Preparation method of phosphorus-containing flame-retardant halogen-free copper clad laminate

Abstract

The present invention relates to the technical field of copper clad laminate preparation and discloses a method for preparing a phosphorus-containing flame-retardant halogen-free copper clad laminate. The method comprises the following steps: uniformly mixing bisphenol A epoxy resin, linear phenolic resin, phosphorus-containing tetraglycidyl ester, etc., applying the mixture to an E-glass fiber cloth, and baking the mixture to obtain a prepreg. Eight prepregs are then stacked, copper foil is applied on both sides, and hot pressing is performed to obtain a phosphorus-containing flame-retardant halogen-free copper clad laminate. The method uses bisphenol A epoxy resin as a main resin, linear phenolic resin as a curing agent, and phosphorus-containing tetraglycidyl ester to the mixture. The flame retardant elements and heat-resistant structure contained in the phosphorus-containing tetraglycidyl ester are utilized to improve the flame retardant properties, heat resistance properties, and mechanical properties of the copper clad laminate material.

Description

Technical Field

[0001] The invention relates to the technical field of copper clad laminate preparation, in particular to a method for preparing a phosphorus-containing flame-retardant halogen-free copper clad laminate. Background Art

[0002] Printed circuit boards (PCBs) are currently an essential component for interconnecting circuits in most electronic products. Copper-clad laminates (CCLs), the substrate material for PCBs, provide electrical conductivity, insulation, and support. Copper-clad laminates are made by impregnating reinforcing materials such as paper and glass cloth with resin, coating one or both sides with copper foil, and then heat-pressing them. However, their flame retardancy does not meet the current requirements for PCBs. Traditional CCLs are manufactured using brominated epoxy resins. However, the combustion of brominated epoxy resins produces large amounts of toxic fumes, causing irreparable damage to the environment and human health. Consequently, the trend in CCL development in recent years has been to reduce the use of bromine-containing materials and to achieve halogen-free production.

[0003] For example, the Chinese patent application number is CN 108146035 A, which discloses a flame-retardant and heat-resistant copper-clad laminate. The copper-clad laminate prepared by this invention has good flame-retardant and heat-resistant properties, but does not improve the mechanical properties of the copper-clad laminate material. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing a phosphorus-containing flame-retardant halogen-free copper clad laminate. The prepared copper clad laminate has good flame retardancy, heat resistance and mechanical properties.

[0006] (2) Technical solution

[0007] A method for preparing a phosphorus-containing flame-retardant halogen-free copper clad laminate, the method comprising the following steps:

[0008] Bisphenol A epoxy resin, linear phenolic resin, and phosphorus-containing tetraglycidyl ester are added to an acetone solvent, stirred and mixed evenly, and then a 2-methylimidazole accelerator is added thereto, stirred and mixed evenly to obtain a glue solution; the glue solution is applied on an E-glass fiber cloth, baked in an oven at 170-180°C for 5-8 minutes, and cooled to room temperature to obtain a semi-cured sheet; 8 semi-cured sheets are stacked, copper foil is applied on both sides, and placed in a vacuum laminator for hot pressing to obtain a phosphorus-containing flame-retardant halogen-free copper clad laminate. In the process of preparing the glue solution, linear phenolic resin is used as a curing agent and bisphenol A epoxy resin is used as a main resin. The epoxy groups contained in the phosphorus-containing tetraglycidyl ester and the epoxy groups contained in the epoxy resin are cured and cross-linked with the linear phenolic resin to form a three-dimensional network structure. Due to the large number of epoxy groups, a larger cross-linking density is generated. This high-density cross-linked network structure can effectively improve the heat resistance and mechanical properties of the material.

[0009] Preferably, the mass ratio of bisphenol A epoxy resin, linear phenolic resin, phosphorus-containing tetraglycidyl ester, and accelerator is 100:30-40:10-20:0.4-0.6.

[0010] Preferably, the preparation method of phosphorus-containing tetraglycidyl ester comprises the following steps:

[0011] Step (1): adding p-formylbenzoic acid to ethanol, stirring and dispersing, then adding an ethanol solution of diethylenetriamine thereto, heating to 60-70°C, reacting for 2-5h, washing with n-hexane after the reaction, filtering, and drying. The obtained product is recorded as target product I, wherein the molar ratio of p-formylbenzoic acid to diethylenetriamine is 2-2.2:1. In this reaction, p-formylbenzoic acid and diethylenetriamine are used as raw materials, and Schiff base reaction is performed to obtain target product I, that is, Schiff base structure and benzene ring structure are introduced into target product I. When heated, the Schiff base structure can absorb heat, open the ring and cross-link to form a network structure, so it has good heat resistance. The benzene ring is a rigid structure and also has good heat resistance. The reaction synthesis route is:

[0012] ;

[0013] Step (2): adding allyl chloride and target product I to ethanol, stirring and mixing uniformly, then adding sodium bicarbonate thereto, controlling the temperature to 50-60°C, reacting for 12-16 hours, washing with deionized water, removing the solvent by rotary evaporation, and drying. The obtained product is recorded as target product II, wherein the molar ratio of allyl chloride, target product I, and sodium bicarbonate is 1:1.5-2:0.8-1.2. In this reaction, allyl chloride and target product I are used as raw materials, and the target product II is obtained through substitution reaction. The reaction synthesis route is:

[0014] ;

[0015] Step (3), under nitrogen atmosphere, add SPDPC-H to N,N-dimethylformamide, heat to 60-70 ° C, stir to dissolve, then add target product II thereto, stir to react for 24-30 hours, after the reaction is completed, wash with dichloromethane, dry, and the obtained product is recorded as target product III, wherein the molar ratio of SPDPC-H to target product II is 1:2.2-2.5. In this reaction, the C=C in target product II reacts with the PH bond in SPDPC-H to obtain target product III. Through the addition reaction, phosphorus-containing structure, nitrogen-containing structure and carbon-containing skeleton are introduced into target product III. When burned, The carbon-containing skeleton can form a protective layer of coke to inhibit further combustion of the matrix; when the phosphorus-containing structure is heated, the PO bond breaks, and phosphoric acid substances are produced during the combustion process to promote the system to degrade into carbon in advance, forming a stable carbon layer, and forming a glass-like substance on the surface of the carbonized material. This layer of structure can effectively inhibit the diffusion of combustible gases produced during the combustion process into the combustion area, isolate oxygen and heat, and thus improve the flame retardant properties of the material; the nitrogen-containing structure decomposes at high temperature to absorb heat and reduce the surface temperature of the material. At the same time, the non-combustible gases such as NH3 and N2 produced by decomposition dilute the air and oxygen concentration, playing a synergistic flame retardant role. The reaction synthesis route is as follows:

[0016] ;

[0017] Step (4), adding the target product III and epichlorohydrin into a flask, stirring and dispersing, heating to 100-110°C, adding tetrabutylammonium bromide thereto, and reacting at a constant temperature for 4-6h. After the reaction is completed, cooling to 60-65°C, adding a 50% by mass sodium hydroxide aqueous solution thereto, and reacting at a constant temperature for 3-5h. After the reaction is completed, washing with saturated sodium chloride, and drying to obtain phosphorus-containing tetraglycidyl ester, wherein the molar ratio of the target product III to epichlorohydrin is 1:8-10, and the amount of tetrabutylammonium bromide is 2-4% of the mass of the target product III. In this reaction, under the action of tetrabutylammonium bromide, the carboxylate of the target product III acts as a nucleophilic reagent to attack the epoxy group in the epichlorohydrin, and a ring-opening esterification reaction occurs. Then, sodium hydroxide is added for a ring-closing reaction to obtain phosphorus-containing tetraglycidyl ester, that is, a tetraepoxy group is introduced into the phosphorus-containing tetraglycidyl ester. The reaction route is:

[0018] ;

[0019] (3) Beneficial technical effects

[0020] The present invention prepares a phosphorus-containing tetraglycidyl ester and uses it as a raw material in combination with an epoxy resin to prepare a phosphorus-containing flame-retardant halogen-free copper-clad laminate. Firstly, the flame-retardant elements contained in the phosphorus-containing tetraglycidyl ester are utilized to improve the flame retardancy of the copper-clad laminate. Secondly, the heat-resistant structures (Schiff base structure, benzene ring structure, and spiro ring structure) contained in the phosphorus-containing tetraglycidyl ester are utilized to improve the heat resistance of the copper-clad laminate. Furthermore, the high-density cross-linked network structure generated by the phosphorus-containing tetraglycidyl ester during curing is utilized to improve the heat resistance and mechanical properties of the copper-clad laminate. This is because the phosphorus-containing tetraglycidyl ester contains a large number of epoxy groups, which can form a high cross-linking density with the curing agent. This results in a high cross-linking density and enhanced thermal stability in the cured product. Furthermore, this high cross-linking density creates larger cross-linking sites. When the material is subjected to external forces, the cross-linking sites can be dispersed to other chains, thereby improving the mechanical properties. In addition, the copper-clad laminate material prepared by the present invention contains a relatively large number of ester groups, ether bonds and other polar structures, which can generate a strong force with the copper foil, effectively improve the adhesion, and further improve the peel strength. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below through specific examples.

[0022] Preparation method of 2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide (SPDPC-H): 0.4 mol of formic acid is added to 0.2 mol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide (SPDPC) at room temperature. Nitrogen is added for protection during the reaction. The reaction is carried out for 2 hours. After the reaction is completed, the mixture is washed with ether and deionized water in sequence and dried to obtain SPDPC-H. The reaction synthesis route is as follows:

[0023] .

[0024] Example 1

[0025] (1) Add 0.2 mol of p-formylbenzoic acid to ethanol, stir and disperse, then add 0.1 mol of diethylenetriamine in ethanol solution, heat to 65 °C, and react for 4 h. After the reaction is completed, wash with n-hexane, filter, and dry. The obtained product is recorded as target product I.

[0026] (2) Add 50 mmol of allyl chloride and 80 mmol of target product I to ethanol, stir and mix evenly, then add 50 mmol of sodium bicarbonate, control the temperature to 55 °C, and react for 15 h. After the reaction is completed, wash with deionized water, evaporate to remove the solvent, and dry. The obtained product is recorded as target product II.

[0027] (3) Under nitrogen atmosphere, 20 mmol of SPDPC-H was added to N,N-dimethylformamide, heated to 65 °C, stirred and dissolved, and then 50 mmol of target product II was added thereto. The mixture was stirred and reacted for 26 h. After the reaction was completed, the mixture was washed with dichloromethane and dried. The obtained product was recorded as target product III.

[0028] (4) 20 mmol of target product III and 180 mmol of epichlorohydrin were added to a flask, stirred and dispersed, and heated to 105°C. 0.6 g of tetrabutylammonium bromide was added thereto, and the temperature was kept constant for 6 h. After the reaction, the temperature was lowered to 60°C, and a 50% by mass sodium hydroxide aqueous solution was added thereto. The temperature was kept constant for 5 h. After the reaction, the mixture was washed with saturated sodium chloride and dried to obtain phosphorus-containing tetraglycidyl ester.

[0029] (5) Add 100g of bisphenol A epoxy resin, 30g of linear phenolic resin, and 10g of phosphorus-containing tetraglycidyl ester to acetone solvent, stir and mix evenly, then add 0.5g of 2-methylimidazole accelerator, stir and mix evenly to obtain glue; apply the glue on E-glass fiber cloth, bake in an oven at 170℃ for 6min, cool to room temperature to obtain a semi-cured sheet; take 8 semi-cured sheets, overlap them, apply copper foil on both sides, put them into a vacuum laminator, and hot press them at 190℃ and 2.5MPa for 100min to obtain a phosphorus-containing flame-retardant halogen-free copper clad laminate.

[0030] Example 2

[0031] (1) Add 0.22 mol of p-formylbenzoic acid to ethanol, stir and disperse, then add 0.1 mol of diethylenetriamine in ethanol solution, heat to 60 °C, and react for 5 h. After the reaction is completed, wash with n-hexane, filter, and dry. The obtained product is recorded as target product I.

[0032] (2) Add 50 mmol of allyl chloride and 100 mmol of target product I to ethanol, stir and mix evenly, then add 60 mmol of sodium bicarbonate, control the temperature to 50 ° C, and react for 16 hours. After the reaction is completed, wash with deionized water, evaporate to remove the solvent, and dry. The obtained product is recorded as target product II.

[0033] (3) Under nitrogen atmosphere, 20 mmol of SPDPC-H was added to N,N-dimethylformamide, heated to 65 °C, stirred and dissolved, and then 45 mmol of target product II was added thereto. The mixture was stirred and reacted for 30 h. After the reaction was completed, the mixture was washed with dichloromethane and dried. The obtained product was recorded as target product III.

[0034] (4) 20 mmol of target product III and 190 mmol of epichlorohydrin were added to a flask, stirred and dispersed, and heated to 105°C. 0.6 g of tetrabutylammonium bromide was added thereto, and the temperature was kept constant for 4 hours. After the reaction was completed, the temperature was lowered to 60°C, and a 50% by mass sodium hydroxide aqueous solution was added thereto. The temperature was kept constant for 4 hours. After the reaction was completed, the mixture was washed with saturated sodium chloride and dried to obtain phosphorus-containing tetraglycidyl ester.

[0035] (5) Add 100 g of bisphenol A epoxy resin, 32 g of linear phenolic resin, and 14 g of phosphorus-containing tetraglycidyl ester to acetone solvent, stir and mix evenly, then add 0.4 g of 2-methylimidazole accelerator, stir and mix evenly to obtain glue; apply the glue on E-glass fiber cloth, bake in an oven at 175 ° C for 6 minutes, cool to room temperature, and obtain a semi-cured sheet; take 8 semi-cured sheets, overlap them, apply copper foil on both sides, put them into a vacuum laminator, and hot press them at 190 ° C and 2.5 MPa for 100 minutes to obtain a phosphorus-containing flame retardant halogen-free copper clad laminate.

[0036] Example 3

[0037] (1) Add 0.2 mol of p-formylbenzoic acid to ethanol, stir and disperse, then add 0.1 mol of diethylenetriamine in ethanol solution, heat to 70°C, and react for 2 h. After the reaction is completed, wash with n-hexane, filter, and dry. The obtained product is recorded as target product I.

[0038] (2) Add 50 mmol of allyl chloride and 75 mmol of target product I to ethanol, stir and mix evenly, then add 50 mmol of sodium bicarbonate, control the temperature to 55 °C, and react for 14 h. After the reaction is completed, wash with deionized water, evaporate to remove the solvent, and dry. The obtained product is recorded as target product II.

[0039] (3) Under nitrogen atmosphere, 20 mmol of SPDPC-H was added to N,N-dimethylformamide, heated to 70 °C, stirred and dissolved, and then 44 mmol of target product II was added thereto. The mixture was stirred and reacted for 25 h. After the reaction was completed, the mixture was washed with dichloromethane and dried. The obtained product was recorded as target product III.

[0040] (4) 20 mmol of target product III and 160 mmol of epichlorohydrin were added to a flask, stirred and dispersed, and heated to 110°C. 0.4 g of tetrabutylammonium bromide was added thereto, and the temperature was kept constant for 6 h. After the reaction was completed, the temperature was lowered to 65°C, and a 50% by mass sodium hydroxide aqueous solution was added thereto. The temperature was kept constant for 3 h. After the reaction was completed, the mixture was washed with saturated sodium chloride and dried to obtain phosphorus-containing tetraglycidyl ester.

[0041] (5) Add 100 g of bisphenol A epoxy resin, 36 g of linear phenolic resin, and 18 g of phosphorus-containing tetraglycidyl ester to acetone solvent, stir and mix evenly, then add 0.6 g of 2-methylimidazole accelerator, stir and mix evenly to obtain glue; apply the glue on E-glass fiber cloth, bake in an oven at 170 ° C for 8 minutes, cool to room temperature, and obtain a semi-cured sheet; take 8 semi-cured sheets, overlap them, apply copper foil on both sides, put them into a vacuum laminator, and hot press them at 190 ° C and 2.5 MPa for 100 minutes to obtain a phosphorus-containing flame retardant halogen-free copper clad laminate.

[0042] Example 4

[0043] (1) Add 0.22 mol of p-formylbenzoic acid to ethanol, stir and disperse, then add 0.1 mol of diethylenetriamine in ethanol solution, heat to 70 °C, and react for 3 h. After the reaction is completed, wash with n-hexane, filter, and dry. The obtained product is recorded as target product I.

[0044] (2) Add 50 mmol of allyl chloride and 80 mmol of target product I to ethanol, stir and mix evenly, then add 40 mmol of sodium bicarbonate, control the temperature to 60 ° C, and react for 12 hours. After the reaction is completed, wash with deionized water, evaporate to remove the solvent, and dry. The obtained product is recorded as target product II.

[0045] (3) Under nitrogen atmosphere, 20 mmol of SPDPC-H was added to N,N-dimethylformamide, heated to 60 °C, stirred and dissolved, and then 50 mmol of target product II was added thereto. The mixture was stirred and reacted for 24 h. After the reaction was completed, the mixture was washed with dichloromethane and dried. The obtained product was recorded as target product III.

[0046] (4) 20 mmol of target product III and 200 mmol of epichlorohydrin were added to a flask, stirred and dispersed, and heated to 100 °C. 0.8 g of tetrabutylammonium bromide was added thereto, and the temperature was kept constant for 4 h. After the reaction was completed, the temperature was lowered to 60 °C, and a 50% by mass sodium hydroxide aqueous solution was added thereto. The temperature was kept constant for 5 h. After the reaction was completed, the mixture was washed with saturated sodium chloride and dried to obtain phosphorus-containing tetraglycidyl ester.

[0047] (5) Add 100 g of bisphenol A epoxy resin, 40 g of linear phenolic resin, and 20 g of phosphorus-containing tetraglycidyl ester to acetone solvent, stir and mix evenly, then add 0.4 g of 2-methylimidazole accelerator, stir and mix evenly to obtain glue; apply the glue on E-glass fiber cloth, bake in an oven at 180 ° C for 5 minutes, cool to room temperature, and obtain a semi-cured sheet; take 8 semi-cured sheets, overlap them, apply copper foil on both sides, put them into a vacuum laminator, and hot press them at 190 ° C and 2.5 MPa for 100 minutes to obtain a phosphorus-containing flame retardant halogen-free copper clad laminate.

[0048] Comparative Example 1

[0049] The preparation method of the copper clad laminate provided in this comparative example is substantially the same as that of Example 1, with the main difference being that phosphorus-containing tetraglycidyl ester is not contained in step (5).

[0050] Flame retardancy test: Use a horizontal-vertical burning tester to test the flame retardancy of the copper clad laminate;

[0051] Heat resistance limit test: Determine heat resistance according to IPC-TM-650-2.4.13.1 method.

[0052] Table 1: Flame retardant and heat resistance test results of Examples 1-4 and Comparative Example 1

[0053]

[0054] As can be seen from the table, the flame retardancy and heat resistance of Examples 1-4 are superior to those of Comparative Example 1. The difference between the two is that Comparative Example 1 does not contain phosphorus-containing tetraglycidyl ester. This is because the phosphorus-containing tetraglycidyl ester prepared by the present invention is added to the copper-clad laminate. On the one hand, the flame retardancy of the copper-clad laminate is improved by utilizing the flame retardant elements contained in the phosphorus-containing tetraglycidyl ester. On the other hand, the rigid structure and Schiff base structure contained in the phosphorus-containing tetraglycidyl ester are used to improve the heat resistance of the material. In addition, during the curing process, due to the presence of tetraepoxy structures, a large number of high-density cross-linked structures are generated. The high cross-linking density structure can also improve the heat resistance of the material. Therefore, the flame retardancy and heat resistance of Comparative Example 1, which does not contain phosphorus-containing tetraglycidyl ester, are inferior to those of Examples 1-4.

[0055] Bending performance test: Use a universal testing machine to test the bending performance of the copper clad laminate;

[0056] Peeling performance test: Peel the copper foil at one end of the sample 10mm away from the substrate. Place the sample on the sample holder of the peeling machine and clamp the peeled copper foil with the sample clamp. The copper foil is perpendicular to the substrate. Start the peeling machine and apply a uniform tensile force. The direction of the tensile force should be perpendicular to the direction of the substrate. Record the minimum value during the peeling process when the length is not less than 25mm. The minimum load required per unit width is the peeling strength.

[0057] Table 2: Mechanical properties test results of Examples 1-4 and Comparative Example 1

[0058]

[0059] As can be seen from the table, the bending strength and peel strength of Examples 1-4 are better than those of Comparative Example 1. In Examples 1-4 in which phosphorus-containing tetraglycidyl ester is added, since phosphorus-containing tetraglycidyl ester contains more polar structures that can generate force with copper foil, the peel strength of the copper clad laminate can be effectively improved; and Examples 1-4 in which phosphorus-containing tetraglycidyl ester is added also produce a three-dimensional cross-linked network during the curing process. The three-dimensional cross-linked network structure can improve the bending strength of the material.

[0060] Therefore, the copper clad laminate prepared by the present invention has good heat resistance, flame retardancy and mechanical properties.

[0061] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a phosphorus-containing flame-retardant halogen-free copper-clad laminate, characterized in that: The preparation method comprises the following steps: Add bisphenol A epoxy resin, linear phenolic resin, and phosphorus-containing tetraglycidyl ester to acetone solvent, stir and mix evenly, then add 2-methylimidazole accelerator and stir and mix evenly to obtain glue; apply the glue on E-glass fiber cloth, bake in an oven at 170-180°C for 5-8 minutes, and cool to room temperature to obtain a prepreg; take 8 prepregs, stack them, apply copper foil on both sides, put them in a vacuum laminator, and perform hot pressing to obtain a phosphorus-containing flame-retardant halogen-free copper clad laminate; The preparation method of the phosphorus-containing tetraglycidyl ester comprises the following steps: Step (1): add p-formylbenzoic acid to ethanol, stir and disperse, then add diethylenetriamine ethanol solution thereto, heat to 60-70°C, react for 2-5h, after the reaction is completed, wash with n-hexane, filter and dry, the obtained product is recorded as target product I, and its structural formula is: ； Step (2): add allyl chloride and target product I to ethanol, stir and mix evenly, then add sodium bicarbonate, control the temperature to 50-60°C, react for 12-16 hours, and after the reaction is completed, wash with deionized water, remove the solvent by rotary evaporation, and dry. The obtained product is recorded as target product II, and its structural formula is: ； Step (3), under nitrogen atmosphere, add SPDPC-H to N,N-dimethylformamide, heat to 60-70°C, stir to dissolve, then add target product II, stir to react for 24-30h, after the reaction is completed, wash with dichloromethane, dry, and the obtained product is recorded as target product III, its structural formula is: ， The structural formula of SPDPC-H is: ； Step (4): add the target product III and epichlorohydrin into a flask, stir and disperse, heat to 100-110°C, add tetrabutylammonium bromide, and react at a constant temperature for 4-6 hours. After the reaction is completed, cool to 60-65°C, add a 50% by mass sodium hydroxide aqueous solution, and heat for 3-5 hours. After the reaction is completed, wash with saturated sodium chloride, and dry. The obtained product is recorded as phosphorus-containing tetraglycidyl ester, and its structural formula is: 。 2. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: The mass ratio of bisphenol A epoxy resin, linear phenolic resin, phosphorus-containing tetraglycidyl ester and accelerator is 100:30-40:10-20:0.4-0.

6.

3. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: In step (1), the molar ratio of p-formylbenzoic acid to diethylenetriamine is 2-2.2:

1.

4. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: In step (2), the molar ratio of allyl chloride, target product I, and sodium bicarbonate is 1:1.5-2:0.8-1.

2.

5. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: In step (3), the molar ratio of SPDPC-H to target product II is 1:2.2-2.

5.

6. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: In step (4), the molar ratio of target product III to epichlorohydrin is 1:8-10.

7. The method for preparing the phosphorus-containing flame-retardant halogen-free copper clad laminate according to claim 1, characterized in that: In step (4), the amount of tetrabutylammonium bromide used is 2-4% of the mass of the target product III.

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