Low-viscosity liquefied dicyandiamide latent curing agent, epoxy resin composition as well as preparation method and application of low-viscosity liquefied dicyandiamide latent curing agent

Abstract

The invention provides a low-viscosity liquefied dicyandiamide latent curing agent, an epoxy resin composition as well as a preparation method and application of the low-viscosity liquefied dicyandiamide latent curing agent. The low-viscosity liquefied dicyandiamide latent curing agent is prepared from raw materials including dicyandiamide and aldehyde compounds in the presence of a catalyst; the preparation method comprises the following steps: uniformly mixing raw materials including dicyandiamide and aldehyde compounds with a solvent to obtain a mixture; and adding a catalyst into the obtained mixture to react, and removing the solvent from the generated product to obtain the low-viscosity liquefied dicyandiamide latent curing agent. The prepared low-viscosity liquefied dicyandiamide latent curing agent is low in viscosity, simple in preparation process and convenient to operate; the epoxy resin composition prepared from the epoxy resin composition has the advantages of low viscosity, long pot life, low curing temperature, high glass transition temperature of a cured product, and high tensile strength and tensile modulus of the cured epoxy resin.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and more particularly to a low-viscosity liquefied dicyandiamide latent curing agent, an epoxy resin composition, and a preparation method and application thereof. Background Art

[0002] Dicyandiamide is a commonly used latent epoxy resin curing agent. Due to the conjugated double bonds and cyanide in the molecule, its mixture with epoxy resin is very stable at room temperature and has a storage period of more than 6 months. Therefore, dicyandiamide is widely used as a curing agent for epoxy resin in coatings, composite materials, adhesives and other fields.

[0003] Dicyandiamide is a white crystalline powder with a melting point of 207-209°C. It has disadvantages such as high curing temperature and low solubility in epoxy resin during use. Therefore, dicyandiamide, as an effective curing agent for epoxy resin, must be crushed into extremely fine powder and suspended in epoxy resin. The preparation process is relatively complicated, which limits its application.

[0004] The current hot topic in the research of latent epoxy resin curing agents is to liquefy the solid dicyandiamide while ensuring the good storage stability of the dicyandiamide / epoxy resin system, and to reduce the curing reaction temperature to the medium temperature range without affecting its performance.

[0005] At present, patent CN102633987A mentions that dicyandiamide is liquefied with epoxy resin diluent to obtain viscous liquid dicyandiamide, which has good compatibility with epoxy resin, is conducive to uniform mixing with epoxy resin, and does not produce precipitation. However, its viscosity is too high and it cannot be used in composite material liquid molding fields such as winding molding, resin transfer molding, wet molding or infusion molding.

[0006] The reaction time of dicyandiamide modified by glycidyl neodecanoate in patent CN1194025C is relatively long, and the product is a viscous liquid with too high viscosity, and cannot be used in composite material liquid molding fields such as winding molding, resin transfer molding, wet molding or infusion molding.

[0007] Therefore, it is necessary to study a low-viscosity liquefied dicyandiamide latent curing agent with low viscosity and long application period, which can be applied to composite material liquid molding fields such as winding molding, resin transfer molding, wet molding or infusion molding. Summary of the invention

[0008] In order to solve the technical problems existing in the prior art, the present invention provides a low-viscosity liquefied dicyandiamide latent curing agent, an epoxy resin composition, and a preparation method and application thereof.

[0009] The invention solves the technical problem that the viscosity of dicyandiamide after liquefaction is too high and it cannot be used in the liquid molding process of composite materials in the prior art. A low-viscosity liquefied dicyandiamide latent curing agent is prepared by reacting an aldehyde compound with dicyandiamide, and the low viscosity and the simple preparation process. The epoxy resin composition prepared by using the prepared low-viscosity liquefied dicyandiamide latent curing agent has low viscosity, long pot life, low curing temperature, and high glass transition temperature of the cured product.

[0010] One of the purposes of the present invention is to provide a low-viscosity liquefied dicyandiamide latent curing agent.

[0011] The low-viscosity liquefied dicyandiamide latent curing agent is prepared from raw materials including dicyandiamide and aldehyde compounds in the presence of a catalyst.

[0012] In a preferred embodiment of the present invention,

[0013] The aldehyde compound is a non-solid aldehyde compound, preferably at least one of aliphatic aldehydes, ester ring aldehydes, aromatic aldehydes and terpene aldehydes, more preferably at least one of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, glyoxal and succinaldehyde;

[0014] The catalyst is at least one of the following compounds and derivatives: quaternary ammonium salts, quaternary phosphonium salts; preferably at least one of the following compounds and derivatives: triphenylphosphine, triphenylphosphine acetate, isopropyltriphenylphosphine iodide, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride.

[0015] In a preferred embodiment of the present invention,

[0016] The molar ratio of the dicyandiamide, the aldehyde compound and the catalyst is 1:(0.2-1.5):(0.005-0.5), preferably 1:(0.4-1.1):(0.01-0.25).

[0017] In a preferred embodiment of the present invention,

[0018] The low-viscosity liquefied dicyandiamide latent curing agent has a viscosity of 50 to 500 mPa·s at 25° C., preferably 100 to 400 mPa·s, for example, 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, etc.

[0019] The second object of the present invention is to provide a method for preparing a low-viscosity liquefied dicyandiamide latent curing agent, comprising the following steps:

[0020] (1) mixing raw materials including dicyandiamide and an aldehyde compound and a solvent to obtain a mixture;

[0021] (2) adding a catalyst to the mixture obtained in step (1) to react, and removing the solvent from the generated product to obtain the low-viscosity liquefied dicyandiamide latent curing agent.

[0022] In a preferred embodiment of the present invention,

[0023] Step (1),

[0024] The solvent is a protic solvent, preferably at least one of a fatty amine solvent, a fatty alcohol solvent, and water; more preferably at least one of methanol, ethanol, and water;

[0025] The mixing temperature is 40 to 80°C, preferably 50 to 70°C;

[0026] The mixing time is 10 to 60 minutes, preferably 15 to 55 minutes;

[0027] The mixing method can adopt the common method of the prior art, such as mechanical stirring, etc.

[0028] Step (2),

[0029] The reaction temperature is 50 to 90°C, preferably 50 to 80°C;

[0030] The reaction time is 30 to 200 min, preferably 60 to 180 min;

[0031] The solvent can be removed by common methods in the prior art, such as vacuuming.

[0032] The third object of the present invention is to provide an epoxy resin composition, comprising the above-mentioned low-viscosity liquefied dicyandiamide latent curing agent; preferably, the epoxy resin composition also includes an epoxy compound and an accelerator.

[0033] In a preferred embodiment of the present invention,

[0034] The epoxy compound is at least one of glycidyl ether epoxy resin, glycidyl ester epoxy resin, and glycidyl amine epoxy resin, preferably bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD ​​epoxy resin, bisphenol S epoxy resin, tetrabromobisphenol A diglycidyl ether, N,N-diglycidyl aniline, N,N-diglycidyl o-toluidine, catechol diglycidyl ether, resorcinol diglycidyl ether, hydroquinone diglycidyl ether, tert-butylhydroquinone diglycidyl ether, 2,5-di-tert-butylhydroquinone diglycidyl ether, and phthalic acid diglycidyl ester; among them, bisphenol A epoxy resin, bisphenol F epoxy resin and other bisphenol epoxy resins are preferred due to their low viscosity and good operability;

[0035] The accelerator is at least one of the following compounds and derivatives: quaternary ammonium salts, quaternary phosphonium salts, tertiary amines, imidazoles; preferably at least one of tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, triphenylphosphine, ethyltriphenylphosphine acetate, isopropyltriphenylphosphine iodide, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanolamine, o-hydroxybenzyldimethylamine, 2-methylimidazole, 1-benzyl-2-ethylimidazole, 2-ethyl-4-methylimidazole, and 1-aminoethyl-2-methylimidazole.

[0036] In a preferred embodiment of the present invention,

[0037] The mass ratio of the epoxy compound, the low-viscosity liquefied dicyandiamide latent curing agent and the accelerator is 100:(3-25):(0.1-10), preferably 100:(5-20):(0.2-5).

[0038] In a preferred embodiment of the present invention,

[0039] The epoxy resin composition has an initial viscosity of 300 to 3000 mPa·s at 25° C., preferably 300 to 1800 mPa·s;

[0040] The epoxy resin composition has a pot life (the time required for the viscosity to double) of ≥48h at 25°C;

[0041] The epoxy resin composition can be cured at a relatively low curing temperature, and the curing temperature is ≤110°C;

[0042] The glass transition temperature of the cured product obtained after the epoxy resin composition is cured and formed is ≥110°C.

[0043] A fourth object of the present invention is to provide a method for preparing an epoxy resin composition comprising the low-viscosity liquefied dicyandiamide latent curing agent, comprising the following steps:

[0044] The epoxy compound, the low-viscosity liquefied dicyandiamide latent curing agent and the accelerator are uniformly mixed to obtain the epoxy resin composition; preferably,

[0045] The mixing temperature is 25 to 100°C, more preferably 25 to 60°C; and / or,

[0046] The mixing time is 3 to 60 minutes, more preferably 3 to 10 minutes.

[0047] The fifth object of the present invention is to provide a low-viscosity liquefied dicyandiamide latent curing agent and an epoxy resin composition for use in the field of composite material liquid molding such as winding molding, resin transfer molding, wet molding or infusion molding.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention prepares a low-viscosity liquefied dicyandiamide latent curing agent by reacting an aldehyde compound with dicyandiamide. The low viscosity of the latent curing agent is 50-500 mPa·s at 25° C. The latent curing agent has the advantages of simple preparation process and convenient operation.

[0050] The epoxy resin composition prepared by using the low-viscosity liquefied dicyandiamide latent curing agent obtained by the present invention has low viscosity after mixing, and the initial viscosity at 25°C is 300-3000 mPa·s; it also has the advantages of long application period, low curing temperature, high glass transition temperature of cured product, etc. The tensile strength and tensile modulus of the cured epoxy resin are high, and the epoxy resin is suitable for winding molding, resin transfer molding, wet molding or infusion molding of composite material liquid molding field. DETAILED DESCRIPTION

[0051] The present invention is described in detail below in conjunction with specific examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0052] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials.

[0053] in,

[0054] Bisphenol A type liquid epoxy resin 1128 is self-made; it is prepared by mixing bisphenol A type liquid epoxy resin 128 and active diluent ethylene glycol diglycidyl ether 669 at a ratio of 8:2 at room temperature;

[0055] Bisphenol F type liquid epoxy resin 1354 is self-made; it is prepared by mixing bisphenol F type liquid epoxy resin NPEF-170 and active diluent ethylene glycol diglycidyl ether 669 in a ratio of 8:2 at room temperature;

[0056] Bisphenol A type liquid epoxy resin 128: Baling Petrochemical Company;

[0057] Bisphenol F type liquid epoxy resin NPEF-170: Nan Ya Plastics Corporation;

[0058] Ethylene glycol diglycidyl ether 669: Anhui Xinyuan Technology Co., Ltd.;

[0059] Dicyandiamide: DICY, Sinopharm Group;

[0060] Aldehyde compounds: acetaldehyde, succinaldehyde, Sinopharm Group;

[0061] Catalyst: Tetrabutylammonium bromide, TBAB, Sinopharm Group;

[0062] Catalyst: triphenylphosphine, TPP, Sinopharm Group;

[0063] Accelerator: ethyl triphenylphosphonium acetate, TPPEA, Sinopharm Group;

[0064] Accelerator: 2-ethyl-4-methylimidazole, EMI24, Sinopharm Group;

[0065] Curing agent: methylhexahydrophthalic anhydride, MHHPA, Sinopharm Group.

[0066] Test method:

[0067] The initial viscosity was measured by a Brookfield CAP2000+L series cone and plate viscometer, with a rotor model of CAP-01, a rotation speed of 100 rpm, and a test temperature of 25°C.

[0068] Pot life of resin matrix: It is tested on CAP2000+L series cone and plate viscometer of Brookfield Company in the United States according to the requirements of GB / T 7123.1~7123.2-2002. The time when the viscosity of the system reaches twice the initial viscosity at the test temperature is taken as the pot life of the system at that temperature.

[0069] The T of the cured epoxy resin composition was determined based on the DSC (TA DSC Q20) measurement method in GB / T 19466-2004. g (Glass transition temperature).

[0070] Based on the determination method using an electronic universal tensile testing machine in GB / T 2567-2008, the mechanical properties of the epoxy resin composition casting were determined.

[0071] [Example 1]

[0072] Preparation of low viscosity liquefied dicyandiamide latent curing agent (L-DICY):

[0073] (1) The molar ratio of dicyandiamide (DICY), acetaldehyde and tetrabutylammonium bromide (TBAB) is 1:0.9:0.2.

[0074] (2) Add DICY, acetaldehyde, and methanol into a container and mechanically stir at 70°C for 30 min until the mixture is uniform;

[0075] (3) TBAB was added into the container and reacted at a reaction temperature of 70°C for 120 min;

[0076] (4) removing the solvent by vacuum to obtain the low-viscosity liquefied dicyandiamide latent curing agent (L-DICY);

[0077] Preparation of epoxy composition:

[0078] The mass ratio of bisphenol A type liquid epoxy resin 1128, L-DICY and ethyl triphenylphosphine acetate (TPPEA) is 100:10:2.

[0079] 1128, L-DICY and TPPEA were mixed evenly at a mixing temperature of 25°C and a mixing time of 10 min, poured into a mold, and cured in an oven at a curing process of 110°C / 2h.

[0080] The relevant performance test results of Example 1 are shown in Table 2

[0081] [Example 2]

[0082] Preparation of low viscosity liquefied dicyandiamide latent curing agent (L-DICY):

[0083] (1) The molar ratio of dicyandiamide (DICY), acetaldehyde and tetrabutylammonium bromide (TBAB) is 1:1.1:0.2.

[0084] (2) Add DICY, acetaldehyde, and methanol into a container and mechanically stir at 50°C for 15 min until the mixture is uniform;

[0085] (3) TBAB was added into the container and reacted at a reaction temperature of 50°C for 180 min;

[0086] (4) removing the solvent by vacuum to obtain the low-viscosity liquefied dicyandiamide latent curing agent (L-DICY);

[0087] Preparation of epoxy composition:

[0088] The mass ratio of bisphenol A type liquid epoxy resin 1128, L-DICY and ethyl triphenylphosphine acetate (TPPEA) is 100:10:2.

[0089] 1128, L-DICY and TPPEA were mixed evenly at a mixing temperature of 60°C and a mixing time of 3 min, poured into a mold, and cured in an oven at a curing process of 110°C / 2h.

[0090] The relevant performance test results of Example 2 are shown in Table 2.

[0091] [Example 3]

[0092] Preparation of low viscosity liquefied dicyandiamide latent curing agent (L-DICY):

[0093] (1) The molar ratio of dicyandiamide (DICY), succinaldehyde and tetrabutylammonium bromide (TBAB) is 1:0.4:0.2.

[0094] (2) Add DICY, acetaldehyde, and methanol into a container and mechanically stir at 50°C for 55 min until the mixture is uniform;

[0095] (3) TBAB was added into the container and reacted at 80°C for 60 min;

[0096] (4) removing the solvent by vacuum to obtain the low-viscosity liquefied dicyandiamide latent curing agent (L-DICY);

[0097] Preparation of epoxy composition:

[0098] The mass ratio of bisphenol F type liquid epoxy resin 1354, L-DICY and ethyl triphenylphosphine acetate (TPPEA) is 100:10:2.

[0099] 1354, L-DICY and TPPEA were mixed evenly at a mixing temperature of 60°C and a mixing time of 3 min, poured into a mold, and cured in an oven at a curing process of 110°C / 2h.

[0100] The relevant performance test results of Example 2 are shown in Table 2.

[0101] [Examples 4 to 10]

[0102] The raw material components and amounts of L-DICY in Examples 4 to 10, and the components and amounts of epoxy compositions prepared using the obtained L-DICY are shown in Table 1.

[0103] Except for the differences in components and amounts in Table 1, the preparation process of the low-viscosity liquefied dicyandiamide latent curing agent (L-DICY) and the preparation process of the epoxy composition in Examples 4 to 10 are the same as those in Example 1.

[0104] The curing process of Examples 4 to 8 is the same as that of Example 1, and the curing process of Examples 9 to 10 is 120° C. / 1 h.

[0105] The performance data of Examples 4 to 6 are shown in Table 2.

[0106] The performance data of Examples 7 to 10 are shown in Table 3.

[0107] [Comparative Example 1]

[0108] Directly use solid powder of dicyandiamide (DICY) to prepare epoxy composition:

[0109] (1) The mass ratio of 1128, DICY and TPPEA is 100:10:2.

[0110] (2) 1128, DICY and TPPEA were mixed evenly at a mixing temperature of 25°C for 10 min, poured into a mold, and cured in an oven at a curing process of 110°C / 2h.

[0111] The relevant performance test results of Comparative Example 1 are shown in Table 3.

[0112] [Comparative Example 2]

[0113] Preparation of epoxy composition using anhydride system curing agent:

[0114] (1) The mass ratio of 1128, methylhexahydrophthalic anhydride (MHHPA) and TPPEA is 100:100:2

[0115] (2) 1128, MHHPA and TPPEA were mixed evenly at a mixing temperature of 25°C for 10 min, poured into a mold, and cured in an oven at a curing process of 110°C / 2h.

[0116] The relevant performance test results of Comparative Example 1 are shown in Table 3.

[0117] Table 1

[0118]

[0119] In Table 1, the ratio of each raw material in L-DICY is a molar ratio, the ratio of each raw material in the epoxy composition is a mass ratio, and the L-DICY in the epoxy composition in each embodiment refers to the L-DICY obtained in this embodiment;

[0120] Among them, 1354 is a homemade bisphenol F type liquid epoxy resin, and EMI24 is 2-ethyl-4-methylimidazole.

[0121] Table 2

[0122]

[0123] Table 3

[0124]

[0125] From the data in Tables 2 and 3, we can see that:

[0126] Compared with Comparative Example 1, Examples 1 to 2, 4, and 6 show:

[0127] The initial viscosity of the epoxy compositions of Examples 1 to 2, 4, and 6 at 25°C is 451 to 1152 mPa·s, which is lower than 14150 mPa·s of Comparative Example 1;

[0128] Cured products T of the epoxy compositions of Examples 1 to 2, 4, and 6 g The temperature of the cured product T g higher;

[0129] The tensile strength of the cured products of the epoxy compositions of Examples 1 to 2, 4, and 6 is 91.5 to 96.1 MPa, which is higher than 82 MPa of Comparative Example 1;

[0130] The tensile modulus of the cured products of the epoxy compositions of Examples 1 to 2, 4, and 6 is 3.4 to 3.6 GPa, which is higher than 2.9 GPa of Comparative Example 1;

[0131] The epoxy compositions of Examples 1 to 2, 4, and 6 can be cured at a temperature below 110° C., while Comparative Example 1 needs to be cured at 120° C., which is a lower curing temperature than Comparative Example 1.

[0132] The above data comparison results prove that after dicyandiamide is modified, it changes from a solid powder to a liquid with lower viscosity, and the obtained epoxy composition has better physical and chemical properties after curing and a lower curing temperature.

[0133] Compared with Comparative Example 2, Examples 1 to 2, 4, and 6 show:

[0134] Although the initial viscosity of the epoxy composition of Comparative Example 2 at 25°C (230 mPa·s) is lower, its pot life at 25°C is only 8 hours; g The tensile strength of the cured product (85.1 MPa) is lower, the tensile modulus of the cured product (2.8 GPa) is lower, and the curing temperature is higher (needs to be cured at 120°C).

[0135] It is proved that although the viscosity reduction effect of methyl hexahydrophthalic anhydride is good, it is at the expense of greatly sacrificing the application period. At the same time, the physical and chemical properties of the epoxy composition obtained after curing are worse, and the curing temperature is higher. The comprehensive use effect is far inferior to the low-viscosity liquefied dicyandiamide latent curing agent prepared in the example.

[0136] The low-viscosity liquefied dicyandiamide latent curing agent prepared in Examples 1 to 10 has a low viscosity of 100 to 400 mPa·s at 25°C, and the preparation process is simple and easy to operate. The epoxy resin composition prepared using the obtained low-viscosity liquefied dicyandiamide latent curing agent has a low viscosity after mixing, and an initial viscosity of 300 to 1600 mPa·s at 25°C. It also has the advantages of a long application period, a low curing temperature, and a high glass transition temperature of the cured product. The cured epoxy resin has high tensile strength and tensile modulus, and is suitable for winding molding, resin transfer molding, wet molding or infusion molding of composite material liquid molding.

Claims

1. A low-viscosity liquefied dicyandiamide latent curing agent is prepared from raw materials including dicyandiamide and aldehyde compounds in the presence of a catalyst.

2. The low-viscosity liquefied dicyandiamide latent curing agent as claimed in claim 1, characterized in that: The aldehyde compound is a non-solid aldehyde compound, preferably at least one of aliphatic aldehydes, ester ring aldehydes, aromatic aldehydes and terpene aldehydes, more preferably at least one of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, glyoxal and succinaldehyde; and / or, The catalyst is at least one of the following compounds and derivatives: quaternary ammonium salts, quaternary phosphonium salts; preferably at least one of the following compounds and derivatives: triphenylphosphine, triphenylphosphine acetate, isopropyltriphenylphosphine iodide, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride.

3. The low-viscosity liquefied dicyandiamide latent curing agent as claimed in claim 1, characterized in that: The molar ratio of the dicyandiamide, the aldehyde compound and the catalyst is 1:(0.2-1.5):(0.005-0.5), preferably 1:(0.4-1.1):(0.01-0.25).

4. The low-viscosity liquefied dicyandiamide latent curing agent according to any one of claims 1 to 3, characterized in that: The viscosity of the low-viscosity liquefied dicyandiamide latent curing agent at 25° C. is 50 to 500 mPa·s, preferably 100 to 400 mPa·s.

5. A method for preparing a low-viscosity liquefied dicyandiamide latent curing agent as claimed in any one of claims 1 to 4, comprising the following steps: (1) mixing raw materials including dicyandiamide and an aldehyde compound and a solvent to obtain a mixture; (2) adding a catalyst to the mixture obtained in step (1) to react, and removing the solvent from the generated product to obtain the low-viscosity liquefied dicyandiamide latent curing agent.

6. The method for preparing a low-viscosity liquefied dicyandiamide latent curing agent as claimed in claim 5, characterized in that: Step (1), The solvent is a protic solvent, preferably at least one of a fatty amine solvent, a fatty alcohol solvent, and water; more preferably at least one of methanol, ethanol, and water; and / or, The mixing temperature is 40 to 80°C, preferably 50 to 70°C; and / or, The mixing time is 10 to 60 minutes, preferably 15 to 55 minutes; and / or, Step (2), The reaction temperature is 50 to 90°C, preferably 50 to 80°C; and / or, The reaction time is 30 to 200 min, preferably 60 to 180 min.

7. An epoxy resin composition, comprising the low-viscosity liquefied dicyandiamide latent curing agent according to any one of claims 1 to 4 or the low-viscosity liquefied dicyandiamide latent curing agent obtained by the preparation method according to any one of claims 5 to 6; preferably, the epoxy resin composition also includes an epoxy compound and an accelerator.

8. The epoxy resin composition according to claim 7, wherein: The epoxy compound is at least one of glycidyl ether epoxy resin, glycidyl ester epoxy resin and glycidyl amine epoxy resin, preferably at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol AD ​​epoxy resin, bisphenol S epoxy resin, tetrabromobisphenol A diglycidyl ether, N,N-diglycidyl aniline, N,N-diglycidyl o-toluidine, catechol diglycidyl ether, resorcinol diglycidyl ether, hydroquinone diglycidyl ether, tert-butylhydroquinone diglycidyl ether, 2,5-di-tert-butylhydroquinone diglycidyl ether and phthalic acid diglycidyl ester; and / or, The accelerator is at least one of the following compounds and derivatives: quaternary ammonium salts, quaternary phosphonium salts, tertiary amines, imidazoles; preferably at least one of tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, triphenylphosphine, ethyltriphenylphosphine acetate, isopropyltriphenylphosphine iodide, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, triethanolamine, o-hydroxybenzyldimethylamine, 2-methylimidazole, 1-benzyl-2-ethylimidazole, 2-ethyl-4-methylimidazole, and 1-aminoethyl-2-methylimidazole.

9. The epoxy resin composition according to claim 7, wherein: The mass ratio of the epoxy compound, the low-viscosity liquefied dicyandiamide latent curing agent and the accelerator is 100:(3-25):(0.1-10), preferably 100:(5-20):(0.2-5).

10. The epoxy resin composition according to any one of claims 7 to 9, characterized in that: The epoxy resin composition has an initial viscosity of 300 to 3000 mPa·s at 25° C., preferably 300 to 1800 mPa·s; and / or, The epoxy resin composition has a shelf life of ≥48h at 25°C; and / or The glass transition temperature of the cured product obtained after the epoxy resin composition is cured and formed is ≥110°C.

11. A method for preparing the epoxy resin composition according to any one of claims 7 to 10, comprising the following steps: The epoxy compound, the low-viscosity liquefied dicyandiamide latent curing agent and the accelerator are uniformly mixed to obtain the epoxy resin composition; preferably, The mixing temperature is 25 to 100°C, more preferably 25 to 60°C; and / or, The mixing time is 2 to 60 minutes, more preferably 3 to 10 minutes.

12. An application of the low-viscosity liquefied dicyandiamide latent curing agent as claimed in any one of claims 1 to 4, the low-viscosity liquefied dicyandiamide latent curing agent obtained by the preparation method as claimed in any one of claims 5 to 6, the epoxy resin composition as claimed in any one of claims 7 to 10, and the epoxy resin composition prepared by the preparation method as claimed in claim 11 in the field of composite material liquid molding by winding molding, resin transfer molding, wet molding or infusion molding.

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