JPH0119986B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a phenolic resin for shell molds, which has a solid resol type phenolic resin as its main component, and particularly for shell molds with good mold strength. The present invention relates to a method for producing phenolic resin. [Prior art] Conventionally, when producing resin coated sand by the shell molding method, the phenolic resin used is generally a mixture of phenols and formaldehyde reacted at a molar ratio of 0.6 to 0.9 in the presence of an acidic catalyst. There are novolac type phenolic resins and resol type phenolic resins reacted in the presence of an alkaline catalyst at a molar ratio of 1 to 2.5. Novolac type phenolic resins are usually made by adding hexamethylenetetramine as a curing agent to the resin.
The resin-coated sand obtained by using 10 to 15% by weight generally has high strength and fast-curing shell properties, but the hexamine used in this method is used during mold making and pouring. When thermally decomposed, nitrogen compounds such as ammonia and amines are generated, causing environmental pollution, and when applied to cast iron or cast steel, the nitrogen compounds generated by thermal decomposition of hexamine may cause pinholes or proholes in cast products. There were disadvantages such as the generation of gas defects such as. Resol type phenolic resins have been used to improve these drawbacks found in novolac type phenolic resins. The resol type phenolic resin is obtained by reacting phenols and formaldehyde at a molar ratio of 1 to 3 in the presence of an alkaline catalyst. In the case of resol type phenolic resins for shell molds, there are generally two types: resins using ammonia as an alkaline catalyst and resins using ammonia and alkali metal hydroxides or alkaline earth metal hydroxides. The former resin is easy to solidify during resin production, but has the drawbacks of low shell mold strength and slow curing speed. The latter resin has the advantage that it is easy to solidify during resin production, has high shell mold strength, and has a fast curing speed. However, resol-type phenolic resins that use ammonia and alkali metal hydroxides or alkaline earth metal hydroxides have better shell mold strength and curing speed than resol-type phenolic resins that use ammonia alone. However, compared to novolak type phenolic resin,
There was still a problem that these physical properties were inferior. [Purpose of the Invention] The present inventors have developed a method for significantly improving the strength of shell molds obtained from resin-coated sand produced using a phenolic resin for shell molds whose main component is a solid resol type phenolic resin. As a result of extensive research, we found that 1.0 to 2.5 moles of formaldehyde were used per mole of phenol, and lithium hydroxide was used as a catalyst for each mole of phenols.
It has been found that the strength of the mold can be significantly improved by reacting with a combination of 0.002 to 0.2 moles of ammonia and 0.05 to 0.8 moles of ammonia, and further adding a novolak type phenolic resin and a lubricant. [Structure of the Invention] Lithium hydroxide in the present invention is a type of alkali metal hydroxide, but other alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and alkaline earth metal hydroxides may also be used. It has been found that resins using lithium hydroxide are significantly more effective in improving the strength of shell molds than resins using magnesium, calcium hydroxide, barium hydroxide, etc. In the presence of a novolak type phenolic resin with a number average molecular weight of 250 to 600 and a fatty acid amide lubricant, why does a phenolic resin whose main component is a solid resol type phenolic resin produced by a combined catalyst of lithium hydroxide and ammonia exhibit high shell strength? is unknown and is considered to be a unique phenomenon. The phenols in the present invention include phenol, orthocresol, metacresol, paracresol, xylenol, bisphenol A,
Resorcinol, hydroquinone, catechol, etc. are used. As formaldehyde, in addition to formalin, paraformaldehyde, trioxane, etc., which are substantial sources of formaldehyde generation, are used. The number average molecular weight of the novolak type phenolic resin used in the present invention is preferably 250 to 600. When the number average molecular weight is less than 250 or more than 600, the shell mold strength decreases. Novolac type phenolic resin is made by combining phenols and aldehydes in a molar ratio of 0.6 to 0.9 with oxalic acid, hydrochloric acid, sulfuric acid, zinc acetate,
It is a phenolic resin obtained by reaction in the presence of an acidic catalyst such as zinc carbonate. The amount of this novolak type phenolic resin to be blended is preferably 2 to 40% by weight in the phenolic resin obtained in the present invention. If it is less than 2% by weight or more than 40% by weight, the shell mold strength will decrease. The lubricant used in the present invention is preferably a fatty acid amide with a melting point of 100°C or higher, such as ethylene bisstearamide, methylene bisstearamide, oxystearamide, and stearamide. The content of these lubricants in the phenolic resin of the present invention is preferably 0.1 to 5% by weight. If it is less than 0.1% by weight or more than 5% by weight, the strength of the shell mold will decrease. In the present invention, when a silane coupling agent is blended with a phenolic resin, the shell strength is further improved. Examples of silane coupling agents include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-aminoethylaminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, etc. epoxysilanes such as aminosilane, γ-glycidoxypropyltrimethoxysilane, and vinylsilanes such as vinyltrichlorosilane and vinyltrimethoxysilane. When producing the phenolic resin in the present invention,
The diameter of the melt after the reaction is 0.5 to 7 m/m, and the length is 0.5
The shell strength is further improved by shaping into beads or rods of ~30 m/m. The method for producing resin coated sand using the phenolic resin for shell molding according to the present invention may be any of the dry hot coating method, semi-hot coating method, cold coating method, and powder solvent method. [Examples] The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples. In addition, "parts" and "%" described in each example and comparative example all indicate "parts by weight" and "% by weight." Production example 1 1000 parts of phenol, 620 parts of 37% formalin, and 10 parts of oxalic acid were charged into a reaction vessel equipped with a condenser, and the temperature was gradually raised. When the temperature reached 96°C, the mixture was refluxed for 120 minutes, and then dehydrated under vacuum. After the reaction was completed, the flask was discharged to obtain 915 parts of novolak type phenolic resin. The number average molecular weight of this novolak type phenolic resin is
It was 395. Example 1 1000 parts of phenol and 1760 parts of 37% formalin were charged into a reaction vessel equipped with a cooler, and then 28 parts of lithium hydroxide monohydrate and 85 parts of 28% aqueous ammonia were added, and the temperature was gradually raised until the temperature reached 96°C. After refluxing for 25 minutes, a dehydration reaction was carried out under vacuum, and when the internal temperature reached 70°C, 100 parts of the novolac type phenolic resin of Production Example 1 and 20 parts of ethylene bissteramide were added. Mixed. Thereafter, it was taken out of the pot and rapidly cooled to obtain 1170 parts of a solid phenolic resin. Example 2 1000 parts of phenol and 1760 parts of 37% formalin were charged into a reaction vessel equipped with a condenser, and then 28 parts of lithium hydroxide monohydrate and 85 parts of 28% aqueous ammonia were added, and the temperature was gradually raised until the temperature reached 96°C. After reflux reaction for 25 minutes, dehydration reaction was carried out under vacuum, and when the internal temperature reached 70°C, 100 parts of the novolak type phenol resin of Production Example 1 and 20 parts of ethylene bisstearamide were added and mixed. . Next, the resin produced from the reaction pot was flowed into a twin-screw extruder, extruded through a die at the tip of the extruder, and the resin was taken out while being air-cooled to form phenol resin 1120 into a rod shape with a diameter of 2 m/m and a length of 9 m/m. I got the department. Example 3 1000 parts of phenol and 1580 parts of 37% formalin were charged into a reaction vessel equipped with a cooler, and then 43 parts of lithium hydroxide monohydrate and 48 parts of 28% aqueous ammonia were added, and the temperature was gradually raised until the temperature reached 96°C. After refluxing for 20 minutes, a dehydration reaction was carried out under vacuum, and when the internal temperature reached 70°C, 200 parts of the novolak type phenolic resin of Production Example 1 and 25 parts of methylene bisstearamide were added and mixed. . Thereafter, it was taken out of the pot and rapidly cooled to obtain 1220 parts of a solid phenolic resin. Comparative Example 1 1000 parts of phenol and 1760 parts of 37% formalin were charged in a reaction vessel equipped with a cooler, and then 210 parts of 28% ammonia water was added, the temperature was gradually raised, and after the temperature reached 96°C, the reaction was refluxed for 40 minutes. A dehydration reaction was carried out under vacuum, and when the internal temperature reached 70°C, it was taken out of the pot and rapidly cooled to obtain 1030 parts of a solid phenol resin. Comparative Example 2 1000 parts of phenol and 1760 parts of 37% formalin were charged into a reaction vessel equipped with a condenser, and then 60 parts of sodium hydroxide and 85 parts of 28% aqueous ammonia were added, and the temperature was gradually raised until the temperature reached 96°C. After a reflux reaction for 25 minutes, a dehydration reaction was performed under vacuum, and when the internal temperature reached 70°C, 20 parts of ethylene bisstearamide was added and mixed. Thereafter, it was taken out of the pot and rapidly cooled to obtain 1060 parts of a solid phenolic resin. Comparative Example 3 1000 parts of phenol and 1760 parts of 37% formalin were charged into a reaction vessel equipped with a cooler, and then 60 parts of sodium hydroxide and 85 parts of 28% aqueous ammonia were added, and the temperature was gradually raised until the temperature reached 96°C. After a reflux reaction for 25 minutes, a dehydration reaction was carried out under vacuum, and when the internal temperature reached 70°C, the novolak type phenolic resin of Production Example 1
100 parts and ethylene bisstearamide
20 parts were added and mixed. Thereafter, it was taken out of the pot and rapidly cooled to obtain 1160 parts of a solid phenolic resin. Using the six types of phenolic resins obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3, six types of resin-coated sand were separately obtained. The manufacturing method is as follows. 7000 parts of Sanei No. 6 silica sand heated to a temperature of 130 to 140°C was charged into a Whirl mixer, and 140 parts of each of the phenolic resins obtained in Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 were added separately. After that, the mixture was kneaded for 40 seconds. Next, 105 parts of cooling water was added, and after kneading the coated sand until it disintegrated, 7 parts of calcium stearate was added, mixed for 30 seconds, the sand was removed, and aeration was performed to obtain resin coated sand. The characteristic values of each resin coated sand are
Shown in the table. The test method is as follows. Bending strength: Based on JACT test method SM-1. Adhesive point: Based on JACT test method C-1. Hot tensile strength: Based on JACT test method SM-10. 【table】

Claims (1)

[Claims] 1. A reaction is carried out using 1.0 to 2.5 moles of formaldehyde per mole of phenols, and 0.002 to 0.2 moles of lithium hydroxide and 0.05 to 0.8 moles of ammonia per mole of phenols as catalysts. 1. A method for producing a phenolic resin for shell molds, characterized in that the resin is made into a resol type phenolic resin, and a novolac type phenolic resin and a lubricant are blended when this resin is melted. 2. The method for producing a phenolic resin for shell mold according to claim 1, characterized in that a silane coupling agent is blended when the phenolic resin is melted. 3 The diameter of the shaped phenolic resin is 0.5 to 7
3. The method for producing a phenolic resin for shell mold according to claim 1 or 2, wherein the phenolic resin is bead-like or rod-like with a m/m length of 0.5 to 80 m/m.