Porous ceramic multilayer body and separation membrane

Abstract

The purpose of the present invention is to provide a porous ceramic multilayer body in which two or more kinds of layers are stacked and separation at a stacking interface is suppressed. The present invention provides a porous ceramic multilayer body in which, on a first porous ceramic layer that is composed of a ceramic bone trabecula and pores, one or more other porous ceramic layers are superposed, wherein the number of branch points of the pores is 1.0 × 106 or more per 1 μm3 of the total volume of the ceramic bone trabecula and the pores. It is preferable that the volume of projected valley parts in the surface of the first porous ceramic layer as determined in accordance with ISO 25178 is more than 0.56 ml / m2.

Description

Porous ceramic laminate and separation membrane

[0001] The present invention relates to a porous ceramic laminate and a separation membrane.

[0002] Porous ceramic bodies are used in various fields as membranes that have functions such as separating, concentrating, or filtering gaseous or liquid fluids, such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, ion exchange membranes, and gas separation membranes.

[0003] It is important that porous ceramic bodies suitable for use in the fields described above be able to fully perform functions such as separation while allowing fluids to flow easily through the porous ceramic body. Therefore, they are usually composed of a laminate of two or more layers, including a functional layer with a small pore diameter and a support layer with a large pore diameter that supports the functional layer.

[0004] Patent Document 1 discloses a ceramic filter comprising at least one layer of porous ceramic membrane laminated on the surface of an alumina porous body as a substrate, the porous body having an average pore diameter smaller than that of the alumina porous body. Patent Document 1 describes that the corrosion resistance to alkaline and acidic solutions can be improved by adjusting the porosity and average pore diameter of the alumina porous body as a substrate and by including a predetermined amount of at least one metal oxide selected from the group consisting of titanium, manganese, and copper relative to the alumina.

[0005] Similarly to Patent Document 1, Patent Document 2 discloses a ceramic filter formed by laminating one or more layers of porous ceramic membranes having an average pore diameter smaller than that of an alumina porous body on the surface of an alumina porous body serving as a substrate. Patent Document 2 describes that by adjusting the porosity and average pore diameter of the alumina porous body serving as a substrate and containing predetermined amounts of titanium oxide and at least one element selected from the group consisting of copper, manganese, calcium, and strontium, the filter can have high initial strength and have improved corrosion resistance to alkaline and acidic solutions.

[0006] JP 2010-228946 A JP 2010-228948 A

[0007] In a laminate in which two or more types of layers are laminated, if the bonding at the lamination interface is not strong when a load is applied to the laminate, peeling will occur at the lamination interface.

[0008] Although Patent Documents 1 and 2 also disclose a laminate as a separation membrane structure, they do not consider peeling at the lamination interface. Therefore, an object of the present invention is to provide a porous ceramic laminate in which two or more types of layers are laminated, in which peeling at the lamination interface is suppressed.

[0009] The present invention, which has achieved the above object, is as follows: [1] A porous ceramic laminate in which one or more other porous ceramic layers are laminated on a first porous ceramic layer composed of ceramic trabeculae and pores, wherein the number of branch points of the pores is within 1 μm of the total volume of the ceramic trabeculae and pores. ３ 1.0 x 10 per ６ [2] A porous ceramic laminate having a protruding valley volume of 0.56 ml / m or more on the surface of the first porous ceramic layer, as determined in accordance with ISO 25178. ２ [3] The porous ceramics laminate according to [1], wherein the other porous ceramics layer is composed of two or more layers. [4] The porous ceramics laminate according to any one of [1] to [3], wherein the other porous ceramics layer is a layer containing small particles having a circle-equivalent particle diameter of less than 1 μm in a cross section parallel to the lamination direction of the laminate, and the small particles and large particles having a circle-equivalent particle diameter of 2 μm to 25 μm are present on the surface of the first porous ceramics layer facing the other porous ceramics layer. [5] The porous ceramics laminate according to [4], wherein the layer containing the small particles is composed of an outer layer containing the small particles but not the large particles, and an intermediate layer containing both the small particles and the large particles. [6] The porous ceramics laminate according to [4], wherein the average circle-equivalent particle diameter of the large particles present on the surface of the first porous ceramics layer is greater than the average pore diameter D of the first porous ceramics layer. ５０[7] The porous ceramic laminate according to any one of [4] to [6], wherein the large particles and the small particles are both inorganic oxides. [8] The porous ceramic laminate according to any one of [1] to [7], which is tubular or monolithic. [9] A separation membrane comprising the porous ceramic laminate according to any one of [1] to [8].

[0010] According to the present invention, it is possible to provide a porous ceramic laminate in which the peel strength between the first porous ceramic layer and another porous ceramic layer laminated thereon is improved.

[0011] Fig. 1 is a schematic diagram showing the pores of a first porous ceramic layer. Fig. 2 is a schematic diagram showing an example of an embodiment of the present invention. Fig. 3 is a schematic diagram showing another example of an embodiment of the present invention. Fig. 4 is a drawing-substitute photograph showing a cross-sectional SEM image of a porous ceramic laminate of the present invention.

[0012] The present invention provides a porous ceramic laminate in which one or more other porous ceramic layers are laminated on a first porous ceramic layer composed of ceramic trabeculae and pores, and the number of branch points of the pores is 1 μm of the total volume of the ceramic trabeculae and pores. ３ (i.e., per 1 μm of the first porous ceramic layer) ３ Per) 1.0 x 10 ６ There are more than one.

[0013] (1) First porous ceramic layer The first porous ceramic layer is composed of ceramic trabeculae and pores (voids). The pores usually extend three-dimensionally in the porous ceramic layer. The pores extending three-dimensionally can also be said to be irregular in shape or not linear. Figure 1 is a diagram showing a schematic representation of the pores in the first porous ceramic layer, and the locations indicated by 11 are branch points. The number of branch points determined by three-dimensional quantitative analysis of the pores in the first porous ceramic layer using the method described below is calculated as follows: ３ 1.0 x 10 per ６The number of branching points is more than 1 μm, and the unevenness of the surface of the first porous ceramic layer increases due to the large number of branching points, so that the bonding strength with other porous ceramic layers laminated on the first porous ceramic layer is strong. ３ 1.1 x 10 per ６ It is preferable that the number is 1.2 × 10 or more, and more preferably 1.2 × 10 ６ more preferably 1.5 × 10 ６ The upper limit is not particularly limited, but for example, 2.5 × 10 ６ That is, the branching points of the pores may be located within 1 μm of the first porous ceramic layer. ３ 1.0 x 10 per ６ ~2.5 x 10 ６ 1.1 × 10 ６ ~2.5 x 10 ６ 1.2 × 10 pieces is more preferable, ６ ~2.5 x 10 ６ 1.5×10 ６ ~2.5 x 10 ６ Individual is even more preferred.

[0014] The number of branch points in the first porous ceramic layer is determined by binarizing a three-dimensional image of the first porous ceramic layer, identifying the pore portions, and then performing a thinning process on the pore portions. A more detailed measurement procedure is as shown in the examples below. First, the first porous ceramic layer is three-dimensionally observed using X-ray CT (Computed Tomography) to obtain a 3D image. The 3D image is binarized using quantitative analysis software TRI / 3D-BON-FCS (manufactured by Ratoc Systems Engineering) to distinguish between the trabecular bone portion and the pores. Then, the structure of the 3D image is analyzed using 3D cancellous bone measurement with the bone measurement option. The number of pore branches and the total volume of the ceramic trabeculae and pores are calculated to determine the thickness of the first porous ceramic layer per 1 μm . ３ The number of branching points is preferably measured within a range of about 600 μm in the depth direction from the surface of the first porous ceramic layer on the side where another porous ceramic is laminated.

[0015] Furthermore, it is preferable that the volume of the protruding valleys on the surface of the first porous ceramic layer, as determined in accordance with ISO 25178, is large, since this increases the volume of the depressions on the surface. Specifically, it is preferable that the volume of the protruding valleys on the surface of the first porous ceramic layer is large. ２ It is preferable that the viscosity is greater than 0.60 ml / m ２ More preferably, it is 0.70 ml / m or more. ２ The upper limit is not particularly limited, but for example, 1.5 ml / m ２ may be.

[0016] It is also preferable that the surface of the first porous ceramic layer satisfies the requirement for the volume of the protruding valleys and further has a small volume of the protruding peaks as determined in accordance with ISO 25178, specifically 0.25 ml / m ２ It is preferably less than 0.22 ml / m ２ More preferably, it is 0.19 ml / m or less. ２ The lower limit is not particularly limited, but for example, 0.05 ml / m ２ That is, the volume of the protruding valley portion may be 0.05 ml / m ２ ~0.25 ml / m ２ Preferably less than 0.05 to 0.22 ml / m ２ More preferably, 0.05 to 0.19 ml / m ２ is more preferred.

[0017] Average pore diameter D of the first porous ceramic layer ５０ As described in the examples below, the average pore diameter D of the first porous ceramic layer is measured by a three-dimensional analysis method (similar to the measurement of the number of branch points described above, the average pore diameter D of the first porous ceramic layer is obtained by performing a structural analysis of a 3D image using the quantitative analysis software and calculating the average length between the connection points Nd of the voids and the average width of the voids). The average pore diameter D of the first porous ceramic layer is, for example, 6.0 μm or more, more preferably 10.0 μm or more, and even more preferably more than 13.0 μm. ５０ is preferably 6.0 to 20 μm, more preferably 10.0 to 18 μm, and even more preferably more than 13.0 μm to 18 μm.

[0018] The first porous ceramic layer preferably contains an inorganic oxide, for example, Li ２ O, BeO, B ２ O ３ , Na ２ O, MgO, Al ２ O ３ , SiO ２ , K. ２ O, CaO, ScO ２ , TiO ２ , V ２ O ５ , Cr ２ O ３ , ZnO, Ga ２ O ３ , GeO ２ , As ２ O ５ , Rb ２ O, SrO, Y ２ O ３ , ZrO ２ , Nb ２ O ５ , Ag ２ O, CdO, In ２ O ３ , SnO ２ , Sb ２ O ５ , TeO ２ , Cs ２ O, BaO, La ２ O ３ , Ta ２ O ５ , W.O. ３ , HgO, Tl ２ O, PbO, PbO ２ , and ThO ２ It is more preferable that the first porous layer contains at least one metal oxide selected from the group consisting of Al ２ O ３ And Al ２ O ３ It is more preferable that the first porous layer contains one or more metal oxides other than Al. ２ O ３ The one or more metal oxides other than the above can be arbitrarily selected from the metal oxides exemplified above, and the first porous layer is Al ２ O ３ and SiO２ It is particularly preferable that the glass contains the following: In this specification, the term "metal" is used to include semi-metals such as Si.

[0019] The shape of the first porous ceramic layer is not particularly limited, and examples thereof include a plate shape, a tube shape, and a monolith shape. A tube shape or a monolith shape is particularly preferred. In any of the above shapes, the corners may be rounded. The monolith shape refers to a columnar (cylindrical, rectangular, elliptical, etc.) shape having a plurality of axially penetrating holes (preferably cylindrical). When the first porous ceramic layer is tubular, the other porous ceramic layer is preferably formed only on the inner circumferential surface, only on the outer circumferential surface, or on both the inner and outer circumferential surfaces of the tube, more preferably only on the inner circumferential surface or only on the outer circumferential surface, and even more preferably only on the inner circumferential surface. When the first porous ceramic layer is monolithic, the other porous ceramic layer is preferably formed only on the inner surface of each through-hole of the monolithic shape.

[0020] The porous ceramic laminate of the present invention comprises a first porous ceramic layer on which one or more other porous ceramic layers are laminated, and has the same shape as the first porous ceramic layer.

[0021] The thickness (average value) of the first porous ceramic layer is preferably 400 μm to 8000 μm. When the first porous ceramic layer is monolithic, the thickness may be the average value of the closest distances between adjacent through holes in a plane perpendicular to the long axis. The longitudinal length of the first porous ceramic layer is, for example, 50 mm to 5000 mm, preferably 500 mm to 3000 mm. The longitudinal length refers to, for example, the length of the long side in the case of a plate-like structure, or the length in the long axis direction in the case of a tubular or monolithic structure. When the first porous ceramic layer is tubular, the outer diameter of the first porous ceramic layer is, for example, 5 mm to 20 mm, and the inner diameter of the tube is, for example, 1 mm to 15 mm. When the first porous ceramic layer is monolithic, i.e., when it has two or more tubes, the outer diameter of the first porous ceramic layer is, for example, 5 mm to 100 mm, and the inner diameter of each tube is, for example, 0.1 mm to 10 mm.

[0022] (2) Other porous ceramic layers The porous ceramic laminate of the present invention has one or more other porous ceramic layers laminated on the first porous ceramic layer described above, and may be a laminate consisting of a first porous ceramic layer 21 and one other porous ceramic layer 22 as shown in Fig. 2, or a laminate consisting of a first porous ceramic layer 31 and other porous ceramic layers 32, 33 (two layers) as shown in Fig. 3, or a laminate in which one or more further porous ceramic layers are laminated on the porous ceramic layer 33 in Fig. 3. It is preferable that the porous ceramic laminate of the present invention is composed of two or more other porous ceramic layers.

[0023] In the porous ceramic laminate of the present invention, it is preferable that the other porous ceramic layer is a layer containing small particles having a circle-equivalent particle diameter of less than 1 μm in a cross section parallel to the stacking direction of the laminate, and that the small particles and large particles having a circle-equivalent particle diameter of 2 μm to 25 μm are present on the surface of the first porous ceramic layer. A porous ceramic laminate of the present invention that satisfies these requirements will be referred to as laminate P below. The configuration of laminate P is advantageous for improving the peel strength between the first porous ceramic layer and the other porous ceramic layer stacked thereon. The lower limit of the circle-equivalent particle diameter of the small particles may be approximately 0.05 μm. The cross section parallel to the stacking direction of the laminate can be, for example, a cross section perpendicular to the longitudinal direction of the laminate (e.g., the axial direction when the outer shape of the laminate is a columnar shape such as a circular cylinder, a rectangular cylinder, or an elliptical cylinder).

[0024] In the laminate P, the layer containing small particles preferably comprises an outer layer containing the small particles but not the large particles, and an intermediate layer containing both the small particles and the large particles. The thickness of the intermediate layer can be, for example, 3 μm to 100 μm, and preferably 3 μm to 60 μm. The thickness of the outer layer is, for example, 5 μm to 100 μm, and more preferably 20 μm to 80 μm. When the layer containing small particles comprises an intermediate layer and an outer layer, one or more other layers may be laminated between the intermediate layer and the outer layer or on the outer layer.

[0025] For the intermediate layer, in a cross section parallel to the stacking direction of the laminate, straight lines are drawn from any five points on the surface of the first porous layer (the surface on the intermediate layer side) in the stacking direction (for example, the thickness direction if the laminate is in the form of a plate, or the radial direction of the through holes if the laminate is in the form of a tube or monolith with cylindrical through holes and the intermediate layer is formed on the inner peripheral surface of the through holes), the lengths of the line segments to the points where they intersect with the interface between the intermediate layer and the outer layer are measured, and the average of the five line segments can be used as the thickness of the intermediate layer. For the outer layer, straight lines are drawn from any five points on the interface between the intermediate layer and the outer layer in the stacking direction, the lengths of the line segments to the points where they intersect with the surface of the outer layer, and the average of the five line segments can be used as the thickness of the outer layer.

[0026] The surface of the porous ceramic laminate of the present invention opposite the first porous ceramic layer is measured by mercury intrusion porosimetry, and the cumulative 50% equivalent diameter calculated from a graph with the pore diameter on the horizontal axis and the cumulative log differential pore volume on the vertical axis is, for example, 0.01 μm to 0.5 μm.

[0027] The average circle-equivalent particle diameter of the large particles present on the surface of the first porous ceramic layer is equal to or smaller than the average pore diameter D of the first porous ceramic layer. ５０ The average value of the circle-equivalent particle diameter of the large particles is preferably 0.3 times or more, more preferably 0.7 times or more, and even more preferably 0.8 times or more of the average pore diameter D of the first porous ceramic layer. ５０ The average circle-equivalent particle diameter of the large particles present on the surface of the first porous ceramic layer can be determined by arbitrarily selecting 20 large particles in a section parallel to the stacking direction of the laminate between the following lines X1 and X0, and calculating the average circle-equivalent particle diameter of the large particles. Note that the large particles in the section between the following lines X1 and X0 mean that at least a portion of the particle is present in the section between the lines X1 and X0. If the target large particle has a portion that protrudes from the lines X1 and X0, the circle-equivalent particle diameter of the entire large particle, including the protruding portion, is measured. Line X1: A line that contacts the first porous ceramic layer at two or more points and does not cross the first porous ceramic layer. Line X0: A parallel line separated by 10 μm from the line X1 toward the interior of the first porous ceramic layer.

[0028] The other porous ceramic layer is preferably composed of an inorganic oxide, that is, in a preferred embodiment, both the large particles and the small particles are preferably inorganic oxides. Examples of inorganic oxides include the metal oxides listed as preferred embodiments of the first porous ceramic layer. In particular, both the large particles and the small particles are preferably Al. ２ O ３ It is preferable that Al ２ O３ As the α-alumina, commercially available α-alumina can be used without any particular limitation, but for large particles, AA-10, AA-5, etc. manufactured by Sumitomo Chemical Co., Ltd. can be used, and for small particles, AKP-3000, AKP-20, etc. manufactured by Sumitomo Chemical Co., Ltd. can be used.

[0029] (3) Manufacturing Method of Ceramic Laminate (3-1) Manufacturing Method of First Porous Ceramic Layer The first porous ceramic layer is made of a ceramic material having a thickness of 1 μm or less, and the number of branching points of the pores measured in the above manner is 1 μm or less. ３ 1.0 x 10 per ６ The first porous ceramic layer may be produced by molding and firing a raw material mixture containing an inorganic raw material powder, which is at least one of an aluminum source powder, a silicon source powder, and a magnesium source powder, a pore-forming agent, a binder, and the like.

[0030] As the aluminum source, alumina, kaolin (Al ２ Si ２ O ５ (OH) ４Examples of the aluminum source include aluminum hydroxide, aluminum salts, aluminum alkoxides, aluminum titanate, and metallic aluminum. Only one aluminum source may be used, or two or more may be used in combination. Examples of the crystalline form of alumina include γ-, δ-, θ-, and α-types, and may be amorphous. Mixtures of these may also be used. Among these, α-type alumina is preferably used. Examples of the crystalline form of aluminum hydroxide include gibbsite, bayerite, norosotranite, boehmite, and pseudoboehmite, and may be amorphous. Amorphous aluminum hydroxide also includes aluminum hydrolysates obtained by hydrolyzing aqueous solutions of water-soluble aluminum compounds such as aluminum salts and aluminum alkoxides. The aluminum salt may be an inorganic salt with an inorganic acid or an organic salt with an organic acid. Specific examples of inorganic aluminum salts include aluminum nitrates such as aluminum nitrate and ammonium aluminum nitrate, and aluminum carbonates such as ammonium aluminum carbonate. Examples of aluminum organic salts include aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate, and aluminum laurate.

[0031] Silicon sources include silicon oxide (quartz, amorphous silica), talc (Mg ３ Si ４ O １０ (OH) ２ ), kaolin (Al ２ Si ２ O ５ (OH) ４ Talc also functions as a magnesium source, and kaolin also functions as an aluminum source. Other silicon sources include silicic acid, silicon carbide, silicon nitride, silicon sulfide, silicon tetrachloride, silicon acetate, sodium silicate, sodium orthosilicate, and glass frit. Only one silicon source may be used, or two or more silicon sources may be used in combination.

[0032] The magnesium source may be magnesia spinel, magnesium oxide, talc (Mg ３ Si ４ O １０ (OH) ２ ), magnesium salts, magnesium alkoxides, magnesium hydroxide, magnesium nitride, metallic magnesium, etc. As the magnesium source, only one type may be used, or two or more types may be used in combination. Specific examples of the magnesium salt include magnesium chloride, magnesium perchlorate, magnesium phosphate, magnesium pyrophosphate, magnesium oxalate, magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium sulfate, magnesium citrate, magnesium lactate, magnesium stearate, magnesium salicylate, magnesium myristate, magnesium gluconate, magnesium dimethacrylate, magnesium benzoate, etc.

[0033] Examples of the pore-forming agent include carbon materials such as graphite; resins such as polyethylene, polypropylene, and polymethyl methacrylate; plant materials such as starch, nut shells, walnut shells, and corn; ice; and dry ice.

[0034] Examples of binders include celluloses such as methyl cellulose, carboxymethyl cellulose, hydroxyalkyl methyl cellulose, and sodium carboxymethyl cellulose; alcohols such as polyvinyl alcohol; salts such as lignin sulfonate; and waxes such as paraffin wax and microcrystalline wax.

[0035] In the molding step, molding into a desired shape may be performed using a molding device such as a commonly used uniaxial press or extruder. To reduce the number of branch points, the constituent particles (aluminum source powder, silicon source powder, or magnesium source powder) may be made larger and / or a pore-forming agent that forms relatively large pores may be used. On the other hand, to increase the number of branch points, the constituent particles may be made smaller and / or a pore-forming agent that forms relatively small pores may be used and mixed uniformly.

[0036] In the firing step, prior to firing the compact, calcination (degreasing) may be performed to remove binders and other substances contained in the compact (raw materials). In firing the compact, the firing temperature is typically 1300°C or higher, preferably 1400°C or higher. The firing temperature is typically 1550°C or lower, preferably 1500°C or lower. The heating rate is not particularly limited, but is typically 1°C / hour to 500°C / hour. When the pore-forming agent is an organic powder or a carbon powder, firing is preferably performed in an oxygen-containing atmosphere. Firing is typically performed using a conventional firing furnace, such as a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a microwave heating furnace, a rotary furnace, a roller hearth furnace, or a gas firing furnace. The firing time may be sufficient to transform the inorganic raw material powder into cordierite-based crystals. While this time varies depending on the amount of raw materials, the type of firing furnace, the firing temperature, the firing atmosphere, and the like, it is typically 5 hours to 24 hours.

[0037] (3-2) Manufacturing Method of Porous Ceramic Laminate The porous ceramic laminate of the present invention can be manufactured by preparing a slurry containing an inorganic oxide, applying the slurry to the lower layer serving as the substrate, heat treating it, and repeating the slurry application and heat treatment as necessary. The composition of the inorganic oxide can be seen in the explanation of the large particles and small particles above. ２ O ３ When it contains Al ２ O ３ Commercially available α-alumina can be used as the inorganic oxide, such as AKP-3000, AKP-20, AA-10, and AA-5 manufactured by Sumitomo Chemical Co., Ltd. The volume-based cumulative 50% equivalent diameter of the inorganic oxide is, for example, about 0.05 μm to 20 μm, and preferably 0.1 μm to 15 μm. The concentration of the inorganic oxide in the slurry is, for example, 5% by mass to 15% by mass.

[0038] The slurry containing an inorganic oxide preferably contains a dispersant, a thickener and a solvent in addition to the inorganic oxide.

[0039] The dispersant can suppress aggregation of inorganic oxide particles in the slurry. The dispersant may be any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. Among these, anionic surfactants such as ammonium polycarboxylates and amine polycarboxylates are preferred, and examples thereof include SN Dispersant 5020, SN Dispersant 5023, SN Dispersant 5027, SN Dispersant 5468, Noparfa D-6010, Nopcol 5200, Nopcosant RFA, Nopcosperse 6100, and Nopcosperse 6150 manufactured by San Nopco. The concentration of the dispersant in the slurry (in terms of active ingredient) is, for example, 0.1% by mass or more and 3% by mass or less, and preferably 0.3% by mass or more and 2% by mass or less. The concentration of the dispersant in the slurry (in terms of active ingredient) is preferably, for example, 0.01% by mass or more and 10% by mass or less with respect to 100% by mass of the inorganic particles in the slurry.

[0040] Examples of thickeners include methyl cellulose, hydroxyethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, polyalkylene oxide, polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, polyacrylamide, polydimethylaminoethyl methacrylate, etc., with hydroxypropyl methyl cellulose being particularly preferred. The amount of thickener added can be adjusted appropriately depending on the target slurry viscosity.

[0041] The solvent may be water or an organic solvent.

[0042] Methods for applying the slurry to the substrate include dip coating, spray coating, roll coating, bar coating, spin coating, slit coating, ball injection, brush coating, etc. After the slurry is applied, a heat treatment (firing) is performed. The heat treatment temperature is, for example, 1000°C or higher and 1500°C or lower, and the heat treatment time is, for example, 1 hour or higher and 8 hours or lower.

[0043] The porous ceramic laminate of the present invention may be produced by applying a slurry containing particles X1 having a volume-based cumulative 50% equivalent diameter of 1 μm to 20 μm and particles X2 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more to less than 1 μm by dipping, spray coating, spin coating, bar coating, or the like onto the first porous ceramic layer and drying it, or after the drying, a slurry containing particles Y1 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more to less than 1 μm (preferably 0.1 μm or more to less than 1 μm) but not containing particles having a volume-based cumulative 50% equivalent diameter of 1 μm to 20 μm (preferably 1 μm to 15 μm) may be applied, dried, and further heat-treated as necessary to produce the porous ceramic laminate of the present invention.

[0044] In particular, when the first porous ceramic layer is tubular or monolithic and the laminate of the present invention is the laminate P described above, the laminate of the present invention may be manufactured by a method of forming the layer on the inner surface of the tube or monolith using a jig (hereinafter referred to as the ball injection method). This will be explained in more detail below.

[0045] The ball injection method is a method for producing a ceramic porous laminate by forming a ceramic porous layer on the inner surface of a tubular or monolithic first porous ceramic layer, i.e., a first porous ceramic layer having one or more tubes (hereinafter sometimes referred to as a substrate), and is a production method comprising a slurry liquid supply step (1) for supplying a slurry liquid containing particles to the inside of the tube, and a coating layer formation step (2) for passing a jig through the tube while supplying the slurry liquid or after supplying the slurry liquid to form a coating layer of the slurry liquid on the inner surface of the tube.

[0046] The particle-containing slurry liquid is a raw material for a ceramic porous layer formed on a substrate. In a preferred embodiment of the ball injection method, a substrate having one or more tubes is provided with a slurry liquid X containing particles X1 having a cumulative 50% equivalent diameter on a volume basis of 1 μm to 20 μm (preferably 1 μm to 15 μm) on the inner surface of the tube through a slurry liquid X supplying step (1X), a coating layer forming step (2X) using the slurry liquid X, and a drying step (3X) to form a coating layer containing particles X1 on the inner surface of the tube, and then a slurry liquid Y supplying step (1Y) using the slurry liquid Y containing particles Y1 having a cumulative 50% equivalent diameter on a volume basis of 0.05 μm or more to less than 1 μm (preferably 0.1 μm or more to less than 1 μm), a coating layer forming step (2Y) using the slurry liquid Y, and a drying step (3Y) to form a coating layer containing particles Y1 on the inner surface of the tube on which the coating layer containing particles X1 has been formed. A heat treatment step (4X) may be further carried out after the drying step (3X), or a heat treatment step (4Y) may be further carried out after the drying step (3Y). Furthermore, it is also preferable that the slurry liquid X contains, in addition to the particles X1, particles X2 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more and less than 1 μm (preferably 0.1 μm or more and less than 1 μm). Particles X1 having a volume-based cumulative 50% equivalent diameter of 1 μm to 20 μm (preferably 1 μm to 15 μm) correspond to the large particles described above, and particles X2 and Y1 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more and less than 1 μm (preferably 0.1 μm or more and less than 1 μm) correspond to the small particles described above.

[0047] In the ball injection method, the slurry preferably contains the above-mentioned dispersant, thickener and solvent in addition to the particles, and all of the above, including the preferred ranges of the types, concentrations and the like, can be referenced.

[0048] When supplying the slurry liquid to the substrate and when passing the jig through the pipe, it is preferable to arrange the substrate so that the axial direction thereof is vertical.

[0049] In the slurry liquid supply step (1), the slurry liquid may be supplied from either end of the substrate, but when the substrate is arranged so that its axial direction is vertical, it is preferable to supply the slurry liquid from the lower end of the substrate. The supply of the slurry liquid may be carried out by injecting the slurry liquid from the end of the substrate, or by masking the end face of the substrate other than the hole of the pipe and the side face of the substrate and immersing it in the slurry liquid, but it is preferable to supply the slurry liquid by injection from the end of the substrate (particularly one end).

[0050] In the coating layer forming step (2) of the slurry liquid, by using a jig, the excess slurry liquid supplied to the inner surface of the tube of the substrate can be discharged, and the slurry liquid can be uniformly applied to the inner surface of the tube of the substrate. The jig may be passed through the tube after the slurry liquid has been supplied, or may be passed through the tube while the slurry liquid is being supplied. It is preferable to supply the slurry liquid to the inside of the tube and then pass the jig after the supply of the slurry liquid, and it is more preferable to supply the slurry liquid to the inside of the tube by injection and then pass the jig after the injection of the slurry liquid.

[0051] The direction of supply of the slurry liquid and the direction of passing the jig may be the same or different. When the substrate is arranged so that its axial direction is vertical, it is preferable to pass the jig from the upper end after the slurry liquid has been supplied from the end of the substrate to the inner surface of the tube of the substrate.

[0052] Methods for passing the jig through the tube of the substrate include (i) flowing a fluid other than the slurry liquid from behind the jig in the direction of jig movement, (ii) sucking the slurry liquid from the direction of travel of the jig, or (iii) performing both of these. Furthermore, when the axial direction of the substrate is vertical, (iv) the jig may be passed through by dropping it from the upper end of the substrate under its own weight. Examples of the fluid include gases such as air. The methods of moving the jig are particularly preferred (i) to (iii), with (i) being more preferred. In the embodiment (i), when a fluid other than the slurry liquid is passed through, the pressure of the fluid may be, for example, 0.01 MPa to 0.5 MPa.

[0053] After the jig is passed through the tube of the substrate, a fluid such as air may be passed through the tube and the tube may be held in a pressurized state for a certain period of time, thereby allowing the solvent, thickener, etc. in the slurry to be discharged to the outside of the tube through the pores of the substrate. The pressurizing pressure is, for example, 0.01 MPa to 0.5 MPa, and the holding time is, for example, 1 minute to 30 minutes.

[0054] The material of the jig is not particularly limited, and jigs made of resin, metal, or ceramic can be used. The shape of the jig, when projected in the direction of jig movement inside the pipe, preferably has at least a portion of the outer periphery of the projection curved. Specific examples include coil, cylindrical, elliptical cylindrical, conical, spherical, and combinations thereof. Shapes obtained by cutting shapes other than the coil shape along one or more planes parallel to the direction of jig movement, removing a portion of the outer periphery while leaving a portion, are also preferred. The jig may be moved inside the pipe while rotating. The shape of the jig is preferably such that the inner periphery of the cross section perpendicular to the axial direction of the pipe is circular. Specifically, it is a cylinder or a sphere, with a sphere being more preferred. The size of the jig may be adjusted appropriately depending on the thickness of the ceramic porous layer to be formed, as long as it can be inserted inside the pipe.

[0055] After forming a coating layer of the slurry liquid on the inner surface of the pipe using the jig, a drying step (3) is usually carried out to dry the coating. Drying is preferably carried out by air-drying the coating layer, and the temperature of the air blown onto the coating may be room temperature or may be hot air in the range of 100°C or less. The speed of the air blown onto the coating surface is, for example, 0.05 m / sec to 1 m / sec.

[0056] After the drying step (3), a heat treatment step (4) is preferably carried out. The heat treatment promotes sintering of particles (preferably inorganic oxides) contained in the slurry liquid, and can improve the strength of the layer formed from the slurry liquid and appropriately adjust the porosity. The heat treatment is preferably carried out at, for example, 300°C to 1500°C. The heat treatment time is, for example, 30 minutes to 10 hours.

[0057] The thickness of the ceramic porous layer formed on the inner surface of the substrate tube may be adjusted by adjusting the viscosity of the slurry liquid; performing a series of steps including the slurry liquid supply step (1) and the slurry liquid coating layer formation step (2) (and, if necessary, the drying step (3) and the heat treatment step (4)) two or more times; adjusting the particle concentration in the slurry; or adjusting the size of the jig.

[0058] (4) Separation Membrane The porous ceramic laminate of the present invention can be used as a microfiltration membrane, an ultrafiltration membrane, or a nanofiltration membrane, and can be further laminated with a functional layer as needed to be used as a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, an ion exchange membrane, a separation membrane for gases, etc. In the separation membrane, it is preferable that a functional layer is provided on the outermost surface of the porous ceramic laminate of the present invention opposite to the first porous ceramic layer.

[0059] Examples of the functional layer include zeolite, MOFs (Metal Organic Frameworks), porous silica membranes, and porous alumina membranes. A separation membrane equipped with a functional layer can be produced by applying a liquid containing inorganic particles or MOFs that constitute the functional layer and allowing it to react. The synthesis conditions can be appropriately selected depending on the functional layer to be laminated, but for example, a temperature of 80°C to 800°C for 1 hour to 72 hours may be sufficient.

[0060] This application claims the benefit of priority based on Japanese Patent Application No. 2023-127032, filed on August 3, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-127032, filed on August 3, 2023, are incorporated herein by reference.

[0061] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and can of course be practiced with appropriate modifications within the scope of the above and below-described aims, all of which are included in the technical scope of the present invention.

[0062] [Method for measuring the number of branch points] Three-dimensional observation was performed using an X-CT (Nano-CT manufactured by Rigaku Corporation) so that the inner periphery of the first porous ceramic layer, the substrates A to D, could be observed from the surface to about 600 μm inside. The observation conditions were: Mo target, tube voltage = 50 kV, tube current = 24 mA, camera length XD = 3 mm, exposure time = 30 s, FOV = 0.65 mm x 0.65 mm, resolution = 0.32 μm / voxel, number of images = 1200, rotation range = 0 ° to 180 °, StepScan mode. Using the captured images, noise removal and ring removal operations were performed using reconstruction software (nano3DX Reconstruction manufactured by Rigaku Corporation) to obtain a 3D model of the porous substrate layer. The image resolution was X, Y, Z = 0.32 μm / pix. The obtained 3D model is trimmed to a size of 350 μm x 350 μm x 350 μm, and a 3D quantitative analysis of the voids in the base material layer is performed. For the 3D quantitative analysis, quantitative analysis software TRI / 3D-BON-FCS (manufactured by Ratoc Systems Engineering) is used. Specifically, the software is opened, and the image is bi-toned using Auto-LW, to distinguish between the trabecular bone and pores (voids) that make up the porous layer. If the bi-tonalization is insufficient or excessive, an image calculation function is used to appropriately extract the data. The voids identified by these processes were subjected to 3D cancellous bone measurement using the software's bone measurement option, with the analysis direction set to the direction in which the outer peripheral surface of the substrate is observed parallel, the MIL effective length = 0.5 × Thickness, the NdNd effective length = 1.5 × Thickness, and the NdTm effective length = 2.0 × Thickness. The number of connection points (bonding points) Nd in the voids of the porous layer, that is, the number of branching points N.Nd, indicates how many voids are branched. The number of branching points N.Nd indicates the total volume of the trabecular bone and voids (i.e., the volume of the entire analysis area), and the total volume of the trabecular bone and voids (i.e., the volume of the entire analysis area) TV (μm ３ ) and calculate the number of branches per unit volume N. Nd / TV. The number of branch points indicates how many branches the voids have, so a large value indicates a large number of paths.

[0063] [Measurement of Pore Diameter] Average pore diameter D of the first porous ceramic layer ５０was calculated from the average value of the length between the connection points (bonding points) Nd of the voids in the porous layer obtained by the three-dimensional analysis using the software and the width of the voids.

[0064] [Measurement of particle size of metal oxide] The particle size distribution of the alumina used in the examples and comparative examples was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3300EX II, manufactured by Microtrac Co., Ltd., 0.2 mass % aqueous solution of sodium hexametaphosphate), and the volume-based cumulative 50% equivalent diameter was measured.

[0065] [Cross-sectional observation of laminate] The cylindrical porous ceramic laminate obtained in the examples was cut at a cross section perpendicular to the axial direction, embedded in resin so that the cut surface could be observed, and mechanically polished. Platinum was vapor-deposited on the polished surface, and the cross section was observed and photographed at 1000x magnification using an FE-SEM (JSM-7500FA (manufactured by JEOL)). The perimeter of the particles observed in the obtained SEM image was determined, and the particle was considered to be a circle with that perimeter. The diameter of the particle was calculated and used as the equivalent circle particle diameter of the particle. The presence of large and small particles was confirmed from the obtained equivalent circle particle diameter. The equivalent circle particle diameter of the small particles was measured at a magnification large enough to confirm the equivalent circle particle diameter (for example, 20,000x).

[0066] [Average value of circle-equivalent particle diameter of large particles present on the surface of the first porous ceramic layer] In the SEM image of the cross section of the laminate, 20 large particles were arbitrarily selected from the portion sandwiched between the following lines X1 and X0, and the average value of the circle-equivalent particle diameter of the large particles was determined. Line X1: A line that contacts the first porous ceramic layer at two or more points and does not cross the first porous ceramic layer. Line X0: A parallel line separated by 10 μm from the line X1 toward the inside of the first porous ceramic layer.

[0067] [Method for measuring the volume of protruding valleys and protruding peaks] Three-dimensional observation was performed using a laser microscope (Keyence Corporation: VK-X3000) to observe the surfaces corresponding to the inner circumference of the first porous ceramic layer, i.e., the substrates A to D. The observation was performed using software for the laser microscope (Keyence Corporation: VK-X3000 Observation Application Ver. 2.3.0.151). The observation conditions were as follows: measurement mode = surface profile, scan mode = laser confocal, measurement size = standard, pitch = 2.00 μm, RPD = ON, average number = 1, optical zoom = 1.0x, Z-axis mode = recommended setting. The head settings were: head = V, objective lens name = Plan, objective lens magnification = 10X, NA = 0.3, field curvature correction = ON, and light intensity eccentricity correction = ON. The laser settings were: received light intensity correction mode = γ correction, γ coefficient = 0.45, offset = 0%. Using the captured image data, correction was performed using analysis software (Keyence Corporation: VK-X3000 Multi-File Analysis Application Ver. 3.3.185) to calculate the volume of the protruding valleys and peaks. The corrections were: height cut level = medium, surface shape correction = cylindrical correction, and surface shape correction = waviness removal (strength: 5). The settings for calculation were: filter type = Gaussian, S-filter (low-pass filter) = none, F-operation (shape correction) = none, L-filter (high-pass filter) = none, and end effect correction: ON.

[0068] Example 1 (Substrate) A commercially available substrate A was used as the first porous ceramic layer. Substrate A contained Al as a main raw material, and also contained Si, O, etc., and was cylindrical with an inner diameter of 7.0 mm, an outer diameter of 9.5 mm, and a length of 10 cm. The pore diameter D50 was 15.4 μm, and the number of branch points per unit volume of the pores measured by the above method was 1.71 × 10 ６ pieces / μm ３ It was.

[0069] (Preparation of Slurry S1) Alumina powder AA-10 (volume-based cumulative 50% equivalent diameter: approximately 14.8 μm) manufactured by Sumitomo Chemical Co., Ltd., hydroxypropyl methylcellulose 65SH-30000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 (active ingredient 41%) as a dispersant were mixed with water to concentrations of 10 mass%, 1.5 mass%, and 1 mass%, respectively, to prepare slurry S1.

[0070] (Formation of Porous Ceramic Layer 1) The slurry S1 was filled into a catheter syringe manufactured by Terumo Corporation, and left standing for 1 hour with the outlet facing downward. A tube was attached to the tip of the catheter syringe manufactured by Terumo Corporation, and one end of the substrate A was placed vertically with the end facing downward (hereinafter referred to as end A; the other end opposite end A is referred to as end B). The tip of the tube was connected to this end, and the slurry S1 was injected onto the entire inner surface of the substrate.

[0071] After injecting the slurry S1, a resin ball X having a diameter of 6.7 mm was set at end B (upper end side) of the substrate, and air was flowed from end B at an air pressure of 0.1 MPa to move the ball from end B to end A, thereby discharging the slurry S1. After that, with the ball held at end A, the pressure was maintained at 0.1 MPa for 30 seconds. Thereafter, while rotating the substrate A at 6.9 rpm, hot air of about 0.1 m / s was blown through the inside of the substrate A to dry it. Thereafter, the substrate A having the slurry S1 applied to its inner surface was heat-treated at 1200°C for 3 hours, and a layer containing AA-10 particles was formed on the inner surface of the substrate A.

[0072] (Preparation of Slurry S2) Subsequently, alumina powder AKP-20 (volume-based cumulative 50% equivalent diameter: approximately 0.42 μm) manufactured by Sumitomo Chemical Co., Ltd., hydroxypropyl methylcellulose 65SH-30000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 as a dispersant were mixed in water at concentrations of 9 mass%, 1.5 mass%, and 1 mass%, respectively, to prepare slurry S2.

[0073] (Formation of Porous Ceramic Layer 2) A catheter syringe manufactured by Terumo Corp. was filled with the slurry S2, and left standing for 1 hour with the outlet facing downward. A tube was attached to the tip of the catheter syringe manufactured by Terumo Corp., and the tip of the tube was connected to the end A of the substrate, which was placed vertically and had a layer containing AA-10 particles formed on its inner surface, with the end A facing downward, and the slurry S2 was injected into the entire inside of the substrate.

[0074] After injecting the slurry S2, a ball Y having a diameter of 6.35 mm was set at the end B of the substrate, and air was flowed from end B at an air pressure of 0.02 MPa to move the ball from end B to end A, thereby discharging the slurry. While rotating the substrate at 6.9 rpm, hot air of about 0.1 m / s was blown over the inner surface of the substrate to dry it, and a layer containing AKP-20 was formed on the layer containing AA-10 particles (an intermediate layer, which also contains AKP-20 from slurry S2). The substrate having a layer containing AA-10 particles and a layer containing AKP-20 formed on its inner surface was heat-treated at 1200 ° C. for 3 hours.

[0075] After the heat treatment, the slurry S2 was applied again in the same manner as in the first application of the slurry S2, except that a ball was set at end A (upper end side) of the substrate, air was blown through end A to discharge the slurry, and a ball Y having a diameter of 6.35 mm was used. After the application, a heat treatment was carried out at 1200°C for 3 hours.

[0076] Example 2 The first porous ceramic layer contained Al as a main raw material, and also contained Si, O, etc., and had a cylindrical shape with an inner diameter of 6.6 mm, an outer diameter of 10.0 mm, and a length of 10 cm. The pore diameter D50 was 14.4 μm, and the number of branch points per unit volume of the pores was 1.26 × 10 ６ pieces / μm ３ The porous ceramic laminate of Example 2 was obtained in the same manner as in Example 1, except that a commercially available substrate B was used, the diameter of the ball X used in applying the slurry S1 and the first application of the slurry S2 was changed from 6.7 mm to 6.35 mm, and the diameter of the ball Y used in applying the slurry S2 the second time was changed from 6.35 mm to 6.0 mm.

[0077] Comparative Example 1 The first porous ceramic layer contained Al as a main raw material, and also contained Si, O, etc., and had a cylindrical shape with an inner diameter of 6.0 mm, an outer diameter of 9.9 mm, and a length of 10 cm. The pore diameter D50 was 12.8 μm, and the number of branch points per unit volume of the pores was 8.49 × 10 ５ pieces / μm ３ A porous ceramic laminate of Comparative Example 1 was obtained in the same manner as in Example 1, except that a commercially available substrate C was used, the diameter of ball X was changed from 6.7 mm to 5.5 mm, and the diameter of ball Y was changed from 6.35 mm to 5.0 mm.

[0078] Comparative Example 2 The first porous ceramic layer contained Al as a main raw material, and also contained Si, O, etc., and had a cylindrical shape with an inner diameter of 6.9 mm, an outer diameter of 10.5 mm, and a length of 10 cm. The pore diameter D50 was 13.0 μm, and the number of branch points per unit volume of the pores was 7.89 × 10 ５ pieces / μm ３ A porous ceramic laminate of Comparative Example 2 was obtained in the same manner as in Example 1, except that a commercially available substrate D having a diameter of 6.7 mm was used, the diameter of ball X was changed from 6.7 mm to 6.35 mm, and the diameter of ball Y was changed from 6.35 mm to 6.0 mm.

[0079] [Peel Strength Test] The porous ceramic laminates obtained in the examples and comparative examples were evaluated according to JIS K5600 General Test Method for Paint Scratch Hardness (Pencil Method) 5-4. A pencil hardness tester (Yasuda Seiki Seisakusho Co., Ltd. 533-M1, weight: 750 g, pencil movement speed: 1 mm / sec) was used to draw a line on the surface of the laminate (the surface opposite the first porous ceramic layer) using a soft pencil (Mitsubishi Pencil Co., Ltd.: Mitsubishi Uni Series 6B-9H), and the surface was observed using a digital microscope (Keyence Corporation: VHX-5000). The hardness just before the hardness at which peeling, dents, or scratches were observed was evaluated as the hardness of the sample. The results are shown in Table 1.

[0080]

[0081] As can be seen from the inner diameter of the substrate and the size of the balls used, the comparative example has a thicker film thickness of the other porous ceramic layer formed on the substrate than the example, which would normally be expected to improve the peel strength since the film strength is improved.However, in the comparative example, the number of branching points of the pores in the substrate did not meet the requirements of the present invention, so the peel strength was inferior despite the film thickness of the other porous ceramic layer being thicker than the example.

[0082] Fig. 4 shows a cross-sectional view of the laminate obtained using the substrate of Example 1. As shown in Fig. 4, it was observed that a layer containing small particles having a circle-equivalent particle diameter of less than 1 µm was laminated on the first porous ceramic layer, and that the small particles and large particles having a circle-equivalent particle diameter of 2 µm to 25 µm were present on the surface of the first porous ceramic layer on the side of the layer containing the small particles, and that the layer containing the small particles was composed of an outer layer containing small particles but not the large particles, and an intermediate layer containing both small particles and large particles.

[0083] 11 Branch point 21, 31 First porous ceramic layer 22, 32, 33 Other porous ceramic layers

Claims

1. A porous ceramic laminate in which one or more other porous ceramic layers are laminated on a first porous ceramic layer composed of ceramic trabeculae and pores, the number of branching points of the pores being within 1 μm of the total volume of the ceramic trabeculae and pores. ３ 1.0 x 10 per ６ The porous ceramic laminate has at least one porous ceramic layer.

2. The volume of the protruding valley of the surface of the first porous ceramic layer, as determined in accordance with ISO 25178, is 0.56 ml / m ２ The porous ceramic laminate according to claim 1, wherein the porous ceramic laminate has a thickness of more than 100 nm.

3. The porous ceramic laminate according to claim 1 or 2, wherein the other porous ceramic layer is composed of two or more layers.

4. A porous ceramic laminate as described in claim 1 or 2, wherein the other porous ceramic layer is a layer containing small particles having a circle-equivalent particle diameter of less than 1 μm in a cross section parallel to the stacking direction of the laminate, and the small particles and large particles having a circle-equivalent particle diameter of 2 μm to 25 μm are present on the surface of the first porous ceramic layer facing the other porous ceramic layer.

5. The porous ceramic laminate according to claim 4, wherein the layer containing small particles comprises an outer layer containing the small particles and not the large particles, and an intermediate layer containing both the small particles and the large particles.

6. The average circle-equivalent particle diameter of the large particles present on the surface of the first porous ceramic layer is equal to or smaller than the average pore diameter D of the first porous ceramic layer. ５０ 5. The porous ceramic laminate according to claim 4, wherein the average particle diameter is 0.3 times or more.

7. The porous ceramic laminate according to claim 4, wherein both the large particles and the small particles are made of an inorganic oxide.

8. The porous ceramic laminate according to claim 1 or 2, which is in the form of a tube or a monolith.

9. A separation membrane comprising the porous ceramic laminate according to claim 1 or 2.

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