JP2013256731A - Method for producing polyimide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyimide fiber which can provide a polyimide fiber having excellent characteristics such as thermal resistance and is low in production cost and low in environmental load, and to provide a polyimide precursor solution and a polyimide precursor fiber used for the same.SOLUTION: The method for producing a polyimide fiber comprises: obtaining a polyimide precursor fiber by spinning using a polyimide precursor solution; and imidizing the obtained polyimide precursor fiber, in which a) the polyimide precursor is a polyamide acid having a carboxylate structure in a part of the molecular structure and b) the solution viscosity of the polyimide precursor solution is 0.1 to 170 Pa s at 30°C.

Description

  The present invention relates to a method for producing a polyimide fiber having a low production cost and a low environmental load, and a polyimide precursor solution and a polyimide precursor fiber used therefor.

  Conventionally, aramid fibers and polyimide fibers have been mainly used as materials for applications requiring heat resistance, such as space / aviation and electrical fields, due to their excellent performance. Specific examples include para-type aramid fibers synthesized from terephthalic acid chloride and p-phenylenediamine, and meta-type aramid fibers synthesized from isophthalic acid chloride and m-phenylenediamine. However, these are manufactured by a so-called wet spinning method, in which a polymer is dissolved in an acidic solvent and extracted and solidified after spinning. Special equipment such as solvent recovery and pollution control is required, and the work is extremely complicated. It will be something. For polyimide fibers, for example, polyimide fibers useful in the space / aviation field or the electronic materials field (see, for example, Patent Document 1) and polyimide nonwoven fabrics (see, for example, Patent Document 2) as heat-resistant bag filters have been proposed. .

  On the other hand, in recent years, fibers (nanofibers) having a nano-order fiber diameter have been widely studied (see, for example, Patent Documents 3 to 6). Examples of a method for producing an aggregate of fibers having a small fiber diameter include a composite spinning method, a high-speed spinning method, and an electrospinning method. Among these, the electrospinning method can perform spinning more easily and with fewer man-hours than other methods. That is, by applying a high voltage to a liquid (for example, a solution containing a polymer that forms a fiber, a molten polymer), the liquid is charged, and the liquid is made to flow toward the counter electrode material to form a fiber. It is. Usually, the polymer forming the fiber is spun out of the solution and forms the fiber until it is captured by the counter electrode material. For example, when a solution containing a polymer that forms a fiber is used, the fiber is formed by solvent evaporation, when a molten polymer is used, by cooling, or by chemical curing (treatment with a curing vapor). ). In addition, the obtained fiber can be collected on a collector arranged as necessary and laminated to obtain a laminate, and if necessary, it can be peeled off and used as an aggregate of fibers. Is possible. Further, since it is possible to directly obtain an aggregate of non-woven fibers, there is no need to form an aggregate of fibers after spinning the fibers once as in other methods, and the operation is simple.

  It has been proposed to produce a polyimide nonwoven fabric by producing polyamic acid microfibers as a polyimide precursor by such an electrospinning method, and subjecting the obtained polyamide acid nonwoven fabric to high temperature heat treatment to cause dehydration and ring closure (for example, (See Patent Document 5). It has also been proposed to produce highly heat-resistant polyimide fine fibers using a polyimide solution having excellent stability (see, for example, Patent Document 6). However, the polyimide having high heat resistance and the polyamic acid which is the polyimide precursor are inferior in solubility, and therefore generally used as a high-boiling amide solvent such as N-methyl-2-pyrrolidone and N, N-dimethylformamide. Need to dissolve. For this reason, there has been a problem that a high-temperature heat treatment of substantially 350 ° C. or more is required in the fiber production process, and the amide solvent is discharged into the environment.

  As described above, in the production of polyimide fibers, it is the present situation that an excellent characteristic such as heat resistance can be expressed and a production method with low production cost and low environmental load has not been found.

Japanese Patent Publication No. 7-42611 JP 9-52308 A Japanese Patent Publication No. 48-1466 JP 2008-202169 A JP 2009-167571 A JP 2011-132651 A

  INDUSTRIAL APPLICABILITY The present invention is capable of obtaining a polyimide fiber having excellent characteristics such as heat resistance, and has a low production cost and a low environmental load, and a polyimide precursor solution and a polyimide precursor used therefor The object is to provide fibers.

The present invention relates to the following items.
1. After obtaining a polyimide precursor fiber by spinning using a polyimide precursor solution, a polyimide fiber manufacturing method for imidizing this,
a) The polyimide precursor is a polyamic acid having a carboxylate structure as part of the molecular structure.
b) The solution viscosity of the polyimide precursor solution at 30 ° C. is 0.1 to 170 Pa · s.
A method for producing a polyimide fiber, characterized in that:
2. further,
c) As a solvent, 50 mass% or more of at least 1 type chosen from water, alcohol, or polyhydric alcohol is contained,
A method for producing a polyimide fiber, characterized in that:
3. 3. The method for producing a polyimide fiber according to any one of items 1 to 2, wherein the polyamic acid having a carboxylate structure in a part of the molecular structure is a polyamic acid represented by the following general formula (1).
(In General Formula (1), A is a tetravalent aromatic group, B is a divalent aromatic group, and one or both of X ₁ and X ₂ are basic compounds.)
4). 4. The method for producing a polyimide fiber according to item 3, wherein the basic compound in the general formula (1) is an amine compound or an alkali metal.
5. A in the said General formula (1) is a tetravalent phenyl group or a biphenyl group, The manufacturing method of the polyimide fiber in any one of the preceding clauses 3-4 characterized by the above-mentioned.
6). B in the said General formula (1) is a bivalent phenyl group or an oxydibenzene group, The manufacturing method of the polyimide fiber in any one of the preceding clauses 3-5 characterized by the above-mentioned.
7). A polyimide precursor solution for producing fibers, heat-resistant filters, heat-resistant nonwoven fabrics, heat-resistant felts or heat-resistant separators having the following characteristics.
a) The polyimide precursor is a polyamic acid having a carboxylate structure as part of the molecular structure.
b) The solution viscosity of the polyimide precursor solution at 30 ° C. is 0.1 to 170 Pa · s.

  The method for producing a polyimide fiber of the present invention has a low production cost and a low environmental load during production. Moreover, the polyimide fiber obtained by this invention has the outstanding characteristics, such as heat resistance, and can be used suitably as a heat resistant filter, a heat resistant nonwoven fabric, a heat resistant felt, and a heat resistant separator.

An example of an electrospinning device

  The present invention relates to a method for producing a polyimide fiber in which a polyimide precursor fiber is obtained from a polyimide precursor solution and then imidized. As a polyimide precursor, a polyamic acid having a carboxylate structure in a part of a molecular structure is used. It is used, and the solution viscosity of the polyimide precursor solution is set within a specific range.

In the present invention, the polyamic acid having a carboxylate structure in a part of the molecular structure means a polyamic acid having a structure in which a carboxylic acid forms a neutral salt with a basic compound in at least a part of the molecular structure of the polyamic acid. For example, the structural unit represented by the following general formula (1) is included in at least a part of the molecular structure of the polyamic acid.
(A in the general formula (1) is a tetravalent group, B is a divalent group, and one or both of X ₁ and X ₂ are basic compounds.)

  The basic compound in the general formula (1) is preferably an amine compound or an alkali metal, and more preferably an imidazole compound or a tertiary amine compound. Examples of the imidazole compound include 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole. Tertiary amine compounds For example, triethylenediamine, triethylamine, N, N, N ′, N ″, N ″ -pentamethyldiethylenetriamine, N, N, N ′, N′-tetramethylpropanediamine, 1,4-dimethylpiperazine, 1 , 4-diethylpiperazine, N, N-dimethylcyclohexylamine, ethylenediaminetetraacetic acid, N, N-dimethylaminoethanol, trimethylamine and the like. These may be used alone or in admixture of two or more. By using the basic compound, the polyimide precursor can be dissolved in various solvents such as water, alcohols and polyhydric alcohols, and can be fired at a low temperature because it becomes a catalyst for imidization reaction.

  The ratio of carboxylate structure in the polyamic acid molecular structure is the ratio of the number of moles of functional groups present as carboxylate to the total number of moles of functional groups of carboxylic acid contained in the polyamic acid (carboxylic acid The number of moles of functional groups present as a salt / the total number of moles of functional groups of carboxylic acid contained in the polyamic acid) is 0.01 or more, preferably 0.1 or more, more preferably 0.5 or more, and particularly preferably 0.8. 8 or more. By setting it to 0.01 or more, the imidization reaction at a low temperature can easily proceed, and by setting it to 0.1 or more, particularly 0.8 or more, the solubility of the polyimide precursor is improved. The ratio of this functional group can be adjusted by the addition amount (number of moles) of the base compound used, and the ratio can be determined by neutralization titration, NMR measurement, and FT-IR measurement.

  A in the general formula (1) represents a residue obtained by removing four carboxylic acids from the tetracarboxylic acids constituting the polyamic acid. The tetracarboxylic acids that can be used in the present invention are not particularly limited, but aromatic tetracarboxylic acids in which A is an aromatic group are preferred. Such tetracarboxylic acids include 3,3,4 ', 4'-biphenyltetracarboxylic acids, 2,3,3', 4'-biphenyltetracarboxylic acids, 2,2 ', 3,3'-biphenyl Tetracarboxylic acids, pyromellitic acids, oxydiphthalic acids, 3,3 ′, 4,4′-benzophenone tetracarboxylic acids, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic acids, m-terphenyl-3,3 ', 4,4'-tetracarboxylic acids, 4,4'-(2,2-hexafluoroisopropylene) diphthalic acids, 2,2'-bis (3,4-dicarboxyphenyl) propanes, 1,4 , 5,8-Naphthalenetetracarboxylic acids, 2,3,6,7-naphthalenetetracarboxylic acids, (1,1 ′: 3 ′, 1 ″ -terphenyl) -3,3 ″, 4,4 ″- Examples include tracarboxylic acids, 4,4 ′-(dimethylsiladiyl) diphthalic acid, 4,4 ′-(1,4-phenylenebis (oxy)) diphthalic acid, etc. Among them, A 3,3,4 ′, 4′-biphenyltetracarboxylic acids, 2,3,3 ′, 4′-biphenyltetracarboxylic acids or 2,2 ′, 3,3′-biphenyltetracarboxylic acids, in which is a biphenyl group, Alternatively, pyromellitic acids in which A is a phenyl group are more preferable, and these tetracarboxylic acids may be used in combination.The tetracarboxylic acids include tetracarboxylic acids and tetracarboxylic acid dicarboxylic acids. Tetracarboxylic acid derivatives such as anhydrides and esterified products of tetracarboxylic acid are included.

On the other hand, B in the general formula (1) represents a residue obtained by removing two amines from diamines constituting the polyamic acid. The diamines that can be used in the present invention are not particularly limited, but aromatic diamines in which B is an aromatic group are preferred. Such diamines include paraphenylene diamine, metaphenylene diamine, 4,4′-oxydianiline, 3,4′-oxydianiline, 4,4′-diaminodiphenylmethane, 2,4-toluenediamine, 3 , 3′-dihydroxy-4,4′-diaminobiphenyl, bis (4-amino-3-carboxyphenyl) methane, 2,4-diaminotoluene and the like. Among them, since the obtained polyimide has excellent characteristics, B is paraphenylenediamine or metaphenylenediamine in which a phenyl group is used, or 4,4′-oxydianiline or 3,4 ′ in which B is an oxydibenzene group. -Oxydianiline is preferred. In particular, paraphenylenediamine, 4,4'-oxydianiline or 3,4'-oxydianiline is preferable from the viewpoint of heat resistance. These diamines can also be used in combination. In addition to the diamine, the diamines include diamine derivatives such as diamine salts and silylated diamines.

  Examples of generally used solvents for polyimide precursor solutions include water, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, methanol, ethanol, propanol, butanol, and the like. Alcohols, ethylene glycol, diethylene glycol, triethylene glycol, glycerin, propylene glycol, dipropylene glycol, methylpropanediol and other polyhydric alcohols, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, diethylene glycol, diethylene glycol dimethyl ether , Ethers such as triethylene glycol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl alcohol Tate, ethyl cellosolve, ptyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α-methyl-γ-butyrolactone Esters such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, ketones such as acetophenone, carbonates such as diethyl carbonate, propylene carbonate, hexane, heptane, octane, benzene, toluene, Hydrocarbons such as xylene, phenols such as phenol, m-cresol, p-cresol, 3-chlorophenol, 4-chlorophenol, etc. , 3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, sulfolane, dimethyl star pen, mineral spirit, petroleum naphtha solvent and the like.

  However, from the viewpoint of environmental burden when volatilized, in particular, a solvent having an amide bond such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone should not be used as much as possible. Preferably, in the present invention, a solvent containing 50% by mass or more of at least one selected from water, alcohols or polyhydric alcohols, particularly a solvent consisting essentially of water, alcohols and polyhydric alcohols. It is preferable to use it. Further, among these, in order to facilitate firing at a low temperature, those having a boiling point of 200 ° C. or lower are preferable, and those having a boiling point of 150 ° C. or lower are more preferable. Moreover, since the stability of a solution is excellent, what has a boiling point of 60 degreeC or more is preferable, what is 80 degreeC or more is more preferable, and what is 100 degreeC or more is more preferable.

The polyimide precursor solution can be synthesized, for example, by the following method.
i) A diamine is dissolved in a solvent, and a tetracarboxylic dianhydride is gradually added to this solution while stirring. Further, a polyamic acid is obtained by stirring in a temperature range of 0 to 100 ° C. A method of adding a compound.
ii) A method in which a basic compound and a diamine are dissolved in a solvent in advance, and tetracarboxylic dianhydride is gradually added to this solution while stirring, and the mixture is further stirred in a temperature range of 0 to 100 ° C.
In particular, the method ii) is preferable because the polyamic acid having a carboxylate structure as a part of the molecular structure is directly synthesized, so that the solubility in a solvent is excellent.

  The solid content concentration of the polyimide precursor solution is determined by the method described in the examples, and is preferably 1 to 50% by mass, more preferably 3 to 45% by mass, and still more preferably 5 to 40% by mass. If the solid content concentration is less than 1% by mass, the fiber productivity may not be sufficient. If it exceeds 50% by mass, the fluidity of the solution may be inferior, resulting in a problem in production stability.

  The logarithmic viscosity of the polyimide precursor (polyamic acid having a carboxylate structure as part of the molecular structure) is determined by the method described in the examples, and is 0.2 or more, preferably 0.4 or more, more preferably Is 0.6 or more, more preferably 0.8 or more, and particularly preferably 1.0 or more. Moreover, the weight average molecular weight calculated | required by GPC of a polyimide precursor is 1,000-1,000,000, Preferably, it is 5,000-500,000. These logarithmic viscosities and molecular weights can be arbitrarily set by adjusting the molar ratio of the tetracarboxylic acid component to be used and the diamine component.

  The solution viscosity of the polyimide precursor solution is determined by the method described in the examples, preferably 0.1 to 170 Pa · s, more preferably 0.5 to 150 Pa · s, and still more preferably 1 to 100 Pa · s. It is. By setting the solution viscosity within this range, the spinnability is excellent and stable production becomes possible. The solution viscosity can be set in a desired range by adjusting the solid content concentration and the logarithmic viscosity and molecular weight of the polyimide precursor.

  For the polyimide precursor solution, catalyst, chemical imidization agent (acid anhydride such as acetic anhydride, amine compound such as pyridine and isoquinoline), antioxidant, filler, dye, pigment, silane coupling, if necessary Agents, flame retardants, antifoaming agents, leveling agents, rheology control agents (additives for flow control purposes), release agents and the like can be added.

  The spinning step in the method for producing a polyimide fiber of the present invention is not particularly limited as long as it is a step of spinning using the polyimide precursor solution, and a known spinning method can be used. For example, the wet spinning method and the dry spinning method described in JP2010-180494A, and the electrospinning method described in JP2009-167571A and JP2011-132651A are preferable. The production method of the present invention can suitably produce fibers having a fiber diameter of 0.001 to 10 μm, particularly 0.01 to 5 μm.

As an example, a case where electrospinning is performed using the electrospinning apparatus shown in FIG. 1 will be described below.
In the electrospinning apparatus shown in FIG. 1, 1 is a discharge means (syringe) for discharging an electrospinning dope (polyimide precursor solution) 3 held in a cylindrical solution holding tank 2, 4 is an orifice of the syringe, 5 is a nozzle installed in the orifice 4, 6 is a fibrous material collecting electrode, and 7 is a high voltage generator.

  The discharge means 1 and the fibrous substance collecting electrode 6 are arranged so that the distance between the tip of the nozzle 5 and the fibrous substance collecting electrode 6 is an appropriate distance. A voltage is applied to the nozzle 5 by the high voltage generator 7. The discharge means 1 guides the electrospinning dope 3 to the tip of the nozzle 5, places the electrospinning dope 3 at an appropriate position in the electrostatic field, and the electric field causes the nozzle 5 to move toward the fibrous material collecting electrode 6. Yarn. The dope 3 for electrospinning is made into a fiber by evaporating the solvent between the tip of the nozzle 5 and the fibrous material collecting electrode 6, and a polyimide fiber / nonwoven fabric is placed on the fibrous material collecting electrode 6. Collected on the collecting substrate. In the present apparatus, the number of nozzles is not limited to one, and it is possible to increase the production rate of polyimide fiber / nonwoven fabric by providing a plurality of nozzles.

If the spinning temperature is about room temperature, the organic solvent usually evaporates before the polyimide fiber / nonwoven fabric is collected on the collection substrate. The degree of evaporation of the organic solvent is not particularly problematic as long as the fiber shape is maintained and can be easily handled. Further, the degree of evaporation of the organic solvent is adjusted as necessary in the post-processing. When evaporation of the organic solvent is insufficient, a drying treatment may be performed after spinning.
The spinning temperature depends on the evaporation behavior of the solvent and the viscosity of the electrospinning dope, but is usually 0 to 50 ° C., preferably 20 to 50 ° C. Further, the humidity is preferably as low as possible in order to evaporate the organic solvent stably and efficiently, and the humidity is preferably 50% or less.

  The solution viscosity of the dope for electrospinning may affect the productivity of the spinning process, and is appropriately adjusted so that a desired fiber can be produced stably. In this invention, Preferably it is 0.1-170 Pa.s, More preferably, it is 0.5-150 Pa.s, More preferably, it is 1-110 Pa.s. If the solution viscosity is lower than this range, it may be difficult to maintain the fiber shape of the dope, and if the solution viscosity is higher than this range, it may be difficult to discharge in a good fiber shape due to poor fluidity. is there.

  In addition, the solid content concentration of the dope for electrospinning may affect the spinnability, and further determines the diameter of the polyimide fine fiber as well as the spinning speed. To be selected. In this invention, Preferably it is 1-50 mass%, More preferably, it is 3-45 mass%, More preferably, it is 5-40 mass%. When the polyimide concentration is out of the above range, it may be difficult to adjust the solution viscosity of the dope or the spinnability may be lowered.

  In the present invention, the polyimide fiber is produced by spinning using a polyimide precursor solution to obtain a polyamic acid fiber having a carboxylate structure in a part of its molecular structure, and then imidizing it. The imidization step is not particularly limited, and a known imidization method for obtaining a polyimide from a polyimide precursor, for example, a thermal imidization method or a chemical imidization method can be used. In the thermal imidization method, a polyimide precursor fiber or a nonwoven fabric thereof is subjected to a maximum temperature of 150 ° C. to 500 ° C., preferably 200 ° C. to 400 ° C., more preferably 200 ° C. to 350 ° C. in air or nitrogen under normal pressure or reduced pressure. It is good to heat-process at 200 degreeC, Especially preferably at 200 to 250 degreeC for 0.1 to 60 minutes, Preferably it is 0.1 to 20 minutes, More preferably, it is 0.5 to 5 minutes. In the method for producing a polyimide fiber of the present invention, since the polyimide precursor (polyamic acid) fiber contains a basic compound, imidization can be completed at a low temperature in a short time, and compared to conventional amide solvents. Since a low boiling point solvent can be used, the solvent can be removed at a low temperature in a short time.

  The polyimide fiber obtained by this invention can be used suitably as a heat resistant filter, a heat resistant nonwoven fabric, a heat resistant felt, and a heat resistant separator.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples.

The measurement methods used in the following examples are shown below.
<Concentration of solid content>
The polyimide precursor solution (whose mass is w1) is heat-treated in a hot air dryer at 120 ° C. for 10 minutes, 250 ° C. for 10 minutes, and then at 350 ° C. for 30 minutes. w2). Solid content concentration [mass%] was computed by the following formula.

<Logarithmic viscosity>
The polyimide precursor solution was diluted so that the concentration was 0.5 g / dl (solvent was water) based on the solid content concentration. This diluted solution was added to Cannon Fenceke No. The flow-down time (T1) was measured using 100. The logarithmic viscosity was calculated from the following formula using the flow time (T0) of blank water.

<Solution viscosity (rotational viscosity)>
The solution viscosity of the polyimide precursor solution is a standard rotor using a cone plate E-type viscometer manufactured by Toki Sangyo Co., Ltd., a rotation speed of 10 rpm or 1 rpm (shear speed 38.3 / s or 3.83 / s), The sample temperature was measured at 30 ° C.

<Preparation of polyimide film sample>
The obtained polyimide precursor solution was applied onto a glass plate of a substrate by a bar coater, and the coating film was defoamed and pre-dried at 25 ° C. for 30 minutes under reduced pressure, and then a hot air dryer under normal pressure. And heated at 80 ° C. for 30 minutes, 120 ° C. for 30 minutes, 200 ° C. for 10 minutes, and then 250 ° C. for 10 minutes to form a polyimide film having a thickness of 50 μm.
Properties were evaluated using this polyimide film.

<Glass transition temperature measurement>
TA Instruments Co., Ltd. Solid Viscoelasticity Analyzer RSAIII (compression mode)
Using dynamic measurement, frequency 62.8 rad / sec (10 Hz), strain amount set to 3% of sample height), each temperature reached from -140 ° C to 450 ° C at a temperature step of 3 ° C in an atmospheric nitrogen stream The measurement was performed 30 seconds later, the temperature was raised to the next temperature, and the measurement was repeated to determine the maximum point of loss elastic modulus (E ″), and the temperature was determined as the glass transition point (Tg).

<Spinning>
The fiber formation of the polyimide precursor by the electrospinning method using the electrospinning apparatus shown in FIG. 1 was evaluated with a laser micrograph or a scanning electron microscope. The case where fiber formation was possible was marked as ◯, the fiber was obtained, but the production stability was poor, Δ, and the case where fiber formation was impossible was marked as x.

<Fiber diameter>
The polyimide fiber obtained by heating imidization of the polyimide precursor fiber was measured for the fiber diameter at any 10 locations from a laser micrograph or a scanning electron micrograph, and the fiber diameter (average fiber diameter) was determined.

The abbreviations of the compounds used in the following examples are described.
s-BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride PPD: p-phenylenediamine ODA: 4,4′-diaminodiphenyl ether 1,2-DMZ: 1,2-dimethylimidazole TEA: Triethylamine DABCO: 1,4-diazabicyclo [2.2.2] octane PG: Propylene glycol EtOH: Ethanol DMAc: N, N-dimethylacetamide

[Reference Example 1]
In a glass reaction vessel with an internal volume of 500 mL equipped with a stirrer and nitrogen gas inlet / outlet pipe, water as a solvent is calculated to a target concentration (previously calculated from the input amount of PPD and s-BPDA to a predetermined concentration). In this case, 9% by weight of 450 g) was added, and to this was added PPD as a diamine, 0.124 mol (13.44 g) and 1,2-DMZ of 0.31 mol (29.87 g diamine). 2.5 moles) was added and stirred at 25 ° C. for 1 hour to dissolve. First, 0.118 mol (0.95 times mol of 34.73 g diamine) of s-BPDA was added to this solution, and the mixture was stirred at 25 ° C. for 8 hours. Further, s-BPDA is added stepwise so that the target solution viscosity (here 5 Pa · s) and solid content concentration (here 9 mass%) are obtained (substantially equimolar with diamine). Dilute with solvent if necessary. Furthermore, it stirred for 2 hours and obtained the uniform polyimide precursor solution. The characteristics of the obtained polyimide precursor solution are shown in Table 1.

[Reference Examples 2 to 11]
A polyimide precursor solution was obtained in the same manner as in Reference Example 1 except that the diamine component, amines, and solvent described in Table 1 were used. The characteristics of the obtained polyimide precursor solution are shown in Table 1. In Example 4, a solvent mixed with water / ethanol (mass ratio: 15/85) was used as the solvent.
Reference Examples 8 and 9 had insoluble components and were non-uniform solutions.

[Example 1]
A polyimide fiber using the polyimide precursor solution obtained in Reference Example 1 was produced by the electrospinning method using the electrospinning apparatus shown in FIG.
A polyimide precursor solution was discharged into the air at a discharge rate of 0.1 cc / H from a nozzle having 0.7 mm pores to which a high voltage of 25 kV was applied, and the substrate was electrically grounded on a collecting electrode. As a material, an aluminum foil (thickness 12 μm), a glass substrate or a polyimide film was used for spinning. The distance from the nozzle to the collecting electrode was 110 mm. A polyimide precursor fiber (nonwoven fabric) was produced by moving the position of the nozzle and the collecting electrode at appropriate times.
The obtained polyimide precursor fiber (nonwoven fabric) was subjected to heat treatment at 200 ° C. for 1 hour in air using a hot air circulating oven to obtain polyimide fibers (nonwoven fabric). (It was confirmed by FT-IR that imidization was completed.)
The evaluation results of the polyimide fiber production are shown in Table 1.

[Examples 2-7, Comparative Examples 1-4]
In the same manner as in Example 1, in Examples 2-7, the polyimide precursor solutions of Reference Examples 2-7 were used, and in Comparative Examples 1-4, the polyimide precursor solutions of Reference Examples 8-11 were used. Manufactured. In view of the spinning state, the discharge amount from the nozzle is in the range of 0.1 to 1 cc / H, the distance from the nozzle to the collecting electrode is in the range of 110 to 200 mm, and the applied high voltage is in the range of 15 to 25 kV. Adjusted. The evaluation results of the polyimide fiber production are shown in Table 1.
In Example 5, when spinning continuously for a long time, the tip of the nozzle was hardened more than before, so it was necessary to remove it as necessary.
On the other hand, in Comparative Examples 1 and 2, since there were insoluble components in the solution, the nozzles were clogged, and polyimide fibers could not be produced. In Comparative Example 3, the solution viscosity was high, and stringing was not possible even under high voltage conditions. .

  As can be seen from the results shown in Table 1, in the method for producing a polyimide fiber of the present invention, fine fibers are obtained, and the solvent used for the polyimide precursor solution does not include an organic solvent or an amide solvent. Organic solvents and amide-based solvents can be reduced as volatile components generated during fiber production. On the other hand, in Comparative Examples 1 to 3, problems occurred in the production of polyimide fibers. In Comparative Example 4, it was possible to produce a polyimide fiber, but it was necessary to use an amide solvent as the solvent because the solubility of the polyimide precursor was poor.

1 Discharge means (syringe)
2 Cylindrical solution holding tank 3 Dope for electrospinning (polyimide precursor solution)
4 Orifice 5 Nozzle 6 Fibrous material collecting electrode 7 High voltage generator

Claims (7)

After obtaining a polyimide precursor fiber by spinning using a polyimide precursor solution, a polyimide fiber manufacturing method for imidizing this,
a) The polyimide precursor is a polyamic acid having a carboxylate structure as part of the molecular structure.
b) The solution viscosity of the polyimide precursor solution at 30 ° C. is 0.1 to 170 Pa · s.
A method for producing a polyimide fiber, characterized in that: further,
c) As a solvent, 50 mass% or more of at least 1 type chosen from water, alcohol, or polyhydric alcohol is contained,
The manufacturing method of the polyimide fiber of Claim 1 characterized by the above-mentioned. 3. The method for producing a polyimide fiber according to claim 1, wherein the polyamic acid having a carboxylate structure as part of the molecular structure is a polyamic acid represented by the following general formula (1): .
(In General Formula (1), A is a tetravalent aromatic group, B is a divalent aromatic group, and one or both of X ₁ and X ₂ are basic compounds.) The method for producing a polyimide fiber according to claim 3, wherein the basic compound in the general formula (1) is an amine compound or an alkali metal. The method for producing a polyimide fiber according to any one of claims 3 to 4, wherein A in the general formula (1) is a tetravalent phenyl group or a biphenyl group. B in said general formula (1) is a bivalent phenyl group or an oxydibenzene group, The manufacturing method of the polyimide fiber in any one of Claims 3-5 characterized by the above-mentioned. A polyimide precursor solution for producing fibers, heat-resistant filters, heat-resistant nonwoven fabrics, heat-resistant felts or heat-resistant separators having the following characteristics.
a) The polyimide precursor is a polyamic acid having a carboxylate structure as part of the molecular structure.
b) The solution viscosity of the polyimide precursor solution at 30 ° C. is 0.1 to 170 Pa · s.