Structure and method for manufacturing structure

Abstract

The present invention addresses the problem of providing a structure having excellent durability against humidity and heat. Moreover, the present invention also addresses the problem of providing a method for manufacturing a structure. This structure has cellulose nanofibers and a porous body having voids composed of continuous holes, and contains at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent.

Description

Structure and method for manufacturing the structure

[0001] This invention relates to a structure and a method for manufacturing the structure.

[0002] Vehicles such as automobiles and trains are required to be both lightweight and quiet. To ensure quietness, sound-insulating materials that block external noise and sound-absorbing materials that absorb noise are used by attaching them to the walls, floors, and ceilings of the vehicles. In particular, sound-insulating and sound-absorbing materials used in automobiles are required to reduce noise across a wide frequency range from low to high frequencies (100 to 10,000 Hz).

[0003] As such sound-absorbing materials, nonwoven fabrics made solely of organic fibers, such as Thinsulate (manufactured by 3M), are known. Furthermore, Patent Document 1 describes "a sound-absorbing material having a nonwoven fabric form, comprising microfibers having a fiber diameter of the micro order and nanofibers having a fiber diameter of the nano order, wherein the nanofibers have a porosity of 92 to 99.9%" ([Claim 1]).

[0004] Japanese Patent Publication No. 2017-181925

[0005] Sound-absorbing materials are sometimes used in high-temperature, high-humidity environments, and therefore, resistance to moist heat is also required. When the present inventors examined the sound-absorbing material (structure) described in Patent Document 1, they found that there is room for improvement in its resistance to moist heat.

[0006] Therefore, the present invention aims to provide a structure with excellent resistance to moist heat. Furthermore, the present invention also aims to provide a method for manufacturing the structure.

[0007] The inventors of this invention have diligently studied and developed the present invention to solve the above problems. Specifically, they have found that the above problems can be solved by the following configuration.

[0008] [1] A structure comprising a porous body having voids consisting of continuous pores and cellulose nanofibers, further comprising at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent. [2] The structure according to [1], further comprising a thin film portion formed in at least a part of the voids. [3] The structure according to [1] or [2], comprising the surface modifier, wherein the surface modifier has a structure represented by formula (A1) described later. [4] The structure according to [3], wherein Cp in formula (A1) represents a group selected from the group consisting of an alkoxysilyl group, a trialkylsilyl group, an epoxy group, a carboxychloride group, an acid anhydride group, an isocyanate group, a thioisocyanate group, and a boronic acid group. [5] The structure according to [3] or [4], wherein Cp in formula (A1) is a group represented by formula (A2) described later. [6] The structure according to any one of [3] to [5], wherein R in formula (A1) is an n-valent hydrocarbon group having 1 to 20 carbon atoms, which may have substituents. [7] The structure according to any one of [3] to [6], wherein R in formula (A1) includes a fluoride alkyl group structure. [8] The structure according to [7], wherein the fluoride alkyl group structure has 4 to 12 carbon atoms. [9] The structure according to any one of [1] to [8], wherein the surface modifier includes a compound represented by formula (A3) described later.

[10] The SP value of the compound represented by formula (A1) is 5.0 to 11.0 (cal / cm²). ３ ) １／２ The structure according to any one of [3] to [8].

[11] The structure according to [1] or [2], comprising the above crosslinking agent, wherein the crosslinking agent is a polyvalent metal salt.

[12] The structure according to

[11] , wherein the metal element contained in the polyvalent metal salt is at least one selected from the group consisting of magnesium, calcium, and aluminum.

[13] The structure according to [1] or [2], comprising the above surface protective agent, wherein the surface protective agent is at least one selected from the group consisting of sizing agents and hydrophobic agents.

[14] The above structure 1 cm ３ The amount of cellulose nanofibers per unit is 1.0 × 10 －３ g / cm ３The structure according to any one of [1] to

[13] .

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

[14] , wherein the porous body includes fibers.

[16] The structure according to

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

[17] The density of the porous body is 10 kg / m³ ３ The above is a structure according to any one of [1] to

[16] .

[18] A structure according to any one of [1] to

[17] , having a film-like or board-like shape.

[19] A structure with a surface density of 0.1 kg / m ２ The above is a structure according to any one of [1] to

[18] .

[20] The structure according to

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

[21] The structure according to

[19] or

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

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

[21] , to be used as a sound insulation material or a sound absorption material.

[23] A method for manufacturing a structure according to any one of [1] to

[22] , comprising contacting a structural precursor having a porous body with voids consisting of continuous holes and cellulose nanofibers with at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent to obtain the above structure.

[0009] According to the present invention, a structure with excellent resistance to moist heat can be provided. Furthermore, according to the present invention, a method for manufacturing the structure can also be provided.

[0010] Figure 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 now be described in detail. The following descriptions of constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] The following represents the meaning of each description in this specification. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Also, in this specification, for a numerical range described stepwise, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other stepwise descriptions. Moreover, for the upper limit value or the lower limit value described in a certain numerical range within the numerical range described in this specification, it may be replaced with the value shown in the examples. Also, in this specification, each component may be used alone with one substance corresponding to each component or in combination of two or more. Here, when two or more substances are used in combination for each component, the content of that component, unless otherwise specified, refers to the total content of the substances used in combination.

[0013] In this specification, a high hygrothermal durability of the structure means that when placed in a high-temperature and high-humidity environment, the properties of the structure (for example, the transmission loss and sound absorption rate of the structure) are difficult to change. Examples of the evaluation method for hygrothermal durability include the methods described in the examples in the following section

[0014] [Structure] The structure of the present invention has a porous body having voids composed of continuous pores and cellulose nanofibers, and further contains at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protector. The structure of the present invention contains cellulose nanofibers, but since it contains at least one selected from the group consisting of the above surface modifier, crosslinking agent, and surface protector, it is considered that the cellulose nanofibers are less likely to deteriorate due to moisture. As a result, the structure of the present invention is considered to have excellent hygrothermal durability.

[0015] Hereinafter, the structure of the present invention will be described separately in a first embodiment containing at least a surface modifier, a second embodiment containing at least a crosslinking agent, and a third embodiment containing at least a surface protector.

[0016] [First Embodiment of the Structure] The first embodiment of the structure of the present invention has a porous body having voids composed of continuous pores and cellulose nanofibers, and further contains at least a surface modifier. When the first embodiment of the structure of the present invention contains a surface modifier, it is considered that it becomes difficult for moisture to reach the cellulose nanofibers, or the cellulose nanofibers are strongly bonded to each other, and the wet heat durability is excellent. Hereinafter, the first embodiment of the structure of the present invention will be described.

[0017] [Porous Body] The porous body included in the first embodiment of the structure of the present invention is a porous body having voids composed 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 a resin (for example, a membrane, a sponge, etc.), a metal porous body containing a metal, a glass porous body containing glass, and a ceramic porous body containing a ceramic.

[0018] Among these, from the reasons that the structure can be made lighter and the thin film portion described later can be formed more easily, it is preferably a fibrous porous body containing fibers, and more preferably a fibrous porous body composed of a fiber aggregate.

[0019] Examples of the above fibers include fibers such as polyester, glass fiber, glass wool, rock wool, cellulose, polyurethane, aramid fiber, polyvinyl chloride, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more. Among these, it is preferably at least one fiber selected from the group consisting of polyester, glass fiber, and cellulose because the thin film in the preferred embodiment described later is easily formed. Also, glass wool, rock wool, aramid fiber, and polyvinyl chloride are preferred, and glass wool is more preferred because the structure has excellent flame retardancy.

[0020] In the present invention, since it becomes easy to form many thin film portions described later, the density (mass per 1 m ３ ) of the porous body is preferably 10 kg / m ３ or more, and preferably 100 kg / m ３It is more preferable that the density is greater than or equal to the above. Furthermore, there is no particular upper limit to the density, but it is 1000 kg / m³. ３ The following is preferable:

[0021] 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. The upper limit of the average pore diameter is not particularly limited, but it is preferably 3000 μm or less, and more preferably 1000 μm or less.

[0022] Furthermore, in the present invention, it is preferable to control the hydrophilicity and hydrophobicity of the surface of the porous body from the viewpoint of controlling the formation of the thin film portion described later.

[0023] [Cellulose Nanofibers] The first embodiment of the structure of the present invention includes cellulose nanofibers (hereinafter also referred to as "CNF"). The CNF is not particularly limited as long as it is a material obtained from a cellulose-based raw material. The cellulose-based raw material is not particularly limited as long as it is a material mainly composed of cellulose, and examples include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing cellulose raw material through mechanical treatment. Commercially available products such as crystalline cellulose made from pulp can be used as the cellulose-based raw material. The cellulose-based raw material may be subjected to chemical treatment such as alkaline treatment to facilitate the penetration of an oxidizing agent.

[0024] The fiber length of CNF is not particularly limited, but is preferably 100 nm to 5000 nm, more preferably 50 nm to 2000 nm, and even more preferably 100 nm to 700 nm. The fiber diameter of CNF is also not particularly limited, but is preferably 1 nm to 100 nm, and more preferably 2 nm to 10 nm.

[0025] The method for obtaining CNF from cellulosic raw materials is not particularly limited, and known methods in the art of the present invention can be used. For example, CNF can be produced by oxidizing cellulosic raw materials with sodium hypochlorite as an oxidizing agent in the presence of a compound having a piperidine skeleton, such as 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter abbreviated as "TEMPO"), as a catalyst.

[0026] Furthermore, CNF may be chemically modified. In chemically modified CNF, some or all of the groups in the cellulose molecular chain are altered by chemical treatment. For example, in chemically modified CNF, the cellulose molecular chain may be substituted with other functional groups, such as some or all of the C6 hydroxyl group in the molecule being oxidized to an aldehyde group, a carboxyl group, etc., some or all of the hydroxyl groups including hydroxyl groups other than the C6 position being oxidized, esterified to nitrate esters, acetate esters, phosphate esters, etc., or etherified to methyl ether, hydroxypropyl ether, carboxymethyl ether, etc. More specifically, the groups introduced by chemical modification include, for example, carboxyl group, acetyl group, sulfate group, sulfonic acid group, acryloyl group, methacryloyl group, propionyl group, propioloyl group, butyryl group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanol group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl group, and Examples of chemically modified groups include acyl groups such as sonicotinoyl, froyl, and cinnamoyl groups, isocyanate groups such as 2-methacryloyloxyethyl isocyanol groups, alkyl groups such as methyl, ethyl, propyl, 2-propyl, butyl, 2-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, myristyl, palmityl, and stearyl groups, oxirane, oxetane, thiirane, and thietan groups. In particular, it is preferable that the groups introduced by chemical modification include at least a carboxyl group.

[0027] Chemical modification of CNF can be carried out by conventional methods. That is, cellulose can be chemically modified by reacting it with a chemical modifier. If necessary, solvents and catalysts may be used, and heating, reduced pressure, etc., may be performed. Examples of chemical modifiers include acids, acid anhydrides, alcohols, halogenating agents, alcohols, isocyanates, alkoxysilanes, and cyclic ethers such as oxiranes (epoxy). These may be used individually or in combination of two or more. Examples of acids include acetic acid, acrylic acid, methacrylic acid, propanoic acid, butanoic acid, 2-butanoic acid, and pentanoic acid. Furthermore, after chemical modification, it is preferable to wash thoroughly with water to terminate the reaction. After thorough washing with water, it is also preferable to further replace with an organic solvent such as alcohol. In this case, the replacement is achieved by immersing the cellulose in an organic solvent such as alcohol.

[0028] In the first embodiment of the structure of the present invention, the CNF content is as follows: ３ per unit, 1.0 x 10 －３ g / cm ３ Preferably, it is 5.0 × 10 －３ g / cm ３ It may be greater than or equal to 10.0 × 10 －３ g / cm ３ The above is also acceptable. Here, the CNF content includes not only the CNF forming the thin film portion described later, but also the CNF contained in the structure in parts other than the thin film portion (for example, CNF attached to the fiber surface constituting the porous body).

[0029] [Surface Modifier] The first embodiment of the structure of the present invention includes a surface modifier. The surface modifier is preferably bonded to the surface of CNF, and is also preferably bonded to the surface of a film formed of CNF (a thin film portion described later). The surface modifier will be described below. Note that the surface modifier included in the structure of the present invention may react and be in a form derived from the surface modifier.

[0030] The surface modifier preferably has a structure represented by the following formula (A1).

[0031]

[0032] In formula (A1), Cp represents a group that can react with CNF to form a chemical bond. If there are multiple Cp groups, they may be the same or different from one another. Examples of Cp groups include those that can react with at least one group selected from the group consisting of hydroxyl groups, carboxyl groups, and phosphate groups of CNF to form a chemical bond. Examples of Cp include structures containing alkoxysilyl groups, trialkylsilyl groups, epoxy groups, carboxychloride groups, acid anhydride groups, isocyanate groups, thioisocyanate groups, boronic acid groups, carboxyl groups, aldehyde groups, and carbonyl groups (e.g., ester structures, ketone structures), halogenated alkyl groups (-RX, where R represents an alkylene group and X represents a halogen atom (selected from F, Cl, Br, and I)), phenylene halogenated alkyl groups (-Ph-RX, where -Ph- represents a phenylene group, R represents an alkylene group and X represents a halogen atom (selected from F, Cl, Br, and I)), sulfonic acid groups, sulfonic acid anhydride groups, sulfonic acid groups, and halogenated sulfonic acid groups (-SO ２ X, where X represents a halogen atom (one selected from F, Cl, Br, and I). Examples of groups selected from the group consisting of alkoxysilyl groups, trialkylsilyl groups, epoxy groups, carboxychloride groups, acid anhydride groups, isocyanate groups, thioisocyanate groups, and boronic acid groups are preferred for Cp, more preferably a group selected from the group consisting of alkoxysilyl groups, trialkylsilyl groups, isocyanate groups, and thioisocyanate groups, and even more preferably an alkoxysilyl group or a trialkylsilyl group. An alkoxysilyl group refers to a group having one to three alkoxy groups bonded to a silicon atom. The isocyanate group may also be a blocked isocyanate group.

[0033] In formula (A1), Cp is also preferably a group represented by the following formula (A2).

[0034] In formula (A2), R ａR represents an alkyl group having 1 to 4 carbon atoms. ａ If there are multiple instances, they may be identical or different from one another. ａ R preferably represents a methyl group or an ethyl group. ｂ R represents an alkyl group having 1 to 4 carbon atoms. ｂ If there are multiple instances, they may be identical or different from one another. ｂ is preferably a methyl group or an ethyl group. p is an integer from 0 to 3. p is preferably 1 to 3, more preferably 2 or 3, and even more preferably 3. When p is 0, the group represented by formula (A2) is a trialkylsilyl group, and when p is 1 to 3, the group represented by formula (A2) is an alkoxysilyl group. * represents the bond position with Sp in the above formula (A1).

[0035] In formula (A1), Sp represents a divalent linking group or single bond which may have substituents. When Sp is a divalent linking group, it represents an alkylene group having 1 to 10 carbon atoms, -COO-, -OCO-, -CONR Ｎ -, -NR Ｎ CO-, -O-, and NR Ｎ Groups selected from the group consisting of -, and groups formed by combining two or more of the above groups. Note that the above R Ｎ Examples include hydrocarbon groups which may have substituents, and R Ｎ The hydrocarbon group portion represented by is preferably 1 to 4 carbon atoms. The alkylene group with 1 to 10 carbon atoms may be linear, branched, or have a cyclic structure. Sp is preferably a single bond.

[0036] In formula (A1), n ​​represents an integer from 1 to 8. Preferably, n is from 1 to 6, more preferably from 1 to 4, even more preferably from 1 to 3, and particularly preferably 1.

[0037] In formula (A1), R represents an n-valent group. R is preferably an n-valent hydrocarbon group having 1 to 20 carbon atoms, which may have substituents. Examples of substituents include halogen atoms (more preferably fluorine atoms). Furthermore, R preferably includes a fluorinated alkyl group structure. If R includes a fluorinated alkyl group structure, the number of carbon atoms in the fluorinated alkyl group structure is preferably 4 to 12. Also, R may be a group obtained by removing three hydrogen atoms bonded to the nitrogen atom of isocyanuric acid, a group obtained by removing one hydrogen atom bonded to the nitrogen atom of biuret from each nitrogen atom, a group obtained by removing one hydrogen atom bonded to the oxygen atom of pentaerythritol from each oxygen atom, or a group obtained by removing one hydrogen atom bonded to the oxygen atom of dipentaerythritol from each oxygen atom.

[0038] The surface modifier preferably includes, for example, a compound represented by the following formula (A3).

[0039]

[0040] In formula (A3), R ａ R represents an alkyl group having 1 to 4 carbon atoms. ａ If there are multiple instances, they may be identical or different from one another. ａ R preferably represents a methyl group or an ethyl group. ｂ R represents an alkyl group having 1 to 4 carbon atoms. ｂ If there are multiple instances, they may be identical or different from one another. ｂ is preferably a methyl group or an ethyl group. p is an integer from 1 to 3. p is preferably 2 or 3, more preferably 3. q is an integer from 0 to 10. q is preferably 0 to 4, more preferably 0 to 2. r is an integer from 0 to 19. r is preferably 1 to 15, more preferably 3 to 11. X is a hydrogen atom or a fluorine atom. X is preferably a fluorine atom.

[0041] The SP value of the compound represented by formula (A1) is 5.0 to 11.0 (cal / cm³). ３ ) １／２It is also preferable that the following conditions are met. In this specification, the SP value is Hildebrand's dissolution parameter. More specifically, when ΔH is the molar heat of vaporization of the compound, V is the molar volume, R is the gas constant, and T is the absolute temperature, ((ΔH - RT) / V) １／２ A quantity defined by (cal / cm³) ３ ) １／２ That is the case.

[0042] Specific examples of surface modifiers include, for example, trimethoxyhexylsilane, triethoxyhexylsilane, trimethoxyphenylsilane, triethoxyphenylsilane, 1,6-bis(trimethoxysilyl)hexane, trimethoxyheptadecafluorodecylsilane, triethoxyheptadecafluorodecylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltrialkoxysilane, 3-ureido Silane compounds such as propyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltrimethoxysilane; silazane compounds such as hexamethylsilazane, 1,3-diphenyltetramethyldisilazane, and 1,3-bis(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane;Examples 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, and xylylene diisocyanate; alicyclic diisocyanates such as 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, and cyclohexane diisocyanate; and aliphatic diisocyanates such as trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate. Furthermore, as described above, the surface modifier included in the first embodiment of the structure of the present invention may be in a form derived from the above compound after the compound has reacted.

[0043] The content of the surface modifier is preferably 0.005 to 30% by mass, more preferably 0.01 to 20% by mass, and even more preferably 0.1 to 10% by mass, relative to the CNF content. Furthermore, the content of the surface modifier is preferably 0.0005 to 3% by mass, more preferably 0.001 to 2% by mass, and even more preferably 0.01 to 1% by mass, relative to the total mass of the structure.

[0044] Furthermore, the first embodiment of the structure of the present invention may include, in addition to the surface modifier, at least one of the crosslinking agent and the surface protective agent described later.

[0045] [Thin Film Section] The first embodiment of the structure of the present invention may also preferably have a thin film section formed in at least a part of the above-mentioned void. The thin film section may also preferably be a film formed of CNF. Note that the thin film section is not a liquid film. In the structure, all of the CNF may be included as a thin film section, or only CNF that does not form a thin film section may be included in the structure. Alternatively, both CNF that does not form a thin film section and CNF that does form a thin film section may be included. In other words, a porous body having voids consisting of continuous holes may have a thin film section formed of at least a part of CNF in at least a part of the void. Furthermore, it is preferable that the thin film section 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). Note that the presence or absence of a thin film section can be confirmed by observing the structure using an optical microscope.

[0046] Figure 1 shows a schematic cross-sectional view illustrating an example of an embodiment of the structure of the present invention. The structure 10 shown in Figure 1 has a porous body 3 having voids 1 consisting of continuous holes, and a thin film portion 4 formed in at least a part of the voids. In Figure 1, reference numeral 2 denotes a fiber, so the porous body 3 is composed of an aggregate of fibers 2 and voids 1. In the embodiment shown in Figure 1, the thin film portion 4 is formed of cellulose nanofibers.

[0047] It is also preferable that at least a portion of the thin film exhibits optical interference fringes. Furthermore, it is preferable that the thin film is a film formed of CNF and that at least a portion of it exhibits optical interference fringes. The above-mentioned optical interference fringes refer to optical interference fringes that can be confirmed by observing the reflected image using an optical microscope. Specifically, they can be confirmed by observing the reflected image using an optical microscope equipped with a light source that can confirm interference fringes with a continuous change in color from blue to green to red or a part thereof, at a magnification that allows observation of the thin film formed in at least a portion of the voids in the porous body. For example, with a Keyence VKX-200 laser microscope, the presence or absence of optical interference fringes can be confirmed by observing with a 10x objective lens in optical microscope image observation mode. Note that the magnification should be selected so that the thin film occupies 20% or more of the observation field area. Then, in any field of view of the surface or cross-section of the structure, 30 thin film portions formed in at least a portion of the voids are observed, and if interference fringes with a continuous change in color from blue to green to red or a part thereof are observed in 50% (i.e., 15 portions) or more, the thin film portion is considered to exhibit optical interference fringes.

[0048] When the first embodiment of the structure of the present invention has a thin film portion, resonance is more likely to occur, resulting in excellent sound insulation and sound absorption, which is preferable. Furthermore, when the thin film portion is formed of CNF, and when the thin film portion exhibits optical interference fringes, resonance is more likely to occur in the thin film portion, resulting in even better sound insulation and sound absorption.

[0049] When the first embodiment of the structure of the present invention includes a thin film portion, the distribution of the included thin film portion is not particularly limited, but it may be uniformly distributed within the structure or may be more abundant on one side. Furthermore, the film thickness, area, etc., may differ depending on the location. If the thin film portion is unevenly distributed, the sound absorption properties (sound absorption coefficient, frequency dependence) may differ depending on the direction in which sound is incident on the film surface of the structure, so it is preferable to adjust it according to the application.

[0050] When the first embodiment of the structure of the present invention includes a thin film portion, the thickness of the thin film portion included in the thin film portion is preferably 1 nm to 10 μm, and more preferably 100 nm to 5 μm.

[0051] When the first embodiment of the structure of the present invention includes a thin film portion, the contact angle of the thin film portion is preferably 60° or more. There is no particular upper limit to the contact angle, but for example, it is 150° or less.

[0052] [Flame Retardant / Protective Layer] In the first embodiment of the structure of the present invention, it is preferable that the structure is flame retardant by incorporating a flame retardant or by adsorbing a flame retardant. There are no particular restrictions on the flame retardant, and known materials can be used. For example, flame retardants described in "Technologies for the Use of Flame Retardants and Flame Retardant Materials" (CMC Publishing) can be used, and generally, halogen-based flame retardants, flame retardants containing phosphorus atoms (hereinafter also abbreviated as "phosphorus-based flame retardants"), and inorganic flame retardants can be suitably used. Among these, when it is desirable to suppress the inclusion of halogens in electronic applications, it is preferable to use phosphorus-based flame retardants and inorganic flame retardants. Examples of phosphorus-based flame retardants include phosphate materials such as triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresylphenyl phosphate, and 2-ethylhexyldiphenyl phosphate; phosphate esters such as aromatic phosphate esters and aromatic condensed phosphate esters; polyphosphates; phosphinate metal salts; red phosphorus; and the like. Examples of inorganic flame retardants include aluminum compounds. In addition, in the first embodiment of the structure of the present invention, a protective layer may be provided on the surface of the porous body for flame retardancy. That is, it may be a laminate of porous body / protective layer. There are no particular limitations on such a protective layer, but examples include a layer formed of a material that is difficult to burn, such as a siloxane film or a metal thin film; a resin layer containing a flame retardant; and so on.

[0053] [Other Functional Layers] The first embodiment of the structure of the present invention may be a laminated structure with other functional layers. Examples of other functional layers include a hard coat film, a heat-resistant layer, a waterproof layer, a moisture-proof layer, and an ultraviolet-blocking layer. Furthermore, the laminated structure with other functional layers may be such that the other functional layers cover part or all of the structure of the present invention. For example, the structure of the present invention may be used in which it is sealed inside a moisture-proof bag, a waterproof bag, an ultraviolet-blocking bag, etc.

[0054] [Physical properties, shape, applications, etc.] The surface density of the first embodiment of the structure of the present invention is 0.1 kg / m², for reasons such as the ease with which a large amount of thin film can be formed. ２ Preferably, it is 0.2 kg / m ２ It is more preferable that the amount be greater than or equal to 0.5 kg / m ２ It is even more preferable that the above conditions are met. The upper limit of the surface density is 3 kg / m³. ２ The following is preferable. Here, 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 dividing (measured mass) by (measured area).

[0055] In the first embodiment of the structure of the present invention, in order to obtain sufficient sound insulation, the transmission loss at 2000 Hz is preferably 3 dB or more, and more preferably 5 dB or more. There is no particular upper limit to the transmission loss, but if you try to obtain a value that is too high, the film thickness tends to become thicker and the mass heavier, so it is preferable to use a value of 30 dB or less. Here, the transmission loss is the value obtained by the following procedure. A sound source is placed upstream of the structure, sound is incident from the sound source, and the transmittance and reflectance of the structure are measured to determine the transmission loss. At this time, the measurement is performed using the transfer function method of four microphone terminals in accordance with the known acoustic tube measurement method (as defined in ASTM E2611). Specifically, first, two pipes are prepared, each with two microphones inserted into an acrylic pipe (10 mm thick, 500 mm long, with two microphone insertion holes on the side) with an inner diameter of 40 mm. Next, the structure is placed near the end of the pipe and connected to another pipe at the end (aligning them so as not to shift, and placing another acrylic ring in the groove from the outer circumference to prevent sound leakage). At this time, there will be two microphones on each side of the structure. When installing the structure inside the pipe, care should be taken to avoid situations where it is pinched in the groove between the pipes or where the structure is larger than the pipe diameter and pressed strongly against the wall, as this will cause vibrations of the structure due to the fixing method and alter the measurement results. Next, a speaker is connected to one end of the pipe, and a wideband sound including the measurement frequency range is played and measured with the microphone. The characteristics are determined by converting the time-series data into frequency data using the Fast Fourier Transform (FFT). Two levels of measurement are performed on the other end of the pipe: when it is hollow and when it is sealed with aluminum (30 mm thick, 60 mm in diameter) to prevent sound leakage. Next, following the acoustic tube measurement method specified in ASTM E2611, reflected sound is separated from two microphones upstream of the structure, and transmitted sound is separated from two microphones downstream. The reflectance and transmittance are then normalized by the incident sound to determine the reflectance and transmittance, and the transmission loss is calculated using the following formula: Transmission loss = 10 × log10(1 / transmittance)

[0056] In the first embodiment of the structure of the present invention, in order to obtain sufficient sound absorption characteristics, the sound absorption coefficient at 2000 Hz is preferably 0.3 or higher, and more preferably 0.5 or higher. There is no particular upper limit to the sound absorption coefficient, but since obtaining a high value tends to result in a thicker film and increased mass, it is preferable to use a value of 0.99 or lower. Here, the sound absorption coefficient is the value obtained by measuring the normal incidence sound absorption coefficient of two microphone terminals according to the known acoustic tube measurement method (as defined in JIS A 1405-2). Specifically, one pipe is prepared by inserting two microphones into an acrylic pipe with an inner diameter of 40 mm (thickness 10 mm, length 500 mm, with two microphone insertion holes processed on the side), and one end of the pipe is connected to a speaker. Next, the structure is placed at the end opposite the speaker. Aluminum (thickness 30 mm, diameter 60 mm) is pressed against the end of the pipe on the side of the structure to prevent sound leakage. At this time, care should be taken to ensure that the structure and aluminum are in contact, as any air gap between them will result in a different sound absorption coefficient than that of the structure itself. Next, following the acoustic tube measurement method specified in JIS A 1405-2, the transmitted sound volume and reflected sound volume are separated and determined, and the sound absorption coefficient is calculated from the following formula: Sound absorption coefficient = 1 - Reflectance = 1 - (Reflected sound volume / Transmitted sound volume)

[0057] The elastic modulus of the first embodiment of the structure of the present invention is preferably higher than that of the embodiment without the thin film portion (i.e., the porous body) because it has the thin film portion described above. Specifically, it is preferably 1 MPa or more higher, and more preferably 2 MPa or more higher.

[0058] The thickness of the first embodiment 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 first embodiment of the structure of the present invention is not particularly limited as it can be changed according to the application, but is preferably in the form of a film or a board. The first embodiment of the structure of the present invention may also be a three-dimensional structure. In the case of a three-dimensional structure, the formation of the three-dimensional structure by pressing or the like may be either a pre-process or a post-process of the liquid filling process described later in the manufacturing method of the structure.

[0059] The first embodiment of the structure of the present invention can be suitably used as a sound-insulating or sound-absorbing material. Furthermore, because the first embodiment of the structure of the present invention has excellent resistance to high temperatures and high humidity, it can be used as a sound-insulating or sound-absorbing material even in high-temperature and high-humidity environments.

[0060] [Second Embodiment of the Structure] The second embodiment of the structure of the present invention comprises a porous body having voids consisting of continuous holes, cellulose nanofibers, and further includes at least a crosslinking agent. When the second embodiment of the structure of the present invention includes a crosslinking agent, the cellulose nanofibers are strongly bonded to each other, and it is believed that the structure has excellent resistance to moist heat. The second embodiment of the structure of the present invention is the same as the first embodiment except for the inclusion of a crosslinking agent, so the description of the other components is omitted. The preferred embodiments other than those including the crosslinking agent are the same as those of the first embodiment.

[0061] [Crosslinking agent] The second embodiment of the structure of the present invention includes a crosslinking agent. The crosslinking agent is preferably bonded to the surface of CNF, and is also preferably bonded to the surface of a film formed of CNF (a thin film portion described later). The crosslinking agent will be described below. Note that the crosslinking agent included in the structure of the present invention may react and be in a form derived from the crosslinking agent.

[0062] The crosslinking agent is preferably a polyvalent metal salt. A polyvalent metal salt is defined as a metal cation with a valence of 2 or higher. Examples of metal elements included in the polyvalent metal salt include at least one selected from the group consisting of magnesium, calcium, strontium, barium, iron, cobalt, nickel, copper, zinc, aluminum, gallium, and tin, with at least one selected from the group consisting of magnesium, calcium, and aluminum being preferred.

[0063] The anions contained in the polyvalent metal salt are not particularly limited, but examples include halide ions (more preferably chloride ions), sulfate ions, nitrate ions, carbonate ions, and phosphate ions, with halide ions being preferred.

[0064] Specific examples of crosslinking agents include magnesium chloride, calcium chloride, strontium chloride, iron chloride, aluminum chloride, gallium chloride, tin chloride, calcium sulfate, magnesium sulfate, iron sulfate, aluminum sulfate, calcium carbonate, and silver nitrate.

[0065] The crosslinking agent content is preferably 0.005 to 30% by mass, more preferably 0.01 to 20% by mass, and even more preferably 0.1 to 10% by mass, relative to the CNF content. Furthermore, the crosslinking agent content is preferably 0.0005 to 3% by mass, more preferably 0.001 to 2% by mass, and even more preferably 0.01 to 1% by mass, relative to the total mass of the structure.

[0066] Furthermore, the second embodiment of the structure of the present invention may include, in addition to the crosslinking agent, at least one of the surface modifier and the surface protective agent described later. Also, the second embodiment of the structure of the present invention may have the configuration of the first embodiment of the structure.

[0067] [Third Embodiment of the Structure] The third embodiment of the structure of the present invention comprises a porous body having voids consisting of continuous holes, cellulose nanofibers, and further includes at least a surface protective agent. When the third embodiment of the structure of the present invention includes a surface protective agent, it is thought that moisture becomes less likely to reach the cellulose nanofibers, or the cellulose nanofibers become strongly bonded to each other, resulting in excellent resistance to moist heat. The third embodiment of the structure of the present invention is the same as the first embodiment except for the inclusion of a surface protective agent, so the description of the other aspects is omitted. The preferred embodiments other than those including a surface protective agent are the same as those of the first embodiment.

[0068] [Surface Protectant] The third embodiment of the structure of the present invention includes a surface protectant. The surface protectant is preferably bonded to the surface of CNF, and also preferably bonded to the surface of a film formed of CNF (a thin film portion described later). The surface protectant will be described below. The surface protectant included in the structure of the present invention may react and take a form derived from the surface protectant.

[0069] Examples of surface protective agents include at least one selected from the group consisting of sizing agents and hydrophobic agents. Examples of sizing agents include those used in papermaking, such as alkyl ketene dimers, rosin, alkenyl succinic anhydride, styrene-unsaturated carboxylic acid systems, higher fatty acid systems, petroleum resin systems, styrene / acrylic acid copolymers, styrene / methacrylic acid copolymers, and wax-based sizing agents.

[0070] Examples of hydrophobic agents include those used to hydrophobize wood and other materials, such as silicone-based hydrophobic agents.

[0071] The content of the surface protective agent is preferably 0.005 to 30% by mass, more preferably 0.01 to 20% by mass, and even more preferably 0.1 to 10% by mass, relative to the CNF content. Furthermore, the content of the surface protective agent is preferably 0.0005 to 3% by mass, more preferably 0.001 to 2% by mass, and even more preferably 0.01 to 1% by mass, relative to the total mass of the structure.

[0072] Furthermore, the third embodiment of the structure of the present invention may include, in addition to the surface protective agent, at least one of the surface modifier and the crosslinking agent. Also, the third embodiment of the structure of the present invention may have the configuration of the first embodiment of the structure.

[0073] [Method for Manufacturing the Structure] The method for manufacturing the structure of the present invention involves contacting a porous body having voids consisting of continuous pores and a structural precursor having cellulose nanofibers with at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent to obtain a structure. The structure of the present invention can be obtained by the method for manufacturing the structure of the present invention. The following describes the steps of obtaining a porous body having voids consisting of continuous pores and a structural precursor having cellulose nanofibers (CNF) (hereinafter also referred to as the "structural precursor manufacturing step") and obtaining a structure by contacting the obtained structural precursor with at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent (hereinafter also referred to as the "contact step").

[0074] [Process for Manufacturing Structural Precursors] Structural precursors are obtained, for example, by a liquid filling process 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 voids of the porous body is filled with the cellulose nanofiber solution. It is also preferable to perform a drying process after the liquid filling process to dry the liquid in the cellulose nanofiber solution. The liquid filling process and the drying process will be described below.

[0075] <Porous material> Examples of porous materials having voids consisting of continuous holes used in the liquid filling process include those similar to the porous material of the structure of the present invention described above.

[0076] <Cellulose Nanofiber Solution> The cellulose nanofiber solution used in the liquid filling process is a solution containing a solvent and cellulose nanofibers, and may also be a dispersion in which the cellulose nanofibers are not dissolved.

[0077] (Solvent) The solvent contained in the cellulose nanofiber solution is not particularly limited, but from the viewpoint of solubility, drying properties, and cost-effectiveness, it is preferable to include water. Furthermore, the solvent may be water alone, or a mixed solvent of water and an organic solvent. Examples of organic solvents include: ester 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 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 solvents such as methanol, ethanol, ethoxypropanol, butanol, methoxybutanol, methylmethoxybutanol, propyl alcohol, and 2-ethylhexanol; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as swazol, shellzol, and mineral spirits; aromatic solvents such as xylene and toluene; and aprotic polar solvents such as acetonitrile and dimethyl sulfoxide. These can be used individually or in combination of two or more.

[0078] (Cellulose Nanofibers) The cellulose nanofibers contained in the cellulose nanofiber solution are the same as those described above as cellulose nanofibers that form the thin film portion of the structure according to the second aspect of the present invention. In particular, it is preferable to use cellulose nanofibers obtained by oxidizing a cellulose-based raw material with sodium hypochlorite, which is an oxidizing agent, in the presence of a TEMPO catalyst.

[0079] The cellulose nanofiber content 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, based on the total mass of the cellulose nanofiber solution. Furthermore, the cellulose nanofiber content 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, based on the total mass of the cellulose nanofiber solution.

[0080] The morphology of the cellulose nanofibers in the cellulose nanofiber solution is not particularly limited, but those with a diameter of 3 to 300 nm and a length of 0.5 to 10 μm are preferred.

[0081] In the liquid filling process, as described above, a cellulose nanofiber solution is supplied to a porous body having voids consisting of continuous holes, filling at least a portion of the voids in the porous body with the cellulose nanofiber solution. It is preferable to fill the voids with the cellulose nanofiber solution so that no voids remain (for example, by dripping from a portion of the continuous holes and filling so that the liquid spreads throughout due to the effects of gravity, suction, surface tension, etc.), and it is more preferable to completely immerse the porous body in the cellulose nanofiber solution (for example, by continuing to drip until it 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, it is more preferable that 95% or more of the voids in the porous body are filled with the cellulose nanofiber solution, and it is even more preferable that 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 inside the porous body are pushed out to the outside of the porous body by the cellulose nanofiber solution, making it easier to form a thin film.

[0082] [Drying Process] The drying process is a process of drying the liquid in the cellulose nanofiber liquid after the liquid filling process described above. Here, it is preferable to set the drying conditions in the drying process to conditions that allow the formation of a thin film portion in the structure of the present invention described above. Conditions that allow the formation of a thin film portion include conditions in which the drying process is carried out while the material is in a liquid state without freezing. When dried under such conditions, a thin film portion made of cellulose nanofibers can be easily formed in at least a part of the voids of the porous material. In other words, if heating drying at a high temperature or freeze-drying is performed in the drying process, it is difficult to form a thin film portion. The method of carrying out the drying process is not particularly limited, and known methods can be applied. For example, methods include letting the porous material stand, heating the porous material, supplying heating gas to the porous material, supplying drying gas to the porous material, and placing the porous material in a reduced-pressure environment. Among these, the method of letting the porous material stand is preferred because it facilitates the formation of a thin film portion.

[0083] [Contact Process] In the contact process, the obtained structural precursor is brought into contact with at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent to obtain a structure. The surface modifier, crosslinking agent, and surface protective agent are as described above.

[0084] In the contact step, a treatment agent containing at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents may be brought into contact with the structural precursor. The treatment agent may contain a solvent. The solvent is not particularly limited as long as it can dissolve or disperse at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents, and known solvents can be selected. The method of bringing the treatment agent into contact with the structural precursor is not particularly limited, but examples include dropping the treatment agent onto the structural precursor and immersing the structural precursor in the treatment agent. Furthermore, when the treatment agent is used in the contact step, the contact step may be carried out in the same manner as the liquid filling step described above.

[0085] Furthermore, the contact step may involve contacting the structural precursor with at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents (particularly preferably a surface modifier) ​​in the gas phase. The following describes a method for contacting the structural precursor with a surface modifier in the gas phase. When supplying the surface modifier to the structural precursor in the gas phase, for example, one method is to store the surface modifier and the structural precursor in a chamber and heat the chamber. Alternatively, the gas containing the surface modifier described above may be supplied to the chamber containing the structural precursor.

[0086] After the above contact step, a cleaning step may be performed. The cleaning step can remove at least one substance selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents that has not reacted with the CNF or is not present on the surface of the CNF. As an example of the cleaning step, one method is to bring the structure that has undergone the above contact step into contact with a cleaning solution. The cleaning solution is not particularly limited, and for example, the solvents mentioned above can be applied as appropriate.

[0087] After the above contact step, a drying step may be performed. If a washing step is performed, the drying step may be performed only before the washing step, only after the washing step, or both before and after the washing step. The drying step removes the solvent contained in the treatment agent and the washing solution used in the washing step from the structure. The drying step can be carried out in the same manner as described above.

[0088] The structure of the present invention may be manufactured by methods other than those described above. For example, the structure of the present invention may be obtained by mixing a cellulose nanofiber solution with at least one selected from the group consisting of a surface treatment agent, a crosslinking agent, and a surface protective agent, and then subjecting the cellulose nanofiber solution to the above liquid filling step.

[0089] The present invention will be described in more detail below based on the following examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0090] [Example 1] [Preparation of Cellulose Nanofibers] 10 g of coniferous kraft pulp was suspended in 1000 g of pure water in which 0.16 g of TEMPO and 1 g of sodium bromide were dissolved. 25 g of a 2 M sodium hypochlorite aqueous solution was added to initiate the oxidation reaction. The temperature in the reaction system was maintained at 25°C, and the pH in the system was maintained at 10 by adding a 0.5 M sodium hydroxide aqueous solution during the reaction. After 2 hours, the oxidation reaction was stopped by adding approximately 100 mL of ethanol to the reaction system. Subsequently, filtration and washing were repeatedly performed using a glass filter with pure water to obtain oxidized cellulose. The obtained oxidized cellulose was passed through a high-pressure homogenizer in 3 passes to prepare a dispersion containing 1% by mass of cellulose nanofibers (cellulose nanofiber dispersion). The obtained cellulose nanofibers had a carboxyl group content of 1.5 mmol / g, a fiber diameter of 3 nm, and a fiber length of 500 nm.

[0091] [Preparation of Cellulose Nanofiber Solution] The cellulose nanofiber dispersion prepared above was mixed with pure water and stirred to prepare a 0.35% by mass cellulose nanofiber solution 1.

[0092] [Preparation of structural precursor] Polyester fibers (QonPET, manufactured by Ribgraphy Co., Ltd.) were cut into a circular shape (40 mm in diameter, 5 mm in thickness) to prepare a porous body 1 having voids consisting of continuous holes. The cellulose nanofiber solution 1 prepared above was dropped onto the porous body 1, and the dropping was continued until the porous body 1 was completely immersed in the cellulose nanofiber solution 1 (liquid filling step). With the porous body 1 completely immersed, it was left to stand in a sealed container for 12 hours. After standing, it was moved to an open environment and dried at room temperature (23°C) and relative humidity of 40-60 RH% for 48 hours to remove moisture (drying step), thereby preparing the structural precursor 1.

[0093] [Preparation of Structure] The obtained structure precursor 1 was placed in a sealed chamber, and 100 mg of trimethoxyheptadecafluorodecylsilane was added as a surface modifier. The chamber was kept warm at 60°C for 1 hour, and triethoxyheptadecafluorodecylsilane was supplied to structure precursor 1 to obtain structure 1. In the table below, triethoxyheptadecafluorodecylsilane will be referred to as "silane coupling agent 1". Triethoxyheptadecafluorodecylsilane has the structure represented by formula (A1) above, and Cp in formula (A1) is the group represented by formula (A2) above. Furthermore, triethoxyheptadecafluorodecylsilane has a structure in which R in formula (A1) includes a fluoride alkyl group structure, and is a compound represented by formula (A3) above. The SP value of triethoxyheptadecafluorodecylsilane is 6.36 (cal / cm²). ３ ) １／２ That is the case.

[0094] [Example 2] Structure 2 was obtained by contacting the structure precursor 1 obtained in the above procedure with a treatment agent containing a solvent. Specifically, a solution containing 5% by mass of vinyltriethoxysilane was adjusted to a pH of 3.5 with acetic acid and dissolved in water to obtain a treatment agent containing a solvent (acetic acid content: 0.18% by mass). Structure precursor 1 was immersed in the obtained solvent-containing treatment agent for 2 hours, and after immersion, it was washed with deionized water. After washing, the liquid was drained and then air-dried to obtain structure 2. In the table below, vinyltriethoxysilane will be referred to as "silane coupling agent 2". The SP value of vinyltriethoxysilane is 7.76 (cal / cm²). ３ ) １／２ That is the case.

[0095] [Example 3] The structural precursor 1 obtained by the above procedure was immersed for 2 hours in an anhydrous N,N-dimethylacetamide solution of acrylic acid chloride (concentration of acrylic acid chloride: 0.18 mol / L), and after immersion, it was washed twice with deionized water. After washing, the liquid was drained and then air-dried to obtain structure 3.

[0096] [Example 4] The structural precursor 1 obtained by the above procedure was immersed in a 1 mol / L aqueous solution of aluminum chloride, and after immersion, it was washed with deionized water. After washing, the liquid was drained, and then it was dried by air to obtain structural 4.

[0097] [Example 5] The structural precursor 1 obtained by the above procedure was immersed in an alkyl ketene dimer (AKD)-based sizing agent solution, and excess solution was removed by dropwise addition. The structural precursor 1 immersed in the AKD-based sizing agent solution was dried at 80°C for 30 minutes to obtain structure 5. As the AKD-based sizing agent solution, SE2360 from Seikoh PMC was used, diluted three times with pure water.

[0098] [Example 6] Structure precursor 6 was obtained in the same manner as in Example 1, except that the drying step for obtaining structure precursor 1 was performed by freeze-drying as described below. Freeze-drying was performed by freezing with liquid nitrogen for 1 minute, followed by drying under reduced pressure of 100 Pa for 12 hours. Structure 6 was obtained in the same manner as in Example 1, except that structure precursor 6 was used in place of structure precursor 1.

[0099] [Example 7] A structural precursor 7 was obtained in the same manner as the procedure for obtaining structural precursor 1, except that a porous body 7 having voids consisting of continuous holes, cut from glass wool (Paraboard GW32k25t, manufactured by Paramount Glass Industry Co., Ltd.), was used instead of the porous body 1. A structure 7 was fabricated in the same manner as in Example 4, except that structural precursor 7 was used.

[0100] [Comparative Example 1] The above structural precursor 1 was used as comparative structure C1.

[0101] [Comparative Example 2] The porous material 1 used to produce the above-mentioned structural precursor 1 was used as comparative structure C2.

[0102] [Comparative Example 3] The above structural precursor 5 was used as comparative structure C3.

[0103] [Measurement] [Thin Film Section] The presence or absence of a thin film section in each structure was measured using the method described above. The measurement results are shown in the table below.

[0104] [Transmission Loss and Sound Absorption Coefficient] The transmission loss TL (unit: dB) and sound absorption coefficient a of each structure were measured using the method described above.

[0105] [Evaluation] A moist heat endurance test was performed on each structure using a high-temperature constant humidity test chamber. The moist heat endurance of each structure was evaluated from the changes in transmission loss TL and sound absorption coefficient a (ΔTL and Δa) before and after the moist heat endurance test. The moist heat endurance test was performed by leaving each structure undisturbed for 1000 hours in an environment of 85°C and 85% relative humidity. The measurement methods for transmission loss TL and sound absorption coefficient a are as described above. ΔTL is TL １ This is the transmission loss before the moist heat endurance test, and TL ２ The transmission loss after the transmission loss test can be calculated using the following equation (1): Equation (1) ΔTL = (TL １ -TL ２ ) / TL １ Also, Δa is a １ Let be the transmission loss before the moist heat endurance test, a ２ The transmission loss after the transmission loss test can be calculated using the following equation (2): Equation (2) Δa = (a １ -a ２ ) / a １ The moisture heat resistance was evaluated based on the above ΔTL and Δa according to the following criteria: • A: Both ΔTL and Δa are less than 3% • B: Both ΔTL and Δa are less than 10%, and at least one of ΔTL and Δa is 3% or more • C: Both ΔTL and Δa are less than 20%, and at least one of ΔTL and Δa is 10% or more • D: At least one of ΔTL and Δa is 20% or more In practical terms, an A or B rating is preferable, with an A rating being more preferable.

[0106] [Results] The fabrication method, measurement results, and evaluation results for each structure are shown in Table 1 below. In Table 1, AKD refers to the alkyl ketene dimer-based sizing agent described above.

[0107]

[0108] The results shown in Table 1 confirm that when the structure has a porous body with voids consisting of continuous holes and cellulose nanofibers, and further includes at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents, it exhibits excellent humid heat resistance (Examples 1-7). On the other hand, when the structure does not include at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents, it exhibits inferior humid heat resistance compared to the structures of the examples (Comparative Examples 1-3). A comparison between Example 6 and Example 1 confirms that when the structure includes a thin film, the transmission loss TL and sound absorption coefficient a are superior. Furthermore, it was confirmed that when the structure includes a thin film, it also exhibits superior humid heat resistance.

[0109] 1. Void 2. Fiber 3. Porous body 4. Thin film portion 10. Structure

Claims

1. A structure comprising a porous body having voids consisting of continuous pores, cellulose nanofibers, and further comprising at least one selected from the group consisting of surface modifiers, crosslinking agents, and surface protective agents.

2. The structure according to claim 1, having a thin film portion formed in at least a part of the void.

3. The structure according to claim 1 or 2, comprising the surface modifier, wherein the surface modifier has a structure represented by the following formula (A1). In formula (A1), Cp represents a group that can react with the cellulose nanofiber to form a chemical bond. If there are multiple Cp groups, they may be the same or different from one another. Sp represents a divalent linking group or single bond which may have substituents. n represents an integer from 1 to 8. R represents an n-valent group.

4. The structure according to claim 3, wherein Cp in formula (A1) represents a group selected from the group consisting of an alkoxysilyl group, a trialkylsilyl group, an epoxy group, a carboxychloride group, an acid anhydride group, an isocyanate group, a thioisocyanate group, and a boronic acid group.

5. The structure according to claim 3, wherein Cp in formula (A1) is a group represented by the following formula (A2). In formula (A2), R ａ R represents an alkyl group having 1 to 4 carbon atoms. ａ If there are multiple instances, they may be identical or different from one another. ｂ R represents an alkyl group having 1 to 4 carbon atoms. ｂ If there are multiple elements, they may be the same or they may be different from one another. p represents an integer from 0 to 3. * represents the bonding position with Sp in the above formula (A1).

6. The structure according to claim 3, wherein R in formula (A1) is an n-valent hydrocarbon group having 1 to 20 carbon atoms, which may have substituents.

7. The structure according to claim 3, wherein R in formula (A1) includes a fluoride alkyl group structure.

8. The structure according to claim 7, wherein the number of carbon atoms in the alkyl fluoride structure is 4 to 12.

9. The structure according to claim 1 or 2, wherein the surface modifier comprises a compound represented by the following formula (A3). In formula (A3), R ａ R represents an alkyl group having 1 to 4 carbon atoms. ａ If there are multiple instances, they may be identical or different from one another. ｂ R represents an alkyl group having 1 to 4 carbon atoms. ｂ If there are multiple values, they may be the same or different from each other. p represents an integer from 1 to 3. q represents an integer from 0 to 10. r represents an integer from 0 to 19. X represents a hydrogen atom or a fluorine atom.

10. The SP value of the compound represented by the formula (A1) is 5.0 to 11.0 (cal / cm ３ ). １／２ The structure according to claim 3, wherein the structure is as defined above.

11. The structure according to claim 1 or 2, comprising the crosslinking agent, wherein the crosslinking agent is a polyvalent metal salt.

12. The structure according to claim 11, wherein the metal element contained in the polyvalent metal salt is at least one selected from the group consisting of magnesium, calcium, and aluminum.

13. The structure according to claim 1 or 2, comprising the surface protective agent, wherein the surface protective agent is at least one selected from the group consisting of sizing agents and hydrophobic agents.

14. The aforementioned structure 1 cm ３ The amount of cellulose nanofiber per unit is 1.0 × 10 －３ g / cm ３ The structure according to claim 1 or 2.

15. The structure according to claim 1 or 2, wherein the porous body includes fibers.

16. The structure according to claim 15, wherein the fiber is at least one fiber selected from the group consisting of polyester, glass fiber, and cellulose.

17. The density of the porous material is 10 kg / m³ ３ The structure according to claim 1 or 2.

18. The structure according to claim 1 or 2, having a film-like or board-like shape.

19. Surface density is 0.1 kg / m³ ２ The structure according to claim 1 or 2.

20. The structure according to claim 19, wherein the transmission loss at 2000 Hz is 3 dB or more.

21. The structure according to claim 19, wherein the sound absorption coefficient at 2000 Hz is 0.3 or more.

22. The structure according to claim 1 or 2, for use as a sound-insulating or sound-absorbing material.

23. A method for manufacturing a structure according to claim 1 or 2, comprising contacting a structural precursor having a porous body with voids consisting of continuous holes and cellulose nanofibers with at least one selected from the group consisting of a surface modifier, a crosslinking agent, and a surface protective agent to obtain the structure.

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