Polyamide-imide resin, polyamide-imide fiber, nonwoven fabric and separators for electronic components

Abstract

The purpose of this invention is to provide a polyamide-imide resin that can be stably spun into nanofibers with fine fiber diameters; and polyamide-imide fibers, nonwoven fabrics, etc. formed therefrom. One polyamide-imide resin contains organic acid salt compounds as constituent units.

Description

Technical Field

[0001] This invention relates to a polyamide-imide resin. More specifically, it relates to a polyamide-imide resin, polyamide-imide fibers formed therefrom, nonwoven fabrics and separators for electronic components, and a method for manufacturing the nonwoven fabric. Prior Technology

[0002] Nanofibers with a diameter of less than 1 μm have been extensively studied in the past. Methods for manufacturing aggregates of small-diameter fibers include composite spinning, high-speed spinning, and electrospinning. Among these, electrospinning is simpler than other methods, requiring less labor. Specifically, a high voltage is applied to a liquid (e.g., a solution containing fiber-forming polymers, or molten polymers) to charge the liquid, which is then drawn towards a counteracting substance to form fibers. Typically, the fiber-forming polymers are drawn out of the solution and formed into fibers as they are captured by the counteracting substance. Fiber formation, for example, is achieved by solvent evaporation when using a solution containing fiber-forming polymers, and by cooling or chemical hardening (using hardening vapor) when using molten polymers. Furthermore, the resulting fibers can be captured and laminated onto appropriately configured capture groups to obtain laminates, which can be peeled off if necessary for use as fiber aggregates. Furthermore, since an aggregate of nonwoven fibers can be obtained directly, it is not necessary to first spin the fibers to form an aggregate of fibers, as is the case with other methods, making the operation simple. Patent Document 1 discloses a technique for manufacturing nonwoven fabrics suitable for use as separators or heat-resistant filters for electronic components by electrospinning a composition comprising polyamide-imide resin and dimethylformamide.

[0003] Non-patent literature 1 discusses and reports on the viscosity or concentration of the resin solution suitable for spinning in electrospinning, and the fiber diameter or the occurrence of droplets referred to as beads in the fiber.

[0004] Patent document 2 discloses a method for manufacturing ultrafine nanofibers by adding an organic quaternary ammonium salt to a spinning solution containing polyamide imide resin. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-026771 [Patent Document 2] Japanese Patent No. 5246652 [Non-patent literature]

[0006] [Non-Patent Literature 1] Polymer, 46, 3372 (2005) Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] In recent years, in the field of separators for electronic components, in addition to the basic requirement of heat resistance, there is an increasing demand for smaller fiber diameters as separators with higher porosity or thinner films are needed to improve battery capacity or output. To address this requirement, the aforementioned method of nonwoven fabric spinning using electrospinning is known. Regarding methods for reducing fiber diameter, commonly known methods such as reducing solution viscosity and concentration can lead to issues like the formation of beads, reduced film strength, or negative effects on residual solvent. Furthermore, methods such as adding organic or inorganic salts, as described in Patent Document 2, can affect intermolecular interactions, increase solution viscosity, and cause nozzle clogging during electrospinning.

[0009] The purpose of this invention is to provide a polyamide-imide resin that can be stably spun into nanofibers with fine fiber diameters, and polyamide-imide fibers, nonwoven fabrics, etc. formed therefrom. [Problem-solving methods]

[0010] Through in-depth research and examination of the aforementioned issues, the inventors discovered that a polyamide-imide resin having the following composition can solve the problems, thus completing the present invention. That is, the present invention is formed by the following composition.

[0011] [1] A polyamide imine resin containing organic acid salt compounds as constituent units. [2] As described in [1], when all the constituent units constituting the polyamide-imide resin are set at 100 mol%, the content of constituent units from organic acid salt compounds is 0.1 to 25 mol. [3] As described in [1] or [2] above, the polyamide imine resin contains an organic acid salt compound that is an organic acid metal salt compound. [4] As described in [1] or [2] above, the polyamide imide resin contains an organic acid salt compound that is a sulfonate metal salt compound. [5] As described in [1] or [2] above, the polyamide imine resin wherein the organic acid salt compound is a metal salt of 3,5-dicarboxybenzenesulfonic acid. [6] The polyamide imide resin of any one of [1] to [5] above, wherein the number average molecular weight is more than 7,000 and less than 30,000. [7] A polyamide-imide fiber, which is spun from a polyamide-imide resin as described in any one of [1] to [6] above. [8] A nonwoven fabric composed of polyamide imide fibers as described above [7]. [9] A separator for electronic components, which is made of nonwoven fabric as described above [8].

[10] A method for manufacturing nonwoven fabric, wherein a solution containing a polyamide-imide resin containing an organic acid salt compound as a constituent unit and an organic solvent is spun by electrospinning and the polyamide-imide fibers are captured onto a capture substrate. [Effects of the Invention]

[0012] The polyamide-imide resin of this invention can be stably spun into nanofibers with fine fiber diameters using electrospinning. Therefore, for example, in separators for electronic components using this fiber, high porosity or thin film can be achieved, thereby increasing battery capacity or battery output. Simple Explanation of the Diagram

[0013] Figure 1 is a schematic cross-sectional view of the electrospinning device. Implementation

[0014] The following describes in detail the embodiments of the present invention. However, the present invention is not limited thereto, and can be implemented in various modified forms within the scope described above.

[0015] <Polyamide-imide resin> Polyamide-imide resin refers to a resin having at least one amide bond and at least one amide bond in its repeating units. The polyamide-imide resin of this invention contains organic acid salt compounds as constituent units. By including organic acid salt compounds as constituent units in the polyamide-imide resin, nozzle clogging or ball formation can be suppressed during electrospinning, allowing for the stable production of nanofibers with fine fiber diameters.

[0016] Organic acid salt compounds are substances that can introduce organic acid salts into the structure of polyamide-imide resins, and are components having organic acid salt groups and functional groups that can react with other monomer components constituting polyamide-imide resins. Examples of organic acids constituting organic acid salts include carboxylic acids and sulfonic acids. Examples of salts constituting organic acid salts include metal salts such as sodium salts, potassium salts, and lithium salts, as well as onium salts such as phosphonium salts and ammonium salts. From the viewpoint of ease of acquisition and reactivity with other monomer components, sulfonic acids are particularly preferred organic acids.

[0017] Examples of such organic acid salt compounds include, for instance, sodium 3,5-dicarboxybenzenesulfonate (also known as sodium 5-sulfoisophthalate, hereinafter referred to as SSIPA), potassium 3,5-dicarboxybenzenesulfonate, lithium 3,5-dicarboxybenzenesulfonate, sodium 3,5-bis(β-hydroxyethoxycarbonyl)benzenesulfonate, potassium 3,5-bis(β-hydroxyethoxycarbonyl)benzenesulfonate, lithium 3,5-bis(β-hydroxyethoxycarbonyl)benzenesulfonate, sodium 2,6-dicarboxynaphthalene-4-sulfonate, sodium 2,6-dicarboxynaphthalene-4,8-disulfonate, sodium 2,5-bis(hydroxyethoxy)benzenesulfonate, potassium 2,5-bis(hydroxyethoxy)benzenesulfonate, sulfonate metal salts of α-sodium sulfosuccinic acid, tetrabutylphosphonium 3,5-dicarboxybenzenesulfonate, ethyltributylphosphonium 3,5-dicarboxybenzenesulfonate, and sulfonate metal salts of sodium 3,5-dicarboxybenzenesulfonate. -Benzyltributylphosphonium dicarboxybenzenesulfonate, phenyltributylphosphonium 3,5-dicarboxybenzenesulfonate, tetraphenylphosphonium 3,5-dicarboxybenzenesulfonate, butyltriphenylphosphonium 3,5-dicarboxybenzenesulfonate, benzyltriphenylphosphonium 3,5-dicarboxybenzenesulfonate, ethyltriphenylphosphonium 3,5-dicarboxybenzenesulfonate, tetrabutylphosphonium 3-carboxybenzenesulfonate, tetraphenylphosphonium 3-carboxybenzenesulfonate, 3,5-di(β-hydroxy) Sulfonate salts of phosphonium salts, such as tetrabutylphosphonium (ethoxycarbonyl)benzenesulfonate, tetraphenylphosphonium 3,5-bis(β-hydroxyethoxycarbonyl)benzenesulfonate, tetrabutylphosphonium 3-(β-hydroxyethoxycarbonyl)benzenesulfonate, tetraphenylphosphonium 4-hydroxyethoxybenzenesulfonate, tetrabutylphosphonium 2,6-dicarboxynaphthalene-4-sulfonate, and α-tetrabutylphosphonium sulfosuccinic acid, are also available. Other biomass feedstocks induced by biomass resources may also be used. One or more of the above compounds may be used alone.

[0018] When the total constituent units of the polyamide-imide resin are defined as 100 mol%, the organic acid salt compound is preferably 0.1 mol% or more, more preferably 1 mol% or more, and even more preferably 2 mol% or more. Furthermore, 25 mol% or less is preferred, 20 mol% or less is more preferred, and 10 mol% or less is even more preferred. If the organic acid salt compound is 0.1 mol% or more, the increased ion concentration and charge during electrospinning will result in finer fibers. Conversely, if it is 25 mol% or less, the short-term charge mitigation caused by excessively high ion concentration can be suppressed. Specifically, nozzle clogging or balling can be suppressed, allowing for continuous and stable spinning.

[0019] Regarding the other monomeric components constituting polyamide-imide resin, and specifically the components forming amide and amide groups, they may include polycarboxylic acid derivatives with anhydride groups, isocyanate components, or amine components as copolymerizing agents. They may also arbitrarily contain carboxylic acid components without anhydride groups, glycol components, etc. Furthermore, when a glycol component is included as a copolymerizing agent, it becomes polyamide-imide urethane resin.

[0020] Polycarboxylic acid derivatives containing anhydride groups are not particularly limited, and examples include trimellitic anhydride (TMA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propionic dianhydride (BisDA), p-phenylene bis(trimethoxy)ester anhydrous, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propionic dianhydride, pyrocalcite dianhydride, ethylene glycol dehydrotrimethoxyester, propylene glycol dehydrotrimethoxyester, 1,4-butanediol dehydrotrimethoxyester, hexamethylene glycol dehydrotrimethoxyester, polyethylene glycol dehydrotrimethoxyester, and polypropylene glycol dehydrotrimethoxyester, etc. Alkyl diol bis(dehydrated) trimellitate, 3,3'-4,4'-benzophenone tetracarboxylic dianhydride, 3,3'-4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 3,3',4,4'-diphenyltriphenyltetracarboxylic dianhydride, meta-triphenyl-3,3',4,4'-tetracarboxylic dianhydride, 4,4'-oxophthalic dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 1,1 Aromatic polycarboxylic acid derivatives of 1,3,3,3-hexafluoro-2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, or 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethylsiloxane dianhydride, etc., as well as butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, hexahydropyrolithic dianhydride, cyclohexyl-1-ene-2,3,5,6-tetracarboxylic dianhydride, 3-ethylcyclohexyl-1-ene-3-(1,2),5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane ... Aliphatic or alicyclic polycarboxylic acid derivatives such as cyclohexyl-1-en-3-(1,2),5,6-tetracarboxylic dianhydride, 1-ethylcyclohexane-1-(1,2),3,4-tetracarboxylic dianhydride, 1-propylcyclohexane-1-(2,3),3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane-1-(2,3),3-(2,3)-tetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2,2,2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2,2,2]oct-7-en-2,3,5,6-tetracarboxylic dianhydride, or hexahydrotriphenylene anhydride can also be used. Other biomass feedstocks induced from biomass resources can also be used. The above compounds may be used alone or in combination with two or more.

[0021] Carboxylic acid components without an anhydride group are not particularly limited, and examples include tetracarboxylic acids such as pyrocalcite, biphenyltetracarboxylic acid, biphenyl ether tetracarboxylic acid, ethylene glycol dipreptyl trimellitate, and propylene glycol dipreptyl trimellitate; tricarboxylic acids such as pyromellitic acid and trimellitic acid; oxalic acid; adipic acid; malonic acid; sericinoleic acid; succinic acid; azelaic acid; and dodecanedicarboxylic acid. Aliphatic dicarboxylic acids such as dicarboxylated polybutadiene, dicarboxylated poly(acrylonitrile-butadiene), and dicarboxylated poly(styrene-butadiene); alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 4,4'-dicyclohexylmethanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, diphenyl ether dicarboxylic acid, and naphthalenedicarboxylic acid. Other biomass feedstocks induced from biomass resources may also be used, such as adipic acid, sericin, succinic acid, terephthalic acid, and difurandicarboxylic acid. One or more of the above compounds may be used alone.

[0022] The diol composition is not particularly limited, and examples include ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexanediol, dimer diols such as polyalkylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutadiene glycol, etc., or hydroxyl-terminated polyesters synthesized from one or more of the above-mentioned dicarboxylic acids and one or more of the above-mentioned diols. Other biomass feedstocks such as 1,3-propanediol and 1,10-decanediol induced from biomass resources can also be used. One of the above compounds may be used alone, or two or more may be used in combination.

[0023] The diisocyanate component is not specifically limited, and examples include diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethyldiphenylmethane-2,4'-diisocyanate, and so on. '-Diethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethoxydiphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenyl ether- 4,4'-Diisocyanate, benzophenone-4,4'-diisocyanate, diphenyl benzoate-4,4'-diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-[2,2-bis(4-phenoxyphenyl)propane]diisocyanate, 3,3'- or 2,2'-dimethylbiphenyl-4,4'- Aromatic diisocyanates such as diisocyanates, 3,3'- or 2,2'-diethylbiphenyl-4,4'-diisocyanates, 3,3'-dimethoxybiphenyl-4,4'-diisocyanates, 3,3'-diethoxybiphenyl-4,4'-diisocyanates, and 1,4-phenyl diisocyanates; aliphatic isocyanates such as hexamethylene diisocyanates; and alicyclic isocyanates such as norcamphene diisocyanates and isofrone diisocyanates. Other biomass feedstocks such as difuran diisocyanates induced from biomass resources can also be used. Considering factors such as heat resistance, aromatic diisocyanates are preferred. If solubility is also a consideration, diphenylmethane-4,4'-diisocyanate (MDI), toluene-2,4- or 2,6-diisocyanate (TDI), and 3,3'-dimethylbiphenyl-4,4'-diisocyanate (ToDI) are preferred. One of these compounds may be used alone, or two or more may be used in combination.

[0024] The diamine component is not particularly limited, and examples include aliphatic diamines such as ethylenediamine, propenyldiamine, and hexamethylenediamine; alicyclic diamines such as 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, isophoronediamine, and 4,4'-dicyclohexylmethanediamine; aromatic diamines such as m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, benzidine, o-toluidine, 2,4-toluidine, 2,6-toluidine, and xylenediamine. Other biomass feedstocks induced by biomass resources can also be used. From the perspective of reactivity, 4,4'-diaminodiphenylmethane and o-toluidine are preferred. One of the above compounds can be used alone or in combination with two or more.

[0025] The number average molecular weight of the polyamide-imide resin of this invention is preferably 7,000 to 30,000. More preferably, it is 8,000 or more, and even more preferably 9,000 or more. Furthermore, 28,000 or less is preferred, and even more preferably 25,000 or less. If the number average molecular weight is 7,000 or more, the nonwoven fabric exhibits good mechanical properties and easily forms beads-free fibers during electrospinning. If the number average molecular weight is 30,000 or less, the solution viscosity or molecular chain entanglement is appropriate, resulting in finer fibers, preventing nozzle clogging, and facilitating stable spinning.

[0026] Manufacturing of Polyamide Imide Resin The polyamide-imide resin of this invention can be manufactured using conventional methods for producing polyamide-imide resins. For example, after adding and dissolving the aforementioned raw materials, polymerization catalyst, and polymerization solvent in a reaction vessel, the mixture is stirred under a nitrogen stream and reacted at a predetermined reaction temperature for at least 2 hours. Then, it is diluted with the polymerization solvent to an appropriate solvent viscosity and cooled to obtain the target polyamide-imide resin. Furthermore, regarding the manufacturing method of the polyamide-imide resin, it can be synthesized using methods such as the chlorohydrin method (using amide and amine), the direct method (using an anhydride and amine), or the isocyanate method (using an anhydride and isocyanate). In methods using amines, since it is necessary to use amide acid, the isocyanate method (using isocyanate) is industrially advantageous.

[0027] In the method for manufacturing the polyamide-imide resin of the present invention, the molar ratio of the amount of diisocyanate and diamine components to the amount of acid and diol components is preferably 0.90 to 1.20, and more preferably 0.95 to 1.15. By setting the value above the aforementioned lower limit, the molecular weight of the polyamide-imide resin can be easily increased. In addition, by setting the value below the aforementioned upper limit, gelation or side reactions of the polyamide-imide resin during polymerization can be suppressed.

[0028] The solvent used in the polymerization of the polyamide-imide resin of this invention is preferably a solvent that dissolves the raw material as a solute and has low reactivity with the isocyanate group. Examples include toluene, xylene, ethylbenzene, nitrobenzene, cyclohexane, isophorone, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, dipropylene glycol methyl ether acetate, diethylene glycol ethyl ether acetate, methyl methoxypropionate, ethyl methoxypropionate, methyl ethoxypropionate, ethyl ethoxypropionate, ethyl acetate, n-butyl acetate, isoamyl acetate, ethyl lactate, acetone, methyl ethyl ketone, cyclohexanone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, γ-butyrolactone, dimethyl sulfoxide, chloroform, dichloromethane, etc. These can be used alone or in combination of two or more. From the perspective of reactivity and solubility, N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), γ-butyrolactone (GBL), and cyclohexanone (CHX) are preferred polymerization solvents. Among these, N,N-dimethylacetamide (DMAc) is the best, as it balances high volatility and reactivity.

[0029] In the manufacturing process of polyamide imide resin, in order to promote the reaction, it can also be reacted in the presence of amines such as triethylamine, dimethylpyridine, methylpyridine, undecene, triethylenediamine (1,4-diazabicyclo[2,2,2]octane), DBU (1,8-diazabicyclo[5,4,0]-7-undecene), alkali metals and alkaline earth metals such as lithium methoxide, sodium methoxide, sodium ethoxide, potassium butoxide, potassium fluoride, and sodium fluoride, or metals and semi-metals such as titanium, cobalt, tin, zinc, and aluminum.

[0030] The reaction temperature for manufacturing polyamide-imide resin is preferably set between 60 and 200°C, with 100 to 180°C being more favorable. Setting the reaction temperature above the aforementioned lower limit shortens the reaction time. Conversely, setting it below the aforementioned upper limit suppresses monomer decomposition and even inhibits gelation caused by the three-dimensional reaction. The reaction can be carried out in multiple stages. The reaction time can be appropriately selected based on batch size, available reaction conditions, and especially the reaction concentration. Within the aforementioned temperature range, a minimum reaction time of 3 hours is preferable to maximize molecular weight.

[0031] The polymer concentration during the polymerization of polyamide-imide resin is 10-50% by weight, preferably 20-40% by weight, based on the solids concentration. By keeping the solids concentration below 50% by weight, the increase in viscosity during synthesis is suppressed, and the stirability becomes better. In addition, by keeping the solids concentration above 10% by weight, the decrease in reaction rate can be suppressed.

[0032] When diluting polyamide-imide resin after polymerization or during electrospinning, the polymer concentration of the polyamide-imide resin solution, based on the solids content, is preferably 5-50% by weight, and preferably 10-40% by weight. A solids content of 5% or higher ensures molecular chain entanglement, allowing for stable spinning of beads-free fibers. A concentration below 50% helps suppress nozzle clogging or fiber diameter increase.

[0033] In addition to the polymerization solvents mentioned above, any solvent that dissolves the polyamide-imide resin without precipitation during dilution can be used for dilution. Examples include highly volatile solvents such as acetone, chloroform, ethanol, isopropanol, methanol, toluene, tetrahydrofuran, water, benzene, benzyl alcohol, 1,4-dimethylamine, propanol, carbon tetrachloride, cyclohexane, cyclohexanone, dichloromethane, phenol, pyridine, trichloroethane, and acetic acid; or N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), and 1-methyl-2-pyrrolidone (NM). Solvents with relatively low volatility, such as ethyl carbonate, propyl carbonate, dimethyl carbonate, acetonitrile, N-methylphosphono-N-oxide, butyl carbonate, γ-butyrolactone, diethyl carbonate, diethyl ether, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolinone, 1,3-dipentane, methyl ethyl carbonate, methyl formate, 3-methylphosphono-2-one, methyl propionate, 2-methyltetrahydrofuran, and cyclobutane, are used in spinning. When these solvents contain many highly volatile solvents, evaporation occurs rapidly, causing resin precipitation and nozzle blockage. Furthermore, because the resin solidifies under insufficient stretching conditions, there is a concern about increased fiber diameter. Conversely, when these solvents contain many less volatile solvents, evaporation is less efficient, resulting in fibers containing beads and residual solvent. Therefore, from the viewpoint of appropriate evaporation rate, N,N'-dimethylacetamide (DMAc), cyclohexanone, and dimethyl sulfoxide (DMSO) are preferred, and from the viewpoint of polymer storage stability, N,N'-dimethylacetamide (DMAc) and cyclohexanone are particularly preferred. Furthermore, two or more of the above solvents can be mixed and used.

[0034] In this invention, to improve various properties of the nonwoven fabric obtained by spinning, additives such as inorganic or organic fillers can be incorporated. In the case of additives with low affinity for polyamide-imide, their size is preferably smaller than the diameter of the obtained polyamide-imide fibers. If the additive is large, it will precipitate during electrospinning, causing fiber breakage. Regarding the method of incorporating additives, examples include methods such as pre-adding a necessary amount of additive to the polyamide-imide polymerization reaction system, and adding a necessary amount of additive after the polyamide-imide polymerization reaction is completed. In the case of additives that do not hinder polymerization, the former method yields a nonwoven fabric with uniformly dispersed additives, and is therefore more suitable.

[0035] In cases where a necessary amount of additive is added after the polymerization reaction of polyamide amide is completed, mechanical forced stirring using methods such as ultrasonic stirring or homogenizers and bead mills can be used. <Polyamide-imide fiber>

[0036] The average fiber diameter of the polyamide-imide fiber of this invention is preferably 0.001~1μm. More preferably 0.005μm~0.8μm, and even more preferably 0.01μm~0.5μm. Within this range, the industrial applicability, such as low-pressure-loss filters or waterproof and breathable membranes, is significantly expanded. If the diameter is less than 0.001μm, not only is manufacturing difficult, but the mechanical strength of the fiber also suffers. On the other hand, if the diameter exceeds 1μm, the surface area is small, and only the same effect as conventional nonwoven fabrics can be obtained.

[0037] The method for manufacturing the polyamide-imide fiber of this invention is not particularly limited, but electrospinning is preferred. The electrospinning method is described in detail below.

[0038] Electrospinning The electrospinning method used in this invention is a type of solution spinning. Generally, it involves applying a positive high voltage to a polymer solution and spraying it onto a grounded or negatively charged surface, resulting in fiber formation. An example of an electrospinning apparatus is shown in Figure 1. In Figure 1, the electrospinning apparatus 1 includes a spinning nozzle 2 that sprays polymer fiber material and a counter electrode 5 positioned opposite the spinning nozzle 2. This counter electrode 5 is grounded. The polymer solution, charged by applying a high voltage, flies out from the spinning nozzle 2 toward the counter electrode 5. At this point, fiber formation occurs. A solution of polyamide amide dissolved in an organic solvent is sprayed into an electrostatic field formed between the electrodes, causing the solution to be drawn toward the counter electrode, allowing the formed fibrous material to accumulate on a collecting substrate, thereby obtaining a nonwoven fabric.

[0039] The material of the solution tank 3 is not particularly limited, as long as it is resistant to the organic solvent used. In addition, the solution in the solution tank 3 can be sprayed into the electric field by mechanical extrusion or by suction by a pump or the like.

[0040] Spinning nozzle 2 is preferably a nozzle with an inner diameter of approximately 0.1 to 3 mm. The nozzle material can be metal or non-metal. If the nozzle is metal, it can be used as a single electrode. If nozzle 2 is non-metallic, by placing an electrode inside the nozzle, the extruded solution can be subjected to an electric field. Multiple nozzles can also be used to improve production efficiency. Generally, a circular cross-section nozzle is used, but nozzles with special cross-sections can also be used depending on the polymer type or application.

[0041] The opposing electrode 5 can be a roller electrode, a flat plate, or a strip metal electrode as shown in Figure 1. Electrodes of various shapes can be used depending on the application.

[0042] Furthermore, the current description focuses on the case where the electrodes also serve as substrates for capturing fibers. However, by placing an object that acts as a substrate between the electrodes, polyamide-imide fibers can also be captured there. In this case, for example, a strip substrate can be placed between the electrodes for continuous production.

[0043] In addition, it is generally formed with a pair of electrodes, but different electrodes can also be introduced. Spinning is performed with a pair of electrodes, and the electric field state can be controlled by introducing electrodes with different potentials, which can also control the spinning state.

[0044] The voltage application device 4 is not particularly limited; in addition to a DC high-voltage generator, a Van de Graaf generator can also be used. Furthermore, the applied voltage is not particularly limited, generally 3~100kV, preferably 5~50kV, and more preferably 5~30kV. Moreover, the polarity of the applied voltage is preferably positive. This is because negative ions, which facilitate conductivity in the gas, have an equivalent mobility approximately four times that of positive ions; with negative polarity, spark discharge will occur rapidly.

[0045] The distance between electrodes depends on the charge, nozzle size, solution flow rate, solution concentration, etc. At 10~15kV, a distance of 5~20cm is appropriate.

[0046] Electrospinning typically takes place in air, but by using a gas, such as carbon dioxide, with a discharge initiation voltage higher than that of air, low-voltage spinning can be achieved, and abnormal discharges such as corona discharge can be prevented. Furthermore, when water is a poor solvent for the polymer, polymer precipitation may occur near the spinning nozzle. Therefore, it is best to conduct the process in a low-humidity environment whenever possible.

[0047] Non-woven fabric The following describes the stage of obtaining the nonwoven fabric accumulated on the collecting substrate. In this invention, during the drawing of the solution onto the collecting substrate, the solvent evaporates depending on the conditions, forming a fibrous material. If it is at normal room temperature, the solvent will completely evaporate during the process until it is collected onto the collecting substrate. If the solvent evaporation is insufficient, drawing can be performed under reduced pressure. Even if the time of collection onto the collecting substrate is late, the fibers of this invention will still be formed. In addition, the drawing temperature depends on the evaporation behavior of the solvent or the viscosity of the spinning solution, and is usually 0~50°C. Thus, porous fibers further accumulate on the collecting substrate, and a nonwoven fabric can be manufactured.

[0048] The basis weight of the nonwoven fabric of this invention can be determined according to its application and is not particularly limited. For example, in air filter applications, 0.05~50 g / m² is preferred. The basis weight mentioned here is based on JIS-L1085. If it is below 0.05 g / m², the filter's collection efficiency is low and therefore undesirable; if it is above 50 g / m², the filter's air resistance becomes too high, and therefore also undesirable.

[0049] The thickness of the nonwoven fabric of this invention can be determined according to the application and is not particularly limited, but 1~100μm is preferred. The thickness mentioned here is measured with a micrometer.

[0050] The nonwoven fabric of this invention can also be post-processed if necessary to suit various applications. For example, it can be subjected to calendering, hydrophilic treatment, water-repellent treatment, surfactant adhesion treatment, pure water washing treatment, etc., to densify or adjust the thickness precision.

[0051] The nonwoven fabric obtained by this invention can be used alone or in combination with other components depending on operability or purpose. For example, the collecting substrate can be made of fabric (nonwoven fabric, woven fabric, knitted fabric) or film that can serve as a support substrate, conductive materials formed of metal or carbon in the shape of rollers, nets, plates, or strips, or non-conductive materials formed of organic polymers. By forming the nonwoven fabric on it, a component combining the support substrate and the nonwoven fabric can be manufactured.

[0052] The nonwoven fabric obtained by this invention can be used in various air filter applications, such as coal dust filters, air purifier filters, precision machine filters, cabin filters and engine filters for automobiles and trains, and air conditioning filters for buildings. It is particularly effective in air purification applications requiring heat resistance, mechanical strength, and thermal stability; liquid filters such as oil filters; insulating substrates for short and thin circuits; separators for electrolytic batteries where the internal temperature becomes high during charging and discharging; separators for electronic components; and dialysis membranes for fuel cell components. It is especially effective in applications exposed to high-temperature environments. It can even be used as a lining material for medical artificial organs, an immobilization support for cell culture and bioreactors, and for various other applications.

[0053] The electronic component separator obtained by this invention is manufactured using the aforementioned nonwoven fabric. The electronic component separator is a material used to prevent short circuits caused by contact between the anode and cathode inside a battery. Conventional electronic component separators use porous thin-film separators made of polyethylene or polypropylene. However, the electronic component separator of this invention uses nonwoven fabric, thus achieving high porosity. Furthermore, the fibers constituting the nonwoven fabric have a fine diameter, eliminating the need to increase film thickness to prevent short circuits, and also allowing for miniaturization and weight reduction.

[0054] The separator for electronic components of the present invention can be obtained by directly electrospinning the electrode to which it is used using the above-mentioned electrospinning method. [Example]

[0055] The present invention is illustrated below by way of examples; however, the present invention is not limited to these examples. Furthermore, the evaluation items in the following examples are carried out according to the means described below.

[0056] <Numerical Average Molecular Weight> The number-average molecular weight of polyamide-imide resins is determined as described below. Molecular weight is calculated using a conversion from standard polystyrene. Device: HLC-8220GPC manufactured by Tosoh Corporation Column:TSKgel SuperAWM-H+TSKgel Super AW2500 Solvent: DMAc / lithium bromide (LiBr) 30mM + phosphoric acid 60mM Flow rate: 0.35 ml / min Concentration: 0.05% Injection volume: 10 μl Temperature: 40℃ Detector: Differential Refraction Detector (RI)

[0057] <Glass transition temperature (Tg)> Polyamide-imide resin solution was coated onto Teflon sheets and dried at 140°C for 3 minutes. The resulting 25 μm thick polyamide-imide film was cut into pieces 4 mm wide and 15 mm long, and measured using a DVA-220 dynamic viscoelasticity measuring device manufactured by IT Measurement & Control Co., Ltd. Vibration at a frequency of 110 Hz was applied, and the temperature was increased from room temperature to 400°C at a rate of 4°C / min. The temperature at which the loss tangent (tanδ) of the dynamic viscoelasticity reaches its maximum value was defined as the glass transition temperature (Tg).

[0058] <Electrospinning conditions> The polyamide-imide resin solution disclosed in the following examples and comparative examples was spun for 10 minutes using the apparatus shown in Figure 1. The spinning nozzle 2 used an 18G needle (inner diameter: 0.8 mm) and was ejected at a flow rate of 1-5 ml / min. A voltage of 10 kV-17 kV was applied during ejection. The distance from the nozzle 2 to the fibrous material trapping electrode 5 coated with aluminum foil was set to 15 cm.

[0059] <Average fiber diameter> Take scanning electron microscope (SEM) images (5000x magnification) of the surface of the nonwoven fabric obtained after spinning under the above conditions. Number all fibers, and then randomly select 10 fibers. Measure the diameter of the 10 selected fibers and calculate the average value. Classify the obtained average fiber diameter according to the following evaluation criteria. ○: Above 0.001μm but below 0.5μm △: 0.5μm and above, 1.0μm and below ×: Exceeding 1.0μm

[0060] <Spinning Stability> Spinning under the above conditions is classified according to the following evaluation criteria. ○: Spinning was continuous without interruption. △: Spinning is interrupted at a frequency of more than once every 10 minutes but less than once every 10 seconds, yet there are very few fiber clumps or beads. ×: Spinning is interrupted at a frequency of more than once every 10 seconds, resulting in many fiber clumps or beads.

[0061] <Nozzle blockage> Spinning under the above conditions is classified according to the following evaluation criteria. ○: The nozzle tip was never clogged, allowing for continuous spinning. ×: Resin curing material is precipitated at the nozzle tip, interrupting the spinning process.

[0062] <Example 1> Trimeric triphthalic anhydride (TMA), sodium 5-sulfoisophthalate (SSIPA), diphenylmethane diisocyanate (MDI), and 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) were mixed to achieve a solids concentration of 35%. This mixture was then placed in a four-necked flask equipped with a thermometer, condenser, and nitrogen inlet tube, along with N,N-dimethylacetamide (DMAc). The mixture was stirred at 80°C for 2 hours, at 110°C for 1 hour, and at 150°C for approximately 3 hours to synthesize polyamide-imide resin. After synthesis, the resin was diluted with N,N-dimethylacetamide (DMAc) to achieve a solids concentration of 33%. The obtained polyamide imide resin has an average molecular weight of 15,000 and a glass transfer temperature of 310°C.

[0063] <Examples 2-8, 10-12, Comparative Examples 1-2> Except for changing the types and proportions of the raw materials to achieve the composition shown in Table 1, polyamide-imide resin was synthesized in the same manner as in Example 1, and the solution was diluted. The number-average molecular weight and glass transition temperature of the obtained polyamide-imide resin are shown in Table 1.

[0064] <Example 9> Except that the reaction conditions were set to stirring at 80°C for 2 hours and at 110°C for 1 hour, polyamide-imide resin was synthesized in the same manner as in Example 1, and the solution was diluted. The number-average molecular weight of the obtained polyamide-imide resin was 6800. Furthermore, the glass transition temperature could not be measured due to the breakage of the measuring film during the measurement process.

[0065] <Comparative Example 3> For the DMAc solution (100 parts by weight of solids) of polyamide imine resin prepared in Comparative Example 1, 1.2 parts by weight of lithium chloride (LiCl) pre-dissolved in DMAc to 5% by weight were added.

[0066] [Table 1] Example Comparative example 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 SSIPA 2.5 1 20 2.5 5 0.5 2.5 12.5 12.5 PHEBS 2.5 15 polyamide TBPSI 2.5 TMA 47.5 47.5 47.5 49 30 42.5 45 49.5 47.5 35 35 35 50 45 50 Imine resin composition BisDA 5 2.5 2.5 5 [mol%] MDI 50 50 50 50 50 50 50 50 50 50 50 50 50 TDI 10 10 ToDI 40 40 Additives[*] LiCl 1.2 Glass transition temperature [°C] 310 303 288 302 287 296 311 309 Unable Measurement 285 289 308 307 300 307 Number average molecular weight 15000 12000 13000 15000 11000 13000 21000 22000 6800 10000 12000 20000 11000 12000 11000 Average fiber diameter [μm] 0.3 0.3 0.4 0.7 0.2 0.3 0.4 0.9 0.3 0.3 0.2 0.3 1.5 1.4 0.3 ○ ○ ○ △ ○ ○ ○ △ ○ ○ ○ ○ × × ○ Spinning stability ○ ○ ○ ○ △ ○ ○ ○ △ △ △ △ ○ ○ × Nozzle blockage ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ × *Parts by weight relative to 100 parts by weight of polyamide-imide resin

[0067] The abbreviations in Table 1 are as follows. SSIPA: Sodium 5-sulfoisophthalate PHEBS: Potassium 2,5-bis(hydroxyethoxy)benzenesulfonate TBPSI: Tetrabutylphosphonium 3,5-dicarboxybenzenesulfonate TMA: Trimethicone BisDA: 2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propionic dianhydride MDI: Diphenylmethane-4,4'-diisocyanate TDI: Toluene-2,4- or 2,6-diisocyanate ToDI: 3,3'-Dimethylbiphenyl-4,4'-diisocyanate LiCl: Lithium chloride

[0068] As shown in Table 1, polyamide-imide resin containing organic acid salt compounds as constituent units can stably produce nanofibers with a fiber diameter of less than 1 μm and uniform fiber diameter. On the other hand, the polyamide-imide resins of Comparative Examples 1 and 2 do not contain organic acid salt compounds as constituent units, therefore the fiber diameter exceeds 1 μm and cannot be reduced in size. In Comparative Example 3, when an inorganic metal salt was added, although the fiber diameter was small, continuous and stable spinning was not possible, and the solution viscosity and hygroscopicity were high, causing nozzle blockage during spinning. [Industry availability]

[0069] The polyamide-imide fiber of this invention, by containing organic acid salt compounds as constituent units in the polyamide-imide resin, is expected to achieve significant fiber diameter reduction during electrospinning. For example, it can achieve high porosity or thin film formation in battery separators, thereby improving battery capacity or output. It can also be used in a wide range of applications, such as as a substitute for low-pressure-loss filters or membranes, which will greatly benefit industry.

[0070] 1: Electrospinning device 2: Spinning nozzle 3: Solution tank 4: High-voltage power supply 5: Opposing electrode (collecting substrate)

Claims

1. A polyamide-imide resin containing an organic acid salt compound as a constituent unit, wherein when all constituent units constituting the polyamide-imide resin are defined as 100 mol%, the content of constituent units from the organic acid salt compound is 2.5 to 25 mol%. The polyamide-imide resin is used to form polyamide-imide fibers with an average fiber diameter of 0.001 μm to 1 μm by electrospinning.

2. The polyamide-imide resin as claimed in claim 1, wherein, This organic acid salt compound is an organic acid metal salt compound.

3. The polyamide-imide resin as claimed in claim 1 or 2, wherein, This organic acid salt compound is a sulfonate metal salt compound.

4. The polyamide-imide resin as claimed in claim 1 or 2, wherein, The organic acid salt compound is a metal salt of 3,5-dicarboxybenzenesulfonic acid.

5. The polyamide-imide resin as claimed in claim 1 or 2, wherein, The number average molecular weight is between 7,000 and 30,000.

6. The polyamide-imide resin mentioned in claim 1 or 2 is used in the manufacture of nonwoven fabrics.

7. A polyamide-imide fiber, which is spun from a polyamide-imide resin as claimed in any one of claims 1 to 6.

8. A nonwoven fabric comprising polyamide-imide fibers as claimed in claim 7 as a constituent material.

9. A separator for electronic components comprising the nonwoven fabric as claimed in claim 8.

10. A method for manufacturing a nonwoven fabric, wherein a solution containing a polyamide-imide resin comprising an organic acid salt compound as a constituent unit and an organic solvent is spun by electrospinning, and the polyamide-imide fibers are collected onto a collection substrate.

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