A kind of purple black polyimide fiber and its preparation method and application

Abstract

The application provides a kind of purple black polyimide fiber and its preparation method and application, which comprises the following steps: (1) dissolving of copper ions: dissolving copper salt in a suitable amount of organic solvent to obtain a solution containing divalent copper ions; (2) preparation of spinning solution: adding dianhydride monomer and diamine monomer according to a certain molar ratio into the solution containing divalent copper ions for synthesis, the molar ratio of divalent copper ions to diamine monomer containing benzimidazole unit is 1:3-1:8, the spinning solution is deaerated and then spun by wet spinning or dry-wet spinning, and the finished fiber is obtained after coagulation, washing, drying and thermal imidization. Compared with the dyeing process, the production process has the advantage of high color fastness, and the method is simple, low in production cost and safe and environmentally friendly.

Description

TECHNICAL FIELD

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

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

[0003] Dyeing in the original solution refers to using appropriate pigments and uniformly dispersing the pigments in the polyamide acid spinning solution. Compared with carrier dyeing and surface modification dyeing methods, dyeing in the original solution can obtain fibers with high color fastness. However, in this method, the pigment particles and the spinning solution form a suspension system which is unstable in thermodynamics and kinetics. Therefore, the pigment particles and the spinning solution need to have high compatibility to avoid the aggregation of the spinning solution during storage.

[0004] By utilizing the designability of the polyimide molecular structure, monomers with color development or light absorption properties can be introduced to obtain colored polyimide fibers. For example, Chinese patent document CN105734710A discloses a preparation method of colored polyimide fibers, which comprises the following steps: (1) first, diamine monomer A and diamine monomer B are added to an organic solvent, stirred at room temperature until completely dissolved, and then dianhydride monomer is added when the temperature of the mixed organic solvent is controlled at -10-20℃. After 2-6 hours of polymerization reaction, colored polyamide acid spinning solution is obtained; (2) the colored polyamide acid spinning solution in step (1) is vacuum degassed and filtered, then transported to a dry spinning duct through a spinning metering pump via a spinneret, a certain amount of hot air is introduced, and after solvent evaporation and original solution solidification, polyamide acid as-spun fiber is obtained; (3) the polyamide acid as-spun fiber in step (2) is treated in a hot environment at 200-350℃ for 1-3 hours, and then stretched to 1-4 times at 350-450℃, to obtain colored polyimide fiber. In the above method, diamine monomer A, i.e. diaminoanthraquinone, is a color developer, and the fiber is blackened by copolymerization. However, anthraquinone itself has certain toxicity and is high in price, which is not conducive to industrial production. SUMMARY

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

[0006] Another objective of this invention is to provide a method for preparing purple-black polyimide fibers that is safer, more environmentally friendly, and more cost-effective.

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

[0008] According to the purpose of this invention, a purple-black polyimide fiber is provided, which contains benzimidazole units in its chemical structure and includes divalent copper ions, wherein 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 of the purple-black polyimide fiber to soap washing is not lower than grade four or grade five.

[0009] The polyimide fiber provided by this invention is purplish-black in color and has a uniform color. In the same roll of purplish-black polyimide fiber, four points are randomly selected and the maximum color difference is ≤2. The color fastness to soap washing reaches level 5. Thus, it can provide polyimide fiber with unique color and excellent performance, making up for the shortcomings of the prior art.

[0010] According to another objective of the present invention, a method for preparing purplish-black polyimide fibers is provided, comprising the following steps:

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

[0012] (2) Preparation of spinning solution: Add dianhydride monomer and diamine monomer to the solution containing divalent copper ions in a certain molar ratio for synthesis, maintain the molar ratio of amino group to anhydride group at 1:1, the molar ratio of divalent copper ions to diamine monomer containing benzimidazole unit at 1:3-1:8, adjust the solid content of the solution to 12%-20% by mass, and then degas.

[0013] (3) Spinning: The defoamed spinning solution is transported to the spinneret by a pipeline under the push of a metering pump for spinning. Wet or dry-wet spinning process is adopted. The spinning solution is spun, coagulated and washed to obtain polyamic acid nascent fiber.

[0014] (4) Thermal imidization: The polyamic acid nascent fiber is dried at 80℃-120℃ and then thermal imidized at 240℃-500℃ to obtain the finished fiber, namely purple-black polyimide fiber.

[0015] In this invention, the copper salt is a salt capable of dissociating 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 this invention, copper chloride is used, but it can be replaced by other types of copper salts.

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

[0017] In this invention, in step (1) above, "appropriate amount of organic solvent" means that the amount of organic solvent is sufficient to dissolve the copper salt in the organic solvent. In step (2) above, "a certain molar ratio" means that the ratio of dianhydride monomer and 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 and diamine monomer.

[0018] In step (2) above, the solid content, expressed as a percentage by mass, can be selected within the range of 12% to 20%, for example, 13%, 14%, 15%, 16%, 17%, 18%, or 19%.

[0019] In the preparation method of this 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 only complex with benzimidazole units, the diamine monomer must contain a benzimidazole unit. The benzimidazole-containing diamine monomer can be selected from commonly used benzimidazole-containing diamine monomers in the art, such as 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), benzimidazole-1,2-diamine, etc. Preferably, the benzimidazole-containing diamine monomer is BIA.

[0020] In this invention, the diamine monomers, in addition to those containing a benzimidazole unit, also include other diamine monomers. These other diamine monomers are those that do not contain a benzimidazole unit. Any diamine monomer commonly used in the art can be used, as long as this condition is met, including diaminodiphenyl ether (ODA), m-phenylenediamine (MDA), 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (MTD), etc. Regarding the dianhydride monomers, any dianhydride monomers commonly used in the art can be used, such as pyromellitic dianhydride (PMDA), including biphenyl dianhydride (BPDA), hexafluorodianhydride (6FDA), diphenyl ether tetracarboxylic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), etc. Preferably, in step (2), the other diamine monomer is p-phenylenediamine (PDA), and the dianhydride monomer is biphenyl dianhydride (BPDA).

[0021] Preferably, in step (2), the diamine monomers, namely PDA and BIA, are first added to a reaction vessel 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 reaction vessel. After the addition is complete, stirring is continued for 2-3 hours, and then the mixture is transferred to a spinning tank for degassing.

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

[0023] The polyimide fibers prepared by the method of this invention are purplish-black in color and have a uniform color. Within the same roll of purplish-black polyimide fibers, four randomly selected points show a maximum color difference of ≤2, and the color fastness to soap washing reaches grade 5. Furthermore, the method of this invention allows for adjustment of 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 includes 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 dianhydride (BPDA), p-phenylenediamine (PDA), and BIA were added to an organic solvent in a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3 for synthesis. The molar ratio of amino groups to anhydride groups was maintained at 1:1, and the molar ratio of copper chloride to 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) was 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 defoamed spinning solution is transported to the spinneret by a metering pump through a pipeline for spinning. Wet or wet-dry spinning processes are used, and the spinning solution is spun, coagulated, and washed to obtain nascent fibers.

[0028] (4) Thermal imidization: After drying the above-mentioned nascent fibers at 80℃-120℃, they are then subjected to gradient imidization at 240℃-500℃ to obtain the finished fiber, namely the purple-black polyimide fiber.

[0029] The fiber color is purplish-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. Its color fastness to soaping reaches level 5.

[0030] Polyimide fibers have strong intermolecular forces and lack active groups on their surface, resulting in poor binding ability between the fiber and dye molecules. Combined with the inherent color of the fiber itself, this limits the applications of polyimide fibers. Solution dyeing can produce polyimide fibers with high color fastness, but the suspension system formed by the pigment particles and spinning solution in this method is thermodynamically and kinetically unstable, making pigment particles prone to aggregation, affecting the stability of fiber fineness and the uniformity of fiber color. In this invention, benzimidazole units complexed with copper ions are used as chromophores, eliminating the need for pigment particle dispersion. This avoids the sedimentation, aggregation, and dispersion problems of pigment particles in conventional solution dyeing processes, thus improving process stability.

[0031] In another aspect, according to the present invention, the present invention provides the application of the above-described purplish-black polyimide fiber or the purplish-black polyimide fiber obtained by the above preparation method in the fields of aerospace, high-temperature protection or textiles.

[0032] On the other hand, the present invention provides a continuous filament, short fiber, woven fabric, nonwoven fabric or powder comprising the above-mentioned purplish-black polyimide fiber or purplish-black polyimide fiber obtained by the above-mentioned 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 aforementioned continuous filaments, short fibers, woven fabrics, nonwoven fabrics, or powders.

[0034] In addition, the present invention also provides a prepreg comprising the above-mentioned purplish-black polyimide fiber or purplish-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 was used as the chromophore, which facilitates cost control, provides good coloring effect, uniform coloring, and avoids the stability problem of the dispersion system.

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

[0038] (3) It does not require changing the main structure of the molecular chain, and does not require adding extra steps in the conventional spinning process, which helps to reduce costs;

[0039] (4) It does not use toxic and expensive anthraquinone compounds, making it safer, more environmentally friendly, and able to effectively reduce production costs. Detailed Implementation

[0040] <fiber>

[0041] The fiber described in this 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, the fiber is in the form of a continuous filament. For the purposes of this document, the term "filament" is defined as a relatively flexible, macroscopically uniform body having a high aspect ratio in a cross-section perpendicular to its length. The cross-section of a filament can be of any shape, but is typically circular. A multifilament wound onto a spool in a package comprises multiple continuous filaments. In the context of this disclosure, the terms filament and fiber are used interchangeably.

[0043] Other suitable forms of fiber materials are short fibers, woven fabrics, non-woven fabrics, or powders—terms well-known in the field of textile fibers.

[0044] The implementation schemes similar to those described above are applicable to filaments, staple fibers, woven fabrics, nonwoven fabrics, or powders.

[0045] <Composite Materials>

[0046] The purplish-black polyimide fibers of this invention can be combined with a matrix resin to form a fiber-reinforced resin composite material. Suitable fiber forms include continuous filaments, short fibers, woven fabrics, nonwoven fabrics, or powders. The resin can be a thermosetting resin or a thermoplastic resin. Typically, the matrix resin accounts for 20% to 50% by weight of the fiber plus resin in the composite material. Suitable thermosetting resins include epoxy resins, phenolic resins, epoxy-thermoplastic phenolic resins, cyanate esters, unsaturated esters, melamine, and maleimide. The fibers can be treated by any of the methods described above.

[0047] The implementation schemes described above are applicable to fibers in filament, staple fiber, woven fabric, nonwoven fabric, or powder form.

[0048] The purplish-black polyimide fibers of this invention can be combined with a matrix resin to form a fiber-reinforced resin composite material. Suitable fiber forms include continuous filaments, short fibers, woven fabrics, nonwoven fabrics, or powders. The resin can be a thermosetting resin or a thermoplastic resin. Typically, the matrix resin accounts for 20% to 50% by weight of the fiber plus resin in the composite material. Suitable thermosetting resins include epoxy resins, phenolic resins, epoxy-thermoplastic phenolic resins, cyanate esters, unsaturated esters, melamine, and maleimide, etc.

[0049] The abbreviations and key terms used in this invention are defined as follows: 2-(4-aminophenyl)-5-aminobenzimidazole is BIA, p-phenylenediamine is PDA, 3,3',4,4'-biphenyltetracarboxylic dianhydride is BPDA, and dimethylacetamide is DMAc. In this invention, nascent fiber refers to fiber formed by the solidification of polymer streams extruded from the spinneret in the spinning field, which is fiber that has not yet undergone heat treatment; finished fiber is fiber obtained by heat treatment of nascent fiber.

[0050] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

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

[0052] Fiber color fastness: Tested using an SW-8A wash fastness tester 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 of these points is used as a reference. The color difference between the other three points and the reference point is calculated according to standard GB / T / 8424.3-2001. The calculation formula is as follows:

[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] Example 1:

[0057] First, copper chloride is dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:4. Synthesis is then carried out according to a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3, with an amino group to anhydride group molar ratio of 1:1, and the solid content of the solution is adjusted to 18%. During synthesis, the diamine monomers PDA and BIA are first added to a solution containing divalent copper ions. After thorough mixing in a reactor for 0.5 hours, BPDA is weighed and slowly added to the reactor for polymerization. After the addition is complete, stirring continues for 2-3 hours, followed by transfer to a spinning tank for degassing.

[0058] After degassing, the spinning solution is transported to the spinneret by a metering pump through a pipeline. Wet spinning is then used to obtain nascent fibers, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

[0059] The polyimide fiber prepared in this embodiment is purplish-black (RGB(29,22,38)), with uniform fiber color. Four random points were taken from the same roll of fiber, and the maximum color difference was 0.79. The color fastness to soap washing was grade 5.

[0060] Example 2:

[0061] Before synthesis, copper acetate was dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:6. Synthesis was carried out according to a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3, maintaining a molar ratio of amine to anhydride groups of 1:1 and a solution solid content of 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA were first added to a solution containing divalent copper ions. After stirring thoroughly in the reactor for 0.5 hours, an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization. After the addition was complete, stirring continued for 2-3 hours, and then the mixture was transferred to a spinning tank for degassing.

[0062] After degassing, the spinning solution is transported to the spinneret via a pipeline by a metering pump. Nascent fibers are obtained using a wet-dry spinning process, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

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

[0064] Example 3:

[0065] Before synthesis, copper chloride was dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:8. Synthesis was carried out according to a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3, maintaining an amino to anhydride molar ratio of 1:1 and a solution solid content of 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA were first added to a reaction vessel and stirred thoroughly for 0.5 hours. An appropriate amount of BPDA was then weighed and slowly added to the reaction vessel for polymerization, with stirring continued for 2-3 hours. The mixture was then transferred to a spinning tank for degassing.

[0066] After degassing, the spinning solution is transported to the spinneret by a metering pump through a pipeline. Wet spinning is then used to obtain nascent fibers, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

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

[0068] Example 4:

[0069] Before synthesis, copper chloride was dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:3. During synthesis, the monomer molar ratio of BPDA:PDA:BIA was 1:0.7:0.3, maintaining a molar ratio of amine to anhydride groups of 1:1 and a solid content of 18% in the solution. During synthesis, the above-mentioned diamine monomers PDA and BIA were first added to the reactor and stirred thoroughly for 0.5 hours. Then, an appropriate amount of BPDA was weighed and slowly added to the reactor for polymerization, and stirring was continued for 2-3 hours. Finally, the mixture was transferred to a spinning tank for degassing.

[0070] During the spinning process, the deaerated spinning solution is transported to the spinneret by a metering pump through a pipeline. Wet spinning is then used to obtain nascent fibers, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

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

[0072] Comparative Example 1:

[0073] During synthesis, the monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3 was used, maintaining a 1:1 molar ratio of amino groups to anhydride groups and a solid content of 18% in the solution. First, the diamine monomers PDA and BIA were added to the reactor and stirred. After thorough mixing for 0.5 hours, an appropriate amount of BPDA was weighed and slowly added to the reactor. After the addition was complete, stirring continued for 2-3 hours, followed by transfer to a spinning tank for degassing.

[0074] After degassing, the spinning solution is transported to the spinneret by a metering pump through a pipeline. Wet spinning is then used to obtain nascent fibers, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

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

[0076] Comparative Example 2:

[0077] First, copper chloride is dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:2. Synthesis is carried out according to a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3, maintaining an amino to anhydride molar ratio of 1:1 and a solution solid content of 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA are first added to the reactor and stirred thoroughly for 0.5 hours. Then, an appropriate amount of BPDA is weighed and slowly added to the reactor for polymerization. After stirring for another 2 hours, the solution becomes gel-like, loses its fluidity, and is unsuitable for spinning.

[0078] Comparative Example 3

[0079] First, copper chloride is dissolved in an appropriate amount of DMAc, with a molar ratio of copper chloride to BIA of 1:10. Synthesis is carried out according to a monomer molar ratio of BPDA:PDA:BIA = 1:0.7:0.3, maintaining an amino to anhydride molar ratio of 1:1 and a solution solid content of 18%. During synthesis, the above-mentioned diamine monomers PDA and BIA are first added to the reactor and stirred thoroughly for 0.5 hours. Then, an appropriate amount of BPDA is weighed and slowly added to the reactor for polymerization, and stirring continues for 2-3 hours. Finally, the mixture is transferred to a spinning tank for degassing.

[0080] After degassing, the spinning solution is transported to the spinneret by a metering pump through a pipeline. Wet spinning is then used to obtain nascent fibers, with a coagulation bath concentration of 6%. The nascent fibers are dried at 120°C and then subjected to a gradient imidization process at 240°C–450°C to obtain the finished fibers.

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

[0082] In Examples 1-4 above, the preparation method of the purple-black polyimide fiber of the present invention is safer, more environmentally friendly, and more cost-effective. Furthermore, by using the preparation method of the present invention, high-performance purple-black polyimide fibers can be obtained with uniform color; the maximum color difference between four randomly selected points from the same roll of fiber is ≤2.0, and the color fastness is good, with a soap washing fastness level of grade four or higher. In contrast, in Comparative Example 1 above, no copper ions were added, and the fiber color was yellowish-brown, which does not meet the requirement of purple-black. In Comparative Example 2, the molar ratio of copper chloride to BIA was greater than 1:3, and the resulting solution could not meet the requirements for spinning. In Comparative Example 3 above, the molar ratio of copper chloride to BIA was less than 1:8, and the fiber color was brown, which also does not meet the requirement of purple-black.

[0083] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends 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, wherein 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, and the color fastness of the purple-black polyimide fiber to soap washing is not lower than level four. The purplish-black polyimide fiber is obtained by a preparation method including the following steps: (1) Dissolution of copper ions: Dissolve copper salt in an appropriate amount of organic solvent to obtain a solution containing divalent copper ions; (2) Preparation of spinning solution: The dianhydride monomer and the diamine monomer are added to the solution containing divalent copper ions in a certain molar ratio for synthesis, maintaining the molar ratio of amino groups to anhydride groups at 1:1, and the molar ratio of divalent copper ions to diamine monomers containing benzimidazole units at 1:3 to 1:

8. The solid content of the solution is adjusted to 12%-20% by mass percentage, and then degassing is performed. (3) Spinning and (4) Thermal imidization: The polyamic acid nascent fiber is obtained by wet spinning or dry-wet spinning, and then thermal imidization is carried out to obtain the finished fiber, namely the purple-black polyimide fiber.

2. The purplish-black polyimide fiber according to claim 1, wherein, The maximum color difference is ≤1.

3. The purplish-black polyimide fiber according to claim 1, wherein, The purplish-black polyimide fiber has a color fastness to soap washing of grade 5.

4. A method for preparing a purple-black polyimide fiber according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Dissolution of copper ions: Dissolve copper salt in an appropriate amount of organic solvent to obtain a solution containing divalent copper ions; (2) Preparation of spinning solution: The dianhydride monomer and the diamine monomer are added to the solution containing divalent copper ions in a certain molar ratio for synthesis, maintaining the molar ratio of amino groups to anhydride groups at 1:1, and the molar ratio of divalent copper ions to diamine monomers containing benzimidazole units at 1:3 to 1:

8. The solid content of the solution is adjusted to 12%-20% by mass percentage, and then degassing is performed. (3) Spinning: During the spinning process, the defoamed spinning solution is transported to the spinneret by the pipeline under the push of the metering pump for spinning, and polyamic acid nascent fibers are obtained by wet spinning or dry-wet spinning. (4) Thermal imidization: After drying the polyamic acid nascent fiber at 80℃-120℃, it is then thermal imidized at 240℃~500℃ to obtain the finished fiber, namely purple-black polyimide fiber.

5. The method for preparing purple-black polyimide fiber according to claim 4, wherein, The copper salt of the divalent copper ion is a salt capable of dissociating into divalent copper ions, and is selected from one or more of copper acetate, copper chloride, copper pyridine sulfate, and copper ethylenediaminetetraacetate; and / or The organic solvent is the solvent used in the synthesis of polyamic acid, and is selected from one or more of tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

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

7. The method for preparing purple-black polyimide fibers according to claim 6, wherein, The diamine monomer containing the benzimidazole unit is 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), the other diamine monomer is p-phenylenediamine (PDA), and the dianhydride monomer is biphenyl dianhydride (BPDA).

8. The method for preparing purple-black polyimide fiber according to claim 4, wherein, In step (2), the diamine monomer is first added to a reaction vessel containing the solution containing divalent copper ions and stirred. After mixing for more than 0.5 hours, an appropriate amount of dianhydride monomer is weighed and slowly added to the reaction vessel. After the addition is complete, stirring continues for 2 to 3 hours. Then, the mixture is transferred to a spinning tank for degassing; and / or In step (3), the concentration of the coagulation bath is 6-9% during spinning.

9. The application of the purple-black polyimide fiber according to any one of claims 1 to 3 or the purple-black polyimide fiber obtained by the preparation method according to any one of claims 4 to 8 in the fields of aerospace, high-temperature protection or textiles.

10. A continuous filament, staple fiber, woven fabric, nonwoven fabric or powder comprising the purple-black polyimide fiber according to any one of claims 1 to 3 or the purple-black polyimide fiber obtained by the preparation method according to any one of claims 4 to 8.

11. A fiber-reinforced composite material, high-temperature protective material, or textile material comprising the continuous filament, short fiber, woven fabric, nonwoven fabric, or powder as described in claim 10.

12. A prepreg comprising purple-black polyimide fibers according to any one of claims 1 to 3 or purple-black polyimide fibers obtained by the preparation method according to any one of claims 4 to 8.