Preparation method and application of halogen-free flame-retardant low-consumption copper-clad plate

Abstract

The application discloses a preparation method of halogen-free flame-retardant low-consumption copper-clad plate and application thereof and belongs to the technical field of copper-clad plate preparation. Modified boehmite is prepared by coating boehmite with silica and grafting silane coupling agent through a sol-gel method, long-chain alkyl modified benzoxazine resin is prepared by condensation reaction of polyformaldehyde after depolymerization, cashew phenol and 4,4'-diamino diphenyl methane, a glue solution is prepared by mixing the two with diphenyl type epoxy resin, a curing agent, a flame retardant and silicon powder, and the copper-clad plate is prepared by laminating after impregnation and drying to obtain a prepreg. Through the synergistic effect of the modified boehmite and the long-chain alkyl modified benzoxazine resin, a reactive interface compatibility and a low-polarity hydrophobic effect are formed in the resin matrix, the dielectric stability and the halogen-free flame-retardant reliability of the copper-clad plate in a high-temperature and high-humidity environment are improved, and the use requirement of a signal integrity of a high-level driving auxiliary system vehicle-mounted electronic control unit is met.

Description

Technical Field

[0001] This invention belongs to the field of copper clad laminate preparation technology, specifically a method for preparing halogen-free flame-retardant low-consumption copper clad laminate and its application. Background Technology

[0002] With the development of automotive intelligence, advanced driver assistance systems (ADAS) place stringent demands on the accuracy of in-vehicle environmental perception and the reliability of signal transmission. As a core sensor in ADAS, millimeter-wave radar's high-frequency signal transmission integrity and phase stability on printed circuit boards (PCBs) are highly dependent on the performance of the copper-clad laminate (CCL) substrate. Furthermore, high-frequency signals exhibit significant thermal effects during transmission, posing stringent requirements on the heat resistance and fire safety of automotive CCL substrates. To meet the high safety standards of automotive electronics, halogen-free flame-retardant CCLs have become the mainstream choice in the industry.

[0003] However, to achieve both flame retardancy and dimensional stability, halogen-free flame-retardant copper clad laminates typically require the addition of inorganic fillers to reduce the curing shrinkage of the resin matrix, improve rigidity, and construct a framework. In the prior art, Chinese patent application CN111718678A discloses a resin adhesive for copper clad laminates, copper clad laminates, and their preparation method. Epoxy resin, curing agent, accelerator, and phosphorus-based flame retardant are dissolved in an organic solvent, and aluminum hydroxide, talc powder, and soft composite silica powder are added as inorganic fillers for physical blending. By combining the phosphorus-based flame retardant with the inorganic fillers, the copper clad laminate achieves both flame retardancy and good thermal reliability.

[0004] However, the aluminum hydroxide filler used in the above-mentioned existing technical solutions has insufficient thermal stability and is prone to thermal decomposition under the conditions of copper clad laminate lamination and curing temperature. This leads to irreversible defects such as micropores at the resin-filler interface. During vehicle service, these micropores will introduce ambient moisture into the material. The adsorbed water molecules have extremely high dielectric constants and loss factors, which will generate significant polarization losses under the action of high-frequency electric fields. This will affect the dielectric stability of the copper clad laminate at high frequencies, cause phase distortion of the high-frequency signal of millimeter-wave radar, and thus threaten the perception accuracy of assisted driving. It is difficult to meet the stringent requirements of advanced driver assistance systems for signal transmission reliability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing halogen-free flame-retardant low-consumption copper-clad laminate and its application. By introducing modified boehmite as a reactive interface modifier filler and synergistically with long-chain alkyl-modified benzoxazine resin into an epoxy resin matrix, the surface reactivity of modified boehmite is utilized to participate in resin curing and cross-linking to improve interface density. In addition, the low polarity and hydrophobic effect of long-chain alkyl-modified benzoxazine resin reduces dielectric loss and moisture absorption, slowing down dielectric performance drift under long-term automotive conditions. At the same time, the combination of phosphorus-based flame retardant and the aluminum-containing component of modified boehmite forms multiple flame-retardant protections, enabling the copper-clad laminate to maintain stable dielectric performance under long-term high temperature and high humidity conditions, meeting the requirements of advanced driver assistance system printed circuit boards for signal transmission integrity and halogen-free flame-retardant reliability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate, comprising the following steps:

[0008] Step 1: Place epoxy resin, styrene-maleic anhydride copolymer, bismaleimide, 2-ethyl-4-methylimidazole, long-chain alkyl-modified benzoxazine resin, butanone, and cyclohexanone in a mixing tank and stir at 200-400 r / min for 2-3 h at 30-40℃. Then add silica powder, phosphorus flame retardant, modified boehmite, antioxidant, defoamer, and dispersant. Disperse the mixture at 2000-3000 r / min for 1-2 h at 25-35℃. Finally, grind the mixture in a sand mill to obtain the resin solution for copper-clad laminates.

[0009] The component contents of the resin adhesive for copper clad laminates mentioned above, by weight, are as follows:

[0010] The composition includes: 80-100 parts epoxy resin, 10-20 parts styrene-maleic anhydride copolymer, 5-15 parts bismaleimide, 0.05-0.15 parts 2-ethyl-4-methylimidazolium, 10-20 parts long-chain alkyl-modified benzoxazine resin, 50-60 parts butanone, 40-50 parts cyclohexanone, 40-60 parts silica powder, 10-30 parts phosphorus flame retardant, 10-20 parts modified boehmite, 0.5-1.0 parts antioxidant, 0.3-0.5 parts defoamer, and 0.5-1.0 parts dispersant.

[0011] The aforementioned phosphorus-based flame retardant is SPB-100; the antioxidant is any one of antioxidant 1010, antioxidant 168, and antioxidant 245; the defoamer is any one of BYK-051, BYK-055, and TEGO Airex 900; and the dispersant is any one of BYK-110, BYK-180, and BYK-9076.

[0012] Furthermore, the specific preparation process of the long-chain alkyl-modified benzoxazine resin is as follows:

[0013] 4,4'-Diaminodiphenylmethane, cashew phenol, and toluene were placed in a reactor equipped with a condenser and a water separator. Under nitrogen protection, the mixture was heated to 75-85°C and stirred for 20-30 minutes. Then, an aqueous formaldehyde solution was slowly added, and the mixture was heated to 85-90°C and reacted for 6-8 hours. The mixture was then cooled to room temperature, distilled under reduced pressure, and dried under vacuum to constant weight to obtain a long-chain alkyl-modified benzoxazine resin.

[0014] The mass ratio of 4,4'-diaminodiphenylmethane, cashew phenol, and toluene is 1:2.8-3.2:5-7; the molar ratio of formaldehyde and 4,4'-diaminodiphenylmethane in the formaldehyde aqueous solution is 4-4.5:1.

[0015] Furthermore, the specific preparation process of formaldehyde aqueous solution is as follows:

[0016] Paraformaldehyde and deionized water are mixed at a mass ratio of 1:5-8. The pH value is adjusted to 8.0-8.5 by adding 0.1mol / L NaOH solution dropwise. The mixture is stirred at 200-300 r / min for 30-40 min at 50-60℃ until completely dissolved. After cooling to room temperature, an aqueous formaldehyde solution is obtained.

[0017] Furthermore, the specific preparation process of modified boehmite is as follows:

[0018] Silica-coated boehmite, anhydrous ethanol, and deionized water were placed in a reaction vessel and ultrasonically dispersed for 20-30 min. The pH of the reaction solution was adjusted to 4.5-5.0 with 1 mol / L acetic acid. γ-glycidoxypropyltrimethoxysilane was added, and the reaction was carried out at 60-70℃ for 2-3 h. After centrifugation and washing, the mixture was vacuum dried to constant weight to obtain modified boehmite.

[0019] The ratio of silica-coated boehmite, anhydrous ethanol, deionized water, and γ-glycidyl etheroxypropyltrimethoxysilane used is 60-100g: 800-1200mL: 80-150mL: 2-5g.

[0020] Furthermore, the specific preparation process of silica-coated boehmite is as follows:

[0021] Boehmite was placed in anhydrous ethanol and deionized water in a reaction vessel and ultrasonically dispersed for 20-30 min. Tetraethyl orthosilicate was slowly added and stirred at 40-45℃ for 20-30 min. Ammonia solution with a concentration of 0.5 mol / L was added to adjust the pH of the reaction solution to 8.5-9.0. The reaction was continued for 4-6 h. After centrifugation and washing, the solution was vacuum dried to constant weight to obtain silica-coated boehmite.

[0022] The ratio of boehmite, anhydrous ethanol, deionized water and tetraethyl orthosilicate used above is 80-120g: 800-1000mL: 150-250mL: 8-14g.

[0023] Step 2: Pass the electronic-grade glass fiber cloth through the impregnation tank containing the resin solution for copper-clad laminate at a traction speed of 1-2 m / min. Then, squeeze out the excess resin solution by the extrusion roller. Then, send the resin-impregnated glass fiber cloth into the drying tunnel and dry it at 160-170℃ for 5-7 minutes. Then, raise the temperature to 170-180℃ and dry it for 8-10 minutes. Finally, roll it up to obtain a semi-cured sheet.

[0024] The thickness of the prepreg is 0.15 mm.

[0025] Step 3: Stack the prepreg sheets to form a slab. Cover the top and bottom surfaces of the slab with an electrolytic copper foil and align them. Place it in a vacuum hot press, evacuate to -0.098 MPa, and heat to 140-160℃ at 2℃ / min, at 30-40 kg / cm². 2 Hot-press under pressure for 10-20 minutes, then increase the temperature to 190-210℃ at a rate of 2℃ / min, at a pressure of 35-45 kg / cm³. 2 The copper-clad laminate is hot-pressed under pressure for 60-80 minutes, then cooled to 40-50℃ at a rate of 1℃ / min to release the pressure and remove the laminate, thus obtaining a halogen-free flame-retardant low-consumption copper-clad laminate.

[0026] The thickness of the aforementioned halogen-free flame-retardant low-consumption copper-clad laminate is 2.0 mm.

[0027] This invention also provides an application of halogen-free flame-retardant low-consumption copper-clad laminate in printed circuit boards for automotive driver assistance systems.

[0028] The beneficial effects of this invention are:

[0029] 1. The halogen-free flame-retardant low-consumption copper-clad laminate prepared by this invention uses epoxy resin as the matrix resin and silica powder as the main filler. Modified boehmite and long-chain alkyl-modified benzoxazine resin are introduced to participate in the curing and cross-linking of the main resin, constructing a halogen-free flame-retardant system and improving the interfacial bonding quality and system uniformity. Modified boehmite exhibits good thermal stability at the lamination temperature, helping to suppress the generation of interfacial micropores caused by the thermal decomposition of fillers and maintaining the structural stability of the resin matrix. Its lamellar morphology complements the spherical silica powder in terms of particle size and morphology, which is beneficial for increasing the packing density of inorganic fillers in the resin matrix and reducing the hygroscopic tendency of the resin-rich areas. Long-chain alkyl-modified benzoxazine resin, as a reactive resin additive, introduces low-polarity side chains into the resin matrix, improving the moisture resistance of the resin matrix. The combined effect of these two components maintains the dielectric stability of the copper-clad laminate under high temperature and high humidity environments, providing a stable foundation for high-frequency signal transmission in advanced driver assistance systems (ADAS) printed circuit boards.

[0030] 2. The halogen-free flame-retardant low-consumption copper-clad laminate prepared by this invention utilizes the gas-phase flame-retardant effect provided by phosphorus-based flame retardants, the nitrogen source charring effect provided by long-chain alkyl-modified benzoxazine resin, and the thermal barrier effect of modified boehmite as a halogen-free aluminum source at high temperatures to form multiple flame-retardant protections. Boehmite is halogen-free, which avoids the contamination of the substrate and copper foil circuitry by corrosive gases generated from the decomposition of halogen-based flame retardants. Simultaneously, the reactive interfacial compatibility of modified boehmite and the long-chain hydrophobic effect of long-chain alkyl-modified benzoxazine work together to improve the interfacial density between the functional filler, the main filler, and the resin matrix, inhibiting water vapor penetration. This helps maintain stable dielectric properties while achieving halogen-free flame retardancy, reducing the risk of phase distortion in high-frequency signals of automotive radar, and providing support for the signal transmission integrity and perception reliability of printed circuit boards in advanced driver assistance systems. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: This example provides a modified boehmite for a halogen-free flame-retardant, low-consumption copper-clad laminate, prepared through the following steps:

[0033] S1: Place 80g boehmite, 800mL anhydrous ethanol and 150mL deionized water in a reaction vessel and sonicate at 200W for 20min. Slowly add 8g tetraethyl orthosilicate and stir at 200r / min at 40℃ for 20min. Add 0.5mol / L ammonia solution to adjust the pH of the reaction solution to 8.5 and continue the reaction for 4h. After the reaction is completed, cool to room temperature and centrifuge at 6000r / min to remove the supernatant. Add anhydrous ethanol and centrifuge twice to wash. Collect the solid and vacuum dry at 60℃ to constant weight to obtain silica-coated boehmite.

[0034] This step employs the sol-gel method, using boehmite as the core. Tetraethyl orthosilicate is hydrolyzed under alkaline conditions to generate silanol groups. The silanol groups undergo dehydration condensation with Al-OH on the surface of boehmite to form Al-O-Si bonds. Simultaneously, the silanol groups self-condense to form a Si-O-Si network, depositing a silica coating layer on the surface of boehmite to obtain silica-coated boehmite.

[0035] S2: 60g of silica-coated boehmite, 800mL of anhydrous ethanol and 80mL of deionized water were placed in a reaction vessel and ultrasonically dispersed at 200W for 20min. The pH of the reaction solution was adjusted to 4.5 with 1mol / L acetic acid. 2g of γ-glycidoxypropyltrimethoxysilane was added and reacted at 200r / min at 60℃ for 2h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 6000r / min to remove the supernatant. The mixture was washed twice by centrifugation with deionized water and anhydrous ethanol, and the solid was collected and vacuum dried at 60℃ to constant weight to obtain modified boehmite.

[0036] This step utilizes γ-glycidoxypropyltrimethoxysilane to chemically modify the surface of silica-coated boehmite. Under weakly acidic conditions, the silane hydrolyzes to generate silanol groups, which dehydrate and condense with Si-OH on the surface of the silica coating to form Si-O-Si bonds. Epoxy groups are then grafted onto the surface of the boehmite to obtain modified boehmite.

[0037] Example 2: This example provides a modified boehmite for a halogen-free flame-retardant, low-consumption copper-clad laminate, prepared through the following steps:

[0038] S1: Place 100g boehmite, 900mL anhydrous ethanol and 200mL deionized water in a reaction vessel and sonicate at 250W for 25min. Slowly add 11g tetraethyl orthosilicate and stir at 250r / min at 42℃ for 25min. Add 0.5mol / L ammonia solution to adjust the pH of the reaction solution to 8.8 and continue the reaction for 5h. After the reaction is completed, cool to room temperature and centrifuge at 7000r / min to remove the supernatant. Add anhydrous ethanol and centrifuge and wash 3 times. Collect the solid and vacuum dry at 70℃ to constant weight to obtain silica-coated boehmite.

[0039] S2: 80g of silica-coated boehmite, 1000mL of anhydrous ethanol and 120mL of deionized water were placed in a reaction vessel and ultrasonically dispersed at 250W for 25min. The pH of the reaction solution was adjusted to 4.8 with 1mol / L acetic acid. 3.5g of γ-glycidoxypropyltrimethoxysilane was added and reacted at 65℃ and 250r / min for 2.5h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 7000r / min to remove the supernatant. The mixture was washed three times by centrifugation with deionized water and anhydrous ethanol, and the solid was collected and vacuum dried at 70℃ to constant weight to obtain modified boehmite.

[0040] Example 3: This example provides a modified boehmite for a halogen-free flame-retardant, low-consumption copper-clad laminate, prepared through the following steps:

[0041] S1: Place 120g boehmite, 1000mL anhydrous ethanol and 250mL deionized water in a reaction vessel and sonicate at 300W for 30min. Slowly add 14g tetraethyl orthosilicate and stir at 300r / min at 45℃ for 30min. Add 0.5mol / L ammonia solution to adjust the pH of the reaction solution to 9.0 and continue the reaction for 6h. After the reaction is completed, cool to room temperature and centrifuge at 8000r / min to remove the supernatant. Add anhydrous ethanol and centrifuge and wash 4 times. Collect the solid and vacuum dry at 80℃ to constant weight to obtain silica-coated boehmite.

[0042] S2: 100g of silica-coated boehmite, 1200mL of anhydrous ethanol and 150mL of deionized water were placed in a reaction vessel and ultrasonically dispersed at 300W for 30min. The pH of the reaction solution was adjusted to 5.0 with 1mol / L acetic acid. 5g of γ-glycidoxypropyltrimethoxysilane was added and reacted at 70℃ and 300r / min for 3h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000r / min to remove the supernatant. The mixture was washed four times by centrifugation with deionized water and anhydrous ethanol, and the solid was collected and vacuum dried at 80℃ to constant weight to obtain modified boehmite.

[0043] Example 4: This example provides a method for preparing a halogen-free flame-retardant low-loss copper-clad laminate, including the following steps:

[0044] Step 1: Mix paraformaldehyde and deionized water at a mass ratio of 1:5. Adjust the pH to 8.0 by adding 0.1 mol / L NaOH solution. Stir at 200 r / min for 30 min at 50℃ until completely dissolved. Cool to room temperature to obtain an aqueous formaldehyde solution. Place 4,4'-diaminodiphenylmethane, cashew phenol, and toluene at a mass ratio of 1:2.8:5 in a reactor equipped with a condenser and a water separator. Purge with nitrogen and heat to 75℃. Stir at 200 r / min for 20 min. Then slowly add the aqueous formaldehyde solution, controlling the molar ratio of formaldehyde to 4,4'-diaminodiphenylmethane to be 4:1. Heat to 85℃ and stir at 200 r / min for 6 h. Stop the reaction when no more water is generated in the water separator. Cool to room temperature and distill the reaction solution under reduced pressure at 60℃ until no solvent is distilled off. Then vacuum dry at 60℃ to constant weight to obtain long-chain alkyl-modified benzoxazine resin.

[0045] This step uses paraformaldehyde as the formaldehyde source, which is depolymerized by heating an alkaline aqueous solution to form an aqueous formaldehyde solution. This solution is then reacted with cashew phenol and 4,4'-diaminodiphenylmethane via a Mannich condensation reaction to synthesize a bifunctional benzoxazine resin. In the reaction, formaldehyde condenses with the amino group of 4,4'-diaminodiphenylmethane and the phenolic hydroxyl group of cashew phenol to form a benzoxazine ring. The diamino group of DDM imparts a bifunctional structure to the resin, and the unsaturated long chain of cashew phenol is introduced into the resin side chain, resulting in a long-chain alkyl-modified benzoxazine resin.

[0046] Step 2: By weight, 80 parts epoxy resin, 10 parts styrene-maleic anhydride copolymer (curing agent), 5 parts bismaleimide, 0.05 parts 2-ethyl-4-methylimidazolium (curing accelerator), 10 parts long-chain alkyl-modified benzoxazine resin prepared in Example 1, 50 parts butanone, and 40 parts cyclohexanone are placed in a mixing tank and stirred at 200 r / min for 2 h at 30 °C. Then, 40 parts silica powder and 10 parts... SPB-100 (phosphorus flame retardant), 10 parts of modified boehmite prepared in Example 1, 0.5 parts of antioxidant 1010 (antioxidant), 0.3 parts of BYK-051 (defoamer), and 0.5 parts of BYK-110 (dispersant) were dispersed at 25°C with high-speed stirring at 2000 r / min for 1 h, and then ground in a sand mill at 1800 r / min until the fineness of the adhesive solution was ≤10 μm to obtain the resin adhesive solution for copper clad laminate.

[0047] Step 3: Pass the electronic-grade glass fiber cloth through the impregnation tank containing the resin solution for copper-clad laminate at a traction speed of 1m / min. Then, squeeze the excess resin solution by the extrusion roller. Then, send the resin-impregnated glass fiber cloth into the drying tunnel. First, dry it at 160℃ for 5 minutes, then raise the temperature to 170℃ and dry it for 8 minutes. Finally, roll it up to obtain a semi-cured sheet with a thickness of 0.15mm.

[0048] Step 4: Stack the prepreg sheets to form a slab. Cover the top and bottom surfaces of the slab with an electrolytic copper foil and align them. Place it in a vacuum hot press, evacuate to -0.098 MPa, and heat to 140℃ at 2℃ / min. Apply pressure at 30 kg / cm². 2 Hot-pressed under pressure for 15 minutes, then heated to 190℃ at a rate of 2℃ / min, at 35 kg / cm². 2 The material was hot-pressed under pressure for 60 minutes, then cooled to 40°C at a rate of 1°C / min to release the pressure and remove it, resulting in a halogen-free flame-retardant low-consumption copper-clad laminate with a thickness of 2.0 mm.

[0049] Example 5: This example provides a method for preparing a halogen-free flame-retardant low-loss copper-clad laminate, including the following steps:

[0050] Step 1: Mix paraformaldehyde and deionized water at a mass ratio of 1:7, add 0.1 mol / L NaOH solution to adjust the pH to 8.3, stir at 250 r / min for 35 min at 55℃ until completely dissolved, cool to room temperature to obtain formaldehyde aqueous solution. Place 4,4'-diaminodiphenylmethane, cashew phenol and toluene at a mass ratio of 1:3:6 in a reaction vessel equipped with a condenser and a water separator, purge with nitrogen, heat to 80℃, stir at 250 r / min for 20 min, then slowly add formaldehyde aqueous solution, controlling the molar ratio of formaldehyde to 4,4'-diaminodiphenylmethane to be 4.2:1, heat to 88℃, stir at 250 r / min for 7 h, stop the reaction when no more water is generated in the water separator, cool to room temperature, distill the reaction solution under reduced pressure at 70℃ until no solvent is distilled off, then vacuum dry at 65℃ to constant weight to obtain long-chain alkyl modified benzoxazine resin.

[0051] Step 2: By weight, 90 parts epoxy resin, 15 parts styrene-maleic anhydride copolymer (curing agent), 10 parts bismaleimide, 0.1 parts 2-ethyl-4-methylimidazolium (curing accelerator), 15 parts long-chain alkyl-modified benzoxazine resin prepared in Example 2, 55 parts butanone, and 45 parts cyclohexanone are placed in a mixing tank and stirred at 300 r / min for 2.5 h at 35 °C. Then, 50 parts silica powder and 20 parts... 15 parts of SPB-100 (phosphorus flame retardant), 15 parts of modified boehmite prepared in Example 2, 0.8 parts of antioxidant 168 (antioxidant), 0.4 parts of BYK-055 (defoamer), and 0.8 parts of BYK-180 (dispersant) were dispersed at 30°C with high-speed stirring at 2500 r / min for 1.5 h, and then ground in a sand mill at 1900 r / min until the fineness of the adhesive solution was ≤10 μm to obtain the resin adhesive solution for copper clad laminate.

[0052] Step 3: Pass the electronic-grade glass fiber cloth through the impregnation tank containing resin solution at a traction speed of 1.5m / min. Then, squeeze the excess resin solution by the extrusion roller. Then, send the resin-impregnated glass fiber cloth into the drying tunnel. First, dry it at 165℃ for 6 minutes, then raise the temperature to 175℃ and dry it for 9 minutes. Finally, roll it up to obtain a semi-cured sheet with a thickness of 0.15mm.

[0053] Step 4: Stack the prepreg sheets to form a slab. Cover the top and bottom surfaces of the slab with an electrolytic copper foil and align them. Place it in a vacuum hot press, evacuate to -0.098 MPa, and heat to 150°C at 2°C / min. Maintain a pressure of 35 kg / cm². 2 Hot-pressed under pressure for 18 minutes, then heated to 200℃ at a rate of 2℃ / min, at 40 kg / cm². 2The material was hot-pressed under pressure for 70 minutes, then cooled to 45°C at a rate of 1°C / min to release the pressure and remove it, resulting in a halogen-free flame-retardant low-consumption copper-clad laminate with a thickness of 2.0 mm.

[0054] Example 6: This example provides a method for preparing a halogen-free flame-retardant low-loss copper-clad laminate, including the following steps:

[0055] Step 1: Mix paraformaldehyde and deionized water at a mass ratio of 1:8, add 0.1 mol / L NaOH solution to adjust the pH to 8.5, stir at 300 r / min for 40 min at 60℃ until completely dissolved, cool to room temperature to obtain formaldehyde aqueous solution. Place 4,4'-diaminodiphenylmethane, cashew phenol and toluene at a mass ratio of 1:3.2:7 in a reaction vessel equipped with a condenser and a water separator, purge with nitrogen, heat to 85℃, stir at 300 r / min for 30 min, then slowly add formaldehyde aqueous solution, controlling the molar ratio of formaldehyde to 4,4'-diaminodiphenylmethane to be 4.5:1, heat to 90℃, stir at 300 r / min for 8 h. The reaction was stopped when no more water was generated in the water separator. The mixture was cooled to room temperature and then distilled under reduced pressure at 80°C until no solvent was distilled off. The mixture was then dried under vacuum at 70°C to constant weight to obtain long-chain alkyl-modified benzoxazine resin.

[0056] Step 2: By weight, 100 parts epoxy resin, 20 parts styrene-maleic anhydride copolymer (curing agent), 15 parts bismaleimide, 0.15 parts 2-ethyl-4-methylimidazolium (curing accelerator), 20 parts long-chain alkyl-modified benzoxazine resin prepared in Example 3, 60 parts butanone, and 50 parts cyclohexanone are placed in a mixing tank and stirred at 400 rpm for 3 hours at 40°C. Subsequently, 60 parts silica powder, 30 parts SPB-100 (phosphorus flame retardant), 20 parts modified boehmite prepared in Example 3, 1.0 part antioxidant 245 (antioxidant), and 0.5 parts TEGO Airex are added. 900 (defoamer) and 1.0 part of BYK-9076 (dispersant) were pre-dispersed at 35℃ and stirred at 3000r / min for 2h. Then, the mixture was ground in a sand mill at 2000r / min until the fineness of the adhesive was ≤10μm to obtain the resin adhesive for copper clad laminate.

[0057] Step 3: Pass the electronic-grade glass fiber cloth through the impregnation tank containing resin liquid at a traction speed of 2m / min. Then, squeeze the excess resin liquid out by the extrusion roller. Then, send the resin-impregnated glass fiber cloth into the drying tunnel. First, dry it at 170℃ for 7 minutes, then raise the temperature to 180℃ and dry it for 10 minutes. Finally, roll it up to obtain a semi-cured sheet with a thickness of 0.15mm.

[0058] Step 4: Stack the prepreg sheets to form a slab. Cover the top and bottom surfaces of the slab with an electrolytic copper foil and align them. Place it in a vacuum hot press, evacuate to -0.098 MPa, and heat to 160°C at 2°C / min. Apply pressure at 40 kg / cm². 2 Hot-pressed under pressure for 20 minutes, then heated to 210℃ at a rate of 2℃ / min, at 45 kg / cm². 2 The material was hot-pressed under pressure for 80 minutes, then cooled to 50°C at a rate of 1°C / min to release the pressure and remove it, resulting in a halogen-free flame-retardant low-consumption copper-clad laminate with a thickness of 2.0 mm.

[0059] Comparative Example 1: The difference from Example 4 is that the modified boehmite prepared in Example 2 is not added in step 2, but replaced with an equal mass of silica powder. The other steps remain unchanged, and a halogen-free flame-retardant low-consumption copper-clad laminate is prepared.

[0060] Comparative Example 2: The difference from Example 4 is that the modified boehmite prepared in Example 2 is not added in step 2, but replaced with commercially available boehmite of equal mass. The other steps remain unchanged, and a halogen-free flame-retardant low-consumption copper-clad laminate is prepared.

[0061] Comparative Example 3: The difference from Example 4 is that the modified boehmite prepared in Example 2 is not added in step 2, but is replaced by the silica-coated boehmite prepared in S1 of Example 2 of equal mass. The other steps remain unchanged, and a halogen-free flame-retardant low-consumption copper-clad laminate is prepared.

[0062] Comparative Example 4: The difference from Example 5 is that in step two, long-chain alkyl-modified benzoxazine resin is not added, but replaced with an equal mass of epoxy resin. The other steps remain unchanged, and a halogen-free flame-retardant low-consumption copper-clad laminate is prepared.

[0063] Comparative Example 5: The difference from Example 5 is that in step two, commercially available benzoxazine resin of medium quality is used instead of the long-chain alkyl-modified benzoxazine resin prepared in step one, while the other steps remain unchanged, to prepare a halogen-free flame-retardant low-consumption copper-clad laminate.

[0064] The boehmite used in the above embodiments and comparative examples is industrial-grade platy boehmite produced by Chinalco Shandong Co., Ltd., D 50≤2μm, aspect ratio ≥10; Paraformaldehyde is industrial-grade paraformaldehyde produced by Nantong Jiangtian Chemical Co., Ltd., with a degree of polymerization of 8-100 (based on formaldehyde units) and a formaldehyde content ≥95%; Epoxy resin is biphenyl-type epoxy resin, model NEC-3000; Styrene-maleic anhydride copolymer is an industrial-grade product, model SMA EF-41, with a maleic anhydride content of 22-26%; Bismaleimide is industrial-grade bismaleimide resin produced by Dongcai Technology Group Co., Ltd., with a softening point of 80-120℃; Silica powder is electronic-grade spherical fused silica powder produced by Jiangsu Lianrui New Materials Co., Ltd., with an average particle size of 2-5μm; Glass fiber cloth is electronic-grade E-glass fiber cloth produced by China Jushi Co., Ltd., model E-2116; Electrolytic copper foil is electronic-grade electrolytic copper foil produced by Jiujiang Defu Technology Co., Ltd., with a thickness of 35μm; Benzoxazine resin is from Shandong... The resin is produced by Shengquan New Materials Co., Ltd., and is a bisphenol A type benzoxazine resin with a softening point of 80-100℃. The phosphorus-based flame retardant is an industrial-grade phosphazene flame retardant produced by Otsuka Chemical, model SPB-100. The antioxidants are industrial-grade antioxidants produced by Tianjin Lianlong New Materials Co., Ltd., including antioxidants 1010, 168, and 245. The defoamers are industrial-grade defoamers produced by BYK Chemical (Shanghai) Co., Ltd., including BYK-051 and BYK-055, and industrial-grade defoamer TEGO Airex 900 produced by Evonik Specialty Chemicals (Shanghai) Co., Ltd. The dispersants are industrial-grade dispersants produced by BYK Chemical (Shanghai) Co., Ltd., including BYK-110, BYK-180, and BYK-9076.

[0065] The halogen-free flame-retardant low-loss copper-clad laminates prepared in Examples 4-6 and Comparative Examples 1-5 were subjected to performance tests, and the test results are shown in Table 1.

[0066] Sample preparation: The copper-clad laminate prepared above was chemically etched to remove the electrolytic copper foil on the upper and lower surfaces to obtain a bare dielectric laminate. The bare laminate was then cut into samples of the corresponding sizes according to the requirements of each test item. After equilibration for 24 hours at 23±2℃ and 50±5% relative humidity, it was ready for testing.

[0067] Glass transition temperature test: The glass transition temperature was determined by dynamic thermomechanical analysis (DMA). The dynamic thermomechanical analyzer was used to heat the sample from room temperature to 250°C at a heating rate of 5°C / min under a nitrogen atmosphere. The test frequency was 1Hz. The glass transition temperature (Tg) of the sample was recorded. The higher the Tg, the better the resin crosslinking density and heat resistance.

[0068] Water absorption rate test: The water absorption rate is determined by the boiling method. The sample is dried in an oven at 105℃±5℃ until constant weight, and the weight is recorded as m1. Then, it is boiled in distilled water at 100℃±2℃ for 48 hours. After removing and wiping off the surface moisture, the weight is recorded as m2. The water absorption rate is calculated according to the formula (m2-m1) / m1×100%. The lower the water absorption rate, the better the interfacial compactness.

[0069] Flame retardant performance testing: A vertical burning test was conducted according to standard UL-94, "Tests for flammability of plastic materials for equipment and appliance components." The flaming time, flameless time, dripping pattern, and whether the sample ignited the absorbent cotton below were recorded. The results were rated as V-0, V-1, or V-2. A higher flame retardant rating indicates better flame retardant performance.

[0070] Referring to standard GB / T 2406.2 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test", the limiting oxygen index (LOI) is the minimum oxygen concentration required for a sample to sustain combustion in a nitrogen-oxygen mixed gas flow, determined using an oxygen index meter. A higher limiting oxygen index indicates better flame retardant performance.

[0071] Dielectric performance testing: The dielectric constant (Dk) and dielectric loss factor (Df) were determined at a frequency of 10 GHz using the resonant cavity method, referring to standard IPC-TM-650 2.5.5.9 "Test method for dielectric constant and loss factor (resonant cavity method)".

[0072] To simulate the actual working conditions of copper-clad laminates, high temperature and high humidity treatment was carried out. The sample was placed in a constant temperature and humidity chamber of 85℃ / 85% relative humidity for 1000 hours and then taken out. The dielectric constant (Dk) and dielectric loss factor (Df) of the sample were measured again according to the above standards. The lower the values ​​of Dk and Df, the better the dielectric performance.

[0073] Table 1 Performance Test Table of Halogen-Free Flame-Retardant Low-Energy Copper Clad Laminates

[0074]

[0075] As shown in Table 1, the halogen-free flame-retardant low-loss copper-clad laminates prepared in Examples 4–6 are superior to the comparative examples in terms of dielectric loss, high-temperature and high-humidity stability, water absorption, and flame-retardant efficiency. Overall, they exhibit good long-term moisture resistance, dielectric stability, and a synergistic effect of halogen-free flame retardancy. This indicates that by introducing modified boehmite into the resin matrix and introducing long-chain alkyl-modified benzoxazine resin additives, the high-temperature structural stability and surface reactive modification of the modified boehmite, along with the C15 hydrophobic long chains of the long-chain alkyl-modified benzoxazine resin and its carbonization with the nitrogen source, complement each other functionally. This helps to suppress the generation of interfacial micropores caused by the thermal decomposition of fillers during lamination, thereby enabling the halogen-free flame-retardant low-loss copper-clad laminate to maintain good dielectric stability under long-term high-temperature and high-humidity conditions.

[0076] The flame retardant properties of the material in Comparative Example 1 decreased significantly, and the dielectric properties also decreased substantially after high-temperature and high-humidity treatment. This may be because although the silica powder can form a certain interfacial bond with the resin matrix after surface treatment, it lacks the layered physical barrier structure of boehmite and the thermal barrier effect of residual aluminum components at high temperatures. Under lamination and long-term high-temperature conditions, the condensed phase carbon layer lacks inorganic thermal barrier reinforcement, making it difficult to maintain the gas-phase quenching efficiency of phosphorus-based flame retardants, thus reducing the flame retardant rating. In addition, although the all-silica powder system has a low initial dielectric constant, the resin matrix has many moisture absorption channels under long-term humid and hot conditions, and water vapor penetration leads to the accumulation of interfacial polarization losses, increasing the dielectric loss factor over time.

[0077] The dielectric stability of the material in Comparative Example 2 was significantly reduced, and the water absorption rate also increased. This may be because the surface of commercially available boehmite is rich in highly polar groups, which have poor compatibility with organic resins, resulting in significant interfacial polarization loss. Furthermore, the unmodified surface lacks active sites that can react with the resin matrix, and interfacial bonding is mainly based on physical adsorption. Under humid and hot conditions, hygroscopic pores are easily formed at the interface, leading to the deterioration of dielectric properties over time. After the modified boehmite surface is coated with silica and grafted with epoxy silane, not only can the polarity be reduced through surface modification, but the epoxy groups on its surface may also participate in the curing and crosslinking of the main resin, improving the compatibility and interfacial density between the filler and the resin matrix.

[0078] The dielectric stability of the material in Comparative Example 3 decreased, and the water absorption rate increased compared to the Example. This may be because although the silica coating can shield some surface polar groups and reduce surface energy, thus improving dispersibility, the surface of the coating lacks active groups that can react with the resin matrix. After curing, the interface is still mainly based on physical adsorption, and under long-term humid heat, interfacial pores and moisture absorption channels are still difficult to avoid, resulting in lower dielectric stability than the Example.

[0079] The flame retardant properties of the material in Comparative Example 4 decreased, and the dielectric properties also decreased significantly after high-temperature and high-humidity treatment. This may be because replacing benzoxazine resin with epoxy resin resulted in a relatively increased concentration of epoxy groups in the system, leading to a more complete reaction with the anhydride curing agent and an increase in crosslinking density, thus raising the glass transition temperature. Due to the lack of nitrogen source provided by benzoxazine resin in the system, it is unable to form an effective phosphorus-nitrogen-aluminum synergistic flame retardant with phosphorus-based flame retardants and modified boehmite, resulting in a decrease in gas-phase free radical capture ability. At the same time, the lack of active groups generated after benzoxazine ring opening to participate in the crosslinking network, and the absence of long-chain alkyl groups to introduce low-polarity hydrophobic microregions, led to the accumulation of interfacial polarization loss under long-term humid and hot conditions, and an increase in the dielectric loss factor over time.

[0080] The glass transition temperature of the material in Comparative Example 5 was higher than that in the Example, and the dielectric properties were significantly deteriorated after high temperature and high humidity treatment. This may be because commercially available benzoxazine does not contain alkyl long chains and the resin skeleton is more rigid, which reduces the flexibility of the cured crosslinking network and increases the glass transition temperature. Although it can provide a nitrogen source to participate in phosphorus-aluminum synergistic flame retardancy, the lack of alkyl long chains in the molecule makes it unable to effectively reduce the local polarity of the resin matrix and the hygroscopicity of the interface, which leads to a decrease in the dielectric stability of the material.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate, characterized in that, Includes the following steps: Step 1: Place epoxy resin, styrene-maleic anhydride copolymer, bismaleimide, 2-ethyl-4-methylimidazolium, long-chain alkyl-modified benzoxazine resin, butanone, and cyclohexanone in a mixing tank and stir at 200-400 r / min for 2-3 h at 30-40℃. Then add silica powder, phosphorus flame retardant, modified boehmite, antioxidant, defoamer, and dispersant. Disperse the mixture by high-speed stirring at 2000-3000 r / min for 1-2 h at 25-35℃. Finally, grind the mixture in a sand mill to obtain the resin solution for copper-clad laminates. Step 2: Pass the electronic-grade glass fiber cloth through the impregnation tank containing the resin solution for copper-clad laminate at a traction speed of 1-2 m / min. Then, squeeze the excess resin solution by the extrusion roller. Then, send the resin-impregnated glass fiber cloth into the drying tunnel. First, dry it at 160-170℃ for 5-7 min, then raise the temperature to 170-180℃ and dry it for 8-10 min. Finally, roll it up to obtain a semi-cured sheet. Step 3: Stack the prepreg sheets to form a slab. Cover the top and bottom surfaces of the slab with an electrolytic copper foil and align them. Place it in a vacuum hot press, evacuate to -0.098 MPa, and heat to 140-160℃ at 2℃ / min, at 30-40 kg / cm². 2 Hot-press under pressure for 10-20 minutes, then increase the temperature to 190-210℃ at a rate of 2℃ / min, at a pressure of 35-45 kg / cm³. 2 The copper-clad laminate is hot-pressed under pressure for 60-80 minutes, then cooled to 40-50℃ at a rate of 1℃ / min to release the pressure and remove the laminate, thus obtaining a halogen-free flame-retardant low-consumption copper-clad laminate.

2. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 1, characterized in that, The content of each component in the resin solution for copper clad laminates mentioned in step one, by mass, is as follows: The composition includes: 80-100 parts epoxy resin, 10-20 parts styrene-maleic anhydride copolymer, 5-15 parts bismaleimide, 0.05-0.15 parts 2-ethyl-4-methylimidazolium, 10-20 parts long-chain alkyl-modified benzoxazine resin, 50-60 parts butanone, 40-50 parts cyclohexanone, 40-60 parts silica powder, 10-30 parts phosphorus flame retardant, 10-20 parts modified boehmite, 0.5-1.0 parts antioxidant, 0.3-0.5 parts defoamer, and 0.5-1.0 parts dispersant.

3. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 1, characterized in that, The specific preparation process of the long-chain alkyl-modified benzoxazine resin in step two is as follows: 4,4'-Diaminodiphenylmethane, cashew phenol, and toluene were placed in a reactor equipped with a condenser and a water separator. Under nitrogen protection, the mixture was heated to 75-85°C and stirred for 20-30 minutes. Then, an aqueous formaldehyde solution was slowly added, and the mixture was heated to 85-90°C and reacted for 6-8 hours. The mixture was then cooled to room temperature, distilled under reduced pressure, and dried under vacuum to constant weight to obtain a long-chain alkyl-modified benzoxazine resin.

4. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 3, characterized in that, The mass ratio of 4,4'-diaminodiphenylmethane, cashew phenol, and toluene is 1:2.8-3.2:5-7; the molar ratio of formaldehyde and 4,4'-diaminodiphenylmethane in the formaldehyde aqueous solution is 4-4.5:

1. The specific preparation process of the formaldehyde aqueous solution is as follows: Paraformaldehyde and deionized water are mixed at a mass ratio of 1:5-8. The pH is adjusted to 8.0-8.5 by adding 0.1 mol / L NaOH solution. The mixture is stirred at 200-300 r / min for 30-40 min at 50-60℃ until completely dissolved. The mixture is then cooled to room temperature to obtain an aqueous formaldehyde solution.

5. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 2, characterized in that, The specific preparation process of the modified boehmite is as follows: Silica-coated boehmite, anhydrous ethanol, and deionized water were placed in a reaction vessel and ultrasonically dispersed for 20-30 min. The pH of the reaction solution was adjusted to 4.5-5.0 with 1 mol / L acetic acid. γ-glycidoxypropyltrimethoxysilane was added, and the reaction was carried out at 60-70℃ for 2-3 h. After centrifugation and washing, the mixture was vacuum dried to constant weight to obtain modified boehmite. The ratio of silica-coated boehmite, anhydrous ethanol, deionized water, and γ-glycidyl etheroxypropyltrimethoxysilane is 60-100g: 800-1200mL: 80-150mL: 2-5g.

6. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 5, characterized in that, The specific preparation process of the silica-coated boehmite is as follows: Boehmite was placed in anhydrous ethanol and deionized water in a reaction vessel and ultrasonically dispersed for 20-30 min. Tetraethyl orthosilicate was slowly added and stirred at 40-45℃ for 20-30 min. Ammonia solution with a concentration of 0.5 mol / L was added to adjust the pH of the reaction solution to 8.5-9.

0. The reaction was continued for 4-6 h. After centrifugation and washing, the solution was vacuum dried to constant weight to obtain silica-coated boehmite. The ratio of boehmite, anhydrous ethanol, deionized water and tetraethyl orthosilicate is 80-120g: 800-1000mL: 150-250mL: 8-14g.

7. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 1, characterized in that, The antioxidant is any one of antioxidant 1010, antioxidant 168, and antioxidant 245; the defoamer is any one of BYK-051, BYK-055, and TEGO Airex 900; the dispersant is any one of BYK-110, BYK-180, and BYK-9076; and the phosphorus-based flame retardant is SPB-100.

8. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 1, characterized in that, The thickness of the semi-cured sheet mentioned in step two is 0.15 mm.

9. The method for preparing a halogen-free flame-retardant low-consumption copper-clad laminate according to claim 1, characterized in that, The thickness of the halogen-free flame-retardant low-consumption copper-clad laminate mentioned in step three is 2.0 mm.

10. The application of a halogen-free flame-retardant low-power copper-clad laminate in printed circuit boards of automotive driver assistance systems, characterized in that... The halogen-free flame-retardant low-consumption copper-clad laminate is prepared by the preparation method described in any one of claims 1-9.

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