JP2013256732A - Method for producing polyimide fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polyimide fiber which can control a fiber diameter and is stable, and to provide a polyimide precursor solution.SOLUTION: The method for producing a polyimide fiber comprises: obtaining a polyimide precursor fiber by an electrospinning method using a polyimide precursor solution, in which a) the polyamide precursor is a polyamide acid represented by the following general formula (1) (A is a tetravalent biphenyl group, B is a bivalent aromatic group, and Xand Xare each independently hydrogen, an alkyl group or an alkylsilyl group), b) the solid concentration is 1 to 50 mass%, c) the solution viscosity is 1 to 150 Pa s at 30°C, and d) the boiling point of a solvent is 65 to 250°C; and imidizing the obtained polyimide precursor fiber.

Description

  The present invention relates to a method for producing a polyimide fiber which can control the fiber diameter and can be stably produced.

  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 Documents 5 and 6). However, in this production method, the fiber diameter is not sufficiently controlled, and fine fibers having an average fiber diameter of 2 μm or less have not been obtained.

  As described above, in the electrospinning method, polyimide is used in spite of the importance of the solution properties (solid content concentration, solution viscosity, logarithmic viscosity, etc.) of the raw material as a factor affecting fiber diameter control and stable spinning. The present condition is that the improvement regarding the solution characteristic of a precursor varnish is not examined.

Japanese Patent Publication No. 7-42611 JP 9-52308 A Japanese Patent Publication No. 48-1466 JP 2008-202169 A International Patent Publication WO2002-92888 JP 2009-167571 A

  An object of this invention is to provide the manufacturing method of the polyimide fiber which can control a fiber diameter and can be manufactured stably, and to provide the polyimide precursor solution used for it.

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) Polyamide acid represented by the following general formula (1):
(A in the general formula (1) is a tetravalent biphenyl group, B is a divalent aromatic group, and X ₁ and X ₂ are each independently hydrogen, an alkyl group, or an alkylsilyl group. )
b) The solid content concentration of the polyimide precursor solution is 1 to 50% by mass,
c) The viscosity of the polyimide precursor solution at 30 ° C. is 1 to 150 Pa · s,
d) the boiling point of the solvent is 65-250 ° C.
The manufacturing method of the polyimide fiber characterized by these.
2. 2. The method for producing a polyimide fiber according to item 1, wherein B in the general formula (1) is a divalent phenyl group or an oxydibenzene group.
3. 4. The method for producing a polyimide fiber according to any one of items 1 to 3, wherein an average fiber diameter of the produced polyimide fiber is 0.001 to 1.5 μm.
4). 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 represented by the following general formula (1).
(A in the general formula (1) is a tetravalent biphenyl group, B is a divalent phenyl group or an oxydibenzene group, and X ₁ and X ₂ are each independently hydrogen, an alkyl group, or an alkylsilyl group. Group or basic compound.)
b) The solid content concentration of the polyimide precursor solution is 1 to 50% by mass.
c) The solution viscosity at 30 ° C. of the polyimide precursor solution is 1 to 150 Pa · s.
d) The boiling point of the solvent is 65 to 250 ° C.

  According to the present invention, excellent fiber characteristics such as heat resistance can be exhibited, the fiber diameter can be controlled, and a polyimide fiber can be more stably produced. 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 Relationship between solid content concentration and average fiber diameter (ODA / s-BPDA composition)

  This invention is a manufacturing method of the polyimide fiber characterized by spinning using a specific polyimide precursor solution.

In the polyimide precursor solution used in the present invention, the polyimide precursor is preferably a polyamic acid represented by the following general formula (1).
(A in the general formula (1) is a tetravalent biphenyl group, B is a divalent aromatic group, and X ₁ and X ₂ are each independently hydrogen, an alkyl group, or an alkylsilyl group. )

  A in the general formula (1) represents a residue obtained by removing four carboxylic acids from the tetracarboxylic acids constituting the polyamic acid, and is preferably a biphenyl group in the present invention. Such tetracarboxylic acids include 3,3,4 ', 4'-biphenyltetracarboxylic acids, 2,3,3', 4'-biphenyltetracarboxylic acids, 2,2 ', 3,3'-biphenyltetra Carboxylic acids can be mentioned. These tetracarboxylic acids can be used in combination. The tetracarboxylic acids include tetracarboxylic acid derivatives as well as tetracarboxylic dianhydrides and tetracarboxylic acid esterified products.

  B in the general formula (1) represents a residue obtained by removing two amines from diamines constituting the polyamic acid, and is preferably an aromatic group in the present invention. Examples of 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 can be mentioned. Among them, since the obtained polyimide has excellent properties, paraphenylenediamine, metaphenylenediamine, 4,4′-oxydianiline or 3,4′-oxydianiline in which B is a phenyl group or an oxydibenzene group is used. Paraphenylenediamine, 4,4′-oxydianiline or 3,4′-oxydianiline is particularly 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 the solvent for the polyimide precursor solution include water, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl-2-pyrrolidone, alcohols such as methanol, ethanol, propanol, and butanol, Polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, propylene glycol, dipropylene glycol, methylpropanediol, dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, ethylene glycol, diethylene glycol, diethylene glycol dimethyl ether, Ethers such as triethylene glycol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl Cetate, 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. 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, sulfolane, dimethyl star pen, mineral spirit, petroleum naphtha solvent and the like can be used. A combination of these can also be used.

  The boiling point of the solvent used in the present invention is preferably 65 ° C. or higher, more preferably 80 ° C. or higher, preferably 250 ° C. or lower, more preferably 200 ° C. or lower, particularly preferably 150 ° C. or lower, 65 It is preferably in the range of ˜250 ° C. When the boiling point is in the above range, the solvent is not excessively volatile, so that it can be stably manufactured and has a volatility that can be removed by heating at a relatively low temperature in the imidization process. It is preferable.

  In a polyimide precursor solution, it is preferable that solid content concentration is 1-50 mass%, It is more preferable that it is 3-40 mass%, It is especially preferable that it is 5-30 mass%. When the solid content concentration is 50% by mass or less, fine fibers are easily obtained, and when it is 1% by mass or more, production stability and production efficiency are high, which is preferable.

  The logarithmic viscosity of the polyimide precursor (polyamic acid) is not particularly limited, but the logarithm measured at a temperature of 30 ° C. and a concentration of 0.5 g / 100 mL (dissolved in the solvent used) based on the solid content concentration resulting from the polyimide precursor. The viscosity is preferably 0.2 or more, more preferably 0.5 or more, particularly preferably 1.0 or more, and 2.5 or less. Moreover, although it does not specifically limit, the weight average molecular weight calculated | required by GPC of the polyimide precursor is 1,000-1,000,000, Preferably, it is 5,000-500,000. If it is this range, it is excellent in the heat resistance of a polyimide fiber, and a mechanical characteristic. Moreover, these logarithmic viscosity and molecular weight can be arbitrarily set by the molar ratio of the tetracarboxylic acid component and the diamine component in the synthesis method described later.

  The polyimide precursor solution preferably has a solution viscosity at 30 ° C. of 1 to 150 Pa · s, and more preferably 5 to 150 Pa · s. By setting the solution viscosity within this range, fine fibers can be easily obtained, excellent spinnability, 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.

  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 1-150 Pa.s, More preferably, it is 5-120 Pa.s. If the solution viscosity is smaller than this range, it may be difficult to maintain the fiber shape of the dope, and if the solution viscosity is larger than this range, it may be difficult to discharge with 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 immobilizing a polyamic acid fiber by spinning using a polyimide precursor solution. 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.

  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.

A method for measuring the characteristics used in the following examples is shown below.
<Concentration of solid content>
The sample solution (whose mass is designated as 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. Measure). Solid content concentration [mass%] was computed by the following formula.

<Logarithmic viscosity>
The sample solution was diluted so that the concentration was 0.5 g / dl based on the solid content concentration (the dilution solvent was the solvent used in the polymerization). 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 was measured using a standard rotor, a rotational speed of 10 rpm or 1 rpm (shear speed of 38.3 / s or 3.83 / s), and a sample temperature of 30 ° C., using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. Measured under conditions.

<Spinnability>
Using the electrospinning apparatus shown in FIG. 1, a polyimide precursor fiber was prepared, followed by heat imidization to obtain a polyimide fiber sample. The obtained sample was evaluated with a laser micrograph or a scanning electron microscope. A sample having no abnormality is indicated by ◎, a component having a slight abnormality is indicated by ◯, and a component having an overall abnormality is indicated by ×.

<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 NMP: N-methyl-2-pyrrolidone DMAc: N, N -Dimethylacetamide

[Reference Example 1]
In a glass reaction vessel with an internal volume of 500 mL equipped with a stirrer and a nitrogen gas introduction / discharge pipe, DMAc as a solvent is calculated from the amount of the target concentration of the polyimide precursor varnish (calculated from the input amount of ODA and s-BPDA, here 10 mass%), 24.83 g (0.124 mol) of ODA was added thereto, and the mixture was stirred at 25 ° C. for 1 hour to dissolve. To this solution, 32.90 g (0.116 mol) of s-BPDA was added and stirred at 25 ° C. for 8 hours. Further, s-BPDA (substantially equimolar to the diamine) and DMAc are set so that the target solution viscosity (here, 62 Pa · s) and the solid content concentration (here, 10 mass%) are obtained. Added from time to time. Furthermore, it stirred for 2 hours and obtained the polyimide precursor solution of the uniform solution. The characteristics of the obtained polyimide precursor solution are shown in Table 1.

[Reference Examples 2 to 7]
In the same manner as in Reference Example 1, a polyimide precursor solution was obtained. In Reference Examples 5, 6, and 8, PPD was used instead of ODA, and in Reference Example 6, NMP was used instead of DMAc.
The characteristics of the obtained polyimide precursor solution are shown in Table 1.

[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, and a polyimide film were 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 using a hot-air circulating oven to obtain polyimide fibers (nonwoven fabric). (It was confirmed by FT-IR that imidization was completed.)

[Examples 2-6, Comparative Examples 1-2]
In the same manner as in Example 1, in Examples 2-6, the polyimide precursor solutions of Reference Examples 2-6 were used, and in Comparative Examples 1-2, the polyimide precursor solutions of Reference Examples 7-8 were used. Manufactured. In addition, 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, so that the spinning state is stable and the thinnest fiber diameter is obtained. The applied high voltage was adjusted in the range of 15 to 25 kV.
In Examples 1-5, the fiber was able to be manufactured stably. In Example 6, fibers could be produced stably, but there were portions where the fiber shape was slightly disturbed. On the other hand, in Comparative Examples 1 and 2, formation of fine fibers was confirmed, but adhesion of particles was confirmed as a whole, and good fibers could not be obtained.

  As can be seen from the results shown in Table 1, in the polyimide fiber manufacturing method of the present invention (Examples 1 to 6), the solution diameter of the polyimide precursor solution is improved, so that the fiber diameter can be controlled. It was confirmed that it can be manufactured stably. On the other hand, when the solution properties of the polyimide precursor solution are out of the range described in the present invention, it is difficult to produce polyimide fibers by electrospinning.

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 (4)

After obtaining a polyimide precursor fiber by spinning using a polyimide precursor solution, a polyimide fiber manufacturing method for imidizing this,
a) Polyamide acid represented by the following general formula (1):
(A in the general formula (1) is a tetravalent biphenyl group, B is a divalent aromatic group, and X ₁ and X ₂ are each independently hydrogen, an alkyl group, or an alkylsilyl group. )
b) The solid content concentration of the polyimide precursor solution is 1 to 50% by mass,
c) The viscosity of the polyimide precursor solution at 30 ° C. is 1 to 150 Pa · s,
d) the boiling point of the solvent is 65-250 ° C.
The manufacturing method of the polyimide fiber characterized by these. B in general formula (1) is a bivalent phenyl group or oxydibenzene group, The manufacturing method of the polyimide fiber of Claim 1 characterized by the above-mentioned. The average fiber diameter of the manufactured polyimide fiber is 0.001-1.5 micrometers, The manufacturing method of the polyimide fiber in any one of Claims 1-2 characterized by the above-mentioned. 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 represented by the following general formula (1).
(A in the general formula (1) is a tetravalent biphenyl group, B is a divalent phenyl group or an oxydibenzene group, and X ₁ and X ₂ are each independently hydrogen, an alkyl group, or an alkylsilyl group. Group or basic compound.)
b) The solid content concentration of the polyimide precursor solution is 1 to 50% by mass.
c) The solution viscosity at 30 ° C. of the polyimide precursor solution is 1 to 150 Pa · s.
d) The boiling point of the solvent is 65 to 250 ° C.