Fluorine-free polyimide-based film and preparation method thereof

Abstract

The invention relates to a fluoride-free polyimide-based film and a preparation method thereof. The method comprises the following steps: S1, preparing a polyamide acid solution; s2, fluorine-free organic silicon serving as a modifier is added into the polyamide acid solution and dispersed, a blended spinning solution is formed, and the solubility parameter difference value of the fluorine-free organic silicon and polyamide acid is 2.0 (MPa) 1 / 2 or below; s3, carrying out electrostatic spinning on the blended spinning solution to form a polyamide acid-based nanofiber layer; and S4, carrying out thermal imidization on the polyamide acid-based nanofiber layer to obtain the fluoride-free polyimide-based film. The film has a structure formed by three-dimensional cross-linking and winding of polyimide-based nanofibers, and the polyimide-based nanofibers are composed of a polyimide base material and fluorine-free organic silicon dispersed in the polyimide base material. The method does not involve fluorine-containing raw materials, and is environment-friendly and high in process compatibility. The film provided by the invention has excellent waterproofness, air permeability and mechanical properties at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and particularly relates to a fluorine-free polyimide-based film and a preparation method thereof, which are applicable to fields such as textile materials, high-temperature gas and / or liquid filtration, and flexible electronic device packaging. Background Art

[0002] With the development of the high-end protective materials field, polyimide (PI) nanofiber membranes have attracted much attention in extreme environment applications such as aerospace and special protective clothing due to their excellent high-temperature resistance, chemical stability, and mechanical strength. However, traditional polyimide nanofiber membranes are hydrophilic by nature and need to be surface-modified to achieve waterproof functionality.

[0003] Currently, the industry mainly uses fluorine-containing compounds (such as perfluoroalkyl acrylates, perfluorooctanoic acid (PFOA) and its derivatives) to modify the waterproofness of polyimide nanofiber membranes. Although such materials can achieve high waterproofness, their inherent defects severely restrict practical applications: fluorine-containing compounds are difficult to degrade and tend to accumulate in organisms. The strict control of fluorine-containing substances by the EU REACH regulation and the US TSCA has forced downstream application manufacturers to seek alternative solutions. In addition, fluorine-containing coatings are prone to thermal decomposition at high temperatures, resulting in a sudden drop in waterproofness, which does not match the high-temperature resistance characteristics of the polyimide matrix.

[0004] So far, there have been many reports on improving the waterproofness of polyimide nanofiber membranes.

[0005] In one study, a waterproof polyimide nanofiber membrane was obtained by blending and electrospinning silica nanoparticles with polyimide, but nanoparticle aggregation led to a decrease in the fiber breaking strength.

[0006] In addition, in another study, polyimide nanofiber membranes were coated with graphene / carbon nanotubes to improve their waterproofness, but this would block the pores of the nanofibers, resulting in a decrease in the porosity of the membrane and the loss of the core advantages of the application.

[0007] In addition, there was also a study using fatty acid esters as coatings to improve their waterproofness, but its high-temperature resistance was insufficient (decomposition temperature < 150 °C), unable to meet the requirements of high-temperature scenarios.

[0008] In summary, the main problems faced by the existing technology are: how to prepare a polyimide nanofiber membrane with excellent waterproofness, breathability, and mechanical properties without using fluorine-containing substances. This technological gap severely restricts the popularization and application of polyimide nanofiber membranes in environmentally demanding fields (such as diaphragms for new energy batteries, high-temperature filtration media).

[0009] Therefore, there is a need to develop a polyimide nanofiber membrane that is environmentally friendly, has strong process compatibility, and balanced performance in all aspects. Summary of the Invention

[0010] Technical problem

[0011] To solve the deficiencies of the prior art, the first object of the present invention is to provide a method for preparing a fluorine-free polyimide-based film. The method does not involve fluorine-containing raw materials, is environmentally friendly, and has strong process compatibility.

[0012] The second object of the present invention is to provide a fluorine-free polyimide-based film that simultaneously has excellent waterproofness, breathability, and mechanical properties.

[0013] Technical solution

[0014] According to one aspect of the present invention, there is provided a method for preparing a fluorine-free polyimide-based film, the method comprising the following steps:

[0015] S1: Prepare a polyamic acid solution;

[0016] S2: Add a fluorine-free organosilicon as a modifier to the polyamic acid solution and disperse it to form a blend spinning solution, wherein the difference in solubility parameter between the fluorine-free organosilicon and the polyamic acid is 2.0 (MPa) 1 / 2 or less;

[0017] S3: Electrospun the blend spinning solution to form a polyamic acid-based nanofiber layer;

[0018] S4: Thermally imidize the polyamic acid-based nanofiber layer to obtain the fluorine-free polyimide-based film.

[0019] In one embodiment, in step S1,

[0020] By dissolving a diamine monomer and a dianhydride monomer in a polar solvent and stirring and reacting for 6 - 20 hours, a polyamic acid solution is obtained, [[ID=3८]]

[0021] the molar ratio of the diamine monomer to the dianhydride monomer is 1:1,

[0022] relative to the weight of the polyamic acid solution, the combined amount of the diamine monomer and the dianhydride monomer is 8 - 15 wt%,

[0023] the diamine monomer is selected from one or more of diaminodiphenyl ether (ODA), all-meta triphenylenediamine (1,3,3-APB), bisphenol A type diamine (BAPP), and 4,4'-diaminodiphenyl sulfone (DDS),

[0024] The dianhydride monomer is one or more selected from diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl ether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA).

[0025] The polar solvent is one or more selected from N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF).

[0026] In one embodiment, in step S2,

[0027] The fluorine-free organosilicon is one or more selected from amino-terminated polydimethylsiloxane (PDMS), epoxy-modified silicone oil, carboxyl-modified silicone oil, and polyether-modified silicone oil.

[0028] The amount of the fluorine-free organosilicon used is 1-8 wt% based on the weight of the polyamic acid solution.

[0029] The dispersion is carried out by a high-shear dispersion emulsifier.

[0030] In one embodiment, in step S3, in the electrospinning,

[0031] The voltage is set to 10-20 kV.

[0032] The distance between the nozzle and the collector is 15 - 20 cm.

[0033] The injection rate of the polyamic acid solution is 1.0-2.5 mL / h.

[0034] In one embodiment, in step S4, the temperature of the thermal imidization is 300-450 °C.

[0035] According to another aspect of the present invention, there is provided a fluorine-free polyimide-based film prepared by the method described above, wherein the fluorine-free polyimide-based film has a structure formed by three-dimensional cross-linking and winding of polyimide-based nanofibers.

[0036] The polyimide-based nanofibers are composed of a polyimide substrate and fluorine-free organosilicon dispersed therein.

[0037] In one embodiment, the hydrostatic pressure resistance value of the fluorine-free polyimide-based film is 100 kPa or more, the air permeability is 8 mm / s or more, and the tensile strength is 22 MPa or more.

[0038] In one embodiment, the thickness of the fluorine-free polyimide-based film is 30-μm.

[0039] In one embodiment, the average diameter of the polyimide-based nanofibers is 200-900 nm.

[0040] Beneficial effects

[0041] In the present invention, a specific fluorine-free silicone is added to the polyimide matrix to form polyimide-based nanofibers. Through the microphase separation of the silicone, a rough surface structure is formed, while the waterproofness and breathability are enhanced. In addition, the hydrophobic group (-Si-O-Si-) of the silicone is complementary to the rigid structure of the polyimide molecular chain, which not only reduces the surface energy but also maintains the fiber strength (i.e., the mechanical properties of the fiber).

[0042] In addition, the fluorine-free silicone of the present invention has a solubility parameter similar to that of polyamic acid (the difference in solubility parameters between the two is 2.0 (MPa) 1 / 2 as follows), to improve the compatibility, so that the fluorine-free silicone can be uniformly dispersed in the polyamic acid (PAA) solution, ensuring no problems such as nozzle blockage and continuous fiber formation during the electrospinning process. Thus, the problems of poor processing stability and high rejection rate caused by phase separation in traditional blend materials are solved.

[0043] Therefore, the present invention overcomes the technical problems that are difficult to balance in terms of waterproofness, breathability, and mechanical properties in the traditional fluorine-free modification process, and prepares a fluorine-free polyimide-based film with synergistically improved waterproofness, breathability, and mechanical properties.

[0044] In addition, the present invention replaces the traditional multi-step modification process with a one-step blending method, shortening the production process, reducing energy consumption and time, with simple operation, stable processing, and easy production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a scanning electron microscope (SEM) image of the fluorine-free polyimide-based film prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0047] Unless otherwise defined, all terms used herein, including technical or scientific terms, shall be interpreted as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, terms such as those defined in common dictionaries shall not be interpreted in an ideal or overly formal sense unless explicitly defined.

[0048] When the conditions and methods for measuring the properties or parameters described in this specification are not specifically described, the measurement conditions and methods commonly used by those skilled in the art can be used to measure the property or parameter.

[0049] Unless otherwise specified, "%" used herein refers to % by weight.

[0050] Method for preparing a fluorine-free polyimide-based film

[0051] According to one aspect of the present invention, there is provided a method for preparing a fluorine-free polyimide-based film, the method comprising the following steps:

[0052] S1: Prepare a polyamic acid solution;

[0053] S2: Add a fluorine-free organosilicon as a modifier to the polyamic acid solution and disperse it to form a blend spinning solution, wherein the difference in solubility parameter between the fluorine-free organosilicon and the polyamic acid is 2.0 (MPa) 1 / 2 hereinafter;

[0054] S3: Electrospun the blend spinning solution to form a polyamic acid-based nanofiber layer;

[0055] S4: Thermally imidize the polyamic acid-based nanofiber layer to obtain the fluorine-free polyimide-based film.

[0056] Hereinafter, each step will be described in detail.

[0057] Step S1: Prepare a polyamic acid solution

[0058] The polyamic acid (PAA) solution can be prepared by a conventional process.

[0059] Generally, a diamine monomer, a dianhydride monomer and a polar solvent are used to form a polyamic acid solution. Suitable diamine monomers, dianhydride monomers and polar solvents, as well as their amounts, can be determined according to conventional selection.

[0060] In one embodiment, a polyamic acid solution is obtained by dissolving a diamine monomer and a dianhydride monomer in a polar solvent and stirring the reaction for 6-20 hours.

[0061] The diamine monomer is a compound containing two amino groups and is a conventional component for preparing a polyamic acid solution. The diamine monomer can be one or more selected from diaminodiphenyl ether diamine (ODA), all-meta terphenyl ether diamine (1,3,3-APB), bisphenol A type diamine (BAPP) and 4,4-diaminodiphenyl sulfone (DDS).

[0062] The dianhydride monomer is a compound containing two carboxylic anhydride groups and is a conventional component for preparing a polyamic acid solution. The dianhydride monomer can be one or more selected from diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl ether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A type dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA).

[0063] The molar ratio of the diamine monomer to the dianhydride monomer can generally be 1:1 to ensure that both react completely.

[0064] Relative to the weight of the polyamic acid solution, the combined dosage of the diamine monomer and the dianhydride monomer can be 8 - 15 wt%, preferably 10 - 12 wt%.

[0065] If the combined dosage is too low, the viscosity of the solution is insufficient, which is not conducive to subsequent spinning and forming, and may cause fiber breakage or discontinuous film formation;

[0066] If the combined dosage is too high, the solution viscosity is too large, the fluidity is poor, it is not easy to stir evenly or causes gelation, affecting the spinning uniformity and stability.

[0067] In addition, the combined weight of the diamine monomer and the dianhydride monomer is equal to the weight of the polyamic acid obtained by the reaction. Relative to the weight of the polyamic acid solution, the content of polyamic acid (also known as the solid content) is equal to the combined dosage of the diamine monomer and the dianhydride monomer.

[0068] The polar solvent is used to dissolve the diamine monomer and the dianhydride monomer, enabling them to undergo a polymerization reaction without a catalyst to form polyamic acid, and at the same time forming a uniformly mixed solution with an appropriate viscosity suitable for spinning. The polar solvent can be one or more selected from N,N - dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N,N - dimethylformamide (DMF), and tetrahydrofuran (THF).

[0069] Step S2: Form a blended spinning solution

[0070] Add a fluorine - free organosilicon as a modifier to the polyamic acid solution and disperse it to form a blend spinning solution, where the difference in solubility parameter between the fluorine - free organosilicon and the polyamic acid is 2.0 (MPa) 1 / 2 below.

[0071] The solubility parameter is a measure of the intermolecular force per unit volume of a material and is a quantitative index used to evaluate the compatibility (i.e., whether it can be fully dissolved) between a solvent and a polymer or monomer. The solubility parameter can be measured according to GB / T21862.1 - 2008.

[0072] In the present invention, the difference (absolute value) between the solubility parameters of the fluorine-free organosilicon and polyamic acid can be 2.0 (MPa) 1 / 2 Preferably, it is 1.5 (MPa) or less 1 / 2 More preferably, it is 1.0 (MPa) or less 1 / 2 Generally, the solubility parameter of polyamic acid can be 20 - 23 (MPa) 1 / 2 ; the solubility parameter of the fluorine-free organosilicon can be 18 - 25 (MPa) 1 / 2 , for example, 20 - 22 (MPa) 1 / 2 . When the difference in solubility parameters satisfies the above range, it can ensure that the fluorine-free organosilicon and polyimide have similar intermolecular forces, thereby enabling uniform blending. Conversely, if the difference in solubility parameters does not satisfy the above range, the fluorine-free organosilicon and polyimide cannot be uniformly blended, thereby reducing the performance of the film obtained by electrospinning.

[0073] The fluorine-free organosilicon is used to improve the water resistance and thermal stability of the film. The fluorine-free organosilicon has a siloxane structure and does not contain fluorine. In addition, the molecular weight range of the fluorine-free organosilicon can generally be 2000 - 5000, preferably 3000 - 4000, to ensure the normal progress of the spinning process.

[0074] Specifically, the fluorine-free organosilicon can be one or more selected from amino-terminated polydimethylsiloxane (PDMS), epoxy-modified silicone oil, carboxyl-modified silicone oil, and polyether-modified silicone oil.

[0075] Relative to the weight of the polyamic acid solution, the amount of the fluorine-free organosilicon used can be 1 - 8 wt%, preferably 1.5 - 5 wt%, more preferably 2 - 3 wt%.

[0076] If the amount of the fluorine-free organosilicon used is too low, the blending effect is not obvious, and it cannot effectively improve the hydrophobicity and flexibility of the obtained fluorine-free polyimide-based film, resulting in limited improvement in water resistance and poor interfacial compatibility;

[0077] If the amount of the fluorine-free organosilicon used is too high, it may cause phase separation or enrichment of the fluorine-free organosilicon in the fibers, affecting the stability and spinnability of the spinning solution.

[0078] Dispersion can be carried out by a conventional process. For example, it can be dispersed by a high-shear dispersion emulsifier. The dispersion time can be 10 - 20 minutes.

[0079] Through dispersion, the agglomeration phenomenon of the fluorine-free organosilicon in the liquid phase can be avoided, and a nano-scale particle size distribution can be formed. The blended spinning solution after dispersion treatment is a transparent or microemulsion-like homogeneous system without obvious stratification, and has good spinning rheological properties.

[0080] Step S3: Electrospinning

[0081] Electrospin the blend spinning solution to form a polyamic acid-based nanofiber layer.

[0082] Electrospinning is a simple and effective technique for producing nanofibers at the nanoscale. It causes a charged polymer solution to flow and deform in an electrostatic field and solidify upon solvent evaporation, thereby forming fibrous substances. Continuous nanofibers can be easily and effectively prepared by electrospinning.

[0083] Electrospinning can be carried out by a conventional process. Specifically, the blend spinning solution can be loaded into a syringe of an electrospinning device, and a stainless-steel needle with an inner diameter of 0.4 - 0.6 mm is selected as the nozzle.

[0084] In the electrospinning process, the voltage can be set to 10 - 20 kV.

[0085] The distance between the nozzle and the collector can be 5 - 20 cm.

[0086] The injection rate of the polyamic acid solution can be 0.5 - 3 mL / h.

[0087] In the electrospinning process, the blend spinning solution is ejected by an electrostatic field to form continuous nanofibers, which are deposited on a receiving device to form a polyamic acid-based nanofiber layer. During electrospinning, the polar solvent evaporates rapidly, and the nanofibers are stretched and shaped in the air, finally forming a uniform and dense polyamic acid-based nanofiber layer.

[0088] The polyamic acid-based nanofiber layer has a high specific surface area, good porosity, and structural integrity, providing a good precursor morphology for subsequent thermal imidization. Through electrospinning, the fluorine-free organosilicon and polyamic acid jointly form nanofibers, endowing the polyamic acid-based nanofiber layer with both good mechanical properties and preliminary hydrophobic characteristics.

[0089] The obtained polyamic acid-based nanofiber layer has a single-layer structure.

[0090] Step S4: Thermal imidization

[0091] Thermally imidize the polyamic acid-based nanofiber layer to obtain the fluorine-free polyimide-based film.

[0092] Thermal imidization can be carried out by a conventional process to cause the polyamic acid to undergo a dehydration cyclization reaction and be converted into a polyimide with thermal stability and chemical inertness.

[0093] The temperature of thermal imidization can be 300 - 450 °C, preferably 320 - 400 °C.

[0094] If the temperature is lower than 300 °C, the thermal imidization reaction is incomplete, and hydrophilic groups remain in the product film, resulting in insufficient thermal stability and waterproofness; if the temperature exceeds 450 °C, the polymer main chain may undergo thermal cracking or carbonization, causing damage to the fiber structure.

[0095] The time for thermal imidization can be 0.5 - 2 hours, preferably 1 - 1.5 hours.

[0096] If the time is too short, the imide cyclization reaction in the polyamic acid molecules is incomplete, and hydrophilic groups remain, resulting in insufficient hydrophobicity, thermal stability, and mechanical properties of the film material.

[0097] If the time is too long, it can cause thermal oxidation or increased crosslinking of the polymer main chain, resulting in fiber embrittlement, color deepening, and even structural degradation, affecting the flexibility and processability of the material.

[0098] There is no particular limitation on the length and width of the film, which can be determined according to needs. For example, the length can be 50 - 200 m, and the width can be 90 - 150 cm.

[0099] The thickness of the film can generally be 30 - 60 μm, preferably 40 - 50 μm.

[0100] The film also has a single-layer structure. In addition, by using fluorine-free raw materials (especially fluorine-free organosilicon as a modifier) in the preparation process, the resulting film is fluorine-free.

[0101] In the film, the average diameter of the polyimide-based nanofibers can be 200 - 900 nm, preferably 200 - 400 nm.

[0102] Fluorine-free polyimide-based film

[0103] According to another aspect of the present invention, there is provided a fluorine-free polyimide-based film prepared by the above method, wherein the fluorine-free polyimide-based film has a structure formed by three-dimensional cross-linking and winding of polyimide-based nanofibers, and the polyimide-based nanofibers are composed of a polyimide substrate and fluorine-free organosilicon dispersed therein.

[0104] The hydrostatic pressure resistance value of the fluorine-free polyimide-based film can be 100 kPa or more, such as 100 - 120 kPa; the air permeability can be 8 mm / s or more, such as 8 - 15 mm / s.

[0105] The hydrostatic pressure resistance value can be measured using the national standard GB / T 4744 - 2013 "Testing method for hydrostatic pressure of textiles - Hydrostatic pressure method", using a fabric water permeability measuring instrument, where the hydrostatic pressure resistance value characterizes the waterproofness. Specifically, the higher the hydrostatic pressure resistance value, the higher the waterproofness; conversely, the lower the waterproofness.

[0106] The air permeability can be measured using the national standard GB / T 5453-1997 with a fully automatic fabric air permeability measuring instrument.

[0107] The mechanical properties of the fluorine-free polyimide-based film can be characterized by the tensile strength. The tensile strength of the fluorine-free polyimide-based film of the present invention can be 22 MPa or more, for example, 24 - 26 MPa. The tensile strength can be measured according to GB / T13773-2008 "Determination of Tensile Properties of Nonwovens".

[0108] The length, width and thickness of the fluorine-free polyimide-based film and the average diameter of the polyimide-based nanofibers are as described above.

[0109] Examples

[0110] Hereinafter, the present invention will be described in detail with reference to examples to specifically describe the present invention. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more fully describe the present invention to those of ordinary skill in the art.

[0111] If the experimental methods in the following examples are not specified in specific conditions, they are usually the conventional conditions in the art or the conditions recommended by the manufacturers; the raw materials and equipment used, unless otherwise specified, are all raw materials and equipment that can be obtained from commercial channels such as conventional markets.

[0112] As follows, films of examples and comparative examples are prepared based on the same gram weight (i.e., areal density, 10 g / m 2 ), and their water resistance, air permeability and mechanical properties are compared.

[0113] Example 1 (Preparation of fluorine-free polyimide-based film)

[0114] A fluorine-free polyimide-based film is prepared by a method including the following steps.

[0115] Step S1: Prepare a polyamic acid solution

[0116] 200.2 g (1 mol) of diaminodiphenyl ether (ODA) and 310.2 g (1 mol) of diphenyl ether tetracarboxylic dianhydride (ODPA) (the molar ratio of the two is 1:1) are dissolved in 4593.7 g of N,N-dimethylacetamide (DMAc), stirred and reacted in a polymerization reactor for 12 hours to obtain a viscous and uniform polyamic acid (PAA) solution.

[0117] Among them, relative to the weight of the polyamic acid (PAA) solution, the content of polyamic acid (i.e., the combined dosage of diamine monomer and the dianhydride monomer) is about 10 wt%.

[0118] Step S2: Form a blended spinning solution

[0119] 102.1 g of amino-terminated polydimethylsiloxane (PDMS) (Hengsheng Silicon Industry, HSi-AM230, molecular weight of 3000) as a modifier was added to the resulting polyamic acid (PAA) solution, and the amount of PDMS used was 2.0 wt% based on the weight of the polyamic acid (PAA) solution.

[0120] Then, a high-shear dispersion emulsifier (IKA, T25) was used for dispersion treatment for 10 minutes to obtain a homogeneous and stable PAA / PDMS blend spinning solution.

[0121] Among them, the solubility parameter of the polyamic acid is 23 (MPa) 1 / 2 ;

[0122] The solubility parameter of the amino-terminated polydimethylsiloxane (PDMS) is 21.3 (MPa) 1 / 2 ;

[0123] The difference in solubility parameters between the two is 1.7 (MPa) 1 / 2 。

[0124] Step S3: Electrospinning

[0125] The above blend spinning solution was loaded into a 10 mL syringe, connected to a stainless steel needle (inner diameter 0.5 mm), and electrospinning was carried out. The working parameters of electrospinning were as follows: the voltage was 18 kV, the distance between the nozzle and the collector was 15 cm, and the injection rate was 1.0 mL / h. The obtained nanofibers were deposited on the collecting plate to obtain a uniform polyamic acid-based nanofiber layer.

[0126] Step S4: Thermal imidization

[0127] The obtained polyamic acid-based nanofiber layer was placed in a vacuum drying oven and heated at 330 °C for 1 hour for thermal imidization treatment to obtain a fluorine-free polyimide-based film.

[0128] The areal density of the fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0129] Example 2 (Increasing the amount of modifier)

[0130] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S2, the amount of amino-terminated polydimethylsiloxane (PDMS) used as a modifier was increased to 2.9 wt%.

[0131] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 39 μm.

[0132] Example 3 (changing the type of modifier)

[0133] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S2, the amino-terminated polydimethylsiloxane (PDMS) used as the modifier was replaced with epoxy-modified silicone oil (Momentive, LMB-7101).

[0134] The solubility parameter of the epoxy-modified silicone oil is 24 (MPa) 1 / 2 ;

[0135] The difference in solubility parameter between the modifier and the polyamic acid is 1 (MPa) 1 / 2 .

[0136] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0137] Example 4 (changing the type of modifier)

[0138] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S2, the amino-terminated polydimethylsiloxane (PDMS) used as the modifier was replaced with carboxyl-modified silicone oil (Wacker, PCS).

[0139] The solubility parameter of the carboxyl-modified silicone oil is 22 (MPa) 1 / 2 ;

[0140] The difference in solubility parameter between the modifier and the polyamic acid is 1 (MPa) 1 / 2 .

[0141] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0142] Example 5 (using different diamine monomers and dianhydride monomers)

[0143] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S1, 1,3,3-aminophenylbenzene (1,3,3-APB) was used as the diamine monomer and biphenyl dianhydride (BPDA) was used as the dianhydride monomer, and the amount of both was 1 mol.

[0144] Among them, the solubility parameter of the obtained polyamic acid is 22.5 (MPa) 1 / 2 ;

[0145] The solubility parameter difference between the modifier and the polyamic acid is 1.2 (MPa). 1 / 2 .

[0146] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0147] Example 6 (using different diamine monomers and dianhydride monomers)

[0148] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S1, bisphenol A diamine (BAPP) was used as the diamine monomer and triphenyl ether dianhydride (HQPDA) was used as the dianhydride monomer, and the amount of both was 1 mol.

[0149] Among them, the solubility parameter of the obtained polyamic acid is 20.5 (MPa). 1 / 2 ;

[0150] The solubility parameter difference between the modifier and the polyamic acid is 0.8 (MPa). 1 / 2 .

[0151] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0152] Comparative Example 1 (omitting the modifier)

[0153] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that step S2 was omitted, that is, the modifier was not used.

[0154] The areal density of the obtained fluorine-free polyimide-based film is 10 g / m 2 , and the thickness is 41 μm.

[0155] Comparative Example 2 (using fluorinated organosilicon as the modifier)

[0156] A fluorine-free polyimide-based film was prepared in the same manner as in Example 1, except that in step S2, a fluorosilane water repellent (DuPont, 7713) was used as the modifier. The solubility parameter of the fluorosilane water repellent is about 12 (MPa). 1 / 2 .

[0157] The solubility parameter difference between the modifier and the polyamic acid is 11 (MPa). 1 / 2 .

[0158] The areal density of the obtained polyimide-based film is 10 g / m 2 , and the thickness is 40 μm.

[0159] Comparative Example 3 (Omit Step S2 and prepare a fluorine-free modifier coating in a new Step S5)

[0160] A thin film was prepared in the same manner as in Example 1, except that Step S2 was omitted. In addition, a modifier coating was prepared in Step S5 to obtain a composite thin film with a bilayer structure.

[0161] Step S5: Prepare a modifier coating

[0162] On the surface of the fluorine-free polyimide-based thin film obtained in Step S4, PDMS with a solid content of 10 wt% (the same as the PDMS used in Example 1) was uniformly sprayed in an amount of 5 ml / m 2 . The coating thickness was about 2 μm, and then it was dried with hot air at 60 °C for 1 hour to obtain a composite thin film with a modifier coating.

[0163] The areal density of the composite thin film was 10 g / m 2 , and the thickness was 41 μm.

[0164] Comparative Example 4 (Using a fluorine-free silicone with too small a solubility parameter)

[0165] A fluorine-free polyimide-based thin film was prepared in the same manner as in Example 1, except that vinyl silicone oil (Dow Corning, PMX-0156) was used as the modifier in Step S2. The solubility parameter of the modifier was about 16.3 (MPa) 1 / 2 .

[0166] The difference in solubility parameter between the modifier and the polyamic acid was 6.7 (MPa) 1 / 2 .

[0167] The areal density of the obtained polyimide-based thin film was 10 g / m 2 , and the thickness was 40 μm.

[0168] Comparative Example 5 (Using a fluorine-free silicone with too large a solubility parameter)

[0169] A fluorine-free polyimide-based thin film was prepared in the same manner as in Example 1, except that sodium methyl silicate (Shandong Dongyue, DY-M50) was used as the modifier in Step S2. The solubility parameter of the modifier was about 28 (MPa) 1 / 2 .

[0170] The difference in solubility parameter between the modifier and the polyamic acid was 5 (MPa) 1 / 2 .

[0171] The areal density of the obtained polyimide-based thin film was 10 g / m 2 , and the thickness was 40 μm.

[0172] Experimental Example 1: Morphology observation using a scanning electron microscope (SEM)

[0173] The microstructure of the fluorine-free polyimide-based film of Example 1 was observed using a scanning electron microscope (TESCAN, model VEGA3) according to GB / T36422-2018 (Determination of micromorphology and diameter of chemical fibers by scanning electron microscopy). Figure 1 shown.

[0174] from Figure 1 It can be seen that the fibers are irregularly staggered and form a three-dimensional network structure with a high porosity, indicating that it has a high air permeability.

[0175] Experimental Example 2 Measurement of Waterproofness, Breathability and Mechanical Properties

[0176] The water resistance of the products of the examples and comparative examples was measured. The water resistance was expressed as a hydrostatic pressure value, which can be measured according to GB / T 4744-2013 "Testing the Water Resistance of Textiles - Hydrostatic Pressure Method".

[0177] Specifically, the hydrostatic pressure resistance values of the products of the examples and comparative examples were measured using a fabric hydrostatic pressure measuring instrument (Wenzhou Darong Textile Equipment Co., Ltd., YG85E) in accordance with GB / T4744-2013. The results are shown in Table 1 below.

[0178] Next, the air permeability of the products of the examples and comparative examples was measured. The air permeability can be measured according to GB / T54531997 (Determination of Air Permeability of Textile Fabrics).

[0179] Specifically, the air permeability (ie, air permeability) of the products of the examples and comparative examples was measured using a digital fabric air permeability meter (Wenzhou Darong Textile Equipment Co., Ltd., YG(B)461) in accordance with GB / T54531997. The results are shown in Table 1 below.

[0180] In addition, the mechanical properties of the products of the examples and comparative examples were measured. The mechanical properties were characterized by tensile strength, which can be measured according to GB / T 13773-2008 "Determination of tensile properties of nonwoven fabrics".

[0181] Specifically, the tensile strength of the products of the examples and comparative examples was measured using a universal material testing machine (Shenzhen Xinsansi Material Testing Co., Ltd., CMT4204) in accordance with GB / T13773-2008. The results are shown in Table 1 below.

[0182] Table 1

[0183]

[0184] As can be seen from Table 1, the products of Examples 1-6 all have high hydrostatic pressure resistance values (i.e., excellent waterproofness), high air permeability rates (i.e., excellent breathability), and relatively high tensile strengths (i.e., excellent mechanical properties).

[0185] In contrast, the products of Comparative Example 1 (without modifier), Comparative Example 2 (using fluorinated organosilicon), Comparative Example 3 (using non-fluorinated organosilicon coating), Comparative Example 4 (using non-fluorinated organosilicon with too small solubility parameter), and Comparative Example 5 (using non-fluorinated organosilicon with too large solubility parameter) have high air permeability rates, but their waterproofness does not meet the requirements.

[0186] In addition, the tensile strength of the product of Comparative Example 1 basically meets the requirements, and the products of Comparative Examples 2-5 have relatively low tensile strengths and do not meet the mechanical property requirements.

[0187] According to the above, in Examples 1-6 of the present invention, by adding specific non-fluorinated organosilicon to polyimide-based nanofibers, the obtained non-fluorinated polyimide-based films simultaneously have excellent waterproofness, breathability, and mechanical properties, while the products of Comparative Examples 1-5 cannot meet the performance in all three aspects at the same time.

[0188] The description of the above examples is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a fluorine-free polyimide-based film, the method comprising the following steps: S1: Prepare a polyamic acid solution; S2: Add fluorine-free organosilicon as a modifier to the polyamic acid solution and disperse it to form a blend spinning solution, where the difference in solubility parameter between the fluorine-free organosilicon and the polyamic acid is 2.0 (MPa). 1 / 2 as follows; S3: Electrospun the blend spinning solution to form a polyamic acid-based nanofiber layer; S4: Thermally imidize the polyamic acid-based nanofiber layer to obtain the fluorine-free polyimide-based film.

2. The method according to claim 1, wherein in step S1, A polyamic acid solution is obtained by dissolving a diamine monomer and a dianhydride monomer in a polar solvent and stirring and reacting for 6-20 hours, The molar ratio of the diamine monomer to the dianhydride monomer is 1:1, Relative to the weight of the polyamic acid solution, the combined dosage of the diamine monomer and the dianhydride monomer is 8-15 wt%, The diamine monomer is one or more selected from diaminodiphenyl ether (ODA), all-meta triphenylenediamine (1,3,3-APB), bisphenol A type diamine (BAPP), and 4,4'-diaminodiphenyl sulfone (DDS), The dianhydride monomer is one or more selected from diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), triphenyl ether dianhydride (HQPDA), benzophenone dianhydride (BTDA), bisphenol A type dianhydride (BPADA), and diphenyl sulfide dianhydride (TDPA), The polar solvent is one or more selected from N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF).

3. The method according to claim 1, wherein in step S2, The fluorine-free silicone is one or more selected from amino-terminated polydimethylsiloxane (PDMS), epoxy-modified silicone oil, carboxyl-modified silicone oil, and polyether-modified silicone oil, Relative to the weight of the polyamic acid solution, the dosage of the fluorine-free silicone is 1-8 wt%, The dispersion is carried out by a high-shear dispersion emulsifier.

4. The method according to claim 1, wherein in step S3, in the electrospinning, The voltage is set to 10-20 kV, The distance between the nozzle and the collector is 5-20 cm, The injection rate of the polyamic acid solution is 0.5-3 mL / h.

5. The method according to claim 1, wherein in step S4, the temperature of the thermal imidization is 300-450 °C.

6. A fluorine-free polyimide-based film prepared by the method according to claim 1, wherein the fluorine-free polyimide-based film has a structure formed by three-dimensional cross-linking and winding of polyimide-based nanofibers, The polyimide-based nanofibers are composed of a polyimide substrate and fluorine-free silicone dispersed therein.

7. The fluorine-free polyimide-based film according to claim 6, wherein the hydrostatic pressure resistance value of the fluorine-free polyimide-based film is 100 kPa or more, the air permeability is 8 mm / s or more, and the tensile strength is 22 MPa or more.

8. The fluorine-free polyimide-based film according to claim 6, wherein the thickness of the fluorine-free polyimide-based film is 30-60 μm.

9. The fluorine-free polyimide-based film according to claim 6, wherein the average diameter of the polyimide-based nanofibers is 200-900 nm.

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