Film for electronic member containing chemically-modified cellulose fibers

Abstract

Provided is a film that uses a biomass material and can be used as an electronic member in an electrochemical device and that can also be treated as an independent solo film. According to the present invention, a film contains chemically-modified cellulose fibers and is to be used as an electronic member. The film has an uneven structure at one or both surfaces, and at the surface that has the uneven structure (a) the arithmetic average surface roughness (Ra) is no more than 0.500 μm and (b) the average height (Rc) of roughness profile elements is at least 0.050 μm.

Description

Films for electronic components containing chemically modified cellulose fibers

[0001] This invention relates to a film for electronic components. More specifically, it relates to a film containing chemically modified cellulose used in applications for electronic components.

[0002] Well-known electrochemical devices include secondary batteries such as lithium-ion batteries (LiB), electric double-layer capacitors (EDLCs), fuel cells, and water electrolyzers. Of these, lithium-ion batteries and electric double-layer capacitors generally use organic solvents as electrolytes from the perspective of voltage resistance. However, because organic solvents are flammable and volatile, there are concerns regarding safety and environmental impact. Therefore, development of electrochemical devices using water-based electrolytes is progressing with the aim of reducing the environmental impact. Furthermore, in response to recent environmental issues, there is a demand for electrolytes that avoid the use of perfluorooctaneous acid compounds (PFAS), and electrolytes using biomass-derived materials are desired.

[0003] In Patent Document 1, the applicant disclosed the use of ion-modified cellulose, which is cellulose into which ionic groups have been introduced, as a charge carrier in an electrolyte for an energy storage device.

[0004] International Publication No. 2024 / 195679

[0005] The electrolyte for energy storage devices containing ion-modified cellulose as a charge carrier described in Patent Document 1 can use water as the main medium and is environmentally friendly and safe because it is biomass-derived and PFAS-free. On the other hand, Patent Document 1 describes the formation of the electrolyte by filling a liquid dispersion of ion-modified cellulose into the space defined by the electrode and gasket, or by coating the dispersion of ion-modified cellulose onto the electrode, and does not demonstrate the formation of an electrolyte as a self-supporting, standalone membrane. Depending on the type of electrode, it may be difficult to fill the space between electrodes with a liquid electrolyte or to form an electrolyte membrane by coating it onto the electrode, and electrolytes that are not self-supporting membranes have the problem of being difficult to apply to various devices. The present invention aims to provide a membrane that can be treated as a self-supporting, standalone membrane, which can be used as an electronic component in electrochemical devices such as capacitors, secondary batteries, primary batteries, and fuel cells, using biomass-derived materials.

[0006] The inventors chemically processed cellulose fibers, which are a biomass-derived material, to produce chemically modified cellulose fibers, and used these to manufacture membranes for electronic components such as electrolyte membranes. In doing so, they found that by imparting an uneven structure that satisfies predetermined parameters to one or both sides of the membrane, the strength of the membrane can be improved, and it can be treated as a self-supporting, standalone membrane. The present invention includes the following: [1] A membrane for electronic components containing chemically modified cellulose fibers, wherein one or both sides of the membrane have an uneven structure, (a) the arithmetic mean roughness (Ra) of the surface having the uneven structure is 0.500 μm or less, and (b) the average height (Rc) of the roughness curve elements of the surface having the uneven structure is 0.050 μm or more. [2] The membrane for electronic components according to [1], further comprising (c) the average length (Rsm) of the roughness curve elements of the surface having the uneven structure being 20.000 μm or less. [3] A membrane for an electronic component according to [1] or [2], wherein the electronic component is selected from an electrolyte membrane, a support for an electrolyte membrane, or a separator. [4] A method for manufacturing a membrane for an electronic component according to any one of [1] to [3], comprising: casting a dispersion containing chemically modified cellulose onto a support having an uneven surface; drying the dispersion cast onto the support at a temperature of 35 to 80°C; and peeling it off the support after drying. [5] A method for manufacturing a membrane for an electronic component according to any one of [1] to [3], comprising: casting a dispersion containing chemically modified cellulose onto a support having an uneven surface; floating a membrane having an uneven surface on the liquid surface of the dispersion cast onto the support; drying the dispersion at a temperature of 35 to 80°C while the membrane cast onto the support having an uneven surface and floating on the liquid surface; and peeling off the support and the membrane on the liquid surface after drying. [6] The method for manufacturing a film for an electronic component according to [4] or [5], wherein the support having irregularities on its surface is a porous film made of polyethersulfone. [7] The method for manufacturing a film for an electronic component according to [5], wherein the film having irregularities on its surface is a porous film made of polyethersulfone.

[0007] According to the present invention, by using chemically modified cellulose fibers made from cellulose fibers derived from biomass, it is possible to provide a PFAS-free and environmentally friendly membrane for electronic components. Furthermore, the biomass-derived membrane of the present invention is expected to be manufactured at a lower cost than conventional membranes mainly composed of PFAS, thus offering economic advantages. Moreover, since the membrane of the present invention can be handled as a self-contained, standalone membrane, it is expected to be usable without limitation in a variety of electrochemical devices such as capacitors, secondary batteries, primary batteries, fuel cells, and air batteries, regardless of the form of components such as electrodes that come into contact with the membrane. In addition, since the membrane of the present invention can use water as the main medium, it is possible to provide a safe device, and it also has the advantage of being easy to handle even when hydrated.

[0008] In the "Performance Evaluation in Fuel Cells" section of the Examples, this is the potential-current curve of a fuel cell incorporating the membrane from Example 3.

[0009] The present invention relates to a membrane containing chemically modified cellulose fibers for use in electronic components. In particular, the membrane of the present invention has an uneven surface on one or both sides that satisfies specific parameters. Specifically, (a) the arithmetic mean roughness (Ra) of the surface of the membrane having the uneven surface is 0.500 μm or less, and (b) the average height (Rc) of the roughness curve elements of the surface of the membrane having the uneven surface is 0.050 μm or more.

[0010] (Chemically Modified Cellulose Fibers) "Chemically modified cellulose fibers" refer to cellulose fibers that have been chemically treated to introduce ionic groups into the molecular chains of cellulose. The membrane of the present invention contains chemically modified cellulose fibers as its main component, thereby achieving high ionic conductivity.

[0011] The type of cellulose fiber used to obtain chemically modified cellulose fibers is not particularly limited. Examples include bleached or unbleached mechanical pulp (e.g., thermomechanical pulp (TMP), wood pulp) and chemical pulp (e.g., sulfite pulp, kraft pulp) made from coniferous trees, hardwoods, cotton, straw, bamboo, hemp, jute, kenaf, etc., as well as dissolved pulp, and any of these can be used as raw materials.

[0012] Chemically modified cellulose fibers can be prepared by introducing ionic groups into cellulose fibers. These ionic groups may be anionic or cationic. The method for introducing these ionic groups is not particularly limited. For example, the method described later can be used.

[0013] (Anionic Modified Cellulose Fibers) Cellulose fibers into which anionic groups have been introduced as ionic groups are called "anionic modified cellulose fibers." The method of introducing anionic groups is not particularly limited, but examples include directly oxidizing the hydroxyl group of the pyranose ring of cellulose to a carboxyl group, or introducing anionic groups through an etherification or esterification reaction at the hydroxyl group portion of the pyranose ring, as will be described later.

[0014] (Carboxylated Cellulose Fibers) As an example of anionic modified cellulose fibers, carboxylated cellulose fibers having a carboxyl group can be cited. The carboxyl group (-COOH) is -COOM (metal salt type) (wherein M is a metal ion) or -COO obtained by ionization of the metal ion. －It may be in any of the above forms, or it may be in the acid form (-COOH). Carboxylated cellulose fibers can be obtained using known methods for oxidizing the hydroxyl group of the pyranose ring of cellulose to a carboxyl group. Examples of methods for oxidizing cellulose include oxidizing cellulose in water using an oxidizing agent in the presence of an N-oxyl compound such as 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and a bromide and / or iodide, or oxidizing cellulose by contacting cellulose fibers with a gas containing ozone as an oxidizing agent. Methods for producing acid-type carboxylated cellulose include desalting metal salt-type carboxylated cellulose with a cation exchange resin, or acid treatment with hydrochloric acid, etc., to replace the metal salt with a proton.

[0015] The amount of carboxyl groups in carboxylated cellulose fibers is preferably 0.4 to 3.0 mmol / g, more preferably 0.6 to 2.0 mmol / g, even more preferably 1.0 to 2.0 mmol / g, and even more preferably 1.1 to 2.0 mmol / g, relative to the oven-dry mass of the carboxylated cellulose fibers. The amount of carboxyl groups in carboxylated cellulose fibers can be adjusted by controlling reaction conditions such as the amount of oxidizing agent added and the reaction time. The amount of carboxyl groups can be measured by the following method: Prepare 60 mL of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose fibers, add a 0.1 M hydrochloric acid aqueous solution to make the pH 2.5, then add a 0.05 N sodium hydroxide aqueous solution dropwise until the pH becomes 11 and measure the electrical conductivity. From the amount of sodium hydroxide consumed in the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), the amount of carboxyl groups is calculated using the following formula: Amount of carboxyl groups [mol / g carboxylated cellulose fiber] = a [mL] × 0.05 / mass of carboxylated cellulose [g].

[0016] (Carboxyalkylated cellulose fibers) As an example of anionic modified cellulose fibers, carboxyalkylated cellulose fibers having a carboxyalkyl group can be cited. In this specification, carboxyalkyl group (-RCOOH) (wherein R is an alkylene group such as a methylene group or an ethylene group) is -RCOOM (metal salt type) (wherein M is a metal ion) or -RCOO from which the metal ion has been ionized. － Any of the above forms is acceptable. As the carboxyalkylated cellulose fiber, carboxymethylated cellulose fiber in which R is a methylene group is most preferred (hereinafter, "carboxymethyl" will be referred to as "CM"). Carboxyalkylated cellulose fiber can be obtained using a known method in which cellulose fiber is treated with a mercerizing agent and then treated with a carboxyalkylating agent to introduce a carboxyalkyl group.

[0017] The degree of carboxyalkyl substitution per anhydrous glucose unit of carboxyalkylated cellulose fibers (hereinafter also simply referred to as "degree of substitution" or "DS") is preferably less than 0.40, as this allows for the production of carboxyalkylated cellulose fibers that easily maintain their fibrous form in water. More preferably, the degree of substitution is 0.10 or more and less than 0.40, even more preferably 0.10 or more and 0.35 or less, and even more preferably 0.15 or more and 0.30 or less.

[0018] Note that anhydrous glucose units refer to individual anhydrous glucose (glucose residues) that make up cellulose, and the degree of substitution indicates the proportion of hydroxyl groups (-OH) in the glucose residues that make up cellulose that are substituted with carboxyalkyl groups (-ORCOOH or -ORCOOM) (the number of carboxyalkyl groups per glucose residue). The degree of substitution can be adjusted by controlling reaction conditions such as the amount of mercerizing agent and reaction time. For example, the degree of CM substitution can be measured by the following method: Accurately weigh about 2.0 g of CM-modified cellulose fiber (dry) and place it in a 300 mL stoppered Erlenmeyer flask. Add 100 mL of a solution made by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol, and shake for 3 hours to convert the metal salt type CM-modified cellulose fiber to hydrogen type CM-modified cellulose fiber. Accurately weigh 1.5 g to 2.0 g of hydrogen type CM-modified cellulose fiber (dry) and place it in a 300 mL stoppered Erlenmeyer flask. Wet the hydrogen-type CM-modified cellulose fibers with 15 mL of 80% by mass methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. Use phenolphthalein as an indicator and add 0.1 N H ２ SO ４ The excess NaOH is back-titrated. The degree of CM substitution (DS) is calculated by the following formula: A = [(100 × F' - (0.1 N H) ２ SO ４ ) (mL) × F) × 0.1] / (Oven-dry mass of hydrogen-type CM-modified cellulose fiber (g)) DS = 0.162 × A / (1 - 0.058 × A) A: Amount of 1N NaOH required to neutralize 1g of hydrogen-type CM-modified cellulose fiber (mL) F: 0.1N H ２ SO ４ Factor F': Factor of 0.1N NaOH The degree of substitution of carboxyalkyl groups other than the CM group can also be measured using the same method as described above.

[0019] (Phosphate-esterified cellulose fibers) Phosphate-esterified cellulose fibers can be cited as an example of anionically modified cellulose fibers. Phosphate-esterified cellulose fibers can be obtained by introducing phosphate groups derived from phosphate compounds into cellulose by mixing the above-mentioned cellulose fibers with a powder or aqueous solution of a phosphate compound, or by adding an aqueous solution of a phosphate compound to a slurry of cellulose fibers. Examples of phosphate compounds include phosphoric acid, polyphosphate, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, or esters or salts thereof. Specifically, examples include, but are not limited to, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, etc. Phosphate groups derived from phosphate compounds can be introduced into cellulose by using one or more of these in combination. In this specification, phosphate groups derived from phosphate compounds include phosphate groups, phosphite groups, hypophosphite groups, pyrophosphate groups, metaphosphate groups, polyphosphate groups, phosphonic acid groups, and polyphosphonic acid groups. Phosphate-esterified cellulose fibers include those in which one or more of these phosphate groups are introduced into the molecular chain of cellulose. When reacting cellulose with a phosphate compound, it is desirable to use the phosphate compound as an aqueous solution in order to ensure uniform reaction and high efficiency in introducing the above groups, and in this case, the pH of the aqueous solution is preferably pH 3 to 7. Nitrogen-containing compounds such as urea may also be added.

[0020] The degree of phosphate group substitution per glucose unit in phosphated cellulose fibers (hereinafter simply referred to as "phosphate group substitution degree") is preferably 0.001 or more and less than 0.40. The degree of phosphate group substitution per glucose unit can be measured by the following method: Prepare a slurry of phosphated cellulose fibers with a solid content of 0.2% by mass. Add 1 / 10 by volume of strongly acidic ion exchange resin (Organo Amberjet 1024, conditioned) to the slurry, shake for 1 hour, and then pour onto a mesh with a mesh opening of 90 μm to separate the resin and slurry and obtain hydrogen-type phosphated cellulose fibers. Next, add 50 μL of 0.1 N sodium hydroxide aqueous solution to the slurry after treatment with the ion exchange resin once every 30 seconds, and measure the change in the electrical conductivity value of the slurry. The amount of alkali (moles) required in the region where the electrical conductivity rapidly decreases from the measurement results is divided by the amount of solids (g) in the slurry being titrated to calculate the amount of phosphate groups (moles / g) per gram of hydrogen-type phosphated cellulose fiber. Furthermore, the degree of phosphate group substitution (DS) per glucose unit of phosphated cellulose fiber is calculated by the following formula: DS = 0.162 × A / (1 - 0.079 × A) where A: amount of phosphate groups per gram of hydrogen-type phosphated cellulose fiber (moles / g).

[0021] (Sulfate-esterified cellulose fibers) As an example of anionic modified cellulose fibers, sulfate-esterified cellulose fibers can be mentioned. Sulfate-esterified cellulose fibers can be obtained by reacting the above-mentioned cellulose fibers with a sulfate-based compound, thereby introducing sulfate-based groups derived from the sulfate-based compound into the cellulose. Examples of sulfate-based compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, or esters or salts thereof. Among these, sulfamic acid is preferred because it has low cellulose solubility and low acidity.

[0022] For example, when sulfamic acid is used as the sulfate compound, the amount of sulfamic acid used can be appropriately adjusted considering the amount of anionic group introduced into the cellulose chain. For example, it can be used in an amount of preferably 0.01 to 50 mol per mol of glucose units in the cellulose molecule, and more preferably in an amount of 0.1 to 3.0 mol.

[0023] The amount of sulfate groups per glucose unit in sulfated cellulose fibers (hereinafter simply referred to as "amount of sulfate groups") is preferably 0.1 to 3.0 mmol / g. The amount of sulfate groups per glucose unit can be measured by the following method: An aqueous dispersion of sulfated cellulose fibers is solvent-substituted with ethanol and then t-butanol, and then freeze-dried. 15 mL of ethanol and 5 mL of water are added to 200 mg of the obtained sample and stirred for 30 minutes. Then, 10 mL of 0.5 N aqueous sodium hydroxide solution is added and stirred at 70°C for 30 minutes, and then stirred at 30°C for 24 hours. Next, phenolphthalein is added as an indicator and titrated with hydrochloric acid, and the amount of sulfate groups is calculated using the following formula: Amount of sulfate groups [mol / g sample] = (5 - (0.1 × volume of hydrochloric acid titration [mL] × 2)) / 0.2.

[0024] (Cation-Modified Cellulose Fibers) Cellulose fibers into which a cationic group has been introduced as an ionic group are called "cation-modified cellulose fibers." The method of introducing the cationic group is not particularly limited. For example, they can be obtained by a known method in which the aforementioned carboxylated cellulose fibers are reacted with a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate or its halohydrin type, and an alkali metal hydroxide catalyst (such as sodium hydroxide or potassium hydroxide) in the presence of water or an alcohol having 1 to 4 carbon atoms.

[0025] The degree of cation substitution per glucose unit in cation-modified cellulose fibers is preferably 0.02 to 0.50. The degree of cation substitution can be adjusted by the amount of cationizing agent added and the composition ratio of water or C1-C4 alcohol. The degree of cation substitution per glucose unit can be measured by the following method: After drying the cation-modified cellulose fibers, the nitrogen content is measured using a total nitrogen analyzer (TN-10, manufactured by Mitsubishi Chemical Corporation), and the degree of cation substitution (average number of moles of substituents per mole of anhydrous glucose unit) is calculated using the following formula: Degree of cation substitution = (162 × N) / (1 - 151.6 × N) N: Nitrogen content.

[0026] (Fibrillation) The chemically modified cellulose fibers obtained as described above may be used in the membrane as is, but it is preferable to subject them to a fibrillation treatment, which reduces the diameter of the cellulose fibers, before use. Fibrillated cellulose with a small fiber diameter and cellulose nanofibers (hereinafter, "cellulose nanofibers" are also referred to as "CNF") are preferable from the viewpoint of ionic conductivity because they are easily dispersed uniformly in the membrane. Known methods for fibrillation include, but are not limited to, wet or dry treatment using high-pressure homogenizers, microfluidizers, refiners, grinders, shear-type stirrers, colloid mills, beaters, kneaders, dispersers, freeze-drying and grinding, ultrasonic fibrillation, etc.

[0027] The degree of fibrillation is not particularly limited. For example, the chemically modified cellulose fiber before fibrillation (e.g., chemically modified pulp), although not limited thereto, often has a fiber diameter of 10 to 50 μm and a fiber length of about 0.5 to 5.0 mm. By fibrillation of this or by partially raising the fiber surface fluff (fibrillation), fibrillated cellulose fibers with an average fiber diameter of about 1 to 10 μm may be used. The average fiber diameter of the fibrillated cellulose fibers is more preferably about 5 to 10 μm. The average fiber length of the fibrillated cellulose fibers is not particularly limited, but is about 0.2 to 3.0 mm, more preferably about 0.3 to 2.5 mm, and even more preferably about 0.5 to 2.0 mm. The average fiber diameter and average fiber length of the fibrillated cellulose fibers can be determined by an image analysis type fiber analyzer such as the L&W Fiber Tester Plus manufactured by ABB or the fractionator manufactured by Valmet. Specifically, it can be measured by the following method: A water dispersion of fibrillated cellulose fibers diluted to a solid content concentration of 0.25% by mass is subjected to a fractionator, and is determined as length-weighted fiber width and length-weighted average fiber length, respectively (n = 2).

[0028] In this specification, what is obtained by fibrillating a chemically modified cellulose fiber may be referred to as a chemically modified fibrillated cellulose fiber. Similarly, for example, what is obtained by fibrillating an anion-modified cellulose fiber may be referred to as an anion-modified fibrillated cellulose fiber.

[0029] Chemically modified cellulose fibers may optionally be defibrated until their diameter is smaller than that of fibrillated cellulose fibers, i.e., until the average fiber diameter is less than 1 μm, to obtain chemically modified CNF. When obtaining chemically modified CNF from chemically modified cellulose fibers, it is preferable to use a wet high-pressure homogenizer. The average fiber diameter of the chemically modified CNF is more preferably about 3 to 500 nm, even more preferably about 3 nm to 150 nm, and even more preferably about 3 nm to 20 nm. The aspect ratio of the chemically modified CNF is preferably 30 or more, more preferably 50 or more, and even more preferably 100 or more. There is no upper limit to the aspect ratio, but it is generally around 500 or less. The average fiber diameter and average fiber length of CNF can be measured by analyzing 200 randomly selected fibers using an atomic force microscope (AFM) when the diameter is less than 20 nm, or a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more, and calculating the average. Furthermore, the aspect ratio can be calculated using the following formula: Aspect ratio = Average fiber length / Average fiber diameter.

[0030] In this specification, chemically modified cellulose fibers obtained by defibrating them to a CNF with an average fiber diameter of less than 1 μm are referred to as chemically modified CNF. Similarly, for example, CNF obtained by defibrating anionically modified cellulose fibers may be called anionically modified CNF, and CNF obtained by defibrating carboxylated cellulose fibers may be called carboxylated CNF.

[0031] (Membrane for Electronic Components) The membrane for electronic components of the present invention is a membrane containing the above-mentioned chemically modified cellulose fibers (hereinafter, when simply referred to as "chemically modified cellulose fibers," unless otherwise specified, this includes unfibrillated chemically modified cellulose fibers, as well as chemically modified fibrillated cellulose and chemically modified CNF obtained by fibrillating chemically modified cellulose fibers). The membrane of the present invention can be used as an electronic component in electrochemical devices such as capacitors, secondary batteries, primary batteries, fuel cells, and air batteries. Examples of electronic components include electrolyte membranes, electrolyte membrane supports, and separators. In particular, it is preferable to use the membrane of the present invention as an electrolyte membrane because it can fully utilize the ion conductivity provided by the chemically modified cellulose fibers.

[0032] The film of the present invention has an uneven structure that satisfies specific parameters, and thus can be treated as a self-standing single film. "Can be treated as a self-standing single film" means that, at the normal area when used as an electronic member, it can maintain the shape as a film even without the presence of other supports. Further, the film of the present invention is difficult to deform and has good handleability when hydrated during use or the like. Although the reason why these advantages are obtained due to the uneven structure that satisfies specific parameters is not clear, the inventors speculate as follows: The film of the present invention has a specific uneven structure on at least one side, so that stress concentration is unlikely to occur during handling, and the stress caused by an external force is dispersed, making it difficult to break. Also, due to the presence of the uneven structure on the surface of at least one side, when hydrated and moisture penetrates into the film, the structural change is reduced, and also during drying, the shrinkage stress is dispersed, an even force is applied to the entire film, making stress concentration unlikely to occur, and suppressing the deformation of the film during hydration.

[0033] (Uneven structure) The uneven structure in the film of the present invention refers to, for example, the unevenness on the surface of the film that can be confirmed in the three-dimensional surface shape image of the film (resolution in the height direction: 0.01 μm) by the white confocal microscope described in the examples below. In the film of the present invention, the uneven structure may be formed on both sides of the film or only on one side of the film.

[0034] The film of the present invention satisfies the following conditions for a surface having an uneven structure: (a) an arithmetic mean roughness (Ra) of 0.500 μm or less, and (b) an average height (Rc) of the roughness curve elements of 0.050 μm or more. In the present invention, (a) the arithmetic mean roughness (Ra) is a value measured by the method described in the examples below. That is, after drying the film at 40°C for 12 hours, the Ra of the film is defined as the average value of Ra measured at three different locations within a 100 μm × 100 μm rectangular area from a three-dimensional surface shape image of the film (height resolution of 0.01 μm) obtained using a white confocal microscope. Ra is an index that shows the average of the absolute values ​​of the height and depth of the roughness curve of the surface unevenness within the measurement range, and can be used to evaluate the overall degree of surface roughness. A smaller Ra indicates a flatter and smoother surface, while a larger Ra indicates a rougher surface. The film of the present invention has an Ra of 0.500 μm or less for a surface having an uneven structure. More preferably, the particle size is 0.200 μm or less, even more preferably 0.100 μm or less, and even more preferably 0.050 μm or less. The lower limit is not particularly limited. As a guideline, it is not limited to these values, but may be around 0.001 μm or more, for example 0.010 μm or more, or for example 0.020 μm or more.

[0035] In the present invention, (b) the average height (Rc) of the roughness curve elements is a value measured by the method described in the examples below, similar to Ra described above. Rc is an index that shows the average length from the bottom of the valley to the top of the protrusion of each individual surface roughness curve within the measurement range, and can be used to evaluate the degree of the average size of the surface roughness. By combining Ra and Rc, it is possible to evaluate the state of the surface roughness that cannot be recognized by Ra alone. In the film of the present invention, the Rc of the surface having a surface roughness structure is 0.050 μm or more. More preferably, it is 0.060 μm or more, even more preferably 0.080 μm or more, and even more preferably 0.100 μm or more. The upper limit is not particularly limited. As a guideline, it is not limited to these, but may be 1.000 μm or less, for example 0.500 μm or less, or for example 0.200 μm or less. Thus, when Rc is above a certain level, while Ra is below a certain level as described above, it indicates that although the degree of unevenness (overall roughness) is not very large, fine protrusions are present.

[0036] In addition to Ra and Rc, the surface of the film of the present invention having an uneven structure preferably has (c) an average length of roughness curve elements (Rsm) of 20,000 μm or less. Rsm is a value measured by the method described in the examples below, similar to Ra and Rc. Rsm is an index that shows the average width of individual protrusions on the roughness curve of the surface unevenness within the measurement range, and can be used to evaluate the degree of spacing between surface unevennesses. Generally, if the unevenness is uniformly present in the film, Rsm tends to be small. Rsm is more preferably 18,000 μm or less, even more preferably 16,000 μm or less, and even more preferably 15,000 μm or less. The lower limit is not particularly limited. As a guideline, it may be 1,000 μm or more, for example 5,000 μm or more, or for example 10,000 μm or more, although it is not limited to these.

[0037] The surface of the film of the present invention having an uneven structure preferably has a maximum peak height (Rp) of 10,000 μm or less, more preferably 5,000 μm or less, and more preferably 1,000 μm or less. Rp is a value that indicates the maximum height of the protrusions on the surface roughness curve within the measurement range. The lower limit of Rp is not particularly limited, but as a guideline, it may be around 0.010 μm or more, for example, 0.080 μm or more.

[0038] Furthermore, the surface of the film of the present invention having an uneven structure preferably has a maximum valley depth (Rv) of 10,000 μm or less, more preferably 5,000 μm or less, and most preferably 1,000 μm or less. Rv is a value that indicates the maximum depth of the valley in the surface roughness curve of the surface unevenness within the measurement range. The lower limit of Rv is not particularly limited, but as a guideline, it may be around 0.010 μm or more, and for example, it may be 0.050 μm or more.

[0039] Furthermore, the surface of the film having an uneven structure of the present invention preferably has a maximum height roughness (Rz) of 20,000 μm or less, preferably 10,000 μm or less, and more preferably 2,000 μm or less. Rz is a value corresponding to the sum of the maximum height of the protrusions and the maximum depth of the valleys in the surface roughness curve of the surface unevenness within the measurement range. The lower limit of Rz is not particularly limited, but as a guideline, it may be around 0.020 μm or more, and for example, it may be 0.120 μm or more.

[0040] Rp, Rv, and Rz can be measured by the method described in the examples below, similar to Ra, Rc, and Rsm described above. The method for producing a film having such an uneven structure is not particularly limited. For example, as described in the examples, it can be produced by casting a dispersion containing chemically modified cellulose fibers onto a support having fine irregularities on its surface, drying it, and then peeling it off the support. Alternatively, a film having an uneven structure on both sides can be produced, for example, by casting a dispersion containing chemically modified cellulose fibers onto a support having fine irregularities on its surface, then, before the dispersion dries, placing a thin film with fine irregularities on the surface of the dispersion (floating it on the surface), so that the fine irregularities come into contact with both sides of the cast dispersion, drying it in this state, and then peeling the support on the bottom surface from the thin film on the liquid surface after drying. Supports and thin films having fine irregularities on their surfaces that can be used in such production methods are not limited to these, but examples include porous films made of resin, metal, or glass, or silicon wafer substrates, glass substrates, metal substrates, ceramic substrates, or resin substrates with fine irregularities on their surfaces. Among these, porous membranes made of resin offer an excellent balance of cost and strength and are therefore suitable for use. The type of resin is not particularly limited, but polyethersulfone is preferred because of its good dimensional stability, wettability of the dispersion, and release properties. For example, a porous membrane made of polyethersulfone with an average pore size of about 0.10 to 2.00 μm, preferably about 0.10 to 1.00 μm, can be used as a support used on the bottom surface and / or as a thin film placed on the liquid surface. When using a porous membrane made of polyethersulfone as a support on the bottom surface, it is preferable to place another hard, flat support (for example, a glass plate or a smooth resin plate) beneath the porous membrane in order to keep it flat.

[0041] When drying a dispersion with fine irregularities on a support or the like in contact with it, it is preferable to dry it slowly at a low temperature under normal pressure so as not to damage the structure of the irregularities transferred from the support or the like as much as possible. For example, it is preferable to dry it at a temperature of about 30 to 80°C, more preferably 35 to 50°C, for 10 hours or more, for example, 12 hours or more. If high temperatures are used, the support and the film may undergo thermal deformation, making peeling difficult or increasing the risk of damage to the irregularities during peeling. For the same reason, it is also undesirable to use pressure filtration or vacuum filtration for dewatering.

[0042] The dispersion contains at least a dispersion medium such as water and chemically modified cellulose fibers. The concentration of solids of the chemically modified cellulose fibers in the dispersion is not particularly limited, as long as it is a concentration that maintains the fluidity of the dispersion. For example, it is about 0.1 to 5.0% (w / v), and more preferably about 0.3 to 1.0% (w / v).

[0043] The dispersion may consist of a dispersion medium and chemically modified cellulose fibers. It may also contain one or more other substances, to the extent that they do not interfere with the function of the chemically modified cellulose fibers, and a membrane produced from such a dispersion may contain such substances in addition to the chemically modified cellulose fibers. Examples of such substances include nonionic cellulose and cellulose derivatives, chitin, chitosan, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride, polyethylene terephthalate, polymethyl methacrylate resin, polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyparabenic acid resin, polyether resin, polyester resin, polyether derivatives, and polymers added to improve mechanical strength, such as polyimine resin, polyamide resin, and polycarbonate resin, as well as ionic liquids and electrolytes other than chemically modified cellulose fibers (e.g., organic acids and their salts, inorganic acids and their salts, perfluorosulfonic acid polymers, etc.). Examples include molecular electrolytes and inorganic electrolytes such as glass ceramics), electrolyte salts (e.g., lithium salts such as lithium hexafluorophosphate, quaternary ammonium salts), ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, vinylene carbonate, 1,3-propanesultone, methanesulfonic acid (R)-1-methyl-2-propynyl, cyclohexylbenzene, tert-amylbenzene, adiponitrile, phthalates, adipicates, trimelliticates, polyesters, phosphate esters, citrate esters, epoxidized vegetable oils, sebacateates, azelaates, maleates, and benzoates.

[0044] The proportion of chemically modified cellulose fibers in the membrane of the present invention is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 80% by mass or more, when dried at 40°C for 12 hours. The upper limit may be 100% by mass (i.e., the membrane consists only of chemically modified cellulose fibers).

[0045] The thickness of the film of the present invention may be appropriately set according to various uses and is not particularly limited. For example, in the state of being dried at 40 °C for 12 hours, it is about 1 to 200 μm, preferably about 5 to 50 μm.

[0046] The basis weight of the film of the present invention may be appropriately set according to various uses and is not particularly limited. For example, in the state of being dried at 40 °C for 12 hours, it is about 1 to 200 g / m ２ and preferably about 5 to 100 g / m ２ degree.

[0047] The film of the present invention may be impregnated with a medium such as water as necessary during use. The medium may be any medium that enables the chemical modified cellulose fiber to be ionized, but from the viewpoints of low environmental impact and safety, it is most preferable to use water. Examples of media other than water include water-soluble organic solvents such as methanol, ethanol, isopropanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, ethylene glycol, ethylene carbonate, propylene glycol, propylene carbonate, and also glymes such as tetraethylene glycol dimethyl ether, sulfones such as sulfolane, and combinations thereof. The proportion of water in the medium is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 100% by mass (the medium is all water). The film swells by impregnating with a medium such as water. The film of the present invention tends to be less likely to undergo shape changes such as breakage during handling in a swollen state after being hydrated. In addition, the ratio of the increase in thickness and basis weight due to swelling tends to be small.

[0048] When the film of the present invention contains a medium, the mass % of the medium is not particularly limited, but from the viewpoint of ensuring ionic conductivity, the proportion of the medium is preferably 0.1 to 99.9% by mass based on the total mass of the film and the medium, and more preferably 10 to 90% by mass.

[0049] The membrane of the present invention contains chemically modified cellulose fibers and therefore possesses ionic conductivity. In the present invention, conductivity represents the ease of ion movement, and higher conductivity means lower resistance to ion movement. The conductivity of the membrane of the present invention is not particularly limited, but when measured by the method described in the examples below, it is preferably 0.01 mS / cm or higher, more preferably 0.10 mS / cm or higher, even more preferably 1.00 mS / cm or higher, and particularly preferably 3.00 mS / cm or higher. Having high conductivity is advantageous when used as a standalone electrolyte membrane, and when used as a support for an electrolyte membrane, it can be utilized as an electronic component that contributes to the overall ionic conductivity of the electrolyte compared to a non-ionic conductive support. Furthermore, when used as a separator, it is possible to support ion conduction while preventing electron conduction.

[0050] (Electrochemical Devices) The film of the present invention can be used as an electronic component in electrochemical devices such as capacitors, secondary batteries, primary batteries, fuel cells, and air batteries. Examples of electronic components include electrolyte membranes, electrolyte membrane supports, and separators. In particular, it is preferable to use the film of the present invention as an electrolyte membrane because it can fully utilize the ion conductivity due to the chemically modified cellulose fibers and the effect of reducing contact resistance due to the increased contact area with electrodes caused by the uneven structure. There are no particular limitations on the components other than the film of the present invention when forming an electrochemical device, and ordinary components used in various electrochemical devices can be used in a normal arrangement.

[0051] For example, when the film of the present invention is applied to a secondary battery or the like and used as an electrolyte film, the components other than the film of the present invention in the secondary battery or the like are not particularly limited, but for example, as the positive electrode material, LiCo ２ NaCoO ２ , LiNiCoMnO ２ LiMn ２ O ４ NaMn ２ O ４ LiFePO ４ Oxide systems such as Li ４ Ti ５ O１２ Spinel-type oxides, sulfide-based materials, phosphide-based materials, Prussian blue analogs, etc., can be used, and as a negative electrode material, lithium metal, sodium metal, lithium titanate (LTO), graphite, silicon alloys, tin alloys, titanium oxides, graphite, carbon nanotubes, carbon materials such as graphene, metal oxides, etc. can be used. When the electrolyte membrane contains other media such as an electrolyte, examples of solvents for the electrolyte include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), acetonitrile (AN), tetrahydrofuran (THF), sulfolane (SL), methylsulfolane, tetraglycerides, etc., lactones such as γ-butyrolactone (γ-BL), ionic liquids, water, and aqueous electrolytes, and lithium hexafluoride phosphate (LiPF) can be used as a salt. ６ ), bis(fluorosulfonyl)imide lithium (LiFSI), bis(trifluoromethanesulfonyl)imide lithium (LiTFSI), lithium perchlorate (LiClO) ４ ), sodium hexafluoride phosphate (NaPF ６ ), bis(fluorosulfonyl)imide sodium (NaFSI), bis(trifluoromethanesulfonyl)imide sodium (NaTFSI), sodium perchlorate (NaClO ４Examples include the above. In addition, predetermined additives can be used. The membrane of the present invention is self-supporting and functions as a fibrous structure, and can be used alone as a separator, but it may also be used in combination with another separator. Such separators are not particularly limited, but examples include polypropylene, polyethylene (PE), ceramic-coated polypropylene / polyethylene (PP / PE), polyamide (nylon), polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polyimide (PI), polyacrylonitrile (PAN), zeolite membranes, glass fibers, and cellulose-based materials. The form of such separators is not particularly limited, and nonwoven fabrics, films, textiles, fibrous structures, multilayer film structures, ceramic composite membranes, etc., can be used. Furthermore, when the membrane of the present invention is used as a support for an electrolyte membrane, self-supporting and ionic conductivity can be imparted to the electrolyte by compounding the membrane of this development with an electrolyte that has low self-supporting properties, such as a compound of the aforementioned medium and salt or a gel electrolyte. The method of compounding is not particularly limited, but examples include impregnating the membrane of the present invention with a predetermined electrolyte, coating, and pressing.

[0052] When the film of the present invention is applied to a capacitor, the components of the capacitor other than the film of the present invention are not particularly limited, but for example, activated carbon with a high specific surface area, carbon-based materials, metal oxides, conductive polymers, and mixtures thereof can be used for the electrodes. Electrolytes containing the aforementioned solvents and salts can also be used.

[0053] When the membrane of the present invention is applied to a fuel cell, components other than the membrane of the present invention in the fuel cell are not particularly limited, but the catalyst can be platinum (Pt), platinum-ruthenium (Pt-Ru) alloy, platinum-cobalt (Pt-Co) alloy, platinum-nickel (Pt-Ni) alloy, palladium (Pd), iridium (Ir), ruthenium (Ru), and alloys thereof, nanoparticle catalysts, and non-precious metal catalysts (e.g., iron-nitrogen-carbon composite (Fe-N-C)). As the gas diffusion layer, carbon-based materials (e.g., carbon paper, carbon cloth, carbon nanotubes (CNTs)), graphite, graphene, porous metal, metal foam, etc. As the separator (bipolar plate), graphite, metal (stainless steel, titanium, nickel), resin-impregnated carbon, composite materials (e.g., carbon polymer composite materials, carbon ceramic composite materials), and these materials that have been gold-plated, nickel-plated, or otherwise surface-treated to improve corrosion resistance and conductivity can be used. When the membrane of the present invention is used as an electrolyte support, fluorinated polymer electrolytes and hydrocarbon polymer electrolytes can be used as the electrolyte, although this is not particularly limited. Examples of fluorinated polymer electrolytes include perfluorosulfonic acid (PFSA) resin, fluorinated ionomer, perfluorocarbon acid resin (Aciplex), and polytetrafluoroethylene-based fluorinated polymers. Examples of hydrocarbon polymer electrolytes include sulfonated polyether ketone (SPEEK), sulfonated polyetherimide (SPI), sulfonated polyethersulfone (SPES), sulfonated polyetherether ketone (PEEK), sulfonated polysulfide (SPSU), sulfonated polyphenylene sulfide (SPPS), sulfonated polyphenylene oxide (SPPO), as well as polybenzimidazole (PBI) and polyarylene ether ketone (PAEK). By compounding these polymer electrolytes with the membrane of the present invention, an electrolyte membrane that is self-supporting, easy to handle, and has good ionic conductivity can be used.

[0054] The film of the present invention has improved strength as a self-supporting film due to its fine irregularities, and also possesses low surface roughness despite the presence of fine irregularities, offering many advantages when used in electrochemical devices. Specifically, when used in contact with electrodes as an electrochemical device, the irregular structure improves contact with the electrodes, resulting in an increased contact area and reduced contact resistance, improved charge transfer efficiency, and overall device performance. Furthermore, suppression of swelling and deformation reduces mechanical stress on the film, leading to a longer lifespan. The irregular structure also increases the surface area of ​​the film, which tends to improve ion conductivity. Moreover, the rate of increase in thickness and basis weight due to swelling when hydrated tends to be small, making it easier to maintain a high ion concentration responsible for ion conduction and ensuring ion conductivity. Due to these characteristics, the film of the present invention contributes to the realization of high-performance electrochemical devices.

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. (Preparation of chemically modified cellulose fibers) 500 g (absolutely dry) of bleached, unbeaten kraft pulp (whiteness 85%) derived from coniferous trees was added to 50 L of an aqueous solution in which TEMPO (Sigma Aldrich) (0.025 mmol / g relative to the cellulose raw material) and sodium bromide (1.0 mmol / g relative to the cellulose raw material) were dissolved, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to a concentration of 5.2 mmol / g relative to the cellulose raw material to start the oxidation reaction. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by sequentially adding an aqueous solution of 3 M sodium hydroxide. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system no longer changed. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp. The pulp yield at this stage was 90%, and the oxidation reaction took 100 minutes. The oxidized pulp (carboxylated cellulose fibers) obtained in the above process was adjusted to 0.5% (w / v) with water, and subjected to five defibration treatments in a high-pressure homogenizer (20°C, 150 MPa) to obtain a dispersion of carboxylated CNF. The amount of carboxyl groups in the obtained carboxylated CNF was 1.30 mmol / g, and the average fiber diameter was 3 nm.

[0056] (Example 1) A silicon frame (10 cm × 10 cm) was placed on a porous membrane (pore size 0.45 μm) made of polyethersulfone (PES), and an aqueous dispersion of carboxylated CNF obtained above (solid content 0.5% (w / v), COONa type) was poured into it. Next, the PES porous membrane was placed on the surface of the dispersion in the silicon frame and dried at 40°C for 12 hours. A clean oven (cleanliness class 100) was used during drying to prevent contamination by foreign matter. After drying, the PES porous membrane was peeled off to obtain a carboxylated CNF membrane. The obtained membrane was self-supporting and showed flexibility that did not crack even when bent. Surface observation with a white confocal microscope revealed surface irregularities.

[0057] (Example 2) A film was obtained in the same manner as in Example 1, except that the PES porous film was not placed on the surface of the dispersion liquid in the silicone frame and the film thickness after drying was changed. The film thickness was adjusted by the amount of aqueous dispersion liquid placed in the silicone frame. The obtained film was self-supporting and showed flexibility that did not crack even when bent.

[0058] (Example 3) A film was obtained in the same manner as in Example 1, except that the pore size of the PES porous film was changed to 0.1 μm and the PES porous film was not placed on the surface of the dispersion liquid in the silicon frame.

[0059] (Comparative Example 1) A film was obtained in the same manner as in Example 1, except that a glass plate was used on the bottom surface instead of the PES porous film, and the PES porous film was not placed on the surface of the dispersion liquid in the silicon frame.

[0060] (Comparative Example 2) A film was obtained in the same manner as in Comparative Example 1, except that a polystyrene petri dish was used instead of a glass plate for the bottom surface.

[0061] (Comparative Example 3) A film was obtained in the same manner as in Comparative Example 1, except that an aqueous solution of carboxymethylcellulose (CMC) (manufactured by Nippon Paper Industries Co., Ltd.: FS350HC, DS0.90) was used instead of an aqueous dispersion of carboxylated CNF.

[0062] (Evaluation of surface condition) A three-dimensional surface shape image of the film (height resolution of 0.01 μm) was obtained using a white confocal microscope (Lasertec OPTELICS HYBRID+). As a result, it was observed that irregularities were formed on the surface of the film on the side that was in contact with the PES porous film in Examples 1 to 3. On the other hand, no irregularities were confirmed on the surface that was not in contact with the PES porous film in Examples 2 and 3, and no irregularities were confirmed on either side of the films in Comparative Examples 1 to 3.

[0063] Furthermore, for the obtained images (images of the surfaces where irregularities were observed in Examples 1-3, and images of the bottom surface in Comparative Examples 1-3), the arithmetic mean roughness (Ra) within a 100 μm × 100 μm rectangular area was measured at three different locations using the software (LMeye7) attached to the above-mentioned microscope, and the average value of the three points was calculated. Similarly, the average height (Rc) of the roughness curve elements, the average length (Rsm) of the roughness curve elements, the maximum peak height (Rp), the maximum valley depth (Rv), and the maximum height roughness (Rz) were also measured, and the average values ​​of the three points were calculated. The evaluation results are shown in Table 1.

[0064]

[0065] The results in Table 1 show that the films of the present invention (Examples 1-3) have fine irregularities formed on one or both sides of the film. On the other hand, the films of Comparative Examples 1-3 show small values ​​for both Ra and Rc, indicating that they are smooth with no significant irregularities on the surface.

[0066] (Evaluation of the effect of water content 1) The area and mass of the film immediately after drying, manufactured as described above, were measured, and the basis weight was calculated. The film thickness was measured using a thickness gauge (Mitutoyo Corporation: Code No. 547-401, measuring force 3.5 N or less). Next, the film was immersed in deionized water for 10 minutes to remove the surface water, and the basis weight and film thickness after water content were measured in the same manner. Furthermore, after water content, the handling properties of the film were evaluated by observing whether the film maintained its shape (whether or not damage or change in shape occurred) when the end of the film was grasped with tweezers, the film was bent 180°, and then returned to its original position. "Maintaining shape" means that the film does not break or change in shape. The results are shown in Table 2. The film of Comparative Example 3 dissolved when immersed in deionized water, so the basis weight and film thickness after water content could not be measured.

[0067]

[0068] The results in Table 2 show that the membranes of Examples 1 to 3 did not change shape even after being immersed in deionized water, and were easy to handle as self-supporting membranes.

[0069] (Evaluation of the effect of moisture content 2) The film produced above, immediately after drying, was prepared as a 10 mm wide strip test piece, and the film thickness was measured using a thickness gauge (Mitutoyo Corporation: Code No. 547-401, measuring force 3.5 N or less) (thickness before moisture content). Next, the tensile strength was measured using a force gauge (IMADA load-displacement measuring unit) at a breaking speed of 20 mm / min. The tensile strength (MPa) was calculated by multiplying the load (N) at the time of breaking by the cross-sectional area (mm²) calculated from the test width (10 mm) and thickness (μm) at the time of measurement. ２ The tensile strength before water absorption was determined by dividing by ( ). In addition, a separate 10 mm wide strip test piece was immersed in deionized water for 1 minute, and after removing the water from the surface, the film thickness and tensile strength were determined in the same manner as above (thickness and tensile strength after water absorption). The results are shown in Table 3. In Comparative Example 3, the film did not stand upright after being immersed in deionized water for 1 minute, so the thickness and tensile strength after water absorption could not be measured.

[0070]

[0071] As shown in Table 3, all films exhibited high tensile strength in their pre-water (dry) state. On the other hand, after water absorption, the films of Examples 1 to 3 exhibited tensile strength more than 10 times higher than the comparative example film. This demonstrates that by imparting an uneven surface structure to the film according to the present invention, the self-supporting and handling properties after water absorption are significantly improved compared to conventional smooth films.

[0072] (Measurement of Conductivity) The membrane was immersed in deionized water for 10 minutes, and after removing the surface water, the conductivity in the thickness direction of the membrane was measured. An impedance measuring device (Keysight 4294A) was used for the measurement, with a frequency range of 100 MHz → 100 Hz and an amplitude of 20 mV. Au electrodes were used, and the conductivity was calculated based on the following formula: σ = {L / (R × A)} × 1000 σ: Conductivity (mS / cm) L: Membrane thickness (cm) R: Resistance (Ω) A: Electrode area (cm) ２ The results are shown in Table 4. The membrane of Comparative Example 3 dissolved when immersed in deionized water, so its conductivity could not be measured.

[0073]

[0074] The results in Table 4 show that the films of Examples 1 to 3 exhibit good conductivity. (Measurement of capacitance) Activated carbon (manufactured by Kureha Corporation) was used as a porous electrode, carbon black (manufactured by Denka Corporation: model number Li-400) as a conductive additive, and styrene-butadiene rubber (SBR) (manufactured by JSR Corporation: model number TRD2001) as a binder were mixed in water in a dry mass ratio of 10:1:0.5. The mixture was dispersed using a rotary-orbit mixer at 2000 rpm for 20 minutes to obtain a carbon dispersion with a concentration of 30% by mass. The carbon dispersion was coated onto etched aluminum foil (25 cm x 20 cm, 20 μm thick) as a current collector substrate, and then moisture was removed in an 80°C dryer to obtain a coating film with a mass of 40 g / m². ２ A porous current collector electrode was obtained. The obtained porous current collector electrode was measured over an area of ​​2 cm². ２ They were punched out to form the positive and negative electrodes.

[0075] The membranes of Examples 1 and 2 and Comparative Example 1 were immersed in deionized water for 10 minutes to create a hydrated state. A coin-type cell was fabricated by placing the hydrated membrane between the positive and negative electrodes. Charge-discharge tests were performed on the obtained cell using an electrochemical evaluation device (Biologic SP-300), and the capacitance (mF) was calculated from the discharge curve of the third cycle. The charge-discharge conditions were as follows: (1) CC charging was performed to 1.2V with a charging current of 1mA, and then CV charging was performed at 1.2V for 5 minutes. (2) Next, CC discharge was performed to 0.1V with a discharge current of 1mA. (3) Next, the capacitance was calculated from the discharge curve with voltage on the vertical axis against time on the horizontal axis. The results are shown in Table 5. The membrane of Comparative Example 1 was difficult to handle when hydrated and could not be incorporated into a coin-type cell.

[0076]

[0077] The results in Table 5 show that the membranes of Examples 1 and 2 are easy to handle when hydrated and can be incorporated into coin-type cells using the above-described manufacturing procedure. (Performance evaluation in fuel cells) 0.8 g of commercially available platinum-supported carbon particles (manufactured by Tanaka Kikinzoku Co., Ltd., platinum support amount to carbon: 40% by mass) were added to 10.4 g of ethylene glycol dimethyl ether and dispersed by ultrasonic treatment. Then, 4.0 g of commercially available 5% by mass Nafion® solution (manufactured by Sigma-Aldrich, USA) was added as an electrolyte resin solution and dispersed further by ultrasonic treatment. Finally, the mixture was stirred with a stirrer to prepare a catalyst paste.

[0078] Next, spread this catalyst paste to 25 cm ２ The material was applied to a support (product name: PTFE tape, thickness 0.1 mm), dried in a hot air dryer at 60°C, and the platinum load on the support was 0.4 mg / cm³. ２ A catalyst layer was fabricated.

[0079] As solid polymer films, the films of Example 3 and Comparative Example 2 were prepared. The catalyst layer was transferred to both sides of these solid polymer films and laminated, and then bonded by hot pressing, resulting in an electrode area of ​​25 cm². ２ A solid polymer film-catalyst layer junction was fabricated.

[0080] A membrane-electrode assembly (MEA) was fabricated using this solid polymer membrane-catalyst layer assembly. To ensure ion conductivity, the prepared MEA was stored immersed in deionized water. In this case, the MEA using the membrane from Comparative Example 2 was damaged during storage in deionized water, and therefore could not be incorporated into the fuel cell.

[0081] A microporous layer (MPL) (gas diffusion layer (GDL)) formed on Toray Industries' TGP-H-060 carbon paper and a graphite separator (bipolar plate) were prepared. The MEA and GDL were then assembled into a polymer electrolyte fuel cell (manufactured by NF Circuit Design Block Co., Ltd., product name: As-510-C25-1H) with a clamping pressure of 1.5 N·m, and the power generation performance was evaluated.

[0082] For power generation, hydrogen gas was supplied to the fuel electrode side with a utilization rate of 70% and air gas to the air electrode side with a utilization rate of 45%. The cell temperature was 30°C and the bubbler temperature was 30°C under full humidification conditions, and the potential-current curve was measured. Figure 1 shows the potential-current curve of the fuel cell incorporating the membrane of Example 3. At this point, the OCV was 0.92V and the maximum current density was 65mA / cm². ２ It was found that the membrane of the present invention has good handling properties when hydrated and can be incorporated into a fuel cell using the above manufacturing procedure.

Claims

1. A film for electronic components containing chemically modified cellulose fibers, wherein the film has an uneven surface on one or both sides, and (a) the arithmetic mean roughness (Ra) of the surface having the uneven surface is 0.500 μm or less, and (b) the average height (Rc) of the roughness curve elements of the surface having the uneven surface is 0.050 μm or more.

2. Furthermore, (c) the film for electronic components according to claim 1, wherein the average length (Rsm) of the roughness curve elements of the surface having an uneven structure of the film is 20,000 μm or less.

3. The membrane for an electronic component according to claim 1 or 2, wherein the electronic component is selected from an electrolyte membrane, a support for an electrolyte membrane, or a separator.

4. A method for producing a film for an electronic component according to claim 1, comprising: casting a dispersion containing chemically modified cellulose onto a support having an uneven surface; drying the dispersion cast onto the support at a temperature of 35 to 80°C; and peeling it off from the support after drying.

5. A method for manufacturing a film for an electronic component according to claim 1, comprising: casting a dispersion containing chemically modified cellulose onto a support having an uneven surface; floating a film having an uneven surface on the surface of the dispersion cast onto the support; drying the dispersion at a temperature of 35 to 80°C while the film cast onto the support having an uneven surface and floating on the liquid surface; and peeling off the support and the film on the liquid surface after drying.

6. The method for manufacturing a film for an electronic component according to claim 4 or 5, wherein the support having irregularities on its surface is a porous film made of polyethersulfone.

7. The method for manufacturing a film for an electronic component according to claim 5, wherein the film having irregularities on its surface is a porous film made of polyethersulfone.

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