JP4578324B2 - Method for producing porous ceramic molded body - Google Patents

Description

  The present invention relates to a porous ceramic molded body, and more particularly to a porous ceramic molded body having pores arranged in one direction and linearly, and a method for manufacturing the same.

  Since ceramics are excellent in heat resistance and chemical resistance, in recent years, porous ceramic molded bodies having a large number of pores in a ceramic substrate are widely used as various filter materials and catalyst support materials. .

  For example, Japanese Patent Application Laid-Open No. 2002-45627 describes a dust collection filter in which alumina fibers are bonded with an inorganic binder. Japanese Patent Application Laid-Open No. 2004-299993 discloses a porous metal ceramic in which pores are formed by impregnating Si into a preform containing carbon fibers and a binder and heating the air in the air to eliminate the carbon fibers. A composite material is disclosed. In this type of conventional porous ceramic molded body, pores having a three-dimensional structure are formed in the ceramic substrate.

  On the other hand, recently, due to the increase in environmental protection, porous ceramic filters are used for automobile exhaust gas treatment and water purification treatment, and are expected especially as exhaust gas purification devices from diesel engines. In these applications, it is important that the pores penetrate in one direction and that the pore diameter is 10 μm or less and constant, rather than the large number of pores as in conventional filters. It is said that.

  As a porous ceramic suitable for such an application, Japanese Patent Application Laid-Open No. 11-13987 discloses a method of accumulating a plurality of rod-shaped ceramic molded bodies in one direction and then compressing them to form a gap between the ceramic molded bodies. A method is disclosed in which a precursor having a unidirectional through hole derived from is formed and sintered. However, although the pores formed by this method penetrate in one direction, it is difficult to control the pore diameter, and the pore diameter of the pores that can actually be manufactured is up to several tens of μm.

JP 2002-45627 A JP 2004-299993 A Japanese Patent Application Laid-Open No. 11-13987

  An object of the present invention is to provide a porous ceramic molded body having a pore diameter of 10 μm or less and constant, having a large number of pores penetrating in one direction, and suitable as a filter, and a method for producing the same. To do.

  In order to achieve the above object, a porous ceramic molded body provided by the present invention has a plurality of straw-shaped pores that penetrate linearly in one direction from one end to the other end in a ceramic substrate. The pore diameters of the fine pores are substantially the same and 10 μm or less. In the porous ceramic molded body of the present invention, the porosity is preferably 20 to 90%.

  The first method for producing a porous ceramic molded body provided by the present invention includes a step A1 of kneading ceramic powder, organic fibers or carbon fibers having a predetermined length and diameter, and an organic binder, and stretching the kneaded product. A process B1 for orienting the fibers in one direction, a process C1 for aligning and forming a plurality of the obtained thin rod-shaped bodies aligned in the axial direction, and simultaneously removing the organic binder by calcining the obtained rod-shaped molded bodies and the fibers A step D1 for burning and disappearing, a step E1 for firing the rod-shaped compact from which the fibers have been disappeared and sintering the ceramic, and a step F1 for cutting the resulting rod-shaped sintered body to the length of the fiber or less. It is characterized by including.

  Further, the second production method of the porous ceramic molded body according to the present invention includes a step A2 of kneading ceramic powder, glass fiber or organic fiber having a predetermined length and diameter and dissolved with an acid, and an organic binder, Step B2 for stretching the kneaded material and orienting the fibers in one direction; Step C2 for aligning and forming a plurality of the obtained thin rod-like bodies in the axial direction; and calcining the obtained rod-like shaped body by organic firing Step D2 for removing the binder, Step F2 for cutting to less than the length of the fiber using the calcined rod-shaped body, Step G2 for dissolving and removing the fiber in the cut rod-shaped body with acid, and disappearance of the fiber And a step E2 of firing the rod-shaped formed body and sintering the ceramic.

  A third method for producing a porous ceramic molded body according to the present invention includes a step A3 of kneading ceramic powder, glass fibers having a predetermined length and diameter, and an organic binder, and stretching the kneaded product to combine the fibers. Step B3 for orienting in a direction, Step C3 for aligning and forming a plurality of the obtained thin rod-like bodies in the axial direction, and firing the obtained rod-like shaped body to make fibers between the ceramic powder particles of the shaped body It includes a step E3 of sintering the ceramic simultaneously with the melt impregnation, and a step F3 of cutting the obtained rod-shaped sintered body to a length of fiber or less.

  In the first, second, and third manufacturing methods of the porous ceramic molded body according to the present invention, the stretched kneaded product is cut in each of the steps B1, B2, or B3, and the cut product is axially cut. It is preferable to repeat the operation of stretching a plurality of times after aligning and accumulating a plurality of times.

  According to the present invention, since the fibers having a predetermined diameter oriented in one direction disappear and the pores are formed, the pores are straw-like pores penetrating in one direction, and the pore diameter is 10 μm or less and constant. A porous ceramic molded body having a large number of pores can be provided.

  Therefore, the porous ceramic molded body of the present invention can be used for exhaust gas purification and water treatment filters, catalyst carriers, highly air-permeable molded bodies, etc., and particularly when used as a filter, the pressure loss is small and the processing speed is low. Therefore, it is suitable as a filter for purifying an exhaust gas from a diesel engine.

  The method for producing the porous ceramic molded body of the present invention will be described according to a first method using organic fibers or carbon fibers. The first method is a process A1 for kneading ceramic powder, fibers, and an organic binder, a process B1 for stretching the kneaded material and orienting the fibers in one direction, and a plurality of the obtained thin rods aligned in the axial direction. Forming step C1, preliminarily firing the rod-shaped compact to decombust the fibers together with the binder, step E1 firing the rod-shaped compact to sinter the ceramic, and the resulting rod-shaped firing And a step F1 of cutting to a length equal to or less than the length of the fiber using the bonded body.

First, in the step A1, the ceramic powder, fiber, and organic binder are sufficiently kneaded. The ceramic powder constitutes the base of the porous ceramic molded body of the present invention, and is alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), silicon carbide (SiC), mullite, cordier. From powder such as light, it can be appropriately selected and used according to the application.

  As the fiber to be kneaded with the ceramic powder, any fiber can be used without limitation as long as it can be burned away in the subsequent step E of debinding. For example, organic synthetic fibers such as vinylon, rayon, polynosic, cupra, acetate, triacetate, promix, nylon, aramid, vinylon, vinylidene, polyvinyl chloride, polyester, acrylic, polyethylene, polypropylene, polyurethane, polyclar, silk and hemp Organic natural fibers, carbon fibers, and the like can be used.

  The organic binder is for temporarily bonding the ceramic powder and the fiber to maintain a predetermined shape, and may be one that is usually used for forming the ceramic powder. For example, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol (PVA), starch and the like can be used. In the usual case, water is added together with the organic binder and kneaded. The kneading means is not particularly limited, and for example, a vacuum kneader or a kneader can be used.

  In the next step B1, the kneaded product obtained in the step A1 is stretched to orient the fibers in one direction. That is, when the kneaded material of ceramic powder, fiber, and organic binder is stretched, the fiber is gradually oriented along the stretching direction. In order to facilitate the orientation of the fibers, the length of the fibers is preferably 20 mm or less, more preferably 5 to 10 mm. Further, it is preferable that the length to be extended is as long as possible. For example, it is desirable to extend the length to 1000 times or more of the original length.

  In this step B1, in order to easily and efficiently stretch the kneaded product to a desired length, the kneaded product once stretched is cut and a plurality of the cut products are accumulated in the axial direction or stretched. It is preferable to repeat the operation of folding and further stretching the kneaded material a plurality of times. By repeating this operation a plurality of times, almost all the fibers in the kneaded product can be regularly orientated reliably in one direction.

  In the next step C1, a plurality of the thin rod-like bodies obtained in the step B1 are accumulated in the axial direction and formed into a rod shape. As a molding method, for example, press molding, piston-type extrusion molding, or the like can be used. By this step C1, a rod-shaped molded body in which a large number of dispersed fibers are oriented in one direction is obtained.

In the next step D1, the rod-shaped molded body obtained in the step C1 is dried as usual to remove moisture, and then calcined to remove the organic binder. Since cracking tends to occur when drying is carried out rapidly, it is preferable to dry at room temperature first and then heat-dry at a temperature of about 110 ° C. In addition, since the calcining temperature for removing the normal organic binder is about 1000 ° C., and this temperature is higher than the combustion temperature of the organic fiber or carbon fiber to be used, in this step D1, the organic fiber or carbon fiber is It burns and becomes CO ₂ , which is released from the gap between the molded bodies and completely disappears. As a result, straw-like pores are formed at the locations where the fibers have disappeared.

  Thereafter, the molded body that has been calcined to burn and extinguish the fibers is fired at a temperature equal to or higher than the sintering temperature of the ceramic in step E1 to obtain a sintered body. Sintering conditions vary depending on the ceramic powder to be used, but usually a sintered body can be obtained by firing at 1500 to 1600 ° C. for about 2 hours.

  In the next step F1, the rod-like sintered body obtained in the step E1 is cut according to the target product. The cutting length (product length) needs to be shorter than the length of the fibers used in order to obtain pores that penetrate linearly in one direction from one end to the other end of the ceramic substrate, and It is preferable to cut it to ½ or less of the length of the used fiber because the probability of penetrating pores increases. In this way, the porous ceramic molded body according to the present invention can be obtained.

  Moreover, in the manufacturing method of the porous ceramic molded body of this invention, glass fiber can also be used in addition to the above-mentioned organic fiber or carbon fiber. That is, as a method for producing a porous ceramic molded body using glass fibers, in the second method of the present invention, glass fibers or organic fibers that dissolve with acid are used, and this is dissolved and removed with acid after calcination. To form pores. In the third method, glass fibers are used, and pores are formed by melting and impregnating the glass fibers between the ceramic powder particles of the molded body during firing.

  Specifically, the steps until the rod-shaped molded body is obtained by the second and third methods, that is, the steps A2, B2 and C2 of the second method and the steps A3, B3 and C3 of the third method are as follows. The same as steps A1, B1 and C1 of the first method. In addition, as a glass fiber which melt | dissolves with the acid used with a 2nd method, there exist borosilicate glass etc., for example. Moreover, as an organic fiber which melt | dissolves in an acid, there exist nylon, rayon, and an acetate, for example, and it can melt | dissolve with a sulfuric acid.

  In the second method, the rod-shaped molded body obtained through the steps A2, B2 and C2 or the steps A3, B3 and C3 is dried in the next step D2, as in the step D1 of the first method. After removing the water, the organic binder is removed by calcination. Next, in step F2, as in step F1 of the first method, the rod-shaped molded body is cut to the length of the fiber or less. Thereafter, the glass fibers that have not disappeared in the step D2 (and the organic fibers if they remain) are dissolved and removed with an acid, whereby straw-like pores can be formed at the locations. Finally, in step E2, as in step E1 of the first method, firing is performed to obtain a sintered body.

  In the third method, the obtained rod-shaped molded body is then fired in step E3 to obtain a sintered body in the same manner as in step E1 of the first method. At the same time, since the glass fibers in the molded body are melted and impregnated between the ceramic powder particles of the molded body, straw-like pores are formed at the locations where the glass fibers have disappeared. Thereafter, in step F3, a porous ceramic molded body is obtained by cutting the rod-shaped sintered body to a length equal to or less than the length of the fiber in the same manner as in step F1 of the first method.

  Since the sintering temperature of the ceramic is sufficiently higher than the melting temperature of the glass fibers, it is possible to melt and impregnate all the glass fibers by firing in the step E3. Further, prior to the step E3, a step D3 of calcination to remove the organic binder in advance may be provided in the same manner as the step D1 of the first method. In that case, a part of the glass fiber may be melted and impregnated in the molded body by calcination, but in order to completely melt and impregnate the glass fiber, the firing in the step E3 is necessary.

  In the porous ceramic molded body of the present invention thus obtained, the portions where the fibers disappeared by combustion, dissolution, and melt impregnation remain as pores. Accordingly, the pores formed in the ceramic substrate are straw-shaped pores that penetrate linearly from one end to the other end of the ceramic substrate in one direction. Further, since the pore diameter of the straw-shaped pores substantially corresponds to the diameter of the lost fiber (there is shrinkage during firing), all the pores have substantially the same pore diameter. In addition, the pore diameter of the straw-shaped pores can be easily controlled by changing the diameter of the fiber used, and the straw-shaped pores having a pore diameter of 10 μm or less, which has been impossible in the past, can be easily obtained.

  The porosity of the porous ceramic molded body is not particularly limited, but is preferably 20 to 90% in applications such as filters.

[Example 1]
500 g of alumina powder having an average particle size of 0.5 μm, 66.5 g of vinylon fiber having a diameter of 8 μm and a length of 3 mm, and 2.5 g of methylcellulose were mixed with 127.5 g of water and kneaded well using a three-roller. . The obtained kneaded material was divided into five equal parts and each was stretched into a rod shape having a length of 40 cm. The stretched kneaded product was cut into four pieces, and a plurality of the four cut products were aligned in the axial direction and further stretched to 40 cm. This operation was repeated 5 times to produce a thin rod-like body.

  A plurality of the thin rod-like bodies thus produced were accumulated in the mold with the axial direction aligned, and press-molded at a pressure of 100 MPa. The molded body was dried at room temperature for 24 hours, and then further heated and dried at 110 ° C. for 24 hours. Next, after calcining at 1000 ° C. for 1 hour, it was fired at 1500 for 2 hours to obtain a sintered body. The obtained rod-shaped sintered body was cut and processed to obtain a porous alumina molded body having both end faces of 1 cm square and a length of 1 mm.

  This porous alumina molded body has a plurality of straw-shaped pores that are linearly penetrated in one direction from one end to the other end in the alumina substrate, and the diameter of the straw-shaped pores is almost all. It was 8 μm. Further, the porosity of the porous alumina molded body was 30% when calculated with the true specific gravity of alumina being 3.9.

[Example 2]
500 g of alumina powder having an average particle diameter of 0.5 μm, 143 g of borosilicate glass fiber having a diameter of 6 μm and a length of 6 mm, and 2.5 g of methylcellulose are mixed with 127.5 g of water and mixed well using a three-roller. did. The obtained kneaded material was divided into five equal parts and each was stretched into a rod shape having a length of 40 cm. The stretched kneaded product was cut into four pieces, and the four cut products were aligned and laminated, and further stretched to 40 cm. This operation was repeated 5 times to produce a thin rod-like body.

  A plurality of thin rod-like bodies produced in this way were aligned in the axial direction, and press-molded at a pressure of 100 MPa. The molded body was dried at room temperature for 24 hours, further dried at 110 ° C. for 24 hours, and calcined at 750 ° C. for 2 hours. The molded body after calcination was cut, and both end faces were processed into 1 cm square and 1 mm length. The cut molded body was immersed in an acid to dissolve and remove the acid-dissolved glass fiber, and then sintered by firing at 1500 ° C. for 2 hours to obtain a porous alumina molded body.

  This porous alumina molded body has a plurality of straw-shaped pores that are linearly penetrated in one direction from one end to the other end in the alumina substrate, and the diameter of the straw-shaped pores is almost all. It was 6 μm. Further, the porosity of the porous alumina molded body was 30% when calculated with the true specific gravity of alumina being 3.9.

[Example 3]
500 g of alumina powder having an average particle size of 0.5 μm, 143 g of E glass fiber having a diameter of 6 μm and a length of 6 mm, and 2.5 g of methylcellulose were mixed with 127.5 g of water, and kneaded well using a three-roller. The obtained kneaded material was divided into five equal parts and each was stretched into a rod shape having a length of 40 cm. The stretched kneaded product was cut into four pieces, and the four cut products were aligned and laminated, and further stretched to 40 cm. This operation was repeated 5 times to produce a thin rod-like body.

  A plurality of thin rod-like bodies produced in this way were aligned in the axial direction, and press-molded at a pressure of 100 MPa. The molded body was dried at room temperature for 24 hours, further dried at 110 ° C. for 24 hours, and then fired at 1000 ° C. for 2 hours to obtain a sintered body. The obtained sintered body was cut and processed to obtain a porous alumina molded body having both end faces of 1 cm square and a length of 1 mm.

This porous alumina molded body has a plurality of straw-shaped pores that are linearly penetrated in one direction from one end to the other end in the alumina substrate, and the diameter of the straw-shaped pores is almost all. It was 6 μm. Further, the porosity of the porous alumina molded body was 30% when calculated with the true specific gravity of alumina being 3.9.

Claims (4)

A step A1 of kneading ceramic powder, organic fiber or carbon fiber having a predetermined length and diameter, and an organic binder, a step B1 of stretching the kneaded material to orient the fibers in one direction, and the obtained thin rod-like body A process C1 in which a plurality of axial directions are aligned and formed, a process D1 in which the obtained rod-shaped molded body is calcined to remove the organic binder and at the same time the fibers are burnt and disappeared, and the rod-shaped molded body in which the fibers are disappeared are fired. The ceramic base is characterized in that it includes a step E1 of sintering the ceramic and a step F1 of cutting the fiber-like sintered body below the length of the fiber using the obtained rod-shaped sintered body. A method for producing a porous ceramic molded body having straw-like pores penetrating linearly in a direction. Step A2 of kneading ceramic powder, glass fiber or organic fiber having a predetermined length and diameter and dissolving with acid, and organic binder, Step B2 of stretching the kneaded material and orienting the fiber in one direction, and obtaining A process C2 in which a plurality of the thin rod-like bodies are aligned and accumulated and formed, a step D2 in which the obtained rod-like shaped body is calcined to remove the organic binder, and a fiber using the calcined rod-shaped body A step F2 for cutting to less than the length of the step, a step G2 for dissolving and removing the fibers in the cut rod-shaped molded body with an acid, and a step E2 for sintering the ceramic by firing the rod-shaped molded body from which the fibers have disappeared. A method for producing a porous ceramic molded body having straw-like pores that linearly penetrate the ceramic substrate from one end to the other in one direction. Step A3 of kneading the ceramic powder, glass fibers having a predetermined length and diameter, and organic binder, Step B3 of stretching the kneaded material and orienting the fibers in one direction, and the obtained rod-like body in the axial direction Step C3 in which a plurality of pieces are integrated and formed, Step E3 in which the obtained rod-shaped molded body is fired to melt and impregnate the fibers between the ceramic powder particles of the molded body, and at the same time, the ceramic is sintered; Including a step F3 of cutting a sintered body to a length equal to or less than the length of the fiber, and having a straw-like pore penetrating through the ceramic substrate from one end to the other in one direction and linearly Method for producing a ceramic product. 2. The process of cutting the stretched kneaded product in the step B1, B2, or B3, accumulating a plurality of the cut products with the axial direction aligned, and then stretching the stretched product a plurality of times. The manufacturing method of the porous ceramic molded object in any one of -3.