JP2013540208A - Copolymerized polyimide / nanofiber nonwoven fabric, production method and application thereof - Google Patents

Abstract

The present invention relates to a copolymerized polyimide / nanofiber nonwoven fabric, a method for producing the same, and an application thereof. In the present invention, a tetracarboxylic dianhydride monomer and a diamine monomer are reacted, a highly polar solvent is used as a reaction medium, and mechanically stirred in a reaction kettle to perform condensation polymerization to form a copolymerized polyamic acid solution. Electrostatic spinning is performed by applying a high piezoelectric field to the polymerized polyamic acid solution, processed into a copolymerized polyamic acid nanofiber non-woven fabric, imidized at high temperature, strong tear resistance, high porosity, high Copolymer polyimide / nanofiber nonwoven fabrics that can withstand low temperatures and have excellent mechanical properties are manufactured and applied mainly to battery separators and capacitor separators.
[Selection figure] None

Description

  The present invention relates to a copolymerized polyimide, a method for producing the same, and an application thereof. Specifically, the present invention relates to a polyimide / nanofiber nonwoven fabric, a production method, and an application thereof as a battery separator.

  Chemical batteries are an extremely important component in modern life, and mobile phone batteries and automobile power batteries under development are all indispensable products for human beings to pursue a high-quality life. . However, battery safety is a serious scientific and social responsibility issue that has attracted people's attention, and the development of a safe battery separator is a technical solution that solves the problem of battery safety. It is the key. Battery separators such as polyethylene (PE) and polypropylene (PP) currently used in the battery industry have a low melting temperature and a too high heat shrinkage rate, thus ensuring their integrity at relatively high temperatures. In the case of overheating, overcharging, etc., it often shrinks due to heat, eventually melts, the battery separator ruptures, and a serious accident such as thermal runaway or explosion occurs due to a short circuit inside the battery There is. Therefore, the development of materials with good heat resistance and resistance to thermal shrinkage and application to battery separators is the key to solving chemical battery safety issues.

  An object of the present invention is to provide a copolymerized polyimide / nanofiber nonwoven fabric having characteristics such as strong tear resistance, high porosity, withstand high and low temperatures, and excellent mechanical performance.

  Another object of the present invention is to provide a method for producing the polyimide nanofiber nonwoven fabric of the present invention.

  Yet another object of the present invention is to apply a polyimide nanofiber nonwoven fabric to a battery separator.

  In order to achieve the above object, the technical technique employed in the present invention is as follows.

  The copolymerized polyimide / nanofiber nonwoven fabric of the present invention is obtained by copolymerizing a copolymerized polyamic acid with three or more monomers among the following four monomers (I), (II), (III), and (IV). Further, it is subjected to electrostatic spinning and imidization.

  In the formula, the copolymerized polyimide has the following chemical structure.

In this case, n is a natural number of 50 to 300, m is a natural number of 50 to 300, R ₁ and R ₃ are residue structures of C _{4 to} C ₃₀ tetracarboxylic acid or dianhydride monomers, R ₂ and R ₄ are residue structures of C _{6 to} C ₃₀ diamine monomers, and the ratio of the total amount of tetracarboxylic dianhydride monomer to the total amount of dianhydride monomer always maintains 1: 1. .

  Preferred copolymerized polyimide nanofiber nonwoven fabrics are obtained by copolymerization of one tetracarboxylic dianhydride monomer and two diamine monomers, that is, the above (I), (III), (IV) or (II). ), (III), and (IV). The molar ratio of the three monomers is (I) :( III) :( IV) or (II) :( III) :( IV) = [1]: [0.05-0.95]: [0. 05 to 0.95].

  A preferable copolymerized polyimide / nanofiber nonwoven fabric may be obtained by copolymerization of two types of tetracarboxylic dianhydride monomers and one type of diamine monomer, and the above (I), (II), (III) or (I ), (II), and (IV), the molar ratio of the three monomers is (I) :( II) :( III) or (II) :( III) :( IV) = [0.05-0.95]: [0.05-0.95]: [1].

  Preferred copolymerized polyimide / nanofiber nonwoven fabric is a copolymer of two kinds of tetracarboxylic dianhydride monomers and two kinds of diamine monomers, that is, the above (I), (II), (III), (IV). The four monomers may be copolymerized with each other in a molar ratio of [(I) + (II)]: [(III) + (IV)] = 1: 1.

Preferably, R ₁ and R ₃ are each one selected from the following tetracarboxylic dianhydride residue structures.

Preferably, R ₂ and R ₄ are each one selected from the following diamine residue structures.

The chemical component of the copolymerized imide nanofiber of the present invention may be a copolymer product of one dianhydride monomer and two diamine monomers, and may be two dianhydride monomers and one kind. It may be a copolymerization product with a diamine monomer, or may be a copolymerization product of two dianhydride monomers and two diamine monomers. Specifically, R ₁ and R ₃ in the formula can be the same residue or different residues, R ₂ and R ₄ can be the same residue or different residues, and R ₁ and R ₃ are the same. In the case where R ₂ and R ₄ are different, similarly, when R ₂ and R ₄ are the same, R ₁ and R ₃ are always different, and the chemical component of the copolymerized imide nanofiber is at least 3 It is guaranteed to be obtained by copolymerization of seed monomers.

The thickness of the copolymerized imide nanofiber nonwoven fabric of the present invention is 10 to 60 μm, the elongation at break is 20% or more, it is not completely dissolved in ordinary organic solvents, and the glass transition temperature is 210 ° C. or more. The thermal decomposition temperature is 510 ° C. or higher, the melting temperature exceeds 350 ° C., and thus does not melt below the decomposition temperature, the porosity is higher than 80%, the mechanical strength is higher than 20 MPa, and the dielectric breakdown strength is 1 × 10 ⁷ V / m is exceeded. The electrospinning copolymerized polyimide / nanofiber nonwoven fabric having such properties has the properties of tear resistance, anti-heat shrinkage, high temperature resistance, high voltage resistance and high current overcharge, and the imide nanofiber nonwoven fabric of the present invention has various high capacity and high capacity. Application to power battery separators and capacitor separators has a huge potential market, such as in the automotive power battery and supercapacitor industries.

  Another object of the present invention is to provide a method for producing a copolymerized polyimide nanofiber nonwoven fabric comprising the following steps.

  (1) After purifying three or more kinds of monomers, they are put together with an appropriate amount of solvent into a polymerization reaction kettle and reacted for a certain time with stirring. Obtain a copolymerized polyamic acid (polyimide precursor) solution, perform electrospinning on the copolymerized polyamic acid solution in a high piezoelectric field, collect the stainless steel drum as a collector, and collect the copolymerized polyamic acid nanofiber nonwoven fabric. obtain.

  The solvent used is a highly polar solvent, and is preferably one of N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMAC). The stirring reaction time is 1 to 10 hours, preferably the reaction time is 5 to 10 hours. The reaction temperature is 0 to 30 ° C., preferably the reaction temperature is 5 to 10 ° C. The electric field strength used in the electrospinning process is preferably 250 to 300 kV / m. The diameter of the stainless steel drum collector is 0.3 m.

  (2) The obtained copolymer polyamic acid nanofiber nonwoven fabric is placed in a high temperature furnace and heated to imidize.

  The imidization is performed in a nitrogen gas atmosphere, and the heating process is performed by heating from room temperature to 200 to 250 ° C. at a heating rate of 20 ° C./min, and retaining at this temperature for 30 minutes, and then 5 ° C. The temperature is raised to 330-370 ° C. at a rate of temperature rise / minute, the temperature is maintained for 30 minutes, and then the power is turned off.

  (3) Characterization: absolute viscosity of copolymerized polyamic acid solution and spinning solution, diameter of electrospun copolymerized polyamic acid nanofiber, thermal decomposition temperature of copolymerized polyimide / nanofiber nonwoven fabric, machine of copolymerized polyimide / nanofiber nonwoven fabric Includes measurement of properties (strength, elongation at break, etc.), glass transition temperature of copolymerized polyimide / nanofiber nonwoven fabric, specific surface area of copolymerized polyimide / nanofiber nonwoven fabric, and dielectric breakdown strength of copolymerized polyimide / nanofiber nonwoven fabric.

  In the present invention, the absolute viscosity of the polyamic acid solution and the spinning solution was measured using an NDJ-8S viscometer (Shanghai Precision Science Equipment Co., Ltd.). The diameter of the electrospun polyamic acid nanofibers was measured with a scanning electron microscope VEGA 3 SBU (Czech Republic). The thermal decomposition temperature of the copolymerized polyimide nanofiber nonwoven fabric was measured using a WRT-3P thermogravimetric analyzer (TGA) (Shanghai Precision Science Equipment Co., Ltd.). The mechanical properties (strength, elongation at break, etc.) of the copolymerized polyimide / nanofiber nonwoven fabric were measured using a CMT8102 type electronic universal testing machine (Shenzhen SANS Material Inspection Co., Ltd.). The glass transition temperature of the copolymerized polyimide nanofibers was measured using a Diamond dynamic mechanical analyzer (DMA) (Perkin-Elmer, USA). The specific surface area of the copolymerized polyimide / nanofiber porous membrane or non-woven fabric described in the present invention was measured using a JW-K type pore distribution / specific surface area measuring device (Beijing Seiko Gaobo Science and Technology Co., Ltd.). The dielectric breakdown strength of the copolymerized polyimide / nanofiber nonwoven fabric was measured using a dielectric breakdown tester DJD-20KV (Beijing Crown Tester Co., Ltd.).

  The porosity of the copolymerized polyimide / nanofiber nonwoven fabric described in the present invention was calculated by the following formula.

Porosity β = [1− (ρ / ρ _o )] × 100
Wherein, [rho is the density of the copolymer polyimide nanofiber nonwoven fabric (g / cm ^3), the [rho _o is the density of the copolymer polyimide solid film (manufactured by solution casting ^method) (g / cm 3) .

  Yet another object of the present invention is the application in battery separators of copolymerized polyimide nanofiber nonwovens.

  In the present invention, dianhydride and diamine are used as reaction raw materials, a highly polar solvent is used as a reaction medium, and condensation polymerization is performed under mechanical stirring to form a copolymerized polyamic acid (co-PI precursor polymer) solution. There are three or more types of dianhydride monomers and diamine monomers, and the total number of functional groups of dianhydride and the total number of functional groups of diamine are equal or approximately equal. The solution obtained by the above synthesis is processed into a copolymerized polyamic acid nanofiber nonwoven fabric by high-pressure electrospinning technology, imidized at a high temperature of 300 ° C or higher, and a high-temperature resistant nanofiber nonwoven fabric battery separator for electrodes in isolated chemical batteries Form. This copolymerized polyimide / nanofiber nonwoven fabric has strong tear resistance, high porosity, can withstand high and low temperatures, has excellent mechanical properties, and has good heat resistance even when applied to battery separators. In the case of overheating, overcharging, etc., it does not shrink easily, and it does not shrink due to heat. As a result, the battery separator bursts, and a phenomenon such as thermal runaway due to a short circuit inside the battery does not occur. In addition, the application of this copolymerized polyimide / nanofiber nonwoven fabric to various high-capacity and high-power battery separators and capacitor separators has a huge potential market in the automotive power battery and supercapacitor industries.

  Next, the present invention will be described in more detail in conjunction with examples.

  The steps of the method for producing a copolymerized polyimide / nanofiber nonwoven fabric of the present invention include the following.

  (1) In principle, the molar total amount of the dianhydride functional group and the molar total amount of the diamine functional group are equal, and a mixture of one dianhydride monomer and two diamine monomers or two dianhydride monomers and 1 An appropriate amount of a mixture of seed diamine monomers or a mixture of two dianhydride monomers and two diamine monomers is taken into a polymerization reaction kettle together with an appropriate amount of solvent and allowed to react for a certain period of time while stirring. Obtain a copolymerized polyamic acid (polyimide precursor) solution, perform electrospinning on the copolymerized polyamic acid solution in a high piezoelectric field, collect the stainless steel drum as a collector, and collect the copolymerized polyamic acid nanofiber nonwoven fabric. obtain. The solvent used is preferably one of N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMAC). The temperature of the reaction kettle is 0-30 ° C. The stirring reaction time is preferably 1 to 10 hours, and the electric field strength of the high piezoelectric field is 250 to 300 kV / m. The diameter of the stainless steel drum collector is 0.3 m.

  (2) The copolymerized polyamic acid nanofiber nonwoven fabric obtained above is placed in a high temperature furnace and heated in a nitrogen gas atmosphere to imidize. The heating process was performed at a heating rate of 20 ° C./min from room temperature to 200 to 250 ° C., kept at this temperature for 30 minutes, and then at a heating rate of 5 ° C./min at 330 to 370 ° C. And let it stay at this temperature for 30 minutes, then turn off the power.

  (3) Characterization: absolute viscosity of copolymerized polyamic acid solution and spinning solution, diameter of electrospun copolymerized polyamic acid nanofiber, thermal decomposition temperature of copolymerized polyimide / nanofiber nonwoven fabric, porous film of copolymerized polyimide / nanofiber or Includes measurement of mechanical properties (strength, elongation at break, etc.) of nonwoven fabric, glass transition temperature of copolymerized polyimide / nanofiber nonwoven fabric, specific surface area of copolymerized polyimide / nanofiber nonwoven fabric, dielectric breakdown strength of copolymerized polyimide / nanofiber nonwoven fabric .

Example 1
One tetracarboxylic dianhydride monomer and two diamine monomers were selected as copolymerization monomers. Purified biphenyl dianhydride (BPDA), p-phenylenediamine (PPD) and oxydianiline (ODA) with a molar ratio of 1: 0.5: 0.5 are mixed and N, N-dimethylformamide (DMF) is mixed. Was carried out by the above reaction step. In the reaction step (1), in this example, the temperature of the reaction kettle was 10 ° C., and the stirring reaction time was 6 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 300 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 350 ° C. at a temperature rising rate of 5 ° C./min. Heated and held at 350 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: Copolymerized polyamic acid (polyimide precursor) solution has a mass concentration of 7%, an absolute viscosity of 5.2 Pa · S, and the diameter of the copolymerized polyamic acid nanofiber is 100 to 400 nm, mainly about 250 nm. The tensile strength of the copolymerized polyimide / nanofiber nonwoven fabric is 25 MPa, the elongation at break is 24%, the glass transition temperature is 285 ° C., the thermal decomposition temperature is 530 ° C., the porosity is 84.2%, and the specific surface area is 37. .4m ² / g, the dielectric breakdown strength was 1.2 × ¹⁰ 5 V / cm or 12V / [mu] m.

Example 2
One tetracarboxylic dianhydride monomer and two diamine monomers were selected as copolymerization monomers. Purified pyromellitic dianhydride (PMDA), oxydianiline (ODA) and benzidine (Bz) in a molar ratio of 1: 0.6: 0.4 are mixed, and N, N-dimethylformamide (DMF) is used as a solvent. In the reaction step (1), in this example, the temperature of the reaction kettle was 5 ° C., and the stirring reaction time was 6 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 250 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 250 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 370 ° C. at a temperature rising rate of 5 ° C./min Heated and allowed to stay at 370 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyamic acid (polyimide precursor) solution is 5%, the absolute viscosity is 4.8 Pa · S, and the diameter of the copolymerized polyamic acid nanofiber is 100 to 400 nm, mainly about 200 nm. The tensile strength of the copolymerized polyimide / nanofiber nonwoven fabric is 24 MPa, the elongation at break is 23%, the glass transition temperature is 298 ° C., the thermal decomposition temperature is 560 ° C., the porosity is 82.0%, and the specific surface area is 38 .8m ² / g, the dielectric breakdown strength was 1.3 × ¹⁰ 5 V / cm or 13V / [mu] m.

Example 3
One tetracarboxylic dianhydride monomer and two diamine monomers were selected as copolymerization monomers. Purified pyromellitic dianhydride (PMDA), diphenylmethanediamine (MDA) and oxydianiline (ODA) with a molar ratio of 1: 0.5: 0.5 are mixed and N, N-dimethylformamide (DMF) is mixed. In the reaction step (1), in this example, the temperature of the reaction kettle was 5 ° C., and the stirring reaction time was 10 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 250 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 250 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 370 ° C. at a temperature rising rate of 5 ° C./min. Heated and allowed to stay at 370 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyimide precursor (copolymerized polyamic acid, co-PAA) solution is 6%, the absolute viscosity is 4.8 Pa · S, and the diameter of the copolymerized polyamic acid nanofiber is 100 to 400 nm. It is distributed mainly at about 250 nm, and the tensile strength of the copolymerized polyimide / nanofiber nonwoven fabric is 20 MPa, the elongation at break is 21%, the glass transition temperature is 296 ° C., the thermal decomposition temperature is 510 ° C., and the porosity is 85.1. %, The specific surface area was 3,6.9 m ² / g, and the dielectric breakdown strength was 1.1 × 10 ⁵ V / cm or 11 V / μm.

Example 4
One tetracarboxylic dianhydride monomer and two diamine monomers were selected as copolymerization monomers. Purified diphenylsulfone dianhydride (DSDA), bisaminophenoxyphenylsulfone (BAPS) and oxydianiline (ODA) with a molar ratio of 1: 0.3: 0.7 were mixed and N, N-dimethylformamide ( DMF) was used as a solvent, and the reaction was carried out by the above steps. In this reaction step (1), in this example, the temperature of the reaction kettle was 5 ° C., and the stirring reaction time was 10 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 250 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 330 ° C. at a temperature rising rate of 5 ° C./min. Heated and held at 330 ° C. for 30 minutes, then turned off and allowed to cool to room temperature.

Characterization: The copolymer polyimide precursor (copolymerized polyamic acid, co-PAA) solution has a mass concentration of 8%, an absolute viscosity of 4.2 Pa · S, and a diameter of the copolymerized polyamic acid nanofiber of 100 to 300 nm. There are mainly distributed about 180 nm, the tensile strength of the copolymerized polyimide / nanofiber nonwoven fabric is 20 MPa, the elongation at break is 25%, the glass transition temperature is 238 ° C., the thermal decomposition temperature is 520 ° C., and the porosity is 81.3 %, The specific surface area was 3,6.9 m ² / g, and the dielectric breakdown strength was 1.4 × 10 ⁵ V / cm or 14 V / μm.

Example 5
Two tetracarboxylic dianhydride monomers and one diamine monomer were selected as polymerization monomers. Purified biphenyl dianhydride (BPDA), pyromellitic dianhydride (PMDA) and oxydianiline (ODA) in a molar ratio of 0.5: 0.5: 1 are mixed and an appropriate amount of N, N-dimethylformamide is mixed. (DMF) was used as a solvent, and the above steps were performed. In the reaction step (1), in this example, the temperature of the reaction kettle was 5 ° C., and the stirring reaction time was 10 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 250 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 250 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 370 ° C. at a temperature rising rate of 5 ° C./min. Heated and allowed to stay at 370 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyamic acid solution is 6%, the absolute viscosity is 5.5 Pa · S, the diameter of the polyamic acid nanofiber is 150 to 400 nm, and is mainly distributed at about 280 nm.・ The tensile strength of nanofiber nonwoven fabric is 23 MPa, elongation at break is 22%, glass transition temperature is 295 ° C., thermal decomposition temperature is 550 ° C., porosity is 85.0%, specific surface area is 36.9 m ² / g, insulation The breaking strength was 1.1 × 10 ⁵ V / cm or 11 V / μm.

Example 6
Two tetracarboxylic dianhydride monomers and one diamine monomer were selected as polymerization monomers. Purified 1,4-bis (3,10-dicarboxyphenoxy) benzene dianhydride (HQDPA), pyromellitic dianhydride (PMDA) and oxydianiline (molar ratio 0.5: 0.5: 1) ODA) and a suitable amount of solvent N, N-dimethylformamide (DMF) were reacted according to the above steps. In the reaction step (1), in this example, the temperature of the reaction kettle was 10 ° C., and the stirring reaction time was 5 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 300 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 350 ° C. at a temperature rising rate of 5 ° C./min. Heated and held at 350 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyamic acid solution is 8%, the absolute viscosity is 4.2 Pa · S, the diameter of the copolymerized polyamic acid nanofiber is 80 to 300 nm, and it is distributed mainly around 150 nm. The tensile strength of the polymerized polyimide / nanofiber nonwoven fabric is 23 MPa, the elongation at break is 24%, the glass transition temperature is 278 ° C., the thermal decomposition temperature is 540 ° C., the porosity is 81.4%, and the specific surface area is 41.8 m ² / g. The dielectric breakdown strength was 1.4 × 10 ⁵ V / cm or 14 V / μm.

Example 7
Two kinds of tetracarboxylic dianhydrides and two kinds of diamines were selected as copolymerization monomers. Purified diphenylsulfone dianhydride (BTDA), pyromellitic dianhydride (PMDA), benzidine (Bz) and oxydianiline (ODA) in a molar ratio of 1: 1: 1: 1 are mixed together and an appropriate amount of N , N-dimethylacetamide (DMAc) was used as a solvent, and the reaction was carried out by the above steps. In the reaction step (1), in this example, the temperature of the reaction kettle was 5 ° C., and the stirring reaction time was 6 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 250 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 250 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 370 ° C. at a temperature rising rate of 5 ° C./min. Heated and allowed to stay at 370 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyamic acid solution is 6%, the absolute viscosity is 4.3 Pa · S, the diameter of the copolymerized polyamic acid nanofiber is 100 to 300 nm, and it is distributed mainly around 150 nm. The tensile strength of the polymerized polyimide / nanofiber nonwoven fabric is 22 MPa, the elongation at break is 24%, the glass transition temperature is 288 ° C., the thermal decomposition temperature is 540 ° C., the porosity is 80.5%, and the specific surface area is 41.8 m ² / g. The dielectric breakdown strength was 1.5 × 10 ⁵ V / cm or 15 V / μm.

Example 8
Two kinds of tetracarboxylic dianhydrides and two kinds of diamines were selected as copolymerization monomers. Purified biphenyl dianhydride (BTDA), 1,4-bis (3,10-dicarboxyphenoxy) benzene dianhydride (HQPDA), p-phenylenediamine (PPD) with a molar ratio of 1: 1: 1: 1 And oxydianiline (ODA) were mixed, and an appropriate amount of N, N-dimethylformamide (DMAc) was used as a solvent, and the reaction was carried out by the above steps. In the reaction step (1), in this example, the temperature of the reaction kettle was 10 ° C., and the stirring reaction time was 10 hours. The electric field strength of the high piezoelectric field used in the electrospinning process was 300 kV / m. The temperature raising procedure in the reaction step (2) is to heat from room temperature to 250 ° C. at a temperature rising rate of 20 ° C./min, hold at this temperature for 30 minutes, and then to 350 ° C. at a temperature rising rate of 5 ° C./min. Heated and allowed to stay at 320 ° C. for 30 minutes, then turned off and allowed to cool naturally to room temperature.

Characterization: The mass concentration of the copolymerized polyamic acid solution is 8%, the absolute viscosity is 4.0 Pa · S, the diameter of the copolymerized polyamic acid nanofiber is 50 to 250 nm, and is distributed mainly at about 150 nm. The tensile strength of the polymerized polyimide / nanofiber nonwoven fabric is 21 MPa, the elongation at break is 23%, the glass transition temperature is 284 ° C., the thermal decomposition temperature is 530 ° C., the porosity is 80.2%, and the specific surface area is 42.0 m ² / g. The dielectric breakdown strength was 1.5 × 10 ⁵ V / cm or 15 V / μm.

  The above examples should not be understood as limitations on the protection scope of the present invention. Non-essential improvements and adjustments made by the person skilled in the art based on the above description of the invention belong to the protection scope of the invention.

Claims (13)

Copolymerized polyamic acid is copolymerized with three or more of the following four types of monomers (I), (II), (III), and (IV), followed by electrospinning and imidization. Copolymerized polyimide / nanofiber nonwoven fabric.
At this time, the copolymerized polyimide has the following chemical structure.
n is a natural number of 50 to 300, m is a natural number of 50 to 300, R ₁ and R ₃ are residue structures of C _{4 to} C ₃₀ tetracarboxylic dianhydride monomers, R ₂ , R ₄ is a residual structure of C ₆ -C ₃₀ diamine monomer, in the copolymerization reaction, the ratio of the total amount of substance of the total material amount and diamine monomer dianhydride monomer is always 1: keep 1.   The copolymerized polyimide nanofiber is obtained by copolymerization of the above three monomers (I), (III), (IV), or (II), (III), and (IV). The molar ratio of (I) :( III) :( IV) or (II) :( III) :( IV) = [1]: [0.05-0.95]: [0.05-0. 95] The copolymerized polyimide nanofiber nonwoven fabric according to claim 1,   The copolymerized polyimide nanofiber is obtained by copolymerization of the above three monomers (I), (II), (III), or (I), (II), and (IV). The molar ratio of (I) :( II) :( III) or (II) :( III) :( IV) = [0.05-0.95]: [0.05-0.95]: [ 1] The copolymerized polyimide nanofiber nonwoven fabric according to claim 1, wherein   The copolymerized polyimide nanofiber is obtained by copolymerization of the above four monomers (I), (II), (III), and (IV), and the relationship between the molar ratios of the four monomers is [ The copolymer polyimide nanofiber nonwoven fabric according to claim 1, wherein (I) + (II)]: [(III) + (IV)] = 1: 1. R ₁ and R ₃ are each one type selected from the following tetracarboxylic dianhydride residue structures, copolymerized polyimides according to any one of claims 1 to 4, Nanofiber nonwoven fabric.
The copolymerized polyimide nanofiber nonwoven fabric according to any one of claims 1 to 4, wherein R ₂ and R ₄ are each one selected from the following diamine residue structures.
The copolymerized imide nanofiber nonwoven fabric has an elongation at break of 20 to 30%, a porosity of 80 to 86%, a tensile strength of 20 to 25 MPa, and a dielectric breakdown strength of 1 × 10 ⁷ to 1. 5. The copolymerized polyimide / nanofiber nonwoven fabric according to claim 1, which has a thermal decomposition temperature of 510 to 560 ° C. and is 5 × 10 ⁷ V / m. The manufacturing method of the copolymerization polyimide nanofiber nonwoven fabric of Claim 1 characterized by including the following.
(1) After purifying 3 or more types of the dianhydride and diamine monomer, they are put into a polymerization reaction kettle together with an appropriate amount of solvent and allowed to react for a certain time with stirring. Obtain a copolymerized polyamic acid (polyimide precursor) solution, perform electrospinning on the copolymerized polyamic acid solution in a high piezoelectric field, collect the stainless steel drum as a collector, and collect the copolymerized polyamic acid nanofiber nonwoven fabric. obtain.
(2) The obtained copolymerized polyamic acid nanofiber nonwoven fabric is placed in a high temperature furnace and heated to imidize.   The method for producing a copolymerized polyimide / nanofiber nonwoven fabric according to claim 8, wherein the solvent is a polar solvent.   The method for producing a copolymerized polyimide / nanofiber nonwoven fabric according to claim 8, wherein the polar solvent is N, N-dimethylformamide (DMF) or N, N-dimethylacetamide (DMAC).   The copolymerization according to claim 8, wherein a polymerization reaction temperature of the reaction kettle is 0 to 30 ° C, a reaction time is 1 to 10 hours, and an electric field strength of a high piezoelectric field is 250 to 300 Kv. Manufacturing method of polyimide nanofiber nonwoven fabric.   The temperature increase procedure of the imidization process is as follows: room temperature to 200 to 250 ° C. at a temperature increase rate of 20 ° C./min, residence at that temperature for 30 minutes, and then 330 ° C. at a temperature increase rate of 5 ° C./min. The method for producing a copolymerized polyimide / nanofiber nonwoven fabric according to claim 8, wherein the method is heated to 370 ° C., kept at the temperature for 30 minutes, and then the power is turned off.   Application in the battery separator of the copolymer polyimide nanofiber nonwoven fabric according to claim 1.