Epoxy system curing agent, flame retardant epoxy resin composite material and preparation method thereof

Abstract

Epoxy system curing agent, flame retardant epoxy resin composite material and preparation method thereof, relate to the technical field of flame retardant epoxy resin, and the existing epoxy resin composite material has problems such as inconsistent flame retardant effect. In a three-necked round-bottom flask, n-octyl phosphoric acid is dissolved in a solvent; then, imidazole or imidazole derivative dissolved in the solvent is added to the above solution, and the reaction is carried out by continuous stirring at room temperature. After the reaction is completed, the solvent is removed by rotary evaporation, and the resulting product is vacuum dried to obtain an epoxy system curing agent. After stirring and mixing evenly with the heated epoxy resin, vacuum is evacuated, and when the mixture has no bubbles in the vacuum, it is poured into a mold, and a composite material is obtained after curing. The present invention realizes the integration of flame retardant and curing agent, and can be widely used in many fields, especially in the fields of electrochemistry and electronic packaging.

Description

Technical Field

[0001] The invention relates to the technical field of flame-retardant epoxy resins, and in particular to an epoxy system curing agent, a flame-retardant epoxy resin composite material and a preparation method thereof. Background Art

[0002] Epoxy resin (EP) is widely used in many industrial fields such as coatings, laminates, electronic devices, adhesives, coatings and resin-based composites due to its excellent mechanical properties, good corrosion resistance, simple processing performance and low cost. However, its own flammability poses a huge safety hazard, which limits its application in industries that require high fire safety standards. Therefore, in order to expand its application in the industrial field, it is urgent and necessary to give it corresponding flame retardant properties.

[0003] In this regard, many methods for modifying epoxy resins have been proposed in existing studies. For example, in the patent document CN116675954A "A Phosphorus- and Nitrogen-Containing Ionic Liquid / Epoxy Resin Composite Material and Its Preparation Method" (published on September 1, 2023), phosphorus and nitrogen elements in phosphorus- and nitrogen-containing ionic liquids produce phosphorus oxygen free radicals and nitrogen when the epoxy resin composite material burns, which quenches the flame, thereby achieving excellent flame retardant properties. However, this ionic liquid can only be used as a flame retardant filler, doped in small amounts in the resin matrix, and an amine curing agent or anhydride curing agent must be added to the system to achieve curing. On the one hand, this additionally added ionic liquid is prone to aggregation or uneven dispersion in the system, resulting in internal stress concentration of the material, thereby reducing the strength, toughness and thermal stability of the material, and the problem of inconsistent flame retardant effects of various parts of the material caused by this phase separation; on the other hand, amine curing agents and anhydride curing agents generally have higher curing temperatures and slower curing rates, which will increase time costs in industrial production.

[0004] The curing behavior and overall performance of epoxy resin systems are mainly determined by curing agents. Therefore, the introduction of flame retardant groups in molecular design can achieve curing and crosslinking of epoxy resin systems without the need for additional flame retardants, which can better control the process and simplify the operation. Imidazole curing agents have attracted extensive attention in the academic and industrial fields because they can use secondary amines to react with epoxy groups for ring-opening addition, and can also use tertiary amines to react with epoxy groups to initiate anionic polymerization to catalyze the homogeneous polymerization and curing of epoxy resins, so that the cured resin has good comprehensive performance. Therefore, the introduction of flame retardant groups into imidazole curing agents can improve the flame retardant properties while enabling them to have fast curing capabilities, which will increase the application scope of imidazole curing agents in the industrial field. Summary of the invention

[0005] In order to solve the problems of inconsistent flame retardant effects of existing epoxy resin composite materials, the present invention provides an epoxy system curing agent, a flame retardant epoxy resin composite material and a preparation method thereof.

[0006] The technical solution of the present invention is as follows:

[0007] An epoxy system curing agent, the structural formula is as follows:

[0008] ;

[0009] Among them, R1 is selected from one of hydrogen, alkyl, and phenyl, R2 is selected from one of hydrogen, alkyl, and phenyl, R3 is selected from one of hydrogen, alkyl, and phenyl, or together with R4, it forms a phenyl, and R4 is selected from one of hydrogen, alkyl, and phenyl, or together with R3, it forms a phenyl.

[0010] Preferably, R1 is hydrogen, R2 is hydrogen, R3 is hydrogen, and R4 is hydrogen.

[0011] The present invention also provides a method for preparing the above epoxy system curing agent, comprising the following steps:

[0012] In a three-necked round-bottom flask, n-octyl phosphoric acid (OPA) is dissolved in a solvent; subsequently, imidazole (MI) or an imidazole derivative dissolved in the solvent is added to the above solution, and the reaction is carried out by continuous stirring at room temperature. After the reaction is completed, the solvent is removed by rotary evaporation, and the resulting product is vacuum dried to obtain an epoxy system curing agent (ZMI).

[0013] Preferably, the solvent is one of methanol, ethanol, water, or a combination of at least two of them.

[0014] Preferably, the continuous stirring time is 3h~6h.

[0015] Preferably, the imidazole or imidazole derivative dissolved in the solvent is added dropwise via a constant pressure dropping funnel.

[0016] Preferably, the temperature of the rotary evaporation is 40°C to 55°C.

[0017] The present invention also provides a flame retardant epoxy resin composite material, which is obtained by curing with the above epoxy system curing agent.

[0018] A method for preparing the flame retardant epoxy resin composite material comprises the following steps:

[0019] The epoxy system curing agent and the heated epoxy resin are stirred and mixed evenly, and then vacuumed. When there are no bubbles in the mixture in the vacuum, pour it into the mold, preheat at 60° C. for 20 minutes, and then cure at 70° C. for 2 hours, and then cure at 140° C. for 2 hours.

[0020] Preferably, the epoxy resin is bisphenol A epoxy resin;

[0021] The heating temperature of the epoxy resin is 55° C. to 65° C., and the heating time is 20 min to 30 min.

[0022] Compared with the prior art, the specific beneficial effects of the present invention are:

[0023] 1. The present invention combines a flexible chain with an ionic compound to modify the imidazole curing agent. The phosphorus-containing flame retardant group is introduced into the imidazole curing agent through an ionic bond, so that the curing ability of the imidazole curing agent is improved while having better flame retardant properties. Since the flame retardant group is embedded in the curing agent through a chemical reaction, it can be closely combined with the cross-linked network of the epoxy resin, has better compatibility and dispersibility, avoids the phase separation problem that may exist in traditional flame retardants, and can more effectively play a flame retardant role. The addition of the flexible chain also makes the epoxy resin material have corresponding toughness, solves the problem of poor toughness brought to the epoxy resin when imidazole is used as a curing agent, and obtains an epoxy composite material with excellent performance.

[0024] 2. The present invention realizes the integration of flame retardant and curing agent, simplifies the formula design and production process, reduces the steps and costs required for additional addition of flame retardant, and has high yield; the provided epoxy resin composite material has low curing temperature, fast curing speed, and has excellent electrochemical stability of ionic compounds, and can be widely used in many fields, especially in the fields of electrochemistry and electronic packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the infrared spectrum of the epoxy system curing agent prepared in Example 1;

[0026] Figure 2 The NMR of the epoxy system curing agent prepared in Example 1 is 31 P spectrum;

[0027] Figure 3 1 is a stress-strain curve diagram of the composite material in each embodiment and comparative example;

[0028] Figure 4 is a bar graph of the limiting oxygen index of the composite materials in each embodiment and comparative example;

[0029] Figure 5 is a viscosity curve of the composite material in each embodiment and comparative example at 120°C;

[0030] Figure 6 It is the curing mechanism diagram of the epoxy system curing agent of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as a limitation to the present invention.

[0032] The raw materials and equipment used in the following examples are all known products, which are obtained by purchasing commercial products.

[0033] Example 1.

[0034] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, imidazole (8.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the resulting product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMI). The infrared spectrum of the epoxy system curing agent is shown in Figure 1 , NMR 31 P spectrum see Figure 2 It can be proved that this embodiment has been carried out smoothly according to the following reaction route:

[0035] .

[0036] 12.5 parts of the prepared ZMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into a mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMI-12.5%.

[0037] Example 2.

[0038] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, imidazole (8.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMI).

[0039] 15 parts of the prepared ZMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into a mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMI-15%.

[0040] Example 3.

[0041] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, imidazole (8.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMI).

[0042] 17.5 parts of the prepared ZMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into a mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMI-17.5%.

[0043] Example 4.

[0044] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, imidazole (8.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMI).

[0045] 20 parts of the prepared ZMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMI-20%.

[0046] Example 5.

[0047] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, imidazole (8.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMI).

[0048] 25 parts of the prepared ZMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into a mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMI-25%.

[0049] Example 6.

[0050] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, 1-ethylimidazole (11.53 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZEMI) with the following structural formula:

[0051] 15 parts of the prepared ZEMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then adjusted to 140°C and cured for 2 hours to obtain the flame-retardant epoxy resin composite material EP / ZEMI-15%.

[0052] Example 7.

[0053] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, 1-methylimidazole (9.85 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZMMI), the structural formula of which is as follows:

[0054] .

[0055] 15 parts of the prepared ZMMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZMMI-15%.

[0056] Example 8.

[0057] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, 2-ethyl-4-methylimidazole (13.21 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the resulting product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZEMMI), the structural formula of which is as follows:

[0058] .

[0059] 18 parts of the prepared ZEMMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain the flame-retardant epoxy resin composite material EP / ZEMMI-18%.

[0060] Example 9.

[0061] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, 4-phenylimidazole (17.30 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the obtained product was vacuum dried for 12 h to obtain an epoxy system curing agent (Z4PMI), the structural formula of which is as follows:

[0062]

[0063] 20 parts of the prepared Z4PMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then the temperature was adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / Z4PMI-20%.

[0064] Example 10.

[0065] In a three-necked round-bottom flask, n-octyl phosphoric acid (11.6 g, 0.06 mol) was dissolved in ethanol. Subsequently, benzimidazole (14.17 g, 0.12 mol) dissolved in ethanol was dripped into the above solution through a constant pressure dropping funnel, and the reaction was continuously stirred for 5 h at room temperature. After the reaction was completed, the solvent was removed by rotary evaporation at 50 ° C, and the resulting product was vacuum dried for 12 h to obtain an epoxy system curing agent (ZPMI), the structural formula of which is as follows:

[0066]

[0067] 20 parts of the prepared ZPMI were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then adjusted to 140°C and cured for 2 hours to obtain a flame-retardant epoxy resin composite material EP / ZPMI-20%.

[0068] Comparison ratio.

[0069] 6 parts of imidazole were added to 100 parts of bisphenol A epoxy resin heated at 60°C for 20 minutes, stirred evenly and then vacuumed. When there were no bubbles in the mixture in the vacuum, the mixed sample was quickly poured into the mold, the mold was preheated at 60°C for 20 minutes, cured at 70°C for 2 hours, and then adjusted to 140°C and cured for 3 hours to obtain the common imidazole-cured epoxy resin composite material EP / MI-6.

[0070] Effect example 1.

[0071] The elongation at break and limiting oxygen index of the epoxy resin composite materials prepared in Examples 1 to 5 and the comparative example were tested.

[0072] The stress-strain curve of the composite material is shown in Figure 3It can be seen that the curing agent prepared by the present invention has a significantly improved elongation at break compared with the conventional imidazole-cured epoxy resin composite material EP / MI-6 when the addition amount is 10% to 20%, and the most significant improvement is when the addition amount is 15%, at which the elongation at break can reach twice that of the imidazole-cured epoxy resin.

[0073] The limiting oxygen index bar graph is shown in Figure 4 It can be seen that the curing agent prepared by the present invention has a significantly improved limiting oxygen index when added in an amount of 10% to 20% compared with the epoxy resin composite material EP / MI-6 cured by ordinary imidazole, which can prove the significant improvement of flame retardant properties.

[0074] The viscosity of the mixture of ZMI and bisphenol A epoxy resin in Examples 1 to 5 and the mixture of imidazole catalyst and bisphenol A epoxy resin in the comparative example were tested at 120°C (the temperature at which ZMI gels fastest) and 100°C (the temperature at which imidazole gels fastest). The viscosity curves are shown in FIG. Figure 5 It can be seen that the curing rate of the curing agent prepared by the present invention at 120°C is improved compared with the conventional imidazole-cured epoxy resin composite material EP / MI-6 when 10 to 20 parts of the curing agent prepared by the present invention are added to 100 parts of the epoxy resin. At the same time, the curing mechanism of EP / ZMI is given in the present application as follows Figure 6 As shown. ZMI and imidazole have the same first step of curing, which is the ring-opening addition reaction between the nitrogen at position 1 on the imidazole ring and the epoxy group. However, compared with the anionic polymerization between the nitrogen at position 3 of imidazole and the epoxy group, the second step of curing of ZMI requires endothermic cleavage of the ionic bond before further anionic polymerization with the nitrogen at position 3 of imidazole. At the same time, the phosphorus-containing group is attached to the polymer network in the form of an ionic bond of an imidazole salt and forms a partial covalent bond at the end of the epoxy chain.

[0075] Effect example 2.

[0076] The fire retardancy of the epoxy resin composite materials prepared in Examples 1 to 10 and the comparative example was tested respectively, and the obtained limiting oxygen index LOI and UL-94 test results are shown in Table 1.

[0077] It can be seen that the limiting oxygen index of the composite materials prepared in Examples 1 to 10 of the present invention is significantly improved, and the flame retardant performance is excellent.

[0078] Table 1

[0079]

[0080] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. An epoxy system curing agent, characterized in that: The structural formula is as follows: ； Among them, R1 is hydrogen, R2 is hydrogen, R3 is selected from one of hydrogen and phenyl or forms a phenyl group together with R4, and R4 is hydrogen or forms a phenyl group together with R3.

2. An epoxy system curing agent, characterized in that: The structural formula is one of the following: ， ， ， ， ， 。 3. A method for preparing an epoxy system curing agent as claimed in claim 1 or 2, characterized in that: The steps include: Dissolve n-octyl phosphoric acid in a solvent, then add imidazole or an imidazole derivative dissolved in the solvent, and react with continuous stirring at room temperature. After the reaction is completed, remove the solvent by rotary evaporation, and vacuum dry the obtained product to obtain an epoxy system curing agent.

4. The method for preparing the epoxy system curing agent according to claim 3, characterized in that: The solvent is one of methanol, ethanol and water or a combination of at least two of them.

5. The method for preparing the epoxy system curing agent according to claim 3, characterized in that: The continuous stirring time is 3h~6h.

6. The method for preparing the epoxy system curing agent according to claim 3, characterized in that: The imidazole or imidazole derivative dissolved in the solvent is added dropwise through a constant pressure dropping funnel.

7. The method for preparing the epoxy system curing agent according to claim 3, characterized in that: The temperature of the rotary evaporation is 40°C to 55°C.

8. A flame retardant epoxy resin composite material, characterized in that: The epoxy curing agent as claimed in claim 1 or 2 is used for curing.

9. A method for preparing a flame-retardant epoxy resin composite material as claimed in claim 8, characterized in that: The steps include: 10 to 20 parts of the epoxy system curing agent and 100 parts of the heated epoxy resin are stirred and mixed evenly, and then vacuumed. When there are no bubbles in the mixture in the vacuum, pour it into the mold, preheat at 60°C for 20 minutes, and then cure at 70°C for 2 hours, and then cure at 140°C for 2 hours.

10. The method for preparing a flame-retardant epoxy resin composite material according to claim 9, characterized in that: The epoxy resin is bisphenol A epoxy resin; The heating temperature of the epoxy resin is 55° C. to 65° C., and the heating time is 20 min to 30 min.

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