JPS6258809B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to thermosetting resin-coated sand for castings and a method for producing the same, and in particular, to reduce the collapsibility of molds after casting, which are mainly used for producing castings with relatively low casting temperatures, such as aluminum castings and alloy castings. The present invention relates to a significantly improved thermosetting resin-coated sand for foundries and a method for producing the same. Generally, the coating binder used for resin-coated sand for thermosetting castings is a resin obtained by reacting phenol and formaldehyde in an acidic or alkaline environment. When applied to a foundry sand mold with a low casting temperature, the mold has poor collapsibility and requires heat treatment at a high temperature of around 500°C for 6 to 12 hours, resulting in extremely large costs and labor for removing sand after casting. is becoming necessary. 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. The inventor of the present invention has developed a resin-coated sand for foundry castings that requires less heat treatment after casting, disintegrates easily, and can perform the same work as the current shell molding method. By using resin-coated sand coated with a composition containing a compound and a resol-type phenolic resin, the disintegration properties after casting are significantly improved, and the work equivalent to the current shell molding method (sand fluidity, curing speed, etc.) is significantly improved. ) was found to be possible. That is, according to the present invention, when the thermosetting resin-coated sand for castings consisting of the 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 resol are dissociated. The methylol groups, hydroxyl groups, etc. of the mold phenolic resin react, and the mold becomes strong due to urethane bonds, reaching a strength that allows it to be removed from the mold. 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,
Examples 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. The resol type phenolic resin used in the present invention is preferably a resol resin using bisphenols to maintain the dryness of sand, and more preferably one that is solid at room temperature. As the resol type phenol resin, any phenol resin having a methylol group can be used, and the synthesis of the resol type phenol resin is not particularly limited, but phenol, cresol, bisphenol A,
Phenols such as bisphenol S and bisphenol F and formaldehyde are mixed with NaOH and Ba.
It is obtained by a conventionally known method by reaction using a synthetic catalyst such as (OH) ₂ , ammonia, or trimethylamine. As a resol type bisphenol resin,
A resin obtained by reacting bisphenols such as bisphenol A, bisphenol S, and bisphenol F with formaldehyde using a catalyst such as NaOH, Ba(OH) ₂ ammonia, or trimethylamine is used. As a resol type bisphenol resin, formaldehyde is 1.5 to 1 mole of bisphenol A.
A resin obtained by reacting 4.0 mol is preferably used. If the amount of formaldehyde is less than 1.5 mol, the number of methylol groups will decrease and the curing rate will be slow, and if the amount of formaldehyde exceeds 4.0 mol, the odor of formaldehyde will become strong during heat curing of the sand mold, which is not preferable. The resin-coated sand for foundries of the present invention is produced by stirring and mixing a solid or solution blocking isocyanate compound and a solid or solution resol-type phenolic resin into foundry sand heated to 90 to 180°C. It is obtained by evaporating the corresponding 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. Also the temperature is 90℃
Temperatures below this are not preferred because the resin coating becomes insufficient and the solvent evaporates insufficiently, lowering the melting point of the resin-coated sand for foundries and causing blocking. In addition, the blending ratio (weight ratio) of the blocked isocyanate compound and resol type phenol resin to be used is
Used in the range of 95:5 to 5:95, preferably
Used in the range of 85:15 to 30:70. If there is too much blocking isocyanate, curing will be delayed, and if there is too much resol type phenolic resin, the disintegrability of the sand mold will deteriorate. 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 blocking isocyanate compound and the resol type phenolic resin in the composition mixed with and coated with the sand is 7.0 to 0.3% by weight, preferably 3.0 to 0.5% by weight, based on the foundry sand. If the total amount of resin added exceeds 7%, it is not good because it not only causes gas defects during casting manufacturing but also increases the price. or
If it is less than 0.3%, 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,
Cobalt stannic chloride naphthenate, etc. may be added, and the amount of catalyst added is 0.01 to 1.0 based on the resin solid content.
Weight%. 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. Examples of the present invention will be shown below. Example 1 (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, 40 g of 20% NaOH aqueous solution was added, and the mixture was reacted at reflux temperature for 2 hours, followed by dehydration and concentration. A solid resin was obtained. (Production method of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
Add 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 resol type phenolic resin obtained above, and stir and mix until the sand disintegrates. 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
100g of Coronate AP Stable and 60g of acetone
A solution consisting of 100 g of the resol type phenolic resin obtained in Example 1 and 60 g of acetone was added and mixed with stirring 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 flattery silica sand heated to 160°C in a kneader
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 mixing for 40 seconds, 60g of the resol type phenolic resin obtained in Example 1 and 30g of methanol were added. Add the solution 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 (Production 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, 4 g of oxalic acid was added, and the mixture was reacted 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
The novolak type phenolic resin obtained above
After adding 160 g and stirring and mixing for 40 seconds, a solution consisting of 24 g of hexamethylenetetramine and 80 g of water was added and mixed with stirring 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: Sand mold characteristics
Shown below. Comparative Example 2 8 kg of flattery silica sand heated to 160℃ in a kneader
100 g of Coronate AP Stable and 60 g of the novolak type phenolic resin obtained in Comparative Example 1 were added to the mixture, and the mixture was stirred and mixed 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. Comparative Example 3 8 kg of flattery silica sand heated to 110℃ in a kneader
100g of Coronate AP Stable and 60g of acetone
A solution consisting of Sannix HS-207 (manufactured by Sanyo Chemical Industries, Ltd., Sucrose polyol with a viscosity of approx.
A solution consisting of 60 g of 170P/25°C) and 30 g of acetone was added and mixed for 3 minutes, then 8 g of calcium stearate was added and mixed for a further 20 seconds to obtain resin-coated sand for foundry use. Table 1 shows the characteristics of the sand mold.

[Table] The thermosetting resin-coated sand for foundries obtained in the present invention is excellent in sand fluidity, sand mold hardening speed, and sand mold disintegration property.

Claims (1)

[Scope of Claims] 1. Resin-coated sand for thermosetting foundries, characterized in that foundry sand is coated with a composition containing a blocked isocyanate compound and a resol type phenolic resin. 2. The resin-coated sand for thermosetting castings according to claim 1, wherein the resol type phenolic resin is a resol type bisphenol resin. 3. Resin-coated sand for thermosetting castings according to claim 2, wherein the resol-type bisphenol resin is a resin obtained by reacting 1.5 to 4.0 moles of formaldehyde with 1 mole of bisphenol A. . 4. A method for producing thermosetting resin-coated foundry sand, which comprises stirring and mixing (a) foundry sand heated to 90 to 180°C, (b) a blocked isocyanate compound, and (c) a resol type phenolic resin. 5. The method for producing thermosetting resin-coated sand for foundries according to claim 4, wherein the blocked isocyanate compound is solid at room temperature. 6. The method for producing thermosetting resin-coated sand for castings according to claim 4, wherein the resol type phenolic resin is solid at room temperature. 7. The method for producing resin-coated sand for thermosetting castings according to claim 4 or 6, wherein the resol type phenolic resin is a resol type bisphenol resin. 8. Resin-coated sand for thermosetting castings according to claim 7, wherein the resol type bisphenol resin is a resin obtained by reacting 1.5 to 4.0 moles of formaldehyde with 1 mole of bisphenol A. manufacturing method.