Composition, porous membrane, and porous membrane equipped with base material

Abstract

Provided is a composition containing ceramic particles α having a primary particle diameter of less than 10 nm, ceramic particles β having a primary particle diameter of 10 nm or greater, a carboxylic acid having fewer than 5 carbon atoms, a binder, and an organic solvent, the ratio (ceramic particles β / ceramic particles α) of the ceramic particles β to the ceramic particles α being 1-20 by mass ratio, and the average primary particle diameter of the ceramic particles β being 20 nm or greater.

Description

Composition, porous membrane, and porous membrane with substrate

[0001] The present invention relates to a composition, a porous membrane formed from the composition, and a substrate-attached porous membrane having the porous membrane. This application claims priority based on Japanese Patent Application No. 2023-141308, filed on August 31, 2023, the contents of which are incorporated herein by reference.

[0002] Porous membranes are widely used in homes as, for example, deodorizers and desiccants, and in industrial applications as, for example, membranes for separating substances.

[0003] Patent Document 1 describes a separation membrane element including a porous molded body and a porous membrane. Patent Document 1 also describes a composition for forming a porous membrane, which contains an inorganic sol (fine particles (particles 1) of about 20 nm), mineral particles (large particles (particles 2) of 300 nm to 10 μm), a binder, and water, in which the ratio of particles 2 to particles 1 (particles 2 / particles 1) is 2.5 or more and 20 or less by mass.

[0004] Patent Document 2 describes a composition for forming a porous film, which contains ceramic sol particles (particles 1) of 5 to 50 nm, ceramic particles (particles 2) of 500 nm to 1000 nm, a binder, and water, and the ratio of particles 2 to particles 1 (particles 2 / particles 1) is 3.3 or more and 100 or less by mass ratio.

[0005] JP-A-63-274407 JP-A-10-235172

[0006] However, the porous films formed using the compositions described in Patent Document 1 and Patent Document 2 have a problem of poor adhesion to the substrate. Furthermore, in Patent Document 1, a surfactant is added to improve wettability to the substrate, and this surfactant remains as carbon after heat treatment, which causes a problem of deteriorating electrical and mechanical properties.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a composition capable of forming a porous film that has excellent adhesion to a substrate and a low content of residual carbon, a porous film that is a film formed from the composition, a porous film with a substrate that has the porous film, and a method for producing the composition.

[0008] The present invention has the following aspects. A first aspect of the present invention is the following composition: [1] A composition comprising ceramic particles α having a primary particle diameter of less than 10 nm, ceramic particles β having a primary particle diameter of 10 nm or more, a carboxylic acid having less than 5 carbon atoms, a binder, and an organic solvent, wherein the ratio of the ceramic particles β to the ceramic particles α (ceramic particles β / ceramic particles α) is 1 or more and 20 or less by mass, and the average primary particle diameter of the ceramic particles β is 20 nm or more. The composition of the first aspect of the present invention preferably has the following characteristics. It is also preferable to combine two or more of the following characteristics: [2] The composition according to [1], wherein the water content is 1 mass% or less. [3] The composition according to [1] or [2], wherein the ceramic particles α and the ceramic particles β are oxides containing zirconium. A second aspect of the present invention is the following porous film: [4] A porous film formed from the composition according to any one of [1] to [3]. The porous film of the second aspect of the present invention also preferably has the following characteristics. [5] The porous membrane according to [4], having a porosity of 30% or more and a residual carbon content of less than 1 mass%. A third aspect of the present invention is the following substrate-attached porous membrane. [6] A substrate-attached porous membrane, comprising: a substrate; and a porous membrane provided on at least one surface of the substrate, wherein the porous membrane is the porous membrane according to [4] or [5]. A fourth aspect of the present invention is the following method for producing a composition.[7] A method for producing the composition according to any one of [1] to [3], comprising: dispersing a mixed liquid containing ceramic particles A1 having an average primary particle size of 1 nm or more and less than 10 nm, a carboxylic acid having less than 5 carbon atoms, and a dispersion medium to produce a dispersion A2 having an average secondary particle size of 1 nm or more and less than 10 nm; dispersing a mixed liquid containing ceramic particles B1 having an average primary particle size of 20 nm or more, a binder, and a dispersion medium to produce a dispersion B2; and mixing the dispersion A2 and the dispersion B2 in a mass ratio of the ceramic particles B1 to the ceramic particles A1 (ceramic particles B1 / ceramic particles A1) of 1 or more and 20 or less to produce a composition, wherein a value obtained by dividing the average secondary particle size of the ceramic particles B1 in the dispersion B2 by the average primary particle size of the ceramic particles B1 is 1 or more and 10 or less.

[0009] According to the present invention, it is possible to provide a composition capable of forming a porous film that has excellent adhesion to a substrate and a low content of residual carbon, a porous film that is a film formed from the composition, a porous film with a substrate having the porous film, and a method for producing the composition.

[0010] Preferred examples of the composition, porous membrane, substrate-attached porous membrane, and method for producing the composition of the present invention will be described. Note that these embodiments are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified. For example, unless otherwise specified, conditions such as materials, amounts, types, numbers, sizes, shapes, positions, and ratios may be changed, added, or omitted as necessary.

[0011] [Composition] A composition according to one embodiment of the present invention comprises ceramic particles α having a primary particle diameter of less than 10 nm, ceramic particles β having a primary particle diameter of 10 nm or more, a carboxylic acid having less than 5 carbon atoms, a binder, and an organic solvent. In addition, in a composition according to one embodiment of the present invention, the ratio of the ceramic particles β to the ceramic particles α (ceramic particles β / ceramic particles α) is, in mass ratio, from 1 to 20. In addition, in a composition according to one embodiment of the present invention, the ceramic particles β have an average primary particle diameter of 20 nm or more.

[0012] "Ceramic particles α, ceramic particles β" The ceramic particles α are not particularly limited as long as they have a primary particle diameter of less than 10 nm. For example, alumina (Al ２ O ３ ), lead zirconate titanate (PZT), barium titanate (BaTiO ３ ), zirconium oxide (ZrO ２ Among these, from the viewpoint of chemical stability, the ceramic particles α are preferably an oxide containing zirconium, and more preferably zirconium oxide.

[0013] The ceramic particles α have a primary particle diameter of less than 10 nm, preferably less than 8 nm, and more preferably less than 5 nm. The lower limit of the primary particle diameter of the ceramic particles α can be selected arbitrarily, and may be 1 nm or more, 2 nm or more, or 3 nm or more. Ceramic particles α having a primary particle diameter of less than 10 nm can enter the gaps between ceramic particles β having an average primary particle diameter of 20 nm or more by the manufacturing method described below. This improves the bonding strength between the ceramic particles, thereby improving the adhesion between the substrate and porous film described below.

[0014] The primary particle diameter of the ceramic particles α can be measured by measuring the major axis of the ceramic particles α using a transmission electron microscope or by converting the specific surface area obtained by gas adsorption surface area measurement. The average primary particle diameter of the ceramic particles α can be calculated using a transmission electron microscope, for example, by taking the arithmetic mean of the major axes of 100 ceramic particles α. The primary particle diameter of the ceramic particles α in the composition of this embodiment can be measured by observing the composition using a transmission electron microscope. When the composition of this embodiment is produced using the production method described below, the primary particle diameter of the ceramic particles α and the primary particle diameter of the ceramic particles α in the composition are approximately the same. Therefore, the primary particle diameter of the ceramic particles α themselves may be used as the primary particle diameter of the ceramic particles α in the composition.

[0015] The ceramic particles β are not particularly limited as long as they have a primary particle diameter of 10 nm or more and an average primary particle diameter of 20 nm or more. For example, alumina (Al ２ O ３ ), lead zirconate titanate (PZT), barium titanate (BaTiO ３ ), zirconium oxide (ZrO ２ Among these, from the viewpoint of chemical stability, the ceramic particles β are preferably an oxide containing zirconium, and zirconium oxide is more preferable. The ceramic particles α and the ceramic particles β may be particles made of the same type of material or may be particles made of different types of materials.

[0016] The ceramic particles β have a primary particle diameter of 10 nm or more, preferably 20 nm or more, and more preferably 40 nm or more. The upper limit of the primary particle diameter of the ceramic particles β may be 10 μm or less, 1 μm or less, 500 nm or less, or 100 nm or less. The ceramic particles β have an average primary particle diameter of 20 nm or more, preferably 30 nm or more, and more preferably 40 nm or more. The upper limit of the average primary particle diameter of the ceramic particles β may be any value that ensures adhesion to the substrate, and may be, for example, 10 μm or less, 1 μm or less, 500 nm or less, or 100 nm or less.

[0017] The primary particle size and average primary particle size of the ceramic particles β can be measured in the same manner as the primary particle size and average primary particle size of the ceramic particles α.

[0018] In the composition of this embodiment, the ratio of ceramic particles β to ceramic particles α (ceramic particles β / ceramic particles α) is, by mass, 1 to 20, preferably 2.5 to 15, more preferably 2 to 10, and even more preferably 3 to 7. The ratio may be 3.5 to 6.5, or 4.0 to 5.5, for example. If the ratio is below the lower limit, the porous film may crack due to shrinkage caused by the ceramic particles α when the composition is formed into a film and then heat-treated. If the ratio exceeds the upper limit, the binding strength of the ceramic particles α is insufficient, resulting in a decrease in the strength of the porous film.

[0019] In the composition of this embodiment, the ceramic particles α and β may be surface-modified to enhance the affinity of the ceramic particles α and β with the organic solvent. The surface modifier is not particularly limited as long as it has functional groups that adsorb to the surfaces of the ceramic particles α and β and terminal groups that have affinity with the organic solvent. Examples of the surface modifier include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, cysteamine, tetramethylammonium hydroxide, and aminoethanediol.

[0020] In the composition of this embodiment, the contents of ceramic particles α and ceramic particles β are not particularly limited as long as the ratio of ceramic particles β to ceramic particles α is 1 to 20 and a coating film can be formed. For example, the content of ceramic particles α in the composition may be 0.1% by mass to 20% by mass, 0.5% by mass to 15% by mass, or 0.8% by mass to 10% by mass. It may also be 1.0% by mass to 8% by mass, or 3% by mass to 6% by mass. For example, the content of ceramic particles β in the composition may be 1% by mass to 50% by mass, 3% by mass to 40% by mass, 5% by mass to 30% by mass, or 5% by mass to 20% by mass. It may also be 7% by mass to 15% by mass, or 10% by mass to 13% by mass, for example. The composition of this embodiment may not contain ceramic particles having a specific primary particle size, if necessary. For example, the composition may be free of ceramic particles having a primary particle diameter of 8 nm to 12 nm, may be free of ceramic particles having a primary particle diameter of 10 nm to 15 nm, may be free of ceramic particles having a primary particle diameter of 15 nm to 20 nm, may be free of ceramic particles having a primary particle diameter of 20 nm to 25 nm, may be free of ceramic particles having a primary particle diameter of 25 nm to 30 nm, and / or may be free of ceramic particles having a primary particle diameter of 30 nm to 35 nm. The particle size distribution of the primary particles of the composition of this embodiment may have two or more completely separated peaks, if necessary.

[0021] "Carboxylic Acid" The composition of this embodiment contains a carboxylic acid having less than 5 carbon atoms. By containing a carboxylic acid having less than 5 carbon atoms, the dispersibility of the ceramic particles α in the composition can be maintained, and the amount of carbon residue when a porous film is formed can be reduced. Examples of carboxylic acids having less than 5 carbon atoms include formic acid, acetic acid, propionic acid, isobutyric acid, and butyric acid. Among these, acetic acid is preferred from the viewpoint of ease of handling of the composition, such as toxicity and odor. Note that "carboxylic acid having less than 5 carbon atoms" has the same meaning as "carboxylic acid having 4 or less carbon atoms."

[0022] In the composition of this embodiment, the content of the carboxylic acid having less than 5 carbon atoms is preferably 0.1% by mass or more. For example, it may be 0.3% by mass or more, or 0.6% by mass or more. By having the content of the carboxylic acid having less than 5 carbon atoms be 0.1% by mass or more, the dispersibility of the ceramic particles α in the composition is maintained, allowing them to be uniformly present in the composition, and allowing them to exhibit binding strength in the porous film. The upper limit of the content of the carboxylic acid having less than 5 carbon atoms is not particularly limited as long as the dispersibility of the ceramic particles α is maintained, and may be 10% by mass or less, 5.0% by mass or less, 3.0% by mass or less, or 1.0% by mass or less.

[0023] "Binder" In this embodiment, the binder contributes to adjusting the viscosity of the composition and forming voids when the composition is made into a porous film. The binder is not particularly limited as long as it is one that is substantially completely decomposed, combusted, or evaporated at or below the heat treatment temperature at which the composition is formed into a film and then heat-treated. It may be selected as needed from known binders having such properties. For example, at least one selected from the group consisting of celluloses such as ethyl cellulose, acrylic-modified ethyl cellulose, and methacrylic-modified ethyl cellulose, polyacrylic acid esters, polymethacrylic acid esters, polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxyethylene alkyl ethers, and polyoxypropylene alkyl ethers may be used. Among these, ethyl cellulose is preferred from the viewpoint of viscosity controllability of the composition.

[0024] In the composition of this embodiment, the binder content is preferably 0.1% by mass or more and 40% by mass or less, more preferably 1% by mass or more and 35% by mass or less, even more preferably 8% by mass or more and 30% by mass or less, and even more preferably 14% by mass or more and 25% by mass or less. If the binder content is above the lower limit, voids are generated in the film formed from the composition and heat-treated. If the binder content is below the upper limit, the ceramic particles in the porous film are bonded together, improving the strength of the porous film.

[0025] "Organic Solvent" The organic solvent is not particularly limited as long as it has affinity with the ceramic particles α and the ceramic particles β and is capable of dissolving the binder. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, ethylene glycol, hexylene glycol, and terpineol; esters such as methyl acetate and ethyl acetate; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, acetylacetone, and acetoacetic ester; acid amides such as N,N-dimethylformamide; and aromatic hydrocarbons such as toluene and xylene. These organic solvents may be used alone or in combination. Among these organic solvents, terpineol is preferred from the viewpoint of ease of handling. The composition of the present embodiment uses an organic solvent as a dispersion medium, and therefore has excellent wettability to the substrate described below, and can improve the adhesion between the substrate and the porous film.

[0026] In the composition of this embodiment, the content of the organic solvent can be selected arbitrarily and can be the remainder of other components. For example, the content of the organic solvent may be 50% by mass or more and 90% by mass or less, 60% by mass or more and 85% by mass or less, 65% by mass or more and 80% by mass or less, or 70% by mass or more and 78% by mass or less. When the content of the organic solvent is within the above range, the ceramic particles α and the ceramic particles β can be uniformly mixed, and the composition can be uniformly applied to a substrate.

[0027] The composition of this embodiment may contain surfactants, preservatives, stabilizers, antifoaming agents, leveling agents, etc., as appropriate, to ensure the dispersion stability of the ceramic particles α and β in the organic solvent and to improve the coating properties, as long as the purpose of the present invention is not impaired. To reduce the content of residual carbon, it is preferable not to contain surfactants. These materials can be selected appropriately so that the average secondary particle size of the ceramic particles α and β in the dispersion or composition, as described below, and the viscosity of the composition fall within the desired range.

[0028] In the composition of the present embodiment, the contents of the surfactant, preservative, stabilizer, antifoaming agent, leveling agent, etc. are not particularly limited, and may be set to a range depending on the application of the composition, etc., so that the viscosity of the composition and the average secondary particle diameter of the ceramic particles α and ceramic particles β in the dispersion liquid or composition described below fall within desired ranges.

[0029] The viscosity of the composition of this embodiment can be selected arbitrarily, but from the viewpoint of facilitating the formation of a coating film, it is preferably from 100 Pa s to 2000 Pa s, more preferably from 300 Pa s to 1700 Pa s, and even more preferably from 500 Pa s to 1500 Pa s. The viscosity of the composition of this embodiment means the value measured with a viscometer at room temperature (25°C) and a shear rate of 1 s.

[0030] The composition of this embodiment is obtained by the manufacturing method described below, and therefore the ceramic particles α can be uniformly present in the gaps between the ceramic particles β. Therefore, when the composition of this embodiment is formed into a porous film, it has excellent adhesion to the substrate.

[0031] "Method for Producing Composition" A method for producing a composition of this embodiment will be described. The method for producing a composition of this embodiment is the same as the method for producing a composition of the above-mentioned embodiment, and includes the steps of dispersing a mixture containing ceramic particles A1 having an average primary particle size of 1 nm or more and less than 10 nm, a carboxylic acid having less than 5 carbon atoms, and a dispersion medium to produce a dispersion A2 having an average secondary particle size of 1 nm or more and less than 10 nm, dispersing a mixture containing ceramic particles B1 having an average primary particle size of 20 nm or more, a binder, and a dispersion medium to produce a dispersion B2, and mixing the dispersion A2 and the dispersion B2 in a mass ratio of the ceramic particles B1 to the ceramic particles A1 (ceramic particles B1 / ceramic particles A1) of 1 to 20 to produce a composition. The value obtained by dividing the average secondary particle size of the ceramic particles B1 in the dispersion B2 by the average primary particle size of the ceramic particles B1 is 1 to 10. The average secondary particle size of the ceramic particles B1 in the dispersion B2 may refer to a value (D50) obtained by measuring the dispersion B2 using, for example, a particle size distribution meter.

[0032] "Step of Preparing Dispersion A2" In this step, a mixture containing ceramic particles A1 having an average primary particle diameter of 1 nm or more and less than 10 nm, a carboxylic acid having less than 5 carbon atoms, and a dispersion medium is dispersed until the average secondary particle diameter of the ceramic particles A1 is 1 nm or more and less than 10 nm, to prepare dispersion A2. The particle diameter of the ceramic particles A1 may be the same as that of the ceramic particles α, or the ceramic particles A1 may be composed of only particles having a primary particle diameter of less than 10 nm, or may be composed of only particles having a primary particle diameter of less than 5 nm. That is, in this step, dispersion A2 may be prepared by dispersing a mixture containing ceramic particles α having a primary particle diameter of less than 10 nm, a carboxylic acid having less than 5 carbon atoms, and a dispersion medium until the average secondary particle diameter of the ceramic particles α is 1 nm or more and less than 10 nm. The particle diameter of the ceramic particles A1 may be the same as that of the ceramic particles α, but as long as the ratio of ceramic particles β / ceramic particles α in the composition is 1 or more and 20 or less, the ceramic particles A1 may contain particles with a primary particle diameter of 5 nm or more or 10 nm or more.

[0033] The average primary particle diameter of ceramic particles A1 is 1 nm or more and less than 10 nm, preferably 2 nm or more and less than 8 nm, and more preferably 3 nm or more and less than 5 nm. The content of ceramic particles A1 in dispersion A2 is not particularly limited as long as the ceramic particles A1 can be dispersed therein, and may be, for example, 1 mass % or more and 50 mass % or less, 5 mass % or more and 40 mass % or less, or 10 mass % or more and 30 mass % or less. The primary particle diameter and average primary particle diameter of ceramic particles A1 and B1 may be measured by the same method as for ceramic particles α and β.

[0034] The carboxylic acid having less than 5 carbon atoms can be the same as described above. The content of the carboxylic acid in the dispersion A2 is not particularly limited as long as the average secondary particle diameter of the ceramic particles A1 is 1 nm or more and 10 nm or less. For example, it may be 0.1 mass % or more and 10 mass % or less, or 1 mass % or more and 8 mass % or less. In this embodiment, the average secondary particle diameter of the ceramic particles A1 refers to the value (D50) when the cumulative volume percentage of the particle size distribution of the dispersion A2 measured with a particle size distribution analyzer is 50%. The particle size distribution may be measured using a dispersion adjusted to contain 1 mass % of the ceramic particles A1. The value (D50 / D90) obtained by dividing the D50 of the dispersion A2 by the value (D90) when the cumulative volume percentage of the particle size distribution of the dispersion A2 is 90% is preferably 0.4 or more and 1.0 or less, more preferably 0.5 or more and 1.0 or less, and even more preferably 0.6 or more and 1.0 or less. When D50 / D90 is 0.4 or more, the ceramic particles A1 (ceramic particles α) can be uniformly present in the gaps between the ceramic particles B1 (ceramic particles β).

[0035] The dispersion medium is not particularly limited as long as it has a high affinity with the ceramic particles A1 and a carboxylic acid having less than 5 carbon atoms. Examples include alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, ethylene glycol, hexylene glycol, and terpineol; esters such as methyl acetate and ethyl acetate; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, acetylacetone, and acetoacetic acid ester; acid amides such as N,N-dimethylformamide; and aromatic hydrocarbons such as toluene and xylene. One type may be used alone, or two or more types may be mixed and used. Among these, water is preferred due to its high affinity with a carboxylic acid having less than 5 carbon atoms. The content of the dispersion medium can be the remainder of other components.

[0036] The method for dispersing ceramic particles A1 (ceramic particles α) in a dispersion medium is not particularly limited, but for example, a wet method is preferred. Furthermore, the dispersing machine used in this wet method can be either an open type or a closed type, and for example, a ball mill, an agitating mill, a jet mill, a vibration mill, an attritor, a high-speed mill, a hammer mill, etc. are preferably used. Examples of the ball mill include a tumbling mill, a vibration mill, and a planetary mill, and examples of the agitating mill include a tower mill, an agitating tank mill, a flow-tube mill, and a tubular mill.

[0037] "Step of Preparing Dispersion B2" In this step, dispersion B2 is prepared by dispersing a mixed liquid containing ceramic particles B1 having an average primary particle diameter of 20 nm or more, a binder, and a dispersion medium. The dispersion is performed until the value obtained by dividing the average secondary particle diameter of the ceramic particles B1 by the average primary particle diameter of the ceramic particles B1 is 1 to 10. The value may be 2 to 8, or 4 to 6, as necessary.

[0038] The particle diameter of the ceramic particles B1 may have the same characteristics as the ceramic particles β described above, and may be composed solely of particles with a primary particle diameter of 10 nm or more, or may be composed solely of particles with a primary particle diameter of 5 nm or more. That is, this step may be a step of preparing dispersion B2 by dispersing a mixture containing ceramic particles β having a primary particle diameter of 10 nm or more or a primary particle diameter of 5 nm or more and an average primary particle diameter of 20 nm or more, a binder, and a dispersion medium until the value obtained by dividing the average secondary particle diameter of the ceramic particles β by the average primary particle diameter of the ceramic particles β is 1 to 10. The particle diameter of the ceramic particles B1 may be the same as that of the ceramic particles β, but as long as the ratio of ceramic particles β / ceramic particles α in the composition is 1 to 20, the ceramic particles B1 may contain particles with a primary particle diameter of less than 5 nm or less than 10 nm. The average primary particle diameter of the ceramic particles B1 is 20 nm or more, or may be 30 nm or more, or may be 40 nm or more. It may be 60 nm or more, or 80 nm or more. Furthermore, the upper limit of the average primary particle diameter of the ceramic particles B1 may be any value that provides adhesion to the substrate, and may be, for example, 10 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, or 100 nm or less. The content of the ceramic particles B1 in the dispersion B2 is not particularly limited as long as the ceramic particles B1 can be dispersed, and may be, for example, 1 mass% or more and 50 mass% or less, 5 mass% or more and 45 mass% or less, or 10 mass% or more and 40 mass% or less.

[0039] The binder may be the same as that described above. The content of the binder in the dispersion B2 is not particularly limited as long as the value obtained by dividing the average secondary particle diameter of the ceramic particles B1 by the average primary particle diameter of the ceramic particles B1 is 1 to 10. For example, it may be 0.1% by mass to 10% by mass, or 1% by mass to 8% by mass. As described above, the average secondary particle diameter of the ceramic particles B1 refers to the D50 value obtained by measuring the volume particle size distribution of the dispersion B2. By dispersing the ceramic particles B1 until the value obtained by dividing the average secondary particle diameter of the ceramic particles B1 by the average primary particle diameter of the ceramic particles B1 is 1 to 10, the ceramic particles A1 (ceramic particles α) can be uniformly present in the gaps between the ceramic particles B1 (ceramic particles β).

[0040] The dispersion medium is not particularly limited as long as it has a high affinity for the ceramic particles B1 and the binder. Examples include alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, ethylene glycol, hexylene glycol, and terpineol; esters such as methyl acetate and ethyl acetate; ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, acetylacetone, and acetoacetic ester; acid amides such as N,N-dimethylformamide; and aromatic hydrocarbons such as toluene and xylene. One type may be used alone, or two or more types may be mixed and used. Among these, alcohol is preferred due to its high affinity with the binder. Ethanol is preferred due to its ease of handling. The content of the dispersion medium can be determined as the remainder of the other components.

[0041] The method for dispersing the ceramic particles B1 in the dispersion medium is not particularly limited, but for example, a wet method is preferred, similar to the method for dispersing the ceramic particles A1 in the dispersion medium described above.

[0042] "Step of Mixing Dispersion A2 and Dispersion B2" In this step, dispersion A2 and dispersion B2 are mixed so that the ceramic particles B1 / ceramic particles A1 mass ratio is 1 to 20, to obtain a composition. A binder or organic solvent may be added as needed in this step to adjust the viscosity or porosity. When ceramic particles A1 contain particles with a primary particle diameter of 5 nm or more or 10 nm or more, or when ceramic particles B1 contain particles with a primary particle diameter of less than 5 nm or less than 10 nm, dispersion A2 and dispersion B2 are mixed so that the ceramic particles β / ceramic particles α mass ratio is 1 to 20. The mass ratio may be 2 to 15, 3 to 10, or 5 to 8, as needed. By mixing dispersion A2 and dispersion B2 so that the mass ratio is within the above range, ceramic particles A1 (ceramic particles α) can be uniformly present in the gaps between ceramic particles B1 (ceramic particles β). The method for mixing the dispersion A2 and the dispersion B2 is not particularly limited, but examples thereof include a propeller mixer.

[0043] "Step of Removing Moisture" This step is a step of removing moisture from the composition when the composition contains moisture. If the composition contains moisture, film-forming properties will be impaired. Therefore, it is preferable to remove moisture from the resulting composition. The composition in this embodiment may not contain water, or if it does contain water, it is preferable that it be in a small amount. For example, the amount of water may be 1.0% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less.

[0044] The method for removing water from the mixture is not particularly limited, and examples thereof include distillation using a rotary evaporator and adsorption dehydration using molecular sieves.

[0045] According to the composition of the present embodiment, a composition can be obtained that has excellent wettability and adhesion to a substrate and can form a porous film with a low content of residual carbon.

[0046] [Porous Film] A porous film according to one embodiment of the present invention is a film formed from the composition of the above-described embodiment. The film formed from the composition may be obtained by applying the composition and heat treating it.

[0047] The porous membrane of this embodiment preferably has an average pore diameter of 1 nm to 200 nm, more preferably 5 nm to 100 nm, and even more preferably 10 nm to 100 nm. When the average pore diameter is equal to or greater than the lower limit, gas and liquid permeability can be ensured. When the average pore diameter is equal to or less than the upper limit, when another ceramic particle-containing composition is applied by laminating it on the porous membrane, the other ceramic particles can be prevented from penetrating into the pores and clogging the pores.

[0048] The porous membrane of this embodiment has a porosity of 30% or more, preferably 40% or more, more preferably 50% or more, even more preferably 52% or more, and particularly preferably 55% or more. That is, in the porous membrane of this embodiment, the proportion of pores with an average pore diameter of 1 nm to 200 nm in the entire porous membrane is more preferably 50% or more. Furthermore, this proportion is more preferably 55% or more, and even more preferably 60% or more. When the porosity is above the lower limit, gas and liquid permeability can be ensured. The upper limit of the porosity can be selected arbitrarily, but may be 90% or less, 85% or less, or 80% or less.

[0049] The pore size and porosity of a porous film can be measured as follows. A porous film is formed by applying the composition of the above-described embodiment to a glass substrate and heat-treating the resulting coating. The resulting porous film is scraped off with the flat side of a metal spatula and peeled off from the glass substrate. The peeled material is measured using a specific surface area measurement device, such as a specific surface area measurement device (trade name: Belsorp-mini II, manufactured by Microtrac-Bell), and the pore size and pore volume of the porous film are calculated by the BJH method (Barrett-Joyner Halenda method) from an adsorption isotherm measured by nitrogen gas adsorption. The average pore size is a value obtained using the pore size and pore volume calculated above, and is the pore size value at which the cumulative pore volume is 1 / 2 of the total pore volume. The porosity of the porous film is calculated from the obtained pore volume of the porous film using the following formula (1). The true density of the ceramic may be used as the density of the ceramic particles in the formula. When the ceramic particles are zirconium oxide particles, the density of the ceramic particles of the following formula (1) is 5.7 g / cm ３ Porosity (%) = pore volume / (pore volume + 1 / ceramic particle density) × 100 (1) In the formula, the unit of pore volume is "mL / g" and the unit of density is "g / cm ３ ". In addition, when the types of ceramic particles α and ceramic particles β in the dispersion liquid containing ceramic particles α and the dispersion liquid containing ceramic particles β are different, the porosity of the porous film is calculated by the following formula (2). Specifically, the porosity of the porous film is calculated by the following formula (2): ３ )) and ceramic particles β (density y (g / cm ３ )) are contained in a mass fraction of X:Y, and the pore volume of the porous membrane is Z (mL / g), the porosity of the porous membrane is calculated by the following formula (2): Porosity (%) = Z / [Z + {X / (X+Y)} / x + {Y / (X+Y)} / y] × 100 (2)

[0050] In the porous membrane of this embodiment, the proportion of pores having a pore diameter of 1 nm or more and 200 nm or less to the total pore volume is preferably 50% or more and 90% or less, more preferably the proportion of pores having a pore diameter of 5 nm or more and 100 nm or less to the total pore volume is 50% or more and 90% or less, and even more preferably the proportion of pores having a pore diameter of 10 nm or more and 100 nm or less to the total pore volume is 50% or more and 90% or less.

[0051] When the proportion of pores having a pore diameter of 1 nm to 200 nm in the total pore volume of the porous membrane is 50% or more, the permeability of gases and vapors can be ensured. Furthermore, when the proportion of pores having a pore diameter of 1 nm to 200 nm in the total pore volume is 90% or more, when another ceramic particle-containing composition or the like is coated and laminated on the porous membrane, the penetration of the other ceramic particles into the porous membrane and blocking of the pores can be suppressed.

[0052] The proportion of the pores having a pore diameter of 1 nm or more and 200 nm or less to the total pore volume in the porous film can be measured by scraping the obtained porous film with the flat side of a metal spatula to peel it off from the glass substrate, and measuring the peeled material using a specific surface area measuring device (trade name: Belsorp-mini II, manufactured by Microtrac-Bell) using the BJH method from an adsorption isotherm measured by a nitrogen gas adsorption method.

[0053] The porous film of this embodiment preferably has a residual carbon content of less than 1% by mass, more preferably 0.9% by mass or less, and even more preferably 0.7% by mass or less. It may be 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less. When the residual carbon content is below the upper limit, deterioration of the electrical and mechanical properties of the porous film due to the residual carbon can be prevented. The residual carbon may refer to carbon-containing residues other than the porous film that remain after the heat treatment during formation.

[0054] The content of residual carbon in a porous film can be measured as follows. The composition of the above-described embodiment is applied to a glass substrate, and the resulting coating is heat-treated to form a porous film. The resulting porous film is scraped off with the flat side of a metal spatula and peeled from the glass substrate. The weight loss of the peeled material is measured using a thermogravimetric analyzer (TG / DTA6300, manufactured by Seiko Instruments Inc.), and the weight loss at 120°C to 800°C is taken as the weight loss of residual carbon. That is, the weight A (g) of the peeled material is measured using an electronic balance, and the weight loss B (g) at 120°C to 800°C is measured using TG-DTA, and the content of residual carbon in the porous film is calculated by B / A x 100.

[0055] "Method for producing porous film" A method for producing the porous film of this embodiment will be described. The porous film of this embodiment can be obtained by applying the composition of the above-mentioned embodiment to the surface of a support such as a substrate, and then heat-treating the resulting coating film.

[0056] The method for applying the composition to the surface of the support is not particularly limited and may be appropriately selected depending on the shape and material of the support. Examples of the method for applying the composition include wash coating, dip coating, screen printing, and ordinary wet coating methods.

[0057] After the composition is applied, the thickness of the coating film may be adjusted by removing excess composition using compressed air or the like to a thickness greater than the thickness of the coating film.

[0058] The composition is applied to a coating film, which is then heat-treated to remove the binder contained therein and form a porous ceramic film. The heat treatment temperature for the coating film is not particularly limited as long as the binder is removed, but is preferably 300°C to 800°C, more preferably 400°C to 700°C, and even more preferably 450°C to 600°C. The heat treatment time for the coating film is preferably 0.25 hours to 10 hours, more preferably 0.5 hours to 5 hours. It may be 1 hour to 3 hours, for example.

[0059] The atmosphere in which the coating film is heat-treated is not particularly limited as long as the binder is removed, and the heat treatment can be carried out in any of the following atmospheres: an oxidizing atmosphere such as air; an inert atmosphere such as nitrogen, argon, neon, or xenon; or a reducing atmosphere such as hydrogen or carbon monoxide.

[0060] According to the porous film of this embodiment, a porous film having excellent adhesion to the substrate and a low content of residual carbon can be obtained.

[0061] [Substrate-attached porous membrane] A substrate-attached porous membrane according to one embodiment of the present invention has a substrate and a porous membrane provided on at least one surface of the substrate, and the porous membrane is the porous membrane of the above-described embodiment.

[0062] The substrate is not particularly limited as long as it is possible to form a porous film on at least one surface thereof, and examples thereof include porous ceramics, glass, and metals such as stainless steel and iron.

[0063] The substrate and the porous membrane may be made of the same material or different materials.

[0064] According to the substrate-attached porous membrane of this embodiment, a substrate-attached porous membrane having excellent adhesion between the substrate and the porous membrane and a porous membrane with a low content of residual carbon can be obtained.

[0065] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0066] [Example 1] ZrO having an average primary particle size of 4 nm ２ Particles A1 (manufactured by Sumitomo Osaka Cement Co., Ltd., equivalent to ceramic particles α) were dissolved in a 5% aqueous acetic acid solution to form a ZrO ２ The ZrO content of Example 1 was dispersed to 20 mass %. ２ Dispersion A2 was prepared. ２ A portion of the dispersion A2 was taken and ZrO ２ The ZrO for evaluation was diluted with water so that the content of ２ Dispersion A3 was prepared. ２The volumetric particle size distribution of Dispersion A3 was measured using a particle size distribution analyzer (product name: SZ-100, manufactured by Horiba, Ltd.), and the results were D10: 4.0 nm, D50: 4.5 nm, D90: 6.3 nm, and D50 / D90: 0.71. The results are shown in Table 1.

[0067] Next, ZrO having an average primary particle size of 50 nm ２ The ZrO particles B1 (manufactured by Daiichi Kigenso Kogyo Co., Ltd., corresponding to ceramic particles β) were dissolved in ethanol so that the content of the particles B1 was 30 mass % and the content of ethyl cellulose as a binder was 3 mass %. ２ The particles and the ethyl cellulose were added and mixed to form the ZrO ２ Slurry dispersion B2 was prepared. ２ A portion of the dispersion B2 was taken and ZrO ２ The ZrO for evaluation was diluted with ethanol so that the content of ２ Dispersion B3 was prepared. ２ The volume particle size distribution of Dispersion B3 was measured using a particle size distribution analyzer (product name: SZ-100, manufactured by Horiba, Ltd.). The results were D10 of 45 nm, D50 of 240 nm, D90 of 830 nm, and D50 / D90 of 0.29. The results are shown in Table 1. ２ The average secondary particle diameter D50 of the dispersion B3 was calculated by ２ When divided by the average primary particle size of particles B1, the result was 4.8.

[0068] ZrO ２ ZrO in solid content ２ 2 parts by mass of dispersion liquid A2, ZrO ２ 9 parts by mass of dispersion B2 and 16 parts by mass of ethyl cellulose were mixed, and ZrO ２ Dispersion medium (water) contained in dispersion A2 and ZrO ２ Terpineol was added to prepare a mixture so that the total amount, excluding the dispersion medium (ethanol) contained in Dispersion B2, was 100 parts by mass. Next, water and ethanol were removed from the mixture using a rotary evaporator to obtain the composition of Example 1. The viscosity of the composition of Example 1 was measured using a viscometer (trade name: MCR102, manufactured by Anton Paar) at room temperature (25°C) and a shear rate of 1 s －１The viscosity was measured under the conditions of 930 Pa s. The composition of Example 1 thus obtained was applied to a glass substrate so that the film thickness after heat treatment would be 1 μm to form a coating film made of the composition of Example 1. The coating film was dried at 150° C. for 3 minutes and then heat-treated in the atmosphere at 450° C. for 1 hour to obtain the porous film of Example 1.

[0069] [Example 2] ZrO ２ The composition of Example 2 was obtained in the same manner as in Example 1, except that in the preparation of Dispersion A2, Dispersion A4 made with a 5% n-butyric acid aqueous solution was used instead of the 5% acetic acid aqueous solution. Using the obtained composition of Example 2, the porous film of Example 2 was obtained in the same manner as in Example 1. ZrO of Example 2 ２ The volume particle size distribution of Dispersion A4 and the viscosity of the composition of Example 2 were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0070] [Example 3] ZrO ２ In the preparation of dispersion A2, ZrO ２ A composition of Example 3 was obtained in the same manner as in Example 1, except that dispersion A5 made from ZrO particles (manufactured by Sumitomo Osaka Cement Co., Ltd., corresponding to ceramic particles α) was used. The obtained composition of Example 3 was used to obtain a porous film of Example 3 in the same manner as in Example 1. ２ The volume particle size distribution of Dispersion A5 and the viscosity of the composition of Example 3 were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0071] [Example 4] ZrO ２ ZrO of Example 1 in terms of solid content ２ Dispersion A2 1.1 parts by mass, ZrO ２ 4.8 parts by mass of dispersion B2 and 12.2 parts by mass of ethyl cellulose were mixed, and ZrO ２ Dispersion medium (water) contained in dispersion A2 and ZrO ２The composition of Example 4 was obtained in the same manner as in Example 1, except that terpineol was added so that the total amount, excluding the dispersion medium (ethanol) contained in Dispersion B2, was 100 parts by mass. Using the obtained composition of Example 4, a porous film of Example 4 was obtained in the same manner as in Example 1. The viscosity of the composition of Example 4 was measured in the same manner as in Example 1. The results are shown in Table 1.

[0072] [Example 5] ZrO ２ ZrO of Example 1 in terms of solid content ２ Dispersion A2 5.6 parts by mass, ZrO ２ 23.8 parts by mass of dispersion B2 and 3.4 parts by mass of ethyl cellulose were mixed, and ZrO ２ Dispersion medium (water) contained in dispersion A2 and ZrO ２ The composition of Example 5 was obtained in the same manner as in Example 1, except that terpineol was added so that the total amount, excluding the dispersion medium (ethanol) contained in Dispersion B2, was 100 parts by mass. Using the obtained composition of Example 5, a porous film of Example 5 was obtained in the same manner as in Example 1. The viscosity of the composition of Example 5 was measured in the same manner as in Example 1. The results are shown in Table 1.

[0073] [Comparative Example 1] ZrO ２ A composition of Comparative Example 1 was obtained in the same manner as in Example 1, except that in the preparation of Dispersion A2, Dispersion A6 made with ion-exchanged water was used instead of the 5% aqueous acetic acid solution. Using the obtained composition of Comparative Example 1, a porous film of Comparative Example 1 was obtained in the same manner as in Example 1. ZrO of Comparative Example 1 ２ The volume particle size distribution of Dispersion A6 and the viscosity of the composition of Comparative Example 1 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0074] [Comparative Example 2] ZrO ２ In the preparation of dispersion A2, ZrO ２ A composition of Comparative Example 2 was obtained in the same manner as in Example 1, except that dispersion A7 made with particles (not corresponding to ceramic particles α) was used. That is, a composition of Comparative Example 2 was obtained that did not contain ceramic particles α having a primary particle diameter of less than 10 nm. Using the obtained composition of Comparative Example 2, a porous film of Comparative Example 2 was obtained in the same manner as in Example 1. ZrO of Comparative Example 2２ The volume particle size distribution of Dispersion A7 and the viscosity of the composition of Comparative Example 2 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0075] [Comparative Example 3] ZrO ２ In the preparation of dispersion A2, ZrO was prepared using a 5% lauric acid-ethanol solution instead of a 5% acetic acid aqueous solution. ２ A composition of Comparative Example 3 was obtained in the same manner as in Example 1, except that Dispersion A8 was used. The obtained composition of Comparative Example 3 was used to obtain a porous film of Comparative Example 3 in the same manner as in Example 1. ZrO of Comparative Example 3 ２ The volume particle size distribution of Dispersion A8 and the viscosity of the composition of Comparative Example 3 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0076] Comparative Example 4: A ZrO dispersion was prepared without using ethyl cellulose as a binder in the preparation of dispersion B2 in Example 1. ２ A composition of Comparative Example 4 was obtained in the same manner as in Example 1, except that Dispersion B4 was used. The obtained composition of Comparative Example 4 was used to obtain a porous film of Comparative Example 4 in the same manner as in Example 1. ZrO ２ The volume particle size distribution of Dispersion B4 and the viscosity of the composition of Comparative Example 4 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0077]

[0078]

[0079] [Evaluation] The porosity, residual carbon content, and adhesion were evaluated for the porous films obtained in Examples 1 to 5 and Comparative Examples 1 to 4. The results are shown in Table 3.

[0080] "Measurement of pore size and porosity" The obtained porous film was scraped off with the flat side of a metal spatula and peeled off from the glass substrate. The peeled material was measured using a specific surface area measuring device (trade name: Belsorp-mini II, manufactured by Microtrac-Bell) and the pore volume was calculated by the BJH method from the adsorption isotherm measured by nitrogen gas adsorption method. From the obtained pore volume, the porosity of the porous film was calculated by the following formula (1): Porosity (%) = Pore volume / (Pore volume + 1 / Density of ceramic particles) × 100 (1) ZrO ２The particle density is 5.7 g / cm ３ It was calculated as:

[0081] "Measurement of residual carbon" The obtained porous film was peeled off from the glass substrate by scraping it off with the flat side of a metal spatula. The weight loss of the peeled material was measured using a thermogravimetric analyzer (TG / DTA6300, manufactured by Seiko Instruments Inc.), and the weight loss from 120°C to 800°C was taken as the weight loss of residual carbon. That is, the weight A (g) of the peeled material was measured using an electronic balance, and the weight loss B (g) from 120°C to 800°C was measured using TG-DTA, and the content of residual carbon in the porous film was calculated by B / A x 100.

[0082] "Adhesion measurement" A 15 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., Cellotape (registered trademark)) with a nominal adhesive strength of 4.7 N / 10 mm was attached to the porous membrane, and the adhesive tape was peeled off in a direction of approximately 60° relative to the porous membrane (horizontal surface) for 0.5 to 1.0 seconds. If the force applied at this time was divided by the tape width and the value was less than 5 N, it was evaluated as "adhesion × (poor adhesion)", and if it was 5 N or more, it was evaluated as "adhesion ○ (good adhesion)". A universal testing machine manufactured by Kyowa Interface Science Co., Ltd. was used to measure adhesion.

[0083]

[0084] From the results in Table 3, it was found that the porous films of Examples 1 to 5 had excellent adhesion to the substrate and contained a small amount of residual carbon. On the other hand, it was found that the porous films of Comparative Examples 1, 2, and 4 had poor adhesion to the substrate. It was also found that the porous film of Comparative Example 3 contained a large amount of residual carbon. From these results, it was found that ZrO ２ A dispersion in which particles are dispersed in a carboxylic acid having a carbon number of less than 5 so that the average secondary particle diameter is 1 nm or more and 10 nm or less, and a dispersion in which particles are dispersed in a carboxylic acid having a carbon number of less than 5 so that the average primary particle diameter is 20 nm or more ２ It was confirmed that a composition obtained by mixing particles in a specific ratio of a dispersion liquid in which the average secondary particle size / average primary particle size is 10 or less has excellent adhesion to the substrate when made into a porous film, a small residual carbon rate, and a porosity of 30% or more.

[0085] The present invention can provide a composition capable of forming a porous film that has excellent adhesion to a substrate and a low residual carbon content, a porous film formed from the composition, a porous film with a substrate having the porous film, and a method for producing the composition.

Claims

1. A composition comprising: ceramic particles α having a primary particle diameter of less than 10 nm; ceramic particles β having a primary particle diameter of 10 nm or more; a carboxylic acid having less than 5 carbon atoms; a binder; and an organic solvent, wherein the ratio of the ceramic particles β to the ceramic particles α (ceramic particles β / ceramic particles α) is 1 or more and 20 or less in mass ratio, and the average primary particle diameter of the ceramic particles β is 20 nm or more.

2. The composition according to claim 1, wherein the water content is 1% by mass or less.

3. The composition according to claim 1, wherein the ceramic particles α and the ceramic particles β are an oxide containing zirconium.

4. A porous film which is a film formed from the composition according to any one of claims 1 to 3.

5. The porous membrane according to claim 4, having a porosity of 30% or more and a residual carbon content of less than 1% by mass.

6. A substrate-attached porous membrane comprising: a substrate; and a porous membrane provided on at least one surface of the substrate, the porous membrane being the porous membrane according to claim 4.

7. A method for producing a composition according to claim 1, comprising the steps of: dispersing a mixed liquid containing ceramic particles A1 having an average primary particle diameter of 1 nm or more and less than 10 nm, a carboxylic acid having less than 5 carbon atoms, and a dispersion medium to produce dispersion liquid A2 having an average secondary particle diameter of 1 nm or more and less than 10 nm; dispersing a mixed liquid containing ceramic particles B1 having an average primary particle diameter of 20 nm or more, a binder, and a dispersion medium to produce dispersion liquid B2; and mixing dispersion liquid A2 and dispersion liquid B2 in a mass ratio of ceramic particles B1 to ceramic particles A1 (ceramic particles B1 / ceramic particles A1) of 1 or more and 20 or less to produce a composition, wherein a value obtained by dividing the average secondary particle diameter of ceramic particles B1 in dispersion liquid B2 by the average primary particle diameter of ceramic particles B1 is 1 or more and 10 or less.

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