JP2005054315A - Method for producing dense meta-type wholly aromatic polyamide fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of producing a meta-type wholly aromatic polyamide fiber excellent in heat property and whiteness and not containing salts in a substantially industrial production level. <P>SOLUTION: (1) A spinning dope composed of a meta-type wholly aromatic polyamide polymer solution dissolving a meta-type wholly aromatic polyamide containing a m-phenylene isophthalamide skeleton as a main component in an amide-based solvent and not substantially containing salts is discharged into a coagulating bath composed of an amide-based solvent and water and not substantially containing salts and kept to 20-70°C and the dope is coagulated as a porous linear body from a spinneret and (2) the coagulated fiber is immersed in a first regulation bath composed of an aqueous solution of an amide-based solvent and kept to 20-40°C and (3) the coagulated fiber is immersed into a second regulation bath composed of an aqueous solution of inorganic metal salt compound and kept to a second swelling temperature (T<SB>2</SB>to T<SB>2</SB>-30°C) and (4) the fiber is stretched in a plasticizing and stretching bath composed of an aqueous solution of amide-based solvent and (5) the stretched fiber is washed with water or an aqueous solution of amide-based solvent and (6) the fiber is heat-treated at 100-250°C and (7) the fiber is further heat-treated at 270-400°C to provide the dense meta-type-wholly aromatic polyamide fiber excellent in whiteness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a meta type wholly aromatic polyamide fiber having a main component of a metaphenylene isophthalamide skeleton having excellent heat resistance and good whiteness by wet spinning with high productivity. .

  It is well known that wholly aromatic polyamides produced from aromatic diamines and aromatic dicarboxylic acid dichlorides are excellent in heat resistance and flame retardancy. It is also well known that these wholly aromatic polyamides are soluble in amide solvents and can be made into fibers from these polymer solutions by methods such as dry spinning, wet spinning and semi-dry semi-wet spinning. Yes.

  Among such wholly aromatic polyamides, fibers of meta-type wholly aromatic polyamides represented by polymetaphenylene isophthalamide (hereinafter sometimes referred to as “meta-aramid”) are particularly useful as heat-resistant and flame-retardant fibers. It is said that such meta-aramid fibers are currently industrially produced mainly by the following two methods (a) and (b), and in addition to these, production of meta-aramid fibers As methods, the following methods (c) to (f) have been proposed.

  (A) A polymetaphenylene isophthalamide solution is prepared by subjecting metaphenylenediamine and isophthalic acid chloride to low-temperature solution polymerization in N, N-dimethylacetamide, and then, by-product hydrochloric acid is hydroxylated. A method for producing polymetaphenylene isophthalamide fiber by dry spinning a polymer solution containing calcium chloride obtained by neutralization with calcium (see Japanese Patent Publication No. 35-14399, US Pat. No. 3,360,595) .

  (B) Contacting an organic solvent system (for example, tetrahydrofuran) that is not a good solvent for the resulting polyamide containing metaphenylenediamine salt and isophthalic acid chloride and an aqueous system containing an inorganic acid acceptor and a soluble neutral salt. A method of isolating a powder of a metaphenylene isophthalalamide polymer (see Japanese Patent Publication No. 47-10863), re-dissolving the polymer powder in an amide solvent, and then performing wet spinning in an inorganic salt-containing aqueous coagulation bath ( (See Japanese Patent Publication No. 48-17551).

  (C) From a meta-aramid solution prepared by dissolving and isolating a meta-aramid synthesized by a solution polymerization method in an amide solvent and containing no inorganic salt or a small amount (2 to 3%) of lithium chloride by a wet molding method. A method for producing a molded product such as a fiber (see JP-A-50-52167).

  (D) A meta-aramid polymer solution containing calcium chloride and water produced by solution polymerization in an amide solvent and neutralized with calcium hydroxide, calcium oxide or the like is extruded into the gas from the orifice, After passing, it introduce | transduces into an aqueous coagulation bath, Then, it passes in inorganic salt aqueous solution, such as calcium chloride, and shape | molds into a thread (refer Unexamined-Japanese-Patent No. 56-31209).

  (E) A meta-aramid polymer solution containing calcium chloride and water produced by solution polymerization in an amide solvent and neutralized with calcium hydroxide, calcium oxide, etc. A method of spinning in a coagulation bath to form a yarn (see JP-A-8-074121 and JP-A-10-88421).

(F) An amide solvent solution containing an inorganic salt of meta-aramid is discharged to a high temperature spinning cylinder, and immediately after leaving the spinning cylinder, it is cooled and swollen with a low temperature aqueous solution, and this is an aqueous solution containing a plasticized salt. A method for producing readily dyeable porous fibers having a density of less than 1.3 g / cm ³ having a large number of very fine pores by stretching in a stretching bath (see Japanese Patent Publication No. 52-43930).

The above method (a) has the advantage that a polymer solution for spinning (spinning stock solution) can be prepared without isolating the polymer, but it is energy for production because of dry spinning using an amide solvent having a high boiling point. If the cost is high and the number of holes per spinneret is increased, the spinning stability rapidly decreases. In addition, since it is often possible to obtain only weak fibers with high devitrification even if this polymer solution is wet-spun into an aqueous coagulation bath, a meta-aramid polymer solution obtained by solution polymerization is still wet-spun using an aqueous coagulation bath. The method is believed to have many difficulties and has not been implemented industrially. On the other hand, the method (b) (c) avoids the above-mentioned problem of dry spinning, but the solvent is different between the polymerization system and the spinning system, and the process for re-dissolving the polymer once isolated In order to obtain a stable solution by re-dissolution, special consideration and meticulous process control are required (see Japanese Patent Publication No. 48-4661). In the method (d), when spinning from the spinneret into the air, increasing the number of holes per spine significantly reduces the spinning stability, resulting in low productivity and inefficiency. Furthermore, although the method (e) gives fibers with good physical properties, there is a problem in productivity because it is difficult to increase the spinning speed. The method (f) is a method for producing porous fibers having a density considerably smaller than 1.3 g / cm ³ , but this is an applied technique of the dry spinning method, and has the same problems as the dry spinning method. Have.

  In addition, meta-aramid fibers are used as electronic materials because of their heat resistance and insulation properties, but in order to use them as electronic materials, it is required to reduce the contamination of ionic substances as much as possible, and if possible inorganic ionic substances Is preferably not contained at all. However, in the production methods known so far, in the spinning process, salts having a high affinity for polymer dopes such as calcium chloride and lithium chloride in the spinning dope and coagulation bath are easily dissolved. It is essential to contain it at a high concentration, and therefore it is inevitable that a large amount of salts is contained in the produced fiber. In order to remove the salt remaining in the fiber, it is necessary to provide a large-scale water washing process, but it is impossible to completely remove the salt of the fiber.

  As a means for improving such a problem, Japanese Patent Laid-Open No. 2001-303365 discloses that a meta type wholly aromatic polyamide mainly composed of metaphenylene isophthalamide obtained by the same method as (b) is dissolved in an amide solvent. The polymer solution substantially free of salts is discharged into a coagulation bath consisting of an amide solvent and water and substantially free of salts to solidify as a porous linear body, Subsequently, this is stretched in a plastic stretching bath made of an aqueous solution of an amide solvent, washed with water, and heat-treated to form a dense meta-type wholly aromatic substantially free of salts (inorganic ionic substances). A method for producing a polyamide fiber is also disclosed in Japanese Patent Application Laid-Open No. 2001-348726, which is also coagulated as a porous linear body, followed by heating and stretching in the air as it is or after impregnation with a plastic liquid, Next Once the method further heat treatment at a high temperature of 250 to 400 ° C. After heat treatment at a low temperature of 100 to 200 ° C. without drying has been proposed.

  Certainly, these methods are excellent as a method for obtaining a meta-aramid fiber substantially free of salts, but because the fiber is likely to be colored (yellowing) due to thermal decomposition of the solvent remaining in the fiber, There is a problem that the equipment for removing the solvent is enlarged.

As described above, a method that can produce a meta-aramid fiber excellent in appearance and containing no salt at a substantially industrial production level has not been proposed yet.
Japanese Patent Publication No. 35-14399 U.S. Pat.No. 3,360,595 Japanese Patent Publication No.47-10863 Japanese Patent Publication No. 48-17551 JP 50-52167 A Japanese Patent Laid-Open No. 56-31209 JP-A-8-074121 JP-A-10-88421 Japanese Patent Publication No. 52-43930 Japanese Patent Publication No. 48-4661 JP 2001-303365 A JP 2001-348726 A

  The present invention has been made in view of the above prior art, and an object thereof is to provide a novel method capable of advantageously producing meta-aramid fibers which are excellent in thermal properties and whiteness and do not contain salts at a practical industrial production level. There is to do.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have immersed a salt-free polymer solution in a first adjustment bath after coagulation to adjust the fiber state, and then immersed in an inorganic metal salt compound aqueous solution. As a result, the solvent can be removed in a short time without allowing the inorganic metal salt compound to enter the fiber, and as a result, the fiber having good whiteness (excellent in appearance) without increasing the size of the equipment. And the present invention has been achieved.

Thus, according to the present invention, a “meta-type wholly aromatic polyamide polymer solution in which a meta-type wholly aromatic polyamide having a metaphenylene isophthalamide skeleton as a main component is dissolved in an amide-based solvent is subjected to wet spinning. In the method for producing a wholly aromatic polyamide fiber, (1) a polymer solution substantially free of salts is used as a spinning stock solution, and this is composed of an amide solvent and water from a spinneret and substantially contains salts. A first adjustment bath having a temperature of 20 to 40 ° C., which is discharged into a coagulation bath having a temperature of 20 to 70 ° C. and solidified as a porous linear body, and comprising an aqueous solution of (2) an amide solvent. Soaked in (3) an aqueous solution of an inorganic metal salt compound, soaked in a second adjustment bath having a temperature of the second swelling temperature T _{2 to} T ₂ + 30 ° C., and (4) an aqueous solution of an amide solvent. Possible Stretching in a plastic stretching bath, (5) washing with water or an aqueous solution of an amide solvent, (6) heat-treating this at a temperature of 100-250 ° C, (7) further at a temperature of 270-400 ° C A process for producing a dense meta-type wholly aromatic polyamide fiber, characterized by heat treatment. "

  At this time, the composition of the amide solvent and water in the coagulation bath in step (1) is 40/60 to 70/30 by weight, and the amide solvent and water in the first adjustment bath in step (2). The composition of the inorganic metal salt compound and water in the second adjustment bath of step (3) is 20/80 to 50/50 by weight ratio. In the step (4), a plastic stretching bath in which the composition of the amide solvent and water is 20/80 to 70/30 by weight and the temperature is 20 to 90 ° C. is used. A dense meta-aramid fiber that is particularly excellent in whiteness and substantially free of salts by being heat-treated in the step (7) under a stretch of 0.7 to 4 times in the range of 10 to 10 times. Can be manufactured with good productivity.

  According to the production method of the present invention, a dense meta-type wholly aromatic polyamide fiber excellent in heat resistance and color tone (color L value of 60 or more, particularly 65 or more) and containing no salt (particularly polymetaphenylene isophthalamide type). Fiber) can be produced with substantially industrial productivity.

  The meta-type wholly aromatic polyamide used in the present invention has metaphenylene isophthalamide as a main repeating unit, and its production method is not particularly limited. For example, it can be produced by solution polymerization or interfacial polymerization using a meta-type aromatic diamine and an aromatic dicarboxylic acid chloride as raw materials.

  As the meta-type aromatic diamine which is one of such raw materials, diamines represented by the following formula are mainly used.

かかるメタ型芳香族ジアミンの具体例としては、メタフェニレンジアミン、２，４−トリレンジアミン、２，６−トリレンジアミン、２，４−ジアミノクロルベンゼン、２，６−ジアミノクロルベンゼン等が挙げられる。その他のメタ型芳香族ジアミンとしては、３，４’−ジアミノジフェニルエーテル、３，４’−ジアミノジフェニルスルホン等が挙げられる。

Specific examples of such meta-type aromatic diamines include metaphenylenediamine, 2,4-tolylenediamine, 2,6-tolylenediamine, 2,4-diaminochlorobenzene, 2,6-diaminochlorobenzene, and the like. It is done. Examples of other meta-type aromatic diamines include 3,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl sulfone.

  In the present invention, among them, metaphenylenediamine or mixed diamine mainly composed of this is preferable. Other aromatic diamines used in combination with metaphenylenediamine include paraphenylenediamine, 2,5-diaminochlorobenzene, 2,5-diaminobromobenzene, aminoanisidine, etc. in addition to the above-mentioned meta-type aromatic diamine. Benzene derivatives, 1,5-naphthylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodipheniketone, bis (aminophenyl) phenylamine, bis (paraaminophenyl) methane and the like are used.

  When a polymer with good solubility is desired, such other aromatic diamines can be used up to about 20 mol% of the whole. However, when a highly crystalline polymer is desired, metaphenylene can be used. It is preferable that diamine is contained at 90 mol% or more, particularly 95 mol% or more.

  On the other hand, the aromatic dicarboxylic acid chloride used in the present invention is isophthalic acid chloride or an aromatic dicarboxylic acid chloride mainly composed thereof. Other aromatic dicarboxylic acid chlorides that can be used in combination with isophthalic acid chloride include terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 4,4′-biphenyldicarboxylic acid chloride, 5 -Chlorisophthalic acid chloride, 5-methoxyisophthalic acid chloride, bis (chlorocarbonylphenyl) ether and the like.

  In the practice of the present invention, when a polymer with good solubility is desired, high-rate mixing (up to about 20 mol%) of these other aromatic dicarboxylic acids is possible. Is desired, isophthalic acid chloride is preferably contained in an amount of 90 mol% or more, particularly 95 mol% or more.

  Among the above-mentioned meta-type wholly aromatic polyamides, a polymer in which 90 to 100 mol% of all polymer repeating units are metaphenylene isophthalamide units, and substantially free of salts is preferably used.

  In the present invention, a polymer solution in which the meta-type wholly aromatic polyamide is dissolved in an amide-based solvent and substantially free of salts (inorganic ionic substances) is supplied to the process described later. Such a polymer solution may be obtained by removing salts from an amide solvent solution containing a meta-type wholly aromatic polyamide obtained by the above solution polymerization or the like, or obtained by the above solution polymerization, interfacial polymerization or the like. A solution obtained by isolating the meta type wholly aromatic polyamide from a solution containing the meta type wholly aromatic polyamide and dissolving it in an amide solvent may be used. Here, “substantially free of salts” means that the total amount of salts in the polymer solution is less than 0.1% by weight, and a very small amount of salts is allowed to be contained. The amount is preferably as small as possible, and is preferably 0 to 0.01% by weight.

  Examples of the amide solvent used here include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylimidazolidinone and the like. N-methyl-2-pyrrolidone is preferable from the viewpoint of the stability of the polymer solution up to the wet spinning process.

  In the present invention, the polymer solution used for the spinning dope may contain water. Such water may be added as necessary, but it may be inevitably produced in the solution preparation process. The concentration may be any concentration as long as the solution is stably present, but it is usually preferably added and contained, for example, in the range of 0 to 60% by weight with respect to the polymer weight, particularly 15% by weight. % Or less is preferable. If the concentration exceeds this, the stability of the polymer solution is impaired, and the spinnability may be significantly impaired by the precipitation and gelation of the polymer.

  In the present invention, when the polymer solution is discharged into the coagulation bath, a multi-hole spinneret can be used. In practice, the upper limit of the number of holes is about 50,000 holes, preferably 300 to 30,000 holes, particularly 3000 to 10,000 holes.

The coagulation bath in the present invention is composed of an aqueous solution substantially free of salts and substantially consisting of two components of an amide solvent and water (H ₂ O). In this coagulation bath composition, the amide solvent can be suitably used as long as it dissolves meta-aramid and is miscible with water. Particularly, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, Dimethylimidazolidinone and the like can be suitably used. In consideration of recovery of the solvent and the like, it is preferable to use the same type of amide solvent in the spinning dope.

  The optimum mixing ratio of the amide solvent and water varies slightly depending on the conditions of the polymer solution, but the concentration of the amide solvent in the coagulation bath liquid is in the range of 40 to 70% by weight, particularly 50 to 65% by weight. It is preferable that Under conditions where the concentration of the amide solvent is below this range, very large voids are likely to be formed in the yarn, which is likely to cause subsequent yarn breakage. On the other hand, under conditions exceeding this range, solidification does not proceed and the yarns tend to adhere to each other (welding, gluing, fusing, etc.).

  The temperature of the coagulation bath is closely related to the composition of the coagulation solution. Generally, a higher temperature is preferable because voids on coarse bubbles called fingers are hardly formed in the formed yarn. However, when the concentration of the coagulating liquid is high, the adhesion between the yarns becomes intense when the temperature is too high, so that the suitable temperature of the coagulating bath is 20 to 70 ° C, more preferably in the range of 40 to 65 ° C. .

  The coagulation liquid is preferably substantially composed of only an amide solvent and water, but may contain a small amount of salts other than this. In particular, salts such as calcium chloride and calcium hydroxide may be extracted from the polymer solution remaining in a trace amount, but this is different from obtaining a porous linear body (porous coagulation). This is not hindered, and there is no problem even if salts are contained at a low concentration of 10% by weight or less, particularly 1% by weight or less, based on the coagulation liquid. Therefore, the preferred concentration of the salt is in the range of 0 to 10% by weight with respect to the coagulating liquid. The immersion time of the yarn in the coagulation bath is preferably 0.1 to 30 seconds. If the dipping time is too short, the formation of the yarn is insufficient and there is a possibility that the yarn breaks.

Next, the first adjustment bath in the present invention, the free of coagulation bath and also salts substantially consists of an aqueous solution consisting essentially of two components with an amide solvent and water (H 2 _O). The optimum mixing ratio of the amide solvent and water varies slightly depending on the conditions of the porous linear body, but the concentration of the amide solvent in the first adjustment bath is 5 to 30% by weight, particularly 10 to 20% by weight. % Is preferable. When the concentration of the amide solvent is less than this range, a large void is formed in the yarn, and the yarn is easily broken in the subsequent steps. On the other hand, when this range is exceeded, solidification of the yarn surface becomes insufficient, so that the salts easily enter the yarn in the second adjustment bath (inorganic metal salt aqueous solution) in the next step.

  The temperature of the first adjusting bath is appropriately 20 to 40 ° C, particularly 25 to 35 ° C. If the temperature is lower than this range, the yarns tend to adhere to each other. On the other hand, if the temperature is higher than this range, voids are easily formed in the yarn.

  Next, examples of the inorganic metal salt compound used in the second adjustment bath of the present invention include calcium chloride, zinc chloride, magnesium chloride, sodium chloride, and aluminum chloride. Of these, calcium chloride is particularly preferred.

  The concentration of the inorganic metal salt compound aqueous solution in the second adjustment bath is suitably in the range of 20 to 50% by weight, particularly preferably in the range of 30 to 40% by weight. When the concentration of the inorganic metal salt compound is less than this range, it is difficult to efficiently remove the solvent in the yarn, and the whiteness of the finally obtained fiber tends to be lowered. On the other hand, when the concentration of the inorganic metal salt compound becomes too high, the compound tends to precipitate. In the second adjustment bath, the above-mentioned N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylimidazolidinone and the like are within the range not impairing the object of the present invention. In general, the total concentration of the inorganic metal salt compound and the amide solvent is in the range of 30 to 50% by weight, preferably in the range of 35 to 45% by weight.

The temperature of the second adjustment bath needs to be in the range of T _{2 to} T ₂ + 30 ° C. when the second swelling temperature of the yarn immediately before being immersed in the bath is T ₂ . When it is less than this range, the whiteness of the finally obtained fiber becomes insufficient. On the other hand, when it exceeds this range, it becomes difficult to stretch in the plastic stretching bath in the next step, and the strength and the like. This is not preferable because the mechanical properties of the resin deteriorate. In addition, the 2nd swelling temperature here is calculated | required with the following method.

About 10 g of sample fiber is sampled, treated for 5 minutes with a centrifuge (number of revolutions 3000 rpm), and the fiber weight W1 is precisely weighed. Next, this fiber is immersed in 200 g of a 60 wt% aqueous solution of N-methyl-2-pyrrolidone (NMP) at a temperature of 20 to 70 ° C. for 10 seconds. The soaked fiber is treated for 5 minutes with a centrifuge (rotation speed: 3000 rpm), and then the fiber weight W2 is precisely weighed. The swelling ratio S (%) is obtained from W1 and W2 by the following formula.
S = (W2-W1) / W1 × 100

The swelling rate at each immersion temperature is plotted as shown in FIG. 1, and in the graph within the temperature range of 20 to 70 ° C., the temperature at which the swelling rate starts from decreasing to increasing is defined as T ₁ and T ₂ from low temperature.

  The yarn thus adjusted needs to be plastically drawn in an aqueous solution of an amide solvent. The amide solvent used here may be any solvent that swells the meta-type wholly aromatic polyamide and is well mixed with water. In particular, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethylimidazo Lydinone or the like can be preferably used. More preferably, the same solvent as that used in the coagulation bath is preferably used. If the same type of solvent as the coagulation bath is used, the recovery process is simplified, which is economically beneficial.

  That is, it is preferable to use the same kind of amide solvents in the polymer solution, the coagulation bath, the first adjustment bath, and the plastic stretching bath. As such solvents, N-methyl-2-pyrrolidone, dimethylacetamide, dimethyl It is convenient to use formamide alone or in combination of two or more.

  The optimum mixing ratio of the amide solvent and water in the plastic stretching bath varies slightly depending on the above conditions, but is 20 to 80% by weight, particularly 40 to 70% by weight, based on the concentration of the amide solvent in the plastic stretching bath. In particular, the range of 50 to 65% by weight is preferable. On the other hand, the temperature of the plastic stretching bath is suitably in the range of 20 to 90 ° C. In regions below this range, plasticization does not proceed sufficiently and it is difficult to obtain a sufficient draw ratio. Above this range, the surface of the yarn dissolves and the yarns tend to adhere to each other, or the single yarn breaks. Often occurs and good spinning becomes difficult.

  The plastic liquid of the plastic stretching bath is preferably substantially composed of an amide solvent and water, like the coagulation liquid, but may contain a small amount of salts in addition to this. For example, if it is a low concentration of 10% by weight or less, particularly 5% by weight or less based on the plastic liquid, there is no problem even if salts are contained. Therefore, the preferred concentration of the salt is in the range of 0 to 10% by weight with respect to the plastic liquid.

  Plastic stretching is usually performed at a magnification of 1.5 to 10 times, preferably 2 to 10 times, and more preferably at a magnification of 2.1 to 6.0 times. By drawing at a high magnification in this way, the strength and elastic modulus of the meta-aramid fiber are improved to show good physical properties, and at the same time, the pores of the porous structure are crushed and are subjected to a heat treatment performed after plastic drawing described later. Densification proceeds well. However, when the film is stretched at an extremely high magnification, the process tone is deteriorated and it becomes difficult to produce a good yarn.

The fibers after the plastic stretching bath have been washed with water or an aqueous solution of an amide solvent. At that time, it is necessary to wash the fibers so as to satisfy the following formula.
0.1 ≦ N / (P + N) ≦ 0.3, preferably 0.15 ≦ N / (P + N) ≦ 0.25
0.4 ≦ W / (P + W) ≦ 0.7, preferably 0.45 ≦ W / (P + W) ≦ 0.65
However, P, N, and W represent the polymer-containing weight ratio, the amide-containing solvent weight ratio, and the water-containing weight ratio in the fiber, respectively.

  By adjusting the water content and the amide solvent content within the above ranges, in the subsequent heat treatment, the fluidity of the polymer during the heat treatment is moderately improved and the orientation proceeds but the crystallization is suppressed. It is considered that the densification of the fiber is promoted.

  Here, if N / (P + N) is less than 0.1, the effect of improving the polymer fluidity at the time of heat treatment becomes insufficient, the fiber is not sufficiently densified, and good fiber properties can be obtained. It becomes difficult. On the other hand, if it exceeds 0.3, crystallization at the time of heat treatment is likely to proceed, and at the same time, adhesion of fibers is likely to occur, and it is difficult to obtain good fiber properties.

  On the other hand, if W / (P + W) is less than 0.4, there is a concern that the fluidity of the polymer is lowered during heat treatment, the fiber is not sufficiently densified, and the fiber properties are lowered. On the other hand, if it exceeds 0.7, it takes time to evaporate water, which is disadvantageous in terms of productivity and energy.

  In addition, as a method of adjusting the water content and the amide-based solvent ratio to the above ranges, after the plastic stretching, a water bath of 20 to 90 ° C. or a mixed bath of amide solvent / water of 20 to 70 ° C. is passed, and the immersion length Can be easily carried out by adjusting the number of yarns depending on the number of threading turns.

  Thus, the washed plastic stretched yarn is once heat-treated at a temperature range of 100 to 250 ° C., preferably 100 to 200 ° C., preferably dry heat-treated by a heating roller, a heating plate, hot air or the like.

  The subsequent heat treatment at a temperature of 270 to 400 ° C. has a close relationship between the treatment temperature and the fiber density, and is preferably treated at a temperature of 300 to 370 ° C. When the treatment is performed at a high temperature exceeding 400 ° C., the yarn is severely deteriorated and colored, and in some cases, the yarn may be broken. On the other hand, when the temperature is lower than 270 ° C., it cannot be sufficiently densified, and it becomes difficult to express desired fiber properties. The treatment temperature here refers to the set temperature of a heating means such as a hot plate or a heating roller, and dry heat treatment is particularly preferred.

  The draw ratio at this time is closely related to the development of the elastic modulus and strength, and can take any ratio as necessary, but is usually 0.7 to 3.0 times, particularly 1.0. By setting it in a range of ˜2.7 times, good heat stretchability, expression of strength and elastic modulus can be obtained. Here, the draw ratio of 0.7 times means that the yarn shrinks by 30% of the original length before the treatment by heat treatment, and the heat treatment of the present invention is a limited shrink heat treatment within a certain range during the treatment. It means that there is no problem. It is preferable to select the draw ratio of the heat treatment in consideration of the above-described plastic draw ratio. From the viewpoint of densification of the yarn, manifestation of physical properties, and realization of stable yarn forming properties, plastic drawing and hot drawing are included. It is more preferable to set the total draw ratio to 3.0 to 12 times, and further to set to 2.5 to 6 times. The meta-aramid fiber according to the present invention has good drawability, and can be drawn smoothly to a high magnification without causing yarn breakage or fluff during plastic drawing or heat drawing.

  Furthermore, the fibers produced in this manner are crimped as necessary, cut into an appropriate fiber length, and provided to spinning and other subsequent processes.

As described above, the meta-type wholly aromatic polyamide (meta-aramid) fiber according to the present invention has a dense structure similar to that of a normal meta-aramid fiber. Moreover, the fiber density is greater than 1.2 g / cm ³ , preferably 1.3 g / cm ³ or more, and the color L value representing the whiteness of the fiber is 60 or more, preferably 65 or more. Provided, and the salt content in the fiber is extremely small, and the salt content in the fiber is 500 ppm or less, preferably 300 ppm or less in terms of the total content of inorganic ionic substances. In a preferred embodiment, the calcium concentration in the fiber, which has a concern about adverse effects on fiber properties, heat resistance, and post-processability, is 0 to 100 ppm, and the chlorination in the fiber adversely affects electrical properties such as electrical insulation. It has the advantage that the concentration of the product is 0 to 150 ppm.

  As described above, the meta-type wholly aromatic polyamide (meta-aramid) fiber according to the present invention can be applied to various uses that make use of its heat resistance and flame resistance, and particularly used for dyeing and mixing of ionic substances. It can be used suitably for the use which dislikes. For example, it is useful as a heat-resistant flame-resistant garment such as fire fighting clothes and protective clothing, flame-resistant bedding, interior materials, woven and knitted alone or in combination with other fibers, especially various industrial materials such as filters as non-woven fabrics, or synthetic paper, In addition to being able to be used effectively as a raw material for composite materials, the content of ionic substances is extremely low, so in the fields of electrical insulation materials, parts for electronic equipment, printed wiring boards, etc. It is particularly effective.

  Hereinafter, the present invention will be described more specifically with reference to examples. In Examples and Comparative Examples, the intrinsic viscosity (IV) was measured at 30 ° C. with a polymer concentration of 100 mg / 100 ml sulfuric acid in concentrated sulfuric acid after the aromatic polyamide polymer was isolated from the polymer solution and dried. It is the value. Further, “parts” and “%” are all based on weight unless otherwise specified, and the quantity ratio indicates a weight ratio unless otherwise specified. Further, the polymer concentration (PN concentration) in the polymer solution (spinning stock solution) used for spinning is the polymer weight% with respect to the total weight part, that is, {polymer / (polymer + solvent + others)} × 100 (% ).

  Moreover, the density of the porous linear body obtained by coagulation was calculated from the fiber diameter and fineness measured according to ASTM D2130.

  The whiteness of the obtained fiber was measured using a color measuring device “Macbeth Color Eye Model CE-3100” manufactured by Masbek Co., Ltd. under the conditions of a 10-degree field of view, a D65 light source, and a wavelength of 360 to 740 nm. An index L * (abbreviated as color L value) and chromaticity b * (abbreviated as color b value) were determined, and L−b was defined as whiteness. In addition, it shows that it is white, so that this value is large.

  The metal concentration in the obtained fiber was quantified using an atomic absorption method for alkali metals and the other metal ion concentrations using ICP. The chloride concentration was determined by the Dorman microcoulometric titration method. The case where the total ionic substance amount was less than 500 ppm was indicated as ◯, and the case where 500 ppm or more was indicated as ×.

  The adhesion rate of the obtained fiber was measured by the following method. That is, about 30 g of a fiber cut to a length of 5 cm is sampled, and after drying, the weight (W1) is precisely weighed, mixed with 30 liters of water and stirred for 15 minutes, then a width of 0.15 mm and a length of 50 mm And passed through a filter having 400 slits. At this time, the weight (W2) after drying of the fiber remaining without passing through the slit was precisely weighed, and the adhesion rate was calculated from the following formula. Here, an adhesion rate of less than 0.1% was represented by ◯, 0.1% or more and less than 1.0% by Δ, and 1.0% or more by x.

The second swelling temperature was determined by the following method. That is, about 10 g of sample fibers are sampled, treated for 5 minutes with a centrifuge (number of revolutions 3000 rpm), and then the fiber weight W1 is precisely weighed. Next, this fiber is immersed in 200 g of a 60 wt% aqueous solution of N-methyl-2-pyrrolidone (NMP) having a temperature of 20 to 70 ° C. for 10 seconds. The soaked fiber is treated for 5 minutes with a centrifuge (rotation speed: 3000 rpm), and then the fiber weight W2 is precisely weighed. The swelling ratio S (%) is obtained from W1 and W2 by the following formula.
S = (W2-W1) / W1 × 100

The swelling rate at each immersion temperature is plotted as shown in FIG. 1, and in the graph within the temperature range of 20 to 70 ° C., the temperature at which the swelling rate starts from decreasing to increasing is defined as T ₁ and T ₂ from low temperature.

[Example 1]
Produced by an interfacial polymerization method according to the method described in JP-B 47-10863. V. = 21.5 parts by weight of polymetaphenylene isophthalamide powder of 1.9 was suspended in 78.5 parts by weight of N-methyl-2-pyrrolidone cooled to −10 ° C. The solution was heated up to be dissolved to obtain a transparent polymer solution A. The inorganic ion concentration of the polymer powder was Na: 730 ppm, K: 8.8 ppm, Ca: 5 ppm, Fe: 2.3 ppm. The polymer concentration of the polymer solution was 21.5%.

  The polymer solution A was spun as a spinning dope from a spinneret having a hole diameter of 0.07 mm and a hole number of 5000 into a coagulation bath having a bath temperature of 50 ° C. This coagulation bath uses a bath having a composition of water / NMP = 40/60, and is passed through at an immersion length (effective coagulation bath length) of 15 cm at a yarn speed of 7 m / min. It was.

  The coagulated yarn was immersed in a first adjustment bath having a composition of water / NMP = 90/10 (weight ratio) and a temperature of 25 ° C. (immersion length 100 cm), and then NMP / calcium chloride / water = 3/40/57. In a second adjustment bath having a composition (weight ratio) of 70 ° C. (immersion length: 30 cm), and then in a plastic stretching bath having a composition of water / NMP = 40/60 (weight ratio) and a temperature of 60 ° C. Drawing was performed at a draw ratio of 3.6 times. After stretching, it was passed through water / NMP = 70/30 at 20 ° C. (immersion length 1.8 m), and further passed through a water bath at 50 ° C. Then, it was wound around a roller having a surface temperature of 120 ° C. and subjected to a dry heat treatment. Furthermore, dry heat treatment was performed at a constant length on a hot plate having a surface temperature of 330 ° C. to obtain polymetaphenylene isophthalamide fibers.

The properties of the obtained fiber were a fineness of 2.2 dtex, a density of 1.36 g / cm ³ , and a whiteness of 71, indicating good numerical values. Moreover, the ion concentration in the fiber was Na 75 ppm, K 5 ppm, Ca 8 ppm, Fe 7 ppm, Cl 103 ppm, and total ionic substances 208 ppm, indicating a very low content.

[Example 2 and Comparative Examples 1 to 5]
The polymer solution A used in Example 1 was used as a spinning stock solution, and spun from a spinning nozzle having a pore diameter of 0.07 mm and a pore number of 5000 into a coagulation bath having a bath temperature of 50 ° C. This coagulation bath had a composition of water / NMP = 40/60, was passed at an immersion length (effective coagulation bath length) of 20 cm at a yarn speed of 7 m / min, and was once drawn into the air to obtain a coagulated yarn.

  Next, polymetaphenylene isophthalamide fibers were obtained in the same manner as in Example 1 except that the conditions of the first adjustment bath, the second adjustment bath, and the plastic stretching bath were changed under the conditions described in Table 1. The results are shown in Table 1.

  According to the method of the present invention, a dense meta-type wholly aromatic polyamide fiber (especially polymetaphenylene isophthalamide fiber) excellent in heat resistance and color tone (whiteness) and substantially free of salts is substantially industrially produced. Can be manufactured with high productivity. Meta-type wholly aromatic polyamide fibers that are substantially free of such salts, that is, the concentration of inorganic ionic substances is extremely low and the color tone is good, have heat resistance, flame retardancy, electrical insulation, etc. In addition to the inherent properties of meta-type wholly aromatic polyamide fibers, it does not contain substantial amounts of inorganic ions that affect electrical properties, etc., so it is particularly suitable for use as an electronic material because it does not impair electrical properties. is there.

It is a graph which shows the relationship between immersion temperature and swelling rate for calculating | requiring 2nd swelling temperature. The temperature at which the swelling rate changes from decreasing to increasing is defined as the first swelling temperature and the second swelling temperature from the low temperature side.

Claims (7)

A meta type wholly aromatic polyamide fiber is produced by wet spinning a meta type wholly aromatic polyamide polymer solution in which a meta type wholly aromatic polyamide mainly composed of a metaphenylene isophthalamide skeleton is dissolved in an amide solvent. In the method, (1) a polymer solution substantially free of salts is used as a spinning dope, and this is composed of an amide solvent and water from a spinneret and a temperature substantially free of salts is 20 to 70 ° C. It is discharged into a coagulation bath and coagulated as a porous linear body, (2) immersed in a first adjustment bath composed of an aqueous solution of an amide solvent at a temperature of 20 to 40 ° C., and (3) inorganic Immerse in a second adjustment bath comprising a metal salt compound aqueous solution and having a temperature of the second swelling temperature T _{2 to} T ₂ + 30 ° C. (4) Next, stretching in a plastic stretching bath comprising an aqueous solution of an amide solvent (5) Washing with an aqueous solution of water or an amide solvent, (6) heat-treating this at a temperature of 100 to 250 ° C., and (7) further heat-treating at a temperature of 270 to 400 ° C. A method for producing aromatic polyamide fibers.   The method for producing a dense meta-type aromatic polyamide fiber according to claim 1, wherein the composition of the amide solvent and water in the coagulation bath in the step (1) is 40/60 to 70/30 by weight ratio.   The method for producing a dense meta-type aromatic polyamide fiber according to claim 1 or 2, wherein the composition of the amide solvent and water in the first adjustment bath in the step (2) is 5/95 to 30/70 by weight. .   The dense meta-type aromatic according to any one of claims 1 to 3, wherein the composition of the inorganic metal salt compound and water in the second adjustment bath in the step (3) is 20/80 to 50/50 by weight ratio. Manufacturing method of polyamide fiber.   In the above step (4), the composition of the amide solvent and water is 20/80 to 70/30 by weight and stretched 1.5 to 10 times in a plastic stretching bath having a temperature of 20 to 90 ° C. The manufacturing method of the precise | minute meta type wholly aromatic polyamide fiber in any one of Claims 1-4 extended | stretched by magnification.   The method for producing a dense meta-type wholly aromatic polyamide fiber according to any one of claims 1 to 5, wherein in the step (7), the heat treatment is performed under stretching of 0.7 to 4 times.   The amide solvent contained in the polymer solution, the coagulation bath and the plastic drawing bath is at least one selected from the group consisting of N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide. The manufacturing method of the precise | minute meta type wholly aromatic polyamide fiber in any one.

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