Epoxy resin composition and preparation method thereof

Abstract

The invention discloses an epoxy resin composition and a preparation method thereof. The epoxy resin composition comprises the following raw materials in parts by mass: 23.6-111.0 parts of liquid resin; 7.5 to 55.5 parts by mass of a solid resin; 2.7-12.5 parts by mass of a curing agent; 0.5 to 3.6 parts by mass of an accelerant; 3.2 to 18.6 parts by mass of a toughening agent; the mass ratio C1 of the toughening agent to the curing agent is 1.04-2.48; and the mass ratio C2 of the accelerant to the curing agent is 0.19-0.40. By adjusting the mass ratio of each raw material component and adopting a step-by-step process, the balance between the curing effect and the toughening effect of the epoxy resin composition and the storage period of the prepreg can be promoted, local agglomeration of a curing agent and an accelerant after the toughening agent is added is avoided, the uniformity of a finished product of the epoxy resin composition can be effectively improved, and the service life of the prepreg is prolonged. And the processing quality and toughness of the prepreg and the composite material are improved.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and in particular to an epoxy resin composition and its preparation method. Background Technology

[0002] Epoxy resins are commonly used as matrix materials in composite materials, and their curing properties directly affect the processing technology, mechanical and thermal properties of the composite material. Among related technologies, latent medium-temperature curing epoxy resin compositions have been widely used in the field of resin-based composite materials due to their low curing temperature, short curing time, and long shelf life in the prepreg state. When toughness is required in the composite material, toughening agents are usually added to the latent medium-temperature curing epoxy resin composition to improve the toughness of the composite material by toughening the resin matrix.

[0003] However, since the curing agent in latent medium-temperature curing epoxy resin compositions is mostly in the form of micro powder, it is insoluble in epoxy resin before curing. Adding toughening agents can easily increase the viscosity of the resin composition and reduce its compatibility. Furthermore, micro powder curing agents are difficult to obtain sufficient shear force in high-viscosity systems, and the curing agent is prone to uneven dispersion and agglomeration, thereby affecting the curing performance and effect of the resin composition, and consequently affecting the quality and mechanical properties of the composite material. Summary of the Invention

[0004] To address the issues of uneven dispersion and easy agglomeration of micronized curing agents in toughening resin compositions, this application provides an epoxy resin composition and its preparation method. In this epoxy resin composition, the toughening agent is fully dissolved, and the curing agent and accelerator are uniformly dispersed, exhibiting excellent curing performance and toughening effect, thus meeting the requirements for preparing prepregs with high toughness, fast curing, low curing temperature, and long storage time.

[0005] According to a first aspect of this application, an epoxy resin composition is provided, the epoxy resin composition comprising the following raw materials in parts by weight: Liquid resin, 23.6-111.0 parts by weight; Solid resin 7.5-55.5 parts by weight; Curing agent 2.7-12.5 parts by weight; Accelerator: 0.5-3.6 parts by weight; Toughening agent 3.2-18.6 parts by weight; The mass ratio (C1) of the toughening agent to the curing agent is 1.04-2.48; The mass ratio of the accelerator to the curing agent, C2, is 0.19-0.40.

[0006] In some embodiments of this application, the liquid resin includes a first liquid resin and a second liquid resin, wherein the composition of the first liquid resin is different from that of the second liquid resin; The mass ratio of the first liquid resin to the second liquid resin, C3, is 0.42-1.00.

[0007] In some embodiments of this application, at 70°C, the viscosity of the epoxy resin composition is 17.3-29.6 Pa·s, and the coefficient of variation of the viscosity is 1.9-2.7%; and / or Within a temperature range of -30℃ to 250℃, the curing enthalpy of the epoxy resin composition is 333-386 J / g, and the coefficient of variation of the curing enthalpy is 1.2-1.6%.

[0008] In some embodiments of this application, the KIC of the casting made from the epoxy resin composition is 2.05-3.86 MPa. 1 / 2 The coefficient of variation of KIC in the cast body is 1.3-1.7%.

[0009] In some embodiments of this application, the curing temperature of the epoxy resin composition is 130-140°C.

[0010] According to a second aspect of this application, a prepreg is provided, which is prepared from any of the epoxy resin compositions described above.

[0011] According to a third aspect of this application, a method for preparing an epoxy resin composition is provided, the method being used to prepare the epoxy resin composition as described in any of the above-described methods, the method comprising the following steps: S1. Under the first preset conditions, the raw materials of the first resin composition are thoroughly stirred to obtain the first resin composition; S2. Under the second preset conditions, the raw materials of the second resin composition are thoroughly stirred to obtain the second resin composition; S3. Under the third preset conditions, a toughening agent is added to the second resin composition and stirred thoroughly to obtain a third resin composition. S4. Under the fourth preset condition, the first resin composition is added to the third resin composition and stirred thoroughly to obtain a mixture of the first resin composition and the third resin composition; S5. Under the fifth preset condition, the mixture is degassed under vacuum to obtain the epoxy resin composition.

[0012] In some embodiments of this application, the first preset conditions include: a stirring temperature of 70-80°C, a stirring speed of 80-105 r / min, and stirring until the first resin composition is uniformly dispersed. The second preset conditions include: raising the temperature to 90-100℃, and when the second resin composition is completely dissolved, setting the stirring speed to 295-320 r / min, and stirring until the second resin composition is uniformly mixed; The third preset conditions include: raising the temperature to 120-130℃, stirring at a speed of 295-320r / min, so that the toughening agent is completely dissolved, and stirring until the third resin composition is uniformly mixed. The fourth preset condition includes: lowering the temperature to 70-80℃, stirring at a speed of 80-105 r / min, and stirring until the mixture is uniformly dispersed; The fifth preset condition includes: degassing temperature of 70-80℃, degassing time of 10-20min, and degassing pressure of 0.070-0.080MPa.

[0013] In some embodiments of this application, the first resin composition comprises the following raw materials in parts by weight: The first liquid resin is 7.8-55.5 parts by weight; Curing agent 2.7-12.5 parts by weight; Accelerator: 0.5-3.6 parts by weight; The first liquid resin includes one or more of bisphenol glycidyl ether epoxy resin and phenolic epoxy resin; The curing agent includes one or more of amine curing agents, acid anhydride curing agents, and imidazole curing agents; The accelerator includes one or more of tertiary amine accelerators, modified amine accelerators, and substituted urea accelerators.

[0014] In some embodiments of this application, the third resin composition comprises the following raw materials in parts by weight: The second liquid resin is 15.8-55.5 parts by weight; Solid resin 7.5-55.5 parts by weight; Toughening agent 3.2-18.6 parts by weight; The second liquid resin includes one or more of bisphenol type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin and glycidyl ester type epoxy resin; The solid resin includes one or more of bisphenol type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin and glycidyl ester type epoxy resin; The toughening agent includes one or more of rubber-based reactive toughening agents and thermoplastic reactive toughening agents.

[0015] The technical solution provided in this application may include the following beneficial effects: This application, based on adjustments to the mass ratio of each raw material in the epoxy resin composition, employs a stepwise process to ensure sufficient dissolution of the toughening agent and uniform dispersion of the curing agent and accelerator. This effectively improves the uniformity and curing performance of the finished epoxy resin composition, effectively avoids poor resin wetting, uneven curing reaction, and bubble formation caused by uneven dispersion of the curing agent, effectively enhances the storage stability of the prepreg, extends the storage period of the prepreg, and improves the processing quality and toughening effect of the composite material.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] Figure 1 This is a stepwise preparation process flow diagram of an epoxy resin composition according to an exemplary embodiment.

[0019] Figure 2 This is an electron microscope photograph of the second resin composition before the toughening agent is dissolved, according to an exemplary embodiment.

[0020] Figure 3 This is an electron microscope image of the second resin composition toughening agent after dissolution, according to an exemplary embodiment.

[0021] Figure 4 This is an electron microscope photograph illustrating the dispersion of curing agents and accelerators in an epoxy resin composition according to an exemplary embodiment.

[0022] Figure 5 This is a rheological profile of an epoxy resin composition according to an exemplary embodiment. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0024] In related technologies, prepregs are key raw materials for manufacturing high-end lightweight structural components in aerospace, automotive, and rail transportation industries, achieving high fiber volume content, low porosity, and reprocessability. To ensure the reliability, economy, and industrial production of prepregs in high-end composite materials, a key research focus has been on improving the toughness, curing efficiency, and extending the shelf life of prepregs while maintaining their lightweight and high strength. The toughening effect and curing behavior of prepregs are primarily influenced by the toughening properties of the resin matrix and the curing temperature.

[0025] Epoxy resins are often used as resin matrix materials for composite materials due to their excellent adhesion, chemical resistance, and designable curing properties. Adding latent curing agents and accelerators to epoxy resins can lower their curing temperature, shorten curing time, and extend the shelf life of prepregs, thus forming latent medium-temperature curing epoxy resin compositions. However, untreated latent medium-temperature curing epoxy resin compositions can form a high-density three-dimensional cross-linked network in a short time, resulting in a high elastic modulus and low impact toughness after curing, exhibiting a significant tendency for brittle fracture. Therefore, toughening agents are usually added to latent medium-temperature curing epoxy resin compositions to improve the toughness of the composite material.

[0026] However, since the curing agents in latent medium-temperature curing epoxy resin compositions are mostly in the form of micronized powders and are insoluble in epoxy resins before curing, the addition of toughening agents significantly increases the viscosity of the system and weakens compatibility. This makes it difficult for the curing agents to obtain sufficient shear force in high-viscosity systems, resulting in uneven dispersion, agglomeration, and even sedimentation. This affects the uniformity of the resin composition, leading to difficulties in fiber impregnation and uneven local crosslinking in the prepreg. During storage, the local aggregation of micronized curing agents is accelerated, causing an abnormal increase in viscosity and a shortened latency period. Ultimately, this results in a narrowed processing window, decreased processing quality, and fluctuations in the strength, modulus, and impact toughness of the cured composite material, making it difficult to meet the high-strength requirements of high-end lightweight structural components. High toughness Low defect requirement.

[0027] Due to insufficient attention paid to the dispersion of curing agents in latent, medium-temperature curing epoxy resin compositions undergoing toughening treatment in related technologies, there may be defects such as complex processes and poor uniformity of finished epoxy resin compositions. This can lead to a narrowing of the processing window for prepregs, a decline in processing quality, reduced production efficiency, economic cost losses, and ultimately, defects in the performance of composite materials.

[0028] This application provides an epoxy resin composition comprising the following raw materials in parts by weight: 23.6-111.0 parts by weight of liquid resin; 7.5-55.5 parts by weight of solid resin; 2.7-12.5 parts by weight of curing agent; 0.5-3.6 parts by weight of accelerator; 3.2-18.6 parts by weight of toughening agent; the mass ratio C1 of toughening agent to curing agent is 1.04-2.48; and the mass ratio C2 of accelerator to curing agent is 0.19-0.40. This application only requires adjusting the mass ratio of each raw material component and employing a step-by-step process to promote a balance between curing effect, toughening effect, and prepreg shelf life. First, by increasing the mass ratio of liquid resin in this application, the viscosity of the system can be reduced, allowing the curing agent to obtain sufficient shear force during stirring or high-speed shearing. This disperses the curing agent agglomerates, resulting in a finer, more uniform dispersed phase in the resin composition. Furthermore, the settling velocity of the curing agent is lower in the low-viscosity system, allowing it to remain suspended in the resin composition for a longer period. Simultaneously, the polar epoxy groups of the liquid resin better wet the surface of the curing agent, reducing the interfacial tension between adjacent curing agents and preventing re-agglomeration, thereby improving the uniformity of curing agent dispersion in the resin composition. Moreover, by controlling the mass ratio (C1) of the toughening agent to the curing agent to be 1.04-2.48, this application not only effectively avoids the local enrichment of the curing agent due to insufficient shear stress caused by excessive addition of toughening agent and increased system viscosity, as well as the deterioration of compatibility between the toughening agent and curing agent phases, but also ensures sufficient crosslinking active sites, allowing the flexible phase of the toughening agent to effectively absorb energy, thus improving the toughening effect of the resin composition. Furthermore, by controlling the mass ratio (C2) of the accelerator to the curing agent to be 0.19-0.40, this application enhances the activation rate of the curing agent, enabling rapid and uniform cross-linking, reducing the curing temperature, and shortening the curing time. Simultaneously, it avoids the weakening of the latent properties of the epoxy resin composition due to excessive accelerator addition. Therefore, the epoxy resin composition of this application possesses excellent curing performance and toughening effect (viscosity: 17.3-29.6 Pa·s, curing temperature: 130-140℃, KIC of the casting made from the epoxy resin composition: 2.05-3.86 MPa). 1 / 2 Furthermore, this application uses a stepwise process to prepare the epoxy resin composition, which further improves the dispersion uniformity of the curing agent (the coefficients of variation of viscosity, curing reaction enthalpy, and KIC of the casting are all less than 2.7% when measured by multiple sampling points in the epoxy resin composition).

[0029] The specific embodiments described below are intended to help those skilled in the art understand this embodiment, but this embodiment is not limited to the specific embodiments described below.

[0030] An exemplary embodiment of this application provides an epoxy resin composition comprising the following raw materials in parts by weight: Liquid resin, 23.6-111.0 parts by weight; Solid resin 7.5-55.5 parts by weight; Curing agent 2.7-12.5 parts by weight; Accelerator: 0.5-3.6 parts by weight; Toughening agent 3.2-18.6 parts by weight; The mass ratio of toughening agent to curing agent (C1) is 1.04-2.48; The mass ratio of accelerator to curing agent (C2) is 0.19-0.40.

[0031] In this embodiment, the liquid resin is the matrix component of the composition, providing the main framework and flowability of the epoxy network. Its content determines the viscosity, processability, and crosslinking density of the system after curing. By increasing the mass percentage of liquid resin, the viscosity of the system can be reduced, allowing the curing agent to obtain sufficient shear force during stirring or high-speed shearing, thereby breaking up curing agent agglomerates and forming a finer, more uniform dispersed phase in the resin composition. Furthermore, the settling velocity of the curing agent is lower in the low-viscosity system, allowing it to remain suspended in the resin composition for a longer period. Simultaneously, the polar epoxy groups of the liquid resin can better wet the surface of the curing agent, reducing the interfacial tension between adjacent curing agents and preventing re-agglomeration, thus improving the uniformity of curing agent dispersion in the resin composition. However, excessively high liquid resin content will dilute the concentration of the curing agent and accelerator, increasing the curing temperature and slowing down the curing rate. Therefore, in this embodiment, the liquid resin content is 23.6-111.0 parts by mass.

[0032] In this embodiment, the solid resin can provide additional crosslinking sites, regulate the curing rate and storage latency, inhibit the aggregation of the curing agent, and prolong the latency. However, excessive addition of solid resin can hinder heat conduction, leading to increased curing temperature and prolonged curing time. Furthermore, too much solid resin can increase the viscosity of the resin composition, weakening the uniform dispersion of the toughening agent and curing agent, thus affecting the toughening effect and curing uniformity. Therefore, in this embodiment, the content of solid resin is 7.5-55.5 parts by weight.

[0033] In this embodiment, the curing agent is a key component in the epoxy resin composition that provides crosslinking activity. It generates a three-dimensional crosslinked network through a ring-opening reaction with epoxy groups, thereby curing the resin. The content of the curing agent directly determines the curing performance, crosslinking density, mechanical properties, and storage latency of the prepreg. If the curing agent content is too low, it will lead to insufficient resin crosslinking, increased curing temperature, prolonged curing time, and reduced strength, modulus, and heat resistance of the prepreg and composite material. Conversely, if the curing agent content is too high, it will lead to excessively rapid and excessive crosslinking, excessively low curing temperature, excessively short curing time, high viscosity and brittleness of the resin composition, shortened prepreg storage period, and uneven dispersion of curing agent particles, resulting in a narrowed processing window, decreased processing quality, and fluctuations in the strength, modulus, and impact toughness of the cured composite material. Therefore, in this embodiment, the curing agent content is 2.7-12.5 parts by weight.

[0034] In this embodiment, the accelerator can promote the activation of the curing agent, reduce the activation energy of the crosslinking reaction, thereby lowering the curing temperature and shortening the curing time. However, excessive accelerator content can lead to excessively low viscosity of the resin composition, and the toughening agent phase may undergo phase separation, weakening the toughening effect. Therefore, in this embodiment, the accelerator content is 0.5-3.6 parts by weight.

[0035] In this embodiment, the toughening agent forms a flexible phase in the cross-linked network, providing energy dissipation and bridging at the crack tip, thereby preventing crack propagation in the resin matrix under impact or stress concentration, thus improving the fracture toughness of the resin matrix. However, the toughening agent can increase the viscosity of the resin composition, weaken the shear dispersion of the curing agent, and thus affect the dispersibility of the curing agent, leading to uneven curing. Therefore, in this embodiment, the content of the toughening agent is 3.2-18.6 parts by weight.

[0036] In this embodiment, since the toughening agent affects the dispersion uniformity of the curing agent, and the curing agent affects the toughening effect of the toughening agent, in order to effectively avoid the local enrichment of the curing agent due to insufficient shear stress caused by the increase in system viscosity due to excessive addition of toughening agent, and the deterioration of the compatibility between the toughening agent phase and the curing agent phase; and to ensure that the flexible phase of the toughening agent can effectively absorb energy to improve the toughening effect of the resin composition while ensuring sufficient crosslinking active sites, it is necessary to control the mass ratio of toughening agent to curing agent. For example, the mass ratio C1 of toughening agent to curing agent is 1.04-2.48. The mass ratio of toughening agent to curing agent can be 1.34, 1.56, 1.89, 2.20, 2.31, 2.45, or any ratio between the exemplary mass ratios, such as any ratio between 1.56 and 2.45.

[0037] In this embodiment, to improve the activation rate of the curing agent, enabling it to achieve rapid and uniform cross-linking, lower the curing temperature, and shorten the curing time, while avoiding excessive addition of the accelerator which would weaken the latent properties of the epoxy resin composition, thus ensuring that the epoxy resin composition of this application possesses both excellent curing performance and toughening effect, it is necessary to control the mass ratio of the accelerator to the curing agent. For example, the mass ratio C2 of the accelerator to the curing agent is 0.19-0.40. The mass ratio of the accelerator to the curing agent can be 0.20, 0.25, 0.30, 0.33, 0.36, or 0.39, or any of the exemplary mass ratios, such as any ratio between 0.20 and 0.39.

[0038] In this exemplary embodiment, by adjusting the content of liquid resin, solid resin, curing agent, accelerator and toughening agent, a balance between curing performance and toughening effect of epoxy resin composition is achieved. The prepreg prepared from this epoxy resin composition has a lower curing temperature, shorter curing time, longer storage period, and uniform curing, resulting in good toughening effect.

[0039] In an exemplary embodiment, the liquid resin includes a first liquid resin and a second liquid resin, wherein the composition of the first liquid resin is different from that of the second liquid resin; the mass ratio C3 of the first liquid resin and the second liquid resin is 0.42-1.00.

[0040] In this embodiment, the liquid resin includes a first liquid resin and a second liquid resin. First, the first liquid resin is used as a solvent matrix at a low temperature, and a predetermined amount of curing agent and accelerator are added to it. At this time, the system viscosity is low, which can provide sufficient fluidity for the dispersion of the curing agent and accelerator and fully wet the curing agent and accelerator. At this time, the low shear force can effectively avoid the local agglomeration of the curing agent in the liquid resin, so as to ensure the formation of a stable and uniform resin composition solution before subsequent temperature rise and curing. The low shear force can also prevent the temperature rise from triggering the crosslinking reaction, forming a first resin composition in which the curing agent and accelerator are uniformly dispersed. Second, the second liquid resin is used to mix with the solid resin to construct the main epoxy body, so as to adjust the overall viscosity of the resin composition and provide a large number of epoxy functional groups for subsequent crosslinking network. At a high temperature, the solid resin can be fully melted and uniformly mixed, finally forming a second resin composition with good fluidity, providing a suitable flow environment for the high-temperature dispersion and dissolution of the toughening agent.

[0041] Since the toughening agent requires a higher temperature to dissolve, and to avoid local sedimentation or agglomeration of the curing agent and accelerator due to the increased resin viscosity caused by the addition of the toughening agent, resulting in deterioration of interfacial compatibility, in this embodiment, a predetermined amount of toughening agent is added to the second resin composition with good flowability. The temperature is then further increased to promote the complete dissolution of the toughening agent and to provide sufficient shear force so that the toughening agent is fully dispersed in the second resin composition, thereby forming a third resin composition with higher uniformity. To avoid triggering the crosslinking reaction of the first resin composition, the first resin composition is added to the third resin composition after the third resin composition is cooled to a certain range. The mixture is then stirred thoroughly under low shear force to obtain a well-uniform mixture. Finally, the epoxy resin composition of this application is obtained by vacuum degassing.

[0042] In this embodiment, the composition of the first liquid resin and the second liquid resin may be the same or different. For example, the first liquid resin may be a bisphenol-type glycidyl ether epoxy resin or a phenolic epoxy resin; the first liquid resin may also be a mixture of various liquid resins selected above. The second liquid resin may be a bisphenol-type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin, or a glycidyl ester-type epoxy resin; the second liquid resin may also be a mixture of various liquid resins selected above.

[0043] In this embodiment, to ensure sufficient fluidity and effectively improve the dispersion uniformity of the curing agent and accelerator in the epoxy resin composition, and to ensure the complete dissolution of the solid resin and toughening agent, it is necessary to control the mass ratio of the first liquid resin to the second liquid resin. For example, the mass ratio C3 of the first liquid resin to the second liquid resin is 0.42-1.00. The mass ratio of the first liquid resin to the second liquid resin can be 0.45, 0.55, 0.62, 0.73, 0.85, or 0.98. The mass ratio of the first liquid resin to the second liquid resin can also be any ratio between the exemplary mass ratios; for example, the mass ratio of the first liquid resin to the second liquid resin can be any ratio between 0.55 and 0.98.

[0044] In one exemplary embodiment, at 70°C, the viscosity of the epoxy resin composition is 17.3-29.6 Pa·s, and the coefficient of variation of the viscosity is 1.9-2.7%; and / or Within the temperature range of -30℃ to 250℃, the curing enthalpy of the epoxy resin composition is 333-386 J / g, and the coefficient of variation of the curing enthalpy is 1.2-1.6%.

[0045] In this embodiment, the viscosity of the epoxy resin composition at 70°C is 17.3-29.6 Pa·s, meaning it maintains good processing fluidity at the processing temperature. This ensures sufficient wetting of the fibers without affecting the impregnation rate and degassing efficiency due to excessive viscosity. Furthermore, under the same batch and temperature conditions, the viscosity variation coefficient at each sampling point is 1.9-2.7%, significantly lower than 3%, indicating that the epoxy resin composition of this application has excellent uniformity, ensuring the repeatability of the subsequent curing process, improving production efficiency, and effectively reducing economic losses and production defects caused by uneven curing.

[0046] In this embodiment, within the temperature range of -30℃ to 250℃, the curing enthalpy of the epoxy resin composition is 333-386 J / g, and the coefficient of variation of the curing enthalpy is 1.2-1.6%. Its narrow enthalpy range and low coefficient of variation can avoid local overheating or thermal shock during casting or prepreg processing, thereby reducing the risk of residual stress and warping, improving the stability and repeatability of the process in industrial production, and further improving production efficiency.

[0047] In one exemplary embodiment, the KIC of the casting made from the epoxy resin composition is 2.05-3.86 MPa. 1 / 2 The coefficient of variation of KIC in the cast body is 1.3-1.7%.

[0048] The fracture toughness of epoxy resin compositions in actual use can be analyzed by measuring the KIC (Mode I critical stress intensity factor) of the cast body. In this embodiment, the epoxy resin composition was heated at 70-80°C to improve its fluidity, poured into a KIC mold, and vacuum degassed at 70-80°C for 10-20 minutes. The temperature was then raised to 130-140°C and held for 115-135 minutes to obtain a cured resin casting sample. The KIC of the sample was tested, and it was found that the epoxy resin composition prepared by the formulation of this application can achieve uniform dispersion of curing agent, accelerator, and toughening agent, and has excellent toughening effect. Moreover, the coefficient of variation of KIC of the cast bodies produced by epoxy resin compositions sampled from different points in the same batch under the same process conditions was 1.3-1.7%, indicating that the epoxy resin composition of this application has excellent uniformity, good process repeatability, and good product quality uniformity.

[0049] In an exemplary embodiment, the curing temperature of the epoxy resin composition is 130-140°C.

[0050] The curing agent itself needs to overcome a certain activation energy to undergo a ring-opening reaction with the epoxy groups. Different types of curing agents have significantly different activation energies; the higher the activation energy, the higher the curing temperature. Furthermore, the amount of curing agent also affects the number of reactive sites in the resin composition, thus influencing the curing temperature. Accelerators, on the other hand, can lower the curing temperature required for the curing reaction by reducing the activation energy of the curing agent. In this embodiment, by controlling the type, content, and mass ratio of the accelerator and curing agent in the epoxy resin composition, the curing temperature can be adjusted, thereby achieving a curing temperature of 130-140°C for the epoxy resin composition in this application and extending its shelf life.

[0051] An exemplary embodiment of this application provides a prepreg prepared from any of the epoxy resin compositions described above. In this embodiment, the prepreg can be obtained from the epoxy resin composition of this application by any of the methods selected from solution impregnation, melt impregnation, film lamination, and spraying / dispensing. Furthermore, due to the excellent finished product uniformity, toughening effect, and medium-temperature curing characteristics of the epoxy resin composition of this application, the curing uniformity, production efficiency, and fracture toughness of the prepreg are effectively improved, and its shelf life is extended, facilitating storage and transportation at room temperature during the production process.

[0052] like Figure 1 As shown, an exemplary embodiment of this application provides a method for preparing an epoxy resin composition. The method for preparing the epoxy resin composition is used to prepare any of the epoxy resin compositions described above, and the method includes the following steps: S1. Under the first preset conditions, the raw materials of the first resin composition are thoroughly stirred to obtain the first resin composition; S2. Under the second preset conditions, the raw materials of the second resin composition are thoroughly stirred to obtain the second resin composition; S3. Under the third preset conditions, a toughening agent is added to the second resin composition and stirred thoroughly to obtain the third resin composition. S4. Under the fourth preset conditions, the first resin composition is added to the third resin composition and stirred thoroughly to obtain a mixture of the first resin composition and the third resin composition. S5. Under the fifth preset condition, the mixture is degassed under vacuum to obtain an epoxy resin composition.

[0053] In this embodiment, a stepwise process is used to prepare the epoxy resin composition, which can effectively improve the dispersion uniformity of the curing agent and the promoter, and ensure the excellent toughening effect of the epoxy resin composition, while avoiding the triggering of crosslinking reaction during the preparation process.

[0054] In this embodiment, the first preset conditions include: a stirring temperature of 70-80℃, a stirring speed of 80-105r / min, and stirring until the first resin composition is uniformly dispersed.

[0055] In this embodiment, the first resin composition comprises the following raw materials in parts by weight: 7.8-55.5 parts by weight of first liquid resin; 2.7-12.5 parts by weight of curing agent; and 0.5-3.6 parts by weight of accelerator. In a low-temperature environment of 70-80°C, by providing sufficient first liquid resin as a solvent matrix and adding a predetermined amount of curing agent and accelerator, the system's low viscosity can be ensured. This provides sufficient fluidity for the dispersion of the curing agent and accelerator, and fully wets them. This allows the curing agent and accelerator to obtain sufficient shear force during stirring or shearing, thereby breaking up curing agent agglomerates and forming a finer, more uniform dispersed phase in the resin composition. Furthermore, the settling velocity of the curing agent is lower in the low-viscosity system, allowing it to remain suspended in the resin composition for a longer period. The stirring speed is set to 80-105 r / min to provide low shear force, which can effectively prevent local agglomeration of the curing agent in the liquid resin, ensuring the formation of a stable and uniform resin composition solution before subsequent temperature curing. The low shear force can also prevent the temperature from rising and triggering the crosslinking reaction, forming a first resin composition in which the curing agent and accelerator are uniformly dispersed. Furthermore, by controlling the type, content, and mass ratio of the accelerator and curing agent in the epoxy resin composition, the curing temperature can be adjusted, thereby enabling the epoxy resin composition in this application to achieve medium-temperature curing and extending its shelf life.

[0056] In this embodiment, the second preset conditions include: raising the temperature to 90-100℃, when the second resin composition is completely dissolved, setting the stirring speed to 295-320 r / min, and stirring until the second resin composition is uniformly mixed.

[0057] In this embodiment, the second resin composition comprises the following raw materials in parts by weight: 15.8-55.5 parts by weight of second liquid resin; and 7.5-55.5 parts by weight of solid resin. At a high temperature of 90-100°C, sufficient second liquid resin is provided to mix with a predetermined amount of solid resin to construct the main epoxy matrix. This adjusts the overall viscosity of the resin composition and provides sufficient epoxy functional groups for subsequent crosslinking networks, ensuring the flowability of the epoxy resin composition and the strength of the prepreg or composite material prepared therefrom. The stirring speed is set to 295-320 r / min, allowing the solid resin to fully melt and mix uniformly at high temperature, ultimately forming a second resin composition with good flowability. This provides a suitable flow environment for the subsequent high-temperature dispersion and dissolution of the toughening agent.

[0058] In this embodiment, the third preset conditions include: raising the temperature to 120-130°C, stirring at a speed of 295-320 r / min, so that the toughening agent is completely dissolved, and stirring until the third resin composition is uniformly mixed.

[0059] In this embodiment, the third resin composition comprises the following raw materials in parts by weight: 15.8-55.5 parts by weight of the second liquid resin; 7.5-55.5 parts by weight of the solid resin; and 3.2-18.6 parts by weight of the toughening agent. Since the toughening agent requires a higher temperature to dissolve, and to avoid localized sedimentation or agglomeration of the curing agent and accelerator due to increased resin viscosity caused by the addition of the toughening agent, resulting in deterioration of interfacial compatibility, in this embodiment, a predetermined amount of toughening agent is added to the free-flowing second resin composition. The temperature is further increased to 120-130°C to promote complete dissolution of the toughening agent, and the stirring speed is set to 295-320 r / min to provide sufficient shear force to ensure sufficient dispersion of the toughening agent in the second resin composition, thereby forming a more uniform third resin composition and maximizing the toughening effect. Figure 2 and Figure 3 The electron microscope images of the toughening agent in the second resin composition before and after dissolution show that the toughening agent in this embodiment was fully dissolved and uniformly dispersed, while the number of bubbles in the resin composition was significantly reduced.

[0060] In this embodiment, the fourth preset condition includes: lowering the temperature to 70-80℃, stirring at a speed of 80-105 r / min, and stirring until the mixture is uniformly dispersed.

[0061] In this embodiment, to avoid triggering the crosslinking reaction of the first resin composition, the third resin composition is cooled to 70-80°C, and then the first resin composition is added to the third resin composition. The stirring speed is set to 80-105 r / min to avoid the thermal effect under high shear. The mixture of the first resin composition and the third resin composition with good uniformity is obtained under low shear force. This not only ensures that the toughening agent is fully dissolved, but also improves the dispersion uniformity of the curing agent and the accelerator.

[0062] In this embodiment, the fifth preset conditions include: a degassing temperature of 70-80℃, a degassing time of 10-20 min, and a degassing pressure of 0.070-0.080 MPa.

[0063] In this embodiment, at a temperature of 70-80℃, the degassing pressure is set to 0.070-0.080 MPa, and the mixture of the first resin composition and the third resin composition is subjected to vacuum degassing treatment for 10-20 minutes. The final product is an epoxy resin composition with uniform dispersion of the curing agent and accelerator, good product uniformity, and few bubbles. Figure 4 As shown.

[0064] For example, such as Figure 5 As shown, the epoxy resin composition in this embodiment has a viscosity of 21.25 Pa·s at 70°C, exhibiting good processing fluidity, which ensures that the resin is fully impregnated between fibers and maintains uniform spreading. Furthermore, at 130°C, the viscosity of the epoxy resin composition begins to increase sharply with increasing temperature, indicating that it can achieve medium-temperature rapid curing.

[0065] In this embodiment, the first liquid resin in the first resin composition can be a bisphenol type glycidyl ether epoxy resin and a phenolic epoxy resin; the first liquid resin can also be a mixture of various liquid resins selected above. The curing agent can be an amine curing agent, an anhydride curing agent, and an imidazole curing agent; the curing agent can also be a mixture of various curing agents selected above. The accelerator can be a tertiary amine accelerator, a modified amine accelerator, and a substituted urea accelerator; the accelerator can also be a mixture of various accelerators selected above.

[0066] In this embodiment, in the third resin composition, the second liquid resin can be a bisphenol-type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin, or glycidyl ester-type epoxy resin; the second liquid resin can also be a mixture of various of the above liquid resins. The solid resin can be a bisphenol-type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin, or glycidyl ester-type epoxy resin; the solid resin can also be a mixture of various of the above solid resins. The toughening agent can be a rubber-based reactive toughening agent or a thermoplastic reactive toughening agent; the toughening agent can also be a mixture of various of the above toughening agents.

[0067] In this embodiment, the composition of the first liquid resin and the second liquid resin may be the same or different. For example, the first liquid resin may be a bisphenol-type glycidyl ether epoxy resin or a phenolic epoxy resin; the first liquid resin may also be a mixture of various liquid resins selected above. The second liquid resin may be a bisphenol-type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin, or a glycidyl ester-type epoxy resin; the second liquid resin may also be a mixture of various liquid resins selected above.

[0068] The epoxy resin composition of this application avoids the problem of uneven dispersion of curing agent and accelerator caused by the increase in system viscosity due to the addition of toughening agent by controlling the content of each raw material component and the mass ratio between toughening agent and curing agent. By controlling the mass ratio C3 of the first liquid resin and the second liquid resin to 0.42-1.00 and adopting a stepwise process, the first liquid resin is used to fully impregnate the curing agent and accelerator at low temperature and low shear force, while fully dispersing the curing agent and accelerator, avoiding local agglomeration and uneven resin curing, and also avoiding the triggering of crosslinking reaction due to excessive temperature. The second liquid resin, under high temperature and high shear force, acts as a solvent matrix and fully mixes with the dissolved solid resin, providing sufficient crosslinking sites and sufficient fluidity for the subsequent addition and mixing of toughening agent. Furthermore, the temperature is further increased to allow the addition of toughening agent to be fully dispersed and dissolved. Finally, the first and third resin compositions were mixed at low temperature and low shear force, and vacuum degassing was performed to obtain the finished epoxy resin composition. This process ensured that the solid resin and toughening agent were fully dispersed and dissolved, as well as that the curing agent and accelerator were uniformly dispersed. It also avoided the problem of difficult temperature control during simultaneous mixing, which could easily trigger crosslinking reactions. Furthermore, this application also lowered the curing temperature of the epoxy resin composition and accelerated the curing speed by adjusting the mass ratio between the accelerator and the curing agent. The final product is an epoxy resin composition with good uniformity, good processing fluidity, capable of medium-temperature rapid curing, long prepreg shelf life, and excellent toughening effect.

[0069] To more clearly explain the technical solution of this application, specific embodiments of epoxy resin compositions are provided. The beneficial effects of selecting the above-mentioned range of raw material contents will be explained through specific experimental data provided in the specific embodiments.

[0070] Example It should be noted that the content of this invention is not limited to the following embodiments.

[0071] Example 1: An epoxy resin composition was prepared by the following method: (1) Preparation of the first resin composition: 20 parts by mass of liquid bisphenol A type epoxy resin, 5 parts by mass of dicyandiamide curing agent, and 2 parts by mass of substituted urea accelerator are added to a stirring tank and mixed. The temperature of the stirring tank is increased to 70°C and the stirring speed is set to 100 r / min. After the curing agent and accelerator powder are evenly dispersed in the dissolved matrix raw material, a pre-dispersed first resin composition containing curing components is obtained. (2) Preparation of the second resin composition: 40 parts by weight of liquid bisphenol A epoxy resin, 32 parts by weight of solid bisphenol A epoxy resin and 8 parts by weight of phenoxy resin were put into the reactor and mixed. The temperature of the reactor was raised to 90°C. After the solid bisphenol A epoxy resin melted into a gel state, the stirring speed was set to 300 r / min to make the two epoxy resins fully mixed to obtain the second resin composition. (3) Preparation of the third resin composition: Set the temperature of the reactor to 130°C, preheat the second resin composition, add 6 parts by mass of polyethersulfone toughening agent powder in batches, set the stirring speed to 300 r / min, so that the toughening agent is fully and uniformly dissolved in the resin solution, observe the dissolution of the toughening agent, and obtain the third resin composition containing toughening components after complete dissolution. (4) Mixing and vacuum degassing treatment: Reduce the temperature of the reactor to 70°C, mix the pre-dispersed first resin composition containing curing components with the third resin composition containing toughening components, set the stirring speed to 100 r / min, and make the two fully mixed. Observe the dispersion state of the curing agent and accelerator powder in the resin solution. After uniform dispersion, a mixture of the first resin composition and the third resin composition is obtained. After degassing under vacuum of 0.075 MPa for 10 min, the final epoxy resin composition is obtained.

[0072] Example 2: An epoxy resin composition was prepared by the following method: (1) Preparation of the first resin composition: 7.8 parts by weight of liquid bisphenol F type epoxy resin, 2.7 parts by weight of acid anhydride curing agent, and 0.5 parts by weight of tertiary amine accelerator are added to a stirring tank and mixed. The temperature of the stirring tank is increased to 80°C and the stirring speed is set to 100 r / min. After the curing agent and accelerator powder are evenly dispersed in the dissolved matrix raw material, a pre-dispersed first resin composition containing curing components is obtained. (2) Preparation of the second resin composition: 15.8 parts by weight of liquid bisphenol S-type epoxy resin and 7.5 parts by weight of solid phenolic polyepoxy resin were added to the reactor and mixed. The temperature of the reactor was raised to 90°C. After the solid phenolic polyepoxy resin melted into a gel state, the stirring speed was set to 300 r / min to fully mix the two epoxy resins and obtain the second resin composition. (3) Preparation of the third resin composition: Set the temperature of the reactor to 125℃, preheat the second resin composition, and add 3.2 parts by mass of polyetherimide toughening agent powder in batches. Set the stirring speed to 300r / min to make the toughening agent fully and uniformly dissolve in the resin solution. Observe the dissolution of the toughening agent. After complete dissolution, the third resin composition containing toughening components is obtained. (4) Mixing and vacuum degassing treatment: Reduce the temperature of the reactor to 80°C, mix the pre-dispersed first resin composition containing curing components with the third resin composition containing toughening components, set the stirring speed to 100 r / min, and make the two fully mixed. Observe the dispersion state of the curing agent and accelerator powder in the resin solution. After uniform dispersion, a mixture of the first resin composition and the third resin composition is obtained. After degassing under vacuum of 0.075 MPa for 20 min, the final epoxy resin composition is obtained.

[0073] Performance testing After cooling the epoxy resin composition to room temperature, multiple samples were taken, and the following tests were performed on samples from different locations of the same epoxy resin composition: (1) The thermal properties were characterized using a rheometer, and the viscosity variation coefficient of the same epoxy resin composition at different sampling points at 70℃ was analyzed. (2) The enthalpy of curing reaction of the same epoxy resin composition at different sampling points in the temperature range of -30℃ to 250℃ was characterized by using a differential scanner, and the coefficient of variation of the enthalpy of curing reaction of samples at different points in this temperature range was analyzed. (3) Samples of the same epoxy resin composition from different sampling points were placed in an oven at 80°C and heated for 15 minutes to make them have good fluidity. They were then poured into KIC molds, placed in a vacuum oven, degassed at 85°C for 20 minutes, and then heated to 135°C and kept at that temperature for 120 minutes to obtain cured epoxy resin composition castings. The KIC of different samples were tested using a universal testing machine to analyze the coefficient of variation of the KIC of different samples.

[0074] To more clearly explain the technical solution of this application, examples 3-8 of epoxy resin are also provided. The formulations and properties of examples 1-8 are shown in Table 1. It should be noted that, except for the parameters listed in Table 1, the specific types of each raw material component in examples 3-8 may be the same as or different from those in examples 1-2.

[0075] In Table 1, the ratio C1 is the mass ratio of toughening agent to curing agent; The ratio C2 is the mass ratio of accelerator to curing agent; The ratio C3 is the mass ratio of the first liquid resin to the second liquid resin; Table 1 Formulation of the epoxy resin compositions in the examples

[0076] As can be seen from Examples 1-8 in Table 1, the epoxy resin compositions prepared by the stepwise process according to the epoxy resin composition formulation of this application have an average viscosity of 17.3-29.6 Pa·s at 70°C. This means that the epoxy resin compositions can maintain good processing fluidity at the processing temperature, which can ensure sufficient wetting of the fibers without affecting the impregnation speed and degassing efficiency due to excessive viscosity.

[0077] As can be seen from Examples 1-8, the viscosity variation coefficient at each sampling point of the same resin composition is less than 2.7%, indicating that the epoxy resin composition of this application has excellent finished product uniformity, which can ensure the repeatability of the subsequent curing process, improve production efficiency, and effectively reduce economic losses and production defects caused by uneven curing. Furthermore, within the temperature range of -30℃ to 250℃, the average curing reaction enthalpy of the epoxy resin composition is 333-386 J / g, and the variation coefficient of the curing reaction enthalpy of the samples at each sampling point of the same resin composition is less than 1.6%. Its narrow curing reaction enthalpy range and low variation coefficient further demonstrate that the epoxy resin composition of this application possesses excellent finished product uniformity, which can avoid local overheating or thermal shock during casting or prepreg processing, thereby reducing the risk of residual stress and warping, improving the stability and repeatability of the process in industrial production, and further improving production efficiency.

[0078] As can be seen from Examples 1-8 in Table 1, the average KIC value of the castings made from the epoxy resin composition is 2.05-3.86 MPa. 1 / 2 Furthermore, the coefficient of variation of KIC of the casting specimens corresponding to samples taken from different points of the same epoxy resin composition is less than 1.7%, indicating that the epoxy resin composition prepared by the formulation of this application can achieve uniform dispersion of curing agent, accelerator and toughening agent, uniform curing and excellent toughening effect.

[0079] In summary, the epoxy resin composition of this application, prepared by controlling the content of each raw material component and using a stepwise process, can effectively avoid the problem of uneven dispersion of curing agent and accelerator caused by the addition of toughening agent, which leads to the increase in system viscosity and deterioration of interfacial compatibility. It can achieve uniform dispersion of curing agent, accelerator and toughening agent, so that the prepreg and composite material can be uniformly cured, reducing product defects and enhancing the toughness of the resin matrix.

[0080] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0081] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An epoxy resin composition, characterized in that, The epoxy resin composition comprises the following raw materials in parts by weight: Liquid resin, 23.6-111.0 parts by weight; Solid resin 7.5-55.5 parts by weight; Curing agent 2.7-12.5 parts by weight; Accelerator: 0.5-3.6 parts by weight; Toughening agent 3.2-18.6 parts by weight; The mass ratio (C1) of the toughening agent to the curing agent is 1.04-2.48; The mass ratio of the accelerator to the curing agent, C2, is 0.19-0.

40.

2. The epoxy resin composition according to claim 1, characterized in that, The liquid resin includes a first liquid resin and a second liquid resin; The mass ratio of the first liquid resin to the second liquid resin, C3, is 0.42-1.

00.

3. The epoxy resin composition according to claim 1 or 2, characterized in that, At 70°C, the viscosity of the epoxy resin composition is 17.3-29.6 Pa·s, and the coefficient of variation of the viscosity is 1.9-2.7%; and / or Within a temperature range of -30℃ to 250℃, the curing enthalpy of the epoxy resin composition is 333-386 J / g, and the coefficient of variation of the curing enthalpy is 1.2-1.6%.

4. The epoxy resin composition according to claim 1 or 2, characterized in that, The KIC of the casting made from the epoxy resin composition is 2.05-3.86 MPa. 1 / 2 The coefficient of variation of KIC in the cast body is 1.3-1.7%.

5. The epoxy resin composition according to claim 1 or 2, characterized in that, The curing temperature of the epoxy resin composition is 130-140℃.

6. A prepreg, characterized in that, The prepreg is prepared from the epoxy resin composition according to any one of claims 1-5.

7. A method for preparing an epoxy resin composition, characterized in that, The method for preparing the epoxy resin composition is used to prepare the epoxy resin composition according to any one of claims 1-6, and the preparation method includes the following steps: S1. Under the first preset conditions, the raw materials of the first resin composition are thoroughly stirred to obtain the first resin composition; S2. Under the second preset conditions, the raw materials of the second resin composition are thoroughly stirred to obtain the second resin composition; S3. Under the third preset conditions, a toughening agent is added to the second resin composition and stirred thoroughly to obtain a third resin composition. S4. Under the fourth preset condition, the first resin composition is added to the third resin composition and stirred thoroughly to obtain a mixture of the first resin composition and the third resin composition; S5. Under the fifth preset condition, the mixture is degassed under vacuum to obtain the epoxy resin composition.

8. The method for preparing the epoxy resin composition according to claim 7, characterized in that, The first preset conditions include: a stirring temperature of 70-80℃, a stirring speed of 80-105 r / min, and stirring until the first resin composition is uniformly dispersed; The second preset conditions include: raising the temperature to 90-100℃, and when the second resin composition is completely dissolved, setting the stirring speed to 295-320 r / min, and stirring until the second resin composition is uniformly mixed; The third preset conditions include: raising the temperature to 120-130℃, stirring at a speed of 295-320r / min, so that the toughening agent is completely dissolved, and stirring until the third resin composition is uniformly mixed. The fourth preset condition includes: lowering the temperature to 70-80℃, stirring at a speed of 80-105 r / min, and stirring until the mixture is uniformly dispersed; The fifth preset condition includes: degassing temperature of 70-80℃, degassing time of 10-20min, and degassing pressure of 0.070-0.080MPa.

9. The method for preparing the epoxy resin composition according to claim 8, characterized in that, The first resin composition comprises the following raw materials in parts by weight: The first liquid resin is 7.8-55.5 parts by weight; Curing agent 2.7-12.5 parts by weight; Accelerator: 0.5-3.6 parts by weight; The first liquid resin includes one or more of bisphenol glycidyl ether epoxy resin and phenolic epoxy resin; The curing agent includes one or more of amine curing agents, acid anhydride curing agents, and imidazole curing agents; The accelerator includes one or more of tertiary amine accelerators, modified amine accelerators, and substituted urea accelerators.

10. The epoxy resin composition according to claim 8, characterized in that, The third resin composition comprises the following raw materials in parts by weight: The second liquid resin is 15.8-55.5 parts by weight; Solid resin 7.5-55.5 parts by weight; Toughening agent 3.2-18.6 parts by weight; The second liquid resin includes one or more of bisphenol type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin and glycidyl ester type epoxy resin; The solid resin includes one or more of bisphenol type glycidyl ether epoxy resin, phenoxy resin, phenolic epoxy resin and glycidyl ester type epoxy resin; The toughening agent includes one or more of rubber-based reactive toughening agents and thermoplastic reactive toughening agents.

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