Lignin-based intrinsic black polyimide film as well as preparation method and application thereof

Abstract

The invention discloses a lignin-based intrinsic black polyimide film as well as a preparation method and application thereof. The method comprises the following steps: reacting a diamine monomer with a dianhydride monomer to prepare polyamide acid, mixing the polyamide acid with lignin, and carrying out thermocuring to obtain the lignin-based intrinsic black polyimide film. Compared with a traditional scheme of adding carbon black, the black polyimide film prepared from the polyamide acid solution combination has excellent electrical insulating property and also has good mechanical property. Lignin and polyimide are combined, the black polyimide film material with good comprehensive performance is obtained, meanwhile, lignin is wide in source and low in cost, and good industrial application prospects and economic effects are achieved.

Description

Technical Field

[0001] This invention belongs to the field of polyimide technology, specifically relating to a lignin-based black polyimide film, its preparation method, and its application. Background Technology

[0002] Polyimide, as a specialty engineering plastic, is a strategic high-end material. Due to its stable chemical and radiation resistance, excellent dimensional and thermal stability, and outstanding insulation and dielectric properties, polyimide exhibits superior overall performance in extreme operating environments, making it irreplaceable in many fields. This has led to its widespread application in consumer electronics, aerospace, mobile communication technology, electronic packaging, and flexible copper-clad laminates.

[0003] Black polyimide, a special variety of polyimide, not only possesses the excellent comprehensive properties inherent in polyimide itself, but also exhibits superior light-shielding performance. Some types can also combine one or more functions such as high insulation, electromagnetic shielding, heat dissipation, and low vacuum evaporation rate. Currently, it is widely used in semiconductor and integrated circuit packaging, optics and displays, consumer electronics and wearable devices, automotive electronics, aerospace, and other fields.

[0004] Most current black polyimides are prepared by physically blending inorganic materials (graphite, carbon black, metal oxides, etc.) or organic black dyes (bituminous coal, perylene black, aniline black, etc.) with polyamic acid to form blended black polyimides, or by preparing a black coating on the surface of polyimides using organic black dyes. For example, patent application CN116253880A discloses a method for preparing a black polyimide film containing phenoxyphosphazene, carbon black, and carbon nanotubes, which improves the electrical strength to 110–170 KV / mm compared to the comparative example. However, due to the addition of black filler, the electrical strength of the material is still not ideal. Patent application CN115521706A discloses a method for preparing a black polyimide film containing a color paste prepared from carbon black and a wetting and dispersing agent. The light transmittance of the film was reduced to ≤1%, but the tensile strength of the film material was only 105–112 MPa, and the elongation at break was only 4.5–7.2%. Patent application CN117165081A discloses a method for preparing black polyimide composite materials using a core-shell structure filler with an matting filler core and a carbon black light-shielding material shell. Its electrical strength was increased to 149–171 KV / mm compared to the comparative example of 137 KV / mm, but it was still significantly reduced compared to the excellent insulation properties of polyimide itself.

[0005] However, existing blended black polyimides have the following problems: inorganic black fillers are difficult to disperse evenly, and adding too much will reduce the mechanical properties of the polyimide material, while reducing electrical insulation properties, increasing dielectric constant and dielectric loss; while organic black dyes cannot maintain black properties during high-temperature processing, and organic black dyes are too expensive. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a lignin-based black polyimide film.

[0007] Another object of the present invention is to provide a lignin-based black polyimide film prepared by the above preparation method.

[0008] Another object of the present invention is to provide the application of the above-mentioned lignin-based black polyimide film.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a lignin-based black polyimide film, comprising the following steps: (1) The diamine monomer and the dianhydride monomer react in an aprotic polar solvent to obtain a polyamic acid solution; (2) Add lignin to a polyamic acid solution, then coat it onto a substrate and heat-cur it to obtain a black polyimide film with basic lignin characteristics.

[0010] Preferably, the diamine monomer in step (1) includes 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,4'-diaminodiphenyl ether, benzidine, (oxodi-4,1-phenylene)bis(3-aminophenyl) ketone (CAS No.: 85884-06-6), 4,4'-bis(3-aminophenoxy)benzophenone, 1,3-bis(4'-aminophenoxy)benzene, 2,2'-bis[4-(3-aminophenoxy)phenyl)]propane, 4,4'-dithiodiphenylamine, 4,4'-[[2-(1,1-dimethylethyl)-1,4-phenylene]bis(oxo)]diphenylamine (CAS No.: 146247-61-2), 1,4-phenylene di[[4-(4-aminophenoxy)] [Phenylacetyl] ketone, 4,4'-bis(4-aminophenoxy)diphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-[(2,2',3,3',5,5',6,6'-octafluorobiphenyl-4,4'-diyl)bis(oxy)]diphenylamine (CAS No.: 68090-63-1), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 9,9-bis(4-aminophenyl)fluorene, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, 1,4-bis(p-aminophenoxy)tetrafluorobenzene (CAS No.: 65247-06-5), 2,2-bis[4-(4-aminophenoxy) [Phenyl]-1,1,1,3,3,3-hexafluoropropane, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 3,6-diaminocarbazole, 4,4'-diaminobenzophenone, 4,4'-diaminotriphenylamine, 3,5-diaminotrifluorotoluene, 4,4'-diaminodiphenylmethane, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]hexafluoropropane, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-(2,2,2-trifluoro-1-phenylethylene) 2,2-Bis(4-aminophenyl)propane, 2,5-dimethyl-1,4-phenylenediamine, 1,5-naphthylenediamine, 4,4'-diamino-3,3'-dimethylbiphenylmethane, 4,4-diaminodiphenyl sulfide, 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine, 4,4'-diamino-2,2',6,6'-tetramethylbiphenyl, 4,4'-methylenebis(2,5-dimethylaniline) (CAS No.: 838-88-0), 4-(4-amino-3,5-dimethylphenoxy)-2,6-dimethylaniline, 2,5-bis(4-aminophenyl)pyrimidine, N,N'-1,At least one of 3-phenylenebis[4-aminobenzamide] (CAS No.: 2362-25-6) and 4,4'-methylenebis(2,6-diethylaniline).

[0011] More preferably, the diamine monomer in step (1) includes at least one of 4,4'-diaminodiphenyl ether and p-phenylenediamine.

[0012] Preferably, the dianhydride monomer in step (1) includes pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 6,6′-diphenyl[5,5′-biisobenzofuran]-1,1′,3,3′-tetraone (CAS No.: 165323-77-3), 5-[4-(1,3-dioxo-2-benzofuran-5-yl)phenyl]-2-benzofuran-1,3-dione (CAS No.: 106070-55-7), 1,4-difluoro-2,3,5,6-benzenetetracarboxylic dianhydride (CAS No.: 46861-94-3), diphenyl sulfide dianhydride (CAS No.: 25884-43-9), and bicyclic [2.2]. 2] Oct-7-en-2,3,5,6-tetracarboxylic acid dianhydride, hexahydro-4,8-methylene-1H,3H-benzo[1,2-c:4,5-c′]difuran-1,3,5,7-tetraone (CAS No.: 114291-20-2), 4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride (CAS No.: 61778-79-8), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]malonium dianhydride, biphenyl diether dianhydride (CAS No.: 26177-82-2), cyclobutanetetracarboxylic acid dianhydride (CAS No.: 4415-87-6), hexahydro-1H,3H-benzo[ [1,2-c:4,5-c']difuran-1,3,5,7-tetraone, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride (CAS No.: 6053-68-5), 4,4′-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride (CAS No.: 90335-01-6), bis[4-(3,4-dicarboxyphenoxy)phenyl]ether dianhydride (CAS No.: 26382-26-3), octahydro-4,10:5,9-dimethylbridged naphtho[2,3-c:6,7-c']difuran-1,3,6,8(3aH,8aH)-tetraone (CAS No.: 131891-42-4), 3,3′,4,4′-diphenylsulfonetetracarboxylic acid dianhydride (CAS No.: 2540-99-0) ), bisphenol S dianhydride (CAS No.: 22711-71-3), 5,5′-[[2,5-bis(1,1-dimethylethyl)-1,4-phenylene]bis(oxy)]bis[1,3-isobenzofurandione] (CAS No.: 135771-48-1), 6,6′-bis(trifluoromethyl)[5,5′-biisobenzofuran]-1,1′,3,3′-tetraone (CAS No.: 165323-75-1), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (CAS No.: 1107-00-2), 1,4-bis(3,4-dicarboxyphenoxy)phenyl dianhydride (CAS No.: 17828-53-4), 5,5′-(1,4-phenylene dicarbonyl)bis[1,3-Isobenzofurandione] (CAS No.: 23602-86-0), 5,5′-[1,5-naphthylbis(oxy)]bis[1,3-isobenzofurandione] (CAS No.: 181487-22-9), 4,4'-oxybisphthalic anhydride, 5,5'-(propane-2,2-diyl)bis(isobenzofuran-1,3-dione) (CAS No.: 1779-17-5), 4-(trifluoromethyl)-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetra- At least one of the following: ketone (CAS No.: 114349-13-2), 4,8-bis(trifluoromethyl)-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetraone (CAS No.: 128082-91-7), and 5,5′-[(2,2′,3,3′-tetrahydro-3,3,3′,3′-tetramethyl-1,1′-spirobis[1H-indene]-6,6′-diyl)bis(oxy)]bis-1,3-isobenzofurandione (CAS No.: 120066-70-8).

[0013] More preferably, the dianhydride monomer in step (1) includes at least one of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0014] Preferably, the ratio of the total moles of the diamine monomer to the total moles of the dianhydride monomer in step (1) is 1:1 to 1:1.4; more preferably, it is 1:1 to 1:1.12.

[0015] Preferably, the aprotic polar solvent in step (1) includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, N,N-dimethylacetamide, N-methylpyrrolidone and tetrahydrofuran.

[0016] Preferably, the ratio of the total molar amount of the diamine monomer and the mass of the aprotic polar solvent in step (1) is 0.145 mol: 250-350 g.

[0017] Preferably, the reaction speed in step (1) is 200 to 2000 rpm.

[0018] Preferably, the reaction time in step (1) is 3 to 30 hours; the temperature is room temperature, which includes 20 to 40°C.

[0019] Preferably, the polyamic acid solution in step (1) has a viscosity of 2500 to 35000 mpa•s at room temperature.

[0020] Preferably, the lignin in step (2) includes at least one of alkali lignin, enzymatically hydrolyzed lignin, and organic solvent lignin.

[0021] Preferably, the particle size of the lignin in step (2) is 1 to 15 µm, more preferably 1 to 10 µm.

[0022] Preferably, the weight-average molecular weight of the lignin in step (2) is not higher than 3500 Da, more preferably not higher than 3000 Da.

[0023] Preferably, the lignin in step (2) is first added to the aprotic polar solvent in step (1) and stirred at 100-800 rpm for 5-50 minutes. The resulting mixture is then added to the polyamic acid solution in step (1) and stirred at 100-1000 rpm for 2-20 hours to obtain a mixed solution.

[0024] More preferably, the concentration of lignin in the mixture is 0.1 to 0.4 g / ml.

[0025] Preferably, in the lignin-based black polyimide film described in step (2), the mass percentage of lignin is 5-60%.

[0026] Preferably, the substrate in step (2) comprises a glass substrate.

[0027] Preferably, the coating in step (2) includes at least one of spin coating, casting, and coating.

[0028] Preferably, the temperature for heat curing in step (2) is 270–400 °C and the time is 0.5–3 hours.

[0029] Preferably, the thickness of the lignin-based black polyimide film in step (2) is 5–75 µm.

[0030] Secondly, the present invention provides a lignin-based black polyimide film obtained by the above preparation method.

[0031] Thirdly, the present invention provides the application of the aforementioned lignin-based black polyimide film.

[0032] Preferably, the application is in the manufacture of flexible printed circuit boards (FPCs), serving as a substrate or cover layer to provide mechanical support and insulation protection. Its opacity prevents light from interfering with circuit signals, while its anti-static properties reduce the risk of damage to sensitive components. An electronic and electrical insulating protective film is used to cover the FPC surface, providing "three-proof" (heat-proof, moisture-proof, and contaminant-proof) protection in high-temperature, humid, or corrosive environments, such as for mobile phone antenna reinforcement and interface insulation.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention selects lignin as an organic filler to combine with polyimide, avoiding the impact of carbon-based materials and metal oxide fillers on the electrical insulation properties of polyimide, and also avoiding the impact of poor filler dispersion on the mechanical properties of the material. Lignin is widely available, abundant, and inexpensive, has good electrical insulation properties, and after being heated and cured in polyamic acid, it has a deep color, appearing black, and has good UV absorption and shielding effects, thus maintaining excellent overall performance while reducing costs. Attached Figure Description

[0034] Figure 1 This is a photograph of the actual thin film obtained in Example 3.

[0035] Figure 2 This is a photograph of the actual thin film obtained in Example 5. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0037] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0038] Example 1 (1) Under a nitrogen atmosphere and a set temperature of 35 °C, 327.95 g of N,N-dimethylacetamide was added to a 500 ml reaction apparatus as a solvent. Then, 0.048 mol of p-phenylenediamine (33 mol%) and 0.097 mol of 4,4'-diaminodiphenyl ether (67 mol%) were added as diamine monomers, and the mixture was completely dissolved under mechanical stirring for approximately 45 minutes. Subsequently, 0.061 mol of pyromellitic dianhydride (42 mol%) and 0.084 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (58 mol%) were added as dianhydride monomers for the reaction. The reaction was carried out under mechanical stirring at 700 rpm for 20 hours to ensure complete reaction, yielding a polyamic acid solution with a certain viscosity.

[0039] (2) 8.12 g of alkali lignin with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 11.5% of the total mass of lignin and polyamic acid) was completely dried. The mixture was stirred at 600 rpm for 30 minutes and then mixed with the solvent N,N-dimethylacetamide to prepare a lignin solution with a concentration of 0.37 g / ml.

[0040] (3) At a set temperature of 40 °C, the mixture from step (2) is added to the polyamic acid solution from step (1). The mixture is stirred mechanically at 450 rpm for 12 hours to obtain a polyamic acid-lignin composition.

[0041] (4) The polyamic acid composition from step (3) is coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent is then removed by drying in an oven at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the black polyimide film is peeled off the glass substrate. A black polyimide film with a thickness of 40 µm ± 1 µm is obtained.

[0042] Example 2 (1) Same as Example 1.

[0043] (2) 13.71 g of alkali lignin (18% of the total mass of lignin and polyamic acid) with a particle size of 5 µm and a weight-average molecular weight of 2800 Da was completely dried. It was then mixed with the solvent N,N-dimethylacetamide under mechanical stirring.

[0044] (3) Same as Example 1.

[0045] (4) Same as Example 1.

[0046] Example 3 (1) Same as Example 1.

[0047] (2) 20.27 g of alkali lignin with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 24.5% of the total mass of lignin and polyamic acid) was completely dried. It was then mixed with the solvent N,N-dimethylacetamide under mechanical stirring.

[0048] (3) Same as Example 1.

[0049] (4) Same as Example 1.

[0050] Example 4 (1) Same as Example 1.

[0051] (2) 28.07 g of alkali lignin (31% of the total mass of lignin and polyamic acid) with a particle size of 5 µm and a weight-average molecular weight of 2800 Da was completely dried. It was then mixed with the solvent N,N-dimethylacetamide under mechanical stirring.

[0052] (3) Same as Example 1.

[0053] (4) Same as Example 1.

[0054] Example 5 (1) Same as Example 1.

[0055] (2) 37.48 g of alkali lignin with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 37.5% of the total mass of lignin and polyamic acid) was completely dried. It was then mixed with the solvent N,N-dimethylacetamide under mechanical stirring.

[0056] (3) Same as Example 1.

[0057] (4) Same as Example 1.

[0058] Table 1 Formulations of Examples and Comparative Examples

[0059] Comparative Example 1 (1) Under a nitrogen atmosphere and a set temperature of 35 °C, 327.95 g of N,N-dimethylacetamide was added to a 500 ml reaction apparatus as a solvent. Then, 0.048 mol of p-phenylenediamine (33 mol%) and 0.097 mol of 4,4'-diaminodiphenyl ether (67 mol%) were added as diamine monomers, and the mixture was completely dissolved in approximately 45 minutes under rotary stirring. Subsequently, 0.061 mol of pyromellitic dianhydride (42 mol%) and 0.0843,3',4,4'-biphenyltetracarboxylic dianhydride (58 mol%) were added as dianhydride monomers for the reaction. The reaction was carried out under mechanical stirring at 700 rpm for 20 hours to ensure complete reaction, yielding a polyamic acid solution with a certain viscosity.

[0060] (2) A polyamic acid with a certain viscosity was coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent was then removed by drying at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the polyimide film material was peeled off from the glass substrate. A lignin-free polyimide film with a thickness of 40 µm ± 1 µm was obtained.

[0061] Comparative Example 2 (1) Same as Comparative Example 1.

[0062] (2) After completely drying 4.13 g of carbon black (6.2% of the total mass of carbon black and polyamic acid), add it to N,N-dimethylacetamide solvent. Mix under mechanical stirring at a rotation speed of 1200 rpm, and then place it in an ultrasonic machine for further treatment. The purpose is to ensure that the carbon black is evenly dispersed.

[0063] (3) At a set temperature of 40 °C, the mixture in step (2) is added to the polyamic acid solution in step (1), and the mixture is stirred at a speed of 450 rpm for 12 hours to mix them evenly and obtain a polyamic acid-carbon black composition.

[0064] (4) The polyamic acid composition from step (3) is coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent is then removed by drying at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the black polyimide film material is peeled off from the glass substrate. A carbon black-containing polyimide film with a thickness of 40 µm ± 1 µm is obtained.

[0065] Comparative Example 3 (1) Under a nitrogen atmosphere and a set temperature of 35 °C, 327.95 g of N,N-dimethylacetamide was added to a 500 ml reaction apparatus as a solvent. Then, 0.048 mol of p-phenylenediamine (33 mol%) and 0.097 mol of 4,4'-diaminodiphenyl ether (67 mol%) were added as diamine monomers, and the mixture was completely dissolved under mechanical stirring for approximately 45 minutes. Subsequently, 0.061 mol of pyromellitic dianhydride (42 mol%) and 0.084 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (58 mol%) were added as dianhydride monomers for the reaction. The reaction was carried out under mechanical stirring at 700 rpm for 20 hours to ensure complete reaction, yielding a polyamic acid solution with a certain viscosity.

[0066] (2) 13.71 g of sodium lignosulfonate with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 18% of the total mass of sodium lignosulfonate and polyamic acid) was completely dried. It was then mixed with the solvent N,N-dimethylacetamide under mechanical stirring at 600 rpm for 30 minutes to prepare a lignin solution with a concentration of 0.37 g / ml.

[0067] (3) At a set temperature of 40 °C, the mixture from step (2) is added to the polyamic acid solution from step (1). The mixture is stirred mechanically at 450 rpm for 12 hours to obtain a polyamic acid-lignin composition.

[0068] (4) The polyamic acid composition from step (3) is coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent is then removed by drying in an oven at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the polyimide composite film is peeled off the glass substrate. A polyimide composite film with a thickness of 40 µm ± 1 µm is obtained.

[0069] Comparative Example 4 (1) Under a nitrogen atmosphere and a set temperature of 35 °C, 327.95 g of N,N-dimethylacetamide was added to a 500 ml reaction apparatus as a solvent. Then, 0.048 mol of p-phenylenediamine (33 mol%) and 0.097 mol of 4,4'-diaminodiphenyl ether (67 mol%) were added as diamine monomers, and the mixture was completely dissolved under mechanical stirring for approximately 45 minutes. Subsequently, 0.061 mol of pyromellitic dianhydride (42 mol%) and 0.084 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (58 mol%) were added as dianhydride monomers for the reaction. The reaction was carried out under mechanical stirring at 700 rpm for 20 hours to ensure complete reaction, yielding a polyamic acid solution with a certain viscosity.

[0070] (2) 3.18 g of lignin with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 4.5% of the total mass of lignin, talc and polyamic acid) was completely dried. The mixture was then stirred at 600 rpm for 30 minutes and mixed with the solvent N,N-dimethylacetamide to prepare a lignin solution with a concentration of 0.37 g / ml.

[0071] (3) After drying 10.59 g of talc powder (accounting for 15% of the total mass of lignin, talc powder, and polyamic acid), add it to N,N-dimethylacetamide solvent, and simultaneously add the lignin solution from step 2. Mix under mechanical stirring at a rotation speed of 1200 rpm, and then place it in an ultrasonic machine for further treatment. The purpose is to ensure that the talc powder is evenly dispersed.

[0072] (4) At a set temperature of 40 °C, the mixture from step (3) is added to the polyamic acid solution from step (1). The mixture is stirred at 450 rpm for 12 hours to obtain a polyamic acid-lignin-talc composition.

[0073] (5) The polyamic acid composition from step (4) is coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent is then removed by drying in an oven at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the polyimide composite film is peeled off the glass substrate. A polyimide composite film with a thickness of 40 µm ± 1 µm is obtained.

[0074] Comparative Example 5 (1) Same as Comparative Example 1.

[0075] (2) After completely drying 8.12 g of carbon black (accounting for 11.5% of the total mass of carbon black and polyamic acid), it was added to N,N-dimethylacetamide solvent. After mixing under mechanical stirring at a rotation speed of 1200 rpm, it was further processed in an ultrasonic machine. The purpose was to ensure that the carbon black was evenly dispersed.

[0076] (3) At a set temperature of 40 °C, the mixture in step (2) is added to the polyamic acid solution in step (1), and the mixture is stirred at a speed of 450 rpm for 12 hours to mix them evenly and obtain a polyamic acid-carbon black composition.

[0077] (4) The polyamic acid composition from step (3) is coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent is then removed by drying at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the black polyimide film material is peeled off from the glass substrate. A carbon black-containing polyimide film with a thickness of 40 µm ± 1 µm is obtained.

[0078] Comparative Example 6 (1) Under a nitrogen atmosphere and a set temperature of 35 °C, 327.95 g of N,N-dimethylacetamide was added to a 500 ml reaction apparatus as a solvent. Subsequently, 0.048 mol of p-phenylenediamine (33 mol%) and 0.097 mol of 4,4'-diaminodiphenyl ether (67 mol%) were added as diamine monomers, along with 20.27 g of completely dried alkali lignin with a particle size of 5 µm and a weight-average molecular weight of 2800 Da (accounting for 24.5% of the total mass of lignin and polyamic acid). The mixture was completely dissolved in about 45 minutes under mechanical stirring. Then, 0.061 mol of pyromellitic dianhydride (42 mol%) and 0.084 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (58 mol%) were added as dianhydride monomers for the reaction. The reaction was carried out for 20 hours under mechanical stirring at 700 rpm to ensure complete reaction, resulting in a polyamic acid solution-lignin composition with a certain viscosity.

[0079] (2) The polyamic acid composition from step (1) was coated onto a glass support substrate to a thickness of approximately 100 µm. The solvent was then removed by drying in an oven at 105 °C, followed by thermal imide curing at 280 °C for 2 hours. After cooling, the black polyimide film was peeled off the glass substrate. A black polyimide film with a thickness of 40 µm ± 1 µm was obtained.

[0080] Test methods Test Method 1. The tensile strength and elongation at break of the material are measured on a universal testing machine. The sample is cut into test strips of 10mm*70mm with a tensile gauge length of 20mm, and tested at 50mm / min.

[0081] Test Method 2. The breakdown strength of the material is measured using a breakdown field strength tester. After drying the sample, a breakdown test is performed using direct current with a voltage ramp rate of 0.5 kV / s.

[0082] Test method 3. Measure the cutoff wavelength of the material using an ultraviolet spectrophotometer.

[0083] Test method 4. Measure the L* value of the material using a colorimeter.

[0084] The test results are shown in Table 2 below.

[0085] Table 2 Test results of the examples and comparative examples

[0086] The test results in Table 2 show that the black polyimide film prepared by lignin blending exhibits both ideal blackness and excellent insulation properties. The addition of lignin did not affect the mechanical properties of the polyimide, which still exhibited a tensile strength greater than 230 MPa, demonstrating superior mechanical properties compared to the film material prepared by carbon black blending in Comparative Example 2. The breakdown strength in the examples was greater than 340 KV / mm, far exceeding the 82 KV / mm obtained by carbon black blending in Comparative Example 2. This indicates that the black polyimide film prepared by the method proposed in this invention has excellent insulation properties. The polyimide film prepared by Comparative Example 3 using lignin sulfonate had a high blackness value (L*), a too small cutoff wavelength, and both tensile strength and electrical breakdown strength were lower than those in the examples, failing to meet the requirements for black polyimide. Comparative Example 4 used a small amount of lignin as a dispersant to disperse talc filler; the resulting polyimide film also had a high blackness value (L*), a too small cutoff wavelength, and both tensile strength and electrical breakdown strength were lower than those in the examples, also failing to meet the requirements for black polyimide. Comparative Example 5 further increased the carbon black doping content, resulting in a film material with better black properties compared to Example 1. However, excessive carbon black was difficult to disperse uniformly and easily agglomerated, leading to a significant reduction in the material's mechanical properties and insulation strength. Comparative Example 6, by adding lignin during the polymerization stage of dianhydride and diamine, prepared a black polyimide film that exhibited comparable black properties to Example 3, but its electrical breakdown strength was still lower than that of Example 3, while its mechanical strength showed a significant decrease.

[0087] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based black polyimide film, characterized in that, Includes the following steps: (1) The diamine monomer and the dianhydride monomer react in an aprotic polar solvent to obtain a polyamic acid solution; (2) Add lignin to a polyamic acid solution, then coat it onto a substrate and heat-cur it to obtain a black polyimide film with basic lignin characteristics.

2. The method for preparing a lignin-based black polyimide film according to claim 1, characterized in that, The lignin in step (2) includes at least one of alkali lignin, enzymatically hydrolyzed lignin, and organic solvent lignin; And / or, in step (2), the particle size of the lignin is 1 to 15 µm, more preferably 1 to 10 µm; And / or, in step (2), the weight-average molecular weight of lignin is not higher than 3500 Da, more preferably not higher than 3000 Da.

3. The method for preparing a lignin-based black polyimide film according to claim 1 or 2, characterized in that, In step (2), the lignin content in the black polyimide film of the basic lignin characteristic is 5-60%.

4. The method for preparing a lignin-based black polyimide film according to claim 1 or 2, characterized in that, The diamine monomers in step (1) include 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,4'-diaminodiphenyl ether, benzidine, (oxodi-4,1-phenylene)bis(3-aminophenyl) ketone, 4,4'-bis(3-aminophenoxy)benzophenone, 1,3-bis(4'-aminophenoxy)benzene, 2,2'-bis[4-(3-aminophenoxy)phenyl)]propane, 4,4'-dithiodiphenylamine, 4,4′-[[2-(1,1-dimethylethyl)-1,4-phenylene]bis(oxo)]diphenylamine, 1,4-phenylene bis[[4-(4-aminophenoxy)phenyl] ketone], 4,4'-bis(4-aminophenoxy) Diphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-[(2,2',3,3',5,5',6,6'-octafluorobiphenyl-4,4'-diyl)bis(oxy)]diphenylamine, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 9,9-bis(4-aminophenyl)fluorene, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]phenylphosphine oxide, 1,4-bis(p-aminophenoxy)tetrafluorobenzene, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, α,α'-bis(4-aminophenyl)-1,4-di Isopropylbenzene, 3,6-diaminocarbazole, 4,4'-diaminobenzoyl aniline, 4,4'-diaminobenzophenone, 4,4'-diaminotriphenylamine, 3,5-diaminotrifluorotoluene, 4,4'-diaminodiphenylmethane, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]hexafluoropropane, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-(2,2,2-trifluoro-1-phenylethylene)bis[aniline], 2,2-bis(4-aminophenyl)propane, 2,5 At least one of the following: dimethyl-1,4-phenylenediamine, 1,5-naphthylenediamine, 4,4'-diamino-3,3'-dimethylbiphenylmethane, 4,4-diaminodiphenyl sulfide, 3,3-bis(trifluoromethyl)-[1,1-biphenyl]-4,4-diamine, 4,4'-diamino-2,2',6,6'-tetramethylbiphenyl, 4,4'-methylenebis(2,5-dimethylaniline), 4-(4-amino-3,5-dimethylphenoxy)-2,6-dimethylaniline, 2,5-bis(4-aminophenyl)pyrimidine, N,N'-1,3-phenylenebis[4-aminobenzamide], and 4,4'-methylenebis(2,6-diethylaniline); And / or, the dianhydride monomers in step (1) include pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 6,6′-diphenyl[5,5′-biisobenzofuran]-1,1′,3,3′-tetraone, 5-[4-(1,3-dioxo-2-benzofuran-5-yl)phenyl]-2-benzofuran-1,3-dione, 1,4-difluoro-2,3,5,6-benzenetetracarboxylic dianhydride, diphenyl sulfide dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, hexahydro-4,8-methylene-1H,3H-benzo[1,2-c:4,5-c′]difuran-1 3,5,7-Tetraone, 4,4′-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]malonine dianhydride, biphenyl diether dianhydride, cyclobutanetetracarboxylic acid dianhydride, hexahydro-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetraone, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, 4,4′-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, bis[4-(3,4-dicarboxyphenoxy)phenyl]ether dianhydride, octahydro-4,10:5,9-dimethylbridged naphtho[2,3-c:6, 7-c']difuran-1,3,6,8(3aH,8aH)-tetraone, 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride, bisphenol S dianhydride, 5,5′-[[2,5-bis(1,1-dimethylethyl)-1,4-phenylene]bis(oxy)]bis[1,3-isobenzofurandione], 6,6′-bis(trifluoromethyl)[5,5′-biisobenzofuran]-1,1′,3,3′-tetraone, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 1,4-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 5,5′-(1,4-phenylene dicarbonyl)bis[1,3-isobenzofurandione], 5,5′-[1,5-naphthylbis(oxy)] At least one of the following: bis[1,3-isobenzofurandione], 4,4'-oxobisphthalic anhydride, 5,5'-(propane-2,2-diyl)bis(isobenzofuran-1,3-dione), 4-(trifluoromethyl)-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetraone, 4,8-bis(trifluoromethyl)-1H,3H-benzo[1,2-c:4,5-c']difuran-1,3,5,7-tetraone, and 5,5′-[(2,2′,3,3′-tetrahydro-3,3,3′,3′-tetramethyl-1,1′-spirobis[1H-indene]-6,6′-diyl)bis(oxo)]bis-1,3-isobenzofurandione; And / or, the ratio of the total moles of the diamine monomer to the total moles of the dianhydride monomer in step (1) is 1:1 to 1:1.

4.

5. The method for preparing a lignin-based black polyimide film according to claim 4, characterized in that, The diamine monomer in step (1) includes at least one of 4,4'-diaminodiphenyl ether and p-phenylenediamine; And / or, the dianhydride monomer in step (1) includes at least one of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride; And / or, the ratio of the total moles of the diamine monomer to the total moles of the dianhydride monomer in step (1) is 1:1 to 1:1.

12.

6. The method for preparing a lignin-based black polyimide film according to claim 1 or 2, characterized in that, The aprotic polar solvent in step (1) includes at least one of dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, N,N-dimethylacetamide, N-methylpyrrolidone and tetrahydrofuran; And / or, the total molar amount of the diamine monomer in step (1) and the mass ratio of the aprotic polar solvent are 0.145 mol: 250-350 g; And / or, the reaction time in step (1) is 3 to 30 hours; the temperature is room temperature, which includes 20 to 40°C; And / or, the viscosity of the polyamic acid solution in step (1) is 2500 to 35000 mpa•s at room temperature.

7. The method for preparing a lignin-based black polyimide film according to claim 1 or 2, characterized in that, The temperature for heat curing in step (2) is 270–400 °C, and the time is 0.5–3 hours; And / or, the thickness of the lignin-based black polyimide film in step (2) is 5–75 µm.

8. The method for preparing a lignin-based black polyimide film according to claim 1 or 2, characterized in that, In step (2), the lignin is first added to the aprotic polar solvent described in step (1) and stirred at 100-800 rpm for 5-50 minutes. The resulting mixture is then added to the polyamic acid solution described in step (1) and stirred at 100-1000 rpm for 2-20 hours to obtain a mixed solution. The concentration of lignin in the mixture is 0.1–0.4 g / ml; And / or, the substrate in step (2) includes a glass substrate; And / or, the coating in step (2) includes at least one of spin coating, casting and coating.

9. A lignin-based black polyimide film obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the lignin-based black polyimide film according to claim 9, characterized in that, Applications in the fabrication of flexible printed circuit boards and in electronic and electrical insulation protective films.

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