End-capped modified latent curing agent as well as preparation method and application thereof

Abstract

The invention discloses an end-capped modified latent curing agent as well as a preparation method and application thereof, and the preparation method of the curing agent comprises the following steps: reacting polyaminopolycyclohexylmethane with dicyandiamide to obtain a biguanide compound, and then adding bis (dimethylamino) phosphorus chlorate for end capping to obtain the end-capped modified latent curing agent. The curing agent prepared by the preparation method disclosed by the invention has excellent flame retardant property, conforms to the current environment-friendly and efficient development trend, and has excellent water resistance, excellent solvent resistance and good mechanical property. The latent curing agent has good application value in the fields of epoxy sheet molding compounds, electronic potting and the like.

Description

Technical Field

[0001] The present invention relates to the field of latent curing agents, and particularly to a blocked and modified latent curing agent, a preparation method thereof, and an application thereof. Background Art

[0002] Epoxy resin belongs to the category of thermosetting resins. With its excellent mechanical properties, heat resistance, adhesion properties, and chemical corrosion resistance, it is widely used in the fields of adhesives, coatings, composite materials, etc. Uncured epoxy resin is just a linear macromolecule with a very low molecular weight of only 300 - 2000. At room temperature, it can be in the form of a liquid or a solid. The epoxy resin in the form of a solid softens and becomes viscous when heated, while the epoxy resin in the form of a liquid has a reduced viscosity when heated, but does not cure. Only after adding a certain proportion of curing agent and curing under certain curing conditions does it become a three-dimensional network structure polymer that is insoluble and infusible, and only then can the excellent properties of epoxy resin be manifested.

[0003] Epoxy curing agents can be divided into two types according to the curing process and characteristics: latent type and latent type. The latent type curing agent means that the curing agent can directly react with epoxy resin after being mixed, while the latent type curing agent will not immediately undergo a curing reaction after being mixed with epoxy resin and has a storage period. Changing external conditions, such as light, heating, etc., will cause the curing reaction to occur. Compared with the latent type curing agent, the latent type curing agent can be pre-mixed with epoxy resin without the need for separate transportation and on-site weighing and other measures, and has obvious commercial value, including shortening the working time and stable performance.

[0004] Dicyandiamide has been a common latent curing agent for a long time. To solve its relatively high curing temperature, it generally needs to be modified. However, the existing modification methods generally change the amino structure, thereby reducing the reaction temperature with epoxy groups, which will lead to a shortening of the storage period. How to ensure an appropriate storage period while increasing the curing speed is one of the problems faced by dicyandiamide curing agents. Summary of the Invention

[0005] To solve the above problems, the present invention provides a blocked and modified latent curing agent, a preparation method thereof, and an application thereof. The curing agent modified by the present invention has excellent water resistance, solvent resistance, good storage stability, and excellent flame retardant properties.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A preparation method of a blocked and modified latent curing agent, comprising the following steps:

[0008] Reacting polyaminopolycyclohexylmethane with dicyandiamide to obtain a biguanide compound, and then adding phosphorus bis(dimethylamino)chloride for end-capping to obtain an end-capped modified latent curing agent. The number of amino groups and cyclohexyl groups in the polyaminopolycyclohexylmethane is ≥2, and its structure is:

[0009]

[0010] In the formula, X takes any integer between 0 and 7, and preferably X = 1 or X = 2.

[0011] The polyaminopolycyclohexylmethane can be a product obtained by hydrogenating polyaminopolybenzylmethane.

[0012] The polyaminopolycyclohexylmethane can be a mixture.

[0013] Furthermore, the polyaminopolycyclohexylmethane includes 45-90 wt% of diaminodicyclohexylmethane, 5-25 wt% of triaminotricyclohexylmethane, and 5-20 wt% of tetraaminotetracyclohexylmethane by mass fraction.

[0014] Furthermore, the molar amount of the dicyandiamide is 0.5-1.5 times, preferably 1.0-1.05 times, the molar amount of -NH 2 in the polyaminopolycyclohexylmethane.

[0015] Furthermore, the reaction of polyaminopolycyclohexylmethane with dicyandiamide is carried out under an inert gas atmosphere. Preferably, the reaction of polyaminopolycyclohexylmethane with dicyandiamide is carried out in a solvent, and the solvent is one or more of water, methanol, and ethanol, preferably water.

[0016] Furthermore, the dicyandiamide is added to the solvent for dissolution, and the dissolution temperature is 25-50 °C, preferably 35-45 °C; after the dicyandiamide is fully dissolved, an acid, preferably hydrochloric acid (more preferably concentrated hydrochloric acid), is added to adjust the pH value of the system to 0.5-5, and then polyaminopolycyclohexylmethane is added. After the system is mixed evenly, the temperature is raised to the reaction temperature for reaction.

[0017] Furthermore, the reaction can be carried out under reflux conditions.

[0018] Furthermore, the reaction temperature is 40-130 °C, preferably 60-100 °C; the reaction time is 0.5-10 h, preferably 3-6 h.

[0019] Furthermore, after the reaction is completed, the biguanide compound is obtained by washing with an alkaline solution.

[0020] Furthermore, the alkaline solution is one or more of an aqueous sodium carbonate solution, an aqueous sodium bicarbonate solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution, preferably an aqueous sodium hydroxide solution.

[0021] In the above reaction, due to the influence of steric hindrance, the primary amino group in the middle position of the polyaminopolycyclohexylmethane structure has relatively low reactivity with dicyandiamide. After the reaction, unreacted primary amines will remain in the system. The primary amine group has relatively high reactivity with epoxy resin and releases a large amount of heat, resulting in a short storage period after mixing with epoxy resin. Therefore, after the reaction, phosphorus bis(dimethylamino)chloride is used to eliminate the primary amine group, introducing phosphorus and nitrogen flame retardant elements while improving the storage stability after mixing with epoxy resin.

[0022] Furthermore, the molar ratio of phosphorus bis(dimethylamino)chloride to -NH in the biguanide compound is 0.5 - 1.5, preferably 1.0 - 1.05. 2

[0023] Furthermore, the reaction of the biguanide compound with phosphorus bis(dimethylamino)chloride is carried out in a solvent, which is one or more of dimethyl sulfoxide, dimethylformamide, and carbon dichloride, preferably dimethyl sulfoxide.

[0024] Furthermore, an acid-binding agent is added to the reaction of the biguanide compound with phosphorus bis(dimethylamino)chloride. The acid-binding agent is one or more of triethylamine, N,N-dimethylaniline, and pyridine, preferably triethylamine.

[0025] Furthermore, first, the biguanide compound is dissolved in the solvent, then the acid-binding agent is added, and then phosphorus bis(dimethylamino)chloride is slowly added dropwise to the biguanide compound for reaction. The reaction time is 12 - 36 h, preferably 20 - 28 h.

[0026] The addition amount of the acid-binding agent and the molar ratio of phosphorus bis(dimethylamino)chloride is 0.5 - 2. Furthermore, the reaction is an exothermic reaction, and the reaction temperature is controlled at 1 - 10 °C, preferably 2 - 8 °C, by a low-temperature water bath. After the reaction, recrystallization separation is carried out to obtain the end-capped modified latent curing agent.

[0027] The reaction route of the end-capping reaction is shown as follows:

[0028]

[0029] where R 1 is or H.

[0030] In the formula, X takes any integer between 0 and 7.

[0031] The present invention also provides a curing agent prepared by the above preparation method.

[0032] The present invention also provides an application of the latent curing agent prepared by the above method in the fields of epoxy sheet molding compound, electronic potting, etc.

[0033] ​The beneficial effects of the present invention are as follows:

[0034] Compared with dicyandiamide curing agent, the latent epoxy curing agent prepared by the present invention not only reduces the curing reaction temperature with epoxy resin and shortens the curing time, but also improves the compatibility with epoxy resin, solving the problem of reduced product performance of the cured product caused by incomplete dispersion of dicyandiamide.

[0035] There are still some primary amine groups remaining in the biguanide compound system, with relatively high reactivity. After mixing with epoxy resin, it can crosslink and cure with epoxy groups, resulting in a relatively low storage period. By using the method of end-capping modification with bis(dimethylamino)phosphoric acid chloride, the present invention improves the storage stability after mixing with epoxy resin. In addition, a phosphorus-nitrogen structure is introduced during the end-capping process. Compared with the C-C organic chain segment, the phosphorus-nitrogen inorganic chain segment has a higher Young's modulus and is difficult to be dissolved into a true solution. The stable inorganic chain segment not only improves the water resistance and solvent resistance, but also the synergistic effect of phosphorus and nitrogen elements shows good flame retardancy, has good thermal stability and low toxicity, and is an environmentally friendly flame retardant system. When its products burn, a uniform carbonaceous foam layer is formed on the surface, which plays a role in heat insulation, oxygen isolation, smoke suppression and preventing dripping, meeting the current trend of environmental protection, low toxicity and less smoke of flame retardants, and having broad application prospects in fields such as epoxy sheet molding compounds and electronic potting. Specific embodiments

[0036] The present invention will be further described in detail below with reference to specific examples and attached tables, but the implementation methods of the present invention and the applicable substrates are not limited thereto.

[0037] The raw materials and their sources are shown in Table 1:

[0038] Table 1 Raw materials and their sources

[0039] Chemical Name Manufacturer Dicyandiamide Azken Chemical Co., Ltd. MDA-45 Wanhua Chemical Group Co., Ltd. MDA-60 Wanhua Chemical Group Co., Ltd. MDA-75 Wanhua Chemical Group Co., Ltd. MDA-85 Wanhua Chemical Group Co., Ltd. IPDA Wanhua Chemical Group Co., Ltd. Bis(dimethylamino)phosphoryl chloride Shanghai Aladdin Biochemical Technology Co., Ltd. Dimethyl sulfoxide Shanghai Aladdin Biochemical Technology Co., Ltd. Dimethylformamide Shanghai Aladdin Biochemical Technology Co., Ltd. Carbon dichloride Shanghai Aladdin Biochemical Technology Co., Ltd. Triethylamine Shanghai Aladdin Biochemical Technology Co., Ltd. N,N-Dimethylaniline Shanghai Aladdin Biochemical Technology Co., Ltd. Pyridine Shanghai Aladdin Biochemical Technology Co., Ltd. E51 Resin Nan Ya Electronic Materials Co., Ltd. Concentrated hydrochloric acid (mass fraction about 37%) Shanghai Aladdin Biochemical Technology Co., Ltd. Organic urea U500 Azken Chemical Co., Ltd. Acetone Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] In the examples of the present invention, polyaminopolycyclohexylmethane is prepared by hydrogenating polyaminopolyarylmethane, and the hydrogenation catalyst is a mixture of rhodium-supported catalyst and ruthenium-supported catalyst.

[0041] The composition of polyaminopolycyclohexylmethane is detected by gas chromatography Agilent 7890B.

[0042] Example 1

[0043] (1) In a 2 L high-pressure autoclave with an internal filter, add 5 g of Rh / Al 2 O 3 and 0.125 g of Ru / Al 2 O 3A catalyst, 500 g of MDA-45 raw material and 500 g of tetrahydrofuran were added simultaneously, and they were respectively displaced three times with N 2 and H 2 After that, it was repressurized to 7 MPa (absolute pressure) with H 2 The temperature was raised to 210 °C, and H 2 was continuously introduced into the reaction kettle through a hydrogen flow controller during the reaction to ensure that the reaction pressure was maintained at 7 MPa (absolute pressure). When the hydrogen flow rate indicated by the hydrogen flow controller was lower than 100 sccm, the introduction of H 2 was stopped. When the pressure drop of the reaction kettle was less than 0.1 bar / min, the reaction was stopped, and the reaction kettle was cooled and depressurized. When the temperature of the reaction kettle dropped to 30 °C, N 2 with an absolute pressure not exceeding 4 MPa was used to filter and separate the product liquid from the catalyst through an internal filter to obtain polyaminopolycyclohexylmethane A1, which included diaminodicyclohexylmethane (55 wt%), triaminotricyclohexylmethane (25 wt%), and tetraaminotetracyclohexylmethane (20 wt%).

[0044] (2) Preparation of bis(dimethylamino)phosphoric acid chloride-terminated biguanide compound:

[0045] Dry N 2 was introduced into a 100 ml three-necked flask equipped with a reflux device for displacement. 4.2 g of dicyandiamide and 40 ml of distilled water were added, and the dissolution temperature was controlled at 35 °C. After the dicyandiamide was fully dissolved, concentrated hydrochloric acid (mass fraction about 37%) was added dropwise until the pH value of the system reached 1. 5.3 g of the above polyaminopolycyclohexylmethane A1 was weighed and added dropwise to the reaction system. After the system was mixed evenly, the temperature was raised to 40 °C, and the reaction was maintained for 3 h. During this period, concentrated hydrochloric acid was continuously added to maintain the pH value at 1. After the reaction was completed, the mother liquor was filtered by suction, and the precipitate was washed with an aqueous sodium carbonate solution to obtain a mixture B1.

[0046] The above mixture B1 was dried and dissolved in 60 ml of dimethyl sulfoxide solution. Subsequently, 2.5 g of triethylamine was added. 4.3 g of bis(dimethylamino)phosphoric acid chloride was slowly added dropwise to the reaction system for reaction. The reaction time was controlled at 20 h. The reaction was an exothermic reaction, and the reaction temperature was controlled at 2 °C by a low-temperature water bath. After the reaction was completed, acetone was used as a recrystallization solvent to separate and obtain the end-capped modified latent curing agent C1.

[0047] Example 2

[0048] A mixture of 90 wt% of diaminodicyclohexylmethane, 5 wt% of triaminotricyclohexylmethane, and 5 wt% of tetraaminotetracyclohexylmethane was prepared by the method in Example 1, with the only difference being that the hydrogenation raw material was selected as MDA-85 to obtain polyaminopolycyclohexylmethane A2.

[0049] Dry N was introduced into a 100 ml three-necked flask equipped with a condensation reflux device. 2 After replacement, 4.2 g of dicyandiamide and 40 ml of methanol were added. The dissolution temperature was controlled at 40 °C. After the dicyandiamide was fully dissolved, concentrated hydrochloric acid (mass fraction about 37%) was added dropwise until the pH value of the system reached 1. 10.6 g of the above-mentioned polyamino polycyclohexylmethane A2 was weighed and added dropwise to the reaction system. After the system was mixed evenly, the temperature was raised to 60 °C and the reaction was maintained for 4 h. During this period, concentrated hydrochloric acid was continuously added to maintain the pH value at 1. After the reaction was completed, the mother liquor was filtered by suction, and the precipitate was washed with an aqueous sodium bicarbonate solution to obtain a mixture B2.

[0050] The above mixture B2 was dried and then dissolved in 60 ml of dimethylformamide solution. Subsequently, 18.2 g of N,N-dimethylaniline was added. 25.5 g of bis(dimethylamino)phosphoric acid chloride was slowly added dropwise to the reaction system for reaction. The reaction time was controlled at 24 h. The reaction was an exothermic reaction, and the reaction temperature was controlled at 5 °C by a low-temperature water bath. After the reaction was completed, acetone was used as the recrystallization solvent to separate and obtain the blocked and modified latent curing agent C2.

[0051] Example 3

[0052] A mixture of 75 wt% of diaminodicyclohexylmethane, 15 wt% of triaminotricyclohexylmethane, and 10 wt% of tetraaminotetracyclohexylmethane was prepared by the method in Example 1, except that the hydrogenation raw material was selected as MDA-75 to obtain a polyamino polycyclohexylmethane mixture A3.

[0053] Dry N was introduced into a 100 ml three-necked flask equipped with a condensation reflux device. 2 After replacement, 12.6 g of dicyandiamide and 40 ml of ethanol were added. The dissolution temperature was controlled at 45 °C. After the dicyandiamide was fully dissolved, concentrated hydrochloric acid (mass fraction about 37%) was added dropwise until the pH value of the system reached 1. 15.9 g of the above-mentioned polyamino polycyclohexylmethane mixture A3 was weighed and added dropwise to the reaction system. After the system was mixed evenly, the temperature was raised to 80 °C and the reaction was refluxed for 6 h. During this period, concentrated hydrochloric acid was continuously added to maintain the pH value at 1. After the reaction was completed, the mother liquor was filtered by suction, and the precipitate was washed with an aqueous sodium hydroxide solution to obtain a mixture B3.

[0054] The above mixture B3 was dried and then dissolved in 60 ml of carbon dichloride solution. Subsequently, 11.8 g of pyridine was added. 25.5 g of bis(dimethylamino)phosphoric acid chloride was slowly added dropwise to the reaction system for reaction. The reaction was an exothermic reaction. The reaction time was controlled at 28 h and the reaction temperature was 7 °C. After the reaction was completed, acetone was used as the recrystallization solvent to separate and obtain the blocked and modified latent curing agent C3.

[0055] Example 4

[0056] Prepare a mixture of 60 wt% of diaminodicyclohexylmethane, 25 wt% of triaminotricyclohexylmethane, and 15 wt% of tetraaminotetracyclohexylmethane using the method in Example 1, with the only difference being that the hydrogenation raw material is selected as MDA-60 to obtain the polyaminopolycyclohexylmethane mixture A4.

[0057] Introduce dry N into a 100 ml three-necked flask equipped with a condensation reflux device 2 Perform replacement, add 12.6 g of dicyandiamide and 40 ml of distilled water, control the dissolution temperature at 40 °C. After the dicyandiamide is fully dissolved, add concentrated hydrochloric acid (mass fraction about 37%) until the pH value of the system reaches 1. Weigh 10.5 g of the above polyaminopolycyclohexylmethane mixture A4 and add it dropwise to the reaction system. After the system is mixed evenly, the temperature is raised to 100 °C, and the reaction reflux is maintained for 6 h. During this period, continuously supplement concentrated HCl to keep the pH value at 1. After the reaction is completed, filter the mother liquor by suction, and wash the precipitate with an aqueous potassium hydroxide solution to obtain the mixture B4.

[0058] Dry the above mixture B4 and dissolve it in 60 ml of dimethyl sulfoxide solution. Subsequently, add 5.1 g of triethylamine. Slowly add 8.5 g of bis(dimethylamino)phosphoryl chloride dropwise to the reaction system for reaction. The reaction is an exothermic reaction. Control the reaction time at 24 h and the reaction temperature at 8 °C. After the reaction is completed, use acetone as the recrystallization solvent to separate and obtain the blocked and modified latent curing agent C4.

[0059] Comparative Example 1

[0060] Physically mix 6 g of dicyandiamide and 1 g of organic urea U500 evenly to obtain the comparative Dicy.

[0061] Preparation of comparative epoxy sheet molding compound

[0062] Put 83 g of E51 epoxy resin, 6 g of internal mold release agent, 0.75 g of defoaming agent, and 0.75 g of wetting agent into a reaction kettle and start stirring to obtain Material 1; put the mixed abrasive composed of 17 g of E51 epoxy resin and the comparative Dicy curing agent into the reaction kettle, stir evenly, and then perform three-roll grinding. After grinding, the particle size of the mixture is less than 10 microns to obtain Material 2; add Material 2 to Material 1, stir and perform vacuum defoaming, add 2.7 g of IPDA, stir evenly to obtain the epoxy resin paste; impregnate the prepared epoxy resin paste with 25 mm disordered chopped glass fibers, roll press it with a sheet machine, and then send it to a 45 °C drying oven for curing for 16 hours to obtain the epoxy sheet molding compound P-Dicy.

[0063] Preparation of epoxy sheet molding compounds in Examples 1-4

[0064] Add 100 g of epoxy resin E51, 1 g of organic urea U500, 6 g of internal mold release agent, 0.75 g of defoaming agent, and 0.75 g of wetting agent into a reaction kettle and start stirring. Then, add the end-capped modified latent curing agent synthesized in the examples according to the equimolar amount (the number of moles of epoxy groups in the epoxy resin = the number of moles of hydrogen on the amino groups (primary amines and secondary amines) in the curing agent). Add 2.7 g of IPDA into the reaction kettle and stir. After mixing evenly, perform vacuum degassing to obtain an epoxy resin paste. Immerse the prepared epoxy resin paste in 25 mm disordered chopped glass fibers. After rolling with a sheet machine, send it into a 45 °C drying oven for curing for 16 hours to obtain the epoxy sheet molding compound P-C.

[0065] Using the above preparation method of epoxy sheet molding compound, the epoxy sheet molding compounds P-C1 to P-C4 are prepared by the above steps with the biguanide compounds capped with C1 to C4 in Examples 1 to 4 respectively.

[0066] Cure and test the epoxy resin paste and epoxy sheet molding compound obtained in the examples and comparative examples respectively. The curing conditions and test standards used are as follows:

[0067] For the mechanical properties of the epoxy resin paste, evacuate and degas, pour resin tensile and flexural specimen strips according to the requirements of GB / T2567-2008, and the curing condition is 150 °C × 5 min to obtain the cured product of the epoxy resin paste.

[0068] Test the mechanical properties of the cured product of the epoxy sheet molding compound: Cure and mold quickly under the curing condition of 150 * 20 min in a mold with dimensions of 500 mm * 500 mm * 4 mm. Cut the cured product plate into tensile, flexural, and impact specimen strips according to the GB / T15568-2008 standard for testing. Conduct the test for the flame retardant grade according to the UL94-2013 test standard. Conduct the water absorption test according to the GB / T1034-2008 standard. Conduct the solvent resistance test according to the GB / T1732-1993 standard.

[0069] The test results are listed in Tables 2 and 3 below.

[0070] Table 2 Comparison of basic parameters of epoxy resin paste and properties of its cured product

[0071]

[0072] Table 3 Comparison of mechanical properties and flame retardant properties of epoxy resin sheet molding compound

[0073] P-C1 P-C2 P-C3 P-C4 P-Dicy Tensile strength / MPa 246.4 244.4 256.6 259.3 230.5 Tensile modulus / GPa 14.2 14.6 15.0 15.2 12.4 Flexural strength / MPa 339.5 340.3 343.8 346.4 320.5 Elongation at break % 2.6 2.3 3.3 2.9 1.7 Whether it is V0-class flame retardant Yes Yes Yes Yes No

[0074] As can be seen from the above comparison table, compared with the traditional dicyandiamide curing agent, the latent curing agent obtained by the present invention is used in the field of epoxy sheet molding compounds. After being mixed with epoxy resin, it has a lower initial viscosity, which is convenient for achieving molecular-level mixing, and the properties of the cured product are improved compared with traditional dicyandiamide. There are primary amine groups in the molecular chain of this latent curing agent. After being end-capped and modified with bis(dimethylamino)phosphoric acid chloride, the viscosity of the epoxy resin paste increases extremely slowly, and it can be stored at room temperature for a long time, thus reducing production and storage costs. At the same time, inorganic segments are introduced during the end-capping process to improve the water and solvent resistance of the cured product. The phosphorus and nitrogen elements enable a uniform carbonaceous foam layer to form on the surface of the product during combustion, inhibiting the progress of combustion and achieving a V0-level flame retardant effect.

[0075] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a blocked modified latent curing agent, characterized in that, it comprises the following steps: Reacting polyaminopolycyclohexylmethane with dicyandiamide to obtain a biguanide compound, and then adding phosphorus bis(dimethylamino)chloride for blocking to obtain the blocked modified latent curing agent.

2. The preparation method according to claim 1, characterized in that, the number of amino groups and cyclohexyl groups in the polyaminopolycyclohexylmethane is both ≥2, and its structure is: In the formula, X takes any integer between 0 and 7, preferably X = 1 or X = 2; Preferably, the polyaminopolycyclohexylmethane can be a product obtained by hydrogenating polyaminopolyphenylmethane; Preferably, the polyaminopolycyclohexylmethane comprises 45-90 wt% of diaminodicyclohexylmethane, 5-25 wt% of triaminotricyclohexylmethane, and 5-20 wt% of tetraaminotetracyclohexylmethane.

3. The preparation method according to claim 1, characterized in that, The molar amount of dicyandiamide is 0.5 to 1.5 times, preferably 1.0 to 1.05 times, the molar amount of -NH in polyaminopolycyclohexylmethane. 2 ​ 4. The preparation method according to claim 1, characterized in that, The reaction of polyaminopolycyclohexylmethane with dicyandiamide is carried out in an inert gas atmosphere. Preferably, the reaction of polyaminopolycyclohexylmethane with dicyandiamide is carried out in a solvent, and the solvent is one or more of water, methanol, and ethanol, preferably water; Preferably, the dicyandiamide is added to the solvent for dissolution. After the dicyandiamide is fully dissolved, an acid is added to adjust the pH value of the system to 0.5-5, and then polyaminopolycyclohexylmethane is added. After the system is mixed evenly, the temperature is raised to the reaction temperature for reaction; Preferably, the dissolution temperature is 25-50 °C, preferably 35-45 °C; Preferably, the reaction temperature is 40-130 °C, preferably 60-100 °C; the reaction time is 0.5-10 h, preferably 3-6 h.

5. The preparation method according to claim 1, characterized in that, After the reaction is completed, the biguanide compound is obtained by washing with an alkaline solution; Preferably, the alkaline solution is one or more of an aqueous sodium carbonate solution, an aqueous sodium bicarbonate solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution, preferably an aqueous sodium hydroxide solution.

6. The preparation method according to claim 1, characterized in that, The molar ratio of phosphorus bis(dimethylamino)chloridate to -NH in the biguanide compound is 0.5 to 1.5, preferably 1.0 to 1.

05. 2 ​ 7. The preparation method according to claim 1, characterized in that, The reaction of the biguanide compound with phosphorus bis(dimethylamino)chloride is carried out in a solvent, and the solvent is one or more of dimethyl sulfoxide, dimethylformamide, and carbon dichloride, preferably dimethyl sulfoxide.

8. The preparation method according to claim 1, characterized in that, A deacidifying agent is also added in the reaction of the biguanide compound with phosphorus bis(dimethylamino)chloride, and the deacidifying agent is one or more of triethylamine, N,N-dimethylaniline, and pyridine, preferably triethylamine; Preferably, the biguanide compound is first dissolved in the solvent, then the deacidifying agent is added, and then phosphorus bis(dimethylamino)chloride is slowly added dropwise to the biguanide compound for reaction. The reaction time is 12-36 h, preferably 20-28 h; Preferably, the molar ratio of the amount of the acid-binding agent added to phosphorus bis(dimethylamino)chlorate is 0.5 - 2; preferably, the reaction temperature of the biguanide compound and phosphorus bis(dimethylamino)chlorate is 1 - 10 °C, preferably 2 - 8 °C.

9. A blocked and modified latent curing agent prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the blocked and modified latent curing agent prepared by the preparation method according to any one of claims 1 - 8 in the fields of epoxy sheet molding compounds and electronic potting.

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