A kind of polyimide fiber and preparation method thereof

Abstract

The present invention relates to a polyimide fiber and a preparation method thereof, the method comprising the following steps: a slightly gelled polyamic acid with a certain pre-imidization degree is extruded through a spinneret according to a dry-wet spinning process, and then the slightly gelled polyamic acid enters a coagulation bath through an air layer; then, partially imidized fibers are obtained after washing and drying; and finally, polyimide fibers are obtained after further thermal cyclization. The spray-to-pulling ratio of the slightly gelled polyamic acid fiber in the air layer stage can reach more than 10, which greatly improves the production efficiency and orientation degree of the polyimide fiber, and the prepared polyimide fiber has more excellent mechanical properties.

Description

Technical Field

[0001] The invention belongs to the field of material science and technology, and specifically relates to a polyimide fiber and a preparation method thereof. Technical Background

[0002] Polyimide fiber has good thermomechanical properties, excellent resistance to ultraviolet radiation, acid and alkali corrosion and flame retardancy, and is widely used in aerospace, atomic energy industry, high-temperature dust removal bags, firefighting clothing and other high-temperature resistant fields.

[0003] Common methods for preparing polyimide fibers mainly include one-step and two-step solution spinning. Among them, the one-step method uses polyimide solution for spinning, and the raw fiber does not need to be subsequently thermally imidized, which avoids the fiber structure defects caused by the removal of water molecules during the two-step spinning process, and is convenient for preparing polyimide fibers with excellent mechanical properties. However, it generally uses phenolic solvents with high toxicity, and the monomer types have certain limitations. Therefore, the preparation of polyimide fibers currently mostly adopts the two-step method.

[0004] The two-step wet spinning process is simple and has low requirements on the properties of the solution. It is the most commonly used two-step spinning method at present. However, the fiber is prone to form a skin-core structure in the coagulation bath stage, which limits its spray-pull ratio in the initial stage, resulting in slow spinning speed and low production efficiency. In order to solve the above problems, dry spinning and dry-wet spinning processes have been developed on the basis of wet spinning. Patent CN 102242415 B uses a dry spinning preparation method to improve the spinnability and post-processing characteristics of polyimide fibers, but the mechanical properties of the prepared polyimide fibers have not been reported. Patent CN 101338452 B discloses a dry-wet method for preparing polyimide fibers. The gradient heating method used in the imide process overcomes the shortcomings of inaccurate temperature control and complex operation of the two-stage hot furnace technology, but its heat treatment temperature range is 50-500°C, the heating rate is 1-10°C / min, and the thermal imidization time takes 1-10 hours, and the production efficiency is not high.

[0005] Although there are studies and improvements on the preparation method of polyimide fibers in the prior art, there are still a series of problems. For example, the fiber is prone to form a skin-core structure in the coagulation bath stage of the current fiber preparation technology, which limits the spray-to-pull ratio in the initial stage of spinning, resulting in a slow spinning speed and low production efficiency. Therefore, it is urgent to develop a preparation method for polyimide fibers that can effectively improve the initial spray-to-pull ratio of the fiber, improve production efficiency and fiber orientation. Summary of the invention

[0006] The purpose of the present invention is to overcome the disadvantages of the conventional two-step wet spinning process that the fiber is prone to crusting and forming defective structures in the coagulation bath stage, thereby affecting the mechanical properties of the fiber, as well as the disadvantages of the existing dry-wet spinning process that the imidization time is long and the production efficiency is low. A polyimide fiber and a preparation method thereof are provided, which can greatly improve the initial fiber spray-to-pulling ratio, improve the production efficiency and fiber orientation, and the prepared polyimide fiber has more excellent mechanical properties.

[0007] The present invention firstly adds an imidization agent into a polyamic acid solution to obtain a polyamic acid with a certain degree of pre-imidization and microgelation, thereby preparing polyamic acid primary fibers with a specific microgelation morphology. The fibers have a high initial strength and can withstand a large spin-to-spin ratio in the air layer stage between the subsequent spinneret and the coagulation bath, thereby improving the fiber production efficiency in the initial stage.

[0008] At the same time, in the process flow of the polyimide fiber preparation method of the present invention, an air layer is reserved between the spinneret and the coagulation bath, which omits the complicated modification of the traditional two-step wet spinning equipment. At the same time, the existence of the air layer increases the effective initial stretching time and aging time, further reduces the surface and internal structural defects of the PI fiber, and is conducive to further improving the mechanical properties of the fiber.

[0009] To achieve the above object, the present invention provides a polyimide fiber and a preparation method thereof, comprising the following steps:

[0010] (1) adding a diamine monomer and a dianhydride monomer into a reaction solvent and stirring them sufficiently to cause a condensation polymerization reaction to obtain a homogeneous polyamic acid solution, wherein the solid content ratio of the polyamic acid solution is controlled to be 10%-30%;

[0011] (2) adding a certain amount of a dehydrating agent and a catalyst in a certain ratio to the above polyamic acid solution and stirring the solution thoroughly to obtain a polyamic acid having a certain degree of pre-imidization and slight gelation, wherein the degree of pre-imidization is 20%-40%;

[0012] (3) spinning the slightly gelled polyamic acid obtained according to the dry-wet spinning process, the spinning solution is extruded through the spinneret and then enters the coagulation bath through the air layer, and the nascent fibers are subjected to high-multiple drafting in this stage; the spinning tank is filled with nitrogen at a pressure of 0.2-0.5 MPa, and the solution is pushed to the spinneret, or pushed to the spinneret by a metering pump;

[0013] (4)) The raw fibers are uniformly passed through a tubular furnace at a temperature of 60-120° C. for drying for 1-6 minutes. Then, the dried fibers are uniformly passed through a tubular furnace at a temperature of 350-500° C. for further thermal cyclization treatment for 1-6 minutes to obtain fully imidized polyimide fibers.

[0014] Preferably, the solid content of the polyamic acid solution in step (1) is 10%-20%. The molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1-1.02:1.

[0015] Preferably, the dianhydride monomer in step (1) is one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride (α-BPDA), bisphenol A dianhydride (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), hexafluoroisopropylenephthalic acid (6FDA), diphenyl sulfide tetracarboxylic dianhydride (TDPA) and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride. The invention relates to a method for preparing an alkyl amine, wherein the alkyl amine is a mixture of one or more of p-phenylenediamine (PDA), m-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), 4,4'-diaminodiphenyl sulfone, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl in any proportion; and the reaction solvent is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-vinylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0016] Preferably, in step (2), the volume ratio of the dehydrating agent to the catalyst is 2:1-1:5.

[0017] Preferably, the dehydrating agent in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, and butyric anhydride; and the catalyst is a mixture of one or more of pyridine, triethylamine, imidazole, isoquinoline, 2-methylpyridine, and 3-methylpyridine.

[0018] Another object of the present invention is to provide a polyimide fiber with excellent mechanical properties prepared by the above method.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The method of the present invention obtains a polyamic acid having a certain degree of pre-imidization and microgelation by adding a certain amount of a dehydrating agent and a catalyst to a polyamic acid solution. The microgelated polyamic acid primary fiber prepared by the method has a high strength and can withstand a large spin-to-spin ratio in the air layer stage between the spinneret and the coagulation bath, thereby improving the fiber production efficiency;

[0021] (2) The polyimide fiber prepared by the method of the present invention has higher orientation degree and mechanical properties;

[0022] (3) The method for preparing polyimide fibers of the present invention only requires reserving an air layer between the spinneret and the coagulation bath, and does not require modification of the conventional two-step wet spinning equipment. The operation is simple and convenient for industrial production. The presence of the air layer reduces the surface and internal structural defects of the PI fibers, which is beneficial to further improve the mechanical properties of the fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the dry-wet spinning process of polyimide fiber;

[0024] Figure 2 The rheological behavior of the solution during the chemical imidization process of Example 1 (the junction of region I and region II is the polyamic acid microgel point);

[0025] Figure 3 This is the infrared spectrum of the polyamic acid microgel point in Example 1.

[0026] The microgel point of the polyamic acid solution in the embodiment can be determined by the rheological curve, and the imidization degree at the microgel point can be determined by the infrared spectrum, and then the addition amount of the imidization agent can be calculated. DETAILED DESCRIPTION

[0027] 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.

[0028] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar modules or modules with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0029] In the description of this specification, the description with reference to the terms "one embodiment", "another embodiment", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0030] The present invention provides a process flow for preparing a polyimide fiber, as follows: Figure 1As shown, the general process includes: preparing raw materials → polymerization reaction → obtaining polyamic acid solution → adding chemical imidization reagent → obtaining microgel polyamic acid spinning solution → spinning → extruding through air layer → high-multiple drawing of filaments → entering coagulation bath → entering water bath → drying → collecting filaments to obtain finished fibers.

[0031] During the entire fiber preparation process, the spinning solution goes through the following related equipment in sequence: spinneret → air layer → spinning roller → coagulation bath → water bath → drying furnace → collecting roller.

[0032] In the preparation process of the polyimide fiber of the present invention, the state and tissue morphology of the gelled polyamic acid spinning solution obtained in the intermediate step have a crucial influence on the subsequent spinning process, and play an important role in preparing fibers with higher strength and capable of withstanding a larger spinning ratio, thereby improving fiber production efficiency.

[0033] The specific embodiments of the present invention are clearly described below.

[0034] Example 1

[0035] (1) adding equimolar amounts of PMDA and ODA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0036] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 40%, wherein the molar ratio of acetic anhydride to PMDA is 0.8:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0037] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry-wet spinning process, wherein the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 30 mm air layer, the spin ratio is 15, and the spinning speed is 120 m / min;

[0038] (4) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 460° C. for thermal cyclization and stretching for 2 min at a stretching ratio of 4.0, thereby obtaining fully imidized polyimide fibers.

[0039] Example 1 Scheme for preparing fibers The rheological behavior of the solution during the chemical imidization process in step (2) is as follows: Figure 2 As shown in the figure, the junction of region I and region II is the polyamic acid microgel point. Figure 3The infrared spectrum at the polyamic acid microgel point is shown, and the amount of the required imidization agent can be accurately determined in the experiment to achieve the purpose of accurately controlling the imidization degree.

[0040] Comparative Example 1

[0041] (1) adding equimolar amounts of PMDA and ODA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0042] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution is extruded from the spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 30 mm air layer, the spin ratio is 8, and the spinning speed is 80 m / min;

[0043] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 460° C. for thermal cyclization and stretching with a stretching ratio of 4.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0044] Comparative Example 2

[0045] (1) adding equimolar amounts of PMDA and ODA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0046] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 20 m / min;

[0047] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 460° C. for thermal cyclization and stretching with a stretching ratio of 4.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0048] Table 1 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0049]

[0050] Example 2

[0051] (1) adding equimolar amounts of BPDA and PDA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 12%;

[0052] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 30%, wherein the molar ratio of acetic anhydride to BPDA is 0.6:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0053] (3) The obtained polyamic acid with a certain degree of pre-imidization and microgelation was spun according to a dry-wet spinning process. The spinning solution was extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then entered a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 35 mm air layer. The spin ratio was 13 and the spinning speed was 105 m / min.

[0054] (4) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. for drying at a uniform speed for 3 min; and then passed through a tubular furnace at a temperature of 470° C. for thermal cyclization and stretching at a stretching ratio of 2.0 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0055] Comparative Example 3

[0056] (1) adding equimolar amounts of BPDA and PDA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 12%;

[0057] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution is extruded from the spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 35 mm air layer, the spin ratio is 7, and the spinning speed is 70 m / min;

[0058] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. at a uniform speed for drying for 3 min; then passed through a tubular furnace at a temperature of 470° C. at a uniform speed for thermal cyclization and stretching with a stretching ratio of 2.0 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0059] Comparative Example 4

[0060] (1) adding equimolar amounts of BPDA and PDA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 12%;

[0061] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 20 m / min;

[0062] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. at a uniform speed for drying for 3 min; then passed through a tubular furnace at a temperature of 470° C. at a uniform speed for thermal cyclization and stretching with a stretching ratio of 2.0 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0063] Table 2 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0064]

[0065] Example 3

[0066] (1) adding BPDA / PMDA / PDA with a molar ratio of 5 / 5 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0067] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 20%, wherein the molar ratio of acetic anhydride to PDA is 0.4:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0068] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry-wet spinning process, wherein the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 50 mm air layer, the spin ratio is 14, and the spinning speed is 130 m / min;

[0069] (4) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 1.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0070] Comparative Example 5

[0071] (1) adding BPDA / PMDA / PDA with a molar ratio of 5 / 5 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0072] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution was extruded from the spinneret under a nitrogen pressure of 0.35 MPa and then passed through a 50 mm air layer into a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio was 7, and the spinning speed was 75 m / min;

[0073] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 1.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0074] Comparative Example 6

[0075] (1) adding BPDA / PMDA / PDA with a molar ratio of 5 / 5 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0076] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 25 m / min;

[0077] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 1.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0078] Table 3 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0079]

[0080] Example 4

[0081] (1) adding BPDA / PDA / ODA in a molar ratio of 10 / 6 / 4 into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0082] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 40%, wherein the molar ratio of acetic anhydride to BPDA is 0.8:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0083] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry-wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 45 mm air layer, the spin ratio is 13, and the spinning speed is 125 m / min;

[0084] (4) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 5.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0085] Comparative Example 7

[0086] (1) adding BPDA / PDA / ODA in a molar ratio of 10 / 6 / 4 into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0087] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution is extruded from the spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 45 mm air layer, the spin ratio is 7, and the spinning speed is 75 m / min;

[0088] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 5.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0089] Comparative Example 8

[0090] (1) adding BPDA / PDA / ODA in a molar ratio of 10 / 6 / 4 into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0091] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 2, and the spinning speed is 22 m / min;

[0092] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 5.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0093] Table 4 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0094]

[0095] Example 5

[0096] (1) adding PMDA / PDA / BIA with a molar ratio of 10 / 5 / 5 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0097] (2) adding acetic anhydride and pyridine to the above polyamic acid solution, stirring thoroughly, to obtain a microgel polyamic acid spinning solution with a pre-imidization degree of 30%, wherein the molar ratio of acetic anhydride to PMDA is 0.6:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0098] (3) The obtained polyamic acid with a certain degree of pre-imidization and microgelation was spun according to a dry-wet spinning process. The spinning solution was extruded from a spinneret under a nitrogen pressure of 0.40 MPa and then passed through a 40 mm air layer into a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%). The spin ratio was 16 and the spinning speed was 155 m / min.

[0099] (4) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. for drying at a uniform speed for 3 min; and then passed through a tubular furnace at a temperature of 490° C. for thermal cyclization and drawing at a uniform speed for 2 min, with a drawing ratio of 1.5, to obtain a fully imidized polyimide fiber.

[0100] Comparative Example 9

[0101] (1) adding PMDA / PDA / BIA with a molar ratio of 10 / 5 / 5 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0102] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution is extruded from the spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 40 mm air layer, the spin ratio is 8, and the spinning speed is 80 m / min;

[0103] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. for drying at a uniform speed for 3 min; and then passed through a tubular furnace at a temperature of 490° C. for thermal cyclization and drawing at a drawing ratio of 1.5 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0104] Comparative Example 10

[0105] (1) adding PMDA / PDA / BIA with a molar ratio of 10 / 5 / 5 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0106] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 4, and the spinning speed is 30 m / min;

[0107] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. for drying at a uniform speed for 3 min; and then passed through a tubular furnace at a temperature of 490° C. for thermal cyclization and drawing at a drawing ratio of 1.5 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0108] Table 5 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0109]

[0110] Example 6

[0111] (1) adding BPDA / ODPA / PDA with a molar ratio of 7 / 3 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0112] (2) adding acetic anhydride and pyridine to the polyamic acid solution, stirring thoroughly, and obtaining a microgel polyamic acid with a pre-imidization degree of 35%, wherein the molar ratio of acetic anhydride to PDA is 0.7:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0113] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry-wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 50 mm air layer, the spin ratio is 12, and the spinning speed is 115 m / min;

[0114] (4) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 3.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0115] Comparative Example 11

[0116] (1) adding BPDA / ODPA / PDA with a molar ratio of 7 / 3 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0117] (2) spinning the polyamic acid solution according to the dry-wet spinning process, the spinning solution is extruded from the spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%) through a 50 mm air layer, the spin ratio is 5, and the spinning speed is 45 m / min;

[0118] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 3.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0119] Comparative Example 12

[0120] (1) adding BPDA / ODPA / PDA with a molar ratio of 7 / 3 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0121] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 2.5, and the spinning speed is 20 m / min;

[0122] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 3.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0123] Table 6 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0124]

[0125] It can be seen from Tables 1-6 that the dry-wet spinning process described in the present invention can greatly improve the spray-to-stretch ratio of the fiber in the air layer stage, improve the fiber production efficiency and orientation, and the prepared polyimide fiber has more excellent mechanical properties.

[0126] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing a polyimide fiber, comprising the following steps: (1) adding a diamine monomer and a dianhydride monomer into a reaction solvent and stirring them sufficiently to cause a condensation polymerization reaction to obtain a homogeneous polyamic acid solution, wherein the solid content ratio of the polyamic acid solution is controlled to be 10%-30%; (2) adding a certain amount of dehydrating agent and catalyst to the above polyamic acid solution in a certain ratio and stirring them fully to obtain a polyamic acid with a certain degree of pre-imidization and slight gelation, wherein the degree of pre-imidization is 20%-40%; the solid content of the polyamic acid solution in step (1) is 10%-30%, and the molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1-1.02:1; the volume ratio of the dehydrating agent to the catalyst in step (2) is 2:1-1:5; the dehydrating agent in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, and butyric anhydride; the catalyst is a mixture of one or more of pyridine, triethylamine, imidazole, isoquinoline, 2-methylpyridine and 3-methylpyridine; (3) spinning the slightly gelled polyamic acid obtained according to the dry-wet spinning process, the spinning solution is extruded through the spinneret and then enters the coagulation bath through the air layer, and the nascent fibers are subjected to high-multiple drafting in this stage; the spinning tank is filled with nitrogen at a pressure of 0.2-0.5 MPa, and the solution is pushed to the spinneret, or pushed to the spinneret by a metering pump; (4) The raw fibers are uniformly passed through a tubular furnace at a temperature of 60-120° C. for drying for 1-6 min, and then the dried fibers are uniformly passed through a tubular furnace at a temperature of 350-500° C. for further thermal cyclization treatment for 1-6 min to obtain fully imidized polyimide fibers.

2. The method according to claim 1, characterized in that The dianhydride monomer in step (1) is a mixture of one or more of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, bisphenol A dianhydride, 4,4'-oxydiphthalic anhydride, diphenyl sulfide tetracarboxylic dianhydride and 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride in any proportion; the diamine monomer is a mixture of one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, 4,4'-diaminodiphenyl sulfone and 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl in any proportion; and the reaction solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-vinyl pyrrolidone and dimethyl sulfoxide.

3. A polyimide fiber prepared according to the method according to any one of claims 1-2.

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