Polyamide-imide resin composition for production of nonwoven fabric

Abstract

To provide a polyamide-imide resin composition that contains an organic solvent that can dissolve a polyamide-imide resin like NMP, and has excellent dryability, and has excellent heat resistance, and can be used suitably for the production of a nonwoven fabric.SOLUTION: An amide imide resin composition for the production of a nonwoven fabric contains (A) polyamide-imide resin with a number average molecular weight of 20,000 or more, and (B) dimethyl acetamide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Embodiments of the present disclosure relate to a polyamideimide resin composition, and more particularly to a polyamide resin composition that can be suitably used for producing nonwoven fabrics. [Background technology]

[0002] Nonwoven fabrics can be used in a variety of fields, for example, as battery separators and various filters. Nonwoven fabrics are produced, for example, through a spinning process using materials selected depending on the application and purpose of use. For example, excellent heat resistance is required for battery separator applications. Excellent heat resistance is also required for filters used in high-temperature environments, and further improvement in heat resistance is desired due to the diversification of these application modes. In response to this, polyamide-imide resins, which have excellent heat resistance as well as excellent chemical and solvent resistance, have attracted attention as fiber or nonwoven fabric materials (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4797863 Summary of the Invention [Problem to be solved by the invention]

[0004] N-methyl-2-pyrrolidone (NMP) is widely used as a good solvent for polyamide-imide resins. However, in recent years, regulations regarding the use of NMP have become stricter from the viewpoints of environmental conservation and safety and health. Furthermore, NMP has a high boiling point of 200°C or higher, which makes it difficult to dry, leading to problems such as stickiness of the fibers after spinning and uneven welding of the fibers during nonwoven fabric production. Therefore, there is a need for a polyamide-imide resin composition suitable for nonwoven fabric production, which uses an organic solvent that can dissolve polyamide-imide resins to the same extent as NMP but has good drying properties at relatively low temperatures.

[0005] Organic solvents capable of dissolving polyamide-imide resins and having relatively low boiling points include dimethylacetamide (DMAC) and dimethylformamide (DMF). However, polyamide-imide resins synthesized using organic solvents such as DMAC and DMF tend to have lower properties, such as mechanical strength and heat resistance, compared to polyamide-imide resins synthesized using NMP. On the other hand, generally, increasing the heat resistance of polyamide-imide resins tends to decrease the solubility of the resin, making it difficult to achieve a balance between heat resistance and solubility. Therefore, when producing fibers and nonwoven fabrics using polyamide-imide resin solutions, increasing the heat resistance of the polyamide-imide resin tends to decrease the solubility of the resin, which can easily cause problems during spinning. For these reasons, further development of polyamide-imide resin compositions is desired in order to realize nonwoven fabrics with excellent heat resistance.

[0006] Therefore, an object of an embodiment of the present invention is to provide a polyamideimide resin composition that contains an organic solvent that can dissolve polyamideimide resin to an extent comparable to that of NMP, has excellent drying properties, and can be suitably used for producing nonwoven fabrics that have excellent heat resistance. [Means for solving the problem]

[0007] Nonwoven fabrics are formed by entangling spun fibers without weaving them into a sheet, and the forming is carried out by applying heat or mechanical or chemical treatment. Through extensive investigations, the present inventors discovered that a resin having a glass transition temperature (Tg) of 270°C or higher is suitable for use in the fiber material to produce a heat-resistant nonwoven fabric. They then discovered that a resin composition containing a polyamide-imide resin having a number-average molecular weight of 20,000 or higher and dimethylacetamide can achieve a good balance between heat resistance and solubility, making it suitable for use in the production of nonwoven fabrics, and thus completed the present invention.

[0008] That is, an embodiment of the present invention relates to a polyamideimide resin composition for producing nonwoven fabric, which comprises (A) a polyamideimide resin having a number average molecular weight of 20,000 or more and (B) dimethylacetamide. Another embodiment relates to a nonwoven fabric formed using the polyamideimide resin composition. [Effects of the Invention]

[0009] According to the present embodiment, a polyamideimide resin composition can be provided that can be suitably used for producing nonwoven fabrics that require excellent heat resistance. The polyamideimide resin composition contains dimethylacetamide as a solvent, which is also preferable from the viewpoints of environmental conservation and safety and hygiene. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments will be described below, but the present invention is not limited to the following embodiments. 1. Polyamide-imide resin composition When the nonwoven fabric is used for heat-resistant filters used in high-temperature environments, such as battery separators and fuel exhaust gas filters, the resin preferably has a glass transition temperature (Tg) of 270°C or higher in order to obtain sufficient heat resistance. The Tg described in this specification refers to a value obtained by measurement according to the TMA (Thermal Mechanical Analysis) method, and details will be described later in the Examples. The Tg of the resin is more preferably 275°C or higher, and even more preferably 280°C or higher. In contrast, in one embodiment, the polyamideimide resin composition contains at least (A) a polyamideimide resin having a number-average molecular weight of 20,000 or more and (B) dimethylacetamide as a solvent. According to the polyamideimide resin composition of the above embodiment, by using a polyamideimide resin having a number-average molecular weight of 20,000 or more, a Tg of 270°C or higher can be easily obtained, and excellent solubility in dimethylacetamide can also be achieved. Therefore, the polyamideimide resin composition can be used to efficiently produce nonwoven fabrics with excellent heat resistance. The nonwoven fabrics are suitable for applications requiring high heat resistance, such as battery separators and heat-resistant filters. The components of the polyamideimide resin composition are described below. In the following description, the polyamideimide resin composition may also be referred to as the "resin composition."

[0011] <Polyamide-imide resin> The polyamide-imide resin of component (A) is a resin obtained by reacting a diisocyanate compound with a tribasic acid anhydride or tribasic acid halide as an acid component. Here, each raw material compound may be used in combination with any of a plurality of types.

[0012] The diisocyanate compound is not particularly limited, but examples thereof include 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, 3,3'-diphenylmethane diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, paraphenylene diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, etc. From the viewpoint of reactivity, it is preferable to use 4,4'-diphenylmethane diisocyanate.

[0013] In one embodiment, the polyamide-imide resin may contain a diamine compound in addition to the diisocyanate, such as 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, xylylenediamine, phenylenediamine, and isophoronediamine.

[0014] The tribasic acid anhydride is not particularly limited, but preferably an aromatic tribasic acid anhydride is used, and among them, trimellitic anhydride is preferred. The tribasic acid halide is also not particularly limited, but preferably a tribasic acid chloride, more preferably an aromatic tribasic acid chloride, such as trimellitic anhydride chloride (trimellitic anhydride chloride), is included. From the viewpoint of reducing the burden on the environment, it is preferred to use trimellitic anhydride, etc.

[0015] As the acid component, in addition to the above-mentioned tribasic acid anhydrides (or tribasic acid halides), saturated or unsaturated polybasic acids such as dicarboxylic acids and tetracarboxylic dianhydrides can be used within a range that does not impair the properties of the polyamideimide resin. Examples of dicarboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, adipic acid, and sebacic acid. Examples of tetracarboxylic dianhydrides include, but are not limited to, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, and biphenyl tetracarboxylic dianhydride. These may be used alone or in any combination of two or more. The total amount of carboxylic acids other than tribasic acids (dicarboxylic acids and tetracarboxylic acids) is preferably used in the range of 0 to 50 mol %, more preferably 0 to 30 mol %, of the total carboxylic acids, from the viewpoint of maintaining the properties of the polyamideimide resin.

[0016] The ratio of diisocyanate (and diamine) to acid component (the total amount of tribasic acid anhydride or tribasic acid anhydride halide and dicarboxylic acid and tetracarboxylic acid dianhydride used as needed) used is preferably 0.8 to 1.1 mol, more preferably 0.95 to 1.08 mol, and particularly preferably 1.0 to 1.08 mol, of diisocyanate compound (and diamine compound) per 1.0 mol of the total amount of acid components, from the viewpoint of the molecular weight and degree of crosslinking of the polyamideimide resin produced.

[0017] In one embodiment, the polyamideimide resin may be a blocked polyamideimide resin in which the terminal isocyanate group is treated with a blocking agent (terminal blocking agent). Examples of usable terminal blocking agents include alcohols, oximes, and lactams. When a blocked polyamide resin is used in a polyamideimide resin composition, decomposition due to hydrolysis is suppressed and stability over time is improved, making it easier to achieve excellent heat resistance.

[0018] In one embodiment, the number-average molecular weight of the polyamide-imide resin is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 15,000 or more, from the viewpoint of ensuring mechanical strength in the spinning process. Furthermore, from the viewpoint of ensuring the desired heat resistance when molded into a nonwoven fabric, the number-average molecular weight is preferably 20,000 or more. On the other hand, from the viewpoint of ensuring solubility in solvents and easily obtaining a viscosity suitable for the spinning process, the number-average molecular weight is preferably 50,000 or less, more preferably 45,000 or less, and even more preferably 40,000 or less. In one embodiment, the number average molecular weight of the polyamideimide resin is preferably in the range of 20,000 to 35,000. When a polyamideimide resin having a number average molecular weight within the above range is used, it becomes easy to obtain a good balance between heat resistance and solubility, and the spinning process can be carried out smoothly.

[0019] The number average molecular weight of the polyamide-imide resin can be controlled within the above-mentioned preferred range by sampling during the resin synthesis, measuring by gel permeation chromatography (GPC) using a calibration curve of standard polystyrene, and continuing the synthesis until the target number average molecular weight is reached. The GPC measurement conditions will be described later.

[0020] The polyamideimide resin is preferably contained in the resin composition in an amount of 1 to 50% by mass in order to fully exert its functions. A combination of multiple polyamideimide resins may be used, and a blocked polyamideimide resin may be contained in part.

[0021] The amount of polyamideimide resin in the resin composition can be set appropriately and is not particularly limited. In a preferred embodiment, from the viewpoint of balance with other components, the amount of polyamideimide resin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. On the other hand, it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. By adjusting the amount of polyamideimide resin in the resin composition within the above range, it becomes easy to obtain fibers having sufficient strength during spinning, and it is possible to suppress a decrease in fluidity and maintain good workability.

[0022] <Dimethylacetamide> The polyamideimide resin composition contains dimethylacetamide as a solvent (B). The polyamideimide resin composition may contain a solvent other than dimethylacetamide as long as the effects of the present invention are not impaired.

[0023] Other solvents that can be used include water and one or more polar solvents selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidine, dimethylacetamide, dimethylformamide, and N-acetylmorpholine. Furthermore, co-solvents may be optionally used, including ether compounds such as anisole, diethyl ether, and ethylene glycol; ketone compounds such as acetophenone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanenone, and cyclopentanone; aromatic hydrocarbon solvents such as xylene and toluene; and alcohols such as ethanol and 2-propanol.

[0024] When a solvent other than dimethylacetamide is used as the solvent to prepare a mixed solvent, the content of dimethylacetamide in the mixed solvent is preferably 50% by mass or more, and more preferably 80% by mass or more, in order to fully exert the effects of the preferred embodiment.

[0025] <Other ingredients> The polyamideimide resin composition may contain any optional components depending on the intended use, in addition to the above-mentioned (A) polyamideimide resin and (B) dimethylacetamide.

[0026] In one embodiment, when forming an aqueous resin composition, the resin composition preferably contains a basic compound to increase the solubility of the polyamideimide resin in water. The basic compound reacts with a carboxyl group contained in the polyamideimide resin to form a salt, thereby increasing the solubility of the resin in water. As the basic compound, alkylamines or alkanolamines can be preferably used. In addition to the basic compound, for example, caustic alkali such as sodium hydroxide or potassium hydroxide, or ammonia water, etc. may be used in combination.

[0027] The basic compound is preferably used in an amount of 2.5 to 10 equivalents, more preferably 4 equivalents or more, and even more preferably 8 equivalents or less, relative to the total acid value of the carboxyl groups and ring-opened acid anhydride groups contained in the polyamideimide resin, from the viewpoint of facilitating the water-solubilization of the resin and improving the strength of the coating film. The acid value can be obtained by the following method. First, approximately 0.5 g of a polyamide-imide resin composition is taken, to which approximately 0.15 g of 1,4-diazabicyclo[2.2.2]octane is added. Approximately 60 g of N-methyl-2-pyrrolidone and approximately 1 mL of ion-exchanged water are then added, and the mixture is stirred until the polyamide-imide resin is completely dissolved. This mixture is titrated using a 0.05 mol / L ethanolic potassium hydroxide solution in a potentiometric titrator to obtain the acid value of the polyamide-imide resin, which is the sum of the carboxyl groups and the carboxyl groups resulting from ring-opening of the acid anhydride groups.

[0028] The salt formation between the polyamideimide resin and the basic compound may be carried out by adding the basic compound to a polyamideimide resin composition containing water, or by adding the basic compound to a water-free organic solvent solution of the polyamideimide resin, followed by adding water. The temperature for forming the salt is preferably 0°C to 200°C, more preferably 40°C to 130°C.

[0029] The polyamide-imide resin composition can be used in various applications, such as a coating agent for various devices, a material for molded articles, etc. In one embodiment, the polyamide-imide resin composition can be suitably used as a fiber material, and more suitably used in particular as a nonwoven fabric material. Depending on the intended use and mode of use, the polyamideimide resin composition may further contain optional components such as pigments, fillers, antifoaming agents, preservatives, surfactants, and thickeners, as needed. In one embodiment, the resin composition may contain a resin other than polyamideimide resin. For example, fluororesins, polyethersulfone resins (PES), polyimide resins (PI), polyamide resins, epoxy compounds, isocyanate compounds, melamine compounds, and the like may be used alone or in combination, as needed. For example, tetrafluoroethylene resin, tetrafluoroethylene-perfluorovinyl ether copolymer, or tetrafluoroethylene-hexafluoropropylene copolymer can be preferably used as the fluororesin. A combination of these may also be used. Adding a fluororesin to a resin composition makes it easier to impart properties such as non-stickiness, corrosion resistance, heat resistance, and chemical resistance.

[0030] Examples of epoxy compounds include bisphenol-type epoxy resins (bisphenol A-type epoxy resins, hydrogenated bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, brominated bisphenol A-type epoxy resins, bisphenol S-type epoxy resins, etc.), biphenyl-type epoxy resins, phenol novolac-type epoxy resins, brominated phenol novolac-type epoxy resins, o-cresol novolac-type epoxy resins, flexible epoxy resins, multifunctional epoxy resins, amine-type epoxy resins, heterocycle-containing epoxy resins, alicyclic epoxy resins, triglycidyl isocyanurate, bixylenol-type epoxy resins, etc. These epoxy compounds may be used alone or in combination. The epoxy compound may be added alone to react with the polyamideimide resin, but may also be added together with a curing agent or a curing accelerator so that unreacted epoxy compound is less likely to remain after molding.

[0031] Examples of the isocyanate compound include polyisocyanates of hexamethylene diisocyanate such as Duranate, polyisocyanates synthesized from 4,4'-diphenylmethane diisocyanate, etc. The mass average molecular weight of this polyisocyanate is preferably 500 to 9,000, more preferably 1,000 to 5,000.

[0032] The melamine compound is not particularly limited, but examples thereof include methylol group-containing compounds obtained by reacting melamine with formaldehyde, paraformaldehyde, etc. The methylol group is preferably etherified with an alcohol having 1 to 6 carbon atoms.

[0033] In a preferred embodiment, the resin composition further contains an epoxy compound (epoxy resin). By blending an epoxy compound, the thermal, mechanical, and electrical properties of the polyamideimide resin composition can be further improved.

[0034] The amount of each of the epoxy compound, isocyanate compound, and melamine compound contained in the resin composition is, for example, preferably 1 part by mass or more, more preferably 5 parts by mass or more, relative to 100 parts by mass of the polyamideimide resin. On the other hand, from the viewpoint of maintaining the heat resistance and strength of the polyamideimide resin composition, the amount is preferably 40 parts by mass or less, more preferably 30 parts by mass or less.

[0035] In one embodiment, when a nonwoven fabric is produced using a resin composition, the resin composition preferably contains a surfactant as needed. The surfactant is not particularly limited, but is preferably one that does not cause layer or phase separation until the resin composition is uniformly mixed and the fibers are dried after spinning, and does not leave much residue when the fibers are assembled to form a nonwoven fabric.

[0036] The content of the surfactant is not particularly limited, but in order to maintain a uniform mixed state of the resin composition and to prevent adverse effects during the production of the nonwoven fabric, it is preferably 0.01 to 10 mass % in the resin composition, and more preferably 0.5 to 5 mass %.

[0037] The resin composition may contain a filler to improve the water resistance, etc., of the nonwoven fabric. The type of filler can be selected depending on the application of the nonwoven fabric, taking into account its water resistance, chemical resistance, etc., and is preferably insoluble in water. Specific examples of fillers include metal powder, metal oxides (aluminum oxide, zinc oxide, tin oxide, titanium oxide, etc.), glass beads, glass flakes, glass particles, ceramics, silicon carbide, silicon oxide, calcium fluoride, carbon black, graphite, mica, and barium sulfate. These may be used alone or in combination.

[0038] 2. Polyamide-imide resin manufacturing method The method for producing a polyamide-imide resin includes a polymerization step of reacting a diisocyanate compound with a tribasic acid anhydride and / or a tribasic acid halide in an organic solvent. In a preferred embodiment, the organic solvent contains dimethylacetamide. The raw material compounds used are as described above in the section on the polyamide-imide resin composition. When a blocked polyamideimide resin is produced, in addition to the above polymerization step, a step of blocking the terminal isocyanate groups of the polyamideimide resin with a blocking agent such as alcohol is further included. As will be described later, the polymerization step and the blocking step may be carried out separately, or both steps, i.e., polymerization and blocking, may be carried out simultaneously.

[0039] In the polymerization step, dimethylacetamide or a solvent containing dimethylacetamide can be used as a polymerization solvent (synthesis solvent), and in that case, the obtained polymerization solution can be used as a polyamideimide resin composition as a material for nonwoven fabrics, etc. That is, dimethylacetamide is used both as a synthesis solvent and as a dilution solvent, which will be described later. Solvents other than dimethylacetamide are as explained in the section on polyamideimide resin compositions above.

[0040] The amount of solvent used during polymerization is not particularly limited, but from the viewpoint of resin solubility, it is preferably 50 to 500 parts by mass per 100 parts by mass of the total amount of the diisocyanate component (and diamine component) and acid component. The reaction temperature is not particularly limited, but is generally preferably 80 to 180°C. The polymerization reaction is preferably carried out in an atmosphere of nitrogen or the like in order to reduce the influence of moisture in the air.

[0041] The polyamide-imide resin can be produced, for example, by the following procedure. (1) A method of synthesizing a polyamide-imide resin by using an acid component and a diisocyanate component (and a diamine component) at the same time and reacting them. (2) A method in which an acid component is reacted with an excess amount of a diisocyanate component (and a diamine component) to synthesize an amide-imide oligomer having an isocyanate group or an amino group at the terminal, and then an acid component is added to react with the terminal isocyanate group (and amino group) to synthesize a polyamide-imide resin. (3) A method in which an excess amount of an acid component is reacted with a diisocyanate component (and a diamine component) to synthesize an amide-imide oligomer having an acid or acid anhydride group at the terminal, and then a diisocyanate component and / or a diamine component is added to react with the terminal acid or acid anhydride group to synthesize a polyamide-imide resin.

[0042] When synthesizing a blocked polyamide-imide resin, the blocking step may be carried out simultaneously with the polymerization step by reacting a blocking agent during the synthesis of the resin, or by reacting a blocking agent with the resin after the polymerization step. In the former case, the blocking agent may be added to the polymerization solvent. The amount of the terminal blocking agent used in blocking is preferably 1.0 to 10.0 parts by mass, and more preferably 2.5 to 5.0 parts by mass, from the viewpoint of the storage stability of the resulting resin composition, when the total amount of diisocyanates used in producing the resin is taken as 100 parts by mass.

[0043] 3. Method for producing polyamide-imide resin composition The polyamideimide resin composition containing at least (A) the polyamideimide resin having a number average molecular weight of 20,000 or more and (B) dimethylacetamide can be produced by using the reaction solution containing the polyamideimide resin obtained by the above-mentioned method for producing a polyamideimide resin as is. If necessary, a dilution solvent may be added. That is, in one embodiment, a method for producing a polyamideimide resin composition includes the steps of: The method includes a polymerization step of reacting a diisocyanate compound with a tribasic acid anhydride and / or a tribasic acid halide in a solvent containing dimethylacetamide. In another embodiment, the manufacturing method further comprises: a polymerization step of reacting a diisocyanate compound with a tribasic acid anhydride and / or a tribasic acid halide in a solvent containing the compound; and and adding a dilution solvent to the obtained resin solution or resin. In this embodiment, the solvent and / or dilution solvent used in the polymerization step includes at least dimethylacetamide. When a blocked polyamideimide resin is used as the polyamideimide resin, a blocking step may be carried out simultaneously with the polymerization step, or a blocking step may be added separately. Furthermore, when an aqueous resin composition is to be prepared, a water-solubilizing step using a basic compound may be carried out after the polymerization step, and water may be used as a dilution solvent.

[0044] 4. Nonwoven fabric and its manufacturing method Polyamideimide resin compositions have excellent heat resistance and good solubility of the resin in the resin composition, so various spinning methods can be used to produce fibers. Among these, although not particularly limited, polyamideimide resin compositions have good solvent drying properties, making them suitable materials for dry spinning. When spinning a polyamideimide resin composition, it is preferable to dilute it with a solvent to achieve an appropriate viscosity for each spinning method. However, from the viewpoint of achieving excellent drying properties, it is preferable that the resin composition be non-aqueous.

[0045] In the dry spinning method, a polyamideimide resin composition (solution) is extruded through a spinning nozzle, and the solvent is dried to obtain fibers. In one embodiment, a nonwoven fabric can be obtained by forming an aggregate of fibers obtained by spinning into a predetermined shape under heat and partially fusing (bonding) the fibers together. The fusing of the fibers together can be achieved not only by heating, but also by spraying a solution containing a binder resin onto an aggregate of fibers made of polyamideimide resin. Examples of binder resins that can be used for bonding include polyethersulfone resin (PES), polyimide resin (PI), polyamide resin, epoxy compound, isocyanate compound, and melamine compound, either alone or in combination. Details of these resins are as described in the section on polyamideimide resin compositions.

[0046] In one embodiment, the nonwoven fabric can be suitably produced by electrospinning (electrospinning). Electrospinning is a method in which a positive high voltage is applied to a resin solution, and the resin solution is sprayed onto a grounded or negatively charged surface, resulting in fiberization. This method can produce fibers with a small fiber diameter and excellent structural uniformity. Furthermore, because the fibers can be formed in a two-dimensionally spread state on the target plate, a nonwoven fabric can be obtained without further processing the fibers after spinning. Thus, because nonwoven fabrics produced by electrospinning are composed of fine fibers, it is easy to obtain high-performance nonwoven fabrics with excellent separability. Therefore, in one embodiment, by using the polyamideimide resin composition (solution) of the above embodiment to produce a nonwoven fabric according to an electrospinning method, it is possible to obtain a high-quality nonwoven fabric that has excellent heat resistance and separability through a simple process. Such a nonwoven fabric can be used for various purposes, such as electrode separators and heat-resistant filters, which require excellent heat resistance. [Example]

[0047] Next, various examples will be described, but the preferred embodiment is not limited to these examples, and it goes without saying that it includes many other embodiments based on the gist of the invention.

[0048] The number average molecular weight of the polyamideimide resin was measured as follows. <Number average molecular weight> GPC model: Tosoh Corporation HLC-8320GPC Detector: RI manufactured by Tosoh Corporation Wavelength: 270nm Data processor: ATT 8 Column: Gelpack GL-S300MDT-5 x 2 Column size: 8mmφ×300mm Column temperature: 40℃ Solvent: DMF / THF = 1 / 1 (liters) + 0.06M phosphoric acid + 0.06M lithium bromide Sample concentration: 5mg / 1mL Injection volume: 5μL Pressure: 49kgf / cm 2 (4.8×10 6 Pa) Flow rate: 1.0mL / min

[0049] Example 1 313.6 g of trimellitic anhydride, 408.5 g of 4,4'-diphenylmethane diisocyanate, and 882.6 g of dimethylacetamide were placed in a flask equipped with a thermometer, stirrer, and condenser. The mixture was stirred in a dry nitrogen stream and gradually heated to 90°C over 1 hour. After continuing heating for 3 hours, the mixture was gradually heated to 140°C, while taking care to avoid the rapid foaming of carbon dioxide gas produced by the reaction. Heating was continued for 4 hours from the start of heating, after which the reaction was stopped, yielding a polyamideimide resin solution (resin composition). After allowing this polyamideimide resin solution to cool to room temperature, its appearance was visually observed and found to be uniform and transparent. The nonvolatile content of this polyamideimide resin solution (200°C / 2 hours) was 40 mass %, and the number average molecular weight of the polyamideimide resin was 25,000.

[0050] <Example 2> 482.6 g of trimellitic anhydride, 631.2 g of 4,4'-diphenylmethane diisocyanate, and 1670.7 g of dimethylacetamide were placed in a flask equipped with a thermometer, stirrer, and condenser. The mixture was stirred in a dry nitrogen stream and gradually heated to 80°C over 1 hour. After continuing heating for 4 hours, the mixture was gradually heated to 150°C, while taking care to avoid the rapid foaming of carbon dioxide gas produced by the reaction. Heating was continued for 5 hours from the start of heating, after which the reaction was stopped, yielding a polyamideimide resin solution (resin composition). After allowing this polyamideimide resin solution to cool to room temperature, its appearance was visually observed and found to be uniform and transparent. The nonvolatile content of this polyamideimide resin solution (200°C / 2 hours) was 35 mass %, and the number average molecular weight of the polyamideimide resin was 30,000.

[0051] Example 3 134.5 g of trimellitic anhydride, 78.8 g of 4,4'-diphenylmethane diisocyanate, 101.8 g of 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, and 585.1 g of dimethylacetamide were placed in a flask equipped with a thermometer, a stirrer, and a condenser. The mixture was gradually heated to 100°C over 2 hours while stirring in a dry nitrogen stream. After continuing heating for 2 hours, the mixture was gradually heated to 140°C, while taking care to avoid the rapid foaming of carbon dioxide gas produced by the reaction. Heating was continued for 6 hours from the start of heating, after which the reaction was stopped, yielding a polyamideimide resin solution (resin composition). After allowing the polyamideimide resin solution to cool to room temperature, its appearance was visually observed and found to be uniform and transparent. The nonvolatile content of this polyamideimide resin solution (200°C / 2 hours) was 32 mass %, and the number average molecular weight of the polyamideimide resin was 20,000.

[0052] <Comparative Example 1> 175.8 g of trimellitic anhydride, 229.0 g of 4,4'-diphenylmethane diisocyanate, and 494.7 g of dimethylacetamide were placed in a flask equipped with a thermometer, a stirrer, and a condenser, and the temperature was gradually raised to 120°C over 1 hour while stirring in a dry nitrogen stream. The temperature was maintained while taking care to avoid the sudden foaming of carbon dioxide gas generated by the reaction. Heating was continued for 8 hours from the start of heating, after which the reaction was stopped, yielding a polyamideimide resin solution (resin composition). This polyamideimide resin solution was allowed to cool to room temperature, and its appearance was visually observed to be uniform and transparent. The nonvolatile content of this polyamideimide resin solution (200°C / 2 hours) was 42 mass %, and the number average molecular weight of the polyamideimide resin was 15,000.

[0053] <Glass transition temperature (Tg)> The polyamideimide resin compositions obtained in each of the above Examples and Comparative Example 1 were applied to a glass plate, pre-dried at 80°C for 30 minutes, and then cured at 270°C for 30 minutes to obtain a film, of which approximately 10 mg was used as a test piece. For this test piece, Tg was determined from the inflection point of the linear expansion curve according to the TMA method using a Hitachi High-Tech Science Corporation "TMA-7100" device. The measurement temperature range during measurement was room temperature to 400°C, and the heating rate was 10°C / min.

[0054] The measurement results are shown in Table 1. [Table 1]

[0055] As can be seen from Table 1, the polyamideimide resin compositions (Examples 1 to 3) containing a polyamideimide resin having a number average molecular weight of 20,000 or more and dimethylacetamide can achieve the desired Tg of 270° C. or more. On the other hand, when a polyamideimide resin having a number average molecular weight of less than 20,000 was used, it was difficult to achieve the desired Tg. From the above, it can be seen that the polyamideimide resin composition according to one embodiment of the present invention can efficiently provide a nonwoven fabric having excellent heat resistance. In addition, dimethylacetamide has a lower boiling point than NMP, which is known as a good solvent for polyamideimide resins, and therefore has excellent drying properties, and is also excellent in terms of the working environment and environmental safety, which provides various benefits in the production of nonwoven fabrics.

Claims

1. An amide-imide resin composition for producing nonwoven fabrics, comprising: (A) a polyamide-imide resin having a number-average molecular weight of 20,000 or more; and (B) dimethylacetamide.

2. A nonwoven fabric formed using the amide-imide resin composition for producing nonwoven fabric according to claim 1.

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