JP2011073571A - Acoustic absorption material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic absorption material using meta wholly aromatic polyamide fibers that has not only heat resistance but also acid resistance, excels in a balance between a breaking strength and a dimensional stability in a high temperature environment, and consequently excels in a long-term durability. <P>SOLUTION: The meta type wholly aromatic polyamide fiber is used, which is obtained by obtaining a porous coagulation yarn by wet spinning with a specific coagulating bath, then plastically stretching the yarn at a specific magnification, and also being applied to specific heat treatment in saturated water vapor. The acoustic absorption material is formed by laminating an epidermic material and a nonwoven material, in particular. The meta wholly aromatic polyamide fiber is used as a primary component of a fiber constituting the epidermic material, where a content of low-molecular-weight component having a molecular weight of under 10,000 is not more than 1.0 mass%, a remaining solvent amount is not more than 1.0 mass%, a dry heat contraction percentage at 300°C is not more than 3.0%, and the breaking strength is not less than 3.0 cN/dtex. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sound-absorbing material, and more particularly, to a sound-absorbing material having heat resistance and acid resistance, excellent balance between breaking strength and dimensional stability in a high-temperature atmosphere, and, as a result, excellent long-term durability. .

  In the engine room of an automobile, a sound absorbing material is usually provided for the purpose of preventing resonance of the sound generated by the engine and reducing noise. In the engine room, particularly in the vicinity of the exhaust muffler, the temperature may be considerably high under conditions of high load and high rotation speed during climbing. Further, since the exhaust gas contains an acidic substance, it becomes a high-temperature acidic atmosphere in long-term operation. Therefore, the sound absorbing material provided in the engine room is required to have mechanical strength that can withstand use and to have heat resistance and acid resistance.

  Therefore, a skin material composed of a fiber sheet mainly composed of wholly aromatic polyamide fibers having a melting temperature or a thermal decomposition temperature of 370 ° C. or higher and a heat-resistant fiber having a melting temperature or a thermal decomposition temperature of 370 ° C. or higher as a main component. A sound-absorbing material laminated with a nonwoven fabric has been proposed (see Patent Document 1). According to Patent Document 1, it is possible to obtain a sound-absorbing material that does not shrink or contract even at 400 ° C. However, para-type wholly aromatic polyamide fiber, which is one of the substrates described as a specific embodiment, is expensive, and a cheaper material has been demanded.

  Conventionally, wholly aromatic polyamides produced from aromatic diamines and aromatic dicarboxylic acid dihalides are known as materials having excellent heat resistance and flame retardancy. Among such wholly aromatic polyamides, meta-type wholly aromatic polyamides (sometimes referred to as “meta-aramid”) fibers represented by polymetaphenylene isophthalamide are particularly useful from the viewpoints of heat resistance and flame retardancy. Is. The meta-type wholly aromatic polyamide fibers are widely used in fields exposed to high temperatures such as bag filters for collecting fine particles in exhaust gas such as municipal waste incinerators, taking advantage of their properties.

  However, although the conventional meta-type wholly aromatic amide has sufficient heat resistance, the low molecular weight component called an oligomer remains, so that it is still not satisfactory for long-term stability in an acidic atmosphere. There wasn't.

  In addition, meta type wholly aromatic polyamide fibers generally use an amide-based organic solvent in the production process, and it is known that the amide-based solvent remains in the fibers (see Patent Document 2). ). The solvent remaining in the fiber not only volatilizes or decomposes during high temperature processing to generate gas, but also inhibits the expression of flame retardancy inherent in the meta-type wholly aromatic polyamide. For this reason, in improving the flame retardancy of the meta-type wholly aromatic polyamide fiber, reducing the amount of residual solvent is also one of the means.

  Therefore, as a method of reducing the solvent contained in the meta-type wholly aromatic polyamide fiber, a polymer solution composed of an amide-based solvent containing meta-type wholly-aromatic polyamide and salts, and a salt consisting essentially of amide-based solvent and water. It is discharged into a coagulation bath not contained in the mixture, solidified as a porous linear body, and subsequently stretched in a plastic stretching bath made of an aqueous solution of an amide solvent, washed with water, and then heat treated. It has been proposed (see Patent Document 3).

  However, in the method described in Patent Document 3, the molecular orientation of the fiber is temporarily increased by stretching in a plastic stretching bath after solidification, but the orientation is achieved by a subsequent water washing and / or warm water washing step. It becomes easy to be eased. For this reason, in order to obtain the fiber which has high intensity | strength, it was necessary to extend | stretch again in the heat processing process, and to improve orientation. However, in the heat treatment step, rapid crystallization proceeds simultaneously with the orientation. Since rapid crystallization results in insufficient crystallization, the resulting fiber has a problem that the thermal shrinkage rate at high temperatures is high. For this reason, according to the method of Patent Document 3, a fiber with a reduced amount of residual solvent can be obtained, but in order to increase the strength, the thermal contraction rate under high temperature must be sacrificed.

  Therefore, meta-type wholly aromatic polyamide fibers having not only heat resistance but also acid resistance, excellent balance between breaking strength and dimensional stability under high temperature atmosphere, and excellent long-term durability were used. Actually, high-performance sound-absorbing materials are not yet known.

JP 2006-138935 A JP 2001-348726 A JP-A-2005-232598

  The present invention solves the problems found in the above-mentioned background art, and its object is to have not only heat resistance but also acid resistance, and has a breaking strength and dimensional stability under a high temperature atmosphere. An object of the present invention is to provide a sound absorbing material using a meta-type wholly aromatic polyamide fiber which is excellent in balance and as a result has excellent long-term durability.

  This inventor repeated earnest research in view of said subject. As a result, a porous coagulated yarn can be obtained by wet spinning using a specific coagulation bath, followed by plastic stretching at a specific magnification, and further by performing a specific heat treatment in saturated steam. By using meta-type wholly aromatic polyamide fiber, it has not only heat resistance but also acid resistance, excellent balance between breaking strength and dimensional stability under high temperature atmosphere, and as a result, sound absorption with excellent long-term durability The present inventors have found that a material can be obtained and have completed the present invention.

  That is, the present invention is a sound absorbing material in which a skin material and a nonwoven fabric are laminated, and the skin material includes a meta-type wholly aromatic polyamide fiber as a main component, and the meta-type wholly aromatic polyamide fiber is: The content of the low molecular weight component having a molecular weight of less than 10,000 is 1.0% by mass or less, the residual solvent amount is 1.0% by mass or less, and the dry heat shrinkage at 300 ° C. is 3.0% or less. A sound absorbing material having a breaking strength of 3.0 cN / dtex or more.

  According to the present invention, not only the heat resistance but also the acid resistance is good, and the balance between the breaking strength and the dimensional stability under a high temperature atmosphere is excellent, and as a result, it is possible to obtain a sound absorbing material with excellent long-term durability. it can. Therefore, the sound-absorbing material obtained in the present invention can suppress heat shrinkage, sag, and strength reduction even when installed in a more severe high-temperature acidic atmosphere, and can withstand long-term use. It becomes. Furthermore, it becomes a sound-absorbing material excellent in flame retardancy, heat insulating properties, and mechanical strength, which is inherent to the meta-type wholly aromatic polyamide fiber. The sound absorbing material of the present invention can be used for a long time as a sound absorbing material for an exhaust duct of a diesel engine, for example.

  Hereinafter, the present invention will be described in detail.

<Sound absorbing material>
The sound absorbing material of the present invention is formed by laminating a skin material and a nonwoven fabric. Below, the constituent material, manufacturing method, etc. of the sound-absorbing material of the present invention will be described.

<Skin material>
[Components of skin material]
The skin material constituting the sound absorbing material of the present invention contains a meta-type wholly aromatic polyamide fiber as a main component. Here, the “main component” means that the meta-type wholly aromatic polyamide fiber is 50% by mass or more as a constituent material of the skin material. The material other than the meta-type wholly aromatic polyamide fiber is not particularly limited. For example, para-type wholly aromatic polyamide fiber, aramid copolymer, polyamide imide, polyoxadiazole, polyimide, poly Examples thereof include ether ether ketone, polyether ketone ketone, polybenzimidazole, polytetrafluoroethylene (PTFE), fibers made of glass, ceramics, etc., carbon fibers, and mixtures of these fibers.
Below, the physical property, material, manufacturing method, etc. of the fiber of the meta type wholly aromatic polyamide which is the main component of the skin material will be described.

[Physical properties of meta-type wholly aromatic polyamide fibers]
[Content of low molecular weight component having a molecular weight of less than 10,000]
The content of the low molecular weight component having a molecular weight of less than 10,000 in the meta-type wholly aromatic polyamide fiber needs to be 1.0% by mass or less based on the entire fiber mass. When the content of the low molecular weight component exceeds 1.0% by mass, hydrolysis of the low molecular weight component in the fiber proceeds remarkably quickly, so that various physical properties in an acidic atmosphere are likely to decrease. The content of the low molecular weight component having a molecular weight of less than 10,000 is more preferably 0.8% by mass or less, and particularly preferably 0.6% by mass or less, based on the entire fiber mass.
In order to make the content of the low molecular weight component having a molecular weight of less than 10,000 in the fiber to be 1.0% by mass or less, it can be realized by using a coagulating liquid substantially free of salt in the fiber manufacturing process. .

In the present invention, the “content ratio of a low molecular weight component having a molecular weight of less than 10,000” refers to a value obtained by measurement by the following measurement method.
(Measuring method)
Fibers are dissolved in a solution in which lithium chloride (LiCl) is dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) to a concentration of 0.01 mol / L, and gel permeation chromatograph (GPC) measurement in terms of polystyrene is performed. To implement. The low molecular weight component amount (OV) is obtained from the following equation from the molecular weight (M) obtained by GPC.
OV (%) = 100 × ΣMi (less than 10,000) Ni / ΣMi (Total) Ni
In the formula, Mi and Ni are as follows.
Mi: molecular weight of i-th elution time obtained from GPC measurement Ni: number of molecular weight Mi

[Residual solvent amount]
Since the meta-type wholly aromatic polyamide fiber is usually produced from a spinning solution in which a polymer is dissolved in an amide-based solvent, it is usually that a few percent of the solvent necessarily remains in the fiber. However, in the meta-type wholly aromatic polyamide fiber that is the main component of the skin material of the present invention, the amount of the solvent remaining in the fiber (residual solvent amount) is 1.0% by mass or less based on the entire fiber mass. It is necessary. When the solvent remains in excess of 1.0% by mass with respect to the total mass of the fiber, the molecular structure is destroyed, so that the strength is remarkably reduced and various physical properties are easily lowered in an acidic atmosphere. Therefore, it is not preferable. In addition, it may cause significant yellowing and deterioration of product quality. The amount of the solvent remaining in the fiber (residual solvent amount) is preferably 0.7% by mass or less, and more preferably 0.5% by mass or less.
In order to reduce the amount of residual solvent in the fiber to 1.0% by mass or less, in the fiber manufacturing process, the components or conditions of the coagulation bath are adjusted so that the coagulation form does not have a skin core, and plasticization is performed at a specific magnification. Stretching is performed, and specific heat treatment is performed in saturated steam.

The “residual solvent amount” in the present invention refers to a value obtained by measurement by the following measurement method.
(Measuring method)
The fibers are sampled on the exit side of the washing step, and the fibers are subjected to a centrifuge (rotation speed 5000 rpm) for 10 minutes, and the fiber mass (M1) at this time is measured. The fiber is boiled for 4 hours in methanol having a mass of 2 g, and the amide solvent and water in the fiber are extracted. The fiber after extraction is dried at 105 ° C. for 2 hours, and the fiber weight (P) after drying is measured. Further, the mass concentration (C) of the amide solvent contained in the extract is determined by gas chromatography.
The amount of solvent (amide solvent mass) N (%) remaining in the fiber is calculated by the following equation using M1, M2, P, and C described above.
N = [C / 100] × [(M1 + M2-P) / P] × 100

[Dry heat shrinkage at 300 ° C]
The meta type wholly aromatic polyamide fiber constituting the fabric of the present invention has a dry heat shrinkage of 300 ° C. of 3.0% or less. It is essential that it is 3.0% or less, preferably 2.9% or less, and more preferably 2.8% or less. When the shrinkage rate exceeds 3.0%, it is not preferable because the product dimensions change when used in a high-temperature atmosphere and the product is damaged.
The dry heat shrinkage at 300 ° C. of the meta-type wholly aromatic polyamide fiber can be controlled by performing a specific heat treatment in saturated steam in the fiber production process. In order to set the 300 ° C. dry heat shrinkage to 3.0% or less, the draw ratio in the saturated steam treatment step may be set in the range of 0.7 to 5.0 times. When the draw ratio exceeds 5.0 times, the single yarn breakage at the time of drawing increases, and fluff and process yarn breakage occur, which is not preferable.

In the present invention, “dry heat shrinkage at 300 ° C.” refers to a value obtained by the following method.
(Measurement method of dry heat shrinkage at 300 ° C)
A load of 98 cN (100 g) is hung on a tow of about 3300 dtex, and points 30 cm apart are marked. After removing the load, the tow is placed in an atmosphere of 300 ° C. for 15 minutes, and then the length L between the marks is measured. Based on the measurement result L, the value obtained by the following equation is defined as 300 ° C. dry heat shrinkage (%).
300 ° C. dry heat shrinkage (%) = [(30−L) / 30] × 100

[Strength retention (acid resistance)]
As the acid resistance of the meta-type wholly aromatic polyamide fiber, it is preferable that the strength retention after being immersed in a 20% by mass sulfuric acid aqueous solution at 25 ° C. for 600 hours is 60% or more. When the strength retention is less than 60%, if the sound absorbing material having a skin material containing the meta-type wholly aromatic polyamide fiber as a main component is used in an acidic atmosphere for a long period of time, the mechanical strength of the fiber Since the sound absorbing material deteriorates due to the lowering and is eventually damaged, it is not preferable. The strength retention after dipping in a 20% by mass sulfuric acid aqueous solution at 25 ° C. for 600 hours is more preferably 65% or more, and particularly preferably 70% or more.
In the present invention, in order to achieve a strength retention of 60% or more, in the fiber production process, the components or conditions of the coagulation bath are adjusted so as to obtain a coagulation form having no skin core, and specified after passing through a washing process. Dry heat treatment is performed at the temperature.

In the present invention, “strength retention after immersion in a 20 mass% sulfuric acid aqueous solution at 25 ° C. for 600 hours” refers to a value obtained by measurement by the following measurement method.
(Measuring method)
A 20 mass% sulfuric acid aqueous solution is put into a separable flask, and 51 mm of fibers are immersed therein. Subsequently, the separable flask is immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the fibers are immersed for 600 hours. For each of the fibers before and after the immersion, the breaking strength is measured, and the strength retention of the fibers after the immersion is obtained.

〔Breaking strength〕
The breaking strength of the meta-type wholly aromatic polyamide fiber is preferably 3.0 cN / dtex or more, more preferably 3.5 cN / dtex or more, and particularly preferably 4.0 cN / dtex or more. When the breaking strength is less than 3.0 cN / dtex, the passability in the processing step is deteriorated, which is not preferable.
The “breaking strength” of the meta-type wholly aromatic polyamide fiber can be controlled by carrying out plastic stretching at a specific magnification in the fiber production process. In order to set the breaking strength to 3.0 cN / dtex or more, the stretching ratio in the plastic stretching bath stretching step may be 1.5 to 10 times.

The “breaking strength” in the present invention refers to a value obtained by measurement under the following conditions based on JIS L 1015.
(Measurement condition)
Grasp interval: 20mm
Initial load: 0.044 cN (1/20 g) / dtex
Tensile speed: 20 mm / min

[Elongation at break]
The breaking elongation of the meta-type wholly aromatic polyamide fiber is preferably 30% or more. It is more preferably 35% or more, and particularly preferably 40% or more. When the elongation at break is less than 30%, passability in post-processing steps such as spinning deteriorates, which is not preferable.
In the present invention, the “breaking elongation” of the meta-type wholly aromatic polyamide fiber can be controlled by optimizing the coagulation bath conditions in the spinning / coagulation step in the production method described later. In order to make it 30% or more, the amide solvent concentration in the coagulation bath may be 40 to 60% by mass, and the coagulation bath temperature may be 20 to 90 ° C.
The “breaking elongation” referred to here is obtained based on JIS L 1015 and measured under the same measurement conditions as the above-mentioned “breaking strength” using a model number 5565 manufactured by Instron as a measuring instrument. Value.

[Meta-type wholly aromatic polyamide fiber material]
The meta-type wholly aromatic polyamide used in the production of the meta-type wholly aromatic polyamide fiber, which is the main component of the skin material, uses a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid component as raw materials, and reacts them. It can be obtained by caulking. Further, other copolymer components such as a para type may be copolymerized within a range not impairing the object of the present invention.
In the present invention, it is a meta-type wholly aromatic polyamide mainly composed of a metaphenylene isophthalamide unit because it has excellent mechanical properties and has heat resistance and flame resistance that can withstand use in a high-temperature atmosphere. preferable. Furthermore, it is desirable that the meta-type wholly aromatic polyamide is composed of metaphenylene isophthalamide units, preferably 90 mol% or more, more preferably 95 mol% or more, particularly preferably 100 mol% of all repeating units.

[Raw material for meta-type wholly aromatic polyamide]
(Meta-type aromatic diamine component)
Meta-type aromatic diamine components used as raw materials for meta-type wholly aromatic polyamides include metaphenylene diamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, etc., and halogens in these aromatic rings, Derivatives having a substituent such as an alkyl group having 1 to 3 carbon atoms, such as 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminochlorobenzene, 2,6-diaminochlorobenzene, etc. Can be illustrated. Especially, it is preferable that it is a mixed diamine which contains only metaphenylenediamine or 70 mol% or more of metaphenylenediamine.

(Meta-type aromatic dicarboxylic acid component)
Examples of the meta-type aromatic dicarboxylic acid component that is a raw material for the meta-type wholly aromatic polyamide include a meta-type aromatic dicarboxylic acid halide. Examples of the meta-type aromatic dicarboxylic acid halide include isophthalic acid halides such as isophthalic acid chloride and isophthalic acid bromide, and derivatives having substituents such as halogen and alkoxy groups having 1 to 3 carbon atoms on the aromatic ring, such as 3 Examples thereof include chloroisophthalic acid chloride and 3-methoxyisophthalic acid chloride. Especially, it is preferable that it is a mixed carboxylic acid halide which contains only isophthalic acid chloride or 70 mol% or more of isophthalic acid chloride.

(Copolymerization component)
Examples of copolymer components that can be used other than the above-mentioned meta-type aromatic diamine component and meta-type aromatic dicarboxylic acid component include, for example, paraphenylene diamine, 2,5-diaminochlorobenzene, 2,5- Benzene derivatives such as diaminobromobenzene and aminoanisidine, 1,5-naphthylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ketone, 4,4′-diaminodiphenylamine, 4,4′- And diaminodiphenylmethane. On the other hand, as the aromatic dicarboxylic acid component, terephthalic acid chloride, 1,4-naphthalenedicarboxylic acid chloride, 2,6-naphthalenedicarboxylic acid chloride, 4,4′-biphenyldicarboxylic acid chloride, 4,4′-diphenylether dicarboxylic acid Examples include chloride.

  If the copolymerization ratio of these copolymerization components is too large, the properties of the meta-type wholly aromatic polyamide are liable to deteriorate. Therefore, the copolymerization ratio is preferably 20 mol% or less based on the total acid component of the polyamide. In particular, a suitable meta-type wholly aromatic polyamide is a polyamide in which 90 mol% or more of all repeating units are metaphenylene isophthalamide units, and polymetaphenylene isophthalamide is particularly preferable.

[Method for producing meta-type wholly aromatic polyamide]
The production method of the meta-type wholly aromatic polyamide is not particularly limited. For example, it is produced by solution polymerization or interfacial polymerization using a meta-type aromatic diamine component and a meta-type aromatic dicarboxylic acid chloride component as raw materials. be able to.

[Method for producing meta-type wholly aromatic polyamide fiber]
The meta-type wholly aromatic polyamide fiber that is the main component of the skin material, for example, using the meta-type wholly aromatic polyamide obtained by the production method described above, for example, a spinning solution preparation step, a spinning / coagulation step described below, It is manufactured through a plastic stretching bath stretching step, a washing step, a saturated steam treatment step, and a dry heat treatment step.

[Spinning solution preparation process]
In the spinning solution preparation step, the meta type wholly aromatic polyamide is dissolved in an amide solvent to prepare a spinning solution (meta type wholly aromatic polyamide polymer solution). In the preparation of the spinning solution, an amide solvent is usually used, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc) alone or at least of these amide solvents. The mixed solvent containing 1 type is mentioned. Of these, NMP or DMAc is preferably used from the viewpoints of solubility and handling safety. The spinning solution may contain a small amount (for example, 10% by mass or less) of an inorganic salt such as calcium chloride or lithium chloride.

  The concentration of the solution may be appropriately selected from the viewpoint of the coagulation rate and the solubility of the polymer in the next spinning and coagulation step. For example, the polymer is polymetaphenylene isophthalamide and the solvent is NMP. In the case of, it is usually preferred to be in the range of 10 to 30% by mass.

[Spinning and coagulation process]
In the spinning / coagulation step, the spinning solution (meta-type wholly aromatic polyamide polymer solution) obtained above is spun and coagulated. Although the spinning method is not particularly limited, it is preferable to employ a wet spinning method or a semi-dry semi-wet spinning method because low molecular weight components remaining in the fiber can be reduced.

The spinning device is not particularly limited, and a conventionally known wet spinning device can be used. Moreover, the number of spinning holes, the arrangement state, the hole shape and the like of the spinneret are not particularly limited as long as they can be stably wet-spun. For example, the number of holes is 500 to 30,000, and the spinning hole diameter is 0.05. A multi-hole spinneret for ˜0.2 mm sufu may be used.
The temperature of the spinning solution (meta-type wholly aromatic polyamide polymer solution) when spinning from the spinneret is suitably in the range of 10 to 90 ° C.

  In order to obtain a fiber with a sufficiently reduced amount of residual solvent, it is necessary to densify the fiber to a sufficient extent. For this purpose, a porous fibrous material formed in the solidification stage of the spinning / coagulation process It is extremely important to make the (coagulated yarn) structure as homogeneous as possible. Here, there is a close relationship between the porous structure and the conditions of the coagulation bath, and selection of the composition and temperature conditions of the coagulation bath is extremely important.

  A coagulation bath for obtaining a meta-type wholly aromatic polyamide fiber as a main component of the skin material is substantially composed of an aqueous solution composed of two components of an amide solvent and water. The amide solvent in this coagulation bath composition is not particularly limited as long as it dissolves the meta-type wholly aromatic polyamide and is miscible with water, but in particular, N-methyl-2-pyrrolidone, Dimethylacetamide, dimethylformamide, dimethylimidazolidinone and the like can be suitably used.

  The optimum mixing ratio of the amide solvent and water varies slightly depending on the conditions of the polymer solution, but generally, the ratio of the amide solvent is in the range of 40% by mass to 60% by mass with respect to the entire aqueous solution. Preferably there is. Under conditions below this range, a firm skin layer is formed on the surface of the coagulated yarn, and the residual amount of low molecular weight components increases. Furthermore, very large voids are likely to be generated in the coagulated yarn, which is likely to cause subsequent yarn breakage. On the other hand, under conditions exceeding this range, solidification does not proceed and fiber fusion tends to occur.

  In order to suppress the formation of a strong skin layer on the surface of the coagulated yarn, it is important to use a coagulating liquid made of an aqueous solution of an amide solvent and substantially free of salt. By using a coagulation liquid substantially free of salt, it is possible to suppress the formation of a strong skin layer on the surface of the coagulated yarn, and as a result, low molecular weight components can be efficiently removed.

  It is preferable that the coagulating liquid substantially containing no salt is substantially composed only of an amide solvent and water. However, since inorganic salts such as calcium chloride and calcium hydroxide are extracted from the polymer solution, the coagulating liquid actually contains a small amount of these salts. A suitable concentration of the salt in industrial implementation is in the range of 0.3% by mass to 10% by mass with respect to the entire coagulating liquid. In order to make the inorganic salt concentration less than 0.3% by mass, the recovery cost for purification in the recovery process of the coagulating liquid becomes remarkably high, which is not appropriate. On the other hand, when the inorganic salt concentration exceeds 10% by mass, the coagulation rate becomes slow, so that the fiber immediately after being discharged from the spinneret is likely to be fused, and the coagulation time is long. Therefore, the coagulation equipment must be enlarged, which is not preferable.

  The temperature of the coagulation bath is closely related to the composition of the coagulation solution, but generally it is preferable to increase the temperature because it is difficult to form pores on coarse bubbles called fingers in the produced fiber. However, when the concentration of the coagulating liquid is relatively high, the fiber is strongly fused when the temperature is too high. For this reason, the suitable temperature range of a coagulation bath is 20-90 degreeC, More preferably, it is 25-85 degreeC.

  In addition, it is preferable to make the immersion time of the fibrous material (thread body) in a coagulation bath into the range of 1.5-30 seconds. When the dipping time is less than 1.5 seconds, the fibrous material is not sufficiently formed, and yarn breakage occurs. On the other hand, when the immersion time exceeds 30 seconds, productivity is lowered, which is not preferable.

[Plastic stretching bath stretching process]
In the plastic drawing bath drawing step, while the fiber bundle made of the porous fibrous material (thread body) obtained by coagulation in the coagulation bath is in a plastic state, the fiber bundle is put in the plastic drawing bath. Stretch treatment.

  The plastic stretching bath for obtaining the meta-type wholly aromatic polyamide fiber used for the skin material of the present invention is composed of an aqueous solution of an amide solvent, and is substantially free of salts. The amide solvent is not particularly limited as long as it swells the meta-type aramid and is well mixed with water. Examples of such amide solvents include N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethylimidazolidinone and the like. Industrially, it is particularly preferable to use the same type of solvent as that used in the coagulation bath as the amide solvent used as the plastic stretching bath liquid. That is, the amide solvents used for the polymer solution, the coagulation bath, and the plastic drawing bath are preferably the same, and a single solvent selected from N-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, or two types It is convenient to use a mixed solvent composed of the above. By using the same kind of amide solvent, the recovery process can be integrated and simplified, which is economically beneficial.

  The temperature and composition of the plastic stretching bath are closely related to each other, but can be suitably used as long as the mass concentration of the amide solvent is 20 to 70% by mass and the temperature is in the range of 20 to 70 ° C. . In a region lower than this range, plasticization of the porous fibrous material does not proceed sufficiently, and it becomes difficult to obtain a sufficient stretching ratio in plastic stretching. On the other hand, in a region higher than this range, the surface of the porous fiber is melted and fused, making it difficult to produce a good yarn.

  In order to obtain the meta-type wholly aromatic polyamide fiber used for the skin material of the present invention, the draw ratio in the plastic drawing bath needs to be in the range of 1.5 to 10 times, preferably 2.0 to 6 The range is 0 times. When the draw ratio is less than 1.5 times, the mechanical properties such as strength and elastic modulus of the obtained fiber are lowered, and it is difficult to achieve the breaking strength necessary for the fiber constituting the filter material of the present invention. Become. In addition, it becomes difficult to sufficiently promote the solvent removal from the porous fibrous material, and it becomes difficult to make the residual solvent amount of the finally obtained fiber 1.0% by mass or less. By stretching at a high magnification in the plastic stretching bath stretching process, fibers exhibiting good physical properties by improving strength and elastic modulus can be obtained, and at the same time, fine pores of the porous fibrous material are drawn. It is crushed and the densification in the subsequent heat treatment process proceeds well. However, it is not preferable to draw at a high magnification such that the draw ratio exceeds 10 times because the condition of the process deteriorates and many fluff and single yarn breakage occur.

[Washing process]
In the washing step, the fiber that has undergone the plastic drawing bath drawing step is sufficiently washed. Washing is preferably performed in multiple stages because it affects the quality of the resulting fiber. In particular, the temperature of the cleaning bath in the cleaning step and the concentration of the amide solvent in the cleaning bath liquid affect the state of extraction of the amide solvent from the fibers and the state of penetration of water from the cleaning bath into the fibers. For this reason, it is preferable to control the temperature condition and the concentration condition of the amide solvent by setting the washing process in multiple stages for the purpose of bringing them into an optimum state. A low molecular weight component can be reduced by making a washing | cleaning process multistage.

  The temperature condition and the concentration condition of the amide solvent are not particularly limited as long as the quality of the finally obtained fiber can be satisfied, but if the initial washing bath is at a high temperature of 60 ° C. or higher, water Intrusion into the fiber occurs at a stretch, generating huge voids in the fiber, leading to quality degradation. For this reason, it is preferable that the first washing bath has a low temperature of 30 ° C. or lower. Subsequently, it is preferable to wash with hot water of 50 to 90 ° C.

[Saturated steam treatment process]
In the saturated steam treatment process, the fibers washed in the washing process are heat-treated in saturated steam. By performing the saturated steam treatment, the orientation can be enhanced while suppressing the crystallization of the fibers. Heat treatment in a saturated steam atmosphere can be uniformly heat-treated to the inside of the fiber bundle as compared with dry heat treatment, and uniform fibers can be obtained.

  Further surprisingly, when heat treatment is performed in a saturated water vapor atmosphere, the fiber surface does not crystallize and a skin layer is not formed. For this reason, the solvent remaining in each single fiber of the fiber bundle can be diffused rapidly and can be removed almost completely from the inside of the fiber. Therefore, by carrying out the saturated steam heat treatment, it is possible to reduce the residual solvent amount in the finally obtained fiber to 1.0% by mass or less.

  The saturated water vapor pressure in the saturated water vapor treatment step is in the range of 0.02 to 0.50 MPa. Preferably it is the range of 0.03-0.30 MPa, More preferably, it is the range of 0.04-0.20 MPa. When the saturated water vapor pressure is less than 0.02 MPa, a sufficient steam treatment effect cannot be obtained, and the effect of reducing the residual solvent amount is reduced, which is not preferable. On the other hand, when the saturated water vapor pressure exceeds 0.50 MPa, crystallization of the fiber is promoted too much and a skin layer is formed on the fiber surface, so that it is difficult to sufficiently reduce the residual solvent amount.

  The draw ratio in the saturated steam treatment process is closely related to the expression of fiber strength. The draw ratio may be arbitrarily selected in consideration of the physical properties required for the product, but is in the range of 0.7 to 5.0 times in the present invention, preferably 1.1 to 2. A range of 0 times is preferable. When the draw ratio is less than 0.7, the convergence of the fiber bundle (yarn) in a saturated water vapor atmosphere is lowered, which is not preferable. On the other hand, when the draw ratio exceeds 5 times, the single yarn breakage at the time of drawing is increased, and fluff and process yarn breakage are not preferable. Moreover, if the draw ratio in the saturated steam treatment step is in the range of 0.7 to 5.0 times, the dry heat shrinkage at 300 ° C. necessary for the fibers constituting the filter material of the invention is 3.0% or less. can do.

  In addition, the draw ratio here is represented by ratio of the fiber length after a process with respect to the fiber length before a process. For example, a draw ratio of 0.7 times means that the fiber is subjected to a limit shrinkage treatment to 70% of the original length by the saturated steam treatment process, and 1.1 times means that the fiber is treated to be stretched by 10%. means.

  The time for the saturated steam treatment is preferably in the range of 0.5 to 5.0 seconds. When processing a traveling fiber bundle continuously, the processing time is determined by the traveling distance and traveling speed of the fiber bundle in the steam treatment tank. That's fine.

[Dry heat treatment process]
In the dry heat treatment step, the fiber that has undergone the saturated steam treatment step is dried and heat treated. The dry heat treatment method is not particularly limited, and examples thereof include a method using a hot plate, a heat roller and the like. By undergoing a dry heat treatment, finally, a meta-type wholly aromatic polyamide fiber constituting the filter material of the present invention can be obtained.

  The heat treatment temperature in the dry heat treatment step is preferably in the range of 250 to 400 ° C, more preferably in the range of 300 to 380 ° C. When the dry heat treatment temperature is less than 250 ° C., the porous fibers cannot be sufficiently densified, so that the obtained fibers have insufficient mechanical properties. On the other hand, if the dry heat treatment temperature is higher than 400 ° C., the fiber surface is thermally deteriorated and the quality is lowered, which is not preferable.

  The draw ratio in the dry heat treatment step is closely related to the expression of the strength of the obtained fiber. The draw ratio can be selected arbitrarily depending on the strength required for the fiber, but is preferably in the range of 0.7 to 4 times, and preferably in the range of 1.1 to 3 times. Further preferred. When the draw ratio is less than 0.7 times, the mechanical tension of the fiber is lowered because the process tension is lowered. On the other hand, when the draw ratio is more than 4, the single yarn breakage during drawing increases. In addition, fluff and process breakage occur. In addition, the draw ratio here is represented by ratio of the fiber length after a process with respect to the fiber length before a stretch process similarly to having demonstrated with the said saturated steaming process. For example, a draw ratio of 0.7 times means that the fiber is subjected to a limit shrinkage treatment to 70% of the original length by a dry heat treatment step, and a draw ratio of 1.0 times means a constant length heat treatment.

  The treatment time in the dry heat treatment step is preferably in the range of 1.0 to 45 seconds. The treatment time can be adjusted by the traveling speed of the fiber bundle and the contact length with a hot plate, a heat roller or the like.

[Crimping process, etc.]
The meta-type wholly aromatic polyamide fiber that has been subjected to the dry heat treatment may be further crimped as necessary. Further, after the crimping process, it may be cut into an appropriate fiber length and provided to the next step. In some cases, it may be wound up as a multifilament yarn.

[Form of skin material]
The skin material constituting the sound-absorbing material of the present invention is in the form of a woven fabric or a nonwoven fabric in which the meta-type wholly aromatic polyamide fiber is processed as described above.
In the case of a woven form, it is preferable that the filament yarn or spun yarn has a woven configuration such as plain weave, twill weave, satin weave or the like. Weight per unit area of the fabric when this is preferably in a 100~700g / ^{m 2,} more preferably from 200 to 400 g / ^{m 2.} If it is less than 100 g / m ^2, the sound absorbing efficiency of the resulting sound absorbing material will be extremely low, while if it exceeds 700 g / m ² , flexibility will be impaired.

In the case of a nonwoven fabric, it is preferable to use a resin binder having a glass transition temperature of 250 ° C. or higher. By including a resin binder with a high glass transition temperature, even if it is a sound absorbing material around a high temperature member such as an engine exhaust duct, the shape can be maintained while suppressing sag, etc., and sound absorbing performance Can be suppressed. Moreover, when a resin binder is not used, the fiber which comprises a fiber sheet tends to fall apart, the thing of a desired shape cannot be obtained, or sound absorption performance falls. The glass transition temperature of the resin binder is more preferably in the range of 280 ° C to 500 ° C.
Examples of such a resin binder include a polyimide resin, a polyamideimide resin, a meta-aramid resin, and the like, and fibers made of these resins may be used.

The basis weight in the case of the nonwoven fabric is preferably ²⁰⁰ to 1,500 g / m ² , more preferably 400 to 600 g / m ² . When it is less than 200 g / m ² , the sound absorption efficiency as the sound absorbing material is extremely low, while when it exceeds 1,500 g / m ² , flexibility is impaired.

<Nonwoven fabric>
The nonwoven fabric which comprises the sound-absorbing material of this invention is not specifically limited, Any of the nonwoven fabric consisting of a short fiber and the nonwoven fabric consisting of a long fiber may be sufficient. For example, a needle punched nonwoven fabric, a water jet punched nonwoven fabric, a melt blown nonwoven fabric, a spunbonded nonwoven fabric, a stitchbonded nonwoven fabric, hard cotton, or a wet nonwoven fabric can be used. Especially, the needle punch nonwoven fabric, water jet punch nonwoven fabric, or wet nonwoven fabric which consists of a short fiber is preferable from a viewpoint of process passage property. Moreover, the nonwoven fabric used may be a single layer or a laminate.

  The material of the nonwoven fabric constituting the sound absorbing material is not particularly limited, but it is preferable to use high-strength fibers from the viewpoint that a sound absorbing material having high strength can be obtained. Examples of the high-strength fibers include para-type polyamide fibers such as polyparaphenylene terephthalamide (PPTA), polyparaphenylene benzoxazole fibers, and wholly aromatic polyester fibers.

<Method for producing sound absorbing material>
The laminated state of the skin material and the nonwoven fabric may be a non-adhesive state, but in order to prevent a decrease in sound absorption performance due to the peeling of the sound absorbing material, the skin material and the nonwoven fabric are laminated in a state where at least a part is bonded. It is preferable.

  The method for laminating the skin material and the nonwoven fabric is not particularly limited. For example, as a method not using an adhesive, there may be mentioned a method using a metal connector in addition to sewing, needle punching or the like. Moreover, the method of attaching a fixing member using a binding machine can also be employ | adopted, For example, the method of using a Bannock pin (trademark) (made by Nippon Bannock) etc. can be mentioned. When using an adhesive agent, the method of using heat-resistant thermoplastic resins, such as a polyimide resin, as an adhesive agent is mentioned, for example.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, the scope of the present invention is not limited by these Examples. “Parts” and “%” in Examples and the like are based on “mass” unless otherwise specified, and “quantity ratio” indicates “mass ratio” unless otherwise specified.

<Measurement method>
Each physical property value in Examples and Comparative Examples was measured by the following method.
[Intrinsic viscosity (IV)]
After the aromatic polyamide polymer was isolated from the polymer solution and dried, it was dissolved in 97% concentrated sulfuric acid so that the polymer concentration was 100 mg / 100 mL, and measured at 30 ° C. using an Ostwald viscometer.

[Polymer concentration of polymer solution (PN concentration)]
The polymer mass% with respect to the total mass part of the polymer solution (spinning solution), that is, the PN concentration was determined by the following equation.
PN concentration (%) = {polymer / (polymer + solvent + other components)} × 100

[Fineness]
Based on JIS-L-1015, the measurement based on A method of a positive fineness was implemented, and it described with the apparent fineness.

[Break strength, elongation at break]
Based on JIS L 1015, it measured on condition of the following.
(Measurement condition)
Grasp interval: 20mm
Initial load: 0.044 cN (1/20 g) / dtex
Tensile speed: 20 mm / min

[Low molecular weight component amount N remaining in fiber (%)]
Fibers are dissolved in a solution in which lithium chloride (LiCl) is dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) to a concentration of 0.01 mol / L, and gel permeation chromatograph (GPC) measurement in terms of polystyrene is performed. Carried out. The low molecular weight component amount N was determined from the following formula from the molecular weight (M) determined by GPC.
N (%) = 100 × ΣMi (less than 10,000) Ni / ΣMi (Total) Ni
In the formula, Mi and Ni are as follows.
Mi: molecular weight of i-th elution time obtained from GPC measurement Ni: number of molecular weight Mi

[Amount of solvent remaining in fiber (amide compound solvent mass) SV (%)]
The fibers were sampled on the exit side of the washing step, and the fibers were subjected to a centrifuge (rotation speed: 5,000 rpm) for 10 minutes, and the fiber mass (M1) at this time was measured. This fiber was boiled in methanol having a mass of 2 g for 4 hours to extract the amide solvent and water in the fiber. The fiber after extraction was dried twice at 105 ° C., and the fiber mass (P) after drying was measured. Moreover, the mass concentration (C) of the amide solvent contained in the extract was determined by gas chromatography.
The amount of solvent (amide solvent mass) SV (%) remaining in the fiber was calculated by the following equation using M1, M2, P, and C described above.
SV = [C / 100] × [(M1 + M2-P) / P] × 100

[300 ° C dry heat shrinkage]
A load of 98 cN (100 g) was hung on a tow of about 3,300 dtex, and points 30 cm apart were marked. After removing the load, the tow was placed in an atmosphere of 300 ° C. for 15 minutes, and then the length L between the marks was measured. Based on the measurement result L, the value obtained by the following formula was defined as 300 ° C. dry heat shrinkage (%).
300 ° C. dry heat shrinkage (%) = [(30−L) / 30] × 100

[Acid resistance of raw cotton]
A 20 mass% sulfuric acid aqueous solution was put into a separable flask, and 51 mm of sample yarn was immersed and fixed. Subsequently, the separable flask was immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and the sample yarn was immersed for 600 hours. For each of the sample yarns before and after immersion, the breaking strength was measured by the measurement method described above, and the strength retention rate of the fiber after immersion was determined.

[Change rate of sound absorption coefficient of sound absorbing material]
A 20 mass% sulfuric acid aqueous solution was put into a separable flask, and the sound absorbing material was immersed and fixed. Subsequently, the separable flask was immersed in a constant temperature water bath, maintained at a temperature of 25 ° C., and immersed for 600 hours. The sound absorption coefficient of the sound absorbing material before and after immersion was measured using an automatic normal incidence sound absorption measuring instrument (manufactured by Sotec Co., Ltd.), and the change rate of the sound absorption coefficient before and after immersion was calculated by the following formula. The sound absorption coefficient was measured according to JIS-A-1405 “Measurement method of normal incidence sound absorption coefficient of building material in pipe method” at each frequency (1000 Hz and 2000 Hz). Moreover, the skin part of the sound absorbing material was attached as the sound source side, and the measurement was carried out.
Sound absorption rate change rate (%) = (sound absorption rate before immersion−sound absorption rate after immersion) / sound absorption rate before immersion

<Example 1>
[Spinning liquid adjustment process]
22.0 parts by mass of polymetaphenylene isophthalamide powder having a reduced viscosity (IV) of 1.9 produced by an interfacial polymerization method according to the method described in Japanese Patent Publication No. 47-10863 is cooled to 0 ° C. The resultant was suspended in 78.5 parts by mass of N-methyl-2-pyrrolidone (NMP) and made into a slurry. Subsequently, the suspension was heated to 60 ° C. to dissolve the polymetaphenylene isophthalamide powder, and a transparent polymer solution was obtained.

[Spinning and coagulation process]
The polymer solution obtained above was spun as a spinning solution by discharging it from a spinneret having a pore diameter of 0.06 mm and a pore number of 5000 into a coagulation bath having a bath temperature of 80 ° C. The composition (mass ratio) of the coagulation bath was water / NMP = 45/55, and spinning was performed by discharging into the coagulation bath at a yarn speed of 10 m / min. The immersion length in the coagulation bath (effective coagulation bath length) was set to 60 cm, and after passing through the yarn at a speed of 10 m / min, the obtained coagulated yarn bundle was once drawn into the air.

[Plastic stretching bath stretching process]
Subsequently, the film was stretched at a stretching ratio of 3 in a plastic stretching bath. The composition (mass ratio) of the plastic stretching bath was water / NMP = 70/30, and the temperature was 80 ° C.

[Washing process]
Subsequent to plastic stretching, the film was sufficiently washed with cold water at 10 ° C. at a yarn speed of 30 m / min (immersion length 20 m), and further sufficiently washed with warm water at 80 ° C. (immersion length 20 m).

[Saturated steam treatment process]
Subsequently, heat treatment with saturated steam was performed at a draw ratio of 1.1 times in a container kept at a saturated steam pressure of 0.05 MPa. At this time, various conditions were adjusted so that the fiber bundle was treated with saturated steam for about 1.0 second.

[Dry heat drawing process]
Subsequently, the film was wound on a drying roller having a surface temperature of 150 ° C. and dried, and subsequently stretched 1.2 times on a hot plate at 320 to 350 ° C. and wound to obtain polymetaphenylene isophthalamide fiber. .

[Fiber properties]
The physical properties of the obtained fiber were a fineness of 2.00 dtex, a breaking strength of 3.25 cN / dtex, and a breaking elongation of 39%. In addition, the low molecular weight component having a molecular weight of less than 10,000 in the fiber is 0.90%, the residual solvent amount is 0.58%, the dry heat shrinkage at 300 ° C. is 2.3%, and in a 20 mass% sulfuric acid aqueous solution at 25 ° C. The strength retention after holding for 600 hours was 68%. Table 1 shows the physical properties of the fibers.

[Production of skin material]
The meta-type wholly aromatic polyamide fiber obtained above was subjected to indentation crimping and cut to a fiber length of about 51 mm to produce a short fiber cotton. After the obtained cotton is opened, needle punching is performed under the conditions of a needle density of 150 / cm ² and a needle depth of 14 mm, and only a meta-type wholly aromatic polyamide short fiber having a basis weight of 100 g / m ² and a thickness of 0.8 mm is obtained. A nonwoven fabric made of

[Production of sound absorbing material]
Using a Tarajin para-aramid fiber (Twaron (registered trademark)) staple (1.7 dtex × 50 mm), a needle punch method, a basis weight of 400 g / m ² , a thickness of 10 mm, a bulk density of 0.04 g / A non-woven fabric of cm ³ was prepared. The obtained nonwoven fabric and the skin material obtained above were laminated and integrated by bonding with metal pins to obtain a sound absorbing material. Table 1 shows the change rate of the sound absorption coefficient of the obtained sound absorbing material.

<Example 2>
A polymetaphenylene isophthalamide was prepared in the same manner as in Example 1 except that the solvent used was changed to N, N-dimethylacetamide (hereinafter abbreviated as DMAc) to produce a polymer solution and this was used as the spinning solution. A fiber was produced. Table 1 shows the physical properties of the obtained fiber.
In addition, a sound-absorbing material was produced in the same manner as in Example 1 using the obtained fiber. Table 1 shows the evaluation of the obtained sound absorbing material.

<Example 3>
[Spinning liquid adjustment process]
In a reaction vessel under a dry nitrogen atmosphere, 721.5 parts by mass of N-methyl-2-pyrrolidone (NMP) having a moisture content of 100 ppm or less was placed, and metaphenylenediamine (hereinafter abbreviated as MPDA) 97.2 was contained in this NMP. A part by mass (50.18 mol%) was dissolved and cooled to 0 ° C. To the cooled diamine solution, 181.3 parts by mass (49.82 mol%) of isophthalic acid chloride (hereinafter abbreviated as IPC) was added while gradually stirring to carry out the polymerization reaction. After the change in viscosity stopped, stirring was continued for another 40 minutes.
Subsequently, 66.6 parts by mass of calcium hydroxide powder (average particle size of 10 μm or less) was added to the polymer solution in which the polymerization reaction was completed, and a neutralization reaction was performed. After the addition of calcium hydroxide was completed, the mixture was further stirred for 40 minutes to obtain a transparent polymer solution. Polymetaphenylene isophthalamide was isolated from the obtained polymer solution, and the reduced viscosity (IV) was measured and found to be 1.30. The polymer concentration of the polymer solution was 20% by mass.

[Spinning and coagulation process]
The obtained polymer solution was used as a spinning solution and spun from a spinneret having a hole diameter of 0.06 mm and a hole number of 5000 into a coagulation bath having a bath temperature of 40 ° C. The composition (mass ratio) of the coagulation bath was water / NMP = 45/55, and spinning was performed by discharging into the coagulation bath at a yarn speed of 7 m / min.

[Plastic stretching bath stretching process]
Subsequently, the film was stretched at a stretch ratio of 5.0 in a plastic stretching bath. The composition (mass ratio) of the plastic stretching bath was water / NMP = 40/60, and the temperature was 40 ° C.

[Washing process]
Subsequent to the plastic stretching, it was washed with a 20 ° C. water / NMP = 70/30 bath (immersion length 5 m) at a yarn speed of 35 m / min, followed by a 20 ° C. water bath (immersion length 15 m). It was thoroughly washed by passing it through a warm water bath (immersion length: 15 m).

[Saturated steam treatment process]
Subsequently, heat treatment with saturated steam was performed at a draw ratio of 1.1 times in a container kept at a saturated steam pressure of 0.05 MPa. At this time, various conditions were adjusted so that the fiber bundle was treated with saturated steam for about 1.0 second.

[Dry heat treatment process]
The washed drawn yarn is wound around a drying roller having a surface temperature of 120 ° C. and dried, and subsequently subjected to a dry heat drawing treatment by 1.2 times with a heat roller having a surface temperature of 360 ° C. to obtain polymetaphenylene isophthalamide fiber. Obtained.

[Fiber properties]
Table 1 shows the physical properties of the obtained fiber.

[Production and evaluation of sound absorbing material]
Using the obtained fiber, a sound absorbing material was produced in the same manner as in Example 1. Table 1 shows the evaluation of the obtained sound absorbing material.

<Example 4>
Except that the solvent to be used was changed to N, N-dimethylacetamide (DMAc), a polymer solution to be a spinning solution was produced in the same manner as in Example 3, and the obtained polymer solution was used as the spinning solution. Similarly, polymetaphenylene isophthalamide fiber was obtained. Table 1 shows the physical properties of the obtained fiber.
In addition, a sound-absorbing material was produced in the same manner as in Example 1 using the obtained fiber. Table 1 shows the evaluation of the obtained sound absorbing material.

<Comparative Example 1>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that a coagulation bath having a composition of 125 ° C. and NMP / water / CaCl ₂ = 18/42/40 was used. The sound absorbing material was obtained. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

<Comparative Example 2>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that a coagulation bath having a temperature of 115 ° C. and a composition of DMAc / water / CaCl ₂ = 18/42/40 was used. The sound absorbing material was obtained. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

<Comparative Example 3>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that a coagulation bath having a composition of 125 ° C. and NMP / water / CaCl ₂ = 18/42/40 was used. The sound absorbing material was obtained. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

<Comparative example 4>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that a coagulation bath having a temperature of 115 ° C. and a composition of DMAc / water / CaCl ₂ = 18/42/40 was used. The sound absorbing material was obtained. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

<Comparative Example 5>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that the plastic draw ratio was 1.25 times, and a sound absorbing material was obtained in the same manner as in Example 1. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

<Comparative Example 6>
A polymetaphenylene isophthalamide fiber was produced in the same manner as in Example 1 except that the saturated water vapor pressure in the saturated water vapor treatment step was 0.0 MPa, and the draw ratio during the saturated water vapor treatment was 1.0 times. A sound absorbing material was obtained in the same manner. Table 1 shows the physical properties of the obtained fibers and the evaluation results of the sound absorbing material.

Claims (3)

A sound absorbing material in which a skin material and a nonwoven fabric are laminated,
The skin material includes a meta-type wholly aromatic polyamide fiber as a main component,
The meta-type wholly aromatic polyamide fiber has a low molecular weight component content of less than 10,000 and a residual solvent content of 1.0% by mass or less and a dry heat shrinkage at 300 ° C. A sound-absorbing material having a rate of 3.0% or less and a breaking strength of 3.0 cN / dtex or more.   The sound absorbing material according to claim 1, wherein the meta-type wholly aromatic polyamide fiber has a strength retention of 60% or more after being immersed in a 20 mass% sulfuric acid aqueous solution at 25 ° C for 600 hours.   The sound absorbing material according to claim 1 or 2, wherein the sound absorbing material is for automobiles.