Nonwoven fabric, and sound-absorbing material using the nonwoven fabric
A nonwoven fabric with cellulose fine and short fibers addresses the lack of mid-to-low frequency sound absorption in existing materials by offering excellent sound absorption across a wide frequency range while being industrially productive.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ASAHI KASEI KOGYO KABUSHIKI KAISHA
- Filing Date
- 2024-10-03
- Publication Date
- 2026-05-12
AI Technical Summary
Existing sound-absorbing materials fail to effectively absorb sounds in the mid-to-low frequency range below 3000 Hz and are not industrially productive due to the use of unproductive manufacturing methods like electrospinning.
A nonwoven fabric composed of cellulose fine fibers with a diameter of 100 nm to 2000 nm and short fibers with a diameter of 0.1 μm to 10 μm, uniformly mixed to create a composite sound-absorbing material with a specific average pore size, providing excellent sound absorption characteristics across a wide frequency range, including the mid-to-low frequencies.
The nonwoven fabric achieves high sound absorption in the medium and low frequency regions with high productivity, suitable for use in automobiles, houses, and household appliances, particularly as a skin material for composite sound-absorbing materials.
Smart Images
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Abstract
Description
[Technical Field]
[0001] This invention relates to a nonwoven fabric and a sound-absorbing material using the nonwoven fabric. [Background technology]
[0002] When a car is in motion, various noises are generated, including engine and drivetrain noise, road noise, and wind noise. Traditionally, sound-absorbing materials have been used to suppress these noises and create a comfortable cabin environment. On the other hand, with the recent advancement of electrification in automobiles, the quietness of the drivetrain in particular has improved. Due to these technological changes, sounds that were not previously recognized as noise, specifically sounds in the mid-to-low frequency range below 3000 Hz, are beginning to be recognized as noise. For the aforementioned regions, nonwoven fabrics containing fine fibers and composite structures with a surface layer on a porous body are known to exhibit excellent sound absorption properties. For example, Patent Document 1 below shows a laminated structure composed only of fibers with a fiber diameter of less than 450 nm, which is shown to have excellent sound absorption in the low frequency range of 1000 Hz or less. However, the fibers contained in this structure are manufactured by electrospinning, which is extremely unproductive and difficult to commercialize industrially. Furthermore, Patent Document 2 below describes a structure in which cellulose nanofibers are coated on one side of a nonwoven fabric, and states that by using this as a surface material for sound-absorbing material, the air permeability resistance can be controlled and suitable sound absorption performance can be obtained. However, it does not describe the sound absorption characteristics in the mid-to-low frequency range. [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] International Publication No. 2018 / 143430 [Patent Document 2] International Publication No. 2017 / 006993 [Overview of the project] [Problems that the invention aims to solve]
[0004] In view of the prior art described above, the problem that the present invention aims to solve is to provide a surface material for a composite sound-absorbing material that has excellent sound absorption properties in the mid-to-low frequency range while also having high productivity. [Means for solving the problem]
[0005] In order to solve the above problems, the inventors diligently studied and conducted numerous experiments, and as a result, they discovered that by uniformly mixing short fibers with a fiber diameter of 0.1 μm to 10 μm and cellulose fine fibers with a fiber diameter of 100 nm to 2000 nm to create a nonwoven fabric having an average pore size within a specific range, a composite sound-absorbing material using this nonwoven fabric as a surface material exhibits excellent sound absorption characteristics in the mid-to-low frequency range of 3000 Hz and below, while also having sound absorption properties across a wide frequency range, thus completing the present invention.
[0006] In other words, the present invention is as follows: [1] A nonwoven fabric comprising cellulose fine fibers having an average fiber diameter of 100 nm or more and 2000 nm or less, and short fibers having an average fiber diameter of 0.1 μm or more and 10 μm or less, characterized in that the average flow diameter measured by a palm porometer is 1 μm or more and 30 μm or less. [2] The nonwoven fabric according to [1], which contains cellulose fine fibers in an amount of 1% by mass or more and less than 20% by mass. [3] The nonwoven fabric according to [1] or [2], wherein the cellulose microfibers are type II cellulose. [4] A nonwoven fabric according to any of [1] to [3] above, which is a wet-laid nonwoven fabric. [5] A sound-absorbing material made of a nonwoven fabric as described in any of [1] to [4] above. [6] A composite sound-absorbing material comprising a nonwoven fabric described in any of [1] to [4] above and a porous material other than the nonwoven fabric, laminated together. [7]In the measurement method of normal incidence conforming to JIS A 1405, the composite sound-absorbing material according to [6] having a maximum sound absorption value at 3000 Hz or lower, the maximum value being 0.5 or more, and the sound absorption rate in all ranges of 2000 to 6000 Hz being 0.2 or more. [Effect of the Invention]
[0007] The non-woven fabric according to the present invention has excellent sound absorption properties in the medium and low frequency regions, has high productivity, and can be suitably used as the skin material of the composite sound-absorbing material. Therefore, it can be particularly suitably used as the skin material of the composite sound-absorbing material used in automobiles, houses, and household appliances. [Brief Description of the Drawings]
[0008] [Figure 1] It is a figure showing the results of sound absorption rate measurement in Example 1, Example 2, and Comparative Example 1. [Modes for Carrying Out the Invention]
[0009] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to these modes. One embodiment of the present invention is a non-woven fabric containing cellulose fine fibers having an average fiber diameter of 100 nm or more and 2000 nm or less, and short fibers having an average fiber diameter of 0.1 μm or more and 10 μm or less, and characterized in that the average flow diameter measured by a palm porometer is 1 μm or more and 30 μm or less.
[0010] (Non-woven fabric) The non-woven fabric of the present embodiment preferably has a structure in which cellulose fine fibers having an average fiber diameter of 100 nm or more and 2000 nm or less and short fibers having an average fiber diameter of 0.1 μm or more and 10.0 μm or less are uniformly integrated. In this embodiment, the nonwoven fabric has a dense structure with fine interfiber gaps and a very small amount of breathability. When sound penetrates the interfiber gaps, the vibrational energy of the sound is converted into thermal energy through friction with the ultrafine fibers, and the fibers themselves also vibrate in response to the vibrational energy of the sound, further converting it into thermal energy.
[0011] (Cellulose microfibers) The nonwoven fabric of this embodiment contains cellulose microfibers. Here, cellulose microfibers are cellulose fibers that have been miniaturized using at least one type of physical means, and are synonymous with common names such as cellulose nanofibers, CNF, CeNF, and MFC (microfibrillated cellulose).
[0012] (Fiber diameter of cellulose microfibers) In this embodiment, the average fiber diameter of the cellulose microfibers in the nonwoven fabric is 100 to 2000 nm, from the viewpoint of the effect of refining the internal structure of the nonwoven fabric by the cellulose microfibers. While highly refined microfibers result in a finer internal structure of the nonwoven fabric, this also worsens the productivity of the cellulose microfibers and significantly restricts airflow due to the pore size of the nonwoven fabric becoming too small, making it difficult to obtain sound absorption effects. On the other hand, if the degree of refinement is low, the internal structure of the nonwoven fabric becomes coarse. Therefore, the average fiber diameter of the cellulose microfibers is preferably 200 to 1000 nm, and more preferably 300 to 800 nm. By adjusting to this range, the refined structure not only restricts airflow in the nonwoven fabric, but the cellulose microfibers themselves vibrate and contribute to sound absorption, resulting in high sound absorption across the entire frequency range.
[0013] In this disclosure, the average fiber diameter of cellulose microfibers refers to the fiber diameter of cellulose microfibers used as a raw material for nonwoven fabrics, and is measured according to the following procedure. (1) Disperse the cellulose microfibers in tert-BuOH so that the solid content concentration is 50 ppm. If the cellulose microfibers are in powder form, adjust the concentration to the above level while taking the solid content concentration into consideration. If the cellulose microfibers are dispersed in a medium such as water or an organic solvent, remove as much of the dispersion medium as possible by filtration or centrifugation, and then disperse them in tert-BuOH in the same way as in the case of a powder. Dispersion into tert-BuOH is performed using a high-shear homogenizer (e.g., IKA product, trade name "Ultra-Turrax T18") under the following conditions: rotation speed 25,000 rpm × 5 minutes. (2) Drop 5 μL of the dispersion onto the Os-coated Si wafer and quickly spread it over the entire surface. (3) Dry the above (2) on a hot plate heated to 130°C or in an oven. (4) Observe the above (3) using a high-resolution scanning microscope (SEM) at a magnification of 500 to 2000 times and capture at least 10 fields of view. (5) In each image obtained in (4) above, measure the fiber diameter of at least 10 randomly selected fibrous materials. If branched fibers are present, measure the diameter of the main part and the branched parts separately. (6) The average of all measured fiber diameters shall be taken as the average fiber diameter of the cellulose microfibers.
[0014] (Cellulose raw material) Raw materials for cellulose microfibers include so-called wood pulps such as coniferous pulp and hardwood pulp, as well as non-wood pulps, which are used as raw materials for type I cellulose. 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 pulping to remove lignin, and refining and bleaching processes aimed at removing hemicellulose. In addition, refined products such as seaweed-derived cellulose and sea squirt cellulose can also be used as raw materials for cellulose microfibers. Furthermore, as raw materials for type II cellulose, cut yarns of regenerated cellulose fibers and cut yarns of cellulose derivative fibers can also be used as raw materials for cellulose microfibers. In addition, 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 can be used individually or in mixtures. The average fiber diameter can be adjusted by mixing multiple raw materials.
[0015] (Fine-graining of cellulose) Cellulose microfibers can be obtained by micronizing the raw materials described above. In one embodiment, a pretreatment process is performed before the micronization process. In the pretreatment process, it is effective to prepare the raw pulp to a state that facilitates micronization by autoclaving under water impregnation at a temperature of 100-150°C, enzymatic treatment, or a combination thereof. These pretreatments not only reduce the burden of the micronization process but also discharge 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, and as a result, they have the effect of increasing the α-cellulose purity of the micronized fibers, which can be effective in improving the heat resistance of the cellulose microfibers.
[0016] In the micronization process, the raw pulp is dispersed in water and micronized using known micronization equipment such as a beater, discreeter (double discreeter), or high-pressure homogenizer. The optimal treatment concentration for micronization varies depending on the equipment used and can be set arbitrarily. The average fiber diameter of cellulose microfibers 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 average fiber diameter may be controlled by combining multiple conditions regarding the cellulose raw material, pretreatment, micronization, etc.
[0017] (Cellulose microfiber content) The nonwoven fabric of this embodiment preferably contains cellulose microfibers in an amount of 1% by mass or more and less than 20% by mass. Here, the cellulose microfiber content refers to the ratio of the solid weight of cellulose microfibers to the solid weight of short fibers contained in the nonwoven fabric. By setting the cellulose microfiber content within this range, the structure of the nonwoven fabric does not become too dense and has the breathability necessary for sound absorption. If the cellulose microfiber content is too low, the sound absorption effect of the cellulose microfibers cannot be obtained, but if it is too high, the rigidity of the entire nonwoven fabric increases, making it less susceptible to vibration and thus making it difficult to obtain the sound absorption effect. Therefore, the cellulose microfiber content is more preferably 3% by mass or more and 15% by mass or less, and most preferably 5% by mass or more and 10% by mass or less.
[0018] (Crystalline form of cellulose) In this embodiment, the crystalline form of the cellulose microfibers is preferably type II cellulose. Type II cellulose fibers tend to be less prone to micronization compared to type I cellulose, making it easier to control the average fiber diameter within a suitable range. Furthermore, type II cellulose is preferred because, during drying in nonwoven fabric manufacturing, the fibers are less likely to aggregate, and sound absorption effects in the low-frequency range are easily obtained.
[0019] (Short fibers) The nonwoven fabric of this embodiment includes short fibers in addition to cellulose fine fibers. Here, short fibers in this disclosure mean fibrous materials made of substances other than cellulose, having a fiber length of 10 mm or less. Natural fibers, synthetic fibers, and semi-synthetic fibers can all be used as short fibers. Examples of polymers constituting the short fibers include thermoplastic resins such as polyolefins, polyesters, polyamides (aromatic or aliphatic), acrylic polymers, polyvinyl alcohol, polylactic acid, polyphenylene ether, 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 aniline resins. These short fibers may be used individually or in combination.
[0020] (Average fiber diameter of short fibers) The short fibers contained in the nonwoven fabric in this embodiment have an average fiber diameter of 0.1 μm to 10.0 μm. By using short fibers with an average fiber diameter in this range, when mixed with cellulose fine fibers, a uniformly mixed and sufficiently finely structured nonwoven fabric is obtained. Furthermore, by using short fibers with a fiber diameter of 10.0 μm or less, the short fibers vibrate easily, making it easier to obtain a sound absorption effect. If the average fiber diameter of the short fibers is too large, localization of cellulose fine fibers and short fibers tends to occur inside the nonwoven fabric, but if it is too small, the internal structure of the nonwoven fabric becomes too dense, and the necessary breathability for sound absorption cannot be obtained. Therefore, it is preferable that the average fiber diameter is between 1.0 μm and 8.0 μm, and most preferably between 1.0 μm and 6.0 μm.
[0021] The average fiber diameter of short fibers is measured using the following procedure. (1) Disperse the short fibers in water at a solid content concentration of 0.05% by mass. Use a household blender or similar device for dispersion. (2) Place the dispersion onto a glass slide to prepare the specimen. (3) Observe the above (2) with a digital microscope at a magnification of 500 to 2000 times and take images of at least 5 fields of view. (4) In each image obtained in (3) above, measure the fiber diameter of at least 10 randomly selected fibrous materials. If branched fibers are present, measure the fiber diameter at the trunk level. (5) The average of all measured fiber diameters shall be taken as the average fiber diameter of the short fibers.
[0022] (Average flow diameter of nonwoven fabric) The nonwoven fabric of this embodiment is characterized by having an average flow diameter measured by a palm porometer in the range of 1.0 μm to 30.0 μm. This range allows the nonwoven fabric to have a very small amount of breathability, resulting in a good sound absorption effect in the mid-to-low frequency range. If the average flow diameter is too small, there will be no breathability and no sound absorption effect will be obtained, but if it is too large, it will not be possible to restrict airflow when used as a surface material. Therefore, the average flow diameter is preferably 3 μm to 20 μm, more preferably 4 μm to 15 μm, and most preferably 5 μm to 13 μm. The average flow diameter of the nonwoven fabric is measured using a palm porometer (model: CFP-1200AEX) manufactured by PMI. Garwick (surface tension = 15.6 dynes / cm) manufactured by PMI is used as the immersion liquid, and the measurement is performed by the half-dry method in accordance with ASTME1294-8.
[0023] (Wet nonwoven fabric) In this embodiment, the nonwoven fabric is preferably a wet-laid nonwoven fabric. Here, a wet-laid nonwoven fabric means a nonwoven fabric manufactured using a papermaking method or a water-flow entanglement method in at least part of the nonwoven fabric manufacturing process. Cellulose microfibers are generally refined in water, and when dried, the refined fibers re-aggregate and do not easily re-disperse. Therefore, it is desirable that the cellulose microfibers be brought into the nonwoven fabrication process in a never-dry state after refinement, and it is preferable that they be nonwoven by a wet method.
[0024] (Balance weight of nonwoven fabric) In the non-woven fabric of this embodiment, the basis weight is preferably in the range of 10 g / m 2 or more and 1000 g / m 2 or less. If it is within this range, it can be efficiently manufactured, and a non-woven fabric with good texture can be obtained, which has appropriate air permeability as a sound-absorbing material. When the basis weight is 10 g / m 2 or more, the thickness of the non-woven fabric increases, and suitable sound-absorbing characteristics can be obtained in the medium and low frequency regions. When the basis weight is 1000 g / m 2 or less, appropriate air permeability can be obtained, and the sound-absorbing effect is easily obtained. Therefore, more preferably, the basis weight is 30 g / m 2 or more and 500 g / m 2 or less, and most preferably 50 g / m 2 or more and 300 g / m 2 or less.
[0025] (Thickness of non-woven fabric) In the non-woven fabric of this embodiment, the thickness is preferably in the range of 0.1 mm or more and 3.0 mm or less. By being within this range, space saving is possible when used as a sound-absorbing material. In addition, the thickness of the non-woven fabric is measured according to the following procedure. (1) Cut out the non-woven fabric into a size of 20 cm × 20 cm. (2) Using an ABS digital indicator ID-CX (manufactured by Mitutoyo Corporation), measure the thickness at five different points on the non-woven fabric. At this time, a flat probe with a diameter of Φ15 mm is used. (3) Take the average value of the five points obtained in (2) as the thickness of the non-woven fabric.
[0026] (Bulk density of non-woven fabric) The bulk density of the non-woven fabric of this embodiment is preferably 0.05 g / cm 3 or more and 0.50 g / cm 3 or less. By having the bulk density within this range, appropriate air permeability can be obtained, and the sound-absorbing effect is easily obtained. More preferably, the bulk density is 0.1 g / cm 3 or more and 0.4 g / cm 3 or more, and even more preferably 0.15 g / cm 3 or more and 0.35 g / cm 3 or more. Furthermore, bulk density is calculated using the following formula. Bulk density [g / cm³] 3 ]=Grain weight [g / m 2 ] / thickness [μm]
[0027] (Air permeability resistance of nonwoven fabric) The air permeability resistance of the nonwoven fabric in this embodiment is preferably 10.0 s / 100 mL or less. An air permeability resistance within this range means that cellulose microfibers are uniformly distributed within the nonwoven fabric, resulting in a finely structured and porous material with slight air permeability. A lower air permeability resistance improves air permeability and makes it easier to obtain sound absorption effects; therefore, it is preferably 5.0 s / 100 mL or less, more preferably 3.0 s / 100 mL or less, and most preferably 2.0 s / 100 mL or less. The air permeability resistance in this disclosure refers to the result of measuring the transmission time of 100 mL of air using a Gurley densometer (e.g., Toyo Seiki Co., Ltd., model G-B2C), and is measured according to the following procedure.
[0028] (1) Cut the nonwoven fabric into 20cm x 20cm pieces. (2) Using a Gurley densometer (e.g., Toyo Seiki Co., Ltd., model G-B2C), measure the air permeability resistance of five different nonwoven fabric samples. However, for samples with air permeability resistance exceeding 1000 s / mL, use a Wang Ken air permeability resistance tester (e.g., Asahi Seiki Co., Ltd., model EG01) instead of a Gurley densometer. (3) The average value of the five points obtained in (2) above is taken as the air permeability resistance of the nonwoven fabric.
[0029] (Uses of nonwoven fabrics) The nonwoven fabric of this embodiment can be suitably used as a sound-absorbing material. It may be used alone or in multiple layers. When used alone, it exhibits low sound absorption in the low-frequency range, and the sound absorption coefficient increases as the frequency increases. When multiple layers are used, it shows a peak sound absorption coefficient originating from surface vibration, and the peak shifts to the lower frequency side depending on the number of layers.
[0030] (Laminated sound-absorbing material) In this embodiment, the nonwoven fabric is preferably used as a surface material, laminated onto a porous material other than the nonwoven fabric, and used as a composite sound-absorbing material. Here, examples of porous materials include nonwoven fabrics, knitted fabrics, fiber sheets such as felt, mats, breathable polyurethane foam, and breathable rubber foam. Such a laminated structure exhibits good sound absorption characteristics.
[0031] (Lamination method with porous materials) The nonwoven fabric of this embodiment can be laminated with a porous material using various means. For example, examples include a method in which the nonwoven fabric is directly heated and joined by heat fusion, or a method in which a hot-melt adhesive is applied to the surface of the nonwoven fabric by a curtain spray method, and then heated from the nonwoven fabric side to perform heat fusion.
[0032] (Sound absorption rate of composite sound-absorbing material) The laminated sound-absorbing material using nonwoven fabric in this embodiment exhibits particularly high sound absorption, i.e., a maximum sound absorption value, in the mid-to-low frequency range of 3000 Hz or less, according to the normal incidence measurement method compliant with JIS-1405, with a maximum value of 0.5 or higher, and preferably a sound absorption coefficient of 0.3 or higher in the entire range from 2000 Hz to 6000 Hz. By having such sound absorption characteristics, it is possible to absorb sound in the mid-to-low frequency range of 3000 Hz or less, which is generally difficult to absorb, while having a sound-absorbing effect over a wide range of frequencies.
[0033] Furthermore, the performance of this nonwoven fabric when used as the surface material for a composite sound-absorbing material will be evaluated as follows. (1) Cut out a circular disc with a diameter of 28.8 mm from the nonwoven fabric, and naturally laminate it with a 10 mm thick coarse felt to create a composite sound-absorbing material. (2) The sound absorption coefficient of the composite sound-absorbing material shall be measured using the DS-2000 normal incidence sound absorption coefficient measurement system (manufactured by Ono Sokki Co., Ltd.) in accordance with JIS A 1405. At this time, the measurement shall be taken so that the nonwoven fabric in this implementation is on the incident side of the sound wave. [Examples]
[0034] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these.
[0035] (Fiber diameter of cellulose microfibers) The average fiber diameter of cellulose microfibers was measured according to the following procedure. (1) An aqueous dispersion of cellulose microfibers was filtered to remove as much water as possible, and then dispersed in tert-BuOH to a solid content concentration of 50 ppm. A high-shear homogenizer (IKA, product name "Ultra-Turrax T18") was used for the dispersion process, and the processing conditions were: rotation speed 25,000 rpm for 5 minutes. (2) 5 μL of the dispersion was dropped onto an Os-coated Si wafer and quickly spread over the entire surface. (3) The above (2) was dried on a hot plate heated to 130°C. (4) The object described in (3) above was observed using a high-resolution scanning microscope (SEM) at a magnification of 2000x, and 10 fields of view were captured. (5) In each image obtained in (4) above, the fiber diameter of 10 fibrous materials was measured at random. When branched fibers were present, the diameter of the main part and the branch part were measured separately. (6) The average of all measured fiber diameters was taken as the average fiber diameter of the cellulose microfibers.
[0036] (Average fiber diameter of short fibers) The average fiber diameter of the short fibers was measured using the following procedure. (1) Short fibers were dispersed in water at a concentration of 0.05% by mass. A household blender or similar device was used for dispersion. (2) The dispersion was dropped onto a glass slide to prepare a specimen. (3) Observe the above (2) with a digital microscope at a magnification of 500x and take images of at least 5 fields of view. (4) In each image obtained in (3) above, 10 fibrous materials were randomly washed and their fiber diameters were measured. (5) The average of all measured fiber diameters was taken as the average fiber diameter of the short fibers.
[0037] (Average flow diameter of nonwoven fabric) The average flow diameter of the nonwoven fabric was measured using a PMI palm porometer (model: CFP-1200AEX). PMI's Gullwick (surface tension = 15.6 dynes / cm) was used as the immersion solution, and the measurement was performed using the half-dry method in accordance with ASTME1294-8.
[0038] (Balance weight of nonwoven fabric) The basis weight of the nonwoven fabric was calculated in accordance with JIS P 8124.
[0039] (Thickness of nonwoven fabric) The thickness of the nonwoven fabric was measured using the following procedure. (1) Cut the nonwoven fabric into 20cm x 20cm pieces. (2) The thickness of five different points of nonwoven fabric 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 (2) above was used as the thickness of the nonwoven fabric.
[0040] (Air permeability resistance of nonwoven fabric) The air permeability resistance of the nonwoven fabric was measured using the following procedure. (1) Cut the nonwoven fabric into 20cm x 20cm pieces. (2) The air permeability resistance was measured for five different nonwoven fabrics using a Gurley densometer (manufactured by Toyo Seiki Co., Ltd., model G-B2C). (3) The average of the five points obtained in (2) above was taken as the air permeability resistance of the nonwoven fabric.
[0041] (Sound absorption rate of composite sound-absorbing material) From the nonwoven fabric in each example and comparative example, a circular disc with a diameter of 28.8 mm was cut out and naturally laminated with a 10 mm thick coarse felt to create a composite sound-absorbing material. The sound absorption coefficient of the composite sound-absorbing material was measured using a DS-2000 normal incidence sound absorption coefficient measurement system (manufactured by Ono Sokki Co., Ltd.) in accordance with JIS A 1405. The measurement was performed with the nonwoven fabric on the incident side of the sound wave. The base materials used for the measurement were prepared and used according to the descriptions of each example and comparative example below.
[0042] (CNF-A, CNF-B) Tencel cut yarn (3 mm long), a regenerated cellulose fiber obtained from Sojitz Corporation, was placed in a washing net, a surfactant was added, and the fibers were repeatedly washed in a washing machine to remove any oil from the fiber surface. After that, the fibers were dispersed in water to a solid content of 1.5% by mass and subjected to a beating treatment using an SDR14 type laboratory refiner (pressure-type disk type) manufactured by Aikawa Iron Works Co., Ltd. as a disk refiner. The cellulose microfiber slurry was subjected to a beating process while periodically measuring the fiber diameter, and the slurry with an average fiber diameter of 950 nm was designated as CNF-A (solid content concentration 1.5% by mass). CNF-A was further subjected to beating treatment using the disc refiner apparatus described above. Subsequently, the beating aqueous slurry was further processed using a high-pressure homogenizer (NS015H, manufactured by Nilo Soavi, Italy) to refine it until the average fiber diameter reached 390 nm. The resulting cellulose fine fiber slurry was designated as CNF-B (solid content concentration 1.5% by mass).
[0043] (CNF-C, CNF-D, CNF-E) Using linter pulp, a natural cellulose obtained from Nippon Paper Pulp Trading Co., Ltd., the linter pulp was immersed in water until it comprised 4% by mass. Then, it was heat-treated in an autoclave at 130°C for 4 hours. The resulting swollen pulp was washed multiple times with water to obtain purified linter pulp impregnated with water. The purified linter pulp was then dispersed in water to a solid content of 1.5% by mass, yielding a 400L dispersion. This dispersion was then subjected to beating treatment using an SDR14 type laboratory refiner (pressure-type disk type) manufactured by Aikawa Iron Works Co., Ltd. The cellulose microfiber slurry was subjected to a beating process while measuring the fiber diameter as needed, and the slurry with an average fiber diameter of 2500 nm was defined as CNF-C (solid content concentration 1.5% by mass). CNF-C was further subjected to beating treatment using the above-mentioned discreeter apparatus, and the cellulose fine fiber slurry obtained when the average fiber diameter became 118 nm was designated as CNF-D (solid content concentration 1.5 mass%). Next, CNF-D was subjected to micronization treatment using a high-pressure homogenizer (NS015H, manufactured by Nilo Soavi, Italy), and the cellulose microfiber slurry at which the average fiber diameter became 98 nm was designated as CNF-E (solid content concentration 1.5% by mass).
[0044] (Short fiber A) Short polyethylene terephthalate fibers (3.0 mm in length) were weighed, water was added, and the mixture was stirred for 4 minutes in a household mixer to obtain a short fiber slurry (solid content concentration: 0.05% by mass). The average fiber diameter of the short fibers in the slurry was 3.0 μm.
[0045] (Short fiber B) Short polypropylene fibers (2.0 mm in length) were weighed, water was added, and the mixture was stirred for 4 minutes in a household mixer to obtain a short fiber slurry (solid content concentration: 0.05% by mass). The average fiber diameter of the short fibers in the slurry was 5.3 μm.
[0046] (Short fiber C) Short polypropylene fibers (3.0 mm in length) were weighed, water was added, and the mixture was stirred for 4 minutes in a household mixer to obtain a short fiber slurry (solid content concentration: 0.05% by mass). The average fiber diameter of the short fibers in the slurry was 9.2 μm.
[0047] (Short fiber D) Short polypropylene fibers (5.0 mm in length) were weighed, water was added, and the mixture was stirred for 4 minutes in a household mixer to obtain a short fiber slurry (solid content concentration: 0.05% by mass). The average fiber diameter of the short fibers in the slurry was 10.6 μm.
[0048] (Example 1) A nonwoven fabric was prepared using CNF-B and short fiber A according to the following procedure. CNF-B and short fiber A were added to pure water in a solid content weight ratio of 5:95, resulting in a final solid content concentration of 0.5%. The slurry was stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 300g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S1. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0049] (Example 2) A nonwoven fabric was prepared using CNF-B and short fiber A according to the following procedure. CNF-B and short fiber A were added to pure water in a solid content weight ratio of 5:95, resulting in a final solid content concentration of 0.5%. The slurry was stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S2. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0050] (Example 3) A nonwoven fabric was prepared using CNF-B and short fiber B according to the following procedure. CNF-B and short fiber B were added to pure water in a solid content weight ratio of 15:85, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S3. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0051] (Example 4) A nonwoven fabric was prepared using CNF-B and short fiber B according to the following procedure. CNF-B and short fiber B were added to pure water in a solid content weight ratio of 15:85, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) equipped with filter cloth (Shikishima Canvas Co., Ltd., TT35) at a basis weight of 50g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed with pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S4. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0052] (Example 5) Nonwoven fabrics were prepared using CNF-B and short fiber C according to the following procedure. CNF-B and short fiber C were added to pure water in a solid content weight ratio of 15:85, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed with pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S5. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0053] (Example 6) A nonwoven fabric was prepared using CNF-D and short fiber A according to the following procedure. CNF-D and short fiber A were added to pure water in a solid content weight ratio of 5:95, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed with pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S6. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0054] (Example 7) A nonwoven fabric was prepared using CNF-A and short fiber B according to the following procedure. CNF-A and short fiber B were added to pure water in a solid content weight ratio of 30:70, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 200g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed with pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric S7. The various physical properties of the obtained nonwoven fabric are shown in Table 1 below.
[0055] (Comparative Example 1) A nonwoven fabric was prepared using CNF-D and short fiber A according to the following procedure. CNF-D and short fiber A were added to pure water in a solid content weight ratio of 20:80, resulting in a final solid content concentration of 0.5%. The slurry was stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric R1. The various physical properties of the obtained nonwoven fabric are shown in Table 2 below.
[0056] (Comparative Example 2) A nonwoven fabric was prepared using CNF-E and short fiber B according to the following procedure. CNF-E and short fibers B were added to pure water in a solid content weight ratio of 15:85, resulting in a final solid content concentration of 0.5%. The slurry was then stirred for 4 minutes in a household mixer to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric R2. The various physical properties of the obtained nonwoven fabric are shown in Table 2 below.
[0057] (Comparative Example 3) Nonwoven fabrics were prepared using CNF-B and short fibers D according to the following procedure. CNF-B and short fibers D were added to pure water in a solid content weight ratio of 30:70, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 100g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2 The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric R3. The various physical properties of the obtained nonwoven fabric are shown in Table 2 below.
[0058] (Comparative Example 4) A nonwoven fabric was prepared using CNF-C and short fiber A according to the following procedure. CNF-C and short fibers A were added to pure water in a solid content weight ratio of 50:50, resulting in a final solid content concentration of 0.5%. The slurry was then stirred in a household mixer for 4 minutes to prepare a papermaking slurry. The prepared papermaking slurry was placed in a batch-type paper machine (Kumagai Riki Kogyo Co., Ltd., automatic square sheet machine, 25cm x 25cm, 80 mesh) with a filter cloth (Shikishima Canvas Co., Ltd. TT35) set up, with a basis weight of 300g / m². 2 The material was added in this manner, and then the papermaking (dewatering) process was carried out with a reduced pressure of 50 kPa relative to atmospheric pressure. The wet paper, consisting of the concentrated composition in a wet state, which was placed on the resulting filter cloth, was peeled off the wire and measured at 1 kg / cm². 2The material was pressed under pressure for 1 minute. Then, it was dried for approximately 120 seconds in a drum dryer set to a surface temperature of 130°C to obtain nonwoven fabric R4. The various physical properties of the obtained nonwoven fabric are shown in Table 2 below.
[0059] [Table 1]
[0060] [Table 2] [Industrial applicability]
[0061] The nonwoven fabric according to the present invention has excellent sound absorption properties in the mid-to-low frequency range, while also possessing high productivity and being suitable for use as a surface material for composite sound-absorbing materials. Therefore, it is particularly suitable for use as a surface material for composite sound-absorbing materials used in automobiles, houses, and home appliances.
Claims
1. A sound-absorbing material comprising a nonwoven fabric containing microfibrillated fine fibers having an average fiber diameter of 100 nm to 2000 nm and short fibers having an average fiber diameter of 0.1 μm to 10 μm, wherein the basis weight of the nonwoven fabric is 50 g / m². 2 The sound-absorbing material is characterized by the above, containing 5% by mass or more of the microfibrillated fine fibers, and having an average flow diameter of the nonwoven fabric measured by a palm porometer of 1 μm or more and 30 μm or less.
2. The sound-absorbing material according to claim 1, wherein the nonwoven fabric is a wet-laid nonwoven fabric.
3. A composite sound-absorbing material comprising a sound-absorbing material according to claim 1 or 2 and a porous material other than the nonwoven fabric, laminated together.
4. The composite sound-absorbing material according to claim 3, wherein, in a measurement method for normal incidence in accordance with JIS A 140 5, it has a maximum sound absorption value at 3000 Hz or less, the maximum value is 0.5 or more, and the sound absorption coefficient is 0.2 or more in the entire range from 2000 to 6000 Hz.
5. A step of preparing a papermaking slurry containing microfibrillated fine fibers having an average fiber diameter of 100 nm to 2000 nm and short fibers having an average fiber diameter of 0.1 μm to 10 μm; The process of making paper from the papermaking slurry to obtain wet paper; and A step of drying the wet paper to obtain a sound-absorbing material made of nonwoven fabric; A method for manufacturing sound-absorbing materials, including, The basis weight of the nonwoven fabric is 50 g / m². 2 A method for producing sound-absorbing material, characterized in that the material contains 5% by mass or more of the microfibrillated fine fibers, and the average flow diameter of the nonwoven fabric, as measured by a palm porometer, is 1 μm or more and 30 μm or less.