Sound insulating material comprising sound insulating resin composition

Abstract

To provide a lightweight material exhibiting an excellent sound insulating effect.SOLUTION: A sound insulating material 1 comprising a resin composition 2 in which cellulose nanofibers 3 are dispersed is used.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sound-insulating material made of a resin composition containing cellulose nanofibers. [Background technology]

[0002] To ensure quietness inside buildings and automobiles, soundproofing materials are used in walls, floors, ceilings, etc. Soundproofing materials are broadly divided into sound-absorbing materials, which absorb indoor sound and prevent echoes, and sound-insulating materials, which reflect outdoor sound and prevent it from entering the room, and they are generally used in combination. Of these, porous materials are mainly used for sound-absorbing materials, while heavy, high-density materials such as steel plates are mainly used for sound-insulating materials. However, there is a demand for the development of lightweight, high-performance soundproofing materials for building materials from the perspective of workability and safety during construction, and for automotive applications from the perspective of improving fuel efficiency through weight reduction.

[0003] Cellulose nanofibers have attracted attention as a new, lightweight material with low environmental impact. Cellulose nanofibers have traditionally been added to resins and rubbers to improve their mechanical strength. In recent years, as shown in Patent Documents 1 and 2, it has been proposed to use cellulose nanofibers to form a fine structure on the surface of existing sound-absorbing materials, thereby improving their sound-absorbing performance.

[0004] Patent Document 1 discloses an automotive insulator that has high sound-absorbing and heat-insulating properties, which is made by impregnating a wool mat with a slurry of a thermosetting resin mixed with cellulose nanofibers, thereby entangling the cellulose nanofibers with the wool fibers and forming minute gaps.

[0005] Furthermore, Patent Document 2 discloses a sound-absorbing material that exhibits high sound-absorbing performance by laminating a fiber layer containing cellulose nanofibers on the surface of a resin porous body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-128373 [Patent Document 2] Japanese Patent Publication No. 2022-185471 Summary of the Invention [Problem to be solved by the invention]

[0007] However, these materials are only intended to improve sound absorption, and no mention is made of sound insulation. As mentioned above, to achieve effective soundproofing, it is necessary to achieve both high sound absorption and sound insulation, but the general method of improving sound insulation is to increase the density of the material, which has the problem of increasing the weight of the component.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a material that is lightweight and exhibits excellent sound insulation properties without increasing the density. [Means for solving the problem]

[0009] The present invention solves the above-mentioned problems by a first solution means, which is a sound-insulating material made of a resin composition in which cellulose nanofibers are dispersed.

[0010] Furthermore, in the first solution of the present invention, A second solution can be adopted, in which the content of the cellulose nanofibers is 0.5% by mass or more and 11% by mass or less.

[0011] Furthermore, in the first or second solving means of the present invention, A third solution can be adopted, in which the number average fiber width of the cellulose nanofibers is 3 nm or more and 20 nm or less.

[0012] Furthermore, the present invention can employ a fourth solution in which the first to third solutions described above are in the form of a sheet having a thickness of 0.1 mm or more and 20 mm or less.

[0013] Furthermore, in the first to fourth solutions described above, the present invention can employ a fifth solution, in which the cellulose nanofibers are regenerated cellulose nanofibers that have been regenerated by removing the xanthate groups from xanthated cellulose nanofibers to have a xanthate substitution degree of 0.01 or less.

[0014] Furthermore, the present invention can employ a sixth solution, which is a method for manufacturing a sound-insulating material, in which a masterbatch made of a resin composition containing cellulose nanofibers is kneaded with an additional resin, and the kneaded mixture is molded to form the sound-insulating material. [Effects of the Invention]

[0015] In sound-insulating materials made from resin compositions with dispersed cellulose nanofibers, the small fiber width of the cellulose nanofibers creates a resin-cellulose nanofiber interface with an extremely large specific surface area. Furthermore, because cellulose nanofibers are rigid and have a higher elastic modulus than resins, a high proportion of sound waves incident on the resin-cellulose nanofiber interface are reflected. As a result, resin compositions containing added cellulose nanofibers are thought to be highly sound-insulating materials that exhibit high sound transmission loss because sound waves are scattered internally, hindering their transmission.

[0016] Furthermore, since a small amount of cellulose nanofibers added to the resin that forms the base of the resin composition provides high sound insulation, it has little effect on the density of the material, and the overall weight can be handled in a manner that is not much different from that of the resin itself. [Brief explanation of the drawings]

[0017] [Figure 1] Image of sound attenuation in the sound-proofing material according to the present invention [Figure 2] Illustration of insufficient sound insulation caused by too much CNF [Figure 3] Schematic diagram showing the measurement of normal incidence sound transmission loss [Figure 4]Schematic diagram showing the exceptional measurement of normal incidence sound transmission loss in Manufacturing Example 1 DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention is described in detail below. The present invention is a sound-insulating material made of a resin composition having cellulose nanofibers dispersed therein.

[0019] The cellulose nanofibers (hereinafter abbreviated as "CNF") used in this invention are cellulose that has been processed to produce fine fibers. They may include not only cellulose whose molecular structure remains unchanged, but also cellulose in which part of the molecular structure has been chemically modified, or cellulose that has been chemically modified and then regenerated into cellulose. The CNF preferably has a sufficiently small fiber width. To obtain CNF with a small fiber width, it is desirable to first chemically modify cellulose to impart functional groups and then defibrate it. Defibration with functional groups present results in a smaller fiber width than defibration without functional groups, making it easier to obtain sufficiently fine nanofibers.

[0020] Examples of chemically modified cellulose include TEMPO-oxidized cellulose (oxidized with TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical), carboxymethyl cellulose, phosphoric acid esterified cellulose, and alkali-treated cellulose to which carbon disulfide has been added to form xanthate groups (-OCSS). - M +Examples include xanthate cellulose, which has been introduced with cellulose esters. Chemically modifying cellulose materials such as pulp makes it easier to create nanofibers than defibrating the cellulose material as is. CNF that has been chemically modified and defibrated is called "chemically modified CNF." Furthermore, among the chemically modified celluloses, phosphate ester cellulose and xanthate cellulose are preferred because they can be easily regenerated back into cellulose. CNF obtained by regenerating the molecular structure of chemically modified cellulose is called "regenerated CNF."

[0021] In the following description of this invention, the term "CNF" refers not only to CNFs obtained by simply defibrating cellulose materials, but also to the aforementioned chemically modified CNFs and regenerated CNFs. Furthermore, regenerated CNFs may include not only those in which hydroxyl groups have been modified to other functional groups, such as xanthate groups, but also those in which some remain as other functional groups, rather than those in which all hydroxyl groups have been restored to their original hydroxyl groups. However, to favorably form an interface between the resin and CNF, it is desirable to minimize the number of functional groups that tend to interfere with the surrounding CNF. For this reason, it is preferable to fully remove the functional groups used for defibration rather than leaving them as they are. The degree of substitution is an index that indicates the average degree to which the three hydroxyl groups present in one glucose, a structural unit of cellulose, have been replaced by other functional groups through chemical modification. Specifically, it is desirable for the degree of substitution to be reduced to 0.01 or less through regeneration. Furthermore, these CNFs may be purified before use, if necessary.

[0022] The CNF preferably contains, as its main component, fine fibers with a fiber width of 3 nm or more and 20 nm or less. Here, "main component" means that 50% or more of the fibers present fall within the above fiber width range. However, fine fibers with a fiber width outside the above range may be included as long as it does not interfere with the production and use of the composition. Furthermore, the number-average fiber width of the CNF is preferably 3 nm or more. While the present invention can be implemented with a width smaller than this, achieving a width less than 3 nm requires a great deal of energy and is not very practical in terms of work efficiency. On the other hand, the number-average fiber width of the CNF is preferably 20 nm or less. The smaller the fiber width of the CNF, the more uniformly it disperses in the resin, forming more interfaces with the resin and reflecting incident sound. This results in scattering of sound waves, resulting in improved sound insulation. On the other hand, the larger the fiber width of the CNF, the easier it is to disperse the CNF in the resin. However, if the number-average fiber width exceeds 20 nm, fibers with larger fiber widths are likely to be mixed in, causing uneven dispersion in the resin, increasing the risk of reduced sound insulation.

[0023] The sound-proofing material of this invention is made of a resin composition with dispersed CNFs. Uniform dispersion of CNFs in the resin results in the formation of numerous resin-CNF interfaces. Because CNFs are rigid and have a higher elastic modulus than resins, incident sound waves are reflected and scattered at the resin-CNF interfaces, resulting in the sound-proofing material, which is a resin composition with dispersed CNFs, blocking the transmission of sound waves. The resulting sound wave transmission within sound-proofing material 1 is shown in the schematic diagram of Figure 1. Sound-proofing material 1 is primarily made of resin composition 2, within which CNFs 3 are dispersed. Propagating sound waves S are reflected and scattered whenever they encounter an interface (reflection surface) with CNFs 3 within resin composition 2, resulting in high sound transmission loss. This results in high sound-proofing properties.

[0024] Examples of resins constituting the resin composition include polyolefin resins such as polyethylene and polypropylene, polyurethane resins, acrylic resins, vinyl chloride resins, vinyl acetate resins, fluororesins, epoxy resins, polyester resins, silicone resins, natural rubber, ethylene propylene rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, and copolymers thereof. Thermoplastic resins and elastomers are preferred in terms of ease of production of the resin composition and ease of dispersing CNFs in the resin. Among these, low-density polyethylene, thermoplastic polyurethane resins, and rubbers with lower rigidity are preferred because they have a greater difference in elastic modulus from the CNFs, and therefore are expected to reflect sound waves.

[0025] In addition to the above-mentioned resins, the materials constituting the resin composition may contain other components such as a vulcanizing agent, a dispersant for filler, a plasticizer, a colorant, an antioxidant, and an antiaging agent, as long as the sound insulation properties are not impaired.

[0026] The resin layer constituting the resin composition may have many closed pores, as these are expected to contribute to sound absorption, but it is preferable to have fewer interconnected pores. If there are many interconnected pores, sound may be transmitted through the pores without hitting the resin-CNF interface, resulting in insufficient sound insulation. Therefore, it is preferable that the length of the interconnected pores does not exceed 70% of the thickness of the resin layer. It is even more preferable that it does not exceed 50%.

[0027] The CNF content in the resin composition is preferably 0.5% by mass or more, and more preferably 1% by mass or more, of the total composition. If it is less than 0.5% by mass, the resin-CNF interface will be reduced, increasing the risk of insufficient sound insulation. On the other hand, a content of 11% by mass or less is preferred, and a content of 10% by mass or less is more preferred. Too much CNF tends to actually reduce sound insulation. This depends on the fiber length of the CNF, but if there is too much CNF, it is thought that CNFs come into contact with each other in the resin, forming a sound transmission path through the CNF, allowing sound to travel without attenuation at the resin-CNF interface, resulting in insufficient sound insulation. A hypothetical schematic diagram of this assumed situation is shown in Figure 2.

[0028] The sound insulating material according to the present invention can be molded by injection molding, extrusion molding, compression molding, etc. From the viewpoint of ease of molding, it is preferable that the resin is a thermoplastic resin or an elastomer.

[0029] The sound-insulating material according to the present invention is preferably in sheet form because it is easy to mold, but is not limited to this and can be in block form or any other shape suited to the installation location. However, since sound insulation cannot be fully achieved unless there is a certain thickness even at the thinnest part, it is preferable that the thickness is 0.1 mm or more. Furthermore, 0.3 mm or more is more preferable. On the other hand, since molding becomes difficult as the thickness increases, it is preferable that the thickness is 20 mm or less. [Example]

[0030] An embodiment of the present invention will be described below. First, the materials used will be described. Using these materials, sound-insulating materials according to the present invention were manufactured using four different methods. <cnf> RCNF (manufactured by Rengo Co., Ltd.: regenerated CNF from xanthated CNF, number average fiber width = 5.9 nm) Mechanically defibrated CNF (manufactured by Sugino Machine Co., Ltd.: BiNFi-s, WFo-10005, referred to as "BiNFi-s" in the text, number average fiber width = 31.2 nm). Microfibrous cellulose (manufactured by Daicel Miraizu Co., Ltd.: Celish, KY100S, referred to as "Cerish" in the text, number average fiber width = 198 nm). <Dispersant> 1,3-Butylene glycol (1,3-butanediol, manufactured by Kanto Chemical Co., Ltd.: special grade reagent) <Resin materials> Thermoplastic polyurethane resin (TPU, manufactured by Nihon Miractoran Co., Ltd.: Miractoran E385, thermoplastic elastomer) Low-density polyethylene resin (LDPE, manufactured by Tosoh Corporation: Petrothene 205, thermoplastic resin) Carboxylic acid-modified polyethylene resin emulsion (Unitika Ltd.: Arrowbase SB-1010, thermoplastic resin) Ethylene propylene rubber (EPDM, manufactured by ENEOS Materials Co., Ltd.: EP T7241, thermosetting elastomer) <Additives> Foaming agent (azodicarbonamide, Fujifilm Wako Pure Chemical Industries, Ltd.: Reagent Grade 1) Crosslinking agent / vulcanizing agent (dicumyl peroxide, manufactured by Nacalai Tesque, Inc.: chemical reagent) Vulcanization aid (zinc oxide, manufactured by Nacalai Tesque, Inc.: Reagent grade 1)

[0031] As examples of production methods using different types of resin and different internal structures in the resin composition, sound insulation materials using thermoplastic polyurethane (Production Example 1: TPU), low-density polyethylene (Production Example 2: LDPE), foamed low-density polyethylene (Production Example 3: foamed LDPE), and ethylene propylene rubber (Production Example 4: EPDM) were produced using the following procedures.

[0032] <Production Example 1: Sound insulation material using thermoplastic polyurethane (TPU)> (Example 1: Compared to Comparative Example 1) (1-1) Preparation of dried RCNF Water was added to the RCNF aqueous suspension to prepare 140 g of diluted RCNF aqueous suspension at a solids concentration of 1.0% by mass. While stirring this diluted RCNF aqueous suspension at 3000 rpm using a Homodisper (Labo-lution, manufactured by Primix Corporation), 7 g of 1,3-butylene glycol was added and the mixture was stirred for 5 minutes. After stirring, the mixture was dried with air at 60°C for 24 hours, yielding 8.4 g of dried RCNF. The CNF content of this dried RCNF was 16.7% by mass and the 1,3-butylene glycol content was 83.3% by mass.

[0033] (1-2) Preparation of RCNF-blended TPU masterbatch 8.4 g of the dried RCNF obtained in (1-1) and 12.6 g of TPU were kneaded for 15 minutes at 160 °C in a small benchtop kneader (Xplore Instruments: DSM Xplore MC15HT) to prepare 14 g of RCNF-blended TPU masterbatch. It is believed that the 7 g of 1,3-butylene glycol contained in the dried RCNF was completely evaporated. The CNF content of this RCNF-blended TPU masterbatch was 10 mass%.

[0034] (1-3) Preparation of RCNF-added TPU sheet 7.5 g of the RCNF-blended TPU masterbatch obtained in (1-2) and 7.5 g of TPU were kneaded for 5 minutes at 180°C using the small benchtop kneader to obtain 15 g of RCNF-added TPU as a resin composition with a CNF content of 5% by mass. The entire RCNF-added TPU was compression molded at 200°C and 5 MPa for 5 minutes to obtain a 1.0 mm-thick RCNF-added TPU sheet.

[0035] [Table 1]

[0036] (Comparative Example 1) In Example 1, the above (1-1) and (1-2) were not carried out, and only the TPU used in (1-3) was used to obtain a TPU sheet with a thickness of 1.0 mm.

[0037] (Example 2: Compared with Comparative Example 2) In Example 1, the mixing ratio of the RCNF-blended TPU masterbatch and TPU in (1-3) above was changed to obtain 15 g of RCNF-added TPU as a resin composition with a CNF content of 3 mass%. 4.5 g of this RCNF-added TPU was compression molded under the same conditions as above, except that the thickness was changed to 0.3 mm, to obtain an RCNF-added TPU sheet.

[0038] (Example 3: Compared to Comparative Example 2) In Example 2, the mixing ratio of the RCNF-blended TPU masterbatch to TPU was changed to obtain an RCNF-added TPU as a resin composition with a CNF content of 5 mass%, and an RCNF-added TPU sheet of the same thickness was obtained.

[0039] (Example 4: Compared to Comparative Example 2) In Example 2, the mixing ratio of the RCNF-blended TPU masterbatch to TPU was changed to obtain an RCNF-added TPU as a resin composition with a CNF content of 10 mass%, and an RCNF-added TPU sheet of the same thickness was obtained.

[0040] (Comparative Example 2) In Example 2, the above (1-1) and (1-2) were not carried out, and only the TPU used in (1-3) was used to obtain a TPU sheet with a thickness of 0.3 mm.

[0041] (Comparative Example 3: Compared to Comparative Example 2) A BiNFi-s-added TPU sheet was obtained in the same manner as in Example 3, except that RCNF was changed to BiNFi-s.

[0042] (Comparative Example 4: Compared to Comparative Example 2) A 0.3 mm thick celish-added TPU sheet was obtained by the same procedure as in Example 3, except that RCNF was replaced with celish.

[0043] <Production Example 2: Sound insulation material using low-density polyethylene (LDPE)> (Example 5: Compared to Comparative Example 6) (2-1) Preparation of RCNF-blended carboxy-modified polyethylene resin masterbatch Water was added to the RCNF aqueous suspension to prepare 2000 g of diluted RCNF aqueous suspension at a solids concentration of 1.0 mass%. While stirring this diluted RCNF aqueous suspension at 3000 rpm with the homodisper, 148.4 g of carboxy-modified polyethylene resin emulsion (solids content: 37.1 g) was added, and the mixture was stirred for 5 minutes. After stirring, the mixture was dried with air at 60°C for 24 hours to obtain 57.1 g of an RCNF-blended carboxy-modified polyethylene resin masterbatch. The CNF content of this RCNF-blended carboxy-modified polyethylene resin masterbatch was 35 mass%.

[0044] (2-2) Preparation of RCNF-added LDPE sheet 2.0 g of the RCNF-blended carboxy-modified polyethylene resin masterbatch obtained in (2-1) and 12.0 g of LDPE were kneaded in the small benchtop kneader at 140°C for 5 minutes to obtain 14.0 g of RCNF-added LDPE as a resin composition with a CNF content of 5% by mass. The entire amount of this RCNF-added LDPE was compression molded at 150°C and 7 MPa for 5 minutes to obtain an RCNF-added LDPE sheet with a thickness of 1.0 mm.

[0045] [Table 2]

[0046] (Comparative Example 5: Compared to Comparative Example 6) In Example 5, an RCNF-added LDPE sheet was obtained by the same procedure as in Example 5, except that the RCNF-blended carboxy-modified polyethylene resin masterbatch and LDPE were mixed by hand instead of kneading with a small benchtop kneader, thereby intentionally worsening dispersibility.

[0047] (Comparative Example 6) In Example 5, the above (2-1) was not carried out, and only the LDPE used in (2-2) was used to obtain an LDPE sheet having a thickness of 1.0 mm.

[0048] (Example 6: Compared to Comparative Example 7) An RCNF-added LDPE sheet was obtained in the same manner as in Example 5, except that 4.2 g of RCNF-added LDPE was used and the sheet thickness was changed to 0.3 mm.

[0049] (Comparative Example 7) In Example 6, the above (2-1) was not carried out, and only the LDPE used in (2-2) was used to obtain an LDPE sheet with a thickness of 0.3 mm.

[0050] <Production Example 3: Sound insulation material using foamed low-density polyethylene (foamed LDPE)> (Example 7: Compared to Comparative Example 8) (3-1) Preparation of RCNF-blended carboxy-modified polyethylene resin masterbatch By the same procedure as in (2-1) above, an RCNF-blended carboxy-modified polyethylene resin masterbatch having a CNF content of 35 mass % was obtained.

[0051] (3-2) Preparation of RCNF-added foamed LDPE sheet A foamed LDPE sheet was prepared by following Example 1 of Japanese Patent No. 4865518, except that no antioxidant or antistatic agent was added. Specifically, 0.6 g of the RCNF-blended carboxy-modified polyethylene resin masterbatch obtained in (3-1), 10 g of LDPE, 2.9 g of foaming agent, and 0.1 g of crosslinking agent were mixed in the compact benchtop mixer at 140°C for 5 minutes to obtain a resin composition containing 2% CNF by mass. This RCNF-blended foamed LDPE was compression-molded at 150°C and 7 MPa for 5 minutes to obtain a 0.3 mm-thick sheet. This sheet was then placed in a 230°C air dryer for crosslinking and foaming, yielding a 7.5 mm-thick RCNF-blended foamed LDPE sheet.

[0052] (Comparative Example 8) In Example 7, the above (3-1) was not carried out, and only the LDPE, foaming agent, and crosslinking agent used in (3-2) were used to obtain a foamed LDPE sheet with a thickness of 7.5 mm.

[0053] [Table 3]

[0054] <Production Example 4: Sound insulation material using ethylene propylene rubber (EPDM)> (Example 8: Compared to Comparative Example 10) (4-1) Preparation of RCNF-blended carboxy-modified polyethylene resin masterbatch By the same procedure as in (2-1) above, an RCNF-blended carboxy-modified polyethylene resin masterbatch having a CNF content of 35 mass % was obtained.

[0055] (4-2) Preparation of RCNF-added EPDM sheet 14.3 g of the RCNF-blended carboxy-modified polyethylene resin masterbatch obtained in (4-1), 100 g of EPDM, 3 g of vulcanizing agent, and 5 g of vulcanization aid were kneaded at 80°C using an open roll to obtain an RCNF-added EPDM resin composition. The CNF content of this RCNF-added EPDM was 4.1 mass% (5 phr: parts by mass relative to 100 parts by mass of rubber). This RCNF-added EPDM was vulcanized at 170°C and 20 MPa for 15 minutes to obtain an RCNF-added EPDM sheet with a thickness of 1.0 mm.

[0056] [Table 4]

[0057] (Example 9: Compared to Comparative Example 10) In Example 8, the mixing ratio of the RCNF-blended carboxy-modified polyethylene resin masterbatch and EPDM was changed to obtain an RCNF-added EPDM with a CNF content of 7.3 mass% (10 phr), and an RCNF-added EPDM sheet of the same thickness was obtained.

[0058] (Comparative Example 9: Compared to Comparative Example 10) In Example 8, the mixing ratio of the RCNF-blended carboxy-modified polyethylene resin masterbatch to EPDM was changed to obtain an RCNF-added EPDM with a CNF content of 12.1 mass% (20 phr), and an RCNF-added EPDM sheet of the same thickness was obtained.

[0059] (Comparative Example 10) In Example 8, the above (4-1) was not carried out, and an EPDM sheet having a thickness of 1.0 mm was obtained using the EPDM, vulcanizing agent, and vulcanization aid used in (4-2).

[0060] <Sound insulation evaluation> A test piece of φ41.5 mm was cut out from each sheet sample and evaluated using the normal incidence sound transmission loss as an index. A WinZac manufactured by Nippon Onkyo Engineering Co., Ltd. was used as the device to measure the normal incidence sound transmission loss in accordance with ASTM E2611. In order to stably stand the sample (11) in the sound tube (10) of the device, a 10 mm thick polyurethane foam (12) (Calmflex F2-10 manufactured by Inoac Corporation) was placed on top of it on the sound source side. A schematic diagram of this evaluation method is shown in Figure 3. Incident sound I i and transmitted sound I t For this, sound transmission loss TL (dB) = 10 × log 10 (I i / I t )

[0061] In addition, since the 0.3 mm thick TPU sheet (Sample 11) in Production Example 1 was particularly weak and difficult to support, Sample 11 was sandwiched between two 10 mm thick polyurethane foam sheets (12). A schematic diagram of this evaluation method is shown in Figure 4.

[0062] The normal incidence sound transmission loss was calculated by averaging the average values ​​for each 1 / 3 octave in the range from 250 Hz to 4000 Hz, and the average increase rate was calculated compared to a sample without CNF (shown as "Comparative" in each table). Samples with an average increase rate of more than 15% were evaluated as having excellent sound insulation.

[0063] <Evaluation of dispersibility> The surface of the resin sheet was observed at a magnification of 20x using a digital microscope: VHX-8000 (manufactured by Keyence Corporation). However, for the foamed LDPE sheets of Example 7 and Comparative Example 8, the sheets were observed before crosslinking and foaming. The obtained images were binarized by brightness using an automatic area measurement function. The threshold was set to 95% (0.95x) of the most frequent value of brightness, and a value of 0.1mm2 in the area of ​​the dark part was used. 2 The above were classified as aggregates. Dispersibility was evaluated as follows: when the area ratio of aggregates to the entire image was 3% or less, the CNF was considered to be sufficiently dispersed in the resin (evaluation: ○), and when the area ratio of aggregates to the entire image was more than 3%, the CNF was considered to be insufficiently dispersed (evaluation: ×).

[0064] <Consideration> About Manufacturing Example 1 A 1.0 mm thick TPU sheet (Example 1), in which RCNF was added to ensure sufficient dispersion in the resin, showed an increase in the average sound transmission loss and improved sound insulation compared to a sheet without RCNF (Comparative Example 1). The same effect was confirmed even when the thickness was reduced to 0.3 mm. Furthermore, the sound insulation improved as the amount of RCNF added increased (Examples 2 to 4, Comparative Example 2). On the other hand, when BiNFi-s or Celish, which have a fiber width larger than RCNF, were used, sound insulation did not improve compared to Comparative Example 2, in which no CNF was added (Comparative Examples 3 and 4). Therefore, it is thought that in order to improve sound insulation, it is necessary to use CNF with a sufficiently small fiber width.

[0065] About Manufacturing Example 2 A 1 mm thick LDPE sheet containing RCNF (Example 5) exhibited improved sound insulation compared to a sheet containing no RCNF (Comparative Example 6). On the other hand, in Comparative Example 5, in which the dispersion of RCNF in the resin was intentionally reduced, the average sound transmission loss did not increase significantly compared to Comparative Example 6. This confirmed that in order to improve sound insulation, it is necessary to sufficiently disperse RCNF in the resin. Furthermore, similar sound insulation was confirmed even when the sheet thickness was reduced to 0.3 mm (Example 6, Comparative Example 7).

[0066] About Manufacturing Example 3 The average sound transmission loss of the 7.5 mm thick foamed LDPE sheet containing RCNF (Example 7) was higher than that of the sheet containing no RCNF (Comparative Example 8). This indicates that sound insulation is improved even when the resin composition is foamed.

[0067] About Manufacturing Example 4 A 1 mm thick EPDM sheet containing RCNF (Example 8) showed significantly improved sound insulation compared to a sheet containing no RCNF (Comparative Example 10). Meanwhile, when the RCNF addition rate was 4.1 mass% (5 phr) or 7.3 mass% (10 phr) (Examples 8 and 9), the average sound transmission loss increased, but when the addition rate was increased to 12.1 mass% (20 phr), the average sound transmission loss did not increase (Comparative Example 9). This indicates that adding too much RCNF does not improve sound insulation. [Explanation of symbols]

[0068] 1. Sound insulation material 2 Resin composition 3. CNF 10 sound tube 11 Sample 12 Polyurethane foam< / cnf>

Claims

1. A sound-proofing material made from a resin composition in which cellulose nanofibers are dispersed.

2. The sound-proofing material according to claim 1, wherein the content of the cellulose nanofibers is 0.5% by mass or more and 11% by mass or less.

3. 2. The sound-proofing material according to claim 1, wherein the cellulose nanofibers have a number average fiber width of 3 nm or more and 20 nm or less.

4. 2. The sound-insulating material according to claim 1, which is in the form of a sheet having a thickness of 0.1 mm or more and 20 mm or less.

5. The sound-insulating material according to any one of claims 1 to 4, wherein the cellulose nanofiber is a regenerated cellulose nanofiber obtained by removing the xanthate group from a xanthated cellulose nanofiber to regenerate a xanthate substitution degree of 0.01 or less.

6. A method for producing a sound-insulating material, comprising kneading a masterbatch made of a resin composition containing cellulose nanofibers with an additional resin, and molding the kneaded mixture to form the sound-insulating material.

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