Temperature visualized flame-retardant and smoke-suppression aryl sulfone composite membrane, preparation method and application

Abstract

This invention discloses a temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film. This composite film exhibits reversible color changes within a temperature range of 0-250℃, with a color-changing response time ≤17 seconds, a limiting oxygen index ≥38%, and a carbon monoxide adsorption rate ≥32%. It is composed of a lower flame-retardant and smoke-suppressing functional layer and an upper thermochromic layer directly formed on the surface of the lower layer via a casting method, hot-pressed together. The upper thermochromic layer includes thermochromic microcapsules and aramid fibers; the amount of thermochromic microcapsules added is 5%~10% of the mass of aramid fibers; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer. The lower flame-retardant and smoke-suppressing functional layer is mainly composed of aramid short fibers, silicon-based Schiff base-modified aluminum hydroxide, and plasma-modified cellulose aerogel. Advantages: It efficiently integrates temperature visualization and early warning with flame-retardant and smoke-suppressing functions; the dense film formed by the casting method can encapsulate the thermochromic microcapsules, improving the durability and service life of the thermochromic layer.

Description

Technical Field

[0001] This invention belongs to the field of high-performance materials technology and relates to an aramid composite film with temperature visualization, flame retardancy, and smoke suppression functions, and its preparation method. Specifically, it relates to an aramid composite film with temperature visualization warning and efficient flame retardancy and smoke suppression functions, and its preparation method, which is suitable for special protection, aerospace, power battery safety, high-rise building escape and other scenarios. Background Technology

[0002] In fields such as aerospace, special protection, and power battery safety, extremely high requirements are placed on early warning and fire safety protection in high-temperature environments. Existing heat-insulating and flame-retardant materials, such as aramid fiber and pre-oxidized fiber, although possessing good heat resistance, have limited functionality and cannot directly reflect changes in ambient temperature, resulting in a problem of delayed early warning.

[0003] In existing technologies, although there are studies on combining thermochromic materials with fabrics, the following defects exist: (1) Most thermochromic materials have poor heat resistance and cannot work stably in a wide temperature range of 0~250℃, and the color change is irreversible or has a single gradient. (2) Traditional coating or printing processes are usually used to attach thermochromic materials to the surface of the substrate, which makes the color-changing materials easy to wear and fall off, and seriously affects the softness and breathability of the substrate. (3) The function is single and lacks the function of adsorbing smoke and toxic gases produced by combustion. In a fire scenario, even if the combustion is delayed, people may still be in danger due to inhaling toxic gases.

[0004] Therefore, there is an urgent need to develop a high-performance composite membrane and its preparation method that can achieve wide temperature range, gradient temperature visualization, and integrate flame retardancy, smoke suppression, and toxic gas adsorption. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to: (1) provide a temperature-visible, flame-retardant, smoke-suppressing aramid fiber composite film, which can intuitively display the temperature through color changes within the range of 0~250℃, and at the same time has excellent flame-retardant, smoke-suppressing, and toxic gas adsorption capabilities at high temperatures. (2) provide a method for preparing the above-mentioned temperature-visible, flame-retardant, smoke-suppressing aramid fiber composite film. (3) provide applications of the above-mentioned temperature-visible, flame-retardant, smoke-suppressing aramid fiber composite film.

[0006] To achieve the above-mentioned objectives, this invention provides a temperature-visualized flame-retardant and smoke-suppressing aramid composite film. This aramid composite film exhibits reversible color changes within a wide temperature range of 0~250℃, with a color change response time ≤17 seconds, a limiting oxygen index ≥38%, and a carbon monoxide adsorption rate ≥32%. The aramid composite film is formed by hot-pressing a lower flame-retardant and smoke-suppressing functional layer and an upper thermochromic layer directly formed on the surface of the lower layer.

[0007] Furthermore, in the temperature-visualized flame-retardant and smoke-suppressing aramid composite film provided by the present invention, the upper thermochromic layer is obtained by casting an aramid casting solution containing thermochromic microcapsules directly onto the surface of the lower layer using a casting method; the solid content of the aramid casting solution is 12%~22%; the amount of thermochromic microcapsules added is 5%~10% of the mass of aramid; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer.

[0008] Furthermore, in the temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film provided by this invention, the spiropyran-styrene copolymer undergoes reversible color change at 0~250℃, with the color changing from dark blue to purple to pink to colorless.

[0009] Furthermore, in the temperature-visible flame-retardant and smoke-suppressing aramid composite film provided by the present invention, the lower flame-retardant and smoke-suppressing functional layer is mainly composed of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel; the mass ratio of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel is (28~32): (48~52): 20.

[0010] Furthermore, in the temperature-visible flame-retardant and smoke-suppressing aramid composite membrane provided by this invention, the plasma-modified cellulose aerogel is prepared by low-temperature plasma treatment of cellulose acetate filter rods.

[0011] Furthermore, in the temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film provided by the present invention, the thickness of the upper thermochromic layer before hot-pressing is 20~500μm; the thickness of the lower flame-retardant and smoke-suppressing functional layer before hot-pressing is 100~1000μm.

[0012] To achieve the above-mentioned objectives, the present invention also provides a method for preparing any of the above-mentioned temperature-visible flame-retardant and smoke-suppressing aramid fiber composite films, comprising the following steps, wherein S1 and S2 can be performed simultaneously or in reverse order:

[0013] S1. Preparation of the lower flame-retardant and smoke-suppressing functional layer: A mixture of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel was prepared into a slurry by adding deionized water and dispersant. After vacuum filtration, the slurry was obtained by hot pressing to obtain the lower flame-retardant and smoke-suppressing functional layer substrate. The mass ratio of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel was (28~32): (48~52): 20. The plasma-modified cellulose aerogel was prepared by low-temperature plasma treatment of cellulose acetate filter rods.

[0014] S2. Preparation of the upper thermochromic aramid resin casting solution: Aramid resin is dissolved in a solvent, heated and stirred to form a homogeneous solution, thermochromic microcapsules are added, and after water bath stirring, the solution is allowed to stand for degassing to obtain the upper thermochromic aramid resin casting solution; the solid content of the upper thermochromic aramid resin casting solution is 12%~22%; the amount of thermochromic microcapsules added is 5%~10% of the mass of aramid resin; the solvent is N,N-dimethylacetamide or N-methylpyrrolidone; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer.

[0015] S3. Double-layer composite molding: The prepared lower flame-retardant and smoke-suppressing functional layer substrate is fixed on a platform and preheated; the prepared upper thermochromic aramid fiber casting liquid is applied to the surface of the preheated substrate by a casting method; after coating, the composite film is subjected to gradient drying treatment, and then the dried composite film is subjected to hot pressing strengthening treatment to obtain a temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film; the thickness of the upper thermochromic layer before hot pressing is 20~500μm; the thickness of the lower flame-retardant and smoke-suppressing functional layer before hot pressing is 100~1000μm.

[0016] Furthermore, in the method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid composite film provided by the present invention, after step S1, the method further includes the step of "post-treatment of the flame-retardant and smoke-suppressing functional layer substrate", which is to perform low-temperature plasma post-treatment on the functional layer substrate.

[0017] Furthermore, in the method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film provided by the present invention, the spiropyran-styrene copolymer undergoes reversible color change at 0~250℃, with the color change being dark blue → purple → pink → colorless.

[0018] Furthermore, in the method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film provided by the present invention, in step S3, the gap between the casting blades is 100~600μm; the gradient drying temperature is 60~180℃, and the time is 5~20 minutes.

[0019] Furthermore, in the method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film provided by the present invention, the hot-pressing strengthening conditions are: temperature 150~230℃, pressure 0.2~1.8MPa, and time 1~10 minutes.

[0020] To achieve the above-mentioned objectives, the present invention also provides the use of any of the above-mentioned temperature-visible flame-retardant and smoke-suppressing aramid fiber composite films or temperature-visible flame-retardant and smoke-suppressing aramid fiber composite films prepared according to any of the above-mentioned temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film preparation methods, applicable to any of the technical fields of special protection, aerospace, power battery safety, and high-rise building escape.

[0021] Compared with the prior art, the present invention has the following technical effects: (1) It efficiently integrates temperature visualization early warning and flame retardant and smoke suppression functions. By presenting reversible and gradient color changes in a wide temperature range of 0~250℃, it realizes intuitive visual early warning of overheating risks and timely detection of hidden dangers before open flames or catastrophic thermal runaway occur. (2) The dense film formed by the casting method can completely encapsulate the thermochromic microcapsules in the polymer matrix, effectively isolating the external environment and significantly improving the durability and service life of the thermochromic layer. (3) It has both temperature visualization early warning and flame retardant and smoke suppression functions, which are integrated into one and applicable to a wider range of scenarios. Detailed Implementation

[0022] This invention aims to provide an aramid composite film and its preparation method that combines temperature visualization and early warning with efficient flame retardancy and smoke suppression, overcoming the technical problems of existing heat insulation and flame retardant materials that cannot intuitively reflect changes in ambient temperature and the easy wear and peeling of existing color-changing materials applied to the substrate surface through coating or printing.

[0023] The invention concept is to integrate the temperature visualization warning layer with the flame-retardant and smoke-suppressing layer to overcome the problem of easy peeling of coatings or printing processes in existing bases; and to completely encapsulate the thermochromic microcapsules in the polymer matrix through a dense, non-porous film formed by casting, thereby improving the durability and service life of the color-changing layer.

[0024] First, the present invention provides a temperature-visualized flame-retardant and smoke-suppressing aramid composite film, which has the following characteristics: it exhibits reversible color change in a wide temperature range of 0~250℃, color change response time ≤17 seconds, limiting oxygen index ≥38%, and carbon monoxide adsorption rate ≥32%.

[0025] The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film provided by this invention includes an upper thermochromic layer and a lower flame-retardant and smoke-suppressing functional layer; the thickness of the upper thermochromic layer is 20~500μm; the thickness of the lower flame-retardant and smoke-suppressing functional layer is 100~1000μm. The upper thermochromic layer is directly formed on the surface of the lower layer by a casting method.

[0026] Regarding the upper thermochromic layer, it mainly consists of aramid sulfones and thermochromic microcapsules. The aramid casting solution containing the thermochromic microcapsules is directly formed on the surface of the lower layer by a casting method. Preferably, the solid content of the aramid casting solution is 12%~22%. Preferably, the amount of thermochromic microcapsules added is 5%~10% of the mass of the aramid sulfones; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer. The spiropyran-styrene copolymer undergoes reversible, multi-gradient color change at 0~250℃, with the color change being dark blue → purple → pink → colorless.

[0027] Regarding the lower flame-retardant and smoke-suppressing functional layer, it is mainly composed of aramid short fibers, silicon-based Schiff base-modified aluminum hydroxide, and plasma-modified cellulose aerogel. The plasma-modified cellulose aerogel is prepared by low-temperature plasma treatment of cellulose acetate filter rods. Preferably, the mass ratio of aramid short fibers, silicon-based Schiff base-modified aluminum hydroxide, and plasma-modified cellulose aerogel is (28~32): (48~52): 20.

[0028] Secondly, the present invention also provides a method for preparing any of the above-mentioned temperature-visible flame-retardant and smoke-suppressing aramid fiber composite films, comprising the following steps:

[0029] S1. Preparation of the lower flame-retardant and smoke-suppressing functional layer: Aramid sulfone short fiber, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel are mixed in proportion, and deionized water and dispersant are added to prepare a slurry. After vacuum filtration and molding, the flame-retardant and smoke-suppressing layer substrate is obtained by hot pressing. The ratio of aramid sulfone short fiber, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel is (28~32): (48~52): 20.

[0030] S2. Preparation of the upper thermochromic casting solution: Dissolve aramid resin in N,N-dimethylacetamide (DMAC) or N-methylpyrrolidone (NMP), add thermochromic microcapsules, stir in a water bath for 2-5 hours and allow to stand to remove bubbles, thus preparing an aramid casting solution containing thermochromic microcapsules; wherein the solid content of the casting solution is 12%-22%; the amount of thermochromic microcapsules added is 5%-10% of the mass of aramid.

[0031] S3. Double-layer composite molding: The lower substrate is laid flat on the casting machine platform, and the lower substrate is uniformly coated on the surface of the lower substrate by controlling the blade gap with an adjustable blade. After gradient drying and hot pressing strengthening, a composite aramid film is obtained. Preferably, the blade casting method uses a blade gap of 100~600μm; the gradient drying temperature is 60~180℃, and the time is 5~20 minutes; the hot pressing strengthening conditions are: temperature 150~230℃, pressure 0.2~1.8MPa, and time 1~10 minutes.

[0032] There is no strict order requirement for S1 "preparing the lower flame-retardant and smoke-suppressing functional layer" and S2 "preparing the upper thermochromic casting liquid" in the above preparation steps. In the specific implementation process, S1 can be performed first and then S2, or S2 can be performed first and then S1, or S1 and S2 can be performed simultaneously.

[0033] Preferably, the above-mentioned method for preparing temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film further includes, following step S1, the step of "post-treatment of the substrate of the lower flame-retardant and smoke-suppressing functional layer", in order to activate the fiber surface and increase surface energy and roughness, the substrate is subjected to low-temperature plasma post-treatment.

[0034] The limiting oxygen index (the minimum oxygen concentration required to maintain stable combustion of a material) in this invention is measured according to GB / T 5454-1997 "Test for Combustion Performance of Textiles - Oxygen Index Method"; color deviation is calculated using a spectrophotometer based on the CIE 1976 color space and compared with the color at a standard color chart or reference temperature; tensile strength is measured according to GB / T 1040.2-2022; reversible cycling is tested by temperature rise and fall cycles within a certain range; CO adsorption rate is tested based on simulated flue gas adsorption analysis by gas chromatography.

[0035] Unless otherwise specified, the chemical reagents, experimental apparatus, and production equipment used in this embodiment are all commercially available.

[0036] Example 1

[0037] The aramid resin, aramid chopped fibers, and plasma-modified cellulose aerogel used in this embodiment were prepared in-house. This embodiment prepares a temperature-visible flame-retardant and smoke-suppressing aramid composite membrane according to the following steps:

[0038] (1) Preparation of the lower flame retardant and smoke suppressant functional layer: Aramid sulfone short chopped fiber, silicon-based Schiff base modified aluminum hydroxide, and plasma modified cellulose aerogel (cellulose acetate filter rod treated by plasma) were prepared in a mass ratio of 30:50:20. Deionized water was added to prepare a slurry with a solid content of 25%. 0.5% dispersant was added and the mixture was stirred at high speed for 30 minutes until uniform. After vacuum filtration, the mixture was hot-pressed at 120°C for 10 minutes to obtain a lower substrate with a smooth surface.

[0039] (2) Preparation of upper thermochromic casting solution: Dissolve aramid resin in N-methylpyrrolidone (NMP) and stir for 2.5 hours to prepare a solution with a solid content of 12%; add 6% thermochromic microcapsules and stir at low speed for 4 hours, during which time the mixture is ultrasonically dispersed twice at 120W; filter through a filter screen and let stand for 30 minutes to remove bubbles, to obtain a uniform and non-agglomerated casting solution.

[0040] (3) Double-layer composite molding: The lower flame-retardant and smoke-suppressing functional substrate is fixed on the casting machine carrier belt; the prepared thermochromic casting liquid is uniformly coated on the surface of the lower substrate, the doctor blade gap is 120μm, the casting speed is 8m / min; the gradient drying temperature is 60~180℃ for 15 minutes; the film is reinforced by hot pressing at 200℃ and 1MPa for 5 minutes to obtain a temperature-visible flame-retardant and smoke-suppressing aramid composite film.

[0041] The limiting oxygen index measured according to the above test methods or test standards is 39%, the color change response time (170℃) is 13 seconds, the color deviation at the same temperature is ΔE1.8, and the color change sensitivity does not decrease after 50 reversible cycles; the tensile strength is 87.5MPa, and the CO adsorption rate is 35%.

[0042] Example 2

[0043] The aramid resin, aramid chopped fibers, and plasma-modified cellulose aerogel used in this embodiment were prepared in-house. This embodiment prepares a temperature-visible flame-retardant and smoke-suppressing aramid composite membrane according to the following steps:

[0044] (1) Preparation of the lower flame retardant and smoke suppressant functional layer: Aramid sulfone short-cut fiber, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel (cellulose acetate filter rod treated by plasma) were mixed in a mass ratio of 28:52:20, and deionized water was added to prepare a slurry with a solid content of 22%; 0.3% dispersant was added and stirred at high speed for 25 minutes until uniform; after vacuum filtration, it was hot-pressed at 0.55MPa and 125℃ for 8 minutes to form the lower substrate, so as to ensure that the substrate has appropriate porosity to facilitate heat conduction.

[0045] (2) Preparation of upper casting solution: Dissolve aramid resin in N,N-dimethylacetamide (DMAC) to form a solution with a solid content of 18%, and add thermochromic microcapsules with smaller particle size and more concentrated distribution. The amount added is 10% of the mass of aramid resin; (3) Cast the casting solution through a 280μm doctor blade gap onto the lower substrate preheated to 75℃, immediately transfer it to a 100℃ forced-air drying oven for rapid drying for 8 minutes, and then vacuum dry at 80℃ for 5 hours; finally, hot press at 205℃ and 1.1 MPa for 4.5 minutes to complete the composite.

[0046] The color change response time (170℃) of this composite membrane is shortened to 10 seconds, the color deviation at the same temperature is ΔE=1.6, the color change performance does not decay after 50 reversible thermal cycles, the tensile strength is 89MPa, the limiting oxygen index is 41.2%, and the CO adsorption rate is 36.2%, achieving a balance between rapid early warning and reliable protection.

[0047] Example 3

[0048] The aramid resin, aramid chopped fibers, and plasma-modified cellulose aerogel used in this embodiment were prepared in-house. This embodiment prepares a temperature-visible flame-retardant and smoke-suppressing aramid composite membrane according to the following steps:

[0049] (1) Preparation of the lower flame retardant and smoke suppressant functional layer: Aramid sulfone short chopped fiber, silicon-based Schiff base modified aluminum hydroxide, and plasma modified cellulose aerogel (cellulose acetate filter rod treated by plasma) were prepared in a mass ratio of 32:48:20. Deionized water and dispersant were added to prepare a high solid content slurry with a solid content of 28%. The slurry was stirred at high speed until uniform. After vacuum filtration, it was hot-pressed for 12 minutes under higher conditions of 0.6MPa and 130℃ to obtain a substrate with an extremely dense structure.

[0050] (2) Preparation of upper casting solution: Dissolve aramid resin in N,N-dimethylacetamide (DMAC) to form a solution with a solid content of 22% to form a thicker protective layer. The amount of thermochromic microcapsules added is 5.5%. The casting process uses a doctor blade gap of 220μm. After coating on the substrate at 85℃, it is first dried at 95℃ for 15 minutes, and then vacuum dried at 85℃ for 7 hours to completely remove the solvent. The final key strengthening step is hot pressing at 210℃ and 1.2 MPa for 6 minutes to achieve deep fusion of the two layers.

[0051] The color change response time (170℃) is 17 seconds, the color deviation at the same temperature is ΔE=2.2, the sensitivity does not decay after 50 reversible thermal cycles, the limiting oxygen index remains at 39.2%, the tensile strength is 91MPa, and the CO adsorption rate is 34.2%, demonstrating excellent environmental stability and ultra-long service life.

Claims

1. A temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film, characterized in that, The aramid composite film exhibits reversible color changes within a wide temperature range of 0~250℃, with a color change response time ≤17 seconds, a limiting oxygen index ≥38%, and a carbon monoxide adsorption rate ≥32%. The aramid composite film is formed by hot pressing a lower flame-retardant and smoke-suppressing functional layer and an upper thermochromic layer directly formed on the surface of the lower layer.

2. The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 1, characterized in that... The upper thermochromic layer is obtained by casting a thermochromic microcapsule-containing aramid fiber casting solution directly onto the surface of the lower layer using a casting method; the solid content of the aramid fiber casting solution is 12%~22%; the amount of thermochromic microcapsules added is 5%~10% of the mass of aramid fiber; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer.

3. The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 2, characterized in that, The spiropyran-styrene copolymer exhibits reversible color change at 0~250℃, with the color changing from dark blue to purple to pink to colorless.

4. The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 1, characterized in that, The lower flame-retardant and smoke-suppressing functional layer is mainly composed of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel; the mass ratio of the aramid short fibers, the silicon-based Schiff base modified aluminum hydroxide, and the plasma-modified cellulose aerogel is (28~32): (48~52):

20.

5. The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 4, characterized in that, The plasma-modified cellulose aerogel was prepared by low-temperature plasma treatment of cellulose acetate filter rods.

6. The temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 1, characterized in that, The thickness of the upper thermochromic layer before hot-pressing is 20~500μm; the thickness of the lower flame-retardant and smoke-suppressing functional layer before hot-pressing is 100~1000μm.

7. A method for preparing a temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film as described in any one of claims 1 to 6, characterized in that... The steps include the following, where S1 and S2 can be performed simultaneously or in a different order: S1. Preparation of the lower flame-retardant and smoke-suppressing functional layer: A mixture of aramid short fibers, silicon-based Schiff base modified aluminum hydroxide, and plasma-modified cellulose aerogel is prepared into a slurry by adding deionized water and a dispersant. After vacuum filtration, the slurry is hot-pressed to obtain the lower flame-retardant and smoke-suppressing functional layer substrate. The mass ratio of the aramid short fibers, the silicon-based Schiff base modified aluminum hydroxide, and the plasma-modified cellulose aerogel is (28~32): (48~52):

20. The plasma-modified cellulose aerogel is prepared by low-temperature plasma treatment of cellulose acetate filter rods. S2. Preparation of the upper thermochromic aramid resin casting solution: Aramid resin is dissolved in a solvent, heated and stirred to form a homogeneous solution, thermochromic microcapsules are added, and after water bath stirring, the solution is allowed to stand for degassing to obtain the upper thermochromic aramid resin casting solution; the solid content of the upper thermochromic aramid resin casting solution is 12%~22%; the amount of thermochromic microcapsules added is 5%~10% of the mass of the aramid resin; the solvent is N,N-dimethylacetamide or N-methylpyrrolidone; the wall material of the thermochromic microcapsules is melamine-formaldehyde resin, and the core is spiropyran-styrene copolymer; S3. Double-layer composite molding: The prepared lower flame-retardant and smoke-suppressing functional layer substrate is fixed on a platform and preheated; the prepared upper thermochromic aramid fiber casting liquid is applied to the surface of the preheated substrate by a casting method; after coating, the composite film is subjected to gradient drying treatment, and then the dried composite film is subjected to hot-press strengthening treatment to obtain a temperature-visible flame-retardant and smoke-suppressing aramid fiber composite film; the thickness of the upper thermochromic layer before hot-pressing composite is 20~500μm; the thickness of the lower flame-retardant and smoke-suppressing functional layer before hot-pressing composite is 100~1000μm.

8. The method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 7, characterized in that, After step S1, the method further includes the step of "post-treatment of flame-retardant and smoke-suppressing functional layer substrate", which is to perform low-temperature plasma post-treatment on the functional layer substrate.

9. The method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 7, characterized in that, The spiropyran-styrene copolymer undergoes reversible color change at 0~250℃, with the color changing from dark blue to purple to pink to colorless.

10. The method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 7, characterized in that, In step S3 "double-layer composite molding", the gap between the casting blades is 100~600μm; the gradient drying temperature is 60~180℃ and the time is 5~20 minutes.

11. The method for preparing a temperature-visualized flame-retardant and smoke-suppressing aramid fiber composite film as described in claim 7, characterized in that, The hot-pressing strengthening conditions are: temperature 150~230℃, pressure 0.2~1.8MPa, and time 1~10 minutes.

12. The use of a temperature-visible flame-retardant and smoke-suppressing aramid composite film according to any one of claims 1-6 or a temperature-visible flame-retardant and smoke-suppressing aramid composite film prepared according to any one of claims 7-11, characterized in that, It can be applied to any technical field, including special protection, aerospace, power battery safety, and high-rise building escape.