JPS6268510A - Method for preparing ceramics filter material - Google Patents

Abstract

PURPOSE:To obtain ceramic filtering material having excellent separation performance, large permeability, and high mechanical strength, by impregnating such substances that can be removed afterward into a porous ceramics before slurry of mineral powder is applied thereon. CONSTITUTION:Porous ceramics support having porosity of 30-60% and average pore diameter of 0.1-30mum is used. Water, organic liquid and solid which are removable after the slurry has been applied are impregnated into this support. When the quantity of slurry which is impregnated is in the range of 80-99.5% of the pore volume, the slurry is impregnated slightly into the body of the support, resulting in higher strength thereof. Under this condition, slurry composed of mineral powder, binder of mineral matter, and dispersion medium is applied over the support. Minute particles of metallic oxides with a diameter of tens - thousands Angstrom are used as mineral powder. Thickness of coating layer is prepared so as to become 1-50mum after firing. Said support is fired at a temperature of 500-1,200 deg.C after impregnated matters have been removed by drying.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a ceramic filter medium particularly suitable for ultrafilter applications.

[Conventional technology]

When performing ultrafiltration using a ceramic porous body as a filter medium, it is desirable to make the filter medium as thin as possible in consideration of its separation efficiency.

However, it is difficult to form a ceramic porous body alone into a thin film, and there are also problems in terms of strength. Therefore, a dual structure consisting of a support layer made of porous ceramics with a large pore size and sufficient strength that does not impede permeation, and a microporous layer as thin as possible with a separation function, or the above-mentioned A multilayered filter medium with an intermediate layer between both layers has been proposed.

In order to produce a filter medium having such a multilayer structure, a method of depositing fine powder on porous ceramics to form a powder layer has been employed. There are two methods for forming this powder layer: a dry method and a wet method. In the dry method, an elastic tube is inserted into a support tube made of porous ceramics, fine powder is filled between the support tube and the tube, and then the pressure inside the tube is increased to remove the fine particles in the void. There is a method of compressing the powder onto the support tube (for example, Japanese Patent Laid-Open No. 77410/1983).

On the other hand, as a wet method, a centrifugal molding method in which a support tube made of porous ceramics is rotated, a fine powder slurry is supplied into the support tube, and the fine powder is adhered by centrifugal force (for example, Japanese Patent Laid-Open No. 19057/1983) , 50-7741
1), and an electrophoresis method in which slurry is deposited on a support tube made of porous ceramics by electrophoresis using the surface potential of the slurry.

Another method for obtaining a ceramic filter medium with a multilayer structure is to fill ceramics made of a coarse porous matrix with fine particles by immersion (for example, in Japanese Patent Laid-Open No. 57-182
No. 964), or a method of immersing a ceramic multilayer structure consisting of a dense layer and a support layer in a slurry containing active layer particles smaller than the particles constituting the dense layer (for example, Japanese Patent Laid-Open No. 60-97023). Public bulletin), etc. have been proposed.

[Problem that the invention seeks to solve]

However, in all of these conventional methods, the mechanical strength of the microporous thin membrane layer that has a separation function is insufficient (for example, when used for ultrafiltration, the thin membrane layer is easily broken due to operations such as washing). In addition, although it is possible to obtain a certain degree of bonding strength between particles by sintering the fine particles that make up the microporous thin film layer, in order to obtain high bonding strength, the sintering of the particles may progress too much. However, there was a problem in that the permeability as a filter medium deteriorated significantly and the separation efficiency decreased.

Therefore, the present invention does not have the problems of the conventional methods described above, has excellent separation performance when applied to ultrafiltration, has high permeability, good separation efficiency, and has excellent mechanical strength. The purpose is to obtain ceramic filter media.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that a support made of porous ceramics having a large pore size and sufficient mechanical strength was impregnated with a substance such as water or an organic solvent in advance. A specific slurry containing fine particles of mineral powder and an inorganic binder such as water glass is applied to this, and by firing this, the fine particles are deposited on the support to create a frit made of the binder. When a microporous thin film layer with a fused structure is formed, it has excellent separation performance when applied to ultrafiltration, has high permeability (and has good separation efficiency, and is easy to use mechanically). After learning that it was possible to obtain a ceramic filter medium with high mechanical strength, he completed this invention.

That is, the present invention is a method in which a slurry containing mineral powder, a dispersion medium, and an inorganic binder soluble in the dispersion medium is applied onto porous ceramics, and then fired to form a microporous thin film layer. The present invention relates to a method for producing a ceramic filter medium, characterized in that porous ceramics before applying the slurry are impregnated with a substance that can be removed after applying the slurry.

In this way, in the method of the present invention, the porous ceramic support is pre-impregnated with a substance that can be removed after the slurry is applied.
The fine powder slurry applied thereon hardly penetrates into the ceramic. Therefore, even though the slurry contains an inorganic binder soluble in a dispersion medium such as water glass, the formed coating layer has a uniform composition.

On the other hand, by including an inorganic binder soluble in the dispersion medium as described above in the fine powder slurry, it becomes easy to form a coating layer on porous ceramics, resulting in a coating layer with good coating properties and no cracks. can be formed. Furthermore, the binder acts as a frit component for the mineral powder particles during firing, meaning that unlike organic binders, the binder does not burn out during firing, but instead melts and appropriately fills the spaces between the mineral powder particles. Since it functions to fuse particles together, it increases the bonding strength between powder particles and also contributes to preventing cracks during the firing stage.

Therefore, the microporous thin film layer formed by the method of the present invention has a fine pore structure in which mineral powder particles are fused and bonded with a uniform composition by a frit made of an inorganic binder, and has a fine pore structure with no cracks. The membrane properties are very good, with no pores, which greatly contributes to improving separation performance when used in ultrafiltration applications, and also brings good results to maintaining permeability, which governs separation efficiency. .

In addition, this microporous thin film layer is bonded and supported by a support made of porous ceramics, but during the firing step, a part of the frit made of an inorganic binder flows into the ceramics, thereby reducing the interfacial strength. Since it greatly contributes to improvement, the bonding strength with the support body becomes extremely high. Therefore, it is possible to provide a ceramic filter medium which has excellent mechanical strength and has no fear that the thin film layer peels off from the support even after long-term use, nor is it easily chipped during cleaning in the event of contamination. becomes possible.

Furthermore, this filter material is essentially ceramic.

Composed only of inorganic substances consisting of mineral powder and inorganic binder, so it is resistant to pressure and heat.

It has excellent chemical resistance, and from this point of view, it is very suitable for separating various fluids, especially for ultrafiltration.

[Structure and operation of the invention]

Examples of porous ceramics used as a support in this invention include silica, alumina, magnesia,
Examples include sintered bodies containing titania, zirconia, etc. as main components. The porosity of this ceramic is usually 30 to 60.
%, and the average pore diameter is usually preferably in the range of 0.1 to 30 μm.

In this invention, the porous ceramic described above is first impregnated with a substance made of water, an organic liquid, or a solid that can be removed after applying a slurry as described below. As the organic liquid, a polar solvent such as alcohol, acetone, or glycerin, or a nonpolar solvent such as toluene or hexane can be used, and as the organic solid, an organic polymer such as polyethylene glycol can be used. Among these substances, it is particularly preferable to use water or a water-soluble organic solvent.

These substances are impregnated into porous ceramics, but at this time, if the amount of impregnation is reduced to a certain extent so that the amount of impregnation is 80 to 99.5% of the pore volume,
In other words, when porous ceramics is impregnated so that only a small portion of the pores are left unimpregnated, the slurry or its liquid component slightly enters the ceramic and is fired in this state, resulting in an anchor ring. The effect can be further enhanced.

Next, a slurry consisting of mineral powder, an inorganic binder, and a dispersion medium is applied to the porous ceramic impregnated with water, an organic solvent, etc. in this manner. As the mineral powder, natural types such as clay and silica, or artificial types such as metal oxides, metal carbides, and metal nitrides can be used. Artificial silica, alumina, titania,
Several liters to several hundreds of metal oxides such as zirconia
Preferably, human microparticles are used.

In addition, the inorganic binder imparts spreadability to the slurry during application and has the function of adhering aggregate, that is, mineral powder, as a frit during firing. Examples include inorganic substances soluble in dispersion media such as polycarbosilane and polycarbosilane. Furthermore, as the dispersion medium, a medium that can be easily volatilized and removed by heating and drying, such as water or alcohol, is preferably used.

The viscosity of this slurry can be adjusted appropriately by the amounts of the dispersion medium and inorganic binder added, but preferably mineral powder:dispersion medium:inorganic binder -5 to 40:! 1
The range is 5-40:0.02-20 (weight ratio).

Further, the amount of the inorganic binder is 0.0% relative to the mineral powder.
If it is less than 5% by weight, the bonding strength of the mineral powder after firing will not be sufficient, and if it is more than 50% by weight, the thin film layer will become non-porous, which is not preferable.

The slurry can be applied by, for example, a doctor blade method if the porous ceramic support is a flat plate, or by passing a ball or bullet-like object smaller than the inner diameter of the tube by the coating thickness if it is a tube. You can use any method you like to apply it to the inner surface of the tube. The coating thickness at this time is preferably such that the thickness of the microporous thin film layer that is finally formed by drying and firing is generally about 1 to 50 μm.

After applying the slurry onto the porous ceramic as described above, it is dried and the substance impregnated in the ceramic is removed in this drying process, or it is not removed in the drying process and is placed in a furnace. By gradually raising the temperature and removing it, and further firing at 500 to 1,200℃, the mineral powder that becomes the aggregate is fused with a frit made of an inorganic binder, and the desired porous ceramic is It is possible to easily produce a filtration medium with excellent separation performance, 2 separation efficiency, and mechanical strength, which is composed of a support layer and a microporous thin film layer.

[Effects of the Invention] As described above, in this invention, a support made of porous ceramics is impregnated with a removable substance in advance, and mineral powder and an inorganic binder soluble in a dispersion medium are added to the support. Separation performance 9 Separation of various fluids with excellent separation efficiency and mechanical strength, as well as excellent pressure resistance, heat resistance, chemical resistance, etc., using a simple method of applying a slurry containing and then firing. It is possible to obtain a ceramic filter medium having a laminated structure suitable for use in applications, especially ultrafiltration.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Alumina-based material with average pore diameter of 0.4 μm and porosity of 5
0.1%, a porous ceramic plate with a thickness of 2.0 fl was immersed in water and the pressure was reduced to completely impregnate the inside of the porous ceramic plate with water. Further, by drying in an oven at 80°C, the filling rate of water into the pores inside this porous ceramic plate was adjusted to 98%.

Next, this impregnated ceramic plate was coated with an average particle size of 20
0 aluminum oxide 28.8 parts by weight and water glass 10
．． A slurry consisting of 5 parts by weight and 60.6 parts by weight of water was applied so that the coating amount was 1.8 x 10-3 g/c4 in terms of solid content. After this coating, the slurry and the water in the ceramic plate were removed by drying at 100°C for 3 hours, and then fired at 900°C to create a support layer made of porous ceramics and a microporous layer with a thickness of 9 μm. A ceramic filter medium consisting of a thin film layer and having good adhesion and bonding strength between both layers was obtained.

When we tried to separate latex using this filter material, we found that
Polystyrene latex of 0.09 μm, which could not be separated using only the support layer, was separated with an exclusion rate of 99.9% by weight. On the other hand, the water permeation rate is 1,0 ml/min.
There was no change in ct-atm compared to the case with only the support layer.

Example 2 Mainly composed of silica, average pore diameter 0.5 μm, porosity 49
．． 0%, thickness 2. The porous ceramic plate of On was immersed in glycerin and the pressure was reduced to completely impregnate the inside of the porous ceramic plate with glycerin. next,
To this impregnated ceramic, 28.8 parts by weight of titanium oxide with an average particle size of 200, 10.5 parts by weight of water glass, and 6 parts by weight of water were added.
A slurry consisting of 0.6 parts by weight is coated with a solid content of 1
．． It was coated at 8×10-'E/crM.

Thereafter, the glycerin was removed by holding at 300°C for 5 hours, and then firing at 1.100°C, resulting in a double layer consisting of a support layer made of porous ceramics and a microporous thin film layer with a thickness of 9 μm. A ceramic filter medium with good adhesion and bonding strength was obtained. When latex separation was attempted using this filter medium, performance similar to that of Example 1 was obtained.

Claims (4)

[Claims] (1) A method in which a slurry containing mineral powder, a dispersion medium, and an inorganic binder soluble in the dispersion medium is applied onto porous ceramics, and then fired to form a microporous thin film layer, A method for manufacturing a ceramic filter medium, characterized in that, before applying the slurry, the porous ceramic is impregnated with a substance that can be removed after the slurry is applied. (2) The method for manufacturing a ceramic filter medium according to claim (1), wherein the mineral powder is a metal oxide having a particle size of several tens to several hundreds of angstroms. (3) The method for producing a ceramic filter medium according to claim (1) or (2), wherein the impregnation rate of the removable substance in the porous ceramic is 80 to 99.5% of the pore volume. . (4) The method for producing a ceramic filter medium according to any one of claims (1) to (3), wherein the removable substance is water or a water-soluble organic solvent.