High-thermal-conductivity colored polyimide composite film and preparation method thereof

Abstract

The invention relates to a high-thermal-conductivity colored polyimide composite film and a preparation method thereof. The composite film is obtained by casting a colored polyimide solution on a conductive substrate containing a nano needle-shaped ZnO crystal array and then performing high-temperature vacuum solvent removal. The composite film provided by the invention not only has wide-range color adjustability, ultraviolet resistance and color uniformity, but also has excellent heat-conducting property, and has application potential in the fields of flexible display, 5G antennas, color bearing films, high-heat-conductivity insulating films, microelectronics and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a high-thermal-conductivity colored polyimide composite film and a preparation method thereof. Background Art

[0002] Polyimide (PI), with its high glass transition temperature, excellent heat resistance, and superior dielectric properties, is widely used in flexible electronics, liquid crystal display (LCD) filters, aerospace, and other fields. However, traditional PI films are mostly yellow or brown, making them difficult to meet the high transmittance requirements of optoelectronic devices and posing a significant obstacle to the preparation of colored polyimide films. Conventional methods for preparing colorless and transparent polyimide films can meet the basic requirements of colorlessness and transparency, but research on UV resistance is relatively lacking, preventing the films from achieving a wider range of applications.

[0003] Traditional PI films typically have low thermal conductivity (0.15-0.25 W / m·K), making them difficult to meet the thermal management requirements of thin high-power devices. Currently, several patents for high-thermal-conductivity polyimide films exist in China. For example, CN119751868A mentions the copolymerization of phosphorus dianhydride and long-chain alkyl diamine to create intramolecular heat-conducting channels to improve the thermal conductivity of polyimide while also providing flame retardancy. While this technology effectively optimizes the PI molecular microstructure, the improvement in thermal conductivity is limited. Furthermore, the design approach primarily focuses on structural adjustments within the main chain, limiting its ability to construct macroscopically ordered heat-conducting channels. CN112812341B discloses a method for preparing a "quadruple-structured composite particle / PI film" that uses nanofillers to form a needle-like arrangement to enhance thermal conductivity. However, this needle-like structure relies on filler self-assembly, resulting in an irregular and poorly controllable arrangement. This also poses challenges in terms of cross-sectional thermal conductivity consistency and reliability. CN101168598A proposes a method for improving thermal conductivity while maintaining a low thermal expansion coefficient by uniformly dispersing nano-thermal conductive materials (such as boron nitride) within PI. However, this technique 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 effectiveness of the thermal conductivity enhancement.

[0004] On the other hand, color polyimide, especially blue / red / green PI, has important application prospects in the fields of flexible display, wearable devices and new optoelectronic devices. However, the color film prepared based on colorless transparent polyimide often uses inorganic or organic dye blending method. For example, CN117166089A uses organic dye blending, realizes dye fixation through intermolecular force, but does not realize the formation of covalent bond, and the color stability is poor. CN114164688A uses inorganic dye blending, which not only easily causes agglomeration due to too strong intermolecular force, but also has high requirements for stirring and dispersion equipment, affects color uniformity, and increases equipment cost investment. Moreover, inorganic dyes often contain heavy metal components, which have great threat to the environment. How to combine environmental protection, low cost, color uniformity and stability, there is currently a lack of polyimide film dyeing scheme on the market that can meet all the needs. SUMMARY

[0005] The present application provides a high-thermal-conductivity color polyimide composite film and a preparation method thereof, which solves the problems of high preparation cost, complicated process and limited thermal conductivity resistance of color PI film in the prior art.

[0006] The present application provides a high-thermal-conductivity color polyimide composite film, which is obtained by casting a color polyimide solution on a conductive substrate containing a nano-needle-like ZnO crystal array, and then removing the solvent at high temperature under vacuum.

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

[0008] Preferably, the mass fraction of the nano-needle-like ZnO crystal array in the composite film is 0.1-40%.

[0009] The present application also provides a preparation method of the high-thermal-conductivity color polyimide composite film, which comprises the following steps:

[0010] (1) The surface of the cleaned and surface-treated conductive substrate is coated with a zinc acetate ethanol layer; zinc ion electrolyte, supporting electrolyte and acetamide are added to deionized water, and the pH is adjusted to 3.0-7.0 to obtain a three-electrode electrolyte; the conductive substrate is placed as a working electrode in the three-electrode electrolyte for water bath reaction, the conductive substrate coated with the zinc acetate ethanol layer generates needle-like ZnO crystals in the vertical direction through electrochemical deposition, and then the conductive substrate containing a nano-needle-like ZnO crystal array is obtained through cleaning, drying and high-temperature annealing treatment;

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

[0012] (3) Cast the colored polyimide solution in step (2) on the conductive substrate containing the nanoneedle ZnO crystal array in step (1) to form a film, and then remove the solvent under high temperature and vacuum to obtain a high-thermal-conductivity colored polyimide composite film.

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

[0014] Preferably, the surface treatment in step (1) is UV ozone or plasma treatment to remove organic contamination 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, NH4NO3, etc. The two electrolytes meet the following requirements: (1) good water solubility; (2) the anions and cations thereof cannot be reduced or oxidized within the deposition potential range and do not participate in the generation reaction of ZnO; (3) the selected ions do not seriously doped into the ZnO crystal lattice (unless intentionally doped); (4) the pH can be easily adjusted with acid and alkali to maintain a weak acidic environment (pH≈4-6).

[0016] Preferably, the concentration of the zinc ion electrolyte and the supporting electrolyte in step (1) is 10-50 mmol / L.

[0017] Preferably, the acetamide in step (1) is used to stabilize the electrode (preferably configured at 1 mol / L), the pH is adjusted to be acidic, and a uniform and transparent electrolyte is obtained, and the pH value is preferably 5.0±0.2.

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

[0019] Preferably, the cleaning and drying in step (1) is performed by alternately washing with deionized water and ethanol, and then drying at high temperature (80) for more than 5 minutes.

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

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

[0022] Preferably, the dye compound is 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-N dimethylformamide, gamma-butyrolactone, dimethylacrylamide, hexamethylphosphoramide.

[0024] Preferably, the coupling reagent in step (2) is one or more of 1-ethyl-(3-dimethylaminopropyl) carbodiimide, dicyclohexyl carbodiimide, 1-hydroxybenzotriazole, 1-hydroxy-7-azobenzotriazole, diethyl pyrocarbonate, which simultaneously meet the requirements of being soluble in water or easily solid at low temperature to remove the two requirements of being useful in catalyzing the dehydration condensation of carboxylic acid and amino; the molar ratio of the coupling reagent to the diamine is 1-5:1.

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

[0026] Preferably, the dehydrating agent in step (2) is one or more of acetic anhydride, bis[alpha,alpha-bis(trifluoromethyl)phenethyl alcohol]-diphenyl sulfide, xanthate, and N-(triethylammonium sulfonyl) methyl carbamate.

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

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

[0029] Preferably, the high-temperature vacuum desolvation in step (3) is performed by vacuumizing and heating to 150-200℃ at a heating rate of 0.5-10℃ / min. Further, the temperature is first raised to 60-80℃ and maintained for 8 hours or more to ensure that low-boiling-point solvents such as DMAC are fully evaporated; after the primary desolvation is complete, the temperature is continued to be slowly raised to 150-200℃ and maintained for 2 hours or more to achieve complete ring closure of the polyamic acid to form a polyimide matrix and to increase the glass transition temperature of the chain segment; the entire process is performed under vacuum to prevent oxidation and solvent residue.

[0030] Advantages

[0031] (1) The present application forms a "directional heat conduction channel" that penetrates the thickness direction of the polyimide film by growing a vertically arranged nanoneedle ZnO crystal array in situ on the surface of the conductive substrate. This structure effectively overcomes the bottleneck of the limited heat conductivity of traditional high polymer materials due to interchain heat dissipation, and realizes the rapid conduction of heat flux in the out-of-plane direction, so that the out-of-plane thermal conductivity of the thin film is significantly improved compared to that of pure PI film.

[0032] (2) The nanoneedle ZnO crystal array is embedded in the polyimide matrix to form a rigid-flexible coupled three-dimensional network channel structure, which not only enhances the heat conduction capacity, 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 electronic and thermal management devices under high temperature deformation conditions.

[0033] (3) The present application realizes high-stability coloring by chemically grafting the dye compound to the polyamide acid segment, and avoids dye migration or discoloring during heat treatment. The obtained film has bright and uniform color, and has small color change under high temperature, high humidity or ultraviolet irradiation, and has good long-term weather resistance and appearance retention.

[0034] (4) The composite film of the present application not only has wide color adjustability, ultraviolet resistance, color uniformity, but also has excellent thermal conductivity, and has application potential in the fields of flexible display, 5G antenna, color bearing film, high-thermal-conductivity insulation film, microelectronics, etc. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Picture of the blue polyimide composite film prepared in Example 1.

[0036] Figure 2 Picture of the blue polyimide composite film prepared in Example 1 under ultraviolet light irradiation.

[0037] Figure 3 Picture of the blue polyimide composite film prepared in Example 1 under ultraviolet light irradiation.

[0038] Figure 4 Picture of the blue polyimide composite film prepared in Example 1 under ultraviolet light irradiation.

[0039] Figure 5 Picture of the colorless polyimide composite film prepared in Comparative Example 1.

[0040] Figure 6 Picture of the nanoparticle blended blue polyimide composite film prepared in Comparative Example 4. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. Furthermore, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope of the appended claims of the present application.

[0042] Example 1

[0043] (1) A 10 cm * 10 cm ITO conductive glass plate with a thickness of 4 mm was sequentially cleaned by ultrasonic cleaning (acetone, deionized water, isopropanol), dried, and then treated by UV ozone or plasma to remove organic contaminants and enhance hydrophilicity. A 30 mmol / L zinc acetate ethanol solution was spotted on the surface of the glass plate in a distribution pattern with a horizontal and vertical spacing of 6 mm, and baked at 100°C for 3 minutes. The spotting was then repeated 3 times with a horizontal and vertical spacing of 2 mm, thereby preparing a ZnO nanoparticle seed layer. A 10 mmol / L ZnCl2 and 10 mmol / L NaNO3 solution was prepared in deionized water, and 0.1 mol / L acetamide was added to adjust the pH to 5.0 ± 0.2, obtaining a uniform and transparent three-electrode electrolyte. The above-mentioned ITO working electrode, platinum counter electrode, and Ag / AgCl reference electrode were immersed in the electrolyte, placed in a 60°C water bath and magnetically stirred at 200 rpm, and a constant potential of -0.9V (relative to Ag / AgCl) was applied to the working electrode by a constant potential method, with a deposition time of 2 hours. After deposition, the substrate was washed with deionized water and ethanol alternately, and then dried at 80°C for 10 minutes. Finally, the substrate was annealed in air at 300°C for 20 minutes to improve the crystallinity, obtaining an ITO conductive glass plate containing a nanoneedle-shaped ZnO crystal array.

[0044] (2) 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluorodiamide were dissolved in dimethylacetamide at a molar ratio of 1:1 according to a solid content of 17%, and reacted at about 0°C for 12 hours under nitrogen to obtain a polyamide acid precursor solution; then 1 / 20 of the molar amount of the diamine was added to the dispersion blue 359 dye powder, and finally 5 times the molar amount of the diamine was added to the coupling reagent 1-ethyl-(3-dimethylaminopropyl) carbonyl diimide. After stirring at room temperature for 6 hours, 5 times the molar amount of the diamine was added to acetic anhydride, and 2 times the molar amount of the diamine was added to pyridine slowly. After stirring at room temperature for 6 hours, a blue polyimide solution was obtained. The solution was slowly poured into deionized water in a thin stream to solidify, and the solidified material was broken into small particles and washed in deionized water for 30 minutes. The particles were filtered and dried, and the clean polyimide solution was prepared by reconfiguring the solution according to the solid content requirement.

[0045] (3) Take the ITO conductive glass plate containing the nanoneedle-like ZnO crystal array after the culture is completed, and gently flush the surface dust with deionized water and air dry, so that the glass plate surface keeps the natural crystal array layer; if single-sided coating is needed, the back of the glass plate can be isolated (such as sticking high-temperature-resistant isolation paper, aluminum foil or coating polytetrafluoroethylene film) to prevent both sides from being coated; then the chemical grafting (or blending) dyeing polyimide solution prepared in step (2) is filtered with a stainless steel mesh to remove a small amount of agglomerated impurities that may exist; the polyimide solution is coated on the surface of the glass plate by using a fixed gap doctor blade or spin coating method, and the thickness is determined according to the target dry film thickness, the height of the needle-like crystal and the solid content of the solution. Ensure that the coating is uniform, without obvious sagging or stratification, then place the coated iron plate on a horizontal plate and let it stand for 10-15 minutes to allow the solvent to evaporate under natural convection conditions; then put the coated glass plate together with the polyimide solution into a vacuum oven or vacuum drying oven, and vacuumize to about 10 kPa below; set the temperature curve: heat to 80°C and keep for 8 hours, then continue to slowly raise the temperature to 180°C and keep for 4 hours, the whole process is carried out under vacuum state to prevent oxidation and solvent residue.

[0046] (4) After the end of curing, turn off the heating and slowly cool to room temperature, keep vacuum for 30 minutes, then take out the sample and place it in a desiccator for standby.

[0047] (5) After the sample cools to room temperature, immerse the glass plate in hot water at 70°C, use the slight water absorption difference between the crystal layer and the PI layer to assist separation, use tweezers to gently lift the adhesive interface at the edge of the film, and gradually peel off the film from the glass plate.

[0048] The picture of the blue polyimide composite film prepared is shown in Figure 1 , the mass fraction of the nanoneedle-like ZnO crystal array in the whole film is 15%, the dielectric constant of the blue film is about 7.5 (1 kHz), the thermal conductivity is 7.8 W / m·K, the tensile strength is about 148 MPa, and the linear expansion coefficient is 21 ppm / ℃, under the irradiation of ultraviolet light with a wavelength of 365 nm and an energy density of 182 mW / cm 2 for 4 hours, the color difference after irradiation is 1.2, and the transmittance is 81%. It can be seen from Figure 2 that after irradiation under high energy density ultraviolet light, the mechanical properties of the composite film decrease slowly, and after 4 hours of continuous irradiation, it still maintains good mechanical properties; it can be seen from Figure 3 and Figure 4 that after irradiation, cracks and wrinkles appear on the originally smooth surface, which macroscopically represents the decrease of mechanical properties.

[0049] Example 2

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

[0051] Example 3

[0052] The dispersion blue 359 in Example 1 was replaced with basic red 9, and the other conditions remained the same as in Example 1 to prepare a red polyimide composite film. The dielectric constant of the red sample was about 7.3 (1 kHz), the tensile strength was 150 MPa, the linear expansion coefficient was 22 ppm / °C, the thermal conductivity was 7.7 W / m·K, and the color difference was 1.4 under the same ultraviolet light test conditions in Example 1.

[0053] Example 4

[0054] The dispersion blue 359 in Example 1 was replaced with reactive yellow 186, and the other conditions remained the same as in Example 1 to prepare a yellow polyimide composite film. The dielectric constant of the yellow sample was about 7.4 (1 kHz), the tensile strength was 150 MPa, the linear expansion coefficient was 23 ppm / °C, the thermal conductivity was 7.8 W / m·K, and the color difference was 1.3 under the same ultraviolet light test conditions in Example 1.

[0055] Example 5

[0056] In step (2) of Example 1, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluoro dianhydride were replaced with 4,4'-diamino diphenyl ether and 3,3',4,4'-biphenyl tetracarboxylic dianhydride (molar ratio = 1:1), respectively, and the other steps remained the same as in Example 1. The tensile strength was measured to be 172 MPa, the linear expansion coefficient was 31 ppm / °C, 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, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and hexafluoro dianhydride were replaced with 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenyl carbonyl amido) biphenyl and cyclobutane tetracarboxylic dianhydride, respectively, and 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 was 7.3 W / m·K, the dielectric constant was 7.1 (1 kHz), the linear expansion coefficient was 23 ppm / °C, and the color difference was 2.0 under the same ultraviolet light test conditions in Example 1.

[0059] Example 7

[0060] The polymerization system solvent N,N-dimethylacetamide in step (2) of Example 1 above was replaced with dimethyl sulfoxide, and the remaining steps were the same. A blue polyimide solution of a different solvent system was prepared and applied to the film forming process. The tensile strength of the finished product was measured to be 142 MPa, the linear expansion coefficient was 26 ppm / ℃, the thermal conductivity was 6.4 W / m·K, the dielectric constant was 7.1 (1 kHz), and the 1 color difference was 2.1 after 4 hours of testing under the same ultraviolet irradiation conditions as Example 1, and at the same time, there was a glue print on the surface and the structure was not uniform and beautiful.

[0061] Comparative Example 1

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

[0063] Comparative Example 2

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

[0065] Comparative Example 3

[0066] Unlike Example 1, the ZnO whiskers were not annealed after deposition, and an irregular vertical ZnO layer with distorted and distorted ZnO whiskers and different particle sizes was obtained. After the PI film was prepared on this substrate, the thermal conductivity was 6.2 W / m·K, the dielectric constant was only 5.3 (1 kHz), and the tensile strength was 132 MPa.

[0067] Comparative Example 4

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

[0069] Comparative Example 5

[0070] The polyamide acid precursor solution prepared in step (2) in Example 1 is directly subjected to chemical cyclization, and then dye molecules are added for blending, and the remaining steps are the same as in Example 1, to obtain a colored polyimide composite film under a blending dyeing process. The dielectric constant of the sample is about 7.4 (1 kHz), the tensile strength is 130 MPa, the thermal conductivity is 7.9 W / m·K, the linear expansion coefficient is 28 ppm / °C, and the color difference measured under the same ultraviolet light test conditions as in Example 1 is 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 macrostructure of ZnO crystals directly and significantly affects the improvement effect of the dielectric properties of the film and other properties. Defects in the structure of ZnO crystals can prevent the formation of good thermal conduction channels, and there are a large number of pores and cracks on the surface of the film, and the dielectric defects increase significantly, and the performance is far inferior to that of a normally prepared film.

[0073] Comparing Example 1 with Comparative Example 4, the thermal conductivity and thermal performance of the latter are inferior to those of the former, reflecting that the construction of thermal conduction channels has a better effect on improving the thermal conductivity than the blending of nanoparticles. At the same time, since the thermal conduction channels are treated by annealing and have a relatively small total surface area in contact with the polyimide, the effect on the thermal performance of the film is small. However, the latter has a certain enhancement effect on the mechanical properties of the film due to the filling effect of the nanoparticles. By comparing the dielectric constant values in each item with those of a traditional PI film, it can be found that the introduction of ZnO also has a certain improvement effect on the dielectric properties of the film, greatly expanding its application scenarios.

[0074] In Example 1 and Comparative Example 5, the mechanical properties and thermal stability of Comparative Example 5 are decreased due to the lack of a grafting process to generate a more stable molecular structure. The color difference obtained under the same test conditions can be found that the grafting of dye molecules on the main chain gives the film uniform and stable coloring properties.

[0075] From the comparison of Example 1 and Example 2, it can be seen that the effect of ZnO on the thermal conductivity of the polyimide film is positively correlated with the mass fraction of ZnO. The greater the proportion of ZnO, the better the thermal conductivity of the composite film. The comparison of Example 1 and Example 3 and 4 reflects that the different types of dyes do not have a significant impact on the overall performance of the composite film. At the same time, compared with Comparative Example 1, it can be found that the dye has a certain influence on the light transmittance. Without dye, the optical transmittance is higher. The comparison of Example 1 and Example 5 shows that the mechanical properties of the two are different. Because the 4,4'-diamino diphenyl ether / 3,3',4,4'-biphenyl tetracarboxylic dianhydride system has a relatively rigid molecular structure, the thermal conductivity is poorer, the mechanical properties are better, and the overall temperature change is more sensitive, the linear expansion coefficient is larger, and the thermal stability is poorer. The comparison of Example 1 and Example 6 shows that because the 2,2'-bis(trifluoromethyl)-4,4'-bis(4-aminophenyl carbonyl amine) biphenyl structure used in Example 6 has moderate rigidity, and the cyclobutane tetracarboxylic dianhydride is an alicyclic structure, the flexibility is higher, reflecting lower tensile properties. In Example 7, the solvent was replaced, and the solubility of dimethyl sulfoxide was better, but the evaporation rate was slower under the same environment, the surface forming was uneven, and the mechanical properties, optical stability and thermal conductivity were all decreased, indicating that the participation of the solvent in the system has a great influence on the performance of the film.

[0076] In summary, the colored polyimide composite film constructed by nano-needle-like ZnO crystal array to build thermal conduction channels and chemical grafting of dye molecules has more excellent dielectric properties and more abundant and stable color performance compared with ordinary polyimide films.

Claims

1. A high thermal conductivity colored polyimide composite film, characterized by: The composite film is obtained by casting a colored polyimide solution on a conductive substrate containing a nano needle-shaped ZnO crystal array and then removing the solvent in a high-temperature vacuum.

2. A method for preparing a high thermal conductivity colored polyimide composite film, characterized in that: The steps include: (1) coating the surface of a cleaned and surface-treated conductive substrate with a zinc acetate ethanol layer; adding a zinc ion electrolyte, a supporting electrolyte, and acetamide to deionized water, and adjusting the pH to 3.0-7.0 to obtain a three-electrode electrolyte; placing the conductive substrate as a working electrode in the three-electrode electrolyte, connecting a power supply to perform a water bath reaction, and electrochemically depositing the conductive substrate coated with the zinc acetate ethanol layer to generate needle-shaped ZnO crystals in a vertical direction, and then washing, drying, and high-temperature annealing to obtain a conductive substrate containing a nano-needle-shaped ZnO crystal array; (2) Dissolve the diamine and the acid anhydride in a polar aprotic solvent at a molar ratio of 0.97 to 1.03:1, and react with nitrogen at 0 to 60 ° C for 6 to 24 hours to obtain a polyamic acid precursor solution; then add the dye compound and the coupling reagent, stir at room temperature for 2 to 6 hours, and then add 1 to 5 times the molar amount of the diamine cyclization catalyst and dehydrating agent, stir and react at 25 to 100 ° C for 2 to 12 hours to prepare a colored polyimide solution; (3) Casting the colored polyimide solution in step (2) into a film on the conductive substrate containing the nano-needle-shaped ZnO crystal array in step (1) and then desolvating it in a high-temperature vacuum to obtain a high-thermal-conductivity colored polyimide composite film.

3. The preparation method according to claim 2, wherein: 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; and the supporting electrolyte includes one or more of alkali metal salts and ammonium salts.

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

5. The preparation method according to claim 2, wherein: 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'-biphenyl]-4,4'-diyl)bis(4-aminobenzamide), 4,4-diaminophenyl sulfone, and 1,4-(4-amino-2-trifluoromethylphenoxy)-2-(3',5'-ditrifluoromethylphenyl)benzene; and the acid anhydride is one or more of hexafluorodianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3'-biphenyl dianhydride, and 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride.

6. The preparation method according to claim 2, wherein: The polar aprotic solvent in step (2) is one or more of dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, N-dimethylformamide, γ-butyrolactone, dimethylpropylene urea, and hexamethylphosphoramide.

7. The preparation method according to claim 2, wherein: 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; and the molar ratio of the coupling reagent to the diamine is 1 to 5:

1.

8. The preparation method according to claim 2, wherein: 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]-diphenylsulfide, xanthate, and methyl N-(triethylammoniumsulfonyl)carbamate.

9. The preparation method according to claim 2, wherein: The colored polyimide solution in step (2) has a solid content of 5 to 25 wt %, and a solution viscosity of 10,000 to 300,000 mPa·s.

10. The preparation method according to claim 2, characterized in that: The high-temperature vacuum desolvation in step (3) is specifically as follows: vacuuming and heating to 150-200°C at a heating rate of 0.5-10°C / min.

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