Preparation method of modified aromatic polyamine curing agent

Abstract

The invention discloses a preparation method of a modified aromatic polyamine curing agent, and belongs to the technical field of epoxy resin curing agents. The method comprises the following steps: (1) dissolving an aromatic amine curing agent and an imidazole first accelerant in an alcohol solvent; (2) mixing epoxy resin with the single / double epoxy diluent compound; (3) reacting under the protection of nitrogen at 40-90 DEG C; and (4) adding a second accelerant after desolventizing under reduced pressure. Through scientific compounding of an innovative two-step accelerant system and a single / double epoxy diluent, low-temperature high-efficiency reaction is realized. The viscosity of the obtained curing agent at 25 DEG C is 1000-4000 mPa.s, the curing agent has excellent mechanical properties, the tensile strength is 70.5-93.5 MPa, the elongation at break is 6.8-7.8%, and the solvent residue is less than or equal to 0.5 wt%. The technical problems of high temperature, high viscosity, dependence on toxic solvents and the like in the traditional process are solved.

Description

Technical Field

[0001] This invention relates to the field of epoxy curing agent preparation, and is applicable to low-temperature curing liquid modified aromatic amine epoxy curing agents, specifically to a method for preparing a modified aromatic polyamine curing agent. Background Technology

[0002] Epoxy resins are thermosetting polymers with excellent adhesive properties. Due to their good dielectric properties, chemical stability, and processability, they are widely used in adhesives, coatings, electronics, electrical appliances, and aerospace. In application, epoxy resins must be combined with a curing agent to form a formulated resin, and under certain conditions, undergo a curing and cross-linking reaction to generate a three-dimensional network structure, thus exhibiting various excellent properties. The properties of the cured product are not only related to the matrix resin, but the quality of the curing agent largely determines the quality of the cured product. Aromatic amine curing agents, due to their rigid benzene ring structure, produce cured products with epoxy resins that have excellent impact, compressive, and tensile strength, and are widely used in lamination and casting materials. Currently, aromatic amine curing agents mainly include diaminodiphenylmethane (DDM), diaminodimethoxydiphenylmethane (DADM), m-phenylenediamine (MDA), and diaminodiphenyl sulfone (DDS).

[0003] However, using a single aromatic amine curing agent also has some drawbacks: First, aromatic amines are mostly solid curing agents, requiring the process to be carried out in a molten state when combined with epoxy resin. This shortens the pot life of the composition, causing inconvenience in operation and adversely affecting process performance. Moreover, aromatic diamines produce vapor at high temperatures, which is detrimental to human health. Therefore, it is necessary to modify aromatic amines to lower their melting point. The simplest and most common method is to blend aromatic diamines to achieve a low eutectic point. Using low eutectic point compounds to cure epoxy resins, whether for castings or laminates, results in superior physical and mechanical properties compared to using a single aromatic diamine curing agent, both before and after aging. Second, aromatic amines contain rigid benzene rings, and epoxy resins also contain many rigid structures. The cured product formed by these two components lacks sufficient toughness. Chemical modification is used to increase toughness.

[0004] To improve the performance of aromatic amine curing agents, researchers have developed various modification methods. CN104327251A discloses a method for modifying aromatic amines using butyl glycidyl ether or phenyl glycidyl ether, with a reaction temperature of 160℃ and a reaction time of 2-3 hours, followed by vacuuming to 300 Pa after the reaction. This method requires high reaction temperature and long reaction time, and the resulting modified aromatic amine has a high viscosity at 25℃, greater than 3800 mPa·s, which makes it difficult to eliminate bubbles when used in combination with epoxy resin. CN103554440A discloses a method for modifying aromatic amines using hexahydrophthalic anhydride and dicyandiamide. This method involves heating the aromatic amine to 150-155℃ to dissolve it and then dripping it into the reaction vessel, resulting in high energy consumption and the volatilization of toxic aromatic amine vapors. CN106046324A discloses a method for modifying aromatic amines using benzyl benzoate byproducts, which requires the addition of 0-20 parts of toluene after the reaction to reduce the viscosity of the modified curing agent. Toluene is a highly volatile organic solvent that can diffuse into the environment and cause pollution during solidification.

[0005] However, existing aromatic amine curing agents still have the following problems: traditional aromatic amine curing agents usually require high temperatures (above 120°C) to fully cure, resulting in high energy consumption and harsh operating conditions; aromatic amine curing agents generally have toxicity issues, especially substances such as diaminodiphenylmethane, which are considered carcinogenic and pose a threat to the health of operators; although existing modified aromatic amine curing agents have improved some properties, they are often too viscous, making it difficult to eliminate air bubbles during construction and affecting the mechanical properties of the cured product; benzene-based solvents, such as toluene and xylene, are often used in the modification process, which are highly volatile and toxic, failing to meet environmental protection requirements; existing modification methods cannot simultaneously meet the multiple performance requirements of curing agents, such as low viscosity, excellent toughness, and corrosion resistance.

[0006] Therefore, there is an urgent need to develop a modified aromatic amine curing agent preparation method that can be carried out at lower temperatures, is non-toxic and environmentally friendly, has low viscosity, and can impart excellent toughness and corrosion resistance to the cured product, so as to meet the application requirements of high-performance epoxy resin systems. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide an environmentally friendly modified aromatic amine curing agent preparation method that addresses the shortcomings of existing aromatic amine epoxy curing agents, such as high energy consumption during high-temperature reaction, high toxicity, high viscosity after modification, difficulty in eliminating bubbles, poor toughness of cured products, and dependence on toxic solvents. This method can be carried out at low temperatures of 40~90℃, and the resulting curing agent has low viscosity, excellent toughness and corrosion resistance, and is free of benzene-based solvents throughout the process.

[0008] To achieve the above-mentioned objectives, the following technical solution is provided: A method for preparing a modified aromatic polyamine curing agent, comprising the following preparation steps: 1) dissolving an aromatic amine curing agent and a first accelerator in an alcohol solvent, stirring until homogeneous to obtain component A, wherein the first accelerator is an imidazole compound, the mass ratio of the first accelerator to the aromatic amine curing agent is 1:50~1:10, and the mass ratio of the alcohol solvent to the aromatic amine curing agent is 0.5:1~2:1; 2) mixing epoxy resin and an epoxy diluent until homogeneous to obtain component B, wherein the molar ratio of the epoxy resin to the aromatic amine curing agent is 0.0. The epoxy diluent comprises mono- and di-epoxy glycidyl ethers in a mass ratio of 10:1 to 1:1; preferably, the epoxy diluent comprises mono- and di-epoxy glycidyl ethers in a mass ratio of 5:1 to 1:1; 3) Component B is slowly added dropwise to component A; 4) After the addition is completed, the reaction is kept at a constant temperature under nitrogen purging, and the solvent is removed under reduced pressure after the temperature is completed; a second accelerator is added, and the mass ratio of the first accelerator to the second accelerator is 1:0.5 to 1:2, to obtain the final modified aromatic amine curing agent, the viscosity of which at 25°C is 1000 to 4000 mPa·s.

[0009] Adding a first accelerator to component A lowers the addition reaction temperature of the aromatic curing agent, making the reaction easier to control. Adding an alcohol solvent allows for more thorough mixing and a more complete reaction. Adding a glycidyl ether epoxy diluent to component B allows for the addition reaction to form chain and network structures, significantly improving the curing effect of the curing agent's tensile strength, elongation at break, and impact strength. Adding another accelerator to react with the polyamine adduct yields a modified aromatic polyamine curing agent, which can accelerate the curing reaction, lower the curing temperature, and extend the curing agent's pot life.

[0010] Further, in step 1), the aromatic amine curing agent is one or two of diaminodiphenylmethane, diaminodimethoxydiphenylmethane, diaminodichlorodiphenylmethane, m-phenylenediamine, or diaminodiphenyl sulfone.

[0011] Further, in step 1), the first promoter is an imidazole compound, specifically at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole.

[0012] Further, in step 1), the alcohol solvent is at least one of isopropanol, n-butanol, and neopentyl alcohol.

[0013] Further, in step 2), the epoxy resin is at least one of epoxy resin E-20, epoxy resin E-44, and epoxy resin E-51.

[0014] Further, in step 2), the epoxy diluent is selected from a mixture of monoepoxy glycidyl ether and polyepoxy glycidyl ether, with a mass ratio of 10:1 to 1:1; wherein the monoepoxy glycidyl ether is selected from at least one of C12-C14 alkyl glycidyl ether, benzyl glycidyl ether, phenyl glycidyl ether, o-tolyl glycidyl ether, or butyl glycidyl ether; and the polyepoxy glycidyl ether is selected from at least one of neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, flexible bisphenol A glycidyl ether, polypropylene glycol diglycidyl ether, or propoxyglycerol triglycidyl ether.

[0015] Furthermore, in step 3), the dropping temperature is 40~90℃ and the dropping time is less than 1 hour.

[0016] Furthermore, in step 4), the nitrogen flow rate is 0.5~1.2 L / min, and the system pressure is maintained at 0.02~0.04 MPa.

[0017] Further, in step 4), the holding temperature is 40~90℃ and the holding time is 1~3h; the solvent is removed by reducing the pressure to -0.08~-0.1Mpa, and the material temperature is controlled below 60℃ during vacuum distillation, and the solvent is removed by reducing the pressure until the residual solvent content is ≤0.5wt%.

[0018] Further, in step 4), the second accelerator is at least one of K54, benzyl dimethylamine, triethylamine, and salicylic acid.

[0019] This invention provides a method for preparing a modified aromatic polyamine curing agent. The main reactants are an aromatic amine curing agent, epoxy resin, epoxy diluent, and curing accelerator. The final cured agent is obtained through an addition modification reaction. It can be completely cured at room temperature without heating, thus extending the pot life; the curing speed is also improved; furthermore, the cured product exhibits better tensile strength, impact strength, and elongation at break. This curing agent has significant advantages over traditional aromatic amine curing agents: 1) This invention employs an innovative two-step accelerator system. Imidazole compounds are used as the first accelerator to lower the reaction activation energy, while a K54 / tertiary amine second accelerator regulates the curing rate, achieving a synergistic effect between the two accelerators. By controlling the mass ratio of the first to the second accelerator to 1:0.5~1:2, a balance is successfully achieved between high-efficiency low-temperature (40~90℃) reaction and a pot life (6~7.5 hours), increasing the curing speed by more than 50%. Compared to existing technologies, the curing time is shortened from 45~49 hours to 19~26 hours, while the pot life is extended from 2.5~3.5 hours to 6~7.5 hours.

[0020] 2) This invention utilizes a scientifically formulated blend of mono- and diepoxy diluents, controlling the mass ratio of mono- and diepoxy glycidyl ethers to 10:1 to 1:1. The mono-epoxy diluent (such as C12-C14 alkyl glycidyl ether) effectively reduces the system viscosity to 1000-4000 mPa·s, while the diepoxy diluent (such as neopentyl glycol diglycidyl ether) constructs a cross-linked network, synergistically achieving a balance between excellent mechanical properties and toughness. The resulting cured product exhibits a tensile strength of 70.5-93.5 MPa, an elongation at break of 6.8-7.8%, and an impact strength of 19.8-27.8 MPa, significantly superior to the tensile strength (56.5-57 MPa), elongation at break (2.2-4.4%), and impact strength (5.67-8.86 MPa) of existing technologies.

[0021] 3) This invention optimizes the low-temperature reaction process control, using a nitrogen flow rate of 0.5~1.2L / min and a micro-positive pressure protection of 0.02~0.04MPa, combined with reduced pressure desolventizing at ≤60℃ (-0.08~-0.1MPa), so that the solvent residue is ≤0.5wt%, which not only solves the bubble problem, but also reduces energy consumption by 50%, realizing a highly efficient and environmentally friendly green production process.

[0022] 4) The curing agent obtained by this invention is in liquid state and can be directly cured with epoxy resin at 25°C. It can be used without heating, and the cured product has better salt spray resistance. The rust width is only 0.5~0.8mm, which is far better than the 2.8~3.2mm of the prior art, indicating that it has excellent corrosion resistance. Detailed Implementation

[0023] A method for preparing a modified aromatic polyamine curing agent includes the following preparation steps: Step 1): Aromatic amine curing agent and a first accelerator are dissolved in an alcohol solvent and stirred until homogeneous to obtain component A; the first accelerator is an imidazole compound, and the mass ratio of the first accelerator to the aromatic amine curing agent is 1:50 to 1:10, while the mass ratio of the alcohol solvent to the aromatic amine curing agent is 0.5:1 to 2:1. The aromatic amine curing agent is one or two of diaminodiphenylmethane, diaminodimethoxydiphenylmethane, diaminodichlorodiphenylmethane, m-phenylenediamine, or diaminodiphenyl sulfone. The first accelerator is an imidazole compound, and more specifically, at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole; The alcohol solvent is at least one of isopropanol, n-butanol, and neopentyl alcohol.

[0024] Step 2): Component B is obtained by uniformly mixing epoxy resin and epoxy diluent, wherein the molar ratio of epoxy resin to aromatic amine curing agent is 0.05:1 to 0.2:1; The epoxy resin is at least one of epoxy resin E-20, epoxy resin E-44, and epoxy resin E-51; The epoxy diluent is selected from a mixture of monoepoxy glycidyl ether and polyepoxy glycidyl ether, with a mass ratio of 10:1 to 1:1; wherein the monoepoxy glycidyl ether is selected from at least one of C12-C14 alkyl glycidyl ether, benzyl glycidyl ether, phenyl glycidyl ether, o-tolyl glycidyl ether, or butyl glycidyl ether; and the polyepoxy glycidyl ether is selected from at least one of neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, flexible bisphenol A glycidyl ether, polypropylene glycol diglycidyl ether, or propoxyglycerol triglycidyl ether. Preferably, the monoepoxy diluent is an alkyl / aryl glycidyl ether with a molecular weight of 200-300 g / mol, and its addition amount is 5-15% of the mass of the aromatic amine; the diepoxy diluent is a glycol diglycidyl ether with a molecular weight of 300-600 g / mol, and its addition amount is 3-10% of the mass of the aromatic amine. Monoepoxy diluents (such as phenyl glycidyl ether) reduce viscosity, while diepoxy diluents (such as neopentyl glycol diglycidyl ether) enhance crosslinking density. When monoepoxy / diepoxy diluents are used simultaneously, their mass ratio needs to be controlled at 10:1 to 1:1, preferably 5:1 to 1:1, to avoid excessive crosslinking leading to increased viscosity.

[0025] Step 3): Component B is slowly added dropwise to component A; the addition temperature is 40~90℃, and the addition time is less than 1 hour.

[0026] Step 4): After the addition is complete, the reaction is maintained at a constant temperature under nitrogen purging. Nitrogen is introduced to maintain an inert atmosphere in the reaction system, and the flow rate is sufficient to form a stable nitrogen layer on the surface of the reactants. The pressure difference between the system and the outside is maintained at ≥0.01 MPa. Based on a reactor volume of 0.2~0.5 VVM, the nitrogen flow rate is 0.5~1.2 L / min, and the system pressure is maintained at 0.02~0.04 MPa. The nitrogen protection must meet the following requirements: nitrogen purity ≥99.5%, water content ≤50 ppm; the venting pipe extends to 1 / 3 of the liquid surface; oxygen content monitoring is installed at the reactor exhaust port and maintained <0.5%; the viscosity of the curing agent at 25℃ is 1000~4000 mPa·s, and further, the viscosity of the curing agent at 25℃ is 2300~3100 mPa·s. The heat preservation temperature is 40~90℃, and the heat preservation time is 1~3h; After the heat preservation is completed, the pressure is reduced to -0.08~-0.1 MPa to remove the solvent. During vacuum distillation, the material temperature is controlled below 60℃. The solvent is removed under reduced pressure until the residual solvent content is ≤0.5wt%.

[0027] A second accelerator is added, with the mass ratio of the first accelerator to the second accelerator being 1:0.5 to 1:2, to obtain the final modified aromatic amine curing agent. The second accelerator is at least one of K54 (chemical name 2,4,6-tris(dimethylaminomethyl)phenol), benzyldimethylamine, triethylamine, and salicylic acid. The two-step accelerator addition involves an imidazole-based first accelerator promoting the low-temperature reaction, while the K54 / tertiary amine-based second accelerator regulates the final curing rate.

[0028] Comprehensive performance testing is conducted on the final product, including: curing speed at different temperatures, impact strength, salt spray resistance, tensile strength, and tensile elongation at break.

[0029] The present invention does not impose any special limitations on the application process, and any method known to those skilled in the art can be used.

[0030] To further illustrate the present invention, the technical solutions of the present invention will be clearly and completely described below with the aid of embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 90g of diaminodiphenylmethane and 90g of m-phenylenediamine were added to a 500ml four-necked flask, along with 2g of 2-methylimidazole, 3g of 2-ethyl-4-methylimidazole, and 80g of n-butanol. After thorough stirring and dissolution, component A was obtained. 12g of phenyl glycidyl ether, 3g of neopentyl glycol diglycidyl ether, and 5g of epoxy resin E-51 were thoroughly stirred to obtain component B. Component A was heated to 60℃, and component B was added dropwise to component A over 1 hour. After the addition was completed, the mixture was kept at 60℃ for 2 hours under nitrogen conditions of 0.5 L / min and 0.02 MPa. The mixture was then heated to 80℃ and the n-butanol was removed under reduced pressure. 5g of accelerator K54 was added, and the mixture was stirred thoroughly to obtain the cured agent with a viscosity of 2650 mPa·s.

[0032] Example 2 257g of diaminodiphenylmethane and 90g of diaminodimethoxydiphenylmethane were added to a 1000ml four-necked flask, along with 16g of 2-methylimidazole, 105g of n-butanol, and 75g of isopropanol. After thorough stirring and dissolution, component A was obtained. 15g of benzyl glycidyl ether, 5g of 1,4-butanediol diglycidyl ether, and 10g of epoxy resin E-51 were thoroughly stirred to obtain component B. Component A was heated to 70℃, and component B was added dropwise to component A over 1 hour. After the addition was completed, the mixture was kept at 70℃ for 3 hours under nitrogen conditions of 1.0 L / min and 0.03 MPa. The mixture was then heated to 80℃ and the n-butanol and isopropanol were removed under reduced pressure. 5g of salicylic acid accelerator was added, and the mixture was stirred thoroughly to obtain the cured agent with a viscosity of 2300 mPa·s.

[0033] Example 3 216g of m-phenylenediamine was added to a 500ml four-necked flask, along with 3.2g of 2-phenylimidazolium, 2.9g of 2-ethyl-4-methylimidazolium, 45g of n-butanol, and 51g of neopentyl alcohol. After thorough stirring and dissolution, component A was obtained. 10g of butyl glycidyl ether, 10g of polypropylene glycol diglycidyl ether, and 12g of epoxy resin E-51 were thoroughly stirred to obtain component B. Component A was heated to 80℃, and component B was added dropwise to component A over 1 hour. After the addition was completed, the mixture was kept at 80℃ for 3 hours under nitrogen conditions of 0.8 L / min and 0.02 MPa. After the heat treatment, n-butanol and neopentyl alcohol were removed under reduced pressure, and 5g of accelerator K54 was added. After stirring thoroughly, the cured agent product with a viscosity of 3100 mPa·s was obtained.

[0034] Example 4 540g of diaminodiphenylmethane and 500g of diaminodiphenyl sulfone were added to a 2000ml four-necked flask, along with 51g of 2-ethyl-4-methylimidazole, 245g of n-butanol, and 151g of isopropanol. After thorough stirring and dissolution, component A was obtained. 18g of o-tolyl glycidyl ether, 9g of flexible bisphenol A glycidyl ether, and 49g of epoxy resin E-51 were thoroughly stirred to obtain component B. Component A was heated to 70℃, and component B was added dropwise to component A over 1 hour. After the addition was completed, the mixture was kept at 70℃ for 3 hours under nitrogen conditions of 1.2 L / min and 0.04 MPa. After the heat treatment, the n-butanol and isopropanol were removed under reduced pressure, and 25g of triethylamine, an accelerator, was added. After stirring thoroughly, the cured agent with a viscosity of 3050 mPa·s was obtained.

[0035] Performance Test Examples The curing agents prepared in Examples 1-4 were used, and two commercially available aromatic amine curing agents, m-phenylenediamine (MPD) and diaminodiphenylmethane (DDM), were selected as comparative examples. Based on the active hydrogen equivalent, they were mixed with epoxy resin E-51, and the final product underwent comprehensive performance testing, including: curing speed at different temperatures, impact strength, salt spray resistance, tensile strength, and tensile elongation at break.

[0036] Viscosity test: Brookfield DV2T viscometer, rotor No. 21, 25℃±0.5℃, rotation speed 50 rpm.

[0037] Curing speed: Touch test, according to GB / T 7123.1-2015 standard.

[0038] Impact strength: according to ASTM D256 standard.

[0039] Salt spray resistance test: According to ASTM B117 standard, after 500 hours of salt spray test, the rust width at the scratch, the surface blistering level, and the loss of adhesion.

[0040] Tensile properties: according to ASTM D638 standard.

[0041] Pot life: The time it takes for the viscosity to reach 200% of its initial value, as determined by ISO 9514.

[0042] The comparative curing agent is a solid and cannot be cured at 25°C. It needs to be melted first and then cooled to a certain temperature for curing. 50°C is the application temperature for the comparative example. Therefore, the applicable period is also the applicable period at this temperature.

[0043] The test results above show that the present invention has the following advantages: The curing agent prepared by the present invention is a liquid and can be directly cured with epoxy resin at 25°C; it has significant advantages over the comparative example. The curing agent prepared by the present invention exhibits better impact strength, tensile strength, and elongation at break after curing with epoxy resin. The rust width of the curing agent of the present invention is only 1 / 4 to 1 / 3 of that of the comparative example, and there is no surface blistering; the adhesion loss is ≤10%, far lower than that of the comparative example (≥30%), proving that its cured product has a denser cross-linked network structure; Example 4, due to its rigid structure containing diaminodiphenyl sulfone, has slightly lower salt spray resistance than other examples, but is still significantly better than the comparative example. The curing agent prepared by the present invention cures with epoxy resin faster and has a longer pot life under conditions that allow for construction.

[0044] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a modified aromatic polyamine curing agent, characterized in that, The preparation steps include the following: 1) Dissolve the aromatic amine curing agent and the first accelerator in an alcohol solvent, stir evenly to obtain component A. The first accelerator is an imidazole compound. The mass ratio of the first accelerator to the aromatic amine curing agent is 1:50 to 1:

10. The mass ratio of the alcohol solvent to the aromatic amine curing agent is 0.5:1 to 2:

1. 2) After uniformly mixing epoxy resin and epoxy diluent, component B is obtained. The molar ratio of epoxy resin to aromatic amine curing agent is 0.05:1 to 0.2:

1. The epoxy diluent contains mono-epoxy glycidyl ether and di-epoxy glycidyl ether in a mass ratio of 10:1 to 1:

1. 3) Slowly add component B to component A dropwise; 4) After the addition is complete, keep the reaction under nitrogen gas and remove the solvent under reduced pressure. Add the second accelerator, and the mass ratio of the first accelerator to the second accelerator is 1:0.5~1:2 to obtain the final modified aromatic amine curing agent. The viscosity of the curing agent at 25℃ is 1000~4000 mPa·s.

2. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 1), the aromatic amine curing agent is one or two of diaminodiphenylmethane, diaminodimethoxydiphenylmethane, diaminodichlorodiphenylmethane, m-phenylenediamine, or diaminodiphenyl sulfone.

3. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 1), the first promoter is an imidazole compound, specifically at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole.

4. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 1), the alcohol solvent is at least one of isopropanol, n-butanol, and neopentyl alcohol.

5. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 2), the epoxy resin is at least one of epoxy resin E-20, epoxy resin E-44, and epoxy resin E-51.

6. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 2), the epoxy diluent is selected from a mixture of monoepoxy glycidyl ether and polyepoxy glycidyl ether, with a mass ratio of 10:1 to 1:1; wherein the monoepoxy glycidyl ether is selected from at least one of C12-C14 alkyl glycidyl ether, benzyl glycidyl ether, phenyl glycidyl ether, o-tolyl glycidyl ether, or butyl glycidyl ether; and the polyepoxy glycidyl ether is selected from at least one of neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, flexible bisphenol A glycidyl ether, polypropylene glycol diglycidyl ether, or propoxyglycerol triglycidyl ether.

7. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 3), the dropping temperature is 40~90℃ and the dropping time is less than 1 hour.

8. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 4), the nitrogen flow rate is 0.5~1.2 L / min, and the system pressure is maintained at 0.02~0.04 MPa.

9. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 4), the holding temperature is 40~90℃ and the holding time is 1~3h; the pressure is reduced to -0.08~-0.1Mpa to remove the solvent. During the vacuum distillation, the material temperature is controlled below 60℃, and the solvent is removed under vacuum until the residual solvent content is ≤0.5wt%.

10. The method for preparing the epoxy curing agent according to claim 1, characterized in that, In step 4), the second accelerator is at least one of K54, benzyl dimethylamine, triethylamine, and salicylic acid.

Images