Spun-dyed polyimide fiber, and preparation method therefor and use thereof

Abstract

The present invention provides a spun-dyed polyimide fiber, and a preparation method therefor and the use thereof. The fiber comprises an organic or inorganic pigment, and the content of the pigment is 0.2-10 wt% of the total mass of the polyimide fiber; in the same roll of spun-dyed polyimide fiber, the maximum color difference in four randomly selected points is less than or equal to 2. The preparation method comprises the following steps: firstly mixing a dried organic or inorganic pigment with a surfactant, then adding a proper amount of a solvent, dispersing same to prepare a dispersion containing pigment particles, respectively conveying a defoamed polyamide acid spinning solution and the dispersion of pigment to a feeding inlet of a dynamic mixer via a pipeline under the pushing of a metering pump, mixing same in the dynamic mixer, and obtaining the spun-dyed polyimide fiber by using a wet / dry-wet spinning process. The production process of the present invention adopts spun-dyeing, which offers the advantages of good color uniformity and high color fastness. Furthermore, the method has a simple process and low production costs.

Description

A colored polyimide fiber, its preparation method and application

[0001] Cross-references to related applications

[0002] This application claims the benefit of Chinese application number 2024119288387, filed on December 25, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of high-performance fiber technology, and in particular to a colored polyimide fiber, its preparation method, and its application. Background Technology

[0004] High-performance polyimide fibers possess excellent comprehensive properties, including mechanical strength, resistance to high and low temperatures, flame retardancy, and low dielectric constant, making them promising for applications in aerospace, electronics, and safety protection. Polyimide fibers are intrinsically golden yellow, but to meet the needs of different applications, it is necessary to construct polyimide fibers of various colors. However, due to their high glass transition temperature and strong surface inertness, it is difficult to obtain colored fibers with high color fastness using methods such as carrier dyeing and surface-modified dyeing. Solution dyeing refers to using suitable pigments, uniformly dispersing them in a polyamic acid spinning solution, and spinning after thorough mixing. Compared with carrier dyeing and surface-modified dyeing methods, solution dyeing can obtain fibers with high color fastness.

[0005] Chinese patent document CN105780177A discloses a method for preparing colored polyimide fibers. In this method, a carbon black dispersion is first prepared in a mixing tank. Then, corresponding monomers are added sequentially and in a specific molar ratio. When the viscosity of the solution is controlled to be 100–1000 ppm, the color paste dispersion is uniformly mixed with the spinning solution inside the tank via an external circulation pipeline. Finally, dianhydride monomer is added and stirred for polymerization for 2–5 hours to obtain a polyamic acid spinning solution. After degassing and filtration, colored polyimide fibers are obtained using a dry spinning process. This invention uses solution dyeing, which has the advantage of high color fastness compared to dyeing processes, and the method is simple. However, in the solution dyeing method, the pigment particles and the spinning solution form a suspension system that is thermodynamically and kinetically unstable. During the static degassing process after mixing the spinning solution and pigment, the sedimentation and aggregation of particles in the system are unavoidable, thus adversely affecting the stability of the spinning process and the uniformity of the fiber color. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, the present invention aims to provide a colored polyimide fiber and its preparation method. This colored polyimide fiber exhibits excellent color uniformity, and the preparation method provides a colored polyimide fiber with high process stability. The fiber has uniform color and high color fastness, solving the problem of pigment particle agglomeration during static degassing in existing solution dyeing technologies. This colored polyimide fiber can be applied in aerospace, electronics, rail transportation, high-temperature protection, textiles, and other fields.

[0007] According to the purpose of this invention, a colored polyimide fiber is provided, the color of which can be controlled by adjusting the content and type of pigment. The content of the pigment is 0.2wt%-10wt% of the total mass of the polyimide fiber. In the same roll of colored polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2. The physical and mechanical properties of the colored polyimide fiber are: tensile strength of 0.5-3.5GPa, initial modulus of 7-180GPa, and color fastness to soap washing of not less than grade four.

[0008] In this invention, the color of the colored polyimide fiber can be adjusted within a certain range according to user requirements. For example, the "black" in black polyimide fiber can be different shades of black, such as dark black, light black, pure black, etc. However, the colored polyimide fiber of this invention has good color uniformity. For example, the same roll of black polyimide fiber presents a uniform black color.

[0009] In this invention, four points are randomly selected from the same roll of colored polyimide fiber, with a maximum color difference ≤2, preferably ≤1. The color difference can be determined using conventional methods in the art. For example, four points are randomly selected from a roll of fiber and tested using a DS620 high-precision colorimeter. Using the CIELAB value of one point 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: ΔE ab * =[(L S * -L R * ) 2 +(a S * -a R * ) 2 +(b S * -b R * ) 2 ] 1 / 2

[0010] Where R and S are the CIELAB values ​​of the reference point and other points, respectively.

[0011] In this invention, the pigment used as a colorant can be selected from any one or more disclosed in the prior art, and can be either inorganic or organic pigments. The color of the pigment can be selected from black, red, orange, blue, and green. Specifically, the black pigment is preferably selected from one or more of CI Pigment Black 6, CI Pigment Black 11, CI Pigment Black 28, CI Pigment Black 27, CI Pigment Black 31, and CI Pigment Black 32; the red pigment is preferably selected from one or more of CI Pigment Red 122, CI Pigment Red 149, CI Pigment Red 177, CI Pigment Red 179, CI Pigment Red 202, and CI Pigment Red 254; the blue pigment is preferably selected from one or more of CI Pigment Blue 15, CI Pigment Blue 28, and CI Pigment Blue 60; the green pigment is preferably selected from one or more of CI Pigment Green 7, CI Pigment Green 36, and CI Pigment Green 47; and the orange pigment is preferably selected from CI Pigment Orange 7, CI Pigment Orange 36, CI Pigment Orange 71, and CI Pigment Orange 77. Furthermore, to obtain a specific fiber color, multiple pigments can be blended as needed. For example, navy blue pigment can be obtained by blending black and blue pigments.

[0012] This invention also provides a method for preparing colored polyimide fibers, which includes the following steps:

[0013] First, the dried organic or inorganic pigments are mixed with surfactants, and then an appropriate amount of organic solvent is added. The mixture is then dispersed by ball milling or without ball milling to prepare a pigment dispersion.

[0014] The degassed polyamic acid spinning solution and the above-mentioned pigment dispersion are respectively transported to the feed port of the dynamic mixer by pipeline under the drive of metering pumps, and the two are mixed in the dynamic mixer.

[0015] Then, the spinning process is carried out directly using wet or dry-wet spinning. The spinning solution is then subjected to spinning, coagulation, washing, drying, and thermal imidization treatment to obtain colored polyimide fibers.

[0016] It should be noted that the above-mentioned "dispersing pigments into a dispersion by ball milling or without ball milling" means that when making a pigment dispersion, if it is an organic pigment, ball milling is not required, while if it is an inorganic pigment, ball milling is required.

[0017] As mentioned above, the preparation method of CN105780177A requires static degassing after synthesis. Pigment particles may agglomerate during this process and cannot be dispersed again, clogging the spinneret and affecting the stability of fineness and color uniformity. In the preparation method of this invention, the spinning solution is degassed first, and then the pigment paste and spinning solution are mixed evenly using a dynamic mixer. After mixing, no further degassing is required; spinning is performed directly. This reduces the residence time of pigment particles in the pipeline and eliminates the need for static degassing, effectively reducing pigment particle agglomeration. This effectively solves the problems of poor fineness stability and poor color uniformity in the prior art and provides good color fastness. Furthermore, in the preparation method of CN105780177A, the pigment content cannot be readjusted after mixing the pigment and spinning solution, and the pipeline and reaction vessel need to be cleaned during cutting, resulting in poor process flexibility. In this process, only the type of pigment injected into the dynamic mixer needs to be changed to adjust the hue and tone of the final product. Switching product types does not require extensive cleaning of the delivery pipeline, resulting in greater process flexibility.

[0018] In this invention, preferably, the above preparation method includes the following steps:

[0019] (1) Preparation of pigment dispersion: After vacuum drying of organic or inorganic pigments at 50-100℃, they are dispersed together with an appropriate amount of surfactant in an appropriate amount of organic solvent. Inorganic pigments are ground in a ball mill for 2-24 hours, while organic pigments do not need to be dispersed by ball milling. A dispersion with a pigment content of 0.5wt%-20wt% is prepared for later use.

[0020] (2) Preparation of spinning solution: Diamine monomer and dianhydride monomer are added to an organic solvent at a monomer molar ratio of 0.995:1-1:1.005 for synthesis. The solid content of the solution is adjusted to 12%-20%. After the synthesis is completed, the solution is vacuumed and allowed to stand for degassing.

[0021] (3) Spinning: The defoamed spinning solution and pigment dispersion are respectively transported to the feed port of the dynamic mixer by pipeline under the push of metering pump. The two are mixed in the dynamic mixer and then transported to the spinneret. Wet or dry-wet spinning is carried out. After coagulation and washing, nascent fibers are obtained.

[0022] (4) Drying and thermal imidization: After drying the above-mentioned nascent fibers at 80℃-120℃, imidization is carried out at 200-600℃ to obtain the finished fiber, namely colored polyimide fiber.

[0023] 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 (DMAc).

[0024] In step (1), the pigment content in the dispersion can be adjusted within the range of 0.5wt%-20wt% according to actual needs and dispersion conditions, for example, 0.5wt%, 2wt%, 6wt%, 8wt%, 10wt%, 20wt%.

[0025] In step (2), the solid content can be selected in the range of 12%-20%, for example, 13%, 14%, 15%, 16%, 17%, 18%, or 19%.

[0026] In the preparation method of this invention, commonly used diamine monomers in the art can be used, including diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), m-phenylenediamine (MPD), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (MTD), 4,4'-diaminodiphenylmethane (MDA), etc. Commonly used dianhydride monomers can also be used, such as pyromellitic dianhydride (PMDA). Commonly used dianhydride monomers in the art can also be used, including biphenyl dianhydride (BPDA), hexafluorodianhydride (6FDA), diphenyl ether tetracarboxylic dianhydride (ODPA), benzophenone tetracarboxylic dianhydride (BTDA), etc. Preferably, the diamine monomer is diaminodiphenyl ether (ODA), and the dianhydride monomer is pyromellitic dianhydride (PMDA).

[0027] In addition, the dynamic mixer used in this invention only needs to be able to achieve the effect of dynamic mixing, and existing dynamic mixers in the prior art can be selected.

[0028] Preferably, the pigment content in the colored polyimide fiber is 0.2wt%-10wt% of the total mass of the polyimide fiber. When the pigment content is less than 0.2wt%, the fiber color cannot meet the coloring requirements; when the pigment content is greater than 10wt%, the fiber linear density stability deteriorates. By controlling the pigment content below 10wt%, good fiber linear density stability can be achieved, and the change in fiber linear density within 12 hours during the spinning process can be less than 2%.

[0029] Preferably, the molar ratio of the dianhydride monomer to the diamine monomer is 0.995:1 to 1:1.005.

[0030] In a preferred embodiment, the diaminodiphenyl ether (ODA) is first added to the reaction vessel along with an appropriate amount of dimethylacetamide (DMAc). After mixing thoroughly for more than 0.5 hours, the pyromellitic methyl ether (PMDA) is weighed out and slowly added to the reaction vessel. After the addition is complete, stirring is continued for 0.5 to 3 hours, and then the mixture is transferred to a spinning tank for degassing.

[0031] Experimental testing revealed that the colored polyimide fibers prepared by the method of this invention exhibit the following physical and mechanical properties: tensile strength of 0.5-3.5 GPa, initial modulus of 7-180 GPa, and color fastness to soap washing of not less than grade four, preferably grade five.

[0032] For polyimide fibers, the strong intermolecular interactions within the fiber endow it with excellent mechanical properties while hindering the penetration of dye molecules into the fiber interior. Simultaneously, the fiber surface lacks active groups, making it difficult to stably adsorb dye molecules over a long period. This difficulty in dyeing, coupled with the inherent golden-yellow color of the fiber itself, limits the applications of polyimide fibers.

[0033] In the production of solution-dyed fibers, by adding pigment dispersions of different colors and thoroughly mixing them before spinning, water and air pollution generated during the dyeing and finishing processes can be avoided, achieving the goal of green and clean production. This method can yield colored polyimide fibers with high coloring rate, uniform coloring, and high color fastness. Simultaneously, using a dynamic mixer to mix the spinning solution and pigment dispersions, and immediately spinning after mixing, avoids problems such as pigment particle sedimentation and agglomeration during prolonged storage, thus improving process stability. Therefore, using a dynamic mixer to mix the spinning solution and pigments for solution dyeing to develop colored polyimide fibers can meet the color requirements of various application fields.

[0034] According to another objective of the present invention, in one aspect, the present invention provides a colored polyimide fiber, which is prepared by the above-described method for preparing colored polyimide fibers.

[0035] On the other hand, the present invention provides applications of the above-mentioned colored polyimide fibers in the fields of aerospace, electronics and power, rail transportation, high temperature protection or textiles.

[0036] In another aspect, the present invention provides a continuous filament, short fiber, woven fabric, nonwoven fabric or powder comprising the above-mentioned colored polyimide fiber or colored polyimide fiber obtained by the above-mentioned preparation method.

[0037] The present invention also provides a prepreg comprising the above-described colored polyimide fibers or colored polyimide fibers obtained by the above preparation method.

[0038] In addition, 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.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) A dynamic mixer is used to inject pigment into the spinning solution after degassing and mix it evenly. This can avoid the aggregation of pigment particles during the long-term storage of the spinning solution, improve the fineness stability, and at the same time retain the advantages of high fiber color fastness and uniform coloring in the original solution coloring process.

[0041] (2) In addition, the product color can be changed simply by changing the type of pigment injected into the dynamic mixer, without the need to clean the complex pipeline, which reduces product loss and lowers maintenance costs.

[0042] (3) The use of surfactants enhances the interaction between pigment particles and polyamic acid molecules, further enhancing the stability of the dispersion system;

[0043] (4) 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 and is easy to implement. Attached Figure Description

[0044] Figure 1 is a schematic diagram of the preparation process of the colored polyimide fiber of the present invention. Detailed Implementation

[0045] <fiber>

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The implementation schemes similar to those described above are applicable to filaments, staple fibers, woven fabrics, nonwoven fabrics, or powders.

[0050] <Composite Materials>

[0051] The colored 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, staple 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.

[0052] The implementation schemes described above are applicable to fibers in filament, staple fiber, woven fabric, nonwoven fabric, or powder form.

[0053] The colored 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.

[0054] The abbreviations and key terms used in this invention are defined as follows: diaminodiphenyl ether is ODA, p-phenylenediamine is PDA, 3,3',4,4'-biphenyltetracarboxylic dianhydride is BPDA, pyromellitic dianhydride is PMDA, dimethylacetamide is DMAC, and 2-(4-aminophenyl)-5-aminobenzimidazole is BIA. 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.

[0055] Figure 1 is a schematic flowchart of the preparation process of the colored polyimide fiber of the present invention. Referring to Figure 1, the spinning solution and the colorant dispersion are mixed in a dynamic mixer via pumps 1 and 2, respectively. Then, they are sequentially fed into a coagulation bath and a water washing bath via pump 3. After drying, thermal imidization, and winding, the colored polyimide fiber is obtained. In this invention, a dynamic mixer is used. After degassing the spinning solution, the pigment dispersion is injected into the spinning solution and mixed evenly. This avoids the agglomeration of pigment particles during long-term storage of the spinning solution, improving fineness stability, while retaining the advantages of high fiber color fastness and uniform coloring in the solution dyeing process.

[0056] 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, equipment, or instruments used, unless otherwise specified by the manufacturer, are all commercially available conventional products.

[0057] The fiber performance testing methods and conditions in the following examples and comparative examples are as follows:

[0058] Fiber mechanical properties: The tensile strength and initial modulus of the fiber were tested using a YG001A-1 fiber electronic tensile tester.

[0059] Fiber linear density: The fiber linear density was tested using a YG086 yarn length measuring machine in accordance with GB / T14343-2008.

[0060] Fiber color fastness: Tested using an SW-8A wash fastness tester in accordance with standard GB / T 3921-2008.

[0061] Color difference: Four points were randomly selected from a roll of fiber and tested using a DS620 high-precision colorimeter. Using the CIELAB value of one of these points as a reference, the color difference between the other three points and the reference point was calculated according to standard GB / T / 8424.3-2001. The calculation formula is: ΔE ab * =[(L S * -L R * ) 2 +(a S * -a R * ) 2 +(b S * -b R * ) 2 ] 1 / 2

[0062] Where R and S are the CIELAB values ​​of the reference point and other points, respectively.

[0063] Example 1:

[0064] Black polyimide fibers were prepared using black pigment. First, the colorant CI pigment black 6 was vacuum dried at 80℃ for 24 hours, then dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a CI pigment black 6 content of 5 wt%. Monomers PMDA and ODA were synthesized at a molar ratio of 1:1, maintaining an amine to anhydride molar ratio of 1:1 and adjusting the solution solid content to 18%. Specifically, the diamine monomer ODA was first added to the reactor along with an appropriate amount of DMAc. After thorough mixing for at least 0.5 hours, PMDA was weighed and slowly added to the reactor. After the addition was complete, stirring continued for 0.5-1 hour, and then the mixture was transferred to a spinning tank for degassing.

[0065] After degassing, the spinning solution and the black pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 80℃ and then subjected to gradient imidization at 240℃~400℃ to obtain the finished fibers. The colorant CI pigment black 6 accounts for 4 wt% of the total mass of the polyimide fibers.

[0066] During the spinning process, the linear density of the fiber changed by less than 1% within 12 hours, demonstrating high linear density stability. The polyimide fiber prepared in this example was tested using a YG001A-1 electronic fiber tensile strength tester, and the tensile strength was measured to be 0.63 GPa, with an initial modulus of 9 GPa. The fiber color was black (RGB(21,17,20)), and the color was uniform. Four random samples from the same roll of fiber showed a maximum color difference of 0.98, and the color fastness to washing was grade 5.

[0067] Example 2:

[0068] Black polyimide fibers were prepared using black pigment. First, the colorant CI pigment black 6 was vacuum dried at 80℃ for 24 hours, then dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a CI pigment black 6 content of 5 wt%. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining an amine to anhydride molar ratio of 1:1 and adjusting the solution solid content to 18%. Specifically, the diamine monomer PDA was first added to the reactor along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, BPDA was weighed and slowly added to the reactor. After the addition was complete, stirring continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0069] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for spinning using a wet-dry spinning process to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. The colorant CI pigment black 6 accounts for 4 wt% of the total mass of the polyimide fibers.

[0070] During the spinning process, the fiber linear density change was less than 1% within 12 hours, indicating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester. The tensile strength was measured to be 1.90 GPa, the initial modulus to be 102 GPa, and the fiber color to be black (RGB(60,62,61)). The fiber color was uniform, and the maximum color difference among four randomly selected points from the same roll of fiber was 0.66. The color fastness to washing was grade 5.

[0071] Example 3:

[0072] Black polyimide fibers were prepared using black pigment. First, the colorant CI pigment black 6 was vacuum dried at 80℃ for 24 hours, then dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a CI pigment black 6 content of 0.5 wt%. Monomers BPDA, BIA, and PDA were synthesized at a molar ratio of 10:3:7, maintaining an amino to anhydride molar ratio of 1:1, and adjusting the solution solid content to 18%. Specifically, the diamine monomer was first added to the reactor along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, the dianhydride monomer was slowly added to the reactor. After the addition was complete, stirring continued for 2.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0073] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 9%. The nascent fibers are dried at 100℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. The colorant CI pigment black 6 accounts for 0.2 wt% of the total mass of the polyimide fibers.

[0074] During the spinning process, the fiber linear density change was less than 0.5% within 12 hours, indicating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester. The tensile strength of the fiber was measured to be 3.4 GPa, the initial modulus to be 178 GPa, the fiber color to be black (RGB(77,79,79)), and the fiber color to be uniform. The maximum color difference was 1.02 when four points were randomly selected from the same roll of fiber, and the color fastness to washing was grade 5.

[0075] Example 4:

[0076] Red-colored polyimide fibers were prepared using a red pigment. First, the colorant, CI pigment red 177, was vacuum dried at 80°C for 24 hours. Then, it was co-dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and stirred for 4 hours to prepare a dispersion with a pigment content of 20 wt%. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining a 1:1 molar ratio of amino to anhydride groups, and adjusting the solid content of the solution to 18%. Specifically, the diamine monomer PDA was first added to a reaction vessel along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, BPDA was weighed and slowly added to the reaction vessel. After the addition was complete, stirring continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0077] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. The colorant, CI Pigment Red 179, accounts for 10 wt% of the total mass of the polyimide fibers.

[0078] During the spinning process, the fiber linear density change was less than 2% within 12 hours, indicating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester. The tensile strength was measured to be 1.3 GPa, the initial modulus to be 85 GPa, and the fiber color to be orange-red (RGB(255,69,0)). The fiber color was uniform, and the maximum color difference among four randomly selected points from the same roll of fiber was 0.54. The color fastness to washing was grade 5.

[0079] Example 5:

[0080] Red-colored polyimide fibers were prepared using a red pigment. First, the colorant, CI pigment red 179, was vacuum-dried at 80°C for 24 hours. Then, it was co-dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and stirred for 4 hours to prepare a dispersion with a pigment content of 20 wt%. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining a 1:1 molar ratio of amino to anhydride groups, and adjusting the solid content of the solution to 18%. Specifically, the diamine monomer PDA was first added to a reaction vessel along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, BPDA was weighed and slowly added to the reaction vessel. After the addition was complete, stirring continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0081] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. The pigment content accounts for 6 wt% of the total mass of the polyimide fibers.

[0082] During the spinning process, the fiber linear density change was less than 1% within 12 hours, indicating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester. The tensile strength was measured to be 1.5 GPa, the initial modulus to be 89 GPa, and the fiber color to be red (RGB(189,19,6)). The fiber color was uniform, and the maximum color difference was 0.62 when four points were randomly selected from the same roll of fiber. The color fastness to washing was grade 5.

[0083] Example 6:

[0084] Orange polyimide fibers were prepared using orange pigment. First, the colorant CI pigment orange 36 was vacuum dried at 80℃ for 24 hours, then dispersed with the surfactant sodium methylene dinaphthalene sulfonate in DMAc and stirred for 4 hours to prepare a dispersion with a pigment content of 15 wt%. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining an amino to anhydride molar ratio of 1:1 and adjusting the solution solid content to 18%. Specifically, the diamine monomer was first added to the reactor along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, the dianhydride monomer was slowly added to the reactor. After the addition was complete, stirring continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0085] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃–440℃ to obtain the finished fibers. The pigment accounts for 4 wt% of the total mass of the polyimide fibers.

[0086] During the spinning process, the fiber linear density change was less than 1% within 12 hours, demonstrating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester, yielding a tensile strength of 2.2 GPa and an initial modulus of 90 GPa. The fiber color was orange (RGB(255,140,0)), with uniform color. Four random samples from the same fiber roll showed a maximum color difference of 1.27, and the color fastness to washing was grade 5.

[0087] Example 7:

[0088] First, the colorant CI Pigment Blue 28 was vacuum dried at 80℃ for 24 hours, then dispersed together with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a pigment content of 10 wt%, which was then set aside. Monomers BPDA, BIA, and PDA were synthesized at a molar ratio of 10:3:7, maintaining an amino to anhydride molar ratio of 1:1, and adjusting the solution solid content to 18%. Specifically, the diamine monomer was first added to the reactor along with an appropriate amount of DMAc, and after thorough mixing for 0.5 hours, the dianhydride monomer was slowly added to the reactor. After the addition was complete, stirring was continued for 2.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0089] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 9%. The nascent fibers are dried at 100℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. CI pigment blue 28 accounts for 5 wt% of the total mass of the polyimide fibers.

[0090] During the spinning process, the fiber linear density change was less than 1% within 12 hours, demonstrating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester, yielding a tensile strength of 3.1 GPa and an initial modulus of 158 GPa. The fiber color was green (RGB(154,205,50)), with uniform color. Four random samples from the same fiber roll showed a maximum color difference of 1.09, and the color fastness to washing was grade 5.

[0091] Example 8:

[0092] First, colorants CI Pigment Blue 28 and CI Pigment Black 6 were vacuum dried at 80℃ for 24 hours, then co-dispersed with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a pigment content of 10 wt%, wherein the mass ratio of CI Pigment Blue 28 to CI Pigment Black 6 was 2:1, and set aside for later use. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining the molar ratio of amine to anhydride groups at 1:1, and adjusting the solid content of the solution to 18%. Specifically, the diamine monomer PDA was first added to the reactor along with an appropriate amount of DMAc. After thorough mixing for 0.5 hours, BPDA was weighed and slowly added to the reactor. After the addition was complete, stirring was continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0093] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. CI pigment blue 28 and CI pigment black 6 account for 8 wt% of the total mass of the polyimide fibers.

[0094] During the spinning process, the fiber linear density change was less than 1% within 12 hours, indicating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 fiber electronic tensile strength tester. The tensile strength of the fiber was measured to be 1.6 GPa, the initial modulus to be 89 GPa, and the fiber color to be navy blue (RGB(32,51,72)). The color was uniform, and the maximum color difference was 0.76 when four points were randomly selected from the same roll of fiber. The color fastness to washing was grade 5.

[0095] Comparative Example 1:

[0096] First, the colorant CI Pigment Black 6 was vacuum dried at 80℃ for 24 hours, then dispersed together with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a pigment content of 5 wt%, which was then set aside. Monomers PMDA and ODA were synthesized at a molar ratio of 1:1, maintaining the amine to anhydride molar ratio at 1:1, and adjusting the solution solid content to 18%. Specifically, the diamine monomer ODA was first added to the reactor along with an appropriate amount of DMAc, followed by the carbon black dispersion. After thorough mixing for 0.5 hours, the dianhydride monomer PMDA was slowly added to the reactor. After the addition was complete, stirring was continued for 0.5-1 hours, and then the mixture was transferred to a spinning tank for degassing.

[0097] Nascent fibers were obtained by wet spinning, with a coagulation bath concentration of 6%. The nascent fibers were dried at 80°C and then subjected to gradient imidization at 240°C–400°C to obtain the finished fibers. Carbon black accounted for 8 wt% of the total mass of the polyimide fibers.

[0098] During the spinning process, the linear density of the fiber decreased by 15% within 8 hours, indicating poor linear density stability. The polyimide fiber prepared in this example was tested using a YG001A-1 electronic fiber tensile strength tester, and the tensile strength was measured to be 0.55 GPa, with an initial modulus of 8 GPa. The fiber color was uneven; four random samples from the same roll of fiber showed a maximum color difference of 4.69, and the color fastness to soap washing was grade 5.

[0099] Comparative Example 2:

[0100] First, the colorant CI pigment black 6 was vacuum dried at 80℃ for 24 hours, then dispersed together with the surfactant sodium dodecylbenzenesulfonate in DMAc and ball-milled for 24 hours to prepare a dispersion with a pigment content of 0.5 wt%, which was then set aside. Monomers BPDA, BIA, and PDA were synthesized at a molar ratio of 10:3:7, maintaining an amine to anhydride molar ratio of 1:1, and adjusting the solution solid content to 18%. Specifically, the diamine monomer was first added to the reactor along with an appropriate amount of DMAc, and after thorough mixing for 0.5 hours, the dianhydride monomer was slowly added to the reactor. After the addition was complete, stirring was continued for 2.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0101] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 9%. The nascent fibers are dried at 100℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. CI pigment black 6 accounts for 0.1 wt% of the total mass of the polyimide fibers.

[0102] During the spinning process, the fiber linear density change was less than 0.5% within 12 hours, demonstrating high linear density stability. The polyimide fiber prepared in this embodiment was tested using a YG001A-1 electronic fiber tensile strength tester, yielding a tensile strength of 3.5 GPa and an initial modulus of 178 GPa. The fiber is dark green (RGB(19,50,42)), with uniform color. Four random samples from the same fiber roll showed a maximum color difference of 1.03, and the color fastness to washing was grade 5.

[0103] Comparative Example 3:

[0104] First, the colorant CI pigment black 6 was vacuum dried at 80℃ for 24 hours, then dispersed together with the surfactant sodium methylene dinaphthalene sulfonate in DMAc, and ball-milled for 2 hours to prepare a dispersion with a pigment content of 20 wt%, for later use. Monomers BPDA and PDA were synthesized at a molar ratio of 1:1, maintaining an amine to anhydride molar ratio of 1:1, and adjusting the solution solid content to 18%. Specifically, the diamine monomer was first added to the reactor along with an appropriate amount of DMAc, and after thorough mixing for 0.5 hours, the dianhydride monomer was slowly added to the reactor. After the addition was complete, stirring was continued for 1.5 hours, and then the mixture was transferred to a spinning tank for degassing.

[0105] After degassing, the spinning solution and pigment dispersion are separately pumped through pipelines to the inlet of the dynamic mixer. They are mixed in the dynamic mixer and then conveyed to the spinneret for wet spinning to obtain nascent fibers. The coagulation bath concentration is 6%. The nascent fibers are dried at 120℃ and then subjected to gradient imidization at 240℃ to 440℃ to obtain the finished fibers. The pigment accounts for 12 wt% of the total mass of the polyimide fibers.

[0106] During the spinning process, the linear density of the fiber decreased by 13% within 12 hours, indicating poor linear density stability. The polyimide fiber prepared in this example was tested using a YG001A-1 electronic fiber tensile strength tester, and the tensile strength was measured to be 1.5 GPa, with an initial modulus of 63 GPa. The fiber color was uneven; the maximum color difference was 4.23 at four random points taken from the same roll of fiber, and the color fastness to soap washing was grade 5.

[0107] In Examples 1-8 above, the method for preparing colored polyimide fibers of the present invention can obtain high-performance colored polyimide fibers with high linear density stability. During the spinning process, the change in fiber linear density is less than 2% within 12 hours. The color is uniform, and the maximum color difference between four randomly selected points from the same roll of fiber is ≤2.0. Furthermore, the color fastness is good, with a soap washing fastness of grade four or higher. In contrast, in Comparative Example 1, CI pigment black 6 was added during the spinning solution synthesis process without using a dynamic mixer. The pigment particles settled during the degassing process of the spinning solution, resulting in a significant decrease in linear density after 8 hours of spinning, poor linear density stability, and uneven fiber color. In Comparative Example 2, when the amount of CI pigment black 6 added was too low (the black pigment content in the fiber was less than 0.2 wt%), the fiber color was dark green, failing to meet the requirement of black. In Comparative Example 3, when the amount of CI pigment black 6 added was too high (the black pigment content in the fiber was greater than 10 wt%), clogging easily occurred during the spinning process, leading to poor linear density stability.

[0108] 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 colored polyimide fiber comprising a pigment, wherein the pigment content is 0.2 wt% to 10 wt% of the total mass of the polyimide fiber; Within the same roll of colored polyimide fiber, four points are randomly selected, and the maximum color difference is ≤2 or ≤1. The physical and mechanical properties of the colored polyimide fiber are as follows: tensile strength of 0.5GPa-3.5GPa, initial modulus of 7GPa-180GPa, and color fastness to soap washing of not less than grade four or grade five.

2. The colored polyimide fiber according to claim 1, wherein, The pigment is an organic pigment or an inorganic pigment, and is selected from one or more of black pigment, red pigment, orange pigment, blue pigment, and green pigment; The black pigment is selected from one or more of CI Pigment Black 6, CI Pigment Black 11, CI Pigment Black 28, CI Pigment Black 27, CI Pigment Black 31, and CI Pigment Black 32. The red pigment is selected from one or more of CI Pigment Red 122, CI Pigment Red 149, CI Pigment Red 177, CI Pigment Red 179, CI Pigment Red 202, and CI Pigment Red 254; The blue pigment is selected from one or more of CI Pigment Blue 15, CI Pigment Blue 28, and CI Pigment Blue 60; The green pigment is selected from one or more of CI pigment green 7, CI pigment green 36, and CI pigment green 47; The orange pigment is selected from one or more of CI Pigment Orange 7, CI Pigment Orange 36, CI Pigment Orange 71, and CI Pigment Orange 77.

3. A method for preparing colored polyimide fibers according to claim 1 or 2, characterized in that, Includes the following steps: First, the pigment powder is dried, mixed with a surfactant, and an appropriate amount of organic solvent is added. The mixture is then dispersed by ball milling or without ball milling to prepare a pigment dispersion. The degassed polyamic acid spinning solution and the pigment dispersion are respectively transported to the feed port of the dynamic mixer by pipeline under the drive of metering pumps, and the two are mixed in the dynamic mixer. Colored polyimide fibers are obtained by using wet or dry-wet spinning processes, where the spinning solution is spun, coagulated, washed, dried, and heat-imidized.

4. The method for preparing colored polyimide fibers according to claim 3, wherein, Includes the following steps: (1) Preparation of pigment dispersion: After vacuum drying of pigment powder at 50-100℃, it is dispersed together with an appropriate amount of surfactant in an appropriate amount of organic solvent. Inorganic pigments are ground in a ball mill for 2-24 hours, while organic pigments do not need to be dispersed by ball milling. The resulting dispersion has a pigment content of 0.5wt%-20wt% and is ready for use. (2) Preparation of spinning solution: Diamine monomer and dianhydride monomer are added to an organic solvent at a molar ratio of 0.995:1-1:1.005 for synthesis. The solid content of the solution is adjusted to 12%-20%. After the synthesis is completed, the solution is vacuumed and allowed to stand for degassing. (3) Spinning: The defoamed spinning solution and pigment dispersion are respectively transported to the feed port of the dynamic mixer by pipeline under the push of metering pump. The two are mixed in the dynamic mixer and then transported to the spinneret. Wet or dry-wet spinning is carried out. After coagulation and washing, nascent fibers are obtained. (4) Drying and thermal imidization: The nascent fibers are dried at 80℃-120℃ and then thermal imidized at 200℃-600℃ to obtain the finished fibers, namely colored polyimide fibers.

5. The method for preparing colored polyimide fibers according to claim 3 or 4, wherein, The surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium methylene dinaphthalenesulfonate, polystyrene maleic anhydride copolyammonium salt, and polyacrylate ammonium salt; and / or The diamine monomer is selected from one or more of diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), m-phenylenediamine (MPD), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (MTD), and 4,4'-diaminodiphenylmethane (MDA); 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).

6. The method for preparing colored polyimide fibers according to claim 3, wherein, Within the same roll of polyimide fiber, four points are randomly selected, with a maximum color difference ≤ 2; and / or The molar ratio of the dianhydride monomer to the diamine monomer is 0.995:1 to 1:1.005; and / or During the spinning process, the change in fiber linear density is less than 2% within 12 hours.

7. The method for preparing colored polyimide fibers according to claim 3 or 4, wherein, First, add the diaminodiphenyl ether (ODA) to the reactor and add an appropriate amount of dimethylacetamide (DMAc). After mixing thoroughly for more than 0.5 hours, weigh out the pyromellitic anhydride (PMDA) and slowly add it to the reactor. After adding all the materials, continue stirring for 0.5 to 3 hours, and then transfer it to a spinning tank for degassing.

8. The application of the colored polyimide fiber according to claim 1 or 2 or the colored polyimide fiber obtained by any one of claims 3-7 in the fields of aerospace, electronics and power, rail transportation, high temperature protection or textiles.

9. A continuous filament, staple fiber, woven fabric, nonwoven fabric, powder or prepreg comprising the colored polyimide fiber of claim 1 or the colored polyimide fiber obtained by any one of claims 3-7.

10. 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 9.

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