Method for producing titanium molded body, method for producing titanium porous body, and titanium porous body

Abstract

This method for producing a titanium molded body in sheet form comprises a joining step for layering multiple dry sheets, which have each been obtained by drying a paste containing a titanium powder, an organic binder, and an organic solvent, and then heating the layered sheets to a temperature of 70℃ to 200℃ while applying pressure of at least 0.1 N / cm2 in the direction of thickness.

Description

Method for manufacturing titanium molded body, method for manufacturing titanium porous body, and titanium porous body

[0001] The present invention relates to a method for producing a sheet-like titanium molded body, a method for producing a porous titanium body, and a porous titanium body.

[0002] Porous titanium bodies produced by sintering titanium powder have air or liquid permeability due to the pores, electrical conductivity, and also high corrosion resistance due to the formation of a passivation film on the surface.

[0003] Porous titanium having such properties is being considered for use in porous transport layers (PTLs) in polymer electrolyte membrane (PEM)-type water electrolysis devices, which are in environments where corrosion may occur. In particular, hydrogen produced in PEM-type or other water electrolysis devices using electricity derived from renewable energy is called "green hydrogen," and great expectations are being placed on it in recent years as efforts to realize a decarbonized society accelerate.

[0004] As a technology relating to titanium porous bodies, for example, Patent Document 1 describes "a method for manufacturing a porous metal laminate consisting of multiple layers including a porous layer in which a plurality of polyhedral voids, the edges of which are formed by the skeleton of a metal sintered body, are formed in a mutually continuous state, the method comprising a laminating step of laminating the porous layer and an adjacent layer made of metal, and a fusing step of fusing the porous layer and the adjacent layer in a stacked state into a desired shape with a laser, wherein in the fusing step, the porous layer and the adjacent layer are melted and solidified with the laser to form a fused bonding layer on the side surfaces of the porous layer and the adjacent layer that bonds the porous layer and the adjacent layer."

[0005] Furthermore, Patent Document 2 describes a composite material including "a first region formed of a metal foam having a conductive metal component with a conductivity of 8 MS / m or more at 20°C, and a second region formed of a metal foam having a soft magnetic metal component."

[0006] Japanese Patent Application Laid-Open No. 2011-106023 Special Publication No. 2021-529891

[0007] When a porous titanium body is used as a porous transport layer in a PEM-type water electrolysis device, the porous titanium body may be pressed against an electrolyte membrane when assembled. In this case, if the pores on the surface of the porous titanium body are large, the electrolyte membrane pressed against the porous titanium body may partially enter the pores, causing significant deformation in the areas adjacent to the pores and potentially damaging the electrolyte membrane.

[0008] Therefore, from the viewpoint of preventing damage to the electrolyte membrane, it is desirable that the pores of the titanium porous body that open to the surface facing the electrolyte membrane are small. Even if the pores on the surface are small, a certain degree of air or liquid permeability can be achieved as long as there are many of them.

[0009] However, if the pores of a porous titanium body are small not only on the surface but throughout the body, it may not be possible to obtain the required level of breathability or liquid permeability, depending on the required level, even if the number of pores is large. To address this, it is conceivable to stack multiple porous layers, positioning a porous layer with small pores on one surface to suppress damage to the electrolyte membrane, while creating a porous titanium body with a large porosity overall that exhibits good breathability and liquid permeability.

[0010] When manufacturing a porous titanium body having multiple porous layers, multiple titanium sintered bodies that will form the porous layers are stacked and heated to bond them together. Each porous layer constituting the porous titanium body is subjected to two relatively high-temperature heating processes: once for sintering during the production of the titanium sintered bodies and once for bonding. As a result, the porous titanium body obtained by bonding multiple titanium sintered bodies has small pores overall, and the desired excellent air or liquid permeability may not be achieved. This applies not only to the manufacture of porous titanium bodies having multiple porous layers with different pore sizes and numbers, but also to the manufacture of porous titanium bodies having multiple porous layers with similar pore sizes and numbers.

[0011] An object of the present invention is to provide a method for manufacturing a titanium molded body, a method for manufacturing a titanium porous body, and a titanium porous body, which are capable of manufacturing a titanium molded body that has multiple porous layers and can be used to manufacture a titanium porous body having a relatively high porosity.

[0012] After extensive research, the inventors came up with the idea of ​​stacking multiple dried sheets obtained by drying a titanium powder paste and bonding them under specified conditions. By debinding and sintering the resulting titanium molded body, the number of high-temperature heating cycles can be reduced compared to bonding pre-sintered pieces. As a result, the final porous titanium body has a relatively high porosity.

[0013] The method for producing a titanium molded body of the present invention is a method for producing a sheet-like titanium molded body, in which a plurality of dried sheets each obtained by drying a paste containing titanium powder, an organic binder, and an organic solvent are stacked, and a pressure of 0.1 N / cm is applied in the thickness direction. 2 The bonding step includes heating the components to a temperature of 70° C. or higher and 200° C. or lower while applying the pressure described above.

[0014] The method for producing the titanium molded body may include a drying step, prior to the joining step, of drying the paste to obtain a sheet-like dried body.

[0015] In the drying step, the paste can be heated to a temperature of 90°C or higher and 165°C or lower.

[0016] The drying of the paste in the drying step can be carried out on a resin substrate.

[0017] In the joining step, the laminated dried sheet bodies can be pressed and heated in a state where the laminated dried sheet bodies are sandwiched between dies from both sides in the thickness direction.

[0018] In this case, in the joining step, it is preferable to perform pressure application and heating with a resin substrate interposed between the sheet-like dried body and the mold. The average particle size of the titanium powder in at least one of the sheet-like dried bodies is preferably 10 μm or more and 20 μm or less. The difference between the average particle size of the titanium powder in the sheet-like dried body on one surface side of the sheet-like dried body and the average particle size of the titanium powder in at least one other sheet-like dried body is preferably 5 μm or more. The paste used to prepare the sheet-like dried body preferably does not contain a foaming agent.

[0019] The method for producing a porous titanium body of the present invention is a method for producing a sheet-like porous titanium body, and includes a binder removal step of heating a titanium molded body produced by any of the above-mentioned methods for producing a titanium molded body to volatilize the organic binder in the titanium molded body, and a sintering step of heating the titanium molded body after the binder removal step to sinter the titanium powder in the titanium molded body.

[0020] The titanium porous body of the present invention is in the form of a sheet, and comprises a plurality of titanium porous layers laminated together by bonding adjacent titanium bonding surfaces in the thickness direction, each having pores and allowing gas and / or liquid to permeate therethrough, and the average area of ​​the pores opening to one surface of the porous layer forming one surface of the plurality of porous layers is 5 μm. 2 More than 15 μm 2 The standard deviation of the area of ​​the hole is 35 μm or less. 2 or less, and the area is 22000 μm 2 The number of holes present within a rectangular region having an aspect ratio of 4:3 is 256 or more, and the overall porosity including the multiple porous layers is 40% or more and 60% or less. The average area of ​​the holes opening onto the other surface located on the back side of one surface is preferably 1.5 times or more the average area of ​​the holes opening onto the one surface. The total thickness is preferably 200 μm or more and 3000 μm or less. The thickness of the porous layer constituting the portion on one surface side is preferably 30% or less of the total thickness.

[0021] According to the method for producing a titanium molded body of the present invention, it is possible to produce a titanium molded body that has a plurality of porous layers and can be used to produce a titanium porous body having a relatively high porosity.

[0022] 1(a) and 1(b) are cross-sectional views along the thickness direction of a dried sheet body that can be used in a method for producing a titanium molded body according to one embodiment of the present invention. 2(a) to 2(d) are cross-sectional views showing an example of a procedure for joining the dried sheet bodies of FIG. 1.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. A method for manufacturing a titanium molded body according to one embodiment of the present invention includes a bonding step of stacking and bonding a plurality of dried sheet bodies.

[0024] To obtain each dried sheet body, a paste preparation step of mixing titanium powder, an organic binder, and an organic solvent, and a drying step of forming the paste into a sheet and drying it can be performed. In the bonding step, a plurality of dried sheet bodies are stacked and bonded together in a thickness direction at a pressure of 0.1 N / cm. 2 While applying the pressure described above, the dried sheets are heated to a temperature of 70° C. or more and 200° C. or less. As a result, the dried sheets are bonded together to form a titanium molded body.

[0025] The titanium molded body is sequentially subjected to a debinding step and a sintering step to produce a porous titanium body. The porous titanium body is produced by stacking and bonding a plurality of dried sheet bodies in a bonding step during its production, and is provided with a porous titanium layer as a sintered body of each dried sheet body. By appropriately setting the particle size of the titanium powder used to form the dried sheet body and other conditions, the porous titanium body can be made to have small pores on one surface against which the electrolyte membrane is pressed, but a relatively large porosity overall, when used as a porous transport layer in, for example, a PEM-type water electrolysis device.

[0026] The porous titanium body produced as described above has been exposed to high-temperature heating, such as during sintering, fewer times than one produced by bonding titanium sintered bodies, and therefore has a relatively high porosity. In other words, if multiple dried sheet bodies are each subjected to binder removal and sintering, and then the resulting multiple sintered titanium bodies are heated and bonded, high-temperature heating is performed at least twice, during sintering and bonding, resulting in increased sintering of the titanium powder and a smaller porosity. In contrast, the embodiment described here can reduce the number of high-temperature heating times, making it possible to produce a porous titanium body with a high porosity, for example.

[0027] (Paste Preparation Step) In the paste preparation step, raw materials including titanium powder, an organic binder, and an organic solvent are mixed using a mixer with an agitator, a rotary mixer, a triple roll mill, etc. At this time, the raw materials may be pulverized using a vibration mill, a bead mill, or other pulverizing mixer, etc.

[0028] As the titanium powder, pulverized powders such as hydrogenated / dehydrogenated titanium powder and hydrogenated titanium powder, spherical powders such as atomized powder, etc. can be used. For example, when fine titanium powder having an average particle size of 10 μm or more and 20 μm or less is used, the porous layer obtained by sintering the sheet-like dried body will have small pores. On the other hand, when coarse titanium powder having an average particle size exceeding 20 μm is used, the sintered porous layer will have large pores and a high porosity.

[0029] From the viewpoint of producing a titanium porous body having small pores opening to one surface but a large overall porosity, it is preferable that the difference in average particle size between the titanium powder used to produce one of the plurality of dried sheet bodies that will form the porous layer located on one surface and the titanium powder used to produce at least one other dried sheet body be 5 μm or more, and even 10 μm or more. However, if the difference in average particle size is too large, the difference in the amount of sintering shrinkage between the dried sheet bodies will be too great, which may result in peeling of the titanium porous layer. Therefore, taking this into consideration, the difference in average particle size may be set to 100 μm or less, and even 50 μm or less.

[0030] The above-mentioned average particle size means a particle size at which the cumulative distribution on a volume basis becomes 50% in the particle size distribution obtained by the laser diffraction scattering method.

[0031] The organic binder used in the paste can be appropriately selected from a variety of materials, including, for example, methyl cellulose, polyvinyl alcohol, ethyl cellulose, acrylic, and polyvinyl butyral. Hydrophobic organic binders are preferred. However, they are not limited to the materials listed here. The organic solvent may be, for example, alcohol (ethanol, isopropyl alcohol, terpineol, butyl carbitol, etc.). As an example, the organic binder may be polyvinyl butyral and the organic solvent may be isopropyl alcohol. The paste may further contain a plasticizer (glycerin, ethylene glycol, etc.), a surfactant (alkylbenzene sulfonate, etc.), etc.

[0032] The paste preferably does not contain water as a solvent. It is also preferable that the paste does not contain a foaming agent. It is acceptable for the paste to contain water as a solvent, although it may contain water that may be unintentionally mixed into the paste due to moisture absorption or the like. When a titanium porous body is manufactured using a paste containing water and / or a foaming agent, large pores may be formed during the manufacturing process, making it impossible to achieve the desired pore size. When a titanium porous body is manufactured using a paste containing water and / or a foaming agent, the resulting porous body has poor surface smoothness and is susceptible to damaging the electrolyte membrane of a solid polymer water electrolysis device.

[0033] (Drying Step) In the drying step, the paste is applied in a relatively thin sheet form and heated, whereby the organic solvent in the paste is mainly evaporated, and a dried sheet is obtained.

[0034] The paste can be applied to a table or the like having a flat surface, but is preferably applied to a resin substrate. The resin substrate to which the paste is applied can be placed on a mold, as described below, but is not limited to this. If the paste is applied directly to a graphite mold, carbon from the mold may be mixed into the paste or the dried sheet during the drying process, which may cause the titanium porous body to become discolored after the sintering process. Resin substrates are relatively inexpensive and flexible, making them easy to handle. Specific materials for the resin substrate include polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), and polyvinyls such as polyethylene, polypropylene, polystyrene, and polyvinyl alcohol. Among these, PET resin substrates are inexpensive and allow the dried sheet to be easily separated from the resin substrate after the drying process.

[0035] If necessary, a release layer may be provided on the resin substrate. When a release layer is provided, a silicone coating or the like can be used as the release layer. For example, a release layer can be provided on the substrate by selecting a substrate pre-coated with such a material, such as Cerapeel (registered trademark) manufactured by Toray Industries, Inc. By providing a release layer on the substrate, the thin sheet-like molded product obtained after the drying process can be easily separated from the substrate.

[0036] The heating temperature during drying can be 90°C or higher and 165°C or lower. When the paste is dried at a temperature within this range, the drying can be completed in a relatively short time while suppressing boiling of components such as organic solvents in the paste. The drying time is not particularly limited and can be determined appropriately, for example, 5 minutes or longer and 300 minutes or shorter. Drying is preferably carried out in an oxygen-containing atmosphere, such as air. This can prevent an increase in manufacturing costs.

[0037] When producing a titanium porous body having multiple porous layers with different thicknesses, the thickness of the paste applied during the production of each sheet-like dried body can be adjusted according to the thickness of the porous layer.

[0038] For example, in each of Figures 1(a) and (b), the thickness of the paste applied to the resin substrates 2 and 12 placed on the molding dies 1 and 11 was adjusted and then dried, thereby obtaining a sheet-like dried body 3 having a thickness Ta and a sheet-like dried body 13 having a thickness Tb thinner than the thickness Ta.

[0039] The sheet-like dried body 3 having a relatively large thickness Ta may use titanium powder with a relatively large average particle size in order to increase the porosity of the titanium porous body as a whole. The sheet-like dried body 13 having a relatively small thickness Tb may be used for a porous layer that forms one surface against which an electrolyte membrane is pressed in a PEM-type water electrolysis device, and titanium powder with a relatively small average particle size may be used.

[0040] The forming dies 1, 11 should have the required heat resistance and a flat surface that comes into contact with the resin substrate 2, 12 or the paste or dried sheet 3, 13, and preferably have excellent heat conductivity. A specific example of the forming dies 1, 11 is a graphite setter. While the forming dies 1, 11 are used here as an example, titanium molded bodies can be produced without using the forming dies 1, 11. Various known techniques can be used for coating the paste. For example, although not shown, a method (the so-called comma coating method) can be used in which a long resin substrate is fed by a roll and a paste is ejected onto the resin substrate from between the roll and a pair of rolls to continuously apply the paste to the resin substrate. Alternatively, although not shown, a doctor blade method can be used.

[0041] (Joining Step) In the joining step, a plurality of dried sheet bodies are stacked and joined together by heating while being pressed in the thickness direction, thereby obtaining a titanium molded body.

[0042] At this time, the pressure applied to the laminated dried sheets in the thickness direction was 0.1 N / cm 2 or more, 0.2 N / cm 2 or more and 5.0 N / cm 2The heating temperature is preferably 70°C or higher and 200°C or lower, and more preferably 100°C or higher and 180°C or lower.

[0043] If the heating temperature or pressure is too low, there is a concern that the multiple dried sheets may not be bonded together sufficiently. In extreme cases, the dried sheets of titanium molded body may partially peel off from each other after the bonding process or the binder removal process described below. Applying a certain amount of pressure while raising the temperature to a certain level is thought to achieve good bonding because the organic binder in each dried sheet is softened and compressed, thereby achieving good bonding. On the other hand, by not applying too high a pressure, it is possible to effectively suppress distortion of the dimensions and shape of the dried sheet due to compression during pressure application. Furthermore, a higher heating temperature tends to shorten the bonding time of multiple dried sheets. However, if the heating temperature is too high, there are concerns that the titanium molded body may dry excessively, resulting in cracking, or that the titanium molded body may deform in response to deformation of the resin substrate.

[0044] The pressure and heat application in the bonding step can be performed while the laminated sheet-like dried bodies are sandwiched between molds on both sides in the thickness direction. This ensures the flatness of the titanium molded body. Preferably, the sandwiched state between the molds is maintained until the temperature is lowered to room temperature after heating. The mold may be the same as that used in the drying step described above, but is not limited to this. Furthermore, the mold may have a flat surface facing the sheet-like dried body so that the titanium molded body described below can be formed into a sheet shape, and the shape of other parts is not particularly important. When a mold is used in the bonding step, the above-mentioned pressure is applied to the sheet-like dried body, taking into account the pressure due to the mold's own weight. In other words, the pressure applied to the sheet-like dried body includes the pressure due to the mold's own weight.

[0045] When a mold is used in the bonding step, it is preferable to perform the pressure application and heating with a resin substrate interposed between the sheet-like dried body and the mold in order to prevent contamination of the sheet-like dried body from the mold during heating during bonding. This resin substrate may also be the same as that used in the drying step described above, but a different one may also be used.

[0046] 1, the surface roughness of the surfaces Sa1 and Sb1 located on the resin substrate 2 and 12 side of the sheet-like dried bodies 3 and 13 during the drying process tends to be smaller than the surface roughness of the surfaces Sa2 and Sb2 on the back side (opposite side). For this reason, the sheet-like dried body 13 for the porous layer, which forms one surface of the titanium porous body against which the electrolyte membrane is pressed, is preferably joined to the sheet-like dried body 3 so that the surface Sb1 on the resin substrate 12 side is oriented outward in the thickness direction of the titanium molded body.

[0047] On the other hand, even if an attempt is made to bond a surface Sa2 on the back side of the surface Sa1 of the sheet-like dried body 3 for the porous layer that forms the other surface of the titanium porous body, which is located on the resin substrate 2 side, to a surface Sb2 on the back side of the sheet-like dried body 13, the surface roughness of both surfaces Sa2 and Sb2 is high, and therefore it may not be possible to bond the surface Sa2, Sb2, on the back side sufficiently firmly. Therefore, it is preferable to bond the surface Sa1 of the sheet-like dried body 3 that was located on the resin substrate 2 side to the surface Sb2 on the back side of the sheet-like dried body 13.

[0048] 2 shows an example of laminating and bonding sheet-like dried bodies 3 and 13. Here, first, the sheet-like dried body 3 after the drying process is peeled off from the mold 1 together with the resin substrate. Then, as shown in FIG. 2( a), another resin substrate 32 is laid on the mold 1, and the sheet-like dried body 3 is placed on the resin substrate 32 so that the surface Sa2 on the back side of the surface Sa1 of the sheet-like dried body 3 facing the resin substrate 2 is in contact with the resin substrate 32. That is, as shown by the arrow in the figure, the sheet-like dried body 3 with the resin substrate 2 bonded thereto is turned over and placed on the other resin substrate 32.

[0049] Next, as shown in FIG. 2( b ), the resin substrate 2 used in the drying step is peeled off from the sheet-like dried body 3 to expose the surface Sa1 of the sheet-like dried body 3 that was located on the resin substrate 2 side.

[0050] Thereafter, as shown in FIG. 2( c), the sheet-like dried body 13 is placed on the sheet-like dried body 3 together with the resin substrate 12 and the mold 11 so that the surface Sb2 of the other sheet-like dried body 13 opposite the surface Sb1 on the resin substrate 12 side faces the exposed surface Sa1 of the sheet-like dried body 3 that was located on the resin substrate 2 side. Note that the resin substrate 12 is often not adhered to the mold 11. In this case, the sheet-like dried body 13 and the resin substrate 12 may be placed on the sheet-like dried body 3 first, and then the mold 11 may be placed thereon, resulting in the arrangement shown in FIG. 2( c). At this time, the mold 11 may be replaced with a mold different from the one used in the drying process. In this state, the sheet-like dried bodies 3 and 13 are pressed and heated as shown by the arrows in the figure to bond them together. As a result, a titanium molded body 31 having the sheet-like dried body 3 and the sheet-like dried body 13 bonded together is obtained, as shown in FIG. 2( d).

[0051] 2(a) to 2(d), for example, the surface Sb1 of the sheet-like dried body 13 made of fine titanium powder, which has the smallest surface roughness and is located on the resin substrate 12 side, becomes one surface of the titanium molded body 31. The other surface of the titanium molded body 31 is the back surface Sa2 of the sheet-like dried body 3 made of coarse titanium powder, which has the largest surface roughness. The back surface Sb2 of the sheet-like dried body 13 comes into contact with the surface Sa1 of the sheet-like dried body 3 on the resin substrate 2 side, which has a lesser surface roughness, and therefore the sheet-like dried body 3 and the sheet-like dried body 13 can be firmly bonded together.

[0052] Although not shown, a titanium molded body may be produced by stacking and bonding three or more dried sheets. Here, an example has been described in which the resin substrate 2 used in the drying process or a resin substrate 32 made of the same material is also used in the bonding process. However, resin substrates made of different materials may be used in the drying process and the bonding process. The properties required for the resin substrate in the drying process include that the paste does not fall off the resin substrate during application and that the dried sheet can be relatively easily separated from the resin substrate after drying. Meanwhile, in the bonding process, a resin substrate that allows the titanium molded body to be relatively easily separated and has heat resistance to a predetermined temperature is required.

[0053] The surface roughness Ra of the surface Sa1 of the sheet-like dried body (corresponding to the sheet-like dried body 3 in FIG. 2 ) to be bonded to the surface Sb2 of the sheet-like dried body used in the bonding process, particularly the surface Sb2 of the sheet-like dried body (corresponding to the sheet-like dried body 13 in FIG. 2 ) that will serve as one surface of the titanium molded body, is preferably 3.0 μm or less, more preferably 0.1 μm or more and 3.0 μm or less, and more preferably 0.2 μm or more and 2.0 μm or less. If the surface roughness Ra is within this range, the surface Sa1 of the sheet-like dried body 3 is smooth, which increases the number of bonding sites with the sheet-like dried body 13, thereby enabling good bonding between the sheet-like dried bodies. The surface roughness Ra means the arithmetic mean roughness and is measured in accordance with ISO 4287-1997. A roughness measuring instrument (model number: SJ-210) manufactured by Mitutoyo Corporation can be used for the measurement.

[0054] (Debinding Step) When producing a titanium porous body, the titanium molded body can be subjected to a binder removal step. In the binder removal step, for example, the resin substrate used in the bonding step is removed, and the titanium molded body, optionally placed on a molding die, is heated to volatilize mainly the organic binder in the titanium molded body. When the binder removal step is performed on a molding die, for example, the titanium molded body 31 obtained in FIG. 2(d) can be placed on either one of the molding dies 1 and 11 and subjected to the binder removal step; in this case, the other molding die does not need to be used. The binder removal step does not require the titanium molded body to be sandwiched between molding dies as in the bonding step.

[0055] In the binder removal step, the titanium molded body is preferably heated to a temperature of, for example, 300° C. or higher and 450° C. or lower. This makes it possible to remove the organic binder while suppressing sintering of the titanium powder due to heating.

[0056] The heating time is not particularly limited, but may be 3 hours or more and 20 hours or less, or 3 hours or more and 12 hours or less. The atmosphere during heating may be an oxygen-containing atmosphere such as air atmosphere. When an oxygen-containing atmosphere is used, it is possible to suppress the increase in costs that occurs when the atmosphere is strictly controlled.

[0057] (Sintering Step) After the binder removal step, the titanium molded body is then subjected to a sintering step to sinter the titanium powder in the molded body, thereby obtaining a sintered porous titanium body.

[0058] In the sintering step, the titanium compact after the debinding step can be heated to a temperature of, for example, 700°C or higher and 1100°C or lower, typically 825°C or higher and 950°C or lower. The above temperature may be maintained for a period of 1 hour or higher and 4 hours or lower. The sintering atmosphere may be, for example, 1.0 x 10 -2 The atmosphere may be a vacuum or reduced pressure atmosphere of 10 Pa or less, or an inert gas atmosphere of Ar or He.

[0059] (Porous titanium body) The sheet-like porous titanium body produced by the above-described production method comprises multiple titanium porous layers formed after debinding and sintering the aforementioned multiple laminated dried sheet bodies. The multiple porous layers are laminated such that adjacent titanium bonding surfaces are bonded to each other in the thickness direction, and each layer has pores that are permeable to gases and / or liquids.

[0060] When a titanium porous body is produced using the above-described production method, titanium powder particles located on adjacent surfaces of each dried sheet body are sintered to form a titanium bonding surface. When adjacent dried sheet bodies are produced using titanium powders with different average particle sizes, the sheet-like porous titanium body obtained after the sintering process will have, when observed from the side, a portion where the size of the skeleton formed by the bonded titanium powder particles changes in the thickness direction, and it can be seen that the titanium bonding surface is located in this portion. It is preferable that the titanium bonding surface of the multiple porous layers is substantially free of metals other than titanium or titanium-free compounds, etc., in order to achieve the required high conductivity at low cost. The titanium porous body used as the porous transport layer of a PEM-type water electrolysis device can be one that is permeable to gas and / or liquid in the thickness direction and in other directions, such as a direction perpendicular to the thickness direction.

[0061] Each porous layer has a skeleton formed by bonding titanium powder particles together, and has a sponge-like three-dimensional network structure in which pores are formed between the mutually bonded titanium powder particles.

[0062] One surface of the porous titanium body is formed by the porous layer that constitutes the portion on that surface side (also referred to as the "porous layer on one side"). In other words, the one surface corresponds to the surface of the porous layer on one side.

[0063] The average area of ​​the pores opening to one surface of the titanium porous body is 5 μm 2 More than 15 μm 2As described above, when the pores on one surface have a relatively small area, the surface can be said to be generally smooth, and damage to the electrolyte membrane in a PEM-type water electrolysis device can be effectively suppressed.

[0064] From this perspective, the average area of ​​the holes on one surface is 7 μm 2 More than 13 μm 2 It is preferable that the average area of ​​the pores on one surface is too small, which may result in reduced air permeability or liquid permeability. On the other hand, if the average area of ​​the pores on one surface is too large, the electrolyte membrane may partially penetrate into the pores, causing significant deformation in the areas adjacent to the pores and potentially damaging the electrolyte membrane.

[0065] From the same viewpoint, the standard deviation of the area of ​​the pores on the surface is 35 μm 2 Further, 3 μm 2 ~25μm 2 , especially 5 μm 2 ~17μm 2 A small standard deviation value means that most of the pores present on one surface are of the required fineness.

[0066] In addition, the area of ​​one surface is 22000 μm 2 The number of pores present in a rectangular region having an aspect ratio of length:width = 4:3 is 256 or more, preferably 290 or more, and more preferably 400 or more. The presence of many fine pores as described above on one surface makes it possible to achieve smoothness while ensuring the required air permeability or liquid permeability. The number of pores within the rectangular region on one surface is not limited to this, but may be, for example, 700 or less, or 550 or less.

[0067] The other surface of the porous titanium body refers to the surface located on the back or opposite side of the one surface, and is formed by the porous layer that constitutes the portion on the other surface side (also referred to as the "porous layer on the other side"). In other words, the other surface corresponds to the surface of the porous layer on the other side.

[0068] In order to improve the air permeability or liquid permeability of the porous titanium body, the average area of ​​the pores opening on the other surface is preferably at least 1.5 times, and even more preferably at least 3 times, the average area of ​​the pores on one surface. By forming the other surface side as a porous layer with large pores, gas and liquid can easily flow through the porous titanium body. The upper limit of the average area of ​​the pores opening on the other surface is not particularly limited, provided that the porous titanium body has the required strength for use in, for example, a PEM water electrolysis device, but may be 10 times or less, 7 times or less, or 5 times or less the average area of ​​the pores on one surface.

[0069] The average value and standard deviation of the area of ​​the pores opening to the surface and the number of pores in a predetermined rectangular area are measured using a scanning electron microscope (Keyence Corporation, ultra-deep multi-angle lens VHX-D510). More specifically, for both the one surface and the other surface, the average value and standard deviation of the area of ​​the pores opening to the surface and the number of pores in a predetermined rectangular area are measured using a scanning electron microscope (Keyence Corporation, ultra-deep multi-angle lens VHX-D510). 2 An SEM image was acquired at 2000x magnification for a rectangular region with an aspect ratio of 4:3. The SEM image was then analyzed using a scanning electron microscope. Half the maximum detected brightness value for the SEM image was used as a threshold, and closed regions with brightness ranging from 0 to the threshold were considered to be individual holes. If necessary, the SEM image may be binarized. After the binarization process, small grain removal (processing to convert black pixels after binarization) was performed on closed regions of 50 pixels or less, and then hole filling (processing to convert white pixels after binarization) was performed on closed regions of 50 pixels or less. This was used to calculate the number and area of ​​each hole, and the standard deviation, expressed as the square root of the variance, was determined. This SEM image analysis was performed on five rectangular regions on the surface, at least partially offset from each other, and the average area and number of holes in these rectangular regions were used as the average area and standard deviation of holes on the surface, and the number of holes in the rectangular regions, respectively. In the case of a surface that is a square or a rectangle in plan view, the five rectangular regions are the five rectangular regions at the center and four corners.

[0070] The thickness of the sheet-shaped porous titanium body (total thickness including all porous layers) may be 200 μm or more and 3000 μm or less. For example, a porous transport layer of a PEM water electrolysis device may require such a relatively thick porous titanium body. On the other hand, if the thickness is too large, the PEM water electrolysis device may become large. The thickness of the porous titanium body may be, for example, 200 μm or more and 1000 μm or less, or even 500 μm or less.

[0071] The thickness of the porous titanium body is measured at five points in total, four points on the periphery and one point in the center, using a digital thickness gauge with a flat probe having a diameter of 10 mm and a measurement accuracy of 0.01 mm, such as a digital thickness gauge (model number 547-321) manufactured by Mitutoyo Corporation, and the average of these measurements is used. When the sheet-like porous titanium body has a rectangular shape in plan view, the four peripheral points are the four corner points.

[0072] The thickness of the porous layer on one side may be 20 μm or more and 120 μm or less, or 35 μm or more and 100 μm or less. The thickness of the porous layer on one side may be 30% or less, 20% or less, or even 15% or less of the total thickness. Because the porous layer on one side is a porous layer with small pores, if its thickness is too large, the overall air permeability or liquid permeability of the titanium porous body will decrease. On the other hand, by increasing the thickness of the porous layer on one side to a certain extent, the required strength is ensured after sintering during the preparation of the corresponding porous material, making the porous layer less likely to crack when pressed against the electrolyte membrane together with other porous layers. It is preferable that the porous layer on one side has the thinnest thickness among the multiple porous layers. By making the porous layer on one side, which has small pores and is less likely to permeate gases or liquids, the air permeability or liquid permeability of the titanium porous body can be significantly improved.

[0073] The thickness of the other porous layer is preferably 100 μm to 2900 μm, or 100 to 1000 μm, or 200 to 600 μm. By making the other porous layer thicker to a certain extent, the air permeability or liquid permeability can be further improved, and by not making the thickness too thick, the water electrolysis device can be made smaller and the electrolysis efficiency per area can be improved.

[0074] The thickness of each porous layer is measured by observing the thickness at five points on a cross section of a resin-embedded and polished titanium porous body in the thickness direction using an SEM, and the average value is used. In this embodiment, since the functions required of each porous layer in the sheet-like titanium porous body are different, portions where differences in the size of the skeleton formed by bonding titanium powder in the stacking direction are apparent are identified, and the thickness of each porous layer is determined by SEM observation of those portions.

[0075] The surface area of ​​the sheet-like porous titanium body in a plan view is not particularly limited and can be determined appropriately depending on various conditions. For example, it is 70 mm 2 More than 600,000 mm 2 Below, 10,000 mm 2 More than 600,000 mm 2 The term "sheet-like" as used herein means a plate-like or foil-like shape having a small thickness relative to the dimensions in a plan view, and the shape in a plan view is not particularly limited.

[0076] The titanium porous body can be constructed of two porous layers, one of which is directly bonded to the other at their titanium bonding surfaces, or it can be constructed with one or more intermediate porous layers between the two. In this case, the pores in the titanium porous body can be gradually enlarged to allow for some control of the flow of gas or liquid.

[0077] The titanium porous body has an overall porosity, including the multiple porous layers, of 40% to 60%, preferably 45% to 55%. A porosity within this range provides the required air or liquid permeability for the intended application, making it suitable for use as a porous transport layer in a solid polymer water electrolysis device. If the porosity is too high, the mechanical strength of the titanium porous body may be insufficient, raising concerns that it may be prone to unintended compressive deformation.

[0078] The porosity ε of the titanium porous body is determined by the ratio of the apparent density ρ' calculated from the volume and mass of the titanium porous body determined from the external dimensions such as width, length, and thickness, and the true density ρ (4.51 g / cm) of titanium constituting the titanium sintered body. 3 ) and calculate using the formula: ε = (1 - ρ' / ρ) x 100.

[0079] The titanium porous body is made of titanium. If it is made of titanium, it can be said that the titanium porous body has high electrical conductivity at a certain relative density. The titanium content of the titanium porous body (and further each porous layer) is preferably 97% by mass or more, and more preferably 98% by mass or more. The upper limit of the titanium content is not limited to this, but may be, for example, 99.8% by mass or less, or 99% by mass or less. This titanium content refers to the purity of titanium, taking into account not only the metal components but also impurities such as gas components such as oxygen. Therefore, the titanium content can be calculated by subtracting the total content of metal components and impurities, including gas components, from 100% by mass.

[0080] The titanium porous body may have a purity, excluding the oxygen content, equivalent to JIS H 4600 (2012) pure titanium grades 1 to 4, typically grades 1 or 2. The oxygen content of the titanium porous body can be measured by inert gas fusion-infrared absorption spectroscopy.

[0081] Next, the methods for producing a titanium molded body and a titanium porous body of the present invention were experimentally carried out to produce prototype titanium porous bodies, which are described below, although the description here is for illustrative purposes only and is not intended to be limiting.

[0082] (Example 1) As shown in Table 1, titanium powder (hydrogenated / dehydrogenated titanium powder) having an average particle size of 14 μm and titanium powder having an average particle size of 21 μm were mixed with an organic solvent (isopropyl alcohol) and an organic binder (polyvinyl butyral) to prepare pastes containing these. The pastes did not contain water or a foaming agent. Each paste was applied in sheet form to a PET resin substrate and dried by heating at a temperature of 150 ° C for 90 minutes to obtain a dried sheet. The PET resin substrate had a silicone coating as a release layer.

[0083] Next, as shown in Figure 2, the sheet-like dried body for the other porous layer was turned upside down together with the resin substrate and placed on another resin substrate placed in a mold. The upper resin substrate was then peeled off and removed, and the sheet-like dried body for one porous layer was turned upside down and placed on top of it together with the resin substrate. A mold was then placed on top of it, and in this state, heating and pressurization were performed at the temperature, pressure, and time shown in Table 1. Note that pressure was applied to the sheet-like dried body by placing a weight on the upper mold. As a result, the sheet-like dried bodies were bonded together to obtain a titanium molded body.

[0084] Next, the titanium molded body was heated in an air atmosphere at a temperature of 380°C for the time shown in Table 1 to separate the organic binder and perform debinding (debindering). After that, the debindered titanium molded body was heated under vacuum conditions at the temperature shown in Table 1 for 1 hour. As a result, the titanium powder in the titanium molded body was sintered, and a porous titanium body was obtained.

[0085] Example 2 A porous titanium body was produced in the same manner as in Example 1, except that the bonding conditions for the dried sheet body were changed as shown in Table 2.

[0086] (Example 3) As shown in Table 3, three dried sheets each having a predetermined surface roughness Ra were prepared, and titanium porous bodies were manufactured in the same manner as in Example 1, except that titanium powder having an average particle size of 21 μm was used to prepare each of them.

[0087] (Example 4) As shown in Table 4, a titanium porous body was produced in the same manner as in Example 1, except that titanium powder with an average particle size of 28 μm was used to prepare the sheet-like dried body for the other porous layer, thereby giving the sheet-like dried body a predetermined surface roughness Ra, and the heating time and sintering temperature for binder removal were changed.

[0088] (Comparative Example 1) An attempt was made to produce a titanium porous body in the same manner as in Example 1, except that zero pressure (no pressure) was applied when bonding the sheet-shaped dried bodies. However, the porous layers of the titanium porous body were easily peeled off by hand, and therefore a titanium porous body could not be produced.

[0089] (Comparative Example 2) An attempt was made to produce a titanium porous body in the same manner as in Example 1, except that when bonding the sheet-shaped dried bodies, pressure was applied but heating was not performed and the bodies were left at room temperature. However, the sheet-shaped dried bodies did not bond, and subsequent steps could not be carried out.

[0090] (Evaluation) For each of the titanium porous bodies in Examples 1 to 4, the total thickness, the thickness of each porous layer (thickness of each layer), the average value of the area of ​​the pores opening on one and the other surfaces (average pore area on the surface), the standard deviation of the pore area (standard deviation of the pore area on the surface), and the average value of the area of ​​22,000 μm were measured according to the method described above. 2 The number of pores present in a rectangular region with an aspect ratio of 4:3 (number of pores on the surface) and the overall porosity were measured. The results are shown in Tables 1 to 4.

[0091] Furthermore, the electrical conductivity (conductivity stack) was measured for each of the one and other surfaces of each titanium porous body. The electrical conductivity was measured using a Mitsubishi Analytech low resistivity meter Loresta GP MCP-T610 by the four-probe method, with the surface to be measured positioned on the upper side. The probe checker used was an MCP-T610 RMH112. The results are also shown in Table 1. It is believed that if the titanium bonding surfaces of the titanium porous layer are sufficiently bonded to each other, the electrical conductivity will be high. Furthermore, if the electrical conductivity is high, it is assumed that the gas / liquid permeable layers are firmly bonded, and therefore the mechanical strength will also be excellent. In Tables 1 to 4, the unit of electrical conductivity is expressed as "E+3S / cm", which means "10 3 × S / cm". For example, the value "4.1" in the "Conductivity Layer" column in Table 1 means 4100 S / cm.

[0092] Tables 1 to 4 also show the thickness, electrical conductivity alone, electrical conductivity stacking, and porosity of titanium sintered bodies (titanium sintered bodies corresponding to each porous layer) obtained by debinding and sintering the sheet-like dried bodies used to produce each titanium porous body without bonding them together. The electrical conductivity alone is the value measured when two or three titanium sintered bodies are individually stacked without being stacked together, while the electrical conductivity stacking is the value measured when two or three titanium sintered bodies are stacked together. Because the electrical conductivity stacking is measured when two or three titanium sintered bodies are simply stacked together, the value tends to be smaller than the electrical conductivity alone due to the large electrical resistance between them. Furthermore, because the sheet-like dried bodies were stacked without being joined, the stacking thickness tends not to match the sum of the thicknesses of the individual titanium sintered bodies.

[0093]

[0094]

[0095]

[0096]

[0097] In Examples 1 to 4, porous titanium bodies were produced by heating the dried sheet body at a predetermined temperature while applying a predetermined pressure, as shown in Tables 1 to 4. These porous titanium bodies had electrical conductivity as high as that of each sintered titanium body (single electrical conductivity), which indicates that the porous layers were sufficiently bonded together at the titanium bonding surfaces.

[0098] The porous titanium bodies described above comprised multiple porous layers, each having pores, bonded together at adjacent titanium bonding surfaces in the thickness direction. For each porous titanium body, the conductivity value for at least one of the surfaces on one side and the other side was approximately 1.5 times or more higher than the conductivity value for the same surface of a simply laminated titanium sintered body, indicating that the porous layers were sufficiently bonded together. Furthermore, for each porous titanium body, the average pore area, standard deviation of the pore area, number of pores, and porosity on one surface (the surface of one porous layer) were all within the desired ranges.

[0099] 1, 11 Mold 2, 12, 32 Resin substrate 3, 13 Sheet-like dried body 31 Titanium molded body Sa1, Sb1 Surface on resin substrate side Sa2, Sb2 Back surface Ta, Tb Thickness

Claims

1. A method for producing a titanium sheet-shaped molded body, comprising: stacking a plurality of sheet-shaped dried bodies obtained by drying a paste containing titanium powder, an organic binder, and an organic solvent, and applying a pressure of 0.1 N / cm in the thickness direction. 2 The method for producing a titanium molded body includes a bonding step of heating the molded body to a temperature of 70°C or more and 200°C or less while applying the pressure at the above pressure.

2. The method for producing a titanium molded body according to claim 1, further comprising a drying step of drying the paste to obtain a sheet-like dried body prior to the joining step.

3. The method for producing a titanium molded body according to claim 2, wherein the paste is heated to a temperature of 90°C or more and 165°C or less in the drying step.

4. The method for producing a titanium molded body according to claim 2 or 3, wherein the paste is dried on a resin substrate in the drying step.

5. A method for producing a titanium molded body according to any one of claims 1 to 4, wherein in the joining step, the sheet-like dried body, which is stacked in multiple layers, is sandwiched between a mold from both sides in the thickness direction and pressurized and heated.

6. The method for producing a titanium molded body according to claim 5, wherein in the joining step, pressure and heat are applied with a resin substrate interposed between the sheet-like dried body and the mold.

7. The method for producing a titanium molded body according to any one of claims 1 to 6, wherein the average particle size of the titanium powder in at least one of the sheet-like dried bodies is 10 µm or more and 20 µm or less.

8. A method for producing a titanium molded body described in any one of claims 1 to 7, wherein the difference between the average particle size of the titanium powder in the sheet-like dried body on one surface side of the sheet-like dried body and the average particle size of the titanium powder in at least one other sheet-like dried body is 5 μm or more.

9. The method for producing a titanium molded body according to any one of claims 1 to 8, wherein the paste used to produce the sheet-like dried body does not contain a foaming agent.

10. A method for producing a sheet-like porous titanium body, comprising: a debinding step of heating a titanium molded body produced by the method for producing a titanium molded body described in any one of claims 1 to 9 to volatilize the organic binder in the titanium molded body; and a sintering step of heating the titanium molded body after the debinding step to sinter the titanium powder in the titanium molded body.

11. A sheet-shaped titanium porous body, comprising a plurality of titanium porous layers laminated by bonding adjacent titanium bonding surfaces in the thickness direction, each having pores and allowing gas and / or liquid to pass through, wherein the average area of ​​the pores opening to one surface of the porous layer forming one surface of the plurality of porous layers is 5 μm 2 More than 15 μm 2 The standard deviation of the area of ​​the hole is 35 μm or less. 2 or less, and the area is 22000 μm 2 the number of holes present within a rectangular region having an aspect ratio of 4:3 is 256 or more, and the overall porosity including the multiple porous layers is 40% or more and 60% or less.

12. A titanium porous body according to claim 11, wherein the average area of ​​the pores opening onto the other surface located behind said one surface is at least 1.5 times the average area of ​​the pores opening onto said one surface.

13. The titanium porous body according to claim 11 or 12, having a total thickness of 200 μm or more and 3,000 μm or less.

14. A titanium porous body according to any one of claims 11 to 13, wherein the thickness of the porous layer constituting one surface side portion is 30% or less of the total thickness.

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