Black polyimide film and preparation method thereof

Abstract

The invention relates to the field of organic materials, in particular to a black polyimide film and a preparation method thereof. According to the black polyimide film provided by the invention, polyimide has a structure as shown in a formula (L). In the preparation method provided by the invention, aniline oligomer diamine as shown in a formula (II) is adopted, and each bridged nitrogen atom is coupled with a protecting group, such as benzyloxycarbonyl and tert-butoxycarbonyl; carrying out homopolymerization or copolymerization on the diamine monomer and a diamine monomer and a dianhydride monomer as shown in a formula (III) to form a resin solution; then, preparing a polyimide / polyamide acid film through a film forming process; and then, carrying out deprotection group treatment to obtain the intrinsic black polyimide film. The polymer prepared by the invention has excellent dissolving property, and meanwhile, after the protecting group is removed, the material shows uniform black property and excellent solvent resistance and mechanical property, and the contradiction among the processability, the solvent resistance and the mechanical property is solved.

Description

Technical Field

[0001] The invention relates to the field of organic materials, and in particular to a black polyimide film and a preparation method thereof. Background Art

[0002] In recent years, the speed of product iteration in the communications industry has continued to accelerate. Flexible displays have the unique advantage of being able to fold and unfold the screen, which can greatly save the space occupied by the device, and are therefore favored by the market. As an important high-temperature resistant insulating material, polyimide film has been widely used in this field due to its good compatibility with copper foil.

[0003] However, with the rapid development of technology and increasingly fierce industry competition, protecting intellectual property rights and technological achievements has become an inevitable choice for enterprises. Technicians have found that when using traditional yellow transparent polyimide film as a coating, the printed circuit design is very easy to be cracked and copied. To address this problem, many manufacturers have begun to use black polyimide film to replace traditional transparent polyimide film.

[0004] In high-end fields such as aerospace, in order to ensure the stable operation of imaging systems, sensors and other sensitive devices, they need to be protected from interference from stray light, and these devices are usually placed in light-proof tooling. With the continuous advancement of aerospace technology, the performance requirements for light-proof tooling are becoming higher and higher, such as strong absorption capacity in the visible light region, light weight, and excellent space resistance. Therefore, many technicians began to explore the use of black polyimide film to prepare such tooling.

[0005] At the same time, in order to adapt to the preparation needs of complex parts and respond to the development trend of low-carbon and environmental protection, the market has also put forward more stringent requirements on the solubility and processability of materials.

[0006] In summary, the market demand for black polyimide film is showing an increasingly strong trend. The development of black polyimide film with excellent optical shielding, mechanical and processing properties not only has broad market prospects, but also contains far-reaching strategic significance.

[0007] At present, there are three main preparation methods for black polyimide films. The first is the in-situ dyeing method, that is, adding additives such as black pigments or dye particles to the polyimide solution, and then using a film-forming process to obtain the target film; the second is the composite method, that is, coating the black resin on the polyimide film, and obtaining the black film through heating and curing; the third is the intrinsic method, that is, adding special monomers to the polyimide system, and the introduced structure has strong absorption in the visible light region.

[0008] Patent CN109867786B uses 4'-bis(4-aminoanilino)benzene and 1,3'-bis(4-aminoanilino)phenylenediamine monomers as diamine monomers, and one or more of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and pyromellitic dianhydride (PMDA) as dianhydride monomers, and polymerizes them in a non-protonic polar solvent to obtain a polyamic acid solution, and then casts, coats, and heat-cures to obtain a black polyimide film. The intrinsic black polyimide film has good electrical insulation properties and can be used in wireless charging antenna insulation protective films, FPC covering films, lithium battery connector covering films, and other black polyimide protective films with high insulation requirements, as well as black high-temperature resistant labels, black polyimide-based films for tapes, and solar energy absorption and storage films.

[0009] Patent CN109180936A uses pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA) and 4,4'-diaminodiphenylamine (NDA) as raw materials to prepare a polyamic acid solution and then uses a high-temperature imidization method to prepare the film. Performance test results show that the black polyimide film exhibits excellent light-shielding properties.

[0010] Patent CN113563212B uses anthraquinone derivative tetraamine monomer, in which only two amine groups can undergo polycondensation reaction, thus obtaining a linear polymer. The black polyimide obtained by the invention has good light-shielding performance, good mechanical properties, thermal stability and dielectric properties, and the optical transmittance of the entire band is less than 1%.

[0011] Patent CN111574426A synthesizes a dark red or black diamine monomer containing an iso-indigo structure. The monomer (other diamines may be added) is subjected to a polycondensation reaction with an aromatic dianhydride to obtain a polyamic acid solution, and a black polyimide is prepared by thermal or chemical imidization. The large planar conjugated strong electron-withdrawing iso-indigo structure gives the material a black property.

[0012] Patent CN115873250B prepares a new type of intrinsic black polyimide material by introducing a pyrrolopyrrole diketo structure with coplanar and macroconjugated characteristics into the polyimide molecular chain. The coplanar and macroconjugated pyrrolopyrrole diketo structure can effectively reduce the π→π* excitation energy of electronic transition, red-shift the absorption spectrum, broaden its visible light absorption range, and improve the visible light absorption capacity of polyimide.

[0013] At present, the disclosed intrinsic method for preparing black polyimide materials usually selects monomers with high absorption coefficients for polymerization to obtain polyimides with stable performance. The structures of these polyimides often contain large conjugated systems or more chromophores. This leads to limited solubility of the polyimide obtained after polymerization, and high-boiling point solvents such as N,N'-dimethylacetamide are often required as reaction solvents. Even so, its solubility is still not high, making it difficult to achieve high-concentration construction. Moreover, the subsequent removal of the solvent consumes a lot of energy. In addition, some researchers have tried to couple alkyl chains to the main structure to improve the solubility of the material, but this method usually reduces the mechanical properties of the material, resulting in a difficult balance between solubility and mechanical properties. At the same time, because these polymerization systems are black, it is difficult to find defects such as foreign matter and bubbles during the polymerization and coating process, which increases the difficulty of quality control. Summary of the invention

[0014] In view of this, the present invention provides a black polyimide film and a preparation method thereof. The polymer prepared by the present invention has excellent solubility. At the same time, after deprotection, the material exhibits uniform black properties, excellent solvent resistance and mechanical properties, which solves the contradiction between processing performance and solvent resistance and mechanical properties; in addition, the polymerization system is still a traditional transparent amber solution, which is easy to observe, easy to find defects, and can effectively control product quality.

[0015] The present invention provides a black polyimide film, wherein the polyimide has a structure shown in formula (L):

[0016]

[0017] in:

[0018] n, m1, m2, and Please refer to the previous text for the selection range and the following text for detailed instructions.

[0019] The present invention also provides a method for preparing the black polyimide film described in the above technical solution, comprising the following steps:

[0020] A) mixing a dianhydride monomer, a diamine monomer and a solvent, and performing a polymerization reaction to obtain a polyamic acid precursor solution;

[0021] B) Film making:

[0022] Casting the polyamic acid precursor solution into a film, drying, and heat treating to obtain a black polyimide film;

[0023] or

[0024] The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and subjected to a deprotection group treatment to obtain a black polyimide film;

[0025] The types, dosages, condition parameters, etc. of each substance are detailed below.

[0026] The present invention provides a black polyimide film and a preparation method thereof. In the preparation method provided by the present invention, an aniline oligomer diamine shown in formula (II) is used, wherein each bridging nitrogen atom is coupled with a protecting group, such as benoxycarbonyl (Cbz) and tert-butoxycarbonyl (Boc); the above diamine monomer is homopolymerized or copolymerized with the diamine monomer and dianhydride monomer shown in formula (III) to form a resin solution; then, the solution can be made into a polyimide / polyamic acid film through a film-forming process; subsequently, the film is subjected to a deprotection group treatment to obtain an intrinsic black polyimide film with excellent performance. Among them, the introduction of the protecting group significantly improves the solubility of the polyimide, enabling it to be dissolved in low-boiling point solvents such as tetrahydrofuran and chloroform, greatly improving the processing performance of the material. After the deprotection group treatment, abundant hydrogen bonds are formed within and between the molecules, so that the material has excellent mechanical properties, effectively solving the contradiction between solubility and mechanical properties. In addition, the solution system and the precursor film still maintain the yellow transparent characteristics of traditional polyimide, which is convenient for process quality control. In the last step, it is transformed into a black film. The obtained product exhibits uniform black properties, excellent solvent resistance and mechanical properties. The present invention cleverly solves the contradiction between processing performance and solvent resistance and mechanical properties, and has a broader application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0028] Figure 1 Schematic diagram of the reaction route of the preparation method of the present invention;

[0029] Figure 2 The appearance of the black polyimide film obtained in each embodiment of the present invention;

[0030] Figure 3 Visible light absorption spectra of black polyimide films obtained in some embodiments of the present invention;

[0031] Figure 4The thermogravimetric graphs of precursor resin powders PI-2 and PI-6;

[0032] Figure 5 The infrared images of the precursor films (PI-2 and PIF-2) before and after heat treatment in Example 2;

[0033] Figure 6 Infrared images of the precursor films (PI-6 and PIF-6) before and after heat treatment in Example 6. DETAILED DESCRIPTION

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0035] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0036] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0037] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0038] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 50-100℃ means that the units of the left endpoint "50" and the right endpoint "100" are both ℃.

[0039] The present invention provides a black polyimide film, wherein the polyimide has a structure shown in formula (L):

[0040]

[0041] in:

[0042] n is 3 to 8, specifically 3, 4, 5, 6, 7, 8;

[0043] The ratio of m2 / (m1+m2) is 0% to 90%; specifically it can be 0% (i.e. m2=0), 10% (i.e. m2 / m1=1 / 9), 20% (i.e. m2 / m1=2 / 8), 30% (i.e. m2 / m1=3 / 7), 40% (i.e. m2 / m1=4 / 6), 50% (i.e. m2 / m1=5 / 5), 60% (i.e. m2 / m1=6 / 4), 70% (i.e. m2 / m1=7 / 3), 80% (i.e. m2 / m1=8 / 2), 90% (i.e. m2 / m1=9 / 1), and more preferably is 70% to 90%; the value of m1 is not limited, preferably 5 to 1000.

[0044] Selected from the structures shown in formula (Ⅰ-1') to (Ⅰ-11'):

[0045]

[0046] Wherein, in formula (I-3'), A is selected from the following groups:

[0047]

[0048] Selected from the structures shown in formula (III-1') to (III-12'):

[0049]

[0050] in,

[0051] R1 is selected from: H, F, CF3; n in formula (III-1') is 1 to 4, specifically 1, 2, 3, 4; R2 is selected from: CF3, CH3;

[0052] Y is selected from: O, S, NH;

[0053] X is selected from the following groups:

[0054]

[0055] The present invention also provides a method for preparing the black polyimide film described in the above technical solution, comprising the following steps:

[0056] A) mixing a dianhydride monomer, a diamine monomer and a solvent, and performing a polymerization reaction to obtain a polyamic acid precursor solution;

[0057] B) Film making:

[0058] Casting the polyamic acid precursor solution into a film, drying, and heat treating to obtain a black polyimide film;

[0059] or

[0060] The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and subjected to a deprotection group treatment to obtain a black polyimide film;

[0061] in:

[0062] The dianhydride monomer is selected from the compounds represented by formula (I-1) to (I-11):

[0063]

[0064] Wherein, in formula (I-3), A is selected from the following groups:

[0065]

[0066] The diamine monomer is a diamine monomer represented by formula (II), or a diamine monomer represented by formula (II) and a diamine monomer represented by formula (III);

[0067]

[0068] In formula (II):

[0069] n is 3 to 8;

[0070] Selected from the following groups including but not limited to:

[0071] The diamine monomer represented by formula (III) is selected from the compounds represented by formulas (III-1) to (III-12):

[0072]

[0073] in,

[0074] R1 is selected from: H, F, CF3; n in formula (III-1) is 1 to 4;

[0075] R2 is selected from: CF3, CH3;

[0076] Y is selected from: O, S, NH;

[0077] X is selected from the following groups:

[0078]

[0079] The reaction route of the dianhydride monomer and the diamine monomer to form a polyimide is shown in the following formula:

[0080]

[0081] The reaction route of the preparation method of the present invention is as follows Figure 1 shown.

[0082] [About Step A]:

[0083] A) A dianhydride monomer, a diamine monomer and a solvent are mixed and polymerized to obtain a polyamic acid precursor solution.

[0084] About Dianhydride Monomer :

[0085] In the present invention, the dianhydride monomer is selected from the compounds represented by formula (I-1) to (I-11):

[0086]

[0087] Wherein, in formula (I-3), A is selected from the following groups:

[0088]

[0089] The present invention has no particular limitation on the source of the dianhydride monomer, which may be a commercial product or one prepared according to a preparation method known in the art.

[0090] About diamine monomers :

[0091] In the present invention, the diamine monomer is a diamine monomer represented by formula (II), or a diamine monomer represented by formula (II) and a diamine monomer represented by formula (III).

[0092] About the diamine monomer represented by formula (II):

[0093] In the present invention, the diamine monomer represented by formula (II) is as follows:

[0094]

[0095] in:

[0096] n is 3 to 8, specifically 3, 4, 5, 7, 7, 8. When n=3, the monomer is aniline tetramer diamine; when n=4, the monomer is aniline pentamer diamine; when n=5, the monomer is aniline hexamer diamine; and so on.

[0097] Selected from the group including but not limited to: (i.e., Boc group), (i.e. Cbz group).

[0098] when When it is a Boc group, taking n=4 as an example, the diamine monomer can be prepared by the following preparation method:

[0099] S1, the compound represented by formula (1) reacts with a p-phenylenediamine reactant to form a compound represented by formula (2);

[0100] The p-phenylenediamine reactant is p-phenylenediamine and / or p-phenylenediamine hydrochloride;

[0101] S2, the compound represented by formula (2) undergoes a Boc coupling reaction with di-tert-butyl dicarbonate to form a compound represented by formula (3);

[0102] S3, the compound represented by formula (3) is subjected to deprotection and hydrogenation reaction to obtain a diamine monomer represented by formula (II);

[0103]

[0104] Regarding step S1:

[0105] The reaction scheme of this step is as follows:

[0106]

[0107] In the present invention, the compound represented by formula (1) is [(4-aminophenyl)(4-bromophenyl)amino]methane acid-2-methylpropan-2-yl ester, and its source is not particularly limited, and it is a commercial product or prepared according to a preparation method known in the art.

[0108] In the present invention, the p-phenylenediamine reactant is p-phenylenediamine and / or p-phenylenediamine hydrochloride, and the source thereof is not particularly limited, and it is a commercial product or prepared according to a preparation method known in the art.

[0109] In the present invention, the molar ratio of the compound represented by formula (1) to the p-phenylenediamine reactant is preferably (2.0-2.5):1, specifically 2.0:1, 2.05:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, and more preferably 2.05:1.

[0110] In the present invention, the reaction is preferably carried out in the presence of a catalyst, a ligand, an alkaline substance, and a solvent medium.

[0111] The catalyst is preferably at least one of a metal ruthenium compound, a metal rhodium compound and a metal palladium compound, and more preferably a metal palladium compound. The metal palladium compound is preferably at least one of Pd(PPh3)4, Pd(OAc)2, PdCl2, PdCl2(dppf), PdCl2(PPh3)2, and Pd2(dba)3. In the present invention, the molar ratio of the catalyst to the compound represented by formula (I) is preferably (0.0002-0.001):1, specifically 0.0002:1, 0.0003:1, 0.0004:1, 0.0005:1, 0.0006:1, 0.0007:1, 0.0008:1, 0.0009:1, 0.001:1, and more preferably (0.0005-0.001):1.

[0112] The ligand is preferably a phosphine-containing ligand, including but not limited to trimethylphosphine, triethylphosphine, tripropylphosphine, triisopropylphosphine, tributylphosphine, tricyclohexylphosphine, triphenylphosphine, triisopropylphosphine, bis(2-diphenylphosphophenyl)ether (DPEPhos), 1,1′-binaphthyl-2,2′-bisdiphenylphosphine (BINAP), 2-dicyclohexylphospho-2′,4′,6′-triisopropylbiphenyl (X-Phos), 4,5-bisdiphenylphospho-9,9-dimethylxanthene (XANTPhos), 2-(dicyclohexylphosphine)-3,6-dimethoxy-2′,4′,6′-tri-I-propyl-11′-biphenyl (BrettPhos), 2-dicyclohexylphospho-2′,6′-diisopropyl-1,1′-biphenyl (RuPhos), 2-di-tert-butylphosphino-2′,4′,6′- At least one of triisopropylbiphenyl (tBuXPhos), 2-(di-tert-butylphosphino)-3,6-dimethoxy-2′,4′,6′tri-1-propyl-1,1′-biphenyl (tBuBrettPhos), 1,1′-bis(diphenylphosphino)ferrocene (Dppf), (R)-(-)-1-[(S)-2-(dicyclohexylphosphino)ferrocene]ethyldi-tert-butylphosphine (CyPFt-Bu), 5-di-tert-butylphosphino-1′,3′,5′-triphenyl-1′H-[1,4′]bipyrazole (BippyPhos), and N-[2-di(1-adamantane)phosphophenyl]morpholine (Mor-DalPhos), and more preferably at least one of DPEpHos, BINAP, X-Phos, XANTPhos, and BrettPhos. In the present invention, the molar ratio of the ligand to the catalyst is preferably (1-10):1, more preferably (1-4):1.

[0113] The alkaline substance includes at least one of a metal compound, an organic base, an inorganic base and an inorganic salt, preferably at least one of sodium tert-butoxide, potassium tert-butoxide, sodium amide, lithium diisopropylamide, sodium bis(trimethylsilyl)amide, lithium bistrimethylsilylamide, 4-dimethylaminopyridine, triethylamine, KOH, NaOH, K2CO3, Na2CO3, Cs2CO3, more preferably at least one of sodium tert-butoxide, potassium tert-butoxide, Cs2CO3. In the present invention, the molar ratio of the alkaline substance to the compound represented by formula (1) is preferably (1.5-10):1, specifically 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0114] The reaction is preferably carried out in a solvent medium. The solvent is preferably an organic solvent, or a mixed solvent of an organic solvent and water. Among them, the organic solvent is preferably a deoxygenated organic solvent, and the type is preferably at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, toluene, and benzene. In the present invention, the solvent is more preferably at least one of tetrahydrofuran, dioxane, toluene, a dioxane-water mixed solvent, and a toluene-water mixed solvent. In the present invention, in the mixed solvent, the volume ratio of the organic solvent to water is preferably (5 to 20): 1. In the present invention, the mass of the solvent is preferably 5 to 20 times the mass of the compound represented by formula (1), and more preferably 10 to 15 times.

[0115] In the present invention, the reaction is preferably carried out under a protective atmosphere, more preferably a nitrogen atmosphere and / or an argon atmosphere.

[0116] In the present invention, the reaction temperature is preferably 50-100°C, specifically 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, more preferably 60-80°C. In the present invention, the reaction time is preferably 6-10h. In the present invention, the reaction is preferably accompanied by stirring. Based on the Buchwald-Hartwig cross-coupling reaction, the compound shown in formula (1) reacts with a p-phenylenediamine reactant to form an aniline pentamer shown in formula (2). In the structure shown in the above formula (2), the Ph- group is a conventional group abbreviation in the art, representing a phenyl group.

[0117] In the present invention, preferably, step S1 specifically comprises: under a protective atmosphere, mixing the compound represented by formula (1), a p-phenylenediamine reactant, a catalyst, a ligand, an alkaline substance and a solvent, and heating the mixture to react to form a compound represented by formula (2).

[0118] In the present invention, after the reaction is completed, the following post-treatment is preferably performed: solid-liquid separation, washing, and drying. Among them, the solid-liquid separation method is preferably filtration. The washing is to rinse the precipitate with an organic solvent, which can be washed while filtering or centrifuged; the organic solvent is preferably the solvent used for the reaction. The drying is preferably vacuum drying. The drying temperature is preferably 80 to 100° C.; the drying time is preferably 5 to 12 hours. After the above post-treatment, the aniline pentamer solid product shown in formula (2) is obtained.

[0119] Regarding step S2:

[0120] The reaction scheme of this step is as follows:

[0121]

[0122] In the present invention, the source of the di-tert-butyl dicarbonate (abbreviated as DIBOC, with the chemical formula abbreviated as (Boc)2O) is not particularly limited, and it can be a commercial product or prepared according to a preparation method known in the art.

[0123] In the present invention, the molar ratio of the compound represented by formula (II) to di-tert-butyl dicarbonate is preferably 1:(3-6), specifically 1:3, 1:4, 1:5, 1:6, and more preferably 1:(4-5).

[0124] In the present invention, the reaction is preferably carried out in the presence of a basic substance or a solvent medium.

[0125] The alkaline substance includes at least one of a metal compound, an organic base, an inorganic base and an inorganic salt, preferably at least one of sodium tert-butoxide, potassium tert-butoxide, sodium amide, lithium diisopropylamide, sodium bis(trimethylsilyl)amide, lithium bis(trimethylsilyl)amide, 4-dimethylaminopyridine, triethylamine, KOH, NaOH, K2CO3, Na2CO3, Cs2CO3, more preferably 4-dimethylaminopyridine. In the present invention, the molar ratio of the alkaline substance to the compound represented by formula (2) is preferably (0.05-5):1, specifically 0.05:1, 0.1:1, 0.25:1, 0.5:1, 0.75:1, 1:1, 2:1, 3:1, 4:1, 5:1.

[0126] The solvent is preferably an organic solvent, more preferably at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and ether, and further preferably at least one of chloroform and tetrahydrofuran. In the present invention, the amount of the solvent is preferably 3 to 10 times the mass of the compound represented by formula (2).

[0127] In the present invention, the reaction temperature is preferably 40-100°C, specifically 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C; the temperature is more preferably 60-70°C, which is also a mild temperature condition. The reaction time is preferably 4-12h. The compound represented by formula (II) is subjected to a Boc coupling reaction with di-tert-butyl dicarbonate to obtain the aniline pentamer -Boc represented by formula (3).

[0128] In the present invention, preferably, step S2 specifically comprises: mixing the compound represented by formula (2), di-tert-butyl dicarbonate, an alkaline substance and a solvent, and subjecting the mixture to a reflux reaction to form a compound represented by formula (3).

[0129] In the present invention, after the above reaction is completed, the following post-treatment is preferably performed: solid-liquid separation, washing, and drying. The solid-liquid separation method is preferably filtration. The washing is eluting with an organic solvent; the organic solvent is preferably ethanol. The drying is preferably vacuum drying. The drying temperature is preferably 80 to 100° C.; the drying time is preferably 5 to 12 hours. After the above post-treatment, the aniline pentamer-Boc solid product shown in formula (3) is obtained.

[0130] Regarding step S3:

[0131] The reaction scheme of this step is as follows:

[0132]

[0133] In the present invention, the Ph2CN- groups at both ends of the compound of formula (3) are deprotected and hydrogenated to obtain a diamine monomer represented by formula (II).

[0134] In the present invention, the reaction in step S3 is preferably carried out in the presence of a hydrogen source reagent, an alkaline substance, and a solvent medium.

[0135] The hydrogen source reagent includes but is not limited to H2, hydroxylamine hydrochloride, ammonium formate, sodium borohydride, etc., preferably at least one of H2, hydroxylamine hydrochloride, and ammonium formate. In the present invention, the molar ratio of the hydrogen source reagent to the compound represented by formula (3) is preferably (3-10):1, more preferably (3-5):1.

[0136] In the present invention, when hydroxylamine hydrochloride is selected as the hydrogen source reagent, the reaction of step C) can be carried out in the presence of an alkaline substance. Wherein, the alkaline substance includes at least one of an organic base and an inorganic base, preferably at least one of sodium acetate, dimethylaminopyridine, triethylamine, pyridine, KOH, and NaOH, and more preferably pyridine and triethylamine. Wherein, when the alkaline substance is pyridine and triethylamine, the molar ratio of pyridine to triethylamine is preferably 1: (2 to 5). In the present invention, the molar ratio of the alkaline substance to the compound represented by formula (3) is preferably (10 to 20): 1.

[0137] In the present invention, when H2 or ammonium formate is selected as the hydrogen source reagent, the reaction in step C) can be carried out under the action of a catalyst. The catalyst is preferably at least one of a palladium-containing catalyst and a nickel-containing catalyst, and more preferably at least one of a Pd / C catalyst and a Pd(OH)2 / C catalyst. In the present invention, the molar ratio of the catalyst to the compound represented by formula (3) is preferably (0.05-0.2):1.

[0138] The solvent is preferably an organic solvent, more preferably at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and ether, and further preferably at least one of dichloromethane, chloroform, and tetrahydrofuran. In the present invention, the amount of the solvent is preferably 5 to 20 times the mass of the compound represented by formula (3).

[0139] In the present invention, the reaction temperature is preferably room temperature to the boiling point of the solvent, more preferably 20 to 50°C, that is, the reaction can be carried out at room temperature. The reaction time is preferably 1 to 6 hours. After the reaction, the aniline pentamer diamine monomer represented by formula (II) is formed.

[0140] In the present invention, preferably, step S3 specifically comprises: mixing the compound represented by formula (3), a hydrogen source reagent, an alkaline substance / catalyst, and a solvent, and performing a deprotection and hydrogenation reaction to form a diamine monomer represented by formula (II).

[0141] In the present invention, when hydroxylamine hydrochloride is selected as the hydrogen source reagent, after the above reaction is completed, the obtained reaction solution is preferably subjected to the following post-treatment: solid-liquid separation, washing, and drying. Among them, the solid-liquid separation method is preferably filtration or centrifugal separation. The washing is eluting with an organic solvent; the organic solvent includes but is not limited to at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and ether, and more preferably at least one of dichloromethane, chloroform, and tetrahydrofuran. The drying is preferably vacuum drying. The drying temperature is preferably 80 to 100°C; the drying time is preferably 5 to 12 hours. After the above post-treatment, a solid product of aniline pentamer diamine monomer shown in formula (II) is obtained.

[0142] In the present invention, when H2 and ammonium formate are selected as hydrogen source reagents, after the above reaction is completed, the obtained reaction solution is preferably subjected to the following post-treatment: solid-liquid separation, washing, extraction, and drying. Among them, the solid-liquid separation method is preferably filtration or centrifugal separation. The washing is eluting with an organic solvent; the organic solvent includes but is not limited to at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and ether, and more preferably at least one of dichloromethane, chloroform, and tetrahydrofuran. The extraction is selected but not limited to using a Soxhlet extractor, and the specific steps are to put the obtained solid into the extractor, select organic solvents such as dichloromethane, chloroform, and tetrahydrofuran, heat and reflux extraction, and the obtained extract is further concentrated to a solid state by a rotary evaporator. Drying is preferably vacuum drying. The drying temperature is preferably 80 to 100°C; the drying time is preferably 5 to 12h. After the above post-treatment, a solid product of aniline pentamer diamine monomer shown in formula (II) is obtained.

[0143] when When it is a Boc group and n is other values, the preparation can be carried out by referring to the preparation method when n=4.

[0144] when For Cbz group, refer to The preparation method of the diamine monomer when it is a Boc group can be used for preparation. The main difference lies in the reaction conditions when coupling the Cbz group. The conditions are as follows: at 0-10°C, add a certain amount of saturated sodium bicarbonate aqueous solution to the organic solution of the compound to be added with the Cbz group, and then add benzyl chloroformate. The reaction mixture is stirred at 0-10°C for 0.5-1 hour, heated to 25°C, and continued to stir at 25°C for 0.5-1 hour. Water is added to the reaction mixture to quench the reaction, and then extracted with ethyl acetate. The combined organic extracts are dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain the target product. Among them, the molar ratio of the compound to be added with the Cbz group to benzyl chloroformate is preferably 1:1-2. The molar ratio of the compound to be added with the Cbz group to sodium bicarbonate is 1:1-2. The organic solvent is preferably a common reagent such as tetrahydrofuran, toluene, and ethyl acetate.

[0145] About the diamine monomer represented by formula (III):

[0146] In the present invention, the diamine monomer represented by formula (III) is selected from compounds represented by formulas (III-1) to (III-12):

[0147]

[0148] in,

[0149] R1 is selected from: H, F, CF3; n in formula (III-1) is 1 to 4, specifically 1, 2, 3, 4;

[0150] R2 is selected from: CF3, CH3;

[0151] Y is selected from: O, S, NH;

[0152] X is selected from the following groups:

[0153]

[0154] The present invention has no particular limitation on the source of the diamine monomer represented by formula (III), and it can be a commercial product or one prepared according to a preparation method known in the art.

[0155] In the present invention, the molar ratio of the diamine monomer represented by formula (II) to the diamine monomer represented by formula (III) is preferably 10:0 to 1:9, specifically 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, and more preferably 1:9 to 3:7.

[0156] In the present invention, the molar ratio of the diamine monomer to the dianhydride monomer is preferably 1:(0.95-1.05), specifically 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99, 1:1.00, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, more preferably 1:(0.98-1.02).

[0157] In the present invention, the solvent is preferably an organic solvent, more preferably including at least one of N, N'-dimethylformamide (DMF), N, N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), m-cresol (m-Cresol), dichloromethane (DCM), chloroform (CF), tetrahydrofuran (THF), dioxane (DX), acetone (ACE), butanone (MEK), toluene (TOL), ethyl acetate (EA), xylene (Xylene), and diethyl ether (EE), and more preferably at least one of DCM, CF, DMF, DMAc, DMSO, and NMP. In the present invention, the amount of the solvent is preferably such that the system concentration is 5wt% to 40wt%, specifically 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, and 40wt%.

[0158] In the present invention, the polymerization reaction temperature is preferably -20 to 40° C., specifically -20° C., -15° C., -10° C., -5° C., 0° C., 5° C., 10° C., 15° C., 20° C., 25° C., 30° C., 35° C., 40° C. The reaction time is preferably 1 to 70 hours, specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours.

[0159] In the present invention, the atmosphere of the polymerization reaction is air or an inert atmosphere. The type of the inert atmosphere is not particularly limited, and it can be any conventional inert atmosphere in the art, such as nitrogen atmosphere, argon atmosphere, etc.

[0160] Step A) polymerizing a dianhydride monomer and a diamine monomer in a solvent to obtain a polyamic acid precursor solution.

[0161] [About step B]:

[0162] B) Film making:

[0163] In the present invention, after the polyamic acid precursor solution is obtained in step A), film formation is performed. The present invention can form a film in two ways: one is to cast the polyamic acid precursor solution into a film, dry it, and perform heat treatment to obtain a black polyimide film; the other is to perform imidization treatment on the polyamic acid precursor solution to obtain a polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and subjected to a deprotection group treatment to obtain a black polyimide film.

[0164] About the first film making method:

[0165] In the present invention, the film-forming by casting is direct film-forming by casting, or film-forming by biaxial stretching after casting. There are no special restrictions on the methods of casting and biaxial stretching, and the conventional casting and biaxial stretching methods known to those skilled in the art can be used.

[0166] In the present invention, after the film is cast, drying is performed. The drying temperature is preferably room temperature to 160° C., which can be selected within the above range according to the type of solvent and must not be higher than the boiling point of the solvent. After drying, a polyamic acid precursor film is obtained.

[0167] In the present invention, after the polyamic acid precursor film is obtained by drying, it is subjected to heat treatment. In the present invention, the heat treatment includes two steps of heat treatment, which are a deprotection group treatment and a thermal imidization treatment.

[0168] in:

[0169] The temperature of the deprotection group treatment is preferably 140-250°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C; the temperature can be programmed or fixed. The time of the deprotection group treatment is preferably 4-12h, specifically 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h. The atmosphere of the deprotection group treatment is preferably a vacuum atmosphere or an inert atmosphere; wherein the inert atmosphere is not particularly limited, such as a nitrogen atmosphere, an argon atmosphere, etc.

[0170] The temperature of the thermal imidization treatment is preferably 150-350°C, specifically 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C. The time of the thermal imidization treatment is preferably 5-90min, specifically 5min, 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min. The atmosphere of the thermal imidization treatment can be air atmosphere, vacuum atmosphere or inert atmosphere; wherein, the inert atmosphere is not particularly limited, such as nitrogen atmosphere, argon atmosphere, etc. After the above two steps of heat treatment, a black polyimide film is obtained.

[0171] About the second film making method:

[0172] In the present invention, the polyamic acid precursor solution is first subjected to imidization treatment. In the present invention, the imidization treatment is preferably a chemical imidization treatment; the process preferably includes: mixing the polyamic acid precursor solution with an imidization agent, then precipitating in a poor solvent, solid-liquid separation and drying to obtain a polyimide powder.

[0173] in:

[0174] The imidization agent is preferably a nitrogen-containing compound and acetic anhydride; wherein the nitrogen-containing compound is preferably at least one of triethylamine, pyridine and picoline. The molar ratio of the nitrogen-containing compound to the diamine monomer used in step A) is preferably (0.5-3.5):1, specifically 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1. The molar ratio of the acetic anhydride to the diamine monomer used in step A) is preferably (0.5-5.5):1, specifically 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.5:1.

[0175] The mixing is preferably stirring and mixing. The rotation speed of the stirring and mixing is preferably 300-1000 rpm, specifically 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm; the time of the stirring and mixing is preferably 0.5-36 h, specifically 0.5 h, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 36 h.

[0176] After mixing, a poor solvent is added to precipitate. The poor solvent includes but is not limited to at least one of water, methanol, ethanol, and ethylene glycol. Among them, the water is preferably deionized water. After precipitation, solid-liquid separation is performed. The method of solid-liquid separation is not particularly limited, and conventional methods in the art can be used, such as filtering. After solid-liquid separation, elution is preferably performed; the elution is preferably performed using the poor solvent used for precipitation. After elution, drying is performed. After drying, polyimide powder is obtained.

[0177] In the present invention, after obtaining the polyimide powder, it is dissolved in a solvent to form a solution. The solvent is preferably an organic solvent, more preferably at least one of DMF, DMAc, DMSO, NMP, m-Cresol, DCM, CF, THF, DX, ACE, MEK, TOL, EA, Xylene, and EE, and most preferably at least one of DCM, CF, DMF, DMAc, DMSO, and NMP. The amount of the solvent is preferably such that the solid content of the obtained solution is 10% to 40%, specifically 10%, 15%, 20%, 25%, 30%, and 35%.

[0178] In the present invention, after the polyimide powder is dissolved in a solvent to form a solution, a film is cast. The film casting is direct film casting, or biaxial stretching after casting. There are no special restrictions on the casting and biaxial stretching methods, and the conventional casting and biaxial stretching methods known to those skilled in the art can be used.

[0179] In the present invention, after the film is cast, drying is performed. The drying temperature is preferably room temperature to 160° C., which can be selected within the above range according to the type of solvent and must not be higher than the boiling point of the solvent. After drying, a polyimide precursor film is obtained.

[0180] In the present invention, after the polyimide precursor film is dried to obtain, it only needs to be subjected to a step of deprotection group treatment, which can be a chemical method or a heat treatment method, preferably a heat treatment method.

[0181] The chemical method refers to immersing the precursor film in a solution containing a deprotecting agent, treating it at a certain temperature, then washing and drying it to obtain the target product. Wherein, the solution containing the deprotecting agent includes an acidic solution, an alkaline solution or a solution containing a catalyst. Wherein, the acidic solution includes an acidic solution such as hydrochloric acid, sulfuric acid or trifluoroacetic acid. The alkaline solution includes a solution of an alkaline substance such as sodium hydroxide, potassium hydroxide or potassium carbonate. The catalyst in the catalyst-containing solution includes a platinum catalyst and a palladium catalyst. The certain temperature is preferably room temperature to the boiling point of the solvent; the heating method is not limited, such as electric heating, microwave heating, etc. The treatment time is preferably 30min to 12h, more preferably 1 to 5h. The solvent used for the cleaning includes but is not limited to deionized water (H2O), DMF, DMAc, DMSO, NMP, m-Cresol, DCM, CF, THF, DX, ACE, MEK, TOL, EA, Xylene, EE, methanol (MeOH) or ethanol (Ethanol), etc., preferably at least one of H2O, MeOH, and Ethanol.

[0182] The heat treatment method is to heat treat the precursor film at a certain temperature and atmosphere for a certain time. Among them, the temperature of the heat treatment is preferably 140-250°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C; the temperature can be programmed or fixed. The time of the heat treatment is preferably 4-12h, specifically 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h. The atmosphere of the heat treatment is preferably a vacuum atmosphere or an inert atmosphere; wherein, the inert atmosphere has no special restrictions, such as a nitrogen atmosphere, an argon atmosphere, etc. After the above treatment, a black polyimide film is obtained.

[0183] In the preparation method provided by the present invention, an aniline oligomer diamine shown in formula (II) is used, wherein each bridging nitrogen atom is coupled with a protecting group, such as benoxycarbonyl (Cbz) and tert-butoxycarbonyl (Boc); the above diamine monomer is homopolymerized or copolymerized with the diamine monomer and dianhydride monomer shown in formula (III) to form a resin solution; then, the solution can be made into a polyimide / polyamic acid film through a film-forming process; subsequently, the film is subjected to a deprotection group treatment to obtain an intrinsic black polyimide film with excellent performance. Among them, the introduction of the protecting group significantly improves the solubility of the polyimide, allowing it to be dissolved in low-boiling point solvents such as tetrahydrofuran and chloroform, greatly improving the processing performance of the material. After the deprotection group treatment, abundant hydrogen bonds are formed within and between the molecules, so that the material has excellent mechanical properties, effectively solving the contradiction between solubility and mechanical properties. In addition, the solution system and the precursor film still maintain the yellow transparent characteristics of traditional polyimide, which is convenient for process quality control, and is only transformed into a black film in the last step.

[0184] The present invention belongs to the intrinsic method, which has the characteristics of stable color and excellent comprehensive performance, and is a relatively ideal preparation method. The principle of the intrinsic black color of the polyimide film prepared by the present invention is as follows: after the protective group in the molecular chain is decomposed, the main chain is converted into a reduced polyaniline segment; the segment is further oxidized to form an oxidized polyaniline segment. Since the polyaniline structure with large conjugation characteristics has a wide absorption range in the visible light region, the material is endowed with excellent visible light absorption ability, so that it exhibits intrinsic black characteristics.

[0185] Traditional polyimide films, because polyimide molecules are rich in aromatic rings, charge transfer occurs between molecules, making them show strong absorption characteristics in the visible light region, and their appearance is usually golden or dark brown. This single color greatly limits its application scenarios and scope. The present invention has developed a method for preparing an intrinsic black polyimide film, which effectively overcomes the problem of insufficient absorption capacity of existing polyimide films in the visible light region, and can fully meet the stringent technical requirements for the optical properties of materials in special fields such as shading and confidentiality.

[0186] Compared with the prior art, the present invention has the following beneficial effects:

[0187] During the preparation process of the present invention, a large number of solubilizing groups are cleverly introduced, successfully solving the problems of poor solubility and poor processing performance of traditional intrinsic black polyimide films, and significantly improving the operability of the film during the processing. It is particularly worth mentioning that the present invention pioneered a deprotection group coloring process, so that the prepared black polyimide film has excellent mechanical properties and solvent resistance, thereby further broadening its application possibilities in different fields. In addition, based on the unique intrinsic properties of the intrinsic black polyimide film, it can appear black without adding color fillers, fundamentally avoiding the adverse effects of color fillers in dyed black films on the comprehensive performance of the film. At the same time, it also avoids the problem that the composite film will crack under extreme environments such as high temperature and high frequency due to problems such as adhesive failure and mismatch of thermal expansion coefficient, thereby affecting its function realization and service life.

[0188] In addition to the above-mentioned black polyimide film, any equivalent replacement or change according to the technical solution and inventive concept of the present invention, including material forms such as fibers, profiles, composite materials, foams, etc., should be covered within the protection scope of the present invention.

[0189] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0190] Example 1

[0191] A) Add Boc-protected aniline pentamer diamine (i.e., diamine monomer represented by formula (II), n=4, PG group is Boc; 0.02 mol, 17.46 g) and 4,4'-phenylenedioxydiphthalic anhydride, i.e., 4,4'-HQDPA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.05 g) to N,N'-dimethylacetamide (154 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0192] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, wash, and dry to obtain white polyimide powder PI-1 (23.55g, yield 95%). Take 10g of the above powder and dissolve it in 40g of chloroform to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate and level it with a scraper, dry it at 50℃ for 5h, then place it together with the substrate in a 3mol / L sulfuric acid solution, soak it at 50℃ for 5h, wash it with deionized water, and dry it at 100℃ for 30min to obtain a black polyimide film PIF-1 (thickness δ=41μm).

[0193] Example 2

[0194] A) Add Boc-protected aniline pentamer diamine (i.e., diamine monomer represented by formula (II), n=4, PG group is Boc; 0.02 mol, 17.46 g) and hexafluorodianhydride i.e., 6FDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.88 g) to N,N'-dimethylacetamide (159 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0195] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, rinse with ethanol, and dry to obtain white polyimide powder PI-2 (24.08g, yield 94%). Take 10g of the above powder and dissolve it in 40g N,N'-dimethylacetamide to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate and level it with a scraper, dry it at 120℃ for 5h, then place it in a high-temperature oven under vacuum conditions together with the substrate as a whole, keep it at a constant temperature of 230℃ for 4h, and obtain a black polyimide film PIF-2 (thickness δ=33μm).

[0196] Example 3

[0197] A) Add Boc-protected aniline pentamer diamine (i.e., diamine monomer represented by formula (II), n=4, PG group is Boc; 0.02 mol, 17.46 g) and pyromellitic dianhydride, i.e., PMDA (i.e., dianhydride monomer represented by formula (I-1); 0.02 mol, 4.36 g) to N,N'-dimethylacetamide (120 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0198] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-3 (thickness δ = 35 μm).

[0199] Example 4

[0200] A) Add Boc-protected aniline pentamer diamine (i.e., diamine monomer represented by formula (II), n=4, PG group is Boc; 0.02 mol, 17.46 g) and ketone anhydride, i.e., BTDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 6.45 g) to N,N'-dimethylacetamide (130 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0201] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-4 (thickness δ = 21 μm).

[0202] Example 5

[0203] A) Add Boc-protected aniline heptamer diamine (i.e., diamine monomer represented by formula (II), n=6, PG group is Boc; 0.02 mol, 25.11 g) and 4,4'-phenylenedioxydiphthalic anhydride, i.e., 4,4'-HQDPA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.05 g) to N,N'-dimethylacetamide (180 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0204] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, rinse with ethanol, and dry to obtain white polyimide powder PI-5 (30.42g, yield 94%). Take 10g of the above powder and dissolve it in 40g of chloroform to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate and level it with a scraper, dry it at 50℃ for 5h, then place it together with the substrate in a 3mol / L sulfuric acid solution, soak it at 50℃ for 5h, wash it with deionized water, and dry it at 100℃ for 30min to obtain a black polyimide film PIF-5 (thickness δ=32μm).

[0205] Example 6

[0206] A) Add Boc-protected aniline heptamer diamine (i.e., diamine monomer represented by formula (II), n=6, PG group is Boc; 0.02 mol, 25.11 g) and hexafluorodianhydride i.e., 6FDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.88 g) to N,N'-dimethylacetamide (190 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0207] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, rinse with ethanol, and dry to obtain white polyimide powder PI-6 (30.66g, yield 93%). Take 10g of the above powder and dissolve it in 40g N,N'-dimethylacetamide to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate, level it with a scraper, dry it at 120℃ for 5h, and then place it in a high-temperature oven under vacuum conditions together with the substrate, keep it at a constant temperature of 230℃ for 4h, and obtain a black polyimide film PIF-6 (thickness δ=25μm).

[0208] Example 7

[0209] A) Add Boc-protected aniline heptamer diamine (i.e., diamine monomer represented by formula (II), n=6, PG group is Boc; 0.02 mol, 25.11 g) and pyromellitic dianhydride, i.e., PMDA (i.e., dianhydride monomer represented by formula (I-1); 0.02 mol, 4.36 g) to N,N'-dimethylacetamide (120 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0210] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-7 (thickness δ = 28 μm).

[0211] Example 8

[0212] A) Add Boc-protected aniline heptamer diamine (i.e., diamine monomer represented by formula (II), n=6, PG group is Boc; 0.02 mol, 25.11 g) and ketone anhydride, i.e., BTDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 6.45 g) to N,N'-dimethylacetamide (130 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0213] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-8 (thickness δ = 29 μm).

[0214] Example 9

[0215] A) Cbz-protected aniline tetramer diamine (i.e., diamine monomer represented by formula (II), n=3, PG group is Cbz; 0.02 mol, 13.64 g) and 4,4'-phenylenedioxydiphthalic anhydride, i.e., 4,4'-HQDPA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.05 g) were added to N,N'-dimethylacetamide (154 mL) and stirred at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0216] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, wash, and dry to obtain white polyimide powder PI-9 (21.61g, yield 96%). Take 10g of the above powder and dissolve it in 40g N,N'-dimethylacetamide to obtain a solution with a solid content of 15%; cast the solution onto a glass substrate and level it with a scraper, dry it at 50℃ for 5h, then place it together with the substrate in a 3mol / L hydrobromic acid solution, soak it at 50℃ for 5h, wash it with deionized water, and dry it at 100℃ for 30min to obtain a black polyimide film PIF-9 (thickness δ=23μm).

[0217] Example 10

[0218] A) Cbz-protected aniline hexamer diamine (i.e., diamine monomer represented by formula (II), n=5, PG group is Cbz; 0.02 mol, 21.28 g) and ketone anhydride, i.e., BTDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 6.45 g) were added to N,N'-dimethylacetamide (170 mL) and stirred at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0219] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-10 (thickness δ = 34 μm).

[0220] Embodiment 11

[0221] A) Add Boc-protected aniline heptamer diamine (i.e., diamine monomer shown in formula (II), n=6, PG group is Boc; 0.002 mol, 2.511 g), 4,4'-diaminodiphenyl ether (i.e., diamine monomer shown in formula (III-3); 0.018 mol, 3.60 g) and hexafluorodianhydride i.e., 6FDA (i.e., dianhydride monomer shown in formula (I-3); 0.02 mol, 8.88 g) to N,N'-dimethylacetamide (85 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0222] B) Add imidization reagent triethylamine (0.042mol, 4.24g) and acetic anhydride (0.05mol, 5.10g) to the above polyamic acid solution, stir at room temperature for 5h, then precipitate in ethanol, crush, filter, rinse with ethanol, and dry to obtain white polyimide powder PI-11 (10.62g, yield 93.6%). Take 6g of the above powder and dissolve it in 40g N,N'-dimethylacetamide to obtain a solution with a solid content of 15%; cast the solution onto a glass substrate and level it with a scraper, dry it at 120℃ for 5h, then place it in a high-temperature oven under vacuum conditions together with the substrate, and keep it at a constant temperature of 230℃ for 4h to obtain a black polyimide film PIF-11 (thickness δ=17μm).

[0223] Example 12

[0224] A) Add Boc-protected aniline pentamer diamine (i.e., diamine monomer represented by formula (II), n=4, PG group is Boc; 0.01 mol, 8.73 g), p-phenylenediamine (i.e., diamine monomer represented by formula (III-1); 0.01 mol, 1.08 g) and hexafluorodianhydride i.e., 6FDA (i.e., dianhydride monomer represented by formula (I-3); 0.02 mol, 8.88 g) to N,N'-dimethylacetamide (106 mL), and stir at room temperature for 24 h to obtain a light yellow viscous polyamic acid solution.

[0225] B) The polyamic acid solution was cast onto a glass substrate and leveled with a scraper, dried at 120°C for 5 h, and then placed in a high-temperature oven under vacuum conditions together with the substrate, maintained at a constant temperature of 230°C for 4 h, and then maintained at a constant temperature of 300°C for 1 h to obtain a black polyimide film PIF-12 (thickness δ = 18 μm).

[0226] Product Testing :

[0227] (1) Mechanical properties test

[0228] The tensile properties of the black polyimide films obtained in each example were tested, and the results are shown in Table 1.

[0229] Table 1: Tensile properties of the black polyimide films obtained in various examples

[0230] sample Tensile strength(MPa) Tensile modulus(GPa) Example 1 (PIF-1) 139.6 2.86 Example 2 (PIF-2) 107.2 2.52 Example 3 (PIF-3) 111.4 2.84 Example 4 (PIF-4) 125.6 2.76 Example 5 (PIF-5) 108.4 2.65 Example 6 (PIF-6) 103.1 2.63 Example 7 (PIF-7) 99.6 2.53 Example 8 (PIF-8) 108.5 2.58 Example 9 (PIF-9) 134.6 2.94 Example 10 (PIF-10) 121.3 2.77 Example 11 (PIF-11) 105.6 2.08 Example 12 (PIF-12) 107.3 2.24

[0231] It can be seen from the test results in Table 1 that the tensile strength of the black polyimide film obtained by the present invention is above 99 MPa, and the modulus is above 2 GPa, showing excellent mechanical properties.

[0232] (2) Product appearance

[0233] The black polyimide film obtained in each embodiment is as follows Figure 2 As shown, the appearance of the films PIF-1 to PIF-12 obtained in Examples 1 to 12 are shown in the figure from the 1st to the 12th samples. Among them, PIF-1 to 10 are films obtained by homopolymerization, and PIF-11 to 12 are films obtained by copolymerization (the ratio of the special diamine monomer shown in formula (II) to the conventional diamine monomer shown in formula (III) is 5:5 and 1:9 respectively). It can be seen from the figure that the homopolymer films are all black and the color is uniform; the copolymer films are thin in thickness and the ratio of the special diamine monomer is reduced, so the blackness of the film is not as good as that of the homopolymerization method, but the overall color is still black.

[0234] (3) Visible light absorption test

[0235] Some of the films obtained by the implementation were tested for visible light absorption, and the results were as follows: Figure 3 As shown. Among them, when the thickness (δ) of the homopolymerized film is greater than 40μm, the visible light in the range of 400-800nm ​​is almost completely absorbed, and the transmittance is close to 0. The film with a thickness less than 40μm has strong absorption in the range of 400-700nm, and the transmittance is also close to 0. The copolymer film has strong absorption in the range of 400-600nm, and the transmittance in the range of 600-700nm is higher than that of the copolymer film.

[0236] (4) Solubility test of intermediates

[0237] The solubility of the intermediate product polyimide resin powder in the example was tested, and the results are shown in Table 2.

[0238] Table 2: Solubility of precursor polyimide resin powder (solid content 10%)

[0239] DMAc DMF NMP THF EA m-Cresol CF TOL ACE MEK PI-1 ++ ++ ++ ++ + ++ ++ + + + PI-2 ++ ++ ++ ++ ++ ++ ++ + ++ ++ PI-5 ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ PI-6 ++ ++ ++ ++ ++ ++ ++ + ++ ++

[0240] Note: ++ means completely dissolved, + means partially dissolved, - means insoluble.

[0241] It can be seen from the test results in Table 2 that the precursor polyimide resin powder in the present invention can be dissolved by a variety of organic solvents, which can achieve diversified operation schemes, among which solvents with low boiling points are more conducive to achieving low-energy consumption operations.

[0242] (5) Solvent resistance test of film products

[0243] The solvent resistance test was performed on the black polyimide film obtained in each example, a small amount of the film was put into the solvent, heated under reflux for 12 hours, and the state of the film was observed. The results are shown in Table 3.

[0244] Table 3: Solvent resistance of black polyimide film products (solid content 0.2%)

[0245] DMAc DMF NMP THF EA m-Cresol CF TOL ACE MEK Ethanol PIF-1 - - - - - - - - - - - PIF-2 - - - - - - - - - - - PIF-3 - - - - - - - - - - - PIF-4 - - - - - - - - - - - PIF-5 - - - - - - - - - - - PIF-6 - - - - - - - - - - - PIF-7 - - - - - - - - - - - PIF-8 - - - - - - - - - - - PIF-9 - - - - - - - - - - - PIF-10 - - - - - - - - - - - PIF-11 - - - - - - - - - - - PIF-12 - - - - - - - - - - -

[0246] Note: ++ means dissolved, + means swelled, - means insoluble.

[0247] It can be seen from the test results in Table 3 that the black polyimide film obtained in the present invention is neither soluble nor swellable in a variety of organic solvents, showing excellent solvent resistance.

[0248] (6) Thermogravimetric analysis and infrared testing

[0249] The heat treatment process of the precursor polyimide resin powder is a thermal decomposition process. The typical thermal weight loss process is as follows: Figure 4 As shown. The protective groups of the resin powder decomposed under heat to form a polyimide with aniline segments in the main chain. The infrared results are shown Figure 5 and Figure 6 shown.

[0250] The present invention provides a black polyimide film and a preparation method thereof. Compared with other intrinsic methods, the polymer prepared by the present invention has excellent solubility, and can be dissolved not only in non-protonic polar solvents such as N, N'-dimethylformamide, N, N'-dimethylacetamide, dimethyl sulfoxide, etc., but also in low-boiling point solvents such as chloroform and tetrahydrofuran, thereby achieving green, environmentally friendly and energy-saving operation. In addition, the polymerization system is still a traditional transparent amber solution, which is easy to observe and easy to find defects (such as foreign matter, bubbles, etc.), and can effectively control product quality. After deprotection, due to the transformation of the molecular chain structure, the material exhibits uniform black properties, excellent solvent resistance and mechanical properties. The invention cleverly solves the contradiction between processing performance and solvent resistance and mechanical properties, and has a broader application prospect.

[0251] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and its core ideas of the present invention, including the best mode, and also enable any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. However, the protection scope of the present invention is not limited to this. It should be pointed out that, for example, the technical solution and the inventive concept of the present invention are equivalently replaced or changed, and the material forms include fibers, profiles, composite materials, foams, etc., which should be covered within the protection scope of the present invention.

Claims

1. A black polyimide film, characterized in that: The polyimide has a structure shown in formula (L): in: n is 3 to 8; the ratio of m2 / (m1+m2) is 0% to 90%; Selected from the structures shown in formula (Ⅰ-1') to (Ⅰ-11'): Wherein, in formula (I-3'), A is selected from the following groups: Selected from the structures shown in formula (III-1') to (III-12'): in, R1 is selected from: H, F, CF3; n in formula (III-1') is 1 to 4; R2 is selected from: CF3, CH3; Y is selected from: O, S, NH; X is selected from the following groups:

2. A method for preparing the black polyimide film according to claim 1, characterized in that: The following steps are involved: A) mixing a dianhydride monomer, a diamine monomer and a solvent, and performing a polymerization reaction to obtain a polyamic acid precursor solution; B) Film making: Casting the polyamic acid precursor solution into a film, drying, and heat treating to obtain a black polyimide film; or The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and subjected to a deprotection group treatment to obtain a black polyimide film; in: The dianhydride monomer is selected from the compounds represented by formula (I-1) to (I-11): Wherein, in formula (I-3), A is selected from the following groups: The diamine monomer is a diamine monomer represented by formula (II), or a diamine monomer represented by formula (II) and a diamine monomer represented by formula (III); In formula (II): n is 3 to 8; Selected from the following groups: The diamine monomer represented by formula (III) is selected from the compounds represented by formulas (III-1) to (III-12): in, R1 is selected from: H, F, CF3; n in formula (III-1) is 1 to 4; R2 is selected from: CF3, CH3; Y is selected from: O, S, NH; X is selected from the following groups:

3. The preparation method according to claim 2, characterized in that: In step A), the molar ratio of the diamine monomer represented by formula (II) to the diamine monomer represented by formula (III) is preferably 10:0 to 1:

9.

4. The preparation method according to claim 2, characterized in that: In step A), the molar ratio of the diamine monomer to the dianhydride monomer is 1:(0.95-1.05).

5. The preparation method according to claim 2, characterized in that: In step A), the solvent includes at least one of N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol, dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, and ether.

6. The preparation method according to claim 2, characterized in that: In step A), the polymerization reaction temperature is -20 to 40° C. and the reaction time is 1 to 70 hours.

7. The preparation method according to claim 2, characterized in that: In step B), the heat treatment comprises two steps of heat treatment, which are a deprotection group treatment and a thermal imidization treatment; in: The temperature of the deprotection group treatment is 140 to 250° C. and the time is 4 to 12 hours; The temperature of the thermal imidization treatment is 150-350° C., and the time is 5-90 minutes.

8. The preparation method according to claim 2, characterized in that: In step B), the imidization treatment is a chemical imidization treatment, and the process includes: mixing the polyamic acid precursor solution with an imidization agent, and then precipitating in a poor solvent, solid-liquid separation and drying to obtain a polyimide powder.

9. The preparation method according to claim 8, characterized in that: The imidization agent is a nitrogen-containing compound and acetic anhydride; wherein the nitrogen-containing compound is at least one of triethylamine, pyridine and picoline; The molar ratio of the nitrogen-containing compound to the diamine monomer used in step A) is (0.5-3.5):1; The molar ratio of the acetic anhydride to the diamine monomer used in step A) is (0.5-5.5):

1.

10. The preparation method according to claim 2, characterized in that: In step B), the deprotection group treatment is a chemical method or a thermal treatment method; The temperature of the heat treatment method is 140-250° C. and the time is 4-12 hours.

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