WO2022242547A1 - Polyimide porous membrane and preparation method therefor - Google Patents

Abstract

The present disclosure relates to the technical field of the preparation of polymer dielectric materials and discloses a polyimide porous membrane and a preparation method therefor. The preparation method comprises: dissolving two different aromatic diisocyanates in a polar solvent, then adding an aromatic dianhydride, fully stirring same to obtain an intermediate product polyamide acid, adding a pore-forming agent to the polyamide acid and mixing same until uniform, then defoaming same, coating a glass plate with same, then carrying out heat treatment, and finally, removing the pore-forming agent to obtain the polyimide porous membrane. By means of the special method, a high-performance polyimide porous membrane with a low dielectric constant, uniform pore distribution, good thermal stability and good dimensional stability is obtained, such that the signal transmission speed can be increased, signal interference and inductive coupling are reduced, and the polyimide porous membrane can be better applied in the integrated circuit industry.

Description

A kind of polyimide porous membrane and preparation method thereof

Cross References to Related Applications

This disclosure claims the priority of the Chinese patent application with the application number "CN202110533302.5" and the title "a polyimide porous membrane and its preparation method" submitted to the China Patent Office on May 17, 2021, the entire content of which Incorporated by reference in this disclosure.

technical field

The disclosure relates to the technical field of preparation of polymer dielectric materials, in particular to a polyimide porous film and a preparation method thereof.

Background technique

With the rapid development of science and technology, the trend of the integrated circuit industry towards low-dimensional, large-scale and even ultra-large-scale integration has become increasingly obvious. In order to speed up signal transmission, reduce signal interference and inductive coupling, materials with low dielectric constant must be used. For a new generation of dielectric materials, the dielectric constant is required to be below 2.2. Polyimide has become the most promising polymer dielectric material because of its outstanding thermal and mechanical properties. Since the dielectric constant of ordinary polyimide is usually between 3 and 4, the synthesis of polyimide materials with lower dielectric constant has become a research hotspot.

According to the Clausius Mossotti equation, the dielectric constant of a material is closely related to its molar susceptibility and molar volume. Therefore, there are currently two main methods for reducing the dielectric constant of PI: (1) introducing substituents with low polarizability to reduce the polarizability of dipoles in the molecule. (2) To reduce the number of dipoles per unit volume by introducing bulky groups or even hole structures inside the material.

Ordinary polyimide films have a dielectric constant of 3 to 4, which cannot meet the needs of integrated circuits at this stage. Traditional polyimide porous films have low dielectric constants, but their pores are not uniformly distributed, and thermal Poor stability and poor dimensional stability.

The above Clausius Mossotti equation is:

Among them, Pm is the molar polarizability of the atomic group, and Vm is the molar volume of the atomic group.

Contents of the invention

The disclosure provides a method for preparing a polyimide porous membrane. Two different aromatic diisocyanates are dissolved in a polar solvent, and then an aromatic dianhydride is added, and the intermediate product polyamic acid is fully stirred to obtain the intermediate product polyamic acid, and then the polyimide The amic acid is coated on a glass plate after defoaming, and then heat-treated to obtain the polyimide porous membrane.

In some embodiments, after obtaining the intermediate product polyamic acid, add a pore-forming agent to mix evenly, and then apply it on a glass plate after defoaming, then perform heat treatment, and finally remove the pore-forming agent to obtain the polyamic acid. imine porous membrane.

In some embodiments, the aromatic diisocyanate is selected from 4-methyl-m-phenylene diisocyanate, 2,6-toluene diisocyanate, 4,4'-methylene bis(phenylisocyanate) , 2,4,6-trimethyl-1,3-benzenediisocyanate or 2,3,5,6-tetramethyl-1,4-benzenediisocyanate; the aromatic dianhydride is selected from From 3,4,3',4'-benzophenone tetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,4,3',4'-biphenyl One of tetracarboxylic dianhydrides.

In some embodiments, the polar solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

In some embodiments, the pore-forming agent is selected from one or more of SiO ₂ , ceramics, aluminum powder, and magnesium powder.

In some embodiments, the conditions for the copolymerization of two different aromatic diisocyanates and aromatic dianhydrides are nitrogen protection and a temperature of 0-40°C.

In some embodiments, two different aromatic diisocyanates and aromatic dianhydrides are thoroughly stirred to obtain an intermediate polyamic acid, and the solid content of the polyamic acid is between 13-16 wt%.

In some embodiments, the heat treatment employs a stepwise increase in temperature.

In other embodiments, the two different aromatic diisocyanates are 4,4'-methylenebis(phenylisocyanate) and 4-methyl-m-phenylene diisocyanate; the aromatic diisocyanate The anhydride is 1,2,4,5-benzenetetracarboxylic dianhydride.

In some embodiments, the sum of the molar weights of 4,4'-methylenebis(phenylisocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4,5-benzene The molar ratio of tetramethylcarboxylic dianhydride is 1:1.

In some embodiments, the molar amount of 4,4'-methylene bis(phenylisocyanate) is less than the molar amount of 4-methyl-m-phenylene diisocyanate.

In other embodiments, the pore-forming agent is SiO ₂ , and the SiO ₂ is nano-scale SiO ₂ .

In some embodiments, the average particle diameter of the nanoscale SiO ₂ is 5-45 nm.

The present disclosure also provides a polyimide porous membrane prepared by any one of the above methods.

In some embodiments, the dielectric constant of the polyimide porous membrane is 1.45-1.98.

In some embodiments, the porosity of the polyimide porous membrane is 68-79%.

In some embodiments, the porosity of the polyimide porous membrane is 73-79%.

In some embodiments, the thermal shrinkage of the polyimide porous membrane is 0.25-0.28% in the MD direction and 0.25-0.30% in the TD direction at 150°C.

The present disclosure also provides the use of the above-mentioned porous imide film in dielectric materials.

Description of drawings

Figure 1 shows 4,4'-methylenebis(phenylisocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4,5-pyrylenetetramethyl in 11 embodiments of the present disclosure The chemical reaction formula of carboxylic dianhydride.

Detailed ways

Embodiments of the present disclosure will be described in detail below. It should be understood that the embodiments described here are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

The disclosure provides a method for preparing a polyimide porous film, which has low dielectric constant, uniform pore distribution, good thermal stability and good dimensional stability.

Some embodiments of the present disclosure provide a method for preparing a polyimide porous membrane, the technical gist of which is: under nitrogen protection and a certain temperature condition, 4,4'-methylene bis(phenylisocyanate), 4-Methyl-m-phenylene diisocyanate is dissolved in a polar solvent, and 1,2,4,5-benzenetetracarboxylic dianhydride is added to stir the reaction to obtain the intermediate product polyamic acid, and the obtained polyamide After the acid is added into the pore-forming agent and mixed evenly, it is vacuum defoamed and then coated on a glass plate, subjected to thermal imidization treatment, and then the pore-forming agent is removed to obtain a polyimide porous membrane.

Here, the polar solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

Here, the pore-forming agent is selected from one or more of SiO ₂ , ceramics, aluminum powder, and magnesium powder.

In some embodiments, the pore-forming agent is SiO ₂ , and the SiO ₂ is nano-scale SiO ₂ . Since nano-scale SiO ₂ has a more porous structure, it can absorb metal ions, reducing the possibility of oxidative yellowing; secondly, nano-scale SiO ₂ pore-forming agent has a larger packing density, which is easier to mix with resin and more Conducive to operation.

In some typical embodiments, the average particle size of nano-scale _SiO2 is 5-45nm, such as 10-45nm, 15-40nm or 25-35nm. Here, too small particle size is not conducive to pore formation, and too large particle size affects membrane Strength of. In some more typical embodiments, the average particle size of the nanoscale SiO ₂ is 30nm.

In some embodiments, 4,4'-methylenebis(phenylisocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4,5-benzenetetramethylcarboxylic dianhydride are copolymerized The reaction temperature is 0-40°C, such as 5-40°C, 10-35°C or 20-30°C. In some typical embodiments, the reaction temperature is a water bath at 25°C.

In some embodiments, the polyamic acid has a solid content of 13-16 wt%, such as 13 wt%, 14 wt%, 15 wt% or 16 wt%.

In some typical embodiments, the solid content of the polyamic acid is 15 wt%.

In some embodiments, the heat treatment adopts a stepwise temperature rise, and the stepwise temperature rise process includes but is not limited to: first raise the temperature to 100°C and keep it for 30 minutes, then raise the temperature to 110°C and keep it for 30 minutes, then raise the temperature to 120°C and keep it for 60 minutes, and then raise the temperature to 140°C and keep it 60min, the stepwise temperature rise is only for the reaction, and has no obvious influence on the dielectric constant.

In some embodiments, the sum of the molar weights of 4,4'-methylenebis(phenylisocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4,5 - The molar ratio of pyromellitic acid dianhydride is 1:1.

In some typical embodiments, the molar ratio of 4,4'-methylene bis(phenylisocyanate) to 4-methyl-m-phenylene diisocyanate is 2-8:2-8, such as 3～8: 3～8, 3～7: 3～7 or 4～6: 4～6;

In some typical embodiments, the molar amount of 4,4′-methylene bis(phenylisocyanate) is less than or equal to the molar amount of 4-methyl-m-phenylene diisocyanate.

In some more typical embodiments, the molar ratio of 4,4'-methylene bis(phenylisocyanate) to 4-methyl-m-phenylene diisocyanate is 1-2:1-4, Such as 1:1, 2:3, 1:4. In some typical embodiments, the moles of 4,4'-methylenebis(phenylisocyanate) and 4-methyl-m-phenylene diisocyanate The ratio is 1:4.

In some embodiments, reactive ion etching is used to remove the porogen. When using this method, the fluorine-containing gas generates free F under the plasma, and the free F reacts with SiO ₂ to generate SiF ₄ and oxygen.

In some embodiments, a hydrofluoric acid/ammonium fluoride buffer is used to remove the porogen. When using this method, the fluorine-containing substance reacts with SiO ₂ to generate SiF ₄ and oxygen.

In some embodiments, the thickness of the coating film is 100-500 μm, such as 150-450 μm, 200-400 μm or 250-350 μm.

In some embodiments, the polyimide porous membrane has a thickness of 8-40 μm, such as 10-35 μm, 15-30 μm or 20-25 μm.

The present disclosure provides a method for preparing a polyimide porous membrane. By adopting two different aromatic diisocyanate and aromatic dianhydride polycondensation reactions, CO ₂ is generated to facilitate the formation of pores, and nano-scale SiO ₂ is added at the same time. Pore-forming agent is more conducive to the formation of pores, and makes the formed pores more uniform and higher in porosity, thereby obtaining high-performance polymers with low dielectric constant, uniform pore distribution, good thermal stability, and good dimensional stability. imide porous membrane.

Example

Hereinafter, the present disclosure will be described in detail through examples.

In the following examples and comparative examples, performance parameters are determined according to the following methods:

(1) Porosity

Using the liquid immersion method, according to the mass change before and after the film is soaked in water, the pore volume V _pores of the membrane is determined. The skeleton volume V _{membrane skeleton} of the membrane can be obtained through the density of the membrane raw material and the dry film quality, and the porosity is V _pores /( V _hole + V _{membrane skeleton} );

(2) Dielectric constant

The dielectric constant of the film was measured by using an Agilent 4284A capacitance meter equipped with an Agilent 16451B dielectric connector. After testing the capacitance of the film, the dielectric constant was obtained by calculation, and the frequency was 1MHz.

(3) Dimensional stability

Cut a piece of film whose traction direction (MD) is 280mm and transverse direction (TD) is 255mm, and punch out a round hole with a diameter of 1mm at each of the four corners of the film at a distance of 13mm from the edge. Place the sample at 23°C, 50% relative humidity for at least 24h, measure the distances A-B, C-D, A-C, B-D between the center of the hole and then place the sample in a thermostat at 150°C for 30min without tension, Take it out and place it at 23°C, relative humidity 50% for 3h, and then measure the distance between the holes. The linear dimension changes in each direction as follows:

(4) T _g /(°C), T _5% /(°C) in the table

The glass transition temperature _Tg is measured by thermomechanical method (TMA)

T _5% measured according to GBT27761-2011

Example 1

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 2

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film was put into a buffer solution of hydrofluoric acid/ammonium fluoride (volume ratio: 3:5), soaked for 30 minutes, and SiO ₂ in the polyimide film was removed to obtain a porous polyimide film.

Example 3

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 5nm to the obtained polyamic acid solution (add 0.05gSiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 4

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 45nm to the obtained polyamic acid solution (add 0.05gSiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise temperature rise (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as protective gas, CHF3 as etching gas), time 1h, removes the SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 5

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) The obtained polyamic acid solution is degassed, and after degassing, it is coated on a clean glass plate with an automatic film coating machine, and the thickness of the coating film is 300 μm. The glass plate is placed in an oxygen-free oven, and the temperature is raised by steps ( Heat up to 100°C for 30 minutes, then heat up to 110°C for 30 minutes, then heat up to 120°C for 60 minutes, then heat up to 140°C for 60 minutes) heat treatment to form polyimide, after cooling to room temperature, take out the glass plate and put it in boiling water , the polyimide film was separated from the glass plate to obtain a porous imide film with a thickness of 18 ± 1 μm.

Example 6

(1) Under the condition of nitrogen protection and 25°C, 0.05mol (8.71g) of 4-methyl-m-phenylene diisocyanate and 0.05mol (12.51g) of 4,4'-methylenebis( Phenyl isocyanate) was dissolved in a three-necked flask with 243.84g NMP, 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylene carboxylic dianhydride was added, stirred for 5h, and the solid content was 15 % intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 7

(1) Under the condition of nitrogen protection and 25°C, 0.02mol (3.48g) of 4-methyl-m-phenylene diisocyanate and 0.08mol (20.02g) of 4,4'-methylenebis( Phenyl isocyanate) was dissolved in a three-necked flask with 256.76g NMP, added 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylene carboxylic acid dianhydride, stirred for 5h, and obtained a solid content of 15 % intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 8

(1) Under the condition of nitrogen protection and 25°C, 0.03mol (5.22g) of 4-methyl-m-phenylene diisocyanate and 0.07mol (17.52g) of 4,4'-methylenebis( Phenyl isocyanate) was dissolved in a three-necked flask with 252.45g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylcarboxylic dianhydride was added, stirred for 5h, and the solid content was 15 % intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 9

(1) Under the condition of nitrogen protection and 25°C, 0.04mol (6.97g) of 4-methyl-m-phenylene diisocyanate and 0.06mol (15.01g) of 4,4'-methylenebis( Phenyl isocyanate) was dissolved in a three-necked flask with 248.14g NMP, added 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylene carboxylic acid dianhydride, stirred for 5h, and obtained a solid content of 15 % intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 10

(1) Under the condition of nitrogen protection and 25°C, 0.06mol (10.45g) of 4-methyl-m-phenylene diisocyanate and 0.04mol (10.01g) of 4,4'-methylenebis( Phenyl isocyanate) was dissolved in a three-necked flask with 239.53g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylene carboxylic dianhydride was added, stirred for 5h, and a solid content of 15 % intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60min) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1μm. The obtained film is put into a reactive ion etching machine and etched (with helium as shielding gas, CHF3 as etching gas), time 1h, removes SiO in the polyimide film pore _- forming agent, obtains porous polyimide imide film.

Example 11

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetracarboxylic dianhydride was added and stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, keep it at 120°C for 2 hours, and heat-treat it to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to make the polyimide The amine film is separated from the glass plate to obtain an imide film with a thickness of 18±1 μm, and the obtained film is placed in a reactive ion etching machine for etching (helium is used as the protective gas, CHF3 is used as the etching gas), and the time 1h, remove the _SiO2 porogen in the polyimide film to obtain a porous polyimide film.

Comparative example 1

(1) Under the condition of nitrogen protection and 25°C, dissolve 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylcarboxylic dianhydride in a three-necked flask containing 237.04g of NMP, and add 0.1 mol (20.02 g) of 1-aminooctadecane was stirred and reacted for 5 h to obtain an intermediate polyamic acid solution with a solid content of 15%.

(2) The obtained polyamic acid solution is defoamed, and after defoaming, it is coated on a clean glass plate with an automatic film coating machine. The thickness of the coating film is 300 μm. The temperature was raised to 175°C at a high speed, kept for 30 minutes, and the solvent DMF was removed. After cooling to room temperature, place it in an oxygen-free oven, and use stepwise heating (heating to 200°C for 30 minutes, then heating to 280°C for 10 minutes, then raising the temperature to 320°C for 5 minutes, then raising the temperature to 370°C for 3 minutes, and finally raising the temperature to 400°C ℃ heat preservation 1min) thermal imidization into polyimide, after cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain a polyimide film with a thickness of 18±1μm .

Comparative example 2

(1) Under the condition of nitrogen protection and 25°C, dissolve 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylcarboxylic dianhydride in a three-necked flask containing 237.04g of NMP, and put 0.1 mol (10.81 g) of 1,4-phenylenediamine was stirred for 5 h to obtain an intermediate polyamic acid solution with a solid content of 15%.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven and heat-treat at 130°C to form polyimide. After cooling to room temperature, take out the glass plate and place it in boiling water to make the polyimide film and Separate the glass plate to obtain an imide film with a thickness of 18±1 μm, put the obtained film into a reactive ion etching machine for etching (using helium as the protective gas and CHF3 as the etching gas) for 1 hour, remove _SiO2 porogen in polyimide film to obtain porous polyimide film.

Comparative example 3

(1) Under the condition of nitrogen protection and 25°C, 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4,4'-methylenebis(iso Phenyl cyanate) was dissolved in a three-necked flask with 230.86g NMP, and 0.1mol (21.81g) of 1,2,4,5-benzenetetramethylene carboxylic dianhydride was added, stirred for 5h to obtain a solid content of 15%. The intermediate product polyamic acid solution.

(2) Add nano-SiO ₂ with an average particle size of 30nm to the obtained polyamic acid solution (add 0.05g SiO ₂ per 100g polyamic acid), mix well and then defoam. On a glass plate, the thickness of the coating film is 300 μm. Place the glass plate in an oxygen-free oven, and use a stepwise heating method (heating to 100°C for 30 minutes, then heating to 110°C for 30 minutes, then heating to 120°C for 60 minutes, and then heating to Heat treatment at 140°C for 60 minutes) to form polyimide. After cooling to room temperature, take out the glass plate and put it in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18±1 μm. Table 1 embodiment 1～11 and the polyimide film property contrast prepared by comparative example 1～3

It can be seen that, compared with Comparative Examples 1-3, the polyimide porous membrane prepared by Implementation 1-11 of the present disclosure has a higher porosity, thereby obtaining a lower dielectric constant and a more uniform pore distribution, A high-performance polyimide porous membrane with higher thermal stability and higher dimensional stability.

At the same time, 4-methyl-m-phenylene diisocyanate, 4,4'-methylene bis(phenylisocyanate), 1,2,4,5-benzenetetramethylcarboxylic acid diisocyanate, The molar ratio of anhydride is 80:20:100, adding SiO ₂ (100g polyamic acid plus 0.05gSiO ₂ ) with an average particle diameter of 30nm, and the porous polyimide film obtained after etching by reactive ion etching machine can be further Improve the thermal stability, dimensional stability, higher porosity and further reduce the dielectric constant of the polyimide porous membrane.

The above content related to common knowledge will not be described in detail, and those skilled in the art can understand it.

The above descriptions are only some embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection of the present disclosure. within range. The technical scope of this disclosure is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Industrial Applicability

The disclosure provides a polyimide porous membrane and its preparation method and application. The polyimide porous membrane prepared by the disclosure has high porosity, low dielectric constant, uniform pore distribution, good thermal stability, and dimensional stability. Good and high performance, can be widely used in the field of dielectric materials, has excellent industrial application value and broad market prospects.

Claims (16)

1. A kind of preparation method of polyimide porous membrane, it is characterized in that: dissolving two kinds of different aromatic diisocyanates in solvent, add aromatic dianhydride again, stir to obtain intermediate product polyamic acid, polyamic acid is carried out defoaming coating, followed by heat treatment to obtain the polyimide porous membrane.
2. The preparation method of polyimide porous membrane according to claim 1, is characterized in that: after obtaining intermediate product polyamic acid, then add pore-forming agent and mix, rear defoaming coating, then carry out heat treatment, finally remove The pore-forming agent obtains the polyimide porous membrane.
3. The preparation method of polyimide porous membrane according to claim 1 or 2, is characterized in that: described aromatic diisocyanate is selected from 4-methyl-m-phenylene diisocyanate, 2,6-toluene diisocyanate , 4,4′-methylenebis(phenylisocyanate), 2,4,6-trimethyl-1,3-benzenediisocyanate or 2,3,5,6-tetramethyl-1, One of 4-phenylene diisocyanates; the aromatic dianhydride is selected from 3,4,3',4'-benzophenone tetracarboxylic dianhydride, 1,2,4,5-benzenetetramethylcarboxylate One of acid dianhydride and 3,4,3',4'-biphenyltetracarboxylic dianhydride.
4. According to the preparation method of polyimide porous membrane according to any one of claims 1-3, it is characterized in that: the solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide One or more of amides and N-methylpyrrolidone.
5. According to the preparation method of polyimide porous membrane according to any one of claims 1-4, it is characterized in that: the pore-forming agent is selected from one or more of SiO ₂ , ceramics, aluminum powder, and magnesium powder. kind.
6. According to the preparation method of polyimide porous membrane described in any one in the claim 1-5, it is characterized in that: two kinds of different aromatic diisocyanates and aromatic dianhydride copolymerization reaction conditions are under nitrogen protection and 0～ 40°C temperature.
7. According to the preparation method of the polyimide porous membrane described in any one in claim 1-6, it is characterized in that: two kinds of different aromatic diisocyanates and aromatic dianhydride are fully stirred to obtain intermediate product polyamic acid, so The solid content of the polyamic acid is between 13 and 16 wt%.
8. The method for preparing a polyimide porous membrane according to any one of claims 1-7, characterized in that: the heat treatment adopts stepwise temperature rise.
9. The preparation method of polyimide porous membrane according to claim 3, is characterized in that: two kinds of different aromatic diisocyanates are 4,4'-methylene bis(phenylisocyanate) and 4-methyl Base-m-phenylene diisocyanate; the aromatic dianhydride is 1,2,4,5-benzenetetramethanecarboxylic dianhydride.
10. The preparation method of polyimide porous membrane according to claim 9, is characterized in that: the 4,4'-methylenebis(phenylisocyanate), 4-methyl-m-phenylenebis The molar ratio of the sum of molar amounts of isocyanate to 1,2,4,5-benzenetetracarboxylic dianhydride is 1:1.
11. The preparation method of polyimide porous membrane according to claim 9 or 10, characterized in that: the molar amount of the 4,4'-methylene bis(phenylisocyanate) is less than 4-methyl -The feeding molar amount of m-phenylene diisocyanate.
12. The preparation method of the polyimide porous membrane according to claim 5, characterized in that: the pore-forming agent is SiO ₂ , and the SiO ₂ is nano-scale SiO ₂ .
13. The preparation method of polyimide porous membrane according to claim 12, characterized in that: the average particle diameter of the nano-scale SiO ₂ is 5-45nm.
14. A polyimide porous membrane, characterized in that it is produced by the preparation method described in any one of claims 1-13.
15. The porous imide membrane according to claim 14, wherein the porous polyimide membrane satisfies at least one of the following features (1) to (3):

    (1) The dielectric constant of the polyimide porous membrane is 1.45～1.98;

    (2) The porosity of the polyimide porous membrane is 73% to 79%;

    (3) The thermal shrinkage of the polyimide porous membrane at 150°C is 0.25-0.28% in the MD direction, and 0.25-0.30% in the TD direction.
16. The use of the imide porous film as claimed in claim 14 or 15 in dielectric materials.

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