Nonwoven fabric

Abstract

This invention provides a soundproofing material that includes a lightweight, thin, and easily moldable nonwoven fabric, which improves sound insulation in the low-frequency range without changing the film thickness by increasing the overall rigidity of the nonwoven fabric through the addition of irregularities. [Solution] A soundproofing material comprising a nonwoven fabric composed of fibrillated fibers and non-fibrillated fibers, wherein the nonwoven fabric contains fibrillated fibers in an amount of 1% by mass or more, has a plurality of irregularities on its surface, and has a tensile modulus of elasticity of 10 MPa or more.

Description

[Technical Field]

[0001] This invention relates to nonwoven fabrics and soundproofing materials and composite soundproofing materials using the same. [Background technology]

[0002] When a car is in motion, various noises are generated, including noise from the engine and drivetrain, road noise, and wind noise. Traditionally, sound-absorbing materials have been used to suppress these noises and create a comfortable interior space by reducing noise emissions. In recent years, with the advancement of electric vehicles and the improvement in the quietness of their drivetrains, sounds that were not previously perceived as noise are now being recognized as noise. The frequency of noise depends on the sound source, and sound-absorbing and sound-insulating materials suitable for each sound source are used. However, porous sound-absorbing materials commonly used in automotive applications, such as nonwoven fabrics and foams, exhibit excellent sound absorption in the high-frequency range, but tend to decrease in sound absorption towards the low-frequency range. Similarly, sound-insulating materials also tend to have lower sound insulation rates at lower frequencies compared to high frequencies.

[0003] Patent Document 1 below describes a method for improving sound absorption without reducing the rigidity of a sound-absorbing material, reducing the weight of the sound-absorbing material, or improving sound absorption and rigidity without increasing the weight of the sound-absorbing material, by forming a bulky nonwoven fabric into a corrugated shape with irregularities. Disclosed is a corrugated sound-absorbing material characterized by being formed by molding. This sound-absorbing material consists of 30 parts by weight of recycled wool, 50 parts by weight of cotton waste, and 20 parts by weight of phenolic resin powder, with a thickness of 25 mm and a surface density of 950 g / m². 2 The bulky nonwoven fabric was heated at 200°C for 45 seconds, at a rate of 5 kg / cm². 2The material is formed by pressure molding under certain conditions, creating a continuous bowl-shaped uneven surface with a height of 2 cm and a diameter of 10 cm, forming a corrugated sound-absorbing material. A thin leaf-shaped surface material made of polyester fibers is then applied to both sides so as to only contact the convex parts of the corrugated sound-absorbing material, and the resulting material is an integrated unit. The nonwoven fabric described in Patent Document 1 does not contain fibrillated fibers and is pressure-molded at high temperatures. Although improvements in sound absorption and rigidity are observed, no studies have been conducted on sound insulation.

[0004] Patent Document 2 discloses a nonwoven fabric containing cellulose fine fibers with an average fiber diameter of 100 nm to 2000 nm and short fibers with an average fiber diameter of 0.1 μm to 10 μm, characterized in that the average flow diameter measured by a palm porometer is 1 μm to 30 μm, in order to provide a surface material for a composite sound-absorbing material that is excellent in sound absorption in the mid-to-low frequency range while having high productivity, and the average flow diameter measured by a palm porometer is 1 μm to 30 μm. A sound-absorbing material composed of this nonwoven fabric is also disclosed. However, the uneven shape, rigidity, and sound insulation properties of the nonwoven fabric described in Patent Document 2 have not been considered.

[0005] Furthermore, Patent Document 3 below describes a textile-like composite sound-absorbing material in which a foam layer is provided as a breathability adjusting layer on a nonwoven fabric obtained by combining fibers of a specific fineness, and it is stated that it has excellent sound absorption properties in the 800Hz to 2000Hz range.

[0006] Furthermore, Patent Document 4 below describes a composite sound-absorbing material in which spunbond nonwoven fabric is bonded in a spotted pattern to melamine foam using hot melt adhesive, and it is stated that it has a thickness of slightly over 10 mm and exhibits excellent sound absorption across the entire frequency range.

[0007] Furthermore, Patent Document 5 below provides a composite molded body that can be suitably used as a ventilation adjustment layer with excellent sound absorption in the low to medium frequency range and also has excellent three-dimensional shapeability, comprising fibrillated fibers and short fibers, wherein the composite molded body has a surface density of 30 g / m². 2 ~1000g / m 2There is disclosed a composite molded body having an air permeability resistance per unit thickness of 15.0 s / (100 mL·mm) or less. In Patent Document 5, it is preferable that the composite molded body is a structure in which short fibers and fibrillated fibers are mixed and molded in a chemically or physically entangled or adhered state to each other. Since the composite molded body has a dense structure with fine fiber gaps and has a very small air permeability resistance, when sound enters the fiber gaps, the vibration energy of the sound is converted into heat energy by friction with the ultrafine fibers, and the composite molded body itself can be further converted into heat energy by membrane vibration, so it is described that it has excellent sound absorption characteristics. However, in Patent Document 5, the uneven shape, rigidity, and sound insulation properties of the non-woven fabric, which is a composite molded body, have not been studied.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, although the conventional technology can increase the sound absorption property by providing an additional layer on the porous material, it has hardly exerted its effectiveness with respect to sound insulation. Also, in order to countermeasure the noise leaking from the inside to the outside of the vehicle such as the driving sound of the engine, it is effective to improve the sound insulation property rather than the sound absorption property of the soundproof material. In view of the above circumstances, the problem that the present invention aims to solve is to provide a soundproofing material that includes a lightweight, thin nonwoven fabric with good moldability, which improves sound insulation in the low-frequency range without changing the film thickness by increasing the overall rigidity of the nonwoven fabric by creating an uneven surface. [Means for solving the problem]

[0010] The inventors of this invention diligently studied and conducted numerous experiments to solve the aforementioned problem. As a result, they unexpectedly discovered that the problem could be solved by creating an uneven surface in a nonwoven fabric composed of fibrillated fibers and non-fibrillated fibers in order to increase the rigidity of the nonwoven fabric, and thus completed the present invention.

[0011] In other words, the present invention is as follows: [1] A soundproofing material comprising a nonwoven fabric composed of fibrillated fibers and non-fibrillated fibers, wherein the nonwoven fabric contains fibrillated fibers in an amount of 1% by mass or more, has a plurality of irregularities on its surface, and has a tensile modulus of elasticity of 10 MPa or more. [2] The soundproofing material according to [1], wherein the surface rigidity of the nonwoven fabric is 0.7 N / mm or more. [3] The soundproofing material according to [1] or [2], wherein the height ratio of the unevenness of the nonwoven fabric is 0.1 or more and 10 or less. [4] The soundproofing material according to [1] to [3] above, wherein the taper angle of the unevenness of the nonwoven fabric is 3° or more and 70° or less. [5] The soundproofing material according to any one of [1] to [4] above, wherein the ratio of the uneven surface area to the total surface area of ​​the nonwoven fabric is 2% or more and 90% or less. [6] The soundproofing material according to any one of [1] to [5] above, wherein the irregularities of the nonwoven fabric are wave-shaped. [7] The soundproofing material according to any one of [1] to [6] above, wherein the irregularities of the nonwoven fabric are selected from the group consisting of W-shaped, grid-shaped, and triangular pyramidal shapes. [8] The soundproofing material according to any of [1] to [7] above, wherein the thickness of the nonwoven fabric is 0.5 mm or more and 10 mm or less. [9] The flow resistance per unit thickness of the nonwoven fabric is 0.1 MNs / m4 More than 1000MNs / m 4 The soundproofing material described in any of the above [1] to [8], which is one of the following:

[10] The basis weight of the nonwoven fabric is 10 g / m² 2 More than 10000g / m 2 The soundproofing material described in any of the above [1] to [9], which is one of the following:

[11] The soundproofing material according to any one of [1] to

[10] above, wherein the porosity of the nonwoven fabric is 40% or more and 90% or less.

[12] The soundproofing material according to any of [1] to

[11] above, wherein the labyrinthiness of the nonwoven fabric is 1.20 or more and 10.0 or less.

[13] The soundproofing material according to any one of [1] to

[12] , wherein the fibrillated fiber is at least one selected from the group consisting of microfibrillated cellulose, acrylic pulp, aramid pulp, chitin nanofibers, chitosan nanofibers, and silk nanofibers.

[14] The soundproofing material according to

[13] , wherein the microfibrillated cellulose is cellulose nanofiber (CNF).

[15] The soundproofing material according to any one of [1] to

[14] above, wherein the fibrillation rate of the fibrillated fiber is 0.3% or more.

[16] The soundproofing material according to any one of [1] to

[15] , wherein the content of the fibrillated fibers is 3% by mass or more and 30% by mass or less, based on the total mass of the nonwoven fabric.

[17] The soundproofing material according to any one of [1] to

[16] , wherein the transmitted sound pressure at an incident of 95 dB is 90 dB or less.

[18] The soundproofing material according to any one of [1] to

[17] , wherein the reverberation chamber sound absorption coefficient (-) at 1250 Hz is 0.1 or more. [Effects of the Invention]

[0012] According to the present invention, by providing an uneven surface to a nonwoven fabric containing fibrillated fibers and non-fibrillated fibers of a specific length and having a tensile modulus of elasticity of a predetermined value or higher, it is possible to provide a lightweight, thin, and easily moldable nonwoven fabric that maintains sound absorption while exhibiting excellent sound insulation in the low-frequency range. Therefore, the soundproofing material according to the present invention is suitably usable in various applications where low-frequency sound absorption and sound insulation rates are required, such as in automotive applications where the electrification of automobiles has progressed and the quietness of the drive system has improved. [Brief explanation of the drawing]

[0013] [Figure 1] These are schematic diagrams illustrating examples of the uneven shapes of nonwoven fabrics: wave-shaped, grid-shaped, triangular pyramid 1A, triangular pyramid 2A, triangular pyramid 1B, and triangular pyramid 2B. [Figure 2] These are photographs that serve as substitutes for drawings of nonwoven fabrics with various textures and irregularities. [Figure 3] This is a photograph illustrating a method for measuring the surface stiffness of nonwoven fabrics. [Figure 4] This is a photograph illustrating the measurement method used in sound insulation testing. [Figure 5] This is a diagram illustrating the method for measuring the sound absorption coefficient of a reverberation chamber. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described in detail below, but the present invention is not limited to the embodiments described below. One embodiment of the present invention is a soundproofing material comprising a nonwoven fabric composed of fibrillated fibers and non-fibrillated fibers, wherein the nonwoven fabric contains fibrillated fibers in an amount of 1% by mass or more, has a plurality of irregularities on its surface, and has a tensile modulus of elasticity of 10 MPa or more.

[0015] <Nonwoven fabric> Nonwoven fabric is a structure formed in which multiple fibers are chemically or physically intertwined or bonded to one another. Furthermore, the nonwoven fabric of this embodiment is characterized by containing fibrillated fibers and non-fibrillated fibers, as described later.

[0016] (Three-dimensional shaping of nonwoven fabrics) Nonwoven fabrics can be easily made into three-dimensional structures, and furthermore, they can be made into structures with a uniform surface and no seams or gaps. In this specification, a three-dimensional structure means that the nonwoven fabric is not a two-dimensional (planar or flat) structure, but has at least one curved structure, and is hereinafter also referred to as "three-dimensional" or "three-dimensional structure". When applying a flat, breathable layer, such as a commonly used nonwoven fabric, to a three-dimensional structure, the breathable layer is arranged on the surface of the sound-absorbing material by cutting, folding, and gluing. However, this inevitably results in overlapping sections, gaps, and folds in the nonwoven fabric. Consequently, variations in breathability occur, making it impossible to obtain uniform sound absorption characteristics across all surfaces. On the other hand, when nonwoven fabric is processed into a three-dimensional structure, the surface is uniform and the structure is free of seams and gaps. Therefore, even when applied to sound sources with complex shapes, consistent sound absorption can be obtained across all surfaces of the nonwoven fabric, resulting in superior sound absorption.

[0017] (Unevenness of nonwoven fabric) As mentioned above, nonwoven fabrics can be molded in three dimensions, allowing for the creation of various uneven surfaces (protrusions and indentations). By creating these protrusions and indentations, the overall rigidity of the nonwoven fabric can be increased in shape without increasing its film thickness, and its weight can also be reduced. Improved rigidity not only extends the service life of the nonwoven fabric, but also, according to the aforementioned rigidity law, can enhance sound insulation in the low-frequency range. Furthermore, by changing the pattern of the protrusions and indentations (the cross-sectional shape of the protrusions and indentations when the nonwoven fabric is viewed perpendicular to a plane), rigidity can be controlled. This allows for isotropic improvement of surface rigidity, or anisotropic improvement of rigidity in specific directions. Factors that control rigidity in the protrusions and indentations include the pattern of the protrusions and indentations, as well as the height of the protrusions and indentations, the taper angle of the protrusions and indentations, and the area ratio of the protrusions and indentations. Additionally, by combining two or more types of protrusions and indentations, it is possible to intentionally control the surface on which sound insulation is desired.

[0018] Since this non-woven fabric also has sound absorption properties, it is possible to enhance the sound absorption properties in the high-frequency range by providing uneven shapes. Thus, the provision of uneven shapes can enhance the sound insulation properties in the low-frequency range and the sound absorption properties in the high-frequency range, and as a result, the quietness in the entire frequency range can be improved.

[0019] (Uneven shape) In the present invention, the shape representations such as squares used to represent uneven patterns do not stop at the narrow geometric concepts, but generally include shapes that can be recognized as the above shapes, and it is naturally allowed to provide so-called fillets or chamfers with curved sides or rounded corners or surfaces that are required for shaping on the corners or surfaces. Also, the parallel representation does not stop at the narrow geometric concept, but generally includes what can be recognized as parallel surfaces. Also, when the non-woven fabric is placed horizontally and viewed from the thickness direction, the lowest horizontal plane (i.e., the plane not involved in the formation of the uneven portions) is designated as the first reference plane, the second lowest horizontal plane is designated as the second reference plane, and the third lowest horizontal plane is designated as the third reference plane. Regarding the height of the planes, it does not stop at the narrow geometric concept, and all planes that can generally be recognized as having the same height are the reference planes with the same designation. The uneven shape is preferably at least one selected from the group consisting of a waveform, a lattice type, a triangular pyramid type, a regular polyhedron type, a semi-regular polyhedron type, a quasi-regular polyhedron type, a star regular polyhedron type, a uniform polyhedron type, an Archimedean dual type, a delta polyhedron type, a Johnson solid type, a star polyhedron type, a zone polyhedron type, a parallel polyhedron type, an equilateral rhombic polyhedron type, a composite polyhedron type, a perforated polyhedron type, a cone type, a pyramid type, a double cone type, a double pyramid type, a twisted double pyramid type, a frustum of a cone type, a frustum of a pyramid type, a cylinder type, a prism type, an anti-prism type, an ellipsoid type, a Rouleau polyhedron type, and a stack pattern. FIG. 1 and FIG. 2 illustrate various uneven shapes. Also, Table 1 below shows the mass, surface area, and basis weight of non-woven fabrics having various unevenness used in the following examples. The mass and basis weight of the non-woven fabric are calculated by the following measurements. Mass (g): Measured with an electronic balance (GX-8K2, manufactured by A&D Company). Surface area (mm 2The convex and concave sides of the nonwoven fabric were measured using a 3D scanner-type three-dimensional measuring machine (VL-500, manufactured by Keyence), and the larger value was taken as the surface area of ​​the nonwoven fabric. Weight (g / m 2 )={weight (g) / surface area (mm 2 )} × 1,000,000.

[0020] The wave-shaped structure has two reference planes, a first reference plane and a second reference plane, and is characterized by the fact that the uneven pattern of the second reference plane is rectangular. The longer the longer side L of the rectangle, the higher the surface rigidity, and when arranging multiple wave-shaped structures, arranging them parallel to each other is preferable as it increases the surface rigidity. The grid-shaped structure has two reference planes, a first reference plane and a second reference plane, and is characterized by the fact that the uneven pattern of the second reference plane is grid-like. The grid-shaped structure with varying heights has three reference planes, a first reference plane, a second reference plane and a third reference plane, and is characterized by the fact that the uneven patterns of the second reference plane and the third reference plane are wave-shaped, and the uneven pattern formed by the second and third reference planes is grid-like. The triangular pyramidal structure is characterized by the fact that the second reference plane is a triangle.

[0021] (Ratio of height of uneven surfaces) The higher the ratio of the surface height to the unevenness, the higher the surface rigidity of the nonwoven fabric and the better the sound insulation. The ratio of the surface height to the unevenness is expressed by the following formula. Ratio of unevenness height = Height of unevenness (mm) / Thickness of nonwoven fabric (mm) The height of the unevenness referred to here is expressed as the absolute difference between the height of the apex or bottom surface of the unevenness and the thickness of the nonwoven fabric when the nonwoven fabric is placed on a horizontal surface. In the case of a nonwoven fabric with a third reference plane or higher, the location with the highest unevenness height is used to calculate the unevenness height ratio in this specification. The unevenness height ratio of the nonwoven fabric is 0.1 or higher. 0.6 or higher is preferred, 2 or higher is more preferred, 3 or higher is even more preferred, and 5 or higher is exceptionally preferred. Furthermore, there is no upper limit set from the viewpoint of physical properties, but considering that three-dimensional molding is not good at molding the sides of unevenness, 150 or less is preferred from the viewpoint of moldability. In addition, when this nonwoven fabric is used in automotive applications, it is desirable that it does not interfere with surrounding parts, and in one embodiment, 30 or less is more preferred, and 10 or less is even more preferred.

[0022] (Taper angle of uneven surface) The smaller the taper angle of the uneven surface, the higher the surface rigidity of the nonwoven fabric and the better the sound insulation. This nonwoven fabric has a taper where the uneven surface narrows towards the tip (vertex or bottom surface), and the taper angle of the uneven surface referred to here is the angle of inclination when viewed from the vertex or bottom surface of the uneven surface. In this specification, the taper may have asymmetrical inclination angles on the left and right sides. The taper angle of the uneven surface is preferably 180° or less. As for the taper angle of the uneven surface, 120° or less is preferred, 90° or less is more preferred, 70° or less is even more preferred, 50° or less is particularly preferred, 30° or less is exceptionally preferred, 10° or less is exceptionally preferred, and 5° or less is most preferred. There is no lower limit set, but theoretically it should be greater than 0°, and from the viewpoint of moldability, 3° or more is preferred.

[0023] (Percentage of uneven surface area) The larger the area ratio of the uneven surface, the higher the surface rigidity of the nonwoven fabric and the better the sound insulation. The area ratio of the uneven surface referred to here is the ratio of the total area of ​​the bottom and sides of all the uneven parts of the nonwoven fabric to the total area of ​​the nonwoven fabric, including tapered sections. The area ratio of the uneven surface is preferably 2% or more. Preferably, it is 10% or more, more preferably 20% or more, even more preferably 25% or more, exceptionally preferably 40% or more, particularly preferably 50% or more, and most preferably 70% or more. Furthermore, if the area ratio is too large, the uneven surfaces become continuous and the boundaries disappear, resulting in lower surface rigidity. Therefore, the area ratio must be less than 100%, preferably 90% or less, and even more preferably 80% or less. (Percentage of area of ​​maximum irregularities) The larger the area ratio of the largest surface irregularity, the higher the rigidity of the nonwoven fabric surface and the better the sound insulation. Here, the largest surface irregularity refers to the irregularity with the largest area among all the irregularities on the nonwoven fabric, and the area ratio of the largest surface irregularity is the ratio of the total area of ​​the bottom and sides of the largest surface irregularity to the total area of ​​the nonwoven fabric. Even if there are two or more largest surface irregularities, only one of them is used in calculating the area ratio of the largest surface irregularity.

[0024] (Surface rigidity of nonwoven fabric) By creating irregularities in the nonwoven fabric, the overall surface rigidity of the nonwoven fabric is improved, resulting in improved sound insulation. In this invention, the surface rigidity of the nonwoven fabric is preferably 0.7 N / mm or more, more preferably 1.5 N / mm or more, even more preferably 3 N / mm or more, and particularly preferably 4.5 N / mm or more, for a sample size of 220 × 220 mm. Furthermore, when measuring surface rigidity, any part of the nonwoven fabric surface may be used for measurement, but the value of the surface rigidity as defined in this invention is the point with the highest rigidity. Surface stiffness is measured using a nonwoven fabric of the same material and an Instron 5969 universal testing machine, by the following indenter removal test. The four outer edges of the nonwoven fabric are gripped and fixed with a jig. A hemispherical indenter is pressed against the center of the nonwoven fabric to obtain a load-displacement diagram. At this time, the displacement is measured as 0 mm when the load becomes 0.2 N. The slope of the load for displacements of 0-1 mm represents the surface stiffness according to the present invention. If the nonwoven fabric has irregularities, the indenter may be applied from either the convex or concave side, and the value with greater stiffness is the surface stiffness value according to the present invention. In the example, to avoid cell crushing when punching from the convex side, the surface stiffness was measured by punching from the concave side. The measurement conditions were as follows (see Figure 3). Number of measurement samples: 10 points (average calculated) Load cell capacity: 5kN Test speed: 2 mm / min (constant speed) Test environment: 24°C, 40%RH Sample size: 220 x 220 mm 2 Opening size: 190 x 190 mm 2 Indenter shape: φ50mm, tip radius 25mm hemisphere

[0025] Furthermore, if surface rigidity cannot be measured from a shape perspective, the nonwoven fabric may be cut to 220mm x 220mm and the surface rigidity calculated. Also, if the sample is small, the surface rigidity may be measured at a size smaller than 220mm square, but it is important to note that the surface rigidity of the nonwoven fabric increases as the area of ​​the nonwoven fabric decreases. The table below shows the method for measuring surface rigidity for 100mm square and 50mm square sample sizes used in the examples. (Measurement method for a 100mm square sample) Number of measurement samples: 10 points (average calculated) Load cell capacity: 500N Test speed: 2 mm / min (constant speed) Test environment: 24°C, 40%RH Sample size: 100 x 100 mm 2 Opening size: 70 x 70 mm 2 Indenter shape: φ50mm, tip radius 25mm hemisphere (Measurement method for a 50mm square sample) Number of measurement samples: 10 points (average calculated) Load cell capacity: 500N Test speed: 2 mm / min (constant speed) Test environment: 24°C, 40%RH Sample size: 50 x 50 mm 2 Opening size: 35 x 35 mm 2 Indenter shape: φ25mm, tip radius 25mm hemisphere

[0026] (Thickness of nonwoven fabric) The thickness of the nonwoven fabric in this embodiment was measured according to the following procedure. (1) Sections measuring 5 cm x 5 cm were obtained from five different locations on the sample. (2) The thickness of each section was measured using an ABS Digimatic Indicator ID-CX (manufactured by Mitutoyo Corporation). A Φ15mm flat measuring probe was used for this measurement. (3) The average of the five points obtained in step (2) above was used as the thickness of the sample. It is generally known that the thicker a material is, the higher its rigidity. In particular, it is known that when the rigidity of a soundproofing material is high, it has high sound insulation properties in the low-frequency range (this is called the rigidity law). If the thickness is within this range, the nonwoven fabric will have self-supporting properties, and therefore the sound insulation properties will also be high. The thickness of the nonwoven fabric is preferably 0.5 mm or more, more preferably 1.0 mm or more, and particularly preferably 3.0 mm or more. Furthermore, since rigidity improves as the thickness increases, there is no particular upper limit, but from the viewpoint of handling properties and post-processing such as pressing, it is preferably 10 mm or less, and more preferably 5 mm or less. Furthermore, thickness can be controlled in two ways: by material control and by processing method control. Material control can be achieved by controlling the content of fibrillated fibers, the fiber diameter of the fibrillated fibers, and the type of fibrillated fibers. For example, increasing the content of fibrillated fibers reduces the bonding distance between the short fibers forming the skeleton, thus decreasing the thickness. Alternatively, the overall thickness can be increased by laminating two or more nonwoven fabrics.

[0027] (Flow resistance per unit thickness of nonwoven fabric) The unit-thickness flow resistance of a nonwoven fabric represents the difficulty of airflow through a 1m thick material. The unit-thickness flow resistance of the nonwoven fabric was measured using a flow resistance system (AirReSys, manufactured by Nippon Acoustic Engineering) in accordance with ISO 9053, following the procedure below. First, a predetermined number of φ42mm circular discs were cut from the nonwoven fabric. Next, air at a flow velocity of 0.5m / s was flowed through the cut nonwoven fabric, and the differential pressure across the nonwoven fabric was read. This result was then normalized and calculated by dividing it by the flow velocity and the thickness of the nonwoven fabric. A higher unit-thickness flow resistance indicates greater air permeability and improved sound insulation of the material. A unit-thickness flow resistance of 0.1MNs / m is preferred. 4 That is all. More preferably 5MNs / m 4 The above is preferable to 10 MNs / m 4 The above is the most preferable, and 50 MNs / m 4 The above is true, and each stage is preferably 90 MNs / m 4That concludes the explanation. On the other hand, if the flow resistance per unit thickness is high, the sound absorption coefficient of the material decreases. Sound absorption by nonwoven fabrics occurs through a mechanism in which vibrations are converted into thermal energy due to friction between the air and fibers as air passes through the nonwoven fabric, thereby suppressing vibrations. If the flow resistance per unit thickness is too high, it becomes difficult for air to pass through the nonwoven fabric in the first place, so the sound absorption coefficient decreases. Therefore, the flow resistance per unit thickness of nonwoven fabric is 1,000 MNs / m 4 The following is often 200 MNs / m 4 The following is preferable: 100 MNs / m 4 The following are preferable.

[0028] (Bulk density of nonwoven fabrics) The bulk density of the nonwoven fabric is 30 kg / m². 3 It is preferable that the bulk density is above this range. Having a bulk density within this range allows for appropriate breathability and facilitates sound absorption. More preferably, the bulk density is 100 kg / m³. 3 The above, and more preferably 200 kg / m 3 The above is the most preferable, and is particularly preferable at 300 kg / m 3 The above is the most preferable, and is particularly preferable at 500 kg / m 3 That concludes the explanation. Furthermore, if the bulk density of the nonwoven fabric is too high, the flow resistance per unit thickness will also become too high, which will conversely impair the sound absorption effect (especially in the high-frequency range). The upper limit of bulk density is preferably 10,000 kg / m³. 3 The following, and more preferably 5,000 kg / m 3 The following, and particularly preferably 1,000 kg / m³ 3 The following, and especially preferably 700 kg / m 3 The following applies: The bulk density of nonwoven fabric is calculated using the following formula. Bulk density [kg / m³] 3 ]=Grain weight [g / m 2 ] / thickness[mm] The bulk density can be controlled by adjusting the thickness of the material, given the same basis weight, and the thickness of the material can be adjusted by the method described above.

[0029] (Balance weight of nonwoven fabric) The basis weight of the nonwoven fabric was determined by measuring the weight of a 4cm square piece of nonwoven fabric using an electronic balance (GX-8K2, manufactured by A&D Company, Limited) and multiplying the result by 625. The thickness of the nonwoven fabric was calculated using the same method. The higher the basis weight of the nonwoven fabric, the greater its rigidity and the improved its sound insulation properties. Preferably, 10 g / m². 2 The above is preferable to 50 g / m². 2 The above, and more preferably 100 g / m² 2 The above is the standard, and a particularly preferred value is 150 g / m². 2 The above is the most preferable, and especially preferable is 300 g / m². 2 That's all. Also, when used in automobiles, if the basis weight is too high, fuel efficiency will decrease, so 10,000 g / m³ is recommended. 2 The following is preferable: 7,000 g / m² 2 The following is more preferable: 3,000 g / m² 2 The following are even more preferable.

[0030] (Porosity of nonwoven fabric) The porosity of a nonwoven fabric is expressed as a percentage of the air content per unit volume of the nonwoven fabric. Therefore, the porosity of a nonwoven fabric is given by the following formula: ε[%]=(1-S1 / S2)×100 {In the formula, ε: porosity, S1: bulk density, S2: true density} It is calculated using the bulk density and true density of the nonwoven fabric accordingly.

[0031] Furthermore, when two types of materials are mixed, the true density of the nonwoven fabric is defined as the sum of the true densities of each material multiplied by their volume ratio. The lower the porosity, the smaller the voids within the nonwoven fabric. Sound is caused by the movement of air particles, and the smaller the gaps between the voids, the faster the particle velocity. A faster particle velocity allows for more efficient conversion of thermal energy due to friction between the air and the fibers within the nonwoven fabric, thus improving the sound absorption coefficient. The porosity of the nonwoven fabric is more preferably 90% or less, even more preferably 85% or less, particularly preferably 80% or less, and especially preferably 60% or less. Also, if the porosity is too low, the flow resistance per unit thickness increases, and the sound absorption coefficient decreases, especially in the high-frequency range. Therefore, the lower limit is preferably 40% or more, and more preferably 50% or more.

[0032] (Maze-like properties of nonwoven fabric) The labyrinth degree of the nonwoven fabric is preferably between 1.20 and 10.0. Here, labyrinth degree is a parameter that embodies the ratio of the length of the fluid path flowing inside the nonwoven fabric to the thickness of the nonwoven fabric. The higher the labyrinth degree, the better the sound absorption of the material. As mentioned above, sound absorption by nonwoven fabric occurs through the conversion of thermal energy due to friction between fibers and air vibrations. A high labyrinth degree means that the frequency of friction between fibers and air increases, and as a result, the sound absorption coefficient of the material also improves. The labyrinth degree of the nonwoven fabric is more preferably 2.0 or higher, even more preferably 2.3 or higher, and particularly preferably 3.5 or higher. Furthermore, if the labyrinth degree is too high, the flow resistance per unit thickness also increases, and the sound absorption coefficient of the material actually decreases, so it is more preferably 7.0 or lower, and even more preferably 5.0 or lower. The labyrinthiness of the nonwoven fabric was measured using a labyrinthiness / characteristic length measurement system (TORVITH, manufactured by Nippon Acoustic Engineering) following the procedure below. First, a predetermined number of φ42mm circular discs were cut from the nonwoven fabric. Next, the square of the sound velocity ratio between the sound velocity in the free space without the nonwoven fabric and the sound velocity of the sound wave passing through the nonwoven fabric was calculated. Specifically, this was determined by measuring the time it took for 300kHz ultrasound to reach the receiver from the transmitter. The square of this sound velocity ratio with and without the nonwoven fabric has a frequency characteristic, and especially in the ultrasonic region, if the reciprocal of the square root of the frequency is taken on the horizontal axis, it becomes a straight line sloping upwards. Since labyrinthiness is defined as the value at the limit of infinite frequency, the value corresponding to the y-intercept at this point was used as the labyrinthiness.

[0033] (Tensile modulus of nonwoven fabric) The tensile modulus of the nonwoven fabric is 10 MPa or higher. If the tensile modulus is within this range, the nonwoven fabric will exhibit sound insulation properties in the low-frequency range due to the rigidity law. More preferably, the tensile modulus is 50 MPa or higher, even more preferably 100 MPa or higher, particularly preferably 150 MPa or higher, exceptionally preferably 200 MPa or higher, and most preferably 250 MPa or higher. Furthermore, there is no particular upper limit, and the theoretical modulus of the nonwoven fabric is 1300 MPa or less, and may be 1000 MPa or less. Note that the tensile modulus of the nonwoven fabric is the modulus of the material itself, regardless of the shape of the nonwoven fabric, and the test specimen consists only of flat parts that do not include any uneven areas of the nonwoven fabric. Furthermore, the higher value among the two measurement methods below represents the tensile modulus of elasticity as specified in this specification. (Calculated using the Tensilon Universal Material Tester (RTG-1250, manufactured by A&D Company, Limited)) Number of measurement samples: 10 Tensile speed: 10 mm / min (constant speed) Type of fixture: Parallel clamping air jaw Load cell type: UR-1kN-D Chuck spacing: 100mm Chuck pressure: 0.48 MPa Environmental temperature: 25℃ Environmental humidity 50% Specimen shape: Strip-shaped Specimen width: 15 mm Length of test specimen: 150 mm Thickness of the test specimen: Same as the thickness of the nonwoven fabric. (Calculated using a universal testing machine, model 5969 (manufactured by Instron)) Number of measurement samples: 10 Tensile speed: 200 mm / min (constant speed) Load cell capacity: 500N Test fixture: 1kN air chuck Gauge length: 25mm vertically, 8mm horizontally Environmental temperature: 23℃ Environmental humidity 5% Specimen shape: JIS K 6251 Dumbbell shape, type 1 Thickness of the test specimen: Same as the thickness of the nonwoven fabric.

[0034] (Fibrillated fiber) In this specification, fibrillated fibers refer to fibers that have split axially, subdivided, and become fuzzy. Fibrillated fibers can be broadly classified into two types: those obtained by physically or chemically destroying part of the structure of fibers without a branched structure, and those obtained by intentionally creating fluffiness during the spinning of polymer compounds to induce fibrillation. Examples of the former include microfibrillated cellulose (cellulose fibers that have been refined using at least one physical or chemical means, and are synonymous with common names such as CNF, CeNF, cellulose nanofiber, MFC, cellulose microfiber, and microfiber-like cellulose), acrylic pulp (fibrillated polyacrylonitrile fibers), synthetic pulps such as aramid pulp, chitin nanofibers, chitosan nanofibers, and silk nanofibers. Examples of the latter include synthetic pulps produced by flash spinning. Generally, fibrillated fibers have a structure in which the fiber diameter is partially thinner compared to ordinary fibers without a branched structure, due to their manufacturing method. As a result, fibrillated fibers tend to have a large surface area and, at the same time, a large number of bent structures. Due to these characteristics, in the nonwoven fabric of this embodiment, fibrillated fibers have the effect of a binder that binds non-fibrillated fibers, described later, together through physical entanglement. Depending on the type of fibrillated fiber, differences in fibrillation rate, fiber diameter, and surface state can affect the properties of the nonwoven fabric, but it is preferable that the fibrillated fibers entangle with each other, increasing the flow resistance and labyrinthiness per unit thickness. From this viewpoint, it is preferable to use at least one selected from the group consisting of microfibrillated cellulose, acrylic pulp, aramid pulp, chitin nanofibers, chitosan nanofibers, and silk nanofibers as the fibrillated fiber. Regardless of the above substances, it is preferable to select a fibrous material made of polymers whose melting point is higher than the thermal decomposition onset temperature, as this facilitates fibrillation.

[0035] (Fibrillation rate of fibrillated fibers) The fibrillation rate of the fibrillated fibers in the nonwoven fabric is preferably 0.3% or higher. Here, the fibrillation rate refers to the ratio of the total length of branched fibers to the length of the stem of the fibrillated fiber. Within this range, sufficient binder effect is obtained, the nonwoven fabric has self-supporting properties, and the shedding of non-fibrillated fibers from the nonwoven fabric is reduced. In addition, the thinned fibers due to fibrillation exhibit an effect on sound absorption in the low frequency range. The fibrillation rate of the fibrillated fibers is more preferably 0.5% or higher, even more preferably 0.8% or higher, particularly preferably 1.8% or higher, exceptionally preferably 2.0% or higher, and most preferably 2.4% or higher. Furthermore, there is no particular upper limit to the fibrillation rate, and it may be 100% or less, 10% or less, or 3.0% or less. Furthermore, the fibrillation rate of fibrillated fibers, as well as the average fiber length, average fiber diameter (Method A), and area fineness (described later), were measured using a fiber image analyzer (TechPap Morfi-Neo) under the condition of 3 minutes of image capture (at least 120,000 fibers were measured) using the following procedure. The minimum fiber length to be measured was set at 20 μm.

[0036] (1) Fibrillated fibers were dispersed in pure water to prepare a 1 L aqueous dispersion. Here, the final solid content concentration of the fibrillated fibers was set to 0.004 mass%. When the aqueous dispersion contained 2 mass% or less of fibrillated fibers, the dispersion treatment was performed by simply mixing with a spatula or the like. When the aqueous dispersion contained 2 mass% or more, or when it was in the form of a hydrated cake or powder, the dispersion treatment was performed using a high-shear homogenizer (IKA, product name "Ultra-Turrax T18") at a rotation speed of 25,000 rpm for 5 minutes. (2) The aqueous dispersion prepared in procedure (1) above was subjected to an autosampler and measured. (3) The mean fiber width, μm, fines-mean length, μm, macro fibrillation index, % (or fiber fibrillation index, %), and fine content in area, % (or fines content, % in area) were read and used as the average fiber diameter (Method A), average fiber length, fibrillation rate, and area fineness rate, respectively.

[0037] In this invention, the fibrillation rate, average fiber diameter (Method A), average fiber length, and area fineness rate can be measured in the slurry state before obtaining the nonwoven fabric (for example, after obtaining fibrillated fibers, they may be measured individually). Alternatively, fibrillated fibers and non-fibrillated fibers may be mixed in a predetermined ratio, and then the fibrillated fibers may be separated from the mixed slurry by methods such as sieving or centrifugation for measurement. Furthermore, after the fibrillated fibers and non-fibrillated fibers are mixed, paper is made, dried, and a nonwoven fabric is formed, the nonwoven fabric may be dispersed in water to break down the fibers, and then the fibrillated fibers may be separated by methods such as sieving or centrifugation for measurement. For example, the following describes a method for separating fibrillated fibers from a mixed paper-making dried nonwoven fabric and measuring the fibrillation rate, average fiber length, average fiber diameter (Method A), and area fineness ratio. (1) 5g of nonwoven fabric (dried) and 300g of pure water are introduced into a juicer mixer (Vitamix 1200i S) and mixed for 3 minutes at rotation level 1. The resulting dispersion is poured into a stainless steel sieve (mesh diameter: φ150μm, mesh opening: 300μm, weave: plain weave, inner height: 45mm), and the filtered dispersion is collected in a tray to obtain dispersion containing only fibrillated fibers. (2) The dispersion water obtained in (1) above was adjusted to a concentration of 1 L of aqueous dispersion with a final solid content concentration of 0.004 mass%, and measured using the fiber image analyzer (TechPap Morfi-Neo) described above, under the condition of taking photographs for 3 minutes. The minimum fiber length to be measured was set at 20 μm. The minimum number of fibers that can be measured by the fiber image analyzer using this method is 500 or more. There is no particular upper limit, and it is acceptable to have 1,000 or fewer fibers.

[0038] (Average fiber length of fibrillated fibers) The average fiber length of the fibrillated fibers in the nonwoven fabric is 25 μm or more. This average fiber length refers to the number-average fiber length (Fines-Fibers Mean length) of fibers 20 μm or longer, as measured by the aforementioned fiber image analyzer (TechPap Morfi-Neo). Within this range, sufficient binder effect can be obtained. Furthermore, the longer the average fiber length of the fibrillated fibers, the easier it is for the fibrillated fibers to crosslink with the non-fibrillated fibers. This crosslinking of fibrillated fibers increases the rigidity of the nonwoven fabric as a binder, so the more crosslinked fibrillated fibers there are, the higher the rigidity of the nonwoven fabric and the higher the sound insulation performance in the low-frequency range. In addition, the more crosslinked fibrillated fibers there are, the greater the flow resistance and labyrinthiness per unit thickness of the nonwoven fabric, improving the sound insulation performance of the nonwoven fabric. Furthermore, fibrillated fibers that do not crosslink will exist clinging to the outer circumference of the non-fibrillated fibers. The contribution of non-crosslinked fibrillated fibers to improving the sound insulation properties of nonwoven fabrics is smaller than that of crosslinked fibrillated fibers. The average fiber length of the fibrillated fibers is more preferably 45 μm or more. As an upper limit for the average fiber length, a length of 200 μm or less is preferable because it allows for excellent mixability with non-fibrillated fibers and results in a uniform molded body. In addition, in the manufacturing process of fibrillated fibers, the average fiber diameter increases as the average fiber length increases, but a larger average fiber diameter weakens the entanglement between fibrillated fibers, reducing their binder effect. The upper limit for the average fiber length of the fibrillated fibers is more preferably 125 μm or less, even more preferably 90 μm or less, particularly preferably 65 μm or less, and most preferably 55 μm or less.

[0039] (Area fineness ratio of fibrillated fibers) The area fineness ratio of fibrillated fibers in the nonwoven fabric is preferably 2% or more. Here, the area fineness ratio is the ratio of the total area of ​​the observed image of fine fibers to the total area of ​​the observed image of all fibers (area of ​​normal fibers + area of ​​fine fibers), and fine fibers refer to fibers with a fiber length of less than 100 μm. The method for measuring the area fineness ratio of fibrillated fibers is as described above. As described above, in the manufacturing process of fibrillated fibers, the average fiber diameter increases as the average fiber length increases, but if the average fiber diameter is large, the entanglement between fibrillated fibers weakens, and the effect as a binder also decreases. If the area fineness ratio is within this range, a sufficient effect as a binder is obtained, the nonwoven fabric has self-supporting properties, and the shedding of non-fibrillated fibers from the nonwoven fabric is reduced. The area fineness ratio is more preferably 3% or more, even more preferably 7% or more, particularly preferably 8% or more, most preferably 9% or more, and most preferably 30% or more. Furthermore, the presence of ordinary fibers with a fiber length of 100 μm or more allows the fine fibers to form entanglements with the ordinary fibers as the main axis, so it is preferable to include a certain amount of ordinary fibers. For this reason, the upper limit of the area fine fiber ratio is preferably 90% or less, more preferably 50% or less, and even more preferably 40% or less.

[0040] (Average fiber diameter of fibrillated fibers by Method A) The average fiber diameter of fibrillated fibers in nonwoven fabrics consists of two parts: the average fiber diameter corresponding mainly to the main fiber portion of the fibrillated fiber (average fiber diameter by method A) and the average fiber diameter including the minute fiber portion up to the fibrillated end (average fiber diameter by method B). The average fiber diameter by method A is preferably 50 μm or less. Within this range, the pore diameter formed inside the composite molded body does not become too small, and appropriate air permeability is obtained. The method for measuring the average fiber diameter of fibrillated fibers (method A) is as described above. The average fiber diameter of fibrillated fibers by method A is more preferably 20 μm or less, even more preferably 15 μm or less, and most preferably 13 μm or less. The lower limit may be 1.5 μm or more, depending on the resolution of the device. Furthermore, in the wet papermaking method and pulp molding method, which are listed as nonwoven fabric manufacturing methods later, 2.5 μm or more is preferable from the viewpoint of water drainage.

[0041] <Average fiber diameter of fibrillated fibers by method B> The average fiber diameter of fibrillated fibers in the nonwoven fabric according to Method B refers to the average fiber diameter including the minute fiber portion up to the fibrillated end. The average fiber diameter is preferably 1000 nm or less. Within this range, entanglement with non-fibrillated fibers is more likely to occur, suppressing fiber shedding from the nonwoven fabric. The average fiber diameter of the entire fibrillated fiber according to Method B is more preferably 800 nm or less, even more preferably 600 nm or less, and most preferably 500 nm or less. There is no particular lower limit, but it is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more.

[0042] Furthermore, the average fiber diameter (Method B) of fibrillated fibers was measured using a specific surface area and pore distribution analyzer (NOVA-4200e, Quantachrome Instruments) following the procedure below. For fibrillated fibers that aggregate upon drying, such as fibrillated cellulose microfibers, the measurement was performed after the following pretreatment. [Pre-processing] (1) A wet cake was prepared by filtering the fibrillated microfiber aqueous dispersion. (2) The obtained wet cake was added to tert-butanol and diluted with tert-butanol so that the fibrillated fiber solid content concentration was 0.5% by weight. Dispersion treatment was performed using a high-shear homogenizer (IKA, trade name "Ultra-Turrax T18") at a rotation speed of 25,000 rpm for 5 minutes. (3) The obtained dispersion is estimated at 10 g / m² 3 The material was weighed to obtain a sheet by filtering it through filter paper. (4) The obtained sheet was not peeled off the filter paper, but was sandwiched between two larger sheets of filter paper together with the filter paper, and the edges of the filter paper were pressed down with weights while it was dried in a 150°C oven for 5 minutes to obtain a porous sheet.

[0043] [Measurement of specific surface area and calculation of fiber diameter] (1) 0.2 g of fibrillated fiber (porous sheet prepared by pretreatment) was dried under vacuum at 120°C for 5 minutes. (2) After drying, the amount of nitrogen gas adsorbed at the boiling point of liquid nitrogen is measured at 5 points within the range of relative vapor pressure (P / P0) of 0.05 or more and 0.2 or less (multi-point method), and the BET specific surface area (m²) is calculated using the same device program. 2 The value per gram ( / g) was calculated. (3) The obtained BET specific surface area value Y(m 2 From ( / g), the average fiber length X (nm) and the density of fibrillated fibers ρ (g / cm³) are obtained. 3 ) as follows: Average fiber diameter (nm) = 1 / (2.5 × ρ × Y × 10) -4 ) The average fiber diameter (Method B) was calculated using the following method.

[0044] (Cellulose raw material) Microfibrillated cellulose is preferred as the fibrillated fiber used in nonwoven fabrics. As raw materials for this microfibrillated cellulose, so-called wood pulp such as coniferous pulp and hardwood pulp, and non-wood pulp can be used as raw materials for type I cellulose. Examples of coniferous pulp raw materials include fir, hemlock, Himalayan cedar, larch, spruce, Japanese red pine, Japanese red spruce, Japanese black pine, Japanese white pine, longleaf pine, spruce, cypress, sawara cypress, Japanese cedar, metasequoia, Japanese yew, Japanese umbrella pine, Japanese juniper, goldcrest, and blue ice. Examples of hardwood pulp raw materials include eucalyptus, poplar, Japanese oak, oak, birch, beech, maple, chestnut, paulownia, birch, elm, and aspen. Examples of non-wood pulps include cotton-derived pulps such as cotton linter pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp. Cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp refer to refined pulps obtained from raw materials such as cotton lint or cotton linter, hemp-based abaca (for example, often from Ecuador or the Philippines), zaisal, bagasse, kenaf, bamboo, and straw through a purification process aimed at deligninization by pulping and removal of hemicellulose, as well as a bleaching process. In addition, refined products such as cellulose derived from bacteria such as acetic acid bacteria, cellulose derived from seaweed, and ascidian cellulose can also be used as raw materials for cellulose microfibers. As raw materials for type II cellulose, cut yarns of regenerated cellulose fibers (rayon, lyocell, Bemberg, etc.) and cut yarns of cellulose derivative fibers, or pulp can also be used as raw materials for cellulose microfibers. Furthermore, cut yarns of ultrafine regenerated cellulose or cellulose derivatives obtained by electrospinning can also be used as raw materials for cellulose microfibers or as cellulose microfibers themselves. These raw materials may be used individually or in mixtures of two or more. The average fiber diameter can be adjusted by mixing multiple raw materials.

[0045] (Crystal form and degree of crystallinity) As mentioned above, the crystalline form of cellulose is not unique, but rather exists in various forms and is broadly classified into type I and type II cellulose. Of the two, type I crystals exhibit high values ​​in terms of rigidity and thermal properties. In particular, it is known that when the rigidity of soundproofing material is high, it exhibits high sound insulation in the low frequency range. Therefore, it is preferable that the cellulose crystalline form of the fibrillated fibers used in the nonwoven fabric of this embodiment also includes type I crystals. To be precise from an academic standpoint, type I cellulose crystals include two types, Iα and Iβ, but the mixing ratio of Iα and Iβ does not need to be considered here. Also, the higher the proportion of crystalline components (degree of crystallinity) in the cellulose, the greater the rigidity of the microfibrillated cellulose. The degree of crystallinity is preferably 60% or more, but may be 100% or less. The degree of crystallinity is more preferably 70% or more, even more preferably 80% or more, particularly preferably 85% or more, and most preferably 90% or more. Crystallinity is determined by X-ray diffraction, where diffraction lines from crystalline materials are detected as peaks, and scattered light from amorphous materials is detected as halos. By fitting these peaks and halos, the following formula is obtained: Crystallinity [%]=100×Ic / (Ic+Ia) The degree of crystallinity can be calculated by substituting {Ic: integrated scattering intensity of the peak, Ia: integrated scattering intensity of the halo} into the formula.

[0046] (Method for producing microfibrillated cellulose) Microfibrillated cellulose can be obtained by micronizing the raw materials described above. In this specification, "micronization" means controlling the fiber length, fiber diameter, fibrillation rate, etc., while reducing the size of the cellulose. In one embodiment, a pretreatment step may be performed before the micronization process. In the pretreatment step, it is effective to prepare the raw material pulp to a state that is easy to micronize by autoclaving under water impregnation at a temperature of 100°C to 150°C, enzymatic treatment, or a combination thereof. These pretreatments not only reduce the burden of the micronization process, but also have the effect of discharging impurities such as lignin and hemicellulose present on the surface and in the gaps of the microfibrils that make up the cellulose fibers into the aqueous phase, thereby increasing the α-cellulose purity of the micronized fibers, and may be effective in improving the heat resistance of microfibrillated cellulose. In the pulping process, the raw pulp is dispersed in water and then pulverized using known pulping equipment such as beaters, single-disc refiners, double-disc refiners, and high-pressure homogenizers. The optimal treatment concentration for pulping varies depending on the equipment used and can be set arbitrarily. The fibrillation rate, average fiber length, and average fiber diameter of microfibrillated cellulose can be controlled by the cellulose raw material, pretreatment conditions before micronization (e.g., autoclaving, enzymatic treatment, beating, etc.), micronization conditions (selection of equipment type, operating pressure, number of passes, etc.), or a combination thereof. Here, the cellulose raw material, pretreatment, micronization, etc., may be controlled by combining multiple conditions.

[0047] (Multi-stage miniaturization) When cellulose is refined in multiple stages, it is effective to combine two or more refinement devices with different refinement mechanisms or shear rates. Here, as a method of multi-stage refinement, it is preferable to refine in multiple stages using disc refiners with different disk configurations, or to refine in a high-pressure homogenizer after refinement in a disc refiner. Here, either a single disc refiner or a double disc refiner may be used.

[0048] (Multi-stage miniaturization using multiple discreeters) When performing multi-stage refinement using multiple disc refiners, it is preferable to use refiners having at least two different disc configurations. By using refiners with different disc configurations, it is possible to control various shape parameters of microfibrillated cellulose, namely the fibrillation rate, average fiber length, and average fiber diameter.

[0049] (Disk structure of the disc refiner) Adjusting the disc structure of the disc refiner is an effective means of controlling various shape parameters of microfibrillated cellulose. Important structural features of the disc refiner include blade width, groove width, and blade-to-groove ratio (blade width divided by groove width), with the blade-to-groove ratio being particularly important for producing fibrillated fibers. A small blade-to-groove ratio results in a greater fiber-cutting effect, leading to shorter fiber lengths, while a large blade-to-groove ratio results in a greater fiber-crushing (beating) effect, leading to a higher fibrillation rate. Since it is important that the nonwoven fabric in this embodiment contains fibrillated fibers, a blade-to-groove ratio of 0.2 or higher is preferable, more preferably 0.4 or higher, and most preferably 0.5 or higher. Furthermore, if the blade-to-groove ratio is constant, smaller absolute values ​​for blade width and groove width result in finer and more uniform microfibrillated cellulose.

[0050] (Distinguishing distance between blades in disc refiner processing) Furthermore, in the miniaturization process using a disc refiner, it is also important to control the distance between the two discs (rotating blade and stationary blade) (hereinafter referred to as the "blade distance"). By controlling the blade distance, it is possible to control the average fiber length of the microfibrillated cellulose; the smaller the blade distance, the smaller the average fiber length. In the initial processing stage, it is preferable to set the blade distance to 0.05 mm or more and 2.0 mm or less, and in the subsequent processing stage, it is preferable to set the blade distance to 0.05 mm or more and 1.0 mm or less. When adjusting the blade distance, it is preferable to gradually narrow it from a wider blade distance to the desired blade distance. By controlling it in this way, clogging and overload of the equipment can be prevented, and highly homogeneous cellulose fibers with a narrow distribution of fiber length and fiber diameter can be obtained.

[0051] (Number of passes in the discriminator process) The degree of refinement can also be controlled by the number of times the cellulose passes through the disc portion (hereinafter referred to as "number of passes"). By increasing the number of passes, cellulose fibers with a uniform distribution of fiber diameter and fiber length can be obtained. In this specification, "number of passes" means the number of times the refiner treatment is performed after the above-mentioned inter-blade distance has been set to the desired value. Preferably, the number of passes for the disc refiner is 5 or more, more preferably 20 or more, and even more preferably 40 or more. A higher number of passes is preferable because the distribution of fiber shape gradually converges to a constant value as the number of passes increases, but considering productivity, the upper limit of the number of passes is 300 or less.

[0052] (Method for controlling the number of passes in the discriminator process) Methods for controlling the number of passes include using one tank for one refiner and simply circulating the slurry, controlling the number of passes based on the flow rate, or using two tanks for one refiner and reciprocating the slurry between the tanks during the refiner process. The former allows for simplification of the equipment. On the other hand, in the latter case, since the cellulose reliably passes through the disc section in each process, a more uniform microfibrillated cellulose can be obtained.

[0053] (Multi-stage miniaturization using a combination of a disc refiner and a high-pressure homogenizer) Another preferred method is to further refine the cellulose fibers, which have been refined by a disc refiner, using a high-pressure homogenizer. Compared to a disc refiner, a high-pressure homogenizer is more effective at thinning the fibers, and by combining it with the refinement performed by the disc refiner, it is possible to obtain long, thin cellulose fibers.

[0054] (Method of manufacturing synthetic pulp) Synthetic pulp can be obtained by methods such as spinning and drawing of pre-existing polymers, flash spinning from solutions or emulsions, strip fiber production by uniaxial stretching of films, and shear polymerization, in which monomers are polymerized under shear stress. Acrylic pulp such as BiPUL (registered trademark, manufactured by Nippon Exlan Industries Co., Ltd.) and aramid pulp such as Kevlar (registered trademark, manufactured by DuPont) or Tiara (registered trademark, manufactured by Daicel Mirise Co., Ltd.) can also be used. Furthermore, synthetic pulp can be produced by high-pressure homogenization, similar to finely milled cellulose.

[0055] (Non-fibrillated fiber) The nonwoven fabric of this embodiment includes non-fibrillated fibers in addition to fibrillated fibers. In this specification, "non-fibrillated fibers" means fibrous material that does not have a branched structure. As non-fibrillated fibers, any of natural fibers, synthetic fibers, semi-synthetic fibers, or inorganic fibers can be used. Examples of polymers constituting non-fibrillated fibers include thermoplastic resins such as polyolefins, polyesters, polyamides (aromatic or aliphatic), acrylic polymers, polyvinyl alcohol, polylactic acid, polyphenylene ethers, polyoxymethylene, and polyphenylene sulfide; thermosetting resins such as epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, urea resins, allyl resins, silicon resins, benzoxazine resins, phenolic resins, unsaturated polyester resins, bismaleimidotriazine resins, alkyd resins, furan resins, melamine resins, polyurethane resins, and aniline resins; cellulose, chitin, chitosan, and the like. Furthermore, examples of inorganic materials constituting non-fibrillated fibers include glass, ceramics, cement, metals, carbon fibers, slugs, carbon nanotubes, and graphene. Additionally, since nonwoven fabrics exhibit higher sound insulation in the low-frequency range the higher their rigidity, it is preferable to include at least one material selected from the group consisting of the aforementioned inorganic materials. Moreover, from the viewpoint of processability into fiber shape, glass, metals, and carbon fibers are more preferable. Furthermore, from the viewpoint of ease of compounding with fibrillated fibers, glass is particularly preferable. Suitable types of glass include soda-lime glass, borosilicate glass, potash glass, crystal glass, optical glass, quartz glass, polarizing glass, double-glazed glass (eco-glass), tempered glass, laminated glass, heat-resistant glass / borosilicate glass, bulletproof glass, glass fiber, photocatalytic cleaning glass, water glass, uranium glass, acrylic glass, dichroic glass, goldstone / brownishite / agatestone / purpleishite, glass ceramics, low-melting-point glass, metallic glass, sapphiret, phase-splitting glass, porous glass, liquid glass, liquid glass, glass paint, hybrid glass (a silicate compound formed by chemically crosslinking silicon compounds such as silicone resin, silanol compounds, and thermoplastics at multiple functional groups, and then softening and rapidly cooling it at room temperature (120-180 degrees Celsius)), and natural glass (obsidian, tektite, moldavite, meteorite, volcanic glass, lightning rock, trinitite, Pele's hair). Furthermore, while glass is generally an amorphous material without a crystalline structure, it is possible to break down its structure and induce crystallization by melting it at a constant high temperature for a long period of time. Crystallized glass (glass ceramic), in which this crystal is homogenized, can also be cited as an example.

[0056] Furthermore, examples of glass fibers usable in this invention include E glass fibers (alkali-free glass), S glass fibers (containing more alumina (AL2O3) than E glass, and also containing more magnesium oxide in addition to alumina), C glass fibers (alkali-containing glass), ECR glass fibers (not containing boron (B2O3) or fluorine (F2)), and AR glass fibers (containing a large amount of zirconia (ZrO2)). These may be used individually or in combination. Preferred glass fibers in terms of compounding with fibrillated fibers include E glass fibers and S glass fibers. More preferably, E glass fibers are used. Furthermore, examples of carbon fiber types include PAN-based carbon fibers obtained by carbonizing PAN precursors (polyacrylonitrile fibers) and pitch-based carbon fibers obtained by carbonizing pitch precursors (pitch fibers obtained from coal tar or heavy petroleum components). Of these, pitch-based carbon fibers have a higher modulus of elasticity compared to PAN-based carbon fibers because the carbon layer surface constituting the fiber has a wide surface area and is arranged parallel to the fiber axis. Therefore, in terms of improving the modulus of elasticity of the nonwoven fabric itself, pitch-based carbon fibers are preferred. These non-fibrillated fibers may be used individually or in combination.

[0057] (Average fiber diameter of non-fibrillated fibers) Non-fibrillated fibers are preferably those with an average fiber diameter of 0.1 μm or more. The average fiber diameter of the non-fibrillated fibers was measured according to the following procedure. (1) The weight [g] of a 1,000m length of non-fibrillated fiber was measured and defined as tex [tex]. (2) The following formula: Average fiber diameter [μm]=2×[T×1,000 / (S×π)] 0.5 {In the formula, T: tex, S: true density of the material [g / cm³] 3 The tex was converted to the average fiber diameter using ]}.

[0058] If the average fiber diameter of the non-fibrillated fibers is less than 0.1 μm, they will not be uniformly mixed when mixed with the fibrillated fibers, and a nonwoven fabric with a sufficiently finely textured interior cannot be obtained. Furthermore, the larger the average fiber diameter of the non-fibrillated fibers, the higher the rigidity of the fibers themselves, and the higher the rigidity of the nonwoven fabric, resulting in high sound insulation in the low-frequency range according to the rigidity law. The average fiber diameter of the non-fibrillated fibers is more preferably 1 μm or more, even more preferably 3 μm or more, and particularly preferably 5 μm or more. Furthermore, examples of nonwoven fabric manufacturing methods include the wet papermaking method (also called papermaking) or the pulp molding method, which will be described later. When using this method, fibrillated fibers intertwine in a complex manner and crosslink between the non-fibrillated fibers. This crosslinking of fibrillated fibers acts as a binder, increasing the rigidity of the nonwoven fabric. Therefore, the more crosslinked fibrillated fibers there are, the higher the rigidity of the nonwoven fabric, and according to the rigidity law, it exhibits high sound insulation in the low-frequency range. In addition, the more crosslinked fibrillated fibers there are, the greater the flow resistance and labyrinthiness per unit thickness of the nonwoven fabric, as mentioned above, improving the sound insulation of the nonwoven fabric. Here, if the average fiber diameter of the non-fibrillated fibers is increased, the number of non-fibrillated fibers per unit volume decreases, and thus the number of crosslinkable fibrillated fibers decreases. At this time, the fibrillated fibers that were not crosslinked will exist clinging to the outer circumference of the non-fibrillated fibers. The contribution of non-crosslinked fibrillated fibers to improving the sound insulation properties of nonwoven fabrics is smaller than that of crosslinked fibrillated fibers. Therefore, the average fiber diameter of non-fibrillated fibers is preferably 300 μm or less, more preferably 150 μm or less, and even more preferably 30 μm or less.

[0059] (Fiber length of non-fibrillated fibers) The fiber length (also called the cut length) of the non-fibrillated fibers is preferably 1 mm or more. This range facilitates the three-dimensional molding described later, resulting in a more uniform nonwoven fabric and a more uniform sound insulation effect. Furthermore, since longer fiber lengths increase the rigidity of the nonwoven fabric, the fiber length of the non-fibrillated fibers is more preferably 3 mm or more, and even more preferably 5 mm or more. As an upper limit, from the viewpoint of moldability of the nonwoven fabric, it is preferable to have a fiber length of 30 mm or less.

[0060] (Tensile modulus of non-fibrillated fibers) The tensile modulus of the non-fibrillated fiber is preferably 1 GPa or higher. Here, the tensile modulus (also called Young's modulus) is expressed as the ratio of the tensile stress per unit cross-sectional area to the elongation in the direction of stress, and represents the dimensional stability (resistance to deformation) of the material. A high tensile modulus of the non-fibrillated fiber results in higher rigidity of the nonwoven fabric, exhibiting high sound insulation performance in the low-frequency range. The tensile modulus of the non-fibrillated fiber is more preferably 5 GPa or higher, even more preferably 10 GPa or higher, particularly preferably 70 GPa or higher, exceptionally preferably 190 GPa or higher, and most preferably 300 GPa or higher. Furthermore, there is no particular upper limit, and in one embodiment, it is preferably 1,000 GPa or less, and more preferably 500 GPa or less. The tensile modulus is measured using a Tensilon universal material tester (RTG-1250, manufactured by A&D Co., Ltd.) with a measurable fiber length of the same material, using the following method (in accordance with JIS L 1013:2010, 8.5.1 (Standard Time Test)). A tensile test is performed by attaching a loosely stretched non-fibrillated fiber to the gripping part of the tester, measuring the load and elongation at which the sample breaks, and calculating the strength and elongation, respectively, using the following formulas. The average values ​​of these values ​​are taken as the strength (average strength) and elongation of the sample. If the breaking strength is less than the strength at the maximum load, the strength at the maximum load and the elongation at that time are measured. Strength (cN / dtex) = Strength at break or strength under maximum load (cN) / Fineness of sample (dtex) Elongation (%) = {Elongation at break or elongation at maximum load (mm) / Grip spacing (mm)} × 100 The measurement conditions are as follows: Number of measurement samples: 10 Tensile speed: 300 mm / min (constant speed) Load cell type: UR-50N-D Chuck spacing: 300mm Chuck pressure: 0.20 MPa Environmental temperature: 25℃ Environmental humidity 55%

[0061] The tensile modulus of the non-fibrillated fibers described above may be measured by mixing fibrillated and non-fibrillated fibers in a predetermined ratio, then separating the non-fibrillated fibers from the mixed slurry using methods such as sieving or centrifugation. Alternatively, the fibrillated and non-fibrillated fibers may be mixed, paper-made, dried to form a nonwoven fabric, and then dispersed in water to break down the fibers, separating the non-fibrillated fibers using methods such as sieving or centrifugation for measurement. Furthermore, the non-fibrillated fibers may be directly extracted from the nonwoven fabric using tweezers or adhesive tape for measurement.

[0062] (Fibrillated fiber content) The nonwoven fabric contains 1% by mass or more of fibrillated fibers based on the total mass of the nonwoven fabric. Within this range, the fibrillated fibers can contribute to sound absorption in the low frequency range. A higher content of fibrillated fibers improves the strength of the nonwoven fabric and reduces fiber shedding from the surface. It also improves the flow resistance per unit thickness, thus improving sound insulation. From these viewpoints, 2% by mass or more is more preferable, 5% by mass or more is particularly preferable, and 10% by mass or more is most preferable. However, if the fibrillated fiber content is too high, it can lead to a decrease in handling performance due to excessive rigidity and a decrease in sound absorption coefficient due to excessive flow resistance per unit thickness. Therefore, it is preferable that the content be 90% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less.

[0063] (Manufacturing method for nonwoven fabrics) There are no particular limitations on the method for manufacturing nonwoven fabrics, but examples include dispersing fibrillated fibers and non-fibrillated fibers in a liquid medium, removing the solvent by filtration and pressing, and drying. Mixing non-fibrillated fibers and fibrillated fibers in a liquid medium yields a nonwoven fabric with a more uniform internal structure. Specifically, wet papermaking and pulp molding are preferred as such molding methods because they allow for processing into any shape. Using wet papermaking yields a two-dimensional planar molded body (which can also be called a nonwoven fabric), while using pulp molding allows for the creation of complex three-dimensional shapes. There are several different methods of pulp molding depending on the desired molded body. These methods include the Thick Wall method, which produces very thick, load-bearing molded bodies with a film thickness of 5mm to 10mm; the Transfer Mold method, which produces molded bodies with a film thickness of 3mm to 5mm and a smooth surface; the Thermoformed Mold method, which produces complex shapes with a film thickness of 1mm to 3mm; the PIM (Pulp Injection Mold) method, which produces more complex shapes such as bosses and ribs, similar to ordinary plastic molded products; and the PF (Pulp Forming) method, which produces lightweight and soft molded products by foaming within the mold. Any method that does not belong to these classifications is acceptable as long as it allows for three-dimensional shaping. Various additives may be added to the liquid medium during molding.

[0064] (Liquid medium used during molding) The liquid medium used during molding is not particularly limited, and known liquid media such as water or organic solvents can be used. While water is preferred due to its ease of handling and environmental impact, nonpolar organic solvents with lower surface tension may be used to prevent aggregation during drying and reduce air permeability resistance per unit thickness. When using water as the liquid medium, surfactants may be added to control surface tension.

[0065] (Additives used during molding) By adding papermaking dispersants, binders, and crosslinking agents as additives during molding, it is possible to control the strength and handling properties of nonwoven fabrics, such as fiber shedding, as well as their structure, such as internal uniformity and surface smoothness. Papermaking dispersants refer to surfactants that facilitate the defibration of bundled fibrillated fibers in a liquid medium, and viscous agents that adjust the viscosity of the liquid medium and prevent fiber aggregation. This allows for improved surface smoothness and homogeneity, and control of the air permeability resistance per unit thickness by homogenizing the internal structure. Note that the added surfactants also affect the surface tension of the liquid medium. Binders refer to adhesive components such as starch, and by bonding fibers together, it is possible to control the structural strength and air permeability resistance per unit thickness. Crosslinking agents refer to isocyanates, polyurethanes, etc., and by chemically or physically crosslinking the entanglement points of fibers, it is possible to prevent fiber shedding and adjust strength. Furthermore, when nonwoven fabrics use fibrillated or non-fibrillated fibers containing hydrophilic functional groups such as hydroxyl groups, carbonyl groups, carboxyl groups, or amino groups, repeated absorption and dehumidification of moisture from the air can cause the fibers to aggregate, altering the microstructure of the nonwoven fabric. By restraining the fibers with a crosslinking agent, it is possible to stop such fiber movement and suppress aggregation. These additives may be used individually or in combination of two or more types.

[0066] (Blackening of nonwoven fabric) For automotive components, it is preferable that dirt and stains are not easily visible, and black components are preferred. One method for blackening nonwoven fabrics is to dye at least one type of fiber, either fibrillated or non-fibrillated, black. Methods for blackening fibrillated and non-fibrillated fibers include coating the fibers with a black colorant or incorporating the black colorant into the fibers beforehand. Examples of colorants include black powders such as carbon black, titanium-based black pigments, iron oxide powder, titanium oxynitride powder, and lower-order titanium oxide powder, as well as black fibers such as carbon fibers and carbon nanotubes. Furthermore, from the perspective of blackening nonwoven fabrics, it is preferable to blacken both fibrillated and non-fibrillated fibers, but considering cost and labor efficiency, it is also possible to blacken only one of them. In that case, from the viewpoint of ease of dyeing and content, it is preferable to blacken the non-fibrillated fibers.

[0067] (Adding flame retardants to nonwoven fabrics) For automotive components, from a safety perspective, it is preferable to use materials with high flame retardancy in case of fire. In this embodiment, the flame retardancy of the nonwoven fabric can be enhanced by adding a flame retardant. Methods for adding a flame retardant to the nonwoven fabric include dispersing the flame retardant in a liquid and attaching it by spraying, brushing, coating, pouring, dipping, or immersion. Alternatively, during the manufacturing of the nonwoven fabric, the flame retardant can also be dispersed in a liquid medium along with the non-fibrillated and fibrillated fibers, thereby forming a nonwoven fabric with the flame retardant already attached. Types of flame retardants include halogen-based flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, and inorganic flame retardants. Specific halogen-based flame retardants include chlorinated paraffins, cyclic aliphatic chlorine compounds (decloran plus), aliphatic bromine compounds, and aromatic bromine compounds. Phosphorus-based flame retardants include phosphate esters (monomer type, condensation type), halogen-containing phosphate esters, phosphinate metal salts, intomessenate (IFR), red phosphorus, APP (ammonium polyphosphate), melamine phosphate, and phosphate ester amides. Nitrogen-based flame retardants include melamine, melamine derivatives, and guanidine compounds. Inorganic flame retardants include magnesium hydroxide, aluminum hydroxide, antimony compounds (Sb2O3), tin compounds (zinc stainate, zinc hydroxyl stainate), boron compounds (zinc borate) MMT, zirconium compounds, and molybdenum compounds (molybdenum oxide). In addition to the above, silicone-based flame retardants, hindered amine compounds, and azoalkane compounds are also used. Among the above, phosphorus-based flame retardants have the characteristic of forming a carbonized film (char) on the material surface through dehydration, thereby blocking oxygen and heat. Therefore, it is preferable to use phosphorus-based flame retardants in nonwoven fabrics, as they can prevent the spread of fire in the event of a fire inside or outside a vehicle.

[0068] <Lamination of nonwoven fabric and support> The nonwoven fabric of this embodiment exhibits higher sound insulation when laminated with a support. Although the nonwoven fabric has sound insulation properties, in the frequency range of the nonwoven fabric's natural frequency, the nonwoven fabric itself vibrates violently, generating secondary frequency sounds. Therefore, in the frequency range of the nonwoven fabric's natural frequency, the sound insulation is reduced compared to other frequency ranges. Therefore, when a support is laminated with a nonwoven fabric, the support suppresses the vibration of the nonwoven fabric itself, making it possible to maintain high sound insulation across the entire frequency range. Types of support materials include plate films and porous materials. Plate films are more effective at suppressing the vibration of the nonwoven fabric than porous materials, and the plate films themselves also function as sound insulation materials, resulting in a laminate specialized for sound insulation. On the other hand, porous materials have lower sound insulation than plate films, but higher sound absorption. Therefore, when porous materials are laminated, the porous materials contribute to soundproofing as sound absorbers, resulting in a composite laminate that combines sound absorption and sound insulation. Furthermore, when laminating the film plates as a support, it is preferable to place the nonwoven fabric on the inside of the sound source relative to the film plates. Although the film plates themselves have almost no sound-absorbing properties, the nonwoven fabric does, so by blocking the sound from the sound source with the film plates and nonwoven fabric, while absorbing the sound with the nonwoven fabric on the inside, a laminate with high sound insulation is created.

[0069] <Material type of support> As described above, the support of this embodiment is broadly classified into a plate-like film and a porous body. Examples of materials constituting the plate-like film include thermoplastic resins such as polyolefins, polyesters, polyamides (aromatic or aliphatic), acrylic polymers, polyvinyl alcohol, polylactic acid, polyphenylene ether, polyoxymethylene, and polyphenylene sulfide, as well as thermosetting resins such as epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, urea resins, allyl resins, silicon resins, benzoxazine resins, phenolic resins, unsaturated polyester resins, bismaleimidotriazine resins, alkyd resins, furan resins, melamine resins, polyurethane resins, and aniline resins. Inorganic materials such as glass, ceramics, cement, metals, and slugs can also be given as examples. Other examples include rubber materials, cellulose, fiber-reinforced resins (reinforcement materials: cellulose fibers, glass fibers, aramid fibers, carbon fibers), and particle-reinforced resins. Furthermore, the fibers constituting the nonwoven fabric and felt within the porous material can be natural fibers, synthetic fibers, semi-synthetic fibers, or inorganic fibers. Examples of polymers constituting the porous material include thermoplastic resins such as polyolefins, polyesters, polyamides (aromatic or aliphatic), acrylic polymers, polyvinyl alcohol, polylactic acid, polyphenylene ethers, polyoxymethylene, and polyphenylene sulfide, as well as thermosetting resins such as epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, urea resins, allyl resins, silicon resins, benzoxazine resins, phenolic resins, unsaturated polyester resins, bismaleimidotriazine resins, alkyd resins, furan resins, melamine resins, polyurethane resins, and aniline resins. Examples of inorganic materials constituting non-fibrillated fibers include glass, ceramics, cement, metals, carbon fibers, and slugs. These fibers may be used individually or in combination. Furthermore, examples of materials that constitute the foam among porous materials include thermoplastic resins such as polyolefins, polyesters, polyamides (aromatic or aliphatic), acrylic polymers, polyvinyl alcohol, polylactic acid, polyphenylene ethers, polyoxymethylene, and polyphenylene sulfide, epoxy resins, thermosetting modified polyphenylene ether resins, thermosetting polyimide resins, urea resins, allyl resins, silicon resins, benzoxazine resins, phenolic resins, unsaturated polyester resins, bismaleimidotriazine resins, alkyd resins, furan resins, melamine resins, polyurethane resins, and thermosetting resins such as aniline resins.

[0070] <Tensile modulus of film material> In this embodiment, the tensile modulus of the film plate in the support is preferably 0.5 GPa or higher. Within this range, the film plate is self-supporting and exhibits its effect as a support for the nonwoven fabric. The higher the tensile modulus of the film plate, the better the vibration of the nonwoven fabric can be suppressed, thus improving the sound insulation performance of the laminate. The tensile modulus of the film plate is more preferably 1 GPa or higher, even more preferably 5 GPa or higher, and particularly preferably 10 GPa or higher. Furthermore, there is no particular upper limit, and in one embodiment it may be 1000 GPa.

[0071] <Method for laminating nonwoven fabric onto a support> The nonwoven fabric of this embodiment can be laminated with a support using various means. As for the lamination method, it is possible to simply overlap the nonwoven fabric and the support without bonding them, but bonding them is preferable because the support acts as a binder for the nonwoven fabric, suppressing vibrations of the nonwoven fabric and improving sound insulation. Examples of methods for bonding the two include heating only the surface of the nonwoven fabric with an IR heater or the like and joining them by heat fusion, applying a hot melt adhesive to the surface of the nonwoven fabric using a curtain spray method or the like and then heating and heat fusion, and fixing them with commercially available adhesive tape. Furthermore, the higher the adhesive strength, the less likely the nonwoven fabric is to delaminate from the porous material due to vibrations caused by sound propagation. A tensile shear strength (according to JIS K6849) of 1 MPa or higher is preferable, and 5 MPa or higher is more preferable. There is no particular upper limit, and in one embodiment, it may be 1 GPa or less.

[0072] <Application> While the use of two-dimensional nonwoven sheets as sound-absorbing materials is a known technology, by seamlessly molding fibrillated or non-fibrillated fibers in a three-dimensional manner using methods such as the pulp molding method, a three-dimensional nonwoven fabric possessing both sound-insulating and sound-absorbing properties can be provided. In particular, by using cellulose as the fiber material, it is possible to mold it into a thin layer, and by creating irregularities, it exhibits surface rigidity within a predetermined range and a high modulus of elasticity, making it usable as a three-dimensional soundproofing material with high sound-insulating properties, especially in the low-frequency range. Furthermore, due to its high moldability, it can conform to the complex mechanical shapes of sound-producing devices and other equipment. In addition, it has excellent heat resistance, making it particularly useful for automotive applications, and its main applications are listed below. For automotive applications, it can be suitably used for large parts such as hood silencers, dash outer silencers, dash inner silencers (dash panel pads), fender liners, wheelhouse liners, cowl inner silencers, dash inner silencers, side door trims, luggage door trims, luggage side trims, luggage mats, floor silencers (floor undercovers, floor carpets), engine silencers, headlinings, rear shelves, tailgate trims, soundproofing ducts, soundproofing sheets, transmission insulators, and engine undercovers (motor undercovers in the case of EVs). It can also be suitably used for medium to small three-dimensional covers such as covers for engines, engine-attached reduction gears, drive shafts, torque converters, gear transmissions, reduction gears, differential gears, and differential limiting devices, as well as covers for electrical components such as electric pumps (water and oil circulation), air conditioner electric compressors, air conditioner ducts, electric actuators, inverters, and converters. In particular, in the case of EVs, it can be suitably used for covers for electric drive devices such as electric motors and reduction gears attached to motors. The soundproofing material of the present invention is suitable for small to medium-sized three-dimensional covers because it can be formed seamlessly in a thin layer. It can be used as a cover for electrical components such as electric pumps (water and oil circulation), air conditioner electric compressors, air conditioner ducts, electric actuators, inverters, and converters that emit noise vibrations in the 200Hz to 2000Hz range, as well as for electric drive devices such as electric motors and motor-attached gearboxes. [Examples]

[0073] The present invention will be specifically explained by the following examples and comparative examples. First, we will explain the evaluation methods for sound insulation and sound absorption used in the examples. (1) Transmitted sound pressure (dB) Incident 95 dB A cube-shaped acrylic resin box with an outer side of 250 mm and an inner side of 235 mm was prepared in an anechoic chamber with a temperature of 22.9~24.2℃ and a humidity of 54.8~58.4%RH. It had a 180 mm square hole in the center of one side. The box was placed on a smooth surface with the hole facing upwards, and a wireless speaker (Bose SoundLink Revolve II Bluetooth speaker) was placed inside. A 220 mm square sample was placed on top of the box so as to completely cover the hole. If the sample had any irregularities, the convex side was placed facing upwards. A 280 mm square, 15 mm thick acrylic resin lid with a 180 mm square hole in the center was then placed over the box, aligning with the hole (Figure 4). A sound level meter (NL-20 RION) was fixed facing downwards so that the center of the tip of the microphone sponge was 25 mm above the center of the sample. If the sample had uneven surfaces, the microphone was placed 25mm above the flat surface (i.e., the microphone position remained the same whether or not there were uneven surfaces). 95dB of white noise was played from a speaker, and the value displayed on the sound level meter in A-weighted, Fast mode was used as the transmitted sound pressure of the sample. The white noise was played for 10 seconds, and the highest value displayed on the sound level meter was used as the transmitted sound pressure.

[0074] (2) Reverberation chamber sound absorption coefficient As shown in Figure 5, in accordance with ISO 354, the reverberation chamber (room volume 8.9 m³) of Japan Acoustic Engineering Co., Ltd. 3 The following equipment was used. Sixteen 220mm square samples were joined together to form an 880mm square for evaluation. The reverberation chamber sound absorption coefficient was measured at 1,250Hz and 4,000Hz. The measurements were taken under environmental conditions of temperature: 21.2~21.9℃ and humidity: 67.0~73.3%RH.

[0075] 《Fibrilized Fiber》 <Fibrilized fiber A> Using eucalyptus pulp (TeL Pellita ECF Bleached Hardwood Kraft Pulp), a type I natural cellulose obtained from Marubeni Corporation, the eucalyptus pulp was immersed in water to a concentration of 2% by mass, and then simply dispersed using a lab pulper (manufactured by Aikawa Iron Works). The liquid was then transferred to a tank and diluted to 1.5% by mass. The slurry was then refined using a 14-inch single-disc refiner (manufactured by Aikawa Iron Works) connected to the tank, which had a disc with a blade width of 2.5 mm and a groove width of 7.0 mm, while circulating the slurry. At this time, operation was started with a blade distance of 2.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.05 mm. After the blade distance reached 0.05 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 30 times. The obtained microfibrillated cellulose was designated as fibrillated fiber A.

[0076] <Fibrilized fiber B> Fibrillated fiber A was further refined using a high-pressure homogenizer (NS015H, manufactured by Nilo Soavi, Italy). The slurry was processed in batches, with 10 processing cycles. The resulting fibrillated fiber was designated fibrillated fiber B.

[0077] <Fibrilized fiber C> Using eucalyptus pulp (TeL Pellita ECF Bleached Hardwood Kraft Pulp), a type I natural cellulose obtained from Marubeni Corporation, the eucalyptus pulp was immersed in water to a concentration of 2% by mass, and then simply dispersed using a lab pulper (manufactured by Aikawa Iron Works). The liquid was then transferred to a tank and diluted to 1.5% by mass. The slurry was then refined using a 14-inch single-disc refiner (manufactured by Aikawa Iron Works) connected to the tank, which had a disc with a blade width of 2.5 mm and a groove width of 7.0 mm, while circulating the slurry. At this time, operation was started with a blade distance of 2.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.15 mm. After the blade distance reached 0.15 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 30 times. The obtained microfibrillated cellulose was designated as fibrillated fiber C.

[0078] <Fibrilized fiber D> Using eucalyptus pulp (TeL Pellita ECF Bleached Hardwood Kraft Pulp), a type I natural cellulose obtained from Marubeni Corporation, the eucalyptus pulp was immersed in water to a concentration of 2% by mass, and then simply dispersed using a lab pulper (manufactured by Aikawa Iron Works). The liquid was then transferred to a tank and diluted to 1.5% by mass. The slurry was then finely refined while circulating it using a 14-inch single-disc refiner (manufactured by Aikawa Iron Works) connected to the tank, which had a disc with a blade width of 2.5 mm and a groove width of 7.0 mm. At this time, operation was started with a blade distance of 2.0 mm, and the blade distance was gradually reduced until the final blade distance was 0.30 mm. After the blade distance reached 0.30 mm, operation was continued while monitoring the flow rate, and the operation was terminated when the entire slurry had passed through the disc section 30 times. The obtained microfibrillated cellulose was designated as fibrillated fiber D.

[0079] <Fibrilized fiber E> Using linter pulp, a type I natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water to a concentration of 1.5% by mass, and then simply dispersed using a juicer mixer (Transgate HBH450) under High settings for 5 minutes. The resulting microfibrillated cellulose was designated as fibrillated fiber E.

[0080] [Example 1] Fibrillated fiber A and non-fibrillated PET short fibers (Teijin Frontier Co., Ltd.: TA04PN, fineness: 0.1T, average fiber diameter: 3.0 μm, cut length: 3 mm) were added to pure water in a solid content weight ratio of 10:90, with a solid content concentration of 0.5% and a total volume of 230 L. This slurry was poured into a 250 L capacity stirring tank (pulper), and the pulper was rotated for 20 minutes using a 30 cm diameter stirring blade at a rotor speed of 750 rpm and a rotor tip speed of 11.7 m / sec. This slurry was poured into a material tank, a shaping mold with a wire mesh surface was immersed in it, and a compressor (Roots type blower CT100) was used to produce a slurry with a solid content basis of 754 g / m². 2 The fibers were laminated by suction to create a specific shape, which was then fixed into the form of the mold. The shape of the mold used at this time was a wave-like shape as shown in Figure 1, with a height of 7.5 mm, a taper angle of 60%, and an area ratio of 49%. A press mold of the same shape was placed over this fiber laminate to compress the moisture. Furthermore, this laminate was sandwiched between two molds that conformed to its shape and dried and solidified by heating and pressing at 140°C until the film thickness reached 1.2 mmt. This was designated as nonwoven fabric 1.

[0081] [Example 2] The shape of the mold was changed to the lattice-type shape with varying heights shown in Figure 1, and the nonwoven fabric 2 was produced by carrying out Example 1.

[0082] [Example 3] The shape of the mold was set to the grid shape shown in Figure 1, and the nonwoven fabric 3 was produced by carrying out Example 1.

[0083] [Example 4] The shape of the mold was set to the triangular pyramid 1A shape shown in Figure 1, and the nonwoven fabric 4 was produced by carrying out Example 1.

[0084] [Example 5] The shape of the mold was set to the triangular pyramid 2A shape shown in Figure 1, and the nonwoven fabric 5 was produced by carrying out Example 1.

[0085] [Example 6] The shape of the mold was set to the triangular pyramid 1B shape shown in Figure 1, and the nonwoven fabric 6 was produced by carrying out Example 1.

[0086] [Example 7] The shape of the mold was set to the triangular pyramid 2B shape shown in Figure 1, and the nonwoven fabric 7 was produced by carrying out Example 1.

[0087] [Example 8] The weight in solids is 377g / m². 2 Nonwoven fabric 8 was prepared in the same manner as in Example 1, except that it was suctioned to achieve a final film thickness of 0.6 mmt.

[0088] [Example 9] The weight in solids is 1885g / m². 2 Nonwoven fabric 9 was prepared in the same manner as in Example 1, except that it was suctioned to achieve a final film thickness of 3 mmt.

[0089] [Example 10] The weight in solids is 3142 g / m². 2 Nonwoven fabric 10 was prepared in the same manner as in Example 1, except that it was suctioned to achieve a final film thickness of 5 mmt.

[0090] [Example 11] The weight in solids is 6283 g / m². 2 Nonwoven fabric 11 was prepared in the same manner as in Example 1, except that it was suctioned to achieve a final film thickness of 10 mmt.

[0091] [Example 12] The weight in solids is 240 g / m². 2Nonwoven fabric 12 was prepared in the same manner as in Example 1, except that it was suctioned in such a way.

[0092] [Example 13] The weight in solids is 360g / m². 2 Nonwoven fabric 13 was prepared in the same manner as in Example 1, except that it was suctioned in the same way as in Example 1.

[0093] [Example 14] The weight in solids is 864 g / m². 2 Nonwoven fabric 14 was prepared in the same manner as in Example 1, except that it was suctioned in the same way as in Example 1.

[0094] [Example 15] Nonwoven fabric 15 was prepared in the same manner as in Example 1, except that a mold with a surface height ratio of 0.5 was used.

[0095] [Example 16] Nonwoven fabric 16 was prepared in the same manner as in Example 1, except that a mold with a surface height ratio of 2 was used.

[0096] [Example 17] Nonwoven fabric 17 was prepared in the same manner as in Example 1, except that a mold with a surface height ratio of 3 was used.

[0097] [Example 18] Nonwoven fabric 18 was prepared in the same manner as in Example 1, except that a mold with a 90° taper angle was used.

[0098] [Example 19] Nonwoven fabric 19 was prepared in the same manner as in Example 1, except that a mold with a 30° taper angle was used.

[0099] [Example 20] Nonwoven fabric 20 was prepared in the same manner as in Example 1, except that a mold with a 6° taper angle was used.

[0100] [Example 21] Nonwoven fabric 21 was prepared in the same manner as in Example 1, except that fibrillated fiber B was used.

[0101] [Example 22] Nonwoven fabric 22 was prepared in the same manner as in Example 1, except that fibrillated fiber C was used.

[0102] [Example 23] Nonwoven fabric 23 was prepared in the same manner as in Example 1, except that fibrillated fiber D was used.

[0103] [Example 24] Nonwoven fabric 24 was prepared in the same manner as in Example 1, except that fibrillated fiber E was used.

[0104] [Example 25] Nonwoven fabric 25 was prepared in the same manner as in Example 1, except that the solid weight ratio of fibrillated fiber A to PET fiber was set to 2:98.

[0105] [Example 26] Nonwoven fabric 26 was prepared in the same manner as in Example 1, except that the solid weight ratio of fibrillated fiber A to PET fiber was set to 5:95.

[0106] [Example 27] Nonwoven fabric 27 was prepared in the same manner as in Example 1, except that the solid weight ratio of fibrillated fiber A to PET fiber was set to 30:70.

[0107] [Example 28] Nonwoven fabric 28 was prepared in the same manner as in Example 1, except that the solid weight ratio of fibrillated fiber A to PET fiber was set to 50:50.

[0108] [Comparative Example 1] The shape of the mold was set to a 220 mm square flat film shape, and the nonwoven fabric S1 was produced by carrying out Example 1.

[0109] [Comparative Example 2] A synthetic fiber needle felt with the same shape as nonwoven fabric 1 and a thickness of 8 mm was prepared and designated as nonwoven fabric S2.

[0110] [Comparative Example 3] Polypropylene with the same shape as nonwoven fabric 1 and a film thickness of 0.5 mmt was formed by injection molding to create PP board S3.

[0111] [Comparative Example 4] Nonwoven fabric 29 was prepared in the same manner as in Example 1, except that the solid weight ratio of fibrillated fiber A to PET fiber was set to 100:0.

[0112] The weight, surface area, and basis weight of the various nonwoven fabrics with irregularities obtained in Examples 1 to 7 are shown in Table 1 below. [Table 1]

[0113] Furthermore, the results of Examples 1-28 and Comparative Examples 1-4 are summarized in Tables 2-4 below. [Table 2]

[0114] [Table 3]

[0115] [Table 4] [Industrial applicability]

[0116] According to the present invention, by providing a nonwoven fabric containing fibrillated and non-fibrillated fibers of a specific length with irregularities that increase the surface rigidity to a predetermined value or higher, it is possible to provide a lightweight, thin-film nonwoven fabric with good moldability that maintains sound absorption while exhibiting excellent sound insulation in the low-frequency range. Therefore, the soundproofing material according to the present invention can be suitably used in various applications where low-frequency sound absorption and sound insulation rates are required, such as in automotive applications where the electrification of automobiles has progressed and the quietness of the drive system has improved.

Claims

1. A soundproofing material comprising a nonwoven fabric composed of fibrillated fibers and non-fibrillated fibers, wherein the nonwoven fabric contains fibrillated fibers in an amount of 1% by mass or more, has a plurality of irregularities on its surface, and has a tensile modulus of elasticity of 10 MPa or more.

2. The soundproofing material according to claim 1, wherein the surface rigidity of the nonwoven fabric is 0.7 N / mm or more.

3. The soundproofing material according to claim 1 or 2, wherein the height ratio of the unevenness of the nonwoven fabric is 0.1 or more and 10 or less.

4. The soundproofing material according to claim 1 or 2, wherein the taper angle of the unevenness of the nonwoven fabric is 3° or more and 70° or less.

5. The soundproofing material according to claim 1 or 2, wherein the ratio of the uneven surface area to the total surface area of ​​the nonwoven fabric is 2% or more and 90% or less.

6. The soundproofing material according to claim 1 or 2, wherein the irregularities of the nonwoven fabric are wave-shaped.

7. The soundproofing material according to claim 1 or 2, wherein the irregularities of the nonwoven fabric are selected from the group consisting of W-shaped, grid-shaped, and triangular pyramidal shapes.

8. The soundproofing material according to claim 1 or 2, wherein the thickness of the nonwoven fabric is 0.5 mm or more and 10 mm or less.

9. The flow resistance per unit thickness of the aforementioned nonwoven fabric is 0.1 MNs / m ４ More than 1000MNs / m ４ The soundproofing material according to claim 1 or 2, which is as follows:

10. The basis weight of the aforementioned nonwoven fabric is 10 g / m². ２ More than 10000g / m ２ The soundproofing material according to claim 1 or 2, which is as follows:

11. The soundproofing material according to claim 1 or 2, wherein the porosity of the nonwoven fabric is 40% or more and 90% or less.

12. The soundproofing material according to claim 1 or 2, wherein the labyrinthiness of the nonwoven fabric is 1.20 or more and 10.0 or less.

13. The soundproofing material according to claim 1 or 2, wherein the fibrillated fiber is at least one selected from the group consisting of microfibrillated cellulose, acrylic pulp, aramid pulp, chitin nanofibers, chitosan nanofibers, and silk nanofibers.

14. The soundproofing material according to claim 13, wherein the microfibrillated cellulose is cellulose nanofiber (CNF).

15. The soundproofing material according to claim 1 or 2, wherein the fibrillation rate of the fibrillated fiber is 0.3% or more.

16. The soundproofing material according to claim 1 or 2, wherein the content of the fibrillated fibers is 3% by mass or more and 30% by mass or less, based on the total mass of the nonwoven fabric.

17. The soundproofing material according to claim 1 or 2, wherein the transmitted sound pressure at an incident of 95 dB is 90 dB or less.

18. The soundproofing material according to claim 1 or 2, wherein the reverberation chamber sound absorption coefficient (-) at 1250 Hz is 0.1 or more.

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