An intrinsically colored polyimide film and its preparation method

Abstract

This invention discloses an intrinsically colored polyimide film and its preparation method. The film is obtained by casting and imidization of low molecular weight intrinsically colored polyamic acid resin and high molecular weight polyamic acid resin. The intrinsically colored polyimide film has a tensile strength >160MPa and an elongation at break >40%. The preparation method includes: (1) preparing or using a polyamic acid composition; (2) imidizing the polyamic acid composition to obtain an intrinsically colored polyimide film. The final product obtained by this invention has a tensile strength >160MPa, an elongation at break >40%, a 60-degree gloss level less than 35, a dehumidifying electrical strength greater than 180kv / mm, and a light transmittance less than 0.1%. The preparation process has the flexibility and simplicity of performance control and has been industrialized.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a polyimide film and its preparation method. Background Technology

[0002] Polyimide (PI) films possess excellent comprehensive properties, particularly in high and low temperature resistance, dimensional stability, mechanical properties, and radiation resistance. Colored PI films, in addition to possessing the inherent excellent properties of PI films, also have good light-shielding properties. Therefore, they can be widely used in fields such as optics, electronics, and aerospace where special light-shielding requirements exist. Taking black polyimide film as an example, in the field of flexible circuit boards, black PI film can protect the circuit design while maintaining a simple and concise appearance. However, it has strict requirements for the film's light-shielding properties, gloss, mechanical properties, and dimensional stability. For example, it requires an elongation at break of greater than 50% and a linear expansion coefficient (50-250℃) of less than 25ppm / ℃.

[0003] The preparation process of black PI film is mainly divided into two types: (1) Adding black inorganic fillers or organic dyes: such as adding carbon black particles, carbon nanotubes, black metal oxides, black organic dyes, etc. to polyamic acid resin after grinding or dispersing, and then preparing the film by thermal or chemical imide method. Such films have shortcomings such as uneven dispersion of inorganic fillers, deterioration of electrical insulation performance, or poor heat resistance of organic dyes and thermal decomposition. (2) Using special monomers to prepare intrinsic black PI film: intrinsic black polyimide film has good electrical insulation and heat resistance properties.

[0004] There are currently two main routes for preparing intrinsic black PI films: (1) Using electron-rich diamine monomers to increase the formation of charge transfer complexes in the PI molecular chain. For example, 4,4'-diaminodiphenylamine and 4,4'-diaminodiphenyl ether are copolymerized with benzoic acid dianhydride. Due to the introduction of electron-rich diamine NDA, the ability to form charge transfer complexes between the diamine monomer and the dianhydride monomer is improved, and the prepared PI has a darker color. Another method is to copolymerize 4,4'-diaminodiphenylamine and 2-(4-aminophenyl)-5-aminobenzamide with benzoic acid dianhydride. Due to the introduction of electron-rich diamine NDA and rigid APBI, the prepared PI has a darker color and a lower linear thermal expansion coefficient CTE. (2) Using aromatic amine monomers containing chromophores and auxochromes: A series of intrinsic black PI films have been designed and synthesized in the Chinese patent publications CN111574426A, CN113563212A, CN115873250A, etc.

[0005] However, the intrinsic black PI films reported in current patents and papers all have the following shortcomings: (1) The resin is prepared by copolymerization of special monomers. Due to the special intrinsic black special monomers, special structures are introduced to make the color develop, resulting in low monomer activity and difficulty in obtaining high molecular weight polymers. The weight average molecular weight of the prepared polyamic acid resins is between 50,000 g / mol and 200,000 g / mol; (2) The mechanical properties of the film are low, and the elongation at break is below 45% or even less than 15% in some cases. At the same time, due to the low elongation at break of the prepared PI film, it is difficult to add matting powder to adjust the gloss of the film in order to avoid further decrease in elongation; (3) It is difficult to easily control the shading rate and linear expansion coefficient by copolymerization. Summary of the Invention

[0006] This invention provides an intrinsically colored polyimide film with good mechanical and optical properties and a simple preparation process, and a method for preparing the same, in order to solve the technical problems existing in the prior art mentioned in the background.

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

[0008] An intrinsically colored polyimide film is obtained by imidizing a polyamic acid composition; the polyamic acid composition comprises a low molecular weight intrinsically colored polyamic acid resin and a high molecular weight polyamic acid resin; the intrinsically colored polyimide film has a tensile strength >160MPa and an elongation at break >40%; when the thickness is greater than or equal to 25μm, the light transmittance of the intrinsically colored polyimide film is less than 0.1%.

[0009] The core effect of this invention lies in its ingenious use of two resins with different properties to circumvent the chemical bottleneck in existing colored PI films, where the selection of specific monomers during production prevents the synthesis of high molecular weight polymers. High molecular weight polyamic acid resin serves as the main resin for the intrinsically colored polyimide film, providing essential properties such as mechanical strength, dimensional stability, and heat resistance. Low molecular weight intrinsically colored polyamic acid resin is added to the main resin as a high-heat-resistant pigment component. During imidization, the low molecular weight intrinsically colored polyamic acid is grafted into the molecular backbone, providing intrinsic coloring and light-shielding properties to the film. The intrinsically colored polyimide film formed by this method directly increases the elongation at break from less than 20% in existing technologies to greater than 40%, while maintaining high tensile strength. This improves overall mechanical properties and solves the core defects of existing intrinsically colored PI film technology.

[0010] As a further preferred embodiment of the above technical solution, the weight-average molecular weight of the low-molecular-weight intrinsically colored polyamic acid resin is less than 50,000 g / mol, and the weight-average molecular weight of the high-molecular-weight polyamic acid resin is greater than 500,000 g / mol. The above molecular weight range represents the optimal molecular weight window for achieving the synergistic effect of this invention. The lower weight-average molecular weight of the intrinsically colored polyamic acid resin facilitates uniform dispersion with the bulk high-molecular-weight polyamic acid resin, thereby improving the uniformity of coloring, light-blocking properties, and mechanical properties after film formation.

[0011] As a further preferred embodiment of the above technical solution, the weight-average molecular weight of the low-molecular-weight intrinsically colored polyamic acid resin is less than 10,000 g / mol; and the weight-average molecular weight of the high-molecular-weight polyamic acid resin is greater than 700,000 g / mol. This preferred method provides a more favorable molecular weight range, making the functional division of the two components clearer and the synergistic effect more significant. It is expected to obtain better mechanical properties and more uniform coloring and light-blocking effect. The extremely high weight-average molecular weight of the high-molecular-weight polyamic acid resin provides a guarantee for the main performance of the PI film.

[0012] As a further preferred embodiment of the above technical solution, the polyamic acid composition further includes a matting agent, the mass of which is 2-5% of the mass of the intrinsically colored polyimide film; the intrinsically colored polyimide film has a gloss level of less than 35 at 60 degrees. Since the basic solution of this invention has significantly improved the elongation at break of the film (>50%), it possesses the "confidence" to withstand the loss of mechanical properties caused by adding matting agent. Therefore, matting agent can be conveniently added to control the surface gloss and obtain a matte effect without significantly impairing the flexibility of the film, thereby enabling the product of this invention to better meet the needs of practical and high-end application scenarios.

[0013] As a further preferred embodiment of the above technical solution, the matting agent is fumed silica with a median particle size of 1-6 micrometers. Suitable particle size and appropriate addition amount result in a film with low gloss.

[0014] As a further preferred embodiment of the above technical solution, the thickness of the intrinsically colored polyimide film is 8~150μm.

[0015] As a further preferred embodiment of the above technical solution, the high molecular weight polyamic acid resin is prepared by polycondensation of aromatic diamine A and aromatic dianhydride A in a solvent.

[0016] As a further preferred embodiment of the above technical solution, the low molecular weight intrinsically colored polyamic acid resin is prepared by polycondensation of aromatic diamine B, aromatic amine C and aromatic dianhydride B in a solvent, wherein the molar ratio of aromatic amine C and aromatic diamine B is (50~100):(0~50).

[0017] The aromatic amine C comprises an aromatic amine monomer containing an auxochrome or chromophore and / or an electron-rich diamine monomer; the aromatic amine monomer containing an auxochrome or chromophore comprises 1,8-dihydroxy-2,4,5,7-tetraamino-9,10-anthraquinone; the electron-rich diamine monomer comprises , , , , and At least one of the following. Low molecular weight intrinsically colored polyamic acid resins can also be copolymerized from aromatic amines and common aromatic diamines. By introducing some common diamines, the properties can be adjusted to a certain extent, providing a wider process control window.

[0018] As a further preferred embodiment of the above technical solution, when preparing the high molecular weight polyamic acid resin, the polycondensation of aromatic diamine A and aromatic dianhydride A can be random copolymerization or block copolymerization. The preferred polycondensation method is block copolymerization, which can give the film better performance uniformity.

[0019] As a further preferred embodiment of the above technical solution, the aromatic amine C is selected from 1,8-dihydroxy-2,4,5,7-tetraamino-9,10-anthraquinone. and At least one of them.

[0020] As a further preferred embodiment of the above technical solution, the ratio of the total molar number of aromatic amine C and aromatic diamine B to the molar number of aromatic dianhydride B is 1:1 to 2:1. The weight-average molecular weight of the low molecular weight intrinsically colored polyamic acid resin color paste can be controlled by adjusting the proportion of aromatic dianhydride.

[0021] As a further preferred embodiment of the above technical solution, the aromatic diamine A and / or aromatic diamine B are selected from p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 2,4'-diaminodiphenyl ether, 2,2'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2, 4'-Diaminodiphenyl sulfone, 2,2'-Diaminodiphenyl sulfone, 4,4'-Diaminodiphenyl sulfide, 3,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfide, 2,4'-Diaminodiphenyl sulfide, 2,2'-Diaminodiphenyl sulfide, o-toluidine, meta-toluidine, 1,5-Diaminonaphthalene, 4,4'-Benzyl ketone diamine, bis-{4-(4'-aminophenoxy)phenyl} sulfone, 2,2 -bis{4-(4'-aminophenoxy)phenyl}propane, 4,4'-diaminodiphenylmethane, bis{4-(3'-aminophenoxy)phenyl}sulfone, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,3-bis(4-aminophenyl) At least one of phenoxybenzene, 1,4-bis(4-aminophenoxy)benzene, 2-(4-aminophenyl)-5-aminobenzimidazole, and 1,3-bis(3-aminophenoxy)benzene; more preferably at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2-bis{4-(4'-aminophenoxy)phenyl}propane, 1,3-bis(4-aminophenoxy)benzene, and 1,4-bis(4-aminophenoxy)benzene.

[0022] The aromatic dianhydride A and / or aromatic dianhydride B are selected from pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4... At least one of 5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4'-oxophthalic dianhydride, hexafluorodianhydride, 4,4'-terephthalophthalic dianhydride, and bisphenol A type diether dianhydride; more preferably at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, and hexafluorodianhydride.

[0023] Based on the same technical concept, the present invention also provides a method for preparing the intrinsically colored polyimide film described above, comprising the following steps:

[0024] (1) Prepare or use low molecular weight intrinsically colored polyamic acid resin and high molecular weight polyamic acid resin to obtain the polyamic acid composition;

[0025] (2) The intrinsically colored polyimide film is prepared by chemical imidization or thermal imidization of the polyamic acid composition.

[0026] As a further preferred embodiment of the above technical solution, the solid content of the low molecular weight intrinsically colored polyamic acid resin is 25%~35%; the solid content of the high molecular weight polyamic acid resin is 15%~25%. A solid content of less than 15% in the high molecular weight polyamic acid resin results in a large waste of solvent, while a solid content of more than 25% results in excessively high apparent viscosity of the resin, which is not conducive to leveling during casting.

[0027] As a further preferred embodiment of the above technical solution, the operation of the chemical imidization method is as follows: at -5℃ to 10℃, the polyamic acid composition is mixed evenly with a chemical imidization accelerator and a matte powder solution, and then the mixture is cast, stretched, and subjected to high-temperature imidization to prepare a matte intrinsically colored polyimide film; the chemical imidization accelerator includes a dehydrating agent and an imidization catalyst.

[0028] As a further preferred embodiment of the above technical solution, the mixing method in the chemical imidization method includes three types: a) low molecular weight intrinsically colored polyamic acid resin, high molecular weight polyamic acid resin, and matting agent solution are pre-mixed evenly in a reaction vessel, and then evenly mixed with the chemical imidization method accelerator in a mixer before the die head before being injected into the die head for casting; b) high molecular weight polyamic acid resin and matting agent solution are pre-mixed evenly in a reaction vessel, and then mixed with low molecular weight intrinsically colored polyamic acid resin through a pipeline mixer, and finally evenly mixed with the chemical imidization method accelerator in a mixer before the die head before being injected into the die head for casting; c) high molecular weight polyamic acid resin and matting agent solution are pre-mixed evenly in a reaction vessel, and then evenly mixed together with low molecular weight intrinsically colored polyamic acid resin and the chemical imidization method accelerator in a mixer before the die head before being injected into the die head for casting; the preferred mixing method is c. This method can avoid contamination of the reaction vessel and pipelines by the low molecular weight intrinsically colored polyamic acid resin, and has better mass production processability.

[0029] As a further preferred embodiment of the above technical solution, the operation of the thermal imidization method is as follows: at 10~35℃, the polyamic acid composition is mixed evenly with the matte powder solution and then directly cast, stretched and subjected to high-temperature imidization to prepare a matte intrinsically colored polyimide film.

[0030] The mixing methods described in the hot imidization process include two types: d) low molecular weight intrinsically colored polyamic acid resin, high molecular weight polyamic acid resin, and matting agent solution are directly mixed evenly in the reaction vessel and then injected into the die for casting; e) high molecular weight polyamic acid resin and matting agent solution are pre-mixed evenly in the reaction vessel, and then mixed evenly with low molecular weight intrinsically colored polyamic acid resin through a pipeline mixer before being injected into the die for casting; mixing method e is preferred. Mixing the resin in a pipeline mixer can avoid contamination of the reaction vessel by the low molecular weight intrinsically colored polyamic acid resin, resulting in relatively better mass production processability.

[0031] Compared with the prior art, the advantages of the present invention are as follows:

[0032] (1) This invention solves the contradiction between mechanical properties and coloring and light-blocking properties by preparing low molecular weight intrinsically colored polyamic acid and uniformly dispersing it in the form of color paste into the main high molecular weight polyamic acid resin, and then preparing PI film by chemical casting method. It completely overcomes the fundamental defects of low molecular weight and poor mechanical properties (especially low elongation at break) caused by the use of special coloring monomers. The excellent mechanical properties provide the possibility of adding matting powder to adjust the surface gloss, so that intrinsically colored films with high coloring and light blocking and matte surface can be easily prepared, which broadens the application scenarios and is more in line with the needs of end applications. The final product has good comprehensive performance: thickness range of 8-150 micrometers, tensile strength >180MPa, elongation at break >50%, gloss of 60 degrees less than 35, dehumidification electrical strength greater than 180kv / mm, and the transmittance of the whole wavelength (400-700nm) can be less than 0.1% when the thickness is 25 micrometers.

[0033] (2) The present invention assigns coloring and light-blocking functions and mechanical functions to two different resins respectively, so that coloring and light-blocking performance (by adjusting the proportion or type of low molecular weight intrinsically colored polyamic acid resin) and mechanical performance (by adjusting the proportion or molecular weight of high molecular weight solution) can be two relatively independent control dimensions, simplifying the formulation design and greatly improving the flexibility and ease of performance control: the formulation of the main high molecular weight polyamic acid resin can be adjusted to match different main performance requirements of PI film, and the optical performance of PI film can also be controlled by adjusting the formulation and addition amount of low molecular weight intrinsically colored polyamic acid resin in the mixing stage before film formation.

[0034] (3) The preparation method of the present invention can realize continuous industrial production. The raw materials and monomers used are all commercial products. The preparation method is compatible with the existing mainstream chemical imidization and thermal imidization processes. The technical solution is mature and reliable, easy to implement and promote, and has extremely high industrial application value. Black and other special monomers of other colors can be prepared by the method of the present invention. It is especially suitable for monomers with low reactivity that cannot be prepared by copolymerization of high molecular weight polyamic acid. Polyimide films of specific colors or specific functions can be prepared by the method of the present invention. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention.

[0036] Figure 1 These are photographs of rolls of the matte intrinsic black polyimide film after slitting, as described in Example 2.

[0037] Figure 2 The transmittance test results are for the matte intrinsic black polyimide film of Example 2. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments.

[0039] Example 1:

[0040] The intrinsically colored polyimide film of this embodiment is an intrinsically black polyimide film with a thickness of 50 micrometers. Its performance test parameters are shown in Table 1.

[0041] The intrinsically colored polyimide film in this embodiment was prepared using the following method:

[0042] (1) Preparation of high molecular weight polyamic acid resin: 836 kg of N-N'-dimethylacetamide and 100 kg of 4,4′-diaminodiphenyl ether (ODA) were added to the reaction vessel. After the diamine monomer was dissolved, 109 kg of pyromellitic dianhydride (PMDA) was added to the reactor in batches. The reaction was carried out at 35 °C for 6 h. The final viscosity was adjusted to 450-500 Pa•S to obtain viscous high molecular weight polyamic acid resin 1#. Its weight average molecular weight was measured to be 705447 g / mol.

[0043] Preparation of low molecular weight intrinsically colored polyamic acid resin: 75 kg of N-N'-dimethylformamide, 18.4 kg of NDA, and 2 kg of 4,4'-diaminodiphenyl ether were added to a reaction vessel. After the diamine monomer dissolved, up to 14.5 kg of pyromellitic dianhydride (PMDA) was added in batches to the reactor. The reaction was carried out at 20-50℃ for 4-10 h to obtain low molecular weight intrinsically colored polyamic acid resin paste #2 with good flowability. The weight-average molecular weight was measured to be 11360 g / mol.

[0044] Preparation of matting powder solution: 81 kg of DMF and 19 kg of fumed silica matting powder (Grace C803) were added to a dispersion tank and the mixture was stirred and dispersed to prepare a matting powder solution.

[0045] Preparation of chemical imine accelerator: 50 kg of acetic anhydride and 8 kg of pyridine were dissolved in 35 kg of N-N'-dimethylacetamide to obtain a chemical casting accelerator.

[0046] (2) Add 200 kg of high molecular weight polyamic acid resin 1# to the reaction vessel, then add 6 kg of matting powder solution and 42 kg of low molecular weight intrinsically colored polyamic acid resin color paste 2# and mix evenly. At -5℃, mix continuously and evenly with chemical imidizing accelerator at a ratio of 100:25 in a mixer before the die head, and then inject into the die head. After casting, stretching and high-temperature imidization, a 50-micron thick matte intrinsically colored polyimide film of this embodiment is prepared. High-temperature imidization is a conventional operation in the field. The high-temperature imidization process of each embodiment is the same and will not be described in detail in this invention.

[0047] Example 2:

[0048] The intrinsically colored polyimide film of this embodiment is an intrinsically black polyimide film with a thickness of 25 micrometers. Its performance test parameters are shown in Table 1, and its appearance is as follows. Figure 1 As shown.

[0049] The intrinsically colored polyimide film in this embodiment was prepared using the following method:

[0050] (1) Preparation of high molecular weight polyamic acid resin: consistent with Example 1, high molecular weight polyamic acid resin 1# was obtained.

[0051] Preparation of low molecular weight intrinsically colored polyamic acid resin: 77 kg of N-N'-dimethylacetamide and 17 kg of 4NADA were added to a reaction vessel. After the diamine monomer dissolved, up to 11 kg of pyromellitic dianhydride (PMDA) was added in batches to the reactor. The reaction was carried out at 35 °C for 6 h to obtain low molecular weight intrinsically colored polyamic acid resin paste #1 with good flowability. The weight-average molecular weight was measured to be 5100 g / mol.

[0052] Preparation of matting powder solution: Same as in Example 1.

[0053] Preparation of chemical imine accelerator: Same as in Example 1.

[0054] (2) Add 200 kg of high molecular weight polyamic acid resin 1# to the reaction vessel, then add 6 kg of matting powder solution and mix evenly. Then mix it evenly with low molecular weight intrinsically colored polyamic acid resin paste 1# through a pipeline mixer at a mass ratio of 103:13. Inject it into the mixer before the die head at 5°C. In the mixer before the die head, continuously and evenly mix it with chemical imide accelerator at a ratio of 100:20. Then inject it into the die head and prepare a 25-micron thick matte intrinsically colored polyimide film of this embodiment by casting, stretching and high temperature imidization.

[0055] The transmittance of the intrinsic black polyimide film of this embodiment was tested (five samples were taken for testing), and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the intrinsic black polyimide film of this embodiment has a good light-blocking effect.

[0056] Example 3:

[0057] The intrinsically colored polyimide film of this embodiment is an intrinsically black polyimide film with a thickness of 25 micrometers. Its performance test parameters are shown in Table 1.

[0058] The intrinsically colored polyimide film in this embodiment was prepared using the following method:

[0059] (1) Preparation of high molecular weight polyamic acid resin: 894 kg of N-N' dimethylformamide, 72 kg of 4,4′-diaminodiphenyl ether (ODA) and 15 kg of p-phenylenediamine (PDA) were added to the reaction vessel. After the diamine monomer was dissolved, up to 109 kg of pyromellitic dianhydride (PMDA) was added to the reactor in batches. The reaction was carried out at 35°C for 6 h. The final viscosity was adjusted to 250-300 Pa•S to obtain viscous high molecular weight polyamic acid resin 2#. Its weight average molecular weight was measured to be 815067 g / mol.

[0060] Preparation of low molecular weight intrinsically colored polyamic acid resin: consistent with Example 2, low molecular weight intrinsically colored polyamic acid resin color paste 1# was obtained.

[0061] Preparation of matting powder solution: Same as in Example 1.

[0062] Preparation of chemical imine accelerator: Same as in Example 1.

[0063] (2) Add 200 kg of high molecular weight polyamic acid resin 2# to the reaction vessel, then add 6 kg of matting powder solution and mix evenly. Inject into the mixer before the die head at 0°C. In the mixer, continuously and evenly mix with intrinsically colored polyamic acid resin paste 1# and chemical imide accelerator at a mass ratio of 103:13:20. Inject into the die head and prepare a 25-micron thick matte intrinsically colored polyimide film of this embodiment by casting, stretching and high temperature imidization.

[0064] Example 4:

[0065] The intrinsically colored polyimide film of this embodiment is an intrinsically black polyimide film with a thickness of 25 micrometers. Its performance test parameters are shown in Table 1.

[0066] The intrinsically colored polyimide film in this embodiment was prepared using the following method:

[0067] (1) Preparation of high molecular weight polyamic acid resin: 901 kg of N-N'-dimethylacetamide and 60 kg of 4,4'-diaminodiphenyl ether (ODA) were added to a reaction vessel and dissolved. 76.3 kg of pyromellitic dianhydride (PMDA) was added and reacted at 35°C for 2 h. Then 16.2 kg of p-phenylenediamine was added and reacted at 35°C for 2 h. Finally, up to 58 kg of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the reaction vessel and reacted at 35°C for 4 h. The final viscosity was adjusted to 300-400 Pa•S to obtain viscous high molecular weight polyamic acid resin 3#. The weight-average molecular weight was measured to be 650096 g / mol.

[0068] Preparation of low molecular weight intrinsically colored polyamic acid resin: consistent with Example 2, low molecular weight intrinsically colored polyamic acid resin color paste 1# was obtained.

[0069] Preparation of matting powder solution: Same as in Example 1.

[0070] Preparation of chemical imine accelerator: Same as in Example 1.

[0071] (2) Add 200 kg of high molecular weight polyamic acid resin 3# to the reaction vessel, then add 6 kg of matting powder solution and mix evenly. Inject into the mixer before the die head at 0°C. In the mixer, continuously and evenly mix with intrinsically colored polyamic acid resin paste 1# and chemical imide accelerator at a mass ratio of 103:12:20. Inject into the die head and prepare a 25-micron thick matte intrinsically colored polyimide film of this embodiment by casting, stretching and high temperature imidization.

[0072] Example 5:

[0073] The intrinsically colored polyimide film of this embodiment is an intrinsically black polyimide film with a thickness of 75 micrometers. Its performance test parameters are shown in Table 1.

[0074] The intrinsically colored polyimide film in this embodiment was prepared using the following method:

[0075] (1) Preparation of high molecular weight polyamic acid resin: consistent with Example 1, high molecular weight polyamic acid resin 1# was obtained.

[0076] Preparation of low molecular weight intrinsically colored polyamic acid resin: 70 kg of N-N'-dimethylformamide, 14.3 kg of NDA, and 0.76 kg of 4,4'-diaminodiphenyl ether were added to a reaction vessel. After the diamine monomer dissolved, up to 14.9 kg of pyromellitic dianhydride (PMDA) was added to the reactor in batches. The reaction was carried out at 35°C for 6 h to obtain low molecular weight intrinsically colored polyamic acid resin paste 3# with good flowability. Its weight average molecular weight was measured to be 22050 g / mol.

[0077] Preparation of matting powder solution: Same as in Example 1.

[0078] Preparation of chemical imine accelerator: Same as in Example 1.

[0079] (2) Add 200 kg of high molecular weight polyamic acid resin 1# to the reaction vessel, then add 6 kg of matting powder solution and mix evenly, then add 34 kg of low molecular weight intrinsically colored polyamic acid resin paste 3# and mix evenly. Inject into the die head and prepare a 75-micron thick matte intrinsically colored polyimide film of this embodiment by casting, stretching and high temperature imidization.

[0080] Comparative Example 1:

[0081] The intrinsically colored polyimide film used in this comparative example is the PI-4 product disclosed in Example 3 of Chinese patent application CN113563212A, and its preparation method is described in Example 3 of the same document.

[0082] Comparative Example 2:

[0083] The intrinsically colored polyimide film used in this comparative example is PI-a, as disclosed in the journal article Liu et al. [Preparation and Properties of Inherently Black Polyimide Films with Extremely Low Coecients of Thermal Expansion and Potential Applications for Black Flexible Copper Clad Laminates. Polymers 2020, 12, 576]. The preparation method is described in the same document.

[0084] Performance tests were conducted on each embodiment and comparative example. The test parameters and methods are shown below, and the test results are shown in Table 1.

[0085] Weight-average molecular weight: determined by gel permeation chromatography (GPC);

[0086] Mechanical properties were tested in accordance with GB / T13542.6-2021;

[0087] Transmittance: The transmittance of visible light in the range of 400-700nm was measured in accordance with GB / T2410-2008. The maximum wavelength corresponding to a transmittance of 0.0% was recorded. The larger the wavelength, the better the light-shielding performance of the film.

[0088] Gloss: The gloss at 60° was tested using a gloss meter according to GB / T9754-2007.

[0089] Coefficient of linear expansion (CTE): CTE is tested by TMA at 50℃-250℃ according to ISO11359-2.

[0090]

[0091]

[0092] As can be seen from Table 1, the intrinsic black polyimide film obtained by the present invention possesses excellent optical and mechanical properties.

[0093] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

Claims

1. An intrinsically colored polyimide film obtained by imidizing a polyamide acid composition; characterized in that, The polyamide acid composition comprises a low molecular weight intrinsic colored polyamide acid resin and a high molecular weight polyamide acid resin; the tensile strength of the intrinsic colored polyimide film is >160 MPa, the elongation at break is >40%; the light transmittance of the intrinsic colored polyimide film is less than 0.1% when the thickness is greater than or equal to 25 μm.

2. The intrinsically colored polyimide film according to claim 1, characterized in that, The weight average molecular weight of the low molecular weight intrinsic colored polyamide acid resin is less than 50,000 g / mol, and the weight average molecular weight of the high molecular weight polyamide acid resin is greater than 500,000 g / mol.

3. The intrinsically colored polyimide film according to claim 2, characterized in that, The weight average molecular weight of the low molecular weight intrinsic colored polyamide acid resin is less than 10,000 g / mol, and the weight average molecular weight of the high molecular weight polyamide acid resin is greater than 700,000 g / mol.

4. The intrinsically colored polyimide film according to claim 1, characterized in that, The polyamide acid composition further comprises a matting powder, and the amount of the matting powder added is 2-5% of the mass of the intrinsic colored polyimide film.

5. The intrinsically colored polyimide film according to claim 1, wherein The thickness of the intrinsic colored polyimide film is 8-150 μm.

6. The intrinsically colored polyimide film according to any one of claims 1 to 5, characterized in that, The high molecular weight polyamide acid resin is prepared by polycondensation of an aromatic diamine A and an aromatic dianhydride A in a solvent; the aromatic diamine A comprises at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2-bis{4-(4'-aminophenoxy)phenyl}propane, 1,3-bis(4-aminophenoxy)benzene and 1,4-bis(4-aminophenoxy)benzene; and the aromatic dianhydride A comprises at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride and hexafluorodiphthalic anhydride.

7. The intrinsically colored polyimide film according to any one of claims 1 to 5, characterized in that, The low molecular weight intrinsic colored polyamide acid resin is prepared by polycondensation of an aromatic diamine B, an aromatic amine C and an aromatic dianhydride B in a solvent, the molar ratio of the aromatic amine C and the aromatic diamine B is (50-100):(0-50), and the ratio of the total moles of the aromatic amine C and the aromatic diamine B to the moles of the aromatic dianhydride B is 1:1 to 2:

1. The aromatic diamine B comprises at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2-bis{4-(4'-aminophenoxy)phenyl}propane, 1,3-bis(4-aminophenoxy)benzene and 1,4-bis(4-aminophenoxy)benzene; and the aromatic dianhydride B comprises at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride and hexafluorodiphthalic anhydride. The aromatic amine C includes an auxiliary color group or chromophore group containing aromatic amine monomer and / or electron-rich diamine monomer; the auxiliary color group or chromophore group containing aromatic amine monomer includes 1,8 dihydroxy-2,4,5,7 tetraamino-9,10-anthraquinone; the electron-rich diamine monomer includes at least one of , , , , and . The aromatic dianhydride B comprises at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride and hexafluorodiphthalic anhydride.

8. The intrinsically colored polyimide film according to claim 7, characterized in that, The aromatic amine C is selected from at least one of 1,8 dihydroxy-2,4,5,7 tetraamino-9,10-anthraquinone, and ​ 9. A method for producing the intrinsically colored polyimide film according to any one of claims 1 to 8, characterized by, The method comprises the following steps: (1) preparing or taking a low molecular weight intrinsic colored polyamide acid resin and a high molecular weight polyamide acid resin to obtain the polyamide acid composition; (2) preparing the intrinsic colored polyimide film from the polyamide acid composition by a chemical imidization method or a thermal imidization method.

10. The method of producing an intrinsically colored polyimide film according to claim 9, wherein The solid content of the low molecular weight intrinsic colored polyamide acid resin is 25-35%, and the solid content of the high molecular weight polyamide acid resin is 15-25%.

11. The method of producing an intrinsically colored polyimide film according to claim 9 or 10, characterized in that, The operation of the chemical imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution and the chemical imine promoter at-5℃ to 10℃, the matte intrinsic color polyimide film is prepared by casting, stretching and high-temperature imidization.

12. The method of producing an intrinsically colored polyimide film according to claim 11, wherein The matting powder solution is uniformly mixed with the high-molecular-weight polyamide acid resin in a reaction container in advance, and then uniformly mixed with the low-molecular-weight intrinsic color polyamide acid resin and the chemical imine promoter in a mixer before a die to be injected into the die for casting.

13. The method of producing an intrinsically colored polyimide film according to claim 9 or 10, characterized in that, The operation of the thermal imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution at 10 to 35℃, the matte intrinsic color polyimide film is directly prepared by casting, stretching and high-temperature imidization.

14. The method of producing an intrinsically colored polyimide film according to claim 13, characterized in that, The high-molecular-weight polyamide acid resin and the matting powder solution are uniformly mixed in a reaction container in advance, and then uniformly mixed with the low-molecular-weight intrinsic color polyamide acid resin by a pipe mixer to be injected into a die for casting.

15. The method of producing an intrinsically colored polyimide film according to claim 9 or 10, wherein The intrinsic color polyimide film is prepared by the chemical imine method in step (2). The operation of the chemical imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution and the chemical imine promoter at-5℃ to 10℃, the matte intrinsic color polyimide film is prepared by casting, stretching and high-temperature imidization. The matting powder solution is uniformly mixed with the high-molecular-weight polyamide acid resin in a reaction container in advance, and then uniformly mixed with the low-molecular-weight intrinsic color polyamide acid resin and the chemical imine promoter in a mixer before a die to be injected into the die for casting. The operation of the thermal imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution at 10 to 35℃, the matte intrinsic color polyimide film is directly prepared by casting, stretching and high-temperature imidization. The high-molecular-weight polyamide acid resin and the matting powder solution are uniformly mixed in a reaction container in advance, and then uniformly mixed with the low-molecular-weight intrinsic color polyamide acid resin by a pipe mixer to be injected into a die for casting. The intrinsic color polyimide film is prepared by the chemical imine method in step (2). The operation of the chemical imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution and the chemical imine promoter at-5℃ to 10℃, the matte intrinsic color polyimide film is prepared by casting, stretching and high-temperature imidization. The matting powder solution is uniformly mixed with the high-molecular-weight polyamide acid resin in a reaction container in advance, and then uniformly mixed with the low-molecular-weight intrinsic color polyamide acid resin and the chemical imine promoter in a mixer before a die to be injected into the die for casting. The operation of the thermal imine method is: after the polyamide acid composition is uniformly mixed with the matting powder solution at 10 to 35℃, the matte intrinsic color polyimide film is directly prepared by casting, stretching and high-temperature imid

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