Long-acting cooling type infrared camouflage polyimide fiber aggregate and preparation method thereof

Abstract

The invention provides a long-acting cooling type infrared camouflage polyimide fiber aggregate and a preparation method thereof, and relates to the field of infrared camouflage, a polyamide acid solution is prepared through condensation polymerization, a centrifugal spinning technology is adopted for spinning, and auxiliary rods are arranged around a centrifugal spinning cup to form polyamide acid fibers of a horizontal layered structure. The preparation method comprises the following steps: putting fibers in an oxygen-containing environment for cyclization reaction, regulating the curvature radius of the fibers through oxygen concentration to obtain bent polyimide fibers, depositing a titanium nitride nano layer on the surfaces of the fibers by adopting an atomic layer deposition technology, crushing the composite fibers into short fibers, and performing electrostatic flocking treatment to form a vertical array structure, thereby obtaining the polyimide / titanium nitride composite fiber. The long-acting cooling type infrared camouflage polyimide fiber aggregate is obtained. The composite material with long-acting cooling and infrared camouflage functions is developed by combining the polyimide fiber, the titanium nitride nano layer and the electrostatic flocking technology, and the composite material has wide application prospects in the fields of military affairs, industry, building decoration and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared camouflage, and in particular to a long-lasting cooling type infrared camouflage polyimide fiber aggregate and a preparation method thereof. Background Art

[0002] Infrared camouflage technology is a key research area in the field of military stealth. Its core objective is to reduce the infrared radiation signature of target objects through material design and structural optimization to evade thermal imaging detection. With the rapid development of infrared detection technology, traditional static low-emissivity materials are gradually becoming limited due to their inability to effectively address the temperature rise caused by heat accumulation. For example, while low-emissivity coatings can reduce surface infrared radiation, they hinder heat dissipation, causing the target's internal temperature to continue to rise. Ultimately, secondary infrared signals are generated due to heat conduction or convection, significantly weakening the camouflage effect.

[0003] Polyimide (PI) fiber has become an important matrix for infrared camouflage materials due to its excellent high temperature resistance, mechanical properties and controllable optoelectronic properties. In recent years, researchers have improved its infrared stealth performance by introducing functional fillers (such as graphene, metal nanoparticles) or constructing multi-level structures, but existing solutions mostly rely on a single functional layer (such as a thermal insulation porous layer or a highly reflective coating), lack cross-scale collaborative design, and are difficult to meet the dual needs of blocking heat flow and channeling heat. In addition, although dynamic modulation technology (such as electrochromic emissivity control devices) can be compatible with heat dissipation and camouflage, it relies on complex circuits and external energy input, making it difficult to apply to flexible or large-area equipment surfaces, and its heat dissipation capacity is insufficient.

[0004] In view of this, it is necessary to design a long-lasting cooling infrared camouflage polyimide fiber aggregate and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a long-lasting cooling infrared camouflage polyimide fiber aggregate and its preparation method, aiming to solve the technical problem that existing infrared camouflage materials are difficult to meet the dual needs of blocking heat flow and conducting heat.

[0006] In a first aspect, the present application provides a method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly, comprising the following steps:

[0007] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to N,N-dimethylformamide solvent and subjected to polycondensation reaction at a predetermined temperature to obtain a polyamic acid solution;

[0008] S2 using centrifugal spinning technology to spin the polyamic acid solution, providing an auxiliary rod around the centrifugal spinning cup to form a horizontal layered structure of polyamic acid fibers;

[0009] S3. The horizontal layered structure of the polyamic acid fiber is placed in an oxygen-containing environment for cyclization reaction, and the curvature radius of the fiber is regulated by the oxygen concentration to obtain a curved polyimide fiber;

[0010] S4. A titanium nitride nanolayer is deposited on the surface of the curved polyimide fiber using atomic layer deposition technology to obtain a polyimide / titanium nitride composite fiber;

[0011] S5. The polyimide / titanium nitride composite fiber is crushed into short fibers, and then subjected to electrostatic flocking treatment to form a vertical array structure to obtain a long-lasting cooling infrared camouflage polyimide fiber aggregate.

[0012] As a further improvement of the present application, in step S1, the mass fraction of the pyromellitic dianhydride is 5-10%, the mass fraction of the 4,4'-diaminodiphenyl ether is 5-10%, and the mass fraction of the triethylamine is 1-8%.

[0013] As a further improvement of the present application, the temperature of the polycondensation reaction is 0-10°C.

[0014] As a further improvement of the present application, in step S2, the spinning speed of the centrifugal spinning technology is 3000-4000 rpm, the spinning temperature is 30-40°C, the spinning humidity is 30-40% RH; the spinneret diameter is 0.1-0.4 mm; and the distance between the centrifugal spinning cup and the collecting cloth is 5-15 cm.

[0015] As a further improvement of the present application, the auxiliary rods have a height of 5 to 15 cm, and are arranged with the centrifugal spinning cup as the center and 3 to 8 auxiliary rods placed at equal intervals with a radius of 5 to 25 cm.

[0016] As a further improvement of the present application, in step S3, the temperature of the cyclization reaction is 300-450° C., the time is 1-3 hours; the oxygen concentration is 5-50%, and the remaining component is nitrogen.

[0017] As a further improvement of the present application, the control range of the curvature radius is 10 to 300 μm.

[0018] As a further improvement of the present application, in step S4, the deposition method is: using titanium tetrachloride as a titanium precursor, ammonia as a nitrogen source, the deposition temperature is 150-300° C., the pressure is 0.1-10 Torr, the titanium tetrachloride pulse time is 0.1-1 s, the ammonia pulse time is 0.5-2 s, and the number of cycles is 100-800 times;

[0019] The thickness of the titanium nitride nanolayer is 5 to 200 nm.

[0020] As a further improvement of the present application, in step S5, the length of the short fibers is 100 to 1000 μm; the flocking voltage of the electrostatic flocking treatment is 20 to 150 kV, the flocking time is 3 to 40 s, the electrode distance is 5 to 30 cm, and the flocking density is 35 to 105 g / m 2 .

[0021] In the second aspect, the present application provides a long-lasting cooling type infrared camouflage polyimide fiber aggregate, which is prepared by the preparation method described in the first aspect. The infrared emissivity of the long-lasting cooling type infrared camouflage polyimide fiber aggregate is ≤0.35, the Nusselt number is ≥15, and the thermal conductivity is ≤0.03W / (m·K).

[0022] The beneficial effects of this application are:

[0023] The present application provides a long-lasting cooling type infrared camouflage polyimide fiber aggregate and its preparation method, wherein a polyamic acid solution is prepared by a condensation reaction, spinning is carried out by centrifugal spinning technology, auxiliary rods are arranged around the centrifugal spinning cup to form a horizontal layered structure polyamic acid fiber, the fiber is placed in an oxygen-containing environment for cyclization reaction, the curvature radius of the fiber is regulated by the oxygen concentration to obtain a curved polyimide fiber, and a titanium nitride nanolayer is deposited on the surface of the curved polyimide fiber by atomic layer deposition technology to obtain a polyimide / titanium nitride composite fiber, the polyimide / titanium nitride composite fiber is crushed into short fibers, and then subjected to electrostatic flocking treatment to form a vertical array structure to obtain a long-lasting cooling type infrared camouflage polyimide fiber aggregate. The present application has developed a composite material with long-lasting cooling and infrared camouflage functions by combining polyimide fibers, titanium nitride nanolayers and electrostatic flocking technology, which has broad application prospects in the fields of military, industry and architectural decoration.

[0024] This application can achieve long-term dynamic thermal management and break through the bottleneck of heat accumulation. The vertical polyimide / titanium nitride composite fiber array significantly improves the Nusselt number (Nu) through microporous channels and high specific surface area design, significantly improving the convective heat dissipation efficiency, quickly evacuating the heat accumulated in the first layer of barrier structure, and avoiding secondary infrared radiation caused by temperature rise. The horizontal curved fiber layer effectively blocks the intrusion of heat flow by extending the heat conduction path; the vertical array promptly evacuates the heat escaping from the surface after long-term insulation, realizing the synergy of the "blocking-drainage" dual mechanism, so that the target surface and ambient temperature are synchronously matched.

[0025] The low infrared emissivity of titanium nitride works synergistically with the geometric orientation of the vertical array to reduce the intensity of normal surface radiation while avoiding the risk of specular reflection exposure associated with the flat surface of traditional metal coatings. In high-temperature environments (>100°C), the rapid heat dissipation of the vertical array keeps the surface temperature below 35°C. Combined with the stable low emissivity of titanium nitride, the target infrared radiation intensity consistently matches the ambient temperature, maintaining stable surface radiation characteristics and achieving compatibility between low infrared emissivity and efficient heat dissipation.

[0026] The fiber network is suitable for curved or dynamic targets. The high temperature resistance of polyimide fiber combined with the oxidation resistance of titanium nitride enables the material to maintain stable performance in extreme environments such as humidity, heat, salt spray, and ultraviolet radiation.

[0027] Centrifugal spinning technology enables the mass production of horizontal, curved fiber layers, while electrostatic flocking allows for precise orientation control of vertical arrays, eliminating the complex lamination process required for traditional multi-layer composite materials. Thermal management is achieved through physical structural design, eliminating the need for complex control systems or external energy input from dynamic technologies like electrochromism and microfluidics, making it suitable for passive camouflage applications (such as long-term latent equipment in the field).

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0030] Figure 1 This is an SEM image of the long-lasting cooling infrared camouflage polyimide fiber assembly provided in Example 1 of the present application;

[0031] Figure 2 Schematic diagram of the structure of the long-lasting cooling infrared camouflage polyimide fiber assembly provided in this application;

[0032] Figure 3 This is an SEM image of the curved polyimide fiber prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0035] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0036] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] Although traditional low-emissivity materials (such as metal coatings) reduce surface radiation, their high reflective properties hinder heat dissipation, forming a "thermal barrier effect" that causes the target temperature to continue to rise and eventually be exposed through thermal convection or thermal conduction. Existing solutions mostly rely on a single functional layer (such as a thermally insulating porous layer or a highly reflective coating), lack cross-scale collaborative design, and are difficult to meet the dual needs of "blocking heat flow" and "conducting heat." Dynamic control technologies such as electrochromism require complex control circuits and external energy sources, are bulky and costly, and are difficult to adapt to extreme environments or flexible equipment requirements.

[0038] In order to solve the technical problem that existing infrared camouflage materials are difficult to meet the dual needs of blocking heat flow and dissipating heat, this application provides a long-lasting cooling infrared camouflage polyimide fiber aggregate and its preparation method, wherein the double-layer structure innovatively combines the functions of heat insulation (horizontal curved fiber layer) and heat dissipation (vertical composite fiber array), and achieves thermal management through physical structure rather than chemical modification. The curved shape of the horizontal layer can increase the length of the heat conduction path and delay the intrusion of external heat flow; while the vertical array strengthens air convection through microporous channels. This "blocking-dissipating" synergistic mechanism breaks through the performance bottleneck of traditional single-layer materials while avoiding the complexity of dynamic technology.

[0039] In a first aspect, the present invention provides a method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly, comprising the following steps:

[0040] S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to N,N-dimethylformamide solvent and subjected to polycondensation reaction at a predetermined temperature to obtain a polyamic acid solution;

[0041] S2 using centrifugal spinning technology to spin the polyamic acid solution, providing an auxiliary rod around the centrifugal spinning cup to form a horizontal layered structure of polyamic acid fibers;

[0042] S3. The horizontal layered structure of polyamic acid fiber is placed in an oxygen-containing environment for cyclization reaction, and the curvature radius of the fiber is controlled by the oxygen concentration to obtain a curved polyimide fiber;

[0043] S4. A titanium nitride nanolayer was deposited on the surface of the curved polyimide fiber using atomic layer deposition technology to obtain a polyimide / titanium nitride composite fiber;

[0044] S5. The polyimide / titanium nitride composite fibers are crushed into short fibers and then subjected to electrostatic flocking treatment to form a vertical array structure, thereby obtaining a long-lasting cooling infrared camouflage polyimide fiber aggregate.

[0045] In the technical solution of the embodiment of the present application, a polyamic acid solution is prepared by a condensation reaction, and the contents of pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA) and triethylamine (TEA) are controlled to adjust the viscosity of the polyamic acid solution, thereby affecting the performance of the final fiber. The flat stacked layer structure of the polyimide curved fiber prepared by centrifugal spinning technology uses the curved shape of the fiber to extend the heat conduction path and achieve external heat flow barrier. The upright array structure of the polyimide / titanium nitride composite fiber constructed by electrostatic flocking technology enhances convective heat dissipation (Nussel number improvement) through microporous channels and high specific surface area, while maintaining low infrared emissivity. The dynamic synergy of "barrier-drainage" of the double-layer structure solves the contradiction of "heat insulation must sacrifice heat dissipation" in traditional materials.

[0046] Furthermore, in some embodiments, in step S1, the mass fraction of pyromellitic dianhydride is 5-10%, the mass fraction of 4,4'-diaminodiphenyl ether is 5-10%, and the mass fraction of triethylamine is 1-8%. In the technical solution of the embodiment of the present application, by adjusting the contents of pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and triethylamine, the viscosity of the polyamic acid solution can be controlled to 30-55 Pa·s, thereby improving the stability and controllability of the spinning process and enhancing the thermal insulation properties of the final polyimide fiber.

[0047] Furthermore, in some embodiments, the temperature of the polycondensation reaction is 0-10°C.

[0048] In the technical solution of the embodiment of the present application, the polycondensation reaction is carried out at low temperature, which can avoid the generation of by-products or uneven molecular weight distribution due to too rapid reaction, improve the stability of the solution, regulate the structure and properties of polyamic acid, and improve the performance of the polyimide fiber finally spun.

[0049] Furthermore, in some embodiments, in step S2, the spinning speed of the centrifugal spinning technology is 3000-4000 rpm, the spinning temperature is 30-40°C, the spinning humidity is 30-40% RH; the spinneret diameter is 0.1-0.4 mm; and the distance between the centrifugal spinning cup and the collecting cloth is 5-15 cm.

[0050] In the technical solutions of the embodiments of this application, high rotation speeds help evenly stretch the solution, forming fibers with consistent diameters. The spinning temperature and humidity maintain the fluidity and stability of the polymer solution, preventing changes in solution viscosity caused by excessively high or low temperatures. The spinneret diameter determines the initial diameter of the filaments, which in turn influences the diameter and properties of the final fibers. An appropriate distance between the centrifugal spinning cup and the collecting cloth reduces the risk of filament breakage during flight, improving fiber integrity and continuity.

[0051] Furthermore, in some embodiments, the auxiliary rods have a height of 5 to 15 cm, and are arranged such that 3 to 8 auxiliary rods are placed at equal intervals with a radius of 5 to 25 cm, centered on the centrifugal spinning cup.

[0052] In the technical solution of the embodiment of the present application, an auxiliary rod is provided to assist in forming a horizontal layered structure. By adjusting the height of the auxiliary rod, the deposition thickness of the fiber on the collecting cloth can be controlled, thereby affecting the thickness and density of the final fiber layer. The auxiliary rods are arranged at equal intervals within a certain radius with the centrifugal spinning cup as the center, which can guide the fibers to be evenly distributed under the action of centrifugal force to form a regular layered structure. By reasonably setting the rod height and arrangement of the auxiliary rods, the deposition and molding process of the fibers can be effectively controlled to form a uniform and regular horizontal layered structure of polyamic acid fibers. This structure helps to improve the mechanical properties, thermal insulation properties and structural stability of the fibers.

[0053] Furthermore, in some embodiments, in step S3, the cyclization reaction temperature is 300-450° C., the reaction time is 1-3 hours, the oxygen concentration is 5-50%, and the remaining component is nitrogen.

[0054] In the technical solution of the embodiment of the present application, by controlling the cyclization reaction conditions during the formation of polyimide, curved polyimide fibers are formed, thereby increasing the strain energy storage of single fibers and the elastic limit strain of the fiber aggregate, thereby enhancing the mechanical stability; at the same time, the porous structure of the curved pore walls formed by the curved fibers enhances phonon scattering, shortens the mean free path of phonons, reduces the equivalent thermal conductivity, and enhances thermal insulation performance.

[0055] Furthermore, in some embodiments, the curvature radius of the fiber is controlled in the range of 10 to 300 μm.

[0056] In the technical solution of the embodiment of the present application, by adjusting the curvature radius, the fibers can achieve different bending shapes, and by adjusting the rod height and setting radius of the long rod, the height and porosity of the layered aggregate can be optimized to obtain the best thermal insulation effect.

[0057] Furthermore, in some embodiments, in step S4, the deposition method is: using titanium tetrachloride as a titanium precursor, ammonia as a nitrogen source, the deposition temperature is 150-300°C, the pressure is 0.1-10 Torr, the titanium tetrachloride pulse time is 0.1-1s, the ammonia pulse time is 0.5-2s, and the number of cycles is 100-800 times; the thickness of the titanium nitride nanolayer is 5-200nm.

[0058] In the technical solution of the embodiment of the present application, atomic layer deposition (ALD) technology is used to controllably grow a titanium nitride (TiN) nanolayer on the surface of a polyimide fiber. Titanium tetrachloride (TiCl4) is selected as a titanium precursor, ammonia (NH3) is used as a nitrogen source, and an atomic layer deposition device is used to deposit a nanolayer of titanium nitride on the surface of the polyimide fiber to prepare a polyimide / titanium nitride composite fiber. By controlling the deposition reaction conditions, the load thickness of the titanium nitride film on the polyimide fiber is obtained to range from 5 to 200 nm. Titanium nitride has a high melting point, which significantly improves the thermal stability of the composite material. At the same time, the high thermal conductivity of titanium nitride helps to quickly dissipate heat, improving the cooling effect of the material.

[0059] Furthermore, in some embodiments, in step S5, the length of the short fibers is 100 to 1000 μm; the flocking voltage of the electrostatic flocking treatment is 20 to 150 kV, the flocking time is 3 to 40 s, the electrode distance is 5 to 30 cm, and the flocking density is 35 to 105 g / m 2 .

[0060] In the technical solution of the embodiment of the present application, the polyimide / titanium nitride composite fiber prepared above is prepared into short polyimide / titanium nitride composite fiber by using a cutting type pulverizer. Polyimide adhesive is selected as the interface adhesive and coated on the surface of the carrier metal plate to fix the fiber. In the high voltage electrostatic field of the electrostatic flocking box, the fiber is subjected to the ectopic voltage and vertically falls to the surface of the carrier metal plate, forming a vertical array structure of polyimide / titanium nitride composite fiber, the structure of which is as follows: Figure 2 shown.

[0061] In the second aspect, an embodiment of the present application provides a long-lasting cooling infrared camouflage polyimide fiber assembly, which is prepared by the preparation method described in the first aspect. The infrared emissivity of the fiber assembly is ≤0.35, the Nusselt number is ≥15, and the thermal conductivity is ≤0.03W / (m·K).

[0062] In the technical solution of the embodiment of the present application, the low infrared emissivity of titanium nitride works synergistically with the geometric orientation of the vertical array to reduce the surface normal radiation intensity, while avoiding the risk of specular reflection exposure caused by the flat surface of traditional metal coatings; the high Nusselt number indicates that the material has good convective heat transfer performance, which helps to quickly dissipate heat and reduce the surface temperature; at the same time, the fiber aggregate can effectively reduce the transfer of internal and external heat, effectively block the intrusion of heat flow, and is suitable for complex application scenarios.

[0063] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0064] Example 1

[0065] This embodiment provides a method for preparing a long-lasting temperature-reducing infrared camouflage polyimide fiber assembly, comprising the following steps:

[0066] S1. PMDA, ODA, and TEA were added to N,N-dimethylformamide solvent and subjected to polycondensation reaction at 3°C to obtain a polyamic acid solution; wherein the mass fraction of PMDA was 8%, the mass fraction of ODA was 8%, and the mass fraction of TEA was 2%;

[0067] S2. A polyamic acid solution was spun using centrifugal spinning technology. Auxiliary rods were placed around the centrifugal spinning cup. Five auxiliary rods, each 5 cm high, were placed evenly spaced at a radius of 10 cm around the centrifugal spinning cup to form a horizontal layered structure of polyamic acid fibers. The spinning speed was 3500 rpm, the spinning temperature was 35°C, the spinning humidity was 38% RH, and the spinneret diameter was 0.2 mm. The distance between the centrifugal spinning cup and the collecting cloth was 10 cm.

[0068] S3. The horizontal layered polyamide acid fiber was placed in an oxygen-containing environment for cyclization reaction. The cyclization reaction temperature was 380 ° C, the time was 2 h, the oxygen concentration was 20%, and the remaining components were nitrogen. The curved polyimide fiber was obtained, and its SEM image is shown as follows. Figure 3 As shown;

[0069] S4. Atomic layer deposition of titanium nitride nanolayers onto the surface of curved polyimide fibers to produce polyimide / titanium nitride composite fibers. Titanium tetrachloride was used as the titanium precursor, and ammonia was used as the nitrogen source. The deposition temperature was 260°C, the pressure was 5 Torr, the titanium tetrachloride pulse time was 0.3 s, the ammonia pulse time was 1.5 s, and the number of cycles was 500.

[0070] S5. The polyimide / titanium nitride composite fiber was crushed into short fibers with an average length of 500 μm using a cutting mill. After electrostatic flocking treatment, a polyimide adhesive was selected as an interface binder and coated on the surface of the carrier metal plate to fix the fibers. In the high-voltage electrostatic field of the electrostatic flocking box, the fibers were subjected to an ectopic voltage and vertically flew to the surface of the carrier metal plate, forming a vertical array structure of polyimide / titanium nitride composite fibers. The flocking voltage was 100 kV, the flocking time was 20 s, and the plate distance was 7 cm. A vertical array structure was formed to obtain a long-lasting cooling infrared camouflage polyimide fiber aggregate, the SEM image and structural schematic of which are shown in FIG. Figure 1 and Figure 2 shown.

[0071] Examples 2-3 and Comparative Examples 1-2

[0072] Examples 2-3 and Comparative Examples 1-2 respectively provide a method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly. Compared with Example 1, the only difference is that the oxygen concentration is different, as shown in Table 1. The other experimental parameters and conditions are basically the same as those in Example 1 and will not be repeated here.

[0073] Examples 4-5 and Comparative Examples 3-4

[0074] Examples 4-5 and Comparative Examples 3-4 respectively provide a method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly. Compared with Example 1, the only difference is that the number of deposition cycles is different. Other experimental parameters and conditions are basically the same as those in Example 1 and will not be repeated here.

[0075] Comparative Example 5

[0076] Comparative Example 5 provides a method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly. Compared with Example 1, the only difference is that the titanium nitride nanolayer is not deposited. Other experimental parameters and conditions are basically the same as those in Example 1 and will not be repeated here.

[0077] Test method:

[0078] Thermal conductivity: tested according to GB / T 10294-2008 Insulation materials - Determination of steady-state thermal resistance and related properties - Guarded hot plate method;

[0079] Infrared emissivity: tested according to GB / T 30127-2013 Testing and evaluation of far-infrared properties of textiles;

[0080] Nusselt number: A self-built device was used to simulate a forced convection environment and calculate the Nusselt number by combining temperature, pressure, and mass flow measurements.

[0081] The test results are shown in Table 1.

[0082] Table 1 Performance test results

[0083]

[0084]

[0085] As can be seen from Table 1, the infrared emissivity is affected by the thickness of the titanium nitride nanolayer. The thicker the titanium nitride nanolayer, the lower the infrared emissivity. The influence of flocking density on the Nusselt number shows a normal distribution trend. The thermal conductivity is synergistically affected by the infrared emissivity and the Nusselt number. The present application adopts the horizontal stacked layer structure of polyimide curved fibers prepared by centrifugal spinning technology, and utilizes the curved shape of the fibers to extend the heat conduction path and realize external heat flow barrier; the upright array structure of polyimide / titanium nitride composite fibers constructed by electrostatic flocking technology enhances convective heat dissipation (Nussel number improvement) through microporous channels and high specific surface area, while maintaining low infrared emissivity; the "barrier-conducting" dynamic synergy of the double-layer structure solves the contradiction of "thermal insulation must sacrifice heat dissipation" in traditional materials; titanium nitride in the vertical fibers is evenly spread on each polyimide short fiber in the form of a nano-thin layer, achieving infrared emissivity ≤0.35 (8-14μm band), Nusselt number (Nu) ≥15 (under wind speed of 2m / s), and thermal conductivity ≤0.03W / (m·K).

[0086] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly, characterized in that: The following steps are involved: S1. Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to N,N-dimethylformamide solvent and subjected to polycondensation reaction at a predetermined temperature to obtain a polyamic acid solution; S2 using centrifugal spinning technology to spin the polyamic acid solution, providing an auxiliary rod around the centrifugal spinning cup to form a horizontal layered structure of polyamic acid fibers; S3. The horizontal layered structure of the polyamic acid fiber is placed in an oxygen-containing environment for cyclization reaction, and the curvature radius of the fiber is regulated by the oxygen concentration to obtain a curved polyimide fiber; S4. A titanium nitride nanolayer is deposited on the surface of the curved polyimide fiber using atomic layer deposition technology to obtain a polyimide / titanium nitride composite fiber; S5. The polyimide / titanium nitride composite fiber is crushed into short fibers, and then subjected to electrostatic flocking treatment to form a vertical array structure to obtain a long-lasting cooling infrared camouflage polyimide fiber aggregate.

2. The method for preparing the long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: In step S1 , the mass fraction of the pyromellitic dianhydride is 5-10%, the mass fraction of the 4,4'-diaminodiphenyl ether is 5-10%, and the mass fraction of the triethylamine is 1-8%.

3. The method for preparing the long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 2, characterized in that: The temperature of the polycondensation reaction is 0-10°C.

4. The method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: In step S2, the spinning speed of the centrifugal spinning technology is 3000-4000 rpm, the spinning temperature is 30-40°C, the spinning humidity is 30-40% RH; the spinneret diameter is 0.1-0.4 mm; and the distance between the centrifugal spinning cup and the collecting cloth is 5-15 cm.

5. The method for preparing the long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 4, characterized in that: The auxiliary rods have a height of 5 to 15 cm, and are arranged in such a manner that 3 to 8 auxiliary rods are placed at equal intervals with a radius of 5 to 25 cm, with the centrifugal spinning cup as the center.

6. The method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: In step S3, the temperature of the cyclization reaction is 300-450° C., the time is 1-3 hours, the oxygen concentration is 5-50%, and the remaining component is nitrogen.

7. The method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: The control range of the curvature radius is 10 to 300 μm.

8. The method for preparing a long-lasting temperature-reducing infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: In step S4, the deposition method is: using titanium tetrachloride as a titanium precursor, ammonia as a nitrogen source, a deposition temperature of 150-300°C, a pressure of 0.1-10 Torr, a titanium tetrachloride pulse time of 0.1-1 s, an ammonia pulse time of 0.5-2 s, and a cycle number of 100-800 times; The thickness of the titanium nitride nanolayer is 5 to 200 nm.

9. The method for preparing a long-lasting cooling infrared camouflage polyimide fiber assembly according to claim 1, characterized in that: In step S5, the length of the short fibers is 100 to 1000 μm; The electrostatic flocking treatment has a flocking voltage of 20 to 150 kV, a flocking time of 3 to 40 s, an electrode distance of 5 to 30 cm, and a flocking density of 35 to 105 g / m 2 .

10. A long-term cooling infrared camouflage polyimide fiber assembly, characterized in that: The long-lasting cooling infrared camouflage polyimide fiber aggregate is prepared by the preparation method according to any one of claims 1 to 9, and has an infrared emissivity of ≤0.35, a Nusselt number ≥15, and a thermal conductivity of ≤0.03W / (m·K).

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