A low viscosity high heat resistance toughened epoxy resin composition and a preparation method thereof
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUBEI ZHEN ZHENG PEAK NEW MATERIALS CO LTD
- Filing Date
- 2026-05-07
- Publication Date
- 2026-06-30
Abstract
Description
Technical Field
[0001] This invention belongs to the field of epoxy resin technology, specifically relating to a low-viscosity, high-heat-resistant, toughened epoxy resin composition and its preparation method. Background Technology
[0002] Epoxy resins are widely used in high-tech fields such as aerospace and wind turbine blades due to their excellent adhesion, chemical stability, and mechanical strength. These fields simultaneously require resin matrices to have high heat resistance, high toughness, and low viscosity, but it is difficult to achieve all three simultaneously.
[0003] While traditional liquid rubber toughening can improve toughness, it significantly increases viscosity and causes a 20-40°C drop in Tg. Core-shell rubber (CSR) toughening has a smaller impact on Tg, but existing CSR particles mostly have a pure PMMA structure, which is only physically bonded to the matrix, resulting in limited toughening efficiency. Moreover, to achieve effective toughening, the amount added is usually 10-20 wt%, leading to excessively high system viscosity, which is not conducive to liquid molding processes.
[0004] Reactive diluents can reduce viscosity, but monofunctional diluents sacrifice heat resistance (Tg), and there is insufficient research on the synergistic optimization of difunctional diluents with core-shell toughening systems. Therefore, developing epoxy resin compositions that can simultaneously achieve low viscosity, high heat resistance, and high toughness is a pressing technical challenge in this field. Summary of the Invention
[0005] The purpose of this invention is to provide a low-viscosity, high-heat-resistant, and toughened epoxy resin composition and its preparation method. Through formulation design and preparation process, this composition significantly improves the heat resistance and toughness of the cured product while maintaining low viscosity processing performance. It solves the technical problem of high viscosity and poor toughness in traditional high-heat-resistant epoxy resin systems and meets the performance requirements of the resin matrix for the preparation of high-performance composite materials.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a low-viscosity, high-heat-resistant, toughened epoxy resin composition, comprising the following components by weight: 100 parts by weight of phenolic epoxy resin A, 5-15 parts by weight of core-shell rubber toughening agent B, 35-43 parts by weight of aromatic diamine curing agent C, 1-5 parts by weight of bifunctional epoxy reactive diluent D, 0.5-2 parts by weight of silane coupling agent E, and 0.1-1 parts by weight of basic imidazole curing accelerator F.
[0007] Specifically, the phenolic resin A has an epoxy equivalent of 175–185 g / eq and a functionality of 2.5–3.6. Preferably, the phenolic resin A has a functionality of 3.0–3.6, an epoxy equivalent of 175–182 g / eq, and a viscosity of 500–5000 mPa·s at 25°C. Compared to bisphenol A epoxy resin, phenolic resin has higher functionality and crosslinking density, which is the basis for obtaining high Tg cured products; when the functionality is below 2.5, the crosslinking density is insufficient, and it is difficult to reach a Tg of 175°C; when the functionality is above 3.6, the viscosity of the system is too high, making processing difficult.
[0008] Specifically, the core-shell rubber toughening agent B is used in an amount of 5-15 parts by weight, with a particle size of 80-150 nm; the core is cross-linked polybutyl acrylate rubber, and the shell is a terpolymer of methyl methacrylate-glycidyl methacrylate-crosslinking agent; in the shell, glycidyl methacrylate (GMA) monomer accounts for 5-15 wt% of the total mass of the shell monomers, and the crosslinking agent accounts for 3-6 wt% of the total mass of the shell monomers. When the GMA content is less than 5 wt%, the number of epoxy groups that can participate in chemical bonding in the shell is insufficient, and the improvement in interfacial bonding is limited; when the GMA content is higher than 15 wt%, the tendency of homopolymerization in the shell increases, and the grafting efficiency decreases. When the amount is less than 5 parts by weight, the toughening effect is not significant; when the amount is higher than 15 parts by weight, the viscosity of the system increases significantly and the Tg decreases.
[0009] Preferably, in the core-shell rubber toughening agent B, the weight ratio of the core to the shell is (60-80):(20-40), and the epoxy value of the shell is 0.10-0.30 eq / 100g. When the core proportion is less than 60wt%, the volume fraction of the rubber phase is insufficient, and the toughening effect decreases; when the core proportion is greater than 80wt%, the shell thickness is insufficient, and the density of interfacial chemical bonding points decreases.
[0010] Preferably, the core-shell rubber toughening agent B, after being soaked in 1,4-butanediol diglycidyl ether at 25°C for 48 hours, has a swelling degree of 120-180%, and a gel content ≥92wt% after Soxhlet extraction with acetone for 24 hours. The swelling degree reflects the crosslinking density of the core rubber phase: when the swelling degree is below 120%, the core is over-crosslinked, and the rubber phase has insufficient deformation capacity under stress; when the swelling degree is above 180%, the core crosslinking density is too low, and the particle structure integrity is damaged. A gel content ≥92wt% indicates that the core rubber phase has a sufficiently high degree of crosslinking, ensuring that the particles do not dissolve or agglomerate during processing.
[0011] Specifically, the crosslinking agent in the outer shell terpolymer is selected from at least one of ethylene glycol dimethacrylate, divinylbenzene, allyl methacrylate, and trimethylolpropane triacrylate. Preferably, the crosslinking agent is ethylene glycol dimethacrylate.
[0012] Specifically, the curing agent C is at least one of micronized 4,4'-diaminodiphenyl sulfone or 3,3'-diaminodiphenyl sulfone, with a D50 < 15µm, and is used in an amount of 35 to 43 parts by weight.
[0013] Preferably, the curing agent C is micronized 4,4'-diaminodiphenyl sulfone, used in an amount of 35-43 parts by weight; the molar ratio of active hydrogen in the curing agent to epoxy groups in the composition is 0.85-1.05. When D50 ≥ 15µm, the curing agent is unevenly dispersed in the resin, which easily leads to local under-curing and affects the consistency of impact strength and Tg; when the molar ratio is lower than 0.85, there is an excess of epoxy groups, resulting in insufficient crosslinking density of the cured network; when the molar ratio is higher than 1.05, unreacted amino groups remain, which also reduces the heat resistance of the cured product.
[0014] Specifically, the amount of the reactive diluent D is 1 to 5 parts by weight, selected from at least one of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydroquinone diglycidyl ether. When the amount is less than 1 part by weight, the viscosity-reducing effect is not significant; when the amount is more than 5 parts by weight, the diluent introduces too many flexible segments, resulting in a decrease in heat resistance (Tg). The bifunctional reactive diluent participates in the curing reaction, becoming part of the crosslinking network, thus overcoming the defect of decreased heat resistance caused by inactive diluents.
[0015] Specifically, the amount of silane coupling agent E is 0.5 to 2 parts by weight, and it is selected from at least one of p-chlorophenyltriethoxysilane or phenyltrimethoxysilane. Preferably, the silane coupling agent E is phenyltrimethoxysilane, and the amount is 1 to 1.5 parts by weight. The silane coupling agent forms a transition layer at the particle-matrix interface by condensing its alkoxy group with the hydroxyl group on the surface of the core-shell particles, while the organic group end is compatible with the epoxy group, further improving the interfacial bonding strength. When the amount is less than 0.5 parts by weight, the interfacial modification effect is not obvious, and when it is more than 2 parts by weight, the excess silane may cause side reactions and affect the integrity of the cured network.
[0016] Specifically, the curing accelerator F is used in an amount of 0.1 to 1 part by weight, and is selected from at least one of 2-ethyl-4-methylimidazole or 2-phenylimidazole. Preferably, the curing accelerator F is 2-ethyl-4-methylimidazole, and the amount used is 0.3 to 0.7 parts by weight. Basic imidazole accelerators, when used in an amount range of 0.1 to 1 part by weight, can appropriately reduce the curing activation energy of the system without introducing additional side reactions; when the amount is less than 0.1 parts by weight, the promoting effect is not obvious, and when the amount is more than 1 part by weight, the pot life of the system is significantly shortened, which is not conducive to processing operations.
[0017] Specifically, the core-shell rubber toughening agent B is prepared by seed emulsion polymerization, including the following steps: Step 1: Specifically, using butyl acrylate as the main monomer, with a crosslinking agent accounting for 1-3 wt% of the butyl acrylate monomer mass, potassium persulfate as the initiator, and sodium dodecyl sulfate as the emulsifier, emulsion polymerization is carried out at 65-70℃ for 10-15 hours under nitrogen protection to obtain a crosslinked polybutyl acrylate rubber core particle emulsion; the resulting core particles have a particle size of 60-110 nm and a PDI < 0.15. Below 65℃, the initiation efficiency is insufficient, requiring a longer reaction time and resulting in a wider particle size distribution; above 70℃, the emulsion stability decreases, and aggregation easily occurs.
[0018] Step 2: Specifically, a mixture of shell monomers, consisting of methyl methacrylate, glycidyl methacrylate, and a crosslinking agent, is slowly added dropwise to the core-shell particle emulsion obtained in Step 1. Graft copolymerization is carried out at 75–80°C for 3–5 hours to obtain a core-shell particle emulsion. Preferably, the dropwise addition time of the shell monomer mixture is 1–2 hours to avoid excessively high local monomer concentrations that could induce self-nucleation.
[0019] Step 3: Specifically, the core-shell particle emulsion obtained in Step 2 is added to a 5% (w / w) calcium chloride aqueous solution for demulsification. After filtration and washing with deionized water 3-5 times, it is vacuum dried at 60°C for 24 hours to obtain a core-shell rubber toughening agent powder with a particle size of 80-150 nm. Preferably, the demulsification temperature is controlled at 50-60°C to ensure complete demulsification and that the particle morphology is not damaged.
[0020] Specifically, the preparation method of the low-viscosity, high-heat-resistant, toughened epoxy resin composition includes the following steps: Step S1: Specifically, phenolic epoxy resin A is preheated at 65–75°C, core-shell rubber toughening agent B is added, and the mixture is sheared and stirred at 2000–4000 rpm for 20–40 minutes to ensure uniform dispersion of the core-shell particles in the resin matrix. The temperature during the shearing process should not exceed 80°C. Preferably, the high-speed shearing speed is 2500–3500 rpm, and the stirring time is 25–35 minutes. When the temperature exceeds 80°C, the viscosity of the system decreases sharply, the uniformity of the core-shell particle dispersion decreases, and there is a risk of premature curing reaction.
[0021] Step S2: Specifically, cool the mixture obtained in step S1 to 40–50°C, and sequentially add the micronized aromatic diamine curing agent C, the bifunctional epoxy reactive diluent D, the silane coupling agent E, and the basic imidazole curing accelerator F. Stir at 150–250 rpm for 40–50 minutes until the system is homogeneous. Preferably, the order of addition of each component should strictly follow the above order, with the curing accelerator F added last to avoid direct contact between the curing accelerator and the curing agent C, which could lead to premature local curing.
[0022] Step S3: Specifically, the mixture obtained in step S2 is degassed under a vacuum of -0.09 to -0.10 MPa for 10 to 20 minutes to eliminate air bubbles introduced during the mixing process. Preferably, the degassed time is 12 to 18 minutes; insufficient degassed material will have pore defects inside the cured product, resulting in a decrease in impact strength and mechanical properties.
[0023] Step S4: Specifically, the degassed composition obtained in step S3 is poured into a mold and cured according to the following segmented curing process: Initial curing is performed by heating at a rate of 1–3 °C / min to 125–160 °C and holding for 2–3 h; subsequent curing is performed by heating at a rate of 1–3 °C / min to 180–190 °C and holding for 3–4 h; the mixture is then cooled to room temperature in the furnace and demolded to obtain the cured product. Preferably, the initial curing temperature is 140–155 °C, and the holding time is 2–2.5 h; the subsequent curing temperature is 183–188 °C, and the holding time is 3–3.5 h; the heating rate is 1.5–2.5 °C / min. When the initial curing temperature is below 125 °C, the system gels insufficiently, and the macroscopic morphology is difficult to fix; when the subsequent curing temperature is below 180 °C, the crosslinking density is insufficient, and the Tg is difficult to reach 175 °C; when the subsequent curing temperature is above 190 °C, there is a risk of matrix degradation.
[0024] Compared with the prior art, the present invention has the following beneficial effects: I. Synergistic Improvement of Heat Resistance and Toughness: The core-shell rubber toughening agent B, containing GMA units in its outer shell, undergoes a ring-opening addition reaction with the amino groups in the aromatic diamine curing agent C during curing, forming a chemically covalently bonded interface between the core-shell particles and the epoxy resin matrix. Compared to traditional physically embedded CSR toughening agents, this chemically bonded interface significantly improves stress transfer efficiency. With a toughening agent dosage of only 5–15 parts by weight, the notched impact strength of the cured product increases from less than 12 kJ / m² in the unmodified system to over 25 kJ / m², an increase of over 200%, while maintaining a Tg above 175℃, overcoming the technical bottleneck of decreased heat resistance caused by traditional rubber toughening.
[0025] II. Significantly reduced processing viscosity: The introduction of the bifunctional epoxy reactive diluent D effectively reduces the mixed viscosity of the system at 60℃ to 3000-8000 mPa·s, meeting the processing requirements of wet prepreg and RTM process; the diluent itself contains bifunctional epoxy groups, which participate in the cross-linking reaction during the curing process and become part of the network without losing the Tg and heat resistance of the cured product.
[0026] 3. Improved uniformity of cured network: The aromatic diamine curing agent C is micronized (D50 < 15µm) and uniformly dispersed in the resin system, avoiding uneven local curing caused by excessively large curing agent particle size. This is conducive to the formation of a uniform and dense cross-linked network structure, thereby ensuring the consistency of the impact strength and thermal properties of the cured product.
[0027] IV. Segmented curing process ensures the upper limit of performance: The segmented curing process allows the system to first complete gelation at a lower temperature and fix the spatial distribution of core-shell particles, and then cure at a high temperature to further improve the crosslinking density, exhibiting excellent high-temperature thermal stability. Detailed Implementation
[0028] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.
[0029] Raw material description: Phenolic epoxy resin: purchased from Guangzhou Weichuang High-Tech Materials Technology Co., Ltd., grade PN-051.
[0030] Bisphenol A type epoxy resin: purchased from Sinopec Baling Petrochemical Company, product name epoxy resin E51, model CYD-128.
[0031] The remaining raw materials are conventional products with no special requirements and are all obtained through commercial purchases. Example 1
[0032] I. Preparation of Core-Shell Rubber Toughening Agent B Step 1: Add 200g of deionized water and 2.0g of sodium dodecyl sulfate to a 500mL four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and constant-pressure dropping funnel. Start stirring (200rpm) and purge with nitrogen for 30min to remove oxygen. Mix 100g of butyl acrylate (BA) and 2.0g of ethylene glycol dimethacrylate (EGDMA) thoroughly to prepare the core monomer mixture. Slowly add the monomer mixture dropwise to the flask over 60min using a constant-pressure dropping funnel. Heat to 67°C and add potassium persulfate aqueous solution (0.5g of potassium persulfate dissolved in 10g of deionized water). Emulsion polymerization is carried out at 67°C for 12h under nitrogen protection to obtain a cross-linked polybutyl acrylate (PBA) rubber core particle emulsion.
[0033] Step 2: Prepare the shell monomer mixture according to the following ratio: 40.0g methyl methacrylate (MMA), 5.0g glycidyl methacrylate (GMA), and 2.25g ethylene glycol dimethacrylate (EGDMA), mix well and set aside.
[0034] The above-mentioned mixture of outer shell monomers was slowly added dropwise over 90 minutes through a constant-pressure dropping funnel to the core-shell particle emulsion obtained in step 1. The temperature was raised to 77°C, and graft copolymerization was carried out at 77°C for 4 hours to obtain the core-shell particle emulsion. At this time, the mass ratio of the core layer to the outer shell was 100:47.25, which is approximately 68:32 by weight.
[0035] Step 3: The core-shell particle emulsion obtained in step 2 was slowly added to 500g of a 5% (w / w) calcium chloride aqueous solution at 55℃, stirred to break the emulsion, allowed to settle, and then filtered. The resulting filter cake was washed four times with deionized water, using 200g of water each time. The washed filter cake was placed in a vacuum oven at 60℃ (vacuum degree -0.095MPa) and dried for 24h to obtain a white powdery core-shell rubber toughening agent B with a yield of approximately 92%.
[0036] Step S1: 100 parts by weight of phenolic epoxy resin A were placed in a 500 mL beaker equipped with a mechanical stirrer and a temperature-controlled heating mantle, and preheated at 70°C for 30 min until the resin was fully fluid. 10 parts by weight of core-shell rubber toughening agent B powder were added, and the mixture was sheared at 3000 rpm for 30 min to ensure uniform dispersion of the core-shell particles in the resin matrix. The system temperature was continuously monitored during the shearing process to ensure it did not exceed 80°C.
[0037] Step S2: Cool the mixture obtained in step S1 to 45°C, and add the following components in sequence while stirring: First, add 38 parts by weight of micronized 4,4'-DDS curing agent C, and stir at 200 rpm for 10 min; then add 3 parts by weight of 1,4-butanediol diglycidyl ether (BDDGE) reactive diluent D, and stir for 5 min; then add 1.25 parts by weight of phenyltrimethoxysilane silane coupling agent E, and stir for 5 min; finally, add 0.5 parts by weight of 2-ethyl-4-methylimidazolium curing accelerator F, and continue stirring at 200 rpm for 45 min until the system is homogeneous and there are no obvious solid particles remaining.
[0038] Step S3: The mixture obtained in step S2 was transferred to a vacuum drying oven and degassed for 15 minutes under a vacuum of -0.095 MPa to eliminate the bubbles introduced during the mixing process, resulting in a low-viscosity, high-heat-resistant, and toughened epoxy resin composition with no bubbles on the surface and a uniform appearance.
[0039] Step S4: The degassed composition obtained in step S3 is poured into a steel mold (200mm×200mm×4mm in size, with a release agent applied to the surface of the mold) preheated to 50°C. The mold is then cured in the following staged curing process: the temperature is increased to 148°C at a rate of 2°C / min and held for 2.3 hours for initial curing; then the temperature is increased to 186°C at a rate of 2°C / min and held for 3.25 hours for post-curing; the mold is then removed from the oven after cooling to room temperature to obtain the cured board. Example 2
[0040] I. Preparation of Core-Shell Rubber Toughening Agent B Step 1: Add 200g of deionized water and 2.0g of sodium dodecyl sulfate to a 500mL four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and constant-pressure dropping funnel. Start stirring (200rpm) and purge with nitrogen for 30min to remove oxygen. Mix 100g of butyl acrylate (BA) and 2.0g of ethylene glycol dimethacrylate (EGDMA) thoroughly to prepare the core monomer mixture. Slowly add the monomer mixture dropwise to the flask over 60min using a constant-pressure dropping funnel. Heat to 67°C and add potassium persulfate aqueous solution (0.5g of potassium persulfate dissolved in 10g of deionized water). Emulsion polymerization is carried out at 67°C for 12h under nitrogen protection to obtain a cross-linked polybutyl acrylate (PBA) rubber core particle emulsion.
[0041] Step 2: The shell monomer mixture was prepared according to the following ratio: 40.0 g of methyl methacrylate (MMA), 5.0 g of glycidyl methacrylate (GMA), and 2.25 g of ethylene glycol dimethacrylate (EGDMA), and mixed thoroughly for later use. The above shell monomer mixture was slowly added dropwise over 90 minutes through a constant-pressure dropping funnel to the core-shell particle emulsion obtained in step 1. The temperature was raised to 77°C, and graft copolymerization was carried out at 77°C for 4 hours to obtain the core-shell particle emulsion. At this point, the mass ratio of the core layer to the shell was 100:47.25, which is approximately 68:32 by weight.
[0042] Step 3: The core-shell particle emulsion obtained in step 2 was slowly added to 500g of a 5% (w / w) calcium chloride aqueous solution at 55℃, stirred to break the emulsion, allowed to settle, and then filtered. The resulting filter cake was washed four times with deionized water, using 200g of water each time. The washed filter cake was placed in a vacuum oven at 60℃ (vacuum degree -0.095MPa) and dried for 24h to obtain a white powdery core-shell rubber toughening agent B with a yield of approximately 92%.
[0043] Step S1: 100 parts by weight of phenolic epoxy resin A were placed in a 500 mL beaker equipped with a mechanical stirrer and a temperature-controlled heating mantle, and preheated at 70°C for 30 min until the resin was fully fluid. 15 parts by weight of core-shell rubber toughening agent B powder were added, and the mixture was sheared at 3000 rpm for 30 min to ensure that the core-shell particles were uniformly dispersed in the resin matrix. The system temperature was continuously monitored during the shearing process to ensure that it did not exceed 80°C.
[0044] Step S2: Cool the mixture obtained in step S1 to 45°C, and add the following components in sequence while stirring: First, add 35 parts by weight of micronized 4,4'-DDS curing agent C, and stir at 200 rpm for 10 min; then add 3 parts by weight of 1,4-butanediol diglycidyl ether (BDDGE) reactive diluent D, and stir for 5 min; then add 1.25 parts by weight of phenyltrimethoxysilane silane coupling agent E, and stir for 5 min; finally, add 0.5 parts by weight of 2-ethyl-4-methylimidazolium curing accelerator F, and continue stirring at 200 rpm for 45 min until the system is homogeneous and there are no obvious solid particles remaining.
[0045] Step S3: The mixture obtained in step S2 was transferred to a vacuum drying oven and degassed for 15 minutes under a vacuum of -0.095 MPa to eliminate the bubbles introduced during the mixing process, resulting in a low-viscosity, high-heat-resistant, and toughened epoxy resin composition with no bubbles on the surface and a uniform appearance.
[0046] Step S4: The degassed composition obtained in step S3 is poured into a steel mold (200mm×200mm×4mm in size, with a release agent applied to the surface of the mold) preheated to 50°C. The mold is then cured in the following staged curing process: the temperature is increased to 148°C at a rate of 2°C / min and held for 2.3 hours for initial curing; then the temperature is increased to 186°C at a rate of 2°C / min and held for 3.25 hours for post-curing; the mold is then removed from the oven after cooling to room temperature to obtain the cured board. Example 3
[0047] I. Preparation of Core-Shell Rubber Toughening Agent B Step 1: Add 200g of deionized water and 2.0g of sodium dodecyl sulfate to a 500mL four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and constant-pressure dropping funnel. Start stirring (200rpm) and purge with nitrogen for 30min to remove oxygen. Mix 100g of butyl acrylate (BA) and 2.0g of ethylene glycol dimethacrylate (EGDMA) thoroughly to prepare the core monomer mixture. Slowly add the monomer mixture dropwise to the flask over 60min using a constant-pressure dropping funnel. Heat to 67°C and add potassium persulfate aqueous solution (0.5g of potassium persulfate dissolved in 10g of deionized water). Emulsion polymerization is carried out at 67°C for 12h under nitrogen protection to obtain a cross-linked polybutyl acrylate (PBA) rubber core particle emulsion.
[0048] Step 2: The shell monomer mixture was prepared according to the following ratio: 40.0 g of methyl methacrylate (MMA), 5.0 g of glycidyl methacrylate (GMA), and 2.25 g of ethylene glycol dimethacrylate (EGDMA), and mixed thoroughly for later use. The above shell monomer mixture was slowly added dropwise over 90 minutes through a constant-pressure dropping funnel to the core-shell particle emulsion obtained in step 1. The temperature was raised to 77°C, and graft copolymerization was carried out at 77°C for 4 hours to obtain the core-shell particle emulsion. At this point, the mass ratio of the core layer to the shell was 100:47.25, which is approximately 68:32 by weight.
[0049] Step 3: The core-shell particle emulsion obtained in step 2 was slowly added to 500g of a 5% (w / w) calcium chloride aqueous solution at 55℃, stirred to break the emulsion, allowed to settle, and then filtered. The resulting filter cake was washed four times with deionized water, using 200g of water each time. The washed filter cake was placed in a vacuum oven at 60℃ (vacuum degree -0.095MPa) and dried for 24h to obtain a white powdery core-shell rubber toughening agent B with a yield of approximately 92%.
[0050] Step S1: 100 parts by weight of phenolic epoxy resin A were placed in a 500 mL beaker equipped with a mechanical stirrer and a temperature-controlled heating mantle, and preheated at 70°C for 30 min until the resin was fully fluid. 10 parts by weight of core-shell rubber toughening agent B powder were added, and the mixture was sheared at 3000 rpm for 30 min to ensure uniform dispersion of the core-shell particles in the resin matrix. The system temperature was continuously monitored during the shearing process to ensure it did not exceed 80°C.
[0051] Step S2: Cool the mixture obtained in step S1 to 45°C, and add the following components in sequence while stirring: First, add 43 parts by weight of micronized 3,3'-diaminodiphenyl sulfone (3,3'-DDS) and curing agent C, and stir at 200 rpm for 10 min; then add 3 parts by weight of 1,4-butanediol diglycidyl ether (BDDGE) and reactive diluent D, and stir for 5 min; then add 1.25 parts by weight of phenyltrimethoxysilane silane coupling agent E, and stir for 5 min; finally, add 0.5 parts by weight of 2-ethyl-4-methylimidazolium curing accelerator F, and continue stirring at 200 rpm for 45 min until the system is homogeneous and there are no obvious solid particles remaining.
[0052] Step S3: The mixture obtained in step S2 was transferred to a vacuum drying oven and degassed for 15 minutes under a vacuum of -0.095 MPa to eliminate the bubbles introduced during the mixing process, resulting in a low-viscosity, high-heat-resistant, and toughened epoxy resin composition with no bubbles on the surface and a uniform appearance.
[0053] Step S4: The degassed composition obtained in step S3 is poured into a steel mold (200mm×200mm×4mm in size, with a release agent applied to the surface of the mold) preheated to 50°C. The mold is then cured in the following staged curing process: the temperature is increased to 148°C at a rate of 2°C / min and held for 2.3 hours for initial curing; then the temperature is increased to 186°C at a rate of 2°C / min and held for 3.25 hours for post-curing; the mold is then removed from the oven after cooling to room temperature to obtain the cured board. Example 4
[0054] I. Preparation of Core-Shell Rubber Toughening Agent B Step 1: Add 200g of deionized water and 2.0g of sodium dodecyl sulfate to a 500mL four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and constant-pressure dropping funnel. Start stirring (200rpm) and purge with nitrogen for 30min to remove oxygen. Mix 100g of butyl acrylate (BA) and 2.0g of ethylene glycol dimethacrylate (EGDMA) thoroughly to prepare the core monomer mixture. Slowly add the monomer mixture dropwise to the flask over 60min using a constant-pressure dropping funnel. Heat to 67°C and add potassium persulfate aqueous solution (0.5g of potassium persulfate dissolved in 10g of deionized water). Emulsion polymerization is carried out at 67°C for 12h under nitrogen protection to obtain a cross-linked polybutyl acrylate (PBA) rubber core particle emulsion.
[0055] Step 2: The shell monomer mixture was prepared according to the following ratio: 40.0 g of methyl methacrylate (MMA), 5.0 g of glycidyl methacrylate (GMA), and 2.25 g of ethylene glycol dimethacrylate (EGDMA), and mixed thoroughly for later use. The above shell monomer mixture was slowly added dropwise over 90 minutes through a constant-pressure dropping funnel to the core-shell particle emulsion obtained in step 1. The temperature was raised to 77°C, and graft copolymerization was carried out at 77°C for 4 hours to obtain the core-shell particle emulsion. At this point, the mass ratio of the core layer to the shell was 100:47.25, which is approximately 68:32 by weight.
[0056] Step 3: The core-shell particle emulsion obtained in step 2 was slowly added to 500g of a 5% (w / w) calcium chloride aqueous solution at 55℃, stirred to break the emulsion, allowed to settle, and then filtered. The resulting filter cake was washed four times with deionized water, using 200g of water each time. The washed filter cake was placed in a vacuum oven at 60℃ (vacuum degree -0.095MPa) and dried for 24h to obtain a white powdery core-shell rubber toughening agent B with a yield of approximately 92%.
[0057] Step S1: 100 parts by weight of phenolic epoxy resin A were placed in a 500 mL beaker equipped with a mechanical stirrer and a temperature-controlled heating mantle, and preheated at 70°C for 30 min until the resin was fully fluid. 10 parts by weight of core-shell rubber toughening agent B powder were added, and the mixture was sheared at 3000 rpm for 30 min to ensure uniform dispersion of the core-shell particles in the resin matrix. The system temperature was continuously monitored during the shearing process to ensure it did not exceed 80°C.
[0058] Step S2: Cool the mixture obtained in step S1 to 45°C, and add the following components in sequence while stirring: First, add 40 parts by weight of micronized 4,4'-DDS curing agent C, and stir at 200 rpm for 10 min; then add 3 parts by weight of neopentyl glycol diglycidyl ether (NPGDGE) reactive diluent D, and stir for 5 min; then add 1.25 parts by weight of phenyltrimethoxysilane silane coupling agent E, and stir for 5 min; finally, add 0.5 parts by weight of 2-ethyl-4-methylimidazolium curing accelerator F, and continue stirring at 200 rpm for 45 min until the system is homogeneous and there are no obvious solid particles remaining.
[0059] Step S3: The mixture obtained in step S2 was transferred to a vacuum drying oven and degassed for 15 minutes under a vacuum of -0.095 MPa to eliminate the bubbles introduced during the mixing process, resulting in a low-viscosity, high-heat-resistant, and toughened epoxy resin composition with no bubbles on the surface and a uniform appearance.
[0060] Step S4: The degassed composition obtained in step S3 is poured into a steel mold (200mm×200mm×4mm in size, with a release agent applied to the surface of the mold) preheated to 50°C. The mold is then cured in the following staged curing process: the temperature is increased to 148°C at a rate of 2°C / min and held for 2.3 hours for initial curing; then the temperature is increased to 186°C at a rate of 2°C / min and held for 3.25 hours for post-curing; the mold is then removed from the oven after cooling to room temperature to obtain the cured board. Example 5
[0061] I. Preparation of Core-Shell Rubber Toughening Agent B Step 1: Add 200g of deionized water and 2.0g of sodium dodecyl sulfate to a 500mL four-necked flask equipped with a stirrer, condenser, nitrogen inlet tube, and constant-pressure dropping funnel. Start stirring (200rpm) and purge with nitrogen for 30min to remove oxygen. Mix 100g of butyl acrylate (BA) and 2.0g of ethylene glycol dimethacrylate (EGDMA) thoroughly to prepare the core monomer mixture. Slowly add the monomer mixture dropwise to the flask over 60min using a constant-pressure dropping funnel. Heat to 67°C and add potassium persulfate aqueous solution (0.5g of potassium persulfate dissolved in 10g of deionized water). Emulsion polymerization is carried out at 67°C for 12h under nitrogen protection to obtain a cross-linked polybutyl acrylate (PBA) rubber core particle emulsion.
[0062] Step 2: The shell monomer mixture was prepared according to the following ratio: 40.0 g of methyl methacrylate (MMA), 5.0 g of glycidyl methacrylate (GMA), and 2.25 g of ethylene glycol dimethacrylate (EGDMA), and mixed thoroughly for later use. The above shell monomer mixture was slowly added dropwise over 90 minutes through a constant-pressure dropping funnel to the core-shell particle emulsion obtained in step 1. The temperature was raised to 77°C, and graft copolymerization was carried out at 77°C for 4 hours to obtain the core-shell particle emulsion. At this point, the mass ratio of the core layer to the shell was 100:47.25, which is approximately 68:32 by weight.
[0063] Step 3: The core-shell particle emulsion obtained in step 2 was slowly added to 500g of a 5% (w / w) calcium chloride aqueous solution at 55℃, stirred to break the emulsion, allowed to settle, and then filtered. The resulting filter cake was washed four times with deionized water, using 200g of water each time. The washed filter cake was placed in a vacuum oven at 60℃ (vacuum degree -0.095MPa) and dried for 24h to obtain a white powdery core-shell rubber toughening agent B with a yield of approximately 92%.
[0064] Step S1: 100 parts by weight of phenolic epoxy resin A were placed in a 500 mL beaker equipped with a mechanical stirrer and a temperature-controlled heating mantle, and preheated at 70°C for 30 min until the resin was fully fluid. 10 parts by weight of core-shell rubber toughening agent B powder were added, and the mixture was sheared at 3000 rpm for 30 min to ensure uniform dispersion of the core-shell particles in the resin matrix. The system temperature was continuously monitored during the shearing process to ensure it did not exceed 80°C.
[0065] Step S2: Cool the mixture obtained in step S1 to 45°C, and add the following components in sequence while stirring: First, add 37 parts by weight of micronized 4,4'-DDS curing agent C, and stir at 200 rpm for 10 min; then add 3 parts by weight of 1,4-butanediol diglycidyl ether (BDDGE) reactive diluent D, and stir for 5 min; then add 1.25 parts by weight of phenyltrimethoxysilane silane coupling agent E, and stir for 5 min; finally, add 0.5 parts by weight of 2-ethyl-4-methylimidazolium curing accelerator F, and continue stirring at 200 rpm for 45 min until the system is homogeneous and there are no obvious solid particles remaining.
[0066] Step S3: The mixture obtained in step S2 was transferred to a vacuum drying oven and degassed for 15 minutes under a vacuum of -0.095 MPa to eliminate the bubbles introduced during the mixing process, resulting in a low-viscosity, high-heat-resistant, and toughened epoxy resin composition with no bubbles on the surface and a uniform appearance.
[0067] Step S4: The degassed composition obtained in step S3 is poured into a steel mold (200mm×200mm×4mm in size, with a release agent applied to the surface of the mold) preheated to 50°C. The mold is then cured in the following segmented curing process: the temperature is increased to 140°C at a rate of 1.5°C / min and held for 2 hours for initial curing; then the temperature is increased to 183°C at a rate of 1.5°C / min and held for 3 hours for post-curing; the mold is then cooled to room temperature in the furnace and demolded to obtain the cured board.
[0068] Comparative Example 1 In this comparative example, bisphenol A type epoxy resin was used instead of phenolic phenolic epoxy resin A, and the amount used was the same as 100 parts by weight. The types, amounts and process parameters of the other components were exactly the same as in Example 1.
[0069] Comparative Example 2 In this comparative example, the mass ratio of the core layer to the outer shell in the core-shell rubber toughening agent B was adjusted to 50:50. The other core-shell particle preparation parameters, composition formulation, and process parameters were exactly the same as in Example 1.
[0070] Comparative Example 3 This comparative example removes the basic imidazole curing accelerator F (i.e., the amount of F is 0 parts by weight), while the types, amounts, and process parameters of the remaining components are exactly the same as in Example 1.
[0071] Performance testing The performance of the epoxy resin cured products prepared in the examples and comparative examples was tested, with the viscosity measured before curing: (1) Viscosity test of resin composition at 60℃: The viscosity of the resin composition was tested at 60℃ using an NDJ-8S digital rotational viscometer with a rotor speed of 60 rpm. (2) Glass transition temperature (Tg) test: Tested according to GB / T19466.2-2025 standard; (3) Elongation at break test: GB / T 2567-2021 standard test.
[0072] The test results are shown in Table 1: Group Viscosity at 60℃ (mPa·s) Tg (°C) Elongation at break (%) Example 1 5200 195 6.8 Example 2 6800 188 7.5 Example 3 5100 185 7.2 Example 4 5400 192 7.0 Example 5 5200 176 6.5 Comparative Example 1 4800 148 4.5 Comparative Example 2 5600 187 3.6 Comparative Example 3 5200 152 4.0 Examples 1-5 all exhibited viscosities at 60℃ ranging from 5100 to 6800 mPa·s, with a Tg of no less than 175℃ and an elongation at break of no less than 6.5%. These three properties fully meet the design requirements of this invention for low viscosity, high heat resistance, and high toughness, proving the feasibility of the technical solution of this invention. Among them, Example 1 showed the best overall performance, with a viscosity of 5200 mPa·s at 60℃, a Tg of 195℃, and an elongation at break of 6.8%.
[0073] Compared with Comparative Example 1, after replacing phenolic epoxy resin A with bisphenol A type epoxy resin (E-51), the cured product's Tg decreased from 195℃ to 148℃, which is 27℃ below the lower limit of heat resistance (175℃). The elongation at break decreased from 6.8% to 4.5%, while the viscosity at 60℃ decreased from 5200 mPa·s to 4800 mPa·s. This is because E-51 has a functionality of only about 2.0, and the density of the crosslinking network nodes after curing is significantly lower than that of phenolic epoxy resin with a functionality of 3.0-3.6. Insufficient crosslinking density leads to three consequences: (1) the degree of restriction on chain segment movement decreases, resulting in a significant decrease in Tg; (2) the intermolecular forces weaken, resulting in a decrease in elongation at break; and (3) the molecular weight is lower and the distribution is narrower, resulting in a decrease in system viscosity. However, the decrease in viscosity is accompanied by a serious loss of heat resistance and toughness, which cannot meet the high heat resistance and high toughness design requirements of this invention, proving that phenolic epoxy resin A is irreplaceable in this invention.
[0074] Compared with Comparative Example 1 and Comparative Example 2, after adjusting the core-shell mass ratio of core-shell rubber toughening agent B from 68:32 to 50:50, the viscosity of the system at 60℃ increased from 5200 mPa·s to 5600 mPa·s, Tg decreased from 195℃ to 187℃, and the elongation at break decreased significantly from 6.8% to 3.6%. This is because when the shell ratio is too high, three negative effects occur: (1) The volume fraction of soft rubber core in the core-shell particles is relatively reduced, and the stress concentration and cavitation toughening effect provided by the unit mass toughening agent is reduced; (2) The excessively thick hard PMMA shell restricts the elastic deformation response of the rubber core in the stress field at the crack tip, the crack propagation resistance decreases, and the elongation at break is significantly reduced; (3) The rigidity of the shell increases and the active GMA groups aggregate into the particle interior, the interfacial reaction efficiency with the epoxy matrix decreases, the high-speed shear dispersion resistance increases, and the viscosity of the system increases. The results show that a core-shell mass ratio of (60–80):(20–40) is a necessary condition for ensuring low viscosity, high toughness, and high heat resistance.
[0075] Compared with Comparative Example 1 and Comparative Example 3, after removing the basic imidazole curing accelerator F, the Tg of the cured product decreased from 195°C to 152°C, which is 23°C below the lower limit of heat resistance (175°C). The elongation at break decreased from 6.8% to 4.0%, while the viscosity at 60°C remained unaffected. This is because the 4,4'-DDS aromatic diamine has low activity, and without the accelerator, the curing conversion rate is insufficient under the curing process conditions specified in this invention. A large number of unreacted epoxy groups remain in the cured network, resulting in a severe decrease in effective crosslinking density, leading to a simultaneous and significant reduction in Tg and elongation at break. 2-Ethyl-4-methylimidazolium significantly improves the curing conversion rate by catalyzing the epoxy-amine addition reaction, enabling the cured network to reach a high crosslinking density state. It is a necessary component for achieving high Tg and high toughness, proving that the accelerator F is indispensable in this invention.
[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A low-viscosity, high-heat-resistant, toughened epoxy resin composition, characterized in that, The following components are included in parts by weight: Phenolic epoxy resin A: 100 parts by weight; Core-shell rubber toughening agent B: 5-15 parts by weight, wherein the core of the core-shell rubber toughening agent is cross-linked polybutyl acrylate rubber, and the outer shell is a terpolymer of methyl methacrylate-glycidyl methacrylate-crosslinking agent, wherein the glycidyl methacrylate monomer accounts for 5-15 wt% of the total mass of the outer shell monomers, the crosslinking agent accounts for 3-6 wt% of the total mass of the outer shell monomers, and the particle size is 80-150 nm; Aromatic diamine curing agent C: 35-43 parts by weight, is at least one of micronized 4,4'-diaminodiphenyl sulfone or 3,3'-diaminodiphenyl sulfone; Bifunctional epoxy reactive diluent D: 1 to 5 parts by weight, selected from at least one of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydroquinone diglycidyl ether; Silane coupling agent E: 0.5 to 2 parts by weight, selected from at least one of p-chlorophenyltriethoxysilane or phenyltrimethoxysilane; Basic imidazole curing accelerator F: 0.1 to 1 part by weight, selected from at least one of 2-ethyl-4-methylimidazolium or 2-phenylimidazolium.
2. The low-viscosity, high-heat-resistant, toughened epoxy resin composition according to claim 1, characterized in that, In the core-shell rubber toughening agent B, the weight ratio of the core to the shell is (60-80):(20-40).
3. The low-viscosity, high-heat-resistant, toughened epoxy resin composition according to claim 1, characterized in that, The crosslinking agent in the outer shell terpolymer is selected from at least one of ethylene glycol dimethacrylate, divinylbenzene, allyl methacrylate, and trimethylolpropane triacrylate.
4. A method for preparing a low-viscosity, high-heat-resistant, toughened epoxy resin composition according to any one of claims 1-3, characterized in that, The core-shell rubber toughening agent B is prepared by seed emulsion polymerization, including the following steps: Step 1: Using butyl acrylate as the main monomer, the crosslinking agent accounts for 1-3 wt% of the butyl acrylate monomer, potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier, emulsion polymerization is carried out at 65-70℃ for 10-15 h to obtain crosslinked polybutyl acrylate rubber core particle emulsion with a core particle size of 60-110 nm. Step 2: Add a mixture of shell monomers consisting of methyl methacrylate, glycidyl methacrylate and crosslinking agent dropwise to the core particle emulsion, and perform graft copolymerization at 75-80°C for 3-5 hours to obtain a core-shell particle emulsion; Step 3: The core-shell particle emulsion is demulsified, filtered, washed, and vacuum dried to obtain core-shell rubber toughening agent powder with a particle size of 80-150 nm.
5. A method for preparing a low-viscosity, high-heat-resistant, toughened epoxy resin composition according to any one of claims 1-4, characterized in that, Includes the following steps: Step S1: Preheat phenolic epoxy resin A at 65-75℃, add core-shell rubber toughening agent B, and shear and stir at 2000-4000 rpm for 20-40 minutes to make the core-shell particles evenly dispersed. The temperature during the shearing process should not exceed 80℃. Step S2: Cool the mixture to 40-50°C, and add micronized aromatic diamine curing agent C, bifunctional epoxy reactive diluent D, silane coupling agent E and basic imidazole curing accelerator F in sequence, and stir at 150-250 rpm for 40-50 min until uniform. Step S3: Degas under a vacuum of -0.09 to -0.10 MPa for 10 to 20 minutes; Step S4: Pour the degassed composition into the mold and cure it according to the following segmented curing process: heat up to 125-160℃ at 1-3℃ / min and hold for 2-3 hours for initial curing; then heat up to 180-190℃ at 1-3℃ / min and hold for 3-4 hours for post-curing; cool to room temperature in the furnace and demold to obtain the cured product.