JP-7857370-B2 - Nonwoven fabric, and sound-absorbing material using the nonwoven fabric

Inventors

• 浅井 大貴
• 小野 博文
• 城野 圭佑

Assignees

• 旭化成株式会社

Dates

Publication Date

20260512

Application Date

20241003

Claims (5)

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 or more, and the microfibrillated fine fibers are contained in an amount of 5% by mass or more, and the average flow diameter of the nonwoven fabric, as measured by a palm porometer, is 1 μm to 30 μm.
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; A step 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, A method for producing sound-absorbing material, characterized in that the basis weight of the nonwoven fabric is 50 g/ m² or more, it 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.

Description

This invention relates to a nonwoven fabric and a sound-absorbing material using the nonwoven fabric. 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. International Publication No. 2018/143430International Publication No. 2017/006993 This figure shows the results of sound absorption coefficient measurements in Example 1, Example 2, and Comparative Example 1. The embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments. One embodiment of the present invention is 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. (Non-woven fabric) In this embodiment, it is preferable that the nonwoven fabric has a structure in which 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 10.0 μm 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. (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). (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. 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