Highly heat-conductive color polyimide composite film and preparation method thereof

Abstract

The present application relates to a kind of high thermal conductive color polyimide composite film and its preparation method, the composite film is obtained by color polyimide solution on the conductive substrate containing nano needle-like ZnO crystal array is cast into film again high temperature vacuum desolventizing after solution.The composite film of the present application not only has wide range of color adjustability, UV resistance, color uniformity, and has excellent thermal conductivity, in the field such as flexible display, 5G antenna, color bearing film, high thermal conductive insulation film, microelectronic, has application potential.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a high thermal conductivity colored polyimide composite film and its preparation method. Background Technology

[0002] Polyimide (PI) is widely used in flexible electronics, liquid crystal display (LCD) filters, aerospace, and other fields due to its high glass transition temperature, good heat resistance, and excellent dielectric properties. However, traditional PI films are mostly yellow or brown, which makes it difficult to meet the high light transmittance requirements of optoelectronic devices and poses a significant obstacle to the preparation of colored polyimide films. Currently, conventional colorless and transparent polyimide film preparation methods can meet the basic requirement of colorlessness and transparency, but research on resistance to ultraviolet radiation is lacking, and the films still cannot achieve a wider range of applications.

[0003] Traditional polyimide (PI) films typically exhibit low thermal conductivity (0.15-0.25 W / m·K), making it difficult to meet the thermal management requirements of high-power devices in thin structures. Currently, several patented technologies for high thermal conductivity polyimide films exist in China. For example, CN119751868A mentions copolymerizing phosphorus-based dianhydrides with long-chain alkyl diamines to construct thermally conductive channels within the molecular chain, thereby improving the thermal conductivity of polyimide while also providing flame retardant properties. While this technology effectively optimizes the PI molecular microstructure, the improvement in thermal conductivity is limited, and the design approach mainly focuses on adjusting the structure within the main chain, limiting its ability to construct macroscopically ordered thermal conductive channels. CN112812341B discloses a method for preparing a "four-needle-structure composite microparticle / PI film," using nanofillers to form a needle-like arrangement to enhance thermal conductivity. However, its needle-like structure relies on filler self-assembly, resulting in an irregular arrangement and poor controllability, and still falls short in terms of the consistency and reliability of thermal conductivity in the cross-sectional direction. CN101168598A proposes a method to improve thermal conductivity while maintaining a low coefficient of thermal expansion by uniformly dispersing nano-thermal conductive materials (such as boron nitride) in polyimide (PI). However, this technology struggles to ensure uniform distribution of the filler, and the matrix's isolation of the thermally conductive filler from the heat source significantly reduces the improvement in thermal conductivity.

[0004] On the other hand, colored polyimides, especially blue / red / green PI, have significant application prospects in flexible displays, wearable devices, and novel optoelectronic devices. Currently, colored films prepared from colorless and transparent polyimides often employ inorganic or organic dye blending methods. For example, CN117166089A uses organic dye blending, achieving dye fixation through intermolecular forces, but it does not achieve covalent bond formation, resulting in poor color stability. CN114164688A uses inorganic dye blending, but this method is prone to agglomeration due to excessively strong intermolecular forces and requires sophisticated stirring and dispersion equipment, affecting color uniformity and increasing equipment costs. Furthermore, inorganic dyes often contain heavy metals, posing a significant environmental threat. Currently, there is a lack of polyimide film dyeing solutions on the market that can simultaneously achieve environmental friendliness, low cost, and color uniformity and stability, meeting all these requirements. Summary of the Invention

[0005] This invention provides a high thermal conductivity colored polyimide composite film and its preparation method, which solves the problems of high cost, complicated process and limited thermal conductivity of colored PI films in the prior art.

[0006] This invention provides a high thermal conductivity colored polyimide composite film, which is obtained by casting a colored polyimide solution onto a conductive substrate containing a nano-needle-shaped ZnO crystal array and then removing the solvent under high temperature and vacuum.

[0007] Preferably, the conductive substrate is ITO glass.

[0008] Preferably, the mass percentage of the nanoneedle-shaped ZnO crystal array in the composite film is 0.1-40%.

[0009] This invention also provides a method for preparing a high thermal conductivity colored polyimide composite film, comprising the following steps:

[0010] (1) Coat the surface of the cleaned and surface-treated conductive substrate with a zinc acetate ethanol layer; add zinc ion electrolyte, supporting electrolyte and acetamide to deionized water and adjust the pH to 3.0~7.0 to obtain a three-electrode electrolyte; place the conductive substrate as the working electrode into the three-electrode electrolyte for a water bath reaction; the conductive substrate coated with zinc acetate ethanol layer is electrochemically deposited to generate needle-like ZnO crystals in the vertical direction; and then cleaned, dried and annealed at high temperature to obtain a conductive substrate containing a nano needle-like ZnO crystal array.

[0011] (2) Dissolve diamine and acid anhydride in a polar aprotic solvent at a molar ratio of 0.97~1.03:1 and react with nitrogen at 0~60 °C for 6~24 hours to obtain a polyamic acid precursor solution; then add dye compound and coupling agent, stir at room temperature for 2~6 hours, then add 1~5 times the molar amount of diamine cyclization catalyst and dehydrating agent, stir at 25~100 °C for 2~12 hours to prepare a colored polyimide solution;

[0012] (3) The colored polyimide solution in step (2) is cast into a film on the conductive substrate containing the nano needle-shaped ZnO crystal array in step (1), and then the solvent is removed under high temperature vacuum to obtain a high thermal conductivity colored polyimide composite film.

[0013] Preferably, the solvents used for cleaning in step (1) include deionized water, acetone, isopropanol, ethanol, etc., and the cleaning is preferably performed in the order of first using acetone, then using deionized water, and finally using isopropanol.

[0014] Preferably, the surface treatment in step (1) is performed by UV ozone or plasma treatment to remove organic pollutants and enhance hydrophilicity.

[0015] Preferably, the zinc ion electrolyte in step (1) includes one or more of zinc sulfate, zinc acetate, zinc nitrate, zinc chloride, zinc bromide, and zinc perchlorate; the supporting electrolyte includes one or more of alkali metal salts and ammonium salts, such as NaCl, KCl, NaNO3, NH4Cl, and NH4NO3. The two electrolytes must meet the following requirements: (1) good water solubility; (2) their anions and cations will not be reduced or oxidized within the deposition potential range and will not participate in the formation reaction of ZnO; (3) the selected ions will not be seriously incorporated into the ZnO lattice (unless deliberately doped); and (4) the pH can be easily adjusted with acid and base to maintain a weakly acidic (pH≈4-6) environment.

[0016] Preferably, the concentrations of the zinc ion electrolyte and the supporting electrolyte in step (1) are both 10~50 mmol / L.

[0017] Preferably, the acetamide in step (1) is used to stabilize the electrode (preferably configured as 1 mol / L), adjust the pH to acidic, and obtain a uniform and transparent electrolyte, preferably with a pH value of 5.0 ± 0.2.

[0018] Preferably, the water bath reaction temperature in step (1) is 60-80℃, the water bath reaction time is 0.5-2h, and the working voltage is -5V~-0.5V.

[0019] Preferably, the cleaning and drying in step (1) involves rinsing with deionized water and ethanol alternately, followed by drying at a high temperature (80) for more than 5 minutes.

[0020] Preferably, the high-temperature annealing treatment in step (1) is annealing at a temperature of not less than 300°C in air for more than 20 minutes to improve crystallinity.

[0021] Preferably, the diamine in step (2) is one or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-diphenyl]-4,4'-diyl)bis(4-aminobenzamide), 4,4-diaminophenyl sulfone, and 1,4-(4-amino-2-trifluoromethylphenoxy)-2-(3',5'-ditrifluoromethylphenyl)benzene; and the anhydride is one or more of hexafluorodianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3'-biphenyl dianhydride, and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

[0022] Preferably, the dye compound has one of the following structures: Yellow: Aniline Yellow, Reactive Yellow 3, Reactive Yellow 3RSA, Reactive Yellow 186, Acid Yellow 147, Basic Yellow 9, Basic Yellow Brown 4BR; Red: Basic Red 9, Basic Red 2, Basic Red 118, Disperse Red 4, Disperse Red 60, Disperse Red 92, Disperse Red 11, Acid Red 37, Acid Red 42, Acid Red 54; Blue: Reactive Blue 4, Reactive Blue 2, Aniline Blue, Acid Blue 25, Disperse Blue 359, Disperse Blue 1, Disperse Blue 35, Disperse Blue 81, Disperse Blue BGL, Disperse Blue 56, Disperse Blue BG, Reactive Blue 4 (blue), Reactive Blue 250, Reactive Blue 192, Reactive Blue 69; Green: Reactive Green 19, Acid Green 111. The molar amount of the dye compound is 0.001~10% of the acid anhydride.

[0023] Preferably, the polar aprotic solvent in step (2) is one or more of dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, N-dimethylformamide, γ-butyrolactone, dimethylacrylurea, and hexamethylphosphoramide.

[0024] Preferably, the coupling agent in step (2) is a reagent that simultaneously meets the requirements of being soluble in water or readily solid at low temperatures for removal and being usable for catalyzing the dehydration condensation of carboxylic acids and amino groups. Preferably, it is one or more of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, dicyclohexylcarbodiimide, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, and diethyl pyrocarbonate. The molar ratio of the coupling agent to the diamine is 1 to 5:1.

[0025] Preferably, the cyclization catalyst in step (2) is one or more of triethanolamine, 1,4-diazobicyclo[2.2.2]octane, quinoline, isoquinoline, pyridine, and 3-methylpyridine, with pyridine being preferred.

[0026] Preferably, the dehydrating agent in step (2) is one or more of acetic anhydride, bis[α,α-bis(trifluoromethyl)phenylethanol]-diphenylsulfonate, xanthate, and N-(triethylammonium sulfonyl)carbamate.

[0027] Preferably, the solid content of the colored polyimide solution in step (2) is 5~25 wt%, and the solution viscosity is 10000~300000 mPa·s.

[0028] Preferably, the thickness of the film cast in step (3) is 4 to 10 times the height of the nanoneedle ZnO crystal array.

[0029] Preferably, the high-temperature vacuum desolventizing in step (3) specifically involves: evacuating the vacuum and heating the temperature to 150-200°C at a rate of 0.5-10°C / min. Further, the temperature is first raised to 60-80°C and maintained for at least 8 hours to ensure the complete evaporation of low-boiling-point solvents such as DMAC. After the initial desolventizing is completed, the temperature is slowly raised to 150-200°C and maintained for at least 2 hours to achieve complete ring closure of polyamic acid to form a polyimide matrix and increase the glass transition temperature of the chain segments. The entire process is carried out under vacuum to prevent oxidation and solvent residue.

[0030] Beneficial effects

[0031] (1) This invention forms a “directional heat conduction channel” that runs through the thickness direction of the polyimide film by growing a vertically arranged array of nanoneedle-shaped ZnO crystals in situ on the surface of a conductive substrate. This structure effectively overcomes the bottleneck of the thermal conductivity of traditional polymer materials being limited by inter-chain heat dissipation, and realizes rapid heat conduction in the out-of-plane direction, which significantly improves the out-of-plane thermal conductivity of the film compared with that of pure PI film.

[0032] (2) The nano needle-shaped ZnO crystal array is embedded in the polyimide matrix to form a rigid-flexible three-dimensional network channel structure, which not only enhances the thermal conductivity, but also maintains the good flexibility and tensile properties of the film. Especially under the condition of regular crystal arrangement and controllable spacing, the film exhibits excellent mechanical strength and low thermal expansion coefficient, which can meet the stable service requirements of flexible electronics and thermal management devices under high temperature deformation conditions.

[0033] (3) This invention achieves high-stability coloring by chemically grafting dye compounds onto polyamic acid segments, thereby completing imidization and avoiding problems such as dye migration or fading during heat treatment. The resulting film has a bright and uniform color, and its color changes little under high temperature, high humidity or ultraviolet irradiation, exhibiting good long-term weather resistance and appearance retention.

[0034] (4) The composite film of the present invention not only has a wide range of color tunability, UV resistance and color uniformity, but also has excellent thermal conductivity, and has application potential in flexible display, 5G antenna, color carrier film, high thermal conductivity insulating film, microelectronics and other fields. Attached Figure Description

[0035] Figure 1 This is an image of the blue polyimide composite film prepared in Example 1.

[0036] Figure 2 The graph shows the change in the mechanical property retention rate of the blue polyimide composite film prepared in Example 1 under ultraviolet light irradiation.

[0037] Figure 3 The image shows a surface SEM image of the blue polyimide composite film prepared in Example 1.

[0038] Figure 4 The image shows the surface SEM image of the blue polyimide composite film prepared in Example 1 after 6 hours of ultraviolet light irradiation.

[0039] Figure 5 This is an image of the colorless polyimide composite film prepared in Comparative Example 1.

[0040] Figure 6 This is an image of the blue polyimide composite film blended with nanoparticles prepared in Comparative Example 4. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] Example 1

[0043] (1) An ITO conductive glass plate with a size of 10cm*10cm and a thickness of 4mm was ultrasonically cleaned (acetone, deionized water, isopropanol) in sequence, dried, and then treated with UV ozone or plasma to remove organic pollutants and enhance hydrophilicity. A 30mmol / L zinc acetate ethanol solution was dotted on its surface at a horizontal and vertical spacing of 6mm, baked at 100°C for 3 minutes, and then dotted again at a horizontal and vertical spacing of 2mm in the same place. This process was repeated 3 times to prepare a ZnO nanoparticle seed layer. 10mmol / L ZnCl2 and 10mmol / L NaNO3 were dissolved in deionized water, and 0.1mol / L acetamide was added to adjust the pH to 5.0±0.2 to obtain a uniform and transparent three-electrode electrolyte. The ITO working electrode, platinum counter electrode, and Ag / AgCl reference electrode were then immersed in the electrolyte, placed in a 60°C water bath, and magnetically stirred at 200 rpm. A constant potential method was used to apply -0.9V (relative to Ag / AgCl) to the working electrode, and the deposition time was 2 hours. After deposition, the substrate was removed and rinsed alternately with deionized water and ethanol, then dried at 80°C for 10 minutes. Finally, it was annealed in air at 300°C for 20 minutes to improve crystallinity, resulting in an ITO conductive glass plate containing an array of nanoneedle-shaped ZnO crystals.

[0044] (2) With a solid content of 17%, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluorodianhydride were dissolved in dimethylacetamide at a molar ratio of 1:1. The reaction was carried out at around 0 °C with nitrogen for 12 hours to obtain a polyamic acid precursor solution. Then, 1 / 20 of the molar amount of diamine was added to disperse blue 359 dye powder. Finally, 5 times the molar amount of diamine was added to the coupling reagent 1-ethyl-(3-dimethylaminopropyl)carbodiimide. After stirring at room temperature for 6 hours, 5 times the molar amount of diamine was added to acetic anhydride. Then, 2 times the molar amount of diamine was slowly added to pyridine. The reaction was stirred at room temperature for 6 hours to prepare a blue polyimide solution. The solution was then slowly poured into deionized water in a thin stream to solidify. The solidified material was then broken into small particles and washed in deionized water for 30 minutes. The particles were filtered and dried. The solution was then prepared again with polyimide particles according to the solid content requirements to obtain a clean polyimide solution.

[0045] (3) Take the ITO conductive glass plate containing the nano needle-shaped ZnO crystal array after cultivation, gently rinse the surface dust with deionized water and air dry it to keep the natural crystal array layer on the surface of the glass plate; if a single-sided coating is required, the back of the glass plate can be isolated (such as pasting high-temperature resistant release paper, aluminum foil or coating with polytetrafluoroethylene film) to prevent film formation on both sides; then filter the chemically grafted (or blended) dyed polyimide solution prepared in step (2) with a stainless steel mesh to remove any possible small amount of agglomerated impurities; use a fixed-gap scraper or spin coating method to coat the polyimide solution onto the surface of the glass plate, and the thickness is determined according to the target dry film thickness, needle crystal height and solution solid content. Ensure the coating is uniform, without obvious drips or breaks. Then, place the coated iron plate on a horizontal surface and let it stand for 10-15 minutes to allow the solvent to initially evaporate under natural convection. Next, place the coated glass plate along with the polyimide solution into a vacuum oven or vacuum drying oven and evacuate to a vacuum level of approximately 10 kPa or below. Set the temperature profile: raise the temperature to 80°C and hold for 8 hours, then continue to slowly raise the temperature to 180°C and hold for 4 hours. The entire process should be carried out under vacuum to prevent oxidation and solvent residue.

[0046] (4) After curing is complete, turn off the heating and slowly cool down to room temperature. After maintaining the vacuum for 30 minutes, take out the sample and place it in a desiccator for later use.

[0047] (5) After the sample cools to room temperature, immerse the glass plate in hot water at 70°C. Use the slight difference in water absorption between the crystal layer and the PI layer to assist in separation. Gently lift the adhesion interface at the edge of the film with tweezers so that the film can be gradually peeled off from the glass plate.

[0048] The image of the prepared blue polyimide composite film is shown below. Figure 1 As shown, the nanoneedle-shaped ZnO crystal array accounts for 15% of the total mass of the film. The measured dielectric constant of the blue film is approximately 7.5 (1 kHz), the thermal conductivity is 7.8 W / m·K, the tensile strength is approximately 148 MPa, and the coefficient of linear expansion is 21 ppm / ℃. The energy density at a wavelength of 365 nm is 182 mW / cm². 2 After 4 hours of ultraviolet light irradiation, the color difference was measured to be 1.2, and the light transmittance was 81%. Figure 2 It can be seen that under high-energy-density ultraviolet irradiation, the mechanical properties of the composite film decrease slowly, and it still maintains good mechanical properties after 4 hours of continuous irradiation; from Figure 3 and Figure 4 The comparison shows that after irradiation, the originally smooth surface developed cracks and wrinkles, which macroscopically indicates a decline in mechanical properties.

[0049] Example 2

[0050] The dot-coating array was adjusted to a spacing of 3 mm, while other conditions remained the same as in Example 1, to prepare a colored polyimide composite film. At this point, the content of the nanoneedle-shaped ZnO crystal array reached 30%. The tensile strength was measured to be 131 MPa, the coefficient of linear expansion was 25 ppm / ℃, the thermal conductivity was 9.2 W / m·K, and the dielectric constant was 8.2 (1 kHz).

[0051] Example 3

[0052] Disperse Blue 359 in Example 1 was replaced with Basic Red 9, while other conditions remained the same as in Example 1, to prepare a red polyimide composite film. The dielectric constant of the red sample was measured to be approximately 7.3 (1 kHz), the tensile strength was 150 MPa, the coefficient of linear expansion was 22 ppm / ℃, the thermal conductivity was 7.7 W / m·K, and the color difference measured under the same UV light testing conditions as in Example 1 was 1.4.

[0053] Example 4

[0054] Disperse Blue 359 in Example 1 was replaced with Reactive Yellow 186, while other conditions remained the same as in Example 1, to prepare a yellow polyimide composite film. The dielectric constant of the yellow sample was measured to be approximately 7.4 (1 kHz), the tensile strength was 150 MPa, the coefficient of linear expansion was 23 ppm / ℃, the thermal conductivity was 7.8 W / m·K, and the color difference measured under the same UV light testing conditions as in Example 1 was 1.3.

[0055] Example 5

[0056] In step (2) of Example 1 above, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluorodianhydride were replaced with 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (molar ratio = 1:1), respectively, while other steps remained the same as in Example 1. The tensile strength was measured to be 172 MPa, the coefficient of linear expansion was 31 ppm / ℃, the thermal conductivity was 6.9 W / m·K, and the dielectric constant was 7.6 (1 kHz).

[0057] Example 6

[0058] In step (2) of Example 1 above, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluorodianhydride were replaced with 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenylcarbonylamino)biphenyl and cyclobutanetetracarboxylic dianhydride, respectively, while the other steps remained the same as in Example 1. The tensile strength of the final product was measured to be 150 MPa, the thermal conductivity to be 7.3 W / m·K, the dielectric constant to be 7.1 (1 kHz), the coefficient of linear expansion to be 23 ppm / ℃, and the color difference measured under the same ultraviolet light testing conditions as in Example 1 to be 2.0.

[0059] Example 7

[0060] The polymerization solvent N,N-dimethylacetamide in step (2) of Example 1 was replaced with dimethyl sulfoxide, and the remaining steps were the same. Blue polyimide solutions with different solvent systems were prepared and applied to the film-forming process. The tensile strength of the obtained product was 142 MPa, the coefficient of linear expansion was 26 ppm / ℃, the thermal conductivity was 6.4 W / m·K, and the dielectric constant was 7.1 (1 kHz). After testing under the same ultraviolet irradiation conditions as in Example 1 for 4 hours, the color difference was 2.1. At the same time, there was adhesive residue on the surface, and the structure was not uniform and aesthetically pleasing.

[0061] Comparative Example 1

[0062] The undyed polyimide solution prepared in step (2) of Example 1 was directly used to prepare a colorless and transparent polyimide film (without adding ZnO) according to the film-forming process in step (3) of Example 1. The image is shown below. Figure 5 As shown. The obtained PI film has a thermal conductivity of 7.6 W / m·K, a dielectric constant of 7.4 (1 kHz), a tensile strength of 160 MPa, and a coefficient of linear expansion of 23 ppm / ℃.

[0063] Comparative Example 2

[0064] The polyimide solution prepared in step (2) of Example 1 was used to directly prepare a blue polyimide film (without adding ZnO) according to the film-forming process in step (3) of Example 1. The film has a dielectric constant of 3.1 (1 kHz), a tensile strength of 158 MPa, a coefficient of linear expansion of 24 ppm / ℃, and a thermal conductivity of 7.3 W / m·K, which is similar to that of a colorless transparent polyimide film. After testing for 4 hours under the same ultraviolet irradiation conditions as in Example 1, the color difference was 1.4.

[0065] Comparative Example 3

[0066] Unlike Example 1, the ZnO whiskers were not annealed after deposition, resulting in a ZnO layer with an irregular vertical crystal structure. The ZnO whiskers were distorted and had varying particle sizes. The PI film prepared from this substrate had a thermal conductivity of 6.2 W / m·K, a dielectric constant of only 5.3 (1 kHz), and a tensile strength of 132 MPa.

[0067] Comparative Example 4

[0068] The blue polyimide solution prepared in step (2) of Example 1 was blended with commercial ZnO nanoparticles, both with a mass fraction of 15%. The resulting blue polyimide composite film was prepared using the same process as in step (3) of Example 1. The image is shown below. Figure 6As shown. Its dielectric constant is 6.5 (1kHz), tensile strength is 162MPa, coefficient of linear expansion is 36ppm / ℃, thermal conductivity is 4.5W / m·K, and light transmittance is 65%.

[0069] Comparative Example 5

[0070] The polyamic acid precursor solution prepared in step (2) of Example 1 was directly chemically cyclized, and then dye molecules were added for blending. The remaining steps were the same as in Example 1 to obtain a colored polyimide composite film under the blending dyeing process. The dielectric constant of the sample was measured to be approximately 7.4 (1 kHz), the tensile strength was 130 MPa, the thermal conductivity was 7.9 W / m·K, the coefficient of linear expansion was 28 ppm / ℃, and the color difference measured under the same ultraviolet light test conditions as in Example 1 was 2.5.

[0071] Comparing Example 1 with Comparative Example 2, it can be found that the thermal conductivity of the composite film after introducing ZnO is significantly higher than that of the pure polyimide substrate.

[0072] Comparing Example 1 with Comparative Example 3, it can be found that the quality of the macroscopic structure of ZnO crystal directly and significantly affects the improvement of the dielectric properties of the thin film and other properties. Defects in the ZnO crystal structure will prevent the formation of good heat conduction channels, and there will be a large number of holes and cracks on the surface of the thin film, resulting in a significant increase in dielectric defects and performance that is far inferior to that of normally prepared thin films.

[0073] Comparing Example 1 and Comparative Example 4, the latter's improvement in thermal conductivity and thermal properties are inferior to the former, reflecting that the construction of thermally conductive channels has a better effect on improving thermal conductivity compared to nanoparticle blending. Furthermore, because the thermally conductive channels are annealed and have a smaller total contact surface area with polyimide, their impact on the film's thermal properties is relatively small. However, the latter, due to the filling effect of nanoparticles, has a certain enhancement effect on the film's mechanical properties. Comparing the values ​​of each dielectric constant with traditional PI films, it can be found that the introduction of ZnO also improves the dielectric properties of the film, greatly expanding its application scenarios.

[0074] In Example 1 and Comparative Example 5, since a more stable molecular structure was not generated through the grafting process, the mechanical properties and thermal stability of Comparative Example 5 decreased. The color difference obtained under the same test conditions shows that the grafting of dye molecules on the main chain endows the film with uniform and stable coloring.

[0075] Comparing Examples 1 and 2, it is evident that the improvement in thermal conductivity of polyimide films by ZnO is positively correlated with the mass fraction of ZnO; the higher the ZnO content, the better the thermal conductivity of the composite film. Comparing Examples 1 with Examples 3 and 4, it is shown that different dye types do not significantly affect the overall performance of the composite film. Furthermore, comparing them with Comparative Example 1 reveals that dyes have a certain impact on light transmittance; the absence of dyes results in higher optical transmittance. Comparing Examples 1 and 5 reveals certain differences in their mechanical properties. Due to the more rigid molecular structure of the 4,4'-diaminodiphenyl ether / 3,3',4,4'-biphenyltetracarboxylic acid dianhydride system, its thermal conductivity is worse, but its mechanical properties are better. Therefore, it is more sensitive to temperature changes, has a larger coefficient of linear expansion, and poorer thermal stability. A comparison of Examples 1 and 6 reveals that the 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenylcarbonylamino)biphenyl structure used in Example 6 exhibits moderate rigidity, while the cyclobutanetetracarboxylic dianhydride is alicyclic, resulting in higher flexibility and thus lower tensile strength. In Example 7, the solvent was changed; dimethyl sulfoxide showed better solubility, but its evaporation rate was slower under the same conditions, leading to uneven surface formation and decreased mechanical, optical, and thermal properties. This indicates that the solvent's involvement in the system significantly impacts the film's performance.

[0076] In summary, the colored polyimide composite film constructed by constructing thermally conductive channels with nano-needle-shaped ZnO crystal arrays and chemically grafting dye molecules exhibits superior dielectric properties and richer, more stable color performance compared to ordinary polyimide films.

Claims

1. A high thermal conductivity colored polyimide composite film, characterized in that: The composite film is obtained by casting a colored polyimide solution onto a conductive substrate containing a nano-needle-shaped ZnO crystal array, followed by high-temperature vacuum solvent removal. The conductive substrate containing the nano-needle-shaped ZnO crystal array is obtained by electrochemical deposition of needle-shaped ZnO crystals in a vertical direction on a conductive substrate coated with a zinc acetate ethanol layer, followed by cleaning, drying, and high-temperature annealing. The colored polyimide solution is obtained by chemically grafting a dye compound onto polyamic acid segments, and the polar aprotic solvent used in the grafting process is one or more of dimethylacetamide and N,N-dimethylformamide.

2. A method for preparing a high thermal conductivity colored polyimide composite film, characterized in that, Includes the following steps: (1) Coat the surface of the cleaned and surface-treated conductive substrate with a zinc acetate ethanol layer; add zinc ion electrolyte, supporting electrolyte and acetamide to deionized water and adjust the pH to 3.0~7.0 to obtain a three-electrode electrolyte; place the conductive substrate as the working electrode into the three-electrode electrolyte, connect the power supply and carry out a water bath reaction. The conductive substrate coated with zinc acetate ethanol layer generates needle-shaped ZnO crystals in the vertical direction through electrochemical deposition. Then, after cleaning, drying and high-temperature annealing, a conductive substrate containing a nano needle-shaped ZnO crystal array is obtained. (2) The diamine and the acid anhydride are dissolved in a polar aprotic solvent at a molar ratio of 0.97 to 1.03:1 and reacted with nitrogen at 0 to 60 °C for 6 to 24 hours to obtain a polyamic acid precursor solution; then the dye compound and coupling agent are added, and the mixture is stirred at room temperature for 2 to 6 hours. Then, 1 to 5 times the molar amount of the diamine cyclization catalyst and dehydrating agent are added, and the mixture is stirred at 25 to 100 °C for 2 to 12 hours to prepare a colored polyimide solution; wherein the polar aprotic solvent is one or more of dimethylacetamide and N,N dimethylformamide; (3) The colored polyimide solution in step (2) is cast into a film on the conductive substrate containing the nano needle-shaped ZnO crystal array in step (1), and then the solvent is removed under high temperature vacuum to obtain a high thermal conductivity colored polyimide composite film.

3. The preparation method according to claim 2, characterized in that: The zinc ion electrolyte in step (1) includes one or more of zinc sulfate, zinc acetate, zinc nitrate, zinc chloride, zinc bromide, and zinc perchlorate; the supporting electrolyte includes one or more of alkali metal salts and ammonium salts.

4. The preparation method according to claim 2, characterized in that: The water bath reaction temperature in step (1) is 60-80℃, the water bath reaction time is 0.5-2h, and the working voltage is -5V~-0.5V.

5. The preparation method according to claim 2, characterized in that: The diamine in step (2) is one or more of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-diphenyl]-4,4'-diyl)bis(4-aminobenzamide), 4,4-diaminophenyl sulfone, and 1,4-(4-amino-2-trifluoromethylphenoxy)-2-(3',5'-ditrifluoromethylphenyl)benzene; the anhydride is one or more of hexafluorodianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3'-biphenyl dianhydride, and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

6. The preparation method according to claim 2, characterized in that: The coupling reagent in step (2) is one or more of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, dicyclohexylcarbodiimide, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, and diethyl pyrocarbonate; the molar ratio of the coupling reagent to the diamine is 1~5:

1.

7. The preparation method according to claim 2, characterized in that: The cyclization catalyst in step (2) is one or more of triethanolamine, 1,4-diazobicyclo[2.2.2]octane, quinoline, isoquinoline, pyridine, and 3-methylpyridine; the dehydrating agent is one or more of acetic anhydride, bis[α,α-bis(trifluoromethyl)phenylethanol]-diphenylsulfonate, xanthate, and N-(triethylammonium sulfonyl)carbamate.

8. The preparation method according to claim 2, characterized in that: The solid content of the colored polyimide solution in step (2) is 5~25 wt%, and the solution viscosity is 10000~300000 mPa·s.

9. The preparation method according to claim 2, characterized in that: The high-temperature vacuum desolventizing process in step (3) specifically involves: drawing a vacuum and heating the temperature to 150-200°C at a rate of 0.5-10°C / minute.

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