High-modulus high-adhesion metal-clad plate and preparation method thereof

Abstract

The invention discloses a high-modulus high-adhesion metal-clad plate which comprises a metal layer, and a first polyimide layer and a second polyimide layer are sequentially stacked on one surface of the metal layer; a first coating liquid of the first polyimide layer comprises a diamine monomer containing a benzimidazole unit, a diamine monomer containing a sulfuryl unit, an active end-capping reagent and a flexible dianhydride monomer; a second coating liquid of the second polyimide layer comprises a diamine monomer of a benzimidazole-benzoxazole unit and a rigid dianhydride monomer which is equal to the diamine monomer in mole. Through compounding of the first polyimide layer and the second polyimide layer, the toughness and the mechanical strength of the composite polyimide film and the adhesive force with a metal plate are flexibly adjusted.

Description

Technical Field

[0001] This invention relates to the field of polymer film technology, specifically to a high-modulus, high-adhesion metal-coated plate and its preparation method. Background Technology

[0002] Polyimide (PI) film, with its unique combination of electrical properties, high-temperature stability, chemical corrosion resistance, and high strength and toughness, has become one of the key materials in the electrical insulation, microelectronic packaging, and flexible display industries. Polyimide film is mainly used as a substrate for H-class and C-class electrical insulation and flexible copper-clad laminates (FCCLs) in flexible printed circuits (FPCs). However, the physicochemical properties of polyimide (PI) and copper foil differ significantly; the former has a low-energy surface, while the latter has a high-energy surface, resulting in poor adhesion between the two. Furthermore, their inconsistent expansion and contraction generate thermal stress, easily leading to interfacial delamination. Summary of the Invention

[0003] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a high-modulus, high-adhesion metal-coated plate. The toughness, mechanical strength, and adhesion to the metal plate of the composite polyimide film can be flexibly adjusted by combining a first polyimide layer and a second polyimide layer.

[0004] To achieve the above-mentioned process effects, the technical solution of the present invention is as follows: a high modulus and high adhesion metal-coated plate, comprising a metal layer, wherein a first polyimide layer and a second polyimide layer are sequentially stacked on one surface of the metal layer; The first coating liquid of the first polyimide layer includes a diamine monomer containing benzimidazole units, a diamine monomer containing sulfone units, an active end-capping agent, and a flexible dianhydride monomer; The second coating liquid of the second polyimide layer comprises a diamine monomer of a benzimidazole-benzoxazole unit and an equimolar rigid dianhydride monomer.

[0005] A preferred technical solution is that the total molar ratio of the diamine monomer containing benzimidazole units and the diamine monomer containing sulfone units to the flexible dianhydride monomer in the first coating solution is (1.01~1.03):1, the molar amount of the diamine monomer containing sulfone units accounts for 15%~30% of the total molar amount of the diamine monomer containing benzimidazole units and the diamine monomer containing sulfone units, and the molar amount of the active capping agent is 6%~9% of the molar amount of the flexible dianhydride monomer.

[0006] A preferred technical solution is that the diamine monomer containing the benzimidazole unit is 2,2'-bibenzimidazole-5,5'-diamine, and the diamine monomer of the benzimidazole-benzoxazole unit is 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine.

[0007] A preferred technical solution is that the diamine monomer containing the sulfone group is any one of 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, and 4,4'-bis(3-aminophenoxy)diphenyl sulfone.

[0008] The preferred technical solution is that the active capping agent is maleic anhydride and 5-norbornene-2,3-dicarboxylic anhydride.

[0009] The preferred technical solution is that the flexible dianhydride monomer is any one of 4,4'-oxobisphthalic anhydride and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride; and the rigid dianhydride monomer is any one of 4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0010] A preferred technical solution is that the solid content of the first coating liquid is 15%~30%, and the solid content of the second coating liquid is 7%~18%; both the first coating liquid and the second coating liquid further include a solvent, wherein the solvent is any one of N,N-dimethylacetamide and N-methylpyrrolidone.

[0011] The second objective of this invention is to overcome the deficiencies in the prior art and provide a method for preparing a high-modulus, high-adhesion metal-coated plate, comprising the following steps: S1: Prepare the first coating solution. After the two types of diamine monomers are completely dissolved, add the active end-capping agent and flexible dianhydride monomer in batches. S2: Prepare the second coating solution. After the diamine monomer containing the benzimidazole unit is completely dissolved, add the rigid dianhydride monomer. S3: A metal plate is sequentially coated with a first coating liquid, a second coating liquid, heated to evaporate the solvent, and subjected to high-temperature thermal imidization to obtain a metal-clad plate having a first polyimide layer and a second polyimide layer stacked sequentially.

[0012] The preferred technical solution is that the temperature for evaporating the solvent is 90~190℃; the temperature program for high-temperature thermal imidization is 100℃ / 2 h, 200℃ / 2 h, 250℃ / 2 h, 350℃ / 1 h; and the gradient temperature interval heating time in the temperature program for high-temperature thermal imidization is 20~30 min.

[0013] The preferred technical solution is that the thickness of the first polyimide layer is 5~50 μm, and the thickness of the second polyimide layer is 5~50 μm.

[0014] The advantages and beneficial effects of this invention are as follows: The toughness, mechanical strength, and adhesion to the metal plate of the composite polyimide film can be flexibly adjusted by combining the first polyimide layer and the second polyimide layer. The first polyimide layer improves the toughness of the composite polyimide film by synergistically combining the amino group in the benzimidazole unit, the sulfone group in the sulfone unit, and the flexible dianhydride monomer. Combined with the use of active end-capping agents to adjust the molecular chain length of polyamic acid, its solid content and viscosity are adjusted, and then crosslinked to obtain a first polyimide layer with high modulus and low coefficient of expansion. The second polyimide layer improves the compatibility with the first polyimide layer through the diamine monomer of the benzimidazole-benzoxazole unit, and enhances the high temperature resistance of the composite polyimide film, thereby maintaining the performance stability of the composite polyimide film during preparation and use. Detailed Implementation

[0015] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0016] diamine monomer The first polyimide layer comprises a diamine monomer containing benzimidazole units and a diamine monomer containing sulfone units.

[0017] The second polyimide layer comprises a diamine monomer of a benzimidazole-benzoxazole unit.

[0018] In this process, the diamine monomer containing the benzimidazole unit was prepared by mixing oxalic acid (8.1 g, 0.09 mol) and 4-nitro-1,2-phenylenediamine (38 g, 0.2 mol), dissolving it in 360 ml of ethylene glycol, adding 20 ml of polyphosphoric acid, and refluxing at 165 °C for 12 h. After purification, 5,5'-dinitro-2,2'-bibenzimidazole was obtained. Then, 5,5'-dinitro-2,2'-bibenzimidazole (6 g, 0.015 mol) was dissolved in 60 ml of 1,4-dioxane, mixed evenly at 80 °C, and 0.6 g of catalyst (palladium catalyst, Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., with an effective component of 0.9%) was added. Then, 7.6 g of hydrazine hydrate was slowly added dropwise, and the reaction was maintained at this temperature for 10 h. After purification, 2,2'-bibenzimidazole-5,5'-diamine was obtained.

[0019] Polyphosphoric acid is a viscous inorganic acid that dissolves organic reactants (diamine and oxalic acid) exceptionally well at high temperatures, forming a homogeneous, high-temperature molten reaction medium. This allows for thorough contact between reactant molecules, significantly improving reaction efficiency. Polyphosphoric acid possesses extremely strong hygroscopic and dehydrating abilities, binding water molecules generated during the reaction and irreversibly shifting the reaction equilibrium towards the formation of products. The strongly acidic environment provided by polyphosphoric acid protonates the carbonyl oxygen of oxalic acid, making its carbon atoms more electrophilic and more susceptible to nucleophilic attack from the amino group in o-phenylenediamine.

[0020] Purification of 5,5'-dinitro-2,2'-bibenzimidazole: After the reaction was completed, the mixture was cooled to 25°C and filtered. The filter cake was dispersed in 280 ml of ultrapure water at 80°C and stirred thoroughly. After cooling naturally to room temperature, the mixture was filtered again. The filter cake was then washed with water several times until no viscous precipitate was found. The filter cake was then dried to remove moisture. The dried filter cake was washed with ethanol several times. Finally, the filter cake was recrystallized using N,N-dimethylacetamide solvent, and the recrystallized product was washed with ethanol. After drying, the purified 5,5'-dinitro-2,2'-bibenzimidazole was obtained.

[0021] Purification of 2,2'-bibenzimidazole-5,5'-diamine: After the reaction was completed, 10 ml of N,N-dimethylformamide was added to the product solution and the temperature was raised to 95 °C. The catalyst was removed by hot filtration. The filtrate was then washed multiple times with ultrapure water and filtered again. The filter cake was dried at 65 °C for 10 h. After purification, 5,5'-dinitro-2,2'-bibenzimidazole was obtained.

[0022] In this reaction, the diamine monomer of the benzimidazole-benzoxazole unit was dissolved in 100 ml of acetic acid with 9.5 g (0.05 mol) of 4-nitro-1,2-phenylenediamine. The reaction solution was kept in an ice bath, and 12 g (0.068 mol) of methyl 2,2,2-trichloroacetylimine was added dropwise. The reaction was carried out at 25 °C for 20 h, and after purification, the intermediate 5-nitro-2-(trichloromethyl)-benzimidazole was obtained. Then, the intermediate (16.5 g (0.052 mol)) was mixed with 9 g (0.058 mol) of 2-amino-4-nitrophenol and dissolved in 200 ml of ethanol. Triethylamine (12 g (0.119 mol) was added, and the reaction was carried out at 80 °C for 36 h. After purification, 5-nitro-2-(5-nitro-1H-benzimidazole)-benzoxazole was obtained. Then, 7.2 g of 5-nitro-2-(5-nitro-1H-benzimidazole)-benzoxazole (0.018 mol) was dissolved in 60 ml of 1,4-dioxane and mixed evenly at 80 °C. 0.7 g of catalyst (palladium catalyst, Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., with an effective component of 0.9%) was added, followed by the slow addition of 9.2 g of hydrazine hydrate. The reaction was maintained at this temperature for 9 h, and after purification, 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine was obtained.

[0023] Purification of 5-nitro-2-(trichloromethyl)-benzimidazole: After the reaction, the product solution was dispersed in 300 ml of ultrapure water to produce a precipitate, which was repeatedly washed, filtered, washed with ethanol several times, and dried to obtain 5-nitro-2-(trichloromethyl)-benzimidazole.

[0024] Purification of 5-nitro-2-(5-nitro-1H-benzimidazole)-benzoxazole: After the reaction was completed, the mixture was cooled and filtered. The filter cake was washed with ethanol several times. Then, the filter cake was recrystallized using N,N-dimethylacetamide solvent. The recrystallized product was washed with ethanol, filtered, and dried to obtain purified 5-nitro-2-(5-nitro-1H-benzimidazole)-benzoxazole.

[0025] Purification of 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine: After the reaction was completed, 10 ml of N,N-dimethylformamide was added to the product solution and the temperature was raised to 95 °C. The catalyst was removed by hot filtration. The filtrate was then washed multiple times with ultrapure water and filtered again. The filter cake was dried at 65 °C for 10 h. After purification, 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine was obtained.

[0026] The sulfone-containing diamine monomer contains sulfone groups, which can promote the formation of complex chemical bonds between the first polyimide layer and the metal plate, thereby improving the adhesion between the two. Furthermore, the sulfone groups in the sulfone-containing diamine monomer give the polymer a folded configuration, resulting in a looser chain arrangement and a larger free volume, which is beneficial for subsequent crosslinking while maintaining good toughness. Further, the sulfone-containing diamine monomer is any one of 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, and 4,4'-bis(3-aminophenoxy)diphenyl sulfone. The benzimidazole-containing diamine monomer possesses -NH- proton donor and -N= proton acceptor hydrogen bonding sites, forming strong hydrogen bonds with the carbonyl and sulfone groups on the polyimide backbone, increasing the cohesive energy density between polymer molecular chains. However, an excessive proportion of diamine monomers containing sulfone units increases the modulus loss of the film. Furthermore, the molar amount of diamine monomers containing sulfone units accounts for 15% to 30% of the total molar amount of diamine monomers containing benzimidazole units and diamine monomers containing sulfone units.

[0027] First polyimide layer The first polyimide layer is formed by compounding a diamine monomer containing a benzimidazole unit and a diamine monomer containing a sulfone unit, and then forming a polyamic acid with a flexible dianhydride monomer in a molar ratio of (1.01~1.03):1. In order to adjust the toughness of the first polyimide layer, the flexible dianhydride monomer is further selected from either 4,4'-oxybisphthalic anhydride or 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride.

[0028] The solid content and viscosity of polyamic acid in the first coating solution are adjusted by using an active end-capping agent. The principle is to first form relatively small molecular weights, and then crosslink them through heating to form large molecular chains. Furthermore, the solid content of the first coating solution is 15%~30%. The thickness of the first polyimide layer is flexibly adjusted, which not only improves the adhesion of the composite polyimide film (first and second polyimide layers) to the metal plate, but also facilitates interfacial interpenetration and tighter bonding between the first and second polyimide layers. It also adjusts the toughness of the composite polyimide film and forms a composite polyimide film with a gradient temperature expansion coefficient. To increase the proportion of longer molecular chain segments, reduce the probability of forming shorter molecular chains, and achieve good film-forming properties, the molar amount of the active end-capping agent is further 6%~9% of the molar amount of the flexible dianhydride monomer. The solid content of the first coating solution controls the number of molecular chains in the crosslinking reaction, the active end-capping agent controls the degree of crosslinking of the first polyimide layer, and combined with the selection of the type of reactive monomer, a tough and high-modulus first polyimide layer is synergistically obtained.

[0029] Preparation of the first coating solution: Diamine monomers containing benzimidazole units and diamine monomers containing sulfone units are mixed, dissolved in a solvent, and stirred until completely dissolved to obtain a transparent solution. Then, an active end-capping agent and flexible dianhydride monomer are added in 3-6 batches, and the mixture is stirred at room temperature for 8 hours. During the reaction, solvent is added to adjust the solid content, resulting in a polyamic acid solution. Since the reaction is exothermic, the temperature of the reaction system gradually increases with the addition of the flexible dianhydride monomer, especially in high-solids-content polyamic acid solutions. Adding the flexible dianhydride monomer all at once can easily cause a rapid increase in the viscosity of the reaction system, leading to rod climbing. Adding the active end-capping agent all at once results in too many small molecular weight chains, leading to excessive subsequent crosslinking density and poor toughness. Therefore, the active end-capping agent and dianhydride monomer are added in batches to control the temperature, molecular weight, and viscosity changes of the polyamic acid.

[0030] Second polyimide layer In the second coating solution used, the diamine monomer of the benzimidazole-benzoxazole unit is 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine, which has weak polarity. When it reacts with rigid dianhydride monomers 4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, or 1,4,5,8-naphthalenetetracarboxylic dianhydride, the resulting second polyimide layer has a tensile strength of over 200 MPa, a tensile modulus of over 9 GPa, and an elongation at break of 5% to 11%.

[0031] Preparation of the second coating solution: The diamine monomer of the benzimidazole-benzoxazole unit is dissolved in a solvent and stirred at room temperature to ensure complete dispersion; then, an equimolar amount of rigid dianhydride monomer is added, and the system is reacted in an ice bath for 5 hours, followed by a further reaction at 25°C for 10 hours. Solvent needs to be replenished as needed during the reaction to ensure the stability of the reaction system.

[0032] Example 1

[0033] The high-modulus, high-adhesion metal-coated plate includes a metal layer, and a first polyimide layer and a second polyimide layer are sequentially stacked on one surface of the metal layer.

[0034] The first coating solution of the first polyimide layer comprises 2,2'-bibenzimidazole-5,5'-diamine, 4,4'-diaminodiphenyl sulfone, maleic anhydride and 4,4'-oxophthalic anhydride in a molar ratio of 0.82:0.2:0.08:1, and the solvent is N,N-dimethylacetamide. The solid content of the first coating solution is 25%.

[0035] The second coating solution for the second polyimide layer comprises 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine and equimolar amounts of 4,4'-biphenyltetracarboxylic dianhydride, with N,N-dimethylacetamide as the solvent, and a solid content of 10%.

[0036] The preparation method of high-modulus, high-adhesion metal-coated plate includes the following steps: S1: The first coating solution is prepared by the above method, and the active end-capping agent and flexible dianhydride monomer are added in 4 batches. S2: Prepare the second coating liquid using the method described above; S3: The surface of a metal plate is sequentially coated with a first coating liquid, a second coating liquid, heated to evaporate the solvent, and subjected to high-temperature thermal imidization. The temperature zones for the solvent evaporation are set sequentially as follows: 90℃, 110℃, 190℃, 190℃, 190℃, 190℃, each zone is 4m long, and the material feed rate is 6m / min. The temperature program for high-temperature thermal imidization is 100℃ / 2 h, 200℃ / 2 h, 250℃ / 2 h, 350℃ / 1 h. The temperature interval for the gradient temperature in the high-temperature thermal imidization temperature program is 30min, that is, the heating time between adjacent temperatures is 30min.

[0037] A metal-clad plate having a first polyimide layer and a second polyimide layer stacked sequentially is obtained. The first polyimide layer has a thickness of 15 μm, and the second polyimide layer has a thickness of 10 μm.

[0038] Example 2

[0039] Example 2 is based on Example 1, except that the solid content of the first coating liquid is 15%, the thickness of the first polyimide layer is 5 μm, the solid content of the second coating liquid remains unchanged, and the thickness of the second polyimide layer also remains unchanged.

[0040] Example 3

[0041] Example 3 is based on Example 1, except that the solid content of the first coating liquid is 30%, the thickness of the first polyimide layer is 50 μm, the solid content of the second coating liquid remains unchanged, and the thickness of the second polyimide layer also remains unchanged.

[0042] Example 4

[0043] Example 4 is based on Example 1, except that the first coating solution for the first polyimide layer comprises 2,2'-bibenzimidazole-5,5'-diamine, 4,4'-diaminodiphenyl sulfone, maleic anhydride, and 4,4'-oxophthalic anhydride in a molar ratio of 0.7:0.32:0.08:1, while other components remain unchanged. The second coating solution for the second polyimide layer remains unchanged. Other factors and processes remain unchanged.

[0044] Example 5

[0045] Example 5 is based on Example 1, except that the diamine monomer containing the sulfone group in the first coating solution is 4,4'-bis(4-aminophenoxy)diphenyl sulfone, while other components remain unchanged. The process also remains the same.

[0046] Example 6

[0047] Example 6 is based on Example 1, except that the second coating solution for the second polyimide layer comprises 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine and equimolar amounts of 1,4,5,8-naphthalenetetracarboxylic dianhydride, the solvent is N,N-dimethylacetamide, and the solid content of the second coating solution is 10%. Other factors and processes remain unchanged.

[0048] Example 7

[0049] Example 7 is based on Example 1, except that the molar amount of the active capping agent in the first coating solution is 11.5% of the molar amount of the flexible dianhydride monomer, while other components remain unchanged. The process also remains the same.

[0050] Comparative Example 1 Comparative Example 1 is based on Example 1, except that the first coating solution does not include diamine monomers containing sulfone groups, while other components remain unchanged. The process also remains the same.

[0051] Comparative Example 2 Comparative Example 2 is based on Example 1, except that the second coating liquid includes 2,2'-bibenzimidazole-5,5'-diamine and equimolar amounts of 4,4'-biphenyltetracarboxylic dianhydride.

[0052] Performance testing of the examples and comparative samples: 1. Tensile strength, elongation and modulus: Tested with a universal testing machine. The composite polyimide film sample without metal plate was cut into 100mm long * 10mm wide, and the tensile rate was 50.8mm / min.

[0053] 2. Peel strength: Cut the metal-coated plate sample into 250mm long * 10mm wide pieces. Use double-sided tape to attach the composite polyimide film to the aluminum plate. Use a universal testing machine to stretch the film at a 90° angle and test the peel strength between the metal plate and the composite polyimide film at a speed of 50.8mm / min. Record the values.

[0054] 3. Coefficient of thermal expansion: The composite polyimide film with metal-coated and demetal-coated plates was cut into 8mm long and 4mm wide pieces and tested with a Discovery TMA450 thermomechanical analyzer at a heating rate of 8℃ / min from 30℃ to 300℃. The average coefficient of thermal expansion from 30℃ to 300℃ was then calculated.

[0055] The performance test results of the examples and comparative examples are as follows:

[0056] Compared to Example 1, Example 2 has a reduced solid content in the first coating liquid, which negatively affects the crosslinking density of the first polyimide layer. Although it can improve toughness, it has a negative impact on the tensile strength and modulus of the composite polyimide film, increases the coefficient of expansion, and the adhesion to the metal plate remains unchanged.

[0057] Compared to Example 1, Example 4 shows an increase in the molar amount of 4,4'-diaminodiphenyl sulfone in the first polyimide layer. Although this can improve toughness, it has a negative impact on the tensile strength and modulus of the composite polyimide film, and also increases the coefficient of thermal expansion.

[0058] Compared to Example 1, the composite polyimide film obtained by 4,4'-bis(4-aminophenoxy)diphenyl sulfone in Example 5 has greater toughness, but its tensile strength and modulus are weakened.

[0059] Compared to Example 1, Example 7 shows that the molar amount of active end-capping agent in the first coating solution is too high, which increases the probability of polyamic acid forming short molecular chains, increases the brittleness of the first polyimide layer, and has a negative impact on elongation, tensile strength and modulus, as well as adhesion.

[0060] Compared to Example 1, Comparative Example 2 shows that the diamine monomers of the benzimidazole-benzoxazole unit and those containing benzimidazole units have similar structures, which improves the compatibility between the first and second polyimide layers. However, the diamine monomers of the benzimidazole-benzoxazole unit have better heat resistance and can maintain the performance stability of the polyimide film after high-temperature thermosetting. Using a diamine monomer containing benzimidazole units in the first polyimide layer is beneficial for improving adhesion to the metal plate.

[0061] The 2,2'-bibenzimidazole-5,5'-diamine in Example 1 has ordered and symmetrical benzimidazole, which improves the filling efficiency and close packing of the polymer molecular chains. Compared with the first polyimide layer formed by 2-(4-aminophenyl)-5-aminobenzimidazole, it has better high temperature resistance, tensile strength and modulus.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-modulus, high-adhesion coated metal plate, comprising a metal layer, characterized in that, A first polyimide layer and a second polyimide layer are sequentially stacked on one surface of the metal layer; The first coating liquid of the first polyimide layer includes a diamine monomer containing benzimidazole units, a diamine monomer containing sulfone units, an active end-capping agent, and a flexible dianhydride monomer; The second coating liquid of the second polyimide layer comprises a diamine monomer of a benzimidazole-benzoxazole unit and an equimolar rigid dianhydride monomer.

2. The high modulus, high adhesion coated metal sheet according to claim 1, characterized in that, The molar ratio of the total molar amount of the diamine monomer containing benzimidazole units and the diamine monomer containing sulfone units to the flexible dianhydride monomer in the first coating solution is (1.01~1.03):

1. The molar amount of the diamine monomer containing sulfone units accounts for 15%~30% of the total molar amount of the diamine monomer containing benzimidazole units and the diamine monomer containing sulfone units. The molar amount of the active capping agent is 6%~9% of the molar amount of the flexible dianhydride monomer.

3. The high-modulus, high-adhesion coated metal sheet according to claim 1 or 2, characterized in that, The diamine monomer containing the benzimidazole unit is 2,2'-bibenzimidazole-5,5'-diamine, and the diamine monomer containing the benzimidazole-benzoxazole unit is 2-(5-amino-1H-benzimidazole)-benzoxazole-5-amine.

4. The high-modulus, high-adhesion coated metal sheet according to claim 1 or 2, characterized in that, The diamine monomer containing the sulfone group is any one of 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, and 4,4'-bis(3-aminophenoxy)diphenyl sulfone.

5. The high-modulus, high-adhesion coated metal sheet according to claim 1 or 2, characterized in that, The active end-capping agents are maleic anhydride and 5-norbornene-2,3-dicarboxylic anhydride.

6. The high-modulus, high-adhesion coated metal sheet according to claim 1 or 2, characterized in that, The flexible dianhydride monomer is any one of 4,4'-oxobisphthalic anhydride and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride; the rigid dianhydride monomer is any one of 4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

7. The high-modulus, high-adhesion coated metal sheet according to claim 1 or 2, characterized in that, The first coating liquid has a solid content of 15% to 30%, and the second coating liquid has a solid content of 7% to 18%. Both the first coating liquid and the second coating liquid further include a solvent, which is any one of N,N-dimethylacetamide and N-methylpyrrolidone.

8. A method for preparing a high-modulus, high-adhesion metal-coated plate, characterized in that, Includes the following steps: S1: Prepare the first coating solution. After the two types of diamine monomers are completely dissolved, add the active end-capping agent and flexible dianhydride monomer in batches. S2: Prepare the second coating solution. After the diamine monomer containing the benzimidazole unit is completely dissolved, add the rigid dianhydride monomer. S3: A metal plate is sequentially coated with a first coating liquid, a second coating liquid, heated to evaporate the solvent, and subjected to high-temperature thermal imidization to obtain a metal-clad plate having a first polyimide layer and a second polyimide layer stacked sequentially.

9. The method for preparing a high-modulus, high-adhesion coated metal plate according to claim 8, characterized in that, The temperature for evaporating the solvent is 90~190℃; the temperature program for high-temperature thermal imidization is 100℃ / 2 h, 200℃ / 2 h, 250℃ / 2 h, 350℃ / 1 h; the gradient temperature interval heating time in the temperature program for high-temperature thermal imidization is 20~30 min.

10. The method for preparing a high-modulus, high-adhesion coated metal plate according to claim 8, characterized in that, The thickness of the first polyimide layer is 5~50 μm, and the thickness of the second polyimide layer is 5~50 μm.

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