KR19980051300A - Manufacturing method of ceramic filter with different pore characteristics in thickness direction - Google Patents

Abstract

The present invention is to manufacture a ceramic green sheet having a constant thickness using a tape casting method, and when manufacturing a ceramic filter using the same, pore characteristics of the porous wall by distributing pore-forming agent to a specific site according to the density of the wall thickness It is to provide a method for producing a ceramic filter having a better direction of surface filtration by changing in the direction.

The ceramic filter manufactured by the method of the present invention can be used in incinerators, coal-fired power plants, coal gasification combined cycle power plants, diesel fuel smoke removal device, water treatment filters, and other applications for separation filters of heat exchangers, gases and fluids Or the support, the catalyst carrier, or the like.

Description

Manufacturing method of ceramic filter with different pore characteristics in thickness direction

The present invention relates to a method for producing a ceramic filter in which the pore characteristics of the porous wall differ in the wall thickness direction when the ceramic filter is manufactured by a tape casting method. More specifically, the present invention relates to a method of manufacturing a ceramic filter in which the pore characteristics of the porous wall are differently controlled in the thickness direction by controlling the dispersion of the pore-forming agent in the thickness direction differently during the tape casting process.

In the case of ceramic filters, since they are excellent in physical properties such as heat resistance and chemical resistance, they are actively used in fields in which existing paper filters or filters made of polymers cannot be used. These fields include various incinerators, coal-fired power plants, coal-gas-fired combined cycle power plants, and diesel soot removal devices. Like other filters, ceramic filters have the same pore volume as the dust characteristics in each application. The key technology is to control the pore size so as to have proper filtration efficiency and back pressure characteristics.

In the case of the conventionally developed ceramic filter, the rod type is generally used most widely, but the back pressure of the filter system is increased because its surface area is not large. Therefore, since the number of filters must be increased to reduce the back pressure, the size of the entire system is increased and the cost is increased. In the case of the ceramic honeycomb filter, as described in European Patent Publication No. 36321, the inlet and the outlet of each hole of the ceramic honeycomb are interchanged and sealed, so that the exhaust gas containing dust must pass through the porous wall of the honeycomb. It is a structure which collects a back on the wall surface.

Such a filter is known to be excellent in the back pressure characteristics because each hole plays the same role as the filter of the rod type described above, but the price is very expensive, there is a problem in practical use.

The reason why the ceramic honeycomb filter is expensive is that the manufacturing process is complicated and automation is not easy. That is, the honeycomb filter first manufactures a flow-through honeycomb in which both ends of each channel are drilled by a process of mixing raw materials, extrusion, drying, and sintering. Such flow-through honeycomb is widely used as a carrier for three-way catalysts in gasoline automobiles. In order to manufacture the honeycomb filter, the flow-through honeycomb should be sealed by interchange of the inlet and the outlet of each hole. This is called a plugging process.

This process is not easy to automate because each hole of the flow-through honeycomb is not uniform in shape or position due to sintering. In addition, secondary sintering is required in order to sinter the plugged material after the plugging process is completed. As such, the manufacturing process is complicated and in some cases, automation is difficult, so the price is high.

In addition, the manufacturing process of the ceramic filter using the tape casting process, which is recently developed, is a method designed to solve the problems of the honeycomb filter described above. How to make it. 1 and 2 show an example of a ceramic filter manufactured by such a tape casting process, Figure 1 is a first manufacturing a ceramic green sheet by a tape casting process and then embossed it, Figure 2 is an embossed ceramic green An example is shown in which a sheet is cut into a predetermined shape and then laminated and sintered.

In FIG. 1, reference numeral 1 denotes a flat portion of the sheet, reference numeral 2 denotes a protruding portion, and in FIG. 2, reference numerals 3 and 3 'denote front and rear ends of the filter, and reference numerals 4 and 4' denote both sides of the filter. will be.

In the case of the ceramic filter manufactured using the tape casting process, the plugging process is not required as compared with the conventional honeycomb filter, and it is expected that the filter can be manufactured more easily and inexpensively because the sintering is performed at one time. .

In the case of the various ceramic filters described above, in order to control the pore characteristics, the pore characteristics of the ceramic porous wall through which the fluid passes are uniform since all of the pores such as graphite are uniformly mixed with the ceramic raw material powder. In addition, in the case of the ceramic filter manufactured by the tape casting process, which has been recently developed, the pore characteristics of the porous wall are all uniform as in the case of the previous case.

On the other hand, not only ceramic filters but also general filters can be broadly classified into deep filtration and surface filtration according to their filtration functions. In the accompanying drawings, the surface filtration is shown in FIG. 3, and the principle of the deep filtration is shown in FIG. 4.

That is, in FIG. 3 and FIG. 4, reference numeral 5 denotes a ceramic filter and reference numeral 6 denotes dust to be removed. In the case of the deep filtration, as the dust is trapped and filtered inside the porous wall of the filter, the collected dust gradually blocks pores in proportion to the use time of the filter, so that the airflow resistance increases, thereby improving the performance of the filter. Lowers. On the other hand, the surface filtration method shown in FIG. 3 is known to not only have a very high air flow rate but also a rapid increase in air resistance by trapping and filtering dust and the like on the surface of the porous wall.

In addition, in the case of surface filtration, fine particles or particulate matter, etc., are not present in the porous wall during periodic regeneration of the filter, but only on the surface thereof.

There are various methods of regenerating the ceramic filter, but in the case of particulate material that does not burn, it is common to blow off the compressed air and the like in the opposite direction of the exhaust gas direction. In addition, in the case of combustible particulate matter, the filtered material is recycled by periodically burning it using an electric heater, a burner, etc., or by regenerating it naturally by lowering the self-ignition temperature of the particulate matter by applying a catalyst or mixing an additive in a fuel. Use the method.

In the case of the above-described surface filtration filter, not only compressed air but also combustible particulate matter accumulates only on the surface of the filter, so that the energy can be regenerated with less energy, and the combustion is uniformly propagated to facilitate regeneration. There is an advantage.

Therefore, in order to improve the surface filtration characteristics of the conventionally developed ceramic filter, a method of coating the membrane by coating a slurry having different pore characteristics with the filter as a support is used, and in this case, the pore size is generally relatively high. Larger filters are first manufactured and then coated with a membrane with a smaller pore size to reduce pressure loss and provide surface filtration effects.

However, in the case of the above process, the filter is first manufactured by sintering, and then the slurry is coated and heat-treated again, and the process is complicated and manufacturing costs are relatively increased.

The present invention is to solve the above problems, the pore-forming agent in the manufacture of the ceramic filter by the tape casting process to be distributed in a specific area automatically according to its density, ultimately the pore characteristics in the thickness direction of the porous wall during the molding process It is an object of the present invention to provide a method for producing a ceramic filter for surface filtration more easily and inexpensively.

1 is a schematic perspective view after embossing a ceramic green sheet.

FIG. 2 is a schematic perspective view of a ceramic filter sintered by stacking the sheets of FIG. 1 in a direction perpendicular to each other. FIG.

3 is a schematic diagram illustrating the principle of surface filtration.

4 is a schematic diagram illustrating the principle of depth filtration.

* Explanation of symbols for main parts of the drawings

1: flat part 2: protruding part

3, 3 ': front and back end of filter

4, 4 ': both sides of the filter 5: ceramic filter

6: dust

7: portion where the pore is present

8: part without vacancy

9: pore-forming agent contained in ceramic green sheet

According to the present invention, in the manufacture of a ceramic filter using a tape casting method, the pore property of the porous wall is changed in the wall thickness direction by distributing the pore-forming agent at a specific site according to its density to improve the characteristics of surface filtration. It is a manufacturing method of the ceramic filter characterized by manufacturing so that it may show.

Here, in the method according to the present invention, the pore-forming agent is not influenced by adding the pore-forming agent during the preparation of the ceramic slurry by adding the ceramic raw material powder and the dispersing agent, and then adding the pore-forming agent after the addition of the binder and the plasticizer. It is characterized in that it is distributed to a specific site according to its density.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

5 is a schematic perspective view of a ceramic green sheet manufactured using the present invention during tape casting, in which reference numeral 9 denotes a pore-forming agent contained in the ceramic green sheet, and reference numeral 7 denotes a portion where the pore-forming agent is mainly present. 8 shows a portion where no pore is present.

The method of manufacturing the ceramic green sheet by a tape casting process is commonly used in ceramic electronic components such as alumina substrates for integrated circuits and multi-layer ceramic capacitors. Generally, ceramic raw materials such as cordierite and mullite are used. , Alumina, silica, silicon carbide, titania, zirconia or silicon nitride are first mixed using a dispersant and a solvent, and then a binder and a plasticizer are added and mixed again, and then molded and dried to a certain thickness using a doctor blade. Ceramic green sheets are produced.

In this case, the dispersant may be added first and then mixed, and then the binder and the plasticizer may be added so that the dispersant may be easily adsorbed onto the ceramic material to separate the condensed or aggregated particles and maintain the separated state.

Therefore, a pore-forming agent, such as graphite, is added to adjust the characteristics of the desired pore amount and pore size even when the ceramic filter is manufactured by tape casting. It is prepared according to the method. Therefore, the ceramic filter made using this method has a porous wall with uniform pore characteristics.

In the case of the present invention, firstly, only the ceramic raw material powder is mixed with a dispersant and a solvent, and then a pore-forming agent such as graphite is added together with the addition of the binder and the plasticizer. While dispersed evenly, the later added pore-forming agent relatively changes in distribution due to the density difference with the ceramic powder.

That is, in general, pore-forming agents such as graphite are less dense than ceramic powder, so they are distributed in the upper portion of the slurry indicated by reference numeral 7 formed on the carrier film during tape casting. Only a small amount of graphite will be present.

Therefore, when the green sheet is sintered, the pore size of the upper portion of the ceramic sheet is coarse, while the lower portion of the green sheet is relatively small, which is shown in FIG. 6. In FIG. 6, reference numerals 7 'and 8' show a shape after the portions 7 and 8 of FIG. 5 have undergone a sintering process. The pores of the portion 7 'are coarse while the pores of the portion 8' are fine. Able to know.

Such a ceramic green sheet has a thickness of about 0.1 to 5 mm and undergoes an embossing process as shown in FIG. 1, in which a part of reference numeral 8 of FIG. 5 and a part of reference numeral 9 of FIG. 5 are manufactured to manufacture a surface filtration filter. Treated green sheets should be laminated sequentially and sintered to produce ceramic filters with better surface filtration than conventional filters.

Although the effects of the present invention will be described in more detail with reference to the following examples, the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

25% by weight kaolin powder, 20% by weight calcined kaolin, 30% by weight talc, 15% by weight alumina are mixed in a ball mill. 1% by weight of fish oil and 30% by weight of a mixture of toluene and ethyl alcohol were added to the mixed powder, followed by mixing in a ball mill. 10 wt% of polyvinyl butyral as a binder, 15 wt% of dioctylphthalate as a plasticizer and 20 wt% of graphite as a pore-forming agent were further wet mixed.

After degassing the prepared slurry under reduced pressure, a ceramic sheet was prepared by adjusting the height of the doctor blade to 2 mm in a tape casting equipment. The ceramic sheet dried for 48 hours was cut into a square shape of 150 mm in consideration of the amount of sintering shrinkage and then laminated after embossing using a roller.

Sintering was carried out at a rate of 1 ° C. per minute up to 500 ° C. and then 4 ° C. per minute in consideration of degreasing of the added binder and plasticizer, followed by sintering at 1450 ° C. for 3 hours.

In order to measure the physical properties of the sintered filter, the fracture surface of the sheet was observed with a scanning electron microscope. As a result, the average pore diameter of the surface of the sheet, which is in contact with the exhaust gas, was 5.3 microns, and the average pore diameter of the opposite side of the sheet was 12.7 microns.

Example 2

To 82% by weight of alumina powder, 1% by weight of silica, magnesia, and calcia as fluxes for the liquid sintering formulation and the abnormal grain growth inhibitor and 15% by weight of graphite as the pore-forming agent were added and mixed in a ball mill. Thereafter, 2% by weight of fish oil was added as a dispersant, and 40% by weight of toluene, ethyl alcohol, and enbutyl alcohol were added and mixed again. Then, a slurry was prepared by adding 12% by weight of nitro cellulose and 17% by weight of dibutyl phthalate as a binder.

The prepared slurry was degassed under reduced pressure to give a viscosity suitable for casting. The slurry was tape cast to a thickness of 1 mm to prepare a ceramic green sheet. The dried sheet was embossed by passing between two rollers having irregularities formed thereon, and then cut into a square shape of 200 mm.

The cut sheets were turned to be perpendicular to each other and laminated, and then sintered. Sintering was carried out at a rate of 1 ° C. per minute up to 500 ° C. and then 4 ° C. per minute for degreasing, and then sintered at 1400 ° C. for 3 hours.

When sintering, the green sheet was cut into four portions in the thickness direction, and the average pore diameters were measured. As a result, the average pore diameters of 118, 14, 5, and 4 microns were shown from the large pore distribution.

In the method of manufacturing a ceramic filter of the present invention, when the ceramic filter is manufactured by a tape casting process, the pore-forming agent is automatically distributed in a specific area according to its density, and ultimately, the pore characteristics are adjusted in the thickness direction of the porous wall during the molding process. There is an effect that can easily and cheaply produce a ceramic filter for surface filtration.

Claims (4)

In the manufacture of ceramic filter using tape casting method, the pore property of the porous wall is changed in the wall thickness direction by distributing the pore-forming agent in a specific area according to its density so that the characteristics of surface filtration are better represented. Method for producing a ceramic filter, characterized in that. The method of claim 1, wherein the ceramic is cordierite, mullite, alumina, silica, silicon carbide, titania, zirconia, or silicon nitride. The pore-forming agent according to claim 1, wherein the pore-forming agent is not affected by the dispersing agent by adding and mixing the ceramic raw material powder and the dispersing agent in the preparation of the ceramic slurry, and then adding the pore-forming agent during the addition of the binder and the plasticizer. Method for producing a ceramic filter, characterized in that to be distributed in a specific region according to the density. The method of claim 1, wherein the thickness of the green sheet is about 0.1 to 5 mm, and the green sheet is embossed using a cooler or a press.