JP2010150697A - Polyimide fiber, utilization of the same, and method for producing polyimide fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polyimide fiber having hydrolysis resistance. <P>SOLUTION: The polyimide fiber is obtained by mixing a chemical imidizing agent in a polyamide acid solution and spinning the partially imidized spinning solution by a dry spinning method. The imidizing agent preferably contains at least an imidizing catalyst. The imidizing agent further preferably contains a dehydration condensation agent. The polyimide fiber can be used for a nonwoven fabric, heat resistant filter, woven fabric, heat resistant protective cloth, or the like. Further, it is preferable to produce the polyimide fiber by spinning the partially imidized spinning solution obtained by mixing the chemical imidizing agent with the polyamide acid solution, with the dry spinning method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyimide fiber, its use, and a method for producing the polyimide fiber.

  Polyimide fibers are superior in high-temperature stability and chemical resistance compared to general organic polymer resin fibers, so that felts constituting heat-resistant bag filters for exhaust gas treatment, woven fabrics for heat-resistant clothing, It is widely used as a base fabric and a reinforcing material for various electric insulating materials as base materials.

As a conventional polyimide fiber, a polyimide fiber obtained by spinning an organic solvent-soluble polyimide resin by a dry spinning method is used (for example, see Patent Document 1). Also known are a method for producing polyimide fibers by a dry spinning method (for example, see Patent Document 2) and a polyimide fiber produced by a wet spinning method (for example, see Patent Document 3).
Japanese Patent Publication No.63-27444 (released on June 3, 1988) Japanese Patent Publication No.42-2936 (published February 8, 1967) Japanese Patent Publication No.59-163416 (published on September 14, 1984)

  In the invention of Patent Document 1, an organic solvent soluble and thermoplastic polyimide resin having an organic group in the side chain and a flexible group in the structure is used to increase the solubility in a solvent. It has been. Although the solubility in organic solvents is increased by having an organic group in the side chain, the heat resistance of the polyimide resin is low by having an organic group in the side chain, and the solvent resistance to the organic solvent is low. There was a low problem. In addition, since it is a thermoplastic polyimide resin with a flexible group, when used in protective clothing, it will melt at high temperatures and will adhere to the skin (drop phenomenon). Has a problem that cannot be used widely.

  The invention described in Patent Document 2 discloses a method for producing a polyimide fiber comprising pyromellitic dianhydride and diaminodiphenyl ether by a dry spinning method. However, after spinning the polyamic acid solution and before imidizing the spun fiber, it is immersed in water and stretched, which causes hydrolysis and the fiber becomes brittle, making the manufacturing process unstable. Since the fiber has undergone hydrolysis, there have been problems such as hydrolysis occurring during long-term use.

  In the invention described in Patent Document 3, there is a method for producing a polyamic acid fiber partially imidized by mixing a curing agent and a catalyst with a polyamic acid solution composed of pyromellitic dianhydride and diaminodiphenyl ether by a wet spinning method. It is disclosed. However, since the wet spinning method is adopted and spinning into water, as in Patent Document 2, hydrolysis occurs during processing, the fiber becomes brittle and the manufacturing process is not stable, and hydrolysis occurs during long-term use. There was a problem such as.

  As a result of intensive studies to solve the above problems, the present inventors use a polyimide fiber obtained by dry spinning a spinning stock solution partially imidized by mixing a chemical imidizing agent with a polyamic acid solution. Thus, it has been found that the production process that solves the above-mentioned problems is stabilized and a polyimide fiber having high hydrolysis resistance can be obtained.

That is, the polyimide fiber of the present invention is a polyimide fiber obtained by spinning a spinning solution, which is partially imidized by mixing a chemical imidizing agent with a polyamic acid solution, by a dry spinning method.
Furthermore, it is a polyimide fiber characterized in that the chemical imidizing agent contains at least a tertiary amine.
Further, the polyimide fiber is characterized in that the chemical imidizing agent contains a tertiary amine and an aliphatic carboxylic acid anhydride.

  Another invention of the present invention is a nonwoven fabric using the polyimide fiber.

  Another invention of the present invention is a heat resistant filter using the polyimide fiber.

  Another invention of the present invention is a woven fabric containing the polyimide fiber.

Moreover, another invention of the present invention is a heat-resistant protective clothing using the polyimide fiber.
Another invention of the present invention is a method for producing the polyimide fiber as described above, wherein a spinning solution obtained by mixing a polyimidic acid solution with a chemical imidizing agent and partially imidizing is spun by a dry spinning method to obtain a polyimide fiber. It is a manufacturing method of the polyimide fiber characterized by manufacturing.

  The polyimide fiber of the present invention is excellent in heat resistance, and can also be used under conditions requiring severe hydrolysis resistance, which has been difficult to use with conventional polyimide fibers. Furthermore, the fiber spinning process is stabilized.

  The polyimide fiber of the present invention is a polyimide fiber obtained by spinning a spinning solution obtained by partially imidizing a polyamic acid solution by mixing a chemical imidizing agent with a dry spinning method.

  The polyamic acid solution in the present invention will be described in detail.

  The polyamic acid solution in the present invention is a polyamic acid solution obtained by reacting an acid dianhydride and a diamine in an organic solvent. Preferably, the amount of the acid dianhydride used is a mole, and the amount of the diamine used. In the case where the molar ratio (a / b) is 0.80 or more and less than 1.00, the hydrolysis resistance of the polyimide fiber finally obtained can be improved. Therefore, it is preferable. In a particularly preferable range, the reaction is more preferably performed so that the molar ratio is 0.90 or more and less than 1.00. The reaction at such a molar ratio is preferable because the molecular weight does not decrease during imidization from the polyamic acid solution to the polyimide, and the hydrolysis resistance of the polyimide fiber is further improved.

  The acid dianhydride in the present invention is, for example, pyromellitic dianhydride, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane dianhydride, 2,2-bis [4. -(3,4-dicarboxyphenoxy) phenyl] hexafluoropropane dianhydride, 2,2-bis (4-hydroxyphenyl) propane dibenzoate-3,3 ', 4,4'-tetracarboxylic dianhydride 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3,4-biphenyltetracarboxylic dianhydride, 2,2′-hexafluoropropylidenediphthalic dianhydride 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, pyro Merit acid 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, methylcyclobutanetetracarboxylic dianhydride 1,2,3,4-tetracarboxybutane dianhydride is used.

  In particular, in order to improve the heat resistance of the finally obtained polyimide resin, improve chemical resistance, and further improve hydrolysis resistance, an aromatic acid dianhydride, pyromellitic acid 2 Anhydride, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 , 4-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′— Diphenylsulfone tetracarboxylic dianhydride is preferably used.

  Examples of the diamine in the present invention include 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, and 4,4′-diaminodiphenylsulfone. 3,3′-diaminodiphenylsulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, (4-aminophenoxyphenyl) (3-aminophenoxyphenyl) phenyl] sulfone, bis [4- (3-amino Phenoxy) phenyl] sulfone, 3,3′-diaminobenzanilide, 3,4′-diaminobenzanilide, 4,4′-diaminobenzanilide, bis [4- (3-aminophenoxy) phenyl] methane, bis [4 -(4-aminophenoxy) phenyl] methane, [ -(4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] methane, 1,1-bis [4- (3-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4 -Aminophenoxy) phenyl] ethane, 1,1- [4- (4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] ethane, 1,2-bis [4- (3-aminophenoxy) Phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 1,2- [4- (4-aminophenoxyphenyl)] [4- (3-aminophenoxyphenyl)] ethane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2- [4- (4-aminophenoxyphene) )] [4- (3-aminophenoxyphenyl)] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3′-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3′-hexafluoropropane, 2,2- [4- (4-aminophenoxyphenyl)] [ 4- (3-aminophenoxyphenyl)]-1,1,1,3,3,3′-hexafluoropropane, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-amino) Phenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- ( 3-Aminophenoxy) Nyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, polytetramethylene oxide -Di-P-aminobenzoate, poly (tetramethylene / 3-methyltetramethylene ether) glycol bis (4-aminobenzoate), trimethylene-bis (4-aminobenzoate), p-phenylene-bis (4-aminobenzoate) M-phenylene-bis (4-aminobenzoate), bisphenol A-bis (4-aminobenzoate) are used.

  In particular, in order to improve the heat resistance of the finally obtained polyimide resin, improve chemical resistance, and further improve hydrolysis resistance, an aromatic diamine, 4,4-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- ( 4-Aminophenoxy) phenyl] methane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, and 1,3-bis (3-aminophenoxy) benzene are preferably used.

In particular, since the polyamic acid solution used in the present invention is excellent in heat resistance, chemical resistance and hydrolysis resistance, a polyamic acid solution having the following combination is preferably used.
1. A polyamic acid solution comprising pyromellitic dianhydride and 4,4-diaminodiphenyl ether.
2. A polyamic acid solution comprising pyromellitic dianhydride, 4,4-diaminodiphenyl ether, and p-phenylenediamine.
3. A polyamic acid solution comprising 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine.
4. A polyamic acid solution comprising 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 4,4-diaminodiphenyl ether, and p-phenylenediamine.
5. A polyamic acid solution comprising 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride and 4,4-diaminodiphenyl ether, and p-phenylenediamine.
6. A polyamic acid solution comprising 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and p-phenylenediamine.
7. A polyamic acid solution comprising 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 4,4-diaminodiphenyl ether, and p-phenylenediamine.
8. A polyamic acid solution composed of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4-diaminodiphenyl ether, and p-phenylenediamine.

  Examples of the organic solvent used in the synthesis of the polyamic acid solution include organic polar amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and γ-butyrolactone, tetrahydrofuran Water-soluble ether solvents such as dioxane and dioxolane, ketone solvents such as acetone and methyl ethyl ketone, water-soluble nitrile solvents such as acetonitrile and propionitrile, and aprotic polar solvents such as dimethyl sulfoxide are used. These solvents may be used alone or in combination of two or more.

  In particular, in the dry spinning method of the present invention, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, dioxolane, and acetone are preferably used from the viewpoint of the drying temperature.

  The polymer concentration of the polyamic acid solution of the present invention is 1 to 50% by weight, particularly preferably 10 to 30% by weight, as the solid content concentration. The solid content concentration in the present invention is calculated from a calculation formula of solid content concentration = (weight of acid dianhydride in polyamic acid solution + weight of diamine in polyamic acid solution) ÷ (weight of polyamic acid solution) × 100. Value.

  The viscosity of the polyamic acid solution is preferably 100 poise or more and 10,000 poise or less at 23 ° C. when measured with a B-type viscometer because spinning can be performed stably. Particularly preferably, the viscosity is controlled to be 200 poise or more and 6000 poise or less, and the particularly preferable solution viscosity is preferably 500 poise or more and 4000 poise or less in order to stabilize spinning. In the present invention, when a partial imidization is carried out by mixing a polyamic acid solution with a polyamic acid solution, the solubility in a solvent is lowered, so that the spinning dope becomes higher than the above viscosity.

  In order to control to such a viscosity, the solution viscosity can be adjusted by appropriately changing the molar ratio of the acid dianhydride and the diamine. In particular, in the preferred polyamic acid solution polymerization method in the present invention, acid dianhydride is added and reacted in a molar ratio of 0.80 or less in a solution in which diamine is dissolved in an organic solvent. Next, a solution of acid dianhydride dissolved in an organic solvent is added with stirring, and the viscosity is adjusted so that the viscosity of the polyamic acid solution is within the above range, thereby preparing a polyamic acid solution having a suitable viscosity. Can do.

  In addition, as polymerization conditions of polyamic acid, the target polyamic acid solution can be polymerized by reacting at −20 to 60 ° C., preferably 0 to 50 ° C. in an inert gas atmosphere.

  Furthermore, the said polyamic acid solution can also mix 1 type, or 2 or more types of various fillers, antioxidant, a flame retardant, an antifoamer, a lubricant, a coloring agent, etc.

The chemical imidization agent in the present invention refers to a reagent that can imidize a polyamic acid solution at a low temperature, and an imidization catalyst that promotes imidization or imidization using a dehydration condensing agent in addition to an imidization catalyst. Means an agent. Examples of the imidization catalyst that can be suitably used in the present invention include tertiary amines such as trimethylamine, triethylamine, pyridine, picoline, quinoline, and isoquinoline, m-aminobenzoic acid, p-aminobenzoic acid, and the like. Benzoic acids, hydroxys such as p-hydroxybenzenesulfonic acid, p-aminophenol, p-hydroxybenzaldehyde, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, p-hydroxyphenylacetic acid, etc. Hydroxy acids and the like. In the present invention, it is particularly preferable to use a tertiary amine as an imidization catalyst that has good imidization efficiency, volatilizes in the spinning tower during dry spinning, and hardly remains in the fiber after spinning. More preferably, among tertiary amines, triethylamine, pyridine, and picoline are preferably used.
Examples of the dehydrating condensing agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride and butyric anhydride, aromatic carboxylic acid anhydrides such as benzoic anhydride, and concentrated sulfuric acid, sulfuric anhydride, Inorganic acids such as fuming sulfuric acid can be used.
It is preferable to use an aliphatic carboxylic acid anhydride that can be removed by volatilization in a spinning tower. In particular, it is preferable to use acetic anhydride.
In the present invention, as a method of preparing a polyamic acid solution partially imidized using a chemical imidizing agent, for example, an imidization catalyst that is a chemical imidizing agent is mixed and heated in a polyamic acid solution. A method of performing imidization or a method of performing imidization while mixing an imidization catalyst and a dehydrating condensing agent and heating appropriately can be used.

 In the case of heating by adding an imidization catalyst, the imidization catalyst is mixed at a ratio of 0.01 mol or more and 3.00 mol or less with respect to 1 mol of the amide group of the polyamic acid, and 50 ° C. or more. A partially imidized polyamic acid solution can be produced by heating in a temperature range of 200 ° C. or lower. The imidation catalyst is preferably mixed with 0.01 mol or more, so that imidization is likely to occur, and the imidization catalyst can be uniformly dissolved in the polyamic acid solution by controlling it in the range of 3.00 mol or less. Moreover, it is preferable that the temperature range is 50 ° C. or higher and 200 ° C. or lower because imidization can be efficiently performed, and a more preferable temperature range is 60 ° C. or higher and 180 ° C. or lower. An excessively high temperature is not preferable because the decomposition reaction of the polyamic acid solution proceeds.

 When imidization is performed by mixing an imidization catalyst and a dehydrating condensing agent, after mixing the imidization catalyst in a ratio of 0.01 mol to 3.00 mol with respect to 1 mol of the amide group of the polyamic acid. It is preferable to imidize a part of the polyamic acid solution by mixing the dehydrating condensing agent at a ratio of 0.01 mol to 0.50 mol and stirring and mixing. Mixing 0.01 mol or more as a chemical imidating agent is preferable because imidization occurs efficiently. The imidation catalyst is preferably controlled to 3.00 mol or less because the imidization catalyst is uniformly dissolved in the polyamic acid solution after mixing the imidization catalyst. The dehydrating condensing agent is preferred because imidization can be promoted by mixing at 0.01 mol or more, and an imidized polyamic acid solution can be dissolved in the solvent by mixing at a ratio of 0.50 mol or less. Particularly preferably, the imidization catalyst is mixed in a proportion of 0.05 mol or more and 0.7 mol or less, and the dehydration condensing agent is mixed in a proportion of 0.05 mol or more and 0.40 mol or less. In the case of this imidization method, the solution temperature is preferably in the temperature range of 10 ° C. or higher and 150 ° C. or lower, more preferably in the temperature range of 20 ° C. or higher and 100 ° C. or lower. If the heating temperature is too high, the dehydrating condensing agent volatilizes and the efficiency is lowered, or problems such as decomposition of the polyamic acid solution may occur.

 In addition, in the present invention, as a result of intensive studies for the purpose of improving the hydrolysis resistance of polyimide fibers, a polyamic acid solution mixed with a chemical imidizing agent in a polyamic acid solution is spun into a partially polyamic acid solution. It was found that hydrolysis resistance can be improved.

 In the present invention, it is preferable to proceed with imidization more efficiently at a low temperature because imidization can be performed without lowering the molecular weight of the polyamic acid. As such a method, an imidization catalyst and a dehydration condensing agent are used in combination. It is preferable to use the crystallization method. Further, when the molecular weight of the polyamic acid solution is lowered, spinning stability is lowered, which is not preferable.

  In the invention of the present application, the chemical imidizing agent is polymerized in a polyamic acid solution and then mixed in the solution, or the polyimidic acid solution and the chemical imidizing agent are mixed just before spinning. The method can be adopted.

   From the viewpoint of the stability of the spinning dope, the chemical imidizing agent is preferably mixed immediately before spinning.

 That is, in order to control the breaking strength retention after processing under conditions of 150 ° C./100% RH / 48 hours, which is an index of hydrolysis resistance, which is a characteristic of the polyimide fiber of the present invention, to 80% or more, Using a polyamic acid solution that has been partially imidized by mixing a chemical imidizing agent with the polyamic acid solution, and controlling so as not to actively contact moisture in the dry spinning process, heating, stretching, and imidization process. Thus, it was found that the fracture strength retention after treatment under conditions of 150 ° C./100% RH / 48 hours, which is an index of hydrolysis resistance, can be controlled to 80% or more. When the breaking strength retention after the hydrolysis test is 80% or more, for example, when it is formed as a nonwoven fabric and used as a bag filter, it is used under high temperature and high humidity conditions. It is preferable because it can be used stably for 3 years or more under conditions. In addition, when it is used after being formed into a woven fabric and processed into protective clothing (for example, fire-fighting clothing), the fiber will deteriorate even if it is used for a longer period than the general actual use years (5 years). This is preferable because it cannot be seen.

 The partially imidized polyamic acid solution in the present invention is a polyamic acid solution in which a part of the amide group in the polyamic acid solution is imidized, and when the imidization proceeds, the polyamic acid solution is pale yellow to yellow, Or it can confirm that it is partially imidized by coloring red. Furthermore, for example, after forming a partially imidized polyamic acid solution into a film, extracting the solvent and imidizing agent in a methanol solution, and then measuring with an infrared spectrometer to observe the absorption peak derived from the imide group It can also be confirmed that imidization is progressing.

  In the present invention, a general dry spinning method can be used. In particular, in the dry spinning of the present invention, in order to suppress the contact of water in the spinning tower as much as possible, an inert gas such as argon gas or nitrogen gas or a polyimide fiber finally obtained by spinning in dry air is used. It is preferable for improving hydrolysis resistance.

  An example of a specific spinning method will be described with reference to the drawings.

  As shown in FIG. 1, the dry spinning in the present invention means that the spun fibers are discharged into the air stream immediately after spinning and the solvent in the spun fibers is volatilized by heat exchange and solvent exchange in the air stream. This is a spinning method that prevents bonding.

  More specifically, the spinning solution (partially imidized polyamic acid solution) is supplied to the spinning nozzle 1 and discharged from the orifice (hole) 2 opened in the spinning nozzle 1 into the air stream. . The diameter of the orifice 2 can be appropriately selected depending on the required fiber diameter. A diameter of a circular orifice having a diameter of 0.01 mm or more and 5.00 mm or less is preferable. A particularly preferable range is a range in which the diameter is 0.05 mm or more and 2.00 mm or less. Such a range is preferable because the pressure at the time of discharging the polyamic acid solution can be kept low. Further, the number of orifices in the spinneret 1 is preferably 10 holes or more and 800 holes or less. As the number of holes in the orifice increases, the amount of spun fibers can be increased, but the amount of solvent in the tower increases, so it is preferable to spin within the above range.

  It is preferable to appropriately select the amount of the stock solution for spinning to the spinneret.

 The airflow in the spinning tower is an airflow generated from the airflow generator 3, and the internal temperature of the spinning cylinder 4 is heated to a temperature at which the solvent is volatilized from the spun fiber. The internal temperature of the spinning cylinder 4 in the present invention is preferably 20 ° C. or higher and 300 ° C. or lower, and particularly preferably 30 ° C. or higher and 260 ° C. or lower. When the temperature in the spinning cylinder 4 is high, the viscosity of the fiber immediately after spinning becomes low and the fiber shape cannot be maintained, which is not preferable. On the other hand, when the temperature in the spinning cylinder 4 is low, it is not preferable because the volatilization amount of the solvent is small and the spinning fibers are easily bonded to each other. For heating in the spinning cylinder 4, the temperature in the spinning cylinder 4 can be raised by supplying high-temperature air supply from the airflow generator 3, but a heat source heater is disposed on the side of the spinning tower, It is preferable for safety to take a mechanism for heating the gas inside from the wall surface. The air flow generated from the air flow generator 3 is preferably an inert gas such as argon gas or nitrogen gas, or dry air, and particularly inert gas such as argon gas or nitrogen gas from the viewpoint of explosion of the solvent gas. A gas is preferred.

  The partially imidized polyamic acid solution discharged from the orifice 2 is dried in the spinning cylinder 4. The polyamic acid fiber 5 which has been dried and formed into a fiber shape is taken up by a bobbin in the form of a tow while being twisted using a twister 6 or the like when taken out from the cylindrical device. The spinning fiber 8 wound on the bobbin by the winding device 7 is preferably heated in the spinning tower and imidized more than the spinning stock solution. Moreover, it is preferable that the residual solvent ratio in the spinning fiber 8 at this time is 1% or more and 70% or less. The residual solvent ratio in the present invention means that a part of the obtained spun fiber 8 is sampled and weighed, the weight is Wa (g), and the sample is dried in a heating oven at 350 ° C. for 20 minutes. When the weight is Wb (g), the residual solvent ratio is a value calculated from a calculation formula of (Wa−Wb) ÷ Wb × 100.

  In the production process of the polyamic acid fiber in the present invention, the temperature in the spinning tower, the amount of spinning solution, the number of spinning, the spinning speed, and the air flow rate sent to the tower are appropriately selected so that the residual solvent ratio is within the above range. It is preferable to do.

<Heating, stretching and imidization process>
The spinning fiber 8 can obtain a polyimide fiber by performing heating, stretching, and imidization using a publicly known apparatus. An example of a more specific heating / stretching / imidizing apparatus will be described with reference to FIG.

  As shown in FIG. 2, the heating / stretching / imidization treatment in the present invention is performed by heating / stretching in the heating / stretching processing device 17 while feeding the spun fiber 8 in the conveying direction 16 and then heating. In the imidation treatment device 18, this is a treatment step for completely removing the solvent that could not be volatilized in the drawing treatment device by heating and obtaining the polyimide fiber 15 by completely imidizing the spun fiber 8. .

  The spun fiber 8 is drawn out by a feeding roll 9. The feeding speed at this time is Ra (m / min). The fed polyamic acid fiber passes through the heating / stretching furnace 10, passes through the speed controller 11, and is transported to the next heating / imidization furnace 13 by the transporting roll 12. Let the conveyance speed of the conveyance roll 12 be Rb (m / min). The draw ratio in the present invention is a value calculated by Rb ÷ Ra from the speeds of the feed roll 9 and the transport roll 12.

  In the present invention, the draw ratio is preferably 1.0 times or more, and particularly preferably drawn in the range of 1.0 times to 3.0 times. By controlling within the above range, the polyimide fiber finally obtained has a breaking elongation of 10% to 100%, and a breaking strength of 1.0 cN / dtex to 8.0 cN / dtex can be preferably controlled. .

  By controlling the elongation at break to 10% or more and 100% or less, it is preferable because polyimide fibers are formed into a woven fabric and are not easily broken against the rubbing of the fibers. Further, it is preferable to control the breaking strength within the range of 1.0 cN / dtex or more to 8.0 cN / dtex because the terminal (fiber) is hardly broken when the polyimide fiber is formed into a woven fabric.

  The speed controller 11 appropriately adjusts the speeds of Rb and Ra. The speed controller is preferably a dancer roll capable of applying a variable load, and controls the film tension in the furnace by varying the load according to the speed.

  It is preferable to perform the stretching process at an atmospheric temperature in the stretching / heating furnace 10 of 140 ° C. or higher, and more preferably to perform the stretching process in a temperature range of 140 ° C. or higher and 300 ° C. or lower. If the stretching is performed within the above temperature range, the temperature can be spread to the inside of the fiber without spotting in a short time, and it can be stretched at a uniform stretching ratio over the entire tow. Moreover, since the elasticity modulus of a spinning fiber falls and it becomes easy to extend | stretch by making it the said temperature, it is preferable. The drawing / heating furnace 10 may be heated by a radiant heating furnace using far-infrared rays, a heating furnace using hot air, a heating furnace using microwaves, or a roll heating furnace containing a heating roll. The heating method is not particularly limited.

  The spun fiber is transported to the heating / imidization process through the heating / stretching process and subjected to a heating / imidization reaction.

  The heating / imidizing furnace 13 in the heating / imidizing step is used to completely remove the solvent remaining in the spun fiber and advance the imidization reaction. The heating / imidization furnace 13 may be a single heating furnace or a plurality of heating furnaces.

  In particular, in order to proceed with imidization of polyimide fibers, it is preferable that two or more furnaces are used in series and the polyamic acid fibers are reciprocated inside the furnace so that imidization can be performed slowly over a long period of time. The heating / imidizing furnace 13 may be a radiation heating furnace using far infrared rays, a heating furnace using hot air, a heating furnace using microwaves, or a roll heating furnace including a heating roll inside. The heating method is not particularly limited.

  When the heating / imidizing furnace 13 is composed of a plurality of heating furnaces, it is preferable to change the temperature from a low temperature to a high temperature. At that time, the lowest ambient temperature is preferably set to the same temperature as the temperature of the drawing / heating furnace 10 or higher. The highest heating furnace atmosphere temperature is preferably 400 ° C. or higher for complete imidization of the polyimide fiber, particularly preferably 420 ° C. or higher. By performing the heat treatment at a temperature of 400 ° C. or higher, the imidization ratio of the polyimide fiber finally obtained can be made 100%.

  In order to improve the hydrolysis resistance of the polyimide fiber, it is preferable to bake at a temperature of 400 ° C. or higher for 1 minute or longer.

  That is, if an example is described, the baking of the polyimide fiber of the present invention will be performed at 350 ° C., 400 ° C. and 430 ° C. when three heating furnaces are installed, for example, each oven is heated for 4 minutes and 3 minutes. The polyimide fiber 15 can be obtained by changing the time for 2 minutes and allowing it to pass through and then firing and then cooling and winding with the winding device 14. In order to change the transport time, the heating time can be changed by changing the transport distance in the furnace by changing the number of times of reciprocating in each heating / imidizing furnace. Furthermore, a heating time can be changed by adding a free roll inside or outside the furnace and passing the roll.

  It is preferable that the winding speed of the polyimide fiber winding device 14 is equal to or higher than the speed of the transport roll 12. It is preferable to wind up the fibers in the furnace without slacking by winding at a speed higher than that of the transport roll 12.

  The obtained polyimide fiber 15 is preferably coated with an oil agent composed of an anionic or cationic surfactant on the surface while being drawn out again by another apparatus for removing static electricity, using a publicly known method. It is preferable to apply an oil appropriately.

  Since the polyimide fiber of the present invention is obtained as a multifilament, it can be molded into a woven fabric using the fiber, and can be suitably used for applications such as heat-resistant clothing and heat-resistant filters. In particular, the polyimide fiber of the present invention has very high heat resistance and can be suitably used for such applications. The fiber of the present invention is a fiber having an elliptical shape with a flatness of the cut surface of 1.1 or more, and is excellent in transportability and the like, so that troubles during textile processing can be reduced.

  In addition, after the multifilament is textured by a publicly known method, it can be cut into a certain length and processed into a chopped fiber, and then processed into a nonwoven fabric by using a needle punch device or the like. A heat-resistant mat or a bag filter can be produced using the nonwoven fabric. In particular, the polyimide fiber of the present invention is preferred because it has high hydrolysis resistance, and can be used to avoid deterioration of the polyimide fiber when used for applications such as bag filters.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

<Fineness>
The weight (Sb (g)) of the polyimide fiber tow made of Sa (book) cut into 10 cm was measured, and the fineness was calculated by the following formula.
Fineness (dtex) = Sb ÷ Sa × 100,000
<Elongation at break and strength at break>
Using a Tensilon universal testing device (RTC-1210A) manufactured by A & D Co., Ltd., measurement was performed in accordance with JIS-L1015.

<Breaking strength retention>
The initial breaking strength Ha (cN / dtex) of the polyimide fiber was measured by the above-described method, and the polyimide fiber was subjected to a decomposition acceleration test under saturated steam at 150 ° C., 100% RH and 4 atm for 20 hours. After the acceleration test, the breaking strength Hb (cN / dtex) of the fiber was measured, and the breaking strength retention was calculated from the calculation formula of Hb / Ha × 100. In the present invention, the larger the breaking strength retention, the better the hydrolysis resistance.

(Synthesis Example 1)
The reaction was carried out in a reactor equipped with a stirring blade for stirring the solution in a 200 L reactor subjected to nitrogen substitution. In the reactor, 31.44 kg of N, N-dimethylformamide was added, and 4.41 kg of 4,4′-diaminodiphenyl ether was added and completely dissolved.
To this solution, 4.32 kg of pyromellitic dianhydride was added and stirred uniformly for 20 minutes. To this solution, a solution obtained by dissolving 0.48 kg of pyromellitic dianhydride in 9.1 kg of N, N-dimethylformamide was added little by little, and the viscosity of the spinning stock solution was 23 ° C. The addition was finished when it reached 2300 poises as measured by. After the uniform viscosity was reached, uniform stirring was continued for 1 hour to obtain a polyamic acid solution. The solid content concentration of the polyamic acid solution was 18.5%.

  The polyamic acid solution was heated to 30 ° C., 1.23 kg of β-picoline (corresponding to 0.30 mol relative to 1 mol of amide groups) was added, and the mixture was stirred uniformly for 1 hour. Next, 0.67 kg of acetic anhydride (corresponding to 0.15 mol with respect to 1 mol of amide group) was added and stirred uniformly for 5 hours.

Example 1
A spinning experiment was conducted using the polyamic acid solution obtained in Synthesis Example 1 (hereinafter referred to as spinning solution). Dry spinning was performed using the same apparatus as in FIG. The experiment was conducted with the number of holes in the orifice 2 of the spinneret 1 being 10 holes. A circular spinneret having an orifice diameter of 0.15 mm was used. Spinning was performed by adjusting the atmospheric temperature in the spinning tower to 220 ° C. to 240 ° C., and it was wound around a bobbin after confirming that the spinning fibers were dried to the extent that the spun fibers were not fused together at the bottom of the spinning tower. The winding speed was 600 m / min.

  Spinning fibers were obtained by adjusting the discharge rate of the spinning solution to 10 g / min. The residual solvent ratio of the spun fiber at this time was 10%.

  This polyimide fiber was stretched, heated and imidized under the conditions shown in Table 1 using the heating / imidizing apparatus of FIG. It has been clarified that the fiber during spinning is stabilized without causing problems such as terminal breakage even if it is largely drawn in the drawing process. Moreover, the breaking strength, breaking elongation, and breaking strength retention of the obtained polyimide fiber were measured. It was revealed that the obtained polyimide fiber was excellent in both breaking strength and breaking elongation, in particular, had a high breaking strength retention and excellent hydrolysis resistance.

(Comparative Example 1)
Table 2 summarizes the results of evaluation of the breaking strength, breaking elongation, and breaking strength retention of a product having a trade name of P84 (average fineness of 2.2 dtex) manufactured by Inspec Fiber.
As compared with the polyimide fibers obtained in the examples, it was revealed that the breaking strength retention ratio was greatly reduced and the hydrolysis resistance was low.

Schematic diagram of dry spinning equipment Schematic diagram of heating and imidization equipment

Explanation of symbols

1 Spinneret for spinning 2 Orifice (hole)
3 Airflow generator 4 Spinning cylinder 5 Polyamic acid fiber 6 Twister (twisting device)
DESCRIPTION OF SYMBOLS 7 Winding device 8 Spinning fiber 9 Feeding roll 10 Heating / stretching furnace 11 Speed controller 12 Transport roll 13 Heating / imidizing furnace 14 Winding device 15 Polyimide fiber 16 Transport direction 17 Heating / stretching processing device 18 Heating / imidation processing device

Claims (8)

  A polyimide fiber obtained by spinning a spinning solution, which is partially imidized by mixing a chemical imidizing agent with a polyamic acid solution, by a dry spinning method. The polyimide fiber according to claim 1, wherein the chemical imidizing agent according to claim 1 contains at least an imidization catalyst. The polyimide fiber according to claim 1, wherein the chemical imidizing agent according to claim 2 further contains a dehydrating condensing agent.   A nonwoven fabric using the polyimide fiber according to claim 1.   A heat-resistant filter using the polyimide fiber according to claim 1.   A woven fabric comprising the polyimide fiber according to claim 1.   A heat-resistant protective clothing using the polyimide fiber according to claim 1. A method for producing a polyimide fiber, comprising producing a polyimide fiber by spinning a spinning solution obtained by mixing a polyimidic acid solution with a chemical imidizing agent and partially imidizing it by a dry spinning method.

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