JPH0318531B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a binder composition that has excellent mold strength and is used in a cold-curing mold forming method. [Prior Art] Room temperature curing mold forming methods include methods using various organic or inorganic binders. A mold using an inorganic binder has poor sand disintegration properties after casting, and it is difficult to recover the sand. As a modeling method using an organic binder, there is a method in which a urea-modified furan resin or a resol type phenol resin is used with a strong acidic substance such as xylene sulfonic acid as a hardening agent. Although this method has a good disintegration property of the mold after casting, it has the disadvantage that the sulfonic acid group in the hardening agent decomposes during casting and generates sulfur dioxide gas, etc., which worsens the working environment. Another method using an organic binder is a modeling method in which a benzyl ether type phenol resin and a polyisocyanate liquid are cured with amines. This method shortens the modeling time and has good workability, but it is difficult to use because of the nitrogen content caused by the polyisocyanate. becomes nitrogen gas during casting, which tends to cause pinholes in the casting. In addition, as a method that does not contain nitrogen, a mold molding method using resol type phenolic resin and organic ester as a binder is published in Japanese Patent Publication No. 61-43132 and Japanese Patent Publication No. 61-37032.
is shown. However, this method has the problem that the obtained mold has extremely low strength, requires a large amount of binder, and its uses are limited. [Purpose of the Invention] As a result of various studies on phenolic resins for mold making using organic esters as curing catalysts, the present inventor found that resol-type polyphenolic resins obtained using polyvalent phenols can produce molds with excellent strength. We found that it is particularly effective for Furthermore, based on this knowledge, we proceeded with the study and completed the present invention. [Structure of the Invention] The present invention provides a binder composition for use in a room-temperature curing mold forming method using a resin and an organic ester, wherein the resin is a resol type polyphenolic resin. A binder composition. Here, the resol type polyhydric phenol resin is a liquid resin obtained by reacting polyhydric phenol and formaldehyde using an alkaline catalyst. Polyhydric phenols are phenols having two or more hydroxyl groups, such as catechol, resorcinol, hydroquinone, pyrogallol, oxyhydroquinone, and phloroglycin, and these can be used alone or in combination. Formaldehyde is usually used in the form of formalin. The molar ratio of formaldehyde to polyhydric phenols is 0.5 to 3.0. The alkaline substances used as catalysts are usually hydroxides or oxides of alkali metals or alkaline earth metals such as potassium hydroxide, sodium hydroxide, lithium hydroxide, calcium hydroxide, etc. Used at a ratio of 0.2 to 2.0. In addition, apply a silane coupling agent such as γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane to the resin at a rate of 0.2
By adding and mixing ~3.0% by weight, a mold with even higher strength can be obtained. The resol type polyhydric phenol resin of the present invention can be used alone or in combination with a normal resol type phenol resin. Organic esters used as curing catalysts include methyl formate, ethyl formate, propyl formate, butyrolactone, ethylene glycol diacetate, triacetin, and the like. The organic ester can be added at the time of mixing the sand and resin, or it can be gasified and added to the mixture of sand and resin. The ratio of organic ester to phenolic resin is suitably 0.1 to 0.5 in terms of weight ratio. If it is less than 0.1, the curing of the phenolic resin will be insufficient, and if it exceeds 0.5, the degree of curing will not increase. Foundry sand includes silica sand, zircon sand, chromite sand,
Olivine sand and recycled sand can be used. Appropriate weight ratios of the resin and organic ester to the foundry sand are 0.005 to 0.04 and 0.001 to 0.02, respectively. [Effects of the Invention] According to the present invention, a mold with high strength and few gas defects can be obtained, so it is extremely suitable as an industrial mold making method. [Example] Hereinafter, the present invention will be explained with reference to Examples. The invention is not limited by the examples. Further, "parts" and "%" shown in Examples, Comparative Examples, and Application Examples are all parts by weight and weight %. Example 1 1000 parts of resorcinol and 1474 parts of 37% formalin were placed in a reaction vessel equipped with a cooler and a stirrer and heated to 60°C.
heated to. Next, add 610 parts of 50% potassium hydroxide aqueous solution to 30
Added in portions. The temperature of the reaction solution was raised to 75-80°C, and the reaction was carried out until the resin viscosity reached 2.5-3.0 poise/25°C. After reaching a predetermined viscosity, the mixture was quickly cooled to 30°C or lower, and 30 parts of γ-aminopropyltriethoxysilane were added and mixed to obtain 3030 parts of a resol-type resorcinol resin with a viscosity of 3.0 poise/25°C. Example 2 A reaction was carried out in the same manner as in Example 1 except that 500 parts of resorcin and 500 parts of catechol were used to obtain 3040 parts of a resol type resorcin/catechol resin having a viscosity of 3.2 poise/25°C. Comparative example: 1,000 parts of phenol and 1,725 parts of 37% formalin were placed in a reaction vessel equipped with a cooler and a stirrer, and the temperature was heated to 60°C.
heated to. Next, add 715 parts of 50% potassium hydroxide aqueous solution to 30
Added in portions. The temperature of the reaction solution was raised to 75-80°C, and the reaction was carried out until the resin viscosity reached 0.8-1.2 poise/25°C, and then 250 parts of water was removed under reduced pressure of 70 Torr. Thereafter, the mixture was quickly cooled to 30°C or lower, and 32 parts of γ-aminopropyltriethoxysilane were added and mixed to obtain 3200 parts of a resol type phenolic resin having a viscosity of 3.0 poise/25°C. Application example: Fremantle silica sand 3000 in Shinagawa tabletop mixer
After mixing for 30 seconds, the resin of Example 1, Example 2 or Comparative Example was added.
60 parts were added and mixed for 60 seconds to prepare mixed sand. Immediately after mixing, the mixed sand was placed in a wooden mold with a 50 mm diameter and 50 mm height mold and was hammered with a plastic hammer.
After pounding, excess sand was removed to smooth the top surface of the shaped mixed sand. After the mixed sand had hardened in the wooden mold, the mold was removed and the compressive strength was measured. The results are shown in Table 1.

[Table] As shown in Table 1, the mold binder composition of the present invention provides a mold with high strength.

Claims (1)

[Scope of Claims] 1. In a binder composition used in a room temperature curing mold making method using a resol type phenolic resin and an organic ester, the resin uses a polyhydric phenol as the phenol and an alkali as a reaction catalyst. The molar ratio of metal or alkaline earth metal hydroxide or oxide to the polyhydric phenol is 0.2.
A binder composition for molds, characterized in that it is a resol type phenolic resin obtained by using the resin at a ratio of ~2.0. 2. Claim 1, wherein the polyvalent phenol is one or more selected from catechol, resorcinol, hydroquinone, pyrogallol, oxyhydroquinone, and phloroglycin.
The binder composition for molds as described in 2.