Structure and method for producing structure

Abstract

The present invention addresses the problem of providing: a structure that is lightweight and exhibits excellent soundproofing properties and sound absorbing properties; and a method for manufacturing a structure. This structure includes: a porous body having voids formed of continuous holes; and a thin film formed in at least some of the voids. At least a section of the thin film has optical interference fringe.

Description

Structure and method for manufacturing the structure

[0001] The present invention relates to a structure and a method for manufacturing a structure.

[0002] Vehicles (for example, automobiles, trains, etc.) and building materials are required to be both lightweight and quiet, and to ensure quietness, sound-insulating materials and sound-absorbing materials are used that are attached to the walls, floors, and ceilings of vehicles, buildings, etc. to insulate and absorb noise from outside the vehicle and outdoors, etc. In particular, sound-insulating materials and sound-absorbing materials used in automobiles and building materials are required to provide quietness over a wide frequency range from low to high frequencies (100 to 10,000 Hz region).

[0003] A known example of such a sound-absorbing material is a nonwoven fabric made solely of organic fibers, such as Thinsulate (manufactured by 3M Co.). Patent Document 1 describes a "sound-absorbing material having a nonwoven fabric form, including microfibers having a fiber diameter on the order of microns and nanofibers having a fiber diameter on the order of nanons, wherein the nanofibers have a void ratio of 92 to 99.9%" (Claim 1).

[0004] Japanese Patent Application Laid-Open No. 2017-181925

[0005] The present inventors have studied Thinsulate and the sound-absorbing material of Patent Document 1 and have found that there is room for improvement in sound absorption. Furthermore, from the perspective of achieving even greater noise reduction, the present inventors have also studied improvements in sound insulation as well as sound absorption, and have found that Thinsulate and the sound-absorbing material of Patent Document 1 are inferior in sound insulation. With the recent trend toward electric vehicles and taller buildings, the requirements for lightweight vehicles and building materials are becoming increasingly high. Under these circumstances, lightweight materials with excellent sound insulation are needed, but the development of such materials requires overcoming the mass law of transmission loss.

[0006] Therefore, an object of the present invention is to provide a lightweight structure that exhibits excellent sound insulation and sound absorption properties, and a method for manufacturing the structure.

[0007] As a result of intensive research into the above-mentioned problems, the present inventors have found that a structure in which a specific thin film is provided in at least some of the pores of a porous body is lightweight and exhibits excellent sound insulation and sound absorption properties, and have completed the present invention. That is, the present inventors have found that the above-mentioned problems can be solved by the following configuration.

[0008] [1] A structure having a porous body having voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein at least a part of the thin film portion exhibits optical interference fringes. [2] The structure according to [1], further having a member different from the porous body, wherein the thin film portion is formed of at least a part of the different member. [3] The structure according to [1], ３ The content of different materials per －３ g / cm ３ [4] A structure according to [2], which comprises a porous body having voids formed of continuous pores and cellulose nanofibers, and which has thin film portions formed of at least a portion of the cellulose nanofibers in at least some of the voids, wherein when a cross section in an in-plane direction dividing the thickness direction of the structure into three equal parts is observed with an optical microscope, at least one of the following conditions 1 and 2 is satisfied in each of five visual fields of 1000 μm vertically and 1400 μm horizontally in each cross section, where the ratios of the following conditions 1 and 2 are respectively values ​​calculated for each visual field in each cross section and averaged over the total number of visual fields. Condition 1: The area of ​​the thin film portions is 25000 μm relative to the total area of ​​the thin film portions. ２ Condition 2: The ratio of the total area of ​​the specific thin film portions that is equal to or less than 25,000 μm to the total number of thin film portions is 10% or more, and the total number of thin film portions is 5 or more. ２ The ratio of the number of specific thin film portions that are equal to or less than the above is 20% or more, and the total number of thin film portions is 5 or more. [5] Structure 1 cm ３ The cellulose nanofiber content per －３ g / cm ３The structure according to [4], wherein the thin film portion is uniformly distributed in the thickness direction of the structure. [6] The structure according to [4] or [5], wherein the thin film portion is uniformly distributed in the thickness direction of the structure. [7] The structure according to any one of [4] to [6], wherein the average film thickness of the thin film portion is 3 μm or less. Here, the average film thickness refers to the average value calculated by measuring the film thicknesses of 20 or more thin film portions in an image obtained by measuring the cross section of the structure with a scanning electron microscope. [8] The structure according to any one of [4] to [7], wherein the thin film portion has a substantial film thickness of 0.05 to 5 μm. Here, the substantial film thickness refers to the film thickness range that includes 80% or more of the measured values ​​measured by measuring the film thicknesses of 20 or more thin film portions in an image obtained by measuring the cross section of the structure with a scanning electron microscope. [9] The structure according to any one of [4] to [8], wherein the thin film portion is free of defects.

[10] The structure according to any one of [4] to [9], wherein at least a portion of the thin film portion exhibits optical interference fringes.

[11] A porous body having voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, the porosity being 80 to 99.99% and the specific surface area being 0.2 m ２ / g or more.

[12] A structure having a porous body having voids formed by continuous pores and thin film portions formed in at least some of the voids, wherein the surface area of ​​the structure is 1.5 times or more the surface area of ​​the porous body.

[13] A structure having a porous body having voids formed by continuous pores and thin film portions formed in at least some of the voids, wherein the thin film portions are uniformly present in the thickness direction of the structure.

[14] A structure having a porous body having voids formed by continuous pores and thin film portions formed in at least some of the voids, wherein the indentation modulus of the thin film portions is 3 GPa or more.

[15] A structure having a porous body having voids formed by continuous pores and thin film portions formed in at least some of the voids, wherein the average film thickness of the thin film portions is 3 μm or less. Here, the average film thickness refers to the average value calculated from the measured film thicknesses of 20 or more thin film portions measured from an image of a cross section of the structure measured by a scanning electron microscope.

[16] A structure comprising a porous body having voids formed by continuous pores and a thin film portion formed in at least a portion of the voids, wherein the thin film portion has a substantial thickness of 0.05 to 5 μm. Here, the substantial thickness refers to the thickness range within which 80% or more of the measured values ​​fall when the thicknesses of 20 or more thin film portions are measured from an image of a cross section of the structure measured by a scanning electron microscope are included.

[17] A structure comprising a porous body having voids formed by continuous pores and a thin film portion formed in at least a portion of the voids, wherein the thin film portion exhibits crystallinity.

[18] A structure comprising a porous body having voids formed by continuous pores and a thin film portion formed in at least a portion of the voids, wherein the thin film portion exhibits orientation anisotropy.

[19] A structure comprising a porous body having voids formed by continuous pores and a thin film portion formed in at least a portion of the voids, wherein the arithmetic mean roughness Ra of the surface of the thin film portion is 1 nm or more.

[20] A structure comprising a porous body having voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein the thin film portion has no defects.

[21] The structure according to any one of

[11] to

[20] , wherein the thin film portion contains cellulose nanofibers.

[22] The structure according to any one of

[11] ,

[12] and

[14] to

[21] , wherein the thin film portion is uniformly present in the thickness direction of the structure.

[23] The structure according to any one of

[11] to

[22] , wherein, when an in-plane cross section of the structure, which divides the thickness direction into three equal parts, is observed with an optical microscope, at least one of the following conditions 1 and 2 is satisfied in each of five visual fields of 1000 μm vertically and 1400 μm horizontally in each cross section. However, the ratios of the following conditions 1 and 2 are values ​​obtained by averaging the ratios calculated for each visual field in each cross section over the total number of visual fields. Condition 1: The area of ​​the thin film portions relative to the total area of ​​the thin film portions is 25000 μm. ２ Condition 2: The ratio of the total area of ​​the specific thin film portions that is equal to or less than 25,000 μm to the total number of thin film portions is 10% or more, and the total number of thin film portions is 5 or more. ２

[24] The structure according to any one of [1] to

[23] , wherein the porous body contains fibers.

[25] The structure according to

[24] , wherein the fibers are at least one type of fiber selected from the group consisting of polyester, glass fiber, and cellulose.

[26] The density of the porous body is 10 kg / m or more. ３

[27] The structure according to any one of [1] to

[26] , which is in the form of a film or a board.

[28] An areal density of 0.1 kg / m ２ The structure according to any one of [1] to

[27] , wherein the sound absorption coefficient at 2000 Hz is 0.3 or more.

[29] The structure according to

[28] , wherein the transmission loss at 2000 Hz is 3 dB or more.

[30] The structure according to

[28] , wherein the sound absorption coefficient at 2000 Hz is 0.3 or more.

[31] The structure according to any one of [1] to

[30] , wherein the structure is used as a sound insulating material or a sound absorbing material.

[32] A method for producing the structure according to any one of [1] to

[31] , comprising a liquid filling step of supplying a cellulose nanofiber solution to a porous body having voids consisting of continuous pores, and filling at least a portion of the voids of the porous body with the cellulose nanofiber solution.

[33] A method for producing the structure according to

[32] , wherein the liquid filling step is a step of filling 90% or more of the voids of the porous body with the cellulose nanofiber solution.

[0009] As will be described below, the present invention can provide a lightweight structure that exhibits excellent sound insulation and sound absorption properties, as well as a method for manufacturing the structure.

[0010] FIG. 1 is a schematic cross-sectional view illustrating an example of an embodiment of the structure of the present invention.

[0011] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] The following describes the meaning of each description in this specification. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. Furthermore, in this specification, in a numerical range described in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. Furthermore, in this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. Here, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified.

[0013] [Structure] The structure according to the first aspect of the present invention comprises a porous body having voids formed by continuous pores and a thin film portion formed in at least a portion of the voids, and at least a portion of the thin film portion exhibits optical interference fringes. The presence or absence of the thin film portion in the structures according to the first aspect of the present invention and the second to twelfth aspects described below can be confirmed by observing the structure using an optical microscope. The optical interference fringes exhibited by at least a portion of the thin film portion refer to optical interference fringes that can be confirmed by observing a reflected image using an optical microscope. Specifically, the presence or absence of optical interference fringes can be confirmed by observing a reflected image using an optical microscope equipped with a light source that can confirm interference fringes that change color continuously from blue to green to red or a portion of the color tone at a magnification that allows the thin film portion formed in at least a portion of the voids in the porous body to be observed. For example, the presence or absence of optical interference fringes can be confirmed by observing with a 10x objective lens in optical microscope image observation mode using a Keyence VKX-200 laser microscope. It is necessary to select a magnification at which the thin film portion is present in 20% or more of the observation field area. Whether or not a structure corresponds to the first aspect of the present invention can be determined by observing 30 thin film portions formed in at least a portion of the voids in any field of view on the surface or cross section of the structure, and if interference fringes in which the color tone changes continuously from blue to green to red or a portion thereof are confirmed in 50% or more (i.e., 15 portions), the thin film portions are considered to exhibit optical interference fringes.

[0014] A structure according to a second aspect of the present invention comprises a porous body having voids formed by continuous pores and cellulose nanofibers, with thin film portions formed of at least a portion of the cellulose nanofibers in at least some of the voids. Furthermore, the structure according to the second aspect of the present invention is a structure that, when an in-plane cross section dividing the thickness direction into three equal parts is observed with an optical microscope, satisfies at least one of the following conditions 1 and 2 in each of five fields of view, each measuring 1000 μm in length and 1400 μm in width, in each cross section. The ratios of the following conditions 1 and 2 are respectively values ​​obtained by averaging the ratios calculated for each field of view in each cross section over the total number of fields (i.e., 4 cross sections × 5 field numbers = 20 total field numbers). Condition 1: The area of ​​the thin film portions is 25000 μm relative to the total area of ​​the thin film portions. ２ Condition 2: The ratio of the total area of ​​the specific thin film portions that is equal to or less than 25,000 μm to the total number of thin film portions is 10% or more, and the total number of thin film portions is 5 or more. ２ The ratio of the number of specific thin film portions that is equal to or less than 20% is 20% or more, and the total number of thin film portions is 5 or more. Here, the in-plane cross section that divides the thickness direction into three equal parts refers to the four surfaces exposed by cutting or the like. Furthermore, the "total area of ​​thin film portions" refers to the sum of the geometric areas of the thin film portions included in each of the above-mentioned fields of view (i.e., planar images). Furthermore, the ratio of the total area of ​​the specific thin film portions under condition 1 refers to the average value of the respective values ​​obtained in each field of view. Similarly, the ratio of the number of specific thin film portions under condition 2 refers to the average value of the respective values ​​obtained in each field of view.

[0015] The structure according to the third aspect of the present invention has a porous body having voids formed of continuous pores and a thin film portion formed in at least a part of the voids, and has a porosity of 80 to 99.99% and a specific surface area of ​​0.2 m ２ Here, the porosity refers to a value calculated from the density (mass / volume) and specific gravity, and specifically, when the density of the material forming the porous body is A (g / cm ３ ) and the specific gravity is B (g / cm ３ ), the porosity is calculated by (1-A / B) x 100 (%). The specific surface area is a value measured by a gas adsorption method.

[0016] A structure according to a fourth aspect of the present invention is a structure having a porous body having voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein the surface area of ​​the structure is 1.5 times or more the surface area of ​​the porous body. Here, the surface areas of the structure and the porous body can be measured by, for example, a gas adsorption method.

[0017] A structure according to a fifth aspect of the present invention comprises a porous body having voids formed of continuous pores and thin film portions formed in at least some of the voids, the thin film portions being uniformly present in the thickness direction of the structure. Here, the state of "uniformly present in the thickness direction of the structure" refers to a state in which, when an in-plane cross section of the structure dividing the thickness direction into three equal parts is observed with an optical microscope, three or more thin film portions are present in each of ten fields of view, each 1000 μm long and 1400 μm wide, in each cross section. A state in which five or more thin film portions are present is preferred, and a state in which seven or more thin film portions are present is more preferred.

[0018] A structure according to a sixth aspect of the present invention comprises a porous body having voids formed of continuous pores and a thin film portion formed in at least a part of the voids, the thin film portion having an indentation modulus of 3 GPa or more, where the indentation modulus of the thin film portion refers to the indentation modulus measured by an atomic force microscope (AFM).

[0019] A seventh aspect of the present invention provides a structure comprising a porous body having voids formed of continuous pores and thin film portions formed in at least some of the voids, the thin film portions having an average thickness of 3 μm or less. Here, the average thickness refers to an average value calculated from the measured values ​​of the thicknesses of 20 or more thin film portions in an image obtained by measuring the cross section of the structure with a scanning electron microscope (SEM).

[0020] A structure according to an eighth aspect of the present invention comprises a porous body having voids formed of continuous pores and thin film portions formed in at least some of the voids, the thin film portions having a substantial thickness of 0.05 to 5 μm. Here, the substantial thickness refers to the thickness range that includes 80% or more of the measured values ​​of 20 or more thin film portions measured from an image of a cross section of the structure measured with a scanning electron microscope.

[0021] A structure according to a ninth aspect of the present invention includes a porous body having voids formed of continuous pores and a thin film portion formed in at least a part of the voids, the thin film portion exhibiting crystallinity. Here, whether or not the thin film portion exhibits crystallinity is determined by the presence or absence of peak detection by X-ray diffraction (XRD), and a thin film portion in which a peak is detected is determined to exhibit crystallinity, while a thin film portion in which no peak is detected is determined to not exhibit crystallinity.

[0022] A tenth aspect of the present invention relates to a structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a portion of the voids, wherein the thin film portion exhibits orientation anisotropy. Here, the state of exhibiting orientation anisotropy refers to a state in which the optical performance or periodic structure has different characteristics in and out of the thin film plane, such as liquid crystallinity, anisotropy of the crystalline structure, or a state in which molecular crystals are arranged with a periodic structure in or out of the plane. Furthermore, whether or not orientation anisotropy is exhibited is determined by optical measurement, X-ray diffraction (XRD), scanning electron microscope (SEM), or atomic force microscope (AFM) to determine whether the physical periodic structure or the associated optical performance exhibits periodicity in a specific direction.

[0023] A structure according to an eleventh aspect of the present invention includes a porous body having voids formed of continuous pores and a thin film portion formed in at least a part of the voids, the thin film portion having a surface with an arithmetic mean roughness Ra of 1 nm or more, where Ra is the arithmetic mean roughness in accordance with JIS B0601:2001 and is calculated from an image taken with an atomic force microscope (AFM).

[0024] A structure according to a twelfth aspect of the present invention comprises a porous body having voids formed by continuous pores and thin film portions formed in at least some of the voids, the thin film portions being free of defects. Here, the term "free of defects in the thin film portions" refers to a state in which, when an in-plane cross section of the structure is observed with an optical microscope, dividing the thickness direction of the structure into three equal parts, 20 or more thin film portions are observed in a field of view of 1000 μm vertically and 1400 μm horizontally on each cross section, and no thin film portions with holes or chips are present, or if any are present, there are two or fewer.

[0025] As described above, the structures according to the first to twelfth aspects of the present invention (hereinafter, when no particular distinction is required, they will be simply referred to as "structures of the present invention") have a predetermined thin film portion in at least a portion of the voids of the porous body, and are therefore lightweight and exhibit excellent sound insulation and sound absorption properties. The reason why the above effects are exhibited is not necessarily clear in detail, but the inventors speculate as follows. That is, in the present invention, it is believed that the thin film portion formed in at least a portion of the voids of the porous body satisfies predetermined characteristics and physical properties, making resonance more likely to occur, and as a result, excellent sound insulation and sound absorption properties are exhibited.

[0026] FIG. 1 shows a schematic cross-sectional view illustrating one embodiment of a structure of the present invention. The structure 10 shown in FIG. 1 includes a porous body 3 having voids 1 formed of continuous pores and a thin film portion 4 formed in at least a portion of the voids. In FIG. 1, the reference numeral 2 represents fibers, and the porous body 3 is composed of an aggregate of fibers 2 and the voids 1. Although not shown in FIG. 1, at least a portion of the thin film portion 4 in the structure according to the first embodiment exhibits optical interference fringes, and the thin film portion in the structure according to the second embodiment is formed of cellulose nanofibers. In the structures according to the second to twelfth embodiments, at least a portion of the thin film portion 4 may exhibit optical interference fringes, as in the first embodiment. Furthermore, in the structures according to the first and third to twelfth embodiments, the thin film portion may be formed of cellulose nanofibers, as in the second embodiment.

[0027] The structure of the present invention will be described in detail below.

[0028] [Porous Body] The porous body of the structure of the present invention is a porous body having voids consisting of continuous pores. Such a porous body is not particularly limited, and examples thereof include a fibrous porous body containing fibers, a resin porous body containing resin (e.g., a membrane, a sponge, etc.), a metal porous body containing metal, a glass porous body containing glass, and a ceramic porous body containing ceramic.

[0029] Of these, a fibrous porous body containing fibers is preferred, and a fibrous porous body consisting of a fiber aggregate is more preferred, because this allows the structure to be made lighter and the thin film portion to be formed more easily.

[0030] Examples of the fibers include polyester, glass fiber, glass wool, rock wool, cellulose, polyurethane, aramid fiber, and polyvinyl chloride. These may be used alone or in combination of two or more. Among these, at least one fiber selected from the group consisting of polyester, glass fiber, and cellulose is preferred because it facilitates the formation of an appropriate thin film. Furthermore, glass wool, rock wool, aramid fiber, and polyvinyl chloride are preferred, with glass wool being more preferred, because it results in a structure with excellent flame retardancy.

[0031] In the present invention, the density of the porous body (1 m ３ Mass per unit mass) is 10 kg / m ３ It is preferable that the saturation is 100 kg / m or more. ３ The upper limit of the density is not particularly limited, but is preferably 1000 kg / m ３ It is preferable that:

[0032] In the present invention, the average pore diameter (i.e., the size of the voids) of the porous body is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 50 μm or more. There is no particular upper limit to the average pore diameter, but it is preferably 3000 μm or less, and more preferably 1000 μm or less.

[0033] In the present invention, it is preferable to control the hydrophilicity or hydrophobicity of the surface of the porous body from the viewpoint of controlling the formation of the thin film portion.

[0034] [Thin Film Portion] The thin film portion of the structure of the present invention is a film formed in at least a part of the pores of the porous body. In a first embodiment, the thin film portion is a film at least a part of which exhibits optical interference fringes, and in a second embodiment, the thin film portion is a film formed of cellulose nanofibers. In a third embodiment, the thin film portion is a structure having a porosity of 80 to 99.99% and a specific surface area of ​​0.2 m ２ / g or more, and in the fourth aspect, the surface area of ​​the structure is 1.5 times or more the surface area of ​​the porous body. In the fifth aspect, the thin film portion is a film that is uniformly distributed in the thickness direction of the structure, and in the sixth aspect, the thin film portion is a film having an indentation modulus of 3 GPa or more. In the seventh aspect, the thin film portion has an average film thickness of 3 μm or less, and in the eighth aspect, the actual film thickness is 0.05 to 5 μm. In the ninth aspect, the thin film portion is a film that exhibits crystallinity, and in the tenth aspect, the thin film portion is a film that exhibits orientation anisotropy. In the eleventh aspect, the thin film portion is a film having an arithmetic mean roughness Ra of 1 nm or more, and in the twelfth aspect, the thin film portion is a film without defects. The thin film portion of the structure of the present invention is not a liquid film. It is preferable that the thin film portion of the structure of the present invention does not have a porous structure, and it is more preferable that it is not a coating covering some substance (i.e., a single film). Furthermore, it is preferable that the thin film portions of the structure of the present invention have no micropores observed when observed with an optical microscope, a scanning electron microscope (SEM), or an atomic force microscope (AFM), and that they account for 80% or more of the total number of thin film portions, more preferably 90% or more, and even more preferably 99% or more.

[0035] The total number of thin film portions in the structure of the present invention is not particularly limited, but is preferably 5 or more, more preferably 7 or more, and even more preferably 10 or more. There is also no particular upper limit to the total number, but from the viewpoint of weight reduction, it is preferably 100 or less.

[0036] The structures according to the first aspect and the third to twelfth aspects of the present invention preferably have a material different from the porous body, and the thin film portion is preferably formed at least in part from the different material. Examples of such different materials include cellulose nanofibers, nanofibers other than cellulose nanofibers (hereinafter also referred to as "other nanofibers"), sugars, celluloses, urethane, acrylic, epoxy, inorganic fillers, etc., and among these, as in the second aspect, cellulose nanofibers and other nanofibers are preferred, with cellulose nanofibers being more preferred.

[0037] <Cellulose nanofibers> Cellulose nanofibers (hereinafter also referred to as "CNF") are not particularly limited as long as they are made from a cellulosic raw material. The cellulosic raw material is not particularly limited as long as it is a material that is mainly made of cellulose, and examples thereof include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing a cellulose raw material through mechanical treatment. Note that commercially available products such as crystalline cellulose made from pulp can be used as the cellulosic raw material as is. The cellulosic raw material may be subjected to chemical treatment such as alkali treatment to facilitate penetration of an oxidizing agent.

[0038] <Other Nanofibers> As the other nanofibers, water-dispersible nanofibers can be suitably used, and specific examples thereof include chitin nanofibers and chitosan nanofibers.

[0039] The fiber length of cellulose nanofibers and other nanofibers is not particularly limited, but the fiber length-weighted average value Lw is preferably 100 nm to 5000 nm, more preferably 600 nm to 3000 nm, and even more preferably 800 nm to 1500 nm. Lw is known to correlate well with the degree of polymerization (see, for example, Biomacromolecules 2012, 13, 842-849). The degree of polymerization corresponding to the above fiber length is preferably 200 to 1300, more preferably 300 to 900, and even more preferably 400 to 600. The fiber diameter of cellulose nanofibers and other nanofibers is not particularly limited, but is preferably 1 nm to 100 nm, more preferably 2 nm to 10 nm, and even more preferably 3 nm to 5 nm.

[0040] The method for obtaining cellulose nanofibers from cellulosic raw materials is not particularly limited, and methods known in the technical field of the present invention (particularly methods for defibrating cellulose fibers) can be used. Examples of methods for defibrating cellulose fibers include physical methods (mechanical defibration), chemical methods (chemical defibration), and biological methods. Examples of mechanical defibration include high-pressure homogenizer methods, microfluidizer methods (such as underwater counter-collision methods and water jet methods), grinder methods, ball mill crushing methods, bead mill crushing methods, and freeze-pulverization methods. Examples of chemical defibration include 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter abbreviated as "TEMPO") catalytic oxidation methods, phosphite esterification methods, phosphate esterification methods, carboxymethylation methods, sulfonation methods, xanthation methods, hypooxidation methods, sulfate esterification methods, acid hydrolysis methods, and ionic liquid selective dissolution methods. Examples of biological methods include production by animals (sea squirts) or bacteria (acetic acid bacteria), and methods of decomposing cellulose into nano-sized particles using specific enzymes (e.g., cellulase). Of these, chemical defibration is preferred because it forms a uniform membrane and can defibrate cellulose fibers as much as possible while avoiding cutting them into short pieces. Furthermore, among chemical defibration methods, TEMPO catalytic oxidation is preferred from the viewpoints of chemical stability and dispersion stability. Specific examples of TEMPO catalytic oxidation include a method in which a cellulosic raw material is oxidized with sodium hypochlorite, an oxidizing agent, in the presence of a TEMPO catalyst.

[0041] In the present invention, the cellulose nanofibers may be crosslinked with a crosslinking agent having an isocyanate group or a blocked isocyanate group. Examples of such crosslinking agents include polyisocyanates, which are polyfunctional isocyanates having two or more isocyanate groups. Examples of polyisocyanates include aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates. Among these, alicyclic polyisocyanates and aliphatic polyisocyanates are preferred because of their low yellowing tendency. Examples of aromatic polyisocyanates include aromatic diisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures thereof (TDI), diphenylmethane-4,4'-diisocyanate (MDI), naphthalene-1,5-diisocyanate, 3,3-dimethyl-4,4-biphenylene diisocyanate, crude TDI, polymethylene polyphenyl diisocyanate, crude MDI, phenylene diisocyanate, xylylene diisocyanate, etc. Examples of alicyclic polyisocyanates include alicyclic diisocyanates such as 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate, etc. Examples of the aliphatic polyisocyanate include aliphatic diisocyanates such as trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate.

[0042] In the structures according to the first aspect and the third to twelfth aspects of the present invention, the content of the different components (particularly, cellulose nanofibers) is ３ Per, 1 x 10 －３ g / cm ３ It is preferable that the ratio is 5×10 or more. －３ g / cm ３ More preferably, it is 10×10 or more. －３ g / cm ３Here, the content of the different material refers to the content including not only the material forming the thin film portion but also the material contained in the structure in a location other than the thin film portion (for example, material attached to the surface of the fiber constituting the porous body).

[0043] Similarly, in the structure according to the second aspect of the present invention, the content of the above-mentioned cellulose nanofibers is ３ Per, 1 x 10 －３ g / cm ３ It is preferable that the ratio is 5×10 or more. －３ g / cm ３ More preferably, it is 10×10 or more. －３ g / cm ３ Here, the content of cellulose nanofibers refers to the content including not only those forming the thin film portion but also those contained in the structure in places other than the thin film portion (for example, those attached to the fiber surfaces that make up the porous body).

[0044] The thin film portion included in the structure according to the fifth aspect of the present invention is uniformly present in the thickness direction of the structure. Furthermore, the distribution of the thin film portion included in the structures according to the first to fourth aspects and the sixth to twelfth aspects of the present invention is not particularly limited, and may be uniformly distributed throughout the structure, or may be distributed predominantly on one side. It is particularly preferable that the thin film portion is uniformly distributed throughout the structure, and that it is uniformly present in the thickness direction of the structure. Furthermore, the film thickness, area, etc. may vary depending on the location. Note that if the thin film portion is distributed unevenly, the sound absorption properties (sound absorption coefficient, frequency dependency) may vary depending on the direction of sound incidence on the membrane surface of the structure, and therefore it is preferable to adjust it according to the application.

[0045] The indentation modulus of the thin film portion included in the structure according to the sixth aspect of the present invention is 3 GPa or more. The indentation modulus of the thin film portion included in the structures according to the first to fifth aspects and the seventh to twelfth aspects of the present invention is preferably 3 GPa or more, for the reason that sound insulation is further improved. While there is no particular upper limit for the indentation modulus of the thin film portion included in the structure of the present invention, it is preferably 30 GPa or less.

[0046] As described above, the thin film portion included in the structure according to the ninth aspect of the present invention exhibits crystallinity. Furthermore, the thin film portion included in the structures according to the first to eighth aspects and the tenth to twelfth aspects of the present invention preferably exhibits crystallinity, because this further improves sound insulation. Whether or not a structure exhibits crystallinity can be determined by the presence or absence of peak detection by X-ray diffraction (XRD), as described above. A narrower half-width peak, i.e., a higher degree of crystallinity, is preferred because it is believed to indicate a larger degree of crystallization and a larger volume. Specifically, the degree of crystallinity is preferably 15% or more, and more preferably 25% or more.

[0047] As described above, the thin film portion included in the structure according to the tenth aspect of the present invention exhibits orientation anisotropy. Furthermore, it is preferable that the thin film portion included in the structures according to the first to ninth aspects and the eleventh to twelfth aspects of the present invention exhibit orientation anisotropy, because this further improves sound insulation.

[0048] The arithmetic mean roughness Ra of the surface of the thin film portion included in the structure according to the eleventh aspect of the present invention is 1 nm or more, but is preferably 1.5 nm or more because sound insulation is further improved. Furthermore, the arithmetic mean roughness Ra of the surface of the thin film portion included in the structures according to the first to tenth aspects and the twelfth aspect of the present invention is preferably 1 nm or more, more preferably 1.5 nm or more, because sound insulation is further improved. The arithmetic mean roughness Ra of the surface of the thin film portion included in the structure according to the present invention is preferably less than 200 nm, more preferably less than 100 nm, and even more preferably less than 50 nm.

[0049] As described above, the thin film portion included in the structure according to the twelfth aspect of the present invention is free of defects. Also, it is preferable that the thin film portion included in the structures according to the first to eleventh aspects of the present invention is free of defects.

[0050] The size of the thin film portion included in the structure of the present invention is 100 to 50,000 μm. ２ is preferred, and 1000 to 40000 μm ２ More preferably, 4000 to 25000 μm ２ is more preferred.

[0051] The thickness of the thin film portion contained in the structure of the present invention is preferably 1 nm to 10 μm, more preferably 100 nm to 5 μm, and even more preferably 100 nm to 2 μm.

[0052] The average film thickness of the thin film portion contained in the structure according to the seventh aspect of the present invention is 3 μm or less, but is preferably 2 μm or less, and more preferably 1 μm or less, because sound insulation is further improved. Furthermore, the average film thickness of the thin film portion contained in the structures according to the first to sixth aspects and the eighth to twelfth aspects of the present invention is preferably 3 μm or less, and more preferably 2 μm or less, and even more preferably 1 μm or less, because sound insulation is further improved. The lower limit of the average film thickness of the thin film portion contained in the structure of the present invention is not particularly limited, but is preferably 0.01 μm or more.

[0053] The substantial film thickness of the thin film portion included in the structure according to the eighth aspect of the present invention is 0.05 to 5 μm, but is preferably 0.1 to 3 μm, and more preferably 0.1 to 2 μm, because sound insulation is further improved. The substantial film thickness of the thin film portion included in the structures according to the first to seventh aspects and the ninth to twelfth aspects of the present invention is preferably 0.05 to 5 μm, and more preferably 0.1 to 3 μm, and even more preferably 0.1 to 2 μm, because sound insulation is further improved.

[0054] The surface area of ​​the structure according to the fourth aspect of the present invention is at least 1.5 times the surface area of ​​the porous body, but is preferably at least twice the surface area of ​​the porous body, and more preferably at least three times the surface area of ​​the porous body, in order to further improve sound insulation. The upper limit of the ratio of the surface area of ​​the structure according to the present invention to the surface area of ​​the porous body is not particularly limited, but is preferably 60 times or less. The surface area of ​​the structures according to the first to third aspects and the fifth to twelfth aspects of the present invention is preferably at least 1.5 times the surface area of ​​the porous body, more preferably at least two times the surface area of ​​the porous body, and even more preferably at least three times the surface area of ​​the porous body, in order to further improve sound insulation.

[0055] The tensile modulus of elasticity of the thin film portion of the structure of the present invention is preferably 3 GPa or more, more preferably 5 GPa or more, and even more preferably 7 GPa or more, because this further improves sound insulation. The upper limit of the tensile modulus of elasticity of the thin film portion of the structure of the present invention is not particularly limited, but is preferably 50 GPa or less. Here, the tensile modulus can be determined by dynamic mechanical analysis (DMA) of a single film of the thin film portion.

[0056] The oxygen permeability of the thin film portion of the structure of the present invention is 20 cc / m because sound insulation is further improved. ２ ・24h・atm or less is preferable, 10cc / m ２ The lower limit of the oxygen permeability of the thin film portion of the structure of the present invention is not particularly limited, but it is preferably 0.1 cc / m ２ The oxygen permeability is preferably 24 h·atm or more. Here, the oxygen permeability can be determined by attaching a thin film to the surface of an oxygen concentration meter electrode and measuring the same.

[0057] [Flame Retardant / Protective Layer] The structure of the present invention is preferably flame-retarded by incorporating or adsorbing a flame retardant. There are no particular limitations on the flame retardant, and known materials can be used. For example, flame retardants such as those described in "Technologies for Utilizing Flame Retardants and Flame-Retardant Materials" (CMC Publishing) can be used. Generally, halogen-based flame retardants, flame retardants containing phosphorus atoms (hereinafter also referred to as "phosphorus-based flame retardants"), and inorganic flame retardants are suitable. Among these, phosphorus-based flame retardants and inorganic flame retardants are preferred for electronic applications where it is desirable to suppress the incorporation of halogens. Examples of phosphorus-based flame retardants include phosphate-based materials such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl phenyl phosphate, and 2-ethylhexyl diphenyl phosphate; phosphate esters such as aromatic phosphate esters and aromatic condensed phosphate esters; polyphosphates; metal phosphinates; and red phosphorus. Examples of inorganic flame retardants include aluminum compounds. The structure of the present invention may have a protective layer on the surface of the porous body to provide flame retardancy. That is, it may be a laminate of porous body and protective layer. Examples of such protective layers include, but are not limited to, layers formed from flame-resistant materials such as siloxane films and thin metal films; resin layers containing flame retardants; and the like.

[0058] [Other Functional Layers] The structure of the present invention may have a laminated structure with other functional layers. Examples of the other functional layers include a hard coat film, a heat resistance-imparting layer, a waterproof layer, a moisture-proof layer, and an ultraviolet-blocking layer. The laminated structure with other functional layers may be a structure in which the other functional layer covers part or the entire structure of the present invention. Therefore, for example, the structure of the present invention may be enclosed in a moisture-proof bag, a waterproof bag, an ultraviolet-blocking bag, or the like.

[0059] [Physical properties, shape, applications, etc.] The surface density of the structure of the present invention is 0.1 kg / m because it is easy to form a large number of thin film portions. ２ It is preferable that the concentration is 0.2 kg / m or more. ２More preferably, it is 0.5 kg / m or more. ２ The upper limit of the surface density is 3 kg / m ２ Here, the surface density can be calculated by measuring the area (area when viewed from a direction perpendicular to the measurement plane) and mass of the structure and then calculating (measured mass) / (measured area).

[0060] As described above, the structure according to the second aspect of the present invention is a structure that, when an in-plane cross section dividing the thickness direction into three equal parts is observed with an optical microscope, satisfies at least one of the following conditions 1 and 2 in each of five fields of 1000 μm vertically and 1400 μm horizontally in each cross section. However, the ratios of the following conditions 1 and 2 are values ​​obtained by averaging the ratios calculated for each field of each cross section over the total number of fields (i.e., number of cross sections: 4 × number of fields: 5 = total number of fields: 20). Condition 1: The area of ​​the thin film portion relative to the total area of ​​the thin film portion is 25,000 μm ２ The ratio of the total area of ​​the specific thin film portion to be 25,000 μm or less (hereinafter referred to as "25,000 μm ２ The area ratio of the thin film portions to the total number of thin film portions is 10% or more, and the total number of thin film portions is 5 or more. Condition 2: The area of ​​the thin film portions to the total number of thin film portions is 25,000 μm ２ The ratio of the number of specific thin film portions that is equal to or less than 25,000 μm (hereinafter referred to as "25,000 μm" ２ The ratio of the number of thin film portions to the total number of thin film portions is 20% or more, and the total number of thin film portions is 5 or more. ２ The area ratio of the thin film portion is preferably 20% or more, more preferably 40% or more. ２ The ratio of the total area of ​​the specific thin film portion to be less than or equal to 15,000 μm ２ The area ratio of the thin film portion (hereinafter also referred to as "area ratio of the thin film portion") is preferably 10% or more, more preferably 20% or more, and even more preferably 40% or more. ２The ratio of the number of the thin film portions is preferably 35% or more, more preferably 50% or more. ２ The ratio of the number of specific thin film portions that is equal to or less than 15000 μm (hereinafter referred to as "15000 μm" ２ The ratio of the number of thin film portions (hereinafter also referred to as "ratio of the number of thin film portions") is preferably 20% or more, more preferably 35% or more, and even more preferably 50% or more.

[0061] Furthermore, when the structures according to the first aspect and the third to twelfth aspects of the present invention are observed with an optical microscope at an in-plane cross section dividing the thickness direction into three equal parts, it is preferable that at least one of conditions 1 and 2 described in the second aspect be satisfied in each of five fields of view of 1000 μm vertically and 1400 μm horizontally in each cross section, and it is more preferable that the structures according to the second aspect be satisfied in the preferred embodiments of conditions 1 and 2 described in the second aspect.

[0062] The structure according to the third aspect of the present invention has a porosity of 80 to 99.99% and a specific surface area of ​​0.2 m ２ / g or more. From the viewpoint of weight reduction, the porosity is preferably 85 to 99%, more preferably 90 to 98%. From the viewpoint of sound insulation, the specific surface area is 0.3 m ２ / g or more, and ２ The upper limit of the specific surface area is not particularly limited, but is preferably 10 m ２ / g or less, and ２ / g or less is more preferable. From the viewpoint of weight reduction, the porosity of the structures according to the first, second, and fourth to twelfth aspects of the present invention is preferably 80 to 99.99%, more preferably 85 to 99%, and even more preferably 90 to 98%. From the viewpoint of sound insulation, the specific surface area of ​​the structures according to the first, second, and fourth to twelfth aspects of the present invention is preferably 0.2 m / g or less. ２ / g or more, and ２ / g or more, and 0.4m ２The upper limit of the specific surface area is not particularly limited, but is preferably 10 m ２ / g or less, and ２ It is more preferable that the SiO2 content is 1 / g or less.

[0063] To achieve sufficient sound insulation, the structure of the present invention preferably has a transmission loss of 3 dB or more at 2000 Hz, more preferably 5 dB or more. While there is no particular upper limit for the transmission loss, attempting to achieve a value that is too high tends to result in a thick film and a heavy mass, so a value of 30 dB or less is preferable. Here, the transmission loss is measured using the following procedure. A sound source is placed upstream of the structure, and sound is incident from the sound source. The transmittance and reflectance of the structure are measured to determine the transmission loss. The measurement is performed using a four-terminal microphone transfer function method in accordance with the well-known acoustic tube measurement method (defined in ASTM E2611). Specifically, two acrylic pipes with an inner diameter of 40 mm (10 mm thick, 500 mm long, with two microphone insertion holes on the side) are first prepared, with two microphones inserted into them. Next, a structure is placed near one end of the pipe and connected to another pipe at that end (aligning them properly and placing another acrylic ring from the outer periphery into the groove to prevent sound leakage). At this point, two microphones are positioned on either side of the structure, centered around the center. When installing the structure inside the pipe, care must be taken to avoid pinching the structure in the groove between the pipes or being pressed hard against the wall because the structure is larger than the pipe diameter, as this will cause vibrations of the structure due to the fixing method to appear and alter the measurement results. Next, a speaker is connected to one end of the pipe, and wideband sound including the measurement frequency band is played and measured with the microphone. The time-series data is converted into frequency data using a fast Fourier transform (FFT) to determine the characteristics. Measurements are performed on the other end of the pipe under two conditions: when it is hollow and when it is blocked by aluminum (30 mm thick, 60 mm diameter) pressed against it to prevent sound leakage. Next, in accordance with the acoustic tube measurement method defined in ASTM E2611, the reflected sound from two microphones upstream of the structure and the transmitted sound from two microphones downstream are separated, and the reflectance and transmittance are determined by normalizing them with the incident sound, and the transmission loss is calculated using the following formula: Transmission loss = 10 × log 10 (1 / transmittance)

[0064] To obtain sufficient sound absorption characteristics, the structure of the present invention preferably has a sound absorption coefficient at 2000 Hz of 0.3 or greater, and more preferably 0.5 or greater. While there is no particular upper limit to the sound absorption coefficient, attempting to obtain a higher value tends to result in a thicker film and increased mass, so a value of 0.99 or less is preferred. Here, the sound absorption coefficient is measured using a normal incidence sound absorption coefficient measurement method with two microphone terminals in accordance with the known acoustic tube measurement method (defined in JIS A 1405-2). Specifically, an acrylic pipe with an inner diameter of 40 mm (10 mm thick, 500 mm long, with two microphone insertion holes on the side) is prepared, with two microphones inserted into it, and one end of the pipe is connected to a speaker. Next, the structure is placed at the end opposite the speaker. Aluminum (30 mm thick, 60 mm diameter) is pressed against the end of the pipe facing the structure to prevent sound leakage. At this time, if there is an air gap between the structure and the aluminum, the result will differ from the original sound absorption coefficient of the structure, so care must be taken to ensure that the structure and the aluminum are in contact. Next, in accordance with the acoustic tube measurement method specified in JIS A 1405-2, the transmitted sound volume and the reflected sound volume are separated and found separately, and the sound absorption coefficient is calculated using the following formula: Sound absorption coefficient = 1 - reflection coefficient = 1 - (reflected sound volume / transmitted sound volume)

[0065] Since the structure of the present invention has the thin film portion described above, the elastic modulus is preferably higher than that of an embodiment not having a thin film portion (i.e., a porous body); specifically, it is preferably higher by 1 MPa or more, and more preferably higher by 2 MPa or more.

[0066] The thickness of the structure of the present invention is not particularly limited, but is preferably 1 to 100 mm, and more preferably 3 to 50 mm. The shape of the structure of the present invention is not particularly limited because it can be changed depending on the application, but is preferably a film or board shape. The structure of the present invention may also be a three-dimensional structure (a three-dimensional structure). When forming a three-dimensional structure, the formation of the three-dimensional structure by pressing or the like may be a process before or after the liquid filling process described in the method for producing a structure below.

[0067] The structure of the present invention can be suitably used as a sound-insulating or sound-absorbing material. Applications for use as a sound-insulating or sound-absorbing material include a wide range of applications requiring light weight and soundproofing, such as in the mobility field (e.g., automobiles, airplanes, drones, etc.); building materials and housing fields (e.g., building ceilings and residential walls); communications fields (e.g., data centers); and electronics components. Furthermore, the structure of the present invention can be suitably used not only as a sound-insulating or sound-absorbing material, but also for other purposes, such as increasing strength and heat insulation.

[0068] [Method for manufacturing a structure] The method for manufacturing a structure of the present invention (hereinafter also abbreviated as "the manufacturing method of the present invention") is a method for manufacturing a structure that manufactures the above-mentioned structure of the present invention. The manufacturing method of the present invention comprises a liquid filling step in which a cellulose nanofiber solution is supplied to a porous body having voids consisting of continuous pores, and at least a portion of the porous voids are filled with the cellulose nanofiber solution. Furthermore, the manufacturing method of the present invention preferably comprises a drying step in which, after the liquid filling step, the body is allowed to stand and the liquid content in the cellulose nanofiber solution is dried.

[0069] [Liquid Filling Step] <Porous Body> Examples of the porous body having voids consisting of continuous pores, which is used in the liquid filling step, include the same porous bodies as those contained in the structure of the present invention described above.

[0070] <Cellulose nanofiber solution> The cellulose nanofiber solution used in the liquid filling step is a solution containing a solvent and cellulose nanofibers, and is preferably a dispersion liquid that the cellulose nanofibers are dispersed in. Here, the method for dispersing the cellulose nanofibers is not particularly limited, but examples include stirring with a blade type mixer, a planetary mixer, a homogenizer, and a bead mill.

[0071] In the manufacturing method of the present invention, the cellulose nanofiber solution used in the liquid filling step preferably has a viscosity reduction due to shearing of 20% or more. The cellulose nanofiber solution preferably gels when left to stand for 24 hours. Higher gelling properties are preferred, with the ratio of loss modulus G" / storage modulus G' preferably being 0.05 or more, and more preferably 0.5 or more. The cellulose nanofiber solution preferably has a viscosity of 10 Pa·s or more, and more preferably 30 Pa·s or more. The cellulose nanofiber solution preferably has a cellulose nanofiber concentration of 0.1% or more, more preferably 0.2% or more, and even more preferably 0.3% or more, because liquid crystallinity is more likely to be exhibited in the thin film portion.

[0072] (Solvent) The solvent contained in the cellulose nanofiber solution is not particularly limited, but from the viewpoints of solubility, drying property, and economy, it is preferable that the solvent contains water. Furthermore, the solvent may be water alone or a mixed solvent of water and an organic solvent. Examples of the organic solvent include: ester-based solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; ether-based solvents such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol isopropyl ether, ethylene glycol-t-butyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), and propylene glycol monobutyl ether; alcohol-based solvents such as methanol, ethanol, ethoxypropanol, butanol, methoxybutanol, methyl methoxybutanol, propyl alcohol, and 2-ethylhexanol; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon-based solvents such as Swazol, Shellsol, and mineral spirits; aromatic solvents such as xylene and toluene; and aprotic polar solvents such as acetonitrile and dimethyl sulfoxide. These may be used alone or in combination of two or more. Of these, it is preferable to use only water from the viewpoints of cost and safety.

[0073] (Cellulose nanofibers) Examples of the cellulose nanofibers contained in the cellulose nanofiber solution include the same cellulose nanofibers as those described above as the cellulose nanofibers that form the thin film portion of the structure according to the second aspect of the present invention. Among these, it is preferable to use cellulose nanofibers obtained by a method in which a cellulose-based raw material is oxidized with sodium hypochlorite as an oxidizing agent in the presence of a TEMPO catalyst.

[0074] The content of cellulose nanofibers in the cellulose nanofiber solution is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, relative to the total mass of the cellulose nanofiber solution. The content of cellulose nanofibers in the cellulose nanofiber solution is preferably less than 10% by mass, more preferably 8% by mass or less, and even more preferably 5% by mass or less, relative to the total mass of the cellulose nanofiber solution.

[0075] The form of the cellulose nanofibers in the cellulose nanofiber solution is not particularly limited, but the fiber length, as a weighted average fiber length value Lw, is preferably 100 nm to 5000 nm, more preferably 600 nm to 3000 nm, and even more preferably 800 nm to 1500 nm. The fiber diameter is preferably 1 nm to 100 nm, more preferably 2 nm to 10 nm, and even more preferably 3 nm to 5 nm.

[0076] In the liquid filling step, as described above, a cellulose nanofiber solution is supplied to a porous body having voids formed by continuous pores, and at least a portion of the voids in the porous body are filled with the cellulose nanofiber solution. Preferably, the cellulose nanofiber solution is filled so that no voids remain (for example, by dripping the solution through some of the continuous pores and filling the entire body so that the liquid spreads due to the effects of gravity, suction, surface tension, etc.). More preferably, the porous body is completely immersed in the cellulose nanofiber solution (for example, by continuing to drip the solution until the porous body is completely immersed). Specifically, it is preferable that 90% or more of the voids in the porous body are filled with the cellulose nanofiber solution, more preferably 95% or more of the voids in the porous body are filled with the cellulose nanofiber solution, and even more preferably 99% or more of the voids in the porous body are filled with the cellulose nanofiber solution. By supplying the cellulose nanofiber solution in this manner, air and bubbles contained within the porous body are pushed out of the porous body by the cellulose nanofiber solution, making it easier to form a thin film portion.

[0077] [Drying Step] The optional drying step included in the production method of the present invention is a step of drying the liquid portion of the cellulose nanofiber liquid by leaving it to stand after the liquid filling step. Here, the drying conditions in the drying step are not particularly limited as long as they are conditions under which the thin film portion of the structure of the present invention described above can be formed, but it is preferable to carry out the drying step while the cellulose nanofiber is in a liquid state without freezing. By carrying out drying under such conditions, it is possible to easily form a thin film portion made of cellulose nanofibers in at least a portion of the voids in the porous body. In other words, if the drying step involves heat drying at a high temperature or freeze-drying, it will not be possible to form the thin film portion of the structure of the present invention. Furthermore, the drying step carried out while the cellulose nanofiber is in a liquid state without freezing is preferably carried out at a temperature of 10 to 50°C for 10 to 200 hours, and more preferably at a temperature of 20 to 40°C for 20 to 75 hours.

[0078] The present invention will be described in more detail below with reference to the following examples. The materials, amounts used, ratios, treatment details, and treatment procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

[0079] Example 1 Preparation of Cellulose Nanofiber A 10 g of softwood kraft pulp was suspended in 1,000 g of pure water containing 0.16 g of TEMPO and 1 g of sodium bromide. 25 g of a 2 M aqueous sodium hypochlorite solution was added to initiate the oxidation reaction. The temperature of the reaction system was maintained at 25°C, and the pH of the system was maintained at 10 by adding a 0.5 M aqueous sodium hydroxide solution during the reaction. After 2 hours, the oxidation reaction was terminated by adding approximately 100 mL of ethanol to the reaction system. The resulting oxidized cellulose was then filtered and washed repeatedly with pure water using a glass filter to obtain oxidized cellulose. The resulting oxidized cellulose was passed through a high-pressure homogenizer three times to prepare a dispersion containing 1% by mass of cellulose nanofiber A (cellulose nanofiber A dispersion). The resulting cellulose nanofiber A had a carboxyl group content of 1.5 mmol / g, a fiber diameter of 3 nm, and a fiber length of 500 nm.

[0080] [Preparation of Cellulose Nanofiber A Solution] Pure water was added to the cellulose nanofiber A dispersion liquid prepared above and mixed with stirring to prepare a 0.35 mass % cellulose nanofiber solution 1.

[0081] [Fabrication of Structure] Polyester fiber (QonPET, manufactured by Livgraphy Co., Ltd.) was cut into a circle (diameter 40 mm, thickness 5 mm) to fabricate porous body 1 having voids consisting of continuous pores. The cellulose nanofiber solution 1 prepared above was added dropwise onto porous body 1, and the addition continued until porous body 1 was completely immersed in the cellulose nanofiber solution 1 (liquid filling step). With the porous body 1 completely immersed, it was allowed to stand in a sealed container for 12 hours. After standing, it was exposed to an open environment and left at room temperature (23°C) and a relative humidity of 40 to 60% RH for 48 hours to remove moisture (drying step), thereby fabricating structure 1.

[0082] Example 2 Structure 2 was produced in the same manner as in Example 1, except that polyester fiber (White Qon ES-10-303, manufactured by Tokyo Bouon Co., Ltd.) was used instead of polyester fiber (QonPET, manufactured by Livgraphy Co., Ltd.).

[0083] Example 3 Structure 3 was produced in the same manner as in Example 1, except that polyester fiber (White Qon ES-7-130, manufactured by Tokyo Bouon Co., Ltd.) was used instead of polyester fiber (QonPET, manufactured by Livgraphy Co., Ltd.).

[0084] Example 4 Cellulose nanofiber A dispersion liquid prepared in the same manner as in Example 1 was mixed with blocked isocyanate (Trixene AQUA BI220, manufactured by GSI Creos Corporation) and pure water to prepare cellulose nanofiber solution 2 containing 0.35 mass% of cellulose nanofibers and 1.4 mass% of blocked isocyanate (hereinafter simply abbreviated as "BI220"). Structure 4 was produced in the same manner as in Example 1, except that cellulose nanofiber solution 2 was used instead of cellulose nanofiber solution 1, and the solution was subjected to the same dropping and drying procedures as in Example 1, followed by heating in an oven at 120°C for 11 hours.

[0085] [Example 5] Structure 5 of Example 5 was produced in the same manner as in Example 1, except that porous body 5 having voids consisting of continuous pores cut out from glass wool (Paraboard GW32k25t, manufactured by Paramount Glass Industry Co., Ltd.) was used instead of porous body 1.

[0086] [Example 6] Structure 6 of Example 6 was produced in the same manner as in Example 1, except that porous body 6 having voids consisting of continuous pores cut out from glass wool (Paraboard GW96k25t, manufactured by Paramount Glass Industry Co., Ltd.) was used instead of porous body 1.

[0087] Example 7 Structure 7 of Example 7 was prepared in the same manner as Example 1, except that cellulose nanofiber B prepared by the following method was used instead of cellulose nanofiber A. [Preparation of Cellulose Nanofiber B] Cellulose nanofiber B with Lw = 930 was synthesized using the method described in Biomacromolecules 2012, 13, 842-849. Specifically, wood cellulose (5 g) was suspended in a solution containing TEMPO (0.08 g) and sodium bromide (0.5 g) in water (500 mL). Oxidation by TEMPO was initiated by adding a known amount of 1.8 M sodium hypochlorite (NaClO, 3.8 mmol per gram of wood cellulose) to the cellulose slurry while stirring at room temperature. The pH of the solution was maintained at 10 by adding 0.5 M sodium hydroxide (NaOH) using a pH stat until the pH no longer decreased (0-4 hours). TEMPO-oxidized cellulose (TOC) was filtered, washed with water, and stored at 4°C without drying. A portion of TOC (approximately 0.5 g) was dissolved in 1% sodium hypochlorite (NaClO) at room temperature at pH 4.8. ２The oxidized cellulose was treated with 50 mL of cellulose acetate (50 mL) for two days to convert the C6-aldehyde in the oxidized cellulose to carboxyl groups. The oxidized cellulose was then thoroughly washed with water to produce cellulose nanofiber B (fiber diameter: 3 nm, fiber length: 930 nm). The carboxyl group content of the oxidized cellulose was measured by conductometric titration. The degree of polymerization was measured using the method described in Biomacromolecules 2012, 13, 842-849. Specifically, 0.04 g of the freeze-dried sample was dissolved in 20 mL of 0.5 M copper ethylenediamine over 30 minutes. The intrinsic viscosity of the solution was measured using a Cannon-Fenske capillary viscometer and converted to the degree of polymerization (DP) using the Mark-Houwink-Sakurada equation: [η] = 0.57 × DP

[0088] Example 8 Structure 8 of Example 8 was produced in the same manner as in Example 1, except that the thickness of the polyester fibers was 15 mm.

[0089] Example 9 Structure 9 of Example 9 was produced in the same manner as in Example 7, except that the thickness of the polyester fibers was 15 mm.

[0090] Comparative Example 1 The porous body used in Example 1 was used as a structure H1 of Comparative Example 1 without being subjected to the dropping treatment using the cellulose nanofiber solution and the subsequent drying treatment.

[0091] Comparative Example 2 The porous body used in Example 2 was used as a structure H2 of Comparative Example 2 without being subjected to the dropping treatment using the cellulose nanofiber solution and the subsequent drying treatment.

[0092] Comparative Example 3 The porous body used in Example 3 was used as structure H3 in Comparative Example 3 without being subjected to the dropping treatment using the cellulose nanofiber solution and the subsequent drying treatment.

[0093] Comparative Example 4 Structure H4 of Comparative Example 4 was produced in the same manner as in Example 1, except that cellulose nanofiber solution 1 was replaced with polyvinyl alcohol (Poval 40-80E, manufactured by Kuraray Co., Ltd.) (hereinafter abbreviated as "PVA") having a concentration of 1.11 mass %.

[0094] [Comparative Example 5] Structure H5 of Comparative Example 5 was produced in the same manner as in Example 1, except that the drying step was carried out by freeze-drying as follows: The freeze-drying was carried out by freezing with liquid nitrogen for 1 minute and then drying under a reduced pressure of 100 Pa for 12 hours.

[0095] Comparative Example 6 Structure H6 of Comparative Example 6 was produced in the same manner as in Comparative Example 1, except that the thickness of the polyester fiber was 15 mm.

[0096] Comparative Example 7 Structure H7 of Comparative Example 7 was produced in the same manner as in Comparative Example 4, except that the thickness of the polyester fiber was 15 mm.

[0097] Comparative Example 8 Structure H8 of Comparative Example 8 was produced in the same manner as in Comparative Example 5, except that the thickness of the polyester fiber was 15 mm.

[0098] [Evaluation] The structures produced in the examples and comparative examples were checked for transmission loss at 2000 Hz, 3000 Hz, and 4000 Hz, sound absorption coefficients at 2000 Hz and 3000 Hz, the presence or absence of a thin film portion, and the presence or absence of optical interference fringes in the thin film portion, as appropriate, using the methods described above. The results are shown in Tables 1 and 2 below. Here, a transmission loss of 3 dB or more at 2000 Hz can be evaluated as having excellent sound insulation. Furthermore, a sound absorption coefficient of 0.3 or more at 2000 Hz can be evaluated as having excellent sound absorption. Furthermore, since the structures produced in the examples and comparative examples were based on a porous body made of polyester fiber, they were all lightweight.

[0099] Furthermore, for the structures produced in the Examples and Comparative Examples, the characteristics of the thin film portions (distribution in the thickness direction, average film thickness, actual film thickness, presence or absence of defects, ratio of the surface area of ​​the structure to the surface area of ​​the porous body, number / area ratio / number ratio of predetermined thin film portions, indentation elastic modulus, presence or absence of crystallinity, presence or absence of orientation anisotropy, arithmetic mean roughness Ra of the surface) and the physical properties of the structures (porosity, specific surface area) were confirmed by the methods described above. The results are shown in Tables 3 and 4 below. Furthermore, the presence or absence of thin film portions inside the structures (hereinafter referred to as "presence or absence of internal films") was confirmed by the following method. That is, when the structure was divided in half (bisected) in the thickness direction, in each of five cross-sectional fields, the number of thin films was less than 3 / cm. ２ If so, it is judged as "no internal membrane", and 3 or more per cm ２ If so, it is judged to have an "internal membrane." The results are shown in Table 4 below.

[0100]

[0101]

[0102]

[0103]

[0104] The results shown in Tables 1 to 4 indicate that porous bodies without thin film portions in the pores have low transmission loss and sound absorption coefficients, resulting in poor sound insulation and sound absorption properties (Comparative Examples 1 to 3 and 6). Furthermore, when PVA was used to form the thin film portion, optical interference fringes were not observed in the thin film portion, indicating poor sound insulation and sound absorption properties (Comparative Examples 4 and 7). Furthermore, even when cellulose nanofibers were used to form the thin film portion, depending on the conditions of the drying process, the thin film portion was not formed, resulting in poor sound insulation and sound absorption properties (Comparative Examples 5 and 8).

[0105] In contrast, a porous body having voids made of continuous pores and thin film portions formed in at least a part of the voids, in which optical interference fringes are exhibited in the thin film portions, or in which the thin film portions are formed of cellulose nanofibers and the number of thin films is 5 or more, and the thickness is 25,000 μm ２ The area ratio of the thin film portion is 10% or more, or 25,000 μm ２It was found that all of the structures in which the ratio of the number of thin film portions below was 20% or more exhibited excellent sound insulation and sound absorption properties (Examples 1 to 9). Furthermore, considering the characteristic values ​​shown in Tables 3 and 4, it was found that the structures according to the third to twelfth aspects of the present invention also exhibited excellent sound insulation and sound absorption properties.

[0106] REFERENCE SIGNS LIST 1 void 2 fiber 3 porous body 4 thin film portion 10 structure

Claims

1. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein at least a part of the thin film portion exhibits optical interference fringes.

2. The structure according to claim 1, further comprising a member different from the porous body, wherein the thin film portion is formed of at least a part of the different member.

3. The content of the different members per 1 cm of the structure ３ is 1 × 10 －３ g / cm ３ or more. The structure according to claim 2 4. A structure having a porous body with voids formed of continuous pores and cellulose nanofibers, and having a thin film portion formed of at least a part of the cellulose nanofibers in at least a part of the voids, wherein when observing a cross-section in the in-plane direction that divides the thickness direction of the structure into three equal parts with an optical microscope, in each of five fields of view with a vertical length of 1000 μm and a horizontal length of 1400 μm in each cross-section, the structure satisfies at least one of the following Conditions 1 and 2. However, the ratios of the following Conditions 1 and 2 are values obtained by averaging the ratios calculated in each field of view of each cross-section with the total number of fields of view. Condition 1: The ratio of the total area of specific thin film portions having an area of 25000 μm ２ or less to the total area of the thin film portions is 10% or more, and the total number of the thin film portions is 5 or more. Condition 2: The ratio of the number of specific thin film portions having an area of 25000 μm ２ or less to the total number of the thin film portions is 20% or more, and the total number of the thin film portions is 5 or more.

5. The content of the cellulose nanofiber per 1 cm of the structure ３ is 1 × 10 －３ g / cm ３ or more. The structure according to claim 4.

6. The structure according to claim 4, wherein the thin film portion is uniformly present in the thickness direction of the structure.

7. The structure according to claim 4, wherein the average film thickness of the thin film portion is 3 μm or less. Here, the average film thickness refers to an average value calculated from the film thicknesses of 20 or more thin film portions measured from an image obtained by measuring a cross section of the structure with a scanning electron microscope.

8. The structure according to claim 4, wherein the substantial film thickness of the thin film portion is 0.05 to 5 μm. Here, the substantial film thickness refers to the film thickness range in which 80% or more of each measured value is included, measured from the film thicknesses of 20 or more thin film portions in an image obtained by measuring a cross section of the structure with a scanning electron microscope.

9. The structure according to claim 4, wherein the thin film portion has no defective portion.

10. The structure according to claim 4, wherein at least a part of the thin film portion exhibits optical interference fringes.

11. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, having a porosity of 80 to 99.99% and a specific surface area of 0.2 m ２ / g or more.

12. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein the surface area of the structure is 1.5 times or more the surface area of the porous body.

13. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein the thin film portion is uniformly present in the thickness direction of the structure.

14. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein the indentation elastic modulus of the thin film portion is 3 GPa or more.

15. A structure having a porous body with voids formed of continuous pores and a thin film portion formed in at least a part of the voids, wherein the average film thickness of the thin film portion is 3 μm or less. Here, the average film thickness refers to an average value calculated from the film thicknesses of 20 or more thin film portions measured from an image obtained by measuring a cross section of the structure with a scanning electron microscope.

16. A structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein a substantial film thickness of the thin film portion is 0.05 to 5 μm. Here, the substantial film thickness refers to a film thickness in a range including 80% or more of the measured values obtained by measuring the film thicknesses of 20 or more thin film portions from an image when the cross section of the structure is measured with a scanning electron microscope.

17. A structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein the thin film portion exhibits crystallinity.

18. A structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein the thin film portion exhibits orientation anisotropy.

19. A structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein an arithmetic mean roughness Ra of the surface of the thin film portion is 1 nm or more.

20. A structure having a porous body with voids consisting of continuous pores and a thin film portion formed in at least a part of the voids, wherein there is no defective portion in the thin film portion.

21. The structure according to any one of claims 11 to 20, wherein the thin film portion contains cellulose nanofibers.

22. The structure according to any one of claims 11, 12, and 14 to 20, wherein the thin film portion is uniformly present in the thickness direction of the structure.

23. When observing a cross-section in the in-plane direction that divides the thickness direction of the structure into three equal parts with an optical microscope, in each of five fields of view with a vertical dimension of 1000 μm and a horizontal dimension of 1400 μm in each cross-section, the structure according to any one of claims 11 to 20, satisfying at least one of the following conditions 1 and 2. However, the ratios of the following conditions 1 and 2 are values obtained by averaging the ratios calculated in each field of view of each cross-section with the total number of fields of view. Condition 1: The ratio of the total area of the specific thin film portions, each of which has an area of 25000 μm ２ or less, to the total area of the thin film portions is 10% or more, and the total number of the thin film portions is 5 or more. Condition 2: The ratio of the number of specific thin film portions, each of which has an area of 25000 μm ２ or less, to the total number of the thin film portions is 20% or more, and the total number of the thin film portions is 5 or more.

24. The structure according to any one of claims 1 to 20, wherein the porous body contains fibers.

25. The structure according to claim 24, wherein the fibers are at least one kind of fiber selected from the group consisting of polyester, glass fiber, and cellulose.

26. The density of the porous body is 10 kg / m ３ or more. The structure according to any one of claims 1 to 20.

27. The structure according to any one of claims 1 to 20, having a film-like or board-like shape.

28. The areal density is 0.1 kg / m ２ or more, and the structure according to any one of claims 1 to 20.

29. The structure according to claim 28, having a transmission loss of 3 dB or more at 2000 Hz.

30. The structure according to claim 28, having a sound absorption rate of 0.3 or more at 2000 Hz.

31. The structure according to any one of claims 1 to 20, used as a sound insulation material or a sound absorption material.

32. A method for manufacturing a structure for manufacturing the structure according to any one of claims 1 to 20, the method comprising a liquid filling step of supplying a cellulose nanofiber solution to a porous body having voids formed of continuous pores and filling at least a part of the voids of the porous body with the cellulose nanofiber solution.

33. The method for manufacturing a structure according to claim 32, wherein the liquid filling step is a step of filling 90% or more of the voids of the porous body with the cellulose nanofiber solution.

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