Modified cardanol epoxy curing agent, preparation method and application thereof

Abstract

The application discloses a modified cardanol epoxy curing agent and a preparation method and application thereof, and the curing agent comprises the following raw material components: cardanol, cysteine, boric acid, polyethylene polyamine and formaldehyde; and the preparation method comprises the following steps: performing two-step Mannich condensation reaction on the raw materials. In the application, the cardanol is used as a basic skeleton, and under the joint action of the cysteine, the boric acid and the polyethylene polyamine, the cardanol epoxy curing agent has the advantages of short low-temperature curing time, high thermal stability, high toughness, good corrosion resistance, low free phenol content, green environmental protection and the like, in particular, the water resistance of the cardanol epoxy curing agent can be remarkably improved through the modification of the boric acid, and when the cardanol epoxy curing agent is used for curing epoxy resin, the gel time is 20-35 min under the condition of-10 DEG C to 0 DEG C, the thermal deformation temperature of the cured product is greater than or equal to 95 DEG C, the tensile strength is greater than or equal to 75 MPa, the water absorption is less than or equal to 0.8%, the salt mist resistance time is greater than or equal to 1200 h, and the adhesion is grade 1.

Description

Technical Field

[0001] This invention belongs to the field of epoxy curing agent technology, and relates to a modified cashew phenol epoxy curing agent, its preparation method and application. Background Technology

[0002] Cashew phenol epoxy curing agent is mainly prepared from cashew phenol as raw material. It has the characteristics of low viscosity, low curing temperature and good flexibility, and shows very good application prospects.

[0003] For example, a cashew phenol epoxy curing agent has been proposed in the prior art. It is made of cashew phenol, diethylenetriamine and formaldehyde, but it has shortcomings such as poor low-temperature curing effect.

[0004] To address the aforementioned shortcomings, existing technologies have proposed a low-temperature curing epoxy curing agent made from cashew nut shell phenol, cysteine / eugenol, and formaldehyde. Using cashew nut shell phenol, cysteine, and eugenol as raw materials can enhance the curing agent's reactivity at low temperatures, significantly increasing the curing speed and enabling rapid film formation even at low temperatures (-15℃ to 0℃). However, the aforementioned low-temperature curing epoxy curing agents also suffer from drawbacks such as long curing times at low temperatures (-15℃ to 0℃), for example, surface drying time at -10℃ can be as long as 45 to 55 minutes. Furthermore, these low-temperature curing agents still exhibit drawbacks such as difficulty in simultaneously achieving thermal stability and toughness, high free phenol content, and poor corrosion resistance.

[0005] In addition, a phenolic amide epoxy curing agent has been proposed in the prior art, which includes cashew phenol, aldehyde, amine, dimer acid, polyethylene glycol diglycidyl ether, and polyvinyl butyral. By utilizing the synergistic effect between the various raw materials, the phenolic amide epoxy curing agent has excellent low-temperature curing properties, toughness, and salt spray corrosion resistance. However, this phenolic amide epoxy curing agent still has the following defects: long curing time at low temperature (-15℃~0℃), poor thermal stability, high free phenol content, high VOC content, and poor water resistance.

[0006] For the reasons stated above, this invention is proposed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a modified cashew phenol epoxy curing agent with short low-temperature curing time, high thermal stability, high toughness, good corrosion resistance, good water resistance, low free phenol content and green environmental protection, as well as its preparation method and application.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A modified cashew nut shell epoxy curing agent, comprising the following raw material components: cashew nut shell, cysteine, boric acid, polyethylene polyamine, and formaldehyde.

[0009] In a further improvement of the above-mentioned modified cashew phenol epoxy curing agent, the molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0:1.5-2.5:0.8-1.2:0.5-1.0:2.0-3.0.

[0010] The modified cashew phenol epoxy curing agent described above is further improved in that the molar ratio of cashew phenol to formaldehyde is 1.0:2.2; the formaldehyde is an aqueous formaldehyde solution or paraformaldehyde; and the mass percentage of the aqueous formaldehyde solution is 37%.

[0011] In a further improvement of the aforementioned modified cashew phenol epoxy curing agent, the polyethylene polyamine is tetraethylenepentamine or pentaethylenehexamine.

[0012] The modified cashew nut phenol epoxy curing agent described above is further improved in that its viscosity at 25°C is 800 mPa·s to 1500 mPa·s; the mass percentage of free phenol in the modified cashew nut phenol epoxy curing agent is ≤2.0%, and the mass percentage of water is ≤1.0%; after the modified cashew nut phenol epoxy curing agent is compounded with bisphenol A epoxy resin at a mass ratio of 1:3 to 5, the gelation time at -10°C to 0°C is 20 min to 35 min, the heat distortion temperature of the cured product is ≥95°C, the tensile strength is ≥75 MPa, the water absorption rate is ≤0.8%, the salt spray resistance time is ≥1200 h, and the adhesion is grade 1.

[0013] As a general technical concept, the present invention also provides a method for preparing a modified cashew phenol epoxy curing agent, wherein the modified cashew phenol epoxy curing agent is prepared by a two-step Mannich condensation reaction using cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde as raw materials.

[0014] In a further improvement to the above preparation method, the molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0:1.5-2.5:0.8-1.2:0.5-1.0:2.0-3.0.

[0015] In a further improvement to the above preparation method, the molar ratio of cashew phenol to formaldehyde is 1.0:2.2; the formaldehyde is an aqueous formaldehyde solution or paraformaldehyde; and the mass percentage of the aqueous formaldehyde solution is 37%.

[0016] In a further improvement to the above preparation method, the polyethylene polyamine is tetraethylenepentamine or pentaethylenehexamine; The above preparation method is further improved in that the modified cashew phenol epoxy curing agent has a viscosity of 800 mPa·s to 1500 mPa·s at 25°C; the mass percentage of free phenol in the modified cashew phenol epoxy curing agent is ≤2.0%, and the mass percentage of water is ≤1.0%; after the modified cashew phenol epoxy curing agent and bisphenol A epoxy resin are compounded at a mass ratio of 1:3 to 5, the gelation time is 20 min to 35 min under conditions of -10°C to 0°C, the heat distortion temperature of the cured product is ≥95°C, the tensile strength is ≥75 MPa, the water absorption rate is ≤0.8%, the salt spray resistance time is ≥1200 h, and the adhesion is grade 1.

[0017] The above preparation method, further improved, includes the following steps: S1. Mix cysteine ​​with deionized water and stir to dissolve cysteine ​​in deionized water. Add cashew phenol and formaldehyde dropwise, controlling the temperature not to exceed 70℃. After the addition is complete, keep the reaction at 60℃~70℃ for 1.5h~2.5h to obtain thiolated cashew phenol intermediate. S2. The thiolized cashew nut intermediate obtained in step S1 is heated to 50℃~60℃, and polyethylene polyamine and boric acid are added in sequence. The temperature is further increased to 80℃~90℃ and the reaction is maintained for 2 h~3 h. The temperature is then reduced to 50℃~60℃, a vacuum is drawn, and heating continues until the temperature reaches 90℃. The vacuum is then stopped to obtain the modified cashew nut epoxy curing agent.

[0018] In a further improvement to the above preparation method, in step S1, the stirring is carried out at a temperature of 50℃~60℃.

[0019] In a further improvement to the above preparation method, in step S2, the vacuum level is controlled to be -0.08 MPa to -0.09 MPa during the vacuuming process.

[0020] As a general technical concept, the present invention also provides the application of the above-mentioned modified cashew phenol epoxy curing agent or the modified cashew phenol epoxy curing agent prepared by the above-mentioned preparation method in the preparation of epoxy resin coatings, electronic component encapsulation or marine anti-corrosion coatings.

[0021] Compared with the prior art, the advantages of the present invention are as follows: (1) In view of the shortcomings of existing cashew phenol epoxy curing agents, such as long curing time at low temperature (-15℃~0℃), poor thermal stability, poor corrosion resistance, poor water resistance, high free phenol content, high VOC content, and secondary pollution, this invention creatively provides a modified cashew phenol epoxy curing agent, comprising the following raw material components: cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde, wherein cashew phenol is used as the basic skeleton, and under the combined action of cysteine, boric acid and polyethylene polyamine, thiol groups are simultaneously introduced ( The cashew phenol epoxy curing agent combines boric acid (-SH) ester bonds with aliphatic amino groups to form a ternary synergistic active molecular structure of "thiol-boron-amine," giving it advantages such as short low-temperature curing time, high thermal stability, high toughness, good corrosion resistance, low free phenol content, and environmental friendliness. In particular, the rigid cross-linking structure introduced through boric acid modification, combined with the hydrophobic side chains of cashew phenol, significantly improves the water resistance of the cashew phenol epoxy curing agent. The modified cashew phenol epoxy curing agent of this invention has a viscosity of 800 at 25°C. The modified cashew phenol epoxy curing agent has a free phenol content of ≤2.0% and a water content of ≤1.0% by mass. Furthermore, when the modified cashew phenol epoxy curing agent is compounded with bisphenol A epoxy resin at a mass ratio of 1:3 to 5, the gelation time is 20 to 35 minutes under conditions of -10℃ to 0℃, the heat distortion temperature of the cured product is ≥95℃, the tensile strength is ≥75 MPa, the water absorption rate is ≤0.8%, the salt spray resistance time is ≥1200 h (GB / T 1771-2007), and the adhesion is grade 1 (cross-cut test, GB / T 9754-2007).

[0022] (2) In the modified cashew phenol epoxy curing agent of the present invention, by optimizing the molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde to 1.0∶1.5~2.5∶0.8~1.2∶0.5~1.0∶2.0~3.0, it is more conducive to improving the overall performance of the modified cashew phenol epoxy curing agent, such as having a shorter low-temperature curing time, higher thermal stability, higher toughness, better corrosion resistance and water resistance, lower free phenol content, and being more environmentally friendly. Taking boric acid as an example, by optimizing the amount of boric acid, the performance of the curing agent can be significantly improved from the dimensions of structure and reactivity, curing performance, mechanical and toughness, thermal stability and flame retardancy, corrosion resistance and media resistance, storage and adaptation period, etc. Specifically: (a) By optimizing the amount of boric acid, boric acid can form borate ester bonds with phenolic hydroxyl groups, thereby constructing a cross-linked network, which is beneficial to improving reactivity and achieving a balance between structural stability and reactivity. However, when the amount of boric acid is low, cross-linking is insufficient and curing is slow; when the amount of boric acid is too high, it will lead to excessive cross-linking, excessively high viscosity, shortened shelf life, and may also leave residual free boric acid, reducing storage stability.

[0023] (b) By optimizing the amount of boric acid, the curing exothermic peak temperature can be reduced, the gel time can be shortened, and the room temperature / low temperature curing efficiency can be improved. However, when boric acid is in excess, the acidity of the system increases, the compatibility with epoxy decreases, and uneven curing and defects are more likely to occur.

[0024] (c) By optimizing the amount of boric acid, the cross-linking density can be increased, thereby enhancing hardness, adhesion, and impact resistance. However, when boric acid is used in excess, the cross-linking becomes too dense, leading to increased brittleness and decreased elongation at break.

[0025] (d) By optimizing the amount of boric acid, the thermal stability and char residue can be improved by utilizing the borate ester bond and boron-oxygen structure, thereby enhancing flame retardancy. However, when boric acid is in excess, it will catalytically degrade at high temperatures, which will actually reduce the char residue and is not conducive to improving flame retardancy.

[0026] (e) By optimizing the amount of boric acid, the cross-linking structure can be optimized, improving water resistance, salt spray resistance, and chemical resistance, thus giving the curing agent both anti-corrosion and media resistance properties. However, when boric acid is used in excess, the residual boric acid will reduce alkali resistance and corrode the metal substrate.

[0027] In particular, if the amount of cysteine ​​is too high, it can easily lead to a decrease in the thermal stability of the curing agent, while if the amount of boric acid is too low, the water resistance of the curing agent will be poor due to insufficient borate bonds.

[0028] (3) The present invention also provides a method for preparing a modified cashew phenol epoxy curing agent. The modified cashew phenol epoxy curing agent with excellent performance is prepared by two-step Mannich condensation reaction using cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde as raw materials. Specifically, in the first step of the Mannich condensation reaction, cashew phenol and cysteine ​​react under the action of formaldehyde. Under the cross-linking action of formaldehyde, cashew phenol and cysteine ​​are linked together, and the thiol group (-SH) contained in cysteine ​​reacts with the phenolic hydroxyl group in cashew phenol to form a thioether bond, thus obtaining a compound containing a thioether bond. On the one hand, the introduced thiol group has strong nucleophilicity and can cure epoxy resin rapidly at low temperature. On the other hand, the compound retains the amino and carboxyl groups of cysteine. The carboxyl group can enhance the reactivity of the curing agent, and the presence of the amino and carboxyl groups also provides possibilities for subsequent reactions with polyethylene polyamines. In particular, by optimizing the reaction temperature to 60℃~70℃, the reaction between thiol and phenolic hydroxyl groups can be promoted, which is more conducive to the rapid synthesis of compounds containing thioether bonds. Specifically, when the reaction temperature exceeds 70℃, the reaction rate is too fast and byproducts are easily generated, while when the temperature is below 60℃, the reaction rate is slow and the yield is low. Based on this, polyethylene polyamine and boric acid are added sequentially to carry out the second step of the Mannich condensation reaction. On the one hand, the polyethylene polyamine added first contains multiple amino groups. The catalyst can react with the carboxyl group in the thiolated cashew nutshell intermediate to form an amide bond, thereby giving the product better crosslinking properties and thermal stability. This also creates conditions for subsequent reactions with boric acid. Furthermore, the added boric acid is a tribasic weak acid that can form stable complexes with compounds containing hydroxyl or amino groups. It can also react with unreacted phenolic hydroxyl groups and amino groups on newly formed amide bonds in the above reaction products to form borate esters or borate-amine complexes (borates), further increasing the product's crosslinking properties, thermal stability, and flame retardancy. More importantly, the prepared product exhibits improved crosslinking properties due to the hydrophobic side chains of cashew nutshell and the rigidity introduced by boric acid modification. The combined effect of the cross-linked structure significantly reduces water absorption, exhibiting excellent water resistance. Furthermore, optimizing the reaction temperature to 80-90℃ ensures effective participation of boric acid in the reaction without causing side reactions. Specifically, when the reaction temperature exceeds 90℃, the water formed during the reaction turns into water vapor, adversely affecting product conversion. Conversely, when the reaction temperature is below 80℃, the reaction rate is slow, resulting in low preparation efficiency. Ultimately, by optimizing the raw materials and the conditions of the two-step Mannich condensation reaction, a modified cashew phenol epoxy curing agent with short low-temperature curing time, high thermal stability, high toughness, good corrosion resistance, low free phenol content, and environmental friendliness can be obtained. In addition, the preparation method of this invention does not use organic solvents, resulting in low VOC content and further enhancing its environmental friendliness. Detailed Implementation

[0029] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0030] The raw materials and instruments used in the following examples are all commercially available; unless otherwise specified, the equipment and preparation processes used are conventional equipment and conventional processes.

[0031] Example 1 A modified cashew phenol epoxy curing agent comprises the following raw material components: cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde.

[0032] In this embodiment, the molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0∶2.0∶1.0∶0.8∶2.2.

[0033] In this embodiment, the formaldehyde used is an aqueous formaldehyde solution, wherein the formaldehyde content in the aqueous formaldehyde solution is 37% by mass.

[0034] In this embodiment, the polyethylene polyamine used is pentaethylenehexamine.

[0035] In other embodiments, the polyethylene polyamine used may also be tetraethylenepentamine. In particular, compared with conventional amines (such as diethylenetriamine), the tetraethylenepentamine and pentaethylenehexamine used in this invention have suitable molecular weights, mild reactivity, and are easy to control in production. At the same time, the resulting curing agent has high crosslinking density and excellent corrosion resistance, which are not found in other amines.

[0036] A method for preparing the modified cashew nut shell epoxy curing agent in Example 1 above specifically involves: using cashew nut shell resin, cysteine, boric acid, polyethylene polyamine, and formaldehyde as raw materials, a two-step Mannich condensation reaction is performed to obtain the modified cashew nut shell epoxy curing agent, wherein the molar ratio of cashew nut shell resin, cysteine, boric acid, polyethylene polyamine, and formaldehyde is 1.0∶2.0∶1.0∶0.8∶2.2, and includes the following steps: S1. Mix cysteine ​​with deionized water and stir at 50°C to dissolve cysteine ​​in deionized water. Add cashew phenol and formaldehyde dropwise, controlling the temperature to not exceed 70°C. After the addition is complete, keep the reaction at 65°C for 2 hours to obtain thiolated cashew phenol intermediate.

[0037] S2. The mercapto-modified cashew phenol intermediate obtained in step S1 is heated to 50°C, and polyethylene polyamine and boric acid are added sequentially. The temperature is then raised to 85°C and kept at this temperature for 2.5 hours. The temperature is then lowered to 50°C, and a vacuum is drawn to control the vacuum degree at -0.08 MPa. The temperature is then continued to be heated until it reaches 90°C. The vacuum is then stopped, and the water and small molecules in the reaction product are removed. The product is then cooled to room temperature to obtain the modified cashew phenol epoxy curing agent.

[0038] Example 2 A modified cashew phenol epoxy curing agent comprises the following raw material components: cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde.

[0039] In this embodiment, the molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0∶2.5∶1.2∶1.0∶3.0.

[0040] In this embodiment, the formaldehyde used is an aqueous formaldehyde solution, wherein the formaldehyde content in the aqueous formaldehyde solution is 37% by mass.

[0041] In this embodiment, the polyethylene polyamine used is pentaethylenehexamine.

[0042] A method for preparing the modified cashew nut shell epoxy curing agent in Example 1 above specifically involves: using cashew nut shell resin, cysteine, boric acid, polyethylene polyamine, and formaldehyde as raw materials, a two-step Mannich condensation reaction is performed to obtain the modified cashew nut shell epoxy curing agent, wherein the molar ratio of cashew nut shell resin, cysteine, boric acid, polyethylene polyamine, and formaldehyde is 1.0∶2.5∶1.2∶1.0∶3.0, and includes the following steps: S1. Mix cysteine ​​with deionized water and stir at 50°C to dissolve cysteine ​​in deionized water. Add cashew phenol and formaldehyde dropwise, controlling the temperature to not exceed 70°C. After the addition is complete, keep the reaction at 65°C for 2 hours to obtain thiolated cashew phenol intermediate.

[0043] S2. The mercapto-modified cashew phenol intermediate obtained in step S1 is heated to 50°C, and polyethylene polyamine and boric acid are added sequentially. The temperature is then raised to 85°C and kept at this temperature for 2.5 hours. The temperature is then lowered to 50°C, and a vacuum is drawn to control the vacuum degree at -0.08 MPa. The temperature is then continued to be heated until it reaches 90°C. The vacuum is then stopped, and the water and small molecules in the reaction product are removed. The product is then cooled to room temperature to obtain the modified cashew phenol epoxy curing agent.

[0044] Comparative Example 1 A cashew phenol epoxy curing agent is basically the same as that in Example 2, except that cysteine ​​and boric acid are not added.

[0045] According to the mass ratio of curing agent to epoxy resin of 1:4, the curing agents of Examples 1-2 and Comparative Example 1, the commercially available cashew phenol aldehyde amine curing agent, the commercially available thiol low-temperature curing agent, and bisphenol A epoxy resin E-51 (epoxy value 0.51 eq / 100g) were mixed evenly. The curing performance was tested at -10℃, 0℃, and 25℃. After curing, the mechanical, thermal, and corrosion resistance properties were tested. Each group of tests was repeated in triplicate and the average value was taken. The results are shown in Table 1.

[0046] Testing standards: Viscosity (GB / T 2794-2013) Gel time (GB / T 14683-2017) Tensile strength (GB / T 2567-2021) Heat distortion temperature (GB / T 1634.2-2019) Water absorption rate (GB / T 1034-2008) Salt spray resistance (GB / T 1771-2007).

[0047] Table 1. Performance comparison of the curing agents in Examples 1-2 and Comparative Example 1, commercially available cashew phenol aldehyde amine curing agent, and commercially available thiol-based low-temperature curing agent.

[0048] In Table 1, the total color difference ΔE refers to the test results before and after 1000 hours of UV aging.

[0049] As shown in Table 1, compared with conventional cashew phenol aldehyde amine curing agents, the modified cashew phenol epoxy curing agent of this invention has the following advantages: (a) It exhibits excellent low-temperature curing performance and can still achieve rapid gelation at a low temperature of -10℃. The modified cashew phenol epoxy curing agents of Examples 1 and 2 can effectively solidify at temperatures ranging from -10℃ to 25℃ when used to cure epoxy resins. In particular, rapid gelation can be achieved in 30 min to 35 min at a temperature of -10℃, which solves the technical bottleneck of poor low-temperature activity of traditional cashew phenol curing agents. In contrast, the unmodified cashew phenol epoxy curing agent in Comparative Example 1 and the commercially available cashew phenol aldehyde amine curing agent cannot be cured at this temperature.

[0050] (b) Excellent thermal stability. When the modified cashew phenol epoxy curing agents of Examples 1 and 2 are used to cure epoxy resins, the resulting cured products exhibit excellent stability at temperatures ranging from 102°C to 108°C. In particular, compared to commercially available thiol-based low-temperature curing agents, the heat distortion temperature of the modified cashew phenol epoxy curing agents of Examples 1 and 2 of this invention is increased by more than 40%, overcoming the deficiency of insufficient thermal stability in thiol curing agents.

[0051] (c) It possesses the characteristics of "high strength, high toughness, and high corrosion resistance". When the modified cashew phenol epoxy curing agents of Examples 1 and 2 are used to cure epoxy resin, the tensile strength of the cured product is ≥75 MPa, the elongation at break is ≥18%, and the salt spray resistance time is ≥1200 h, which are not available in conventional cashew phenol epoxy curing agents.

[0052] (d) Low viscosity. The modified cashew phenol epoxy curing agents of Examples 1 and 2 have a viscosity of 800 mPa·s to 1500 mPa·s at 25°C.

[0053] (e) Good water resistance. When the modified cashew phenol epoxy curing agents of Examples 1 and 2 are used to cure epoxy resins, the water absorption rate of the resulting cured product is ≤0.8%.

[0054] (f) Low free phenol content, environmentally friendly. When the modified cashew phenol epoxy curing agents of Examples 1 and 2 are used to cure epoxy resin, the free phenol content of the resulting cured product is ≤1.8%, which is far lower than the ≤3.5% specified in GB / T 34006-2017 standard. Moreover, the solvent-free synthesis process is adopted, resulting in extremely low VOC content, which is more environmentally friendly than traditional curing agents.

[0055] In addition, the modified cashew phenol epoxy curing agent of this invention can also be used for sealing electronic components and for preparing marine anti-corrosion coatings.

[0056] Therefore, the modified cashew nut phenol epoxy curing agent of the present invention uses cashew nut phenol as the basic skeleton, and under the combined action of cysteine, boric acid, and polyethylene polyamine, the cashew nut phenol epoxy curing agent has the advantages of short low-temperature curing time, high thermal stability, high toughness, good corrosion resistance, low free phenol content, and green environmental protection. In particular, the rigid cross-linking structure introduced by boric acid modification, under the combined action of the hydrophobic side chains of cashew nut phenol, can also significantly improve the water resistance of the cashew nut phenol epoxy curing agent. The modified cashew nut phenol epoxy curing agent of the present invention has a viscosity of 800 mPa·s to 1500 mPa·s at 25°C; the mass percentage of free phenol in the modified cashew nut phenol epoxy curing agent is ≤2.0%, and the mass percentage of water is ≤1.0%; at the same time, after the modified cashew nut phenol epoxy curing agent and bisphenol A epoxy resin are compounded at a mass ratio of 1:3 to 5, the gel time is 20 to 35 minutes under the conditions of -10°C to 0°C. The cured product has the following properties: heat distortion temperature ≥95℃, tensile strength ≥75 MPa, water absorption ≤0.8%, salt spray resistance time ≥1200 h (GB / T 1771-2007), and adhesion grade 1 (cross-cut test, GB / T 9754-2007).

[0057] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A modified cashew nut phenol epoxy curing agent, characterized in that, The modified cashew phenol epoxy curing agent comprises the following raw material components: cashew phenol, cysteine, boric acid, polyethylene polyamine, and formaldehyde.

2. The modified cashew phenol epoxy curing agent according to claim 1, characterized in that, The molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0:1.5-2.5:0.8-1.2:0.5-1.0:2.0-3.

0.

3. The modified cashew phenol epoxy curing agent according to claim 2, characterized in that, The molar ratio of cashew nut shell extract to formaldehyde is 1.0:2.2; the formaldehyde is an aqueous formaldehyde solution or paraformaldehyde; the formaldehyde aqueous solution has a mass percentage of 37%. The polyethylene polyamine is tetraethylenepentamine or pentaethylenehexamine.

4. The modified cashew phenol epoxy curing agent according to any one of claims 1 to 3, characterized in that, The modified cashew phenol epoxy curing agent has a viscosity of 800 mPa·s to 1500 mPa·s at 25°C; the mass percentage of free phenol in the modified cashew phenol epoxy curing agent is ≤2.0%, and the mass percentage of water is ≤1.0%; after the modified cashew phenol epoxy curing agent and bisphenol A epoxy resin are compounded at a mass ratio of 1:3 to 5, the gel time is 20 min to 35 min under conditions of -10°C to 0°C, the heat distortion temperature of the cured product is ≥95°C, the tensile strength is ≥75 MPa, the water absorption rate is ≤0.8%, the salt spray resistance time is ≥1200 h, and the adhesion is grade 1.

5. A method for preparing a modified cashew phenol epoxy curing agent, characterized in that, The preparation method involves using cashew phenol, cysteine, boric acid, polyethylene polyamine, and formaldehyde as raw materials, followed by a two-step Mannich condensation reaction to obtain a modified cashew phenol epoxy curing agent.

6. The preparation method according to claim 5, characterized in that, The molar ratio of cashew phenol, cysteine, boric acid, polyethylene polyamine and formaldehyde is 1.0:1.5-2.5:0.8-1.2:0.5-1.0:2.0-3.

0.

7. The preparation method according to claim 6, characterized in that, The molar ratio of cashew nut shell extract to formaldehyde is 1.0:2.2; the formaldehyde is an aqueous formaldehyde solution or paraformaldehyde; the formaldehyde aqueous solution has a mass percentage of 37%. The polyethylene polyamine is tetraethylenepentamine or pentaethylenehexamine; The modified cashew phenol epoxy curing agent has a viscosity of 800 mPa·s to 1500 mPa·s at 25°C; the mass percentage of free phenol in the modified cashew phenol epoxy curing agent is ≤2.0%, and the mass percentage of water is ≤1.0%; after the modified cashew phenol epoxy curing agent and bisphenol A epoxy resin are compounded at a mass ratio of 1:3 to 5, the gel time is 20 min to 35 min under conditions of -10°C to 0°C, the heat distortion temperature of the cured product is ≥95°C, the tensile strength is ≥75 MPa, the water absorption rate is ≤0.8%, the salt spray resistance time is ≥1200 h, and the adhesion is grade 1.

8. The preparation method according to any one of claims 5 to 7, characterized in that, Includes the following steps: S1. Mix cysteine ​​with deionized water and stir to dissolve cysteine ​​in deionized water. Add cashew phenol and formaldehyde dropwise, controlling the temperature not to exceed 70℃. After the addition is complete, keep the reaction at 60℃~70℃ for 1.5h~2.5h to obtain thiolated cashew phenol intermediate. S2. The thiolized cashew nut intermediate obtained in step S1 is heated to 50℃~60℃, and polyethylene polyamine and boric acid are added in sequence. The temperature is further increased to 80℃~90℃ and the reaction is maintained for 2 h~3 h. The temperature is then reduced to 50℃~60℃, a vacuum is drawn, and heating continues until the temperature reaches 90℃. The vacuum is then stopped to obtain the modified cashew nut epoxy curing agent.

9. The preparation method according to claim 8, characterized in that, In step S1, the stirring is carried out at a temperature of 50℃~60℃; In step S2, the vacuum level is controlled to be -0.08 MPa to -0.09 MPa during the vacuuming process.

10. The application of a modified cashew phenol epoxy curing agent as described in any one of claims 1 to 4 or a modified cashew phenol epoxy curing agent prepared by the preparation method described in claims 5 to 9 in the preparation of epoxy resin coatings, electronic component encapsulation or marine anti-corrosion coatings.

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