Porous ceramic laminate and separation membrane

Abstract

The purpose is to provide a porous ceramic laminate in which two or more layers are laminated and peeling at the lamination interface is suppressed. The present invention is a porous ceramic laminate characterized in that a layer containing small particles having a circle-equivalent particle size of less than 1 μm in a cross-section parallel to the lamination direction of the laminate is laminated on a first porous ceramic layer, and the small particles and large particles having a circle-equivalent particle size of 2-25 μm are present on the surface of the first porous ceramic layer.

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] For example, Patent Document 1 discloses a filter element comprising a porous, hard support layer made of sintered mineral particles and having relatively large pores with diameters of approximately several microns to several tens of microns, and an additional porous layer provided on the support layer, the porous layer comprising a first coating layer made of sintered mineral particles having a diameter almost equal to the pore diameter of the support layer, and a second coating layer made of sintered mineral particles having a diameter smaller than the pore diameter of the support layer, the first coating layer and the second coating layer being fixed to the support layer in this order by a sintering method, and the material of the additional porous layer being present on the support without substantially penetrating into the pores of the support layer.

[0005] Special Publication No. 59-48646

[0006] 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.

[0007] The aforementioned Patent Document 1 also discloses a laminate as a separation membrane structure, but does 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.

[0008] The present invention, which has achieved the above-mentioned object, is as follows: [1] A porous ceramic laminate, characterized in that a first porous ceramic layer is laminated with 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 to 25 μm are present on the surface of the first porous ceramic layer. [2] The average circle-equivalent particle diameter of the large particles is less than the average pore diameter D of the first porous ceramic layer. ５０[3] The laminate according to [1], wherein, when observed in a cross section parallel to the stacking direction of the laminate, the proportion of small particles present on the surface of the first porous ceramic layer, represented by the ratio of L2 to L1 below: L2 / L1, is 10% or more. L1: length within the observation field of a line X1 that contacts the first porous ceramic layer at two or more locations and does not cross the first porous ceramic layer L2: total length within the observation field of the surface of the first porous ceramic layer where small particles are present [4] The laminate according to any of [1] to [3], wherein, when observed in a cross section parallel to the stacking direction of the laminate, the proportion of the area of ​​the large particles in the part sandwiched between the following lines X1 and X0 is 4% or more.

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[0105] Line X1: a line that contacts the first porous ceramic layer at two or more points but does not cross the first porous ceramic layer. Line X2: a parallel line that is 10 μm apart from the line X1 in the outermost surface direction of the layer containing the small particles from the surface of the first porous ceramic layer. [7] The laminate according to [5] or [6], in which another layer is further laminated between the intermediate layer and the outer layer or on top of the outer layer. [8] The laminate according to any one of [1] to [7], in which the large particles and the small particles are inorganic oxides. [9] The laminate according to any one of claims [1] to [8], which is tubular or monolithic.

[10] A separation membrane comprising the laminate according to any one of [1] to [9].

[11] The laminate according to any one of [4] to [9], in which, when observed at a cross section parallel to the lamination direction of the laminate, the area ratio of particles having a circle-equivalent particle diameter of more than 25 μm in the portion sandwiched between the line X1 and the line X0 is 2% or less.

[0009] According to the present invention, it is possible to provide a porous ceramic laminate in which peeling at the lamination interface is suppressed.

[0010] Fig. 1 is a photograph showing the procedure for measuring the proportion of small particles on the surface of the first porous ceramic layer. Fig. 2 is a photograph showing an SEM image of a cross section of the laminate obtained in Example 2. Fig. 3(a) is a photograph showing an SEM image of the surface of the first porous ceramic layer used in the example. Fig. 3(b) is a photograph showing an SEM image of the surface of the laminate obtained in Example 2. Fig. 3(c) is a photograph showing an SEM image of the surface of the sample obtained in Comparative Example 1.

[0011] The porous ceramic laminate of the present invention is a porous ceramic laminate in which 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 is stacked on a first porous ceramic layer, and the small particles and large particles having a circle-equivalent particle diameter of 2 to 25 μm are present on the surface of the first porous ceramic layer (the surface on the side of the layer containing the small particles).

[0012] As described above, porous ceramic bodies used for fluid separation, concentration, filtration, etc. typically have a functional layer with a smaller pore diameter than a support layer with a larger pore diameter laminated on top of the support layer to reduce pressure loss of the fluid flowing through the porous ceramic body while fully performing functions such as separation. However, if a layer made of large particles is laminated directly on the support layer, the interfacial bonding strength is insufficient. On the other hand, as shown in the comparative example described below, if an attempt is made to laminate a layer made of small particles on the support layer, the small particles will enter the pores of the support layer, making it impossible to form a layer. In the porous ceramic laminate of the present invention, a layer containing small particles is formed on the surface of the first porous ceramic layer that serves as the support layer, and since both small and large particles are present on the surface of the first porous ceramic layer, a layer can be formed on the support layer and the interfacial bonding strength can be improved.

[0013] 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, with a tube shape or a monolith shape being 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 (cylindrical shape is preferred). When the first porous ceramic layer is tubular, the layer containing small particles is preferably formed on the inner circumferential surface of the tube. When the first porous ceramic layer is monolithic, the layer containing small particles is preferably formed on the inner circumferential surface of each through-hole of the monolithic shape.

[0014] The porous ceramic laminate of the present invention comprises a first porous ceramic layer and a layer containing small particles laminated on the first porous ceramic layer, and has the same shape as the first porous ceramic layer.

[0015] The thickness (average value) of the first porous ceramic layer is preferably 400 to 8000 μm. When the first porous ceramic layer is monolithic, the thickness may be the average value of the closest distances between adjacent tubes in a plane perpendicular to the long axis. The axial length of the first porous ceramic layer is, for example, 50 to 5000 mm, preferably 500 to 3000 mm. 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.

[0016] 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 ceramic 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 ceramic layer contains one or more metal oxides other than Al. ２ O ３ The one or more metal oxides other than the above may be arbitrarily selected from the metal oxides exemplified above, and the first porous ceramic layer is Al ２ O ３ and SiO ２ 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.

[0017] The average pore diameter D of the first porous ceramic layer measured by mercury intrusion porosimetry ５０is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more, and is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. ５０ The average pore diameter D is preferably 0.1 to 20 μm, more preferably 1 to 18 μm, and even more preferably 5 to 15 μm. ５０ means the cumulative 50% equivalent diameter in a graph in which the horizontal axis represents pore diameter and the vertical axis represents log differential pore volume.

[0018] In the present invention, the laminate is observed at a cross section parallel to the stacking direction of the laminate, and particles having a circle-equivalent particle diameter of less than 1 μm at the cross section are defined as small particles. The lower limit of the circle-equivalent particle diameter of small particles may be about 0.05 μm. On the other hand, particles having a circle-equivalent particle diameter of 2 μm to 25 μm at the cross section are defined as large particles. 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 (for example, the axial direction when the laminate is cylindrical).

[0019] In the present invention, it is also preferable to adjust the ratio of large particles to small particles on the surface of the first porous ceramic layer. When observing a cross section of the laminate parallel to the lamination direction, the ratio of small particles present on the surface of the first porous ceramic layer, expressed as the ratio of L2 to L1 below: L2 / L1, is preferably 10% or more. By setting the ratio of small particles to a predetermined value or more, the bonding strength between the first porous ceramic layer and the layer thereon can be improved. L1: length within the observation field of view of a straight line X1 that contacts the first porous ceramic layer at two or more points and does not cross the first porous ceramic layer. L2: total length within the observation field of view along the surface of the portion where small particles are present on the surface of the first porous ceramic layer

[0020] Figure 1 shows the procedure for measuring the proportion of small particles on the surface of the first porous ceramic layer. As shown in Figure 1(a), a straight line X1 (symbol 11a) is drawn that contacts the first porous ceramic layer at two or more points but does not cross the first porous ceramic layer, and the length L1 of the line X1 within the observation field is measured. Next, as shown in Figure 1(b), portions 11b and 12b on the surface of the first porous ceramic layer where small particles exist are identified, and their total length L2 is measured to calculate L2 / L1.

[0021] When there are multiple lines X1 in the observation field, the shortest line is used as X1. In addition, in a rectangular observation field with the stacking direction being the up-down direction on the paper, even if a line touches the first porous ceramic layer at two or more points, a line that does not intersect with the right and left ends of the observation field is not used as X1. Observation is performed using an SEM at a magnification of 1000x.

[0022] As described above, L2 / L1 is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, even more preferably 25% or more, still more preferably 30% or more, and particularly preferably 40% or more, and the upper limit may be, for example, 85%. That is, L2 / L1 is preferably 10 to 85%, more preferably 15 to 85%, even more preferably 20 to 85%, even more preferably 25 to 80%, still more preferably 30 to 85%, and particularly preferably 40 to 85%.

[0023] Furthermore, when observing a cross section of the laminate parallel to the lamination direction, the proportion of large particles on the surface of the first porous ceramic layer is preferably 4% or more, as evaluated by the area proportion of the large particles in the portion sandwiched between the following lines X1 and X0: 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.

[0024] The area ratio of the large particles is preferably 4% or more, more preferably 10% or more, even more preferably 15% or more, and particularly preferably 22% or more. This range is preferable because it facilitates the formation of a layer on the first porous ceramic layer. On the other hand, setting the area ratio of the large particles to a predetermined value or less is preferable because it facilitates improving the bonding strength at the interface between the first porous ceramic layer (which serves as the support layer) and the layer above it. From this perspective, the upper limit of the area ratio of the large particles is, for example, 35%, preferably 30% or less. That is, the area ratio of the large particles may be 4 to 35%, 10 to 30%, 15 to 30%, or 22 to 30%.

[0025] In the present invention, it is preferable that the surface of the first porous ceramic layer contains as few particles as possible having a circle-equivalent particle diameter of more than 25 μm. Specifically, the area ratio of particles having a circle-equivalent particle diameter of more than 25 μm in the part of the observation field sandwiched between the lines X1 and X0 is preferably 2% or less, more preferably 1% or less, and even more preferably 0%.

[0026] The large particles (having a circle-equivalent particle diameter of 2 to 25 μm) present on the surface of the first porous ceramic layer have an average circle-equivalent particle diameter of 2 to 25 μm, which is smaller than the average pore diameter D of the first porous ceramic layer. ５０ The average diameter of the large particles is preferably 0.3 times or more, more preferably 0.6 times or more, and by doing so, it is possible to prevent the large particles from being taken into the pores of the first porous ceramic layer that serves as the support layer. ５０ That is, the average circle-equivalent particle diameter of the large particles is preferably 2.8 times or less than the average pore diameter D of the first porous ceramic layer. ５０The average circle-equivalent particle diameter of the large particles present on the surface of the first porous ceramic layer is preferably 0.3 to 2.8 times, more preferably 0.6 to 2.8 times. 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 the portion sandwiched between the lines X1 and X0 and calculating the average circle-equivalent particle diameter of the large particles. Note that the large particles in the portion sandwiched between the lines X1 and X0 below refer to particles in which at least a portion is present in the portion sandwiched between the lines X1 and X0. If the target large particle has a portion extending beyond the lines X1 and X0, the circle-equivalent particle diameter of the entire large particle, including the portion extending beyond the lines X1 and X0, is measured.

[0027] In the porous ceramic laminate of the present invention, a layer containing small particles is laminated on the first porous ceramic layer, and this 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 average circle-equivalent particle diameter of the small particles in the outer layer and the average circle-equivalent particle diameter of the small particles in the intermediate layer may be the same or different. The thickness of the intermediate layer can be, for example, 3 to 100 μm, preferably 3 to 60 μm. The thickness of the outer layer is, for example, 5 to 100 μm, more preferably 20 to 80 μm.

[0028] For the intermediate layer, in a cross section parallel to the stacking direction of the laminate, straight lines are drawn from any three or more points on the surface of the first porous layer (the surface on the intermediate layer side), each 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), and 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 three or more line segments can be used as the thickness of the intermediate layer. For the outer layer, straight lines are drawn from any three or more points on the interface between the intermediate layer and the outer layer, each in the stacking direction, and the lengths of the line segments to the points where they intersect with the surface of the outer layer can be used as the thickness of the outer layer.

[0029] When the layer containing small particles includes an intermediate layer and an outer layer, the ratio of large particles in the intermediate layer, evaluated by the area ratio of the large particles in the portion sandwiched between the above-mentioned line X1 and the following line X2, is preferably 1 to 60% when observing a cross section of the laminate parallel to the lamination direction. Line X2: A parallel line 10 μm apart from the line X1 toward the outermost surface of the layer containing small particles from the surface of the first porous ceramic layer.

[0030] The proportion of large particles in the intermediate layer is 5% or more, more preferably 10% or more, even more preferably 25% or more, and particularly preferably 35% or more, and the upper limit may be, for example, 90% or 80%. That is, the proportion of large particles in the intermediate layer is preferably 5 to 90%, more preferably 10 to 80%, even more preferably 25 to 80%, and particularly preferably 35 to 80%.

[0031] In the laminate of the present invention, it is also preferable that L2 / L1 is 30 to 85%, the area ratio of the large particles in the portion sandwiched between line X1 and line X0 is 10 to 30%, and further the area ratio of the large particles in the portion sandwiched between line X1 and line X2 below is 25 to 80%.

[0032] Furthermore, when the layer containing small particles includes an intermediate layer and an outer layer, another layer may be laminated between the intermediate layer and the outer layer or on top of the outer layer.

[0033] The large particles and the small particles are preferably inorganic oxides. In a preferred embodiment, the above-mentioned examples of metal oxides contained in the first porous ceramic layer can be referred to. In particular, both the large particles and the small particles are Al. ２ O ３ It is preferable that Al ２ O ３ 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.

[0034] The method for producing the porous ceramic laminate of the present invention is not particularly limited, and the laminate may be produced by applying a slurry containing particles X1 having a volume-based cumulative 50% equivalent diameter of 1 to 20 μm and particles X2 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more but less than 1 μm onto a first porous ceramic layer by dipping, spray coating, spin coating, bar coating, or the like, and then drying the slurry. Alternatively, the laminate may be produced by further applying and drying a slurry containing particles Y1 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more but less than 1 μm, but not containing particles having a volume-based cumulative 50% equivalent diameter of 1 to 20 μm. Particles X2 and Y1 may be the same or different.

[0035] Particles having a volume-based cumulative 50% equivalent diameter of 1 to 20 μm correspond to the above-mentioned large particles, and particles having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more and less than 1 μm correspond to the above-mentioned small particles.

[0036] In particular, when the first porous ceramic layer is tubular or monolithic, it may be produced by a method of forming a particle-containing slurry on the inner surface of a tube or monolith using a jig (hereinafter referred to as a ball injection method). This will be explained in more detail below.

[0037] 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.

[0038] The particle-containing slurry liquid is a raw material for the ceramic porous layer formed on the 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 volume-based cumulative 50% equivalent diameter of 1 to 20 μm through a slurry liquid X supply step (1X), a coating layer formation 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. Then, on the inner surface of the tube on which the coating layer containing particles X1 has been formed, a slurry liquid Y supply step (1Y) containing particles Y1 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more to less than 1 μm is provided, a coating layer formation step (2Y) using the slurry liquid Y, and a drying step (3Y) to form a coating layer containing particles Y1. A heat treatment step (4X) may be performed after the drying step (3X), or a heat treatment step (4Y) may be performed after the drying step (3Y). Furthermore, the slurry liquid X preferably contains particles X2 having a volume-based cumulative 50% equivalent diameter of 0.05 μm or more and less than 1 μm in addition to the particles X1. Particles X1 having a volume-based cumulative 50% equivalent diameter of 1 to 20 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 correspond to the small particles described above. Particles X2 and Y1 may be the same or different.

[0039] The slurry preferably contains particles as well as a dispersant, a thickener, and a solvent.

[0040] The dispersant can suppress aggregation of inorganic 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 of such surfactants that can be used 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 preferably, for example, 0.01% by mass or more and 10% by mass or less, relative to 100% by mass of the inorganic particles in the slurry.

[0041] 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.

[0042] The solvent may be water or an organic solvent.

[0043] 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.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 to 30 minutes.

[0049] 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.

[0050] 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 to 1 m / sec.

[0051] 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 to 1500°C. The heat treatment time is, for example, 30 minutes to 10 hours.

[0052] 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.

[0053] The ceramic porous laminate obtained by the present invention can be used as a microfiltration membrane, an ultrafiltration membrane, or a nanofiltration membrane, and if necessary, can be further laminated with a functional layer 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.

[0054] 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 to the surface of the ceramic porous laminate obtained by the present invention and allowing the reaction to occur. The synthesis conditions can be appropriately selected depending on the functional layer to be laminated, but for example, a temperature of 80 to 800°C for 1 to 72 hours may be sufficient.

[0055] This application claims the benefit of priority based on Japanese Patent Application No. 2023-127030, filed on August 3, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-127030, filed on August 3, 2023, are incorporated herein by reference.

[0056] 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.

[0057] The examples and comparative examples described below were evaluated according to the following methods.

[0058] (1) Method for measuring the pore diameter of the substrate: Pore diameter D of the substrate ５０The substrate was dried at 120°C for 4 hours, and then measured by mercury intrusion porosimetry using an Autopore IV9520 (manufactured by Micromeritics). Mercury intrusion porosimetry produced a graph with the pore diameter on the horizontal axis and the cumulative log differential pore volume on the vertical axis, and the cumulative 50% equivalent diameter was obtained. The details of the measurement conditions are as follows: Adv. Contact Angle: 140.0° Rec. Contact Angle: 140.0° Mercury Temperature: 21°C Sample Mass: 1.0g Assembly Mass: 1.0g Penetrometer Volume: 1.0mL Penetrometer Mass: 1.0g Report Range: 1.07 to 59,256.30 psia

[0059] (2) Method for Measuring Particle Diameter of Inorganic 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 analyzer (Microtrac MT3300EX II, manufactured by Microtrac Co., Ltd., 0.2% by mass aqueous solution of sodium hexametaphosphate), and the volume-based cumulative 50% equivalent diameter was measured.

[0060] (3) Cross-sectional observation of laminate The cylindrical porous ceramic laminate obtained in the example 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).

[0061] (4) Proportion of small particles on the surface of the first porous ceramic layer In the SEM image obtained in (3) above, the following lengths L1 and L2 were determined, and the ratio of L2 to L1, L2 / L1, was calculated. L1: length within the observation field of view of a straight line X1 that contacts the first porous ceramic layer at two or more points and does not cross the first porous ceramic layer. L2: total length within the observation field of view along the surface of the first porous ceramic layer of the portion where small particles exist.

[0062] (5) Area ratio of large particles on the surface of the first porous ceramic layer In the SEM image obtained in (3) above, the total area of ​​the large particles in the portion sandwiched between the following lines X1 and X0 was measured, and divided by the area of ​​the portion sandwiched between the lines X1 and X0 in the observation field to calculate the area ratio of large particles on the surface of the first porous ceramic layer. 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. Furthermore, 20 large particles were randomly selected from the portion sandwiched between the lines X1 and X0, and the average circle-equivalent particle diameter of the large particles was calculated.

[0063] (6) Area ratio of large particles in intermediate layer In the SEM image obtained in (3) above, the total area of ​​the large particles in the part sandwiched between the following lines X1 and X2 was measured, and divided by the area of ​​the part sandwiched between the lines X1 and X2 in the observation field to calculate the area ratio of large particles in the intermediate layer. 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 X2: A parallel line that is 10 μm apart from the line X1 in the direction of the outermost surface of the layer containing the small particles from the surface of the first porous ceramic layer.

[0064] (7) Observation of sample surfaces The surface of the first porous ceramic layer, the surface of the laminate obtained in Example 2 described below, and the surface of the sample obtained in Comparative Example 1 were each observed using a scanning electron microscope TM4000 manufactured by Hitachi High-Tech Corporation.

[0065] (8) Measurement of peel strength 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). A pencil hardness tester (Yasuda Seiki Seisakusho Co., Ltd. 553-M1, weight: 750 g, pencil movement speed: 1 mm / sec) was used to draw a line from a soft pencil (Mitsubishi Pencil Co., Ltd.: Mitsubishi Uni Series 6B to 9H) on the surface of the laminate, and the surface was observed using a digital microscope (Keyence Corporation: VHX-5000). The hardness of the sample was evaluated as the hardness just before the hardness at which peeling, dents, or scratches were observed. Samples with a hardness of 9H to H were evaluated as ◯, samples with a hardness of F to HB were evaluated as △, and samples with a hardness of B to 6B were evaluated as ×.

[0066] Example 1 (First porous ceramic layer) A first porous ceramic layer was formed using alumina and SiO ２ Alumina substrate CRM0107 (cylindrical, with an inner diameter of 6.5 mm, an outer diameter of 10.0 mm, and a length of 12.5 cm, an average pore diameter D ５０ The thickness was approximately 6.1 μm.

[0067] (Preparation of Slurry for Intermediate Layer) Alumina powder AA-5 (volume-based cumulative 50% equivalent diameter is approximately 6.6 μm) and AKP-3000 (volume-based cumulative 50% equivalent diameter is approximately 0.67 μm) manufactured by Sumitomo Chemical Co., Ltd., hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd. as a thickener, and SN Dispersant 5468 (active ingredient 41%) as a dispersant were mixed in water at concentrations of 13.5 mass%, 1.5 mass%, 3.2 mass%, and 1.5 mass%, respectively, and the mixture was defoamed to prepare slurry S1.

[0068] (Formation of intermediate layer) The slurry was filled into a catheter syringe manufactured by Terumo Corp., 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 one end of the substrate was placed vertically downward, with the end (hereinafter referred to as end A; the other end opposite end A is referred to as end B) connected to the tip of the tube, and the slurry S1 was injected into the entire inside of the substrate.

[0069] After injecting the slurry S1, a ball having a diameter of 5.5 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 discharging the slurry S1, the pressure was maintained at 0.1 MPa for 600 seconds with the ball held at end A. After 600 seconds, the substrate was rotated at 6.9 rpm and hot air of about 0.1 m / s was blown across the inner circumferential surface of the substrate to dry it, and a layer (intermediate layer) containing AA-5 particles and AKP-3000 particles was formed on the inner circumferential surface of the substrate.

[0070] (Preparation of Slurry for Outer Layer) Alumina powder AKP-3000 manufactured by Sumitomo Chemical Co., Ltd., a thickener hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd., and a dispersant SN Dispersant 5468 were mixed in water at concentrations of 9.0 mass %, 3.2 mass %, and 0.9 mass %, respectively, and the mixture was degassed to prepare slurry S2.

[0071] (Formation of outer layer 1) A catheter syringe manufactured by Terumo Corp. was filled with the slurry, 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 end A of a substrate having a layer containing AA-5 particles and AKP-3000 particles formed on its inner surface, which was placed vertically, with end A facing downward, and the slurry S2 was injected into the entire inside of the substrate.

[0072] After injecting the slurry S2, a ball having a diameter of 5.5 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-3000 was formed on the layer containing AA-5 particles and AKP-3000 (intermediate layer). The substrate having a layer containing AA-5 particles and AKP-3000 particles and a layer containing AKP-3000 formed on its inner surface was heat-treated at 1200 ° C. for 3 hours.

[0073] (Formation of outer layer 2) After the heat treatment, the same operation as in "Formation of outer layer 1" was carried out to obtain a porous ceramic laminate.

[0074] Example 2 A porous ceramic laminate of Example 2 was obtained in the same manner as in Example 1, except that the concentrations of the alumina powders AA-5 and AKP-3000 in the slurry S1 were 12.0 mass % and 3.0 mass %, respectively.

[0075] Example 3 A porous ceramic laminate of Example 3 was obtained in the same manner as in Example 1, except that the concentrations of the alumina powders AA-5 and AKP-3000 in the slurry S1 were set to 10.5 mass % and 4.5 mass %, respectively.

[0076] Example 4 A porous ceramic laminate of Example 4 was obtained in the same manner as in Example 1, except that the concentrations of the alumina powders AA-5 and AKP-3000 in the slurry S1 were set to 6.0% by mass and 9.0% by mass, respectively.

[0077] Example 5 A porous ceramic laminate of Example 5 was obtained in the same manner as in Example 1, except that the concentrations of the alumina powders AA-5 and AKP-3000 in the slurry S1 were set to 3.0 mass % and 12.0 mass %, respectively.

[0078] Comparative Example 1 As the first porous layer, the same alumina substrate CRM0107 manufactured by Nanjing Tangent Fluid Technology Co., Ltd. as in Example 1 was used.

[0079] Alumina powder AKP-3000 manufactured by Sumitomo Chemical Co., Ltd., a thickener hydroxypropyl methylcellulose 60SH-4000 manufactured by Shin-Etsu Chemical Co., Ltd., and a dispersant SN Dispersant 5468 were mixed with water at concentrations of 9.0 mass%, 3.2 mass%, and 0.9 mass%, respectively, and the mixture was degassed to prepare a slurry. A catheter syringe manufactured by Terumo Corporation was filled with the slurry, and the syringe was allowed to stand for 1 hour with the outlet facing downward.

[0080] A tube was attached to the tip of a catheter syringe manufactured by Terumo Corporation, and the tip of the tube was connected to one end A of the substrate placed vertically with the end A facing downward, and the slurry was injected into the entire inside of the substrate.

[0081] After the slurry was poured, a ball having a diameter of 5.0 mm was set at end B of the substrate opposite end A, 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. After the slurry was discharged, the ball was held at end A and maintained at 0.1 MPa for 600 seconds. After 600 seconds, the substrate was rotated at 6.9 rpm and hot air of about 0.1 m / s was blown through the inner circle of the substrate to dry it, and an attempt was made to form a layer containing AKP-3000 particles on the inner surface of the substrate.

[0082] Figure 2 shows an SEM image of the cross section of the laminate obtained in Example 2 according to (3) above. As shown in Figure 2, in Example 2, a layer containing small particles 22 with a circle-equivalent particle diameter of less than 1 μm was laminated on the first porous ceramic layer 21, and it was confirmed that large particles 23 with a circle-equivalent particle diameter of 2 to 25 μm and the small particles 22 were present on the surface of the first porous ceramic layer 21. A similar state was observed in the other Examples. Furthermore, in Examples 1 to 4, it was confirmed that an intermediate layer containing both small and large particles and an outer layer containing small particles but not the large particles were formed on the first porous ceramic.

[0083] Figure 3 shows the results of surface observation according to (7) above. Figure 3(a) is the surface of the first porous ceramic layer, Figure 3(b) is the surface of the laminate of Example 2, and Figure 3(c) is the surface of the sample of Comparative Example 1. In Figure 3(b), it can be seen that a layer different from the first porous ceramic layer shown in Figure 3(a) has been formed, while in Figure 3(c), it can be seen that the AKP-3000 particles have entered the pores of the first porous ceramic layer, and it can be seen that a layer different from the first porous ceramic layer has not been formed.

[0084] The results of measurements made according to the above (4), (5), (6) and (8) are shown in Table 1. In Table 1, the first porous ceramic layer is referred to as the "first layer."

[0085]

[0086] In all of Examples 1 to 5, the average circle-equivalent particle diameter of the large particles in the portion sandwiched between the lines X1 and X0 was 4.5 μm. In addition, in all of Examples 1 to 5, the area ratio of particles having a circle-equivalent particle diameter of more than 25 μm in the portion sandwiched between the lines X1 and X0 was 2% or less.

[0087] For Examples 2 to 4, in which an outer layer and an intermediate layer were observed in the layer containing small particles, the cylindrical porous ceramic laminate was observed in a cross section perpendicular to the axial direction, and straight lines were drawn from any five points on the surface of the first porous layer (the surface on the intermediate layer side) in the stacking direction (radial direction of a circle) to the point where they intersected with the outer layer side surface of the AA-5 particles. The average value of the five line segments was calculated as the thickness of the intermediate layer, which was about 18 μm in Example 2, about 22 μm in Example 3, and about 22 μm in Example 4. Furthermore, the cylindrical porous ceramic laminate was observed in a cross section perpendicular to the axial direction, and straight lines were drawn from any five points on the interface between the intermediate layer and the outer layer in the stacking direction (radial direction of a circle) to the point where they intersected with the outer layer surface. The average value of the five line segments was calculated as the thickness of the outer layer, which was about 61 μm in Example 2, about 56 μm in Example 3, and about 53 μm in Example 4.

Claims

1. A porous ceramic laminate comprising a first porous ceramic layer and a layer containing small particles having a circular 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 circular equivalent particle diameter of 2 to 25 μm are present on the surface of the first porous ceramic layer.

2. The average circle-equivalent particle diameter of the large particles is equal to or smaller than the average pore diameter D of the first porous ceramic layer. ５０ The laminate according to claim 1, wherein the thickness is 0.3 times or more.

3. The laminate according to claim 1, in which, when observed at a cross section parallel to the lamination direction of the laminate, the ratio of small particles present on the surface of the first porous ceramic layer, represented by the ratio of L2 to L1 below: L2 / L1, is 10% or more: L1: length within the observation field of view of a straight line X1 that contacts the first porous ceramic layer at two or more points and does not cross the first porous ceramic layer, L2: total length within the observation field of view along the surface of the portion where small particles are present on the surface of the first porous ceramic layer 4. The laminate according to claim 1, wherein the area ratio of the large particles in a portion between the following lines X1 and X0 is 4% or more when observed in a cross section parallel to the lamination direction of the laminate: 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 in the direction toward the inside of the first porous ceramic layer 5. The laminate according to claim 1, 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 laminate according to claim 5, wherein, when observed at a cross section parallel to the lamination direction of the laminate, the area ratio of the large particles in a portion sandwiched between the following lines X1 and X2 is 1 to 60%: 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 X2: a parallel line separated from the line X1 by 10 μm in the direction of the outermost surface of the layer containing the small particles from the surface of the first porous ceramic layer 7. The laminate according to claim 5, further comprising another layer laminated between said intermediate layer and said outer layer or on said outer layer.

8. The laminate according to claim 1, wherein said large particles and small particles are inorganic oxides.

9. The laminate according to claim 1, which is in the form of a tube or a monolith.

10. A separation membrane comprising the laminate of claim 1.

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