JPH0617276B2 - Method for manufacturing multi-layer ceramic filter - Google Patents

Description

The present invention relates to a novel method for producing a multilayer ceramic filter.

[Conventional technology]

Conventionally, as a method for producing a multilayer ceramic sheet, as described in JP-A-58-213684, a non-porous green sheet is produced by a papermaking method using a slurry in which an inorganic fine powder and a combustible substance are mixed. A method is known in which raw sheets having high porosity are separately prepared, and then the raw sheets in a wet state are laminated and integrated, followed by drying and firing.

[Problems to be solved by the invention]

However, since any of the above-mentioned ceramic sheets contains a combustible substance such as pulp in all the raw sheets, the size of the pores on the sheet surface or inside formed by burning the raw sheet to burn off the combustible substance is in the order of micron. However, it has a drawback that it cannot be used as a ceramic filter for separating extremely fine particles, because it cannot be controlled to a predetermined size.

[Means for solving problems]

The present inventors have conducted various studies on a method for producing a multilayer ceramic filter capable of controlling the size of pores on the order of microns and having a small overresistance (a large amount of permeated water). The present invention was arrived at by finding that the above problems can be solved by forming a filter layer on the surface of the green support layer by coating.

That is, the gist of the present invention is to form a ceramic raw support layer by making a ceramic slurry containing organic fibers, and then to the surface of the ceramic raw support layer containing no organic fibers and for the support layer. The method for producing a multi-layer ceramic filter comprises applying a slurry containing a ceramic powder having an average particle size smaller than that used in (1), then drying and firing, and filtering from the filter layer toward the support layer.

The raw materials for the ceramic slurry used in the present invention include ceramic powder, organic fibers, an adhesive and an aggregating agent for the support layer, and finer ceramic powder and an adhesive for the filter layer.

The permeation pore size of the multilayer ceramic filter intended by the present invention is about 2 μm or less. Therefore, it is necessary to select a raw material suitable for the filter layer, and the average particle size is 5 μm.
The following ceramic powders are used. Also, if the particle size of the ceramic powder for the support layer is extremely different from that for the filter layer, it may cause cracks or warpage in the firing process, so it is 15 μm.
It is desirable to use the following:

The material of the ceramic powder may be appropriately selected depending on the use of the filter, and examples thereof include alumina, silica, titanium oxide, barium titanate, ferrite, zirconia, mullite, silicon carbide, and silicon nitride. One kind or a mixture of two or more kinds can be used.

As the organic fiber, one having a fiber diameter of 1 to 30 μm and a fiber length of about 1 to 30 mm, for example, natural pulp, synthetic pulp and synthetic fibers such as vinylon, polyester, polyvinyl alcohol and nylon can be used.

Inorganic fibers are used as needed, and the inorganic fibers have an average fiber diameter of 1 to 15 μm and a fiber length of 1 to 30 mm.
From the viewpoint of papermaking, those of glass fiber, rock wool, alumina fiber, alumina silica fiber and the like are used.

Examples of the adhesive include rubber latex such as SBR, ACM, NBR, and NR, and examples of the aggregating agent include anionic acrylic amide polymer, anion-modified starch, or cationic cation-modified polyacrylic amide, and tertiary amine-containing high content. Molecules are included. When the coagulant is used together with an adhesive, the ceramic powder is made into larger secondary particles so that the ceramic powder does not escape from the wire during papermaking.

Next, the raw material mixing ratios for the support layer and the filter layer will be described. The raw material mixing ratio for the support layer is ceramic powder 70 to 95% by weight organic fiber 1 to 15 inorganic fiber 0 to 15 adhesive 1 to 15 coagulant 0.01 to 1. The raw material compounding ratio for the filter layer is 80 to 99% by weight of ceramic powder and 1 to 20 of adhesive agent.

It is one of the features of the present invention that the raw material for the filter does not contain an organic fiber which is a combustible substance. By doing so, the pore diameter becomes uniform and it becomes difficult to form the pore diameter of 2 μm or more.

Next, a method for manufacturing the multilayer ceramic filter of the present invention will be described.

First, the support layer is made into a slurry having a concentration that facilitates paper making, for example, a concentration of 5%, by sequentially adding ceramic powder, an adhesive, and an aggregating agent while sufficiently stirring and dispersing organic fibers in water. The slurry is made into paper by a Fourdrinier paper making machine to form a raw support layer having a thickness of about 0.3 to 1.5 mm.

On the other hand, an adhesive is added and mixed with water to form an adhesive solution. Ceramic powder is added to this and sufficiently dispersed by stirring to a concentration of 40-80.
Make a% slurry for the filter layer. The slurry is applied to the surface of the green support layer to obtain a green multilayer ceramic body.

There are various coating methods, and it may be selected depending on the concentration of the slurry for the filter layer and the coating thickness.For example, after coating the ceramic slurry for the filter layer on one surface of the green support, air is blown at a constant pressure to obtain an extra amount. Remove the slurry of. A so-called air knife coater method, a so-called blade coater method, in which a filter layer slurry is applied in the same manner and then excess slurry is scraped off by a blade, can be employed. When coated by such a method, the green filter layer can be made very thin, and a filter layer having a thickness of 100 μm or less can be obtained.

In order to increase the layer thickness for the purpose of increasing the strength of the multilayer ceramic filter, a plurality of green support layers may be superposed and then the filter layer slurry may be applied.

The obtained raw multilayer ceramic body is dried, then heated in an oxidizing atmosphere and fired at a temperature at which the ceramic powder is sintered,
A multilayer ceramic filter can be obtained by cooling after firing. The pulp is burned out during the temperature rising process and becomes voids in the support layer. These voids are formed in a direction perpendicular to the thickness direction for forming the green support layer by papermaking, and since the holes are communicated with each other, they are effective in reducing over-resistance.

〔Example〕

Examples 1 to 5 5 kg of hardwood kraft pulp adjusted to have a fiber diameter of 20 μm or less and a fiber length of 10 mm or less, and an average fiber diameter of 3 μm and a fiber length of 1
80 kg of calcined alumina adjusted to an average particle size shown in Table 1 while thoroughly stirring and dispersing 5 kg of alumina-silica ceramic fiber adjusted to 0 mm or less in water, 5 kg of titanium oxide adjusted to about 0.3 μm, 5 kg of SBR and anion-modified den 100 g of powder is sequentially added to obtain a ceramic slurry for a support layer having a concentration of about 5%, and the slurry is formed into a paper having a thickness of 1.
A 1 mm raw support layer was made.

On the other hand, 90 kg of calcined alumina having an average particle size shown in Table 1 and about 0.3 μm were added to a solution obtained by adding 5 kg of SBR to 70 kg of water and stirring.
Titanium oxide (5 kg) prepared as above was added to form a ceramic slurry for a filter layer having a concentration of about 60%, and the slurry was coated on the surface of the green support layer by about 100 μm by a blade coater method.
It was applied to a thickness of m to obtain a green multilayer ceramic body. This one
Cut into 0 cm square pieces, dry at room temperature for 1 week, and then raise the temperature from room temperature to 1500 ° C in an electric furnace in an oxidizing atmosphere. 2
Held for hours. Then, it was cooled to obtain a multilayer ceramic filter.

The physical properties of the obtained multilayer ceramic filter are shown in Table 1. The pore diameter of the filter layer in the table is an average value measured by a mercury porosimetry porosimeter.

[Effect of the invention] In the present invention, since the filter layer does not use a flammable substance such as pulp that burns to form pores,
By properly selecting the particle size of the ceramic powder, the pore size of the filter layer can be controlled on the order of microns.

Also, because the filter layer is formed by coating, it can be made extremely thin, over resistance can be reduced, and it can be generated in the filter layer by selecting the particle size of the ceramic powder used for the filter layer and that used for the support layer. Almost no cracks that tend to occur can be eliminated.

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Claims (1)

[Claims] 1. A ceramic slurry containing organic fibers is produced to form a ceramic raw support layer, and the surface of the ceramic raw support layer contains no organic fibers and is used for the support layer. A method for producing a multilayer ceramic filter in which a slurry containing a ceramic powder having an average particle size smaller than that of the above-mentioned one is applied, and then dried and fired to filter from a filter layer toward a support layer.