Intrinsic flame-retardant epoxy resin containing DOPO-based s-triazine ring curing agent and preparation method of intrinsic flame-retardant epoxy resin

Abstract

The invention discloses an intrinsic flame-retardant epoxy resin containing a DOPO-based s-triazine ring curing agent and a preparation method thereof, and the preparation method comprises the following steps: (1) adding 2, 4-diamino-6-(4-pentenyl)-1, 3, 5-triazine into a hydrochloric acid aqueous solution, stirring, and filtering to obtain hydrochloride of 2, 4-diamino-6-(4-pentenyl)-1, 3, 5-triazine; (2) carrying out vacuum drying on the hydrochloride, adding an organic solvent and DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), uniformly stirring, heating to 90 + / -10 DEG C, dropwise adding a catalyst azodiisobutyronitrile solution, and carrying out heat preservation reaction; and (3) after the reaction is finished, carrying out reduced pressure distillation to remove the solvent, washing, and carrying out vacuum drying to obtain the s-triazine ring curing agent. And (4) mixing the s-triazine ring curing agent with bisphenol A epoxy resin, heating and curing to obtain the intrinsic flame-retardant epoxy resin. The prepared epoxy resin is excellent in flame retardant property, LOI reaches 42.5% or above, and the maximum LOI can reach 48.3%. And the process is simple, and the curing temperature of the curing agent can be as low as 100 DEG C or below.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and in particular to an intrinsically flame-retardant epoxy resin containing a DOPO-based triazine ring curing agent. Background Technology

[0002] Flame-retardant epoxy resins are used in many important fields, such as electronics and electrical engineering, automotive industry, building materials, aerospace, and military and protective materials.

[0003] Currently, there are various methods for flame-retardant modification of epoxy resins. The most practically valuable method is chemical structural modification of epoxy resins to ultimately obtain intrinsically flame-retardant epoxy resins containing phosphorus. To obtain flame-retardant epoxy resins, curing agents with flame-retardant properties are typically used, such as acid anhydrides, amines, and phenolic curing agents.

[0004] Triazine rings possess a stable six-membered ring formed by C=N conjugation, resulting in excellent thermal stability. During combustion, triazine rings can promote the formation of a char layer and release nitrogen gas at high temperatures to dilute the oxygen concentration in the flame. Furthermore, their low toxicity, biodegradability, and low volatility indicate that their introduction into epoxy resins can yield excellent green flame retardants.

[0005] However, common triazine ring flame retardant curing agents have very high melting points, such as melamine at 354°C. Furthermore, they exhibit poor solubility in common solvents and tend to settle when dispersed in epoxy resins, leading to demanding curing conditions, such as high curing temperatures. Therefore, there is an urgent need for a method to improve their solubility, thereby promoting their application in the field of epoxy resin flame retardancy.

[0006] Chinese invention patent CN101376665 discloses a flame-retardant compound containing a mestriazine structure, oxaphosphine-phenanthrene, with the following structural formula:

[0007] This compound contains phosphorus and nitrogen flame-retardant elements and can be used as a flame retardant in epoxy resins. When added at 15 wt%, i.e., with a phosphorus content of 1.28 wt%, the epoxy resin can pass the UL94V-0 flame retardancy rating with an LOI of 34.2%. However, the hydroxyl groups in this compound have high steric hindrance, low reactivity, and no curing effect, so it cannot be used to prepare intrinsically flame-retardant epoxy resins and can only be used as an additive flame retardant. Furthermore, its LOI value is below 40%, indicating that its flame-retardant effect still needs improvement. Summary of the Invention

[0008] The purpose of this invention is to provide an intrinsically flame-retardant epoxy resin containing a DOPO-based triazine ring curing agent. A chemical modification method for the triazine ring (using a 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine compound in this paper) yielded a triazine ring flame-retardant curing agent with good solubility and excellent flame-retardant properties. The intrinsically flame-retardant epoxy resin was then obtained through a curing reaction with a bisphenol A type curing agent.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an intrinsically flame-retardant epoxy resin containing a DOPO-based triazine ring curing agent, comprising the following steps: (1) 2,4-Diamino-6-(4-pentenyl)-1,3,5-triazine was added to an aqueous hydrochloric acid solution and stirred. The mixture was then filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. (2) The above hydrochloride salt was dried under vacuum, and organic solvent and DOPO were added and stirred evenly. Then the temperature was raised to 90±10℃, and the catalyst azobisisobutyronitrile solution was added dropwise. After the addition was completed, the reaction was kept at the temperature. (3) After the reaction is completed, the solvent is removed by vacuum distillation, washed, and dried under vacuum to obtain DOPO-based triazine ring curing agent; (4) Mix DOPO-based triazine ring curing agent with bisphenol A epoxy resin and heat to cure to obtain intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0010] Preferably, the volume-to-mass ratio of the hydrochloric acid aqueous solution to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 10-20 L / kg, and the concentration of the hydrochloric acid aqueous solution is 0.5-2.0 mol / L.

[0011] Preferably, the mass ratio of DOPO to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 0.5 to 1.5.

[0012] Preferably, the volume-to-mass ratio of the organic solvent to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 3-15 mL / g, and the organic solvent is toluene, xylene, dioxane, or acetonitrile.

[0013] Preferably, the mass ratio of the azobisisobutyronitrile to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 0.1% to 1.5%; the solvent of the azobisisobutyronitrile solution is toluene, xylene, dioxane, or acetonitrile, and the volume-to-mass ratio of the solvent to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride is 0.1-0.5 mL / g.

[0014] Preferably, the mass ratio of the DOPO-based triazine ring curing agent to the bisphenol A epoxy resin is 0.05-0.10.

[0015] Preferably, the bisphenol A epoxy resin includes one or more of glycidyl ether, glycidyl ester, glycidyl amine, aliphatic epoxy resin, and alicyclic epoxy resin.

[0016] Preferably, the vacuum drying conditions in steps (2) and (3) are: vacuum drying at 40±5℃ for 10±5h; the washing in step (3) is performed by washing with ethanol and sodium hydroxide aqueous solution respectively.

[0017] Preferably, the heat preservation reaction time in step (2) is 24±6h; the heating curing conditions in step (4) are curing at a temperature of 80±10℃ for 1~2h.

[0018] Compared with the prior art, the present invention has the following advantages: (1) This invention selects a 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine compound, which is converted into a hydrochloride salt. Then, its double bond is used to undergo an addition reaction with the pH bond of DOPO, followed by neutralization to obtain a DOPO-based triazine ring curing agent with good solubility. The DOPO structural unit is chemically bonded to the molecular backbone of the triazine ring. During the epoxy resin curing reaction, the DOPO flame-retardant group is permanently fixed in the entire cross-linked network structure of the epoxy resin, avoiding the problems of uneven dispersion, poor interfacial compatibility, and the decrease in flame-retardant performance over time due to migration or exudation caused by the currently common practice of directly adding DOPO.

[0019] (2) The intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent of the present invention has a suitable phosphorus content and a high residual carbon rate, excellent flame retardant performance, and an LOI of more than 42.5%, with a maximum of 48.3%.

[0020] (3) The process of the present invention is simple and the curing temperature of the curing agent is greatly reduced, down to below 100°C. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific examples.

[0022] The bisphenol A epoxy resin used in the examples and comparative examples was PA964736, purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0023] Example 1 100 g of 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine was added to 1.116 L of 1 mol hydrochloric acid aqueous solution, stirred at room temperature for 5 h, and filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. The hydrochloride was dried under vacuum at 40 °C for 10 h. Then, 140.73 g of the dried hydrochloride was added to a reaction flask equipped with a reflux condenser, along with 500 ml of toluene and 77 g of DOPO. The mixture was stirred until homogeneous, then heated to 90 °C, and 0.33 g of azobisisobutyronitrile (AIB) in 20 ml of toluene solution was added dropwise. After the addition was complete, the reaction was maintained at this temperature for 24 h. The solvent was removed by vacuum distillation, and the mixture was then washed with 500 ml of ethanol and 1.116 L of 1 mol sodium hydroxide aqueous solution, respectively. Finally, it was dried under vacuum at 40 °C for 10 h to obtain the DOPO-based homotriazine ring curing agent. DOPO-based triazine ring curing agent was mixed with bisphenol A epoxy resin at a mass ratio of 0.067 and cured at 80℃ for 1-2 hours to obtain an intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0024] Example 2 100 g of 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine was added to 1.252 L of 1 mol hydrochloric acid aqueous solution, stirred at room temperature for 5 h, and filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. The hydrochloride was dried under vacuum at 40 °C for 10 h. Then, 140.73 g of the dried hydrochloride was added to a reaction flask equipped with a reflux condenser, along with 750 ml of toluene and 84 g of DOPO. The mixture was stirred until homogeneous, then heated to 90 °C, and 0.45 g of azobisisobutyronitrile (AIB) in 20 ml of toluene solution was added dropwise. After the addition was complete, the reaction was maintained at this temperature for 24 h. The solvent was removed by vacuum distillation, and the mixture was washed with 500 ml of ethanol and 1.252 L of 1 mol sodium hydroxide aqueous solution, respectively. Finally, it was dried under vacuum at 40 °C for 10 h to obtain the DOPO-based homotriazine ring curing agent. DOPO-based triazine ring curing agent was mixed with bisphenol A epoxy resin at a mass ratio of 0.062 and cured at 80℃ for 1-2 hours to obtain an intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0025] Example 3 100 g of 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine was added to 1.374 L of 1 mol hydrochloric acid aqueous solution, stirred at room temperature for 5 h, and filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. The hydrochloride was dried under vacuum at 40 °C for 10 h. Then, 140.73 g of the dried hydrochloride was added to a reaction flask equipped with a reflux condenser, along with 800 ml of toluene and 92 g of DOPO. The mixture was stirred until homogeneous, then heated to 90 °C, and 0.79 g of azobisisobutyronitrile (AIB) in 20 ml of toluene solution was added dropwise. After the addition was complete, the reaction was maintained at this temperature for 24 h. The solvent was removed by vacuum distillation, followed by washing with 600 ml of ethanol and 1.374 L of 1 mol sodium hydroxide aqueous solution, respectively. Finally, the mixture was dried under vacuum at 40 °C for 10 h to obtain the DOPO-based homotriazine ring curing agent. DOPO-based triazine ring curing agent was mixed with bisphenol A epoxy resin at a mass ratio of 0.058 and cured at 80℃ for 1-2 hours to obtain an intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0026] Example 4 100 g of 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine was added to 1.434 L of 1 mol hydrochloric acid aqueous solution, stirred at room temperature for 5 h, and filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. The hydrochloride was dried under vacuum at 40 °C for 10 h. Then, 140.73 g of the dried hydrochloride was added to a reaction flask equipped with a reflux condenser, along with 770 ml of toluene and 92 g of DOPO. The mixture was stirred until homogeneous, then heated to 90 °C, and 0.94 g of azobisisobutyronitrile (AIB) in 20 ml of toluene solution was added dropwise. After the addition was complete, the reaction was maintained at this temperature for 24 h. The solvent was removed by vacuum distillation, followed by washing with 500 ml of ethanol and 1.434 L of 1 mol sodium hydroxide aqueous solution, respectively. Finally, the mixture was dried under vacuum at 40 °C for 10 h to obtain the DOPO-based homotriazine ring curing agent. DOPO-based triazine ring curing agent was mixed with bisphenol A epoxy resin at a mass ratio of 0.053 and cured at 80℃ for 1-2 hours to obtain an intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0027] Example 5 100 g of 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine was added to 1.672 L of 1 mol hydrochloric acid aqueous solution, stirred at room temperature for 5 h, and filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. The hydrochloride was dried under vacuum at 40 °C for 10 h. Then, 140.73 g of the dried hydrochloride was added to a reaction flask equipped with a reflux condenser, along with 1.2 L of toluene and 103 g of DOPO, and stirred until homogeneous. The temperature was then raised to 90 °C, and 1.3 g of azobisisobutyronitrile (AIB) in 50 mL of toluene solution was added dropwise. After the addition was complete, the reaction was maintained at this temperature for 24 h. The solvent was removed by vacuum distillation, and the mixture was washed with 1.1 L of ethanol and 1.672 L of 1 mol sodium hydroxide aqueous solution, respectively. Finally, it was dried under vacuum at 40 °C for 10 h to obtain the DOPO-based homotriazine ring curing agent. DOPO-based triazine ring curing agent was mixed with bisphenol A epoxy resin at a mass ratio of 0.05 and cured at 80℃ for 1-2 hours to obtain an intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

[0028] Comparative Example 1 2,4-Diamino-6-(4-pentenyl)-1,3,5-triazine was mixed with bisphenol A epoxy resin at a mass ratio of 0.05 and cured at 80°C for 1-2 hours to obtain epoxy resin cured with triazine ring curing agent.

[0029] Comparative Example 2 4,4'-Diaminobenzane and bisphenol A epoxy resin were mixed at a mass ratio of 0.21 and cured at 80°C for 1-2 hours to obtain epoxy resin cured with curing agent.

[0030] Comparative Example 3 4,4'-Diaminobenzane, bisphenol A epoxy resin, and flame retardant trimethylolphosphine oxide were mixed in a mass ratio of 100:18:5 and cured at 80°C for 1-2 hours to obtain a phosphorus-containing flame-retardant epoxy resin cured by the curing agent.

[0031] Comparative Example 4 Two parts of epoxy resin A, 4,4'-diaminobenzane, and DOPO were mixed in a mass ratio of 100:18:5 and cured at 100℃ for 1-2 hours to obtain a phosphorus-containing flame-retardant epoxy resin containing DOPO.

[0032] The materials of the examples and comparative examples were tested according to UL 94 (Underwriters Laboratories 94) standards and LOI (Limiting Oxygen Index), and the results are shown in Table 1.1.

[0033] Table 1.1 UL-94 and LOI test data for the examples and comparative examples

[0034] Experimental results show that the intrinsically flame-retardant epoxy resin containing DOPO-based triazine ring curing agent obtained in this invention is an epoxy resin with excellent flame-retardant properties.

[0035] The above description represents the preferred embodiments of the present invention. It should be noted that improvements and modifications made by those skilled in the art without departing from the principles of the present invention are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing an intrinsically flame-retardant epoxy resin containing a DOPO-based triazine ring curing agent, characterized in that: Includes the following steps: (1) 2,4-Diamino-6-(4-pentenyl)-1,3,5-triazine was added to an aqueous hydrochloric acid solution and stirred. The mixture was then filtered to obtain 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride. (2) The above hydrochloride salt was dried under vacuum, and organic solvent and DOPO were added and stirred evenly. Then the temperature was raised to 90±10℃, and the catalyst azobisisobutyronitrile solution was added dropwise. After the addition was completed, the reaction was kept at the temperature. (3) After the reaction is completed, the solvent is removed by vacuum distillation, washed, and dried under vacuum to obtain DOPO-based triazine ring curing agent; (4) Mix DOPO-based triazine ring curing agent with bisphenol A epoxy resin and heat to cure to obtain intrinsic flame-retardant epoxy resin containing DOPO-based triazine ring curing agent.

2. The preparation method according to claim 1, characterized in that: The volume-to-mass ratio of the hydrochloric acid aqueous solution to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 10-20 L / kg, and the concentration of the hydrochloric acid aqueous solution is 0.5-2.0 mol / L.

3. The preparation method according to claim 1, characterized in that: The mass ratio of DOPO to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 0.5 to 1.

5.

4. The preparation method according to claim 1, characterized in that: The volume-to-mass ratio of the organic solvent to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 3-15 mL / g, and the organic solvent is toluene, xylene, dioxane, or acetonitrile.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the azobisisobutyronitrile to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine is 0.1% to 1.5%; the solvent of the azobisisobutyronitrile solution is toluene, xylene, dioxane, or acetonitrile, and the volume-to-mass ratio of the solvent to 2,4-diamino-6-(4-pentenyl)-1,3,5-triazine hydrochloride is 0.1-0.5 mL / g.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the DOPO-based triazine ring curing agent to the bisphenol A epoxy resin is 0.05-0.

10.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The bisphenol A epoxy resin includes one or more of glycidyl ether, glycidyl ester, glycidyl amine, aliphatic epoxy resin, and alicyclic epoxy resin.

8. The preparation method according to any one of claims 1 to 6, characterized in that: The vacuum drying conditions in steps (2) and (3) are: vacuum drying at 40±5℃ for 10±5h; the washing in step (3) is done with ethanol and sodium hydroxide aqueous solution respectively.

9. The preparation method according to any one of claims 1 to 6, characterized in that: The heat preservation reaction time in step (2) is 24±6h; the heating curing conditions in step (4) are curing at a temperature of 80±10℃ for 1~2h.

10. An intrinsically flame-retardant epoxy resin containing a DOPO-based triazine ring curing agent prepared by the method of any one of claims 1 to 9.

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