Halogen-free flame-retardant benzoxazine modified epoxy glass cloth laminated board and preparation method thereof

Abstract

The invention relates to a halogen-free flame-retardant benzoxazine modified epoxy glass cloth laminated board and a preparation method thereof, and belongs to the field of insulating laminated board materials. A benzoxazine modified epoxy resin composition is used as a resin matrix, glass cloth is used as a base material, the benzoxazine modified epoxy resin composition is used for impregnating the glass cloth to prepare a prepreg, and then the prepreg is subjected to hot press molding to obtain the halogen-free flame-retardant benzoxazine modified epoxy glass cloth laminated board. The benzoxazine modified epoxy resin composition is prepared from the following raw materials in parts by weight: 100 parts of epoxy resin, 5 to 25 parts of benzoxazine, 50 to 500 parts of solvent, 15 to 45 parts of curing agent, 0.05 to 1 part of accelerant, 5 to 25 parts of flame retardant and 0 to 80 parts of filler. The benzoxazine modified epoxy glass cloth laminated board has the flame retardant capacity reaching the vertical combustion grade V-0, meanwhile, the glass transition temperature (TMA test) is not lower than 185 DEG C, and the bending strength is not lower than 500 MPa. In addition, the laminated board does not contain halogen, and has excellent environmental protection property.

Description

Technical Field

[0001] The invention relates to a halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate and a preparation method thereof, belonging to the technical field of insulating laminates. Background Art

[0002] In recent years, with the increasingly urgent requirements for high performance and lightweight in the fields of aerospace, new energy vehicles, motors, power transmission and distribution, etc., the research on resin-based composite materials has received attention. Epoxy resin glass cloth laminates are widely used in the above fields due to their excellent comprehensive performance and relatively low cost. However, since epoxy resin itself does not have flame retardant ability, this type of laminate has a great fire hazard. To solve this problem, halogen-containing epoxies are traditionally used or halogen-containing flame retardants are introduced into the resin system. However, this solution poses a great hazard to both the environment and human health. Therefore, the preparation of halogen-free flame-retardant epoxy resin systems and further preparation of laminate materials are the current mainstream research directions. Existing solutions include introducing P and N flame retardants into the resin system, or introducing structures containing the above elements into the epoxy resin structure to prepare new epoxy with intrinsic flame retardancy. For example, Song Tianyou (Study on Benzoxazine-Modified Epoxy Resin and Its Synergistic Flame Retardancy) introduced benzoxazine into the epoxy system and reacted with the epoxy molecular chain to prepare a benzoxazine-modified epoxy resin with intrinsic flame retardancy. CN202011550444.4 introduced P-containing benzoxazine, maleimide resin, etc. into the epoxy resin system to improve the flame retardancy of the resin.

[0003] However, such solutions often have the following problems: (1) The addition of P-containing flame retardants or the introduction of flame retardant structures significantly reduces the heat resistance of the material. (2) Due to the low flame retardant efficiency, a large amount of external flame retardants are required to achieve the V-0 flame retardant level, resulting in the deterioration of the mechanical properties and process properties of the material. If the amount introduced is reduced, the flame retardant ability of the V-0 level is often not achieved. For practical applications, epoxy resin laminates with high flame retardancy, high strength, high heat resistance, and excellent electrical properties can meet the needs. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate and a preparation method thereof. The specific technical scheme is as follows:

[0005] The invention discloses a halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate, which uses a benzoxazine-modified epoxy resin composition as a resin matrix and a glass cloth as a substrate. The benzoxazine-modified epoxy resin composition is used to impregnate the glass cloth to prepare a prepreg, the prepreg is stacked, and finally the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate is obtained by hot pressing.

[0006] As a further improvement, the preparation process of the benzoxazine-modified epoxy resin composition comprises the following steps:

[0007] Step 1, heating the epoxy resin to a first reaction temperature;

[0008] Step 2, adding benzoxazine to the epoxy resin, and stirring to react at a first reaction temperature;

[0009] Step 3, adding a solvent, then adjusting the system temperature to a second reaction temperature, adding a curing agent, and reacting by stirring and keeping warm at the second reaction temperature;

[0010] Step 4: cool the system to room temperature, then add an accelerator, a flame retardant, and a filler, stir thoroughly until uniform, and finally add a solvent to adjust the solid content to obtain the benzoxazine-modified epoxy resin composition.

[0011] As a further improvement, the epoxy resin, benzoxazine, solvent, curing agent, accelerator, flame retardant and filler are mixed in the following proportions:

[0012] 100 parts of epoxy resin, 5-25 parts of benzoxazine, 50-500 parts of solvent, 15-45 parts of curing agent, 0.05-1 part of accelerator, 5-25 parts of flame retardant, and 0-80 parts of filler.

[0013] As a further improvement, the epoxy resin is o-cresol epoxy, the first reaction temperature is 140-180° C., and the reaction time at the first reaction temperature is 0.5-8 h.

[0014] The structural formula of the o-cresol epoxy is shown in Formula I:

[0015]

[0016] Where n is a positive integer.

[0017] As a further improvement, the structural formula of the benzoxazine is shown in Formula II:

[0018]

[0019] Among them, A is

[0020] In a further improvement, the solvent is one or more of dimethylformamide, dimethylacetamide, ethylene glycol methyl ether, ethylene glycol ethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, toluene, xylene, acetone, butanone, and methyl ethyl ketone;

[0021] and / or,

[0022] The second reaction temperature is 75-135°C, and the stirring reaction time at the second reaction temperature is 0.1-2h;

[0023] and / or,

[0024] The curing agent is one or more of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenyl sulfone;

[0025] and / or,

[0026] The accelerator is one or more of an imidazole anionic polymerization accelerator (including but not limited to 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole) and a boron trifluoride complex cationic polymerization accelerator (including but not limited to boron trifluoride monoethylamine);

[0027] and / or,

[0028] The flame retardant is an alkyl hypophosphite or alkyl hypophosphite dimer flame retardant, and the structural formula of the alkyl hypophosphite dimer flame retardant is shown in Formula III:

[0029]

[0030] Wherein, R1 and R2 are the same or different C1-C6 alkyl groups, and R3 is C1-C 10 Olefins or C6-C 10 Aromatic hydrocarbons, M is one of Al, Mg, Ca, Zn, Fe, Na, and K; m, n, and x are all positive integers of 1 to 4;

[0031] and / or,

[0032] The filler is one or more of aluminum hydroxide, magnesium hydroxide, silicon powder, calcium carbonate, calcium silicate, mica powder, kaolin, and montmorillonite;

[0033] and / or,

[0034] The solid content of the obtained benzoxazine-modified epoxy resin composition is 30-80%.

[0035] As a further improvement, the glass cloth includes one or more of electronic cloth (including but not limited to type 7628 / 7629), alkali-free cloth (including but not limited to type EW-100, EW-140, EW-180), medium-alkali cloth (including but not limited to type CW-140, CW-200), gingham cloth (including but not limited to 300g / 400g / 600g untwisted coarse yarn gingham cloth), and glass felt.

[0036] As a further improvement, the method for preparing the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate comprises the following steps:

[0037] Step 1, dipping the glass cloth into a paint tank containing a benzoxazine-modified epoxy resin composition;

[0038] Step 2: putting the impregnated glass cloth into an oven, keeping warm and drying it, and taking it out to obtain a prepreg;

[0039] Step 3, laying the prepreg;

[0040] Step 4: placing the prepreg after layering into a hot press for hot pressing;

[0041] Step 5: After the hot pressing is completed, the product is cooled and taken out to obtain the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate.

[0042] In a further improvement, in step 1, the duration of the dipping process is 1-10 minutes;

[0043] In step 2, the prepreg is kept in an oven at a temperature of 130-180° C. for a drying time of 1-10 minutes; the prepreg has a glue content of 20-60%.

[0044] For further improvement, in step 4, the hot pressing conditions are:

[0045] Set the initial temperature to 130-170℃, the initial pressure to 4MPa, then gradually increase the pressure to 30MPa, and gradually increase the temperature to 170-220℃, and keep the temperature and pressure for 1-6h.

[0046] The beneficial effects of the present invention are:

[0047] The present invention uses benzoxazine with a specific phosphorus-containing structure to modify o-cresol epoxy resin to prepare a phosphorus-containing, benzoxazine-containing epoxy resin, which enables the epoxy resin to have high heat resistance, high strength and a certain intrinsic flame retardancy. On this basis, an appropriate amount of an organic phosphorus flame retardant with a specific structure is further added to the resin composition. Through the synergistic effect of the intrinsic & additive flame retardants, the material has a flame retardancy of vertical combustion grade V-0, and the glass transition temperature (TMA test) is not less than 185°C, and the bending strength is not less than 500MPa. In addition, the laminate does not contain halogen and has excellent environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a physical photo of the laminate obtained in Example 1;

[0049] Figure 2 This is a photo of the laminate obtained in Example 2;

[0050] Figure 3 This is a photo of the laminate obtained in Example 3;

[0051] Figure 4 This is a photo of the laminate obtained in Example 4. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1

[0054] 1. Preparation of benzoxazine-modified epoxy resin composition

[0055] Heat 241g of o-cresol epoxy resin to 160°C, add 45g of benzoxazine as shown in Formula 4, stir and keep warm for 3h. Add dimethylformamide, adjust the system to 110°C, add 60g of 4,4'-diaminodiphenyl sulfone, keep warm and stir for 2h. Then cool the system to room temperature, add 0.6g of 2-methylimidazole, 24g of diethyl aluminum hypophosphite, and 36g of magnesium hydroxide. After sufficient stirring, add dimethylformamide to adjust the solid content to 70% to obtain a benzoxazine-modified epoxy resin composition.

[0056]

[0057] 2. Preparation of prepreg

[0058] The 7628 type electronic cloth was immersed in a paint tank containing a benzoxazine modified epoxy resin composition, taken out after immersion for 5 minutes, sent into an oven, and dried at 150°C for 3 minutes. After taking out, a prepreg was obtained, and its glue content was 60%.

[0059] 3. Hot pressing

[0060] The prepreg is laid and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 220°C and the temperature is maintained for 3 hours. After the hot press is completed, the laminate is cooled and taken out to obtain a laminate. Figure 1 shown.

[0061] Example 2

[0062] 1. Preparation of benzoxazine-modified epoxy resin composition

[0063] Heat 241g of o-cresol epoxy resin to 140°C, add 24g of benzoxazine as shown in Formula 5, stir and keep warm for 0.5h. Add propylene glycol monomethyl ether, adjust the system to 100°C, add 96.4g of 4,4'-diaminodiphenylmethane, keep warm and stir for 0.5h. Then cool the system to room temperature, add 2.41g of 2-phenylimidazole and 60.25g of dimethyl calcium hypophosphite. After sufficient stirring, add dimethylacetamide to adjust the solid content to 30%, and obtain a benzoxazine-modified epoxy resin composition.

[0064]

[0065] 2. Preparation of prepreg

[0066] The EW-100 alkali-free cloth was immersed in a paint tank containing a benzoxazine-modified epoxy resin composition, taken out after immersion for 7 minutes, sent into an oven, and dried at 140° C. for 6 minutes. After taking out, a prepreg was obtained, and the glue content of the prepreg was 20%.

[0067] 3. Hot pressing

[0068] The prepreg is laid and then placed in a hot press. The initial temperature is set to 170°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 220°C and the temperature is maintained for 4 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate. Figure 2 shown.

[0069] Example 3

[0070] 1. Preparation of benzoxazine-modified epoxy resin composition

[0071] 241g of o-cresol epoxy resin was heated to 180°C, 60.25g of benzoxazine as shown in Formula 4 was added, and the mixture was stirred and kept warm for 5h. Dimethylacetamide was added, the system was adjusted to 135°C, 48.2g of 4,4'-diaminodiphenyl ether was added, and the mixture was stirred and kept warm for 1h. The system was then cooled to room temperature, 1.5g of monoethylamine boron trifluoride, 35g of sodium diethyl hypophosphite, and 122g of filler (including 42g of aluminum hydroxide and 60g of silicon powder) were added. After sufficient stirring, propylene glycol ethyl ether and acetone (mass ratio 1:1) were added to adjust the solid content to 60%. A benzoxazine-modified epoxy resin composition was obtained.

[0072] 2. Preparation of prepreg

[0073] The 7629 electronic cloth was immersed in a paint tank containing a benzoxazine-modified epoxy resin composition, taken out after immersion for 2 minutes, sent into an oven, and dried at 170° C. for 1 minute. After being taken out, a prepreg was obtained, and its glue content was 40%.

[0074] 3. Hot pressing

[0075] The prepreg is laid and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 170°C and the temperature is maintained for 6 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate. Figure 3 shown.

[0076] Example 4

[0077] 1. Preparation of benzoxazine-modified epoxy resin composition

[0078] Heat 241g of o-cresol epoxy resin to 165°C, add 50g of benzoxazine as shown in Formula 4, stir and keep warm for 2.5h. Add propylene glycol ethyl ether, adjust the system to 115°C, add 70g of 4,4'-diaminodiphenyl sulfone, keep warm and stir for 1.5h. Then cool the system to room temperature, add 0.9g of 2-ethyl-4-methylimidazole, 35g of potassium diethyl hypophosphite, 40g each of calcium carbonate and calcium silicate. After sufficient stirring, add ethylene glycol monomethyl ether to adjust the solid content to 55%. Obtain a benzoxazine-modified epoxy resin composition.

[0079] 2. Preparation of prepreg

[0080] 300g of roving gingham cloth was immersed in a paint tank containing benzoxazine-modified epoxy resin composition, taken out after immersion for 4 minutes, sent into an oven, and dried at 150°C for 3 minutes. After taking out, a prepreg was obtained, and its glue content was 50%.

[0081] 3. Hot pressing

[0082] The prepreg is laid and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 210°C and the temperature is maintained for 4 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate. Figure 4 shown.

[0083] Comparative Example 1

[0084] 1. Preparation of epoxy resin composition

[0085] Heat 241g of o-cresol epoxy resin to 110°C, add 60g of 4,4'-diaminodiphenyl sulfone, and stir to react for 2h. Then cool the system to room temperature, add 0.6g of 2-methylimidazole, 24g of diethylaluminum hypophosphite, and 36g of magnesium hydroxide. After sufficient stirring, add dimethylformamide to adjust the solid content to 70%. Obtain an epoxy resin composition.

[0086] 2. Preparation of prepreg

[0087] The 7628 electronic cloth was immersed in a paint tank containing an epoxy resin composition, taken out after immersion for 5 minutes, sent into an oven, and dried at 150°C for 3 minutes. After being taken out, a prepreg was obtained, and its glue content was 60%.

[0088] 3. Hot pressing

[0089] The prepreg is layered and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 220°C and the temperature is maintained for 3 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate.

[0090] Comparative Example 2

[0091] 1. Preparation of benzoxazine-modified epoxy resin composition

[0092] Heat 241g of o-cresol epoxy resin to 160°C, add 45g of benzoxazine as shown in Formula 4, stir and keep warm for 3h. Add dimethylformamide, adjust the system to 110°C, add 60g of 4,4'-diaminodiphenyl sulfone, keep warm and stir for 2h. Then cool the system to room temperature, add 0.6g of 2-methylimidazole and 36g of magnesium hydroxide. After sufficient stirring, add dimethylformamide to adjust the solid content to 70%. Obtain a benzoxazine-modified epoxy resin composition.

[0093] 2. Preparation of prepreg

[0094] The 7628 type electronic cloth was immersed in a paint tank containing a benzoxazine modified epoxy resin composition, taken out after immersion for 5 minutes, sent into an oven, and dried at 150°C for 3 minutes. After taking out, a prepreg was obtained, and its glue content was 60%.

[0095] 3. Hot pressing

[0096] The prepreg is layered and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 220°C and the temperature is maintained for 3 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate.

[0097] Comparative Example 3

[0098] 1. Preparation of benzoxazine-modified epoxy resin composition

[0099] Heat 241g of o-cresol epoxy resin to 160°C, add 45g of benzoxazine as shown in Formula 4, stir and keep warm for 3h. Add dimethylformamide, adjust the system to 110°C, add 60g of 4,4'-diaminodiphenyl sulfone, keep warm and stir for 2h. Then cool the system to room temperature, add 0.6g of 2-methylimidazole, 24g of triethyl phosphate, and 36g of magnesium hydroxide. After sufficient stirring, add dimethylformamide to adjust the solid content to 70%. Obtain a benzoxazine-modified epoxy resin composition.

[0100] 2. Preparation of prepreg

[0101] The 7628 type electronic cloth was immersed in a paint tank containing a benzoxazine modified epoxy resin composition, taken out after immersion for 5 minutes, sent into an oven, and dried at 150°C for 3 minutes. After taking out, a prepreg was obtained, and its glue content was 60%.

[0102] 3. Hot pressing

[0103] The prepreg is layered and then placed in a hot press. The initial temperature is set to 130°C and the initial pressure is 4MPa. The pressure is gradually increased to 30MPa. At the same time, the temperature is gradually increased to 220°C and the temperature is maintained for 3 hours. After the hot press is completed, it is cooled and taken out to obtain a laminate.

[0104] The properties of the laminates of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 and Table 2:

[0105] Table 1

[0106]

[0107] Table 2

[0108]

[0109] It can be seen from the data in Tables 1 and 2 that the introduction of a specific phosphorus-containing benzoxazine structure (adding benzoxazine as shown in Formula II to react with epoxy) is beneficial to improving the mechanical properties of epoxy laminates (Example 1 vs. Comparative Example 1), and through its compounding with alkyl hypophosphite flame retardants, flame retardancy of V-0 level can be achieved at a lower addition amount, and the heat resistance of the material will not be affected. If other phosphorus-containing flame retardants are introduced (Comparative Example 3), due to their lower flame retardant efficiency, the flame retardant ability of the system still cannot reach the V-0 level. If diethyl aluminum hypophosphite is not added to the system, only relying on the intrinsic flame retardant ability of the benzoxazine-modified epoxy resin composition and the filling flame retardant (magnesium hydroxide), the V-0 level of flame retardancy cannot be achieved, even if the amount of magnesium hydroxide is increased, and it will also significantly affect the mechanical properties of the laminate.

[0110] In addition, it should be noted that if the triethyl phosphate in Comparative Example 3 is replaced with an equal mass of ammonium polyphosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), triphenyl phosphate or melamine polyphosphate, the vertical burning grade (thickness 1 mm, 3 mm) of the final laminate is V-1; even if the amount of ammonium polyphosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), triphenyl phosphate or melamine polyphosphate is increased to twice that of triethyl phosphate, the vertical burning grade (thickness 1 mm, 3 mm) of the final laminate is still V-1, and the mechanical properties (such as bending strength) are significantly reduced.

[0111] Therefore, in the present invention, by introducing a specific phosphorus-containing benzoxazine structure and compounding it with an alkyl hypophosphite flame retardant, the best flame retardant effect can be achieved, and at the same time, the material is endowed with the characteristics of high mechanical properties and high heat resistance.

[0112] 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Halogen-free flame retardant benzoxazine modified epoxy glass cloth laminate, characterized by: The benzoxazine-modified epoxy resin composition is used as a resin matrix and the glass cloth is used as a substrate. The benzoxazine-modified epoxy resin composition is impregnated into the glass cloth to prepare a prepreg, the prepreg is stacked, and finally a halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate is obtained by hot pressing.

2. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 1, characterized in that: The preparation process of the benzoxazine-modified epoxy resin composition comprises the following steps: Step 1, heating the epoxy resin to a first reaction temperature; Step 2, adding benzoxazine to the epoxy resin, and stirring to react at a first reaction temperature; Step 3, adding a solvent, then adjusting the system temperature to a second reaction temperature, adding a curing agent, and reacting by stirring and keeping warm at the second reaction temperature; Step 4: cool the system to room temperature, then add an accelerator, a flame retardant, and a filler, stir thoroughly until uniform, and finally add a solvent to adjust the solid content to obtain the benzoxazine-modified epoxy resin composition.

3. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 2, characterized in that: The proportions of the epoxy resin, benzoxazine, solvent, curing agent, accelerator, flame retardant and filler are as follows: 100 parts of epoxy resin, 5-25 parts of benzoxazine, 50-500 parts of solvent, 15-45 parts of curing agent, 0.05-1 part of accelerator, 5-25 parts of flame retardant, and 0-80 parts of filler.

4. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 2, characterized in that: The epoxy resin is o-cresol epoxy, the first reaction temperature is 140-180° C., and the reaction time at the first reaction temperature is 0.5-8 h.

5. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 2, characterized in that: The structural formula of the benzoxazine is shown in Formula II: Among them, A is 6. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 2, characterized in that: The solvent is one or more of dimethylformamide, dimethylacetamide, ethylene glycol methyl ether, ethylene glycol ethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, toluene, xylene, acetone, butanone, and methyl ethyl ketone; and / or, The second reaction temperature is 75-135°C, and the stirring reaction time at the second reaction temperature is 0.1-2h; and / or, The curing agent is one or more of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenyl sulfone; and / or, The accelerator is one or more of an imidazole anionic polymerization accelerator and a boron trifluoride complex cationic polymerization accelerator; and / or, The flame retardant is an alkyl hypophosphite or alkyl hypophosphite dimer flame retardant, and the structural formula of the alkyl hypophosphite dimer flame retardant is shown in Formula III: Wherein, R1 and R2 are the same or different C1-C6 alkyl groups, and R3 is C1-C 10 Olefins or C6-C 10 Aromatic hydrocarbons, M is one of Al, Mg, Ca, Zn, Fe, Na, and K; m, n, and x are all positive integers of 1 to 4; and / or, The filler is one or more of aluminum hydroxide, magnesium hydroxide, silicon powder, calcium carbonate, calcium silicate, mica powder, kaolin, and montmorillonite; and / or, The solid content of the obtained benzoxazine-modified epoxy resin composition is 30-80%.

7. The halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 2, characterized in that: The glass cloth includes one or more of electronic cloth, alkali-free cloth, medium-alkali cloth, lattice cloth and glass felt.

8. The method for preparing the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1, immersing the glass cloth in a paint tank containing a benzoxazine-modified epoxy resin composition; Step 2: putting the impregnated glass cloth into an oven, keeping warm and drying it, and taking it out to obtain a prepreg; Step 3, laying the prepreg; Step 4: placing the prepreg after layering into a hot press for hot pressing; Step 5: After the hot pressing is completed, the product is cooled and taken out to obtain the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate.

9. The method for preparing the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 8, characterized in that: In step 1, the dipping process lasts for 1-10 minutes; In step 2, the prepreg is kept in an oven at a temperature of 130-180° C. for a drying time of 1-10 minutes; the prepreg has a glue content of 20-60%.

10. The method for preparing the halogen-free flame-retardant benzoxazine-modified epoxy glass cloth laminate according to claim 8, characterized in that: In step 4, the hot pressing conditions are: Set the initial temperature to 130-170℃, the initial pressure to 4MPa, then gradually increase the pressure to 30MPa, and gradually increase the temperature to 170-220℃, and keep the temperature and pressure for 1-6h.

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