JPH0148232B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a ceramic foam by firing a polyurethane foam molded product containing a ceramic raw material. (Prior Art) Conventionally, a method of manufacturing a ceramic foam by firing a polyurethane foam molded product containing a ceramic raw material is known. For example, (a) a first component consisting of an isocyanate capped polyoxyalkylene polyol having a functionality greater than 2 and being hydrophilic, the polyol containing at least 60 mole percent ethylene oxide units; a second component comprising an aqueous reactant having a sinterable ceramic material dispersed therein, the ratio of the number of moles of H ₂ O in said second component to the number of moles of NCO groups in said first component being from about 6.5 to about 390, and (c) an optional third component consisting of a cross-linking agent having a functionality greater than 2;
If the above-mentioned polyoxyalkylene/
The functionality of the polyol may be equal to 2.
-34228) is known. As another example, 40 parts by weight of water for 100 parts by weight of ceramic raw material.
~60 parts by weight is added to form a slurry, and to this slurry ceramic is added an ethylene oxide/propylene oxide copolymer with an average molecular weight of 1,500 to 3,500 and an ethylene oxide content of 70 to 90% by weight, and two or more isocyanate groups at the terminals. A free isocyanate group obtained by reacting with a polyisocyanate compound having 4
Hydrophilic urethane polymer containing ~8% 20-40
After mixing parts by weight and injecting this mixed composition into a mold to cause reaction foaming, the urethane foam is dried and fired to produce porous ceramic molded products.
56-145153) is known. In all of the above known methods, the ethylene oxide content of the polyoxyalkylene polyol for producing the urethane prepolymer is 60 mol% or more, and the number of functional groups (NCO groups) in the urethane prepolymer using this is 2. In order to exceed the
After mixing the ceramic slurry and the urethane prepolymer, the viscosity increases rapidly, making moldability difficult. Therefore, it is necessary to adjust the viscosity by adding water during the reaction process, but the mixing with water becomes non-uniform, making it difficult to expect a smooth foaming reaction.
In addition, if the ethylene oxide content of the polyoxyalkylene polyol is high, the polyurethane molded product will easily retain water, and water will need to be added during the molding process, so the shrinkage rate of the molded product after drying the polyurethane foam molded product becomes larger, causing distortion, waviness,
Warpage is likely to occur, resulting in a defective product. Furthermore, since the number of functional groups in the urethane prepolymer exceeds 2, its reactivity is high, making uniform stirring difficult, and separation within the polyurethane foam and expansion of the molded product immediately after release from the mold are likely to occur. The above problems make it difficult to produce uniform polyurethane moldings. Therefore, by reducing the ethylene oxide content of polyoxyalkylene polyol,
Since the water retention and reactivity of polyurethane foam molded products decrease, the drying shrinkage rate can be reduced, and the amount of water mixed in the ceramic slurry can be limited to a small amount, improving the moldability of polyurethane molded products. It is possible to improve drying properties and reduce irregular shrinkage such as warping and waviness. However, on the other hand, the dispersibility of the ceramic slurry and the urethane prepolymer is reduced, so the reaction is slow and the polyurethane foam becomes difficult to cure. Furthermore, since the water retention property is lowered, the ability to retain the ceramic raw material is lowered, resulting in a disadvantage that the hardness of the polyurethane molded product is lowered and it becomes brittle. (Object of the Invention) The object of the present invention is to improve the above drawbacks while maintaining the advantages of reducing the ethylene oxide content of polyoxyalkylene polyols. (Structure of the Invention) This invention comprises adding (a) 20 to 80 parts by weight of water, (b) a surfactant with an HLB value of 9 or more and/or tannic acid or its salt to 100 parts by weight of the ceramic raw material. Mix to form a ceramic slurry, and add (c) ethylene oxide content of 30 to this ceramic slurry.
Terminal NCO group 2 obtained by reacting a polyoxyalkylene polyol containing ~60% by weight and having two or more functional groups and an average molecular weight of 1,000 to 10,000 with a polyisocyanate compound such that the NCO/OH equivalent ratio is 2 or more. 5 to 40 parts by weight of a urethane prepolymer having 100 parts by weight of ceramic raw materials are mixed, and this mixed composition liquid is poured into a mold to cause reaction foaming, and then the polyurethane foam molded product is dried and fired. This is a method for producing ceramic foam characterized by the following. (Description of constituent elements) Ceramic raw materials used in this invention can generally be turned into sintered bodies by heating to high temperatures, including kaolin, clays, silica, alumina, feldspar, pottery stone, and mullite. , zircon, zirconia, titania, silicon carbide, cordierite, etc., and a mixture of these various raw materials. The amount of water (a) mixed with the above ceramic raw material is 20 to 80 parts by weight per 100 parts by weight of the ceramic raw material. If the amount of water is less than 20 parts by weight, the viscosity of the ceramic slurry becomes high and workability is increased. On the other hand, if it exceeds 80 parts by weight, the ceramic component tends to settle, and the water content in the polyurethane foam increases, resulting in a high drying shrinkage rate of the foam molded product. The molded product obtained tends to have closed cells. The amount of water mixed above is adjusted depending on the particle size of the ceramic raw material, and it is preferable that the larger the particle size, the smaller the amount of water mixed, and the smaller the particle size, the larger the amount of water mixed. In addition to the purpose of slurrying the ceramic raw material, this water also serves to react and foam the urethane prepolymer, which will be described later. (b) Surfactant and/or tannic acid or its salt mixed in the production of ceramic slurry is one of the features of this invention. Any of anionic, cationic, nonionic and amphoteric surfactants can be used as the surfactant. Anionic types include higher alcohol sulfate salts, alkylbenzene sulfonates, dialkyl sulfocarboxylic acid ester salts, and polyoxyethylene alkyl ether sulfate salts; cationic types include amide-bonded pyridinium salts and ester-bonded amines; nonionic types include polyoxyethylene Examples of amphoteric systems include alkyl ethers, polyoxyethylene/polyoxypropylene copolymers, polyoxyethylene carboxylic acid esters, polyoxyethylene alkyl phenyl ethers, and betaine and imidazoline carboxylic acids. From the viewpoint of mold releasability and low shrinkage of polyurethane foam, the effectiveness of each of the above surfactants is reduced in the following order: anionic, cationic, amphoteric, and nonionic.
Nonionic foams are superior in terms of viscosity stability immediately after mixing the ceramic slurry and urethane prepolymer and the hardness of the polyurethane foam. Overall, nonionic polyoxyethylene alkyl phenyl ether is preferred. The reason why polyoxyethylene alkyl phenyl ether is preferable is not clear, but it is presumed that by containing a phenyl group, it has good affinity with the urethane prepolymer and improves dispersibility. The HLB value of the surfactant is 9 or more, preferably 17 or more, and if the HLB value is less than 9, it will not contribute to improving the hardness of the polyurethane foam or the dispersibility of the ceramic slurry. The mixing amount of the surfactant is 0.05 to 2.0 parts by weight, preferably 0.3 to 0.8 parts by weight, per 100 parts by weight of the ceramic raw material; if it is less than 0.05 parts by weight, the effect cannot be obtained, and if it exceeds 2.0 parts by weight. and the drying shrinkage rate of polyurethane foam tends to increase. Examples of tannic acid or its salt include fivefold tannin, pyrogallol tannin, and their sodium salts, which are processed natural products containing complex components. This tannic acid or its salt has a phenolic hydroxyl group,
And since the water content is much higher, it is unlikely that it acts as a crosslinking agent by reaction with NCO groups, but the result is clearly improved hardness, shrinkage, and reactivity of the polyurethane foam. A synergistic effect between the dispersion effect and the catalytic effect is observed. The amount of tannic acid or its salt mixed is
0.01 to 2.0 parts by weight per 100 parts by weight, preferably
The amount is 0.04 to 0.08 parts by weight, and if it is less than 0.01 parts by weight, there is no effect, and if it exceeds 2.0 parts by weight, no improvement in the effect can be obtained. Tannic acid or its salt has conventionally been used as a useful protective colloid, but the phenomenon of improving the reactivity and hardness of polyurethane foams as described above is simply due to the stable dispersion of ceramic slurry. When you look at it, you have to say it's unique. The surfactant and tannic acid or its salt may be used alone or in combination. When used in combination, the mixing amount may be slightly smaller than the mixing amount when each is used alone. The above ceramic slurry contains peptizers such as sodium pyrophosphate, sodium silicate, hexametaphosphoric acid, sodium aluminate, sodium hydroxide, diethylamine, and pyridine, or viscosity modifiers such as carboxymethyl, hydroxyethylcellulose, methylcellulose, and polyvinyl alcohol. may be added. The mixing amount of these peptizers and viscosity modifiers is based on 100 parts by weight of ceramic.
0.01 to 0.1 part by weight is preferred. When reacted with the above ceramic slurry, the urethane prepolymer has an ethylene oxide content of 30~
A polyisocyanate compound is added to 52% by weight polyoxyalkylene polyol having two or more functional groups and an average molecular weight of 1000 to 10000 using NCO/OH.
It has two or more terminal NCO groups obtained by reacting at a quantitative ratio of two or more. The ethylene oxide content of the polyoxyalkylene polyol is 30 to 52% by weight (34 to 59 mol%), preferably 40 to 50% by weight. If the ethylene oxide content is less than 30% by weight, the reactivity of the urethane prepolymer will decrease, resulting in poor dispersibility in ceramic slurry.On the other hand, if the ethylene oxide content exceeds 52% by weight, the heat shrinkage rate of the polyurethane foam will increase and cracks may occur. becomes more likely to occur. The number of functional groups in the polyoxyalkylene polyol is 2 or more, preferably more than 2 and 3 or less. If the number of functional groups is less than 2, the polyurethane foam will not harden. If the average molecular weight of the polyoxyalkylene polyol is less than 1,000, the dispersibility of the urethane prepolymer will decrease, making it difficult for the polyurethane foam to cure.On the other hand, if the average molecular weight exceeds 10,000, the viscosity will be large and the reaction will be difficult. . The above polyoxyalkylene polyol is
Glycerin, trimethylolpropane, or triethanolamine is used as an initiator, and propylene oxide or ethylene oxide is added to these, or propylene oxide or ethylene oxide is added to a difunctional glycol such as ethylene glycol or 1,4-butadiol. mixed with the above polyol (3 or more functional groups),
Furthermore, an example of an initiator is a mixture of two or more functional groups and three or more functional groups, to which propylene oxide or ethylene oxide is added. The polyisocyanate compound has two terminals.
Those having an NCO group include tolylene diisocyanate (TDI), diphenmethane diisocyanate (MDI), and polymethylene polyphenylene diisocyanate (PAPI), with TDI and crude MDI being preferred from the viewpoint of cost. The NCO/OH molar ratio between the polyoxyalkylene polyol and the polyisocyanate compound is 2 or more, and the urethane prepolymer has 2 or more terminal NCO groups. If the NCO/OH molar ratio is less than 2, the polyurethane foam will not cure. The amount of urethane prepolymer mixed into the ceramic slurry is 5 to 40 parts by weight based on 100 parts by weight of the ceramic raw material. If the amount of the urethane prepolymer mixed is less than 5 parts by weight, the foaming power during the polyurethane reaction will be low, the porosity will be low, the specific gravity will be high, and the strength of the polyurethane foam will be low. On the other hand, if it exceeds 40 parts by weight, the expansion ratio will increase, shrinkage and deformation of the polyurethane foam during drying will increase, and the strength of the ceramic sintered foam will decrease. An open cell agent can be added to the urethane prepolymer. A preferred open-cell agent is polydimethylsiloxane/polyoxyalkylene copolymer, and the appropriate amount to be added is 1 to 2 parts by weight per 100 parts by weight of the ceramic raw material. The open cell agent is used as an open cell stabilizer for rigid urethane foam, and some of the cells generated during polyurethane foaming are destroyed to obtain an open cell polyurethane foam. This open cell polyurethane foam is
Shrinkage and deformation during drying and cracking and deformation during firing are reduced. The open-cell agent described above has poor dispersibility in water, and if it is directly mixed into the ceramic slurry, it will increase the viscosity of the ceramic slurry and may be hydrolyzed. Therefore, the open-cell agent is mixed with the urethane prepolymer. It is preferable to keep it. Furthermore, a catalyst widely used in polyurethane foaming, such as sigtyltine dilaurate or triethanolamine, may be added to the urethane prepolymer. The mixed composition liquid obtained by mixing the above-described ceramic slurry and urethane prepolymer and stirring sufficiently is poured into a mold, and is reacted and foamed in the mold to obtain a polyurethane foam molded product. The reaction in the mold is carried out at room temperature to 50°C for 3 to 5 minutes. After the polyurethane foam molded in the mold is removed from the mold, it is dried at 80 to 100°C for 15 to 24 hours to remove moisture contained in the polyurethane foam. The dried polyurethane foam is then heated in a high temperature oven. This heating is to thermally decompose the polyurethane and sinter the ceramic raw material, and the former process is carried out at temperatures ranging from room temperature to 400°C, during which time the polyurethane is gradually oxidized and decomposed, or oxygen is released. Pyrolysis occurs in insufficient atmosphere, and the latter step is usually carried out at temperatures above 1100°C, depending on the ceramic raw material. After sintering, the product is allowed to cool gradually and then taken out from the heating furnace. EXAMPLE A ceramic slurry is prepared by adding water, a surfactant, a five-fold tannin, and a peptizer in the amounts shown in Table 1 to a ceramic raw material prepared by mixing various ceramic materials, and uniformly mixing and stirring the mixture. On the other hand, ethylene oxide using ethylene glycol as an initiator
A urethane prepolymer is produced by mixing 1 mole of propylene copolymer and several moles of tolylene diisocyanate and reacting at 120°C for 3 hours. , manufactured by Nippon Unica Co., Ltd.) and mix. Next, the urethane prepolymer was added to the ceramic slurry and stirred to mix uniformly, and the mixed composition was molded into a polyvinyl chloride cylindrical mold (diameter 50 mm, length 280mm) and react and foam for 5 minutes. After taking out this polyurethane foam molding device from the mold, it was immediately dried in a dryer for 24 hours, and then the dried urethane foam was placed in an electric furnace and heated to 400°C for 5 hours and then to a high temperature for 2 hours. The mixture was heated, held at a high temperature for 2 hours and fired, and cooled 15 hours after firing to obtain a ceramic foam. Table 2 shows the conditions and physical property values for each of the above steps.

【table】

【table】

[Table] In Table 1, type of surfactant (a) is nonyl phenyl ether (nonionic type), (b) is the product name Emulget-9 (nonionic type), and (c) is the product name Monogen Y.
-500 (anionic type), (d) is a trade name of Cationogen L (cationic type), and (e) is a brand name of Neugen EA33 (nonionic type), and both are products of Daiichi Kogyo Seiyaku Co., Ltd. The type of peptizer (F) is sodium pyrophosphate, and (G) is sodium hexametaphosphate. The water retention properties in Table 2 are for urethane prepolymer
When foaming is performed by adding 0.5 g of additive and the specified amount of water to 20 g, the maximum amount of water retained in the foam after 5 minutes is measured. A calculated amount of urethane prepolymer is mixed with this by stirring for 10 to 15 seconds, and when this mixed composition is poured into a mold, it is judged as good if it can flow without remaining in the cup, and bad if a considerable amount remains in the cup. did. The hardness after 5 minutes of molding in Table 2 was measured using a JIS hardness meter type C. As shown in Table 2, in Comparative Example No. 1, in which no surfactant and five-fold tannin were added, the polyurethane foam cured slowly, and although it could be demolded in 10 minutes, the shape was deformed, so it was not baked. Ta. Comparative Example No. 2, in which the ethylene oxide content of the polyol was 70%, was not fired because its drying shrinkage was greater than that of the Examples. Comparative Example No. 3, in which the HLB value of the surfactant was small, had extremely low hardness after 5 minutes of molding, and could not be fired because it lost its shape and was difficult to demold. (Operations and Effects of the Invention) The present invention reduces the drying shrinkage rate of polyurethane foam molded products by reducing the ethylene oxide content of polyoxyalkylene polyol for producing urethane prepolymers to 30 to 52% by weight. This maintains the length stability during drying and the length stability of the fired product, which in turn reduces the occurrence of defective ceramic foam products. In addition, surfactants and/or tannic acid are added to the ceramic slurry to prevent the above-mentioned decrease in ethylene oxide content, which lowers the dispersibility of the prepolymer, the water retention capacity of the polyurethane foam, and the strength of the polyurethane foam. By adding it, the above-mentioned dispersibility and water retention are improved, and the strength of the polyurethane foam and ceramic foam is maintained.

Claims (1)

[Claims] 1. (a) 20 parts by weight of water for 100 parts by weight of ceramic raw material.
~80 parts by weight, (b) a surfactant with an HLB value of 9 or more and/or tannic acid or its salt are added and mixed to form a ceramic slurry, and to this ceramic slurry, (c) an ethylene oxide content of 30 to 52% by weight. , the number of functional groups is 2 or more and the average molecular weight is 1000~
10,000 polyoxyalkylene polyol and a polyisocyanate compound at an NCO/OH equivalent ratio of 2.
Terminal NCO obtained by reacting as above
5 to 40 parts by weight of a urethane prepolymer having two or more groups is mixed with 100 parts by weight of ceramic raw material,
A method for producing a ceramic foam, which comprises injecting this mixed composition into a mold to cause reaction foaming, and then drying and firing the polyurethane foam molded product. 2. The method for producing a ceramic foam according to claim 1, wherein the amount of surfactant mixed is 0.05 to 2.0 parts by weight based on 100 parts by weight of the ceramic raw material. 3. The method for producing a ceramic foam according to claim 1, wherein the amount of tannic acid or its salt mixed is 0.01 to 2.0 parts by weight based on 100 parts by weight of the ceramic raw material.