DOPO derivative flame retardant containing P / N / S for V0 grade insulation material and preparation method and application thereof

Abstract

The present invention discloses a DOPO derivative flame retardant containing P / N / S for V0-grade insulating materials, as well as its preparation method and application, belonging to the technical field of flame retardant materials. The method comprises: reacting furfural with 2-amino-5-ethylbenzothiazole at 60-80°C in a solvent; obtaining an intermediate product after the reaction is complete, and then adding DOPO; reacting at 80-100°C to obtain a flame retardant; the molar ratio of furfural to 2-amino-5-ethylbenzothiazole is 1:1-2, and the molar ratio of DOPO to the intermediate product is 1:1-2. The flame retardant is used in epoxy resins with 4,4'-diaminodiphenylmethane as a curing agent. The flame retardant contains phosphorus, nitrogen, and sulfur, and can achieve phosphorus-nitrogen-sulfur synergistic flame retardancy. When applied to epoxy resin materials, it has a good flame retardant effect. It can effectively inhibit the release of heat and smoke during the combustion of epoxy resin, promote the formation of a char layer, and has significant flame retardant properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardants, and particularly relates to a P / N / S-containing DOPO derivative flame retardant for V0-grade insulating materials, a preparation method thereof, and an application thereof, and is specifically used for flame retardancy of epoxy resins. Background Art

[0002] Epoxy resin (EP) has excellent electrical insulation properties, high mechanical properties, good adhesion, and chemical resistance, and is therefore widely used in various industries. However, the flammability of EP limits its application in areas with high fire safety factors. DOPO derivatives have the advantages of low toxicity and low smoke, and are currently widely used in polymer materials including EP, and exhibit excellent flame retardant efficiency. DOPO molecules contain active PH bonds that can react with a variety of functional groups (C=N, C=C, C=O, etc.). Therefore, other flame retardant elements (nitrogen, sulfur, boron, etc.) can be introduced through molecular design to synthesize a series of DOPO derivatives to improve their flame retardant efficiency. Prior art 1 synthesized a P / N derivative flame retardant (DOPO-BNM) using DOPO, 2-aminobenzimidazole, and 3-nitrobenzaldehyde as raw materials. When the DOPO-BNM content in the epoxy resin reached 8 wt%, the EP / 8% DOPO-BNM sample passed the UL-94 V-0 classification, and its LOI increased to 32.5%. Notably, the PHRR, THR, PSPR, and TSP of the EP / 8% DOPO-BNM sample were 13.0%, 28.8%, 33.3%, and 47.9% lower than those of the EP sample, respectively, demonstrating that DOPO-BNM suppresses heat and smoke emissions from EP thermosets. Prior art synthesized a triazole-containing DOPO derivative (DOPO-SGA) from syringaldehyde, 3,5-diamino-1,2,4-triazole (GA), and DOPO and incorporated it into EP. With just 3 wt% DOPO-SGA, the LOI of EP was increased to 33.2%, raising the UL-94 rating to V-0 and reducing smoke and heat emissions. The incorporation of DOPO-SGA also improved the tensile and impact strength of EP. Prior Art 3 also synthesized a triazole-containing DOPO derivative (VDG) via a nucleophilic addition reaction using 3,5-diamino-1,2,4-triazole, vanillin, and DOPO as raw materials. An epoxy resin cured product was then prepared using DDM as a curing agent and VDG as a co-curing agent. VDG exhibited exceptional flame retardancy. A 2.0 wt% VDG content increased the LOI of the epoxy resin to 37.0%, achieving a UL-94 V-0 rating. It also effectively suppressed heat release during combustion of the epoxy resin, reducing the PHRR and THR by 47.5% and 34%, respectively. This significantly improved the flame retardancy of the epoxy resin. Prior Art 4 synthesized a novel reactive flame retardant (PABO) via a one-pot reaction using p-aminobenzonitrile, p-hydroxybenzaldehyde, and DOPO as raw materials, and applied it to epoxy resin. Thermogravimetric analysis showed that PABO had a higher degradation temperature, a lower thermal decomposition rate, and an increase in Char800 (carbon residue at 800 °C) from 1.5% to 26.5 wt% compared with DOPO.EP / PABO-5, with only 5wt% PABO content, achieved a LOI of 32.7% and passed the UL-94 V-0 rating. Furthermore, the PHRR, THR, and TSP of EP / PABO-5 decreased by 19.7%, 19.0%, and 19.4%, respectively, compared to EP. The calculated flame retardancy index (FIGRA) indicates that EP / PABO-5 offers superior fire safety to EP / DOPO-5. Given the chemical properties of DOPO, which reacts with a variety of functional groups, the rational introduction of other flame-retardant elements into DOPO derivatives is promising for the development of new epoxy resin flame retardants with superior performance. Summary of the Invention

[0003] This patent successfully synthesized a new flame retardant containing P / N / S through the addition reaction of DOPO with a Schiff base intermediate generated by the reaction of 2-amino-5-ethylbenzothiazole and furfural. This flame retardant is effective in epoxy resins using 4,4'-diaminodiphenylmethane as a curing agent. The technical solution is as follows:

[0004] On the one hand, an embodiment of the present invention provides a DOPO derivative flame retardant containing PNS for B1-level flame retardant cable materials, the structural formula of which is as follows:

[0005] .

[0006] The flame retardant is a gray powder containing nitrogen, sulfur and phosphorus elements. It has good compatibility with epoxy resin (characterized by not changing the transparency of epoxy resin). The applicant named it DBF.

[0007] In another aspect, the present invention also provides a method for preparing the aforementioned flame retardant, comprising: reacting furfural with 2-amino-5-ethylbenzothiazole in a solvent at 60-80°C; adding DOPO to an intermediate product obtained after the reaction; and continuing the reaction at 80-100°C to obtain the flame retardant. The molar ratio of furfural to 2-amino-5-ethylbenzothiazole is 1:1-2, and the molar ratio of DOPO to the intermediate product is 1:1-2.

[0008] Wherein, the solvent is selected from anhydrous ethanol and the like.

[0009] The preparation method provided in this embodiment includes:

[0010] (1) Furfural and 2-amino-5-ethylbenzothiazole are added to anhydrous ethanol and reacted at 60-80° C. for 12-24 hours to obtain an intermediate product.

[0011] (2) DOPO is dissolved in anhydrous ethanol and added to the reaction solution of step (1), and the reaction is carried out at 80-100° C. for 12-24 hours. After the reaction is completed, the flame retardant is obtained by cooling, solid-liquid separation, ethanol washing and drying.

[0012] Among them, the number of ethanol washings is 3-6 times.

[0013] The drying temperature is 55-65°C and the drying time is 8-15h.

[0014] Specifically, the preparation method provided in this embodiment includes:

[0015] (1) Furfural and 2-amino-5-ethylbenzothiazole are added to anhydrous ethanol and reacted at 60-80°C for 12-24 hours to obtain an intermediate product. The molar ratio of furfural to 2-amino-5-ethylbenzothiazole is 1:1-2. The reaction equation is as follows:

[0016] .

[0017] (2) DOPO is dissolved in anhydrous ethanol and added to the reaction solution of step (1). The reaction is carried out at 80-100°C for 12-24 hours. After the reaction is completed, the temperature is cooled to room temperature, filtered, and the filter residue is washed with ethanol 3-6 times. Finally, the product is dried at 55-65°C for 8-15 hours to obtain the product. The reaction equation is as follows:

[0018] .

[0019] In another aspect, the present invention further provides the use of the aforementioned flame retardant in an epoxy resin containing 4,4'-diaminodiphenylmethane as a curing agent. The flame retardant is added in an amount of 1-6% by weight of the epoxy resin, specifically 4%. The epoxy resin is selected from E51 epoxy resin, E54 epoxy resin, and the curing agent is added in an amount of 2-30% by weight of the epoxy resin.

[0020] Specifically, the process for preparing the modified epoxy resin material using a curing agent, flame retardant, and epoxy resin is as follows: The flame retardant is slowly added to the epoxy resin according to the proportions, and stirred at 125-135°C until transparent, resulting in a homogeneous mixture. The resulting epoxy resin is then stirred with 4,4'-diaminodiphenylmethane at 75-85°C until the 4,4'-diaminodiphenylmethane is completely dissolved. Finally, the epoxy resin mixture is poured into a mold and cured at a temperature of 110-160°C. The curing process is as follows: curing at 120°C for 120 minutes and at 150°C for 240 minutes.

[0021] The present invention has the following advantages: the novel flame retardant DBF obtained by the present invention contains a DOPO structural unit with low toxicity, low smoke and obvious flame retardant effect in its molecular structure, and at the same time introduces flame retardant elements such as nitrogen and sulfur, thereby further enhancing the flame retardant effect of the DOPO structural unit. After being applied to epoxy resin materials, phosphorus-nitrogen-sulfur synergistic flame retardancy can be achieved, effectively inhibiting the release of heat and smoke during the combustion of epoxy resin, while also promoting the formation of a char layer, resulting in a significant flame retardant effect. In addition, the flame retardant has good compatibility with epoxy resin and will not have a negative impact on the mechanical properties of the epoxy resin substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the infrared spectrum of the flame retardant prepared in Example 1;

[0023] Figure 2 This is the H-NMR spectrum of the flame retardant prepared in Example 1. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] Example 1 provides a method for preparing a flame retardant, the method comprising the following steps:

[0027] (1) Furfural (0.02 mol, 1.92 g), 2-amino-5-ethylbenzothiazole (0.02 mol, 3.00 g), and 50 mL of anhydrous ethanol were added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. The mixture was heated to 65°C and maintained at this temperature for 14 h with constant stirring.

[0028] (2) Add 30 mL of anhydrous ethanol solution containing DOPO (0.02 mol, 4.32 g), raise the system temperature to 84°C, and continue stirring for 15 h. After the reaction is complete, cool naturally to room temperature, and collect the crude product by filtration. The crude product is washed three times with ethanol and dried in vacuo at 60°C for 12 h to obtain a gray powder DBF.

[0029] The infrared spectrum of the prepared DBF is shown in Figure 1 As shown: 2436cm in the infrared spectrum of DBF -1 There is no absorption peak of PH bond at 3226cm -1 The characteristic absorption peak of NH appeared, indicating that the reaction of DOPO with the Schiff base-containing intermediate was complete. In addition, at 1598 cm -1 and 1478cm -1There is an absorption signal at 1240cm, which is generated by the vibration of P-Ph; -1 and 1117cm -1 There is also an absorption signal at 932cm, which is caused by the vibration of P=O. -1 and 750cm -1 The absorption peak at is the characteristic absorption peak of PO-Ph. The H-NMR spectrum of the prepared DBF is shown in Figure 2 Shown: H-NMR: 7.94ppm (4H), 7.67-7.28ppm (6H), 7.06ppm (3H), 6.54ppm (1H), 6.40ppm (1H), 6.28ppm (1H), 5.85ppm (1H), 1.28ppm (2H), 0.88ppm (3H).

[0030] Example 2

[0031] Example 2 provides a method for preparing a flame retardant, the method comprising the following steps:

[0032] (1) Furfural (0.02 mol, 1.92 g), 2-amino-5-ethylbenzothiazole (0.03 mol, 4.50 g), and 60 mL of anhydrous ethanol were added to a three-necked flask equipped with a magnetic stirrer and a reflux condenser. The mixture was heated to 70°C and maintained at this temperature for 13 h with constant stirring.

[0033] (2) Add 30 mL of anhydrous ethanol solution containing DOPO (0.024 mol, 5.18 g), raise the system temperature to 85°C, and continue stirring for 16 h. After the reaction is complete, cool naturally to room temperature, and collect the crude product by filtration. The crude product is washed four times with ethanol and dried in vacuo at 60°C for 12 h to obtain a gray powder DBF.

[0034] Example 3

[0035] Example 3 provides a method for preparing a modified epoxy resin material, using the flame retardant synthesized in Example 1 as a flame retardant modifier and 4,4'-diaminodiphenylmethane as a curing agent to prepare a modified E51 epoxy resin material. The process is as follows:

[0036] The flame retardant prepared in Example 1 (1.0 g) was weighed and slowly added to E51 epoxy resin (39.2 g). The mixture was stirred at 130°C until transparent, yielding a homogeneous mixture. The resulting epoxy resin was then stirred with 4,4'-diaminodiphenylmethane (9.8 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, yielding a modified epoxy resin material containing 1.96 wt% flame retardant.

[0037] In this example, the flame retardant was completely dissolved in the epoxy resin without changing the transparency of the epoxy resin.

[0038] Example 4

[0039] Example 4 provides a method for preparing a modified epoxy resin material, using the flame retardant synthesized in Example 1 as a flame retardant modifier and 4,4'-diaminodiphenylmethane as a curing agent to prepare a modified E54 epoxy resin material. The process is as follows:

[0040] The flame retardant prepared in Example 1 (1.5 g) was weighed and slowly added to E54 epoxy resin (38.8 g). The mixture was stirred at 130°C until transparent, yielding a homogeneous mixture. The resulting epoxy resin was then stirred with 4,4'-diaminodiphenylmethane (9.7 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, yielding a modified epoxy resin material containing 3 wt% flame retardant.

[0041] In this example, the flame retardant was completely dissolved in the epoxy resin without changing the transparency of the epoxy resin.

[0042] Example 5

[0043] Example 5 provides a method for preparing a modified epoxy resin material, using the flame retardant synthesized in Example 1 as a flame retardant modifier and 4,4'-diaminodiphenylmethane as a curing agent to prepare a modified E51 epoxy resin material. The process is as follows:

[0044] The flame retardant prepared in Example 1 (2.0 g) was weighed and slowly added to E51 epoxy resin (38.4 g). The mixture was stirred at 130°C until transparent, yielding a homogeneous mixture. The resulting epoxy resin was then stirred with 4,4'-diaminodiphenylmethane (9.6 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, yielding a modified epoxy resin material containing 4 wt% flame retardant.

[0045] Comparative Example 1

[0046] Comparative Example 1 provides a method for preparing a modified epoxy resin material, using 4,4'-diaminodiphenylmethane as a curing agent and no flame retardant to prepare E51 epoxy resin material. The process is:

[0047] 38.4 g of E51 epoxy resin was weighed and stirred at 130°C until transparent, yielding a homogeneous epoxy resin liquid. The resulting epoxy resin was then stirred with 9.6 g of 4,4'-diaminodiphenylmethane at 80°C for 5 minutes until the curing agent was completely dissolved, yielding an epoxy resin mixture. Finally, the epoxy resin mixture was poured into a mold and cured at elevated temperatures. The curing schedule was 120°C for 120 minutes and 150°C for 240 minutes, yielding a flame retardant-free epoxy resin material.

[0048] Comparative Example 2

[0049] Comparative Example 2 provides a method for preparing a modified epoxy resin material, using DOPO as a flame retardant modifier and 4,4'-diaminodiphenylmethane to prepare a modified E51 epoxy resin material. The process is:

[0050] DOPO (2.0 g) was slowly added to E51 epoxy resin (38.4 g) and stirred at 130°C until transparent, resulting in a homogeneous mixture. The resulting epoxy resin was then stirred with 4,4'-diaminodiphenylmethane (9.6 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, producing a modified epoxy resin material with a DOPO content of 4 wt%.

[0051] The epoxy resin materials obtained in Comparative Examples 1, 2, and Example 5 were tested for flame retardancy, mechanical properties, and thermal stability. The UL-94 vertical burning test was conducted using the GB / T2408 standard; the oxygen index was tested using the GB / T8924 standard; and the tensile and flexural tests were conducted according to the GB / T2006 standard. The test results are shown in Table 1.

[0052] Table 1

[0053]

[0054] As shown in Table 1, for pure epoxy resin with an oxygen index of 26 and no flame retardant grade, the tensile and flexural strengths are 87.7 MPa and 112 MPa, respectively. When the flame retardant content of this patent is 4%, the flexural strength is improved, while the tensile strength remains essentially unchanged. The UL-94 vertical combustion test achieves V-0. The effect of DBF on the mechanical properties of epoxy resin was investigated through tensile, flexural, and notched impact tests. The results demonstrate that DBF has no adverse effect on the mechanical properties of EP and can impart excellent flame retardancy to EP without compromising mechanical properties. Furthermore, the sample of Example 5 emits virtually no smoke during combustion.

[0055] Comparative Example 3

[0056] Comparative Example 3 provides a method for preparing a modified epoxy resin material. The flame retardant synthesized in Example 1 is used as a flame retardant modifier and dicyandiamide is used as a curing agent to prepare a modified E51 epoxy resin material. The process is as follows:

[0057] The flame retardant prepared in Example 1 (2.0 g) was weighed and slowly added to E51 epoxy resin (38.4 g). The mixture was stirred at 130°C until transparent, yielding a homogeneous mixture. The resulting epoxy resin was then stirred with dicyandiamide (9.6 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, yielding a modified epoxy resin material containing 4 wt% flame retardant.

[0058] Comparative Example 4

[0059] Comparative Example 4 provides a method for preparing a modified epoxy resin material, using the flame retardant synthesized in Example 1 as a flame retardant modifier and 4,4'-diaminodiphenyl sulfone as a curing agent to prepare a modified E51 epoxy resin material. The process is as follows:

[0060] The flame retardant prepared in Example 1 (2.0 g) was weighed and slowly added to E51 epoxy resin (38.4 g). The mixture was stirred at 130°C until transparent, yielding a homogeneous mixture. The resulting epoxy resin was then stirred with 4,4'-diaminodiphenyl sulfone (9.6 g) at 80°C for 5 minutes until the curing agent was completely dissolved. Finally, the epoxy resin mixture was poured into a mold and cured at 120°C for 120 minutes and 150°C for 240 minutes, yielding a modified epoxy resin material containing 4 wt% flame retardant.

[0061] The flame retardancy, mechanical properties and thermal stability of the epoxy resin materials obtained in Comparative Example 3, Comparative Example 4 and Example 5 were tested. The test results are shown in Table 2:

[0062] Table 2

[0063]

[0064] As can be seen from Table 2, the flame retardant of this patent is generally effective when used in epoxy resins with other curing agent systems, and is not as effective as in epoxy resins based on 4,4'-diaminodiphenylmethane.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. DOPO derivative flame retardant containing P / N / S for V0 grade insulation material, characterized in that: The structural formula is as follows: 。 2. The method for preparing a flame retardant according to claim 1, wherein: The method comprises: reacting furfural with 2-amino-5-ethylbenzothiazole at 60-80° C. in a solvent; after the reaction is completed, an intermediate product is obtained, and DOPO is added; and reacting at 80-100° C. to obtain a flame retardant; the molar ratio of the furfural to the 2-amino-5-ethylbenzothiazole is 1:1-2, and the molar ratio of the DOPO to the intermediate product is 1:1-2.

3. The method according to claim 2, characterized in that The solvent is selected from anhydrous ethanol.

4. The method according to claim 2, characterized in that The method comprises: (1) adding furfural and 2-amino-5-ethylbenzothiazole to anhydrous ethanol and reacting at 60-80° C. for 12-24 hours to obtain an intermediate product; (2) DOPO is dissolved in anhydrous ethanol and added to the reaction solution of step (1), and the reaction is carried out at 80-100° C. for 12-24 hours. After the reaction is completed, the flame retardant is obtained by cooling, solid-liquid separation, ethanol washing and drying.

5. The method according to claim 4, characterized in that The number of ethanol washes was 3-6 times.

6. The method according to claim 4, characterized in that The drying temperature is 55-65℃ and the drying time is 8-15h.

7. Use of the flame retardant according to claim 1 in epoxy resin with 4,4'-diaminodiphenylmethane as a curing agent.

8. The use according to claim 7, characterized in that The added amount of the flame retardant is 1-6% of the weight of the epoxy resin.

9. The use according to claim 8, characterized in that The epoxy resin is selected from E51 epoxy resin and E54 epoxy resin, and the amount of the curing agent is 2-30% by weight of the epoxy resin.

10. The use according to claim 9, characterized in that The process of preparing the modified epoxy resin material with a curing agent, a flame retardant and an epoxy resin is as follows: slowly adding the flame retardant to the epoxy resin according to the ratio, and stirring at 125-135°C until it becomes transparent; then stirring the obtained epoxy resin with 4,4'-diaminodiphenylmethane at 75-85°C until the 4,4'-diaminodiphenylmethane is completely dissolved; finally, pouring the epoxy resin mixture into a mold for heating and curing, and the curing temperature is 110-160°C.

Images