Purple black polyimide fiber as well as preparation method and application thereof

Abstract

The invention provides a purple black polyimide fiber and a preparation method and application thereof, and the preparation method comprises the following steps: (1) dissolving copper ions: dissolving copper salt in a proper amount of organic solvent to obtain a solution containing bivalent copper ions; (2) preparing a spinning solution, namely adding a dianhydride monomer and a diamine monomer into the solution containing the bivalent copper ions according to a certain molar ratio to synthesize, defoaming the spinning solution, spinning by adopting a wet method or a dry-wet method, and solidifying, washing, drying and carrying out thermal imidization, so as to obtain the bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole unit-containing bivalent copper ion / benzimidazole compound. Finished fibers are obtained. Compared with a dyeing process, the production process disclosed by the invention has the advantage of high color fastness, and the method is simple in process, relatively low in production cost, safe and environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of high-performance fibers, and in particular to a colored polyimide fiber and a preparation method and application thereof. Background Art

[0002] High-performance polyimide fibers have broad application prospects in aerospace, electronic power, safety protection and other fields due to their high specific strength, high specific modulus, excellent heat resistance, flame retardancy, low dielectric, and corrosion resistance. Polyimide fibers are inherently golden yellow. In order to meet the needs of different application fields, polyimide fibers of different colors need to be constructed. However, due to their high glass transition temperature and strong surface inertness, it is difficult to obtain colored fibers with high color fastness by using methods such as carrier dyeing and surface modification dyeing.

[0003] Solution coloring refers to using appropriate pigments and evenly dispersing the pigments in the polyamic acid spinning solution, and spinning after sufficient mixing. Compared with carrier dyeing and surface modification dyeing methods, solution coloring can obtain fibers with high color fastness. However, in this method, the suspension system composed of pigment particles and spinning solution is a thermodynamically and kinetically unstable system, which requires high compatibility between the pigment particles and the spinning solution to avoid agglomeration of the spinning solution during storage.

[0004] By utilizing the designability of the polyimide molecular structure and introducing monomers with coloring or light absorption properties, colored polyimide fibers can be obtained. For example, Chinese patent document CN105734710A discloses a method for preparing colored polyimide fibers, which comprises the following steps: (1) firstly adding diamine monomer A and diamine monomer B into an organic solvent, stirring at room temperature until completely dissolved, adding dianhydride monomer while controlling the temperature of the mixed organic solvent at -10-20°C, and performing polymerization reaction for 2-6 hours to obtain colored polyimide fibers. Amine acid spinning stock solution; (2) the colored polyamic acid spinning stock solution in step (1) is subjected to vacuum degassing and filtration treatment, and then transported to a dry spinning tunnel through a spinning metering pump through a spinneret, a certain amount of hot air is introduced, and after the solvent is evaporated and the stock solution is solidified, polyamic acid primary fibers are obtained; (3) the polyamic acid primary fibers in step (2) are treated in a hot environment of 200-350°C for 1-3 hours, and then drawn to 1-4 times at 350-450°C, to obtain colored polyimide fibers. In the above method, the diamine monomer A diaminoanthraquinone is a color developer, and the fiber is made black by copolymerization, but anthraquinone itself has certain toxicity and is relatively expensive, which is not conducive to industrial production. Summary of the invention

[0005] In view of the above problems existing in the prior art and in order to make up for the deficiencies existing in the prior art, the object of the present invention is to provide a purple-black polyimide fiber having a special color, uniform color and high color fastness.

[0006] Another object of the present invention is to provide a method for preparing purple-black polyimide fiber, which is safer, more environmentally friendly and more cost-effective.

[0007] Another object of the present invention is to provide an application of the purple-black polyimide fiber.

[0008] According to the purpose of the present invention, the present invention provides a purple-black polyimide fiber, whose chemical structure contains benzimidazole units and divalent copper ions, and the molar ratio of the divalent copper ions to the benzimidazole units is 1:3 to 1:8; in the same roll of purple-black polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2 or ≤1, and the color fastness to soap washing of the purple-black polyimide fiber is not less than level four or level five.

[0009] The polyimide fiber provided by the present invention is purple-black in color, and the fiber color is uniform. In the same roll of purple-black polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2, and the color fastness to soaping reaches level 5, thereby providing a polyimide fiber with unique color and excellent performance, and making up for the shortcomings in the prior art.

[0010] According to another object of the present invention, the present invention provides a method for preparing purple-black polyimide fiber, which comprises the following steps:

[0011] (1) Dissolution of copper ions: dissolving a copper salt in an appropriate amount of an organic solvent to obtain a solution containing divalent copper ions;

[0012] (2) Preparation of spinning solution: adding dianhydride monomer and diamine monomer in a certain molar ratio to the solution containing divalent copper ions for synthesis, maintaining the molar ratio of amine group to anhydride group at 1:1, the molar ratio of divalent copper ions to diamine monomer containing benzimidazole units at 1:3-1:8, adjusting the solid content of the solution to 12%-20% by mass, and then degassing;

[0013] (3) Spinning: The defoamed spinning solution is transported to the spinneret through a pipeline driven by a metering pump for spinning. A wet spinning process or a dry-wet spinning process is adopted. The spinning solution is spun, coagulated, and washed to obtain polyamic acid primary fibers.

[0014] (4) Thermal imidization: The polyamic acid primary fiber is dried at 80°C-120°C, and then thermally imidized at 240°C-500°C to obtain a finished fiber, i.e., purple-black polyimide fiber.

[0015] In the present invention, the copper salt is a salt that can dissociate copper ions, for example, it can be one or more copper salts selected from copper acetate, copper chloride, copper pyridine sulfate, copper ethylenediaminetetraacetate, etc. In a preferred embodiment of the present invention, copper chloride is used, but it can be replaced by other types of copper salts.

[0016] In the present invention, the organic solvent used is the solvent used in synthesizing polyamic acid (PAA), which can generally be selected from tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, etc., preferably dimethylacetamide.

[0017] In the present invention, in the above step (1), "appropriate amount of organic solvent" means that the amount of organic solvent can make the copper salt dissolve in the organic solvent, and in the above step (2), "certain molar ratio" means that the ratio of dianhydride monomer to diamine monomer can meet the needs of synthesizing polyamic acid. Based on this, those skilled in the art can appropriately adjust the amount of "organic solvent" and the molar ratio of dianhydride monomer to diamine monomer.

[0018] In the above step (2), the solid content can be selected in the range of 12%-20% by mass, for example, 13%, 14%, 15%, 16%, 17%, 18%, 19%.

[0019] In the preparation method of the present invention, suitable dianhydride monomers and diamine monomers can be used according to performance requirements and the monomer ratio in the spinning solution can be adjusted. However, since copper ions are only complexed with benzimidazole units, diamine monomers containing benzimidazole units must be included in the diamine monomers. The diamine monomer containing benzimidazole units can be selected from diamine monomers containing benzimidazole units commonly used in the art, such as 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), benzimidazole-1,2-diamine, etc. Preferably, the diamine monomer containing benzimidazole units is BIA.

[0020] In the present invention, the diamine monomers, in addition to the diamine monomers containing benzimidazole units, also include other diamine monomers, which are diamine monomers that do not contain benzimidazole units. As long as the conditions are met, the diamine monomers commonly used in the art can be used, including diaminodiphenyl ether (ODA), m-phenylenediamine (MDA), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (MTD), etc. Regarding the dianhydride monomers, the dianhydride monomers commonly used in the art can be used, such as pyromellitic anhydride (PMDA), including biphenyl dianhydride (BPDA), hexafluorodianhydride (6FDA), diphenyl ether tetracarboxylic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), etc. Preferably, in step (2), the other diamine monomers are p-phenylenediamine (PDA), and the dianhydride monomers are biphenyl dianhydride (BPDA).

[0021] Preferably, in step (2), the diamine monomers, namely PDA and BIA, are first added to a reactor containing the solution containing divalent copper ions and stirred. After being fully mixed for 0.5 hours, an appropriate amount of BPDA is weighed and slowly added to the reactor. After the addition of the materials, stirring is continued for 2 to 3 hours, and then the mixture is transferred to a spinning tank for degassing.

[0022] Preferably, in step (3), during spinning, the concentration of the coagulation bath is 6-9%.

[0023] The polyimide fiber prepared by the method of the present invention is purple-black in color, and the fiber color is uniform. In the same roll of purple-black polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2, and the color fastness to soaping reaches level 5. In addition, the method of the present invention can adjust the fiber color according to actual needs by adjusting the molar ratio of copper ions to benzimidazole units.

[0024] In a preferred embodiment, the preparation method of the present invention comprises the following steps:

[0025] (1) Dissolution of copper ions: dissolve copper chloride in an appropriate amount of organic solvent;

[0026] (2) Preparation of spinning solution: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), p-phenylenediamine (PDA) and BIA were added to an organic solvent at a monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3 for synthesis, the molar ratio of amine group to anhydride group was maintained at 1:1, the molar ratio of copper chloride to 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) was maintained at 1:4, the solid content of the solution was adjusted to 12%-20%, and then degassing was performed;

[0027] (3) Spinning: During the spinning process, the degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump for spinning. The spinning solution is spun, coagulated, and washed to obtain primary fibers by wet or dry-wet spinning.

[0028] (4) Thermal imidization: The as-spun fibers are dried at 80°C-120°C and then subjected to gradient imidization at 240°C-500°C to obtain finished fibers, i.e., purple-black polyimide fibers.

[0029] The fiber color is purple-black (RGB (29, 22, 38)) and the color is uniform. In the same roll of colored polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2. The color fastness to soap washing reaches level 5.

[0030] The intermolecular forces inside the polyimide fiber are strong and the fiber surface lacks active groups, the fiber has poor binding ability with dye molecules, and the inherent color of the fiber itself limits the application of the polyimide fiber. The polyimide fiber with high color fastness can be obtained by using the stock solution coloring method, but the suspension system composed of the pigment particles and the spinning solution in this method belongs to a thermodynamically and kinetically unstable system, and the pigment particles are prone to agglomeration, which affects the stability of the fiber fineness and the uniformity of the fiber color. In the present invention, the benzimidazole unit after complexing with copper ions is used as the chromophore, and there is no need to carry out the dispersion process of the pigment particles, which avoids the sedimentation, agglomeration and dispersion problems of the pigment particles in the general stock solution coloring process, and improves the stability of the process.

[0031] According to another object of the present invention, on the one hand, the present invention provides the use of the purple-black polyimide fiber or the purple-black polyimide fiber obtained by the above preparation method in the fields of aerospace, high temperature protection or textile.

[0032] On the other hand, the present invention provides a continuous filament, a staple fiber, a woven fabric, a nonwoven fabric or a powder, which comprises the purple-black polyimide fiber or the purple-black polyimide fiber obtained by the above preparation method.

[0033] The present invention also provides a fiber-reinforced composite material, a high-temperature protective material or a textile material, which comprises the above-mentioned continuous filaments, short fibers, woven fabrics, nonwoven fabrics or powders.

[0034] In addition, the present invention also provides a prepreg, which comprises the purple-black polyimide fiber or the purple-black polyimide fiber obtained by the above preparation method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The benzimidazole unit complexed with copper ions is used as the chromophore, which is convenient for cost control and has good coloring effect, uniform coloring, and avoids the stability problem of the dispersed system;

[0037] (2) By adjusting the molar ratio of BIA to copper ions, the fiber color can be controlled to a certain extent;

[0038] (3) There is no need to change the main structure of the molecular chain, and no need to add additional steps in the conventional spinning process, which is conducive to reducing costs;

[0039] (4) It does not use toxic and expensive anthraquinone compounds, is safer and more environmentally friendly, and can effectively reduce production costs. DETAILED DESCRIPTION

[0040] <Fiber>

[0041] The fiber of the present invention is a polyimide fiber. As used herein, the term polyimide filament refers to a filament made of a polyimide polymer.

[0042] In some embodiments, fiber is in the form of continuous filaments. For the purpose of this paper, the term "filament" is defined as a relatively flexible, macroscopically uniform and body with a high aspect ratio on a cross section perpendicular to its length. The filament cross section can be any shape, but is typically circular. The multifilament wound onto the bobbin in a package comprises multiple continuous filaments. In the context of the present disclosure, the terms filament and fiber are used interchangeably.

[0043] Other suitable forms of fiber materials are staple fibers, wovens, nonwovens or powders, which terms are well known in the field of textile fibers.

[0044] Embodiments similar to those described above are applicable to filaments, staple fibers, wovens, nonwovens or powders.

[0045] <Composite Materials>

[0046] The purple-black polyimide fiber of the present invention can be combined with matrix resin to form a fiber-reinforced resin composite material. Suitable fiber forms include continuous filaments, staple fibers, woven fabrics, nonwovens or powders. Resin can be a thermosetting resin or a thermoplastic resin. Usually, in composite materials, matrix resin accounts for 20% to 50% by weight of the weight of fiber plus resin. Suitable thermosetting resins include epoxy resins, phenolic resins, epoxy-thermoplastic novolac resins, cyanate esters, unsaturated esters, melamine and maleimide. Fiber can be processed by any of the above methods.

[0047] Embodiments similar to those described above are applicable to fibers in filament, staple, woven, nonwoven or powder form.

[0048] Purple-black polyimide fiber of the present invention can be merged with matrix resin to form fiber-reinforced resin composite material. Suitable fiber forms include continuous filament, staple fiber, woven fabric, nonwoven fabric or powder. Resin can be thermosetting resin or thermoplastic resin. Usually, matrix resin accounts for 20 wt % to 50 wt % of the weight of fiber plus resin in composite material. Suitable thermosetting resin includes epoxy resin, phenolic resin, epoxy-thermoplastic novolac resin, cyanate ester, unsaturated ester, melamine and maleimide etc.

[0049] The abbreviations and key terms used in the present invention are defined as follows: 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), p-phenylenediamine (PDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and dimethylacetamide (DMAc); in the present invention, nascent fibers refer to fibers formed by solidifying polymer streams extruded from spinnerets in a spinning field, and are fibers that have not been heat-treated; finished fibers are fibers obtained by heat-treating nascent fibers.

[0050] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0051] The fiber performance testing methods and conditions in the following examples and comparative examples are as follows:

[0052] Fiber color fastness: SW-8A washing color fastness tester is used for testing in accordance with standard GB / T 3921-2008.

[0053] Color difference: Four points are randomly selected from a roll of fiber and tested using a DS620 high-precision colorimeter. The CIELAB value of one point is used as the reference. The color difference between the other three points and the reference point is calculated in accordance with standard GB / T / 8424.3-2001. The calculation formula is:

[0054] ΔE ab * =[(L S * -L R * ) 2 +(a S * -a R * ) 2 +(b S * -b R * ) 2 ] 1 / 2

[0055] Where R and S are the CIELAB values ​​of the reference point and other points respectively.

[0056] Embodiment 1:

[0057] First, dissolve cupric chloride in an appropriate amount of DMAc, and the molar ratio of cupric chloride to BIA is 1:4. Synthesis is carried out according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, the molar ratio of amine group to anhydride group is 1:1, and the solid content of the solution is adjusted to 18%. During the synthesis, the diamine monomers PDA and BIA are first added to the solution containing divalent copper ions, and after fully stirring and mixing in the reactor for 0.5 hours, BPDA is weighed and slowly added to the reactor for polymerization. After adding the materials, continue stirring for 2-3 hours, and then transfer to the spinning tank for degassing.

[0058] The degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the wet spinning process is used to spin the raw fiber, wherein the concentration of the coagulation bath is 6%. The raw fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0059] The polyimide fiber prepared in this embodiment is purple-black (RGB (29, 22, 38)), the fiber color is uniform, four points are randomly selected from the same roll of fiber, the maximum color difference is 0.79, and the color fastness to soap washing is level 5.

[0060] Embodiment 2:

[0061] Before synthesis, firstly, copper acetate is dissolved in an appropriate amount of DMAc, and the molar ratio of copper chloride to BIA is 1:6. Synthesis is carried out according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, the molar ratio of amine group to anhydride group is maintained at 1:1, and the solid content of the solution is 18%. During the synthesis, the above-mentioned diamine monomers PDA and BIA are first added to the solution containing divalent copper ions, and after being fully stirred in the reactor for 0.5 hours, an appropriate amount of BPDA is weighed and slowly added to the reactor for polymerization. After adding the materials, stirring is continued for 2 hours to 3 hours, and then transferred to the spinning tank for degassing.

[0062] The deaerated spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the dry-wet spinning process is used to spin the primary fiber, wherein the coagulation bath concentration is 6%. The primary fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0063] The polyimide fiber prepared in this embodiment is purple-black (RGB (76, 60, 74)), and the fiber color is uniform. Four points are randomly selected from the same roll of fiber, and the maximum color difference is 0.65. The color fastness to soap washing is level 5.

[0064] Embodiment 3:

[0065] Before synthesis, cupric chloride was first dissolved in an appropriate amount of DMAc, and the molar ratio of cupric chloride to BIA was 1:8. Synthesis was performed according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, the molar ratio of amine group to anhydride group was maintained at 1:1, and the solid content of the solution was 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA were first added to the reactor, and after fully stirring for 0.5 hours, an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization, and continued to stir for 2 hours to 3 hours, and then transferred to the spinning tank for degassing.

[0066] The degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the wet spinning process is used to spin the raw fiber, wherein the concentration of the coagulation bath is 6%. The raw fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0067] The polyimide fiber prepared in this embodiment is purple-black (RGB (54, 42, 50)), and the fiber color is uniform. Four points are randomly selected from the same roll of fiber, and the maximum color difference is 0.83. The color fastness to soap washing is level 5.

[0068] Embodiment 4:

[0069] Before synthesis, cupric chloride was first dissolved in an appropriate amount of DMAc, and the molar ratio of cupric chloride to BIA was 1:3. During synthesis, the synthesis was carried out according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, the molar ratio of amine group to anhydride group was maintained at 1:1, and the solid content of the solution was 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA were first added to the reactor and fully stirred for 0.5 hours, and then an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization, and continued to stir for 2 hours to 3 hours, and then transferred to the spinning tank for degassing.

[0070] During the spinning process, the degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the wet spinning process is used to spin the raw fiber, wherein the coagulation bath concentration is 6%. The raw fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0071] The polyimide fiber prepared in this embodiment is purple-black (RGB (18, 15, 17)), and the fiber color is uniform. Four points are randomly selected from the same roll of fiber, and the maximum color difference is 0.76. The color fastness to soap washing is level 5.

[0072] Comparative Example 1:

[0073] During the synthesis, the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3 was used for synthesis, the molar ratio of amine group to anhydride group was maintained at 1:1, and the solid content of the solution was 18%. First, the diamine monomers PDA and BIA were added to the reactor and stirred. After being fully mixed for 0.5 hours, an appropriate amount of BPDA was weighed and slowly added to the reactor. After adding the materials, stirring was continued for 2-3 hours, and then transferred to the spinning tank for degassing.

[0074] The degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the wet spinning process is used to spin the raw fiber, wherein the concentration of the coagulation bath is 6%. The raw fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0075] The color of the polyimide fiber prepared in this comparative example is yellow-brown (RGB (218, 165, 32)).

[0076] Comparative Example 2:

[0077] First, cupric chloride was dissolved in an appropriate amount of DMAc, and the molar ratio of cupric chloride to BIA was 1:2. Synthesis was performed according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, and the molar ratio of amine group to anhydride group was maintained at 1:1. The solid content of the solution was 18%. During the synthesis, the above diamine monomers PDA and BIA were first added to the reactor and fully stirred for 0.5 hours, and then an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization. After stirring for 2 hours, the solution became gel-like and lost fluidity, which was not suitable for spinning.

[0078] Comparative Example 3

[0079] First, cupric chloride was dissolved in an appropriate amount of DMAc, and the molar ratio of cupric chloride to BIA was 1:10. Synthesis was performed according to the monomer molar ratio of BPDA:PDA:BIA=1:0.7:0.3, the molar ratio of amine group to anhydride group was maintained at 1:1, and the solid content of the solution was 18%. During the synthesis, the above diamine monomers PDA and BIA were first added to the reactor and fully stirred for 0.5 hours, and then an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization, and continued to stir for 2 hours to 3 hours, and then transferred to the spinning tank for degassing.

[0080] The degassed spinning solution is transported to the spinneret through a pipeline driven by a metering pump, and the wet spinning process is used to spin the raw fiber, wherein the concentration of the coagulation bath is 6%. The raw fiber should be dried at 120°C, and then subjected to gradient imidization at 240°C to 450°C to obtain the finished fiber.

[0081] The color of the fiber prepared in this comparative example is brown (RGB (112, 66, 20)), the fiber color is uniform, four points are randomly selected from the same roll of fiber, the maximum color difference is 0.48, and it has good color fastness, and the color fastness to soap washing is level 5.

[0082] In the above-mentioned embodiments 1 to 4, the preparation method of the purple-black polyimide fiber of the present invention is safer, more environmentally friendly and cost-saving. In addition, by adopting the preparation method of the present invention, a purple-black high-performance polyimide fiber can be obtained, the color is uniform, and the maximum color difference of four points randomly taken from the same roll of fiber is ≤2.0, and the color fastness is good, and the color fastness to soaping reaches level 4 or above. In contrast, in the above-mentioned comparative example 1, no copper ions are added, and the fiber color is yellow-brown, which cannot meet the requirements of purple-black. In comparative example 2, the molar ratio of copper chloride to BIA is greater than 1:3, and the resulting solution cannot meet the needs of spinning. In the above-mentioned comparative example 3, the molar ratio of copper chloride to BIA is less than 1:8, and the fiber color is brown, which cannot meet the requirements of purple-black.

[0083] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A purple-black polyimide fiber, the chemical structure of which contains benzimidazole units and divalent copper ions, and the molar ratio of the divalent copper ions to the benzimidazole units is 1:3 to 1:8; In the same roll of purple-black polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2 or ≤1, and the color fastness to soap washing of the purple-black polyimide fiber is not less than level four or level five.

2. A method for preparing the purple-black polyimide fiber according to claim 1, characterized in that: The following steps are involved: (1) Dissolution of copper ions: dissolving a copper salt in an appropriate amount of an organic solvent to obtain a solution containing divalent copper ions; (2) Preparation of spinning solution: adding dianhydride monomer and diamine monomer to the solution containing divalent copper ions in a certain molar ratio for synthesis, maintaining the molar ratio of amine group to anhydride group at 1:1, the molar ratio of divalent copper ions to the diamine monomer containing benzimidazole units at 1:3-1:8, adjusting the solid content of the solution to 12%-20% by mass, and then degassing; (3) Spinning: During the spinning process, the degassed spinning solution is transported to the spinneret through a pipeline under the push of a metering pump for spinning, and polyamic acid primary fibers are obtained by wet spinning or dry-wet spinning; (4) Thermal imidization: The polyamic acid primary fiber is dried at 80°C-120°C, and then thermally imidized at 240°C-500°C to obtain a finished fiber, i.e., a purple-black polyimide fiber.

3. The method for preparing the purple-black polyimide fiber according to claim 2, wherein: The copper salt of divalent copper ions is a salt that can dissociate into divalent copper ions, and is one or more selected from copper acetate, copper chloride, copper pyridine sulfate, and copper ethylenediaminetetraacetate; and / or The organic solvent is a solvent used in synthesizing polyamic acid, and is one or more selected from tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

4. The method for preparing the purple-black polyimide fiber according to claim 2, wherein: The diamine monomer containing a benzimidazole unit is one or more selected from 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), benzimidazole-1,2-diamine; and / or Among the diamine monomers, other diamine monomers except the diamine monomer containing benzimidazole units are one or more selected from diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), m-phenylenediamine (MDA), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (MTD); and / or The dianhydride monomer is one or more selected from pyromellitic anhydride (PMDA), biphenyl dianhydride (BPDA), hexafluoro dianhydride (6FDA), diphenyl ether tetracarboxylic dianhydride (ODPA), and benzophenone tetracarboxylic dianhydride (BTDA).

5. The method for preparing the purple-black polyimide fiber according to claim 4, wherein: The diamine monomer containing benzimidazole units is 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), the other diamine monomer is p-phenylenediamine (PDA), and the dianhydride monomer is biphenyl dianhydride (BPDA).

6. The method for preparing the purple-black polyimide fiber according to claim 2, characterized in that: In step (2), firstly, the diamine monomer is added into the reactor containing the solution containing divalent copper ions and stirred, and after being fully mixed for more than 0.5 hour, an appropriate amount of dianhydride monomer is weighed and slowly added into the reactor, and after the addition of the materials, stirring is continued for 2 to 3 hours, and then the mixture is transferred to a spinning tank for degassing; and / or In step (3), during spinning, the coagulation bath concentration is 6-9%.

7. Use of the purple-black polyimide fiber according to claim 1 or the purple-black polyimide fiber obtained by the preparation method according to any one of claims 2 to 6 in the fields of aerospace, high temperature protection or textile.

8. A continuous filament, staple fiber, woven fabric, nonwoven fabric or powder, comprising the purple-black polyimide fiber of claim 1 or the purple-black polyimide fiber obtained by the preparation method of any one of claims 2 to 6.

9. A fiber-reinforced composite material, high temperature protective material or textile material, comprising the continuous filament, short fiber, woven fabric, nonwoven fabric or powder according to claim 8.

10. A prepreg comprising the purple-black polyimide fiber according to claim 1 or the purple-black polyimide fiber obtained by the preparation method according to any one of claims 2 to 6.