Polyimide composite film, method for manufacturing the same, and flexible printed wiring board

Abstract

A polyimide composite film and its preparation method, and a flexible printed wiring board, belong to the field of membrane materials. The composite film includes at least three layers, namely a first surface layer, a non-thermoplastic polyimide layer, and a second surface layer. The non-thermoplastic polyimide layer is disposed between the first and second surface layers. The first and second surface layers are both thermoplastic polyimide layers, and the glass transition temperatures of the first and second surface layers are different. By controlling the difference in glass transition temperatures between the two surface layers of the polyimide composite film, the polyimide composite film has good dimensional stability.

Description

Technical Field

[0001] This application relates to the field of membrane materials, and more specifically, to a polyimide composite membrane and its preparation method, and a flexible printed wiring board. Background Technology

[0002] In recent years, with the rapid development of high performance, high functionality, and miniaturization of electronic devices, there is a growing demand for smaller and lighter electronic components. To meet these requirements, semiconductor packaging methods and wiring boards for mounting semiconductor components also need to possess high density, high functionality, and high performance.

[0003] Flexible printed circuit boards (FPCs) are essential electronic components. FPCs are circuit boards with excellent flexibility and adaptability, and due to their thinness, bendability, and rollability, they are widely used in consumer electronics, automobiles, medical devices, and other fields. FPC manufacturing typically uses a flexible, thin insulating film layer as the core film (also called the base film or substrate), usually a polyimide film layer. A metal foil layer is then bonded to the surface of this core film via a thermoforming process, separated by an adhesive layer composed of various adhesive materials, to create a flexible metal-clad laminate. Further, circuit patterns are formed on the flexible metal-clad laminate, and a cover layer (protective film) is formed on the surface of these circuit patterns, thus manufacturing the FPC.

[0004] In the photolithography process of copper-clad laminates or the mounting process of FPCs, various processes such as bonding, cutting, exposure, and etching are performed based on alignment marks set in the copper-clad laminate. The processing accuracy in these processes becomes important in maintaining the reliability of electronic devices equipped with FPCs. However, copper-clad laminates have a structure that stacks copper layers and polyimide film layers with different coefficients of thermal expansion. Therefore, stress is generated between the layers due to the difference in the coefficients of thermal expansion of the copper layer and the polyimide film layer. Some or all of this stress is relieved when the copper layer is etched for wiring, resulting in expansion and contraction, which leads to dimensional changes in the wiring pattern. Therefore, dimensional changes ultimately occur in the FPC stage, becoming a cause of poor contact between wirings or between wirings and terminals, reducing the reliability or yield of the circuit board. Therefore, dimensional stability is a very important characteristic for copper-clad laminates as circuit board materials, and the dimensional stability of the polyimide film is a key factor affecting the dimensional stability of copper-clad laminates. Summary of the Invention

[0005] This application provides a polyimide composite film and its preparation method, as well as a flexible printed wiring board, which can improve the dimensional stability of the polyimide composite film.

[0006] In a first aspect, embodiments of this application provide a polyimide composite film, the composite film comprising at least three layers, including a first surface layer, a non-thermoplastic polyimide layer and a second surface layer, the non-thermoplastic polyimide layer being disposed between the first surface layer and the second surface layer, the first surface layer and the second surface layer being both thermoplastic polyimide layers, and the glass transition temperatures of the first surface layer and the second surface layer being different.

[0007] In the technical solution of this application embodiment, by controlling the different glass transition temperatures of the two surfaces of the polyimide composite film, the first and second surfaces on the steel strip side and the air side are composited with the non-thermoplastic polyimide layer of the intermediate layer during the preparation process, thereby making the polyimide composite film have better dimensional stability.

[0008] As an optional implementation, the difference in glass transition temperature between the first and second surface layers is 20–40°C.

[0009] In the above implementation process, the difference in glass transition temperature between the first and second surface layers is an important factor affecting the dimensional stability of the polyimide composite film. By controlling the difference in glass transition temperature between the first and second surface layers to be 20-40℃ through the via, the dimensional stability of the polyimide composite film can be improved.

[0010] As an optional implementation, the glass transition temperature of the first surface layer is 220–260°C; and / or

[0011] The glass transition temperature of the second surface layer is 200–240 °C.

[0012] In the above implementation process, by controlling the glass transition temperature of the first surface layer to be 220–260°C and the glass transition temperature of the second surface layer to be 200–240°C, the polyimide composite film exhibits good dimensional stability. Simultaneously, the polyimide composite film also possesses good mechanical properties and thermodynamic stability.

[0013] As an optional implementation, the glass transition temperature of the non-thermoplastic polyimide layer is ≥360°C.

[0014] In the above implementation process, the glass transition temperature of the non-thermoplastic polyimide layer has a significant impact on the overall performance of the polyimide composite film. By controlling the glass transition temperature of the non-thermoplastic polyimide layer to ≥360℃, the polyimide composite film can have better mechanical and thermodynamic properties.

[0015] As an alternative implementation method, the composite film is prepared by co-extrusion.

[0016] Secondly, embodiments of this application provide a method for preparing a polyimide composite film, the method comprising:

[0017] Obtain at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids, wherein the thermoplastic polyamic acid includes a first thermoplastic polyamic acid and a second thermoplastic polyamic acid;

[0018] A composite film is prepared by combining at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids to obtain a preliminary product;

[0019] The initial product is subjected to imidization treatment to obtain a polyimide composite film. The composite film includes a first surface layer, a non-thermoplastic polyimide layer and a second surface layer. The non-thermoplastic polyimide layer is disposed between the first surface layer and the second surface layer. The raw material of the first surface layer includes a first thermoplastic polyamic acid, and the raw material of the second surface layer includes a second thermoplastic polyamic acid. The glass transition temperatures of the first surface layer and the second surface layer are different.

[0020] As an optional implementation, preparing a composite film from at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids includes:

[0021] At least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids are co-extruded from a composite slit die to obtain an intermediate with a multilayer structure;

[0022] The intermediate is placed on a receiving platform for casting, wherein the layer with a higher glass transition temperature formed in the intermediate by the first thermoplastic polyamic acid and the second thermoplastic polyamic acid is in contact with the receiving platform.

[0023] In the above implementation process, by having a layer with a higher glass transition temperature formed in the intermediate by the first thermoplastic polyamic acid and the second thermoplastic polyamic acid come into contact with the receiving platform, the dimensional stability of the polyimide composite film can be further improved.

[0024] As an alternative implementation, the thermoplastic polyamic acid is prepared by condensation polymerization of a first diamine and a first dianhydride; and / or

[0025] The first diamine includes at least one of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 4,4'-diaminodiphenyl ether; and / or

[0026] The primary dianhydride includes at least one of alicyclic dianhydrides and aromatic dianhydrides; and / or

[0027] Alicyclic dianhydrides include at least one of 1,2,4,5-cyclohexanetetracarboxylic dianhydride and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride; and / or

[0028] Aromatic dianhydrides include at least one of 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0029] As an optional implementation, the molar proportion of alicyclic monomers in the first diamine and the first dianhydride is 10% to 30%.

[0030] In the above implementation process, by controlling the molar proportion of alicyclic monomers in the first diamine and the first dianhydride to be 10% to 30%, the thermoplastic polyimide can have a better glass transition temperature, which is beneficial to the dimensional stability, mechanical properties and thermodynamic properties of the polyimide composite film.

[0031] As an optional implementation, the first diamine comprises 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, wherein the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane is 10% to 50% of the total molar amount of the first diamine and the first dianhydride.

[0032] In the above implementation process, by controlling the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane to be 10% to 50% of the total molar amount of the first diamine and the first dianhydride, the thermoplastic polyimide can have a better glass transition temperature, which is beneficial to the dimensional stability, mechanical properties and thermodynamic properties of the polyimide composite film.

[0033] As an alternative implementation, the non-thermoplastic polyamic acid is prepared by condensation polymerization of a second diamine and a second dianhydride; and / or

[0034] The second diamine includes at least one selected from p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 1,3-bis(4-aminophenoxy)benzene, 4,4'-diaminobenzoyl aniline, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4-aminophenyl benzoate; and / or

[0035] The second dianhydride includes at least one of phenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 4,4'-biphenyl ether dianhydride, 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, and p-phenylene-bisphenyltriester dianhydride.

[0036] Thirdly, embodiments of this application provide a flexible printed wiring board, which includes the polyimide composite film provided in the first aspect or the polyimide composite film prepared by the method provided in the second aspect. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 Schematic diagram of the polyimide composite film structure provided in the embodiments of this application Figure 1 ;

[0040] Figure 2 Schematic diagram of the polyimide composite film structure provided in the embodiments of this application Figure 2 ;

[0041] Figure 3 A flowchart illustrating the method provided in the embodiments of this application;

[0042] Figure 4 This is a schematic diagram of the system structure provided in the embodiments of this application;

[0043] Figure 5 This is a schematic diagram of the dimensional stability test process provided in an embodiment of this application.

[0044] Icons: 1-First reactor; 2-Second reactor; 3-Third reactor; 4-First tank; 5-Second tank; 6-Needle mixer; 7-Composite slit mold head; 8-Receiving platform; 9-Polyimide composite film; 91-First surface layer; 92-Non-thermoplastic polyimide layer; 93-Second surface layer. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0047] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0048] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b or c" or "at least one of a, b and c" can both mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0049] Copper-clad laminates (CCLs) consist of copper layers with different coefficients of thermal expansion (COPs) and polyimide films. This difference in COPs creates interlayer stress. Some or all of this stress is relieved during copper etching for wiring, resulting in expansion and contraction and dimensional changes in the wiring pattern. Consequently, dimensional changes occur during the FPC (Flexible Printed Circuit) stage, causing poor contact between wirings or between wirings and terminals, thus reducing the reliability or yield of the circuit board. Therefore, dimensional stability is a crucial characteristic for CCLs as circuit board materials, and the dimensional stability of the polyimide film is a key factor affecting the dimensional stability of CCLs.

[0050] Therefore, this application intends to provide a polyimide composite film and a method for preparing the same, which can improve the dimensional stability of the polyimide composite film.

[0051] Figure 1 and Figure 2 This is a schematic diagram of the polyimide composite film structure provided in the embodiments of this application, as shown below. Figure 1 and Figure 2 As shown, this application provides a polyimide composite film, which includes at least three layers. The composite film includes a first surface layer 91, a non-thermoplastic polyimide layer 92, and a second surface layer 93. The non-thermoplastic polyimide layer 92 is disposed between the first surface layer 91 and the second surface layer 93. The first surface layer 91 and the second surface layer 93 are both thermoplastic polyimide layers, and the glass transition temperatures of the first surface layer 91 and the second surface layer 93 are different.

[0052] The composite film comprising at least three layers means that the composite film has at least three layers. For example, the number of layers can be 3, 4, 5, 6, 7, 8, etc. The first surface layer 91 and the second surface layer 93 refer to the two layers furthest apart in the polyimide composite film 9, that is, the two layers located on the two surfaces of the polyimide composite film 9. For example, when the polyimide composite film 9 has three layers, please refer to [further details]. Figure 1 The polyimide composite film 9 comprises a first surface layer 91, a non-thermoplastic polyimide layer 92, and a second surface layer 93, which are sequentially stacked. When the polyimide composite film 9 has three or more layers, please refer to [further details needed]. Figure 2 The first surface layer 91 and the second surface layer 93 are located on the two outermost sides. The remaining layers, including the non-thermoplastic polyimide layer 92, are located between the first surface layer 91 and the second surface layer 93. The positional relationship between the non-thermoplastic polyimide layer 92 and the remaining layers is not limited.

[0053] The glass transition temperature refers to the temperature at which an amorphous polymer (including the non-crystalline portion of a crystalline polymer) transitions from a glassy state to a rubbery state, or vice versa. It is the lowest temperature at which the macromolecular chains of an amorphous polymer can move freely. It can be determined using instruments and methods known in the art. For example, it can be determined according to GB / T 29611-2013 "Determination of Glass Transition Temperature of Raw Rubber - Differential Scanning Calorimetry (DSC)," using a Mettler-Toledo DSC-3 differential scanning calorimeter.

[0054] Non-thermoplastic polyimides typically refer to polyimides with a glass transition temperature higher than 350°C. Thermoplastic polyimides typically refer to polyimides with a glass transition temperature lower than 250°C.

[0055] The polyimide composite film 9 exhibits good dimensional stability by controlling the different glass transition temperatures of its two surfaces.

[0056] In some embodiments, the difference in glass transition temperature between the first surface layer 91 and the second surface layer 93 is 20–40°C. This difference in glass transition temperature is a crucial factor affecting the dimensional stability of the polyimide composite film 9. Controlling the glass transition temperature difference between the first surface layer 91 and the second surface layer 93 to 20–40°C via through-holes can effectively improve the dimensional stability of the polyimide composite film 9. For example, the difference in glass transition temperature between the first surface layer 91 and the second surface layer 93 can be 20°C, 25°C, 30°C, 35°C, or 40°C, or any value within the range of 20–40°C.

[0057] In some embodiments, the glass transition temperature of the first surface layer 91 is 220–260°C; the glass transition temperature of the second surface layer 93 is 200–240°C. By controlling the glass transition temperature of the first surface layer 91 to 220–260°C and the glass transition temperature of the second surface layer 93 to 200–240°C, the polyimide composite film 9 exhibits good dimensional stability. Simultaneously, the polyimide composite film 9 also exhibits good mechanical properties and thermodynamic stability. For example, the glass transition temperature of the first surface layer 91 can be 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, or 260°C, or any value within the range of 220–260°C. The glass transition temperature of the second surface layer 93 can be 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃ or 240℃, or any value within the range of 200 to 240℃.

[0058] In some embodiments, the glass transition temperature of the non-thermoplastic polyimide layer 92 is ≥360°C. The glass transition temperature of the non-thermoplastic polyimide layer 92 has a significant impact on the overall performance of the polyimide composite film 9. By controlling the glass transition temperature of the non-thermoplastic polyimide layer 92 to be ≥360°C, the polyimide composite film 9 exhibits better mechanical and thermodynamic properties. For example, the glass transition temperature of the non-thermoplastic polyimide layer 92 can be 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, or 420°C, or any value within the range ≥360°C.

[0059] In some embodiments, the composite film is prepared by a co-extrusion process.

[0060] Figure 3 A flowchart of the method provided in the embodiments of this application is shown below. Figure 3 As shown in the embodiment of this application, a method for preparing a polyimide composite film 9 is provided, the method comprising:

[0061] S1. Obtain at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids, wherein the thermoplastic polyamic acid includes a first thermoplastic polyamic acid and a second thermoplastic polyamic acid;

[0062] In some embodiments, the thermoplastic polyamic acid is prepared by condensation polymerization of a first diamine and a first dianhydride; wherein the first diamine includes at least one of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 4,4'-diaminodiphenyl ether; the first dianhydride includes at least one of alicyclic dianhydride and aromatic dianhydride; the alicyclic dianhydride includes at least one of 1,2,4,5-cyclohexanetetracarboxylic dianhydride and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride; and the aromatic dianhydride includes at least one of 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[0063] In some embodiments, the molar percentage of alicyclic monomers in the first diamine and the first dianhydride is 10% to 30%. By controlling the molar percentage of alicyclic monomers in the first diamine and the first dianhydride to be 10% to 30%, the thermoplastic polyimide can have a better glass transition temperature, which is beneficial to the dimensional stability, mechanical properties, and thermodynamic properties of the polyimide composite film 9. For example, the molar percentage of alicyclic monomers in the first diamine and the first dianhydride can be 10%, 15%, 20%, 25%, or 30%, or any value within the range of 10% to 30%.

[0064] In some embodiments, the first diamine comprises 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane is 10% to 50% of the total molar amount of the first diamine and the first dianhydride. By controlling the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane to be 10% to 50% of the total molar amount of the first diamine and the first dianhydride, the thermoplastic polyimide can have a better glass transition temperature, which is beneficial to the dimensional stability, mechanical properties, and thermodynamic properties of the polyimide composite film 9. Exemplarily, the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% of the total molar amount of the first diamine and the first dianhydride, or it can be 10% to 50%.

[0065] In some embodiments, the non-thermoplastic polyamic acid is prepared by condensation polymerization of a second diamine and a second dianhydride; the second diamine includes at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 1,3-bis(4-aminophenoxy)benzene, 4,4'-diaminobenzoylaniline, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4-aminophenyl benzoate; the second dianhydride includes at least one of phenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and p-phenylene-bisphenyltriester dianhydride.

[0066] S2. Prepare a composite film by combining at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids to obtain a preliminary product.

[0067] In some embodiments, preparing a composite film from at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids includes:

[0068] S2.1. At least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids are co-extruded from the composite slit die 7 to obtain an intermediate with a multilayer structure;

[0069] S2.2. The intermediate is placed on the receiving platform 8 for casting, wherein the layer with a higher glass transition temperature formed in the intermediate by the first thermoplastic polyamic acid and the second thermoplastic polyamic acid is in contact with the receiving platform 8.

[0070] By having a layer with a higher glass transition temperature, formed from the first and second thermoplastic polyamic acids in the intermediate, in contact with the substrate 8, the dimensional stability of the polyimide composite film 9 can be further improved. This improvement is particularly significant when the difference in glass transition temperature between the first surface layer 91 and the second surface layer 93 is large, for example, greater than 25°C.

[0071] S4. The initial product is subjected to imidization treatment to obtain a polyimide composite film 9. The composite film includes a first surface layer 91, a non-thermoplastic polyimide layer 92, and a second surface layer 93. The non-thermoplastic polyimide layer 92 is disposed between the first surface layer 91 and the second surface layer 93. The raw material of the first surface layer 91 includes a first thermoplastic polyamic acid, and the raw material of the second surface layer 93 includes a second thermoplastic polyamic acid. The glass transition temperatures of the first surface layer and the second surface layer are different.

[0072] The present application is 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 application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0073] Example 1 of the preparation of thermoplastic polyamic acid

[0074] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 878.89 kg of N,N dimethylformamide (DMF) is added. After reaching the set temperature, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 81.2 kg of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 5.02 kg of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) is added, and polymerization continues for another 4 hours. Then, 1.26 kg of HPMDA is dissolved in 16.18 kg of DMF. The HPMDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0075] Example 2 of the preparation of thermoplastic polyamic acid

[0076] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 855.09 kg of N,N dimethylformamide (DMF) is added. After the temperature is reached, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 63.16 kg of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 17.57 kg of 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) is added, and polymerization continues for another 4 hours. Then, 1.26 kg of HPMDA is dissolved in 16.18 kg of DMF. The HPMDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0077] Example 3 of the preparation of thermoplastic polyamic acid

[0078] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 883.43 kg of N,N dimethylformamide (DMF) is added. After reaching the set temperature, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 81.2 kg of 3,3',4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 6.86 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added, and polymerization continues for another 4 hours. Then, 1.72 kg of HBPDA is dissolved in 22.11 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0079] Example 4 of the preparation of thermoplastic polyamic acid

[0080] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 879.56 kg of N,N dimethylformamide (DMF) is added. After the temperature is reached, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 63.16 kg of 3,3',4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 24.01 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added and polymerization continues for another 4 hours. Then, 1.72 kg of HBPDA is dissolved in 22.11 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0081] Example 5 of the preparation of thermoplastic polyamic acid

[0082] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 887.6 kg of N,N-dimethylformamide (DMF) is added. After reaching the set temperature, 67.73 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and 33.04 kg of 4,4'-diaminodiphenyl ether (ODA) are added for dissolution. After 1 hour, 95.7 kg of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 8.09 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added, and polymerization continues for another 4 hours. Then, 2.02 kg of HBPDA is dissolved in 26.06 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0083] Example 6 of the preparation of thermoplastic polyamic acid

[0084] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 883.04 kg of N,N-dimethylformamide (DMF) is added. After the temperature is reached, 67.73 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and 33.04 kg of 4,4'-diaminodiphenyl ether (ODA) are added for dissolution. After 1 hour, 3,3',4,4'-benzophenone tetracarboxylic acid is added. 74.44 kg of bis(bicyclohexyl)-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) was added after 4 hours of polymerization. The polymerization continued for another 4 hours. Then, 2.02 kg of HBPDA was dissolved in 26.06 kg of DMF. The HBPDA solution was gradually added until the viscosity reached 1000 poise, resulting in a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the solution was heated to 35°C and held for 4 hours.

[0085] Example 7 of the preparation of thermoplastic polyamic acid

[0086] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 867.65 kg of N,N dimethylformamide (DMF) is added. After the temperature is reached, 78.09 kg of diamine 4,4'-diaminodiphenyl ether (ODA) is added for dissolution. After 1 hour, 113.1 kg of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 9.56 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added and polymerization continues for another 4 hours. Then, 2.39 kg of HBPDA is dissolved in 30.79 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0087] Example 8 of the preparation of thermoplastic polyamic acid

[0088] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 862.28 kg of N,N dimethylformamide (DMF) is added. After reaching the set temperature, 78.09 kg of diamine 4,4'-diaminodiphenyl ether (ODA) is added for dissolution. After 1 hour, 87.97 kg of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is added. After 4 hours of polymerization, 33.45 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added and polymerization continues for another 4 hours. Then, 2.39 kg of HBPDA is dissolved in 30.79 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0089] Example 9 of the preparation of thermoplastic polyamic acid

[0090] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 883.98 kg of N,N dimethylformamide (DMF) is added. After the temperature is reached, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 88.42 kg of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA) is added. After polymerization for 8 hours, 1.8 kg of BTDA is dissolved in 23.06 kg of DMF. The BTDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0091] Example 10 of the preparation of thermoplastic polyamic acid

[0092] A thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 865.51 kg of N,N dimethylformamide (DMF) is added. After the temperature is reached, 114.94 kg of diamine 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is added for dissolution. After 1 hour, 84.05 kg of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) is added. After polymerization for 8 hours, 1.72 kg of HBPDA is dissolved in 22.10 kg of DMF. The HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0093] Example 1 of preparation of non-thermoplastic polyamic acid

[0094] A non-thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 878.56 kg of N-dimethylformamide (DMF) is added. After reaching the set temperature, 52.06 kg of diamine 4,4'-diaminodiphenyl ether (ODA) and 25.43 kg of 4-aminobenzoic acid 4-aminophenyl ester (APAB) are added for dissolution. After 1 hour, 74.31 kg of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is added. After 4 hours of polymerization, 51.07 kg of p-phenylene-bis(phenyltriterpenoid) dianhydride (TAHQ) is added, and polymerization continues for another 4 hours. Then, 2.19 kg of BPDA is dissolved in 28.17 kg of DMF. HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0095] Example 2 of preparation of non-thermoplastic polyamic acid

[0096] A non-thermoplastic polyamic acid is prepared as follows: The polymerization reactor temperature is set to ≤5℃. 878.85 kg of N,N dimethylformamide (DMF) is added. After reaching the set temperature, 66.08 kg of diamine 4,4'-diaminodiphenyl ether (ODA) and 15.29 kg of p-phenylenediamine (PDA) are added and dissolved. After 1 hour, 94.32 kg of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is added. After 4 hours of polymerization, 28.32 kg of pyromellitic dianhydride (PMDA) is added and polymerization continues for another 4 hours. Then, 2.77 kg of BPDA is dissolved in 35.75 kg of DMF, and HBPDA solution is gradually added until the viscosity reaches 1000 poise, yielding a thermoplastic polyamic acid solution with a solid content of 18.44%. Finally, the temperature is raised to 35℃ and held for 4 hours.

[0097] The following example illustrates the preparation of a three-layer polyimide composite film. All examples and comparative examples use the following... Figure 4 The system shown is used for the preparation of polyimide composite films. Please refer to [link / reference]. Figure 4 The system includes a first reactor 1, a second reactor 2, a third reactor 3, a first tank 4, a second tank 5, a needle mixer 6, a composite slit die 7, and a receiving platform 8. The first reactor 1, second reactor 2, third reactor 3, first tank 4, and second tank 5 are connected to multiple slits of the composite slit die 7. The first tank 4 and second tank 5 are connected to the same slit of the composite slit die 7 via the needle mixer 6 and the third reactor 3. The receiving platform 8 is located below the composite slit die 7 to receive the intermediate material extruded from the composite slit die 7. The receiving platform 8 can be a conveyor belt made of steel. In all embodiments and comparative examples, the thickness of the thermoplastic polyimide layers on both sides is controlled at 2.5 μm, and the thickness of the non-thermoplastic polyimide layer in the middle is controlled at 20 μm. The maximum imidization temperature in all embodiments and comparative examples is controlled at 370°C. The specific imidization process can be as follows: room temperature to 160℃, heating rate of 0.5℃ to 2℃, holding time of 30min to 90min; then 160℃ to 220℃, heating rate of 1℃ to 3℃, holding time of 30min to 90min; then 220℃ to 280℃, heating rate of 1℃ to 5℃, holding time of 15min to 60min; then 280℃ to 370℃, heating rate of 1℃ to 10℃, holding time of 5min to 30min; after imidization, it can also be annealed at a temperature of 300℃ to 400℃ for a time of 30min to 60min.

[0098] Example 1

[0099] The thermoplastic polyamic acid provided in Thermoplastic Polyamic Acid Preparation Example 1 and Thermoplastic Polyamic Acid Preparation Example 6 were transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Non-thermoplastic Polyamic Acid Preparation Example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0100] Example 2

[0101] The thermoplastic polyamic acid provided in thermoplastic polyamic acid preparation example 2 and thermoplastic polyamic acid preparation example 5 were transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in non-thermoplastic polyamic acid preparation example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0102] Example 3

[0103] The thermoplastic polyamic acid provided in thermoplastic polyamic acid preparation example 3 and thermoplastic polyamic acid preparation example 4 were transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in non-thermoplastic polyamic acid preparation example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0104] Example 4

[0105] The thermoplastic polyamic acid provided in Example 4 and Example 3 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0106] Example 5

[0107] The thermoplastic polyamic acid provided in Example 5 and Example 2 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0108] Example 6

[0109] The thermoplastic polyamic acid provided in Preparation Example 6 and Preparation Example 1 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Preparation Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0110] Example 7

[0111] The thermoplastic polyamic acid provided in Preparation Example 1 and Preparation Example 2 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Preparation Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0112] Example 8

[0113] The thermoplastic polyamic acid provided in Preparation Example 2 and Preparation Example 1 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Preparation Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0114] Example 9

[0115] The thermoplastic polyamic acid provided in Example 4 and Example 10 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0116] Example 10

[0117] The thermoplastic polyamic acid provided in thermoplastic polyamic acid preparation example 10 and thermoplastic polyamic acid preparation example 4 were transferred to the first reactor 1 and the second reactor 2, respectively, and the non-thermoplastic polyamic acid provided in non-thermoplastic polyamic acid preparation example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0118] Example 11

[0119] The thermoplastic polyamic acid provided in thermoplastic polyamic acid preparation example 4 and thermoplastic polyamic acid preparation example 9 were transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in non-thermoplastic polyamic acid preparation example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0120] Example 12

[0121] The thermoplastic polyamic acid provided in Example 9 and Example 4 was transferred to the first reactor 1 and the second reactor 2, respectively. The non-thermoplastic polyamic acid provided in Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0122] Comparative Example 1

[0123] The thermoplastic polyamic acid provided in Example 7 was transferred to the first reactor 1 and the second reactor 2, respectively, and the non-thermoplastic polyamic acid provided in Example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0124] Comparative Example 2

[0125] The thermoplastic polyamic acid provided in Example 8 was transferred to the first reactor 1 and the second reactor 2, respectively, and the non-thermoplastic polyamic acid provided in Example 1 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4, and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0126] Comparative Example 3

[0127] The thermoplastic polyamic acid provided in Example 9 was transferred to the first reactor 1 and the second reactor 2, respectively, and the non-thermoplastic polyamic acid provided in Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0128] Comparative Example 4

[0129] The thermoplastic polyamic acid provided in Example 10 was transferred to the first reactor 1 and the second reactor 2, respectively, and the non-thermoplastic polyamic acid provided in Example 2 was transferred to the third reactor 3. The reactor temperature was set to 0°C. The chemical curing agent was placed in the first tank 4 and the solvent was placed in the second tank 5. The materials in the first tank 4 and the second tank 5 were mixed with the materials in the third reactor 3 through the needle mixer 6 and then flowed together with the materials in the first reactor 1 and the second reactor 2 into the composite slit die 7 for extrusion to obtain a polyimide three-layer gel film (initial product). After imidization and biaxial stretching, a polyimide composite film was obtained.

[0130] Dimensional stability tests were performed on the polyimide composite films provided in each embodiment and comparative example. The dimensional stability test can be performed with reference to standard IPC TM 650 2.2.4, and the specific method is as follows:

[0131] 1. Sample taken: composite membrane with dimensions of 270mm × 290mm;

[0132] 2. Punching: Use a punch to make a cross mark at each of the four corners of the sample. Label these points A, B, C, and D respectively. AB and CD represent the MD direction, and AC and BD represent the TD direction. (See [reference needed]) Figure 5 ;

[0133] 3. Use a dimension measuring instrument to measure and record the distances between the four points A, B, C, and D, and record the data results;

[0134] 4. Place the sample in an oven at 150℃ for 30 minutes; cool to room temperature (23℃±2℃) and humidity (50%±5%) for 24 hours.

[0135] 5. Re-measure the distances between points A, B, C, and D using a dimensional measuring instrument;

[0136] 6. Calculate the dimensional changes based on the values ​​measured on both sides:

[0137]

[0138]

[0139] in,

[0140] MD = Percentage of dimensional change in the machining direction;

[0141] TD = Percentage change in vertical dimension;

[0142] I = Initial test results;

[0143] F = Final measurement result;

[0144] AB = the distance between points A and B;

[0145] AC = the distance between points A and C;

[0146] CD = the distance between points C and D;

[0147] BD = the distance between points B and D.

[0148] The parameter control and test results for each embodiment and comparative example are shown in the table below:

[0149]

[0150]

[0151]

[0152] As can be seen from the data in the table above, by comparing the data of each embodiment and comparative example, it can be concluded that when the glass transition temperatures of the two surfaces of the polyimide composite film are different, the polyimide composite film has good dimensional stability, and the dimensional stability can be controlled below -0.03%.

[0153] Comparison of data from Examples 2 and 5, Examples 3 and 4, and Examples 7 and 8 shows that when the layer with a higher glass transition temperature formed by the thermoplastic polyimide in the intermediate comes into contact with the substrate, and the difference in glass transition temperature between the two thermoplastic polyimides is greater than 25°C, the dimensional stability of the polyimide composite film is significantly improved.

[0154] The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A polyimide composite film, characterized in that, The composite film comprises at least three layers, including a first surface layer, a non-thermoplastic polyimide layer, and a second surface layer. The non-thermoplastic polyimide layer is disposed between the first surface layer and the second surface layer. Both the first surface layer and the second surface layer are thermoplastic polyimide layers, and the glass transition temperatures of the first surface layer and the second surface layer are different. The difference between the glass transition temperatures of the first surface layer and the second surface layer is 20~40℃. The glass transition temperature of the first surface layer is 220~260℃, and the glass transition temperature of the second surface layer is 200~240℃.

2. The polyimide composite film according to claim 1, characterized in that, The glass transition temperature of the non-thermoplastic polyimide layer is ≥360℃.

3. The polyimide composite film according to claim 1, characterized in that, The composite film is prepared by co-extrusion process.

4. A method for preparing a polyimide composite film, characterized in that, The method includes: To obtain at least one non-thermoplastic polyamic acid and at least two thermoplastic polyamic acids, wherein the thermoplastic polyamic acid comprises a first thermoplastic polyamic acid and a second thermoplastic polyamic acid; A composite film is prepared by combining at least one of the non-thermoplastic polyamic acids and at least two of the thermoplastic polyamic acids to obtain a preliminary product; The initial product is subjected to imidization treatment to obtain a polyimide composite film. The composite film includes a first surface layer, a non-thermoplastic polyimide layer, and a second surface layer. The non-thermoplastic polyimide layer is disposed between the first surface layer and the second surface layer. The raw material of the first surface layer includes a first thermoplastic polyamic acid, and the raw material of the second surface layer includes a second thermoplastic polyamic acid. The glass transition temperatures of the first surface layer and the second surface layer are different, and the difference between the glass transition temperatures of the first surface layer and the second surface layer is 20~40℃. The glass transition temperature of the first surface layer is 220~260℃, and the glass transition temperature of the second surface layer is 200~240℃.

5. The method for preparing the polyimide composite film according to claim 4, characterized in that, The step of preparing a composite film from at least one of the non-thermoplastic polyamic acids and at least two of the thermoplastic polyamic acids includes: At least one of the non-thermoplastic polyamic acids and at least two of the thermoplastic polyamic acids are co-extruded from a composite slit die to obtain an intermediate with a multilayer structure; The intermediate is placed on a receiving platform for casting, wherein the layer with a higher glass transition temperature formed in the intermediate by the first thermoplastic polyamic acid and the second thermoplastic polyamic acid is in contact with the receiving platform.

6. The method for preparing the polyimide composite film according to claim 4, characterized in that, The thermoplastic polyamic acid is prepared by condensation polymerization of a diamine and a dianhydride; and / or The first diamine comprises at least one of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 4,4'-diaminodiphenyl ether; and / or The first dianhydride includes at least one of alicyclic dianhydrides and aromatic dianhydrides; and / or The alicyclic dianhydride includes at least one selected from 1,2,4,5-cyclohexanetetracarboxylic dianhydride and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride; and / or The aromatic dianhydride includes at least one of 4,4'-(4,4'-isopropyldiphenoxy) phthalic anhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

7. The method for preparing the polyimide composite film according to claim 6, characterized in that, The molar percentage of alicyclic monomers in the first diamine and the first dianhydride is 10% to 30%.

8. The method for preparing the polyimide composite film according to claim 6, characterized in that, The first diamine comprises 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, wherein the molar amount of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane is 10% to 50% of the total molar amount of the first diamine and the first dianhydride.

9. The method for preparing the polyimide composite film according to claim 4, characterized in that, The non-thermoplastic second polyamic acid is prepared by condensation polymerization of a second diamine and a second dianhydride; and / or The second diamine includes at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 1,3-bis(4-aminophenoxy)benzene, 4,4'-diaminobenzoylaniline, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, and 4-aminophenyl benzoate; and / or The second dianhydride includes at least one of phenyltetracarboxylic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 4,4'-biphenyl ether dianhydride, 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, and p-phenylene-bisphenyltriester dianhydride.

10. A flexible printed wiring board, characterized in that, The flexible printed wiring board comprises the polyimide composite film according to any one of claims 1 to 3 or the polyimide composite film prepared by the method according to any one of claims 4 to 9.

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