Method for producing porous ceramics and porous ceramics

Abstract

To provide a manufacturing method of porous ceramic according to which a bubble is difficult to foam, the deviation of foams is suppressed, and a large number of pores of relatively small diameter are formed and porous ceramic.SOLUTION: The above problem is solved by: a manufacturing method of porous ceramic that includes a step of mixing and foaming a powdered ceramic raw material, a foaming agent, fine fibrous cellulose, and a thickener to form a bubble former, wherein the fine fibrous cellulose has an average fiber width of 3 to 100 nm; and the porous ceramic being formed through the step of forming a bubble former by mixing and foaming a powdered ceramic raw material, a foaming gent, fine fibrous cellulose and a thickener, and having a maximum value in the range of 0.1 to 1 μm in a pore diameter distribution curve.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing porous ceramics that can be used as bone fillers and the like.

Background Art

[0002] Conventionally, ceramic materials containing calcium phosphate have attracted attention as bone fillers and are excellent in biocompatibility and safety. Therefore, they are used in applications such as artificial bone materials, drug carrier materials for drug delivery systems (DDS), and scaffold materials for cell culture. In addition, calcium phosphate-based ceramic materials are also used in the treatment of bone-related diseases, such as tumors and degenerative diseases.

[0003] As described above, calcium phosphate-based ceramic materials are used as bone fillers, and research and development related to them have been carried out conventionally. As a document that discloses a technique related to calcium phosphate-based ceramic materials, Patent Document 1 below can be exemplified. Patent Document 1 discloses a technique related to a bioabsorbable implant formed of a bioabsorbable ceramic and having a porous structure that satisfies predetermined conditions. According to this technique, it is said that while maintaining excellent bone-bonding ability, the shape can be maintained not only during the filling operation but also until the filling operation is completed, and high utility can be maintained.

[0004] Another document, Patent Document 2, discloses a technique related to an artificial bone characterized in that bone marrow cells are incorporated inside porous ceramics made of β-tricalcium phosphate. According to this technique, it is possible to obtain an artificial bone material that can favorably promote bone formation, and by combining mechanical stimuli such as isotropic pressure and cell growth factors such as VEGF, bone formation can be more reliably achieved and the utility can be improved.

[0005] Patent Document 3 discloses a porous body manufactured using cellulose nanofibers with respect to a technique related to ceramics having open pores and closed pores.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-184878 [Patent Document 2] Japanese Patent Publication No. 2002-282285 [Patent Document 3] Japanese Patent Publication No. 2020-196649 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the invention described in Patent Document 2 involves mixing a surfactant with a porous ceramic raw material to form a slurry, foaming it, and then drying and sintering it to produce porous ceramics. If left unattended, the bubbles formed in the slurry gradually rise to the surface, burst, or merge to become larger. As a result, the porous ceramics produced have pores concentrated in the upper part of the porous ceramic, resulting in an uneven distribution of pores. While the porous ceramics of Patent Document 3 resolve the uneven distribution of pores seen in Patent Document 2, relatively larger pores have shapes that deviate from spherical (for example, angular shapes, rough or polyhedral pore formation surfaces, or shapes where only a part of the pore formation surface protrudes).

[0008] The porous ceramics described in Patent Document 1 use flammable organic particles to form pores. However, since these flammable organic particles have a uniform particle size, the pores formed will have a uniform diameter. This makes it difficult to obtain porous ceramics with small-diameter pores.

[0009] When porous ceramics are used as bone graft materials, a greater number of small-diameter pores is considered beneficial in the processes of osteogenic cell migration and settlement, bone formation, and bone marrow cell incorporation.

[0010] Therefore, the main problem that the present invention aims to solve is to provide a method for producing porous ceramics in which air bubbles are less likely to burst and a large number of relatively small-diameter pores are formed, as well as to provide porous ceramics. [Means for solving the problem]

[0011] The embodiments for solving the above problems are as follows: (First aspect) The process includes a forming step of mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent to foam and form a bubble-forming body. The aforementioned fine fibrous cellulose has an average fiber width of 3 to 100 nm. A method for producing porous ceramics characterized by the following:

[0012] (Second aspect) The porous ceramics mentioned above are The total volume of pores with a diameter greater than 0.3 μm and less than or equal to 1.0 μm is 60% or more of the total volume of all pores in the porous ceramic. A method for producing porous ceramics according to claim 1.

[0013] (Third aspect) The thickening agent is one or more selected from water-soluble polymers. A method for producing porous ceramics according to a first embodiment.

[0014] (Fourth aspect) The bubble retention rate of the bubble-forming body is 90% or more. A method for producing porous ceramics according to a first embodiment. Here, the stomatal maintenance rate is the value obtained by the following formula ([Equation 1]). [Mathematics 1] Bubble retention rate (%) = Bubble height after 60 minutes (H 60 ) / Initial height of bubble (H0) × 100

[0015] (Fifth aspect) The forming step is a step of obtaining a mixed slurry by mixing a powdery ceramic raw material, a foaming agent, microfibrous cellulose, and a thickening agent, and foaming the mixed slurry to form a foam structure. The B-type viscosity of the mixed slurry is 1000 to 25000 cps. A method for manufacturing a porous ceramic according to the first aspect.

[0016] (The sixth aspect) The porous ceramic has a maximum value within the range of 0.1 to 1 μm in the pore size distribution curve. A method for manufacturing a porous ceramic according to the first aspect. (The seventh aspect)

[0017] The porous ceramic has a total porosity of 50% or more and 90% or less, and a closed porosity of 0% or more and 5% or less. A method for manufacturing a porous ceramic according to the first aspect. <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0022] In another embodiment, a bubble-forming body containing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent has a three-dimensional network structure formed by the fine fibrous cellulose interacting with each other via hydroxyl groups, and also has a predetermined viscosity, thus restricting the flow of generated bubbles. For example, in conventional foam mixtures, bubbles combine to form larger bubbles, but in the present invention, bubbles do not flow easily, so their combination is not promoted, and the generation of relatively large-diameter bubbles is suppressed. Also, because bubbles do not flow easily, their buoyancy is suppressed, and the porous ceramics produced have a suppressed uneven distribution of small-diameter pores throughout the porous ceramic. Furthermore, the porous ceramics of the embodiment of the present invention have a maximum value within the aforementioned range in the pore size distribution curve, and more pores within this range are formed than in conventional porous ceramics. [Effects of the Invention]

[0023] According to the present invention, the primary effect is a method for producing porous ceramics in which air bubbles are less likely to burst and a relatively large number of small-diameter pores are formed. Additionally, a secondary effect is that the resulting porous ceramics also have a relatively large number of small-diameter pores. [Brief explanation of the drawing]

[0024] [Figure 1] This is a SEM image of β-TCP. [Figure 2] This is the XRD pattern of β-TCP powder. [Figure 3] This is the FT-IR spectrum of β-TCP powder. [Figure 4] This is a SEM image of porous ceramics. [Figure 5] This is a SEM image of porous ceramics. [Figure 6] This is a SEM image of porous ceramics. [Figure 7] This is a SEM image of porous ceramics. [Figure 8]This is a conceptual diagram of bubbles formed by a foaming agent and fine fibrous cellulose. [Figure 9] This figure shows the pore size distribution curve and the cumulative pore size distribution curve of porous ceramics. [Modes for carrying out the invention]

[0025] This section describes embodiments for carrying out the present invention. Note that this embodiment is just one example of the present invention. The scope of the present invention is not limited to this embodiment.

[0026] The method for manufacturing porous ceramics in this embodiment includes, for example, a forming step of mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent and foaming to form a bubble-forming body, characterized in that the fine fibrous cellulose has an average fiber width of 3 to 100 nm. Furthermore, porous ceramics in this embodiment are formed, for example, through a forming step of mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent and foaming to form a bubble-forming body, and are characterized in that the maximum value in the pore size distribution curve is within the range of 0.1 to 1 μm.

[0027] Next, we will explain the bubbles formed from ceramic raw materials, fine fibrous cellulose, and a blowing agent. In the manufacture of porous ceramics, it is of course possible to manufacture them without the fine fibrous cellulose from the aforementioned forms, but adding fine fibrous cellulose and a blowing agent has the following effects. As an example of a method for manufacturing porous ceramics, one can cite a method in which a blowing agent is added to ceramic raw materials to cause foaming and obtain a bubble-forming body. If the foamed bubbles are left standing, they will rise to the surface or burst over time due to buoyancy. Here, as shown in Figure 8, if fine fibrous cellulose 20 is included together with the ceramic raw material 10 and the blowing agent 30, there is an effect of suppressing the rising and bursting of bubbles 40. This is thought to be because the fine fibrous cellulose 20 is dispersed in the foamed liquid, so the flow of bubbles 40 is hindered by the fine fibrous cellulose 20, and the fine fibrous cellulose 20 becomes part of the surface on which bubbles 40 are formed, making it difficult for bubbles 40 to disappear. In Figure 8, (a) is a bubble-forming body, showing bubbles 40 formed from the foaming agent 30, fine fibrous cellulose 20, and thickener 50 (hatched area), and (b) is a sintered body, showing pores 41 formed from the ceramics 11 by the sintering process.

[0028] (Ceramic raw materials) As ceramic raw materials, one or more can be selected and used from, for example, alumina, zirconia, mullite, cordierite, titania, sialon, carbon, silicon carbide, silicon nitride, spinel, nickel aluminate, aluminum titanate, calcium phosphate, etc. However, when using porous ceramics of this form as a bone graft material, it is preferable to use calcium phosphate.

[0029] As calcium phosphate, one or more types can be selected and used from, for example, hydroxyapatite, tricalcium phosphate, dicalcium phosphate, tetracalcium phosphate, octacalcium phosphate, calcium phosphate-based glass, etc. However, the use of β-type tricalcium phosphate (β-Ca3(PO4)2) (hereinafter also simply referred to as "β-TCP") is particularly preferred.

[0030] The ceramic raw material is preferably in the form of a powder with an average particle size of 500 μm or less, and more preferably in the form of a powder with an average particle size of 10 to 500 μm.

[0031] β-TCP powder is preferably prepared by the following method. First, calcium carbonate (CaCO3) and calcium hydrogen phosphate dihydrate (CaHPO4·2H2O) are mixed with pure water using a mixer such as a ball mill or kneader. This mixing is preferably carried out for 24 to 48 hours. The pure water can be at room temperature, but it is preferable to heat it to 70 to 90°C as this facilitates the dispersion of the powder.

[0032] Next, the mixture obtained from this mixing is dried. This drying is preferably carried out at, for example, 60-70°C. Furthermore, this drying is preferably carried out for 24-48 hours.

[0033] The dried material obtained by this drying process is then pulverized. This pulverization is preferably carried out until the average particle size is, for example, 0.3 to 0.5 μm. This pulverization can be carried out using grinding equipment such as an agate mortar and pestle, an automatic mortar and pestle, a stamp mill, a dry ball mill, or a hammer mill.

[0034] Next, the pulverized material obtained from this grinding is calcined. This calcination is preferably carried out at, for example, 700-800°C. In this case, the heating rate can be, for example, 3°C / min. This calcination is preferably carried out for 8-24 hours.

[0035] The calcined material obtained from this calcination is then crushed again. This crushing is preferably carried out until the average particle size is, for example, 0.3 to 0.5 μm. This crushing is also preferably carried out using the crushing equipment described above.

[0036] As described above, powdered β-TCP is obtained.

[0037] (Fine fibrous cellulose) In this invention, the fine fibrous cellulose functions as a foaming aid. Conventional porous ceramics were manufactured, for example, by foaming a foaming agent to obtain a bubble-forming body, and then sintering this bubble-forming body. On the other hand, in the embodiment of this invention, the fine fibrous cellulose acts to suppress the flow and disappearance of bubbles formed by foaming. This action reduces the uneven distribution of pores formed in the manufactured porous ceramics, and the formation of extremely large diameter pores is suppressed, making it suitable for use as a bone graft material.

[0038] As the fine fibrous cellulose added to the ceramic raw material, for example, multiple types of cellulose fibers with different fiber widths, cellulose fibers with a single fiber width, or cellulose fibers and aggregates of cellulose fibers can be used, and it is particularly preferable to use fine fibrous cellulose with an average fiber width of 3 to 100 nm. Cellulose fibers are thermally decomposable and have the property of disappearing by vaporizing when heated. When fine fibrous cellulose with an average fiber width exceeding 100 nm is used, the porous ceramics produced may have relatively large diameter pores, and may also have many pores that are irregularly shaped and deviate from a perfect sphere.

[0039] Here, we will explain the meaning of "multiple types of cellulose fibers with different fiber widths." In this embodiment, multiple types of cellulose fibers with different fiber widths refer to cases where there are multiple types of cellulose fibers, based on the premise that cellulose fibers with an average fiber width within a predetermined range are counted as one type, and cellulose fibers with an average fiber width outside this range are counted as another type.

[0040] As raw materials for fine fibrous cellulose, one or more types can be selected and used from wood pulp made from hardwoods, softwoods, etc., non-wood pulp made from straw, bagasse, etc., recycled paper pulp (DIP) made from recycled waste paper, waste paper, etc.

[0041] However, in order to avoid the inclusion of impurities as much as possible, it is preferable to use wood pulp. As for wood pulp, one or more types can be selected and used from chemical pulps such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), and mechanical pulp (TMP), etc. Hardwood kraft pulp may be bleached hardwood kraft pulp, unbleached hardwood kraft pulp, or semi-bleached hardwood kraft pulp. Similarly, softwood kraft pulp may be bleached softwood kraft pulp, unbleached softwood kraft pulp, or semi-bleached softwood kraft pulp. Furthermore, as mechanical pulp, one or more types can be selected and used from, for example, stone gland pulp (SGP), pressurized stone gland pulp (PGW), refiner gland pulp (RGP), chemigland pulp (CGP), thermo gland pulp (TGP), gland pulp (GP), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), refiner mechanical pulp (RMP), bleached thermomechanical pulp (BTMP), etc.

[0042] (Pre-processing) In producing fine fibrous cellulose, cellulose fibers can be pretreated with alkali treatment, enzyme treatment, acid treatment, oxidation treatment, beating, etc. By pretreating the pulp fibers prior to defibration, the number of defibration steps can be significantly reduced, thereby reducing the energy required for defibration.

[0043] Alkaline treatment prior to defibration partially dissociates the hydroxyl groups of the hemicellulose and cellulose molecules in the pulp, causing the molecules to become anionic. This weakens intramolecular and intermolecular hydrogen bonds, promoting the dispersion of cellulose fibers during defibration.

[0044] Examples of alkalis that can be used for alkaline treatment include sodium hydroxide, lithium hydroxide, potassium hydroxide, aqueous ammonia solution, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and benzyltrimethylammonium hydroxide, among other organic alkalis. However, from the viewpoint of manufacturing cost, sodium hydroxide is preferred.

[0045] Prior to defibration, enzymatic, acidic, or oxidative treatments can lower the water retention of the fine fibrous cellulose, increase its crystallinity, and improve its homogeneity. In this regard, a lower water retention of the fine fibrous cellulose makes it easier to dry, thus preventing cracking of the ceramic raw material during the drying of the mixture of ceramic raw material and fine fibrous cellulose. From this perspective, the water retention of the fine fibrous cellulose is preferably 350% or less, and more preferably 300% or less. The water retention can be arbitrarily adjusted through raw material selection, pretreatment, defibration, etc.

[0046] On the other hand, enzymatic, acid, and oxidation treatments decompose the amorphous regions of hemicellulose and cellulose in the pulp, thereby reducing the energy required for the micronization process and improving the uniformity and dispersibility of the fibers. Fiber uniformity is directly related to pore uniformity. Furthermore, these pretreatments increase the proportion of crystalline regions in the overall fiber, improving the dispersibility of the fine fibrous cellulose. However, since pretreatment reduces the aspect ratio of the fine fibrous cellulose, it is preferable to avoid excessive pretreatment.

[0047] The defibration of the raw material can be carried out by beating it using, for example, a homogenizer such as a beater, high-pressure homogenizer, or high-pressure homogenization device; a millstone-type friction machine such as a grinder or crusher; a single-screw kneader; a multi-screw kneader; a kneader refiner; or a jet mill. However, it is preferable to carry out the defibration using a refiner or a jet mill.

[0048] (physical properties, etc.) The degree of crystallinity of the fine fibrous cellulose is preferably 50% or higher, and more preferably 55% or higher. Furthermore, the degree of crystallinity is preferably 99% or lower, and more preferably 95% or lower. If the degree of crystallinity falls within the above range, the fine fibrous cellulose is suitable for use as a foaming aid. The degree of crystallinity can be arbitrarily adjusted, for example, by selecting raw materials, pre-treatment, defibration, etc.

[0049] Furthermore, the pulp viscosity of the fine fibrous cellulose is preferably 1.5 cps or higher, and more preferably 2.0 cps or higher. If the pulp viscosity is within the above range, the fine fibrous cellulose is suitable for use as a foaming aid.

[0050] The B-type viscosity of the slurry (1% concentration) obtained by dispersing fine fibrous cellulose in water is preferably 100 to 100,000 cps, more preferably 200 to 70,000 cps, and particularly preferably 500 to 50,000 cps. Keeping the B-type viscosity of the slurry within this range facilitates mixing with ceramic raw materials, drying of the mixture, and molding processes.

[0051] To form macropores with relatively large pore sizes, one could, for example, use cellulose fibers with a wider fiber width. However, it is also possible to increase the pore size by controlling the amount of additives such as dispersants. In addition, macropores can be formed using cellulose fiber aggregates or foaming agents. However, it is preferable to use cellulose fiber aggregates rather than foaming agents. Using cellulose fiber aggregates makes pore formation easier and helps to equalize the pore size.

[0052] (Foaming agent) The use of foaming agents (foaming methods) is currently preferred because it has the advantage of having many empirical rules. While any surfactant can be used as the foaming agent, nonionic surfactants are particularly preferred. Specifically, one or more of the following can be selected and used: polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene alkylamines, polyethylene glycol fatty acid esters, alkanolamides, polyethylene glycol / polypropylene glycol copolymers, etc. Furthermore, ethylene oxide can be added to these nonionic surfactants to create a foaming agent.

[0053] In particular, polyoxyethylene alkyl ethers are very low in toxicity and pose little harm to the human body. Furthermore, they exhibit weak effervescence, generating numerous moderately sized bubbles, and large-diameter pores do not tend to dominate, making them suitable as porous ceramics for bone graft applications.

[0054] The HLB value of the blowing agent is 7 to 16, preferably 8 to 15, and more preferably 9 to 14. The inventors have found that when the HLB value exceeds 16, the shape of the pores does not easily become spherical. This is probably because the blowing agent is hydrophobic, which destabilizes micelle formation. On the other hand, when the HLB value is less than 7, the effect of suppressing the surface tension of water is strong, resulting in the generation of many small-diameter pores. The HLB value was calculated according to Griffaine's method.

[0055] (Thickening agent) In this embodiment of the method for manufacturing porous ceramics, a thickening agent is added for the purpose of suppressing bubble bursting and making the shape of the bubbles rounded. Conventionally, when a mixed slurry containing ceramic raw materials and a blowing agent (this mixed slurry is usually mixed with a liquid such as water) is foamed, bubbles push aside the ceramic raw materials in the mixed slurry and form spherical shapes. However, if fine fibrous cellulose is dispersed in the mixed slurry, the dispersion stability of the fine fibrous cellulose suppresses the flow of the ceramic raw materials, so the bubbles do not become spherical but instead form angular shapes like polyhedra. Moreover, the angular shape becomes more pronounced in larger diameter bubbles. On the other hand, in this embodiment of the method for manufacturing porous ceramics, the mixed slurry contains a thickening agent in addition to ceramic raw materials, a blowing agent, and fine fibrous cellulose, so the formation of large diameter bubbles is suppressed, and as a result the formation of a large number of relatively small diameter bubbles, the bubbles become rounded. Furthermore, since the rise of air bubbles is suppressed by the thickening agent and fine fibrous cellulose, the bursting of air bubbles is also suppressed.

[0056] As a thickening agent, one or more types selected from the group consisting of polyhydric alcohols, polysaccharides, and water-soluble polymers can be used.

[0057] Examples of polyhydric alcohols that can be used include glycerin, propylene glycol, butylene glycol, pentanediol, dipropylene glycol, hexanediol, and heptanediol, but are not limited to these. Glycerin is particularly preferred from the viewpoint of thickening properties and dispersibility of fine fibrous cellulose.

[0058] Polysaccharides that can be used include, but are not limited to, quince seed, bee gum, xanthan gum, and hyaluronic acid. Hyaluronic acid is particularly preferred from the viewpoint of thickening properties and dispersibility of fine fibrous cellulose.

[0059] Examples of water-soluble polymers include, but are not limited to, polyvinyl alcohol, polyvinylpyrrolidone, carboxyvinyl polymer, polyethylene glycol, carrageenan, sodium carboxymethylcellulose, ammonium carboxymethylcellulose, pectin, gelatin, agar, xanthan gum, and other gelling agents, as well as glycerols, alkyl phosphate salts, alkali metal pyrophosphates, acrylic alkali thickeners, polyethylene oxide, xanthan gum, and sodium polyacrylate, which are also used as humectants. In particular, ammonium carboxymethylcellulose, when sintered, has a low ash content and is therefore suitable for use in bone graft materials.

[0060] The ratio of the thickener to 1 part by mass (oven-dry mass) of fine fibrous cellulose is 0.25 to 2.0 parts by mass, preferably 0.3 to 2 parts by mass, and more preferably 0.5 to 1.5 parts by mass. If the ratio exceeds 2.0 parts by mass, the fine fibrous cellulose will not be sufficiently dispersed, and if the ratio is less than 0.25 parts by mass, an uneven distribution of pores will occur in the porous ceramics.

[0061] (Formation process) The process for forming a bubble-forming body can be carried out using the following procedure, as an example: A foaming agent, fine fibrous cellulose, and a thickening agent are added to powdered ceramic raw materials, and foaming is performed to form a bubble-forming body. Adding an appropriate amount of water is recommended for foaming.

[0062] In addition to the procedure described above, the formation process can also be carried out according to the following procedure. Specifically, a dispersant is further added, and the dispersant, the fine fibrous cellulose, and the thickener are mixed to form a first mixture, and the ceramic raw material and the foaming agent are added to the first mixture and mixed to foam and form a bubble-forming body. This procedure makes it less likely for uneven distribution of bubbles to occur. As the dispersant, one or more water-soluble polymer compounds can be selected and used from among polyacrylic acid, polyacrylic acid derivatives such as polyacrylic acid salts and ammonium polycarboxylates.

[0063] However, when adding a dispersant, it is preferable to use a dispersant that has the function of dispersing both cellulose fibers and ceramic raw materials. Ammonium polyacrylate (PAA) is a preferred dispersant. PAA is used as a decoagulant for ceramic raw materials when a foaming agent is used for pore formation, but it has also been found to be useful when cellulose fibers are used as a foaming aid.

[0064] The concentration of PAA is preferably high, preferably 10% by volume or more of the total amount of the mixed slurry before foaming (the total amount of the mixed slurry with the dispersant added), more preferably 25-45% by volume, and particularly preferably 30-40% by volume. It is also possible to increase the amount added instead of increasing the concentration, but increasing the amount added increases the load on the subsequent drying process, requiring a longer drying time or a higher drying temperature. However, these measures make the ceramic raw material more prone to shrinkage, which can cause cracking.

[0065] On the other hand, if the PAA concentration is too high, the resulting porous ceramics tend to crumble easily.

[0066] For mixing, the ceramic raw material, fine fibrous cellulose, and dispersant are mixed together, a foaming agent is added to this mixture, and the mixture is further mixed using a mixer such as a ball mill or kneader. This mixing is preferably carried out for 5 to 10 minutes. This mixing operation is preferable if performed while applying ultrasound to promote foaming.

[0067] When 0.2 to 0.9 parts by mass, preferably 0.3 to 0.9 parts by mass, and more preferably 0.4 to 0.9 parts by mass are present per 1 part by mass of ceramic raw material, the shape of the pores becomes rounded, and the formation of ultra-macropores is suppressed, which is preferable. If the amount of fine fibrous cellulose exceeds 0.9 parts by mass per 1 part by mass of ceramic raw material, the contribution of the fine fibrous cellulose becomes strong, and there is a risk that a large number of bubbles with shapes other than spherical will be generated. Also, if the amount of fine fibrous cellulose is less than 0.2 parts by mass per 1 part by mass of ceramic raw material, the effect of adding fine fibrous cellulose is difficult to obtain.

[0068] Next, the mixed slurry obtained by this mixing may generate extremely large bubbles, so it is advisable to tap it to de-foam the large bubbles. After that, a dried body is formed by drying at a low temperature. The drying conditions can be as follows: The temperature is, for example, 35 to 70°C, preferably 38 to 42°C. The drying time is, for example, 2 to 5 days, preferably 3 days. In this embodiment, by using fine fibrous cellulose, it is possible to form micropores, macropores, and ultramicropores, so gentle drying is suitable. Note that if this drying is performed too rapidly, it will cause cracking of the ceramic raw material. The drying conditions can also be multi-stage as follows: For example, first the temperature is 35 to 45°C, preferably 38 to 44°C, and the drying time is 24 to 48 hours. Next the temperature is 65 to 75°C, preferably 68 to 72°C, and the drying time is 24 to 48 hours. The inventors have found that, in addition to the effects mentioned above, multi-stage drying imparts the effect of increasing the compressive strength of the resulting porous ceramics.

[0069] (Bubble retention rate) A mixed slurry can be defined as a liquid containing ceramic raw materials and a foaming agent, and may also contain a dispersant, a thickener, and fine fibrous cellulose. If the mixed slurry contains fine fibrous cellulose or a thickener, the bubbles will be maintained and less likely to disappear even if the bubble-forming material is left standing. The degree to which bubbles are maintained can be measured using an index called the bubble retention rate, as follows.

[0070] A beaker containing 64 ml of mixed slurry is subjected to ultrasound (43 Hz) for 5 minutes to obtain a bubble-forming body. This bubble-forming body is immediately poured into a 500 ml graduated cylinder, and the height of the bubbles (including the liquid portion) (initial bubble height (H0)) is measured. After standing for 60 minutes, the height of the bubbles (including the liquid portion) of the bubble-forming body is measured again (60-minute bubble height (H0)). 60 )) is measured. Then, the bubble retention rate is calculated using the following formula for bubble retention rate ([Formula 1]). The measurement is performed in a room at 1 atmosphere and 25°C. [Mathematics 1] Bubble retention rate (%) = Bubble height after 60 minutes (H 60 ) / Initial height of bubble (H0) × 100

[0071] The bubble retention rate of the bubble-forming material can be adjusted by the amount of fine fibrous cellulose and thickener added to the mixed slurry, preferably 60% or more, and more preferably 80% or more. If the bubble retention rate of the bubble-forming material is less than 60%, the resulting porous ceramic may have a low number of pores and may not be suitable for use as a bone graft material. In this case, if a mixed slurry is made without adding fine fibrous cellulose but with a thickener added, the height of the bubbles will decrease over time, resulting in a lower bubble retention rate than that of a mixed slurry with both fine fibrous cellulose and a thickener added. Also, if a mixed slurry is made with fine fibrous cellulose but without a thickener, many large-diameter, angular bubbles will be formed, which may not be in line with the effects required in this invention.

[0072] The B-type viscosity of the mixed slurry is preferably 1,000 to 25,000 cps, more preferably 5,000 to 24,000 cps, and more preferably 10,000 to 23,000 cps. If the B-type viscosity exceeds 25,000 cps, the fine fibrous cellulose may not be uniformly dispersed in the mixed slurry. On the other hand, if the B-type viscosity is less than 1,000 cps, an uneven distribution of pores in the porous ceramics is likely to occur.

[0073] (Sintering process) The bubble-forming material obtained by drying is then sintered. This sintering is carried out by heating the bubble-forming material. The heating is not particularly limited, but it is preferable to perform it in two or more stages to suppress cracking of the ceramics. For example, if the sintering process includes a constant temperature step of maintaining 950 to 1100°C for at least 0.5 to 24 hours, cracking of the porous ceramics can be suppressed. Another example is the more preferable two-stage sintering process, consisting of low-temperature sintering and high-temperature sintering. When sintering is performed in two stages, it is preferable that the sintering is performed at a low temperature of 180-300°C (preferably 200-250°C) followed by high-temperature sintering at 800-1100°C (preferably 1000-1100°C). In this configuration, the ceramic raw material is mainly sintered at low temperature, and foaming aids such as cellulose fibers are mainly vaporized and removed at high temperature. Because the low-temperature sintering precedes the removal of the foaming aids, the ceramic raw material is reliably solidified, thus ensuring the formation of small-diameter open pores.

[0074] The low-temperature sintering time is, for example, 2 to 6 hours, preferably 3 to 5 hours. The high-temperature sintering time is, for example, 40 to 300 minutes, preferably 40 to 240 minutes. By slowly sintering at a low temperature and then rapidly removing the foaming aid at a high temperature, cracking of the ceramic raw material can be prevented as much as possible. The heating rate can be, for example, 1 to 5°C / minute.

[0075] Furthermore, sintering in four stages is preferable. When sintering is performed in four stages, the first stage is sintering at 150-200°C (preferably 160-180°C) for 2-6 hours, the second stage is sintering at 250-350°C (preferably 280-320°C) for 2-6 hours, the third stage is sintering at 350-450°C (preferably 380-420°C) for 2-6 hours, and the fourth stage is sintering at 950-1100°C (preferably 1000-1050°C) for 0.5-24 hours. Among the four-stage sintering methods, a particularly preferred method is one having the following steps: a first heating step in which the temperature is raised at 4-5°C / min to 170-190°C and maintained for 3-4 hours; a second heating step in which the temperature is raised at 4-5°C / min to 290-310°C and maintained for 3-4 hours after the first heating step; a third heating step in which the temperature is raised at 4-5°C / min to 390-410°C and maintained for 3-4 hours after the second heating step; and a fourth heating step in which the temperature is raised at 4-5°C / min to 1000-1120°C and maintained for 3-4 hours after the third heating step. In this configuration, foaming agents such as cellulose fibers are mainly vaporized and removed during the first to third stages of sintering, and ceramic raw materials are sintered during the fourth stage of sintering. By gradually increasing the temperature, bubble-building agents and other contaminants are removed, and then the ceramic raw materials are sintered, ensuring the formation of large and small diameter pores.

[0076] The sintered body obtained after the sintering process and cooling can be used as is, or further processed (polished, cut, pressed, etc.) depending on the application to become a porous ceramic.

[0077] The ash content of the thickening agent is 5% or less, preferably 3% or less, and particularly preferably 1%. A thickening agent with an ash content exceeding 20% ​​may be unsuitable for use as a bone graft material. The ash content can be adjusted mainly by the amount of inorganic components in the thickening agent; it can be reduced by using a thickening agent with a low inorganic content. An example of a thickening agent with a low inorganic content is carboxymethylcellulose ammonium.

[0078] The ash content was measured in accordance with JIS P8251:2003.

[0079] (Porous ceramics) The porous ceramics of this form manufactured as described above have numerous pores. These pores consist of open pores that communicate with the surface of the porous ceramics and closed pores that exist inside the porous ceramics and do not communicate with the surface. Patent document, Japanese Patent Publication No. 63-40782, states that all sintered products had open pores without any closed pores. However, the inventors have found that with conventional methods (foaming methods) using a foaming agent as a foaming aid, the closed porosity can reach as high as 30%.

[0080] The porous ceramics of this form have a total porosity of 50% or more and 95% or less, preferably 60% or more and 90% or less, and more preferably 70% or more and 90% or less. If the total porosity exceeds 95%, it may be insufficient in strength for use as a bone graft material. On the other hand, if the total porosity is less than 50%, it may be difficult to use as a scaffold for good cell extension.

[0081] The closed porosity of the porous ceramic in this embodiment is preferably 0% or more and 5% or less, more preferably 1% or more and 3% or less. If the closed porosity exceeds 5%, it may become difficult for osteogenic cells to migrate into the porous ceramic.

[0082] Here, total porosity can be calculated as (total pore volume / volume of porous ceramic) × 100 (%), open porosity as (volume of open pores / volume of porous ceramic) × 100 (%), and closed porosity as (volume of closed pores / volume of porous ceramic) × 100 (%).

[0083] In this form of porous ceramic, the percentage of open porosity to total porosity is 70% or more, preferably 80% or more, and more preferably 90% or more, while the percentage of closed porosity to total porosity is kept below 30%, preferably below 20%, and more preferably below 10%. By increasing the percentage of open porosity to total porosity in this way, the percentage of open porosity can be kept at the same level as or higher than conventional materials without making the total porosity extremely high. Therefore, there is no risk of a decrease in the strength of the porous ceramic. In this regard, for example, in the case of bone graft material, the bone graft material is filled into the bone defect, reinforces the bone defect in the initial stage until the bone defect is repaired, and is absorbed into the living bone after the bone defect has been repaired. Therefore, the strength of the bone graft material is extremely important. Furthermore, by increasing the percentage of open porosity in this way, it becomes possible for micro-open pores and macro-open pores to coexist, as will be explained next.

[0084] In this embodiment of porous ceramics, the pores consist of first micropores (first microopen pores and first microclosed pores) with a pore diameter in the range of greater than 1 μm and 30 μm or less, preferably greater than 1 μm and 20 μm or less, and more preferably greater than 1 μm and 10 μm or less, and macropores (macroopen pores and macroclosed pores) with a pore diameter exceeding the aforementioned predetermined range. By having micropores and macropores, particularly microopen pores and macroopen pores, coexist in this way, when this embodiment of porous ceramics is used as a bone graft material, for example, it becomes a porous ceramic that can accommodate the migration and fixation of both blood vessels and cells, as well as nutrients and proteins.

[0085] The pore size of the macropores is greater than 30 μm and less than or equal to 1000 μm, preferably greater than 35 μm and less than or equal to 1000 μm, and more preferably greater than 40 μm and less than or equal to 1000 μm.

[0086] In this form of porous ceramic, more preferably, a second micropore with a pore diameter smaller than the range of the first micropore and a supermicropore (supermicro open pores and supermicro closed pores) with a diameter smaller than the range of the second micropore coexist. In this form, there are four types of pores: supermicropores, first micropores, second micropores, and macropores. For example, when this form of porous ceramic is used as a bone graft material, it is more in line with the demand. However, since the applications of supermicropores are limited, they do not need to be distributed in large quantities.

[0087] In porous ceramics, the number of second micropores can be adjusted by changing the proportion of fine fibrous cellulose and thickener during the formation process, and the pore diameter is greater than 0.3 μm and less than or equal to 1 μm, preferably greater than 0.4 μm and less than or equal to 1 μm. Furthermore, the ultramicropores are formed when the aforementioned cellulose particles (foaming aid) are burned away at high temperatures during the sintering process. In addition, the pore diameter of the above-mentioned minute diameter range, i.e., the pore diameter of the ultramicro open pores, is preferably 0.3 μm or less.

[0088] Micropores are formed when bubbles created by stirring a foaming agent into ceramic raw materials, which mainly contain a thickening agent, are sintered. Furthermore, if fine fibrous cellulose is included, the micropores become even smaller in diameter. On the other hand, macropores are formed when large-diameter bubbles, which are formed by the coalescence of micropore-sized bubbles, are sintered. Depending on the amount of foaming agent, fine fibrous cellulose, ceramic raw materials, and thickening agent added, as well as the mixing and tapping of the mixture containing these, the bubbles may become small or large in diameter.

[0089] In this form of porous ceramic, the pore roundness is preferably 0.2 or less, more preferably 0.15 or less, and more preferably 0.1 or less. Pores with a roundness exceeding 0.2 may not allow for smooth migration and settlement of osteogenic cells. The method for measuring roundness is as follows: Ten pores with a diameter in the range of 50 to 600 μm are randomly selected from an SEM image (50x magnification). For each selected pore, the longest diameter (major axis) and the shortest diameter (minor axis) are measured, and the ratio of the major axis to the minor axis is determined. The major axis is then normalized to 1, and the length of the minor axis (normalized minor axis) is calculated from this ratio. This is done for all 10 points. The average value of the normalized minor axes of the 10 points is calculated. The roundness is determined by the following formula. (Roundness) = (1 - Mean value of normalized minor axis) / 2 The closer the roundness is to 0, the closer the pore is to being perfectly round.

[0090] The porous ceramics of this form have a compressive strength of 1 MPa or more, preferably 1.5 to 10 MPa, and more preferably 2 to 10 MPa. If the compressive strength is less than 1 MPa, handling during surgery will be poor. On the other hand, there is no particular upper limit to the compressive strength, but for example, if it is 10 MPa or less, bone formation will occur without resistance and bone defect repair will be performed smoothly, which is preferable. The compressive strength is measured in accordance with JIS-R1608 (2003) at a crosshead speed of 0.5 mm / min.

[0091] The porous ceramics of this form, manufactured through a sintering process, are not particularly limited in shape, but can take the form of a rectangular prism, for example. An example of a rectangular prism is 9 cm wide x 6 cm deep x 3 cm high. Other shapes such as cubes (e.g., 5 cm per side), hexahedrons, spheres, etc., can also be provided. To obtain porous ceramics of this size, it is advisable to manufacture a large porous ceramic and then cut it to the appropriate size. Manufacturing a large piece and then cutting it into smaller pieces results in more homogenized porous ceramics.

[0092] The porous ceramics of this form have a pore size distribution curve with a maximum value (maximum value) in the range of 0.1 to 1 μm, more preferably in the range of 0.11 to 1 μm. Porous ceramics with a maximum value of less than 0.1 μm may have limited material flow into the pores, potentially suppressing the speed of bone formation. The pore size distribution curve, as explained with reference to Figure 9, plots the relationship between the pore size and the total volume of the pores (ml / g) formed in porous ceramics, with the horizontal axis representing the pore size (μm) and the vertical axis representing the total volume of the pores (ml / g). The total volume of the pores refers to the sum of the volumes of individual pores at a specific pore size.

[0093] When the forming process involves mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent and foaming them to form a bubble-forming body, the total volume of pores with a diameter greater than 0.3 μm and less than or equal to 1.0 μm is 60% or more, more preferably 70% or more, and even more preferably 80% or more of the total volume of all pores in the porous ceramic, resulting in the formation of a large number of small-diameter pores and suppressing the uneven distribution of pores, which is preferable.

[0094] Furthermore, porous ceramics in which the total volume of pores with a diameter greater than 0.3 μm and 1.0 μm or less is 60% or more of the total volume of all pores in the porous ceramics, and the total volume of pores with a diameter of 0.3 μm or less is 1.0% or less of the total volume of all pores in the porous ceramics, are also preferable as they do not have an excessively large proportion of ultramicropores.

[0095] (Application) This form of porous ceramic can preferably be used as a bone graft material. However, in addition to being a biomaterial such as a bone graft material, it can also be used as an additive in, for example, filters, electrodes for fuel cells and gas / humidity sensors, catalyst carriers, thermal insulation materials, oral drugs, processed foods, beverages, various adsorption column materials, cosmetics, toothpaste, deodorants, odor removers, bath additives, facial cleansers, shampoos, toiletries, and other products.

[0096] (others) In this specification, open porosity is the value measured by the Archimedes method. Closed porosity is the value obtained by subtracting open porosity from total porosity, and total porosity is the value calculated using the bulk density obtained by the Archimedes method and the calculated density (theoretical density).

[0097] In this specification, "bone graft material" refers to porous ceramics used as a biological implant material for replacing bone, teeth, tooth roots, etc.

[0098] In this specification, the average fiber width (diameter) of cellulose fibers, including fine fibrous cellulose, is the value measured as follows. First, 100 ml of an aqueous dispersion of cellulose fibers with a solid content concentration of 0.01-0.1% by mass is filtered through a Teflon® membrane filter, and the solvent is replaced once with 100 ml of ethanol and three times with 20 ml of t-butanol. Next, the dispersion is freeze-dried and coated with osmium to obtain the sample. This sample is observed using an electron microscope (SEM) at a magnification of 5000x, 10000x, or 30000x depending on the width of the constituent fibers. Specifically, two diagonal lines are drawn on the observed image, and three arbitrary straight lines are drawn passing through the intersection of the diagonals. Furthermore, the width of a total of 100 fibers that intersect these three straight lines is measured visually. The median diameter of the measured values ​​is then taken as the average fiber width.

[0099] In this specification, the degree of crystallinity is a value measured by X-ray diffraction in accordance with the "General Rules for X-ray Diffraction Analysis" of JIS-K0131 (1996). Cellulose fibers have amorphous and crystalline portions, and the degree of crystallinity refers to the proportion of the crystalline portion in the entire cellulose fiber.

[0100] In this specification, pulp viscosity is measured in accordance with JIS-P8215 (1998). A higher pulp viscosity indicates a higher degree of polymerization of cellulose fibers.

[0101] In this specification, the B-type viscosity of the fine fibrous cellulose slurry is a value measured in accordance with the "Method for Measuring the Viscosity of Liquids" of JIS-Z8803 (2011). The measurement conditions for the B-type viscosity were a temperature of 20°C and a rotation speed of 12 rpm.

[0102] In this specification, the water retention capacity is a value measured according to the water retention capacity measurement method in accordance with JAPAN TAPPI No.26:2000. [Examples]

[0103] Next, embodiments of the present invention will be described. Porous ceramics (porous materials) were manufactured from β-TCP powder and fine fibrous cellulose, and tests were conducted to measure the average pore size, porosity, open porosity, closed porosity, compressive strength, porosity distribution, and bulk density of the pores present in the obtained porous materials. In this test, a fine fibrous cellulose slurry of "ELEX®-S" (average fiber width 54 nm, 3 mass%) manufactured by Daio Paper Corporation was used as the fine fibrous cellulose.

[0104] (Synthesis of β-TCP powder) First, 0.1125 mol of calcium carbonate (99.5% purity, Wako Pure Chemical Industries, Wako Special Grade) and 0.225 mol of calcium hydrogen phosphate dihydrate (98.0% purity, Pure Special Grade) (Ca / Pmol ratio = 1.50) were added to 450 ml of pure water at 80°C, and the mixture was wet-mixed for 24 hours using a zirconia pot (Nikkatoh) and zirconia balls (Nikkatoh, 600 g of 5 mm diameter balls and 900 g of 10 mm diameter balls). Next, this mixture was dried at 70°C for 24 hours. The resulting dried material was pulverized using an agate mortar and pestle, and then calcined at 750°C for 10 hours in an air atmosphere. The heating rate was 3°C / min. The resulting calcined material was pulverized into a powder (β-TCP powder). An SEM image of this powder is shown in Figure 1.

[0105] The XRD pattern of the obtained β-TCP powder is shown in Figure 2, and the FT-IR spectrum is shown in Figure 3. From the XRD pattern, the diffraction pattern of the obtained β-TCP powder matched that of the β-TCP crystal structure. Furthermore, since the peaks seen in byproducts were not observed, the obtained β-TCP powder was identified as β-TCP. From the FT-IR results, the PO present in β-TCP was identified. 4 The angular vibration is 420 cm -1 ,580cm -1 Nearby, PO 4 The extension and vibration range is 800-1200cm -1 Because they were found in close proximity to each other, the obtained β-TCP powder was identified as β-TCP.

[0106] (Creation of porous ceramics) Test samples and reference samples were manufactured using the following procedure. <Test Example 1> 1. Preparation process for foamed slurry (bubble-forming material) 30 ml of 30% ammonium polyacrylate (PAA, Wako Grade 1) aqueous solution, 0.9 g of ammonium carboxymethylcellulose (CMC-NH4, Wako Pure Chemical Industries, Ltd., chemical grade), and 30 ml of 3% by mass fine fibrous cellulose (corresponding to "CNF aqueous dispersion 3%" in Table 1) were placed in a container and stirred with a stirrer for 1 hour. 30 g of the aforementioned β-TCP powder was added and stirred with a hand mixer for 5 minutes while applying ultrasonic waves to ensure uniform dispersion. The ultrasonic waves were applied by immersing the container in an ultrasonic water bath (AS ONE Corporation). Subsequently, 4 ml of foaming agent was added to the container and stirred for 5 minutes to induce foaming and obtain a bubble-forming material. A nonionic surfactant (NIKKOL, BT-7) was used as the foaming agent.

[0107] 2. Forming Process and Sintering Process The obtained bubble-forming material was poured into a square container (60 mm long x 60 mm wide), tapped to a height of 25 mm, and then dried. The drying conditions were as follows: the tapped foam was left at 40°C for 48 hours, and then left at 70°C for 24 hours to obtain a dried body. The obtained dried body was sintered. The sintering process was carried out in multiple stages, specifically as follows: In the first stage, the temperature was raised at a rate of 5°C / min to 180°C and maintained at this temperature for 4 hours. Next, in the second stage, the temperature was raised at a rate of 5°C / min to 300°C and maintained at this temperature for 4 hours. Furthermore, in the third stage, the temperature was raised at a rate of 5°C / min to 400°C and maintained at this temperature for 4 hours. In addition, in the fourth stage, the temperature was raised at a rate of 5°C / min to 1000°C and maintained at this temperature for 4 hours. After that, it was allowed to cool to obtain the porous ceramic of Test Example 1.

[0108] <Reference example 1> 1. Preparation process for foamed slurry 30 ml of 30% ammonium polyacrylate (PAA, Wako Grade 1) aqueous solution and 0.9 g of ammonium carboxymethylcellulose were placed in a container and stirred with a stirrer for 1 hour. 30 g of the aforementioned β-TCP powder was added and stirred with a hand mixer for 5 minutes while applying ultrasonic waves to ensure uniform dispersion. The ultrasonic waves were applied by immersing the container in an ultrasonic water bath. Subsequently, 4 ml of foaming agent was added to the container and stirred for 5 minutes to induce foaming. A nonionic surfactant was used as the foaming agent.

[0109] 2. Forming Process and Sintering Process The forming and sintering processes were carried out using the same operating procedures as described in "2. Forming and Sintering Processes" of Test Example 1 above, to obtain the porous ceramics of Reference Example 1.

[0110] <Reference example 2> 1. Preparation process for foamed slurry 30 ml of a 30% ammonium polyacrylate aqueous solution and 30 ml of 3% by mass fine fibrous cellulose were placed in a container and stirred with a stirrer for 1 hour. 30 g of the aforementioned β-TCP powder was added and stirred with a hand mixer for 5 minutes while applying ultrasonic waves to ensure uniform dispersion. The ultrasonic waves were applied by immersing the container in an ultrasonic water bath. Then, 4 ml of foaming agent was added to the container and stirred for 5 minutes to induce foaming. A nonionic surfactant was used as the foaming agent.

[0111] 2. Forming Process and Sintering Process The forming and sintering processes were carried out using the same operating procedures as described in "2. Forming and Sintering Processes" of Test Example 1 above, to obtain the porous ceramics of Reference Example 2.

[0112] <Reference example 3> 1. Preparation process for foamed slurry 30 ml of a 30% ammonium polyacrylate aqueous solution and 30 g of the aforementioned β-TCP powder were placed in a container and stirred with a hand mixer for 5 minutes while applying ultrasound to ensure uniform dispersion. The ultrasound was applied by immersing the container in an ultrasonic water bath. Then, 4 ml of foaming agent was added to the container and stirred for 5 minutes to induce foaming.

[0113] 2. Forming Process and Sintering Process The forming and sintering processes were carried out using the same operating procedures as described in "2. Forming and Sintering Processes" of Test Example 1 above, to obtain the porous ceramics of Reference Example 3.

[0114] Table 1 shows the reagents and other materials used in the aforementioned test examples and reference examples.

[0115] [Table 1]

[0116] The porous ceramics obtained using the above procedure were cut horizontally to divide each piece in half vertically, resulting in two pieces (upper and lower). SEM images of the upper and lower pieces of the test example and reference example are shown in Figures 4-7, respectively.

[0117] Test Example 1 ,Reference examples 1~3 For this material, the total porosity A, open porosity B, closed porosity C, the percentage of open porosity to total porosity (B / A), bulk density, ash content, and compressive strength were measured. The measurement results are shown in Table 2.

[0118] [Table 2]

[0119] Pore ​​size distribution was measured for the test example and reference example. The measurement results are shown in Figure 9.

[0120] Next, test examples and reference The bubble retention rate was measured for each example. The measurement results are shown in Table 3.

[0121] [Table 3]

[0122] Test example 1 This resulted in a higher bubble retention rate compared to Reference Example 2. [Industrial applicability]

[0123] The present invention relates to a method for producing porous ceramics that can be used as bone graft material, etc., and to a porous ceramic that can be used as such.

Claims

1. The process includes a forming step of mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent to foam and form a bubble-forming body. The aforementioned fine fibrous cellulose has an average fiber width of 3 to 100 nm. The amount of fine fibrous cellulose is 0.2 to 0.9 parts by mass per 1 part by mass of ceramic raw material. The ratio of the thickening agent to 1 part by mass (dry mass) of the fine fibrous cellulose is 0.25 to 2.0 parts by mass. A method for producing porous ceramics characterized by the following:

2. The porous ceramics are The total volume of pores with a diameter greater than 0.3 μm and less than or equal to 1.0 μm is 60% or more of the total volume of all pores in the porous ceramic. A method for producing porous ceramics according to claim 1.

3. The thickening agent is one or more selected from water-soluble polymers. A method for producing porous ceramics according to claim 1.

4. The bubble retention rate of the bubble-forming body is 90% or more. A method for producing porous ceramics according to claim 1. Here, the stomatal maintenance rate is the value obtained by the following formula ([Equation 1]). [Mathematics 1] Bubble retention rate (%) = Bubble height after 60 minutes (H ６０ ) / Initial height of the bubble (H ０ ) × 100

5. The aforementioned forming step involves mixing powdered ceramic raw materials, a foaming agent, fine fibrous cellulose, and a thickening agent to obtain a mixed slurry, and then foaming the mixed slurry to form a bubble-forming body. The B-type viscosity of the mixed slurry is 1,000 to 25,000 cps. A method for producing porous ceramics according to claim 1.

6. The porous ceramic has a pore size distribution curve with a maximum value within the range of 0.1 to 1 μm. A method for producing porous ceramics according to claim 1.

7. The porous ceramic has a total porosity of 50% or more and 90% or less, and a closed porosity of 0% or more and 5% or less. A method for producing porous ceramics according to claim 1.

8. The roundness of the porous ceramic is 0.1 or less. A method for producing porous ceramics according to claim 1.

9. The foaming agent is a nonionic surfactant. A method for producing porous ceramics according to claim 1.

10. The ash content of the aforementioned thickener is 5% or less. A method for producing porous ceramics according to claim 1.

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