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

Abstract

To provide a method for manufacturing a titanium molded body having a plurality of porous layers and capable of manufacturing a titanium porous body having a relatively high void ratio, a method for manufacturing the titanium porous body, and the titanium porous body.SOLUTION: A method for manufacturing a sheet-like titanium molded body includes a joining step of laminating a plurality of sheet-like dried bodies obtained by drying a paste containing a titanium powder, an organic binder and an organic solvent to obtain a plurality of sheet-like dried bodies, and heating the laminated sheet-like dried bodies to a temperature of 70°C or more and 200°C or less while pressing the laminated sheet-like dried bodies with a pressure of 0.1 N / cm2 or more in a thickness direction.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] A titanium porous body manufactured by sintering titanium powder has air permeability or liquid permeability due to pores, electrical conductivity, and also has high corrosion resistance due to the formation of a passive film on the surface.

[0003] A titanium porous body having such characteristics has been considered for use in a porous transport layer (PTL) or the like in an environment where corrosion can occur in a polymer electrolyte membrane (PEM) type water electrolysis device. In particular, hydrogen produced by a water electrolysis device such as a PEM type using electric power derived from renewable energy is called green hydrogen, and great expectations are placed on it in recent years as the movement towards realizing a decarbonized society accelerates.

[0004] As a technology related to a titanium porous body, for example, Patent Document 1 describes "a method for manufacturing a porous metal laminate composed of a plurality of layers including a porous layer in which a plurality of polyhedral voids whose sides 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 cutting step of cutting the laminated porous layer and adjacent layer into a desired shape by a laser, and in the cutting step, melting and solidifying the porous layer and the adjacent layer by the laser to form a fusion bonding layer that bonds the porous layer and the adjacent layer on the side surfaces of the porous layer and the adjacent layer."

[0005] In addition, 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."

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] When a titanium porous body is used as a porous transport layer in a PEM type water electrolysis device, the titanium porous body may be pressed against and incorporated into the electrolyte membrane. At this time, if the pores on the surface of the titanium porous body are large, the electrolyte membrane against which the titanium porous body is pressed may partially enter the pores, and may be greatly deformed at locations close to the pores, leading to damage to the electrolyte membrane.

[0008] Therefore, from the perspective of suppressing the occurrence of damage to the electrolyte membrane, it is desirable that the titanium porous body has small pores opening on the surface side facing the electrolyte membrane. Even if the surface pores are small, if the number of pores is large, a certain degree of air permeability or liquid permeability can be exhibited.

[0009] However, if the pores are small not only on the surface of the titanium porous body but also throughout the whole body, even if the number of pores is large, it may not be possible to obtain the required air permeability or liquid permeability depending on the required level. To address this, by laminating a plurality of porous layers, a porous layer with small pores is positioned on one surface side to suppress damage to the electrolyte membrane, while the titanium porous body has a large porosity so that good air permeability or liquid permeability can be exhibited as a whole.

[0010] When manufacturing a titanium porous body having a plurality of porous layers, when a plurality of titanium sintered compacts to be porous layers are laminated and heated for joining, each porous layer constituting the titanium porous body is subjected to relatively high-temperature heating twice: heating for sintering during the production of the titanium sintered compact and heating during the joining. As a result, in the titanium porous body obtained by joining a plurality of titanium sintered compacts, the pore portions may become smaller as a whole, and it may not be possible to obtain the desired excellent air permeability or liquid permeability. This is the case not only in the production of a titanium porous body having a plurality of porous layers with different pore sizes and numbers, but also in the production of a titanium porous body having a plurality of 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 capable of manufacturing a titanium molded body that can be used in the manufacture of a titanium porous body having a plurality of porous layers and a relatively high porosity, a method for manufacturing a titanium porous body, and a titanium porous body.

Means for Solving the Problems

[0012] As a result of intensive studies, the inventor has devised a method of laminating a plurality of sheet-like dried bodies obtained by drying a paste of titanium powder and joining them under predetermined conditions. By performing debinding and sintering on the titanium molded body thus obtained, the number of times of high-temperature heating can be reduced as compared with the case of joining pre-sintered ones. As a result, the finally manufactured titanium porous body has a relatively high porosity.

[0013] The method for manufacturing a titanium molded body of the present invention is a method for manufacturing a sheet-like titanium molded body, wherein a plurality of sheet-like dried bodies respectively obtained by drying a paste containing titanium powder, an organic binder, and an organic solvent are laminated, and 0.1 N / cm 2 or more pressure while heating to a temperature of 70°C or higher and 200°C or lower, and includes a joining step.

[0014] The manufacturing method of the titanium formed body described above may include a drying step of drying the paste to obtain a sheet-like dried body before the joining step.

[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 performed on a resin base material.

[0017] In the joining step, the plurality of laminated sheet-like dried bodies can be pressed and heated while being sandwiched between moldings from both sides in the thickness direction.

[0018] In this case, in the joining step, it is preferable to perform pressing and heating in a state where a resin base material is interposed between the sheet-like dried body and the molding.

[0019] The manufacturing method of the titanium porous body of this invention is a method for manufacturing a sheet-like titanium porous body, including a debinding step of heating the titanium formed body manufactured by the manufacturing method of any of the above titanium formed bodies to volatilize the organic binder in the titanium formed body, and a sintering step of heating the titanium formed body after the debinding step to sinter the titanium powder in the titanium formed body.

[0020] The titanium porous body of this invention is sheet-like, and is composed of a plurality of titanium-made porous layers that are laminated by bonding titanium bonding surfaces adjacent to each other in the thickness direction, each having pore portions and being permeable to gas and / or liquid. Among the plurality of porous layers, the average value of the area of the pore portions opening on the surface of the porous layer forming one surface is 5 μm 2 or more and 15 μm 2 or less, the standard deviation value of the area of the pore portions is 35 μm 2 or less, and the area is 22000 μm 2The number of the holes existing within a rectangular area having an aspect ratio of 4:3 is 256 or more, and the overall porosity of the multiple layers of the porous layers is 40% or more and 60% or less.

Advantages of the Invention

[0021] According to the method for manufacturing a titanium molded body of this invention, a titanium molded body that includes multiple layers of porous layers and can be used for manufacturing a titanium porous body having a relatively high porosity can be manufactured.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of this invention will be described in detail. The method for manufacturing a titanium molded body according to an embodiment of this invention includes a joining step of laminating and joining multiple sheet-like dried bodies.

[0024] To obtain each sheet-like dried 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 shape and drying it can be performed. In the joining step, while applying a pressure of 0.1 N / cm or more in the thickness direction to the multiple laminated sheet-like dried bodies, they are heated to a temperature of 70°C or more and 200°C or less. As a result, the multiple sheet-like dried bodies are joined to each other to form a titanium molded body. 2 above, the multiple sheet-like dried bodies are joined to each other to form a titanium molded body.

[0025] The above titanium formed body is sequentially subjected to a debinding process and a sintering process to become a titanium porous body. The titanium porous body includes a porous layer made of titanium as a sintered body of each sheet-like green body by laminating and joining a plurality of sheet-like green bodies in the joining process during its production. By appropriately setting the particle size and other conditions of the titanium powder used when forming the sheet-like green body, the titanium porous body can have, for example, smaller pore portions on the surface where the electrolyte membrane is pressed when used as a porous transport layer in a PEM type water electrolysis device, but can have a relatively large porosity as a whole.

[0026] Compared with a titanium porous body manufactured by joining titanium sintered bodies, the titanium porous body manufactured as described above is exposed to high-temperature heating such as during sintering fewer times, so it has a somewhat higher porosity. In other words, when debinding and sintering are performed on each of a plurality of sheet-like green bodies, and the resulting plurality of titanium sintered bodies are heated and joined, as a result, at least two high-temperature heatings are performed during sintering and joining, and the sintering of the titanium powder proceeds, reducing the porosity and the like. In contrast, according to the embodiment described here, the number of high-temperature heatings can be reduced, so for example, a titanium porous body with a high porosity can be manufactured.

[0027] (Paste preparation process) In the paste preparation process, a raw material containing titanium powder, an organic binder, and an organic solvent is mixed using a mixer with a stirrer, a rotary mixer, a three-roll mill, or the like to prepare a paste. At this time, it may be pulverized using a vibration mill, a bead mill, or other pulverizing mixers.

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

[0029] From the viewpoint of manufacturing a titanium porous body having small pores opening on one surface but a large overall porosity, among a plurality of sheet-like dried bodies, the difference between the average particle size of the titanium powder used for producing one sheet-like dried body that becomes the porous layer located on one surface side and the average particle size of the titanium powder used for producing at least one other sheet-like dried body is preferably 5 μm or more, more preferably 10 μm or more. However, if the difference in the above average particle size is too large, the difference in the sintering shrinkage amount of each sheet-like dried body becomes too large, and the porous layer made of titanium may peel off. Therefore, considering this, it may be 100 μm or less, more preferably 50 μm or less.

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

[0031] As the organic binder used for the paste, various ones can be appropriately selected and used. For example, methyl cellulose-based, polyvinyl alcohol-based, ethyl cellulose-based, acrylic-based, polyvinyl butyral-based, etc. can be mentioned. An organic binder showing hydrophobicity is preferable. However, it is not limited to those listed here. The organic solvent is, 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] Preferably, the paste does not contain water as a solvent. It is also preferable that the paste does not contain a foaming agent. Note that the paste only needs not to contain water as a solvent, and the inclusion of water that may be mixed into the paste unintentionally, such as by moisture absorption, is acceptable. If 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, and it may not be possible to achieve the desired pore size. When a titanium porous body with large pore sizes is manufactured because the paste contains water and / or a foaming agent, the titanium porous body will have poor surface smoothness and will be likely to damage the electrolyte membrane of a solid polymer type water electrolyzer.

[0033] (Drying process) In the drying process, the above paste is applied thinly in a sheet shape and heated. As a result, mainly the organic solvent in the paste evaporates, and a sheet-shaped dried body is obtained.

[0034] The paste can be applied on a flat surface such as a table, but it is preferably applied on a resin substrate. The resin substrate on which the paste is applied can be placed on a molding die described later, but is not limited thereto. Note that if the paste is directly applied on a graphite molding die, carbon from the molding die may be mixed into the paste or the sheet-shaped dried body during the drying process, which may cause the titanium porous body to be colored after the sintering process. Since the resin substrate is relatively inexpensive and flexible, it is easy to handle. Specific materials for the resin substrate include, for example, polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), and polyvinyls such as polyethylene, polypropylene, polystyrene, and polyvinyl alcohol. Among them, a resin substrate made of PET is inexpensive, and the sheet-shaped dried body can 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 providing a release layer, a silicone coating or the like can be used as the release layer. For example, by selecting a substrate on which such a material has been pre-coated, such as Celapil (registered trademark) manufactured by Toray Industries, Inc., a release layer can be provided on the substrate. By providing a release layer on the substrate, it becomes possible to easily separate the thin sheet-shaped molded body obtained after the drying process 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, it is possible to complete drying in a relatively short time while suppressing the boiling of components such as organic solvents in the paste. The drying time is not particularly limited and can be appropriately determined. For example, it can be 5 minutes or more and 300 minutes or less. Drying is preferably performed in an atmosphere containing oxygen, such as in the air atmosphere. This can suppress an increase in manufacturing cost.

[0037] When manufacturing a titanium porous body having a plurality of porous layers with different thicknesses, the coating thickness of the paste can be adjusted according to the thickness of the above-mentioned porous layer when producing each sheet-shaped dried body.

[0038] For example, in each of FIGS. 1(a) and 1(b), by adjusting the coating thickness of the paste on the resin substrates 2 and 12 placed on the molds 1 and 11 and drying them respectively, a sheet-shaped dried body 3 having a thickness Ta and a sheet-shaped dried body 13 having a thickness Tb thinner than Ta are obtained.

[0039] The sheet-shaped dried body 3 with a relatively thick thickness Ta may use titanium powder with a relatively large average particle size in order to increase the porosity of the entire titanium porous body. Also, the sheet-shaped dried body 13 with a relatively thin thickness Tb may be used for the porous layer forming one surface on which the 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] As the forming dies 1 and 11, those having required heat resistance and having a flat surface in contact with the resin base materials 2 and 12 or the paste or sheet-like dried bodies 3 and 13 are sufficient, and those having excellent heat conductivity are desirable. Specifically, as the forming dies 1 and 11, for example, a setter made of graphite can be mentioned. Here, although the forming dies 1 and 11 are used as an example, it is possible to manufacture a titanium molded body without using the forming dies 1 and 11, and various known techniques can be adopted for the coating of the paste. For example, although not shown, a method of continuously coating the paste on the resin base material by discharging the paste between a roll and a roll paired with the roll while feeding a long resin base material with a roll (so-called comma coating method) can also be adopted. Alternatively, although not shown either, a doctor blade method may be adopted.

[0041] (Bonding step) In the bonding step, a plurality of sheet-like dried bodies are laminated and heated while being pressed in the thickness direction to bond them. Thereby, a titanium molded body is obtained.

[0042] At this time, the pressure applied in the thickness direction to the plurality of sheet-like dried bodies laminated on each other is 0.1 N / cm 2 or more and 0.2 N / cm 2 or more and 5.0 N / cm 2 or less is preferable. Further, the heating temperature is 70°C or more and 200°C or less, and preferably 100°C or more and 180°C or less.

[0043] If the heating temperature is too low or the pressure is too small, there is a concern that multiple sheet-like green compacts may not be sufficiently joined. In such a case, in the worst case, the sheet-like green compacts of the titanium compact may be partially peeled off from each other after the joining process or after the debinding process described later. When the temperature is raised to a certain extent and a pressure of a predetermined magnitude is applied, the sheet-like green compacts are compressed while the organic binder softens, so it is considered that good joining can be achieved. On the other hand, by not making the pressure too large, it is possible to satisfactorily suppress the disturbance of the dimensions and shape of the sheet-like green compacts due to compression during pressurization. Also, the higher the heating temperature, the more likely it is that the joining of multiple sheet-like green compacts will be completed in a short time. However, if the heating temperature is too high, there are concerns such as the titanium compact drying excessively and cracking, and the titanium compact deforming following the deformation of the resin base material.

[0044] Pressurization and heating in the joining process can be performed with the sheet-like green compacts stacked in multiple layers sandwiched between mold halves from both sides in the thickness direction. Thereby, the flatness of the titanium compact is ensured. Preferably, the state of being sandwiched between mold halves is maintained until the temperature drops to room temperature after heating. The mold may be the same as that used in the drying process described above, but is not limited thereto. Also, as the mold, any mold having a flat surface on the sheet-like green compact side may be used as long as the titanium compact can be formed into a sheet shape later, and there are no particular restrictions on the shape of the other parts. When using a mold in the joining process, the above-described pressure is applied to the sheet-like green compacts in consideration of the pressure due to the self-weight of the mold. That is, the pressure applied to the sheet-like green compacts includes the pressure due to the self-weight of the mold.

[0045] When using a mold in the joining process, in order to suppress contamination from the mold to the sheet-like green compacts during heating at the time of joining, it is preferable to perform pressurization and heating with a resin base material interposed between the sheet-like green compacts and the mold. This resin base material may also be the same as that used in the drying process described above, but a different material may be used.

[0046] As shown in FIG. 1, the surface roughness of the surfaces Sa1 and Sb1 of the sheet-like dried body, which were located on the resin base material 2 and 12 sides of the sheet-like dried bodies 3 and 13 in the drying process, tends to be smaller than that of the surfaces Sa2 and Sb2 on the back side (opposite side). For this reason, for the sheet-like dried body 13 for the porous layer that forms one surface of the titanium porous body on which the electrolyte membrane is pressed, it is preferable that the surface Sb1 on the resin base material 12 side is joined to the sheet-like dried body 3 in a direction that is on the outer side in the thickness direction of the titanium molded body.

[0047] On the other hand, even if the surface Sa2 on the back side of the surface Sa1 located on the resin base material 2 side of the sheet-like dried body 3 for the porous layer that forms the other surface of the titanium porous body is opposed to the surface Sb2 on the back side of the sheet-like dried body 13 and attempts to join with the surface Sb2, there may be a case where neither of the surfaces Sa2 and Sb2 can be joined firmly enough due to the rough surface roughness. Therefore, it is preferable to join the surface Sa1 located on the resin base material 2 side of the sheet-like dried body 3 and the surface Sb2 on the back side of the sheet-like dried body 13.

[0048] FIG. 2 shows an example of the case where the sheet-like dried bodies 3 and 13 are laminated and joined. Here, first, the sheet-like dried body 3 after the drying process is once peeled off from the mold 1 together with the resin base material. Then, as shown in FIG. 2(a), another resin base material 32 is laid on the mold 1, and the sheet-like dried body 3 is arranged on the resin base material 32 in a direction in which the surface Sa2 on the back side of the surface Sa1 located on the resin base material 2 side of the sheet-like dried body 3 contacts the resin base material 32. That is, as shown by the arrow in the figure, the sheet-like dried body 3 in a state where the resin base material 2 is adhered is turned over and arranged on another resin base material 32.

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

[0050] Thereafter, as shown in Fig. 2(c), the sheet-like drying body 13 is arranged on the sheet-like drying body 3 together with the resin base material 12 and the molding die 11 such that the back surface Sb2 of the sheet-like drying body 13, which is on the side of the resin base material 12, faces the exposed surface Sa1 located on the side of the resin base material 2 of the sheet-like drying body 3. Note that the resin base material 12 is often not adhered to the molding die 11. In this case, the sheet-like drying body 13 and the resin base material 12 may be first arranged on the sheet-like drying body 3, and then the molding die 11 may be placed thereon to obtain the arrangement shown in Fig. 2(c). At this time, the molding die 11 may be replaced with another one different from that used in the drying process. In this state, the sheet-like drying bodies 3 and 13 are pressed and heated as indicated by the arrows in the figure to join them together. As a result, as shown in Fig. 2(d), a titanium molded body 31 having the sheet-like drying body 3 and the sheet-like drying body 13 joined to each other is obtained.

[0051] When the joining process is performed as shown in Figs. 2(a) to 2(d), for example, the surface Sb1 on the resin base material 12 side of the sheet-like drying body 13 with the smallest surface roughness, which uses fine titanium powder, becomes one surface of the titanium molded body 31. On the other surface of the titanium molded body 31, the back surface Sa2 with the largest surface roughness of the sheet-like drying body 3, which uses coarse titanium powder, is located. Since the back surface Sb2 of the sheet-like drying body 13 is in contact with the surface Sa1 on the resin base material 2 side of the sheet-like drying body 3, which is not so rough, the sheet-like drying body 3 and the sheet-like drying body 13 can be firmly joined together.

[0052] Although not shown, a titanium molded body may be manufactured by laminating and joining three or more sheet-like dried bodies. Here, an example in which the resin base material 2 used in the drying step and the resin base material 32 of the same material are also used in the joining step has been described, but resin base materials having different materials, etc. may be used in the drying step and the joining step. Examples of the properties required for the resin base material in the drying step include that the paste does not fall off from the resin base material during coating, and that the sheet-like dried body after drying can be relatively easily separated from the resin base material. On the other hand, in the joining step, a resin base material is required that allows the titanium molded body to be relatively easily separated and has heat resistance against a predetermined temperature.

[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) joined to the surface Sb2 of the sheet-like dried body used in the joining step, particularly the sheet-like dried body (corresponding to the sheet-like dried body 13 in FIG. 2) that becomes 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 even 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, more adhesion sites with the sheet-like dried body 13 can be formed, and the sheet-like dried bodies can be adhered well. The surface roughness Ra means the arithmetic mean roughness and is measured in accordance with ISO4287-1997. For the measurement, a roughness measuring instrument (model number: SJ-210) manufactured by Mitutoyo Corporation can be used.

[0054] (Debinding process) When manufacturing a titanium porous body, the above titanium formed body can be subjected to a debinding process. In the debinding process, for example, the resin base material used in the above joining process is removed, and the titanium formed body is heated, sometimes while placed on a mold, to volatilize mainly the organic binder in the titanium formed body. When performing the debinding process on a mold, for example, the titanium formed body 31 obtained in Fig. 2(d) can be placed on either one of the molds 1 and 11 and subjected to the debinding process. In this case, the other mold does not need to be used. The debinding process does not require sandwiching the titanium formed body with a mold as in the joining process.

[0055] In the debinding process, for example, it is preferable to heat the titanium formed body to a temperature of 300°C or higher and 450°C or lower. Thereby, the organic binder can be removed while suppressing sintering of the titanium powder due to heating.

[0056] The heating time is not particularly limited, but it 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 can be an atmosphere containing oxygen such as an air atmosphere. When using an atmosphere containing oxygen, an increase in cost as in the case of precisely adjusting the atmosphere can be suppressed.

[0057] (Sintering process) Thereafter, a sintering process is performed on the titanium formed body that has undergone the debinding process to sinter the titanium powder in the formed body. After the sintering process, a titanium porous body as a sintered body is obtained.

[0058] In the sintering process, the titanium formed body after the debinding process 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 1 hour or more and 4 hours or less. The atmosphere during sintering can be, for example, a vacuum or reduced pressure atmosphere of 1.0×10 -2 Pa or less, or an inert gas atmosphere of Ar or He.

[0059] (Titanium porous body) The sheet-like titanium porous body produced by the manufacturing method described above includes a plurality of porous layers made of titanium formed after debinding and sintering of the plurality of sheet-like dried bodies stacked as described above. The plurality of porous layers are bonded and laminated to each other at titanium bonding surfaces adjacent to each other in the thickness direction, each having pore portions, and being permeable to gas and / or liquid.

[0060] When a titanium porous body is manufactured by the manufacturing method as described above, the titanium powders located on the adjacent surfaces of each sheet-like dried body are sintered and bonded to each other to form titanium bonding surfaces. When adjacent sheet-like dried bodies are produced using titanium powders having different average particle sizes, in the sheet-like titanium porous body obtained after the sintering process, when observing the side surface from the side, there is a portion where the size of the skeleton formed by the bonding of the titanium powders changes in the thickness direction, and it can be understood that the above-mentioned titanium bonding surface is located at that portion. It is preferable that substantially no metal other than titanium, compounds not containing titanium, etc. exist on the titanium bonding surfaces of the plurality of porous layers in terms of realizing a required high conductivity at low cost. Note that, as the titanium porous body as the porous transport layer of the PEM type water electrolysis device, those permeable to gas and / or liquid in the thickness direction and other directions such as the direction perpendicular to the thickness direction can be used.

[0061] Each porous layer has a sponge-like three-dimensional network structure in which titanium powders are bonded to form a skeleton, and pore portions are formed between the mutually bonded titanium powders.

[0062] One surface of the titanium porous body is formed by a porous layer (also referred to as "porous layer on one side") constituting the portion on the one surface side. That is, one surface corresponds to the surface of the porous layer on one side.

[0063] The average value of the area of the pore portions opening on one surface of the titanium porous body is 5 μm 2 or more and 15 μm 2The following is the case. If the hole portion on one surface has a relatively small area in this way, it can be said that the surface is generally smooth, and damage to the electrolyte membrane in the PEM type water electrolysis device can be well suppressed.

[0064] From this viewpoint, the average value of the area of the hole portions on one surface is 7 μm 2 or more and 13 μm 2 or less, which is preferable. If the average value of the area of the hole portions on one surface is too small, there is a risk that the air permeability or liquid permeability will decrease. On the other hand, if the average value of the area of the hole portions on one surface is too large, the electrolyte membrane may partially enter the hole portions and be greatly deformed at locations close to the hole portions, leading to damage to the electrolyte membrane.

[0065] Also, from the same viewpoint, the standard deviation value of the area of the hole portions on the surface is 35 μm 2 or less, more preferably 3 μm 2 to 25 μm 2 , particularly preferably 5 μm 2 to 17 μm 2 , which is preferable. A small standard deviation value means that many of the hole portions existing on one surface are of the required fineness.

[0066] Also, the number of hole portions existing within a rectangular region on one surface with an area of 22000 μm 2 and an aspect ratio of length:width = 4:3 is 256 or more, preferably 290 or more, and more preferably 400 or more. When many fine hole portions as described above exist on one surface, it is possible to ensure the required air permeability or liquid permeability while realizing smoothness. The number of hole portions 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 titanium porous body means the surface located on the back side or the opposite side of one surface, and is formed by a porous layer (also referred to as the "porous layer on the other side") that constitutes a portion on the other surface side. In other words, the other surface corresponds to the surface of the porous layer on the other side.

[0068] In order to enhance the air permeability or liquid permeability of the titanium porous body, the average value of the area of the holes opening to the other surface is preferably 1.5 times or more, and more preferably 3 times or more, the average value of the area of the holes on one surface. By configuring the other surface side with a porous layer of large holes in this way, gases and liquids can flow more easily inside the titanium porous body. The upper limit of the average value of the area of the holes opening to the other surface is not particularly limited on the premise of having the required strength that can be used when incorporated into, for example, a PEM type water electrolysis device, but may be 10 times or less, 7 times or less, or 5 times or less the average value of the area of the holes on one surface.

[0069] The average value, standard deviation value, and number within a predetermined rectangular region of the area of the holes opening to the surface described above are measured with a scanning electron microscope (Keyence Corporation's ultra-depth multi-angle lens VHX-D510). More specifically, for both the one surface and the other surface, for a rectangular region on the surface with an area of 22000 μm 2 and an aspect ratio of 4:3, an SEM image is acquired at a magnification of 2000 times. Then, the SEM image is analyzed using a scanning electron microscope, and a value half of the maximum detected value of the luminance of the SEM image is used as the threshold value, and a closed region within the range of luminance from 0 to the threshold value is regarded as one hole. At this time, if necessary, the SEM image may be subjected to binarization processing. After the binarization processing, a small particle removal process (processing to black pixels after binarization) is performed on closed regions of 50 pixels or less, and then a hole filling process (processing to white pixels after binarization) is performed on closed regions of 50 pixels or less. Using this, the number and area of each hole are calculated, and the standard deviation value as the square root of the variance is obtained. Such analysis of the SEM image is performed for 5 rectangular regions where at least a part of the surface is shifted from each other, and the average value of the area of the holes and the average value of the number in those rectangular regions are respectively taken as the average value of the area of the holes, the standard deviation value, and the number within the rectangular region on the surface. In the case of a surface that is a square or rectangle in plan view, the above 5 rectangular regions are the 5 rectangular regions at the center and the four corners.

[0070] The thickness of the sheet-like titanium porous body (total thickness including all porous layers) may be 200 μm or more and 3000 μm or less. For example, a titanium porous body of such a certain thickness may be required for the porous transport layer of a PEM type water electrolysis device. On the other hand, if the thickness is too thick, there is a risk of increasing the size of the PEM type water electrolysis device. The thickness of the titanium porous body may be, for example, 200 μm or more, 1000 μm or less, and further 500 μm or less.

[0071] The thickness of the titanium porous body is measured for a total of five points, namely four points on the periphery and one point at the center of the titanium porous body, using a digital thickness gauge such as a Mitutoyo Corporation digital thickness gauge (model number 547-321) with a measuring head of Φ10 mm and a measuring accuracy of 0.01 mm, and the average value of these measured values is taken. When the sheet-like titanium porous body is rectangular in plan view, the four peripheral points mentioned above are the four corner points.

[0072] The thickness of one porous layer may be 20 μm or more and 120 μm or less, or 35 μm or more and 100 μm or less. Also, the thickness of one porous layer may be 30% or less, 20% or less, or further 15% or less of the above total thickness. Since one porous layer is composed of a porous layer with small pores, if its thickness is too thick, the air permeability or liquid permeability of the entire titanium porous body will decrease. On the other hand, by making the thickness of one porous layer somewhat thick, the required strength can be ensured after sintering during the production of the corresponding porous material, and the porous layer is less likely to crack when pressed against the electrolyte membrane together with other porous layers. It is preferable that one porous layer has the thinnest thickness among the plurality of porous layers. By making the thickness of one porous layer, which has small pores and through which gas or liquid hardly permeates, the thinnest, the air permeability or liquid permeability of the titanium porous body can be greatly increased.

[0073] The thickness of the porous layer on the other side is preferably 100 μm to 2900 μm, also preferably 100 to 1000 μm, and also preferably 200 μm to 600 μm. By making the thickness of the porous layer on the other side somewhat thicker, the air permeability or liquid permeability can be further enhanced. Also, by not making it too thick, miniaturization of the water electrolysis device becomes possible, and the electrolysis efficiency per unit area can be improved.

[0074] The thickness of each porous layer is measured by observing with SEM the thicknesses at five points in the thickness direction of the cross-section of the titanium porous body filled with resin and polished, and adopting the average value thereof. Since the functions required for each porous layer are different in the sheet-like titanium porous body in this embodiment, a portion where a difference in the size of the skeleton formed by bonding titanium powder in the stacking direction can be seen is specified, and the thickness of each porous layer is determined by SEM observation of the said portion.

[0075] The surface area of the sheet-like titanium porous body in plan view is not particularly limited since it can be appropriately determined according to various conditions. For example, it can be 70 mm 2 or more and 600000 mm 2 or less, or also 10000 mm 2 or more and 600000 mm 2 or less. The above-mentioned "sheet-like" means a plate-like or foil-like shape with a small thickness relative to the dimensions in plan view, and the shape in plan view is not particularly limited.

[0076] Incidentally, the titanium porous body can be composed of two porous layers in which the porous layer on one side and the porous layer on the other side are directly bonded at their titanium bonding surfaces. However, it is also possible to provide one or more porous layers as an intermediate layer between the porous layer on one side and the porous layer on the other side. In this case, the pore portions in the titanium porous body can be gradually enlarged to control the flow of gas or liquid to some extent.

[0077] The titanium porous body includes a plurality of porous layers, and the overall porosity is 40% or more and 60% or less, preferably 45% or more and 55% or less. If the porosity is within this range, it has the required air permeability or liquid permeability according to the application, and can be preferably used as a porous transport layer of a solid polymer type water electrolysis device or the like. If the porosity is too high, there is a concern that the mechanical strength of the titanium porous body is insufficient and unintentional compression deformation is likely to occur.

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

[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 also 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, 99% by mass or less. This titanium content means the purity of titanium considering not only metal components but also impurities such as gas components. Therefore, the titanium content is obtained by subtracting the total content of the metal component and the impurity component including the gas component from 100% by mass.

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

Examples

[0081] Next, the manufacturing method of the titanium molded body and the manufacturing method of the titanium porous body of this invention were experimentally carried out, and a titanium porous body was prototyped. Therefore, it will be described below. However, the description here is for the purpose of mere exemplification and is not intended to be limited thereto.

[0082] (Example 1) As shown in Table 1, titanium powder (hydrogenated dehydrogenated titanium powder) with an average particle size of 14 μm and titanium powder with an average particle size of 21 μm were each used and mixed with an organic solvent (isopropyl alcohol) and an organic binder (polyvinyl butyral) to prepare a paste containing these. Note that the paste does not contain water and a foaming agent. Each paste was applied in a sheet form onto a resin substrate made of PET and heated and dried at a temperature of 150°C for 90 minutes to obtain each sheet-like dried body. Note that the resin substrate made of PET had a silicone coating as a release layer.

[0083] Next, as shown in FIG. 2, the sheet-like dried body for the porous layer on the other side was turned over together with the resin substrate and placed on another resin substrate laid on a molding die. Then, the resin substrate on the upper side was peeled off and removed, and on it, the sheet-like dried body for the porous layer on one side was turned over together with the resin substrate and placed. Further, a molding die was placed thereon, and in this state, heating and pressurization were performed at the temperature, pressure, and time shown in Table 1. Note that the pressure was applied to the sheet-like dried body by placing a weight on the upper molding die. Thereby, the sheet-like dried bodies were joined to obtain a titanium molded body.

[0084] Subsequently, the above titanium molded body was heated at a temperature of 380°C in an air atmosphere for the time shown in Table 1 to separate the organic binder and perform debinding. Thereafter, the titanium molded body that had undergone debinding was heated at the temperature shown in Table 1 for 1 hour under vacuum conditions. As a result, the titanium powder in the titanium molded body was sintered to obtain a titanium porous body.

[0085] (Example 2) As shown in Table 2, a titanium porous body was produced in the same manner as in Example 1, except that the bonding conditions of the sheet-like dried body were changed.

[0086] (Example 3) As shown in Table 3, a titanium porous body was produced in the same manner as in Example 1, except that three sheet-like dried bodies with a predetermined surface roughness Ra were used and titanium powder with an average particle size of 21 μm was used for the production of 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 for the production of the sheet-like dried body for the porous layer on the other side, and as a result, the sheet-like dried body had a predetermined surface roughness Ra, and the heating time and sintering temperature of the debinder were changed.

[0088] (Comparative Example 1) When attempting to produce a titanium porous body in the same manner as in Example 1, except that the pressure was set to zero (unpressurized) when bonding the sheet-like dried bodies, each porous layer of the titanium porous body was easily peeled off by hand, so the titanium porous body could not be produced.

[0089] (Comparative Example 2) When attempting to produce a titanium porous body in the same manner as in Example 1, except that the sheet-like dried bodies were pressurized but not heated and kept at room temperature, the sheet-like dried bodies did not bond, and the subsequent steps could not be carried out.

[0090] (Evaluation) For each of the titanium porous bodies of Examples 1 to 4, in accordance with the method described above, the total thickness, the thickness of each porous layer (each layer thickness), the average value of the area of the pores opening on each of the one and the other surfaces (average pore area of the surface), the standard deviation of the area of the pores (standard deviation of the pore area of the surface), the number of the pores existing in a rectangular region with an aspect ratio of 4:3 and an area of 22000 μm 2 (pore number on the surface), and the overall porosity were measured respectively. The results are shown in Tables 1 to 4.

[0091] In addition, for each of one surface and the other surface of each titanium porous body, the conductivity (conductivity of the laminate) was measured. The conductivity was measured by the four-probe method using a low resistivity meter Loresta GP MCP-T610 manufactured by Mitsubishi Analytical Technology, with the surface to be measured among the above-mentioned surfaces positioned on the upper side. The probe checker used was MCP-T610 RMH112. The results are also shown in Table 1. If the titanium bonding surfaces of the titanium porous layers are sufficiently bonded, it is considered that the conductivity will be high. Also, when the conductivity is high, since each gas-liquid permeable layer is firmly bonded, it is presumed that the mechanical strength is also excellent. In Tables 1 to 4, the unit of conductivity is described as "E+3 S / cm", which means "10 3 × S / cm". For example, the value "4.1" in the "Conductivity of laminate" column in Table 1 means 4100 S / cm.

[0092] Also shown in Tables 1 to 4 are the thickness, conductivity of a single body, conductivity of the laminate, and porosity of titanium sintered bodies (titanium sintered bodies corresponding to each porous layer) obtained by performing debinding and sintering on each of the sheet-like green bodies used for manufacturing each titanium porous body without bonding them. The conductivity of a single body is the value obtained by measuring the conductivity separately without overlapping two or three titanium sintered bodies, and the conductivity of the laminate is the value obtained by measuring the conductivity in a state where two or three titanium sintered bodies are overlapped. Since the conductivity of the laminate is measured in a state where two or three titanium sintered bodies are simply overlapped, the value tends to be smaller than the conductivity of a single body due to the large electrical resistance between them. Also, since the sheet-like green bodies were laminated without bonding, the laminate thickness tends not to match the sum of the thicknesses of each titanium sintered body.

[0093]

Table 1

[0094]

Table 2

[0095]

Table 3

[0096]

Table 4

[0097] In Examples 1 to 4, as shown in Tables 1 to 4, titanium porous bodies could be produced by heating a sheet-like dried body at a predetermined temperature while applying a predetermined pressure. Since these titanium porous bodies have a conductivity as high as that of each titanium sintered body (conductivity alone), it is considered that the porous layers are sufficiently joined at the titanium bonding surfaces.

[0098] In addition, the above titanium porous bodies were each composed of a plurality of porous layers having pores, with the titanium bonding surfaces adjacent to each other in the thickness direction being bonded to each other and laminated. For any of the titanium porous bodies, the value of conductivity lamination for at least one of the surfaces on one side and the other side is about 1.5 times or more higher than the value of conductivity lamination for the same surface of the simply laminated titanium sintered body, indicating that the porous layers are sufficiently joined. Also, for any of the titanium porous bodies, the average value of the area of the pores, the standard deviation of the area of the pores, the number of the pores, and the porosity on one surface (the surface of the porous layer on one side) each became a respective predetermined desirable value.

Explanation of Reference Numerals

[0099] 1, 11 Molds 2, 12, 32 Resin Substrates 3, 13 Sheet-like Dried Bodies 31 Titanium Molded Bodies Sa1, Sb1 Surfaces on the Resin Substrate Side Sa2, Sb2 Back Surfaces Ta, Tb Thickness

Claims

1. A method for manufacturing a sheet-shaped titanium compact, comprising: A plurality of sheet-like dried bodies respectively obtained by drying a paste containing titanium powder, an organic binder, and an organic solvent are laminated, and while applying a pressure of 0.1 N / cm or more in the thickness direction, 2 A method for manufacturing a titanium molded body, including a joining step of heating to a temperature of 70°C or higher and 200°C or lower while applying pressure.

2. The method for manufacturing a titanium compact according to claim 1, further comprising a drying step of drying the paste before the bonding step to obtain a sheet-shaped dried body.

3. The method for manufacturing a titanium compact according to claim 2, wherein in the drying step, the paste is heated to a temperature of 90°C or higher and 165°C or lower.

4. The method for manufacturing a titanium compact according to claim 2, wherein the drying of the paste in the drying step is performed on a resin substrate.

5. The method for manufacturing a titanium compact according to claim 1, wherein in the bonding step, the plurality of laminated sheet-shaped dried bodies are sandwiched between a pair of mold halves in the thickness direction, and pressure and heat are applied.

6. The method for manufacturing a titanium compact according to claim 5, wherein in the bonding step, pressure and heat are applied with a resin substrate interposed between the sheet-shaped dried body and the mold halves.

7. A method for manufacturing a sheet-shaped titanium porous body, comprising: a debinding step of heating a titanium compact manufactured by the method for manufacturing a titanium compact according to any one of claims 1 to 6 to volatilize an organic binder in the titanium compact; and a sintering step of heating the titanium compact after the debinding step to sinter titanium powder in the titanium compact. The method for manufacturing a titanium porous body as described above.

8. A sheet-shaped titanium porous body, comprising: a plurality of porous layers made of titanium, each having pores and being capable of allowing gas and / or liquid to permeate, and being bonded and laminated to each other between adjacent titanium bonding surfaces in the thickness direction; and Among the plurality of porous layers, the average value of the areas of the holes opening in the surface of the porous layer forming one surface is 5 μm 2 or more and 15 μm 2 or less, and the standard deviation value of the areas of the holes is 35 μm 2 or less, and the number of the holes existing in a rectangular region having an area of 22000 μm 2 and an aspect ratio of 4:3 is 256 or more a titanium porous body having a total porosity of 40% or more and 60% or less including the plurality of porous layers.

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