ethanol, filter it, and dilute the filtrate to 100 mL with anhydrous ethanol. Take the solution to measure the absorbance at the maximum absorption wavelength, and calculate the total content of TPP in the microcapsules based on the standard curve. The encapsulation efficiency was determined according to the following formula: Embedment rate = (1-surface content / total content) × 100%.
[0032] Comparative Example 1 is the same as Example 1, except that the modified GO powder in Example 1 is replaced by an equal amount of silicon dioxide powder (purchased from Aladdin, with an average particle size of 15±5 nm, and hydrophobically modified SiO2 obtained by modification with diphenyldimethoxysilane (DMDPS)).
[0033] Comparative Example 2 is the same as Example 1, except that step (9) of Comparative Example 2 is as follows: The obtained microcapsule precipitate was washed three times with deionized water and freeze-dried for 24 hours to obtain white microcapsule powder, namely, microcapsule-type latent curing accelerator.
[0034] Comparative Example 3 is the same as Example 1, except that the MEMA in Example 1 is replaced by divinylbenzene (DVB) in the same molar amount.
[0035] Specific applications
[0036] Thermal curing properties: Application 1 Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Example 1 into a beaker. Add 8 g of methylhexahydrophthalic anhydride (MHHPA) and pre-disperse under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) and add it to the dispersion. Stir thoroughly to obtain a uniform mixture. Degas the mixture under vacuum for 1 hour and then pour it into a mold. Curing schedule: 95°C / 2 h → 120°C / 2 h → 140°C / 2 h.
[0037] Comparative Application 1 is the same as Application 1, except that the microcapsule-type latent curing accelerator obtained in Example 1 is not added to Comparative Application 1.
[0038] The test results show that the epoxy resin curing systems of Application 1 and Comparative Application 1 were successfully cured.
[0039] Storage stability at room temperature: Lay the container flat and observe the fluidity of the system every 24 hours.
[0040] Application 2
[0041] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Example 1 into a beaker, then add 8 g of methylhexahydrophthalic anhydride (MHHPA) and pre-disperse under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) and add it to the dispersion. Stir evenly to obtain an epoxy resin coating. The epoxy resin coating obtained in Application 2 exhibits good room temperature storage stability. The coating system maintains good fluidity for 45 days and has room temperature storage stability exceeding 45 days.
[0042] Application 3
[0043] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Example 2 into a beaker, then add 8 g of methylhexahydrophthalic anhydride (MHHPA) and pre-disperse under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) and add it to the dispersion. Stir evenly to obtain an epoxy resin coating. The epoxy resin coating obtained in Application 3 exhibits good storage stability at room temperature. The coating system maintains good fluidity for 45 days and has a room temperature storage stability exceeding 45 days.
[0044] Application 4
[0045] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Example 3 into a beaker, then add 8 g of methylhexahydrophthalic anhydride (MHHPA) and pre-disperse under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) and add it to the dispersion. Stir evenly to obtain an epoxy resin coating. The epoxy resin coating obtained in Application 4 exhibits good storage stability at room temperature. The coating system maintains good fluidity for 45 days and has a room temperature storage stability exceeding 45 days.
[0046] Comparison Application 2
[0047] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Comparative Example 1 into a beaker, then add 8 g of methylhexahydrophthalic anhydride (MHHPA) and pre-disperse under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) was added to the dispersion and stirred evenly to obtain an epoxy resin coating. Although the epoxy resin coating obtained in Comparative Example 1 had good fluidity, it had a short storage life at room temperature, losing its fluidity after 21 days.
[0048] Comparison Application 3
[0049] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Comparative Example 2 into a beaker, then weigh 8 g of methylhexahydrophthalic anhydride (MHHPA) and add it to the mixture. Pre-disperse the mixture under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) was added to the dispersion and stirred evenly to obtain an epoxy resin coating. The epoxy resin coating obtained in Comparative Application 3 exhibited poor room-temperature storage stability, lasting no more than five days. After five days, the coating lost fluidity and completely solidified. This was because the TPP adhering to the microcapsule surface was not removed during the washing of the microcapsule precipitate with deionized water. This allowed the residual TPP to react directly with the epoxy resin system, causing it to cure too quickly.
[0050] Comparison Application 4
[0051] Weigh 1 g of the microcapsule-type latent curing accelerator obtained in Comparative Example 3 into a beaker, then weigh 8 g of methylhexahydrophthalic anhydride (MHHPA) and add it. Pre-disperse the mixture under magnetic stirring for 1 hour to obtain a dispersion. Then, weigh 9 g of E51 (epoxy value 0.48) and add it to the dispersion. Stir evenly to obtain an epoxy resin coating. The epoxy resin coating obtained in Comparative Application 4 loses fluidity and solidifies after storage at room temperature for no more than 25 days. This is because the polymer chains formed by MEMA contain flexible hydroxyethyl side chains (-CH2CH2OH), which significantly lower the Tg of the resulting cross-linked polymer. At the curing temperature of the epoxy resin, the MEMA-based wall material becomes softer, more fluid, or swellable, making the core material easier to release.
[0052] Comparison Application 5
[0053] Weigh 1 g of TPP into a beaker, then add 8 g of methylhexahydrophthalic anhydride (MHHPA). Pre-disperse the mixture under magnetic stirring for 1 hour to obtain a dispersion. Then, add 9 g of E51 (epoxy value 0.48) to the dispersion and stir thoroughly to obtain an epoxy resin coating. The epoxy resin coating obtained in Comparative Application 5 lost fluidity after storage at room temperature for no more than 25 days.
[0054] Comparison of the flow properties of epoxy resin coatings obtained in Application 5 and Application 2 is shown in the attached manual. Figure 5 As shown in the image, the fluidity of the system with TPP added decreased significantly within 24 hours, the fluidity was hindered after 48 hours, and the fluidity was completely lost at 25 days. In contrast, the system containing microcapsules still had fluidity after being placed at room temperature for 45 days. This shows that compared with the system with TPP added, the system with microcapsules added has significantly improved storage performance at room temperature.
[0055] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.
Claims
1. A microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer, characterized in that: The preparation method comprises the following steps: (1) Graphene oxide reacts with diethanolamine-adipic acid condensation polymer to form an amide bond to obtain modified graphene oxide; (2) uniformly dispersing the modified graphene oxide in deionized water to obtain an aqueous phase; (3) Mix TPP, St, MEMA, cross-linking agent and initiator to obtain an oil phase; (4) Add the oil phase to the water phase at a volume ratio of 1:4 and homogenize and emulsify to obtain a stable O / W Pickering emulsion; (5) The Pickering emulsion is transferred to a reactor. After deoxygenation, St and MEMA are subjected to a heating copolymerization reaction under the protection of nitrogen or inert gas. After the reaction is completed, it is cooled to room temperature and solid-liquid separation is performed to obtain a solid product. The obtained solid product is washed with hydrochloric acid, ammonia water, and deionized water in sequence, and then freeze-dried to obtain a microcapsule-type latent curing accelerator.
2. A microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that, The graphene oxide is graphene oxide obtained by an improved Hummer's method.
3. A microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that, Diethanolamine-adipic acid polycondensate is a product obtained by amidation polycondensation reaction of diethanolamine and adipic acid.
4. A microcapsule type latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer according to claim 3, characterized in that, The molar ratio between diethanolamine and adipic acid is 1:
1.
5. A microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that, The mass percentage of modified graphene oxide in the aqueous phase is 0.24%.
6. The microcapsule latent curing accelerator prepared by a Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that The dosage ratio of TPP to St, MEMA, cross-linker and initiator in the oil phase is 2.0 g:8.0 mL:2.0 mL:0.3 g:0.2 g.
7. The microcapsule latent curing accelerator prepared by Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that: The cross-linking agent is DVB.
8. The microcapsule latent curing accelerator prepared by Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that: The initiator is AIBN.
9. The microcapsule latent curing accelerator prepared by Pickering emulsion method using modified graphene as a stabilizer according to claim 1, characterized in that: The steps of homogenization and emulsification are as follows: Premix at an initial speed of not less than 5000 rpm for at least 1 min, then increase the speed to not less than 16000 rpm and mix for at least 15 min, with the temperature controlled in an ice bath at ≤25°C throughout the process.
10. A heat-curing epoxy resin coating, characterized in that: The microcapsule latent curing accelerator according to any one of claims 1 to 9 is used as the latent curing accelerator for thermal curing.