A low dielectric polyimide film and preparation method thereof

Abstract

The present invention discloses a low-dielectric polyimide film, which is obtained by casting a polyamic acid copolymer solution into a film, then subjecting it to thermal imidization and biaxial stretching. The polyamic acid copolymer solution is obtained by polymerization of the following raw materials in an aprotic, strongly polar solvent: diamine, dianhydride, and amino-containing thermally unstable polymer nanoparticles. The present invention also discloses a method for preparing the low-dielectric polyimide film. The polyimide film of the present invention has the characteristics of high mechanical strength, low dielectric constant, high heat resistance, and good dimensional stability, and can be applied in 5G communications, integrated circuits, electronics, microelectronics, aerospace, and other fields.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide films, in particular to a low-dielectric polyimide film and a preparation method thereof. Background Art

[0002] The advent of the 5G era has made people's lives more information-based and intelligent. Various electronic and electrical devices are becoming increasingly portable and lightweight, significantly improving operational efficiency and elevating the human-computer interaction experience to a new level. 5G communications feature ultra-high-speed signal transmission, ultra-low latency, and multi-user connectivity. These characteristics also make the parasitic effects of the resistance (R) of metal connecting wires and the capacitance (C) of insulating dielectric layers within electronic devices increasingly pronounced, leading to problems such as signal transmission delays, crosstalk, and high power consumption, limiting device performance and impacting user experience. Therefore, reducing the dielectric constant of interlayer insulating materials to ensure accurate and effective signal transmission under high-frequency and high-speed conditions has become the most basic and important material performance requirement in the current 5G era.

[0003] Polyimide (PI) refers to a class of polymers containing an imide ring (-CO-N-CO-) in the main chain. It has excellent heat resistance, mechanical properties, electrical properties and chemical stability, and has been widely used in aerospace, rail transportation, automotive medical, electrical and electronic and other technical fields.

[0004] Polyimide film has been used for many years in integrated circuits and microelectronics as an indispensable insulating material. However, the dielectric constant of traditional polyimide film is relatively high, ranging from 3.0 to 3.5, limiting its application in high-frequency substrates used in 5G communication components. Therefore, polyimide film modification is often required to lower its dielectric constant and enable wider application in the 5G communication field. At present, there are mainly the following methods to reduce the dielectric constant of polyimide films: 1) Introducing fluorine-containing monomers. Fluorine atoms are extremely electronegative and can bind electrons through the electron-withdrawing induction effect, thereby reducing the electronic polarization rate. However, the large volume of fluorine atoms will affect the reaction activity and reduce the heat resistance and mechanical properties of the film; 2) Adding inorganic nanoparticles. Introducing nanoparticles with a microporous structure into the PI matrix can effectively reduce the dielectric constant of the film. However, the addition of inorganic particles has poor compatibility with the PI matrix on the one hand, and may also reduce the mechanical properties of the film on the other hand; 3) Adding porogens. Porogens can form air micropores inside the PI film, thereby reducing the dielectric constant of the film. However, porogens will cause uneven pore formation and reduce the mechanical properties of the film. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a low-dielectric polyimide film and a preparation method thereof.

[0006] The low-dielectric polyimide film proposed in the present invention is obtained by casting a polyamic acid copolymer solution into a film, then subjecting it to thermal imidization and biaxial stretching. The polyamic acid copolymer solution is obtained by polymerizing the following raw materials in an aprotic, highly polar solvent: diamine, dianhydride, and amino-containing heat-unstable polymer nanoparticles.

[0007] The diamine comprises 70 to 100 mol% of a diamine monomer having a non-coplanar super-twisted structure and 0 to 30 mol% of other diamine monomers, wherein the structural formula of the diamine monomer having a non-coplanar super-twisted structure is one of the structural formulas shown in Formulas I-1 to I-4;

[0008]

[0009] Preferably, the average particle size of the amino-containing heat-unstable polymer nanoparticles is 200 to 500 nm.

[0010] Preferably, the component of the amino-containing heat-unstable polymer nanoparticles is at least one of the polymers having the structural formulas shown in II-1 to II-6:

[0011]

[0012] Wherein, the relative molecular mass of the polymer having the structural formula shown in II-1 to II-6 is 10,000 to 20,000 g / mol.

[0013] Preferably, the molar ratio of the diamine to the dianhydride is 1:(0.95-1.015).

[0014] Preferably, the other diamine monomer is at least one of 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4-diaminodiphenylmethane, 4,4-diaminodiphenyl ketone, and bisphenol A diether diamine.

[0015] Preferably, the dianhydride is at least one of bisphenol A diether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-biphenyl ether tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and pyromellitic dianhydride.

[0016] Preferably, the mass of the amino-containing heat-unstable polymer nanoparticles accounts for 1 to 20% of the total mass of the diamine and dianhydride.

[0017] Preferably, the method for preparing the polyamic acid copolymer solution comprises the following steps:

[0018] (1) dissolving a diamine in an aprotic strong polar solvent, then adding dianhydride to carry out a polymerization reaction to obtain a polyamic acid resin solution;

[0019] (2) Adding amino-containing heat-unstable polymer nanoparticles into the polyamic acid resin solution, dispersing them evenly, and then performing a polymerization reaction to obtain a polyamic acid copolymer solution.

[0020] Preferably, in step (1), the viscosity of the polyamic acid resin solution is 50 to 120 Pa·s.

[0021] Preferably, in step (2), the viscosity of the polyamic acid copolymer solution is 80 to 120 Pa·s.

[0022] Preferably, in step (1), the reaction temperature is 25-50° C., and the reaction time is 4-6 h.

[0023] Preferably, in step (2), the reaction temperature is 30-60° C., and the reaction time is 2-5 h.

[0024] Preferably, in S2, the specific method for uniform dispersion is: stirring and dispersing at 2500-3000 r / min for 2-3 hours.

[0025] A method for preparing a low dielectric polyimide film comprises the following steps:

[0026] S1, casting the polyamic acid copolymer solution on a support to form a film to obtain a self-supporting film;

[0027] S2, thermally imidizing the self-supporting film under the condition of a gradient temperature increase of 100 to 450° C., and stretching the self-supporting film longitudinally and transversely to obtain the self-supporting film.

[0028] Preferably, in S1, the casting temperature is 150-200° C., and the casting speed is 3-6 m / min.

[0029] Preferably, in S2, the step of thermal imidization of the self-supporting film under the condition of gradient heating at 100-450°C is: heating at 100-120°C for 10-20s, heating at 140-160°C for 10-20s, heating at 180-220°C for 10-20s, heating at 240-260°C for 10-20s, heating at 280-320°C for 10-20s, heating at 340-360°C for 10-20s, heating at 380-420°C for 10-20s, and heating at 440-460°C for 10-20s.

[0030] Preferably, in S2, the longitudinal stretching ratio is 1.0 to 1.15, and the transverse stretching ratio is 1.0 to 1.25.

[0031] The beneficial effects of the present invention are as follows:

[0032] The invention obtains a polyamic acid copolymer solution by polymerizing dianhydride, a diamine with a non-coplanar super-twisted structure and heat-unstable polymer nanoparticles containing amino groups. After the solution is cast into a film, the solution is subjected to thermal imidization and biaxial stretching to obtain a polyimide film. The present invention introduces a non-coplanar super-twisted structure diamine monomer, which can effectively destroy the structural regularity of the polyimide molecular chain and reduce the symmetrical structure, thereby effectively reducing the packing density of the molecular chain, increasing the molecular distance, reducing the intermolecular force, increasing the free volume of the system, and macroscopically manifesting a reduction in the dielectric constant. Nanoparticles formed by introducing a low-molecular-weight, thermally unstable high-molecular polymer undergo a polymerization reaction to form an ABA-type or grafted polyamic acid copolymer, which is made into a whole. Unlike the introduced inorganic particles dispersed in the matrix, which are incompatible and unevenly dispersed, the mechanical properties of the film can be made more stable. Since the low-molecular-weight polymer is a thermally unstable component, it can decompose at 200-400° C. to produce uniformly dispersed nanopores. This temperature is below the Tg of the PI molecular chain, and its decomposition does not significantly affect the relative molecular mass and physical and mechanical properties of the PI. Moreover, the uniformly dispersed nanopores are equivalent to introducing air into the interior of the PI film, which can significantly reduce the dielectric constant of the film. In summary, this invention can obtain a polyimide film with low dielectric constant and good mechanical properties. It has the characteristics of high mechanical strength, low dielectric constant, high heat resistance, and good dimensional stability. It can be applied to 5G communications, integrated circuits, electronics, microelectronics, aerospace and other fields. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below through specific embodiments.

[0034] In the following examples and comparative examples, diamino-terminated polystyrene nanoparticles and diamino-terminated polymethyl methacrylate nanoparticles were purchased from commercial sources.

[0035] Example 1

[0036] Preparation of polyamic acid copolymer solution:

[0037] (1) dissolving a diamine monomer as shown in Formula I-1 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-1 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0038] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 3% of the sum of the masses of the diamine monomer and pyromellitic dianhydride shown in Formula I-1; the structural formula of the diamino-terminated polystyrene is as shown in Formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0039] Preparation of low dielectric polyimide film:

[0040] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0041] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0042] Example 2

[0043] The only difference between Example 2 and Example 1 is that the amount of diamino-terminated polystyrene nanoparticles used is different. The details are as follows:

[0044] Preparation of polyamic acid copolymer solution:

[0045] (1) dissolving a diamine monomer as shown in Formula I-1 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-1 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0046] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 6% of the sum of the masses of the diamine monomer and pyromellitic dianhydride shown in Formula I-1; the structural formula of the diamino-terminated polystyrene is as shown in Formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0047] Preparation of low dielectric polyimide film:

[0048] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0049] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0050] Example 3

[0051] The only difference between Example 3 and Example 1 is that the diamine monomer with the structural formula shown in Formula I-2 is used instead of the diamine monomer with the structural formula shown in Formula I-1. The details are as follows:

[0052] Preparation of polyamic acid copolymer solution:

[0053] (1) dissolving a diamine monomer as shown in Formula I-2 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-2 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0054] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 3% of the sum of the masses of the diamine monomer shown in Formula I-2 and pyromellitic dianhydride; the structural formula of the diamino-terminated polystyrene is as shown in Formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0055] Preparation of low dielectric polyimide film:

[0056] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0057] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0058] Example 4

[0059] The only difference between Example 4 and Example 1 is that the diamine monomer represented by the structural formula of Formula I-2 is used instead of the diamine monomer represented by the structural formula of Formula I-1; and the amount of diamino-terminated polystyrene nanoparticles used is different. The details are as follows:

[0060] Preparation of polyamic acid copolymer solution:

[0061] (1) dissolving a diamine monomer as shown in Formula I-2 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-2 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0062] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 6% of the sum of the masses of the diamine monomer and pyromellitic dianhydride shown in formula I-2; the structural formula of the diamino-terminated polystyrene is shown in formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0063] Preparation of low dielectric polyimide film:

[0064] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0065] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0066] Example 5

[0067] The only difference between Example 5 and Example 1 is that diamino-terminated polymethyl methacrylate nanoparticles are used instead of diamino-terminated polystyrene nanoparticles. The details are as follows:

[0068] Preparation of polyamic acid copolymer solution:

[0069] (1) dissolving a diamine monomer as shown in Formula I-1 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-1 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0070] (2) Add diamino-terminated polymethyl methacrylate nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polymethyl methacrylate nanoparticles is 3% of the sum of the masses of the diamine monomer shown in Formula I-1 and pyromellitic dianhydride; the structural formula of the diamino-terminated polymethyl methacrylate is shown in Formula II-5, and the molecular weight is 10,000 to 13,000 g / mol.

[0071] Preparation of low dielectric polyimide film:

[0072] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0073] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0074] Example 6

[0075] The only difference between Example 6 and Example 1 is that diamino-terminated polymethyl methacrylate nanoparticles are used instead of diamino-terminated polystyrene nanoparticles, and the amount of diamino-terminated polymethyl methacrylate nanoparticles used is different. The details are as follows:

[0076] Preparation of polyamic acid copolymer solution:

[0077] (1) dissolving a diamine monomer as shown in Formula I-1 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer as shown in Formula I-1 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0078] (2) Add diamino-terminated polymethyl methacrylate nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 6% of the sum of the masses of the diamine monomer shown in Formula I-1 and pyromellitic dianhydride; the structural formula of the diamino-terminated polymethyl methacrylate is shown in Formula II-5, and the molecular weight is 10,000 to 13,000 g / mol.

[0079] Preparation of low dielectric polyimide film:

[0080] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0081] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0082] Example 7

[0083] The only difference between Example 7 and Example 1 is that another diamine monomer is added, as follows:

[0084] Preparation of polyamic acid copolymer solution:

[0085] (1) dissolving a diamine monomer and diaminodiphenyl ether as shown in formula I-1 in N,N-dimethylacetamide, then adding pyromellitic dianhydride, and polymerizing at 45° C. for 6 hours to obtain a polyamic acid resin solution with a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer and diaminodiphenyl ether as shown in formula I-1 is 7:3, and the ratio of the sum of the moles of the diamine monomer and diaminodiphenyl ether as shown in formula I-1 to the mole of pyromellitic dianhydride is 1:0.98 to 1.011;

[0086] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 3% of the sum of the masses of the diamine monomer, diaminodiphenyl ether and pyromellitic dianhydride shown in formula I-1; the structural formula of the diamino-terminated polystyrene is as shown in formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0087] Preparation of low dielectric polyimide film:

[0088] S1, casting the polyamic acid copolymer solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0089] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0090] Comparative Example 1

[0091] Conventional polyimide films are as follows:

[0092] Preparation of polyamic acid resin solution:

[0093] 4,4-Diaminodiphenyl ether is dissolved in N,N-dimethylacetamide, and then pyromellitic dianhydride is added. The mixture is polymerized at 45°C for 6 hours to obtain a polyamic acid resin solution with a viscosity of 50 to 120 Pa·s. The molar ratio of 4,4-diaminodiphenyl ether to pyromellitic dianhydride is 1:0.98 to 1.011.

[0094] Preparation of low dielectric polyimide film:

[0095] S1, casting the polyamic acid resin solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0096] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0097] Comparative Example 2

[0098] Polyimide films using only special diamine monomers, as follows:

[0099] Preparation of polyamic acid resin solution:

[0100] A diamine monomer represented by the structural formula of Formula I-1 is dissolved in N,N-dimethylacetamide, and then pyromellitic dianhydride is added, and polymerization reaction is carried out at 45° C. for 6 hours to obtain a polyamic acid resin solution having a viscosity of 50 to 120 Pa·s; wherein the molar ratio of the diamine monomer represented by the structural formula of Formula I-1 to pyromellitic dianhydride is 1:0.98 to 1.011;

[0101] Preparation of polyimide film:

[0102] S1, casting the polyamic acid resin solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0103] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0104] Comparative Example 3

[0105] Polyimide film to which only thermally unstable polymer nanoparticles are added, specifically as follows:

[0106] Preparation of polyamic acid copolymer solution:

[0107] (1) 4,4-diaminodiphenyl ether is dissolved in N,N-dimethylacetamide, and then pyromellitic dianhydride is added, and the mixture is polymerized at 45°C for 6 hours to obtain a polyamic acid resin solution with a viscosity of 50 to 120 Pa·s; wherein the molar ratio of 4,4-diaminodiphenyl ether to pyromellitic dianhydride is 1:0.98 to 1.011.

[0108] (2) Add diamino-terminated polystyrene nanoparticles with an average particle size of 200 nm to a polyamic acid resin solution, stir and disperse at 2800 r / min for 2.5 hours, and then polymerize at 50°C for 4 hours to obtain a polyamic acid copolymer solution with a viscosity of 80 to 120 Pa·s; wherein the mass of the diamino-terminated polystyrene nanoparticles is 3% of the sum of the masses of the diamine monomer and pyromellitic dianhydride shown in Formula I-1; the structural formula of the diamino-terminated polystyrene is as shown in Formula II-1, and the molecular weight is 10,000 to 12,000 g / mol.

[0109] Preparation of low dielectric polyimide film:

[0110] S1, casting the polyamic acid resin solution prepared above on a mirror steel belt at a casting temperature of 150-180° C. and a casting speed of 3.5 m / min to obtain a self-supporting film;

[0111] S2. The self-supporting film is thermally imidized under the condition of a gradient temperature increase of 100 to 450°C, and the specific steps are: heating at 100 to 120°C for 10 to 20s, heating at 140 to 160°C for 10 to 20s, heating at 180 to 220°C for 10 to 20s, heating at 240 to 260°C for 10 to 20s, heating at 280 to 320°C for 10 to 20s, heating at 340 to 360°C for 10 to 20s, heating at 380 to 420°C for 10 to 20s, and heating at 440 to 460°C for 10 to 20s; and performing longitudinal stretching and transverse stretching, with the longitudinal stretching ratio being 1.0 and the transverse stretching ratio being 1.15, to obtain the product.

[0112] The performance of the polyimide films prepared in Examples 1-6 and Comparative Examples 1-3 was tested, and the results are shown in Table 1:

[0113] Table 1 Polyimide film performance test results

[0114]

[0115] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A low dielectric polyimide film, characterized in that: The polyamic acid copolymer solution is cast into a film, and then subjected to thermal imidization and biaxial stretching; the polyamic acid copolymer solution is obtained by polymerization reaction of the following raw materials in a non-proton strong polar solvent: diamine, dianhydride, and amino-containing heat-unstable polymer nanoparticles; The structural formula of the diamine is the structural formula shown in Formula I-1; Ⅰ-1 ； The dianhydride is pyromellitic dianhydride; The average particle size of the amino-containing heat-unstable polymer nanoparticles is 200-500 nm; The components of the amino-containing heat-unstable polymer nanoparticles are at least one of the polymers having the structural formula shown in II-1 or II-5: Ⅱ-1 ； Ⅱ-5 ； Wherein, the relative molecular mass of the polymer having the structural formula shown in II-1 or II-5 is 10,000 to 20,000 g / mol; The mass of the amino-containing heat-unstable polymer nanoparticles accounts for 1-20% of the total mass of the diamine and the dianhydride.

2. The low dielectric polyimide film according to claim 1, wherein The molar ratio of the diamine to the dianhydride is 1:(0.95-1.015).

3. The low dielectric polyimide film according to claim 1, wherein: The preparation method of the polyamic acid copolymer solution comprises the following steps: (1) dissolving diamine in a non-proton strong polar solvent, then adding dianhydride to carry out polymerization reaction to obtain a polyamic acid resin solution; (2) Adding amino-containing heat-unstable polymer nanoparticles into the polyamic acid resin solution, dispersing them evenly, and then performing a polymerization reaction to obtain a polyamic acid copolymer solution.

4. The low dielectric polyimide film according to claim 3, characterized in that In step (1), the reaction temperature is 25-50°C, and the reaction time is 4-6 hours; in step (2), the reaction temperature is 30-60°C, and the reaction time is 2-5 hours.

5. A method for preparing a low dielectric polyimide film according to any one of claims 1 to 4, characterized in that: The steps include: S1, casting the polyamic acid copolymer solution on a support to form a film to obtain a self-supporting film; S2. The self-supporting film is subjected to thermal imidization under the condition of a gradient temperature increase of 100-450° C., and is longitudinally stretched and transversely stretched to obtain the self-supporting film.

6. The method for preparing a low dielectric polyimide film according to claim 5, wherein: In S1, the casting temperature is 150~200℃, and the casting speed is 3~6m / min; In S2, the step of thermal imidization of the self-supporting film under the condition of gradient heating of 100~450°C is as follows: heating at 100~120°C for 10~20s, heating at 140~160°C for 10~20s, heating at 180~220°C for 10~20s, heating at 240~260°C for 10~20s, heating at 280~320°C for 10~20s, heating at 340~360°C for 10~20s, heating at 380~420°C for 10~20s, and heating at 440~460°C for 10~20s; In S2, the longitudinal stretching ratio is 1.0 to 1.15, and the transverse stretching ratio is 1.0 to 1.25.

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