JP5993411B2 - Porous material and method for producing the same - Google Patents

Description

  The present invention relates to a porous body comprising cellulosic nanofibers.

  With the progress of industrial use of nanotechnology, recent advances in nanofiber utilization technology are remarkable. Nanofibers generally have a number average fiber diameter in the range of 1 to 100 nm. However, at present, in the nanofiber manufacturing technology including electrospinning, the number average fiber diameter often exceeds 100 nm. In such technical trends, the present inventors have examined the use of cellulosic nanofibers having a number average fiber diameter of 1 to 100 nm.

  In this specification, the cellulosic nanofibers are (1) fine cellulose nanofibers (cellulose fibers) having a number average fiber diameter of 1 to 100 nm or (2) fine cellulose nanofibers chemically treated (modified). Say. As the cellulose nanofiber (1), for example, microfibrated cellulose (hereinafter abbreviated as MFC) having a number average fiber diameter of 100 nm or less obtained by shearing and defibrating cellulose fibers under high pressure or a microorganism is produced. Bacterial cellulose having a fine network structure with a number average fiber diameter of 100 nm or less (hereinafter abbreviated as BC). Examples of the modified cellulose nanofibers (2) include cellulose nanowhiskers (hereinafter abbreviated as CNW) or wood pulp obtained by treating natural cellulose with 40% or more concentrated sulfuric acid. Microfibers having an average fiber diameter of about 3 to 5 nm and isolated as an aqueous dispersion by mild chemical treatment and mild mechanical treatment at normal temperature and normal pressure, and fine cellulose fibers having a uniform fiber diameter (for example, (See Patent Document 1).

  Cellulosic nanofibers are derived from plants or organisms, and therefore have a feature that the burden on the environment during production and disposal is smaller than nanofibers made of petroleum-derived thermoplastic polymers. Therefore, it is expected that a porous body is formed using cellulose-based nanofibers and applied to various fields and applications such as functional filters, wiping materials, electronic device materials, and regenerative medical materials.

  As a method of forming a porous body using nanofibers, for example, a film obtained by coating a dispersion obtained by dispersing fine cellulose fibers (cellulosic nanofibers) in water, an organic solvent or a mixed solvent thereof by a coating method or a papermaking method. And the technique of obtaining a nonwoven fabric is disclosed (for example, refer patent document 2). However, due to the cohesive strength of cellulose nanofibers, a dried product obtained by drying an aqueous dispersion of cellulose nanofibers becomes a film having a high gas barrier property (for example, Patent Document 3). (See Non-Patent Document 1). In Patent Document 2, as a means for obtaining a porous body that is permeable to gas or liquid, a higher porosity than in the case where the dispersion medium is water by using a hydrophobic organic solvent as the dispersion medium in the coating method. It is disclosed that a nonwoven fabric having a rate can be obtained. Further, in the papermaking method, it is disclosed that a non-woven fabric having a higher porosity can be obtained by substituting the dispersion medium from water to an organic solvent and then drying, rather than using water as the dispersion medium and heat drying as it is. Has been.

  A method for producing a nanofiber structure in which nanofibers are attached to a support in a network form by attaching a dispersion of nanofibers made of a thermoplastic polymer to the support and naturally drying or thermally drying the dispersion medium. (For example, refer to Patent Document 4). In addition, by attaching a nanofiber dispersion to the support and freeze-drying the dispersion medium, the nanofiber has a three-dimensional network structure in the pores of the support, and the collection efficiency and air permeability of the fine particles are improved. A higher porous body and a method for producing the same are disclosed (for example, see Patent Document 5).

  In addition, in the method for producing a fine fibrous cellulose sheet, as a method for solving the phenomenon that fine fibrous cellulose becomes difficult to be dehydrated due to high density during suction filtration, by blending a cellulose coagulant with fine fibrous cellulose, A technique that facilitates dehydration is disclosed because fine fibrous cellulose forms a network, and the network maintains the voids contained in the network without being crushed by the pressure of suction filtration (for example, Patent Document 6). See).

JP 2008-1728 A WO2006 / 004012 Publication JP 2009-57552 A JP 2005-330639 A JP 2008-101315 A JP 2010-168716 A

Biomacromolecules, 10, 162-165 (2009)

  As described above, development of a porous body using a fluid-permeable cellulose nanofiber that can be mass-produced at low cost is desired from the viewpoint of expanding application development of the cellulose nanofiber. However, at present, there is no method that can mass-produce a porous body using a fluid-permeable cellulose nanofiber at low cost.

  In the cellulose-based nanofiber having a number average fiber diameter of several nanometers described in Patent Document 1, a part or all of the C6 hydroxyl group of the cellulose molecule on the fiber surface is substituted with a carboxyl group having higher hydrophilicity than the hydroxyl group. Further, since the surface free energy per unit mass generally increases as the fiber diameter becomes thinner, the cohesive force between fibers that stabilizes the surface when dried increases. Therefore, when the aqueous dispersion of cellulose-based nanofibers described in Patent Document 1 is dried as it is, it is agglomerated due to hydrophilicity derived from cellulose hydroxyl groups and carboxyl groups and strong surface tension of water, and has a network structure. It is difficult to obtain a mass.

  In the method of using an organic solvent as a dispersion medium such as Patent Document 2 and the method of drying after replacing the dispersion medium with an organic solvent, special consideration must be given to the environment in consideration of implementation at an industrial level. I must. The total amount of organic solvent used must be recovered from the environment and facilities, including the fact that the entire amount must be recovered, the facility to handle flammable liquids, and the health of workers. There is a problem of not getting.

  Patent Document 4 discloses a method for producing a nanofiber structure in which nanofibers made of a thermoplastic polymer are attached to a support in a network form. Nanofibers made of a thermoplastic polymer and cellulose-based nanofibers are Since the surface states are different, the means for dispersing the cellulose nanofibers in the dispersion medium is different from the means for dispersing the nanofibers made of the thermoplastic polymer in the dispersion medium. In addition, freeze-drying including Patent Document 5 requires high pressure because a decompression device is required, continuous production cannot be performed, energy consumption is large compared to thermal drying, and sublimation of the dispersion medium takes time. It becomes. Patent Document 6 discloses a method for efficiently producing a fine fibrous cellulose sheet by utilizing the formation of a network of fine fibrous cellulose, but the fine fibrous cellulose sheet obtained by drying is disclosed. Is not a porous body.

  An object of the present invention is to provide a fluid-permeable porous body containing a cellulose nanofiber having a very small fiber diameter and high hydrophilicity, and to produce the porous body at low cost.

  As a result of repeated studies to solve the above problems, the present inventors have completed the present invention. That is, by arranging cellulose nanofibers having a number average fiber diameter of 1 to 100 nm in pores of a porous support body in which a large number of pores communicate with each other, a network composed of cellulose nanofibers is stretched. It was found that a porous body having a different structure can be obtained. Moreover, the dispersion medium is obtained by drying a nanofiber dispersion liquid in which cellulose nanofibers having a number average fiber diameter of 1 to 100 nm are dispersed in a dispersion medium in a state where the nanofiber dispersion is attached to a porous support having a large number of pores in communication. It has been found that a porous body can be obtained by using a production method for removing the.

The porous body according to the present invention is a porous body in which nanofibers are entangled to form a network structure in the pores of a porous support body in which a large number of pores communicate with each other. And the number average fiber diameter is 1 to 4 nm, the average pore diameter of the support is 0.01 to 0.8 μm, and the network structure is composed of the nanofibers. The mesh is stretched in the hole of the support member, traverses the hole, and is not laminated on the surface of the portion excluding the hole of the support member .

  In the porous body according to the present invention, the support is preferably either a porous film or a fiber sheet. Cellulosic nanofibers can easily form a network-like nanofiber structure in the pores of the support, and can maintain a network structure even after drying.

  In the porous body according to the present invention, the average pore diameter of the support is preferably 0.01 to 20 μm. Cellulosic nanofibers can easily form a network-like nanofiber structure in the pores of the support, and can disperse the cohesive force generated on the nanofibers during drying. The structure can be maintained.

  In the porous body according to the present invention, the network structure contains a surfactant, and the content of the surfactant is 0.10 to 10% in terms of solid content with respect to the dry mass of the nanofiber. It is preferable that it is 100 mass%. It is possible to weaken the aggregation of cellulosic nanofibers during drying and maintain a network structure.

In the porous body according to the present invention, the surfactant is preferably a cationic surfactant. Easily adsorbed on the surface of the cellulose-based nanofibers, the effect of weakening the aggregation of cellulose nanofibers after drying of Ru more Takama.

The method for producing a porous body according to the present invention is a method for producing a porous body according to the present invention, wherein a nanofiber dispersion in which cellulose nanofibers having a number average fiber diameter of 1 to 4 nm are dispersed in a dispersion medium. A step of preparing a dispersion, and the dispersion is attached to a porous support having a large number of pores in communication and an average pore diameter of 0.01 to 0.8 μm. An adhesion step of forming a thin film of the dispersion in the pores of the body; and a drying step of drying the support to which the dispersion is adhered to remove the dispersion medium.

  In the method for producing a porous body according to the present invention, the dispersion medium is preferably water. Excellent in terms of safety, environment and facilities.

  In the method for producing a porous body according to the present invention, the dispersion preferably contains the nanofiber in a concentration of 0.001 to 0.500% by mass with respect to the total mass of the dispersion. A nanofiber network structure can be efficiently formed in the pores of the support.

In the method for producing a porous body according to the present invention, the dispersion further contains a surfactant, and the surfactant is contained in a concentration of 0.0001 to 1. It is preferable to contain 0000 mass%. It is possible to weaken the aggregation of cellulosic nanofibers during drying and maintain a network structure. In the method for producing a porous body according to the present invention, it is preferable that a removal step of removing the dispersion liquid attached to the surface of the support is provided between the attachment step and the drying step.

  INDUSTRIAL APPLICABILITY The present invention can provide a fluid-permeable porous body including a cellulose nanofiber having a very small fiber diameter and high hydrophilicity, and can produce the porous body at low cost. Further, the porous body according to the present invention can increase the surface area because the nanofibers are entangled in the pores of the porous support body in which a large number of pores communicate with each other to form a network structure. it can.

1 is a view showing an observation image by SEM of a porous body having a network structure of cellulosic nanofibers of Example 1. FIG. It is a figure which shows the observation image by SEM of the porous body which has the network-like structure body of the cellulose nanofiber of Example 6. FIG. FIG. 6 is a view showing an observation image by SEM of a porous body having a network structure of cellulose nanofibers of Example 8.

  Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

  The porous body according to the present embodiment is a porous body in which nanofibers are intertwined to form a network structure in the pores of a porous support body in which a large number of pores communicate with each other. And a number average fiber diameter of 1 to 100 nm.

<Cellulose nanofiber>
In the present embodiment, the cellulose-based nanofiber includes a cellulose nanofiber or a chemically treated (modified) cellulose nanofiber. Cellulose nanofibers form a bundle of two or more cellulose molecules. The phrase “cellulose molecules form a bundle of two or more” refers to a state in which two or more cellulose molecules are aggregated to form an aggregate called microfibril. In the present embodiment, the cellulose molecule is one in which part or all of the hydroxyl group at the C6 position in the molecule is oxidized to an aldehyde group, a carboxyl group or the like, or part or all of the hydroxyl group containing a hydroxyl group other than the C6 position is a nitrate ester. It includes forms substituted with other functional groups such as those esterified such as acetate and those etherified such as methyl ether, hydroxypropyl ether and carboxymethyl ether.

  The number average fiber diameter of the cellulosic nanofiber is in the range of 1 to 100 nm. The number average fiber diameter of the nanofiber is more preferably 1.5 to 50 nm, and particularly preferably 2 to 10 nm. When the number average fiber diameter is less than 1 nm, the single fiber strength of the nanofibers is weak, and a network structure cannot be formed. If it exceeds 100 nm, it is difficult to form a network structure in the pores. Here, the number average fiber diameter is calculated according to the following. Cellulosic nanofibers cast on a carbon film-coated grid are observed with an electron microscope image using a transmission electron microscope (TEM). Random axes of 2 vertical and horizontal axes are drawn per image, and the fiber diameter of the fiber intersecting the axis is visually read. At this time, it is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. In addition, a sample or a magnification shall be the conditions on which 20 or more fibers intersect the axis. In this way, at least three images of the non-overlapping surface portion are taken with an electron microscope, and the value of the fiber diameter of the fiber intersecting each of the two axes is read. Therefore, at least 20 pieces × 2 × 3 = 120 pieces of fiber information are obtained. The number average fiber diameter was calculated from the fiber diameter data thus obtained.

  Nanofibers are dispersed in a dispersion medium. The form of the nanofibers in the dispersion is, for example, a form in which the nanofibers are dispersed separately or a form in which the fibers are partially aggregated. The number average fiber length of the nanofibers is preferably 0.05 to 20 μm. More preferably, it is 0.10-10 micrometers. When the number average fiber length is less than 0.05 μm, the nanofibers are close to particles and it is difficult to form a network structure. When it exceeds 20 μm, the entanglement between the nanofibers increases and there is a possibility of forming an aggregate. The number average fiber length is calculated by observing an electron microscope image using a scanning electron microscope (SEM, Scanning Electron Microscope) obtained by thinly casting a cellulose nanofiber dispersion on a substrate and freeze-drying it. Ten independent fibers are randomly selected for each observed image, and the fiber length is read visually. At this time, it is performed at a magnification of either 5000 times or 10000 times depending on the length of the constituent fibers. Note that the sample or the magnification is the one in which the start point and the end point of the fiber are within the same image. In this way, a minimum of 12 non-overlapping surface images are taken with an SEM and the fiber length is read. Accordingly, at least 10 × 12 = 120 pieces of fiber information can be obtained. The number average fiber length can be calculated from the fiber diameter data thus obtained. The cross-sectional shape of the nanofiber is, for example, a circular shape, an elliptical shape, a flat shape, a quadrangular shape, a triangular shape, or a rhombus shape. Among these, a rectangular shape is preferable. In addition, this embodiment is not restrict | limited to the number average fiber length and cross-sectional shape of a nanofiber.

  The kind of nanofiber is, for example, the above-mentioned MFC, BC, CNW, and cellulose-based nanofiber described in Patent Document 1. MFC is characterized in that the fiber diameter distribution is wide because cellulose fibers are sheared by mechanical processing into nanofibers. BC is characterized by having a relatively uniform fiber diameter. CNW has a relatively uniform fiber diameter, but is characterized by a short fiber length of 0.1 to 0.2 μm. As described in Patent Document 1, the cellulose-based nanofiber described in Patent Document 1 oxidizes a cellulosic raw material using an oxidizing agent in the presence of an N-oxyl compound, bromide, iodide, or a mixture thereof. In addition, the oxidized cellulose is further processed by wet atomization, fibrillated, and converted into nanofibers, which are produced as an aqueous dispersion and have a uniform fiber diameter. Among these, the fine cellulose described in Patent Document 1 is particularly preferable because it requires less energy than other cellulose fibers and has high productivity.

  The cellulose-based nanofiber described in Patent Document 1 is a cellulose single microfibril. In natural cellulose, microfibrils are bundled to form a high-order solid structure. Here, the microfibrils are strongly aggregated by the hydrogen bond derived from the hydroxyl group in the cellulose molecule. Cellulose single microfibrils refer to microfibrils isolated by subjecting natural cellulose to chemical treatment and light mechanical treatment. In the cellulose-based nanofiber described in Patent Document 1, a part of the hydroxyl group of the cellulose molecule is oxidized to at least one functional group selected from the group consisting of a carboxyl group and an aldehyde group, and a cellulose I-type crystal structure is obtained. Have. The maximum fiber diameter is 1000 nm or less. This cellulose nanofiber becomes a transparent liquid when dispersed in water.

  The cellulose raw material used as the raw material of the cellulose nanofiber is not particularly limited. For example, kraft pulp derived from various woods such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), sulfite pulp, Waste paper pulp such as deinked pulp (DIP), ground pulp (GP), pressurized groundwood pulp (PGW), refiner groundwood pulp (RMP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), chemimechanical pulp (CMP), mechanical pulp such as Chemi-Grand Pulp (CGP), powdered cellulose obtained by pulverizing them with a high-pressure homogenizer, a mill or the like, and microcrystalline cellulose powder purified by chemical treatment such as acid hydrolysis can be used. Plants such as kenaf, hemp, rice, bagasse, bamboo, and cotton can also be used. This embodiment is not limited to the raw material and manufacturing method of nanofibers.

  The manufacturing method of a nanofiber is the manufacturing method described in patent document 1, for example. According to Patent Document 1, a method for producing nanofibers uses natural cellulose as a raw material, N-oxyl compound as an oxidation catalyst in water, and oxidizes the natural cellulose by acting a co-oxidant to obtain a reactant fiber. An oxidation reaction step, a purification step for obtaining a reaction product fiber impregnated with water by removing impurities, a dispersion step for dispersing the reaction product fiber impregnated with water in a dispersion medium, and a dispersion obtained in the dispersion step A drying step of drying the dispersion medium from the body.

  In the oxidation reaction step, a dispersion in which natural cellulose is dispersed in water is prepared. The dispersion medium of natural cellulose in the reaction is water. And the natural cellulose density | concentration in reaction aqueous solution is arbitrary if it is a density | concentration in which sufficient spreading | diffusion of a reagent is possible, Usually, it is 5 mass% or less with respect to the mass of reaction aqueous solution.

  Numerous N-oxyl compounds that can be used as oxidation catalysts for cellulose have been reported ("Cellulose" Vol. 10, 2003, pages 335 to 341, using "TEMPO derivatives by I. Shibata and A. Isogai. Article entitled “Catalyzed Oxidation of Cellulose: HPSEC and NMR Analysis of Oxidation Products”). Among these, TEMPO, 4-acetamido-TEMPO, 4-carboxy-TEMPO, and 4-phosphonooxy-TEMPO are particularly preferable in the reaction rate at room temperature in water. A catalytic amount is sufficient for the addition of these N-oxyl compounds. That is, it is added to the reaction aqueous solution preferably in the range of 0.1 to 4 mmol / l, more preferably 0.2 to 2 mmol / l. If it is less than 0.1 mmol / l, the catalytic effect may be inferior. If it exceeds 4 mmol / l, it may become insoluble in water.

  The co-oxidant is, for example, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, and a perorganic acid. Alkali metal hypohalite is preferable. Examples of the alkali metal hypohalite are sodium hypochlorite and sodium hypobromite. When sodium hypochlorite is used, it is preferable in terms of reaction rate to advance the reaction in the presence of an alkali metal bromide such as sodium bromide. The amount of the alkali metal bromide added is preferably 1 to 40 times the molar amount of the N-oxyl compound. More preferably, it is 10 to 20 times the molar amount. If the amount is less than 1 time, the reaction rate may be inferior. When the amount exceeds 40 times mol, the reaction rate may be inferior. The pH of the aqueous reaction solution is preferably maintained in the range of 8-11. Although the temperature of aqueous solution is arbitrary in 4-40 degreeC, reaction can be performed at room temperature and does not require temperature control especially. The amount of the co-oxidant added is preferably in the range of 0.5 to 8 mmol with respect to 1 g of natural cellulose. The reaction is preferably 5 to 120 minutes, and is completed within 240 minutes at the longest.

  The purification step is a step of removing impurities such as unreacted hypochlorous acid and various by-products from the oxidized cellulose slurry obtained in the oxidation reaction step. In the stage after the oxidation reaction step, since the nanofiber unit is not normally dispersed, the normal purification method, that is, the water washing step and the filtration step is repeated to obtain a high purity (99% by mass or more). Let it be a refined oxidized cellulose slurry. The purified oxidized cellulose slurry thus obtained is preferably in the range of 10 to 50% by mass as the solid content (cellulose) concentration in a squeezed state. More preferably, it is 15-30 mass%. Considering a dispersion step performed later, a solid content concentration higher than 50% by mass is not preferable because extremely high energy is required for dispersion.

  In the dispersion step, the oxidized cellulose slurry obtained in the purification step is further dispersed in a dispersion medium to obtain a cellulose-based nanofiber dispersion. As the dispersion medium, a dispersion medium exemplified as a dispersion medium that can be used in the dispersion liquid preparation step of the porous body production method described later can be used. As the disperser, a general-purpose disperser as an industrial production machine can be used. General-purpose dispersers are, for example, screw-type mixers, paddle mixers, disper-type mixers, and turbine-type mixers. In addition, the use of more powerful and defeating devices such as homomixers, high-pressure homogenizers, ultra-high-pressure homogenizers, ultrasonic dispersion processing, beaters, disc type refiners, conical type refiners, double disc type refiners, and grinders under high-speed rotation. By doing so, more efficient and advanced downsizing becomes possible.

  The drying step is a step of drying the cellulose nanofiber dispersion obtained in the dispersion step to remove the dispersion medium and separating the fine cellulose fibers. For example, when the dispersion medium of the dispersion is water, the drying method is a freeze-drying method. When the dispersion medium of the dispersion is a mixed solution of water and an organic solvent, drying with a drum dryer, spray dryer is used. By spray drying.

<Porous support>
In the present embodiment, the support is porous with many pores communicating with each other. Here, the term “pores” includes both regularly formed micropores or voids between fibers formed by intertwining fibers. The term “hole communicates” refers to a state in which a void is continuously connected linearly or curvedly from one surface to the other surface. The support is not particularly limited as long as it has a porous structure in which a large number of pores communicate with each other. For example, a fiber sheet obtained by processing fibers such as nonwoven fabric, paper, woven fabric, and knitted fabric into a sheet, porous film, porous ceramic, sponge, and the like. These are a composite of many voids communicating with each other. The fiber sheet is, for example, an inorganic fiber sheet, a chemical fiber sheet, a natural fiber sheet, or a metal fiber sheet. The inorganic fiber sheet is, for example, a glass fiber sheet or a carbon fiber sheet. The chemical fiber sheet is, for example, a regenerated fiber sheet made of cellulose such as rayon, cupra, and tencel, a semi-synthetic fiber sheet made of chemically treated cellulose such as acetate, polyamide, vinylon, polyester, polyvinylidene chloride, A synthetic fiber (organic fiber) sheet made from a thermoplastic resin such as acrylic, polyolefin, or aramid. The natural fiber sheet is, for example, a vegetable fiber sheet such as cotton, hemp, or linen, or an animal fiber sheet such as wool, silk, or cashmere. The metal fiber sheet is, for example, stainless steel, iron, gold, silver, or aluminum. The porous film is, for example, a membrane filter.

  In the porous body according to the present embodiment, the average pore diameter of the support is preferably 0.1 to 20 μm. More preferably, it is 0.5-10 micrometers. If it is less than 0.1 μm, the fluid permeability may be inferior. If it exceeds 20 μm, it may be difficult for the cellulose-based nanofibers to form a network structure uniformly in the pores of the support. Here, the average pore diameter is a value measured according to ASTM E1294-89 “Half Dry Method”.

  The support has an air permeability resistance (Oken) measured according to JIS P 8117: 2009 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method” of 10,000 s or less. preferable. More preferably, it is 100 s or less. If it exceeds 10,000 s, the fluid permeability of the porous body may be lowered.

  When the nanofiber dispersion medium is water, the support is desirably hydrophilic. If the support is hydrophobic, the dispersion will not easily penetrate into the interior. In the porous body according to the present embodiment, the support is preferably either a porous film or a fiber sheet. Since the porous film or the fiber sheet can be easily selected from those having different hole shapes and sizes, the amount and speed at which the dispersion penetrates into the pores of the support can be controlled, and the pores are more uniform in the pores. A network-like nanofiber structure can be easily formed, and the network structure can be maintained even after drying.

  A porous film has micropores of various shapes as pores. The material of the porous film is not particularly limited in the present embodiment, and examples thereof include cellulose, cellulose mixed ester, cellulose acetate, polyethylene, polypropylene, polyurethane, polystyrene, polyester, and polycarbonate. A polycarbonate membrane filter is more preferable in that the pore diameter is uniform. The average pore diameter of the porous film is preferably 0.1 to 20 μm. More preferably, it is 0.5-10 micrometers. If it is less than 0.1 μm, the fluid permeability may be inferior. If it exceeds 20 μm, it may be difficult for the cellulose-based nanofibers to form a network structure uniformly in the pores of the support.

  A fiber sheet has the space | gap between the fibers formed by the fiber entangled as a hole. Although the material of a fiber sheet is not specifically limited in this embodiment, It is more preferable that it is glass fiber at the point used as the fiber sheet material which has a smaller hole diameter, without reducing fluid permeability. The average pore diameter of the fiber sheet is preferably 0.1 to 20 μm. More preferably, it is 0.5-10 micrometers. If it is less than 0.1 μm, the fluid permeability may be inferior. If it exceeds 20 μm, it may be difficult for the cellulose-based nanofibers to form a network structure uniformly in the pores of the support.

The basis weight of the fiber sheet is preferably 10 to 1000 g / m ² . More preferably 40~200g / ^{m 2.} If it is less than 10 g / m ² , the physical strength may be insufficient. If it exceeds 1000 g / m ² , the fluid permeability may be inferior.

<Surfactant>
In the porous body according to the present embodiment, the network structure contains a surfactant, and the content of the surfactant is 0.10 to 100 mass in solid concentration with respect to the dry mass of the nanofiber. % Is preferred. More preferably, it is 0.5-50.0 mass%. Especially preferably, it is 1-40 mass%. If it is less than 0.10% by mass, the effect of adding the surfactant may not be obtained. If it exceeds 100% by mass, it may be difficult for the cellulosic nanofibers to maintain the fiber state.

  In the present embodiment, a cationic surfactant, an anionic surfactant, a nonionic surfactant, or an amphoteric surfactant can be used as the surfactant. In the porous body according to the present embodiment, the surfactant is preferably a cationic surfactant. Since the surface of the cellulosic nanofiber is anionic, the cationic surfactant is easily adsorbed on the surface of the nanofiber, and the effect of weakening the aggregation of the cellulosic nanofibers during drying is further enhanced. Cationic surfactants are, for example, quaternary ammonium salts, alkylamine salts, sulfonium salts, and phosphonium salts. In view of high water solubility, a quaternary ammonium salt is more preferable. Surfactants have the effect of reducing the surface tension of the liquid, and the hydrophilic part of the surfactant is adsorbed to the cellulose nanofibers, and the hydrophobic part is directed outwards. It is thought that it works to weaken the aggregation between fibers.

  The porous body according to this embodiment has an air permeability resistance (Oken) measured in accordance with JIS P 8117: 2009 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method”. It is preferable that it is 10,000 s or less. More preferably, it is 100 s or less. If it exceeds 10,000 s, fluid permeability may be inferior.

  In the porous body according to the present embodiment, the network formation rate is preferably 10% or more. More preferably, it is 50% or more. If it is less than 10%, the effect of forming the network structure may be inferior. Here, the network formation rate is determined by selecting an arbitrary area of 10 μm × 10 μm from the electron microscope image obtained using the SEM on the surface of the porous body, and the network structure with respect to the number of holes present therein. The ratio of the number of holes formed was calculated. This operation was carried out at any five locations, and the average value was determined.

  The porous body according to the present embodiment preferably has a porosity of 10 to 99%. More preferably, it is 50 to 90%. If it is less than 10%, the fluid permeability may be inferior. If it exceeds 99%, the physical strength may be weakened. Here, the porosity is selected from an electron microscope image obtained using SEM on the surface of the porous body, and an arbitrary area of 5 μm × 5 μm is selected, and the pores in which the network structure is present are blocked. The ratio of the total area of the unexposed portion to the entire hole was calculated. This operation was carried out for any 10 locations, and the average value was determined.

  The method for producing a porous body according to the present embodiment includes a dispersion liquid preparing step of preparing a nanofiber dispersion in which cellulose nanofibers having a number average fiber diameter of 1 to 100 nm are dispersed in a dispersion medium, and a large number of dispersion liquids. An adhering step for adhering to the porous support with which the pores communicated, and a drying step for drying the support adhering the dispersion to remove the dispersion medium.

<Dispersion preparation process>
First, a nanofiber dispersion in which cellulose nanofibers are dispersed in a dispersion medium is prepared. The dispersion is prepared by diluting the cellulose nanofiber dispersion to obtain a dispersion having a desired concentration, or adding the cellulose nanofiber to a dispersion medium so as to obtain a desired concentration. May be. Here, the cellulose-based nanofiber dispersion is, for example, a cellulose-based nanofiber dispersion obtained in the dispersion step in the cellulose nanofiber manufacturing method described in Patent Document 1 described above, and is manufactured or commercially available. It doesn't matter whether you use goods. Cellulose nanofibers are, for example, cellulose nanofibers separated from the dispersion medium obtained in the drying step in the method for producing cellulose nanofibers described in Patent Document 1 described above. It doesn't matter whether you use it. The method of diluting the nanofiber dispersion is more preferable in that the nanofiber is less aggregated and has a uniform fiber diameter. In the present embodiment, the method is not limited to a method of diluting a cellulose nanofiber dispersion or a method of dispersing cellulose nanofibers in a dispersion medium. For example, a screw mixer, a paddle mixer, a disper mixer, a turbine mixer, etc. A known dispersion machine can be used as a dispersion. In addition, by using a device with powerful beating ability such as homomixer, high pressure homogenizer, ultrasonic dispersion treatment, beater, disc type refiner, conical type refiner, double disc type refiner, grinder, etc. under high speed rotation. A nanofiber dispersion can be obtained.

  The dispersion preferably contains 0.001 to 0.500% by mass of nanofibers in terms of solid content with respect to the total mass of the dispersion. More preferably, it is 0.010-0.100 mass%, Most preferably, it is 0.03-0.100 mass%. If it is less than 0.001% by mass, a network structure may not be formed in the pores of the support. When it exceeds 0.500 mass%, nanofibers may be laminated at the time of drying, resulting in a film without air permeability.

  In this embodiment, it is preferable that the dispersion medium is water from the viewpoints of safety, environment, and facilities. However, a hydrophilic organic solvent can be used as needed. Examples of the hydrophilic organic solvent include methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, glycerol and other alcohols, ethylene glycol dimethyl ether, 1 , 4-dioxane, ethers such as tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethyl sulfoxide.

  In the present embodiment, it is preferable that the dispersion further contains a surfactant, and the surfactant is contained in a concentration of 0.0001 to 1.000% by mass with respect to the total mass of the dispersion. More preferably, it is 0.0010-0.1000 mass%, Most preferably, it is 0.0100-0.0500 mass%. Thereby, the aggregation suppressing effect of the nanofibers can be obtained, the aggregation of the cellulose nanofibers can be weakened during drying, and the network structure can be maintained in the pores of the support. If it is less than 0.0001% by mass, the effect of the surfactant may not be obtained. When it exceeds 1.000 mass%, the shape of the nanofiber cannot be maintained, and a network structure may not be formed in the pores of the support.

<Adhesion process>
The method for attaching the dispersion to the support is not limited in the present embodiment, and examples thereof include an impregnation method, a coating method, and a spray method. The wet adhesion amount of the dispersion is appropriately adjusted according to the thickness, material and average pore diameter of the support, but is preferably 1 to 1000 g / m ² per unit area of the support. More preferably, it is 10-500 g / m < ² >. If it is less than 1 g / m ² , the dispersion may not spread over the entire support. When it exceeds 1000 g / m ² , the dispersion liquid becomes excessive, which may result in a porous body with poor fluid permeability.

  Examples of the impregnation method include a method in which the support is completely immersed in the dispersion and a method in which only the surface of the support is immersed. The method of completely immersing the support in the dispersion allows the dispersion to penetrate efficiently and surely into the inner part of the hole of the support, so that a more uniform nanofiber network structure Is excellent in that it can be formed. Further, if the pressure is reduced while the support is completely immersed in the dispersion, air in the support is easily removed, which is more effective for infiltrating the dispersion. In addition, it is preferable that the excessively attached dispersion liquid is squeezed out with a roll dehydrator or the like, or removed with a water absorbent felt, water absorbent paper or the like. The method of immersing only the surface of the support is effective in providing a density difference between the network structures in the holes in the thickness direction of the support.

  The coating method is a method of coating the dispersion on the surface of the support with a known coating machine. Known coating machines are, for example, air knife coaters, roll coaters, bar coaters, comma coaters, blade coaters and curtain coaters. The coating method is excellent in that it is easy to control the amount of the dispersion attached to the support.

  The spraying method is a method of spraying the dispersion onto the surface of the support using a known sprayer such as spraying or spraying. The spraying method is effective, for example, when the nanofiber network structure is formed only in the vicinity of the surface of the support in the pores, and when the thickness of the network structure is desired to be reduced.

<Drying process>
As a drying method, it is preferable to select forced drying by heat, reduced pressure, etc., or natural drying by leaving it in the atmosphere. The temperature for the heat drying must be a temperature at which the support and the nanofibers are not decomposed or deformed. The drying temperature varies depending on the type of support and nanofibers. For example, when a polycarbonate type membrane filter is used as the support and the nanofiber described in Patent Document 1 is used as the nanofiber, the drying temperature is 20 to 120 ° C. It is preferable that More preferably, it is 50-110 degreeC. If it is less than 20 ° C., it takes time to dry, which is not efficient. If it exceeds 120 ° C, the support may be deformed beyond the softening point of the support. Moreover, when using glass fiber as a support body and using the nanofiber of patent document 1 as nanofiber, it is preferable to set it as 20-200 degreeC. More preferably, it is 50-120 degreeC. If it is less than 20 ° C., it takes time to dry, which is not efficient. If it exceeds 200 ° C., the cellulose nanofibers may be thermally decomposed. In the present embodiment, by using a porous support, the cohesive force generated on the nanofibers when the dispersion is dried is dispersed, and furthermore, a large number of micro thin films are formed in each hole of the support. By drying, it is considered that the nanofibers dispersed in the fine thin film remain in a network structure even when water evaporates.

  In the method for producing a porous body according to this embodiment, it is important that the dispersion liquid exists uniformly in the pores of the support. In the present embodiment, it is preferable that the dispersion medium for dispersing the nanofibers is water and the support is a hydrophilic support. Furthermore, it is particularly preferable to use the cellulose nanofiber of Patent Document 1 as the nanofiber. Cellulosic nanofibers have high hydrophilicity due to the hydrophilic functional groups in the molecule, so that a dispersion liquid in which nanofibers are more uniformly dispersed can be obtained by using water as the dispersion medium. In particular, in the cellulose-based nanofiber of Patent Document 1, a part of the hydroxyl group in the molecule is substituted with a carboxyl group having a negative charge, and an electrostatic repulsive force works between the nanofibers. In addition, a stable dispersion can be obtained. Furthermore, by making the support hydrophilic, the aqueous dispersion of nanofibers can be uniformly present in the pores of the support, and as a result, the nanofibers can be uniformly present in the pores. In addition, by making the support hydrophilic, a fine thin film of nanofiber dispersion can be stably formed, and even when water as a dispersion medium is removed by heat drying or natural drying, the network structure is uniform. The formed porous body can be obtained. By further containing a cationic surfactant in the dispersion, the surface tension of the dispersion can be reduced, and the wettability to the support can be further increased. Furthermore, aggregation of nanofibers can be weakened during drying. On the other hand, in a porous body using a thermoplastic polymer as a nanofiber including Patent Document 5, since the thermoplastic polymer is hydrophobic, it is difficult to uniformly disperse the nanofiber in the minute thin film. .

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” represent “parts by mass” and “mass%”, respectively, unless otherwise specified.

[Preparation of nanofiber dispersion 1]
NBKP (mainly consisting of fibers with a fiber diameter exceeding 1000 nm) equivalent to 2.00 g dry weight, 0.025 g TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical), , 0.25 g of sodium bromide was dispersed in 150 ml of water, and then a 13% sodium hypochlorite aqueous solution was added so that the amount of sodium hypochlorite was 5.00 mmol with respect to 1.00 g of pulp. To the reaction, sodium hypochlorite was added to initiate the reaction. During the reaction, 0.50 mol / l sodium hydroxide aqueous solution was added dropwise to keep the pH at 10. After reacting for 2 hours, the reaction product was filtered and sufficiently washed with water to obtain an oxidized cellulose slurry. 0.15 mass% oxidized cellulose slurry was defibrated for 8 minutes at 15000 rpm using a homogenizer (model NS-56, manufactured by Microtec Nithion), and after removing coarse fibers by centrifugation, The fiber was defibrated for 4 minutes with an ultrasonic homogenizer (model US-300T, manufactured by Nippon Seiki Seisakusho Co., Ltd.) to obtain a transparent and viscous cellulose nanofiber dispersion 1. As a result of analyzing this nanofiber dispersion liquid 1 from an observation image observed with a TEM at a magnification of 50000 times, the number average fiber diameter was 4 nm and the number average fiber length was 1.1 μm.

[Preparation of nanofiber dispersion 2]
A cellulose-based nanofiber aqueous dispersion 2 was obtained in the same manner as the nanofiber dispersion 1 except that LBKP (mainly composed of fibers having a fiber diameter exceeding 1000 nm) was used as a raw material. As a result of analyzing this nanofiber dispersion liquid 2 from an observation image observed at a magnification of 50000 using TEM, the number average fiber diameter was 4 nm and the number average fiber length was 1.0 μm.

Example 1
[Dispersion preparation process]
The nanofiber dispersion liquid 1 was diluted so that the solid content concentration of the nanofiber was 0.050% with respect to the total mass of the dispersion liquid to obtain a nanofiber dispersion liquid. Cetyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) as a cationic surfactant was added to the dispersion so that the solid concentration was 0.010% with respect to the total mass of the dispersion. The total solid content concentration of the dispersion was 0.060%.

[Adhesion process]
A polycarbonate type membrane filter (manufactured by ADVANTEC) having an average pore diameter of 0.8 μm was used as a porous support in which a large number of pores communicated, and the entire support was immersed in the dispersion. Excess dispersion liquid adhering to the membrane filter surface after immersion was removed with water absorbent paper. When the difference in the mass of the support before and after being immersed in the dispersion was calculated as the amount of adhesion, the amount of adhesion was 10 g / m ² .

[Drying process]
The support to which the dispersion was adhered was dried using a dryer under drying conditions of a drying temperature of 105 ° C. and a drying time of 5 minutes to obtain a porous body. Here, the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Example 2)
A porous material was obtained in the same manner as in Example 1 except that the nanofiber dispersion 2 was used.

(Example 3)
In the drying step of Example 1, a porous body was obtained in the same manner as in Example 1 except that the drying conditions were a drying temperature of 30 ° C. and a drying time of 1 hour.

Example 4
In the dispersion liquid adjusting step of Example 1, the solid content concentration of the nanofiber is 0.010% with respect to the total mass of the dispersion liquid, and the surfactant is solid concentration with respect to the total mass of the dispersion liquid. A porous body was obtained in the same manner as in Example 1 except that the content was 0.0020%. Here, the adhesion amount of the dispersion liquid to the support was 10 g / m ² , and the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Example 5)
In the dispersion adjusting step of Example 1, the nanofiber dispersion 1 is concentrated, the solid content concentration of the nanofiber is 0.60% with respect to the total mass of the dispersion, and the surfactant is dispersed. A porous material was obtained in the same manner as in Example 1 except that the solid concentration was 0.12% with respect to the total mass of the liquid. Here, the adhesion amount of the dispersion liquid to the support was 10 g / m ² , and the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Example 6)
In the adhesion step of Example 1, the same as Example 1 except that a glass fiber sheet having a basis weight of 64 g / m ² and an average pore diameter of 2.7 μm was used as the support, and the adhesion amount was 150 g / m ^2. The dispersion was adhered to the support. Furthermore, in the drying process of Example 1, a porous body was obtained in the same manner as in Example 1 except that the drying conditions were a drying temperature of 105 ° C. and a drying time of 10 minutes. Here, the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Example 7)
Support in the same manner as in Example 1 except that a glass fiber sheet having a basis weight of 40 g / m ² and an average pore diameter of 15 μm was used as the support in the adhesion process of Example 1 and the adhesion amount was 150 g / m ^2. The dispersion was attached to the body. Furthermore, in the drying process of Example 1, a porous body was obtained in the same manner as in Example 1 except that the drying conditions were a drying temperature of 105 ° C. and a drying time of 10 minutes. Here, the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Example 8)
A porous material was obtained in the same manner as in Example 1 except that the surfactant was not used in the dispersion liquid adjusting step of Example 1. Here, the adhesion amount of the dispersion liquid to the support was 10 g / m ² .

Example 9
In the dispersion liquid adjusting step of Example 1, instead of the nanofiber dispersion liquid 1, slurry-like MFC (Serish KY-100G, manufactured by Daicel Chemical Industries, Ltd.) was used as the nanofiber. Here, after the MFC was disaggregated with a household mixer, coarse fibers were removed by centrifugation. As a result of analysis from an observation image observed at a magnification of 10,000 using an electron microscope, the number average fiber diameter of the nanofibers was 64 nm, and the number average fiber length was 6.2 μm. The nanofiber dispersion was prepared so that the solid content concentration was 0.150% with respect to the total mass of the dispersion to obtain a nanofiber dispersion. As a dispersion obtained by adding cetyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) as a cationic surfactant to the dispersion to a solid content concentration of 0.030% with respect to the total mass of the dispersion A porous material was obtained in the same manner as in Example 1 except that it was used. The total solid concentration of the dispersion was 0.180%. Moreover, the adhesion amount of the dispersion liquid to the support was 10 g / m ² , and the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

(Comparative Example 1)
The dispersion obtained in the dispersion preparation step of Example 1 was poured into a glass petri dish so that the basis weight was 2 g / m ² and dried at a drying temperature of 105 ° C. and a drying time of 6 hours to obtain a transparent sheet.

(Comparative Example 2)
In the dispersion liquid adjusting step of Example 1, instead of the nanofiber dispersion liquid 1, slurry-like MFC (Serish KY-100G, manufactured by Daicel Chemical Industries, Ltd.) was used as the nanofiber. Here, a porous material was obtained in the same manner as in Example 9, except that the MFC was disaggregated with a household mixer and then a precipitate from which fine fibers were removed by centrifugation was used. As a result of analyzing from an observation image observed at a magnification of 5000 using an electron microscope, the number average fiber diameter of the nanofibers was 430 nm. Although it was confirmed that the number average fiber length of the nanofibers exceeded 20 μm, the total length could not be confirmed from the observation image. Moreover, the adhesion amount of the dispersion liquid to the support was 10 g / m ² , and the content of the surfactant in the network structure was 20% with respect to the dry mass of the nanofiber.

  The obtained porous bodies of Examples and Comparative Example sheets and porous bodies were evaluated by the following methods, and the evaluation results are shown in Table 1.

"Air permeability resistance increase value"
JIS P 8117: 2009 “Paper and paperboard—air permeability and air resistance test method (intermediate region) —Gurley method for the support, the porous body of the example obtained and the sheet and porous body of the comparative example The measurement was performed using a Oken type smoothness air permeability tester (model KY-5, manufactured by Asahi Seiko Co., Ltd.). The air resistance (A) of the support only and the air resistance (B) of the porous body with nanofibers attached to the support are obtained, and the difference between A and B is used as the air resistance increase value. Calculated. Here, the air resistance in the blank of the support used in the present invention was 4 s or less.

"Nanofiber network state"
The network structure formed with nanofibers was observed using a scanning electron microscope (SEM), and visually evaluated according to the following criteria. FIG. 1 shows an SEM image of the porous body of Example 1, FIG. 2 shows an SEM image of the porous body of Example 6, and FIG. 3 shows an SEM image of the porous body of Example 8.
A: The network formation rate is 80% or more, the open area ratio is 50% or more and 90% or less, the aggregation and / or lamination of nanofibers is small, and the uniform network structure in all the pores of the support The body is formed (practical level).
◯: The network formation rate is 10% or more and less than 80%, and the open area rate is 50% or more and 90% or less, and there is little aggregation and / or lamination of nanofibers. The network structure is not formed (practical level).
(Triangle | delta): A network formation rate is 10% or more, and a hole area rate is 10% or more and less than 50%, and aggregation and / or lamination | stacking of nanofiber are partially (practical use lower level).
X: The network formation rate is less than 10%, or the network formation rate is 10% or more, and the open area rate is less than 10%, and the nanofibers are aggregated and / or laminated. Is not formed (level not suitable for practical use).

  As can be seen from Table 1 and FIGS. 1 to 3, the porous bodies of Examples 1 to 9 have a network-like structure formed by stretching cellulose nanofibers in the pores of the support, and have a surface area. The air permeability resistance of the porous body was 10000 s or less and had fluid permeability. It was confirmed that a fluid-permeable porous body containing a cellulose nanofiber having a very small fiber diameter and high hydrophilicity can be obtained by a relatively simple production method.

  In Examples 1 to 3, a uniform nanofiber network structure was formed in most of the pores of the support. In Example 4, since the solid content concentration of the nanofibers in the dispersion was smaller than that in Example 1, the nanofiber network structure was not formed in some of the pores of the support, and the air permeability resistance However, it was smaller than Example 1. In Example 5, since the solid content concentration of the nanofibers in the dispersion was higher than in Example 1, lamination of nanofibers was observed in the pores of the support, and the air resistance was higher than in Example 1. became. In Example 8, a nanofiber network structure was not formed in some of the pores of the support. This is probably because the surfactant was not added to the dispersion, and thus it was less likely to penetrate into the pores of the support of the dispersion than in Example 1, and the effect of the surfactant could be confirmed. did it. In Example 9, a finer MFC was used as the nanofiber, but a uniform nanofiber network was formed in the pores of the support. Moreover, although Example 6 and Example 7 use a glass fiber sheet as a support and have an average pore diameter larger than that of the membrane filter used in Example 1, a nanofiber network structure is formed in the holes of the support. As a result, a porous body in which was formed was obtained.

  In Comparative Example 1, since the support was not used, the nanofibers aggregated, the air resistance was high, and the fluid permeability was poor. In Comparative Example 2, since the number average fiber diameter of the nanofibers exceeded 100 nm, no network structure was formed in the pores of the support.

  The porous body according to the present invention includes a cellulose nanofiber having a very small fiber diameter and high hydrophilicity, and can provide a fluid-permeable porous body at low cost. Therefore, the porous body according to the present invention can be suitably used in various fields and applications such as functional filters, wiping materials, electronic device materials, and regenerative medical materials.

Claims (9)

A porous body in which nanofibers are entangled to form a network structure in the pores of a porous support body in which a large number of pores communicate with each other,
The nanofiber is a cellulosic nanofiber, and the number average fiber diameter is 1 to 4 nm,
The average pore diameter of the support is 0.01 to 0.8 μm,
The network structure is formed by stretching a network composed of the nanofibers into the holes of the support body and crossing the holes, and on the surface of the portion excluding the holes of the support body. A porous body characterized by not being laminated .   The porous body according to claim 1, wherein the support is one of a porous film and a fiber sheet. The network structure contains a surfactant,
3. The porous body according to claim 1, wherein the content of the surfactant is 0.10 to 100% by mass in solid concentration with respect to the dry mass of the nanofiber.   The porous body according to claim 3, wherein the surfactant is a cationic surfactant. It is a manufacturing method of the porous body according to any one of claims 1 to 4,
A dispersion preparation step of preparing a dispersion of nanofibers in which cellulose nanofibers having a number average fiber diameter of 1 to 4 nm are dispersed in a dispersion medium;
A large number of pores communicate with each other and the dispersion adheres to a porous support having an average pore diameter of 0.01 to 0.8 μm, and the dispersion is placed in the pores of the support. An adhesion process to form a thin film;
Drying the support to which the dispersion is adhered to remove the dispersion medium;
A method for producing a porous body, comprising: The method for producing a porous body according to claim 5 , wherein the dispersion medium is water. The porous body according to claim 5 or 6 , wherein the dispersion contains the nanofiber in a solid content concentration of 0.001 to 0.500 mass% with respect to the total mass of the dispersion. Manufacturing method. The dispersion further contains a surfactant, and the surfactant is contained in a solid content concentration of 0.0001 to 1.000 mass% with respect to the total mass of the dispersion. The manufacturing method of the porous body as described in any one of 5-7 . The porous body according to any one of claims 5 to 8 , further comprising a removing step of removing the dispersion liquid adhered to the surface of the support body between the attaching step and the drying step. Manufacturing method.