CN113248773B - Polyimide porous membrane and preparation method thereof - Google Patents
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Abstract
The invention relates to the technical field of preparation of polymer dielectric materials, and discloses a preparation method of a polyimide porous membrane. By the special method, the high-performance polyimide porous membrane with low dielectric constant, uniform pore distribution, good thermal stability and good size stability is obtained, so that the signal transmission speed can be increased, signal interference and inductive coupling are reduced, and the polyimide porous membrane is better applied to the integrated circuit industry.
Description
Technical Field
The invention relates to the technical field of preparation of polymer dielectric materials, in particular to a polyimide porous membrane and a preparation method thereof.
Background
With the development of scientific technology, the trend of the integrated circuit industry towards low-dimensional, large-scale and even ultra-large-scale integration is increasingly obvious. In order to increase the signal transmission speed and reduce signal interference and inductive coupling, a material with a low dielectric constant must be used. For the next generation of dielectric materials, a dielectric constant of 2.2 or less is required. Polyimide is the most promising polymer dielectric material due to its outstanding thermal and mechanical properties. Because the dielectric constant of common polyimide is usually between 3 and 4, the synthesis of polyimide materials with lower dielectric constant has become a hot spot of current research.
The dielectric constant of a material is closely related to its molar polarizability and molar volume according to the Clausius Mossotti equation. Therefore, there are two main types of methods for reducing the PI dielectric constant: (1) substituents with low polarizability are introduced to reduce the polarizability of dipoles in the molecule. (2) The number of dipoles in a unit volume is reduced by introducing bulky groups or even pore structures inside the material.
The dielectric constant of a common polyimide film is 3-4, and the common polyimide film cannot meet the requirements of integrated circuits at the present stage, while the traditional polyimide porous film has a lower dielectric constant, but the pore distribution is not uniform, the thermal stability is poor, and the dimensional stability is poor.
The Clausius Mossotti equation is as follows:
wherein Pm is the molar polarizability of the atomic group, and Vm is the molar volume of the atomic group.
Disclosure of Invention
In view of the above, the present invention is to provide a method for preparing a polyimide porous membrane, which has a low dielectric constant, uniform pore distribution, good thermal stability, and good dimensional stability.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention aims to provide a preparation method of a polyimide porous membrane, which comprises the following steps: dissolving two different aromatic diisocyanates in a polar solvent, adding aromatic dianhydride, fully stirring to obtain an intermediate product polyamic acid, defoaming the polyamic acid, coating the polyamic acid on a glass plate, and performing heat treatment to obtain the polyimide porous membrane.
Further, after the intermediate product polyamic acid is obtained, a pore-forming agent is added to be uniformly mixed, the mixture is defoamed and coated on a glass plate, then heat treatment is carried out, and finally the pore-forming agent is removed to obtain the polyimide porous membrane.
Further, the aromatic diisocyanate is selected from one of 4-methyl-m-phenylene diisocyanate, 2, 6-toluene diisocyanate, 4' -methylene bis (phenyl isocyanate), 2,4, 6-trimethyl-1, 3-benzene diisocyanate or 2,3,5, 6-tetramethyl-1, 4-benzene diisocyanate;
further, the aromatic dianhydride is selected from one of 3,4,3 ', 4' -benzophenone tetracarboxylic dianhydride, 1,2,4, 5-pyromellitic dianhydride, and 3,4,3 ', 4' -biphenyl tetracarboxylic dianhydride.
Further, the polar solvent is selected from one or more of N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
Further, the pore former is selected from SiO2One or more of ceramic, aluminum powder and magnesium powder.
Further, the copolymerization reaction conditions of the two different aromatic diisocyanates and the aromatic dianhydride are under the protection of nitrogen and at the temperature of 0-40 ℃.
Further, two different aromatic diisocyanates and aromatic dianhydride are fully stirred to obtain an intermediate product polyamic acid, and the solid content of the polyamic acid is 13-16 wt%.
Further, the solid content of the polyamic acid was 15 wt%.
Further, the heat treatment adopts step heating, and the step heating process is as follows: heating to 100 deg.C, maintaining for 30min, heating to 110 deg.C, maintaining for 30min, heating to 120 deg.C, maintaining for 60min, heating to 140 deg.C, and maintaining for 60 min.
Further, the two different aromatic diisocyanates are 4, 4' -methylenebis (phenyl isocyanate) and 4-methyl-m-phenylene diisocyanate;
still further, the aromatic dianhydride is 1,2,4, 5-benzenetetracarboxylic dianhydride.
Specifically, the molar ratio of the sum of the molar amounts of the 4, 4' -methylenebis (phenyl isocyanate) and the 4-methyl-m-phenylene diisocyanate to the 1,2,4, 5-pyromellitic dianhydride is 1:1 during the feeding reaction.
Preferably, the charged molar amount of the 4, 4' -methylenebis (phenyl isocyanate) is less than the charged molar amount of 4-methyl-m-phenylene diisocyanate.
More preferably, the molar ratio of 4, 4' -methylenebis (phenyl isocyanate) to 4-methyl-m-phenylene diisocyanate is 1: 4.
Further, the pore-forming agent is SiO2Said SiO2Is nano-scale SiO2。
In particular, the nano-scale SiO2The average particle diameter of (B) is 5 to 45 nm.
Preferably, the nano-scale SiO2Has an average particle diameter of 30 nm.
Further, a reactive ion etching method is used to remove the porogen.
Further, a hydrofluoric/ammonium fluoride buffer was used to remove the porogen.
The present invention also provides a polyimide porous film produced by any of the above-mentioned methods.
Further, the polyimide porous film has a dielectric constant of 1.45 to 1.98.
Further, the polyimide porous film has a dielectric constant of 1.45 to 1.74.
Preferably, the polyimide porous film has a dielectric constant of 1.45 to 1.63, more preferably 1.45 to 1.60, and most preferably 1.45 to 1.49.
Further, the polyimide porous membrane has a porosity of 68 to 79%.
Further, the polyimide porous membrane has a porosity of 73 to 79%.
Further, the polyimide porous membrane has a thermal shrinkage of 0.25 to 0.28% in the MD direction and a thermal shrinkage of 0.25 to 0.30% in the TD direction at 150 ℃.
The invention has the following beneficial effects:
the invention provides a preparation method of a polyimide porous membrane, which generates CO by adopting polycondensation reaction of two different aromatic diisocyanates and aromatic dianhydride 2Is beneficial to the formation of pores, and simultaneously nano SiO is added2The pore-forming agent is more beneficial to the formation of pores, ensures that the formed pores are more uniform and the porosity is higher, thereby obtaining the porous ceramic material with low dielectric constant and uniform pore distributionAnd a high-performance polyimide porous membrane having good thermal stability and dimensional stability.
Drawings
FIG. 1 shows the chemical reaction formula of 4, 4' -methylenebis (phenyl isocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4, 5-pyromellitic dianhydride in 11 embodiments of the present invention.
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The specific embodiment of the invention provides a preparation method of a polyimide porous membrane, which has the technical key points that: under the protection of nitrogen and at a certain temperature, 4' -methylene bis (phenyl isocyanate) and 4-methyl-m-phenylene diisocyanate are dissolved in a polar solvent, 1,2,4, 5-benzene tetracarboxylic dianhydride is added to be stirred and reacted to obtain intermediate product polyamic acid, the obtained polyamic acid is added with a pore-forming agent to be uniformly mixed, the mixture is defoamed in vacuum and then coated on a glass plate, thermal imidization treatment is carried out, and then the pore-forming agent is removed, so that the polyimide porous membrane is obtained.
Here, the polar solvent is one or more selected from N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
Here, the pore-forming agent is selected from SiO2One or more of ceramic, aluminum powder and magnesium powder.
Preferably, the pore-forming agent is SiO2The SiO is2Is nano-scale SiO2. Due to the nano-SiO2The porous structure can adsorb metal ions, so that the possibility of oxidation and yellowing is reduced; second nano-scale SiO2The pore-forming agent has larger bulk density, is easier to mix with resin and is more beneficial to operation.
Further preferred is nanoscale SiO2The average particle diameter of (2) is 5 to 45nm, wherein an excessively small particle diameter is not favorable for pore formation, and an excessively large particle diameter is favorable for film strength, and more preferably an average particle diameter of 30 nm.
Here, the copolymerization reaction temperature of 4, 4' -methylenebis (phenyl isocyanate), 4-methyl-m-phenylene diisocyanate and 1,2,4, 5-pyromellitic dianhydride is 0 to 40 ℃, and a water bath at 25 ℃ is preferable.
Here, the solid content of the polyamic acid is between 13 and 16 wt%.
Preferably, the solid content of the polyamic acid is 15 wt%.
Here, the heat treatment employs a step heating process, and the step heating process is: firstly heating to 100 ℃ and preserving heat for 30min, then heating to 110 ℃ and preserving heat for 30min, then heating to 120 ℃ and preserving heat for 60min, then heating to 140 ℃ and preserving heat for 60min, and adopting step heating only for reaction, and having no obvious influence on dielectric constant.
Here, the molar ratio of the sum of the molar amounts of 4, 4' -methylenebis (phenyl isocyanate) and 4-methyl-m-phenylene diisocyanate to 1,2,4, 5-pyromellitic dianhydride in the charging reaction was 1: 1.
Preferably, the molar ratio of the 4, 4' -methylene bis (phenyl isocyanate) to the 4-methyl-m-phenylene diisocyanate is 2-8: 2-8;
more preferably, the charged molar amount of the 4, 4' -methylenebis (phenyl isocyanate) is not more than the charged molar amount of 4-methyl-m-phenylene diisocyanate.
Still more preferably, the molar ratio of 4, 4' -methylenebis (phenyl isocyanate) to 4-methyl-m-phenylene diisocyanate is 1:1, 2:3, 1:4, most preferably 1: 4.
Here, a reactive ion etching method is used to remove the porogen. When the method is adopted, the fluorine-containing gas generates free F, free F and SiO under plasma2Reaction to form SiF4And oxygen.
Here, a hydrofluoric acid/ammonium fluoride buffer is used to remove the porogen. When the method is adopted, the fluorine-containing substance and SiO2Reaction to form SiF4And oxygen.
Here, the coating film thickness is 100 to 500 μm.
The thickness of the polyimide porous membrane is 8 to 40 μm.
The present invention will be described in detail below by way of examples.
In the following examples and comparative examples, the performance parameters were determined as follows:
(1) porosity factor
Determining the pore volume V of the membrane by adopting an immersion method according to the mass change before and after the membrane is immersed in waterHole(s)Skeleton volume V of the filmMembrane skeletonCan be obtained by the density of the membrane raw material and the quality of a dry membrane, and has the porosity of VHole(s)/(VHole(s)+VMembrane skeleton)；
(2) Dielectric constant
The dielectric constant of the film was determined by using an Agilent 4284A capacitance meter equipped with an Agilent 16451B dielectric connector, and the dielectric constant was obtained by calculation after measuring the capacitance of the film, and the frequency was 1 MHz.
(3) Dimensional stability
One film sheet with a drawing direction (MD) of 280mm and a Transverse Direction (TD) of 255mm is cut, and circular holes with the diameter of 1mm are punched at the positions, 13mm away from the edge, of four corners of the film. The samples were placed at 23 ℃ at 50% relative humidity for at least 24h, the distances A-B, C-D, A-C, B-D between the centers of the wells were measured, the samples were then placed in a 150 ℃ incubator without tension for 30min, taken out at 23 ℃ at 50% relative humidity for 3h, and the distances between the wells were measured. The linear dimensional changes in each direction are as follows:
(4) in table Tg/(℃)、T5％/(℃)
Glass transition temperature T gMeasurement by Thermomechanical Method (TMA)
T5％Measured according to GBT27761-2011
Example 1
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average grain diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on a clean glass plate by using an automatic coating machine, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating process (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (taking helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h 2Pore-forming agent to obtain the porous polyimide film.
Example 2
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average grain diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on clean glass plate with an automatic coating machine after defoaming, coating the film with a thickness of 300 μm, placing the glass plate in an oxygen-free oven, heating by steps (heating to 100 deg.C and maintaining for 30min, then heating to 110 deg.C and maintaining for 30min, then heating to 120 deg.C and maintaining for 60min, then heating to 140 deg.C and maintaining for 60min60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18 +/-1 μm, soaking the obtained film in a buffer solution of hydrofluoric acid/ammonium fluoride (volume ratio of 3:5) for 30min, and removing SiO in the polyimide film 2And obtaining the porous polyimide film.
Example 3
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average grain diameter of 5nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on a clean glass plate by using an automatic coating machine, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating process (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (taking helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h 2Pore-forming agent to obtain the porous polyimide film.
Example 4
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Will be provided withAdding nanometer SiO with average particle diameter of 45nm into the obtained polyamic acid solution2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on a clean glass plate by using an automatic coating machine, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating process (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (taking helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h 2Pore-forming agent to obtain the porous polyimide film.
Example 5
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Defoaming the obtained polyamic acid solution, coating the polyamic acid solution on a clean glass plate by an automatic coating machine after defoaming, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating (heating to 100 ℃ and preserving heat for 30min, then heating to 110 ℃ and preserving heat for 30min, then heating to 120 ℃ and preserving heat for 60min, and then heating to 140 ℃ and preserving heat for 60min) to form polyimide, taking out the glass plate after cooling to room temperature, and placing the glass plate in boiling water to separate the polyimide film from the glass plate to obtain the porous imide film with the thickness of 18 +/-1 mu m.
Example 6
(1) 0.05mol (8.71g) of 4-methyl-m-phenylene diisocyanate and 0.05mol (12.51g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 243.84g of NMP under nitrogen protection at 25 ℃ and 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on a clean glass plate by using an automatic coating machine, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating process (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (taking helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Example 7
(1) 0.02mol (3.48g) of 4-methyl-m-phenylene diisocyanate and 0.08mol (20.02g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 256.76g of NMP under nitrogen protection at 25 ℃ and 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Debubbling after mixing, coating on clean glass plate with automatic coating machine to film thickness of 300 μm, placing the glass plate in oxygen-free oven, heating to 100 deg.C for 30min, then to 110 deg.C for 30min, then to 120 deg.C for 60min, then to 140 deg.C for 60min to form polyimide, cooling to room temperature, taking out the glass plate, placing in boiling water to separate the polyimide film from the glass plate to obtain imide film with thickness of 18 + -1 μm, and etching the film in reactive ion etcher with helium as protective gas, CHF3As etching gas) for 1h, removing SiO in the polyimide film2Pore-forming agent to obtain the porous polyimide film.
Example 8
(1) 0.03mol (5.22g) of 4-methyl-m-phenylene diisocyanate and 0.07mol (17.52g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 252.45g of NMP under nitrogen atmosphere at 25 ℃ and 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Debubbling after mixing, coating on a clean glass plate with a film coating thickness of 300 μm by an automatic film coating machine after debubbling, placing the glass plate in an oxygen-free oven, heating to 100 deg.C for 30min, heating to 110 deg.C for 30min, heating to 120 deg.C for 60min, heating to 140 deg.C for 60min to form polyimide, cooling to room temperature, taking out the glass plate, placing in boiling water to separate the polyimide film from the glass plate to obtain an imide film with a thickness of 18 + -1 μm, placing the obtained film in a reactive ion etcher for etching (with helium as a protective gas and CHF3 as an etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Example 9
(1) 0.04mol (6.97g) of 4-methyl-m-phenylene diisocyanate and 0.06mol (15.01g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 248.14g of NMP under nitrogen atmosphere at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average grain diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on clean glass plate with an automatic coating machine to a coating thickness of 300 μm, and coatingPlacing the glass plate in an oxygen-free oven, performing heat treatment by using step heating (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, taking out the glass plate after cooling to room temperature, placing the glass plate in boiling water to separate the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (with helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Example 10
(1) 0.06mol (10.45g) of 4-methyl-m-phenylene diisocyanate and 0.04mol (10.01g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 239.53g of NMP under nitrogen protection at 25 ℃ and 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average grain diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Mixing uniformly, defoaming, coating on a clean glass plate by using an automatic coating machine, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using a step heating process (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (taking helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Example 11
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Defoaming after mixing uniformly, coating on a clean glass plate with an automatic coating machine after defoaming, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, keeping the temperature at 120 ℃ for 2h, performing heat treatment to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etching machine for etching (with helium as protective gas and CHF3 as etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Comparative example 1
(1) 0.1mol (21.81g) of 1,2,4, 5-pyromellitic dianhydride was dissolved in a three-necked flask containing 237.04g of NMP under nitrogen atmosphere at 25 ℃ and 0.1mol (20.02g) of 1-aminooctadecane was added thereto and the mixture was stirred for reaction for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) And (3) defoaming the obtained polyamic acid solution, coating the polyamic acid solution on a clean glass plate by using an automatic coating machine after defoaming, wherein the coating thickness is 300 mu m, placing the glass plate in an oven, heating to 175 ℃ at the speed of 1 ℃/min, keeping the temperature for 30min, and removing a solvent DMF. Cooling to room temperature, placing in an oxygen-free oven, performing thermal imidization to form polyimide by using step heating (heating to 200 ℃ and keeping the temperature for 30min, then heating to 280 ℃ and keeping the temperature for 10min, then heating to 320 ℃ and keeping the temperature for 5min, then heating to 370 ℃ and keeping the temperature for 3min, and finally heating to 400 ℃ and keeping the temperature for 1min), cooling to room temperature, taking out the glass plate, placing in boiling water, and separating the polyimide film from the glass plate to obtain the polyimide film with the thickness of 18 +/-1 mu m.
Comparative example 2
(1) 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was dissolved in a three-necked flask containing 237.04g of NMP under nitrogen atmosphere at 25 ℃ and 0.1mol (10.81g) of 1, 4-benzenediamine was introduced thereinto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) Defoaming after mixing uniformly, coating on a clean glass plate with an automatic coating machine after defoaming, wherein the coating thickness is 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment at 130 ℃ to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, separating the polyimide film from the glass plate to obtain an imide film with the thickness of 18 +/-1 mu m, placing the obtained film in a reactive ion etcher for etching (helium is used as protective gas, CHF3 is used as etching gas), and removing SiO in the polyimide film for 1h2Pore-forming agent to obtain the porous polyimide film.
Comparative example 3
(1) 0.08mol (13.93g) of 4-methyl-m-phenylene diisocyanate and 0.02mol (5g) of 4, 4' -methylenebis (phenyl isocyanate) were dissolved in a three-necked flask containing 230.86g of NMP under nitrogen protection at 25 ℃, 0.1mol (21.81g) of 1,2,4, 5-benzenetetracarboxylic dianhydride was added thereto and stirred for 5 hours to obtain an intermediate polyamic acid solution having a solid content of 15%.
(2) Adding the obtained polyamic acid solution into nano SiO with the average particle diameter of 30nm2(0.05 gSiO per 100g polyamic acid2) The preparation method comprises the steps of mixing uniformly, defoaming, coating on a clean glass plate by an automatic coating machine after defoaming, coating with the thickness of 300 mu m, placing the glass plate in an oxygen-free oven, performing heat treatment by using step heating (heating to 100 ℃ and keeping the temperature for 30min, then heating to 110 ℃ and keeping the temperature for 30min, then heating to 120 ℃ and keeping the temperature for 60min, and then heating to 140 ℃ and keeping the temperature for 60min) to form polyimide, cooling to room temperature, taking out the glass plate, placing the glass plate in boiling water, and separating the polyimide film from the glass plate to obtain the imide film with the thickness of 18 +/-1 mu m.
TABLE 1 comparison of the Properties of polyimide films prepared in examples 1 to 11 and comparative examples 1 to 3
It can be seen that the molar ratio of 4-methyl-m-phenylene diisocyanate, 4' -methylenebis (phenyl isocyanate), 1,2,4, 5-benzenetetracarboxylic dianhydride was 80: 20: 100, adding SiO with average particle size of 30nm2(100g Polyamic acid plus 0.05 gSiO)2) The porous polyimide film obtained by etching by adopting the reactive ion etcher has better thermal stability and dimensional stability, higher porosity and lower dielectric constant.
The above matters related to the common general knowledge are not described in detail and can be understood by those skilled in the art.
The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.
Claims (10)
1. A method for preparing a polyimide porous membrane is characterized by comprising the following steps: dissolving two different aromatic diisocyanates in a solvent, adding aromatic dianhydride, stirring to obtain an intermediate product polyamic acid, defoaming and coating the polyamic acid, and then performing heat treatment to obtain the polyimide porous membrane;
wherein the two different aromatic diisocyanates are 4, 4' -methylenebis (phenyl isocyanate) and 4-methyl-m-phenylene diisocyanate;
wherein the aromatic dianhydride is 1,2,4, 5-benzenetetracarboxylic dianhydride;
wherein the heat treatment adopts step heating or is kept at 120 ℃ for 2 hours, and the step heating process comprises the following steps: firstly heating to 100 ℃ and preserving heat for 30 minutes, then heating to 110 ℃ and preserving heat for 30 minutes, then heating to 120 ℃ and preserving heat for 60 minutes, and then heating to 140 ℃ and preserving heat for 60 minutes.
2. The method for producing a polyimide porous film according to claim 1, characterized in that: and after the intermediate product polyamic acid is obtained, adding a pore-forming agent for mixing, defoaming and coating, performing heat treatment, and finally removing the pore-forming agent to obtain the polyimide porous membrane.
3. The method for producing a polyimide porous membrane according to claim 1 or 2, characterized in that: the solvent is one or more selected from N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
4. The method for producing a polyimide porous membrane according to claim 2, characterized in that: the pore-forming agent is selected from SiO2One or more of ceramic, aluminum powder and magnesium powder.
5. The method for producing a polyimide porous membrane according to claim 1 or 2, characterized in that: the copolymerization reaction conditions of the two different aromatic diisocyanates and the aromatic dianhydride are under the protection of nitrogen and at the temperature of 0-40 ℃.
6. The method for producing a polyimide porous membrane according to claim 1 or 2, characterized in that: two different aromatic diisocyanates and aromatic dianhydride are fully stirred to obtain intermediate product polyamic acid, and the solid content of the polyamic acid is between 13 and 16 weight percent.
7. The method for producing a polyimide porous membrane according to claim 1, characterized in that: the molar ratio of the sum of the molar amounts of the 4, 4' -methylenebis (phenyl isocyanate) and the 4-methyl-m-phenylene diisocyanate to the 1,2,4, 5-pyromellitic dianhydride is 1: 1.
8. The method for producing a polyimide porous membrane according to claim 2, characterized in that: the pore-forming agent is SiO2Said SiO2Is nano-scale SiO2。
9. The method for producing a polyimide porous membrane according to claim 8, characterized in that: the nano SiO2The average particle diameter of (B) is 5 to 45 nm.
10. A polyimide porous film characterized by: is prepared by the preparation method of any one of claims 1 to 9.
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