Halogen-free flame-retardant epoxy resin copper clad plate and preparation method thereof

Abstract

The present application relates to the field of copper-clad plate, and particularly discloses a halogen-free flame-retardant epoxy resin copper-clad plate and a preparation method thereof. The composite flame retardant is prepared by loading an intumescent flame retardant on mesoporous silica, and is mixed with modified aluminum hydroxide. The intumescent flame retardant is loaded on mesoporous silica, and the foam carbon layer structure formed after combustion can isolate air and heat conduction, protect the polymer main body, and achieve the purpose of flame retardation. Meanwhile, the modified aluminum hydroxide is introduced. The aluminum hydroxide has good flame retardation, and can promote the generation of carbon layer in the combustion process. On the other hand, the silica and aluminum hydroxide as inorganic fillers can improve the mechanical properties of the copper-clad plate, and make up for the problem of decreased impact resistance caused by the introduction of the intumescent flame retardant. At the same time, the mesoporous carbon dioxide loaded flame retardant can fix the intumescent flame retardant inside the resin, reduce the migration rate, and ensure that the flame retardation performance of the copper-clad plate does not decrease during long-term storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of copper-clad plate, in particular to a halogen-free flame-retardant epoxy resin copper-clad plate and a preparation method thereof. BACKGROUND

[0002] Copper-clad plate, full name copper-clad foil laminated plate (CCL), is a kind of plate-shaped material made of glass fiber cloth immersed in resin, one side or both sides covered with copper foil and hot pressed, which is the core substrate of printed circuit board (PCB). Epoxy resin refers to a kind of high molecular compound containing two or more than two epoxy groups in the molecular structure. Epoxy resin has the advantages of good chemical resistance, dimensional stability, low price, high bonding strength, etc., so it is widely used in CCL. However, epoxy resin is flammable and emits a large amount of toxic gas during combustion, so in the production of CCL, flame retardants are added to improve its performance. At present, the most commonly used in the market is halogen-based flame retardant, but this flame retardant will produce toxic substances when burning, which has great safety hidden danger; in addition, inorganic flame retardants can also be used, but in order to achieve good results, a large amount of inorganic materials need to be added, which will affect the overall performance of CCL; another method is to introduce phosphorus-containing flame retardants into the resin material, which can achieve good results, but with the continuous expansion of the use of electronic products, electronic waste containing phosphorus will cause great pressure on the environment over time.

[0003] In summary, it is of great significance to solve the above problems and manufacture a halogen-free flame-retardant epoxy resin copper-clad plate. SUMMARY

[0004] The present application aims to provide a halogen-free flame-retardant epoxy resin copper-clad plate and a preparation method thereof to solve the problems raised in the background.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: a preparation method of a halogen-free flame-retardant epoxy resin copper-clad plate, comprising the following steps:

[0006] S1: preparing vinyl mesoporous silica by co-condensation of silane mixed precursors under acidic conditions;

[0007] S2: obtaining polyvinyl acetate modified mesoporous silica by copolymerization, and then preparing polyvinyl alcohol modified mesoporous silica by alcoholysis reaction;

[0008] S3: (1) mixing polyvinyl alcohol modified mesoporous silica as carbon source with acid source and gas source, and then connecting them by using aldehyde as reaction reagent to prepare a composite flame retardant; (2) treating aluminum hydroxide with silane coupling agent to obtain modified aluminum hydroxide;

[0009] S4: mixing bisphenol A type epoxy resin, curing agent, curing accelerator, solvent, composite flame retardant and modified aluminum hydroxide, stirring uniformly to obtain a pre-impregnation solution, dipping glass fiber cloth in the pre-impregnation solution for 5-20 minutes, and obtaining a prepreg after curing at 60-90℃ for 10-30 minutes;

[0010] S5: laminating the prepreg in one or more layers, covering both sides of the prepreg with copper foil, and pressing at 5-30 MPa and 120-200℃ for 3-6 hours and holding for 1-3 hours to obtain a halogen-free flame-retardant epoxy resin copper-clad plate.

[0011] Preferably, the mass fractions of the raw materials for preparing the vinyl mesoporous silica are as follows: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid, and 3000-4000 parts of deionized water.

[0012] Preferably, the mass fractions of the raw materials for preparing the vinyl mesoporous silica are as follows: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid, and 3000-4000 parts of deionized water.

[0013] Preferably, the mass fractions of the raw materials for preparing the vinyl mesoporous silica are as follows: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid, and 3000-4000 parts of deionized water.

[0014] Preferably, the mass fractions of the raw materials for preparing the vinyl mesoporous silica are as follows: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid, and 3000-4000 parts of deionized water.

[0015] Preferably, the mass fractions of the raw materials for preparing the vinyl mesoporous silica are as follows: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid, and 3000-4000 parts of deionized water.

[0016] Among them, in S3, the preparation process of the composite flame retardant is: mixing the acid source, the gas source, and the aldehyde uniformly, heating to 40-60°C, stirring continuously, reacting for 1-3 hours, adding polyvinyl alcohol-modified mesoporous silica, stirring continuously at 40-60°C, and reacting for 12-24 hours to obtain the composite flame retardant;

[0017] Preferably, the composite flame retardant comprises the following raw materials in the following weight parts: 1-3 parts of polyvinyl alcohol-modified mesoporous silica, 3-8 parts of acid source, 1-3 parts of gas source, and 0.1-2 parts of aldehyde.

[0018] Preferably, the acid source includes but is not limited to one of amino-containing sulfhydryls and amino-containing benzenesulfonates; the gas source includes but is not limited to one of melamine and melamine derivatives;

[0019] More preferably, the acid source is sodium p-aminobenzenesulfonate; the gas source is melamine;

[0020] Wherein, in S3, the modified aluminum hydroxide preparation process is: adding aluminum hydroxide, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and anhydrous ethanol into a ball mill, ball milling for 1 to 5 hours, and then taking out without drying to obtain modified aluminum hydroxide;

[0021] Preferably, the modified aluminum hydroxide comprises the following raw materials in the following mass fractions: 10 to 30 parts of aluminum hydroxide, 1 to 5 parts of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and 1 to 5 parts of anhydrous ethanol;

[0022] The raw materials of the prepreg are as follows: 80-120 parts by weight of bisphenol A epoxy resin, 5-15 parts by weight of curing agent, 2-8 parts by weight of curing accelerator, 40-80 parts by weight of solvent, 20-50 parts by weight of composite flame retardant, and 5-20 parts by weight of modified aluminum hydroxide.

[0023] Preferably, the curing agent includes but is not limited to one of dicyandiamide and phenolic resin; the curing accelerator includes but is not limited to one of imidazoles and tertiary amines; the solvent includes but is not limited to one of acetone, dimethylformamide, ethylene glycol methyl ether, and toluene.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present application uses nitrogen-containing intumescent flame retardant instead of traditional flame retardant, uses polyvinyl alcohol with multiple hydroxyl groups as carbon source, which can be quickly deprived of water by dehydrating agent to form carbon layer when combustion occurs; sodium p-aminobenzenesulfonate as acid source, which can decompose to produce acid during combustion, then esterification with carbon source to dehydrate; melamine will release non-toxic gas after heating, so that the carbon layer has a good foam structure, which can isolate air and heat conduction, protect the polymer matrix, and achieve the purpose of flame retardation. However, the compatibility of intumescent flame retardant with resin is poor, which can affect the impact resistance of copper-clad plate after use, on the other hand, the intumescent flame retardant is easy to seep out in the resin system, which affects the long-term storage stability of the copper-clad plate.

[0026] Mesoporous silica can be used as an adsorbent material due to its unique hexagonal structure. By synthesizing vinyl mesoporous silica and then alcoholysis with vinyl acetate copolymerization, polyvinyl alcohol modified mesoporous silica can be obtained. By using aldehyde as a reaction reagent to connect it with acid source and gas source, the intumescent flame retardant can be fixed on the mesoporous silica, limiting its flow, which can improve the long-term stability of the copper-clad plate. On the other hand, silica as a commonly used copper-clad plate filler can improve the thermal stability, mechanical properties and dielectric properties of the copper-clad plate.

[0027] In addition, the composite flame retardant is used in combination with modified aluminum hydroxide, which can improve the overall flame retardancy of the copper-clad plate, and on the other hand, a proper amount of aluminum hydroxide can also improve the overall impact resistance of the copper-clad plate. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] The following examples contain the following raw materials: hydrochloric acid (CAS No.: 7647-01-0), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic P123) (CAS No: 9003-11-6), tetraethoxysilane (CAS No.: 78-10-4), vinyltriethoxysilane (CAS No.: 78-08-0), vinyl acetate (CAS No.: 108-05-4), azobisisobutyronitrile (CAS No.: 78-67-1), methanol (CAS No.: 67-56-1), sodium hydroxide (CAS No.: 1310-73-2), sodium p-aminobenzenesulfonate (CAS No.: 15898-43-8), melamine (CAS No.: 108-78-1), formaldehyde (CAS No.: 50-00-0), aluminum hydroxide (CAS No.: 21645-51-2), gamma-(2,3-epoxypropoxy)propyltrimethoxysilane (CAS No.: 2530-83-8), absolute ethanol (CAS No.: 64-17-5), bisphenol A type epoxy resin (CAS No.: 25085-99-8), dicyandiamide (CAS No.: 461-58-5), 2-ethyl-4-methylimidazole (CAS No.: 931-36-2), acetone (CAS No.: 67-64-1), silicon dioxide (CAS No.: 7631-86-9).

[0030] Example 1: S1: 250 parts of hydrochloric acid was dissolved in 4000 parts of deionized water to obtain a hydrochloric acid solution, 65 parts of Pluronic P123 was dissolved in the hydrochloric acid solution, 105 parts of tetraethoxysilane was added while stirring, after 2h of reaction, 95 parts of vinyltriethoxysilane was added while stirring, after 2h of reaction, the temperature was raised to 80°C, and it was left to stand for 24h, after filtration, it was extracted with ethanol by Soxhlet extraction for 24h, and finally it was dried at 80°C for 12h to obtain vinyl mesoporous silica;

[0031] S2: 50 parts of vinyl mesoporous silica, 180 parts of vinyl acetate, 0.5 parts of azobisisobutyronitrile, 80 parts of methanol were mixed uniformly, and stirred at 65°C to react, when the reactants became viscous, an appropriate amount of methanol was added for dilution, after cooling, the product was dried and crushed to obtain polyvinyl acetate modified mesoporous silica; 30 parts of polyvinyl acetate modified mesoporous silica, 4 parts of sodium hydroxide, 100 parts of methanol were mixed uniformly, and continuously stirred at 45°C, after the reaction was completed, it was filtered and dried to obtain polyvinyl alcohol modified mesoporous silica;

[0032] S3: (1) 4 parts of sodium p-aminobenzenesulfonate, 2 parts of melamine, 1 part of formaldehyde were mixed uniformly, heated to 50°C, continuously stirred, 2 hours after reaction, 2 parts of polyvinyl alcohol modified mesoporous silica was added, continuously stirred at 50°C, 24 hours after reaction, a composite flame retardant was obtained; (2) 20 parts of aluminum hydroxide, 1 part of γ-(2, 3-epoxypropoxy) propyl trimethoxysilane, 1 part of anhydrous ethanol were added into a ball mill, taken out after ball milling for 3 hours, without drying, modified aluminum hydroxide was obtained;

[0033] S4: 100 parts of bisphenol A type epoxy resin were heated to 50°C, 10 parts of dicyandiamide, 5 parts of 2-ethyl-4-methylimidazole, 60 parts of acetone, 50 parts of composite flame retardant, 5 parts of modified aluminum hydroxide were added, stirred for 5 min, a pre-impregnation solution was obtained; glass fiber cloth was immersed in the pre-impregnation solution for 15 minutes, cured at 80°C for 15 minutes, a prepreg was obtained;

[0034] S5: a single layer of prepreg was covered with copper foil on both sides, hot pressed in a press at 15Mpa, 200°C for 4h, after holding for 2h, a halogen-free flame retardant epoxy resin copper clad plate was obtained.

[0035] Example 2: S1: 250 parts of hydrochloric acid was dissolved in 4000 parts of deionized water to obtain a hydrochloric acid solution, 65 parts of Pluronic P123 was dissolved in the hydrochloric acid solution, 105 parts of tetraethoxysilane was added while stirring, reacted for 2h, 95 parts of vinyl triethoxysilane was added while stirring, reacted for 2h, heated to 80°C, stood for 24h, filtered, Soxhlet extracted with ethanol for 24h, finally dried at 80°C for 12h, to obtain vinyl mesoporous silica;

[0036] S2: 50 parts of vinyl mesoporous silica, 180 parts of vinyl acetate, 0.5 parts of azobis isobutyronitrile, 80 parts of methanol were mixed uniformly, stirred and reacted at 65°C, when the reactants became viscous, appropriate amount of methanol was added for dilution, after cooling, the product was dried and crushed, to obtain polyvinyl acetate modified mesoporous silica; 30 parts of polyvinyl acetate modified mesoporous silica, 4 parts of sodium hydroxide, 100 parts of methanol were mixed uniformly, continuously stirred at 45°C, after reaction was completed, filtered, dried to obtain polyvinyl alcohol modified mesoporous silica;

[0037] S3: (1) 5 parts of sodium p-aminobenzenesulfonate, 3 parts of melamine, 1.2 parts of formaldehyde were mixed uniformly, heated to 50°C, continuously stirred, 2 hours after reaction, 3 parts of polyvinyl alcohol modified mesoporous silica was added, continuously stirred at 50°C, 24 hours after reaction, a composite flame retardant was obtained; (2) 20 parts of aluminum hydroxide, 1 part of γ-(2, 3-epoxypropoxy) propyl trimethoxysilane, 1 part of anhydrous ethanol were added into a ball mill, taken out after ball milling for 3 hours, without drying, modified aluminum hydroxide was obtained;

[0038] S4: 120 parts of bisphenol A type epoxy resin was heated to 50℃, 12 parts of dicyandiamide, 6 parts of 2-ethyl-4-methyl imidazole, 65 parts of dimethyl formamide, 30 parts of composite flame retardant, 15 parts of modified aluminum hydroxide were added, stirred for 5 min, and a pre-impregnation solution was obtained; the glass fiber cloth was immersed in the pre-impregnation solution for 15 min, and cured at 80℃ for 15 min to obtain a prepreg;

[0039] S5: The three-layer prepreg was laminated with copper foil on both sides, and hot-pressed in a press at 15Mpa, 200℃ for 4h, and then cooled for 2h to obtain a halogen-free flame-retardant epoxy resin copper clad plate.

[0040] Example 3: S1: 250 parts of hydrochloric acid was dissolved in 4000 parts of deionized water to obtain a hydrochloric acid solution, 65 parts of Pluronic P123 was dissolved in the hydrochloric acid solution, 105 parts of tetraethoxysilane was added while stirring, reacted for 2h, 95 parts of vinyl triethoxysilane was added while stirring, reacted for 2h, and then the temperature was raised to 80℃, and then the mixture was left to stand for 24h. After filtration, ethanol was used for Soxhlet extraction for 24h, and finally dried at 80℃ for 12h to obtain a vinyl mesoporous silica;

[0041] S2: 50 parts of vinyl mesoporous silica, 180 parts of vinyl acetate, 0.5 parts of azobisisobutyronitrile, and 80 parts of methanol were mixed uniformly, and stirred at 65℃. When the reactants became viscous, appropriate amount of methanol was added for dilution. After cooling, the product was dried and crushed to obtain a polyvinyl acetate modified mesoporous silica. 30 parts of polyvinyl acetate modified mesoporous silica, 4 parts of sodium hydroxide, and 100 parts of methanol were mixed uniformly, and continuously stirred at 45℃. After the reaction was completed, the mixture was filtered and dried to obtain a polyvinyl alcohol modified mesoporous silica;

[0042] S3: (1) 3 parts of sodium p-aminobenzenesulfonate, 3 parts of melamine, and 1.5 parts of formaldehyde were mixed uniformly, and the temperature was raised to 50℃. After stirring for 2h, 3 parts of polyvinyl alcohol modified mesoporous silica was added, and the mixture was continuously stirred at 50℃ for 24h to obtain a composite flame retardant; (2) 20 parts of aluminum hydroxide, 1 part of γ-(2,3-epoxypropoxy) propyl trimethoxysilane, and 1 part of anhydrous ethanol were added into a ball mill, and the mixture was ball milled for 3h. Without drying, a modified aluminum hydroxide was obtained;

[0043] S4: 100 parts of bisphenol A type epoxy resin was heated to 50℃, 10 parts of dicyandiamide, 5 parts of 2-ethyl-4-methyl imidazole, 60 parts of acetone, 20 parts of composite flame retardant, and 20 parts of modified aluminum hydroxide were added, and stirred for 5 min to obtain a pre-impregnation solution. The glass fiber cloth was immersed in the pre-impregnation solution for 15 min, and cured at 80℃ for 15 min to obtain a prepreg;

[0044] S5: The five layers of prepreg were laminated and double coated with copper foil, and a halogen-free flame-retardant epoxy resin copper clad plate was obtained by hot pressing in a press at 15 MPa and 200°C for 4h and holding for 2h.

[0045] Comparative Example 1: As a control, the modified aluminum hydroxide was removed from Example 1, and the rest of the process remained unchanged.

[0046] Comparative Example 2: S1: (1) 4 parts of sodium p-aminobenzenesulfonate, 2 parts of melamine, and 1 part of formaldehyde were mixed uniformly, heated to 50°C, and continuously stirred for 2h. Then 2 parts of polyvinyl alcohol were added, and the mixture was continuously stirred at 50°C for 24h to obtain an intumescent flame retardant. (2) 20 parts of aluminum hydroxide, 20 parts of silicon dioxide, 2 parts of γ-(2,3-epoxypropoxy) propyl trimethoxysilane, and 2 parts of anhydrous ethanol were added to a ball mill, and the mixture was ball milled for 3h. The modified inorganic filler was obtained without drying.

[0047] S2: 100 parts of bisphenol A type epoxy resin were heated to 50°C, and 10 parts of dicyandiamide, 5 parts of 2-ethyl-4-methylimidazole, 60 parts of acetone, 50 parts of intumescent flame retardant, and 15 parts of modified inorganic filler were added. The mixture was stirred for 5min to obtain a pre-impregnation solution. Glass fiber cloth was immersed in the pre-impregnation solution for 15min and cured at 80°C for 15min to obtain a prepreg.

[0048] S3: A single layer of prepreg was double coated with copper foil on the front and back, and a halogen-free flame-retardant epoxy resin copper clad plate was obtained by hot pressing in a press at 15 MPa and 200°C for 4h and holding for 2h.

[0049] Comparative Example 3: S1: Deionized water was heated to 70°C, and then 20 parts of polyvinyl alcohol were added while stirring. The temperature was maintained at 70-90°C until the polyvinyl alcohol was completely dissolved. Then 50 parts of mesoporous silica were added to the solution, and the mixture was stirred at 70°C for 3h. The polyvinyl alcohol modified mesoporous silica was obtained by filtration and freeze-drying.

[0050] S2: (1) 4 parts of sodium p-aminobenzenesulfonate, 2 parts of melamine, and 1 part of formaldehyde were mixed uniformly, heated to 50°C, and continuously stirred for 2h. Then 2 parts of polyvinyl alcohol modified mesoporous silica were added, and the mixture was continuously stirred at 50°C for 24h to obtain a composite flame retardant. (2) 20 parts of aluminum hydroxide, 1 part of γ-(2,3-epoxypropoxy) propyl trimethoxysilane, and 1 part of anhydrous ethanol were added to a ball mill, and the mixture was ball milled for 3h. The modified aluminum hydroxide was obtained without drying.

[0051] S3: 100 parts of bisphenol A type epoxy resin was heated to 50℃, 10 parts of dicyandiamide, 5 parts of 2-ethyl-4-methylimidazole, 60 parts of acetone, 50 parts of composite flame retardant, 5 parts of modified aluminum hydroxide were added, and stirred for 5 min to obtain a pre-impregnation solution; the glass fiber cloth was immersed in the pre-impregnation solution for 15 min, and cured at 80℃ for 15 min to obtain a prepreg;

[0052] S4: The single-layer prepreg was covered with copper foil on the front and back, and hot-pressed in a press at 15Mpa, 200℃ for 4h, and after holding for 2h, a halogen-free flame-retardant epoxy resin copper-clad plate was obtained.

[0053] Test Experiment 1: The prepregs prepared in Examples 1-3 and Comparative Examples 1-3 were cut into samples of 80x10x2.5mm, and their impact resistance was tested according to standard ASTM D256-2010; their limiting oxygen index was detected according to standard ASTM D2863-2008, and the data are shown in Table 1.

[0054] impact strength / (KJ / m 2 )]]> Oxygen index / % Example 1 6.41 34.4 Example 2 6.39 33.8 Example 3 6.43 33.7 Comparative Example 1 5.87 29.4 Comparative Example 2 6.19 31.5 Comparative Example 3 6.37 32.8

[0055] Table 1

[0056] Test Experiment 2: The prepregs prepared in Example 1 and Comparative Examples 2 and 3 were stored in a dry environment avoiding direct sunlight for 12 months, and after taking out, the surface was observed for moisture, and their limiting oxygen index was detected according to standard ASTM D2863-2008, and the test data are shown in Table 2.

[0057] Surface wet or not Oxygen index / % Oxygen index decrease rate Example 1 No 34.1 0.87％ Comparative Example 2 Yes 23.8 24.4％ Comparative Example 3 Yes 27.3 16.8％

[0058] Table 2

[0059] Conclusion: By comparing the results of Examples 1-3, it can be seen that as the mass fraction of the composite flame retardant decreases and the mass fraction of the modified aluminum hydroxide increases, the oxygen index gradually decreases and the flame retardancy gradually decreases, but the difference in impact strength performance is small, therefore, the performance of Example 1 is the best. By comparing Example 1 with Comparative Example 1, it can be found that the use of a simple composite flame retardant not only cannot guarantee the impact performance, but also has poorer flame retardancy than the modified aluminum hydroxide flame retardant, because aluminum hydroxide has the effect of promoting charring and can act as a synergist for intumescent flame retardants. By analyzing the data of Example 1 and Comparative Example 2 in Tables 1 and 2, it can be seen that it is feasible in the short term to directly add an intumescent flame retardant to the resin and ensure its flame retardancy and mechanical properties by adding inorganic fillers, but as the storage time increases, the intumescent flame retardant not loaded by mesoporous silica in Comparative Example 3 has a leakage phenomenon, at which time the performance gap in flame retardancy between the product of Example 1 is large; by analyzing the results of Example 1 and Comparative Example 3, it can be seen that the composite flame retardant prepared by directly using polyvinyl alcohol modified mesoporous silica has a large gap in flame retardancy with Example 1 after long-term storage, because the present application first copolymerizes mesoporous silica and vinyl acetate to introduce polyvinyl acetate on the surface of mesoporous silica, and then alcoholysis is performed to obtain polyvinyl alcohol modified mesoporous silica, the polyvinyl alcohol and mesoporous silica are connected by chemical bonds, while in Comparative Example 3, the polyvinyl alcohol and mesoporous silica are directly mixed and freeze-dried, the two are connected only by hydrogen bonds, therefore, Example 1 can better reduce the migration of the composite flame retardant and ensure its stable performance after long-term storage.

[0060] Finally, it should be noted that: the above only describes the preferred embodiments of the present application and is not intended to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a halogen-free flame-retardant epoxy resin copper-clad laminate, characterized in that: The method comprises the following steps: S1: preparing vinyl mesoporous silica by co-condensation of silane mixed precursors under acidic conditions; S2: obtaining polyvinyl acetate modified mesoporous silica by copolymerization, and then preparing polyvinyl alcohol modified mesoporous silica by alcoholysis reaction; S3: (1) preparing a composite flame retardant by connecting polyvinyl alcohol modified mesoporous silica as a carbon source with an acid source and a gas source after mixing, using aldehyde as a reaction reagent; (2) treating aluminum hydroxide with a silane coupling agent to obtain modified aluminum hydroxide; S4: mixing bisphenol A type epoxy resin, a curing agent, a curing accelerator, a solvent, the composite flame retardant and the modified aluminum hydroxide, stirring uniformly to obtain a pre-impregnation solution, dipping glass fiber cloth in the pre-impregnation solution for 5-20 minutes, and curing at 60-90°C for 10-30 minutes to obtain a prepreg; S5: laminating the prepreg in one or more layers, covering both sides of the prepreg with copper foil, and pressing at 5-30 MPa and 120-200°C for 3-6 hours and keeping warm for 1-3 hours to obtain a halogen-free flame-retardant epoxy resin copper-clad plate; In S1, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) is dissolved in a hydrochloric acid solution, tetraethoxysilane is added while stirring, the reaction is carried out for 1-3 hours, vinyl triethoxysilane is added while stirring, the reaction is carried out for 1-3 hours, the temperature is raised to 60-100°C, the mixture is left to stand for 18-24 hours, filtration is carried out, ethanol is used for Soxhlet extraction for 18-24 hours, and finally drying is carried out at 60-100°C for 8-16 hours to obtain the vinyl mesoporous silica. In S2, the vinyl mesoporous silica, vinyl acetate, azobisisobutyronitrile and methanol are mixed uniformly, stirring reaction is carried out at 50-80°C, when the reaction mixture becomes viscous, an appropriate amount of methanol is added for dilution, the product is dried and pulverized after cooling to obtain polyvinyl acetate modified mesoporous silica; the polyvinyl acetate modified mesoporous silica, sodium hydroxide and methanol are mixed uniformly, continuous stirring is carried out at 30-60°C, filtration is carried out after the reaction is completed, and drying is carried out to obtain polyvinyl alcohol modified mesoporous silica. The polyvinyl acetate modified mesoporous silica comprises the following components in the following amounts: 30-80 parts of vinyl mesoporous silica, 100-300 parts of vinyl acetate, 0.1-1 part of azobisisobutyronitrile and 60-90 parts of methanol; the polyvinyl alcohol modified mesoporous silica comprises the following components in the following amounts: 20-50 parts of polyvinyl acetate modified mesoporous silica, 2-6 parts of sodium hydroxide and 100-150 parts of methanol.

2. The preparation method of the halogen-free flame-retardant epoxy resin CCL according to claim 1, characterized in that: The vinyl mesoporous silica comprises the following components in the following amounts: 50-80 parts of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 90-120 parts of tetraethoxysilane, 80-100 parts of vinyl triethoxysilane, 200-300 parts of hydrochloric acid and 3000-4000 parts of deionized water.

3. The method for preparing a halogen-free flame-retardant epoxy resin CCL according to claim 1, characterized in that: In S3, the preparation process of the composite flame retardant is as follows: uniformly mixing the acid source, the gas source and the aldehyde, heating to 40-60 DEG C, continuously stirring, adding the polyvinyl alcohol modified mesoporous silica after 1-3 hours of reaction, continuously stirring at 40-60 DEG C, and obtaining the composite flame retardant after 12-24 hours of reaction.

4. The method for preparing a halogen-free flame-retardant epoxy resin CCL according to claim 3, characterized in that: The mass fraction of each raw material of the composite flame retardant is as follows: 1-3 parts of polyvinyl alcohol modified mesoporous silica, 3-8 parts of the acid source, 1-3 parts of the gas source, and 0.1-2 parts of the aldehyde; the acid source includes one of a thiol containing amino group and a benzene sulfonate containing amino group; and the gas source includes one of melamine and a melamine derivative.

5. The method of claim 1, wherein the method further comprises: adding 0.5-2 wt% of the halogen-free flame retardant to the epoxy resin to form a mixture; and adding 0.5-2 wt% of the inorganic filler to the mixture to form the halogen-free flame retardant epoxy resin copper clad plate. The mass fraction of each raw material of the pre-impregnation solution is as follows: 80-120 parts of bisphenol A type epoxy resin, 5-15 parts of a curing agent, 2-8 parts of a curing accelerator, 40-80 parts of a solvent, 20-50 parts of the composite flame retardant, and 5-20 parts of modified aluminum hydroxide.

6. A halogen-free flame-retardant epoxy resin copper-clad plate prepared by the preparation method of the halogen-free flame-retardant epoxy resin copper-clad plate according to any one of claims 1-5.