Thiol curing agent as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: mixing 20-40 parts by mass of substituted hydroxymethyl glycoluril, 45-85 parts by mass of mercaptocarboxylic acid and 0.5-3 parts by mass of an acidic catalyst, stirring and reacting for 1-10 hours at the temperature of 50-150 DEG C under the pressure condition of-0.01 to-0.1 MPa, adding 300-800 parts by mass of an organic solvent for diluting after the reaction is finished, washing and purifying with deionized water, and collecting an organic layer, thereby obtaining the mercaptan curing agent. Concentrating and drying to obtain the mercaptan curing agent. According to the thiol curing agent, the rigid glycoluril group is introduced, so that the rigidity of a cured product structure is improved, and the mechanical property, the adhesive property, the heat resistance and the damp-heat aging resistance of a cured product are improved; four tertiary amine groups in the substituted glycoluril have a certain self-promotion effect on a thiol curing epoxy reaction, and the curing reaction temperature is reduced under the condition that an accelerant is not added; the glycoluril-containing thiol epoxy resin curing agent disclosed by the invention has good application value and development prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of epoxy resin curing agents, and relates to thiol epoxy curing agents, their preparation methods and applications, specifically to an ester-containing glyceryl urea-thiol epoxy resin curing agent, its preparation method and applications. Background Technology

[0002] Epoxy resin is a type of thermosetting resin, and the curing agent is an essential component in the application of epoxy resin, significantly influencing the preparation process and performance of epoxy resin materials. Compounds with multiple thiol groups within their molecules can be used as curing agents for epoxy resins; these are called thiol curing agents. When tertiary amine accelerators are added, thiol curing agents can achieve rapid curing of epoxy resins at room temperature or even low temperatures. Thiol curing agents possess unique chemical structures, and their cured epoxy resins exhibit excellent electrical insulation properties, thermal stability, and optical properties, making them promising candidates for applications in electronic packaging, optical applications, and aerospace.

[0003] With the continuous upgrading and iteration of electronic products, smart devices, and aerospace components, higher requirements are being placed on the heat resistance and hygrothermal aging resistance of thiol-cured epoxy resin systems. Traditional thiol curing agents containing ester groups (such as trimethylolpropane tris(3-mercaptopropionic acid) ester), compared to aliphatic thiol curing agents, exhibit improved bulk strength due to the polar ester groups, but are prone to degradation under hygrothermal conditions, leading to performance decline. Therefore, improving the hygrothermal aging resistance of epoxy resin thiol-cured products is an important development direction for thiol curing agents. Introducing a rigid heat-resistant framework and hydrophobic structures into the thiol structure is one way to improve its hygrothermal aging resistance. Furthermore, the curing process of thiol curing agents also needs improvement. Without accelerators, the curing temperature of thiol curing agents is too high; while adding accelerators achieves rapid curing at room temperature or low temperature, the operating time is short and curing is difficult to control. Summary of the Invention

[0004] The purpose of this invention is to improve the resistance to humid heat aging of epoxy resin thiol curing agents, and to provide an ester-based glycourea-based thiol epoxy resin curing agent, its preparation method, and its application. This invention introduces a glycourea group into the structure of the thiol curing agent. Glycourea is a fused-ring diurea compound whose four -NH groups can be substituted to form four tertiary amine groups, and the hydrogens on the two bridging carbon atoms can also be substituted. The glycourea derivatives formed by these two substitution modifications are also called substituted glycourea. The dual-rigid structure endows glycourea and substituted glycourea molecules with high rigidity, good heat resistance, and good hydrophobicity. This invention proposes to introduce the substituted glycourea structure into the ester-based thiol curing agent to improve its resistance to humid heat aging. Simultaneously, the tertiary amine groups of the substituted glycourea play a certain promoting role in curing, lowering the curing temperature of the ester-based thiol curing agent without the use of an accelerator.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A thiol curing agent, the general structural formula of which is shown in (I):

[0007]

[0008] A method for preparing the above-mentioned thiol curing agent, wherein the method comprises mixing substituted hydroxymethyl glycourea, mercaptocarboxylic acid and an acidic catalyst, and carrying out an esterification reaction under heating conditions.

[0009] Further, the method specifically involves mixing substituted hydroxymethyl urea, mercaptocarboxylic acid, and an acidic catalyst in a mass ratio of 20~40:45~85:0.5~3, stirring and reacting at 50~150 °C for 1~10 h under a pressure of -0.01~-0.1 MPa. After the reaction is completed, 300~800 parts of organic solvent are added for dilution, and the mixture is washed and purified with deionized water. The organic layer is collected, concentrated, and dried to obtain the thiol curing agent.

[0010] Further, the substituted hydroxymethyl glycourea is one or more of tetrahydroxymethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-dimethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-diethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-diphenyl glycourea, and 1,3,4,6-tetra(hydroxymethyl)-3,4-diethoxyformyl glycourea. Preferably, it is one of tetrahydroxymethyl glycourea or 1,3,4,6-tetra(hydroxymethyl)-3,4-dimethyl glycourea.

[0011] Further, the thiocarboxylic acid is one or more selected from mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutyric acid, 4-mercaptobutyric acid, 4-mercaptovalerate, 5-mercaptovalerate, and 6-mercaptohexanoic acid. Preferably, it is one of 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutyric acid, or 4-mercaptobutyric acid.

[0012] Further, the acidic catalyst is one or more selected from benzenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, trifluoroacetic acid, hydrochloric acid, phosphoric acid, and concentrated sulfuric acid. Preferably, it is p-toluenesulfonic acid or benzenesulfonic acid.

[0013] Further, the organic solvent is one or more selected from ethyl acetate, butyl acetate, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, toluene, and xylene. Preferably, it is ethyl acetate or chloroform.

[0014] An application of the above-mentioned thiol curing agent is described as follows: taking the thiol curing agent and a commercially available thiol curing agent at a mass ratio of 1:1 to 10 and mixing them evenly to obtain a thiol curing agent; taking epoxy resin and thiol curing agent at a mass ratio of 100:60 to 100 and mixing them evenly, and curing at 80 to 170 °C for 0.2 to 3 h.

[0015] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention utilizes a substituted hydroxymethyl glycourea to undergo an esterification reaction with a mercaptocarboxylic acid under an acidic catalyst to prepare a reactive curing agent containing ester-based glycourea-based thiol epoxy resin. The introduced glycourea group has a rigid structure, which improves the rigidity of the cured product structure, thereby enhancing its mechanical properties, adhesive properties, heat resistance, and resistance to damp heat aging. Furthermore, the four tertiary amine groups in the substituted glycourea have a certain self-promoting effect on the thiol-cured epoxy reaction, lowering the curing reaction temperature without the addition of an accelerator. The ester-based glycourea-based thiol epoxy resin curing agent of this invention has a simple synthesis process and is easy for industrial production. This invention is of great significance for improving the performance of thiol curing agents and expanding the variety of thiol curing agents. Attached Figure Description

[0016] Figure 1 These are Fourier transform infrared spectra of the curing agents prepared in Examples 1 and 5;

[0017] Figure 2 The images show the 1H NMR spectra of the curing agents prepared in Examples 1 and 5.

[0018] Figure 3 These are the dynamic thermomechanical curves of the epoxy resin thiol cured products obtained in Examples 1-4 and Comparative Example 1.

[0019] Figure 4 These are the dynamic thermomechanical curves of the epoxy resin thiol cured products obtained in Examples 5-8 and Comparative Example 1.

[0020] Figure 5 These are DSC curves of the curing agent and epoxy resin in Examples 1-4 and Comparative Example 1;

[0021] Figure 6 These are DSC curves of the curing agent and epoxy resin in Examples 5-8 and Comparative Example 1. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] Preparation steps of ester-based glycourea-thiol epoxy resin curing agent: Take 39 parts by weight of tetramethylolpropionic acid, 60 parts by weight of 2-mercaptopropionic acid, and 1 part by weight of p-toluenesulfonic acid as an acidic catalyst. React at 80℃ for 3 h under a pressure gauge reading of -0.08 MPa. After the reaction, add 350 parts by weight of ethyl acetate for dilution, wash and purify with deionized water, collect the organic layer, concentrate and dry to obtain ester-based glycourea-thiol curing agent 1 (2-MAMEG), whose structural formula is as follows:

[0025]

[0026] Its infrared spectrum is shown below. Figure 1 See the proton NMR spectrum. Figure 2 . Figure 1 The middle is 2544 cm -1 The presence of a characteristic stretching vibration peak of -SH nearby indicates that the product is a thiol compound. Figure 2 For curing agent 1 (2-MAMEG) 1 H-NMR spectral analysis: =5.61 ppm corresponds to a single peak of hydrogen proton signal on the methylene carbon atom at the bridging position of glycourea (N-CH-N, 2H); =4.90 ppm corresponds to the hydrogen proton absorption peak on the methylene carbon atom connected to N and O atoms (N-CH2-O, 8H); =3.59 ppm corresponds to the hydrogen proton absorption peak on the carbon atom of the methylene group connected to the ester group and the mercapto group (C-CH2-SH, 4H); =1.53 ppm corresponds to a single peak of hydrogen proton signal on the methyl carbon atom (-CH3, 12H); =1.49 ppm corresponds to a single peak of hydrogen proton signal (-SH, 4H) on the thiol group, indicating that 2-MAMEG was successfully synthesized.

[0027] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 1 is mixed with the commercially available thiol curing agent trimethylolpropane tris(3-mercaptopropionic acid) ester (TMPMP). Weigh 100 parts by weight of E51 epoxy resin, 61.2 parts by weight of commercially available thiol curing agent TMPMP, and 6.8 parts by weight of ester-based glyceryl thiol curing agent 1, stir and mix evenly, and place in a constant temperature oven at 140 ℃ for curing for 2.5 h.

[0028] Example 2

[0029] The preparation steps of the ester-containing glyceroyl thiol epoxy resin curing agent are the same as in Example 1.

[0030] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 1 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 54.4 parts of commercially available thiol curing agent TMPMP, and 13.6 parts of ester-based glyceryl thiol curing agent 1 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 120 ℃ for curing for 2 h.

[0031] Example 3

[0032] The preparation steps of the ester-containing glyceroyl thiol epoxy resin curing agent are the same as in Example 1.

[0033] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 1 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 47.6 parts of commercially available thiol curing agent TMPMP, and 20.4 parts of ester-based glyceryl thiol curing agent 1 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 100 ℃ for curing for 1.5 h.

[0034] Example 4

[0035] The preparation steps of the ester-containing glyceroyl thiol epoxy resin curing agent are the same as in Example 1.

[0036] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 1 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 40.8 parts of commercially available thiol curing agent TMPMP, and 27.2 parts of ester-based glyceryl thiol curing agent 1 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 100 ℃ for curing for 1 h.

[0037] Example 5

[0038] Preparation steps of ester-based glycourea-based thiol epoxy resin curing agent: 35 parts by weight of tetramethylolpropionic acid, 115 parts by weight of 3-mercaptopropionic acid, and 0.9 parts by weight of benzenesulfonic acid as an acidic catalyst were taken and reacted at 90 °C for 6 h under a pressure gauge reading of -0.08 MPa. After the reaction, 500 parts by weight of chloroform were added for dilution, and the mixture was washed and purified with deionized water. The organic layer was collected, concentrated, and dried to obtain ester-based glycourea-based thiol curing agent 2 (M3-MG), whose structure is as follows:

[0039]

[0040] Its infrared spectrum is shown below. Figure 1 See the proton NMR spectrum. Figure 2 . Figure 1 The middle is 2544 cm -1The presence of a characteristic stretching vibration peak of -SH nearby indicates that the product is a thiol compound. Figure 2 For curing agent 2 (M3-MG) 1 H-NMR spectral analysis: =5.82ppm corresponds to a single peak of hydrogen proton signal on the carbon atom of the methylene group at the bridging position of glycyrrhizin (N-CH-N, 2H); =4.78 ppm and 4.40 ppm correspond to the hydrogen proton absorption peaks on the methylene carbon atoms connected to N and O atoms (N-CH2-O, 8H); = 2.63 ppm corresponds to a single peak of hydrogen proton signal (-O-CH2, 8H) on the methylene carbon atom connected to the ester group. =2.53 ppm corresponds to a single peak of hydrogen proton signal on the methylene carbon atom linked to the thiol group (-CH2-SH, 8H); =2.48 ppm corresponds to a singlet signal (-SH, 4H) of hydrogen protons on the thiol group. This indicates that the product M3-MG was successfully synthesized.

[0041] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 2 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 61.2 parts of commercially available thiol curing agent TMPMP, and 6.8 parts of ester-based glyceryl thiol curing agent 2 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 160 ℃ for curing for 2.5 h.

[0042] Example 6

[0043] The preparation steps of the ester-containing glyceryl urea-thiol epoxy resin curing agent are the same as in Example 5.

[0044] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 2 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 54.4 parts of commercially available thiol curing agent TMPMP, and 13.6 parts of ester-based glyceryl thiol curing agent 2 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 140 ℃ for curing for 2 h.

[0045] Example 7

[0046] The preparation steps of the ester-containing glyceryl urea-thiol epoxy resin curing agent are the same as in Example 5.

[0047] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 2 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 47.6 parts of commercially available thiol curing agent TMPMP, and 20.4 parts of ester-based glyceryl thiol curing agent 2 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 120 ℃ for curing for 1.5 h.

[0048] Example 8

[0049] The preparation steps of the ester-containing glyceryl urea-thiol epoxy resin curing agent are the same as in Example 5.

[0050] Application method of ester-based glyceryl thiol epoxy resin curing agent: The prepared ester-based glyceryl thiol curing agent 2 is mixed with commercially available thiol curing agent TMPMP. Weigh 100 parts of E51 epoxy resin, 40.8 parts of commercially available thiol curing agent TMPMP, and 27.2 parts of ester-based glyceryl thiol curing agent 2 according to the following weight ratios, stir and mix evenly, and place in a constant temperature oven at 120 ℃ for curing for 1 h.

[0051] Comparative Example 1

[0052] In this comparative example, E51 epoxy resin and commercially available curing agent TMPMP were mixed evenly at a mass ratio of 100:69.4 and placed in a constant temperature oven at 180 ℃ for 3 h.

[0053] The dynamic thermomechanical curves of the epoxy resin cured products obtained in Examples 1-8 and Comparative Example 1 are shown below. Figure 3 and Figure 4 The determination was performed using a Netzsch dynamic thermomechanical analyzer (NDA). Epoxy resin cured products were prepared as samples measuring 32 mm × 10 mm × 4 mm, and tested using a single cantilever mode. Experimental parameters were set as follows: constant frequency 1.0 Hz, dynamic vibration amplitude 20 μm, and a heating rate of 5 ℃ / min from 30 ℃ to 150 ℃. The peak value of the curve was measured as the glass transition temperature (Tg) of the cured product. g The results are shown in Table 1.

[0054] Table 1 Comparison of glass transition temperature, tensile strength and flexural strength of epoxy resin cured products

[0055]

[0056] As shown in Table 1, the epoxy resin cured by incorporating the ester-containing glyceryl thiol curing agent of the present invention into the commercially available thiol curing agent TMPMP exhibits an increased glass transition temperature compared to Comparative Example 1, which used only the commercially available curing agent TMPMP. Furthermore, the glass transition temperature of the cured product increases with the increase in the proportion of the thiol curing agent of the present invention, indicating that the curing agent of the present invention can improve the heat resistance of the cured product. Table 1 also shows that the curing agent of the present invention can improve the tensile strength and flexural strength of the cured product.

[0057] Epoxy resin adhesives were prepared using the thiol curing agents from Examples 1, 7, and Comparative Example 1. Single-lap tensile shear specimens (GB / T 7124-2008) were prepared using Q235 low-carbon steel sheets, and their tensile shear strength was tested. Accelerated damp heat aging tests (double 85) were also conducted. The test was performed in a constant environment of 85℃ and 85% RH, and the adhesive's resistance to damp heat was tested through 21 consecutive days of damp heat exposure. The results are shown in Table 2.

[0058] Table 2 Comparison of the damp heat aging properties of epoxy resin cured products

[0059]

[0060] As shown in Table 2, the introduction of the ester-containing glyceryl thiol curing agent of the present invention into the commercially available thiol curing agent TMPMP improved the tensile shear strength of the epoxy resin adhesive and the tensile shear strength after the accelerated damp heat aging test, indicating that the curing agent can improve the bonding performance and damp heat aging resistance of epoxy resin.

[0061] Figure 5 and Figure 6 These are the DSC curves (heating rate 20 °C / min) of the epoxy resin systems cured by the curing agent in Examples 1-8 and Comparative Example 1. Figure 5 and Figure 6 It can be seen that two exothermic peaks appeared in Examples 1 to 8, and the peak temperatures of the exothermic peaks were all lower than those in Comparative Example 1, which demonstrates that the curing agent of the present invention has the ability to promote the curing reaction.

[0062] As can be seen, this invention introduces the glycourea structure into the thiol curing agent molecule through an esterification reaction of substituted hydroxymethylglycourea and mercaptocarboxylic acid catalyzed by an acidic catalyst, thus preparing an ester-containing glycourea-based thiol epoxy resin curing agent. The introduction of the glycourea structure increases the rigidity of the curing agent molecule, effectively improving the heat resistance and mechanical properties of the cured epoxy resin, as well as enhancing its adhesion and resistance to humid heat aging. Simultaneously, the substitution of the four tertiary amine structures in the glycourea promotes the curing reaction of the thiol curing agent, exhibiting a certain self-promoting effect. Therefore, the glycourea-based thiol epoxy resin curing agent of this invention has excellent application value and development prospects.

[0063] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A thiol curing agent, characterized in that: The general structural formula of the thiol curing agent is shown in (I):

2. A method for preparing the thiol curing agent according to claim 1, characterized in that: The method involves mixing substituted hydroxymethyl glycourea, mercaptocarboxylic acid, and an acidic catalyst, and then carrying out an esterification reaction under heating conditions.

3. The method for preparing the thiol curing agent according to claim 2, characterized in that: The method specifically involves mixing substituted hydroxymethyl urea, mercaptocarboxylic acid, and an acidic catalyst at a mass ratio of 20~40:45~85:0.5~3, stirring and reacting at 50~150 ℃ for 1~10 h under a pressure of -0.01~-0.1 MPa. After the reaction is completed, 300~800 parts of organic solvent are added for dilution, and the mixture is washed and purified with deionized water. The organic layer is collected, concentrated, and dried to obtain the thiol curing agent.

4. The method for preparing the thiol curing agent according to claim 2 or 3, characterized in that: The substituted hydroxymethyl glycourea is one or more of tetrahydroxymethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-dimethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-diethyl glycourea, 1,3,4,6-tetra(hydroxymethyl)-3,4-diphenyl glycourea, and 1,3,4,6-tetra(hydroxymethyl)-3,4-diethoxyformyl glycourea.

5. The method for preparing the thiol curing agent according to claim 2 or 3, characterized in that: The thiocarboxylic acid is one or more of the following: thioacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutyric acid, 4-mercaptobutyric acid, 4-mercaptovalerate, 5-mercaptovalerate, and 6-mercaptohexanoic acid.

6. The method for preparing the thiol curing agent according to claim 2 or 3, characterized in that: The acidic catalyst is one or more of benzenesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid, trifluoroacetic acid, hydrochloric acid, phosphoric acid, and concentrated sulfuric acid.

7. The method for preparing the thiol curing agent according to claim 3, characterized in that: The organic solvent is one or more of ethyl acetate, butyl acetate, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, toluene, and xylene.

8. The application of the thiol curing agent according to claim 1, characterized in that: The application is as follows: take thiol curing agent and commercially available thiol curing agent in a mass ratio of 1:1 to 10 and mix them evenly to obtain thiol curing agent; take epoxy resin and thiol curing agent in a mass ratio of 100:60 to 100 and mix them evenly, and cure at 80 to 170 ℃ for 0.2 to 3 h.

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