An ultra-thin flame-retardant halogen-free epoxy fiberglass board and its preparation method

Abstract

This invention discloses an ultrathin flame-retardant halogen-free epoxy fiberglass sheet and its preparation method, belonging to the technical field of epoxy fiberglass materials. The preparation process includes preparing a resin solution by mixing phosphorus-containing epoxy resin, bisphenol A phenolic epoxy resin, o-cresol phenolic epoxy resin, benzoxazine resin, phosphorus-containing phenolic flame-retardant curing agent, toughening agent, catalyst, coupling agent, and a mixed solvent. Composite fillers and flame-retardant synergists are added, and the mixture is dispersed at high speed and then impregnated with fiberglass cloth. After drying, a semi-cured sheet is obtained, which is then stacked and hot-pressed to obtain the finished product. Compared with existing technologies, the ultrathin fiberglass sheet obtained by this invention meets the UL94 V-0 halogen-free flame-retardant standard, has a high glass transition temperature, and maintains excellent electrical insulation performance and dimensional stability even at ultrathin thicknesses. During processing, the resin flow is uniform and there is no bubble delamination. This sheet is environmentally friendly and halogen-free, with excellent comprehensive performance, and is suitable for automotive insulation, electronic packaging, and printed circuit boards.

Description

Technical Field

[0001] This invention relates to the field of epoxy fiberglass materials technology, and in particular to an ultrathin flame-retardant halogen-free epoxy fiberglass sheet and its preparation method. Background Technology

[0002] With the rapid development of the electronics and information industry and the new energy vehicle industry, the demand for epoxy fiberglass-based insulation sheets in printed circuit boards, automotive electronic packaging, and power battery insulation is increasing. Traditional epoxy fiberglass-based sheets often use halogens as flame retardants, but halogen-containing materials produce carcinogenic substances such as dioxins when burned, posing a serious threat to the environment and human health, and have been gradually restricted by regulations in various countries. In recent years, halogen-free flame-retardant epoxy systems have become a research hotspot in this field. Among them, reactive phosphorus-containing flame-retardant curing agents have received widespread attention because they can chemically bond phosphorus elements into the cross-linking network, exhibiting advantages such as good flame-retardant durability and no precipitation or migration. Simultaneously, with the trend towards thinner and lighter electronic products and lighter automobiles, the combined requirements of ultra-thinness, high heat resistance, and high insulation safety place more stringent performance demands on epoxy fiberglass sheets.

[0003] Patent document CN110561855A discloses a halogen-free, medium-Tg, high-CTI flame-retardant epoxy fiberglass cloth base plate and its preparation method. It involves compounding phosphorus-containing epoxy resin with phenolic epoxy resin, introducing phenolic resin and benzoxazine resin for curing, and using aluminum hydroxide and / or silica as fillers to obtain a copper-clad laminate product with medium Tg and high CTI. However, this patent focuses on copper-clad laminates and lacks targeted optimization for the production of ultra-thin insulating boards, and does not address the synergistic effects and ratio optimization of phosphorus-containing phenolic curing agents. Patent document CN114589993A discloses a preparation process and method for a halogen-free flame-retardant fiberglass board. It employs a combination of water-soluble flame retardant and expanded graphite, using glass fiber and polypropylene fiber as substrates, and preparing the fiberglass board through needle punching reinforcement and polyurethane adhesive bonding. However, the sheet material prepared by this patent is mainly used in the field of automotive interior parts. It has poor electrical properties such as insulation stability at high temperature, high heat resistance and high CTI. Moreover, it is formed by needle punching and gluing, and the strength, heat resistance uniformity and ultra-thin dimensional accuracy of the sheet material are difficult to meet the requirements of electronic insulation or automotive motor insulation.

[0004] Therefore, achieving a high glass transition temperature, high CTI, and low water absorption rate at ultra-thin thicknesses while ensuring a halogen-free flame retardant rating of UL94 V-0 is a pressing technical challenge in this field. Particularly during the processing of ultra-thin sheets, avoiding uneven resin flow and thickness deviations due to excessive resin fluidity, as well as bubble delamination caused by excessive volatiles, are key factors restricting the industrial application of ultra-thin insulating sheets. Furthermore, existing research on the synergistic compounding of phosphorus-containing phenolic flame retardant curing agents is insufficient. The differences in the flame retardant mechanisms of different types of phosphorus-containing phenolic curing agents and their impact on flame retardant efficiency and heat resistance have not been systematically revealed. There is an urgent need to develop an epoxy fiberglass sheet and its preparation method that can balance flame retardant performance, heat resistance, and ultra-thin processing capabilities. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide an ultra-thin flame-retardant halogen-free epoxy fiberglass sheet and its preparation method.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: An ultra-thin flame-retardant halogen-free epoxy fiberglass board comprises the following raw materials in parts by weight: 40-60 parts phosphorus-containing epoxy resin, 20-40 parts bisphenol A type phenolic epoxy resin, 130-170 parts o-cresol phenolic epoxy resin, 60-90 parts benzoxazine resin, 120-150 parts phosphorus-containing phenolic flame retardant curing agent, 3-8 parts toughening agent, 0.2-0.6 parts catalyst, 1-2 parts coupling agent, 300-500 parts mixed solvent, 40-80 parts composite filler, 3-8 parts flame retardant synergist, and fiberglass cloth; The phosphorus-containing phenolic flame retardant curing agent is at least one of the following: flame retardant ODOPB, bis(4-hydroxyphenyl)phenylphosphine oxide, tri(4-hydroxyphenyl)phosphine oxide, and 4-hydroxyphenyl phosphate.

[0007] The mixed solvent is composed of butanone and propylene glycol methyl ether in a mass ratio of 4-6:2-4.

[0008] The composite filler is composed of magnesium hydroxide and silicon dioxide in a mass ratio of 1-3:0.5-2.

[0009] The catalyst is at least one of triphenylphosphine and dimethylimidazole.

[0010] The toughening agent is at least one of terminal epoxy-terminated nitrile rubber, styrene-butadiene rubber, butadiene rubber, and ethylene propylene rubber.

[0011] The coupling agent is at least one of titanate coupling agents and silane coupling agents.

[0012] The flame retardant synergist is at least one of zinc borate, melamine cyanurate, and nano zinc oxide.

[0013] Preferably, the phosphorus-containing phenolic flame retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate.

[0014] More preferably, the phosphorus-containing phenolic flame retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 1-3:1.

[0015] More preferably, the phosphorus-containing phenolic flame retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 2:1.

[0016] The preparation method of the ultrathin flame-retardant halogen-free epoxy fiberglass board is as follows: Step 1: Take phosphorus-containing epoxy resin, bisphenol A type phenolic epoxy resin, o-cresol phenolic epoxy resin, benzoxazine resin, phosphorus-containing phenolic flame retardant curing agent, toughening agent, catalyst, and coupling agent, and add them sequentially to the mixed solvent. Stir at 500-1000 r / min for 10-50 minutes to form a uniform low-viscosity resin solution. Add composite filler and flame retardant synergist while stirring. After the addition is complete, increase the speed to 1000-2000 r / min and disperse at high speed for 1-5 hours to obtain a uniform adhesive solution. Step 2: Impregnate the fiberglass cloth with the above adhesive solution through the impregnation tank at a speed of 3-8 m / min. After impregnation, dry the fiberglass cloth at a temperature of 100-150℃ for 1-10 minutes to obtain a semi-cured sheet. Step 3: Cut and stack 2-8 prepreg sheets, place a layer of PTFE release cloth on the top and bottom surfaces of the stack, and then place the whole assembly between two stainless steel mirror panels to form the unit to be pressed. Step 4: Place the unit to be pressed into a vacuum hot press to cure the resin. Then, under pressure, cool it to below 50°C at 3-10°C / min. Release the pressure, remove the board, and peel off the release cloth to obtain the ultra-thin flame-retardant halogen-free epoxy fiberglass board.

[0017] In the vacuum hot press, the resin is cured by evacuating to a residual pressure of 4-6 mmHg, applying a pressure of 2-5 MPa, heating to 180-200°C at a heating rate of 1-3°C / min, and holding at the temperature and pressure for 30-120 minutes.

[0018] The thickness of the ultra-thin flame-retardant halogen-free epoxy fiberglass sheet is 0.05-0.20 mm.

[0019] In existing technologies, without the addition of phosphorus-containing phenolic flame retardant curing agents, the system relies solely on phosphorus-containing epoxy resin and inorganic fillers for flame retardancy and curing. This results in low phosphorus content and insufficient crosslinking density, leading to poor flame retardant and heat resistance properties. This invention introduces a phosphorus-containing phenolic flame retardant curing agent, utilizing the phenolic hydroxyl groups in its molecule to undergo a ring-opening reaction with the epoxy resin, participating in the formation of a crosslinking network, increasing the crosslinking density and glass transition temperature. Simultaneously, the introduction of additional phosphorus enhances flame retardant efficiency, thereby significantly improving the overall performance of the board. Furthermore, it was discovered that different structures of phosphorus-containing phenolic curing agents exhibit varying effects. Among them, the flame retardant ODOPB, containing a DOPO cyclic phosphate ester structure and bisphenol hydroxyl groups, has a rigid heterocyclic structure that effectively improves the thermal stability of the crosslinking network. During combustion, it can both release phosphorus-containing free radicals by breaking PO bonds to achieve gas-phase flame retardancy and promote charring on the substrate surface to achieve condensed-phase flame retardancy.

[0020] Based on a single phosphorus-containing phenolic curing agent, this invention further discovers that not every combination of two phosphorus-containing phenolic curing agents can produce a synergistic effect. Specifically, when the flame retardant ODOPB is combined with 4-hydroxyphenyl phosphate, the DOPO ring structure of the flame retardant ODOPB dominates flame retardancy at high temperatures through a gas-phase free radical quenching mechanism, while the arylphosphonic acid structure of 4-hydroxyphenyl phosphate promotes char formation in the condensed phase through dehydration condensation to generate polyphosphoric acid. The two act on the gas phase and the condensed phase respectively, forming a complementary double-barrier flame retardant system, resulting in a significant synergistic effect.

[0021] After confirming the synergistic effect between flame retardant ODOPB and 4-hydroxyphenyl phosphate, this invention further investigated the influence of different compounding ratios on performance. The results showed that when the mass ratio of ODOPB to 4-hydroxyphenyl phosphate was 2:1, the flame retardant contribution of gas-phase free radical quenching and condensed phase dehydration to char formation reached the optimal balance, and the crosslinking density distribution of the cured network was the most uniform. If the proportion of 4-hydroxyphenyl phosphate was too high, the strong acidity of its phosphonic acid groups would lead to excessively rapid local curing reaction, uneven crosslinking, and increased hygroscopicity of the cured product, thus reducing heat resistance stability. If the proportion of ODOPB was too high, the density of the char layer formed by the condensed phase would be insufficient, reducing heat barrier capacity, and the excessive rigid heterocycles would increase the brittleness of the cured network and raise internal stress. This invention optimizes the ratio of the two to achieve optimal synergistic complementarity between the gas phase and condensed phase, resulting in the most complete crosslinking structure, thereby obtaining an ultra-thin sheet with optimal overall flame retardant and heat resistance performance.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects: 1) This invention introduces phosphorus-containing phenolic flame retardant curing agents, benzoxazine resin, and inorganic fillers to achieve the high-level halogen-free flame retardant standard in the field of epoxy resin materials by introducing synergistic effects, while avoiding the environmental hazards of traditional halogen flame retardants.

[0023] 2) This invention utilizes phosphorus-containing phenolic flame retardant curing agents and benzoxazine resin to jointly improve crosslinking density, significantly increasing the glass transition temperature of the board and meeting the needs of automotive electronics and high heat-resistant insulation applications.

[0024] 3) By optimizing the compounding ratio of flame-retardant components, this invention maintains excellent flame-retardant and mechanical properties at ultra-thin thicknesses, and solves process problems such as uneven glue flow and bubble stratification during processing. Detailed Implementation

[0025] The sources or parameters of some substances are as follows: Phosphorus-containing epoxy resin: epoxy equivalent 305-325 g / eq, phosphorus content 2.2±0.1wt%, solid content 74-76%.

[0026] Bisphenol A type phenolic epoxy resin: epoxy equivalent 190-220 g / eq, softening point 75-85℃.

[0027] o-Cresol-formaldehyde epoxy resin: epoxy equivalent 190-220 g / eq, softening point 60-95℃.

[0028] Benzoxazine resin: Grade: Araldite MT35600, Manufacturer: Huntsman.

[0029] Epoxy-terminated nitrile butadiene rubber: Acrylonitrile content 17~26%, epoxy equivalent 2000-4000 g / eq.

[0030] Triphenylphosphine: CAS No. 603-35-0, purity ≥99.5%.

[0031] Coupling agent KH550: KH550 is γ-aminopropyltriethoxysilane, CAS number 919-30-2, purity ≥98%.

[0032] Flame retardant ODOPB: Chemical name 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide, CAS number 99208-50-1, purity ≥99%.

[0033] Bis(4-hydroxyphenyl)phenylphosphine oxide: CAS No. 795-43-7, purity ≥98%.

[0034] Tris(4-hydroxyphenyl)phosphine oxide: CAS No. 797-71-7, purity ≥98%.

[0035] 4-Hydroxyphenyl phosphate: CAS No. 33795-18-5, purity ≥97%.

[0036] Magnesium hydroxide: Particle size D 50≤1.5μm, purity ≥98%.

[0037] Silica: Specific surface area of ​​150-200 m² 2 / g, particle size 5-40 nm.

[0038] Fiberglass cloth: Commercially available E-type alkali-free fiberglass open-fiber cloth, 0.01mm thick, with a single filament diameter of 5-7μm.

[0039] In the embodiments and comparative examples of this invention, all raw materials are commercially available products.

[0040] Example 1

[0041] A method for preparing an ultrathin flame-retardant halogen-free epoxy fiberglass board is as follows, in parts by weight: Step 1: Take 50 parts of phosphorus-containing epoxy resin, 30 parts of bisphenol A type phenolic epoxy resin, 150 parts of o-cresol phenolic epoxy resin, 75 parts of benzoxazine resin, 135 parts of phosphorus-containing phenolic flame retardant curing agent, 5 parts of terminal epoxy group nitrile rubber, 0.4 parts of triphenylphosphine, and 1.5 parts of coupling agent KH550, and add them sequentially to a mixed solvent of 250 parts of butanone and 150 parts of propylene glycol methyl ether. Stir at 800 r / min for 30 minutes to form a uniform low-viscosity resin solution. While stirring, add 65 parts of composite filler, which is composed of magnesium hydroxide and silicon dioxide in a mass ratio of 2:1, and 5 parts of zinc borate. After the addition is complete, increase the speed to 1500 r / min and disperse at high speed for 3 hours to obtain a uniform adhesive solution. Step 2: Impregnate the fiberglass cloth with the above adhesive solution through the impregnation tank at a speed of 4.8 m / min. After impregnation, dry the fiberglass cloth at a temperature of 135°C for 3 minutes to obtain a semi-cured sheet. Step 3: Cut and stack 4 prepreg sheets, place a layer of polytetrafluoroethylene release cloth on the top and bottom surfaces of the stack, and then place the whole assembly between two stainless steel mirror panels to form the unit to be pressed. Step 4: Place the unit to be pressed into a vacuum hot press, evacuate to a residual pressure of 5 mmHg, apply a pressure of 3.0 MPa, heat to 195°C at a heating rate of 1.8°C / min, and hold at the temperature and pressure for 90 minutes to allow the resin to fully cure. Then, under pressure, cool to below 50°C at a rate of 7°C / min, release the pressure, remove the board, and peel off the release cloth to obtain the ultra-thin flame-retardant halogen-free epoxy fiberglass board with a thickness of 0.10 mm.

[0042] The phosphorus-containing phenolic flame retardant curing agent is the flame retardant ODOPB.

[0043] In the curing system of this invention, the phenolic hydroxyl groups of the phosphorus-containing phenolic curing agent can act as promoters for the ring-opening polymerization of benzoxazine, accelerating the ring-opening of the oxazine ring and participating in its cross-linking network. Simultaneously, the phenolic hydroxyl groups undergo ring-opening addition reactions with epoxy groups. The phenolic hydroxyl groups and secondary amine groups generated after the ring-opening of benzoxazine can also react with epoxy groups to form an epoxy-benzoxazine copolymer structure. Under heating conditions, these three components synergistically construct a uniform and dense cross-linking network, without competing side reactions.

[0044] Example 2

[0045] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is bis(4-hydroxyphenyl)phenylphosphine oxide.

[0046] Example 3

[0047] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is tris(4-hydroxyphenyl)phosphine oxide.

[0048] Example 4

[0049] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is 4-hydroxyphenyl phosphate.

[0050] Example 5

[0051] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 1:1.

[0052] Example 6

[0053] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is composed of bis(4-hydroxyphenyl)phenylphosphine oxide and tri(4-hydroxyphenyl)phosphine oxide in a mass ratio of 1:1.

[0054] Example 7

[0055] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 2:1.

[0056] Example 8

[0057] The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 3:1.

[0058] Comparative Example 1 The preparation method of an ultra-thin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the phosphorus-containing phenolic flame-retardant curing agent is not added.

[0059] Comparative Example 2 The preparation method of an ultrathin flame-retardant halogen-free epoxy fiberglass board is basically the same as that in Example 1, except that the zinc borate is not added.

[0060] Test Example 1 Flame retardant performance test: Five 125mm × 13mm samples were cut from the boards obtained in each embodiment and comparative example. After conditioning for 48 hours at a temperature of 23±2℃ and a relative humidity of 50±5%, the samples were subjected to a UL94 vertical burning test according to GB / T2408-2021 "Determination of the flammability of plastics - Horizontal and Vertical Methods". During the test, the sample was vertically fixed on the fixture, and a Bunsen burner was used to apply a blue flame with a flame height of 20±1mm. After the first application of the flame for 10 seconds, the flame was removed, and the flaming time t1 was recorded. If the sample extinguished, the flame was immediately applied a second time for 10 seconds at the same position, and the second flaming time t2 and afterglow time t3 were recorded. At the same time, it was observed and recorded whether any molten drips ignited the degreased cotton placed 300mm below the sample. The UL94 rating was determined according to the GB / T2408-2021 standard, and the average total afterglow time of the five samples was taken as the evaluation index. The results are summarized in Table 1.

[0061] Table 1

[0062] Test Example 2 Glass transition temperature test: A 15 mg sample was cut from the center of the plates prepared in each embodiment and comparative example, placed in an aluminum crucible and sealed, with an empty crucible as a reference. Tests were conducted under a nitrogen atmosphere at a gas flow rate of 50 mL / min. The heating program was set as follows: heating from 30°C to 250°C at a rate of 20°C / min, holding at that temperature for 2 minutes to eliminate thermal history; cooling to 30°C at a rate of 20°C / min, and then heating again to 250°C at a rate of 20°C / min. The temperature corresponding to the inflection point of the heat flux step change in the second heating curve was taken as the glass transition temperature, automatically calculated using the midpoint method (half-width method) of the thermal analysis instrument software. Three parallel samples were tested for each embodiment, and the arithmetic mean was taken. The relevant test data are summarized in Table 2.

[0063] Table 2

[0064] Comparative Example 1 did not add phosphorus-containing phenolic flame retardant curing agent. The system relied solely on phosphorus-containing epoxy resin and inorganic fillers for flame retardancy and curing. The phosphorus content was low and the curing crosslinking density was insufficient, resulting in poor flame retardancy and heat resistance. Compared with Comparative Example 2, Example 1 added zinc borate and phosphorus-containing phenolic flame retardant curing agent synergistically promoted char formation, formed a dense char layer, and inhibited flame spread, increasing the flame retardancy rating from V-1 to V-0. Examples 1 to 4 respectively introduced phosphorus-containing phenolic flame retardant curing agents. These substances participate in the formation of cross-linking networks through the ring-opening reaction of phenolic hydroxyl groups with epoxy resin, thereby increasing the cross-linking density and glass transition temperature. They also introduce additional phosphorus elements to enhance flame retardant efficiency. Therefore, their overall performance is significantly better than that of Comparative Example 1. Among them, the flame retardant ODOPB used in Example 1 contains a DOPO cyclic phosphate ester structure and bisphenol hydroxyl groups. Its rigid heterocyclic structure has a good effect on improving the thermal stability of the cross-linking network. Moreover, the DOPO structure can release phosphorus-containing free radicals by breaking PO bonds during combustion to achieve gas-phase flame retardancy, and can also promote char formation on the substrate surface to achieve condensed-phase flame retardancy. The dual mechanism makes its flame retardant efficiency higher than that of other single components.

[0065] Example 5 uses a combination of flame retardant ODOPB and 4-hydroxyphenyl phosphate. The DOPO ring structure of ODOPB dominates flame retardancy at high temperatures through a gas-phase free radical quenching mechanism, while the arylphosphonic acid structure of 4-hydroxyphenyl phosphate promotes char formation in the condensed phase through dehydration condensation to generate polyphosphoric acid. The two act on the gas phase and condensed phase respectively, forming a complementary double-barrier flame retardant system. Therefore, the synergistic efficiency is higher than that of the single use in Example 1 or Example 4. In contrast, Example 6 uses a combination of bis(4-hydroxyphenyl)phenylphosphine oxide and tri(4-hydroxyphenyl)phosphine oxide. Both have a structure of phosphine oxide linked to p-hydroxyphenyl, and their phosphorus chemical forms and thermal decomposition mechanisms are exactly the same. Both use char formation in the condensed phase as the main flame retardant pathway. There is no gas-phase flame retardant complementarity. The superposition only has an additive effect of flame retardants and cannot produce a synergistic effect. Therefore, its performance is only between that of the two single substances.

[0066] Example 7 uses a 2:1 mass ratio of flame retardant ODOPB to 4-hydroxyphenyl phosphate. At this ratio, the flame retardant contribution of gas-phase free radical quenching and condensed phase dehydration to char formation is optimally balanced, and the crosslinking density distribution of the cured network is most uniform. If the proportion of 4-hydroxyphenyl phosphate is too high, the strong acidity of its phosphonic acid groups will lead to localized excessively rapid curing reaction, uneven crosslinking, and increased hygroscopicity of the cured product, which will reduce heat resistance stability. If the proportion of flame retardant ODOPB is too high, the density of the char layer formed by the condensed phase will be insufficient, the heat barrier capacity will decrease, and too many rigid heterocycles will increase the brittleness of the cured network and increase internal stress. Therefore, the 2:1 ratio makes the gas phase and condensed phase synergistic complementarity optimal, and the crosslinking structure most perfect. Thus, the overall performance is better than that of Example 5 and Example 8.

Claims

1. An ultra-thin flame-retardant halogen-free epoxy fiberglass sheet, characterized in that, The raw materials include the following parts by weight: 40-60 parts phosphorus-containing epoxy resin, 20-40 parts bisphenol A type phenolic epoxy resin, 130-170 parts o-cresol phenolic epoxy resin, 60-90 parts benzoxazine resin, 120-150 parts phosphorus-containing phenolic flame retardant curing agent, 3-8 parts toughening agent, 0.2-0.6 parts catalyst, 1-2 parts coupling agent, 300-500 parts mixed solvent, 40-80 parts composite filler, 3-8 parts flame retardant synergist, and glass fiber cloth; The flame retardant synergist is zinc borate; The thickness of the ultra-thin flame-retardant halogen-free epoxy fiberglass sheet is 0.05-0.20 mm; The phosphorus-containing phenolic flame retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 1-3:

1.

2. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The mixed solvent is composed of butanone and propylene glycol methyl ether in a mass ratio of 4-6:2-4.

3. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The composite filler is composed of magnesium hydroxide and silicon dioxide in a mass ratio of 1-3:0.5-2.

4. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The catalyst is at least one of triphenylphosphine and dimethylimidazole.

5. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The toughening agent is at least one of terminal epoxy-terminated nitrile rubber, styrene-butadiene rubber, butadiene rubber, and ethylene propylene rubber.

6. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The coupling agent is at least one of titanate coupling agents and silane coupling agents.

7. The ultra-thin flame-retardant halogen-free epoxy fiberglass sheet as described in claim 1, characterized in that, The phosphorus-containing phenolic flame retardant curing agent is composed of flame retardant ODOPB and 4-hydroxyphenyl phosphate in a mass ratio of 2:

1.

8. A method for preparing an ultrathin flame-retardant halogen-free epoxy fiberglass sheet as described in any one of claims 1-7, characterized in that, The method is as follows: Step 1: Take phosphorus-containing epoxy resin, bisphenol A type phenolic epoxy resin, o-cresol phenolic epoxy resin, benzoxazine resin, phosphorus-containing phenolic flame retardant curing agent, toughening agent, catalyst, and coupling agent, and add them sequentially to the mixed solvent. Stir at 500-1000 r / min for 10-50 minutes to form a uniform low-viscosity resin solution. Add composite filler and flame retardant synergist while stirring. After the addition is complete, increase the speed to 1000-2000 r / min and disperse at high speed for 1-5 hours to obtain a uniform adhesive solution. Step 2: Impregnate the fiberglass cloth with the above adhesive solution through the impregnation tank at a speed of 3-8 m / min. After impregnation, dry the fiberglass cloth at a temperature of 100-150℃ for 1-10 minutes to obtain a semi-cured sheet. Step 3: Cut and stack 2-8 prepreg sheets, place a layer of PTFE release cloth on the top and bottom surfaces of the stack, and then place the whole assembly between two stainless steel mirror panels to form the unit to be pressed. Step 4: Place the unit to be pressed into a vacuum hot press to cure the resin. Then, under pressure, cool it to below 50°C at 3-10°C / min. Release the pressure, remove the board, and peel off the release cloth to obtain the ultra-thin flame-retardant halogen-free epoxy fiberglass board.

9. The method as described in claim 8, characterized in that, In the vacuum hot press, the resin is cured by evacuating to a residual pressure of 4-6 mmHg, applying a pressure of 2-5 MPa, heating to 180-200°C at a heating rate of 1-3°C / min, and holding at the temperature and pressure for 30-120 minutes.

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