JPH0254304B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing porous ceramic bodies.

A method is known in which a ceramic porous body is manufactured by firing a polyurethane foam mixed with ceramic raw materials to remove the polyurethane and sintering the ceramic raw materials.This ceramic porous body has excellent corrosion resistance, heat resistance, and strength. Because of their excellent properties, they are used in a wide variety of applications, including materials, ion exchange resins, diaphragms, adsorbents, catalyst carriers, firebricks, heat-resistant materials, and construction materials.

An example of a conventional method for manufacturing a ceramic porous body is to react an ethylene oxide/propylene oxide copolymer and a polyisocyanate compound having two or more isocyanate groups at the end with a ceramic mud made by adding water to a ceramic raw material. Mix the hydrophilic urethane prepolymer obtained by
A method for manufacturing a porous ceramic molded product is known (see Japanese Patent Laid-Open No. 145153/1983), in which this mixed composition liquid is injected into a mold, reacted and foamed, and then the urethane foam is dried and fired. This method is called the prepolymer method. In this prepolymer method, a large amount of water is mixed with the ceramic raw material, and a large amount of water is present in the urethane foam that is reacted and foamed in the mold. Therefore, when this water is removed by drying, the urethane foam shrinks extremely as the water evaporates, causing distortion and warpage in the urethane foam. Therefore, the shape of the ceramic porous body after firing is also not good.

In addition, as another method for manufacturing porous ceramic materials, an organic isocyanate compound is added to a mixed solution of a ceramic raw material, a polyol compound having two or more active hydrogen atoms in the molecule, a blowing agent, and water. A manufacturing method is known in which a composition liquid is foamed in a mold to form a urethane foam, and then the urethane foam is dried and fired (see JP-A-55-71659). It is called the one-shot method. This one-stage method has a smaller shrinkage rate during drying than the prepolymer method described above, but the amount of polyurethane resin is large, which makes firing difficult, and only lightweight products with low specific gravity are produced, and the cost is high. Become.

Porous ceramic bodies are required to have a high degree of dimensional stability depending on their use. The dimensional stability of porous ceramics is inhibited by the shrinkage of the urethane foam during drying and the shrinkage of the dried urethane foam during firing. Since there appears to be a correlation, it is thought that by suppressing shrinkage during drying, shrinkage during firing will also be considerably suppressed.

Heat shrinkage during drying increases as the amount of water mixed into the ceramic raw material increases, so the best way to reduce heat shrinkage is to suppress the amount of water added, but if the amount of water added is too small, There are disadvantages in that the mixing reaction of the composition is not uniform and the molding with a mold does not proceed smoothly.

In order to solve the above-mentioned problems, this invention changes the blending order and blending ratio of each raw material component.

In other words, this invention combines (a) a polyalkylene polyol with an average molecular weight of 3,000 to 10,000 having two or more OH groups, and (b) an organic isocyanate compound having two or more NCO groups, in a molar ratio of OH groups/NCO groups. The ratio is
(c) a crosslinking agent having two or more functional groups;
Aqueous ceramic slurry is mixed with the above premix at a molar ratio of the functional group of the crosslinking agent (c) to the NCO group of the organic isocyanate compound of (b) from 0.29 to 7.5, and the premix and the slurry are mixed together. Ceramic is blended so that the total weight of the above components (a), (b), and (c) is 10 to 35 parts by weight based on 100 parts by weight of the ceramic raw material, and this blended composition liquid is molded. This is a method for producing a porous ceramic body, which is characterized in that the urethane foam is injected, reacted and foamed, and then dried and fired.

The polyalkylene polyol as component (a) used in this invention is prepared by adding propylene oxide using glycerin, trimethylolpropane, pentaerythritol, etc. as an initiator, and preferably having 2 or more functional groups to which ethylene oxide is added to a part of the polyalkylene polyol. It is a conventional hydrophobic polyol having an average molecular weight of 3,000 to 10,000, preferably 5,000 to 7,000.
If the average molecular weight of the polyalkylene polyol is less than 3000, the strength of the molded urethane foam will be low;
It becomes difficult to release from the mold, and the average molecular weight is 10,000.
If it exceeds 50%, the viscosity is high and the OH equivalent is low, making it difficult to release from the mold.

Mixed with the above (a) polyalkylene polyol
The organic isocyanate compound of component (b) contains two or more
Those having an NCO group, being liquid at room temperature, and having an aromatic group such as toluylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and isophorone diisocyanate are preferred.

The crosslinking agent (c) mixed into the aqueous ceramic slurry has two or more functional groups such as OH groups and NH ₂ groups at its terminals, is water-soluble or water-dispersible, and has diethanolamine, triethanolamine, etc. Examples include ethanolamine, tributanolamine, trimethylolpropane, glycerin, trimethylenediamine, ethylene glycol, diethylene glycol, and the like.

Ceramic raw materials can generally be turned into sintered bodies by heating to high temperatures, and include kaolin, clays, silica, alumina, feldspar, pottery stone, mullite, zircon, zirconia, titania, silicon carbide, and cordierite. For example, it is a mixture of these various raw materials.

The amount of water added to the ceramic raw material is 10 to 100 parts by weight, preferably 30 to 60 parts by weight, based on 100 parts by weight of the ceramic, and is preferably as small as possible to mix the aqueous ceramic slurry with the premix. If the amount of water is less than 10 parts by weight, the viscosity becomes high and molding becomes difficult, and if it exceeds 100 parts by weight,
The amount of polyurethane becomes smaller than the total amount of ceramic raw materials and water, and the polyurethane becomes too diluted, reducing the strength of the molded urethane foam.
It becomes difficult to release the mold and the heat shrinkage of the urethane foam increases when drying. This aqueous ceramic slurry contains peptizers such as sodium pyrophosphate and soda carbonate, which are used in the general ceramics industry.
Protective colloids such as tannic acid and lignin may be added, and the amount of each added is 0.01
~0.1 part by weight is preferred.

The characteristics of this invention are the mixing order of the above-mentioned raw materials and their mixing ratios.

When producing a premix by mixing the above (a) polyalkylene polyol and (b) organic isocyanate compound, the blending ratio is as follows:
(a) Polyalkylene polyol to NCO group
The molar ratio of OH groups, OH groups/NCO groups, is 0.01 to 0.5, preferably 0.02 to 0.1. If the OH group/NCO group molar ratio is less than 0.01, the polyol content will be small and the dispersion between the premix and water will be poor, making it difficult for the reaction to proceed smoothly, and an excessive amount of NCO
Since the group reacts with a crosslinking agent having two or more functional groups or with water, the resulting foam is brittle and does not undergo a polymerization reaction to have the strength and elasticity required for a foam. When the OH group/NCO group molar ratio exceeds 0.5, the polyol content becomes too large and the reaction between the polyol component and the isocyanate component becomes slow, and the amount of crosslinking agent added decreases as the polyol component increases. Polymerization reaction is insufficient and solidification does not occur.

Next, the amount of crosslinking agent (c) added to the ceramic slurry, which is a mixture of ceramic raw materials and water, is (b)
It depends on the amount ratio of (b) the NCO group of the organic isocyanate compound to the (c) functional group of the crosslinking agent (represented by the OH group).
The molar ratio of OH group/NCO group is 0.29 to 7.5, preferably 0.5 to 4.0. This OH group/NCO group molar ratio is
If it is less than 0.29, the amount of crosslinking agent is small, resulting in insufficient polymerization and poor solidification. In this case, water is supposed to act as a crosslinking agent, but in reality solidification is poor, and although the reason for this is not clear, it is thought to be a problem in the balance between foaming and gelation. If the molar ratio of OH group/NCO group exceeds 7.5, the hard segments of the produced polyurethane will be the main focus due to the small amount of polyol, making it difficult to solidify or only crumbly products will be produced.

Next, a composition solution in which the above premix and mud-like ceramic containing a crosslinking agent are mixed is reacted and cured in a mold, and (a) polyalkylene polyol, (b) organic isocyanate compound and (c) The total weight of the polyurethane component consisting of the crosslinking agent is 5 parts by weight based on 100 parts by weight of the ceramic raw material.
~40 parts by weight. If the amount of polyurethane component is less than 5 parts by weight, there will be too little polyurethane component and it will not harden, and if it exceeds 40 parts by weight, the amount of polyurethane will be too large, and the specific gravity of the sintered ceramic porous body will become too small. The strength decreases,
Moreover, the cost is high.

It is preferable to add a surfactant during the production of the above premix. As the surfactant, polydimethylsiloxane/polyoxyalkylene copolymer is suitable, and the amount of surfactant added is 1 to 20% based on the total amount of (a) polyalkylene polyol and (b) organic isocyanate compound. Parts by weight are preferred. If the amount is less than 1 part by weight, the premix has poor dispersibility in water, and it appears that the ceramic slurry will not harden unless the amount of polyurethane is increased. Moreover, if it exceeds 20 parts by weight, the cost will be high.

A catalyst can be added to the ceramic mud prepared by mixing the crosslinking agent and the ceramic slurry, and N-alkylmorpholine, N-alkylmorpholine,
Examples include 1,8 diazocyclo[5,4,0]undecacene (DBU), trimethylamine, ethylenediamine, etc. Examples of the tin-based catalyst include dibutyltin dilaurate, and these catalysts may be used in combination.

A mixed composition liquid obtained by mixing the premix and mud ceramic described above and thoroughly stirring the mixture is poured into a mold, and is reacted and foamed in the mold to obtain a urethane foam. The reaction in the mold is carried out at room temperature to 50°C for 3 to 5 minutes.

The urethane foam molded in the mold is removed from the mold and then dried at 80 to 100°C for 15 to 24 hours to remove moisture contained in the urethane foam. The dried urethane foam is then heated in a high temperature furnace. This heating is to thermally decompose the polyurethane and sinter the ceramic raw material. The former process is carried out at a temperature in the range of 400°C from room temperature, during which time the polyurethane gradually oxidizes and decomposes or is exposed to oxygen. Thermal decomposition occurs in an insufficient atmosphere, and the latter step is usually carried out at temperatures above 1100°C, although this varies depending on the ceramic raw material. After sintering, it is allowed to cool down gradually and then taken out from the heating furnace.

Examples of the present invention will be described below.

Example 1 Ceramic raw materials of 50 parts by weight of synthetic mullite, 10 parts by weight of Kibushi clay, 20 parts by weight of kaolin, and 20 parts by weight of talc, 40 parts by weight of water, 4 parts of tributanolamine (crosslinking agent), and 0.1 parts by weight of sodium hexametaphosphate. and 0.5 parts by weight of a catalyst (trade name: U-cat2600, manufactured by Sunabott Co., Ltd.) to form a mud-like ceramic.
On the other hand, 5 parts by weight of crude MDI, 3 parts by weight of polypropylene glycol (average molecular weight 6000, number of functional groups 3), and 1 part by weight of a surfactant (trade name Y-6827, manufactured by Nippon Unica Co., Ltd.) were mixed, and this mixture was added to the above slurry. Mix and stir the ceramic material and pour it into the mold. The urethane foam solidified in the mold and removed from the mold has a shrinkage rate of 2 to 3 after drying at 80℃ for 12 hours in a hot air circulation dryer.
% and had excellent dimensional stability. This dried body was heated to 1350° C. for 12 hours in a firing gas furnace, held for an additional hour, cooled, and taken out. The obtained ceramic porous body has no cracks and has high strength.

In addition, the (a) component OH group/(b) component in the premix
NCO group is 0.07, (c) component OH group/(b) component NCO group is
2.43, (a) + (b) + (c) for 100 parts of ceramic raw material
The quantity is 12 parts.

Example 2 66 parts by weight of alumina (average particle size: 5 microns), 28 parts by weight of alumina (average particle size: 0.5 microns), 30 parts by weight of kaolin, 0.5 parts by weight of magnesium carbonate, 2.5 parts by weight of calcium carbonate, 45 parts by weight of water, Add 5 parts by weight of triethanolamine to form a ceramic slurry. In advance, 13.6 parts by weight of TDI, polypropylene glycol (average molecular weight 5000, number of functional groups 3)
) 5 parts by weight, surfactant (trade name SF-8428,
The slurry ceramic was mixed and stirred into a premix containing 0.5 parts by weight of Toray Silicone Co., Ltd.) and poured into a mold. After being removed from the mold and dried in the same manner as in Example 1, the shrinkage rate was 4% and no abnormal warpage was observed. The temperature of this dried product was raised to 1700° C. over 20 hours in a gas furnace, maintained for 2 hours, and then cooled. No cracks or warpage were observed in the sintered ceramic porous body.

In addition, the (a) component OH group/(b) component in the premix
NCO group is 0.02, (c) component OH group / (b) component NCO group is
0.7, and the amount of (a) + (b) + (c) was 23.6 parts with respect to 100 parts of ceramic raw material.

Example 3 Water was added to a ceramic mixture of 20 parts by weight of kaolin, 40 parts by weight of feldspar, 30 parts by weight of anti-firestone, and 10 parts by weight of Kibushi clay.
Add 50 parts by weight, 0.05 parts by weight of sodium pyrophosphate, and 5 parts by weight of triethanolamine to form a mud-like ceramic. On the other hand, 6 parts by weight of crude MDI, 2.8 parts by weight of polypropylene glycol (average molecular weight 7000, average number of functional groups 2.5), surfactant (trade name
A dried polyurethane foam was obtained in the same manner as in Example 1 by mixing and stirring the slurry ceramic into a premix containing 1.5 parts by weight of PRX-607 (manufactured by Toray Silicone Co., Ltd.). The shrinkage rate of this dry product is 3
%, and no abnormal warpage was observed.

In addition, the (a) component OH group/(b) component in the premix
The NCO group was 0.04, the component (c) OH group/(b) component NCO group was 4, and the amount of (a)+(b)+(c) was 13.8 parts based on 100 parts of the ceramic raw material.

Comparative Example 1 In Example 1, the crude MDI, polypropylene glycol, surfactant, catalyst, etc. were mixed separately and simultaneously into the ceramic mud and stirred without being mixed in advance, but the mixture did not harden at all.

Comparative Example 2 Ceramic raw materials of 50 parts by weight of synthetic mullite, 10 parts by weight of Kibushi clay, 20 parts by weight of kaolin, and 20 parts by weight of talc, 40 parts by weight of water, and sodium hexametaphosphate.
0.1 part by weight, hydrophilic urethane prepolymer (polyethylene with an average molecular weight of 5000 containing 2.5 mol of tolylene diisocyanate and 90% ethylene oxide).
15 parts by weight of the reaction product with 1 mol of polypropylene glycol were mixed and reacted, and injection molded into a mold. The drying shrinkage rate of this urethane foam, similar to that of Example 1, was 13%, and abnormal shrinkage was observed at the four corners.

According to the method of this invention, since the polyalkylene polyol and the organic isocyanate compound are hydrophobic, when the mud-like ceramic and the premix are mixed, the premix does not react with the water in the mud-like ceramic, so that the viscosity increases. Since the rise is small, the amount of water added to the muddy ceramic can be reduced. In the conventional hydrophilic prepolymer method, the premix is hydrophilic and the viscosity of the composition increases significantly, so it is necessary to add a large amount of water. In addition, in this invention, the polyalkylene polyol and the organic isocyanate compound are in contact with each other in molecular units in the premix, so they easily react.
Since the resin is immediately polymerized by the reaction, the amount of urethane resin required for molding the urethane foam can be small. Furthermore, since the present invention uses a hydrophobic urethane foam, the urethane foam does not swell with water, so the shrinkage rate of the urethane foam when drying is small, and warpage does not occur. Furthermore, since the present invention requires only a small amount of water to be added to the aqueous ceramic slurry, the energy and time required for drying the urethane foam can be saved, making it economical.

Claims (1)

[Scope of Claims] 1 (a) Average molecular weight of 3,000 or more with two or more OH groups
10,000 polyalkylene polyol and (b) an organic isocyanate compound having two or more NCO groups at a molar ratio of OH group/NCO group of 0.01 to 0.5. A crosslinking agent having more than 100 functional groups and an aqueous ceramic slurry are combined with the above (b) organic isocyanate compound NCO
The molar ratio of the functional group of the crosslinking agent (c) to the group is from 0.29 to
Mix in a ratio of 7.5 to produce mud ceramic,
The above premix and the mud ceramic
Components (a), (b), and (c) are mixed so that the total weight is 10 to 35 parts by weight based on 100 parts by weight of the ceramic raw material, and this mixed composition liquid is poured into a mold to form a reaction foam. 1. A method for producing a porous ceramic body, which comprises drying and firing the urethane foam. 2. The method for producing a porous ceramic body according to claim 1, wherein a surfactant is added when producing a premix by mixing (a) a polyalkylene polyol and (b) an organic isocyanate compound.