JPS6235852B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to thermosetting resin-coated sand for castings and a method for producing the same. The present invention relates to a resin-coated sand for heat-curable castings that significantly improves mold disintegration properties, and a manufacturing method. [Prior Art] Generally, the coating binder used in resin-coated sand for thermosetting castings is a resin obtained by reacting phenol and almaldehyde in acidic or alkaline conditions. When this method is applied to foundry sand molds with low casting temperatures, such as aluminum castings, the molds tend to disintegrate and require heat treatment for 6 to 12 hours at a high temperature of around 500°C, making it difficult to remove sand after casting. This requires a huge amount of cost and effort. Therefore, a method of adding a halogen compound or a phosphorus compound to the phenolic resin has been proposed in order to improve the disintegration properties of the mold, but sufficient disintegration properties have not yet been obtained. In particular, recently there has been a call for energy savings, and there is a strong demand for thermosetting resin-coated sand for castings that reduces heat treatment and can perform operations equivalent to the current shell molding method. [Problems to be Solved by the Invention] The present invention provides resin-coated sand for heat-curable castings that reduces post-casting heat treatment, easily disintegrates, and has excellent mold strength that allows work equivalent to the current shell molding method. This is what you get. [Means to solve the problem] Block isocyanate compound and 1.5 to 1.5 to 1 mole of formaldehyde per mole of bisphenol A in foundry sand.
The use of resin-coated sand coated with a composition containing an ammonia resol resin obtained by reacting 4.0 mol of ammonia or 0.01 to 0.5 mol of hexamethylenetetramine significantly improves the disintegration properties after casting, and improves the disintegration properties of current shell molds. It can perform the same work as the method (sand fluidity, hardening speed), and in particular, it can greatly improve mold strength. That is, according to the present invention, when the thermosetting resin-coated sand for foundries as described above is filled into a mold heated to 150°C to 350°C, the blocking agent of the blocking isocyanate compound dissociates, and the generated isocyanate compound and ammonia The methylol groups, amino groups, imino groups, hydroxyl groups, etc. of the resol resin react, and the urethane bonds make the mold strong enough to allow it to be removed. Furthermore, the disintegration properties of the mold are significantly improved. This seems to be due to the use of urethane bonding in forming the template. As the blocking isocyanate compound in the composition used in the present invention, an addition reaction product of a polyisocyanate compound and an isocyanate blocking agent is used. As the polyisocyanate compound, any conventionally known isocyanate compound having two or more isocyanate groups can be used, and these polyisocyanate compounds and ethylene glycol, propylene glycol, trimethylolpropane, glycerin, and polyether polyols can be used. A terminal isocyanate group-containing compound obtained by reacting an active hydrogen compound such as is also used. As the isocyanate blocking agent, any conventionally used one can be used, including phenols such as phenol, cresol, and xylenol nonylphenol, tertiary alcohols such as t-butyl alcohol, acetylacetone, and malonic acid. Active methylene compounds such as diesters, aromatic amines such as methylaniline and diphenylamine, imides such as phthalic acid imide,
These include lactams such as ε-caprolactam, imines such as ethyleneimine, ureas, oximes, bisulfites, and boric acids. The blocked isocyanate compound used in the present invention can be obtained by reacting the above-mentioned isocyanate compound with an isocyanate blocking agent by a conventionally known method. In addition, the ammonia resol resin used in the present invention is preferably solid at room temperature in order to maintain the dryness of the sand, and bisphenol A is preferably used in order to improve the disintegration property.
Ammonia aresol resin is used. Ammonia resol resin of bisphenol A contains 1.5 to 4.0 formaldehyde per mole of bisphenol A.
A resin obtained by reacting 0.01 to 0.5 moles of ammonia or hexamethylenetetramine is used. If the amount of formaldehyde is less than 1.5 mol, the number of methylol groups decreases and the curing rate becomes slow, which is not preferable. Further, if the formaldehyde content exceeds 4.0 moles, the odor of formaldehyde will be strong during heat curing of the sand mold, which is not preferable. Ammonia or hexamethylenetetramine
If it is less than 0.01 mol, the effect of improving mold strength will be small or
If the amount exceeds 0.5 mol, the resin becomes too polymeric and the strength of the mold decreases, which is not preferable. There are no particular limitations on the method of synthesizing the ammonia aresol resin. The resin-coated sand for foundries of the present invention is produced by stirring and kneading a solid or solution blocking isocyanate compound and a solid or solution ammonia aresol resin into foundry sand heated to 90 to 180°C, and adding as needed during this kneading process. Obtained by evaporating the solvent. When the temperature of the foundry sand exceeds 180° C., the blocked isocyanate compound begins to dissociate, which not only shortens the life of the foundry resin-coated sand but also reduces the strength of the sand mold, which is undesirable. Furthermore, if the temperature is less than 90°C, the resin coating becomes insufficient and the solvent evaporates insufficiently, which lowers the melting point of the resin-coated sand for foundries and causes blocking, which is not preferable. Also, the blending ratio (weight ratio) of the blocking isocyanate compound and ammonia resol resin to be used is
Used in the range of 95:5 to 5:95, preferably
Used in the range 85:15 to 30:770. If there is too much blocking isocyanate, curing will be delayed, and if there is too much ammonia resol resin, the disintegrability of the sand mold will be poor. Furthermore, when producing resin-coated sand for foundries, there is no particular limitation on the method of mixing the blocked isocyanate compound and the resol-type phenolic resin, and even if the two components are mixed in advance before stirring and mixing with the sand, they may be mixed separately at the time of mixing. You can also put it in. Further, the foundry sand used in the present invention may be any of those commonly used for foundries, and zircon sand and olivine sand can also be used. The total amount of the blocked isocyanate compound and the resol type phenolic resin in the composition to be kneaded with the sand and coated is 4.0 to 0.5% by weight, preferably 3.0 to 1.0% by weight, based on the foundry sand. If the total amount of resin added exceeds 4%, this is not good as it not only causes gas defects during casting manufacturing but also increases the price. or
If it is less than 0.5%, the strength of the sand mold will be too low to be of practical use. Furthermore, any of the conventionally known dissociation catalysts for blocked isocyanate compounds can be used for the foundry resin-coated sand obtained in the present invention, such as dibutyl tin dilaurate,
Tinnic chloride, cobalt naphthenate, calcium octylate, cobalt octylate, etc. may be added, and the amount of the catalyst added is 0.01 to 20% by weight based on the solid content of the resin. In addition, a lubricant such as calcium stearate used in the shell mold method may be added to the resin-coated sand for foundries to improve fluidity, and the amount of the lubricant added is 0.05 to 0.2 to the foundry sand. weight%
It is. [Example] Examples of the present invention will be shown below. Example 1 (Synthesis of ammonia resol resin) 2280 g of bisphenol A 37% and 1620 g of formalin were added to a 4-necked flask equipped with a reflux condenser to give a concentration of 25%.
After adding 136 g of ammonia aqueous solution and reacting at 80°C for 2 hours, dehydration and concentration were performed to obtain a solid resin. (Production method of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
Then, 120 g of Coronate AP Stable (manufactured by Nippon Polyurethane Co., Ltd., phenol-masked isocyanate compound, softening point: approximately 100°C) and 40 g of the ammonia resol resin obtained above were added, and the mixture was stirred and kneaded until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 2 8 kg of flattery silica sand heated to 110°C in a kneader
and Coronate AP stable 100g and acetone 60g
A solution consisting of 100 g of the ammonia aresol resin obtained in Example 1 and 60 g of acetone was added to the mixture, and the mixture was stirred and kneaded until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 3 8 kg of phthalate silica sand heated to 160°C in a kneader
and Clelan cross-linking agent UT
(Manufactured by Sumitomo Bayer Urethane Co., Ltd., isocyanate compound masked with ε-caprolactam, softening point approximately 100°C) After adding 100g and stirring and kneading for 40 seconds, a solution consisting of 60g of ammonia resol resin obtained in Example 1 and 30g of methanol. Add and mix until the sand is broken down. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 4 Resin-coated sand for foundries was obtained in the same manner as in Example 3, except that 1.6 g of dibutyltin dilaurate was added. Table 1 shows the characteristics of the sand mold. Comparative Example 1 (Manufacture of novolac type phenolic resin) 1880 g of phenol, 244 g of 37% formalin, and 488 g of 80% paraformaldehyde were put into a four-necked flask equipped with a reflux condenser, and 4 g of oxalic acid was added, followed by reaction at reflux temperature for 3 hours. After dehydration and concentration, a solid resin was obtained. (Manufacture of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
and the novolak type phenolic resin obtained above.
After adding 160 g and stirring and kneading for 40 seconds, a solution consisting of 24 g of hexamethylenetetramine and 80 g of water was added, and the mixture was stirred and kneaded until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 of sand mold characteristics
Shown below. Comparative Example 2 8 kg of flattery silica sand heated to 160℃ in a kneader
Then, 100 g of Coronate AP Stable and 60 g of the novolak type phenolic resin obtained in Comparative Example 1 were added, and the mixture was stirred and mixed until the sand disintegrated. Then add 8g of calcium stearate and mix for another 20 seconds.
Resin-coated sand for foundries was obtained. Table 1 of sand mold characteristics
Shown below. Comparative Example 3 (Synthesis of resol type phenolic resin) 2280 g of bisphenol A and 1620 g of 37% formalin were put into a four-necked flask equipped with a reflux condenser.
After adding 40 g of 20% NaOH and reacting at reflux temperature for 2 hours, dehydration and concentration were performed to obtain a solid resin. (Production method of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
Then, 120 g of Coronate AP stable and 40 g of the resol type phenolic resin obtained above were added, and the mixture was stirred and kneaded until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated sand for foundry use. Table 1 shows the characteristics of the sand mold.

〔Effect of the invention〕

According to the present invention, resin-coated sand for foundries with excellent disintegrability, workability, and strength was obtained.

Claims (1)

[Claims] 1 Foundry sand containing blocked isocyanate compound and formaldehyde per mole of bisphenol A.
1. Resin-coated sand for thermosetting castings, characterized in that it is coated with a composition containing an ammonia resol resin obtained by reacting 1.5 to 4.0 moles of ammonia or 0.01 to 0.5 moles of hexamethylenetetramine. 2 (a) Foundry sand heated to 90 to 180°C, (b) blocked isocyanate compound, and (c) bisphenol A1
For mole, formaldehyde 1.5-4.0 mole, ammonia or hexamethylenetetramine 0.01-
1. A method for producing resin-coated sand for thermosetting castings, which comprises stirring and kneading an ammonia aresol resin obtained by reacting 0.5 mol of ammonia aresol resin. 3. The method for producing thermosetting resin-coated sand for foundries according to claim 2, wherein the blocked isocyanate compound is solid at room temperature. 4. The method for producing thermosetting resin-coated sand for castings according to claim 3, wherein the ammonia aresol resin is solid at room temperature.