Soundproofing and sound absorbing material and method of producing the same

Abstract

To provide a soundproofing and sound absorbing material with good soundproofing performance that is lightweight and easy to handle.SOLUTION: The soundproofing and sound absorbing material has membranes containing cellulose nanofibers in inter-fiber spaces or air bubbles etc. of porous sheets.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sound insulation and absorption material having a fine film made of cellulose nanofibers and a method for producing the same. [Background technology]

[0002] In buildings and automobiles, soundproofing materials are used in walls, floors, ceilings, etc. to ensure quietness inside the building. Soundproofing materials are broadly divided into sound-absorbing materials that absorb indoor sound and prevent echoes, and sound-proofing materials that reflect outside 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, and high-density heavy materials such as steel plates are mainly used for sound-proofing materials. However, there is a demand for the development of lightweight, high-performance soundproofing materials from the viewpoints of workability and safety during construction in building materials applications, and of improving fuel efficiency through weight reduction in automobile applications.

[0003] A nanofiber-attached sound-absorbing material has been proposed as a lightweight sound-absorbing material, in which a nonwoven fabric made of microfibers with a fiber width on the order of microns is impregnated with a dispersion containing cellulose nanofibers with a fiber width on the order of nanons, and then freeze-dried (Patent Document 1). This material has a structure in which a network of cellulose nanofibers is formed in the gaps between the microfibers, and it has been confirmed that the material has excellent deformation recovery and shape retention properties, as well as improved sound absorption in some sound ranges. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6493276 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the sound-absorbing material described in Patent Document 1 has improved deformation recovery and shape retention compared to sound-absorbing materials that do not contain cellulose nanofibers, no improvement was observed in sound insulation performance.

[0006] Therefore, an object of the present invention is to provide a sound insulating and absorbing material which is lightweight, easy to handle, and has excellent sound insulating properties. [Means for solving the problem]

[0007] The present invention solves the above-mentioned problems by providing a sound insulation and absorption material having a film containing cellulose nanofibers in voids such as between fibers or air bubbles in a porous sheet.

[0008] In the sound insulating and absorbing material according to the present invention, a configuration can be adopted in which an inorganic material or an organic material is selected for the porous sheet.

[0009] In addition, the present invention makes it possible to produce the above-mentioned sound-insulating and sound-absorbing material by papermaking a raw material slurry containing cellulose nanofibers into a porous sheet, and forming a membrane containing cellulose nanofibers between the fibers inside the sheet.

[0010] Furthermore, the present invention also enables the production of the above-mentioned sound-insulating and sound-absorbing material by a method in which a porous sheet such as a fiber aggregate or a foam is coated or impregnated with a slurry of cellulose nanofibers to form a membrane containing cellulose nanofibers in voids between the fibers or in air bubbles within the sheet. Effect of the Invention

[0011] Conventional sound-absorbing materials have utilized a fine network of gaps between fibers or bubbles on the micro (μm) order, such as in nonwoven fabrics and foams, but the gaps themselves were not blocked, so sufficient sound insulation effect was not achieved. In the sound-insulating and absorbing material of this invention, cellulose nanofibers are not added simply for reinforcement, but a cellulose nanofiber membrane is formed in all or part of the gaps between fibers or bubbles on the μm order, resulting in a greatly improved sound-insulating effect in addition to the original sound-absorbing effect of the porous sheet, as the gaps between fibers or bubbles are blocked, preventing sound from passing through as is.

[0012] Even if the cellulose nanofiber has a relatively large fiber width, it does not exhibit such sound absorbing and sound insulating effects. It is believed that if the fiber width is large, it is difficult to produce a uniform film, and even if a film is produced, holes are likely to appear due to the unevenness caused by the thick fibers mixed in. By using cellulose nanofibers with a smaller fiber width, a suitable film with small unevenness, uniformity, and few holes can be produced, and sound absorbing and sound insulating effects can be exhibited.

[0013] As a method for producing a sound-insulating and sound-absorbing material, a membrane can be formed in the gaps between the fibers inside a porous sheet by making a raw material slurry containing cellulose nanofibers. On the other hand, a membrane can also be formed by coating or impregnating a porous sheet with a cellulose nanofiber slurry, and various production methods are available, making it easy to produce. [Brief description of the drawings]

[0014] [Figure 1] SEM photo of the sound-insulating and sound-absorbing material of Example 1 [Diagram 2] SEM photo of the sound-insulating and sound-absorbing material of Example 7 [Diagram 3] SEM photo of sound-insulating and sound-absorbing material of Example 8 [Figure 4] SEM photo of sound-insulating and sound-absorbing material of Example 10 [Diagram 5] SEM photo of sound-insulating and sound-absorbing material of Example 12 [Figure 6]SEM photo of sound-insulating and sound-absorbing material of Comparative Example 10 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention is described in detail below. The present invention is a sound insulation and absorption material having a film containing cellulose nanofibers in voids such as between fibers or air bubbles inside a porous sheet.

[0016] As the porous sheet, a sheet-like inorganic material or organic material having voids on the order of μm can be used. For example, inorganic materials include sheets as fiber aggregates made of rock wool, glass wool, ceramic fiber, alkaline earth silicate wool, alumina fiber, carbon fiber, stainless steel fiber, etc. Organic materials include sheets as fiber aggregates made of wood pulp, cotton, olefin fiber, ester fiber, acrylic fiber, aramid fiber, vinyl chloride fiber, urethane fiber, etc., and foams made of olefin resin, urethane resin, melamine resin, acrylic resin, epoxy resin, vinyl acetate resin, vinyl chloride resin, silicone resin, latex, rubber, cellulose, etc. Basically, any sheet-like porous material used as a conventional sound absorbing material can be used. Note that voids on the order of μm mean that gaps of about 1 μm to 100 μm are formed. Note that even if the material has finer voids on the order of nm, it can be used without any particular problem. It is sufficient that these voids are blocked by the film.

[0017] Among these, inorganic materials are preferable because it is easy to ensure a sufficient thickness for sound absorption effect and to impart flame retardancy. Among inorganic materials, rock wool is inexpensive and has a fiber width of about 2 to 20 μm, so that the membrane constituting the present invention can be easily formed in the formed void and the membrane can be easily blocked. In addition, silicon dioxide, which is the main component of rock wool, is particularly preferable because it forms hydrogen bonds with cellulose nanofibers and is easily fixed.

[0018] The thickness of the porous sheet is not particularly specified, but generally, a thickness of 200 μm or more and 25 mm or less is advantageous in terms of handling during production or processing. When producing a porous sheet with a cellulose nanofiber membrane formed by papermaking, the thickness is sufficient as long as the sheet can be made into paper. When forming a membrane by coating, there is no particular problem even if the porous sheet is thick, as long as it can be manufactured or processed. On the other hand, when forming a membrane by impregnation, if the porous sheet is too thick, it takes time for the slurry to penetrate into the inside, and production efficiency is likely to decrease.

[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 whose molecular structure has been partially chemically modified, and cellulose that has been chemically modified and then regenerated into cellulose.

[0020] Examples of chemically modified cellulose include TEMPO-oxidized cellulose (TEMPO-oxidized cellulose), carboxymethyl cellulose (carboxymethyl cellulose), phosphoric acid ester cellulose, and cellulose treated with alkali and carbon disulfide to form xanthate groups (-OCSS). - M + Examples include xanthate cellulose, which is a compound that has been introduced with cellulose phosphate. Chemically modifying cellulose materials made from materials such as pulp makes it easier to convert them into nanofibers than defibrating the cellulose materials as is. CNF that has been chemically modified and defibrated is called "chemically modified CNF." Among the chemically modified celluloses, cellulose phosphate and xanthate are preferred because they can be easily regenerated back to cellulose. CNF obtained by regenerating the molecular structure of the chemically modified cellulose of chemically modified CNF back to cellulose is called "regenerated CNF."

[0021] In the following description of the present invention, the term CNF refers not only to CNFs obtained by simply defibrating cellulose materials, but also to the above-mentioned chemically modified CNFs and regenerated CNFs. In addition, the regenerated CNFs may include not only those in which the hydroxyl groups have been once modified to other functional groups such as xanthate groups, but also those in which some remain as other functional groups, as well as those in which all of the functional groups have been returned to the original hydroxyl groups. In the case of regenerated CNFs, it is preferable to use CNFs in which the substitution degree of functional groups remaining in the regeneration is reduced to 0.01 or less, since this keeps the viscosity of the raw material slurry low, makes it easier to form a uniform membrane in the porous sheet, and prevents the productivity from decreasing due to the decrease in drainage during papermaking. Furthermore, these CNFs may be purified before use if necessary.

[0022] The CNF preferably contains fine fibers having a fiber width of 3 nm or more and 100 nm or less as the main component. Here, the term "main component" means that 50% or more of the fibers present fall within the above fiber width condition. However, fine fibers having a fiber width outside the above range may be contained as long as it does not interfere with the production or use of the composition. In addition, the number average fiber width of the CNF is preferably 3 nm or more. The present invention can be carried out with a width smaller than this, but making it less than 3 nm requires a lot 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 100 nm or less. If it exceeds 100 nm, fibers with a large fiber width are mixed in, so a uniform film is not formed and sound insulation may be reduced.

[0023] In this invention, the film in the porous sheet is formed by adding CNF to the raw material slurry of the sheet when making the porous sheet, by applying a slurry containing CNF to the porous sheet by means of a bar coater, gravure coater, reverse roll coater, kiss coater, roll knife coater, die coater, spray, or the like, or by immersing and impregnating the porous sheet in a slurry containing CNF, so as to block all or part of the voids formed between the fibers or in the bubbles inside the porous sheet. Not only does the void become smaller as in the past, but the voids are blocked by the film, which greatly improves sound insulation.

[0024] In papermaking, the amount of CNF added to the raw material slurry of the porous sheet is preferably 0.5% by mass or more and 10% by mass or less. If it is less than 0.5% by mass, sufficient sound insulation and reinforcing effects cannot be obtained, and if it exceeds 10% by mass, the viscosity of the raw material slurry increases, the drainage during papermaking deteriorates, and productivity decreases. In addition, if more than necessary is added, the sound insulation and reinforcing effects may reach a plateau.

[0025] On the other hand, as the slurry containing CNF used for coating or impregnation, a general slurry dispersed in water can be used. The solid content of CNF in the slurry (hereinafter referred to as "CNF concentration") is preferably 0.05 mass% or more and 2 mass% or less. If it is less than 0.05 mass%, the CNF is too thin and the film formed cannot sufficiently close the voids, which may reduce the sound insulation effect, and a large amount of energy is required for drying. If it exceeds 2 mass%, the viscosity of the slurry increases, the dispersibility of CNF decreases, making it difficult to form a uniform film in the porous sheet, and coating or impregnation may become difficult.

[0026] When a porous sheet is manufactured by papermaking, the raw material slurry may contain a binder that facilitates membrane formation, and when the porous sheet is manufactured by coating or impregnation, the CNF slurry may contain a binder that facilitates membrane formation. Depending on the shape and size of the voids formed in the porous sheet, a sufficient membrane may not be formed with a slurry of CNF alone, but the presence of a binder makes it easier to form a membrane. Examples of binders include emulsions of acrylic resins, urethane resins, olefin resins, ester resins, etc.

[0027] When the slurry contains a binder, the binder content is preferably a binder:CNF mass ratio of about 1:5 to 5:1. If the binder content is too small, the film formation assisting effect of adding it cannot be obtained, and if the binder content is too large, blocking will mainly be caused by the binder film rather than the CNF, and there is a risk that a sufficient sound insulation effect will not be obtained.

[0028] The raw material slurry used for papermaking may contain additives such as paper strength agents and coagulants. For example, polyacrylamide-based and polymethyl methacrylate-based paper strength agents can be used, and aluminum sulfate (aluminum sulfate), quaternary ammonium salts, polyamines, and diallyl dimethyl ammonium chloride can be used as coagulants. Coagulants have the effect of uniformly distributing CNF in the sheet and improving the texture of the porous sheet. Meanwhile, the CNF slurry used for coating or impregnation may contain other additives such as antifoaming agents.

[0029] In the manufacture of the sound-insulating and sound-absorbing material according to the present invention, after adding CNF to the raw material slurry of the porous sheet or coating or impregnating the CNF slurry, normal drying methods such as natural drying or heated air drying can be used to remove moisture from the porous sheet. When drying by air drying, the temperature is preferably 60°C or higher and 150°C or lower. If the temperature is too low, the drying takes too long. On the other hand, if the temperature is too high, the porous sheet may be deformed or the film formed may become unstable. Furthermore, when the foam is coated or impregnated, the porosity may be lost. Note that if moisture is removed by freeze-drying, a film is not formed and a network structure of CNF with fine voids remains, so moisture removal by freeze-drying must be avoided. EXAMPLES

[0030] An embodiment of the present invention will be described below. First, the materials used will be described. Using these materials, sound insulation and absorption materials according to the present invention were manufactured by three different methods.

[0031] <Porous sheet material> Inorganic material: Rock wool (JFE Rock Fiber Corp.: Rockceram granular cotton) Organic material: Polyester fiber (Teijin Frontier Co., Ltd.: Tepyrus, fiber diameter: 0.3 dtex, fiber length: 3 mm) <Porous sheet> Glass wool sheet (Koizumi Wireless Co., Ltd.: AS Fabric Glass Wool GW5090) Polyester non-woven sound absorbing material (3M: Thinsulate ThinPL) -Polyurethane foam sheet (INOAC Corporation: Calmflex F2-10)

[0032] <cnf> (Sample 1: Preparation of regenerated CNF) RCNF was prepared as the regenerated CNF according to Example 1 of Patent No. 7195126. That is, after the NBKP of the kraft pulp was treated with alkali, it was subjected to a xanthation treatment with carbon disulfide, and then defibrated using a high-pressure homogenizer to prepare xanthated CNF, which was then regenerated to obtain a regenerated CNF slurry. The degree of substitution of the xanthate group (xanthate substitution degree) contained in the regenerated CNF was less than 0.001, which is the lower limit of measurement. Hereinafter, when simply referring to RCNF, this regenerated CNF is referred to. The RCNF slurry with a CNF concentration of 1.0 mass% obtained above was redispersed using a high-pressure homogenizer.

[0033] [Xanthate Substitution Degree Measurement] The degree of xanthate substitution of RCNF was measured by the Bredee method. The degree of xanthate substitution is a value relative to the degree of introduction of xanthate groups per glucose unit of cellulose. The procedure of the Bredee method was as follows. 40 g of the RCNF slurry was weighed, 50 mL of 0.5 M sodium hydroxide aqueous solution (5 ° C.) was added and stirred. After leaving it for 15 minutes, it was neutralized with 1.5 M acetic acid aqueous solution. 100 mL of distilled water was added thereto and stirred well, and 10 mL of 1.5 M acetic acid aqueous solution and 10 mL of 0.05 mol / L iodine aqueous solution were added. This solution was titrated with 0.05 mol / L sodium thiosulfate aqueous solution, and the degree of xanthate substitution was calculated from the following formula (1) from the titration amount of the sodium thiosulfate aqueous solution and the cellulose content in the sample.

[0034] Xanthate substitution degree = (0.05 x 10 x 2 - 0.05 x sodium thiosulfate titration (m L))÷1000÷(Cellulose content in sample (g) / 162.1)……(1)

[0035] [Measurement of CNF fiber width] A dye solution was added to a slurry of RCNF diluted with distilled water to a CNF concentration of 0.01% by mass, and the slurry was dried on a support film to prepare a dried specimen. The specimen was observed using a field emission scanning electron microscope (FE-SEM, Hitachi High-Tech Corporation, S-4800) at an accelerating voltage of 25 kV. 50 nanofibers were randomly selected from the 130,000x image and measured. The fiber width was in the range of 3.9 nm to 9.7 nm, and the number average fiber width was 6.4 nm.

[0036] (Sample 2: Mechanically defibrated CNF) The CNF obtained by mechanical fiberization was BiNFi-s (product number: WFo-10005) manufactured by Sugino Machine Ltd. When measured in the same manner as Sample 1, the fiber width was in the range of 24.1 to 53.2 nm, and the number average fiber width was 31.2 nm.

[0037] (Sample 3: TEMPO oxidized CNF) TEMPO-oxidized CNF was prepared as chemically modified CNF according to the reference example of Japanese Patent No. 6668558, and a slurry of TEMPO-oxidized CNF with an average oxidation degree of 2 mmol / g was obtained. This CNF was defibrated as chemically modified cellulose substituted with carboxyl groups. The obtained TEMPO-oxidized CNF was measured in the same manner as Sample 1, and the fiber width was in the range of 3.7 to 7.9 nm, and the number average fiber width was 6.3 nm.

[0038] <Fine cellulose> Microfibrous cellulose (Cerish, manufactured by Daicel Miraizu Co., Ltd., product number: KY100S. In this text, this will be referred to as "Cerish") For the cellish, the wet product was first diluted with distilled water to a solid content concentration of 0.03% by mass, redispersed in a homogenizer, and then the solvent was replaced with tert-butyl alcohol and freeze-dried. The dried specimen was observed with the above-mentioned FE-SEM, and 50 fine cellulose fibers were randomly selected from the 20,000x image and measured. The fiber width was in the range of 48 nm to 570 nm, and the number average fiber width was 198 nm. <Binder> Acrylic emulsion (DIC Corporation: AN-678A-E) Olefin-based emulsion (Sumitomo Seika Chemicals Co., Ltd.: Zaixen A) Ester emulsion (Toyobo MC Co., Ltd.: Vylonal MD-2000) <Additives> Aluminum sulfate (manufactured by Rengo Co., Ltd.: 8% by weight aluminum sulfate aqueous solution)

[0039] <Production of porous sheets by papermaking of rock wool> (Examples 1 and 2) (a) Rock wool as a material for a porous sheet of inorganic material was added to water and dispersed with a disintegrator (manufactured by Nippon TMC Co., Ltd.: D-438) to prepare a 1.88 mass % inorganic material dispersion slurry. (b) On the other hand, an acrylic emulsion binder was added to a slurry of RCNF (CNF) while stirring with a Three-One Motor (manufactured by Shinto Scientific Co., Ltd.) to obtain a binder mixture with a CNF concentration of 0.5 mass% and a solids ratio of binder:CNF = 5:3 (Example 1) and 5:6 (Example 2) converted into mass. (c) The binder mixture was added to the inorganic material dispersion slurry while stirring with a three-one motor. The solid content ratio was rock wool:binder:CNF = 97:5:3 (Example 1) or 94:5:6 (Example 2) by mass, and aluminum sulfate was added and mixed until the pH of the inorganic material dispersion slurry reached 5.0. (d) The mixture obtained in (c) is then made into paper, the wet paper is dehydrated, dried for 2 hours at 120°C in a blower dryer (Yamato Scientific Co., Ltd.: DKN602), and further dried for 280 seconds at 120°C in a drum dryer (Japo Co., Ltd.: L-3D) to obtain a basis weight of 600 g / m 2 As a result, a sound-proofing and sound-absorbing material was obtained.

[0040] Comparative Example 1 A porous sheet (rock wool sheet 1) was obtained in the same manner as in Example 1, except that in (b) no CNF was added, and in (c) only a binder was added instead of the binder mixture.

[0041] <Production of porous sheets with different basis weights by rock wool papermaking> (Examples 3 and 4) In Example 1, the basis weight is 900 g / m 2 (Example 3), 1,500 g / m 2 A sound-insulating and sound-absorbing material was obtained in the same manner as in Example 4.

[0042] (Comparative Examples 2 and 3) In Comparative Example 1, the basis weight was 900 g / m 2 (Comparative example 2), 1,500g / m 2 A porous sheet was obtained in the same manner as in Comparative Example 3, except that the comparative example was used.

[0043] <Production of porous sheets with different binders by rock wool papermaking> (Examples 5 and 6) Sound insulation and absorption materials were obtained in the same manner as in Example 1, except that the binder was an olefin-based emulsion (Example 5) or an ester-based emulsion (Example 6).

[0044] <Production of porous sheets with different types of CNFs by papermaking of rock wool> (Examples 7 and 8) Sound-insulating and sound-absorbing materials were obtained in the same manner as in Example 1, except that mechanically defibrated CNF (sample 2 used: Example 7) and TEMPO-oxidized CNF (sample 3 used: Example 8) were used instead of RCNF.

[0045] Comparative Example 4 A porous sheet was obtained in the same manner as in Example 1, except that selish (fine cellulose) was used instead of CNF.

[0046] <Production of porous sheets by papermaking of polyester fibers> Example 9 (a) Polyester fibers, which are a material for an organic porous sheet, were added to water and dispersed in the disintegrator to prepare a 1.88% by mass organic material dispersion slurry. (b) To this organic material dispersion slurry, RCNF slurry diluted with distilled water to a CNF concentration of 0.5% by mass was added while stirring with the three-one motor, so that the solids ratio by mass was polyester fiber:CNF = 97:3, and aluminum sulfate was added and mixed until the pH of the organic material dispersion slurry reached 5.0. (c) The mixture obtained in (b) is then made into paper, the wet paper is dehydrated, dried in the blower dryer at 120°C for 2 hours, and further dried in the drum dryer at 120°C for 280 seconds to obtain a basis weight of 900 g / m 2 As a result, a sound-proofing and sound-absorbing material was obtained.

[0047] Comparative Example 5 A porous sheet was obtained in the same manner as in Example 9, except that no CNF was added in (b).

[0048] <Production by spraying onto rock wool sheet> Example 10 (a) The RCNF slurry was diluted with distilled water to obtain a CNF slurry with a CNF concentration of 0.5 mass%. (b) As the porous sheet, the rock wool sheet 1 of the above-mentioned Comparative Example 1 was used. This was dried in an air dryer at 110° C. for 2 hours, and the bone dry mass was measured. (c) The CNF slurry of (a) was applied to the rock wool sheet 1 by spraying it with a spray container. After that, it was dried at 120°C for 15 minutes with a blower dryer to obtain a sound insulation and sound absorbing material with a film formed. At this time, the amount of CNF added was calculated from the mass difference before and after drying.

[0049] Example 11 Instead of (a) in Example 10, the binder was added to the CNF slurry while stirring with a Homo Disper (Labo-lution, manufactured by Primix Corporation) so that the CNF concentration was 0.5% by mass and the solid content ratio was binder:CNF=5:3 by mass. After the addition was completed, the mixture was further stirred at 500 rpm for 3 minutes to obtain a binder-mixed CNF slurry that was sufficiently dispersed. This binder-mixed CNF slurry was used instead of the CNF slurry in Example 10 (c) to obtain a sound-insulating and sound-absorbing material.

[0050] Example 12 <Manufacturing by applying bar coater coating to rock wool sheet> In (c) of Example 10, the CNF slurry was applied using a bar coater (Bar Coater No. 40, manufactured by Daiichi Rika Co., Ltd.) instead of a spray, and the drying time using a blower dryer was set to 5 minutes. Except for this, sound-insulating and sound-absorbing materials were obtained by the same procedure as in Example 10.

[0051] Comparative Example 6 In Comparative Example 1, the concentration of the inorganic material dispersion slurry was 3.75 mass% in (a), and the basis weight was 1800 g / m 2 A porous sheet (rock wool sheet 2) was obtained by the same procedure except for the above.

[0052] <Production by spraying onto rock wool sheets of different thicknesses> (Example 13) A sound insulating and absorbing material was obtained in the same manner as in Example 10, except that rock wool sheet 2 was used as the porous sheet (b).

[0053] <Production by spraying onto glass wool sheet> Example 14 A sound insulating and absorbing material was obtained in the same manner as in Example 10, except that a glass wool sheet was used instead of the rock wool sheet 1 in (b).

[0054] Comparative Example 7 A blank glass wool sheet with no coating was used.

[0055] <Production by spraying and coating onto nonwoven sound absorbing material> Example 15 A sound-insulating and sound-absorbing material was obtained in the same manner as in Example 10, except that (b) a polyester nonwoven sound-absorbing material was used instead of the rock wool sheet 1, and (c) the drying in the air dryer was performed for 20 minutes.

[0056] (Example 16) A sound insulating and absorbing material was obtained in the same manner as in Example 11, except that a polyester nonwoven sound absorbing material was used instead of the rock wool sheet 1, and the drying in the air dryer (c) was performed for 20 minutes.

[0057] Comparative Example 8 A blank polyester nonwoven sound-absorbing material with no coating was used.

[0058] <Production by spraying onto a polyurethane foam sheet> (Example 17) A sound-insulating and sound-absorbing material was obtained in the same manner as in Example 10, except that a foamed polyurethane sheet was used instead of the rock wool sheet 1 (b) and drying in a blower dryer (c) was performed at 60°C for 16 hours.

[0059] Comparative Example 9 A blank polyurethane foam sheet with no coating was used.

[0060] <Manufactured by spraying, coating and then freeze-drying> Comparative Example 10 In (c) of Example 10, sound-insulating and sound-absorbing materials were obtained by the same procedure as in Example 10, except that in place of blowing air to dry the porous sheet coated with the CNF slurry, it was frozen at -25°C for 16 hours and then freeze-dried for 64 hours using a freeze dryer (FD-1, manufactured by Tokyo Rikakikai Co., Ltd.).

[0061] <Production by immersion, impregnation and then freeze-drying> Comparative Example 11 (a) RCNF was dispersed in water to contain 0.1% by mass of CNF to obtain a CNF slurry. (b) Rock wool sheet 1 was used as the porous sheet. This was dried in a blower dryer at 110° C. for 2 hours, and the bone dry mass was measured. (c) The rock wool sheet 1 (b) was immersed in the CNF slurry (a) and left to stand at room temperature for 16 hours (immersion), and the CNF slurry was impregnated into the rock wool sheet 1. The sheet was then taken out and the slurry attached to the surface of the sheet was wiped off with filter paper to remove it. Then, the sheet was freeze-dried in the same manner as in Comparative Example 10 to obtain a sound-insulating and sound-absorbing material. At this time, the amount of CNF added was calculated from the mass difference before and after drying.

[0062] <Sound absorption and sound insulation evaluation> A test piece with a diameter of 41.5 mm was cut out from each sheet sample, and the normal incidence sound absorption coefficient was used as an evaluation index for sound absorption, and the normal incidence sound transmission loss was used as an evaluation index for sound insulation. The normal incidence sound absorption coefficient was measured in accordance with JIS A 1405-2, and the normal incidence sound transmission loss was measured in accordance with ASTM E2611 using a WinZac made by Nihon Onkyo Engineering Co., Ltd. The samples in Examples 10 to 17 and Comparative Example 10, in which CNF was sprayed or coated by a bar coater, were placed so that the coated surface faced the sound source and measured. The normal incidence sound absorption coefficient and normal incidence sound transmission loss were each averaged at 1 / 3 octave intervals.

[0063] The normal incidence sound absorption coefficient 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 of the normal incidence sound absorption coefficient was calculated for samples (Comparative Examples 1-3, 5-9) that were made of the same material and manufactured by the same method, and to which Celish and CNF were not added. Samples for which the average increase rate of the normal incidence sound absorption coefficient for the corresponding comparative example was greater than 0% were determined to maintain the sound absorption properties of the original base material.

[0064] As for the normal incidence sound transmission loss, unlike the normal incidence sound absorption coefficient, almost no difference was observed in the high frequency range, so the average values ​​for each 1 / 3 octave in the low to mid frequency range from 250 Hz to 1000 Hz were averaged, and the average increase rate was calculated in the same way as for the sound absorption coefficient. Those that had an average increase rate of normal incidence sound transmission loss of more than 40% compared to the base material (Comparative Examples 1 to 3, 5 to 9) that was made of the same material and manufactured by the same method, and to which Celish and CNF were not added, were judged to have sound insulation properties in the low to mid frequency range.

[0065] <Sheet density measurement> The width, length, and thickness of the obtained sound-proofing and sound-absorbing material were measured, and the density (g / cm 3 ) was calculated.

[0066] <Tensile strength measurement> A rectangular test piece 20 mm wide was cut out from the obtained sound-insulating and sound-absorbing material, and a tensile test was performed using a tensile testing machine (Kumagaya Riki Kogyo Co., Ltd.: Tensilon universal material testing machine RTE-1210) with a gripping width of 20 mm and a tensile speed of 100 mm / min. The average stress at break (n=3) was taken as the tensile strength of the test piece.

[0067] <Results: Addition during rock wool sheet papermaking> The results of the sound insulation and absorbing material obtained by papermaking are shown in Table 1. The rock wool sheets (Examples 1 and 2) made by adding RCNF as CNF showed a significant improvement in sound insulation in the low-mid range (250 to 1000 Hz) compared to those without RCNF (Comparative Example 1: Rock Wool Sheet 1). In addition, when the basis weight of the sheet was increased (Examples 3 and 4), the average sound absorption coefficient and transmission loss increased compared to those without CNF (Comparative Examples 2 and 3), but the sound insulation was improved by adding CNF. On the other hand, when the type of binder was changed (Examples 5 and 6), although there was a difference in tensile strength, the improvement in sound insulation was the same. Furthermore, even when mechanically defibrated CNF (Example 7) or TEMPO oxidized CNF (Example 8) was used as CNF, it was possible to provide further sound insulation in the low-mid range while maintaining the same strength, compared to the sound insulation and absorbing material with added Celish as a conventional reinforcing agent (Comparative Example 4), by replacing Celish with CNF. Since the sound insulation improvement effect is low for Cerish with an average fiber width of 198 nm, this effect is considered to be specific to nanofibers that have been defibrated to an average fiber width of about 3 nm to 100 nm. In addition, when comparing Example 1 and Example 2, it was confirmed that sound insulation improves by increasing the CNF addition rate.

[0068] [Table 1]

[0069] <Results: Addition during polyester fiber papermaking> The results for the sound-insulating and sound-absorbing material obtained by papermaking polyester fiber as an organic material are shown in Table 2. The polyester fiber sheet (Example 9) made by adding RCNF and papermaking without adding a binder showed improved sound insulation in the low and mid-range, similar to rock wool, compared to the sheet without adding CNF (Comparative Example 5), confirming the effect of improving sound insulation by CNF even without a binder.

[0070] [Table 2]

[0071] <Results: Spraying onto rock wool sheet and coating with a bar coater> Table 3 shows the results of adding CNF to a rock wool sheet by spraying or coating with a bar coater. Sound insulation improved with either method (Examples 10, 11, and 12). Sound insulation improved whether the coating liquid used in production was a CNF slurry without a binder (Examples 10 and 12) or a binder-mixed CNF slurry with a binder (Example 11). This confirmed that a film that improves sound insulation can be formed by CNF, regardless of the presence or absence of a binder. It was also confirmed that sound insulation improved when the thickness of the substrate was changed from Example 10 (Example 13).

[0072] [Table 3]

[0073] <Results: Spray coating on other substrates> Tables 4 and 5 show the results of adding CNF to substrates other than rock wool sheets by spray coating. Sound insulation was improved when a glass wool sheet, another inorganic material, was used as the substrate (Example 14), and when a polyester nonwoven sound absorbing material (Examples 15 and 16) or a foamed polyurethane sheet (Example 17), both of which are organic materials, were used. In addition, sound insulation was improved when the coating liquid used in the production was a CNF slurry without a binder (Example 15) or a binder-mixed CNF slurry with a binder (Example 16). Therefore, it was confirmed that sound insulation can be improved regardless of whether the material is inorganic or organic, and regardless of the presence or absence of a binder.

[0074] [Table 4]

[0075] [Table 5]

[0076] <Confirmation of film formation> The surfaces of the sheets of Example 1 (addition at the time of papermaking: RCNF), Example 7 (addition at the time of papermaking: BiNFi-s), Example 8 (addition at the time of papermaking: TEMPO-oxidized CNF), Example 10 (coating by spraying), and Example 12 (coating with a bar coater) were observed by SEM. Photographs of each are shown in Figures 1 to 5. In all cases, a membrane was formed to block the voids in the rock wool. This membrane is thought to be formed by CNF. Since the membrane contains CNF with a narrow fiber width, it has fine irregularities, so the surface area that comes into contact with sound, i.e., air vibrations, is large. Therefore, it is highly efficient in converting air vibrations into membrane vibrations, which again vibrates the air, scattering the sound in random directions and preventing sound transmission. In addition, since there was no change in the density of the sheet with or without incorporation or before and after coating, it is thought that the CNF membrane did not impair the porosity of the substrate itself and maintained its original sound absorption properties.

[0077] As a method corresponding to conventional sound-absorbing materials, sound-insulating and absorbing materials (Comparative Examples 10 and 11) were obtained by coating by spraying or impregnating by immersion and then drying by freeze-drying. The results of evaluating the sound absorption and sound insulation properties of these materials are shown in Table 5, but no improvement in sound insulation was observed in any of them. In addition, the results of observing the surface of Comparative Example 10 with an SEM are shown in Figure 6. It was confirmed that a CNF film was not formed, and a nonwoven form was formed, that is, a CNF network was formed between the fibers, and the voids were not blocked but were merely fragmented and remained. Therefore, it is considered that the sound insulation was improved by blocking the voids between the fibers in the porous sheet with a film containing CNF.< / cnf>

Claims

1. A sound-insulating and sound-absorbing material having a membrane containing cellulose nanofibers in the voids in a porous sheet.

2. 2. The sound insulating and absorbing material according to claim 1, wherein the porous sheet is made of an inorganic material or an organic material.

3. A method for producing a sound-insulating and sound-absorbing material, comprising papermaking a raw material slurry containing cellulose nanofibers into a porous sheet, and forming a membrane containing cellulose nanofibers between the fibers inside the sheet.

4. A method for producing a sound-insulating and sound-absorbing material, comprising coating or impregnating a porous sheet with a slurry of cellulose nanofibers to form a membrane containing cellulose nanofibers in the voids inside the sheet.

5. The method for producing a sound insulating and absorbing material according to claim 3 or 4, wherein the slurry contains a binder.

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