Polyimide film and preparation method thereof

Abstract

The invention provides a polyimide film and a preparation method thereof. The preparation method of the polyimide film comprises the following steps: mixing cyclodextrin, an inorganic nano material and water, stirring for a certain time to form an inclusion compound, removing water, and adding a polar aprotic solvent to form an inclusion compound solution I; mixing a polar aprotic solvent containing a diamine monomer with the inclusion compound solution I to obtain an inclusion compound solution II; mixing the inclusion compound solution II with a dianhydride monomer to obtain a reaction system; carrying out polymerization reaction on the reaction system to obtain a polyamide acid solution; and preparing the polyimide film by using the polyamide acid solution. On the basis of ensuring the appearance and mechanical properties of the polyimide film, the thermal expansion coefficient of the polyimide film is reduced, and the thermal stability of the polyimide film is improved.

Description

Technical Field

[0001] This invention belongs to the field of polyimide film preparation technology, specifically relating to a polyimide film and its preparation method. Background Technology

[0002] Polyimide films possess excellent high and low temperature resistance, mechanical properties, insulation properties, and chemical stability, and are widely used in electronics, microelectronics, displays, aerospace, and new energy fields. As an important flexible substrate and interlayer node material, polyimide films come into contact with other materials such as glass and copper foil during device fabrication. After high-temperature processing, significant thermal stress often forms at the interface between these materials, causing dimensional deformation problems such as delamination and warping, severely affecting device performance and reliability. The generation of thermal stress is closely related to the thermal expansion behavior of the two materials during heating. The coefficient of thermal expansion (CTE) of inorganic or metallic materials is typically around 5-15 ppm / ℃, while most polyimide film materials have a higher CTE. This mismatch in CTE leads to significant residual stress at the contact interface at high temperatures, resulting in varying degrees of thermal deformation. Therefore, developing polyimide films with low CTE that match the conductive layer of the packaging circuit is of great significance. Methods to reduce the CTE of polyimide mainly include designing the main chain molecular structure and doping with inorganic nanomaterials.

[0003] One of the most important methods in designing the main chain molecular structure is to introduce linear rigid units, such as spirocyclic and caloric structures, into the molecular backbone. These structures can disrupt the regularity of the molecules, thereby reducing the coefficient of thermal expansion of polyimide. While the introduction of rigid monomers can reduce the coefficient of thermal expansion of the film, it also leads to greater brittleness and makes the film difficult to manufacture.

[0004] Regarding nanomaterial doping, for example, adding carbon nanotubes (CNTs) to polyimide results in the lowest CTE (Coefficient of Thermal Expansion) in the composite film when the CNT content is 0.1%, indicating that the addition of carbon nanotubes can improve the thermal stability of polyimide. Another example is the effective combination of polyimide with surface-hydroxylated modified silica, resulting in a polyimide film with a low coefficient of thermal expansion. While nanomaterial doping can improve the thermal and dimensional stability of materials, nanomaterials are often inorganic. Uneven dispersion and aggregation of inorganic materials in polyimide can lead to poor film appearance and reduced overall mechanical properties.

[0005] Therefore, there is an urgent need to study technical solutions that can improve the dimensional stability of polyimide films while maintaining their overall performance (mainly appearance and mechanical properties), especially their dimensional stability at higher temperatures and over a wider temperature range. Summary of the Invention

[0006] The purpose of this invention is to provide a technical solution that can reduce the coefficient of thermal expansion and improve the thermal stability of polyimide films while ensuring their appearance and mechanical properties.

[0007] To achieve the above objectives, the present invention provides the following technical solution.

[0008] In a first aspect, the present invention provides a method for preparing a polyimide film, wherein the preparation method includes:

[0009] Cyclodextrin, inorganic nanomaterials, and water were mixed and stirred for a certain period of time to form an inclusion complex. The water was removed, and a polar aprotic solvent was added to form inclusion complex solution I. A polar aprotic solvent containing a diamine monomer was mixed with inclusion complex solution I to obtain inclusion complex solution II.

[0010] The inclusion complex solution II was mixed with the dianhydride monomer to obtain the reaction system; the reaction system underwent a polymerization reaction to obtain a polyamic acid solution.

[0011] Polyimide films were prepared using polyamic acid solutions.

[0012] Cyclodextrins (CDs) are a class of cyclic oligosaccharides composed of glucose molecules linked by α-1,4-glycosidic bonds, possessing a unique cyclic structure. They are typically classified as α-CD, β-CD, and γ-CD, composed of 6, 7, and 8 glucose molecules, respectively. The molecular structure of cyclodextrins results in a hydrophobic internal cavity and a hydrophilic external surface, a property that allows them to form inclusion complexes with various organic compounds. The method for preparing polyimide films provided in this invention fully utilizes the strong inclusion ability of cyclodextrins.

[0013] In the polyimide film preparation method provided by this invention, cyclodextrin and inorganic nanomaterials are added simultaneously. The inclusion of cyclodextrin with the inorganic nanomaterials prevents the agglomeration of the inorganic nanomaterials, thus solving the problem of insufficient appearance and mechanical properties of the polyimide film caused by the agglomeration of inorganic nanomaterials. Furthermore, the inclusion of cyclodextrin with the polyimide molecular chains restricts the movement of the molecular chains to a certain extent, increases the rigidity of the molecular chains, improves the thermal stability of the polyimide film, and reduces the coefficient of thermal expansion of the polyimide film. With the cooperation of cyclodextrin, the inorganic nanomaterials are uniformly doped into the polyimide film, improving the dimensional stability of the polyimide film and reducing its coefficient of thermal expansion. In short, the polyimide film preparation method provided by this invention, through the combination of cyclodextrin and inorganic nanomaterials, achieves the goal of reducing the coefficient of thermal expansion and improving the thermal stability of the polyimide film while ensuring its appearance and mechanical properties.

[0014] According to the specific implementation of the first aspect, when cyclodextrin, inorganic nanomaterials and water are mixed, the order of addition is not important, as long as they can be evenly dispersed; preferably, cyclodextrin and water are mixed first, and then inorganic nanomaterials are added.

[0015] According to a specific embodiment of the first aspect, the cyclodextrin can be selected from existing types of cyclodextrin; preferably, the cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin and derivatives of cyclodextrin; more preferably, the cyclodextrin includes β-cyclodextrin and / or γ-cyclodextrin.

[0016] According to the specific implementation of the first aspect, the inorganic nanomaterial can be any existing type of inorganic nanomaterial; preferably, the inorganic nanomaterial includes at least one of graphene, carbon nanotubes (CNTs), silicon dioxide, silicon carbide, zirconium oxide and boron nitride (BN); more preferably, the inorganic nanomaterial includes carbon nanotubes and / or silicon dioxide.

[0017] According to the specific embodiments of the first aspect, the diamine can be any existing type of diamine; preferably, the diamine includes at least one of aromatic diamine and aliphatic diamine; more preferably, the diamine includes at least one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, ethylenediamine and 1,6-hexanediamine.

[0018] According to the specific embodiments of the first aspect, the polar aprotic solvent in the inclusion solution I and the polar aprotic solvent containing the diamine monomer can be independently selected from existing types of polar aprotic solvents; preferably, the polar aprotic solvent in the inclusion solution I includes at least one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; preferably, the polar aprotic solvent containing the diamine monomer includes at least one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

[0019] According to the specific implementation of the first aspect, the dianhydride can be any existing type of dianhydride; preferably, the dianhydride includes at least one of aromatic dianhydride and aliphatic dianhydride; more preferably, the dianhydride includes at least one of pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride and cyclopentanetetracarboxylic dianhydride.

[0020] According to the specific implementation of the first aspect, preferably, the molar ratio of cyclodextrin, diamine, and dianhydride is (0.1-0.6):1:(1-1.1); preferably, the molar ratio of cyclodextrin, diamine, and dianhydride is (0.2-0.4):1:(1-1.05).

[0021] According to a specific embodiment of the first aspect, preferably, the mass of the inorganic nanomaterial is 0.5%-1.5% of the total mass of the diamine and dianhydride.

[0022] According to a specific implementation of the first aspect, preferably, the mass content of the polar aprotic solvent in the reaction system is 0.7-0.9.

[0023] According to a specific embodiment of the first aspect, preferably, the mass content of the polar aprotic solvent in the inclusion complex solution I is 0.6-0.9%.

[0024] According to a specific embodiment of the first aspect, preferably, the mass content of the polar aprotic solvent containing the diamine monomer is 0.6-0.9%.

[0025] According to the specific implementation of the first aspect, preferably, the reaction temperature for the polymerization reaction of the reaction system is 15-30°C.

[0026] According to the specific implementation of the first aspect, preferably, the reaction time for the polymerization reaction in the reaction system is 1-8 hours.

[0027] According to a specific embodiment of the first aspect, preferably, the solid content in the polyamic acid solution is 10%-30%.

[0028] According to a specific embodiment of the first aspect, preferably, the preparation of a polyimide film using a polyamic acid solution includes:

[0029] The polyamic acid solution is coated, and then vacuum degassing, vacuum heat treatment, demolding, and vacuum drying are performed sequentially to obtain the polyimide film.

[0030] More preferably, the temperature for vacuum degassing is 80-100℃;

[0031] More preferably, the vacuum degassing time is 3-12 hours; even more preferably, the vacuum degassing time is 5-8 hours.

[0032] More preferably, the vacuum heat treatment process is as follows: heating sequentially to 100°C, 150°C, 200°C, 250°C, and 300°C, and holding each temperature for 1 hour.

[0033] In a second aspect, the present invention provides a polyimide film, wherein the polyimide film is prepared by the polyimide film preparation method provided in the first aspect.

[0034] The technical solution provided by this invention achieves a reduction in the coefficient of thermal expansion and an improvement in the thermal stability of polyimide films by combining cyclodextrin with inorganic nanomaterials, while maintaining the appearance and mechanical properties of the polyimide film. Specifically:

[0035] On the one hand, in the technical solution provided by the present invention, the cyclodextrin itself is a macrocyclic compound with a cavity structure, which can form an inclusion complex with the polyimide molecular chain. This inclusion complex can restrict the movement of the molecular chain to a certain extent. At the same time, the cyclodextrin molecule itself has a certain rigidity, which can increase the rigidity of the polyimide molecular chain and reduce the thermal expansion coefficient of the polyimide film to a certain extent.

[0036] On the other hand, the technical solution provided by the present invention, when using inorganic nanomaterials to dope polyimide to improve its dimensional stability, utilizes the inclusion of cyclodextrin macrocyclic molecules with inorganic nanomaterials to solve the problem of inorganic nanomaterial agglomeration, avoids the problems of poor film appearance and mechanical properties caused by inorganic nanomaterial agglomeration, and ensures the appearance and mechanical properties of the obtained polyimide film.

[0037] Furthermore, in the technical solution provided by this invention, when using inorganic nanomaterials to dope polyimide to improve its dimensional stability, the inclusion of cyclodextrin macrocyclic molecules with nanoparticles further reduces the coefficient of thermal expansion of the polymer film. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0039] Thermal expansion coefficient test of the film: A certain length of polyimide film was taken and its dimensional changes upon heating were tested. The test temperature range was room temperature to 300℃, and the heating rate was 10℃ / min. The calculation method for the thermal expansion coefficient is shown below:

[0040] CTE=△L / L×△T

[0041] In the formula: △L is the elongation of the polyimide film when heated (mm), L is the original length of the film material (mm), and △T is the heating temperature range of the material (°C).

[0042] Mechanical property testing: The prepared polyimide film was pressed into standard dumbbell-shaped specimens using a punching machine. The stress area was 2 cm long and 4 mm wide. The thickness of the samples was measured and recorded using a digital thickness gauge. The specimens were placed at 25°C for 24 hours to avoid unstable data results from the standard test temperature. A universal tensile testing machine was used to stretch the specimens at 10 mm / min at room temperature (25°C) to obtain the tensile strength, tensile modulus, and elongation at break of the polyimide film.

[0043] Example 1

[0044] This embodiment provides a polyimide film.

[0045] The polyimide film was prepared by the following method:

[0046] (1) Mix 2.39g β-cyclodextrin, 3.43g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 64.02g N-methylpyrrolidone to form inclusion complex solution I;

[0047] (2) Add 2.2792 g (21.08 mmol) of p-phenylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0048] (3) Add 4.5742 g (20.97 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0049] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0050] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0051] The prepared polyimide film has a coefficient of thermal expansion of 2 ppm / ℃, a tensile strength of 203 MPa, an elongation at break of 16%, a stretching weight of 5.8 GPa, and no crystalline points on the film surface.

[0052] Example 2

[0053] This embodiment provides a polyimide film.

[0054] The polyimide film was prepared by the following method:

[0055] (1) Mix 4.18g β-cyclodextrin, 4.9g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 59.34g N,N-dimethylformamide to form inclusion complex solution I;

[0056] (2) Add 3.6911 g (18.43 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0057] (3) Add 4.0408 g (18.53 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0058] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0059] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0060] The prepared polyimide film has a coefficient of thermal expansion of 3 ppm / ℃, a tensile strength of 210 MPa, an elongation at break of 18%, a stretching weight of 6.0 GPa, and no crystalline points on the film surface.

[0061] Example 3

[0062] This embodiment provides a polyimide film.

[0063] The polyimide film was prepared by the following method:

[0064] (1) Mix 11.72g β-cyclodextrin, 6.23g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 56.95g N,N-dimethylacetamide to form inclusion complex solution I;

[0065] (2) Add 2.7921 g (25.82 mmol) of p-phenylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0066] (3) Add 7.5964 g (25.82 mmol) of biphenyltetracarboxylic dianhydride to inclusion complex solution II, stir at -5℃ for 3 h to obtain polyamic acid solution;

[0067] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0068] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0069] The prepared polyimide film has a coefficient of thermal expansion of 4 ppm / ℃, a tensile strength of 208 MPa, an elongation at break of 17%, a stretching weight of 5.7 GPa, and no crystalline points on the film surface.

[0070] Example 4

[0071] This embodiment provides a polyimide film.

[0072] The polyimide film was prepared by the following method:

[0073] (1) Mix 21.3g β-cyclodextrin, 12.18g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 64.44g N-methylpyrrolidone to form inclusion complex solution I;

[0074] (2) Add 3.7580 g (62.53 mmol) of ethylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0075] (3) Add 13.6388 g (62.53 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0076] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0077] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0078] The prepared polyimide film has a coefficient of thermal expansion of 4 ppm / ℃, a tensile strength of 211 MPa, an elongation at break of 17%, a stretching weight of 5.8 GPa, and no crystalline points on the film surface.

[0079] Example 5

[0080] This embodiment provides a polyimide film.

[0081] The polyimide film was prepared by the following method:

[0082] (1) Mix 18.83g β-cyclodextrin, 5.57g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 51.60g N,N-dimethylformamide to form inclusion complex solution I;

[0083] (2) Add 7.3822 g (36.86 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0084] (3) Add 8.0816 g (37.06 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at 10 °C for 3 h to obtain polyamic acid solution;

[0085] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0086] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0087] The prepared polyimide film has a coefficient of thermal expansion of 2 ppm / ℃, a tensile strength of 214 MPa, an elongation at break of 18%, a stretching weight of 5.8 GPa, and no crystalline points on the film surface.

[0088] Example 6

[0089] This embodiment provides a polyimide film.

[0090] The polyimide film was prepared by the following method:

[0091] (1) Mix 23g β-cyclodextrin, 16.2g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 51.60g N,N-dimethylformamide to form inclusion complex solution I;

[0092] (2) Add 7.3822 g (36.86 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0093] (3) Add 8.0816 g (37.06 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at 10 °C for 3 h to obtain polyamic acid solution;

[0094] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0095] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0096] The prepared polyimide film has a coefficient of thermal expansion of 3 ppm / ℃, a tensile strength of 205 MPa, an elongation at break of 17%, a stretching weight of 5.9 GPa, and no crystalline points on the film surface.

[0097] Example 7

[0098] This embodiment provides a polyimide film.

[0099] The polyimide film was prepared by the following method:

[0100] (1) Mix 2.39g β-cyclodextrin, 3.85g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 64.02g N-methylpyrrolidone to form inclusion complex solution I;

[0101] (2) Add 2.2792 g (21.08 mmol) of p-phenylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0102] (3) Add 4.5742 g (20.97 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0103] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0104] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0105] The prepared polyimide film has a coefficient of thermal expansion of 2 ppm / ℃, a tensile strength of 210 MPa, an elongation at break of 17%, a stretching weight of 5.7 GPa, and no crystalline points on the film surface.

[0106] Example 8

[0107] This embodiment provides a polyimide film.

[0108] The polyimide film was prepared by the following method:

[0109] (1) Mix 4.18g β-cyclodextrin, 5.21g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 59.34g N,N-dimethylformamide to form inclusion complex solution I;

[0110] (2) Add 3.6911 g (18.43 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0111] (3) Add 4.0408 g (18.53 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0112] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0113] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0114] The prepared polyimide film has a coefficient of thermal expansion of 5 ppm / ℃, a tensile strength of 232 MPa, an elongation at break of 19%, a stretching weight of 6.4 GPa, and no crystalline points on the film surface.

[0115] Example 9

[0116] This embodiment provides a polyimide film.

[0117] The polyimide film was prepared by the following method:

[0118] (1) Mix 11.72g β-cyclodextrin, 6.11g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 56.95g N,N-dimethylacetamide to form inclusion complex solution I;

[0119] (2) Add 2.7921 g (25.82 mmol) of p-phenylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0120] (3) Add 7.5964 g (25.82 mmol) of biphenyltetracarboxylic dianhydride to inclusion complex solution II, stir at -5℃ for 3 h to obtain polyamic acid solution;

[0121] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0122] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0123] The prepared polyimide film has a coefficient of thermal expansion of 4 ppm / ℃, a tensile strength of 215 MPa, an elongation at break of 18%, a stretching weight of 5.9 GPa, and no crystalline points on the film surface.

[0124] Example 10

[0125] This embodiment provides a polyimide film.

[0126] The polyimide film was prepared by the following method:

[0127] (1) Mix 21.3g β-cyclodextrin, 12.45g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 64.44g N-methylpyrrolidone to form inclusion complex solution I;

[0128] (2) Add 3.7580 g (62.53 mmol) of ethylenediamine to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0129] (3) Add 13.6388 g (62.53 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at -5℃ for 3 h to obtain polyamic acid solution;

[0130] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0131] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0132] The prepared polyimide film has a coefficient of thermal expansion of 6 ppm / ℃, a tensile strength of 205 MPa, an elongation at break of 17%, a stretching weight of 5.8 GPa, and no crystalline points on the film surface.

[0133] Example 11

[0134] This embodiment provides a polyimide film.

[0135] The polyimide film was prepared by the following method:

[0136] (1) Mix 18.83g β-cyclodextrin, 5.78g carbon nanotubes and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 51.60g N,N-dimethylformamide to form inclusion complex solution I;

[0137] (2) Add 7.3822 g (36.86 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0138] (3) Add 8.0816 g (37.06 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at 10 °C for 3 h to obtain polyamic acid solution;

[0139] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0140] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0141] The prepared polyimide film has a coefficient of thermal expansion of 7 ppm / ℃, a tensile strength of 199 MPa, an elongation at break of 15%, a stretching weight of 5.5 GPa, and no crystalline points on the film surface.

[0142] Example 12

[0143] This embodiment provides a polyimide film.

[0144] The polyimide film was prepared by the following method:

[0145] (1) Mix 23g β-cyclodextrin, 15.5g silica and 100mL water, stir for 2h to form inclusion complex, heat to remove water, and then add 51.60g N,N-dimethylformamide to form inclusion complex solution I;

[0146] (2) Add 7.3822 g (36.86 mmol) of 4,4'-diaminodiphenyl ether to inclusion complex solution I and stir thoroughly to obtain inclusion complex solution II;

[0147] (3) Add 8.0816 g (37.06 mmol) of pyromellitic dianhydride to inclusion complex solution II, and stir at 10 °C for 3 h to obtain polyamic acid solution;

[0148] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0149] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0150] The prepared polyimide film has a coefficient of thermal expansion of 3 ppm / ℃, a tensile strength of 217 MPa, an elongation at break of 18%, a stretching weight of 5.8 GPa, and no crystalline points on the film surface.

[0151] Comparative Example 1

[0152] This comparative example provides a polyimide film.

[0153] The only difference between the preparation method used and the polyimide film preparation method in Example 1 is that cyclodextrin and inorganic nanomaterials are not added. The specific process is as follows:

[0154] (1) Mix 2.2792g (21.08mmol) of p-phenylenediamine with 64.02g of N-methylpyrrolidone and stir thoroughly to dissolve;

[0155] (3) Add 4.5742 g (20.97 mmol) of pyromellitic dianhydride to the solution in step (1), and stir at -5℃ for 3 h to obtain a polyamic acid solution;

[0156] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0157] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0158] The prepared polyimide film has a coefficient of thermal expansion of 55 ppm / ℃, a tensile strength of 160 MPa, an elongation at break of 10%, a stretching weight of 2.9 GPa, and no crystalline points on the film surface.

[0159] Comparative Example 2

[0160] This comparative example provides a polyimide film.

[0161] The only difference between the preparation method used and the polyimide film preparation method in Example 1 is that no inorganic nanomaterials are added. The specific process is as follows:

[0162] (1) Mix 2.39g of β-cyclodextrin with 100mL of water, stir for 2h, heat to remove water, and then add 64.02g of N-methylpyrrolidone to form solution I;

[0163] (2) Add 2.2792 g (21.08 mmol) of p-phenylenediamine to solution I and stir thoroughly to obtain solution II;

[0164] (3) Add 4.5742 g (20.97 mmol) of pyromellitic dianhydride to solution II, stir at -5℃ for 3 h to obtain polyamic acid solution;

[0165] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0166] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0167] The prepared polyimide film has a coefficient of thermal expansion of 40 ppm / ℃, a tensile strength of 172 MPa, an elongation at break of 12%, a stretching weight of 2.4 GPa, and no crystalline points on the film surface.

[0168] Comparative Example 3

[0169] This comparative example provides a polyimide film.

[0170] The only difference between the preparation method used and the polyimide film preparation method in Example 1 is that cyclodextrin is not added. The specific process is as follows:

[0171] (1) Mix 3.43g of carbon nanotubes with 100mL of water, stir for 2h, heat to remove water, and then add 64.02g of N-methylpyrrolidone to form solution I;

[0172] (2) Add 2.2792 g (21.08 mmol) of p-phenylenediamine to solution I and stir thoroughly to obtain solution II;

[0173] (3) Add 4.5742 g (20.97 mmol) of pyromellitic dianhydride to solution II, stir at -5℃ for 3 h to obtain polyamic acid solution;

[0174] (4) The obtained polyamic acid solution was coated onto the steel plate with a doctor blade to a thickness of 0.6 mm, and then vacuum degassed for 5 hours.

[0175] (5) Heat to 100℃, 150℃, 200℃, 250℃ and 300℃ in sequence and keep warm for 1 hour each time. Demold and vacuum dry at 60℃ for 24 hours to obtain polyimide film.

[0176] The prepared polyimide film has a coefficient of thermal expansion of 8 ppm / ℃, a tensile strength of 120 MPa, an elongation at break of 6%, a stretching weight of 1.3 GPa, and crystalline points on the film surface.

[0177] The embodiments described above are for the purpose of better explaining the present invention. For those skilled in the art, it is not difficult to make various modifications to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and variations made to the present invention by those skilled in the art based on the principles and spirit of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide film, wherein, The preparation method includes: Cyclodextrin, inorganic nanomaterials, and water were mixed and stirred for a certain period of time to form an inclusion complex. The water was removed, and a polar aprotic solvent was added to form inclusion complex solution I. A polar aprotic solvent containing a diamine monomer was mixed with inclusion complex solution I to obtain inclusion complex solution II. The inclusion complex solution II was mixed with the dianhydride monomer to obtain the reaction system; the reaction system underwent a polymerization reaction to obtain a polyamic acid solution. Polyimide films were prepared using polyamic acid solutions.

2. The preparation method according to claim 1, wherein, Cyclodextrins include at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives of cyclodextrin; Preferably, the cyclodextrin includes β-cyclodextrin and / or γ-cyclodextrin.

3. The preparation method according to claim 1, wherein, Inorganic nanomaterials include at least one of graphene, carbon nanotubes, silicon dioxide, silicon carbide, zirconium oxide, and boron nitride; Preferably, the inorganic nanomaterials include carbon nanotubes and / or silicon dioxide.

4. The preparation method according to claim 1, wherein, Diamines include at least one of aromatic diamines and aliphatic diamines; Preferably, the diamine includes at least one selected from p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, ethylenediamine, and 1,6-hexanediamine.

5. The preparation method according to claim 1, wherein, The polar aprotic solvent in inclusion complex solution I includes at least one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; The polar aprotic solvents containing diamine monomers include at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

6. The preparation method according to claim 1, wherein, Dihydrides include at least one of aromatic dianhydrides and aliphatic dianhydrides; Preferably, the dianhydride includes at least one selected from pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, and cyclopentanetetracarboxylic dianhydride.

7. The preparation method according to claim 1, wherein, The molar ratio of cyclodextrin, diamine, and dianhydride is (0.1-0.6):1:(1-1.1); Preferably, the molar ratio of cyclodextrin, diamine, and dianhydride is (0.2-0.4):1:(1-1.05).

8. The preparation method according to claim 1, wherein, The mass of the inorganic nanomaterial is 0.5%-1.5% of the total mass of the diamine and dianhydride.

9. The preparation method according to claim 1, wherein, In the reaction system, the mass content of the polar aprotic solvent is 0.7-0.

9. In inclusion complex solution I, the mass content of polar aprotic solvent is 0.6-0.9%. In polar aprotic solvents containing diamine monomers, the mass content of the polar aprotic solvent is 0.6-0.9%.

10. The preparation method according to claim 1, wherein, The reaction temperature for polymerization in the reaction system is 15-30℃; The reaction time for polymerization in the reaction system is 1-8 hours.

11. The preparation method according to claim 1, wherein, The preparation of polyimide films using polyamic acid solutions includes: The polyamic acid solution is coated, and then vacuum degassing, vacuum heat treatment, demolding, and vacuum drying are performed sequentially to obtain the polyimide film. Preferably, the temperature for vacuum degassing is 80-100℃; Preferably, the vacuum degassing time is 3-12 hours; Preferably, the vacuum heat treatment process is as follows: heating sequentially to 100℃, 150℃, 200℃, 250℃, and 300℃, and holding each temperature for 1 hour.

12. A polyimide film, wherein, The polyimide film is prepared by the polyimide film preparation method according to any one of claims 1-11.