CN113150501B - A kind of benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding and its preparation method - Google Patents

Abstract

The invention belongs to the field of high-temperature resistant materials of high-molecular resin compositions, and provides benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding and a preparation method thereof. The flame-retardant modified epoxy resin consists of benzoxazine resin, epoxy resin, phosphate flame retardant, curing agent and accelerator. The preparation method comprises the following steps: preparing the raw materials according to the weight ratio; heating, stirring and uniformly mixing benzoxazine resin and epoxy resin, taking out and cooling to room temperature; sequentially adding a phosphate flame retardant, an amine curing agent and an accelerator into the mixture and uniformly stirring; vacuum defoaming the obtained mixture at room temperature to remove air; pouring the mixture subjected to vacuum defoaming into a mold treated by a mold release agent for thermosetting and demolding to obtain the benzoxazine flame-retardant modified epoxy resin. The flame-retardant modified epoxy resin is suitable for a vacuum infusion composite material forming process, has low viscosity and excellent flame retardant property, and the flame retardant grade of a body reaches UL94V-0.

Description

A benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding and its preparation method

technical field

The invention relates to the field of high-molecular resin composition high-temperature-resistant materials, in particular to a benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding and a preparation method.

Background technique

Epoxy resin (EP) is an important class of thermosetting resins. It refers to a high polymer containing two or more epoxy groups that can form a three-dimensional network of thermosetting products through the reaction of epoxy groups. Due to its good physical and chemical properties, it is widely used in the national economy. However, epoxy resins are highly flammable resins, which limits their application in scenarios with flame retardant requirements, such as vehicle interior parts and electronic assemblies, etc., so their flame retardant modification came into being.

Halogen-containing epoxy resins or halogen-containing flame retardants are mostly used in the initial modification of epoxy resins, but due to their smoke toxicity, hydrogen halides, dioxins and other toxic substances will be produced, which will greatly damage human health and environmental protection , subject to strict restrictions on environmental protection regulations, this method was gradually abandoned, so halogen-free flame retardant has become the development direction. Many halogen-free flame retardants have been used to improve the flame retardancy of epoxy resins, but most of them are solid powder flame retardants, such as inorganic phosphates, melamine and salt, aluminum hydroxide, magnesium hydroxide, etc. , the particle size is usually at the micron level, and in the infusion molding process of composite materials, since the solid flame retardant will be filtered by the reinforcing fiber, it cannot be evenly distributed in the part, and it will not have a good flame retardant effect, and at the same time there will be surface The blooming phenomenon affects the appearance of the part, so it is difficult for solid powder flame retardants to be used in vacuum infusion molding of composite materials. The use of liquid halogen-free flame retardants compatible with epoxy resins is a common method in the prior art, but to achieve a certain flame retardant effect, the amount of liquid flame retardants usually added is very large, and the side effects are very obvious, such as bringing cured products Decrease in glass transition temperature (T _g ), loss of physical mechanical properties and lack of flame retardant durability.

On the other hand, as a composite material resin used in a vacuum infusion process, it is required that the resin viscosity is appropriate under the infusion conditions, usually not higher than 800mpa·s. Because resin viscosity decreases with increasing temperature, many infusion resins must be infused under heated conditions, which further increases process difficulty and production costs. Due to higher requirements for resin viscosity in room temperature infusion, many commonly used epoxy resins cannot meet the requirements, and the flame retardant modification of them is more restricted and more difficult. For example, when using hexaphenoxycyclotriphosphazene flame retardant, if the flame retardant level reaches UL 94V-0, the addition amount needs to reach 40 parts by mass of the whole, and the compatibility with epoxy resin is poor. Poor, easy to separate out and stratify, and the viscosity is as high as several thousand mpa.s at 25°C. If poured under this condition, the flame retardant cannot be uniformly dispersed, which will greatly reduce its flame retardant performance. If it is only ensured that it does not precipitate after being dissolved in epoxy resin, the addition amount can be reduced to about 10 parts. Although the infusion process is satisfied, its flame retardant performance will be greatly reduced; another example is liquid phosphate flame retardants. The phosphorus content is as high as 25%. When the UL94V-0 level is met, the T _g of the cured resin is only 33°C, and the loss of mechanical properties is very serious. However, liquid silicon-based flame retardants (tetraethyl orthosilicate, etc.) also cannot meet the requirements of not only meeting the flame retardant performance, but also ensuring that the mechanical properties are not lost. Therefore, there is currently no resin system that satisfies low viscosity, high flame retardancy and can be poured at room temperature, which undoubtedly becomes a technical problem that researchers in this field need to solve urgently.

In the case that liquid halogen-free flame retardants cannot effectively meet the requirements of normal temperature pouring flame retardant resins, the flame retardant modification of bulk resins has become an option. However, due to severe limitations of resin viscosity and curing chemical compatibility, the choice of modified resins is very limited. Phenolic resin with excellent flame retardant properties is one of the choices, but the water molecules produced during the curing process of phenolic resin will affect the curing of epoxy resin, and the desired effect cannot be achieved.

Benzoxazine is a six-membered heterocyclic compound containing oxygen and nitrogen atoms, belonging to a special structure of phenolic resin. Benzoxazine not only maintains the excellent mechanical and flame-retardant properties of traditional phenolic resins, but also overcomes the problem of water molecules generated during the curing process of traditional phenolic resins, making it more compatible with the curing chemistry of epoxy resins compatibility. Another feature is that the molecular weight of benzoxazine resin is low, which contributes little to the viscosity of epoxy resin and is suitable for vacuum infusion process. Other advantages include polybenzoxazine's high glass transition temperature and almost zero curing shrinkage, which is conducive to maintaining the service temperature and mechanical properties of the part.

CN 109705353B discloses a non-curing agent benzoxazine modified epoxy resin flame retardant, the highest flame retardant level that the system can achieve is UL94V-1, which cannot reach UL94V-0, and is not suitable for vacuum infusion Technology; CN101914265B discloses that benzoxazine type epoxy resin, tetraphenol-based ethane epoxy resin, inorganic filler etc. have prepared the resin that green environmental protection flame retardancy can reach UL94V-0, but only be applicable to printed circuit board adhesive The hot-pressing process used in the sheet cannot be used for vacuum infusion.

Therefore, the current heat-resistant varieties of vacuum infusion resins at home and abroad are still missing, so high-performance vacuum infusion composite material systems are still a research and development hotspot.

Contents of the invention

In view of this, the object of the present invention is to provide a benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding and a preparation method thereof. The invention adopts the resin system of benzoxazine-modified epoxy resin, which has low viscosity, good resin fluidity, long operation period, and meets the requirements of vacuum infusion process. While ensuring high glass transition temperature, the resin body can reach UL94 V -0 flame retardant level, the prepared cured product has excellent mechanical properties at the same time.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

A benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding, comprising the following raw materials in parts by weight:

Preferably, the epoxy resin is bisphenol F epoxy resin, the phosphonate flame retardant is dimethyl methyl phosphonate, the amine curing agent is methylcyclohexanediamine, and the accelerator The agent is 2,4,6-tris(dimethylaminomethyl)phenol.

Formula ①Molecular structure of bisphenol F epoxy resin

Compared with bisphenol A epoxy resin, bisphenol F epoxy resin has the characteristics of low viscosity, and after curing, it has excellent physical and chemical properties such as strong adhesion to metal, chemical corrosion resistance, high mechanical strength, and good electrical insulation. performance, so the basic resin selected by the present invention is bisphenol F type epoxy resin.

Formula ② Molecular structure of benzoxazine

The molecular weight of benzoxazine is low, which contributes little to the viscosity of the overall resin system. It has a certain flame retardant performance and good compatibility with epoxy resin. The curing shrinkage rate is almost zero, and the size and shape of the cured part are good. Therefore the present invention selects benzoxazine resin modified epoxy resin for use.

Formula ③ Molecular structure of dimethyl methylphosphonate

Dimethyl methylphosphonate (DMMP) not only has the characteristics of low viscosity, but also has a phosphorus content of up to 25%, which is the highest among phosphonate flame retardants. Therefore, the present invention selects dimethyl methylphosphonate as the phosphonic acid Ester flame retardants.

Formula ④Methylcyclohexanediamine Molecular Structural Formula

Methylcyclohexanediamine is colorless, transparent, and insoluble in water. Its viscosity at 25°C is only 10-20mpa·s. Therefore, the present invention uses methylcyclohexanediamine as the amine curing agent.

Formula ⑤ Molecular structural formula of 2,4,6-tris(dimethylaminomethyl)phenol

2,4,6-three (dimethylaminomethyl) phenol has the characteristics of low viscosity equally, and the resin cured by this accelerator has characteristics such as high temperature resistance and flame resistance, so the present invention selects 2,4,6-three (two methylaminomethyl)phenol as accelerator.

Another object of the present invention is to provide a method for preparing a benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding, comprising the following steps:

Step (1): preparing each raw material according to the weight ratio;

Step (2): Warm up the benzoxazine resin and epoxy resin and stir, mix well, take out and cool to room temperature;

Step (3): adding a phosphonate flame retardant, an amine curing agent, and an accelerator in sequence to the cooled mixture in step (2), and stirring until uniform;

Step (4): vacuum defoaming the mixture obtained in step (3) at room temperature to remove the air mixed in during the stirring process;

Step (5): Pour the mixture after vacuum defoaming into a mold treated with a release agent for thermal curing, and demould after curing to obtain the required benzoxazine flame-retardant modification for vacuum infusion molding. permanent epoxy resin.

Preferably, the stirring temperature in step (2) is 80-100°C, and the stirring time is 0.5-2h.

Preferably, the addition amount of benzoxazine resin in step (2) is 25-35 parts, and the addition amount of epoxy resin is 65-75 parts.

Preferably, 20-25 parts of dimethyl methylphosphonate (DMMP) are added in step (4);

Preferably, the release agent used in step (5) is a water-based release agent, and before the mixture after the vacuum defoaming obtained in step (4) is thermally cured, it is evenly added dropwise on the curing mold, and the consumption is to promote 0.5%-1% of the weight of the agent;

Preferably, the thermal curing described in step (5) is divided into two stages, the curing temperature of the first stage is 80°C, and the curing time is 4-6h; the curing temperature of the second stage is 190°C, and the curing time 1-3h.

The benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding provided by the present invention has the following components in its structure:

Formula ⑥ Benzoxazine self-polymerization

Formula ⑦ Ring-opening polymerization of benzoxazine and epoxy resin

Formula ⑧ epoxy resin reacts with methylcyclohexanediamine

Compared with the prior art, the present invention has the following advantages:

1. The nitrogen element in the benzoxazine and the phosphorus element in the DMMP in the present invention can have a good synergistic flame retardant effect, and the body flame retardant effect can reach UL94V-0 level, and the product does not contain halogen, which meets the requirements of RoHS directive requirements, friendly to the environment.

2. No powder filler is used in the present invention, which does not affect the appearance of the product. And the selected liquid flame retardant is added in a small amount, which can ensure good mechanical properties of the parts.

3. The epoxy resin composition of the present invention, when applied to vacuum infusion molding composite materials, has good flame retardancy and can meet the requirements of use.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is the viscosity scatter diagram of benzoxazine flame-retardant modified epoxy resin of the present invention;

Fig. 2 is the DSC curve chart of the benzoxazine flame-retardant modified epoxy resin of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Analytical operation method and flow process among the present invention are all conventional techniques, wherein analytical instrument and parameter are as follows:

Viscosity test: the instrument is Viscotester IQ rotary rheometer, Germany HAAKE company. Viscosity was measured using a rotational viscometer. Weigh the sample and stir it evenly, slowly pour it into the container for viscosity test, the test temperature is 25°C, measure 5 times continuously, and get the average value, which is the viscosity of the mixture.

Differential scanning calorimetry (DSC) analysis of curing behavior: NETZSCH DSC214 differential scanning calorimeter was used to characterize the curing behavior of the resin. Sample quality The sample is 5-10mg, the test temperature range is 25-250°C, the heating rate is 10°C/min, and the test is carried out under nitrogen protection.

Dynamic thermomechanical analysis (DMA): The cured product is tested by TADMAQ800 dynamic mechanical analyzer, the test temperature range is 25-200°C, and the heating rate is 3°C/min. The test mode is a three-point bending double cantilever beam mode. The cured spline is placed on two fulcrums with a distance of 10mm, and the push rod applies a load to the spline from above.

Limiting oxygen index analysis: According to the standard GB/T2406, this invention uses an oxygen index meter to test the oxygen index of the flame-retardant cured product. The size of the cured product is 100mm×10mm×4mm, and 10 test samples are used.

UL-94 vertical burning test: test according to the standard GB-2408, the size of the sample is 125mm×13mm×3mm, and 5 samples are prepared for each sample for the test.

Example 1

Step (1): Prepare the raw materials of each component according to the weight ratio, 65 parts of bisphenol F epoxy resin, 35 parts of benzoxazine resin, 25 parts of dimethyl methylphosphonate (DMMP), 13 parts of methyl Cyclohexanediamine, 0.2 parts of 2,4,6-tris(dimethylaminomethyl)phenol.

Step (2): Heat benzoxazine resin and bisphenol F epoxy resin in an oil bath to 80°C and stir for 0.5h. After mixing evenly, take out and cool to room temperature;

Step (3): adding dimethyl methylphosphonate, methylcyclohexanediamine and 2,4,6-tris(dimethylaminomethyl)phenol to the cooled mixture in turn, stirring until uniform;

Step (4): vacuum defoaming the mixture obtained in step (3) at room temperature to remove the air mixed in during the stirring process;

Step (5): Pour the mixture after vacuum defoaming into a mold treated with 0.5% of accelerator weight Diwa release agent for thermal curing. Thermal curing is divided into two stages, and the first stage curing temperature is 80 °C, the curing time is 4h; the second stage curing temperature is 190°C, and the curing time is 1h. After the curing is completed, demoulding is carried out to obtain the required benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding.

Example 2

Step (1): Prepare the raw materials of each component according to the weight ratio, 65 parts of bisphenol F epoxy resin, 35 parts of benzoxazine resin, 20 parts of dimethyl methylphosphonate (DMMP), 13 parts of methyl Cyclohexanediamine, 0.2 parts of 2,4,6-tris(dimethylaminomethyl)phenol. (The temperature of the oil bath is 80°C, and the amount of release agent added is 0.75% of that of the accelerator)

Step (2): Heat benzoxazine resin and bisphenol F epoxy resin to 90°C in an oil bath and stir for 1 hour. After mixing evenly, take out and cool to room temperature;

Step (3): adding dimethyl methylphosphonate, methylcyclohexanediamine and 2,4,6-tris(dimethylaminomethyl)phenol to the cooled mixture in turn, stirring until uniform;

Step (4): vacuum defoaming the mixture obtained in step (3) at room temperature to remove the air mixed in during the stirring process;

Step (5): Pour the mixture after vacuum defoaming into a mold treated with 0.65% of accelerator weight Diwa release agent for thermal curing. Thermal curing is divided into two stages, and the first stage curing temperature is 80 °C, the curing time is 4.5h; the second stage curing temperature is 190°C, and the curing time is 1.5h. After the curing is completed, demoulding is carried out to obtain the required benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding.

Example 3

Step (1): Prepare the raw materials of each component according to the weight ratio, 75 parts of bisphenol F epoxy resin, 25 parts of benzoxazine resin, 25 parts of dimethyl methylphosphonate (DMMP), 15 parts of methyl Cyclohexanediamine, 0.2 parts of 2,4,6-tris(dimethylaminomethyl)phenol.

Step (2): Heat benzoxazine resin and bisphenol F epoxy resin to 95°C in an oil bath and stir for 1.5 hours. After mixing evenly, take out and cool to room temperature;

Step (3): adding dimethyl methylphosphonate, methylcyclohexanediamine and 2,4,6-tris(dimethylaminomethyl)phenol to the cooled mixture in turn, stirring until uniform;

Step (4): vacuum defoaming the mixture obtained in step (3) at room temperature to remove the air mixed in during the stirring process;

Step (5): Pour the mixture after vacuum defoaming into a mold treated with 0.85% of accelerator weight Diwa release agent for thermal curing. Thermal curing is divided into two stages, and the first stage curing temperature is 80 °C, the curing time is 5h; the second stage curing temperature is 190°C, and the curing time is 2h. After the curing is completed, demoulding is carried out to obtain the required benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding.

Example 4

Step (1): Prepare the raw materials of each component according to the weight ratio, 75 parts of bisphenol F epoxy resin, 25 parts of benzoxazine resin, 20 parts of dimethyl methylphosphonate (DMMP), 15 parts of methyl Cyclohexanediamine, 0.2 parts of 2,4,6-tris(dimethylaminomethyl)phenol.

Step (2): Heat benzoxazine resin and bisphenol F epoxy resin in an oil bath to 100°C and stir for 2 hours. After mixing evenly, take out and cool to room temperature;

Step (3): adding dimethyl methylphosphonate, methylcyclohexanediamine and 2,4,6-tris(dimethylaminomethyl)phenol to the cooled mixture in turn, stirring until uniform;

Step (4): vacuum defoaming the mixture obtained in step (3) at room temperature to remove the air mixed in during the stirring process;

Step (5): Put the mixture after vacuum defoaming into the mold processed by the Diwa release agent of 1% accelerator weight and carry out thermal curing. The thermal curing is divided into two stages, and the first stage curing temperature is 80 °C, the curing time is 6h; the second stage curing temperature is 190°C, and the curing time is 3h. After the curing is completed, demoulding is carried out to obtain the required benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding.

Comparative example 1

Mix epoxy resin, methylcyclohexanediamine, and 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 100:20:0.4, and then stir evenly. Vacuum defoaming of the obtained mixture to remove the air mixed in the stirring process, pour the vacuum defoamed mixture into a mold treated with a release agent, put it into an oven for thermal curing, the curing temperature is 80 ° C, and the time is After 4 hours, demoulding was carried out after the curing was completed, and the desired comparison sample of the blended cured product was obtained.

Comparative example 2

Mix epoxy resin, dimethyl methylphosphonate, methylcyclohexanediamine, and 2,4,6-tris(dimethylaminomethyl)phenol in a mass ratio of 100:40.1:20:0.4 and stir uniform. The resulting mixture is vacuum defoamed in a vacuum oven to remove the air mixed in the stirring process, the mixture after vacuum defoaming is poured into a mold treated with a release agent, and put into an oven for thermal curing. The curing temperature is 80 ℃, the time is 4h, after the curing is completed, the demoulding is carried out to obtain the desired comparison sample of the blended cured product.

See Table 1 for the selection of raw materials for the components of Examples 1-4 and Comparative Example 1-2.

Table 1 embodiment and comparative example component raw material selection table

Performance Test 1: Viscosity Analysis

Figure 1 shows the viscosity data of the flame retardant, which was tested using a rotational viscometer. Weigh the sample and stir it evenly, slowly pour it into the container for viscosity test, the test temperature is 25°C, measure 5 times continuously, and get the average value, which is the viscosity of the mixture.

It can be seen from Figure 1 that DMMP can be used not only as a flame retardant, but also as a diluent because of its low viscosity. The vacuum infusion molding process requires that the viscosity should be lower than 800mpa·s. According to the measured data, it can be known that the prepared system can meet the infusion requirements at room temperature.

Performance test 2: DSC test analysis

The curing behavior of the resin was characterized by differential scanning calorimetry. Sample quality The sample is 5-10mg, the test temperature range is 25-250°C, the heating rate is 10°C/min, and the test is carried out under nitrogen protection. The DSC test data in Fig. 2 can clearly reflect the temperature required for curing and the exothermic value of each embodiment and comparative example. In Fig. 2, comparative examples 1-2 are all single peaks, and examples 1-4 are double peaks, inherently two Onset temperature, peak temperature, and end temperature, so there are two corresponding exothermic enthalpy. Separated by "/" in Table 2.

It can be seen from Figure 2 that the initial heat release is around 80°C, so 80°C is selected as the first stage curing temperature. Benzoxazine will not only undergo copolymerization reaction with epoxy resin, but also undergo self-polymerization reaction at high temperature. Therefore, it is judged that the exothermic reaction at 190°C is the reaction of benzoxazine itself. In order to fully cure, implement The curing of Example 1-4 is divided into two stages: the first stage curing temperature is 80°C and the curing time is 4h; the second stage curing temperature is 190°C and the curing time is 1h. The specific data are shown in Table 2:

Table 2 DSC analysis of halogen-free benzoxazine flame retardant modified epoxy resin

Performance test 3: DMA test analysis

Dynamic thermomechanical analysis (DMA): The cured product is tested by TADMAQ800 dynamic mechanical analyzer, the test temperature range is 25-200°C, and the heating rate is 3°C/min. The test mode is a three-point bending double cantilever beam mode. The cured spline is placed on two fulcrums with a distance of 10mm, and the push rod applies load to the spline from above. The test results are shown in Table 3.

Table 3 DMA analysis of halogen-free benzoxazine flame retardant modified epoxy resin

From the data in Table 3, we can see that the storage modulus T _g of Comparative Example 1 is 109°C, while the T _g of Comparative Example 2 dropped rapidly to 33°C due to the addition of DMMP. The movement of the molecular chain segment makes the T _g of the spline decrease greatly. However, the _Tg of the present invention increases after adding benzoxazine, which shows that the crosslinking density increases after adding benzoxazine, and the storage modulus _Tg of Examples 1-4 of the present invention are all greater than 90 ° C, in line with actual production process requirements.

Performance Test 4: Flame Retardancy

Table 4 shows the UL94 vertical burning and limiting oxygen index test data of the benzoxazine flame-retardant modified epoxy resin blended cured product, the experimental result data obtained in the experiment, including the vertical burning level, the average duration after the first ignition Burning time t1, the average continuous burning time t2 after the second ignition, whether there is a droplet, whether the flame reaches the fixture, and the vertical burning level.

Table 4 Vertical combustion analysis of halogen-free benzoxazine flame retardant modified epoxy resin

As can be seen from the data in Table 4, adding benzoxazine and dimethyl methyl phosphonate can improve the flame retardancy of epoxy resin, so the inventors think that the phosphorus element in dimethyl methyl phosphonate and the content of benzoxazine The nitrogen element makes the system form a dense carbon layer during combustion, and the nitrogen element in benzoxazine and the phosphorus element in dimethyl methylphosphonate have a good synergistic effect, achieving a good flame retardant effect.

To sum up, adding DMMP to the benzoxazine modified epoxy resin system, according to a certain curing process, can well increase the flame retardant performance, so that the flame retardant level of the resin body can reach UL94 V-0, and get Resin system with suitable viscosity.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. The benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding is characterized by comprising the following raw materials in parts by weight:

2. the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 1, wherein the accelerator is 2,4, 6-tris (dimethylaminomethyl) phenol.

3. The benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 1, wherein the bisphenol F epoxy resin has the structure:

4. the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 1, wherein the benzoxazine resin structure is:

5. the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 1, wherein the dimethyl methylphosphonate has the structure:

6. the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 1, wherein the methylcyclohexanediamine has the structure:

7. the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 2, wherein the 2,4, 6-tris (dimethylaminomethyl) phenol has the structure:

8. a method for preparing a benzoxazine fire retardant modified epoxy resin for vacuum infusion molding according to any one of claims 1-7, comprising the following steps:

step (1): preparing raw materials according to the weight ratio;

step (2): heating and stirring benzoxazine resin and bisphenol F epoxy resin, uniformly mixing, taking out and cooling to room temperature;

and (3): sequentially adding dimethyl methylphosphonate, methylcyclohexanediamine and an accelerator into the mixture cooled in the step (2), and stirring uniformly;

and (4): performing vacuum defoaming on the mixture obtained in the step (3) at room temperature, and removing air mixed in the stirring process;

and (5): and pouring the mixture subjected to vacuum defoaming into a mold treated by a release agent for thermosetting, and demolding after curing to obtain the benzoxazine flame-retardant modified epoxy resin for vacuum infusion molding.

9. The method for preparing the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 8, wherein the stirring temperature in the step (2) is 80-100 ℃ and the stirring time is 0.5-2h.

10. The preparation method of the benzoxazine flame retardant modified epoxy resin for vacuum infusion molding according to claim 8, wherein the thermosetting in step (5) is divided into two stages, the curing temperature in the first stage is 80 ℃, and the curing time is 4-6h; the curing temperature of the second stage is 190 ℃, and the curing time is 1-3h.

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