An epoxy resin-based flame-retardant circuit board and its preparation method

Abstract

This invention relates to the field of epoxy resin-based circuit boards, and discloses an epoxy resin-based flame-retardant circuit board and its preparation method. The invention introduces 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide into an intermediate prepared from 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde, successfully introducing a flame retardant component into the epoxy resin monomer. This improves the flame retardant properties of the epoxy resin while maintaining its excellent mechanical properties. The dense charred layer formed by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide effectively reduces heat transfer between the ignition zone and the epoxy resin, while also reducing the release of toxic gases. Synergistically with 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde, it further restricts the diffusion of pyrolysis products into the air.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin-based circuit boards, specifically to an epoxy resin-based flame-retardant circuit board and its preparation method. Background Technology

[0002] Epoxy resins (EP), as well-known multifunctional thermosetting polymers, possess many advantageous properties, including chemical and corrosion resistance, excellent mechanical properties, and superior electrical properties. These properties make them ideal for a wide range of applications, including aerospace, metal coatings, molding compounds, automotive, and microelectronics materials.

[0003] However, a significant drawback of epoxy resin is its high flammability; its poor heat resistance and flammability limit its application in fields such as printed circuit boards (PCBs). Since PCBs generate heat during use, the epoxy resin substrate used to fabricate them must possess high thermal stability and flame-retardant properties.

[0004] There are generally two common methods to improve the flame retardant properties of materials: one is to add flame retardants to the polymer matrix, and the other is to introduce halogenated elements into the polymer molecular structure. Traditional flame retardants, including ATH, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), always contain halogenated elements that are harmful to the atmosphere and may produce toxic gases after combustion. In 2004 and 2008, the European Union banned the use of PBDEs due to several potential hazards. The addition of flame retardants can lead to a decrease in the mechanical properties of epoxy resins; introducing halogenated elements into the molecular structure can avoid a decline in the overall thermosetting properties after curing. Flame retardancy can be improved by synergistic use of nitrogen and phosphorus elements, while simultaneously increasing high-temperature char residue and maintaining mechanical properties.

[0005] Therefore, inventing an epoxy resin-based flame-retardant circuit board is of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide an epoxy resin-based flame-retardant circuit board and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] A method for preparing an epoxy resin-based flame-retardant circuit board includes the following steps:

[0009] S1: Mix the epoxy monomer and curing agent evenly, pour into a mold, remove air bubbles, heat and cure to obtain flame-retardant epoxy resin;

[0010] S2: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0011] Furthermore, in step S1, the epoxy monomer is prepared according to the following method:

[0012] 3,5-Diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde were added to anhydrous ethanol and mixed evenly. The mixture was refluxed at 50-70°C for 1-2 hours, rotary evaporated, allowed to stand for 24 hours, washed three times with deionized water and ethanol, and dried under vacuum at 50°C for 24 hours to obtain a light yellow intermediate.

[0013] The light yellow intermediate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to anhydrous ethanol, heated to 70-75°C and stirred for 24 hours, cooled to room temperature, filtered, washed three times with acetone, anhydrous diethyl ether and ethanol, and dried under vacuum at 60°C to obtain a solid.

[0014] The solid, epichlorohydrin and tetrabutylammonium bromide were mixed evenly and refluxed at 80-85℃ for 12 h. The reaction temperature was then lowered to 60℃, and 40% sodium hydroxide solution was added. The mixture was reacted at 60℃ for 6 h, washed, and rotary evaporated to obtain the epoxy resin monomer.

[0015] Furthermore, the mass ratio of 3,5-diamino-1,2,4-triazole to 3,5-diethyl-4-hydroxybenzaldehyde is 1:(3-3.2).

[0016] Furthermore, the mass ratio of 3,5-diethyl-4-hydroxybenzaldehyde to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1.4-1.5).

[0017] Furthermore, the mass ratio of the solid to epichlorohydrin is 1:(4.8-5.2).

[0018] Furthermore, the curing agent is 4,4'-diaminodiphenylmethane, and the mass ratio of epoxy monomer to curing agent is 5:1.

[0019] Furthermore, in step S1, the heating and curing temperature is 180-200℃, and the time is 1-2 hours.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention introduces 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide into the intermediate prepared from 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde, and successfully introduces the flame retardant component into the epoxy resin monomer. This can effectively avoid the problem of reduced flame retardant performance and mechanical properties caused by uneven mixing of flame retardant, curing agent and epoxy resin in the traditional flame retardant epoxy resin preparation process.

[0021] The introduction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide leads to steric hindrance of the phosphaphenanthrene group, which is detrimental to the curing reaction and reduces the crosslinking density of the epoxy resin, resulting in a decrease in the glass transition temperature. The presence of diethyl groups in the intermediate prepared by 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde can effectively increase the crosslinking density of the epoxy resin. The ethyl groups carried on both sides of 3,5-diethyl-4-hydroxybenzaldehyde can crosslink and interpenetrate during the curing process, forming a tight structure and enhancing the curing reaction.

[0022] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide releases phosphorus-containing substances under thermal degradation, causing esterification and dehydration of the epoxy resin matrix, thereby producing a carbonized layer. The dense structure of the carbonized layer can serve as a potential heat insulation layer, effectively reducing heat transfer between the fire zone and the epoxy resin, while also reducing the release of toxic gases.

[0023] The epoxy resin prepared by combining 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide with 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde exhibits synergistic effects of its Schiff base structure and triazole ring, resulting in the release of fewer volatile products during thermal decomposition, thus reducing further combustion and fuel supply in the ignition zone. Simultaneously, the high carbonization capacity of the Schiff base structure and triazole ring, in synergy with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, further enhances the smoke suppression effect of the epoxy resin. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the following examples, 3,5-diamino-1,2,4-triazole, 3,5-diethyl-4-hydroxybenzaldehyde, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 4,4'-diaminodiphenylmethane, epichlorohydrin, tetrabutylammonium bromide, sodium hydroxide, and ethanol were provided by Aladdin Reagents (Shanghai) Co., Ltd.

[0026] Example 1

[0027] S1: 20g of 3,5-diamino-1,2,4-triazole and 60g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0028] S2: Add the light yellow intermediate and 84g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250mL of anhydrous ethanol, heat to 70℃ and stir for 24h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and vacuum dry at 60℃ to obtain a solid.

[0029] S3: Mix 20g solid, 96g epichlorohydrin and 2g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 12g 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0030] S4: Mix 50g of epoxy monomer and 10g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0031] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0032] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0033] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0034] The test results are shown in the table below.

[0035] Example 2

[0036] S1: 20g of 3,5-diamino-1,2,4-triazole and 62g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0037] S2: Add the light yellow intermediate and 86.8 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250 mL of anhydrous ethanol, heat to 70 °C and stir for 24 h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and dry under vacuum at 60 °C to obtain a solid.

[0038] S3: Mix 20g solid, 100g epichlorohydrin and 2.2g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0039] S4: Mix 50g of epoxy monomer and 10g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0040] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0041] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0042] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0043] The test results are shown in the table below.

[0044] Example 3

[0045] S1: 20g of 3,5-diamino-1,2,4-triazole and 64g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0046] S2: Add the light yellow intermediate and 96g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250mL of anhydrous ethanol, heat to 70℃ and stir for 24h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and vacuum dry at 60℃ to obtain a solid.

[0047] S3: Mix 20g solid, 104g epichlorohydrin and 2.4g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0048] S4: Mix 50g of epoxy monomer and 10g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0049] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0050] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0051] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0052] The test results are shown in the table below.

[0053] Example 4

[0054] S1: 20g of 3,5-diamino-1,2,4-triazole and 64g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0055] S2: Add the light yellow intermediate and 96g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250mL of anhydrous ethanol, heat to 70℃ and stir for 24h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and vacuum dry at 60℃ to obtain a solid.

[0056] S3: Mix 20g solid, 104g epichlorohydrin and 2.4g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0057] S4: Mix 50g of epoxy monomer and 15g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0058] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0059] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0060] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0061] The test results are shown in the table below.

[0062] Example 5

[0063] S1: 20g of 3,5-diamino-1,2,4-triazole and 64g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0064] S2: Add the light yellow intermediate and 96g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250mL of anhydrous ethanol, heat to 70℃ and stir for 24h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and vacuum dry at 60℃ to obtain a solid.

[0065] S3: Mix 20g solid, 104g epichlorohydrin and 2.4g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0066] S4: Mix 50g of epoxy monomer and 20g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0067] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0068] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0069] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0070] The test results are shown in the table below.

[0071] Comparative Example 1

[0072] S1: Mix 50g of bisphenol A type epoxy resin and 10g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h, heat to 180℃ for 2h, and cure at 200℃ for 1h to obtain flame-retardant epoxy resin;

[0073] S2: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0074] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0075] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0076] The test results are shown in the table below.

[0077] Comparative Example 2

[0078] S4: Mix 50g of bisphenol A type epoxy resin, 10g of 4,4'-diaminodiphenylmethane and 1g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0079] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0080] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0081] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0082] The test results are shown in the table below.

[0083] Comparative Example 3

[0084] S1: 20g of 3,5-diamino-1,2,4-triazole and 60g of 3,5-diethyl-4-hydroxybenzaldehyde were added to 250mL of anhydrous ethanol and mixed evenly. The mixture was refluxed at 50℃ for 1h, rotary evaporated, allowed to stand for 24h, washed three times with deionized water and ethanol, and vacuum dried at 50℃ for 24h to obtain a light yellow intermediate.

[0085] S3: Mix 20g of light yellow intermediate, 96g of epichlorohydrin and 2g of tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 12g of 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0086] S4: Mix 50g of epoxy monomer, 10g of 4,4'-diaminodiphenylmethane and 1g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0087] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0088] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0089] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0090] The test results are shown in the table below.

[0091] Comparative Example 4

[0092] S1: Add 20g of 3,5-diamino-1,2,4-triazole and 60g of 4-hydroxybenzaldehyde to 250mL of anhydrous ethanol and mix well. Reflux at 50℃ for 1h, rotary evaporate, stand for 24h, wash three times with deionized water and ethanol, and vacuum dry at 50℃ for 24h to obtain a light yellow intermediate.

[0093] S2: Add the light yellow intermediate and 84g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to 250mL of anhydrous ethanol, heat to 70℃ and stir for 24h, cool to room temperature, filter, wash three times with acetone, anhydrous diethyl ether and ethanol, and vacuum dry at 60℃ to obtain a solid.

[0094] S3: Mix 20g solid, 96g epichlorohydrin and 2g tetrabutylammonium bromide evenly, reflux at 80℃ for 12h, lower the reaction temperature to 60℃, add 12g 40% sodium hydroxide solution, react at 60℃ for 6h, wash, and rotary evaporate to obtain epoxy resin monomer.

[0095] S4: Mix 50g of epoxy monomer and 10g of 4,4'-diaminodiphenylmethane at 120℃ until homogeneous, pour into a mold, and remove air bubbles at 60℃ for 12h, 70℃ for 12h, 80℃ for 12h, 90℃ for 12h, 100℃ for 2h, 120℃ for 2h, and 150℃ for 2h. Then heat to 180℃ for 2h and cure at 200℃ for 1h to obtain flame-retardant epoxy resin.

[0096] S5: Flame-retardant epoxy resin is processed into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board.

[0097] Test: Flame retardancy: The sample was cut into pieces with dimensions of 125mm × 13mm × 3mm and tested in a UL-94 vertical combustion chamber according to ASTM D3801-10.

[0098] Limiting oxygen index: The sample was cut into pieces with dimensions of 100mm × 6.5mm × 3mm and tested on an HC-2LOI instrument according to ASTM D2863-97.

[0099]

[0100]

[0101] Conclusion: Examples 1-5 show that when the amount of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide increases, the amount of curing agent added also increases, which can effectively improve the LOI. The reason is that the steric hindrance effect of the phosphaphenanthrene group of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is not conducive to the curing reaction and will reduce the crosslinking density of epoxy resin. Increasing the amount of curing agent can increase the crosslinking density and thus have stronger flame retardant properties during combustion.

[0102] Comparative Examples 1-3 show that by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide instead of introducing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide into the intermediate prepared from 3,5-diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde, the resulting epoxy resin exhibits poor flame retardant properties.

[0103] In Comparative Example 4, the use of 4-hydroxybenzaldehyde instead of 3,5-diethyl-4-hydroxybenzaldehyde reduced the crosslinking density during the curing process of the epoxy resin, resulting in a decrease in flame retardant properties.

[0104] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention 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 substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an epoxy resin-based flame-retardant circuit board, characterized in that: The following steps are involved: S1: Mix the epoxy monomer and curing agent evenly, pour into a mold, remove air bubbles, heat and cure to obtain flame-retardant epoxy resin; S2: Flame-retardant epoxy resin is made into copper-clad laminate using a PCB manufacturing machine. After grinding the copper-clad laminate, circuit printing, etching, ink removal, and solder resist printing are performed to obtain an epoxy resin-based flame-retardant circuit board. In step S1, the epoxy monomer is prepared according to the following method: 3,5-Diamino-1,2,4-triazole and 3,5-diethyl-4-hydroxybenzaldehyde were added to anhydrous ethanol and mixed thoroughly. The mixture was refluxed, rotary evaporated, allowed to stand, washed, and dried to obtain a light yellow intermediate. The pale yellow intermediate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added to anhydrous ethanol, heated and stirred, cooled, filtered, washed, and dried to obtain a solid. The solid, epichlorohydrin and tetrabutylammonium bromide were mixed evenly, refluxed, washed and rotary evaporated to obtain epoxy resin monomer.

2. The method for preparing an epoxy resin-based flame-retardant circuit board according to claim 1, characterized in that: The mass ratio of 3,5-diamino-1,2,4-triazole to 3,5-diethyl-4-hydroxybenzaldehyde is 1:(3-3.2).

3. The method for preparing an epoxy resin-based flame-retardant circuit board according to claim 1, characterized in that: The mass ratio of 3,5-diethyl-4-hydroxybenzaldehyde to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(1.4-1.5).

4. The method for preparing an epoxy resin-based flame-retardant circuit board according to claim 1, characterized in that: The mass ratio of solids to epichlorohydrin is 1:(4.8-5.2).

5. The method for preparing an epoxy resin-based flame-retardant circuit board according to claim 1, characterized in that: The curing agent is 4,4'-diaminodiphenylmethane, and the mass ratio of epoxy monomer to curing agent is 5:(1-2).

6. The method for preparing an epoxy resin-based flame-retardant circuit board according to claim 1, characterized in that: In step S1, the heating and curing temperature is 180-200℃, and the time is 1-2 hours.

7. The epoxy resin-based flame-retardant circuit board prepared by the method of preparing an epoxy resin-based flame-retardant circuit board according to any one of claims 1-6.

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