A fast-curing polythiol curing agent for epoxy resin and preparation method thereof

Abstract

The present invention provides a fast-curing epoxy resin polythiol curing agent and a preparation method, and relates to the technical field of polythiol compounds. The preparation method of the present invention comprises the following steps: aniline, modified cashew nut shell oil and formaldehyde are stirred to react to obtain a modified alcohol mixture; the modified alcohol mixture is esterified with thioglycolic acid to obtain a polythiol curing agent; wherein, the preparation of the modified cashew nut shell oil includes: cashew nut shell oil and bromomethyl phenyl sulfone are stirred and mixed at 60-80°C to obtain a mixed solution; the mixed solution is dropwise added with iodine-promoting solution at 100-120°C and refluxed for 5-7h, and then cooled to room temperature to obtain modified cashew nut shell oil. The polythiol curing agent prepared by the present invention can effectively shorten the curing time of epoxy resin, and improve the heat resistance and mechanical strength of epoxy resin products.

Description

Technical Field

[0001] The invention relates to the technical field of polythiol compounds, and in particular to a fast-curing polythiol curing agent for epoxy resin and a preparation method thereof. Background Art

[0002] Epoxy resin adhesive is a polymer compound containing epoxy groups, usually with bisphenol A and epichlorohydrin as the main raw materials, produced by addition reaction. The molecular structure of epoxy resin contains two or more epoxy groups, which can react with a variety of compounds through ring-opening reaction to form a network structure. These structures give epoxy resin excellent mechanical properties, bonding properties, chemical corrosion resistance and electrical insulation. Due to the excellent performance of epoxy resin, it is widely used in coatings, adhesives, composite materials, electronic materials and building materials. In addition, it also has important applications in aerospace, automotive industry, electronics and electrical fields.

[0003] In the curing process of epoxy resin, it is usually completed by addition reaction with curing agent, and there are many types of curing agents, including amines, anhydrides, phenolic resins, polythiols, etc. In the curing reaction, epoxy resin reacts with curing agent to form a network structure for curing, so the choice of curing agent directly affects the curing speed and performance of epoxy resin after curing. Polythiols are a type of compound with multiple thiol groups. The thiol group has high reactivity and can undergo a ring-opening addition reaction with the epoxy group, thereby achieving rapid curing of epoxy resin.

[0004] According to the different molecular structures, polythiols can be divided into linear polythiols and cyclic polythiols, wherein linear polythiols are mainly prepared by reacting polymers such as polyethylene glycol and polypropylene glycol with thiol compounds, while cyclic polythiols are mainly prepared by reacting epoxy resin with thiol compounds. However, although polythiols have a fast curing rate and a low curing temperature for epoxy resin, the synthesis method of polythiols is relatively complicated, and the heat resistance and mechanical strength of the cured product obtained after curing with epoxy resin are inferior to those of other curing agents. Therefore, it is urgent to provide a solution to improve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a fast-curing polythiol curing agent for epoxy resin and a preparation method thereof, wherein cashew nut shell liquid is modified by using bromomethyl phenyl sulfone, thereby improving the stability and reactivity of the molecular structure, and containing more reactive groups after reacting with aniline and formaldehyde, thereby forming a curing agent with a denser and more stable cross-linked structure with thioglycolic acid, so that after curing the epoxy resin, the curing time of the epoxy resin can be effectively shortened, and the heat resistance and mechanical strength of the epoxy resin product can be improved.

[0006] In a first aspect, the present invention provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps: stirring aniline, modified cashew nut shell oil and formaldehyde to obtain a modified alcohol mixture; esterifying the modified alcohol mixture with thioglycolic acid to obtain a polythiol curing agent; wherein the preparation of the modified cashew nut shell oil comprises: stirring and mixing cashew nut shell oil and bromomethyl phenyl sulfone at 60-80° C. to obtain a mixed solution; adding an iodine-promoting solution dropwise to the mixed solution at 100-120° C. and refluxing for 5-7 hours, and then cooling to room temperature to obtain the modified cashew nut shell oil.

[0007] When preparing the modified cashew nut shell liquid, the cashew nut shell liquid and bromomethyl phenyl sulfone are fully mixed in advance, which is helpful for the subsequent reaction. In addition, bromomethyl phenyl sulfone is used as a modifier, and phenyl and sulfone groups are introduced by reacting with the cashew nut shell liquid to increase the crosslinking and stability between molecules. When the reaction is carried out, the iodine-promoting solution can activate the reaction system and promote the reaction of the cashew nut shell liquid and the bromomethyl phenyl sulfone to generate the modified cashew nut shell liquid.

[0008] When preparing the curing agent, aniline reacts with formaldehyde to generate methyleneaniline compounds, which can react with modified cashew nut shell oil as a bridge to generate a modified alcohol mixture with more reactive groups. After the active sites on the modified cashew nut shell oil participate in the reaction, the molecular chain length and the number of crosslinking points can be further increased to improve the mechanical properties and heat resistance of the curing agent product. In addition, when reacting with thioglycolic acid, the hydroxyl group in the modified alcohol mixture reacts with the thiol group to form a stable ester group, and the obtained curing agent has high reactivity and can quickly cure the epoxy resin at a lower temperature and in a shorter time.

[0009] Optionally, the mass mixing ratio of the aniline, the modified cashew nut shell oil and the formaldehyde is 1:(3-5):(2-5).

[0010] Optionally, the mass mixing ratio of the modified cashew nut shell liquid to the thioglycolic acid is 1:(5-6).

[0011] Optionally, when aniline, modified cashew nut shell oil and formaldehyde are stirred to react to obtain a modified alcohol mixture, the method includes: stirring and mixing aniline and formaldehyde to obtain an aldehyde-amine mixture; heating the aldehyde-amine mixture to 80-90° C. and reflux for 3-5 hours, then adding the modified cashew nut shell oil dropwise into the aldehyde-amine mixture, and refluxing for 2-3 hours to obtain the modified alcohol mixture.

[0012] Optionally, when the modified alcohol mixture is subjected to an esterification reaction with thioglycolic acid to obtain the polythiol curing agent, the process comprises: subjecting the modified alcohol mixture and thioglycolic acid to a reflux reaction in an acidic environment for 5-8 hours, and then cooling and dehydrating to obtain the polythiol curing agent.

[0013] Optionally, after the modified alcohol mixture is mixed with thioglycolic acid, an acidic regulator is added to adjust the pH of the system to 2-3, and then a reflux reaction is carried out for 5-8 hours.

[0014] Optionally, the acidic regulator includes one of citric acid and methanesulfonic acid.

[0015] Optionally, when cashew nut shell liquid and bromomethyl phenyl sulfone are mixed, the mass mixing ratio of the cashew nut shell liquid to the bromomethyl phenyl sulfone is 1:(0.2-0.5).

[0016] Optionally, the solute in the iodine-promoting solution includes one of iodine and iodic acid.

[0017] In a second aspect, the present invention also provides a polythiol curing agent prepared by any of the above optional preparation methods. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with general skills in the field to which the present invention belongs.

[0019] The present invention provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0020] S1, stirring and reacting aniline, modified cashew nut shell liquid and formaldehyde to obtain a modified alcohol mixture;

[0021] S2. Esterifying the modified alcohol mixture with thioglycolic acid to obtain a polythiol curing agent.

[0022] Specifically, the method for preparing the modified cashew nut shell liquid used in step S1 comprises the following steps:

[0023] S0.1, stirring and mixing cashew nut shell liquid and bromomethyl phenyl sulfone at 60-80° C. to prepare a mixed solution;

[0024] S0.2. Add the iodine-promoting solution dropwise to the mixture at 100-120°C and reflux for 5-7 hours, then cool to room temperature to obtain modified cashew nut shell liquid.

[0025] In some embodiments, when executing step S0.1, the mass mixing ratio of cashew nut shell liquid to bromomethyl phenyl sulfone is 1:(0.2-0.5), and in step S0.2, the solute in the iodine-promoting solution includes one of iodine and iodic acid.

[0026] In some embodiments, when performing step S1, the mass mixing ratio of aniline, modified cashew nut shell liquid and formaldehyde is 1:(3-5):(2-5), and when performing step S2, the mass mixing ratio of modified cashew nut shell liquid and thioglycolic acid is 1:(5-6).

[0027] In some embodiments, the step S1 includes: stirring and mixing aniline and formaldehyde to obtain an aldehyde-amine mixture; heating the aldehyde-amine mixture to 80-90° C. and reflux for 3-5 hours, then adding the modified cashew nut shell oil dropwise into the aldehyde-amine mixture, and refluxing for 2-3 hours to obtain a modified alcohol mixture.

[0028] In some embodiments, the step S2 includes: reflux reaction of the modified alcohol mixture and thioglycolic acid in an acidic environment for 5-8 hours, followed by cooling and dehydration to obtain a polythiol curing agent. In practice, after the modified alcohol mixture and thioglycolic acid are mixed, an acidic regulator is added to adjust the system pH to 2-3, followed by reflux reaction for 5-8 hours. Specifically, the acidic regulator includes one of citric acid and methanesulfonic acid.

[0029] Preparation Example 1

[0030] This preparation example 1 provides a method for preparing modified cashew nut shell oil, comprising the following steps:

[0031] S0.1. In a 75°C water bath, cashew nut shell liquid (purchased from Hubei Chengfeng Chemical Co., Ltd., purity 99%) and bromomethyl phenyl sulfone (CAS: 19169-90-5) were ultrasonically mixed at a mass ratio of 1:0.2 to obtain a mixed solution;

[0032] S0.2. In an oil bath environment at 110°C, add hydroiodic acid solution dropwise to the mixed solution, control the dropping time to 30 minutes, and control the total amount of hydroiodic acid added to 1 / 10 of the mass of bromomethylphenyl sulfone; after the addition is completed, reflux the mixed solution for 5 hours, cool to room temperature, and dry it with anhydrous sodium sulfate to obtain modified cashew nut shell oil.

[0033] Preparation Example 2

[0034] This preparation example 2 provides a method for preparing modified cashew nut shell oil, comprising the following steps:

[0035] S0.1. In a 75°C water bath, cashew nut shell liquid (purchased from Hubei Chengfeng Chemical Co., Ltd., purity 99%) and bromomethyl phenyl sulfone (CAS: 19169-90-5) were ultrasonically mixed at a mass ratio of 1:0.5 to obtain a mixed solution;

[0036] S0.2. In an oil bath environment at 110°C, add hydroiodic acid solution dropwise to the mixed solution, control the dropping time to 30 minutes, and control the total amount of hydroiodic acid added to 1 / 10 of the mass of bromomethylphenyl sulfone; after the addition is completed, reflux the mixed solution for 5 hours, cool to room temperature, and dry it with anhydrous sodium sulfate to obtain modified cashew nut shell oil.

[0037] Preparation Example 3

[0038] This preparation example 3 provides a method for preparing modified cashew nut shell oil, comprising the following steps:

[0039] S0.1. In a 75°C water bath, cashew nut shell liquid (purchased from Hubei Chengfeng Chemical Co., Ltd., purity 99%) and maleic anhydride (CAS: 108-31-6) were ultrasonically mixed at a mass ratio of 1:0.5 to obtain a mixed solution;

[0040] S0.2. In an oil bath environment at 110°C, add hydroiodic acid solution dropwise to the mixed solution, control the dropping time to 30 minutes, and control the total amount of hydroiodic acid added to 1 / 10 of the mass of bromomethylphenyl sulfone; after the addition is completed, reflux the mixed solution for 5 hours, cool to room temperature, and dry it with anhydrous sodium sulfate to obtain modified cashew nut shell oil.

[0041] Preparation Example 4

[0042] This preparation example 4 provides a method for preparing modified cashew nut shell oil, comprising the following steps:

[0043] S0.1. In a 75°C water bath, cashew nut shell liquid (purchased from Hubei Chengfeng Chemical Co., Ltd., purity 99%) and isopropyl-2-bromoethyl ether (CAS: 54149-16-5) were ultrasonically mixed at a mass ratio of 1:0.5 to obtain a mixed solution;

[0044] S0.2. In a water bath at 80°C, add hydroiodic acid solution dropwise to the mixed solution, control the adding time to 30 minutes, and control the total amount of hydroiodic acid added to 1 / 13 of the mass of isopropyl-2-bromoethyl ether; after the addition is completed, reflux the mixed solution for 5 hours, cool it to room temperature, and dry it with anhydrous sodium sulfate to obtain modified cashew nut shell oil.

[0045] Example 1

[0046] This embodiment 1 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0047] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) were ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture was heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then the modified cashew nut shell oil prepared in Preparation Example 1 was added dropwise to the aldehyde-amine mixture, and the total dripping time was controlled to be 1 hour. After the dripping was completed, the mixture was refluxed for 2 hours and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, modified cashew nut shell oil and formaldehyde was 1:4:3;

[0048] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0049] Example 2

[0050] This embodiment 2 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0051] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) were ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture was heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then the modified cashew nut shell oil prepared in Preparation Example 2 was added dropwise to the aldehyde-amine mixture, and the total dripping time was controlled to be 1 hour. After the dripping was completed, the mixture was refluxed for 2 hours and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, modified cashew nut shell oil and formaldehyde was 1:4:3;

[0052] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0053] Comparative Example 1

[0054] This comparative example 1 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0055] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) are ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture is heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and cashew nut shell oil (purchased from Hubei Chengfeng Chemical Co., Ltd., purity 99%) is added dropwise to the aldehyde-amine mixture, and the total dripping time is controlled to be 1 hour. After the dripping is completed, the mixture is refluxed for 2 hours, and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, cashew nut shell oil and formaldehyde is 1:4:3;

[0056] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0057] Comparative Example 2

[0058] This comparative example 2 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0059] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) were ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture was heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then cardanol (purchased from Shandong Qilin Chemical Co., Ltd., item number 0220) was added dropwise to the aldehyde-amine mixture, and the total dripping time was controlled to be 1 hour. After the dripping was completed, the mixture was refluxed for 2 hours, and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, cardanol and formaldehyde was 1:4:3;

[0060] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0061] Comparative Example 3

[0062] This comparative example 3 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0063] S0.1. In a 75°C water bath, ultrasonically mix cardanol (purchased from Shandong Qilin Chemical Co., Ltd., item number 0220) and bromomethylphenyl sulfone (CAS: 19169-90-5) at a mass ratio of 1:0.3 to obtain a mixed solution;

[0064] S0.2. In an oil bath environment at 110°C, add hydroiodic acid solution dropwise to the mixed solution, control the dropping time to 30 minutes, and control the total amount of hydroiodic acid added to be 1 / 10 of the mass of bromomethylphenylsulfone; after the addition is completed, reflux the mixed solution for 5 hours, cool it to room temperature, and dry it with anhydrous sodium sulfate to obtain modified cardanol;

[0065] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) are ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture is heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then modified cardanol is added dropwise to the aldehyde-amine mixture, and the total dripping time is controlled to be 1 hour. After the dripping is completed, the mixture is refluxed for 2 hours, and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, modified cardanol and formaldehyde is 1:4:3;

[0066] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0067] Comparative Example 4

[0068] This comparative example 4 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0069] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) were ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture was heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then the modified cashew nut shell oil prepared in Preparation Example 3 was added dropwise to the aldehyde-amine mixture, and the total dripping time was controlled to be 1 hour. After the dripping was completed, the mixture was refluxed for 2 hours and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, modified cashew nut shell oil and formaldehyde was 1:4:3;

[0070] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) are stirred and mixed at a mass ratio of 1:0.3, citric acid is added to adjust the pH to 3, and the mixture is refluxed at 80° C. for 6 hours. The mixture is cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent.

[0071] Comparative Example 5

[0072] This comparative example 5 provides a method for preparing a fast-curing polythiol curing agent for epoxy resin, comprising the following steps:

[0073] S1. Aniline (CAS: 62-53-3) and formaldehyde (CAS: 50-00-0) were ultrasonically mixed at 45°C to obtain an aldehyde-amine mixture; in a water bath environment, the aldehyde-amine mixture was heated to 85°C at a rate of 5°C / min and then refluxed for 4 hours, and then the modified cashew nut shell oil prepared in Preparation Example 4 was added dropwise to the aldehyde-amine mixture, and the total dripping time was controlled to be 1 hour. After the dripping was completed, the mixture was refluxed for 2 hours and then cooled to room temperature to obtain a modified alcohol mixture; wherein the mass mixing ratio of aniline, modified cashew nut shell oil and formaldehyde was 1:4:3;

[0074] S2. The modified alcohol mixture and thioglycolic acid (CAS: 68-11-1) were stirred and mixed at a mass ratio of 1:0.3, citric acid was added to adjust the pH to 3, and the mixture was refluxed at 80°C for 6 hours, cooled to room temperature and dried with anhydrous sodium sulfate to obtain a polythiol curing agent. Performance test

[0075] The polythiol curing agent prepared in Examples 1 to 2 and Comparative Examples 1 to 5, and the quick-drying epoxy curing agent with the brand GL1810 purchased from Guangzhou Green New Materials Co., Ltd. were used as Comparative Example 6, and were uniformly mixed with NPEL128 Nan Ya epoxy resin (purchased from Shanghai Kain Chemical Co., Ltd.) at a volume ratio of 1:1 to prepare a mixed glue, and the following tests were performed:

[0076] Based on the method described in GB / T 12007.7-1989, the curing time was recorded after curing at 10°C, 20°C, and 30°C, and the average value was taken after repeating five times. The results are shown in Table 1 below;

[0077] Based on the method described in GB / T 7124-2008, the mixed adhesives corresponding to Example 1 and Comparative Examples 1 to 4 were applied on two iron sheets and cured, and then the shear strength was measured after curing at 25°C and 50% humidity for 4 hours; the tensile strength was measured after curing at 25°C and 50% humidity for 7 days, and the results are shown in Table 1 below.

[0078] Based on the method described in ISO 11357-2:2013, the mixed glue corresponding to Example 1 and Comparative Examples 1 to 4 was applied on two iron sheets for curing, and then the Tg value was measured after curing at 25°C and 50% humidity for 7 days. The results are shown in Table 1 below.

[0079] Table 1 Performance comparison data of Example 1, Comparative Examples 1 to 4

[0080]

[0081] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A method for preparing a fast-curing polythiol curing agent for epoxy resin, characterized in that: The following steps are involved: Aniline, modified cashew nut shell liquid and formaldehyde are stirred and reacted to prepare a modified alcohol mixture; The modified alcohol mixture is subjected to an esterification reaction with thioglycolic acid to obtain a polythiol curing agent; wherein the preparation of the modified cashew nut shell oil comprises: stirring and mixing cashew nut shell oil and bromomethyl phenyl sulfone at 60-80° C. to obtain a mixed solution; adding an iodine-promoting solution dropwise to the mixed solution at 100-120° C. and refluxing the solution for 5-7 hours, and then cooling the mixed solution to room temperature to obtain the modified cashew nut shell oil; the solute in the iodine-promoting solution comprises one of iodine and iodic acid.

2. The preparation method according to claim 1, characterized in that: The mass mixing ratio of the aniline, the modified cashew nut shell oil and the formaldehyde is 1:(3-5):(2-5).

3. The preparation method according to claim 1, characterized in that: The mass mixing ratio of the modified cashew nut shell oil to the thioglycolic acid is 1:(5-6).

4. The preparation method according to claim 1, characterized in that: When aniline, modified cashew nut shell oil and formaldehyde are stirred to react to obtain a modified alcohol mixture, the method comprises: stirring and mixing aniline and formaldehyde to obtain an aldehyde-amine mixture; heating the aldehyde-amine mixture to 80-90° C. and refluxing for 3-5 hours, adding the modified cashew nut shell oil dropwise into the aldehyde-amine mixture, and refluxing for 2-3 hours to obtain the modified alcohol mixture.

5. The preparation method according to claim 1, characterized in that: When the modified alcohol mixture is subjected to esterification reaction with thioglycolic acid to obtain the polythiol curing agent, the process comprises: subjecting the modified alcohol mixture and thioglycolic acid to reflux reaction in an acidic environment for 5-8 hours, and then cooling and dehydrating to obtain the polythiol curing agent.

6. The preparation method according to claim 5, characterized in that: After the modified alcohol mixture is mixed with thioglycolic acid, an acidic regulator is added to adjust the pH of the system to 2-3, and then a reflux reaction is carried out for 5-8 hours.

7. The preparation method according to claim 6, characterized in that: The acidic regulator includes one of citric acid and methanesulfonic acid.

8. The preparation method according to claim 1, characterized in that: When cashew nut shell liquid and bromomethyl phenyl sulfone are mixed, the mass mixing ratio of the cashew nut shell liquid to the bromomethyl phenyl sulfone is 1:(0.2-0.5).

9. A polythiol curing agent prepared by the preparation method according to any one of claims 1 to 8.

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