JP2023027449A - Nonwoven fabric for sound absorption material, sound absorption material, and method of manufacturing nonwoven fabric for sound absorption material - Google Patents

Abstract

To provide a nonwoven fabric for a sound absorption material, the sound absorption material, and a method for manufacturing the nonwoven fabric for the sound absorption material that, in particular, excel in sound absorption performance in a low frequency range and in productivity.SOLUTION: There is provided a nonwoven fabric for a sound absorption material having a laminated structure composed of a nonwoven fabric A and a nonwoven fabric B, wherein the nonwoven fabric A contains fibers A with a mode of a single fiber diameter of 0.05 to 0.80 μm and fibers B with a mode of a single fiber diameter of 5.00 to 30.00 μm, and a number ratio of the fibers A to the fibers B in the nonwoven fabric A (the number of the fibers A to the number of the fibers B) is 94.0:6.0 to 99.5:0.5, and a difference between the mode of the single fiber diameter of the fibers A and that of the fibers B in the nonwoven fabric A (the mode of the single fiber diameter of the fibers B minus the mode of the single fiber diameter of the fibers A) is 4.00 to 28.00 μm, and the nonwoven fabric B contains 80 mass % or more of fibers C with a mode of a single fiber diameter of 5.00 to 30.00 μm for the whole nonwoven fabric B.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a nonwoven fabric for a sound absorbing material, a sound absorbing material, and a method for producing the nonwoven fabric for a sound absorbing material.

2. Description of the Related Art In recent years, quietness has become more important than ever as one of the commercial values of products in automobiles, electric appliances, and the like. Generally speaking, it is effective to increase the mass and thickness of sound absorbing materials, which are part of noise countermeasures. There is a demand for compactness and compactness. Furthermore, in the field of automobiles, there is a demand for heat resistance that can be applied around engines and the like.

Patent Document 1 proposes a sound absorbing material in which a porous sound absorbing material and a nanofiber nonwoven fabric are laminated. Further, Patent Document 1 discloses that the nanofiber nonwoven fabric has an average fiber diameter of less than 1 μm.

Further, Patent Document 2 proposes a method for manufacturing a sound absorbing structure in which short fibers having a single fiber diameter of 10 to 1000 nm are sprayed onto a fiber structure by a spray method.

Further, Patent Document 3 proposes a laminated nonwoven fabric having a skin layer having fibers with a single fiber diameter of 1 to 5000 nm and a base layer.

JP 2017-82346 A JP 2010-102236 A International Publication No. 2016/143857

According to the findings of the present inventors, the sound absorbing material disclosed in Patent Document 1, the sound absorbing structure disclosed in Patent Document 2, and the laminated nonwoven fabric disclosed in Patent Document 3 all contain ultrafine fibers. , the sound absorption performance tends to be relatively excellent.

However, Patent Document 1 has a configuration in which a multifilament is irradiated with a laser and a nanofiber nonwoven fabric having a single-layer structure generated by the vibration is laminated on a base nonwoven fabric, and there is a problem of poor productivity. In addition, in order to improve the sound absorbing performance of the sound absorbing material described in Patent Document 1, it is necessary to increase the basis weight of the nanofiber nonwoven fabric laminated on the base nonwoven fabric, resulting in poor productivity. . That is, the sound absorbing material described in Patent Document 1 has a problem that it is difficult to achieve both sound absorbing performance and productivity.

Further, Patent Document 2 has a configuration in which a dispersion of ultrafine fibers is sprayed onto a fiber structure by a spray method, and is inferior in productivity as described above. In addition, in order to make the sound absorption performance of the sound absorbing structure described in Patent Document 2 excellent, it is necessary to spray a large amount of a dispersion of ultrafine fibers on the fiber structure. A fiber layer needs to be formed on the fiber structure, resulting in poor productivity. That is, the sound absorbing structure described in Patent Document 2 also has a problem that it is difficult to achieve both sound absorbing performance and productivity.

In response to the problem that it is difficult to achieve both productivity and sound absorption performance, Patent Document 3 discloses a skin layer having a nanofiber layer and a thicker fiber layer. Since the nanofiber layer of is a dense layer consisting only of nanofibers, surface reflection of sound occurs, resulting in poor sound absorption performance. Therefore, the laminated nonwoven fabric described in Patent Document 3 also has the problem that it is difficult to achieve both sound absorption performance and productivity.

Therefore, in view of the above circumstances, the present invention provides a nonwoven fabric for sound absorbing material that can be used as a sound absorbing material having excellent sound absorbing performance (especially sound absorbing performance in the low frequency range) and excellent productivity, and the above sound absorbing material. An object of the present invention is to provide a sound absorbing material using a nonwoven fabric for sound absorption and a method for manufacturing the nonwoven fabric for sound absorbing material.

In order to solve the above problems, the present invention has the following configurations. i.e.
(1) It has a laminated structure of a nonwoven fabric A and a nonwoven fabric B, and the nonwoven fabric A includes a fiber A having a single fiber diameter mode of 0.05 to 0.80 μm and a single fiber diameter mode of 5. .00 to 30.00 μm of the fiber B, and the number ratio of the fiber A and the fiber B in the nonwoven fabric A (number of fiber A: number of fiber B) is 94.0: 6.0 to 99 .5: 0.5, and the difference in the mode of the single fiber diameter of the fiber A and the fiber B in the nonwoven fabric A (the mode of the single fiber diameter of fiber B - the maximum of the single fiber diameter of fiber A) frequency) is 4.00 to 28.00 μm, and the nonwoven fabric B contains 80% by mass or more of the fibers C having a single fiber diameter mode of 5.00 to 30.00 μm with respect to the entire nonwoven fabric B. It is a nonwoven fabric for sound absorbing material,
(2) The nonwoven fabric for sound absorbing material according to (1), wherein the fiber A has a single fiber diameter Cv value of 20% or less and the fiber B has a single fiber diameter Cv value of 15% or less. is preferred,
(3) The fabric weight ratio of the nonwoven fabric A and the nonwoven fabric B (the fabric weight of the nonwoven fabric A/the fabric weight of the nonwoven fabric B) is 0.5 to 1.7, and the fabric weight of the nonwoven fabric B is 70 to 200 g/m ^{2 .} It is preferable that the nonwoven fabric for sound absorbing material according to (1) or (2) is
(4) It is preferable that the nonwoven fabric for sound absorbing material according to any one of (1) to (3) has a density of 0.07 to 0.40 g/cm ³ ,
(5) of (1) to (4), wherein the tensile strength of the fibers B and the fibers C is 3 cN/dtex or more, and the initial tensile resistance of the fibers B and the fibers C is 30 cN/dtex or more; It is preferable that the nonwoven fabric for sound absorbing material according to any one of
(6) The nonwoven fabric for sound absorbing material according to any one of (1) to (5), wherein the fibers A, the fibers B, and the fibers C are polyester short fibers.

(7) The nonwoven fabric for a sound absorbing material according to any one of (1) to (6), and a layered material comprising a fibrous porous material, a foam, or an air layer, wherein the layered material is and a sound absorbing material laminated on one surface of the nonwoven fabric for sound absorbing material, wherein the layered material has a thickness of 5 to 50 mm.

(8) The method for producing a nonwoven fabric for sound absorbing material according to any one of (1) to (6), which includes the following steps (a) to (h).
(a) a step of spinning a sea-island composite fiber comprising two or more resins using a composite spinneret; (b) a step of crimping and cutting the sea-island composite fiber to obtain a sea-island composite staple fiber; ) The sea-island composite staple fibers and the staple fibers B having a mode of single fiber diameter of 5.00 to 30.00 μm are subjected to a fiber opening treatment to form a mixed fiber web of the sea-island composite staple fibers and the fibers B. Step (d) of obtaining a web of the fibers C by subjecting short fiber-shaped fibers C having a mode of single fiber diameter of 5.00 to 30.00 μm to obtain a web of the fibers C (e) the mixed fiber web and (f) subjecting the laminated web to entangling by a needle punching method or a water jet punching method to obtain a laminated nonwoven fabric; (g) applying the laminated nonwoven fabric to an alkaline Step (h) of removing the sea component from the sea-island composite short fibers with an aqueous solution to develop fibers A having a single fiber diameter mode of 0.05 to 0.80 μm; lamination after the step of (g); A process of drying the nonwoven fabric.

According to the present invention, by using ultrafine fibers having a predetermined fiber diameter, it is possible to provide a nonwoven fabric for sound absorbing material with excellent sound absorption performance (especially sound absorption performance in the low frequency range) and productivity.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.

The nonwoven fabric for sound absorbing material of the present invention has a laminated structure of the nonwoven fabric A and the nonwoven fabric B. The nonwoven fabric A contains fibers A having a single fiber diameter mode of 0.05 to 0.80 μm and fibers B having a single fiber diameter mode of 5 to 30 μm.

The nonwoven fabric A contains fibers A having a mode of single fiber diameter of 0.05 to 0.80 μm, so that the nonwoven fabric A can form a porous portion having a large number of fine pores. As a result, when sound passes through the voids (that is, the porous part) between the fibers, it can be efficiently converted into heat by air friction with the fibers around the voids, and when used as a sound absorbing material. excellent sound absorption can be obtained. In addition, since the nonwoven fabric A contains fibers B having a mode value of the single fiber diameter of 5.00 to 30.00 μm, the nonwoven fabric A containing the fibers A is suppressed from becoming dense and has appropriate voids. As a result, surface reflection of sound can be suppressed, sound can be efficiently converted into heat by air friction, and excellent sound absorption can be obtained when used as a sound absorbing material.

By setting the mode of the single fiber diameter of the fiber A to 0.05 μm or more, the surface reflection of sound on the surface of the nonwoven fabric A can be reduced, and the sound is absorbed by the air friction between the fiber A contained in the nonwoven fabric A and the sound. can enhance sexuality. On the other hand, by setting the mode value of the single fiber diameter of the fiber A to 0.80 μm or less, it is possible to enhance the sound absorption, particularly at low frequencies, due to the film vibration effect of the nonwoven fabric for sound absorbing material. In view of the above, the mode of the single fiber diameter of Fiber A is preferably 0.15 to 0.70 μm, more preferably 0.20 to 0.65 μm.

In addition, by setting the mode of the single fiber diameter of the fiber B to 5.00 μm or more, the nonwoven fabric A containing the fiber A is suppressed from becoming dense, and by having an appropriate void, the surface reflection of sound is reduced. sound can be efficiently converted into heat by air friction, and excellent sound absorption can be obtained when used as a sound absorbing material. On the other hand, by setting the mode of the single fiber diameter of the fiber B to 30.00 μm or less, it is possible to suppress the gap from becoming excessively large, and to efficiently convert sound into heat by air friction in the fine gap. , excellent sound absorption can be obtained when used as a sound absorbing material. In view of the above, the mode of the single fiber diameter of the fiber B is preferably 6.00 to 27.00 μm, more preferably 7.00 to 23.00 μm.

In the nonwoven fabric A of the present invention, the number ratio of the fibers A and the fibers B in the nonwoven fabric A (number of fibers A:number of fibers B) is 94.0:6.0 to 99.5:0.5, and , the difference in the mode of the single fiber diameters of the fibers A and B in the nonwoven fabric A (the mode of the single fiber diameter of the fiber B - the mode of the single fiber diameter of the fiber A) is 4.00 to 28. 00 μm. With the above configuration, the nonwoven fabric A can form a porous portion having a large number of fine pores, and by having an appropriate amount of voids, sound can be transmitted while suppressing surface reflection of sound. Sound can be efficiently converted into heat by air friction with the fibers when the material is used, and excellent sound absorption can be obtained when used as a sound absorbing material.

By setting the ratio of the number of fibers A to 94.0 or more when the total number of fibers A and B is 100, the number of fibers A increases with respect to the number of fibers B. It is possible to form a porous part with many fine holes inside, and it is possible to efficiently convert sound into heat by air friction with fibers when sound passes through, resulting in excellent sound absorption. can. On the other hand, when the total number of fibers A and B is 100, by setting the ratio of the number of fibers A to 99.5 or less, the number of fibers B increases with respect to the number of fibers A, so that the sound is reduced. It suppresses surface reflection, can efficiently convert sound into heat by air friction, and can provide excellent sound absorption when used as a sound absorbing material.

By setting the ratio of the number of fibers B to 0.5 or more when the total number of fibers A and B is 100, the number of fibers B increases with respect to the number of fibers A. It can have moderate voids inside, suppress surface reflection of sound, can efficiently convert sound into heat by air friction, and can obtain excellent sound absorption when used as a sound absorbing material. . On the other hand, by setting the ratio of the number of fibers B to 6.0 or less when the total number of fibers A and B is 100, the number of fibers A increases with respect to the number of fibers B, so that voids are formed. It is possible to suppress an excessive increase in size, efficiently convert sound into heat by air friction caused by fine voids, and obtain excellent sound absorption when used as a sound absorbing material. In view of the above, the number ratio of fibers A and fibers B in nonwoven fabric A (number of fibers A: number of fibers B) is preferably 97.0:3.0 to 99.5 to 0.5, More preferably 98.5:1.5-99.5-0.5.

The difference in the mode of the single fiber diameters of the fibers A and B in the nonwoven fabric A (the mode of the single fiber diameter of the fiber B - the mode of the single fiber diameter of the fiber A) should be 4.00 μm or more. As a result, fine voids for increasing air friction and voids for suppressing surface reflection of sound coexist inside nonwoven fabric A, and the sound entering inside nonwoven fabric A is heated by air friction. can be efficiently converted to, and excellent sound absorption can be obtained when used as a sound absorbing material. On the other hand, the difference in the mode of the single fiber diameters of the fibers A and B in the nonwoven fabric A (the mode of the single fiber diameter of the fiber B - the mode of the single fiber diameter of the fiber A) is 28.00 μm or less. By doing so, it is possible to suppress the gaps from becoming excessively large, and to efficiently convert sound into heat by air friction in the fine gaps, and to obtain excellent sound absorption when used as a sound absorbing material. In the above point, the difference in the mode of the single fiber diameters of the fiber A and the fiber B (the mode of the single fiber diameter of the fiber B - the mode of the single fiber diameter of the fiber A) is 6.00-25. 00 μm, more preferably 7.00 to 22.00 μm. The mode of the single fiber diameter referred to in the present invention is the maximum value in the distribution of the single fiber diameter.

The nonwoven fabric for sound absorbing material of the present invention comprising the nonwoven fabric A having the above structure has excellent sound absorbing performance (especially sound absorbing performance in the low frequency range) even if the basis weight of the nonwoven fabric A is small. will also be excellent. Therefore, with the nonwoven fabric for sound absorbing material of the present invention, it is possible to achieve both excellent sound absorbing performance and excellent productivity.

The nonwoven fabric for sound absorbing material of the present invention has a nonwoven fabric B, and the nonwoven fabric B contains 80% by mass or more of the fibers C having a single fiber diameter mode of 5.00 to 30.00 μm with respect to the entire nonwoven fabric B. . The nonwoven fabric B has the role of increasing the mass of the nonwoven fabric for sound absorbing material and improving the sound absorption of low frequencies, suppressing the dimensional change of the nonwoven fabric in the process of manufacturing the nonwoven fabric for sound absorbing material, and having the desired fine voids. Nonwoven fabric A is laminated to obtain a nonwoven fabric for lumber. By including the nonwoven fabric B, the mass of the nonwoven fabric for sound absorbing material can be increased, the resonance frequency in the membrane vibration sound absorbing effect can be shifted to low frequencies, and the low frequency sound absorption performance can be enhanced. In addition, since the nonwoven fabric B contains 80% by mass or more of the fibers C having a mode of single fiber diameter of 5.00 to 30.00 μm with respect to the whole nonwoven fabric B, The deformation of the nonwoven fabric due to the process tension in the process can be suppressed, and the nonwoven fabric for sound absorbing material with excellent sound absorption performance can be efficiently obtained without collapsing the uniform fine voids of the nonwoven fabric A, and the productivity can be improved. can. By setting the mode of the single fiber diameter of the fiber C to 5.00 μm or more, the deformation of the nonwoven fabric can be suppressed and the sound absorbing performance can be enhanced. On the other hand, by setting the mode of the single fiber diameter of the fiber C to 30.00 μm or less, it is possible to increase the entanglement of the nonwoven fabric and suppress the deformation of the nonwoven fabric in the needle punching or the entangling process using water flow, which will be described later, and improve the sound absorption performance. can be enhanced. In view of the above, the mode of the single fiber diameter of the fiber B is preferably 6.00 to 27.00 μm, more preferably 7.00 to 23.00 μm.

Further, the fiber C may be a fiber different from the fiber B as long as the mode of the single fiber diameter is 5.00 to 30.00 μm, but the productivity of the nonwoven fabric for sound absorbing material is more excellent. It is preferable that the fiber C is the same fiber as the fiber B because it is the same fiber.

The Cv value of the single fiber diameter of the fiber A of the present invention is preferably 20% or less, and the Cv value of the single fiber diameter of the fiber B is preferably 15% or less. By reducing the Cv value of the single fiber diameter of each fiber, that is, the variation in the single fiber diameter, fine and uniform voids are formed between the fibers A and B in the interior of the nonwoven fabric A. It can efficiently convert sound into heat by air friction, and when used as a sound absorbing material, excellent sound absorption can be obtained. In view of the above, the Cv value of the single fiber diameter of the fiber A is preferably 15% or less, more preferably 10% or less. The Cv value of the single fiber diameter of the fiber B is preferably 10% or less, more preferably 8% or less. The Cv value of single fiber diameter in the present invention is calculated by the following formula after measuring the single fiber diameter of each fiber with a scanning electron microscope (SEM).
Cv value of single fiber diameter (%) = (standard deviation of single fiber diameter / average value of single fiber diameter) x 100 (%)
The basis weight ratio of nonwoven fabric A and nonwoven fabric B (nonwoven fabric A/nonwoven fabric B) is 0.5 to 1.7, and the basis weight of nonwoven fabric B is 70 to 200 g/m ² . is preferred. By setting the basis weight ratio of nonwoven fabric A and nonwoven fabric B to 0.5 or more, sound can be efficiently converted into heat by air friction with fibers due to fine voids in nonwoven fabric A, and it can be used as a sound absorbing material. Excellent sound absorption can be obtained when On the other hand, by setting the weight ratio between the nonwoven fabric A and the nonwoven fabric B to 1.7 or less, deformation of the nonwoven fabric due to process tension in the manufacturing process of the nonwoven fabric for sound absorbing material, especially in the sea removal process, is suppressed, and the nonwoven fabric A is uniform. It is possible to efficiently obtain a nonwoven fabric for a sound absorbing material with excellent sound absorbing performance without collapsing the fine voids, thereby increasing the productivity. In view of the above, the ratio of basis weight between nonwoven fabric A and nonwoven fabric B is preferably 0.6 to 1.5, more preferably 0.65 to 1.3. In addition, by setting the basis weight of the nonwoven fabric B to 70 g/m ² or more, the mass of the nonwoven fabric for sound absorbing material can be increased, the resonance frequency in the membrane vibration sound absorbing effect can be shifted to a low frequency, and the low frequency sound absorption performance while suppressing deformation of the nonwoven fabric due to process tension in the manufacturing process of the nonwoven fabric for sound absorbing material, especially in the sea removal process, without collapsing the uniform fine voids of the nonwoven fabric A, and having excellent sound absorbing performance. can be obtained efficiently and productivity can be improved. On the other hand, by setting the basis weight of the nonwoven fabric B to 200 g/m ² or less, it is possible to increase the entanglement of the nonwoven fabric, suppress the deformation of the nonwoven fabric, and improve the sound absorption performance in the needle punching or the entangling process using water flow, which will be described later. . In view of the above, the nonwoven fabric B preferably has a basis weight of 75 to 180 g/m ² , more preferably 80 to 160 g/m ² .

The density of the nonwoven fabric for sound absorbing material of the present invention is preferably 0.07 to 0.40 g/cm ³ . By setting the density to 0.07 g/cm ³ or more, the nonwoven fabric for sound absorbing material has a dense structure, fine voids are formed by the fibers A and B, and sound is more efficiently converted into heat by air friction. As a result, when the nonwoven fabric for sound absorbing material is used as a sound absorbing material, the sound absorbing performance becomes more excellent. Furthermore, on the other hand, by setting the density to 0.40 g/cm ³ or less, the surface reflection of sound is suppressed by having moderate voids, and the sound that enters the interior of the nonwoven fabric for sound absorbing material is reduced by air friction. It can be efficiently converted into heat, and when used as a sound absorbing material, it can improve its excellent sound absorbing performance. From the above points, the density is preferably 0.09 to 0.35 g/cm ³ , more preferably 0.10 to 0.32 g/cm ³ .

The tensile strength of the fibers B and C of the present invention is preferably 3 cN/dtex or more, and the initial tensile resistance of the fibers B and C is preferably 30 cN/dtex or more. By setting the tensile strength and the initial tensile resistance of the fibers B and C within the ranges described above, deformation of the nonwoven fabric during the manufacturing process of the nonwoven fabric for sound absorbing material, particularly in the sea removal process, is suppressed, and the nonwoven fabric A is uniformly fine. It is preferable because it is possible to efficiently obtain a nonwoven fabric for a sound absorbing material having excellent sound absorbing performance without collapsing the voids, and furthermore, it is possible to increase the productivity. In view of the above, it is more preferable that the fibers B and C have a tensile strength of 3.3 cN/dtex or more, and that the fibers B and C have an initial tensile resistance of 34 cN/dtex or more. The upper limits of the tensile strength and the initial tensile resistance of the fibers B and C are not particularly limited, but the tensile strength is preferably 10 cN/dtex or less in order to increase the entanglement of the nonwoven fabric and suppress the deformation of the nonwoven fabric. , the initial tensile resistance of the fiber B is preferably 80 cN/dtex or less.

Thermoplastic resins such as polyester-based resins, polyamide-based resins, acrylic-based resins, and polyolefin-based resins can be used for the materials that constitute the fibers A, fibers B, and fibers C of the present invention. Among these, both fiber A and fiber B are made of polyester resin in that they have excellent heat resistance, that is, they can reduce deformation and discoloration in high-temperature environments of nonwoven fabrics for sound absorbing materials when used in engine rooms of automobiles. It is preferable that the fibers (polyester fibers) are made of polyester resin, and short fibers (polyester short fibers) made of a polyester resin are preferable in terms of efficiently dispersing the fibers by the carding process described later. Among them, short fibers made of polyethylene terephthalate resin (polyethylene terephthalate short fibers), which are particularly excellent in heat resistance, are preferred in terms of heat resistance and productivity.

Next, a preferred manufacturing method for manufacturing the nonwoven fabric for sound absorbing material of the present invention will be described. A preferred method for producing the nonwoven fabric for sound absorbing material of the present invention includes the following steps.

(Production of conjugate fiber as precursor of fiber A)
(a) A step of spinning a sea-island composite fiber comprising two or more resins using a composite spinneret.
(b) A step of crimping and cutting sea-island composite fibers to obtain sea-island composite staple fibers.

(Manufacture of laminated nonwoven fabric)
(c) Sea-island composite short fibers and short fiber-shaped fibers B having a mode of single fiber diameter of 5.00 to 30.00 μm (hereinafter referred to as short fibers B) are subjected to a fiber opening treatment to obtain a sea-island composite. A step of obtaining a mixed fiber web of short fibers and short fibers B;
(d) A step of subjecting short fibers C having a mode of single fiber diameter of 5.00 to 30.00 μm to an opening treatment to obtain a web of short fibers C;
(e) A step of laminating a mixed fiber web of sea-island composite staple fibers and staple fibers B and a web of staple fibers C to obtain a laminated web.
(f) A step of entangling the laminated web by a needle punching method or a water jet punching method to obtain a laminated nonwoven fabric.

(Manufacturing nonwoven fabric for sound absorbing material)
(g) A step of removing the sea component of the sea-island composite fiber from the laminated nonwoven fabric with an alkaline aqueous solution to develop the fiber A;
(h) A step of drying the laminated nonwoven fabric after the sea removal treatment.

Details of these steps (a) to (h) will be described below.

(Production of conjugate fiber as precursor of fiber A)
First, (a) the step of spinning a sea-island composite fiber composed of two or more resins using a composite spinneret will be described. In the process of spinning a composite fiber, the resin that constitutes the island component and the resin that constitutes the sea component are separately melted and weighed, and the sea component and the island component are put into a spinning pack using a distribution plate with distribution holes. A sea-island composite fiber can be obtained by injecting a molten resin and discharging a composite polymer flow from a discharge hole for melt spinning and drawing.

Next, in the step (b) of crimping and cutting the sea-island composite fibers to obtain sea-island composite staple fibers, the sea-island composite fibers are heated, introduced into a crimper to be mechanically crimped, and then rotated. The sea-island composite staple fiber can be obtained by cutting it into a predetermined length with a cutter.

(Manufacture of laminated nonwoven fabric)
Next, the step (c) of subjecting the sea-island composite staple fibers and the staple fibers B to an opening treatment to obtain a mixed fiber web of the sea-island composite staple fibers and the staple fibers B will be described. First, the step of opening the sea-island composite staple fibers and the staple fibers B (opener step) included in the above steps will be described. In the opener step, the sea-island composite short fibers and the short fibers B (hereinafter also referred to as short fibers) are weighed so that the content of the fibers A and the content of the fibers B in the nonwoven fabric for sound absorbing material are as desired. Using air or the like, each short fiber is sufficiently opened and mixed.

Next, a process (carding process) of forming a web from a mixture of the sea-island composite staple fibers and the staple fibers B will be described. In the carding process, the mixed short fibers obtained in the opener process are pulled together by a carding roller to obtain a mixed fiber web.

On the other hand, (d) the step of subjecting the short fibers C to opening treatment to obtain a web of the short fibers C comprises opening the short fibers C using the opener described above, arranging the short fibers C by a carding step, and A web of fibers C can be obtained.

(e) The step of laminating a mixed fiber web of sea-island composite staple fibers and staple fibers B and a web of staple fibers C to obtain a laminated web is to obtain a laminated web by laminating the above webs on a conveyor. can be done.

Next, (f) the step of entangling the laminated web by a needle punching method or a water jet punching method to obtain a laminated nonwoven fabric will be described. The water jet punch method is a hydroentanglement method. In the entangling step, the entangling of the short fibers may be mechanically entangled by a needle punch method or a water jet punch method (hydroentangling method). This is preferable in that it can be suppressed.

When the staple fibers are entangled by a needle punch method, it is preferable to perform the entanglement treatment with a needle density of 200/cm ² or more. More preferably, the needles are entangled at a needle density of 250 needles/cm ² or more, particularly preferably 300 needles/cm ² or more. By setting the above needle density, each short fiber can be sufficiently entangled, and in the sea removal process described later, deformation of the laminated nonwoven fabric due to process tension is suppressed, and the uniform fine voids of the nonwoven fabric A are collapsed. Therefore, it is possible to efficiently obtain a nonwoven fabric for sound absorbing material having excellent sound absorbing performance, and to increase productivity.

When the short fibers are entangled by the water jet punch method, it is preferable to pass the fibers through the water jet punch nozzle at a pressure of 12.0 MPa or more three times or more. Under these conditions, the short fibers can be sufficiently entangled in the same manner as described above, and deformation of the laminated nonwoven fabric due to process tension is suppressed in the sea removal process described later, and the nonwoven fabric A has uniform fine voids. It is possible to efficiently obtain a nonwoven fabric for a sound absorbing material having excellent sound absorbing performance without collapsing, and to increase productivity.

(Manufacturing nonwoven fabric for sound absorbing material)
Next, (g) the step of removing the sea component of the sea-island composite fiber from the laminated nonwoven fabric with an alkaline aqueous solution to develop the fiber A will be described. The laminated nonwoven fabric is treated with an alkaline aqueous solution containing sodium hydroxide or the like at a temperature of 80 to 100° C. to remove the sea component of the sea-island composite fiber and develop the fiber A as the island component.

(h) In the step of drying the sea-removed laminated nonwoven fabric, the sea-removed laminated nonwoven fabric is washed with water and dried with a dryer such as a pin tenter to obtain a sound absorbing nonwoven fabric.

In the above-mentioned sea removal step and drying step, the uniform fine voids of the fibers A contained in the nonwoven fabric A may collapse due to the process tension when the laminated nonwoven fabric is conveyed, and the sound absorption performance may be reduced. By using the fiber B and the fiber C described in the specification, adjusting the basis weight of the nonwoven fabric B, and performing the entangling treatment described in this specification, deformation of the laminated nonwoven fabric is suppressed, and the nonwoven fabric A is uniform. It is possible to efficiently obtain a nonwoven fabric for a sound absorbing material having excellent sound absorbing performance without collapsing fine voids, thereby increasing productivity.

Next, the sound absorbing material will be explained. A sound absorbing material comprising the nonwoven fabric for sound absorbing material of the present invention includes the nonwoven fabric for sound absorbing material of the present invention and a layered material comprising a fiber-based porous layer, a foam layer, or an air layer, and The layered material is laminated on one surface of the nonwoven fabric for sound absorbing material. In such a sound absorbing material, the sound absorbing performance of the sound absorbing material is improved by using the sound absorbing material such that the layered material is positioned on the surface opposite to the sound incident side of the sound absorbing nonwoven fabric. will be excellent.

Moreover, the thickness of the layered material is preferably 5 to 50 mm. The layered material is preferably a fibrous porous material, a foam, or an air layer. That is, the nonwoven fabric for sound absorbing material of the present invention has a fiber-based porous body using thermoplastic resin fibers having a thickness of 5 to 50 mm or fibers using inorganic fibers on the surface opposite to the surface on which the sound is incident. The sound absorbing performance of these composite products (sound absorbing materials) is extremely excellent by using a base material made of a porous material or a base material made of a foam such as urethane foam. In addition, by providing an air layer having a thickness of 5 to 50 mm on the surface opposite to the sound incident side of the nonwoven fabric for sound absorbing material of the present invention, a composite product (sound absorbing material) of the laminated nonwoven fabric for sound absorbing material and the air layer The sound absorption performance of the material) is extremely excellent. Furthermore, with the configuration as described above, the air contained in the fiber-based porous material, the foam, or the air layer resonates with the nonwoven fabric for the sound absorbing material. sound absorption is improved. The thickness of the layered material can be measured by using a metal ruler to measure the length of the side surface of the layered material in the thickness direction.

The measurement method used in this example will be described later.

(Measuring method)
(1) Mode of single fiber diameter of fiber A Separate each layer of nonwoven fabric for sound absorbing material, observe the cross section with a scanning electron microscope (SEM) (S-3500N type manufactured by Hitachi High-Tech), and randomly A site to be photographed was selected and a cross-sectional photograph was taken at a magnification of 10,000. Fibers with a single fiber diameter of less than 1 μm were randomly selected in this photograph and the single fiber diameter of these fibers was measured. Then, the work from taking a cross-sectional photograph to measuring the single fiber diameter was repeated until the total number of fibers A reached 100, and the single fiber diameter of the fiber A was measured. In addition, when the cross-sectional shape of the fiber is an irregular cross-sectional shape, the cross-sectional area of the fiber is measured from the cross-sectional photograph, and the single fiber diameter of the fiber A is obtained by converting the cross-sectional area into the diameter of a perfect circle. Using the above-obtained single fiber diameter data with a total of 100 fibers, the maximum value of the distribution frequency was determined and taken as the mode value of the single fiber diameter of fiber A. Note that the distribution interval was 0.01 μm.

(2) Mode of single fiber diameters of fiber B and fiber C The method described in (1) Method for measuring single fiber diameter of fiber A above, except that the magnification of the cross-sectional photograph was 1,000 times. Similarly, a cross-sectional photograph was taken with a scanning electron microscope (SEM) (SU8010 model manufactured by Hitachi High-Tech). Fibers having a single fiber diameter of 1 μm or more were randomly selected in this photograph, and the single fiber diameters of these fibers were measured. Then, the operation from taking a cross-sectional photograph to measuring the single fiber diameter was repeated until the total number of fibers B or C reached 100, and the single fiber diameter of fiber B or fiber C was measured. When the cross-sectional shape of the fiber is an irregular cross-sectional shape, the cross-sectional area of the fiber is measured from the cross-sectional photograph, and the single fiber diameter of the fiber B or the fiber C is obtained by converting the cross-sectional area into the diameter of a perfect circle. . Using the data on the single fiber diameter of 100 total fibers obtained above, the maximum value of the distribution frequency was obtained and taken as the mode value of the single fiber diameter of the fiber B or the fiber C. Note that the distribution interval was set to 1 μm.

(3) Cv value of single fiber diameter of fiber A and fiber B Use the data of the single fiber diameter of 100 total number measured in (1) and (2) above, and use the standard deviation and average value. Then, the Cv value of the single fiber diameter of fiber A and fiber B was calculated by the following formula.
Cv value (%) of single fiber diameter of fiber A = (standard deviation of single fiber diameter of fiber A / average value of single fiber diameter of fiber A) × 100
Cv value (%) of single fiber diameter of fiber B=(standard deviation of single fiber diameter of fiber B/average value of single fiber diameter of fiber B)×100.

(4) Number ratio of fiber A and fiber B Separate each layer of the nonwoven fabric for sound absorbing material, observe the cross section with a scanning electron microscope (SEM) (S-3500N model manufactured by Hitachi High-Tech), and randomly photograph parts was selected, and a cross-sectional photograph was taken at a magnification of 2,000. The number of fibers corresponding to fiber A and the number of fibers corresponding to fiber B were counted for all fibers present in this cross-sectional photograph. The number of fibers A and B was obtained by repeating the operation from taking the cross-sectional photograph to counting the number of fibers 10 times. Then, the number of each fiber was expressed as a percentage of the total number of fibers A and B, which was taken as a number ratio.

(5) Difference between the mode values of the single fiber diameters of fiber A and fiber B Using the values, the difference between the modes of Fiber A and Fiber B was obtained by the following formula.
Difference in the mode of single fiber diameters of fiber A and fiber B (μm) = Mode of single fiber diameter of fiber B (μm) - Mode of single fiber diameter of fiber A (μm)
(6) Material and content of each fiber constituting nonwoven fabric for sound absorbing material Separate nonwoven fabric A and nonwoven fabric B, and for each nonwoven fabric, JIS L 1030-1: 2006 "Test method for mixing rate of textile products - Part 1 : Fiber identification", and JIS L 1030-2: 2005 "Testing method for mixing ratio of textile products-Part 2: Fiber mixing ratio", the correct mixing ratio (mass ratio of each fiber in the standard state) is measured. This was taken as the content (% by mass) of the fibers constituting the nonwoven fabric for sound absorbing material. As a result, the fiber materials constituting the sound absorbing nonwoven fabrics (nonwoven fabric A and nonwoven fabric B) and the content (% by mass) of each fiber material were specified.

(7) Content of fiber C in nonwoven fabric B 6. of JIS L 1030-2:2005 "Testing method for mixing ratio of textile products-Part 2: Fiber mixing ratio" in (6) above. The remaining nonwoven fabric of nonwoven fabric B in the dissolution method was observed with a scanning electron microscope (SEM) (SU8010 type manufactured by Hitachi High-Tech), 30 observation areas were randomly selected, and cross-sectional photographs were taken. The single fiber diameter was measured for all fibers having a single fiber diameter of 1 μm or more in this photograph, and fibers corresponding to fiber C were extracted. Then, the cross-sectional areas of the fibers corresponding to the fiber C and the other fibers (fibers with a fiber diameter of less than 1 μm) are measured, and from the total cross-sectional area of each fiber and the specific gravity of the fiber, the fiber in the nonwoven fabric B is calculated by the following formula. The content of C (% by mass) was calculated.
Content of fiber C in nonwoven fabric B (% by mass) = (total cross-sectional area of fiber C (μm ² ) × specific gravity of fiber) / ((total cross-sectional area of fiber C (μm ² ) × specific gravity of fiber) + (that Cross-sectional area of fibers other than (μm ² ) × specific gravity of fibers)) × 100
In addition, when the nonwoven fabric B has a plurality of fiber materials, the content of the fiber C is measured for each fiber material using the residual nonwoven fabric in the dissolution method, and the content of the fiber C in the nonwoven fabric B ( % by mass) was calculated.

(8) Fabric weight of nonwoven fabric for sound absorbing material Measured based on JIS L 1913:1998 6.2. Three test pieces of 300 mm×300 mm were taken from a sample of the nonwoven fabric for sound absorbing material using a steel ruler and a razor blade. The mass of the test piece in the standard state was measured, the basis weight, which is the mass per unit area, was determined by the following formula, and the average value was calculated. The basis weights of the nonwoven fabric A and the nonwoven fabric B were measured in the same manner after the nonwoven fabric A and the nonwoven fabric B were separated.
ms=m/s
ms: Mass per unit area (g/m ² )
m: Average mass (g) of test piece of nonwoven fabric for sound absorbing material
S: Area of test piece of nonwoven fabric for sound absorbing material (m ² )
(9) Thickness of nonwoven fabric for sound absorbing material Measured based on JIS L1913:1998 6.1.2 A method. Five test pieces of 50 mm×50 mm were taken from a sample of the nonwoven fabric for sound absorbing material. Using a thickness gauge (a constant pressure thickness gauge manufactured by TECLOCK, model PG11J), the thickness was measured by applying a pressure of 0.36 kPa to the test piece for 10 seconds under standard conditions. The measurement was performed for each test piece (five pieces), and the average value was calculated.

(10) Density of nonwoven fabric for sound absorbing material Density of nonwoven fabric for sound absorbing material was obtained from the basis weight of the nonwoven fabric for sound absorbing material in (8) above and the thickness of the nonwoven fabric for sound absorbing material in above (9) by the following formula.
Density of nonwoven fabric for sound absorbing material (g/cm ³ )=basis weight of nonwoven fabric for sound absorbing material (g/m ² )/thickness of nonwoven fabric for sound absorbing material (mm)/1000
(11) Nonwoven fabric A and nonwoven fabric B Nonwoven fabric A and nonwoven fabric B are separated from the nonwoven fabric for sound absorbing material, and the basis weights of nonwoven fabric A and nonwoven fabric B are obtained in the same manner as the basis weight of the nonwoven fabric for sound absorbing material in (8) above. asked for

(12) Ratio of nonwoven fabric A to nonwoven fabric B Based on the basis weight of nonwoven fabric A and nonwoven fabric B determined in (11) above, the ratio was obtained by the following formula.

Ratio of basis weight of nonwoven fabric A and nonwoven fabric B = basis weight of nonwoven fabric A (g/m ² ) / basis weight of nonwoven fabric B (g/m ² )
(13) Tensile strength of fiber B and fiber C Based on JIS L 1015 (1999) 8.7.1, each short fiber is loosely stretched along the division line with a spatial distance of 20 mm, and both ends are attached to a piece of paper with an adhesive. Stick and fix, and make each section one sample. Attach the sample to the grip of the tensile tester, cut the paper strip near the upper grip, pull it at a grip interval of 20 mm, a tensile speed of 20 mm / min, and measure the load (N) and elongation (mm) when the sample is cut. The tensile strength (cN/dtex) was calculated from the measurement and the following formula.
Tb=SD/F0
Tb: Tensile strength (cN/dtex)
SD: load at break (cN)
F0: sample fineness (dtex)
S={(E2−E1)/(L+E1)}×100
(14) Initial tensile resistance of fiber B and fiber C Based on JIS L 1015 (1999) 8.11, the load-elongation curve obtained from the tensile strength of fiber B and fiber C in (13) above, the load - The maximum point A of load change (maximum point of contact angle) with respect to the change in elongation was obtained near the origin of the elongation curve, and the initial tensile resistance (cN/dtex) was calculated by the following formula.
Tri=P/((L′/L)×F0)
Tri: initial tensile resistance (cN/dtex)
P: load (cN) at the maximum point A of the contact angle
F0: sample fineness (dtex)
L: test length (mm)
L': Length of TH (mm) (H is the foot of the perpendicular line, T is the intersection of the tangent line and the horizontal axis)
(15) Normal Incidence Sound Absorption Coefficient of Nonwoven Fabric for Sound Absorbing Material It was measured according to the normal incidence sound absorption measurement method (in-pipe method) of JIS A 1405 (1998). Three circular test pieces with a diameter of 92 mm were taken from a sample of the nonwoven fabric for sound absorbing material. As a testing device, an automatic perpendicular incidence sound absorption coefficient measuring instrument (model 10041A) manufactured by Denshi Sokki Co., Ltd. was used. The test piece was attached to one end of an impedance tube for measurement by setting a spacer so that an air layer with a thickness of 20 mm was formed between the test piece and the metal reflector. A value obtained by multiplying the measured sound absorption coefficient by 100 was adopted as the sound absorption coefficient for each frequency. The average value of the obtained sound absorption coefficients at 1000 Hz was defined as the low frequency sound absorption coefficient (%).

(Example 1)
(Composite fiber)
Polyethylene terephthalate (PET, melt viscosity: 160 Pa s) as the island component and PET (copolymerized PET, melt viscosity: 95 Pa s) obtained by copolymerizing 8.0 mol% of 5-sodium sulfoisophthalic acid as the sea component were mixed at 290°C. After separately melting and weighing, a known composite spinneret (for example, a composite spinneret with the arrangement disclosed in FIG. 6(b) of WO 12/173116) is incorporated, and one discharge hole is used for the island component. A spinning pack using a distribution plate with 1,000 distribution holes perforated is flowed into a composite ratio of sea/island components of 40/60, and the composite polymer stream is discharged from the discharge holes for melt spinning, An undrawn fiber was obtained. This was drawn at a draw ratio of 4.0 times to obtain a sea-island composite fiber of 150 dtex-15 filaments. The above sea-island composite fibers were heated to 100° C., introduced into a crimper, mechanically crimped, and then cut to a length of 51 mm by a rotary cutter to obtain sea-island composite short fibers.

(Laminated nonwoven fabric)
80% by mass of the above sea-island composite short fibers, and 20 polyethylene terephthalate (PET) short fibers having a single fiber diameter of 18.50 μm, a fiber length of 51 mm, a strength of 3.5 cN/dtex, and an initial tensile resistance of 35 cN/dtex as fiber B. % by mass, each short fiber was subjected to an opener process and then to a carding process to obtain a mixed fiber web.

On the other hand, 100% by mass of the fiber B was used as the fiber C, and the staple fiber was subjected to an opener process and then to a carding process to obtain a web composed of the fiber C.

After laminating the mixed fiber web and the web made of the fiber C to form a laminated web, the laminated web was entangled in a needle punching process at a needle density of 350 needles/cm ² to obtain a laminated nonwoven fabric.

(Nonwoven fabric for sound absorbing material)
The above laminated nonwoven fabric is immersed in an aqueous solution of 0.5% by mass of sodium hydroxide heated to a temperature of 95°C for 30 minutes to remove the sea component, and dried in a hot air dryer at a temperature of 130°C for 10 minutes. Fiber A with a mode single fiber diameter of 0.41 μm and a Cv value of 5.9%, and Fiber B with a mode single fiber diameter of 18.50 μm and a Cv value of 5.5% Nonwoven fabric A with a fiber count ratio of 99.1:0.9, a difference in the mode of the single fiber diameter between fiber A and fiber B of 18.09 μm, a basis weight of 100 g / m ² , and a basis weight of 100 g / made of fiber C A nonwoven fabric for sound absorbing material having a nonwoven fabric B of 2 m ² , a basis weight of 200 g/m ² , a thickness of 1.6 mm, a nonwoven fabric density of 0.125 g/cm ³ , and a basis weight ratio between the nonwoven fabric A and the nonwoven fabric B of 1.0 is obtained. rice field.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 1 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 1 was excellent.

(Example 2)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1 except that the compounding ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 60% by mass and the compounding ratio of the fiber B was changed to 40% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 98.0:1.0, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 2 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 2 was excellent.

(Example 3)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 70% by mass and the blending ratio of the fiber B was changed to 30% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included in a number ratio of 98.7:1.3, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 3 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 3 was excellent.

(Example 4)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 90% by mass and the blending ratio of the fiber B was changed to 10% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included in a number ratio of 99.4:0.6, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 4 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 4 was excellent.

(Example 5)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the draw ratio of the undrawn fibers was changed to 5.0 times.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 75% by mass and the blending ratio of the fiber B was changed to 25% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dried. Fiber B with a mode of 18.50 μm and a Cv value of 5.5% is included in a number ratio of 99.0:1.0, respectively, and the difference in the mode of single fiber diameter between Fiber A and Fiber B is 18 .19 μm, a nonwoven fabric A with a basis weight of 100 g/m ² and a nonwoven fabric B made of a fiber C with a basis weight of 100 g/m ² , with a basis weight of 200 g/m ² , a thickness of 1.5 mm, a nonwoven fabric density of 0.133 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 5 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 5 was excellent.

(Example 6)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the draw ratio of the undrawn fibers was changed to 3.0 times.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 85% by mass and the blending ratio of the fiber B was changed to 15% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.2:0.8, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 17 A nonwoven fabric A with a basis weight of .91 μm and a basis weight of 100 g/m ² and a nonwoven fabric B made of fibers C and with a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm, and a nonwoven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 6 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 6 was excellent.

(Example 7)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the draw ratio of the undrawn fibers was changed to 2.0 times.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 90% by mass and the blending ratio of the fiber B was changed to 10% by mass.

(Nonwoven fabric for sound absorbing material)
The above laminated nonwoven fabric was dried under the same process and conditions as in Example 1, and the fiber A with a mode of single fiber diameter of 0.72 μm and a Cv value of 5.9% Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 17 .78 μm, a nonwoven fabric A having a basis weight of 100 g/m ² and a nonwoven fabric B made of fibers C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm, and a nonwoven fabric density of 0.125 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 7 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 7 was excellent.

(Example 8)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
The fiber B used for the mixed fiber web was changed to a polyethylene terephthalate (PET) short fiber having a single fiber diameter of 8.50 μm, a fiber length of 51 mm, a strength of 3.7 cN/dtex, and an initial tensile resistance of 36 cN/dtex. The steps and conditions were the same as in Example 1, except that the blending ratio of the fiber was changed to 90% by mass, the blending ratio of the fiber B to 10% by mass, and the fiber of the web made of the fiber C was changed to the above fiber B. processed to obtain a laminated nonwoven fabric.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 8.50 μm and a Cv value of 5.6% is included at a number ratio of 99.2:0.8, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 8 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 8 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 8 was excellent.

(Example 9)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
The fiber B used for the mixed fiber web was changed to a polyethylene terephthalate (PET) short fiber having a single fiber diameter of 25.50 μm, a fiber length of 51 mm, a strength of 3.4 cN/dtex, and an initial tensile resistance of 33 cN/dtex. The steps and conditions were the same as in Example 1, except that the blending ratio of the fiber was changed to 70% by mass and the blending ratio of the fiber B to 30% by mass, and the fiber of the web made of the fiber C was changed to the above fiber B. processed to obtain a laminated nonwoven fabric.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 25.50 μm and a Cv value of 5.5% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 25 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.7 mm, and a non-woven fabric density of 0.118 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 9 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 9 was excellent.

(Example 10)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the composite ratio of the sea/island components was changed to 50/50.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the compounding ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 82% by mass and the compounding ratio of the fiber B was changed to 18% by mass.

(Nonwoven fabric for sound absorbing material)
The above laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dried. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 .10 μm, a nonwoven fabric A with a basis weight of 100 g/m ² and a nonwoven fabric B made of a fiber C with a basis weight of 100 g/m ² , with a basis weight of 200 g/m ² , a thickness of 1.6 mm, a nonwoven fabric density of 0.125 g/cm ³ A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 10 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 10 was excellent.

(Example 11)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the composite ratio of the sea/island components was changed to 70/30.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 90% by mass and the blending ratio of the fiber B was changed to 10% by mass.

(Nonwoven fabric for sound absorbing material)
The above laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dried. Fiber B with a mode of 18.50 μm and a Cv value of 5.5% is included in a number ratio of 99.0:1.0, respectively, and the difference in the mode of single fiber diameter between Fiber A and Fiber B is 18 08 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fibers C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm, and a non-woven fabric density of 0.125 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 11 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 11 was excellent.

(Example 12)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
The fiber B used for the mixed fiber web was changed to a polyethylene terephthalate (PET) short fiber having a single fiber diameter of 18.50 μm, a fiber length of 51 mm, a strength of 2.6 cN / dtex, and an initial tensile resistance of 27 cN / dtex. A laminated nonwoven fabric was obtained by performing the same process and under the same conditions as in Example 1, except that the fibers of the first web were changed to the above fibers B.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.6% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 12 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 12 was excellent.

(Example 13)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the nonwoven fabric B of the sound absorbing nonwoven fabric had a basis weight of 80 g/m ² .

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fibers C and having a basis weight of 80 g/m ² , having a basis weight of 180 g/m ² , a thickness of 1.5 mm and a non-woven fabric density of 0.120 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of nonwoven fabric A to nonwoven fabric B of 1.3 was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 13 was high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 13 was excellent.

(Example 14)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the nonwoven fabric B of the sound absorbing nonwoven fabric had a basis weight of 55 g/m ² .

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.1:0.9, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 09 μm and a basis weight of 100 g/m ² , and a non-woven fabric B made of fiber C and having a basis weight of 55 g/m ² , having a basis weight of 155 g/m ² , a thickness of 1.5 mm, and a non-woven fabric density of 0.103 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of nonwoven fabric A to nonwoven fabric B of 1.8 was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Example 14 was relatively high. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Example 14 was excellent.

(Comparative example 1)
(Composite fiber)
Sea-island composite short fibers were obtained by the same process and conditions as in Example 1, except that the draw ratio of the undrawn fibers was changed to 1.5 times.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 93% by mass and the blending ratio of the fiber B was changed to 7% by mass.

(Nonwoven fabric for sound absorbing material)
The above laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dried, and the fiber A having a single fiber diameter mode of 0.92 μm and a Cv value of 5.7% and a single fiber diameter of Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.2:0.8, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 17 .58 μm, a nonwoven fabric A with a basis weight of 100 g/m ² and a nonwoven fabric B made of a fiber C with a basis weight of 100 g/m ² , with a basis weight of 200 g/m ² , a thickness of 1.6 mm, and a nonwoven fabric density of 0.125 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 1 was low.

(Comparative example 2)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 95% by mass and the blending ratio of the fiber B was changed to 5% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included at a number ratio of 99.8:0.2, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.6 mm and a non-woven fabric density of 0.125 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 2 was low.

(Comparative Example 3)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same process and under the same conditions as in Example 1, except that the blending ratio of the sea-island composite staple fibers in the mixed fiber web was changed to 40% by mass and the blending ratio of the fiber B was changed to 60% by mass.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fiber B with a mode value of 18.50 μm and a Cv value of 5.5% is included in a number ratio of 93.8:6.2, respectively, and the difference in the mode value of the single fiber diameter between fiber A and fiber B is 18 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.7 mm, and a non-woven fabric density of 0.118 g/cm ³ . A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 3 was low.

(Comparative Example 4)
(Composite fiber)
The sea-island composite short fibers of Example 1 were used.

(Laminated nonwoven fabric)
The fiber B used for the mixed fiber web was changed to a polyethylene terephthalate (PET) short fiber having a single fiber diameter of 30.50 μm, a fiber length of 51 mm, a strength of 3.4 cN/dtex, and an initial tensile resistance of 34 cN/dtex. The steps and conditions were the same as in Example 1, except that the blending ratio of the fiber was changed to 70% by mass and the blending ratio of the fiber B to 30% by mass, and the fiber of the web made of the fiber C was changed to the above fiber B. processed to obtain a laminated nonwoven fabric.

(Nonwoven fabric for sound absorbing material)
The above-mentioned laminated nonwoven fabric was subjected to the same process and conditions as in Example 1 to remove the seawater and dry. Fibers B with a mode value of 30.50 μm and a Cv value of 5.4% are included at a number ratio of 99.2:0.8, respectively, and the difference in the mode value of the single fiber diameter between Fiber A and Fiber B is 30 09 μm and a basis weight of 100 g/m ² and a non-woven fabric B made of fiber C and having a basis weight of 100 g/m ² , having a basis weight of 200 g/m ² , a thickness of 1.8 mm and a non-woven fabric density of 0.111 g/cm ³ , A sound-absorbing nonwoven fabric having a basis weight ratio of 1.0 between nonwoven fabric A and nonwoven fabric B was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 4 was low.

(Comparative Example 5)
(Composite fiber)
A sea-island composite fiber was obtained in the same process and under the same conditions as in Example 1, except that the draw ratio of the undrawn fiber was changed to 2.0 times. The above sea-island composite fibers were heated to 100° C., introduced into a crimper, mechanically crimped, and then cut to a length of 1 mm by a rotary cutter to obtain sea-island composite short fibers.

(Nonwoven fabric for sound absorbing material)
The above sea-island composite short fibers were immersed in an aqueous solution of 0.5% by mass of sodium hydroxide heated to a temperature of 95° C. for 30 minutes to remove the sea component, and fibers A were obtained. 80% by mass of the fiber A, and 20% by mass of polyethylene terephthalate (PET) short fiber having a single fiber diameter of 3.50 μm, a fiber length of 3 mm, a strength of 3.6 cN/dtex, and an initial tensile resistance of 37 cN/dtex as the fiber B. The fibers A and B were put into water so that the slurry concentration was 0.1% by mass, and stirred for 10 minutes to obtain a slurry. Using a spray nozzle, the resulting slurry was sprayed onto a polyethylene terephthalate spunbond nonwoven fabric having a basis weight of 15 g/m ² for 5 minutes, and dried in a hot air dryer at a temperature of 130°C for 10 minutes to remove the spunbond nonwoven fabric. Then, fiber A with a mode of single fiber diameter of 0.72 μm and a Cv value of 5.9% and fiber B with a mode of single fiber diameter of 3.50 μm and a Cv value of 5.6% are obtained. Consists only of nonwoven fabric A with a fiber count ratio of 95.2: 4.8, a difference in the mode of the single fiber diameter of fiber A and fiber B of 2.78 μm, and a basis weight of 5 g / m ² , basis weight 5 g / m ^2. A nonwoven fabric for sound absorbing material having a thickness of 0.1 mm and a nonwoven fabric density of 0.050 g/cm ³ was obtained.

The nonwoven fabric for sound absorbing material of Comparative Example 5 was excellent in productivity, but the low frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 5 was low.

(Comparative Example 6)
(Composite fiber)
The sea-island composite staple fiber of Comparative Example 5 was used.

(Nonwoven fabric for sound absorbing material)
The process and conditions were the same as in Comparative Example 5 except that the spraying time of the slurry was 200 minutes. Fibers B with a mode diameter of 3.50 μm and a Cv value of 5.6% are included in a number ratio of 95.2:4.8, respectively, and the difference in the mode of the single fiber diameter between Fiber A and Fiber B A sound-absorbing nonwoven fabric having a basis weight of 200 g/m ² , a thickness of 1.4 mm, and a nonwoven fabric density ^of 0.143 g/cm ³ was obtained.

The low-frequency sound absorption coefficient of the nonwoven fabric for sound absorbing material of Comparative Example 6 was low. Moreover, the productivity of the nonwoven fabric for sound absorbing material of Comparative Example 5 was inferior.

Tables 1 to 4 summarize the configurations and properties of the nonwoven fabrics for sound absorbing materials of Examples and Comparative Examples.

The nonwoven fabric for sound absorbing material of the present invention is particularly excellent in sound absorbing performance in a low frequency region and productivity, and is therefore suitable for use as a sound absorbing material for automobiles.

Claims (8)

Having a laminated structure of nonwoven fabric A and nonwoven fabric B,
The nonwoven fabric A contains fibers A with a mode of single fiber diameter of 0.05 to 0.80 μm and fibers B with a mode of single fiber diameter of 5.00 to 30.00 μm,
The number ratio of the fibers A and the fibers B in the nonwoven fabric A (number of fibers A:number of fibers B) is 94.0:6.0 to 99.5:0.5,
The difference in the mode of the single fiber diameter between the fiber A and the fiber B in the nonwoven fabric A (the mode of the single fiber diameter of the fiber B - the mode of the single fiber diameter of the fiber A) is 4.00 to 28.00 μm,
A nonwoven fabric for a sound absorbing material, wherein the nonwoven fabric B contains 80% by mass or more of fibers C having a mode of single fiber diameter of 5.00 to 30.00 μm with respect to the entire nonwoven fabric B. 2. The nonwoven fabric for sound absorbing material according to claim 1, wherein the fiber A has a single fiber diameter Cv value of 20% or less, and the fiber B has a single fiber diameter Cv value of 15% or less. The ratio of the basis weight of the nonwoven fabric A and the nonwoven fabric B (the basis weight of the nonwoven fabric A/the basis weight of the nonwoven fabric B) is 0.5 to 1.7,
3. The nonwoven fabric for sound absorbing material according to claim 1, wherein said nonwoven fabric B has a basis weight of 70 to 200 g/m ² . The nonwoven fabric for sound absorbing material according to any one of claims 1 to 3, having a density of 0.07 to 0.40 g/cm ³ . The tensile strength of the fiber B and the fiber C is 3 cN/dtex or more,
5. The nonwoven fabric for sound absorbing material according to claim 1, wherein said fibers B and said fibers C have an initial tensile resistance of 30 cN/dtex or more. The nonwoven fabric for sound absorbing material according to any one of claims 1 to 5, wherein said fibers A, said fibers B and said fibers C are all polyester short fibers. A nonwoven fabric for a sound absorbing material according to any one of claims 1 to 6, and a layered material comprising a fiber-based porous material, a foam, or an air layer,
The layered material is laminated on one surface of the nonwoven fabric for sound absorbing material,
A sound absorbing material, wherein the layered material has a thickness of 5 to 50 mm. 7. The method for producing a nonwoven fabric for sound absorbing material according to any one of claims 1 to 6, comprising the following steps (a) to (h).
(a) a step of spinning a sea-island composite fiber comprising two or more resins using a composite spinneret; (b) a step of crimping and cutting the sea-island composite fiber to obtain a sea-island composite staple fiber; ) The sea-island composite staple fibers and the staple fibers B having a mode of single fiber diameter of 5.00 to 30.00 μm are subjected to a fiber opening treatment to form a mixed fiber web of the sea-island composite staple fibers and the fibers B. Step (d) of obtaining a web of the fibers C by subjecting short fiber-shaped fibers C having a mode of single fiber diameter of 5.00 to 30.00 μm to obtain a web of the fibers C (e) the mixed fiber web and (f) subjecting the laminated web to entangling by a needle punching method or a water jet punching method to obtain a laminated nonwoven fabric; (g) applying the laminated nonwoven fabric to an alkaline Step (h) of removing the sea component from the sea-island composite short fibers with an aqueous solution to develop fibers A having a single fiber diameter mode of 0.05 to 0.80 μm; lamination after the step of (g); A process of drying the nonwoven fabric.