EP3636819A1

EP3636819A1 - Fiber structure, molded body and sound-absorbing material

Info

Publication number: EP3636819A1
Application number: EP18813160.1A
Authority: EP
Inventors: Kazuhisa Nakayama; Toru Ochiai; Kimihiko HOUHASHI; Yasuhiro Shirotani; Masahiro Sasaki; Yasutomi MATSUSHIMA
Original assignee: Kuraray Kuraflex Co Ltd
Current assignee: Kuraray Kuraflex Co Ltd
Priority date: 2017-06-08
Filing date: 2018-05-28
Publication date: 2020-04-15
Anticipated expiration: 2038-05-28
Also published as: EP3636819A4; JP7104695B2; CN110709552A; EP3636819B1; TWI759493B; TW201908166A; JPWO2018225568A1; WO2018225568A1

Abstract

Provided are a fiber structure which has moldability while having heat resistance, a molded body thereof, and a sound-absorbing material which uses the molded body. The fiber structure 12 comprises thermoplastic resin fibers formed from a thermoplastic resin having a glass transition temperature higher than or equal to 80°C, wherein the thermoplastic resin fibers have an average fiber diameter of smaller than or equal to 10 µm, and an elongation at break in at least one of a machine direction and a cross direction of the fiber structure is greater than or equal to 10%. The molded body 10 comprises at least the fiber structure 12 and a support 11. The molded body can cover an object 13 to be covered.

Description

CROSS REFERENCE TO THE RELATED APPLICATION

This application is based on and claims Convention priority to Japanese Patent Application No. 2017-113821 filed on June 8, 2017 in Japan, the entire disclosure of which is herein incorporated by reference as a part of this application.

TECHNICAL FIELD

The present invention relates to a fiber structure which has moldability while having heat resistance, a molded body thereof, and a sound-absorbing material which uses the molded body.

BACKGROUND OF THE INVENTION

Sound-absorbing materials have been conventionally used for many products, such as electrical products, construction wall materials, and vehicles. In particular, sound-absorbing materials are broadly used for vehicles, especially automobiles in order to reduce noises such as acceleration noise outside vehicle, idling noise, exhaust noise, or in order to prevent noises impeding inside vehicles. In particular, in engine areas where noise insulation is required, because of their exposure to high temperature, aluminum materials have been conventionally used as sound-absorbing materials to these parts. The aluminum materials control sound wave transmission by reflection of the sound by aluminum, the aluminum materials, however, are insufficient in sound absorption performance, so that sound-absorbing materials with higher sound-absorbing performance have been demanded.
As sound-absorbing materials excellent in sound absorption performance, fiber structures have been known. Patent Document 1 ( JP Patent No. 5819650 ) recites a sound-absorbing surface material formed of an embossed nonwoven fabric comprising melt-blown fibers.
Patent Document 2 ( JP Patent No. 5812786 ) recites a fiber structure which is excellent in heat resistance, that is a melt-blown nonwoven fabric comprising as the main component a fully aromatic polyester capable of forming liquid crystal in melt phase.

RELATED ART DOCUMENT

PATENT DOCUMENT

Patent Document 1 JP Patent No. 5819650
Patent Document 2 JP Patent No. 5812786

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

The fiber structure recited in Patent Document 1 was insufficient in moldability because embossing processing of the fiber structure is indispensable.
The fiber structure recited in Patent Document 2 enhances its strength by performing heat-treatment to the melt-blown nonwoven fabric for a long period. As the heated fibers are too firmly bonded because of the heat treatment, there is a room for improvement in moldability of the fiber structure.
For example, the sound-absorbing materials used under high temperature environments, such as car engine surroundings, are frequently demanded to have moldability in addition to heat resistance and sound absorption performance. In particular, as one construction of the sound-absorbing material, a sound-absorbing body comprising a bulky fibrous material is frequently used in combination with a sound-absorbing surface material which covers the surface of the sound-absorbing body. Although such a construction enables to achieve further improvement in sound absorption performance, since a sound-absorbing surface material has to be molded (shaped) in accordance with the shape of the sound-absorbing body, the sound-absorbing surface material has to have moldability, i.e., followability to other shape at the time of molding.
The object of the present invention is to provide a fiber structure which has moldability while being excellent in heat resistance, a molded body thereof, and a sound-absorbing material using such a fiber structure as well as molded body.

MEANS FOR SOLVING THE PROBLEM

The present inventors have conducted extensive studies for achieving the objects described above, and found the following problems. (1) Where a fiber structure with a small average fiber diameter is produced by spinning a resin having a high glass transition temperature (Tg) using a melt-blown method etc., it is necessary to carry out spinning with spinning nozzle or the like at high temperature conditions depending on the high glass transition temperature of the resin. As a result, fibers are firmly bonded in the obtained fiber structure to achieve enhanced strength of the fiber structure. Such a fiber structure, however, is deteriorated in moldability because of the firm bonding of fibers, resulting in deteriorated moldability for the required shape. (2) In order for a fiber aggregate with a small average fiber diameter to enhance its strength required at the time of subsequent process, the obtained fiber aggregate is ordinally subjected to post-processing, such as calendar processing or embossing processing, to make fibers bonded or fused. The post-processing can enhance bonding or fusing between fibers so as to increase strength of fiber structure, whereas flexibility of fiber movement in the fiber structure is rather deprived so that moldability of the fiber structure is reduced. In order to solve the above problems, the inventors of the present invention have further inquired and have finally found that (3) as for the fiber structure containing fibers of thermoplastic resin having a specific high glass transition temperature, a fiber structure not only having an extra-fine fiber structure and heat resistance but also achieving moldability can be obtained by forming a nonwoven primary fiber aggregate and carrying out entangling treatment of the primary fiber aggregate. Based on these findings, the present inventors have accomplished the present invention.
That is, the present invention may comprise the following aspects.

Aspect 1
A fiber structure containing thermoplastic resin fibers formed from a thermoplastic resin having a glass transition temperature higher than or equal to 80°C (preferably higher than or equal to 100°C, more preferably higher than or equal to 120°C, still more preferably higher than or equal to 150°C, particularly higher than or equal to 180°C), wherein the thermoplastic resin fibers have an average fiber diameter of smaller than or equal to 10 µm (for example, from 0.1 to 10 µm, preferably from 0.5 to 7 µm, more preferably from 1 to 5 µm, still more preferably from 1.5 to 4.5 µm, particularly preferably from 2 to 4 µm), and an elongation at break in at least one of a machine direction and a cross direction of the fiber structure is greater than or equal to 10% (preferably greater than or equal to 20%, more preferably greater than or equal to 30%).
Aspect 2
The fiber structure given in aspect 1, wherein the fiber structure has a total elongation at break in the machine direction and the cross direction of greater than or equal to 30% (preferably greater than or equal to 40%, more preferably greater than or equal to 50%, still more preferably greater than or equal to 60%).
Aspect 3
The fiber structure given in aspect 1 or 2, wherein the fiber structure has a strength at break in at least one of the machine direction and the cross direction of greater than or equal to 10 N/5 cm (preferably greater than or equal to 20 N/5 cm, more preferably greater than or equal to 30 N/5 cm, still more preferably greater than or equal to 50 N/5 cm, particularly preferably 100 N/5 cm).
Aspect 4
The fiber structure given in any one of aspects 1 to 3, wherein the fiber structure has an air permeability of 5 to 50 cm³/cm²/s (preferably lower than or equal to 30 cm³/cm²/s, more preferably lower than or equal to 20 cm³/cm²/s, still more preferably lower than or equal to 15 cm³/cm²/s) at a differential pressure of 125 Pa measured in accordance with Frazir type method described in JIS L 1913.
Aspect 5
The fiber structure given in any one of aspects 1 to 4, wherein the fiber structure has a basis weight of 10 to 100 g/m² (preferably 20 to 90 g/m², more preferably 40 to 80 g/m²).
Aspect 6
The fiber structure given in any one of aspects 1 to 5, wherein the fiber structure has a shrinkage percentage under heat of less than or equal to 60% (preferably less than or equal to 50%, more preferably less than or equal to 20%, still more preferably less than or equal to 10%, particularly preferably less than or equal to 5%) in at least one of the machine direction and the cross direction after the fiber structure is allowed to stand for 3 hours under atmosphere at 250°C.
Aspect 7
The fiber structure given in any one of aspects 1 to 6, wherein the thermoplastic resin fibers comprise liquid crystal polyester fibers.
Aspect 8
The fiber structure given in any one of aspects 1 to 7, wherein the fiber structure is a melt-blown nonwoven fabric subjected to entangling treatment.
Aspect 9
A production method for the fiber structure recited in any one of aspects 1 to 8, the production method comprising entangling a nonwoven primary fiber aggregate, wherein the nonwoven primary fiber aggregate comprises thermoplastic resin fibers having an average fiber diameter of smaller than or equal to 10 µm (for example from 0.1 to 10 µm, preferably from 0.5 to 7 µm, more preferably from 1 to 5 µm, still more preferably from 1.5 to 4.5 µm, particularly preferably from 2 to 4 µm), and the thermoplastic resin fibers are formed from a thermoplastic resin having a glass transition temperature of higher than or equal to 80°C (preferably higher than or equal to 100°C, more preferably higher than or equal to 120°C, still more preferably higher than or equal to 150°C, especially preferably higher than or equal to 180°C).
Aspect 10
The production method wherein the primary fiber aggregate may have a restricted fiber group in which restricted fibers have restricted movement and a non-restricted fiber group in which fibers are not substantially restricted their movement, and the entanglement process enables the fibers in the non-restricted fiber group to be stirred so as to form entangled portions and non-entangled portions in the fiber structure.
Aspect 11
A molded body which comprises at least the fiber structure recited in any one of aspects 1 to 8.
Aspect 12
The molded body obtained by heat-molding the fiber structure recited in any one of aspects 1 to 8.
Aspect 13
A molded body comprising at least the fiber structure recited in any one of aspects 1 to 8 and a support.
Aspect 14
The molded body given in aspect 13, wherein the support is a bulky fibrous material.
Aspect 15
A sound-absorbing material (acoustic insulation material) comprising at least the fiber structure as recited in any one of aspects 1 to 8 or the molded body as recited in any one of aspects 11 to 14.

According to the present invention, the MD direction (machine direction) means a feeding direction of a fiber structure at the time of manufacture, and the machine direction can be determined in view of the fiber orientation direction in the fiber structure. CD direction (cross direction) means a direction perpendicularly crossed with the Machine direction. Hereinafter, the Machine direction is sometimes referred to as longitudinal direction, the cross direction is also sometimes referred to as lateral direction or width direction. The present invention encompasses any combination of at least two features disclosed in the claims and/or the specification and/or the drawings. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention.

EFFECT OF THE INVENTION

According to one embodiment of the present invention, since entangling treatment is performed to a nonwoven primary fiber aggregate of heat-resistant fibers having a specific average fiber diameter, even if the fiber structure comprises fine fibers, it is possible to obtain a fiber structure that achieves not only heat resistance but also moldability. In the production method of the fiber structure, the fiber structure which achieves outstanding performances described above can be produced in an efficient way.
According to another embodiment of the present invention, a molded body utilizing the forming processability of the above-mentioned fiber structure can be obtained.
According to another embodiment of the present invention, the above-mentioned fiber structure can be used as a sound-absorbing material. The above fiber structure is applicable to portions used under high temperature environments, such as environment near automobile engine. Since the fiber structure can be molded into various shapes, it can be conveniently used as, for example, a sound-absorbing surface material and others. Accordingly, the sound-absorbing material constituting such a sound-absorbing moldable material can be used as a sound-absorbing material applicable to wider environment than those used in the conventional sound-absorbing materials and can have high forming flexibility.

BRIEF DESCRIPTION OF THE DRAWINGS

In any event, the present invention will become more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views.

FIG. 1 is a SEM (scanning electron microscope) photograph showing a cross-section of a fiber structure 1 in the thickness direction.
FIG. 2 is a cross sectional schematic view illustrating a cross-section of a molded body (sound-absorbing material) 10 according to the present invention in the thickness direction.
FIG. 3 is a schematic view illustrating a metallic mold used for evaluation of the moldability of the fiber structure in Examples.

DESCRIPTION OF EMBODIMENTS

The fiber structure according to the present invention is a fiber structure containing the thermoplastic resin fibers formed from a thermoplastic resin having a glass transition temperature of higher than or equal to 80°C.

Thermoplastic Resin Fiber

The thermoplastic resin fibers which constitute the fiber structure are fibers formed from a thermoplastic resin having a glass transition temperature of higher than or equal to 80°C.
In the present invention, the glass transition temperature (temperature at which polymer molecules begin their micro movement) is an index for heat resistance of thermoplastic resins, thus the fiber structure excellent in heat resistance can be obtained from thermoplastic resin fibers having a glass transition temperature of higher than or equal to 80°C.
The glass transition temperature can be determined by measuring the temperature dependence of loss tangent (tanδ) at a frequency of 10 Hz and an elevating temperature of 10°C/minute to find a peak temperature of the tanδ using a solid dynamic viscoelasticity measuring apparatus "Rheospectra DVE-V4" produced by Rheology Co. Ltd. Here, the peak temperature of tanδ is a temperature at which the first differential value of the change in tanδ with respect to the temperature is zero.
From the viewpoint of improving heat resistance of the fiber structure, the thermoplastic resin used for thermoplastic fibers preferably has a glass transition temperature of higher than or equal to 100°C, more preferably higher than or equal to 120°C, still more preferably higher than or equal to 150°C, particularly preferably higher than or equal to 180°C. As for the spinnability, the thermoplastic resin preferably has a glass transition temperature of lower than or equal to 250°C, and more preferably lower than or equal to 230°C.
The thermoplastic resin fibers are not particularly limited as long as they are formed from a thermoplastic resin having a glass transition temperature of higher than or equal to 80°C, and may include, for example, meta-aramid fibers, para-aramid fibers, melamine fibers, polybenzoxazole fibers, polybenzoimidazole fibers, polybenzothiazole fibers, an amorphous polyarylate fibers, polyether sulfone fibers, liquid crystal polyester fibers, polyimide fibers, polyether imide fibers, polyether ether ketone fibers, polyether ketone fibers,
polyether ketone ketone fibers, polyamideimide fibers, semi-aromatic polyamide fibers (for example, polyamide fibers comprising aliphatic diamine units and aromatic dicarboxylic acid units), polyphenylene sulfide fibers, and others. These fibers may be used alone and may be used as a mixture of two or more species.
The thermoplastic resin fibers according to the present invention are formed from a thermoplastic resin which has a glass transition temperature of higher than or equal to substantially 80°C, and may be a polymer blend with another polymer component as long as the polymer component does not spoil the effect of the present invention. Examples of such a polymer component may include thermoplastic polymers, such as a polyethylene terephthalate, a modified-polyethylene terephthalate, a polybutylene terephthalate, a polycyclohexynedimethylene terephthalate, a polyolefin, a polycarbonate, a polyamide, a fluoro-resin and other thermoplastic polymers; and a thermoplastic elastomer, and others. These polymer components may be used alone and may be used as a mixture of two or more species, as long as they do not spoil the function of the present invention.
Additives may be added in the thermoplastic resin fiber in the range which does not spoil the effect of the present invention. For example, as additives, there may be mentioned carbon black; a colorant such as dye and paints; inorganic fillers such as titanium oxide, kaolin, silica, and barium oxide; an antioxidant; an ultraviolet ray absorbent; and a light stabilizer; and other ordinally used additives.
Among these fibers, from viewpoints of melt-spinnability and heat resistance, preferred fibers may include liquid crystal polyester fibers, polyether imide fibers, polyphenylene sulfide fibers, semi-aromatic polyamide fibers (for example, polyamide fibers comprising terephthalic acid unit as the aromatic dicarboxylic acid unit and 1,9-nonandiamine unit and/or 2-methyl-1,8-octanediamine unit as the aliphatic diamine unit), and others.

Liquid Crystallinity Polyester Fiber

Liquid crystallinity polyester fiber (sometimes referred to as polyarylate-series liquid crystal resin fiber) can be obtained by melt-spinning liquid crystal polyester (LCP). The liquid crystal polyester comprises repeating structural units originating from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc. As long as the effect of the present invention is not spoiled, the repeating structural units originating from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids arc not limited to a specific chemical composition. The liquid crystal polyester may include the structural units originating from aromatic diamines, aromatic hydroxy amines, or aromatic aminocarboxylic acids in the range which does not spoil the effect of the present invention. For example, the preferable structural units may include units shown in Table 1.

Table 1

In the formula, X is selected from the following structures.

m is an integer from 0 to 2, Y is a substituent selected from hydrogen atom, halogen atoms, aryl groups, aralkyl groups, alkoxy groups, aryloxy groups, aralkyloxy groups.

Y independently represents, as from one substituent to the number of substituents in the range of the replaceable maximum number of aromatic ring, a hydrogen atom, a halogen atom (for example, fluorine atom, chlorine atom, bromine atom and iodine atom), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group and t-butyl group), an alkoxy group (for example, methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), an aryl group (for example, phenyl group, naphthyl group, etc.), an aralkyl group [benzyl group (phenylmethyl group), phenethyl group (phenylethyl group)], an aryloxy group (for example, phenoxy group etc.), an aralkyloxy group (for example, benzyloxy group etc.), and others.
As the preferable structural units, there may be mentioned structural units as described in Examples (1) to (18) shown in the following Tables 2, 3, and 4. It should be noted that where the structural unit in the formula is a structural unit which can show a plurality of structures, combination of two or more units may be used as structural units for a polymer.
In the structural units shown in Tables 2, 3, and 4, n is an integer of 1 or 2, among each of the structural units, n= 1 and n= 2 may independently exist, or may exist in combination; each of the Y1 and Y2 independently represents, hydrogen atom, a halogen atom, (for example, fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group, and t-butyl group, etc.), an alkoxy group (for example, methoxy group, ethoxy group, and isopropoxy group, n-butoxy group, etc.), an aryl group (for example, phenyl group, naphthyl group, etc.), an aralkyl group [benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.], an aryloxy group (for example, phenoxy group etc.), an aralkyloxy group (for example, benzyloxy group etc.), and others. Among these, the preferable Y may include a hydrogen atom, a chlorine atom, a bromine atom, and methyl group.
Z may include substitutional groups denoted by following formulae.
Preferable liquid crystal polyesters may comprise a combination of a structural unit having a naphthalene skeleton. Especially preferable one may include both the structural unit (A) derived from hydroxybenzoic acid and the structural unit (B) derived from hydroxy naphthoic acid. For example, the structural unit (A) may have a following formula (A), and the structural unit (B) may have a following formula (B). From the viewpoint of improvement in melt-spinnability, the ratio of the structural unit (A) and the structural unit (B) may be in a range of former/latter of 9/1 to 1/1, more preferably from 7/1 to 1/1, still preferably from 5/1 to 1/1.
The total proportion of the structural units of (A) and (B) may be, based on all the structural units, for example, greater than or equal to 65 mol %, more preferably greater than or equal to 70 mol %, and still more preferably greater than or equal to 80 mol %. The liquid crystal polyester having the structural unit (B) at a proportion of 4 to 45 mol % is especially preferred among polymers.
Further, as the constitution of liquid crystal polyester (polyarylate-series liquid crystal resin) for forming liquid crystal polyester fibers, a constitution comprising para-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid as the main components, or a constitution comprising para-hydroxybenzoic acid, 2-hydroxy 6-naphthoic acid, terephthalic acid, and biphenol as the main components are preferred.
The liquid crystal polyester may preferably have a melt-viscosity at 310 °C of lower than or equal to 20 Pa·s or less from the viewpoint of reduced oligomer generation at the time of polymerization as well as facilitation of finer fiber formation. In view of easier spinnability, liquid crystal polyester may preferably have a melt-viscosity at 310°C of higher than or equal to 5 Pa s.
The liquid crystal polyester suitably used in the present invention preferably has a melting point of in the range from 250 to 360°C, and more preferably from 260 to 320°C. The melting point here means a main absorption peak temperature measured and observed in accordance with JIS K7121 examining method using a differential scanning calorimeter (DSC; "TA3000" produced by Mettler). More concretely, after taking 10 to 20 mg of a sample into the above-mentioned DSC apparatus to enclose the sample in an aluminum pan, nitrogen as carrier gas is introduced at a flow rate of 100 cc/minute and a heating rate of 20°C/minute, the position of an appearing endothermic peak is measured. In some kinds of polymer, where a clear peak does not appear in the first run in the DSC measurement, after heating the sample to a temperature 50°C higher than the flow temperature expected with a heating rate of 50°C/minute so as to make the sample to be completely molten for 3 minutes, and the melt is quenched to 50°C at a rate of -80°C/minute. Subsequently, the quenched material is reheated at a heating rate of 20°C/minute, and the position of an appearing endothermic peak may be recorded.
As the liquid crystal polyester, there may be exemplified a fully aromatic polyester capable of forming liquid crystal in melt phase which comprises a copolymerization product of para-hydroxybenzoic acid and 6-hydroxy 2-naphthoic acid ("Vectra L type" produced by Polyplastics, Inc.).

Polyetherimide Fiber

Polyetherimide fibers can be obtained by melt-spinning polyether imide polymer (PEI). The polyetherimide may comprise an ether unit of aliphatic unit, alicycle unit, or aromatic unit and a cyclic imide unit as repeating structural units. As long as the effect of the present invention is not spoiled, the polyetherimide polymer may comprise a structure unit(s) other than cyclic imide unit and the ether bond unit. The structure unit(s) may include, for example, an aliphatic ester unit, an alicycle ester unit, or an aromatic ester unit, an oxycarbonyl unit, and others. The polyetherimide may be crystalline or amorphous, and preferably an amorphous polymer.
The polyetherimide polymer may be a polymer comprising a combination of repeating structural units as shown below. In the formula, R1 represents a divalent aromatic residue having 6 to 30 carbon atoms; R2 represents a divalent organic group selected from the group consisting of a divalent aromatic residue having 6 to 30 carbon atoms, an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 2 to 20 carbon atoms, and a polydiorganosiloxane group in which the chain is terminated by an alkylene group having 2 to 8 carbon atoms.
The preferable R1 and R2 include, for example, an aromatic residue and an alkylene group (e.g., m = 2 to 10) shown in the following formulae.
In the present invention, from the viewpoint of melt-spinnability and cost reduction, a preferable polymer may include a condensate of 2,2-bis4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride and m-phenylenediamine, having a structural unit shown by the following formula as a main constituent. Such an amorphous polyetherimide is available from SABIC Innovative Plastics Holding under the trademark of "ULTEM".
The resin forming a polyetherimide fiber may preferably contain a polymer having a unit represented by the above general formula at a proportion of greater than or equal to 50 mass %, more preferably greater than or equal to 80 mass %, still more preferably greater than or equal to 90 mass %, and particularly preferably greater than or equal to 95 mass %.
As the preferable polyetherimide, there may be used an amorphous polyetherimide having a melt viscosity of 900 Pa·s at a shear rate of 1200 sec^-1 at a temperature of 330°C using a capilograph 1B produced by Toyo Seiki Seisaku-sho, Ltd.

(Polyphenylene sulfide fiber)

Polyphenylene sulfide fibers can be obtained by melt-spinning polyarylene sulfide. The polyarylene sulfide may comprise a repeating structural unit of arylene sulfide represented by -Ar-S- (Ar is an arylene group). The arylene group may include p-phenylene, m-phenylene, naphthylene groups or others. From the viewpoint of heat resistance, preferable repeating structural unit may be p-phenylene sulfide.
The resin forming the polyphenylene sulfide fibers may preferably contain a polymer having an arylene sulfide repeating structural unit at a proportion of greater than or equal to 50 mass % based on the resin, preferably greater than or equal to 80 mass %, more preferably greater than or equal to 90 mass %.
The average fiber diameter of the thermoplastic resin fibers may be smaller than or equal to 10 µm from the viewpoint of sound absorption performance and moldability. In view of moldability, the average fiber diameter of the thermoplastic resin fibers may be preferably greater than or equal to 0.1 µm. The average fiber diameter of the thermoplastic resin fibers may be more preferably from 0.5 to 7 µm, still more preferably from 1 to 5 µm, further preferably from 1.5 to 4.5 µm, and particularly preferably from 2 to 4 µm.
In general, it is known that the air permeability can be used as an index for sound absorption performance of fiber structures, and lower the air permeability is, more excellent in sound absorption performance is. Where the fiber structure has an average fiber diameter of smaller than or equal to 10 µm, it is possible to achieve low air permeability of the fiber structure, resulting in enhanced sound absorption performance. Further, it also enables to reduce the thickness of fiber structure, so that the fiber structure having an improved moldability can be obtained. Furthermore, where the fiber structure has an average fiber diameter of greater than or equal to 0.1 µm, it is possible to achieve suitable strength required at the time of molding of the fiber structure, so that moldability of the fiber structure is improved.

Production Method for Fiber Structure

Next, a production method for the fiber structure of the present invention will be described.
The production method for the fiber structure according to the present invention includes an entangling step of performing entangling treatment on a nonwoven primary fiber aggregate containing thermoplastic resin fibers having an average fiber diameter of smaller than or equal to 10 µm. Here, the nonwoven primary fiber aggregate refers to a preliminary nonwoven fiber aggregate having weak bonding (adhesion) between fibers, or a preliminary fiber aggregate having a nonwoven shape in a state where fibers are not adhered to but entangled with each other. Weak adhesion between fibers can be confirmed, for example, by low strength at break per unit weight, or by fluffing occurring when the surface is rubbed with a finger.
In the production method for the fiber structure of the present invention, a later-described object to be subjected to the entangling treatment is formed from fine fibers having an average fiber diameter of smaller than or equal to 10 µm. Thus, the fiber diameter of the fine fibers is too small to be subjected to normal entangling treatment, so that a nonwoven primary fiber aggregate in which fibers are preliminarily adhered to each other in advance such that entangling treatment can be performed on the nonwoven primary fiber aggregate is preferably used.
As used herein, the term "bonding (adhesion)" refers to a state where fibers are softened by heating and deformed and engaged with each other by the force generated when the fibers overlap with each other at intersections thereof, and/or a state where the fibers are melted and integrated with each other. In some cases, "fusion" is used in the same meaning as "bonding (adhesion)".
Meanwhile, regarding a conventional fiber structure in which fibers are firmly fused to each other, even when entangling treatment is performed on the conventional fiber structure, the fibers basically do not move, and thus the elongation of the fiber structure cannot be improved.
The nonwoven primary fiber aggregate can be obtained, for example, as a direct-spun type nonwoven fabric of the above-described thermoplastic resin. The spinning means is not particularly limited as long as the nonwoven primary fiber aggregate can be formed, and, for example, a melt blowing method, a spunbonding method, an electro-spinning method, or the like is possible. The spinning method may be either melt spinning or solution spinning, but melt spinning is preferable from the viewpoint of controlling adhesiveness. Among them, the melt blowing method is preferable from the viewpoint that the production efficiency is excellent and the average fiber diameter can be reduced. The apparatus used for the melt blowing method is not particularly limited.
In the present invention, it is preferable to suppress excessive fusion between the fibers in the primary fiber aggregate. For example, in the case of spinning through direct spinning such as the melt blowing method, the degree of freedom of movement of the fibers can be increased by setting the temperature in the vicinity of a spinning nozzle or at a fiber collection surface to be low so as to deliberately suppress fusion between the fibers. Then by performing specific entangling treatment on the primary fiber aggregate, appropriate strength at break and elongation at break can be imparted to such a primary fiber aggregate. Thus, it is possible to impart the followability required at the time of molding while ensuring the strength required when handling the fiber structure. In addition, for the fiber structure of the present invention, from the viewpoint of increasing the degree of freedom of movement between the fibers and improving moldability, it is preferable not to perform post-processing such as calendering, roll pressing, and embossing after spinning.
In the case of the melt blowing method, a conventionally known melt blowing apparatus can be used as the spinning apparatus. Regarding the spinning nozzle to be used, from the viewpoint of suppressing nozzle clogging and breakage of extruded yarns, a nozzle hole diameter is preferably from 0.1 to 0.5 mm and further preferably from 0.12 to 0.35 mm.
Moreover, regarding the spinning nozzle to be used, from the viewpoint of good productivity and being able to suppress yarn breakage, the ratio (L/D) of a nozzle hole length and the nozzle hole diameter is preferably from 5 to 50 and further preferably from 8 to 45.
Moreover, the interval between nozzle holes (nozzle hole pitch) is preferably 0.2 to 1.0 mm and further preferably 0.25 to 0.75 mm. Where the interval between the nozzle holes is in the preferable range, fusion between the adjacent fibers at immediate extruded points can be suppressed, so that there are few yarn clumps, and the gaps between the fibers are appropriate, whereby excellent uniformity is achieved.
The spinning conditions can be appropriately set according to the type of resin forming the fibers. Spinning is preferably performed under conditions of a spinning temperature of 300 to 450°C, a hot air temperature of 300 to 450°C, and an air volume (per 1 m of nozzle length) of 5 to 30 Nm³/min.
Moreover, from the viewpoint of improving the degree of freedom of the fibers in the nonwoven primary fiber aggregate, the temperature in the vicinity of the spinning nozzle and the temperature at the collection surface may be set to be lower than usual as necessary. For example, in the case of polyetherimide, the temperature in the vicinity of the spinning nozzle may be set to about 20 to 80°C. In addition, the temperature at the collection surface may be set to about 50 to 150°C. For other resins, as necessary, the temperature in the vicinity of the spinning nozzle may be a low temperature in the range of 100 to 200°C with respect to the glass transition temperature. In addition, the temperature at the collection surface may be a low temperature in the range of 100 to 200°C with respect to the glass transition temperature. These temperatures may be low temperatures in the range of 50 to 150°C.
Moreover, from the viewpoint of improving the degree of freedom of the fibers in the nonwoven primary fiber aggregate and enhancing an effect of later-described entangling treatment, the fiber fusion ratio of the nonwoven primary fiber aggregate may be less than or equal to 90%, preferably less than or equal to 70%, more preferably less than or equal to 30%, further preferably less than or equal to 10%, and particularly preferably less than or equal to 5%. Here, the fiber fusion ratio (%) can be obtained by the same method as for a later-described fiber fusion ratio of the fiber structure of the present invention.
The method of the entangling treatment is not particularly limited as long as the fibers can be pushed (shoved) in the thickness direction of a premolded body to improve the moldability of the fiber structure, and the method may be a spunlace method, a needle punching method, or the like, and the spunlace method is particularly preferable from the viewpoint of being able to impart more excellent moldability to the fiber structure.
In the case of the spunlace method, for example, by performing entangling treatment using a nozzle having orifices provided therein at a specific interval, the fiber structure has portions that are particularly exposed to water flow and portions that are not relatively exposed to water flow so as to generate entangled portions and non-entangled portions, respectively.
At the time of the entangling treatment, a punching drum and/or a net support may be used as a support for the fiber structure. For example, the punching drum is preferable from the viewpoint of facilitating partial exposure of the fiber structure to water flow. The net support is preferable from the viewpoint of easily adjusting an entanglement ratio.
For example, in the case of performing entangling treatment by the spunlace method, the primary fiber aggregate after spinning is placed on a punching drum support having a specific aperture ratio and hole diameter and continuously transferred in the longitudinal direction (machine direction), and, at the same time, high-pressure water flow is jetted from above, using a nozzle having orifices provided therein at a specific interval, to perform the entangling treatment, whereby the fiber structure can be produced.
In this case, the entanglement ratio of the fiber structure can also be adjusted on the basis of the interval between the orifices of the nozzle, the aperture ratio and the hole diameter of the support such as a punching drum or a net support, etc. For example, the net support may have a plain weave shape, and, for example, may have a fiber diameter of about from 0.10 to 1.50 mm and a mesh of about from 5 to 100 (yarns/inch), preferably a mesh of about from 7 to 50 (yarns/inch).
Moreover, the entangling treatment may be performed a plurality of times. For example, the fibers forming the primary fiber aggregate may be loosen by preliminary entangling treatment (pre-entangling treatment) in the first half, to increase the degree of freedom of the fibers, and the loosen fibers may be subjected to movement of fibers by entangling treatment in the second half, to impart a predetermined elongation to the fiber structure. In this case, the water pressure in the entangling treatment to be performed last (main entangling treatment) may be higher than the water pressure in the entangling treatment to be performed first, and, for example, the water pressure in the last entangling treatment may be about 2 to 8 times the water pressure in the first entangling treatment, and may be preferably about 2.5 to 5 times the water pressure in the first entangling treatment. In this case, a different support may be used in each entangling treatment. For example, entangling treatment may be preferably performed using a punching drum as a support, and then performed using a net support. By performing entangling treatment at a plurality of times, favorable entangling treatment may be performed on the fiber structure so as to obtain a fiber structure having improved moldability.
FIG. 1 is a SEM (scanning electron microscope) photograph showing a cross-section, in the thickness direction of a fiber structure 1 according to Example 2 of the present invention, obtained by cutting the fiber structure 1 in a cross direction. In FIG. 1, regions 2 having widths indicated by white arrows are entangled portions, and other regions 3 are non-entangled portions.
In the present invention, the "entangled portion" refers to a portion where the fibers are pushed (shoved) in the thickness direction of the fiber structure as a result of the above entangling treatment being performed. When a cross-section of the fiber structure is observed using a SEM or the like, a region where the fibers are pushed in the thickness direction is observed as an entangled portion distinguished from a non-entangled portion.
Moreover, in entangled portions, more fibers tend to be oriented in the thickness direction than in non-entangled portions, and entangled portions and non-entangled portions may be distinguished from each other by using such characteristics as a secondary basis for judgment.
For example, in the case of the spunlace method, in the fiber structure, locations where water flow has passed most strongly are observed as entangled portions since the fibers are pushed in the thickness direction at the locations. In addition, in the case of the needle punching method, a location where the fibers are pushed in the thickness direction due to passing of a needle is observed as an entangled portion.
The non-entangled portion is a portion where the entangling treatment is not performed and the fibers are almost unpushed (unshoved) in the thickness direction. For example, in the case where the fiber structure is a melt-blown nonwoven fabric, if entangling treatment is not particularly performed on a melt-blown-spun fiber web, the entirety of the fiber structure becomes a non-entangled portion, and, if entangling treatment is performed partially on the melt-blown-spun fiber web, for example, if the melt-blown-spun fiber web is entangled by partially passing water flow such as using a nozzle having orifices provided therein at a specific interval, portions where the water flow does not pass and the state of the fibers has not substantially changed from the time of spinning are non-entangled portions.
Moreover, in a fiber structure in which fibers are firmly fused to each other, even if entangling treatment is performed in a region, the fibers are not pushed in the thickness direction, so that such a region is also regarded as a non-entangled portion.
In the present invention, entangled portions and non-entangled portions preferably coexist in the fiber structure by subjecting the fiber structure to be partially entangled. In such a case, when the fiber structure is visually observed, the entangled portions may be overserved as a dot state where the entangled portions are similar to scattered holes on at least one surface.
In the present invention, the "entanglement ratio" is a proportion of entangled portions in the entirety of the fiber structure, and is specifically a value obtained by a method described in EXAMPLES. The entanglement ratio can be appropriately set as long as a predetermined elongation at break is imparted to the fiber structure. The entanglement ratio of the fiber structure is preferably greater than or equal to 5%. If the entanglement ratio is less than 5%, the elongation at break required at the time of molding is not exhibited, and thus good moldability is not obtained in some cases. The entanglement ratio is more preferably greater than or equal to 10%, still more preferably greater than or equal to 20%, and further preferably greater than or equal to 40%. In addition, from the viewpoint of moldability, the entanglement ratio is preferably less than or equal to 90%, more preferably less than or equal to 80%, and further preferably less than or equal to 70%. Where the fiber structure has an appropriate entanglement ratio as a result of performing the entangling treatment, the fiber structure can have an elongation at break that is sufficient for handleability. Moreover, where entanglement between the fibers is increased by the entangling treatment, the strength at break of the fiber structure can be also improved. The followability required at the time of molding is exhibited by the entangling treatment, so that the fiber structure can have improved moldability. In the entangling treatment, the entanglement ratio imparted to the fiber structure is not particularly limited. For example, if the entanglement ratio is less than or equal to 90%, the fiber structure has further improved moldability because the fiber structure has entangled portions and non-entangled portions. In other words, coexistent of both the portions that do not easily stretch and the portions that easily stretch makes it possible to impart appropriate strength and elongation required at the time of molding.

Fiber Structure

The fiber structure contains the above-described thermoplastic resin fibers having an average fiber diameter of smaller than or equal to 10 µm, and an elongation at break of greater than or equal to 10% in at least one of the machine direction and the cross direction of the fiber structure. The shape of the fiber structure can be selected according to the application thereof, but is normally a sheet shape or a plate shape.
Moreover, regarding the elongation at break of the fiber structure, from the viewpoint of moldability, the elongation at break in at least one of the machine direction and the cross direction of the fiber structure is greater than or equal to 10%. The elongation at break is more preferably greater than or equal to 20% and further preferably greater than or equal to 30%. In addition, each of the elongations at break in the machine direction and the cross direction is preferably greater than or equal to 5% and more preferably greater than or equal to 10%. Moreover, the total of the elongations at break in the machine direction and the cross direction is preferably greater than or equal to 30%, and may be, preferably, greater than or equal to 40%, more preferably greater than or equal to 50%, and further preferably greater than or equal to 60%. Furthermore, the total of the elongations at break in the machine direction and the cross direction may be greater than or equal to 100%.
Moreover, regarding the strength at break of the fiber structure, from the viewpoint of moldability and handleability, the fiber structure may have a strength at break of preferably greater than or equal to 10 N/5 cm, and may be more preferably greater than or equal to 20 N/5 cm, further preferably greater than or equal to 30 N/5 cm in at least one of the machine direction and the cross direction, much more preferably greater than or equal to 55 N/5 cm, and particularly preferably greater than or equal to 100 N/5 cm. From the viewpoint of improving flexibility in molding, each of the strengths at break in the machine direction and the cross direction of the fiber structure may be greater than or equal to 10 N/5 cm, preferably greater than or equal to 20 N/5 cm, and more preferably greater than or equal to 30 N/5 cm.
The air permeability of the fiber structure can be used as an index of sound absorption performance of the fiber structure, and the lower the air permeability is, the better the sound absorption performance is. Thus, the air permeability at a differential pressure of 125 Pa measured in accordance with the Frazir type method described in JIS L 1913 is preferably less than or equal to 50 cm³/cm²/s, and may be, more preferably less than or equal to 40 cm³/cm²/s, still more preferably less than or equal to 30 cm³/cm²/s, further preferably less than or equal to 20 cm³/cm²/s, and particularly preferably less than or equal to 15 cm³/cm²/s. In addition, from the viewpoint of suppressing reflection of sound and enhancing sound absorption performance, the air permeability is preferably greater than or equal to 5 cm³/cm²/s. If the air permeability is excessively low, sound is reflected, which is disadvantageous in sound absorption performance in some cases.
From the viewpoint of improving handleability while contributing to weight reduction, the basis weight of the fiber structure may be, for example, 10 to 100 g/m², and may be preferably 20 to 90 g/m² and more preferably 30 to 80 g/m².
From the viewpoint of heat resistance, the fiber structure may have a shrinkage percentage under heat of less than or equal to 60% in at least one of the machine direction and the cross direction of when the fiber structure is heat-treated at 250°C for 3 hours, and preferably less than or equal to 55%, more preferably less than or equal to 50%, still more preferably less than or equal to 20%, further preferably less than or equal to 10%, and particularly preferably less than or equal to 5%. In addition, the fiber structure may preferably have shrinkage percentages under heat in any of the above-described ranges in each of the machine direction and the cross direction.
In order to have high followability, the fiber structure according to the present invention may preferably have a structure in which the fibers are not adhered to each other, a structure in which the fibers are adhered to each other with low adhesive strength, or a structure in which the fibers are adhered to each other with a small adhesion area. As a result, the fiber structure can exhibit high followability because of weak bonding strength by the adhesion between the fibers and flexible positional relationship between the fibers.
The fiber structure according to the present invention may have a fiber fusion ratio of less than or equal to 90%, preferably less than or equal to 70%, more preferably less than or equal to 30%, further preferably less than or equal to 10%, and particularly preferably less than or equal to 5%. Here, in a photograph obtained by photographing a cross-section in the thickness direction of the fiber structure at a magnification of 1000 times using a scanning electron microscope, the fiber fusion ratio (%) can be calculated as the proportion of the number of fiber cut surfaces (fiber cross-sections) of fused fibers based on the total number of fiber cut surfaces visually observed. The proportion of the number of fiber cross-sections where two or more fibers are fused, based on the total number of fiber cross-scctions that can be seen in each region is represented as a percentage on the basis of the following equation: $Fiber fusion ratio (%) = (the number of fiber cross-sections where two or more fibers are fused) / (total number of fiber cross-sections) \times 100 .$
For each photograph, all of the fibers whose cross-sections can be seen are counted. If the number of fiber cross-sections is less than or equal to 100, a photograph to be observed is added such that the total number of fiber cross-sections exceeds 100. In addition, if it is difficult to identify individual fiber cross-sections since the fibers are partially dense and fused with each other, the number of fiber cross-sections may be obtained by dividing an estimated area of the fused fiber surfaces by the average fiber diameter.
The thickness of the fiber structure is not particularly limited, but, from the viewpoint of moldability, the thickness of the fiber structure may be, for example, smaller than or equal to 5 mm, preferably smaller than or equal to 1.0 mm, more preferably smaller than or equal to 0.80 mm, and further preferably smaller than or equal to 0.60 mm. In addition, from the viewpoint of sound absorption performance and strength, the thickness of the fiber structure may be preferably greater than or equal to 0.01 mm, more preferably greater than or equal to 0.05 mm, and further preferably greater than or equal to 0.10 mm.
Moreover, a plurality of the fiber structures of the present invention may be used in combination. In this case, the total thickness of the plurality of the fiber structures, for example, may be smaller than or equal to 100 mm, smaller than or equal to 50 mm, or smaller than or equal to 10 mm.

Molded Body

The molded body of the present invention contains at least a fiber structure. For example, the molded body may be a molded body obtained by a plurality of fiber structures being integrated with each other by adhesion or the like, or may be a molded body containing at least a fiber structure and a support. Even if the fiber structure according to the present invention is formed from fine fibers, the fiber structure has a predetermined elongation, and thus the handleability of the fiber structure at the time of molding can be improved. Accordingly, the fiber structure can be molded into a desired shape, while preventing occurrence of wrinkles in the fiber structure.
The molded body of the present invention is useful, for example, for covering a to-be-covered surface having a non-flat surface (a curved surface or a stepped surface) by using the moldability of the fiber structure.
In the molded body, a fiber structure may be integrated with an adhesive, or the molded body may be obtained by heat-molding the fiber structure by means of the thermoplastic property of the fiber structure. In the case of the molded body obtained by heat-molding, since the fiber structure of the present invention has improved moldability, the fiber structure can be transformed (molded) into a desired shape. Heat-molding enables to impart a desired molded shape to the fiber structure, at the same time, the fibers are fusion with each other, thereby obtaining a molded body in which the molded shape is fixed and to which strength is imparted.
Moreover, in the case of heat-molding the fiber structure according to the present invention, heating in the molding process makes it possible to fuse the fibers to each other in a state where a molded shape is maintained. As a result, a molded body that has a molded shape and that also has strength equivalent to that of a conventional fiber structure can be obtained.
Moreover, in the molded body including at least the fiber structure and a support, the fiber structure and the support may be integrated with each other by an adhesive, or may be integrated with each other by thermal pressure bonding of either the fiber structure or the support.
FIG. 2 is a schematic cross-sectional view of a molded body 10 including at least a fiber structure 12 and a support 11. The fiber structure is adhered or fused to the support 11 in order to improve handleability 12 since the fiber structure is formed from fine fibers. In FIG. 2, the fiber structure 12 is disposed on one surface of the support 11, but the fiber structure 12 may be disposed on each of both surfaces of the support 11. In addition, the molded body 10 may have a structure in which multiple supports and multiple fiber structures are alternately combined with each other.
The support 11 can be appropriately selected depending on the application as long as the support 11 can support the fiber structure 12, and the support 11 may be, for example, a film-shaped support, a porous support, or the like, and may be particularly a bulky fibrous material formed from fibers (a bulky fiber aggregate) or the like.
The molded body 10 can cover an object 13 to be covered on a to-be-covered surface. The molded body 10 excellent in moldability can favorably cover the to-be-covered surface, for example, even if the to-be-covered surface has a non-flat surface (for example, a curved surface or a stepped surface).
Since the fiber structure of the present invention has both heat resistance and moldability, the molded body including the fiber structure can be molded into a desired shape, and is useful as, for example, various materials in the industrial materials field, the medical/sanitary materials field, electrical and electronic field, the construction/civil engineering field, the agricultural material field, the aircraft/automobile/ship field, and the like, as, for example, interior materials, packaging materials, sanitary materials, especially, covering materials, etc.

Sound-Absorbing Material

Next, a sound-absorbing material in which a fiber structure is used will be described. An embodiment of the sound-absorbing material of the present invention will be described using FIG. 2. In FIG. 2, the above-described molded body 10 corresponds to a sound-absorbing material 10, the support 11 corresponds to a sound absorbing body 11, the fiber structure 12 corresponds to a sound-absorbing surface material 12, and the object 13 to be covered corresponds to an object 13.
The sound-absorbing material 10 in FIG. 2 includes the sound absorbing body 11 and the sound-absorbing surface material 12. In the case of the embodiment of FIG. 2, the sound absorbing body 11 is, for example, a bulky fibrous material formed from fibers, and the sound-absorbing surface material 12 is the fiber structure 1 according to the present invention. As described above, the sound-absorbing surface material 12 enhances the sound absorption performance and the durability of the sound-absorbing material 10 by covering the surface of the sound absorbing body 11.
The sound-absorbing material 10 is used such that, for example, the sound-absorbing material 10 is attached to the object 13 which is a sound absorbing target. Thus, it is necessary to mold the shape of the sound-absorbing material 10 according to the surface shape of the object 13, and the sound-absorbing surface material 12 (fiber structure 1) particularly needs to have followability with respect to the shape of the object which is a sound absorbing target, or the shape of the sound absorbing body.
Moreover, since the fiber structure of the present invention has excellent heat resistance and sound absorption performance and also has moldability, the fiber structure of the present invention can be suitably used, for example, for sound-absorbing materials for vehicles such as automobiles, trains, airplanes, ships, two-wheeled vehicles, helicopters, and submarines, can be suitably used particularly for sound-absorbing materials for automobiles, for example, automotive interior components such as ceiling materials, dashboards, and carpets, and can also be suitably used for an under cover, a bulk head, an engine head cover, and the like near engine surroundings. Furthermore, the sound-absorbing material of the present invention can be suitably used for electrical products such as vacuum cleaners, dishwashers, washing machines, dryers, refrigerators, microwave ovens, multifunctional microwave ovens, air conditioners, heaters, audio systems, TV sets, sewing machines, photocopiers, telephones, facsimiles, personal computers, and word processors, construction materials such as wallpapers, floorings, tatami mats, ceiling materials, roofing materials, house wraps, and heat insulating materials, civil engineering materials such as highway soundproof walls, Shinkansen (high-speed rails) soundproof walls, tunnel water shielding sheets, and railway ground reinforcement materials, etc.
Moreover, it is possible to use the fiber structure of the present invention at any portion of a sound-absorbing material. For example, in the case where a sound-absorbing material is composed of a sound absorbing body and a sound-absorbing surface material, the fiber structure of the present invention can be used as the sound absorbing body as well as as the sound-absorbing surface material. In particular, the fiber structure of the present invention can be suitably used as a sound-absorbing surface material that requires not only small thickness but also heat resistance and sound absorption performance and moldability to be molded according to the shape of the sound absorbing body.
In the case where the sound-absorbing material that comprises a sound absorbing body and a sound-absorbing surface material, where the fiber structure of the present invention is used as the sound-absorbing surface material, the species of the sound absorbing body is not particularly limited, and may be any bulky fibrous material or the like. The sound absorbing body may be, for example, glass wool or felt. The sound absorption performance and the heat resistance of the sound-absorbing material can be improved by laminating the fiber structure of the present invention on the bulky fibrous material.
It is known among those skilled in the art that there is a so-called "tunnel" between the driver's seat and the passenger seat especially in automobiles, and this "tunnel" is a section that is close to the engine area so as to become hot and also to be a source of noise. The conventional art has not successfully provided a suitable sound-absorbing material used in the "tunnel", the material which is superior in sound absorption performance than aluminum material. Since the fiber structure of the present invention has moldability while enabling sound absorption performance and heat resistance, the fiber structure of the present invention can be suitably used in the "tunnel" or the like so as to provide a sound-absorbing material that allows flexible design in shape, moldability, strength, etc., as compared to aluminum material or the like. Therefore, the fiber structure of the present invention has a much wider application range than the conventional sound-absorbing materials in terms of temperature environment, shape, etc., while having high strength comparable to that of the conventional fiber structure depending on the molding conditions. Thus, the technical significance of the fiber structure of the present invention is extremely high.

EXAMPLES

Hereinafter, the present invention will be described based on Examples. In addition, the present invention is not limited to these Examples, modifications and variations of these Examples can be made based on the gist of the present invention, and they are not excluded from the scope of the present invention.
Each physical property value in Examples and Comparative Examples was measured by a method described below.

Measurement of Basis Weight

According to "6 Test methods 6.2 Mass per unit area (ISO method)" in "Test methods for nonwovens" of JIS L 1913, a fiber structure was cut into a size of 2.5 cm wide × 25 cm long and measured, and a basis weight (g/m²) was calculated from the measurement values.

Measurement of Thickness

According to "6 Test methods 6.1 Thickness (ISO method)" in "Test methods for nonwovens" of JIS L 1913, the thickness (mm) of a fiber structure was measured at a pressing pressure of 12 g/cm² with a measuring instrument having a pressing plate with a diameter of 1 inch.

Measurement of Apparent Density

An apparent density (g/cm³) was calculated from the value of the measured basis weight and the value of the measured thickness using the following equation (1). $Apparent density (g / {cm}^{3}) = basis weight / thickness$

Measurement of Strength at Break and Elongation at Break

According to "6 Test methods 6.3 Tensile strength and elongation" in "Test methods for nonwovens" of JIS L 1913, strength at break (tensile strength) and elongation at break (elongation) were measured. The strength at break was measured in a machine direction (flow direction of a fiber structure, hereinafter also referred to as longitudinal direction) and in a cross direction (direction transverse to the machine direction, hereinafter also referred to as lateral direction or width direction).

Measurement of Air Permeability

According to "6 Test methods 6.8 Permeability (JIS method) 6.8.1 Frazir type method" in "Test methods for nonwovens" of JIS L 1913, air permeability (permeable property) was measured at a differential pressure of 125 Pa.

Measurement of Shrinkage Percentage Under Heat

A fiber structure that was cut in a size of 150 mm in the machine direction and 150 mm in the cross direction, and four dots in total were put on the cut fiber structure at positions away in both the machine direction and the cross direction by 50 mm from the intersection of the diagonal lines of the fiber structure as a center. After the fiber structure was allowed to stand for 3 hours at 250°C under atmosphere, the distance x (mm) between the dots in the machine direction and the distance y (mm) between the dots in the cross direction were measured, and a MD shrinkage percentage under heat "a" (%)and a CD shrinkage percentage under heat "b" (%)were calculated from the following equations, respectively. $MD shrinkage percentage under heat ‶ a ″ (%) = x / 100 \times 100$
$CD shrinkage percentage under heat ‶ b ″ (%) = y / 100 \times 100$
A fiber structure having a width (length in the cross direction) of 10 mm was cut in the cross direction, and the cross-section thereof was observed with a scanning electron microscope at a magnification of 50 times. The width (length in the cross direction) "z" (mm) of an entangled portion observed in the fiber structure having a width of 10 mm, and an entanglement ratio "c" (%) was calculated by the following equation. When an entangled portion had a tapered shape in the observation region, the length of the longest portion in the cross direction was regarded as "z". $Entanglement ratio c (%) = z (mm) / 10 (mm) \times 100$

Measurement of Average Fiber Diameter

A test piece (length × width = 5 cm × 5 cm) was taken from a fiber structure, and a central portion (portion centered on the intersection of diagonal lines) on a surface of the test piece was photographed at a magnification of 1000 times using a scanning electron microscope (SEM). A circle with a radius of 30 cm was drawn so as to be centered on the center (intersection of the diagonal lines) of the obtained photograph, 100 fibers were randomly selected from the inside of the circle, the fibers at or close to a central portion in the length direction were measured with calipers, and the average of the measurement values was calculated and regarded as an average fiber diameter (number average fiber diameter). Upon measurement, all the fibers shown in the SEM photograph were used as targets without distinguishing whether each of the fibers shown in the photograph was located on the outermost surface of the fiber structure or within the fiber structure, and the average fiber diameter (µm) was obtained.

Evaluation of Moldability

A fiber structure was molded using a mold (a mold frame 21 and a mold upper lid 22) schematically shown in FIG. 3, the appearance of the molded fiber structure was observed, and the moldability of the fiber structure was evaluated according to the following criteria.
Good: No wrinkles and the like are seen on the appearance.
Poor: Wrinkles, holes, etc., are seen on the appearance.

Example 1

Production of Fiber Structure

A fully aromatic polyester capable of forming liquid crystal in melt phase (VECTRA L type, manufactured by Polyplastics Co., Ltd.), a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid having a glass transition temperature (Tg) of 193°C, a melting point of 300°C and a melt viscosity at 310°C of 15 Pa·s, was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.15 mm, L/D (ratio of nozzle hole length to nozzle hole diameter) = 30, and 4000 holes per 1 meter of width (interval of 0.25 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.05 g/minute, a resin temperature of 310°C, a hot air temperature of 310°C, and 35 Nm³/minute to obtain a nonwoven fabric (primary fiber aggregate) having a basis weight of 60 g/m². The nonwoven fabric had a value of 0.4 N·m²/g that was a value calculated from strength at break (N) in the cross direction per 5 cm of width divided by the basis weight (g/m²), and the adhesive strength between fibers was very weak.
This nonwoven fabric was placed on a punching drum support with an aperture ratio of 25% and a hole diameter of 0.3 mm, and was continuously transferred in the longitudinal direction (machine direction) at a speed of 30 m/minute. At the same time, high-pressure water flow was jetted from above to perform pre-entangling treatment, to produce a fiber web (nonwoven fabric). Upon the entangling treatment, two nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used (the distance between the adjacent nozzles was 20 cm), the water pressure of high-pressure water flow jetted from the first-row nozzle was set to 3.0 MPa, and the water pressure of high-pressure water flow jetted from the second-row nozzle was set to 5.0 MPa.
The obtained nonwoven fabric was placed on a plain-woven net support having a fiber diameter of 0.90 mm and a mesh of 10 (yarns/inch) and being flat as a whole and was transferred continuously, and, at the same time, high-pressure water flow was jetted to the other surface of the nonwoven fabric to perform main entangling treatment, thereby transferring the irregularities of the net to the surface of the nonwoven fabric. In the entangling treatment, by using three nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web, the entangling treatment was performed under a condition of a water pressure of 10.0 MPa of high-pressure water flow from each nozzle. Furthermore, the nonwoven fabric was dried at 135°C to obtain a fiber structure.

Example 2

Production of Fiber Structure

A fully aromatic polyester capable of forming liquid crystal in melt phase (VECTRA L type, manufactured by Polyplastics Co., Ltd.), a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid having a melting point of 300°C and a melt viscosity at 310°C of 15 Pa·s, was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.15 mm, L/D = 30, and 4000 holes per 1 meter of width (interval of 0.25 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.05 g/minute, a resin temperature of 310°C, a hot air temperature of 310°C, and 35 Nm³/minute to obtain a nonwoven fabric (primary fiber aggregate) having a basis weight of 60 g/m².
This nonwoven fabric was placed on a punching drum support with an aperture ratio of 25% and a hole diameter of 0.3 mm, and was continuously transferred in the longitudinal direction (machine direction) at a speed of 30 m/minute. At the same time, high-pressure water flow was jetted from above to perform pre-entangling treatment, to produce a fiber web (nonwoven fabric). Upon the entangling treatment, two nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used (the distance between the adjacent nozzles was 20 cm), the water pressure of high-pressure water flow jetted from the first-row nozzle was set to 2.0 MPa, and the water pressure of high-pressure water flow jetted from the second-row nozzle was set to 4.0 MPa.
The obtained nonwoven fabric was placed on a plain-woven net support having a fiber diameter of 0.90 mm and a mesh of 10 (yarns/inch) and being flat as a whole and was transferred continuously, and, at the same time, high-pressure water flow was jetted to the other surface of the nonwoven fabric to perform main entangling treatment, thereby transferring the irregularities of the net to the surface of the nonwoven fabric. In the entangling treatment, three nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used, and the entangling treatment was performed under a condition of a water pressure of 6.0 MPa of high-pressure water flow from each nozzle. Furthermore, the nonwoven fabric was dried at 135°C to obtain a fiber structure.

Example 3

Production of Fiber Structure

An amorphous polyetherimide having a melt viscosity at 330°C of 900 Pa·s was used, extruded using an extruder, fed to a melt blowing apparatus having a nozzle with a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length)/D = 10, and a nozzle hole pitch of 0.75 mm, and discharged at a single-hole discharge rate of 0.09 g/minute, a spinning temperature of 420°C, a hot air temperature of 420°C, and 10 Nm³/minute per 1 m of nozzle width. During this time, the direct distance "d" between the tip of the spinning nozzle and a receiving surface of a roller receiving the spun fibers was 10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned on a hemispherical outer periphery of a radius x = 5 cm centered on the tip of the spinning nozzle was 41°C. Furthermore, the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned 1 cm from a collection surface on the straight line relative to the direct distance "d" between the tip of the spinning nozzle and the collection surface of the spun fibers was 110°C. In this way, a nonwoven fabric (primary fiber aggregate) having a basis weight of 50 g/m² was obtained. The strength at break (N) in the cross direction per 5 cm of width of this nonwoven fabric was very weak and was not able to be measured.
This nonwoven fabric was placed on a punching drum support with an aperture ratio of 25% and a hole diameter of 0.3 mm, and was continuously transferred in the longitudinal direction (machine direction) at a speed of 30 m/minute. At the same time, high-pressure water flow was jetted from above to perform pre-entangling treatment, to produce a fiber web (nonwoven fabric). Upon the entangling treatment, two nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used (the distance between the adjacent nozzles was 20 cm), the water pressure of high-pressure water flow jetted from the first-row nozzle was set to 3.0 MPa, and the water pressure of high-pressure water flow jetted from the second-row nozzle was set to 5.0 MPa.
The obtained nonwoven fabric was placed on a plain-woven net support having a fiber diameter of 0.90 mm and a mesh of 10 (yarns/inch) and being flat as a whole and was transferred continuously, and, at the same time, high-pressure water flow was jetted to the other surface of the nonwoven fabric to perform main entangling treatment, thereby transferring the irregularities of the net to the surface of the nonwoven fabric. In the entangling treatment, three nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used, and the entangling treatment was performed under a condition of a water pressure of 10.0 MPa of high-pressure water flow from each nozzle. Furthermore, the nonwoven fabric was dried at 135°C to obtain a fiber structure.

Example 4

Production of Fiber Structure

An amorphous polyetherimide having a melt viscosity at 330°C of 900 Pa·s was used, extruded using an extruder, fed to a melt blowing apparatus having a nozzle with a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length)/D = 10, and a nozzle hole pitch of 0.75 mm, and discharged at a single-hole discharge rate of 0.09 g/minute, a spinning temperature of 420°C, a hot air temperature of 420°C, and 10 Nm³/minute per 1 m of nozzle width. During this time, the direct distance "d" between the tip of the spinning nozzle and a receiving surface of a roller receiving the spun fibers was 10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned on a hemispherical outer periphery of a radius x = 5 cm centered on the tip of the spinning nozzle was 41°C. Furthermore, the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned 1 cm from a collection surface on the straight line relative to the direct distance "d" between the tip of the spinning nozzle and the collection surface of the spun fibers was 110°C. In this way, a nonwoven fabric (primary fiber aggregate) having a basis weight of 50 g/m² was obtained.
This nonwoven fabric was placed on a punching drum support with an aperture ratio of 25% and a hole diameter of 0.3 mm, and was continuously transferred in the longitudinal direction (machine direction) at a speed of 30 m/minute. At the same time, high-pressure water flow was jetted from above to perform pre-entangling treatment, to produce a fiber web (nonwoven fabric). Upon the entangling treatment, two nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used (the distance between the adjacent nozzles was 20 cm), the water pressure of high-pressure water flow jetted from the first-row nozzle was set to 2.0 MPa, and the water pressure of high-pressure water flow jetted from the second-row nozzle was set to 4.0 MPa.
The obtained nonwoven fabric was placed on a plain-woven net support having a fiber diameter of 0.90 mm and a mesh of 10 (yarns/inch) and being flat as a whole and was transferred continuously, and, at the same time, high-pressure water flow was jetted to the other surface of the nonwoven fabric to perform main entangling treatment, thereby transferring the irregularities of the net to the surface of the nonwoven fabric. In the entangling treatment, three nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used, and the entangling treatment was performed under a condition of a water pressure of 6.0 MPa of high-pressure water flow from each nozzle. Furthermore, the nonwoven fabric was dried at 135°C to obtain a fiber structure.

Comparative Example 1

Production of Fiber Structure

A fully aromatic polyester capable of forming liquid crystal in melt phase (VECTRA L type, manufactured by Polyplastics Co., Ltd.), a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid having a melting point of 300°C and a melt viscosity at 310°C of 15 Pa·s, was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.15 mm, L/D = 30, and 4000 holes per 1 meter of width (interval of 0.25 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.05 g/minute, a resin temperature of 310°C, a hot air temperature of 310°C, and 35 Nm³/minute to obtain a nonwoven fabric, and a fiber structure having a basis weight of 30 g/m² was obtained.

Comparative Example 2

Production of Fiber Structure

A fully aromatic polyester capable of forming liquid crystal in melt phase (VECTRA L type, manufactured by Polyplastics Co., Ltd.), a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid having a melting point of 300°C and a melt viscosity at 310°C of 15 Pa·s, was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.15 mm, L/D = 30, and 4000 holes per 1 meter of width (interval of 0.25 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.05 g/minute, a resin temperature of 310°C, a hot air temperature of 310°C, and 35 Nm³/minute to obtain a nonwoven fabric. Then, the nonwoven fabric was treated for 6 hours at 300°C in the air to obtain a fiber structure having a basis weight of 10 g/m².

Comparative Example 3

Production of Fiber Structure

A fully aromatic polyester capable of forming liquid crystal in melt phase (VECTRA L type, manufactured by Polyplastics Co., Ltd.), a copolymer of para-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid having a melting point of 300°C and a melt viscosity at 310°C of 15 Pa·s, was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.15 mm, L/D = 30, and 4000 holes per 1 meter of width (interval of 0.25 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.05 g/minute, a resin temperature of 310°C, a hot air temperature of 310°C, and 35 Nm³/minute to obtain a nonwoven fabric. Then, the nonwoven fabric was treated for 6 hours at 300°C in the air to obtain a nonwoven fabric having a basis weight of 10 g/m². The nonwoven fabric had a value of 1.9 N·m²/g that was a value calculated from strength at break (N) in the cross direction per 5 cm of width divided by the basis weight (g/m²), and the adhesive strength between fibers was strong.
This nonwoven fabric was placed on a punching drum support with an aperture ratio of 25% and a hole diameter of 0.3 mm, and was continuously transferred in the longitudinal direction (machine direction) at a speed of 30 m/minute. At the same time, high-pressure water flow was jetted from above to perform pre-entangling treatment, to produce a fiber web (nonwoven fabric). Upon the entangling treatment, two nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used (the distance between the adjacent nozzles was 20 cm), the water pressure of high-pressure water flow jetted from the first-row nozzle was set to 3.0 MPa, and the water pressure of high-pressure water flow jetted from the second-row nozzle was set to 5.0 MPa.
The obtained nonwoven fabric was placed on a plain-woven net support having a fiber diameter of 0.90 mm and a mesh of 10 (yarns/inch) and being flat as a whole and was transferred continuously, and, at the same time, high-pressure water flow was jetted to the other surface of the nonwoven fabric to perform main entangling treatment, thereby transferring the irregularities of the net to the surface of the nonwoven fabric. In the entangling treatment, three nozzles each having orifices with a hole diameter of 0.10 mm provided at an interval of 0.6 mm along the width direction (cross direction) of the web were used, and the entangling treatment was performed under a condition of a water pressure of 10.0 MPa of high-pressure water flow from each nozzle. Furthermore, the nonwoven fabric was dried at 135°C to obtain a fiber structure.

Comparative Example 4

Production of Fiber Structure

An amorphous polyetherimide having a melt viscosity at 330°C of 900 Pa·s was used, extruded using an extruder, fed to a melt blowing apparatus having a nozzle with a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length)/D = 10, and a nozzle hole pitch of 0.75 mm, and discharged at a single-hole discharge rate of 0.09 g/minute, a spinning temperature of 390°C, a hot air (primary air) temperature of 420°C, and 10 Nm³/minute per 1 m of nozzle width, to produce a nonwoven fabric. At this time, a hot air blowing apparatus was provided such that hot air (secondary air) was blown into the tip of the spinning nozzle of the melt blowing apparatus, and hot air (secondary air) at a temperature of 260°C was blown at an air volume of 2 Nm³/minute toward the tip of the spinning nozzle. The direct distance "d" between the tip of the spinning nozzle and the receiving surface of a roller receiving the spun fibers was 10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned on a hemispherical outer periphery of a radius x = 5 cm centered on the tip of the spinning nozzle was 253°C. Furthermore, the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned 1 cm from a collection surface on the straight line relative to the direct distance "d" between the tip of the spinning nozzle and the collection surface of the spun fibers was 261°C. In this way, a fiber structure having a basis weight of 25 g/m² was obtained.

Comparative Example 5

Production of Fiber Structure

An amorphous polyetherimide having a melt viscosity at 330°C of 900 Pa·s was used, extruded using an extruder, fed to a melt blowing apparatus having a nozzle with a nozzle hole diameter D (diameter) of 0.3 mm, L (nozzle length)/D = 10, and a nozzle hole pitch of 0.75 mm, and discharged at a single-hole discharge rate of 0.09 g/minute, a spinning temperature of 390°C, a hot air (primary air) temperature of 420°C, and 10 Nm³/minute per 1 m of nozzle width, to produce a nonwoven fabric. At this time, a hot air blowing apparatus was provided such that hot air (secondary air) was blown into the tip of the spinning nozzle of the melt blowing apparatus, and hot air (secondary air) at a temperature of 260°C was blown at an air volume of 2 Nm³/minute toward the tip of the spinning nozzle. The direct distance "d" between the tip of the spinning nozzle and the receiving surface of a roller receiving the spun fibers was 10 cm, and the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned on a hemispherical outer periphery of a radius x = 5 cm centered on the tip of the spinning nozzle was 253°C. Furthermore, the temperature measured by a thermometer (AD-5601A (manufactured by A&D Company, Limited)) provided so as to be positioned 1 cm from a collection surface on the straight line relative to the direct distance "d" between the tip of the spinning nozzle and the collection surface of the spun fibers was 261°C. In this way, a nonwoven fabric having a basis weight of 25 g/m² was obtained. The nonwoven fabric had a value of 1.0 N·m²/g that was a value calculated from strength at break (N) in the cross direction per 5 cm of width divided by the basis weight (g/m²), and the adhesive strength between fibers was strong.
Entangling treatment (pre-entangling treatment and main entangling treatment) was performed on the nonwoven fabric in the same manner as Example 1, to obtain a fiber structure.

Comparative Example 6

A semi-random web was produced by means of a carding method from liquid crystal polyester fibers ("VECTRAN", manufactured by Kuraray Co., Ltd.) having a fineness of 2.8 dtex and a fiber length of 51 mm. Entangling treatment was performed on the semi-random web in the same manner as Example 1, to obtain a fiber structure.

Comparative Example 7

Comparative Example 8

A semi-random web was produced by means of a carding method from polyetherimide fibers ("KURAKISSS", manufactured by Kuraray Co., Ltd.) having a fineness of 2.2 dtex and a fiber length of 51 mm. Entangling treatment was performed on the semi-random web in the same manner as Example 1, to obtain a fiber structure.

Comparative Example 9

Comparative Example 10

A polybutylene terephthalate resin (200FP, manufactured by Polyplastics Co., Ltd.) was extruded using a twin-screw extruder, fed to a melt-blowing apparatus having a nozzle with a nozzle hole diameter of 0.3 mm, L/D = 10, and a hole number of 3000 per 1 meter of width (interval of 0.75 mm between nozzle holes), and discharged at a single-hole discharge rate of 0.3 g/minute, a resin temperature of 290°C, a hot air temperature of 290°C, and 32 Nm³/minute to obtain a fiber structure.

The obtained fiber structures were measured for basis weight, thickness, apparent density, average fiber diameter, strength at break, elongation at break, air permeability, shrinkage percentage under heat, and entanglement ratio. The obtained results are shown in Table 5.

[Table 5]

			Ex. 1	Ex. 2	Ex. 3	Ex. 4	Com Ex. 1	Com Ex. 2	Com Ex. 3	Com Ex. 4	Com Ex. 5	Com Ex. 6	Com Ex. 7	Com Ex. 8	Com Ex. 9	Com Ex. 10
Resin			LCP	LCP	PEI	PEI	LCP	LCP	LCP	PEI	PEI	LCP	LCP	PEI	PEI	PBT
Tg of used resin		°C	193	193	217	217	193	193	193	217	217	193	193	217	217	50
Basis weight		g/m²	60	60	52	52	30	10	10	25	25	55	110	57	101	32
Thickness		mm/sheet	0.24	0.27	0.47	0.50	0.15	0.05	0.05	0.12	0.12	0.50	0.80	0.61	1.00	0.21
Density		g/cm³	0.25	0.23	0.11	0.10	0.20	0.22	0.23	0.21	0.20	0.11	0.14	0.09	0.10	0.15
Strength at break	MD	N/5cm	108.4	55.8	132.6	78.3	12.5	42.1	35.7	47.2	32.9	91.1	232.0	145.6	193.4	11.8
Strength at break	CD	N/5cm	62.4	62.7	37.7	31.9	10.7	18.9	13.6	25.1	13.3	36.0	112.9	68.8	95.8	11.0
Elongation at break	MD	%	18.6	12.0	58.6	23.7	1.5	3.0	2.9	9.0	4.3	46.7	37.4	108.5	131.7	10.5
	CD	%	47.3	51.7	124.1	131.2	1.6	5.3	8.6	9.0	4.2	94.8	72.2	172.9	195.3	10.7
	Total	%	65.9	63.7	182.7	154.9	3.1	8.3	11.5	18.0	8.5	141.5	109.6	281.4	327.0	21.2
Air Permeability (cm³/cm²/s) at differential pressure of 125 Pa			13.6	15.0	26.4	31.3	50.8	327.0	347.0	50.7	50.5	140.8	82.7	237.7	150.3	35.1
Heat shrinkage 250°C × 3h	MD	%	0	0	52	50	0	0	0	51	52	0	0	55	53	N.G. (molten)
Heat shrinkage 250°C × 3h	CD	%	0	0	42	41	0	0	0	41	40	0	0	59	58	N.G. (molten)
Entanglement ratio		%	62	45	60	43	0	0	0	0	0	43	59	45	60	0
Average fiber diameter (µm)			3.01	3.01	3.83	3.83	3.01	3.01	3.01	3.83	3.83	12.33	12.33	13.16	13.16	4.01
Moldability			Good	Good	Good	Good	Poor	Poor	Poor	Poor	Poor	Good	Good	Good	Good	Poor

LCP: liquid crystal polyester; PEI: polyetherimide; PBT: polybutylene terephthalate

As shown in Table 5, the fiber structures of Examples 1 to 4 containing a thermoplastic resin having a glass transition temperature higher than or equal to 80°C have high elongation at break, and exhibit good moldability. In addition, even if the basis weight of the fiber structures of Examples 1 to 4 was small, the fiber structures also have good strength at break.
On the other hand, regarding the fiber structure of Comparative Example 1 without subjecting to entangling treatment, the entanglement ratio thereof was 0%, the elongation at break was low, and the moldability was poor. In addition, the strength at break was very low as compared to those of the Examples, so that the handleability was also deteriorated. Furthermore, since the air permeability was also higher than those of the Examples, the fiber structure of Comparative Example 1 is considered to be inferior in terms of sound absorption performance.
The fiber structure of Comparative Example 2 had good strength at break due to the firmly fused fibers with each other by the heat treatment. However, the fiber structure had entanglement ratio of 0%, resulting in low elongation at break and deteriorated moldability. Furthermore, the air permeability was also higher than those of the Examples, and thus the fiber structure of Comparative Example 2 is considered to be inferior in terms of sound absorption performance.
As for Comparative Example 3 obtained by performing entangling treatment on the fiber structure of Comparative Example 2, since the fiber structure had firmly fused fibers with each other, the fiber structure had entanglement ratio of 0% because of no entangled portion even when performing entangling treatment. Similar to Comparative Example 2, the fiber structure had good strength at break. However, the fiber structure had low elongation at break, resulting in deteriorated moldability. Furthermore, the air permeability was also higher than those of the Examples, and thus the fiber structure of Comparative Example 3 is considered to be inferior in terms of sound absorption performance.
The fiber structure of Comparative Example 4 had firmly fused fibers with each other even at the time of spinning. Accordingly, the fiber structure had good strength at break, but low elongation at break, resulting in deteriorated moldability.
As for Comparative Example 5 obtained by performing entangling treatment on the fiber structure of Comparative Example 4, since the fiber structure had firmly fused fibers with each other, the fiber structure had entanglement ratio of 0% because of no entangled portion even when performing entangling treatment. Similar to Comparative Example 3, the fiber structure had good strength at break. However, the fiber structure had low elongation at break resulting in deteriorated moldability.
Comparative Example 6 was obtained by performing hydroentangling treatment using the liquid crystal polyester fiber web by the carding method, and the fiber structure had large average fiber diameter. As a result, the denseness of the fiber structure was not increased, so that the air permeability was higher than those of the Examples.
Comparative Example 7 was intended to make the basis weight higher than that in Comparative Example 6 to increase the denseness of the fiber structure. However, since the denseness of the fiber structure was not able to be increased, the fiber structure failed to have sufficiently decreased air permeability.
Comparative Examples 8 and 9 were obtained by performing hydroentangling treatment using the polyetherimide fiber web by the carding method. Similar to Comparative Examples 6 and 7, they have large average fiber diameters, so that the fiber structures were unable to have increased denseness, and had higher air permeabilities than those of the Examples.
As for the melt-blown nonwoven fabric of polybutylene terephthalate fibers in Comparative Example 10, since the glass transition temperature of the resin forming the fibers in the nonwoven fabric was low, heat resistance of the nonwoven fabric was not sufficient. Furthermore, the elongation at break was lower than those of the Examples, and thus, the moldability was deteriorated.
Moreover, the fiber structures of Examples 1 and 3 in which entangling treatment was performed at higher pressure had higher total elongation at break in the machine direction and the cross direction than those of the fiber structures of Examples 2 and 4. In addition, the fiber structures of Examples 1 and 3 show highest strength at break among the strengths at break in the machine direction and the cross direction, compared with the fiber structures of Examples 2 and 4. Further, the fiber structures of Examples 1 and 3 achieves lower air permeability than those of the fiber structures of Examples 2 and 4.
Furthermore, although heat shrinkage was occurred in Examples 3 and 4 when heating for 3 hours at 250°C exceeding the glass transition temperatures thereof, it is predicted that no heat shrinkage will occur when heating in a range not exceeding the glass transition temperature, for example, at 215°C or lower.

INDUSTRIAL APPLICABILITY

Since the fiber structure of the present invention has good moldability as well as heat resistance, the fiber structure of the present invention can be usefully applicable as a covering material that is used under high temperatures (for example, 100°C or higher, preferably 120°C or higher, more preferably 150°C or higher, further preferably 180°C or higher, particularly preferably 200°C or higher, particularly more preferably 230°C or higher). The fiber structure having particularly low permeability can be effectively used as a constituent material of a sound-absorbing material or the like.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included therein.

[Reference Numerals]

1, 12 ····: fiber structure (sound-absorbing surface material)
10 ····: molded body (sound-absorbing material)
11 ····: bulky fibrous material (sound absorbing body)

Claims

A fiber structure comprising thermoplastic resin fibers formed from a thermoplastic resin having a glass transition temperature higher than or equal to 80°C, wherein
the thermoplastic resin fibers have an average fiber diameter of smaller than or equal to 10 µm, and
an elongation at break in at least one of a machine direction and a cross direction of the fiber structure is greater than or equal to 10%.
The fiber structure according to claim 1, wherein the fiber structure has a total elongation at break in the machine direction and the cross direction of greater than or equal to 30%.
The fiber structure according to claim 1 or 2, wherein a strength at break in at least one of the machine direction and the cross direction of the fiber structure is greater than or equal to 10 N/5 cm.
The fiber structure according to any one of claims 1 to 3, wherein the fiber structure has an air permeability of 5 to 50 cm³/cm²/s at a differential pressure of 125 Pa measured in accordance with Frazir type method described in JIS L 1913.
The fiber structure according to any one of claims 1 to 4, wherein the fiber structure has a basis weight of 10 to 100 g/m².
The fiber structure according to any one of claims 1 to 5, wherein the fiber structure has a shrinkage percentage under heat of less than or equal to 60% in at least one of the machine direction and the cross direction after the fiber structure is allowed to stand for 3 hours under atmosphere at 250°C.
The fiber structure according to any one of claims 1 to 6, wherein the thermoplastic resin fibers comprise liquid crystal polyester fibers.
The fiber structure according to any one of claims 1 to 7, wherein the fiber structure is a melt-blown nonwoven fabric subjected to entangling treatment.
A production method for the fiber structure as claimed in any one of claims 1 to 8, the production method comprising:
entangling a nonwoven primary fiber aggregate,

wherein the nonwoven primary fiber aggregate comprises thermoplastic resin fibers having an average fiber diameter of smaller than or equal to 10 µm, and the thermoplastic resin fibers are formed from a thermoplastic resin having a glass transition temperature of higher than or equal to 80°C.
The production method according to claim 9, wherein the nonwoven primary fiber aggregate is produced by a melt blowing method, a spunbonding method, or an electro-spinning method.
A molded body comprising at least the fiber structure as claimed in any one of claims 1 to 8.
A molded body obtained by heat-molding the fiber structure as claimed in any one of claims 1 to 8.
A molded body comprising at least the fiber structure as claimed in any one of claims 1 to 8 and a support.
The molded body as claimed in claim 13, wherein the support is a bulky fibrous material.
A sound-absorbing material comprising at least the fiber structure as claimed in any one of claims 1 to 8 or the molded body as claimed in any one of claims 11 to 14.