Titanium paste and method for manufacturing green body and sheet-like titanium porous body using the same

Abstract

To provide methods for manufacturing a titanium paste, a green body, and a sheet-like titanium porous body with good yield.SOLUTION: A method for manufacturing a titanium paste for manufacturing a sheet-like titanium porous body includes preparing a mixture by mixing a solution of an acrylic-polymer-based binder and a diluting solvent, and thereafter mixing the mixture and titanium powder. In this method, a foaming agent is not added. In addition, in this method, a plasticizer may further be added at the time of preparing the mixture or at the time of mixing the mixture and titanium powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a titanium paste for producing a sheet-shaped porous titanium body. Another embodiment of the present invention relates to a green body and a method for producing a sheet-shaped porous titanium body using the titanium paste as a raw material. [Background technology]

[0002] Sheet-shaped porous titanium containing titanium (zero-valent titanium) is widely used in filters, secondary battery electrodes, solid polymer fuel cell current collectors, catalyst supports, and the like. One method for producing sheet-shaped porous titanium is the paste method. For example, in the method described in Patent Document 1, a slurry containing titanium powder, an organic binder, a foaming agent, and a plasticizer is prepared, and the slurry is then applied and foamed to produce a foamed body. The foamed body is then degreased and sintered to produce a sheet-shaped porous titanium. In the method described in Patent Document 2, titanium powder and a solid organic binder are simultaneously added to an organic solvent and mixed to prepare a titanium paste, which is then applied and dried to produce a molded body called a green body. The molded body is then degreased and sintered to produce a sheet-shaped porous titanium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-102701 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-84505 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a titanium paste that is a raw material for a sheet-shaped porous titanium body, a method for producing the same, and a method for producing a green body and a sheet-shaped porous titanium body from the titanium paste. Alternatively, an object of one embodiment of the present invention is to provide a method for producing a titanium paste, a green body, and a sheet-shaped porous titanium body with good yield. [Means for solving the problem]

[0005] One embodiment of the present invention is a method for producing a titanium paste for producing a sheet-shaped porous titanium body, which includes mixing a solution of an acrylic polymer binder with a diluent solvent to prepare a mixture, and then mixing the mixture with titanium powder.

[0006] One embodiment of the present invention is a titanium paste for producing a sheet-shaped porous titanium body, which contains titanium powder, an acrylic polymer binder, an organic solvent, and a plasticizer, but does not contain a foaming agent.

[0007] One embodiment of the present invention is a method for producing a green body for producing a sheet-shaped porous titanium body, which method comprises applying the titanium paste produced by the method described above or the titanium paste to a sheet, followed by drying.

[0008] One embodiment of the present invention is a method for producing a sheet-shaped porous titanium body, which includes degreasing the green body produced by the above-described method to obtain a brown body, and sintering the brown body. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart showing a method for producing a sheet-shaped porous titanium body according to one embodiment of the present invention. [Figure 2]Photographs of the titanium paste of Example 1 applied to a substrate. Right: immediately after application, Left: 1 minute after application. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a titanium paste for producing a sheet-shaped porous titanium body, a method for preparing the same, and a method for producing a green body and a sheet-shaped porous titanium body using the titanium paste according to an embodiment of the present invention will be described with reference to FIG.

[0011] 1. Overview of the manufacturing method for porous titanium sheet Porous titanium sheets have high liquid permeability, air permeability, electrical conductivity, and excellent corrosion resistance, and are therefore used as electrode materials and filters that can be used in highly corrosive environments. In particular, porous titanium sheets with thicknesses of several tens to several hundreds of micrometers are useful as porous transport layers (PTLs) in polymer electrolyte membrane (PEM)-type water electrolysis systems that are exposed to strongly acidic and strongly oxidizing conditions.

[0012] Here, "sheet-like" means a plate-like or foil-like shape with a thickness small relative to the dimensions in a plan view. The shape of the sheet-like porous titanium body in a plan view is not particularly limited, and may be rectangular, such as a square or rectangle, with an aspect ratio of 1:1 to 1:3, or may be a rhombus, other polygons, an ellipse, or a circle, such as a perfect circle. The corners of a polygonal porous titanium body in a sheet-like shape may be chamfered.

[0013] FIG. 1 is a flowchart illustrating a method for producing a sheet-shaped porous titanium body according to one embodiment of the present invention. As shown in FIG. 1, first, a titanium paste containing titanium powder is prepared. The titanium paste is then applied to a substrate in the form of a sheet, and the solvent contained in the titanium paste is volatilized (i.e., the titanium paste is dried) to obtain a green body formed on the substrate. This green body is then peeled from the substrate and heated to decompose (degrease) at least a portion of the binder and additives contained in the titanium paste, thereby obtaining a brown body. Sintering the brown body, or dehydrogenating and then sintering the brown body, can produce a sheet-shaped porous titanium body consisting essentially of titanium. Although not shown, the surface of the sheet-shaped porous titanium body may also be coated with a platinum group metal, which has excellent corrosion resistance and electrical conductivity. These steps are described in detail below.

[0014] 1-1.Preparation of titanium paste The titanium paste is a fluid containing titanium powder, and in addition to the titanium powder, it also contains a binder and an organic solvent. The titanium paste may also contain a plasticizer. In addition to water, the titanium paste may also contain one or more additives such as an antifoaming agent, a dispersant, and a leveling agent. However, the titanium paste does not contain a foaming agent.

[0015] (1) Titanium powder There are no limitations on the manufacturing method of titanium powder, the raw material for titanium paste. Hydrogenated and dehydrogenated titanium powder (also known as HDH powder) obtained by hydrogenating and pulverizing titanium sponge or the like and then dehydrogenating it is preferred. The average particle size D50 of the titanium powder is, for example, 1 μm to 150 μm, 10 μm to 50 μm, or 10 μm to 20 μm. By using such fine titanium powder, a porous titanium sheet can be obtained that has a porosity suitable for use as a PTL, is less likely to break, and is easy to handle. Furthermore, the use of finer titanium powder tends to result in a porous titanium sheet with superior surface smoothness. The average particle size D50 is the particle size at which the cumulative volume distribution reaches 50% in the particle size distribution obtained by laser diffraction scattering.

[0016] The shape of the titanium particles constituting the titanium powder can be selected arbitrarily, but titanium powder containing titanium particles that are circular or angular in plan view is preferred. In the former case, titanium powder containing titanium particles with a spherical or nearly spherical shape (e.g., an average circularity of 0.95 or more) can be used. However, the use of titanium powder containing titanium particles with a low average circularity (e.g., less than 0.95) and a shape that deviates from a spherical shape (typically, titanium powder containing HDH powder) as in the latter case increases the number of junctions between titanium particles. As a result, a sheet-shaped porous titanium body can be obtained that has a sponge-like three-dimensional network structure with numerous internal pores. The above-mentioned average circularity is the average ratio of the perimeter of the projected surface of titanium particles (e.g., approximately 1000 to 1500 particles) to the perimeter of a circle with an area equal to the area of ​​the projected surface.

[0017] The purity of the titanium powder is preferably high, and it is preferable to use titanium powder with a composition known as commercially pure titanium (although a high oxygen content is acceptable). For example, the titanium powder has a titanium content of 97% by mass or more, 98% by mass or more, or 99% by mass to 100% by mass, and an oxygen content of 0.1% by mass to 0.7% by mass, or 0.1% by mass to 0.6% by mass. Using titanium powder with a low oxygen content allows for the production of a highly conductive sheet-shaped porous titanium body. In addition to oxygen, the titanium powder may contain trace amounts of other components, such as nonmetallic elements such as carbon and nitrogen, or metallic elements such as chromium, aluminum, copper, zinc, tin, and iron.

[0018] The purity of titanium powder can be determined by measuring components other than titanium and subtracting them from the total (100% by mass). Metallic or semi-metallic components other than titanium, such as iron, aluminum, silicon, manganese, and magnesium, can be measured using inductively coupled plasma (ICP) atomic emission spectrometry. Non-metallic components can also be measured using known methods, as appropriate. Chlorine can be measured using the silver nitrate method, carbon using the high-frequency combustion-infrared absorption method, nitrogen using the ammonia distillation separation-amidosulfuric acid titration method, oxygen using the inert gas fusion-infrared absorption method, and hydrogen using the inert gas fusion-thermal conductivity method.

[0019] (2) Binder The binder used is an acrylic polymer-based binder containing an acrylic polymer. Examples of acrylic polymers include homopolymers of (meth)acrylic acid esters, binary or multi-component copolymers of multiple (meth)acrylic acid esters, or binary or multi-component copolymers of one or more (meth)acrylic acid esters with other monomers. Examples of substituents on the ester oxygen of the acrylic acid ester include aromatic substituents or linear, branched, or cyclic alkyl groups. One or more hydrogen atoms of the aromatic substituent or alkyl group may be substituted with functional groups such as hydroxyl groups, amino groups, ether groups, sulfonyl groups, thiol groups, and thioether groups. Examples of other monomers include (meth)acrylic acid, olefins such as ethylene, propylene, and styrene, vinyl ethers, vinyl acetate, and dienes. The vinyl acetate units contained in the main skeleton of the acrylic polymer may be partially hydrolyzed.

[0020] Although the acrylic polymer itself is solid, when preparing the titanium paste, the binder is not solid, but is used as a solution in which the acrylic polymer is dissolved. Examples of solvents for dissolving the acrylic polymer (hereinafter, the solvent for dissolving the acrylic polymer will be referred to as the auxiliary solvent) include aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, and tetralin; linear, branched, or cyclic aliphatic hydrocarbons such as hexane, heptane, octane, and cyclohexane; ketones such as methyl ethyl ketone and cyclohexanone; alcohols with 1 to 4 carbon atoms such as ethanol, n-propanol, isopropyl alcohol, n-butanol, isobutyl alcohol, and sec-butanol; phenols such as phenol and m-cresol; cyclic ethers such as tetrahydrofuran and dioxane; monoterpene alcohols such as terpineol; and ethylene glycol monoalkyl ethers such as butyl carbitol. The auxiliary solvent may be composed of multiple auxiliary solvents. For example, even if a co-solvent has a low dissolving power for the acrylic polymer, it is possible to use a co-solvent that can maintain the binder as a uniform solution by mixing it with a co-solvent that has a high dissolving power for the acrylic polymer.

[0021] (3) Organic Solvent The organic solvent may include the auxiliary solvent described above and a solvent added during the preparation of the titanium paste (hereinafter referred to as the diluting solvent). The diluting solvent can be a solvent that is compatible with the auxiliary solvent and does not separate from the auxiliary solvent upon mixing. Therefore, the diluting solvent can be appropriately selected from the various solvents exemplified as auxiliary solvents. The diluting solvent and auxiliary solvent may be the same or different. Preferably, a solvent with a relatively low boiling point is selected as the diluting solvent. More specifically, it is preferable to select a solvent with a boiling point of 70°C or higher and 120°C or lower, and suitable examples include toluene, which is a general-purpose solvent, and alcohols such as ethanol, isopropyl alcohol, and isobutyl alcohol. Among these, it is preferable to use alcohols, which have relatively low environmental impact and toxicity, as the organic solvent. By using a low-boiling-point solvent as the diluting solvent, the drying process described below can be performed at a lower temperature (e.g., room temperature), thereby shortening the drying time. As a result, the cost required for the drying process can be reduced.

[0022] Multiple solvents may be used as dilution solvents. In this case, a low-boiling solvent with a boiling point of 70°C to 120°C and a high-boiling solvent with a boiling point above 120°C may be used. Examples of high-boiling solvents include amide solvents such as N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. When using such a mixed solvent, the amount of high-boiling solvent in the titanium paste can be determined based on the purpose. For example, high-boiling solvents are less likely to volatilize from the titanium paste and are useful for preventing deterioration of the titanium paste during storage after preparation and before application. Therefore, the required amount of high-boiling solvent may be mixed into the titanium paste after considering storage conditions, etc. High-boiling solvents can prevent the titanium paste from drying out too quickly, thereby preventing aggregation of titanium powder and precipitation of binder in the film-forming equipment used in the application process described below.

[0023] (4)Water As described above, the titanium paste may contain water. By adding water to the titanium paste, it is possible to reduce the burden on the environment and prevent the titanium paste from drying out too quickly. The amount of water in the titanium paste may be appropriately selected within a range that does not cause the binder to precipitate.

[0024] (5) Additives As mentioned above, the titanium paste may further contain additives such as a plasticizer, an antifoaming agent, a dispersant, and a leveling agent.

[0025] A wide range of plasticizers can be used that can impart flexibility to the dried titanium paste green body. Specific examples include glycerin, ethylene glycol, triethylene glycol, or their ether or ester derivatives. Alternatively, monoesters, diesters, or triesters of glycerin with unsaturated fatty acids such as ricinoleic acid, oleic acid, or linoleic acid, or saturated fatty acids such as palmitic acid or stearic acid, may also be used.

[0026] A wide range of defoaming agents can be used, including those that can suppress the generation of bubbles in the titanium paste or that can quickly break or defoam any bubbles that do occur. For example, defoaming agents include those containing a polymer, such as polyolefin, acrylic polymer, polyvinyl ether, diene polymer, or silicone polymer, and a solvent.

[0027] A wide range of dispersants can be used that facilitate dispersion of titanium powder in the titanium paste, including, for example, ionic surfactants such as alkylbenzene sulfonates and polycarboxylic acid amine salts, and nonionic surfactants such as polyethylene glycol fatty acid esters, such as polyoxyethylene monolaurate.

[0028] Acrylic polymer-based leveling agents, silicone-based leveling agents, and fluorine-based leveling agents can be used as leveling agents. The leveling agent may contain a solvent. Examples of solvents include aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, and ethers. Using a (meth)acrylic acid ester with an ester group of the above structure allows for the production of a highly hydrophilic acrylic polymer, making it possible to obtain a uniform leveling agent even when using a highly polar solvent such as ethanol. The use of a leveling agent significantly reduces the surface tension of the titanium paste, thereby improving the flatness of the titanium paste applied to the substrate and the green body obtained by drying it. As a result, a sheet-shaped titanium porous body with uniform thickness and high surface smoothness can be obtained.

[0029] (6) Titanium paste preparation method The titanium paste is prepared using at least a binder, a diluent, and titanium powder. The titanium paste may contain additional additives, and the timing of additive addition during the preparation of the titanium paste can be determined as appropriate. Specifically, the binder, diluent, and additives are first mixed and stirred. Alternatively, the binder and diluent may be mixed, and then all or part of the additives may be added. Water may also be added at this stage. As described above, the binder is used as a solution in the preparation of the titanium paste. Therefore, the binder, diluent, and additives mixed at this stage are all liquids, allowing for rapid mixing and a homogeneous solution. This feature significantly differs from conventional methods that use only solid binders, such as polyvinyl butyral (PVB), to prepare titanium paste. It prevents the solid binder from remaining in the titanium paste as solid lumps due to insufficient dissolution. If solid lumps remain in the titanium paste, they are difficult to dissolve even when the titanium paste is further stirred or mixed. Paste containing residual solid lumps cannot be used to manufacture a sheet-shaped porous titanium body (it is essentially discarded).

[0030] Furthermore, when a solid binder is mixed with a liquid such as an organic solvent, the titanium paste tends to foam, and once foaming occurs, it is difficult to eliminate the foam, and in some cases it is impossible to eliminate the foam. Furthermore, if a foamed titanium paste is used, it is not possible to produce a sheet-shaped porous titanium body with excellent surface smoothness, and as a result, the production yield in the production of the sheet-shaped porous titanium body decreases due to foaming. However, if a binder solution is used, such problems can be prevented and a sheet-shaped porous titanium body can be produced with a good yield.

[0031] The mixing ratio of the binder and the dilution solvent may be selected appropriately depending on the structure and characteristics of each. For example, the mass ratio of the solid components of the binder to the organic solvent (auxiliary solvent and dilution solvent) (solid components of the binder: (auxiliary solvent + dilution solvent); if the titanium paste contains water, solid components of the binder: (auxiliary solvent + dilution solvent + water)) may be set in the range of 1:20 to 1:2 by mass.

[0032] Titanium powder is then added and further stirred. Any remaining additives can be added at this time or after the titanium powder is mixed. The titanium powder can also be crushed or pulverized using a grinding mixer such as a vibrating mill or a bead mill before mixing. Mixing the dilution solvent and binder solution first and then mixing the titanium powder results in a uniform titanium paste. The titanium paste composition can be appropriately determined. For example, the amounts of titanium powder, binder solids, and organic solvent (auxiliary solvent and dilution solvent) can be adjusted so that the ratio of titanium powder:binder solids:organic solvent (if the titanium paste contains water, titanium powder:binder solids:(auxiliary solvent + dilution solvent + water)) is in the range of 22:1:3 to 22:4:12 by mass. For example, the amount of binder solids should be 3 to 15 g and the amount of organic solvent (if the titanium paste contains water, the total amount of organic solvent and water) should be 25 to 45 g per 100 g of titanium powder. Each of the additives may be added in an amount of, for example, 0.01% by mass to 10% by mass, or 0.01% by mass to 5% by mass, relative to the total amount of the titanium paste.

[0033] The mixing method can also be selected arbitrarily. For example, a mixture containing titanium powder, an organic solvent, a binder, and at least some of the additives can be appropriately mixed using a mixer with an agitator, a rotary mixer, or a three-roll mill. The titanium paste obtained by mixing is then subjected to the subsequent coating process. The temperatures described below for drying, degreasing, dehydrogenation, and sintering are ambient temperatures. Each process can be performed by adjusting the ambient temperature inside the apparatus or furnace where each process is performed to the temperature described below.

[0034] 1-2. Application and drying Next, the titanium paste is applied to a substrate in the form of a sheet. Examples of the substrate include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene, polypropylene, and polystyrene, polyvinyl acetate polymers such as polyvinyl acetate and partially saponified polyvinyl acetate, and polylactic acid. Among these, polyethylene terephthalate is preferred because it can be molded into a film with high flexibility and sufficient strength, and is inexpensively available.

[0035] The titanium paste application method is not limited, and various techniques, such as doctor blade, lip coating, offset printing, and gravure printing, may be used. For example, various deposition devices, such as a rear doctor coater, blade coater, rod coater, knife coater, squeeze coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, kiss roll coater, slot die coater, cast coater, spray coater, curtain coater, calendar coater, extrusion coater, and bar coater, may be used. Among these, the doctor blade method, which allows continuous application of titanium paste to a long substrate, is preferred. For long substrates, a sheet-like green body can be wound into a roll, which is advantageous for storage and transportation. A release agent may be applied to the substrate before applying the titanium paste. Alternatively, a substrate pre-applied with a release agent may be used. Examples of release agents include a solution or dispersion of a fluororesin or silicone resin. Applying a release agent facilitates separation of the dried titanium paste from the substrate.

[0036] The thickness of the titanium paste after application can be adjusted in consideration of the thickness of the porous titanium sheet to be produced, which is often in the range of several tens to several hundreds of micrometers.

[0037] The coated titanium paste is then dried. This involves volatilizing the organic solvent contained in the titanium paste. Some additives may also be volatilized during this process. If the titanium paste contains water, the water is also volatilized or evaporated during drying. This results in a green body on the substrate. Drying can be performed under either atmospheric or reduced pressure. Because the organic solvent volatilizes from the titanium paste, it is preferable to quickly remove the volatilized organic solvent by, for example, blowing air onto the titanium paste on the substrate. The drying atmosphere can be freely selected, and drying can be performed in an atmosphere of air, nitrogen, oxygen, helium, argon, or a mixture of these gases. The drying temperature can also be freely selected, but is preferably below the glass transition temperature of the substrate and the boiling point of the organic solvent. Drying under these conditions not only prevents deformation of the substrate but also prevents pinholes and a decrease in surface smoothness due to rapid evaporation and boiling of the organic solvent. The drying time can also be appropriately selected depending on the thickness of the titanium paste and the boiling point of the organic solvent. Typical drying conditions are atmospheric pressure, a temperature of 20°C to 190°C, or 80°C to 190°C, or 90°C to 180°C, and a drying time of 1 minute to 300 minutes.

[0038] When a long substrate is used, the laminate of the substrate and the green body may be wound into a roll after drying, and the green body may be stored and transported in a compact form. In particular, by adding a plasticizer to the titanium paste, the green body exhibits flexibility or its flexibility is improved, so that the green body will not be damaged even when wound into a roll, and can be stored and transported safely and in a compact form.

[0039] 1-3. Degreasing Next, debinding is performed to remove binders and additives from the green body. Specifically, the green body is peeled off from the substrate and heated (preheated). There are no restrictions on the method of peeling the green body; it can be physically peeled off from the substrate. For example, one end of the substrate-green body stack can be bent, adhesive tape or a roller with an adhesive surface can be used to peel off the substrate or green body, compressed air can be blown between the substrate and green body, or a sharp knife-like tool can be inserted to partially peel off the substrate from the green body, and the peeled portion can be used as a starting point to separate the green body from the substrate. Heating can also be performed on a plate called a setter, which can be made of a high-melting-point metal such as molybdenum or tantalum, a ceramic such as boron nitride, or graphite.

[0040] Debinding is performed at a temperature at which the binder and additives decompose and / or volatilize. For example, debinding can be performed by heating the green body in an oxygen-containing atmosphere, such as air, at a temperature between 300°C and 450°C for a period of 2 to 20 hours. This debinding process can remove all or most of the binder and additives from the green body. The sheet-like compact obtained by debinding the green body is called a Brownian body.

[0041] 1-4.Dehydrogenation After debinding, the brown body may be dehydrogenated. In particular, when the titanium powder contains a large amount of hydrogen, it is preferable to dehydrogenate the brown body prior to sintering in order to reduce the hydrogen content. Dehydrogenation is often carried out at a higher temperature than debinding, for example, by treating the green body at a temperature of more than 450°C and less than 700°C, or from 500°C to 700°C. The treatment time is, for example, from 30 minutes to 360 minutes. Dehydrogenation is carried out under reduced pressure (for example, 10 -4 Pa or more 10 -2 It is preferable to carry out the dehydrogenation at a pressure of 1000 Pa or less. By carrying out the dehydrogenation under reduced pressure, it is possible to prevent an increase in the oxygen content. The dehydrogenation may also be carried out while the Brown body is placed on the setter described above.

[0042] 1-5.Sintering A sheet-shaped titanium porous body can be obtained by sintering a debound brown body or a brown body that has been debound and then dehydrogenated. Sintering is performed at a higher temperature than debinding or dehydrogenation, and the sintering temperature is appropriately selected from temperatures of, for example, 750°C to 1100°C, 775°C to 1000°C, or 800°C to 950°C. Sintering is performed at atmospheric pressure or reduced pressure. When sintering at atmospheric pressure, it is preferable to sinter the brown body in an atmosphere with low concentrations of oxygen and nitrogen, for example, a rare gas atmosphere such as helium or argon, in order to prevent the formation of oxides and nitrides. When sintering under reduced pressure, the pressure is, for example, 1×10 -4 Pa or more 1×10 -2 The sintering time may also be set appropriately taking into consideration the thickness of the brown body, and may be selected, for example, from the range of 1 hour to 8 hours.

[0043] 2. Characteristics of porous titanium sheet The porous titanium sheet produced by the above-described method is essentially composed of high-purity titanium. Specifically, the titanium content in the porous titanium sheet is, for example, 97% by mass or more and 99% by mass or less. The content of other metal elements mixed into the titanium powder used as raw material is also low, typically 0.3% by mass or less. The oxygen content can also be reduced, for example, to within a range of 0.5% by mass or more and 2.0% by mass or 0.5% by mass or more and 1.5% by mass or less. Therefore, the porous titanium sheet has high compression resistance, low brittleness, and excellent handling. The titanium content can be determined by subtracting the trace amounts of other elements mixed in from the total amount (100%) of the porous titanium sheet. The purity of the porous titanium sheet can be measured in the same manner as for the titanium powder described above.

[0044] As mentioned above, if a foaming agent is used in preparing the titanium paste, a large amount of bubbles will be generated during paste preparation or drying, and the bubbles will remain in the resulting porous titanium sheet. When a porous titanium sheet with a rough surface caused by foaming is pressed against an electrolyte membrane in a PEM water electrolysis system, problems such as damage to the electrolyte membrane or the formation of through-holes may occur. Furthermore, if the surface is unevenly uneven due to foaming, when a compressive force is applied in the thickness direction in a PEM water electrolysis system, the compressive force will be unevenly applied, which could damage the porous titanium sheet itself.

[0045] In contrast, as described above, since no foaming agent is used during the preparation of the titanium paste, the inclusion of air bubbles is effectively suppressed. Furthermore, in the method for producing a sheet-shaped porous titanium body, an acrylic polymer-based binder is used as a solution during the preparation of the titanium paste, effectively preventing the binder from remaining as solid lumps in the titanium paste (and thus in the green body after drying). Therefore, the titanium paste applied to the substrate is free of irregularities caused by lumps of binder or air bubbles. As a result, the thickness of the titanium paste on the substrate is uniform, and the surface is highly smooth. This allows for uniform thickness and high surface smoothness to be achieved not only in the green body and brown body obtained from the titanium paste, but also in the sheet-shaped porous titanium body obtained after sintering. For example, the maximum height Rz, which is an index of surface roughness on one side of the sheet-shaped porous titanium body (the surface of the corresponding green body facing the substrate), can be controlled to 10 μm or less, or 7 μm or less. The maximum height Rz can sometimes be 1.0 μm or more. The average surface roughness Ra of the above surface can also be controlled to 2 μm or less. The maximum height Rz and the average surface roughness Ra may be determined in accordance with ISO (International Organization for Standardization) 4287-1997.

[0046] The thickness of the titanium sheet-like porous body can be controlled, for example, by adjusting the thickness of the green body. For example, titanium sheet-like porous bodies having thicknesses of 30 μm to 500 μm, 40 μm to 500 μm, 60 μm to 400 μm, or 80 μm to 300 μm can be produced. By adjusting the thickness within the above range, the titanium sheet-like porous body can be more suitably used as a PTL in a PEM water electrolysis system. The thickness is measured at five points on the titanium sheet-like porous body, including four points on the periphery and one point in the center, using a digital thickness gauge with a 10 mm diameter flat probe and a measurement accuracy of 0.001 to 0.01 mm, such as the Mitutoyo Digital Thickness Gauge (Model No. 547-321), and the average of these measurements is used. When the titanium sheet-like porous body is rectangular in plan view, the four peripheral points are the four corner points.

[0047] The porosity of the porous titanium sheet obtained according to the above-mentioned production method is, for example, 30% to 60% or 30% to 55% or 30% to 50%. This makes it possible to provide a porous titanium sheet that maintains good air and liquid permeability, while also having high compression resistance and low brittleness. The porosity is calculated by multiplying the apparent density ρ' calculated from the volume and mass determined from the width, length, and thickness of the porous titanium sheet by the true density ρ (4.51 g / cm) of titanium that constitutes the porous titanium sheet. 3 ) and calculate using the formula: ε = (1 - ρ' / ρ) × 100. [Example]

[0048] 1. Titanium Paste Preparation (1) Example 1 A titanium paste was prepared with the composition shown in Table 1. Specifically, an acrylic polymer binder, a diluent, and additives were sealed in a 300 mL container and stirred by rotating the container at 1000 rpm for 5 minutes. Visual observation of the mixture at this stage confirmed the absence of residual air bubbles. Titanium powder (HDH powder, average particle size between 10 μm and 20 μm) was then added to the mixture, the container was sealed, and the container was again stirred by rotating at 1000 rpm for 5 minutes to prepare a titanium paste. As a result, a titanium paste was obtained in which the titanium powder was well dispersed and almost free of air bubbles. Furthermore, the same experiment was performed a total of 10 times, and similar results were obtained in each experiment.

[0049] [Table 1]

[0050] (2) Comparative Example 1 All materials listed in Table 1 were sealed in a 300 mL container according to the composition in Table 1, and the container was stirred by rotating at 1000 rpm for 10 minutes. As a result, lumps of titanium powder formed in the mixture, and a uniform titanium paste could not be obtained. Furthermore, of the same experiment conducted a total of 10 times, only three experiments produced a uniform titanium paste without lumps of titanium powder, while the remaining seven experiments failed to produce a uniform titanium paste. Furthermore, even when further stirring was performed in the experiments in which an inhomogeneous titanium paste was produced, a uniform titanium paste could not be obtained.

[0051] (3) Comparative Example 2 In Comparative Example 2, a solid binder was used. Specifically, titanium powder was not used. All materials listed in Table 2 according to the composition in Table 2 were sealed in a 300 mL container, and the container was stirred by rotating at a rotation speed of 1000 rpm for 5 minutes. This experiment was performed 10 times. In eight experiments, no residual binder was observed, and a homogeneous solution was obtained. However, in two experiments, residual binder was observed, resulting in an inhomogeneous mixture. Furthermore, even when the mixture with residual binder was further stirred, a homogeneous solution was not obtained.

[0052] [Table 2]

[0053] The above results clearly demonstrate that a uniform titanium paste can be obtained with good reproducibility by using a solution containing a binder and a co-solvent, and then preparing a mixture containing a binder and an organic solvent, followed by adding titanium powder and stirring. This means that by applying the embodiments of the present invention, it is possible to produce a sheet-shaped porous titanium body with a good yield, a uniform thickness, and high surface smoothness.

[0054] 2. Preparation of green bodies The titanium paste obtained in Example 1 was applied in sheet form to a polyethylene terephthalate resin film (Cerapeel®, manufactured by Toray Industries, Inc.) with a silicone coating as a release agent. Figure 2 shows photographs of the titanium paste taken immediately (right) and one minute after application (left). As can be seen from the photograph on the right, the peripheral area of ​​the titanium paste was gray even immediately after application, confirming that the organic solvent had rapidly evaporated from the peripheral area. Furthermore, one minute after application, the entire titanium paste was gray, suggesting that the organic solvent had evaporated from most of the titanium paste surface within about one minute of application. From this, it can be seen that by applying an embodiment of the present invention, which allows the use of a solvent with a relatively low boiling point as a dilution solvent, the titanium paste on the substrate can be dried in a short time, allowing for efficient production of a green body at low cost.

[0055] Separately, the titanium paste obtained in Example 1 was applied in sheet form to the resin film and dried at 120°C for 10 minutes to obtain a green body. The dried green body was subsequently peeled from the film, and it was confirmed that a highly flexible green body capable of being wound into a roll was obtained. Furthermore, the green body could be wound into a roll together with the film. When a similar experiment to Example 1 was performed, but with the same amount of isobutyl alcohol added instead of the plasticizer (i.e., when a titanium paste without plasticizer was used in Example 1), a similar drying rate was obtained. Furthermore, although a green body with sufficient flexibility to be wound into a roll was not obtained, it was confirmed that a relatively hard sheet-like green body could be produced. This suggests that the properties of the green body can be controlled by adjusting the amount of plasticizer added.

[0056] 3. Preparation of porous titanium sheet The green body peeled off from the film was placed on a graphite setter and degreased at 380°C for 8 hours in an air atmosphere to obtain a brown body. The brown body was then placed on the graphite setter and degreased under reduced pressure (1 × 10 -2 A porous titanium sheet was produced by sintering at 800°C for 1 hour at a pressure of 100 Pa or less. The thickness of the resulting porous titanium sheet was 200 μm, and the porosity was 40%. The maximum height Rz of the surface on the side of the titanium paste or green body that had been in contact with the film was 10 μm or less, and the average surface roughness Ra was 2 μm or less. This confirms that a porous titanium sheet with a smooth surface can be produced by applying an embodiment of the present invention.

[0057] Based on the above-described embodiments of the present invention, those skilled in the art may add, delete, or modify components, or add, omit, or modify processes, as appropriate, as long as they comply with the spirit of the present invention. Even if the effects and advantages provided by the above-described embodiments are different from those provided by the present invention, those that are clear from the description in this specification or that can be easily predicted by those skilled in the art are naturally considered to be provided by the present invention.

Claims

1. A method for producing a titanium paste for producing a sheet-shaped porous titanium body, comprising: mixing a solution containing an acrylic polymer binder and a co-solvent with a dilution solvent to prepare a mixture; and then mixing the mixture with titanium powder.

2. 10. The method of claim 1, wherein no blowing agent is used during preparation of the mixture, during mixing of the mixture with the titanium powder, or after mixing of the mixture with the titanium powder.

3. The method of claim 1 further comprising adding a plasticizer during preparation of the mixture, during mixing of the mixture with the titanium powder, or after mixing of the mixture with the titanium powder.

4. A titanium paste for producing a sheet-shaped porous titanium body, comprising titanium powder, an acrylic polymer binder, an organic solvent, and a plasticizer, but not containing a foaming agent.

5. A method for producing a green body for producing a sheet-shaped porous titanium body, comprising applying the titanium paste produced by the method according to any one of claims 1 to 3 or the titanium paste according to claim 4 to a sheet, and then drying it.

6. degreasing the green body produced by the method of claim 5 to obtain a brown body; and A method for producing a sheet-shaped porous titanium body, comprising sintering the brown body.

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