Curing-type organic urethane binder for casting mold, and casting sand composition and casting mold both obtained using same

Abstract

Provided is a curing-type organic urethane binder with which it is possible to advantageously produce a casting mold exhibiting excellent casting mold properties, while reducing influences on the environment as compared with conventional ones.　The curing-type organic urethane binder is for use in producing urethane-based casting molds and is composed of two liquids, an A liquid comprising a polyol compound as a main component and a B liquid comprising a polyisocyanate compound as a main component. The A liquid includes (a) a saturated fatty acid ester having a boiling point of 110-300°C and having a structure represented by structural formula (1) and (b) a C6-C20 aliphatic hydrocarbon, as a solvent. (In the formula (1), R1 is a C1-C12 hydrocarbon group and R2 is a C1-C10 hydrocarbon group.)

Description

Urethane-curing organic binder for molds, and molding sand composition and mold obtained using the same

[0001] The present invention relates to an organic mold binder used in the production of urethane-based gas-hardening molds or self-hardening molds used in sand casting, a molding sand composition obtained using the same, and a mold obtained by molding such a molding sand composition.

[0002] Conventionally, one of the typical organic molds used in sand casting is a urethane mold, for example, a phenol-urethane mold, which is produced by using a polyol compound such as a phenolic resin and a polyisocyanate compound such as diphenylmethane diisocyanate as binders and utilizing their polyaddition reaction (urethanization reaction). Widely known urethane molds such as phenol-urethane molds include mass-produced gas-hardening molds produced by the amine cold box method using amine gas as a catalyst, which does not require heating during molding, and non-mass-produced self-hardening molds produced by a room-temperature self-hardening method.

[0003] Specifically, gas-hardening molds using the amine cold box method are usually produced by kneading foundry sand with an organic foundry binder consisting of a phenolic resin solution and a polyisocyanate compound solution using a mixer to produce a foundry sand composition in which the surface of the foundry sand is coated with the organic binder, and then injecting the foundry sand composition into a predetermined mold to form a mold, and then passing an amine catalyst gas through the mold to harden it. Self-hardening molds using the room-temperature self-hardening method are produced by kneading granular refractory foundry sand with an organic foundry binder consisting of a phenolic resin solution and a polyisocyanate compound solution, while also mixing in a hardening catalyst, and then immediately molding the resulting mixture into the desired shape.

[0004] The phenolic resin solution and polyisocyanate solution constituting the organic mold binder as described above generally contain a predetermined solvent. As such a solvent, aromatic hydrocarbons have been widely used, as described in, for example, paragraph

[0060] of Patent Document 1 (JP-A 2012-533433). Traditionally, aromatic hydrocarbons used as such solvents have often been refined (petroleum products) from crude oil refining, etc. However, in recent years, there has been a social demand to move away from petroleum products from the perspectives of environmental conservation and carbon neutrality. Therefore, there is a demand for new solvents that can replace some or all of the aromatic hydrocarbons, which are petroleum products, for the solvents used in organic mold binders.

[0005] Special Publication No. 2012-533433

[0006] Under these circumstances, the present inventors conducted extensive research into the solvents constituting organic binders for urethane-setting molds. They discovered that organic binders for urethane-setting molds, which contain a combination of a specific saturated fatty acid ester and a specific aliphatic hydrocarbon as the solvent in a solution primarily composed of a polyol compound, can produce molds with excellent strength, similar to conventional organic binders for urethane-setting molds that use an aromatic hydrocarbon as the solvent. This discovery led to the completion of the present invention. The present invention was made in light of the above-mentioned circumstances, and aims to provide a urethane-setting organic binder that can advantageously produce molds with excellent mold properties while minimizing the environmental impact compared to conventional binders. Another objective of the present invention is to provide a foundry sand composition that uses such a urethane-setting organic binder and is capable of imparting excellent mold properties, and a foundry sand composition that is molded using such a foundry sand composition and has excellent properties.

[0007] In order to solve the above problems, the present invention can be suitably implemented in various aspects as listed below. Note that the aspects described below can be employed in any combination, and it should be understood that the aspects and technical features of the present invention are not limited to those described below, but can be recognized based on the inventive idea grasped from the entire description of the specification.

[0008] (1) A urethane-curing organic binder for use in the production of urethane-based casting molds, which is composed of two liquids: Liquid A, which contains a polyol compound as a main component, and Liquid B, which contains a polyisocyanate compound as a main component; wherein Liquid A contains a saturated fatty acid ester and an aliphatic hydrocarbon as a solvent, the saturated fatty acid ester having a boiling point of 110 to 300°C, and its structure is represented by the following structural formula (1), and the aliphatic hydrocarbon has 6 to 20 carbon atoms. (However, in the above formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms, and R 2 is a hydrocarbon group having 1 to 10 carbon atoms.) (2) The urethane-curing organic binder for foundry molds according to aspect (1), wherein the aliphatic hydrocarbon accounts for 1 to 50 mass% of the solvent in liquid A. (3) The urethane-curing organic binder for foundry molds according to aspect (1) or (2), wherein liquid A and / or liquid B further contain a dicarboxylic acid ester. (4) A foundry sand composition comprising the urethane-curing organic binder for foundry molds according to aspect (1) or (2), and foundry sand. (5) A foundry mold comprising a cured product of the foundry sand composition according to aspect (4).

[0009] Thus, the urethane-setting organic binder for foundry molds according to the present invention contains a specific aliphatic hydrocarbon and a specific saturated fatty acid ester as solvents for Liquid A, which is primarily composed of a polyol compound. By using such a specific aliphatic hydrocarbon and saturated fatty acid ester in combination, molds obtained using the urethane-setting organic binder for foundry molds according to the present invention can exhibit mold properties comparable to or even superior to those obtained using conventional urethane-setting organic binders. Furthermore, because the binder contains a specific aliphatic hydrocarbon as a solvent, it is possible to reduce or completely eliminate the use of aromatic hydrocarbons, which are commonly used as solvents in conventional urethane-setting organic binders for foundry molds. Therefore, the urethane-setting organic binder for foundry molds according to the present invention significantly contributes to improving the environment during mold-making and reducing the environmental impact during casting using the resulting molds. Furthermore, the use of aliphatic hydrocarbons, for example, derived from plants, can significantly contribute to achieving carbon neutrality.

[0010] The urethane-curing organic binder for molds (hereinafter simply referred to as the organic binder) according to the present invention is composed of two liquids having different main components. The polyol compound that is the main component of one of the two liquids (liquid A) is not particularly limited, and may be appropriately selected from various known polyol compounds that have been conventionally used in molding urethane-based curing molds. Specific examples include phenolic resins, polyether polyols, polypropylene polyols, polybutadiene polyols, polymer polyols, polypropylene glycols, polyethylene glycols, polytetramethylene ether glycols, polyoxybutylene glycols, copolymers of ethylene oxide and propylene oxide, copolymers of tetrahydrofuran and ethylene oxide, copolymers of tetrahydrofuran and propylene oxide, and copolymers of tetrahydrofuran and 3-methyltetrahydrofuran.

[0011] Among these, various known phenolic resins used in molding phenol-urethane molds can be suitably used as polyol compounds for molding urethane-based molds. Specifically, examples include organic solvent-soluble benzyl ether-type phenolic resins, resol-type phenolic resins, and novolac-type phenolic resins, which are obtained by subjecting phenols and aldehydes to an addition / condensation reaction in the presence of a reaction catalyst, generally in a ratio of 0.5 to 3.0 moles of aldehydes per mole of phenols. These various phenolic resins, both unmodified (unmodified phenolic resins) and modified (modified phenolic resins), can be used in the present invention. One or more of these unmodified and modified phenolic resins can be appropriately selected and used. For example, orthocresol-modified phenolic resins modified with orthocresol, preferably benzyl ether-type orthocresol-modified phenolic resins, and mixtures thereof are suitable for use in the present invention because they not only have excellent solubility in organic solvents and compatibility with polyisocyanate compounds, but also effectively improve the strength (early strength) of the resulting mold. Furthermore, examples of modified phenolic resins other than orthocresol-modified phenolic resins include lignin-modified phenolic resins and alkyl alcohol-modified phenolic resins, and modified phenolic resins other than these can also be used in the present invention. Raw materials (modifying raw materials) used together with phenol in producing (synthesizing) the modified phenolic resin include orthocresol, lignin, and alkyl alcohols used in the modified phenolic resins described above, as well as naphthols, alkylphenols, bisphenol A, and the like. Regarding such modifying raw materials, first, as naphthols, 1-naphthol and 2-naphthol are advantageous examples from the standpoints of ease of availability and cost, and these can be used alone or as a mixture.Examples of alkylphenols include o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, 2,3-xylenol, 3,5-xylenol, 2,5-xylenol, 3,4-xylenol, 2-propylphenol, 2-isopropylphenol, 3-propylphenol, 3-isopropylphenol, 4-isopropylphenol, 4-propylphenol, 2-sec-butylphenol, 2-tert-butylphenol, 3-sec-butylphenol, 3-tert-butylphenol, 4-sec-butylphenol, 4-te Examples include rt-butylphenol, 2-cyclohexylphenol, 3-cyclohexylphenol, 4-cyclohexylphenol, 2-nonylphenol, 3-nonylphenol, 4-nonylphenol, 2-dodecylphenol, 3-dodecylphenol, 4-dodecylphenol, 2-octadecylphenol, 3-octadecylphenol, 4-octadecylphenol, 2-isopropyl-5-methylphenol, 2-tert-butyl-4-methylphenol, 3-methyl-6-tert-butylphenol, 2,3,5-trimethylphenol, and 2,3,5-triethylphenol.

[0012] The catalyst used in the addition / condensation reaction between the phenols and the aldehydes described above is not particularly limited, and various catalysts conventionally used in the production of phenolic resins, including known acidic and basic catalysts, may be used appropriately depending on the type of phenolic resin desired. Examples of such catalysts include metal salts containing metal elements such as tin, lead, zinc, cobalt, manganese, and nickel. More specific examples include lead naphthenate, zinc naphthenate, lead acetate, zinc chloride, zinc acetate, zinc borate, and lead oxide, as well as combinations of acids and bases capable of forming such metal salts. When such metal salts are used as reaction catalysts, the amount used is not particularly limited, but is generally about 0.01 to 5 parts by mass per 100 parts by mass of the phenols.

[0013] Examples of phenols that can give phenolic resins include alkylphenols such as phenol, cresol, xylenol, p-tert-butylphenol, and nonylphenol, polyhydric phenols such as resorcinol, bisphenol F, and bisphenol A, and mixtures thereof, while examples of aldehydes include formaldehyde, formalin, paraformaldehyde, polyoxymethylene, glyoxal, furfural, and mixtures thereof.

[0014] Furthermore, as described above, examples of orthocresol-modified phenolic resins, which are one of the phenolic resins advantageously employed in the present invention, include (1) co-condensation orthocresol-modified phenolic resins of orthocresol and phenol obtained by reacting orthocresol and phenol with aldehydes in the presence of a reaction catalyst such as a metal salt, (2) a mixed orthocresol-modified phenolic resin of an orthocresol resin and a phenolic resin, (3) a modified orthocresol-modified phenolic resin obtained by modifying the resins (1) and (2) with a modifier, and a mixture of two or more of (1), (2), and (3). Note that the orthocresol-modified phenolic resins (1), (2), and (3) are all well known, and such known resins can be used as they are in the present invention. The phenol / orthocresol ratio is 1 / 9 to 9 / 1, preferably 3 / 7 to 7 / 3, and more preferably 4 / 6 to 6 / 4, on a mass basis.

[0015] These polyol compounds such as phenolic resins are used by dissolving them in a predetermined organic solvent from the viewpoints of low viscosity, compatibility with the polyisocyanate solution described below, coating properties on foundry sand, mold properties, etc., and a major technical feature of the present invention resides in the fact that the solvent contains a specific saturated fatty acid ester and a specific aliphatic hydrocarbon. While various petroleum-derived solvents, including aromatic hydrocarbons, are commonly used as solvents for dissolving the above-mentioned polyol compounds from the viewpoints of ease of availability and mold properties, even an organic binder using a solvent containing a specific saturated fatty acid ester and a specific aliphatic hydrocarbon as in the present invention can achieve effects comparable to or even superior to those of an organic binder using a petroleum-based solvent in terms of compatibility with the polyisocyanate solution, coating properties on foundry sand, mold properties, etc. Furthermore, the organic binder according to the present invention significantly contributes to improving the environment during mold making operations and reducing the environmental load during casting using the resulting molds. In addition, by using, for example, plant-derived aliphatic hydrocarbons, it can also significantly contribute to achieving carbon neutrality.

[0016] In the present invention, the first essential component constituting the solvent of Solution A, which contains a polyol compound as a main component, is a saturated fatty acid ester having a boiling point of 110 to 300°C and a structure represented by the following structural formula (1): (However, in the above formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms, and R 2 is a hydrocarbon group having 1 to 10 carbon atoms.) If a saturated fatty acid ester having a boiling point of less than 110°C is used, it may be difficult to reduce the burden on the environment, while if a saturated fatty acid ester having a boiling point of more than 300°C is used, the various properties of the final mold may not be sufficient. The boiling point of the saturated fatty acid ester used in the present invention is preferably 145 to 250°C, more preferably 160 to 220°C. In addition, R in the above formula (1) 1Examples of the R include alkyl groups and cycloalkyl groups having 1 to 12 carbon atoms, preferably 3 to 9, and more preferably 5 to 7 carbon atoms, and among these, alkyl groups having 1 to 12 carbon atoms, preferably 3 to 9, and more preferably 5 to 7 carbon atoms are desirable. 2 Examples of the alkyl group include alkyl groups and cycloalkyl groups having 1 to 10 carbon atoms, preferably 1 to 8, more preferably 1 to 6, and even more preferably 1 to 4 carbon atoms. Among these, alkyl groups having 1 to 10 carbon atoms, preferably 1 to 8, more preferably 1 to 6, and even more preferably 1 to 4 carbon atoms are desirable. In addition, the saturated fatty acid ester used in the present invention preferably has a total of 5 to 14 carbon atoms in one molecule, more preferably 7 to 12, and even more preferably 8 to 10 carbon atoms. Examples of saturated fatty acid esters that can be used in the present invention include butyl acetate (boiling point: 126°C), butyl butyrate (boiling point: 164°C), ethyl hexanoate (boiling point: 167°C), methyl octanoate (boiling point: 193°C), 2-ethylhexyl acetate (boiling point: 200°C), ethyl octanoate (boiling point: 208°C), and ethyl decanoate (boiling point: 243°C).

[0017] In the present invention, the second essential component constituting the solvent of Solution A is an aliphatic hydrocarbon having 6 to 20 carbon atoms. The number of carbon atoms in the aliphatic hydrocarbon used in the present invention is preferably 8 to 16, more preferably 10 to 14. Aliphatic hydrocarbons having fewer than 6 carbon atoms or more than 20 carbon atoms may not fully exhibit the desired function as a solvent for an organic binder. In the present invention, any aliphatic hydrocarbon having 6 to 20 carbon atoms, including saturated and unsaturated aliphatic hydrocarbons, as well as aliphatic hydrocarbons having a chain structure and aliphatic hydrocarbons having a cyclic structure in whole or in part, can be used. However, saturated aliphatic hydrocarbons are preferred, and alkanes having a chain structure are even more preferred. Examples of aliphatic hydrocarbons that can be used in the present invention include hexane (6 carbon atoms), undecane (11 carbon atoms), hexadecane (16 carbon atoms), and octadecane (18 carbon atoms).

[0018] The proportions of the saturated fatty acid esters and aliphatic hydrocarbons used in Liquid A of the present invention are not particularly limited, but the saturated fatty acid esters and aliphatic hydrocarbons are preferably used so that the proportion of aliphatic hydrocarbons in the solvent in Liquid A is 1 to 50 mass%, more preferably 5 to 45 mass%, and even more preferably 10 to 40 mass%. If this proportion exceeds 50 mass%, depending on the saturated fatty acid esters and aliphatic hydrocarbons used, they may not be able to effectively dissolve the phenolic resin and may not fully function as a solvent. Note that, in the present invention, the solvent in Liquid A refers to all liquid substances blended into Liquid A to dissolve the polyol compound (phenolic resin), and is intended to exclude liquid substances added to Liquid A for other purposes.

[0019] In the present invention, the solvents constituting Solution A are not limited to the saturated fatty acid esters and aliphatic hydrocarbons described above, and various solvents that have conventionally been used to dissolve polyol compounds such as phenolic resins, for example, aromatic hydrocarbons, can also be used together with saturated fatty acid esters and aliphatic hydrocarbons, so long as they do not impair the object of the present invention. When aromatic hydrocarbons are used as the solvent constituting Solution A of the present invention, the proportion of aromatic hydrocarbons in the solvent is preferably 50 mass % or less, more preferably 40 mass % or less, even more preferably 30 mass % or less, and most preferably 20 mass % or less.

[0020] The solution A of the present invention preferably contains a dicarboxylic acid ester as a solvent together with the saturated fatty acid ester and the aliphatic hydrocarbon described above. In the present invention, any dicarboxylic acid ester can be used without any particular limitation as long as it can function as a solvent for the solution A. However, a dicarboxylic acid ester represented by the formula: R a OOC-R b -COOR c Here, R a and R c are each independently an alkyl group having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, and Rb is a linear or branched hydrocarbon group having 1 to 7 carbon atoms. In the present invention, a dibasic acid ester, which is a mixture of dimethyl succinate, dimethyl glutarate, and dimethyl adipate and is commercially available from DuPont, USA, is advantageously used.

[0021] Furthermore, liquid A of the present invention can also contain various known additives such as anti-staining agents and silane coupling agents.

[0022] For example, the silane coupling agent is an organosilicon compound having a structure in which an organic group having a basic group such as an amino group is bonded to silicon (Si). Examples of the silane coupling agent include alkoxysilanes having an amino group such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, as well as basic silane compounds having a ureido group such as hexamethyldisilazane and 3-ureidopropyltrialkoxysilane. Among the basic silane compounds described above, basic alkoxysilanes are preferred, and among these, alkoxysilanes having an amino group are more preferred. N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-ureidopropyltrialkoxysilane are even more preferred. These amino-group-containing alkoxysilanes are the most suitable because, in addition to their ease of availability, the alkoxy groups are hydrolyzed by the water in the polyol compound to hydroxyl groups, thereby strengthening adhesion to foundry sand (aggregates, etc.) and enabling the development of high mold strength. Furthermore, reaction products of the above-described basic silane compounds with acids or their halides can also be used in the present invention.The acid or its halide to be reacted with the basic silane compound may be an inorganic acid, an organic acid, or a halide thereof. Examples of such an acid or halide include inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, and boric acid; organic sulfonic acids such as benzenesulfonic acid, paratoluenesulfonic acid, and trifluoromethanesulfonic acid; organic carboxylic acids such as formic acid, acetic acid, and benzoic acid; and organic phosphonic acids. Of these, hydrochloric acid, hydrobromic acid, phosphoric acid, hydrofluoric acid, benzenesulfonic acid, paratoluenesulfonic acid, and trifluoromethanesulfonic acid are advantageously used. The halides include halides of organic acids such as the above-mentioned organic sulfonic acids, organic carboxylic acids, and organic phosphonic acids, such as phenylphosphonic acid dichloride, isophthalic acid chloride, benzoyl chloride, caprylic acid chloride, lauric acid chloride, myristic acid chloride, palmitic acid chloride, isopalmitic acid chloride, stearic acid chloride, isostearic acid chloride, oleic acid chloride, and sebacic acid dichloride, among which phenylphosphonic acid dichloride and lauric acid chloride are preferably used. In addition to the above-mentioned, various conventionally known silane coupling agents such as tetraethoxysilane, methacrylsilane, vinylsilane, mercaptosilane, isocyanatesilane, and epoxysilane can also be used in the present invention.

[0023] Then, a polyol compound such as a phenolic resin, the specific saturated fatty acid ester and specific aliphatic hydrocarbon described above, and the dicarboxylic acid ester and additives used as needed are uniformly mixed to prepare a solution having a concentration of the polyol compound such as a phenolic resin of about 30 to 80 mass %, preferably 40 to 70 mass %, and more preferably 45 to 60 mass %, which is used as Liquid A in the present invention.

[0024] Meanwhile, Liquid B, which together with Liquid A constitutes the urethane-curing organic binder for foundry molds according to the present invention, is primarily composed of a polyisocyanate compound. This polyisocyanate compound has two or more isocyanate groups in its molecule that can undergo a polyaddition reaction with the active hydrogen of a polyol compound, such as a phenolic resin, to chemically bond the foundry sand together through urethane bonds, such as those in phenolic urethane bonds. Specific examples of such polyisocyanate compounds include aromatic, aliphatic, and alicyclic polyisocyanates, such as diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanate (hereinafter referred to as "polymeric MDI"), hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate, as well as various other conventional polyisocyanates, such as prepolymers containing two or more isocyanate groups obtained by reacting these compounds with polyols. These compounds may be used alone or in combination of two or more.

[0025] Furthermore, for the same reasons as those for polyol compounds such as phenolic resins described above, in the present invention, such polyisocyanate compounds are used as a solution obtained by dissolving them in a predetermined solvent to a concentration of about 40 to 99.9% by mass, preferably 50 to 90% by mass, and more preferably 60 to 85% by mass. Depending on the type of polyisocyanate compound used, it is not necessarily necessary to dissolve it in a solvent, and it is also possible to use the undiluted solution as is. In this specification and claims, the term "liquid ... containing a polyisocyanate compound as a main component" encompasses both a undiluted solution of a polyisocyanate compound and a solution obtained by dissolving a polyisocyanate compound in a solvent.

[0026] Here, the solvent for dissolving the polyisocyanate compound is not particularly limited as long as it is non-reactive with the polyisocyanate compound and is a good solvent for the solute to be dissolved (polyisocyanate compound or polyol compound). In addition to the solvents described above for the solution A containing a polyol compound as the main component, a combination of i) a polar solvent for dissolving the polyol compound such as a phenolic resin and ii) a non-polar solvent for dissolving the polyisocyanate compound in an amount that does not cause separation of the polyol compound such as the phenolic resin is generally used.

[0027] More specifically, examples of the polar solvents of i) above include dicarboxylic acid alkyl esters, vegetable oil methyl esters such as rapeseed oil methyl ester, as well as ketones such as isophorone, ethers such as isopropyl ether, furfuryl alcohol, etc. Furthermore, examples of the nonpolar solvents of ii) above include petroleum hydrocarbons such as paraffins, naphthenes, and alkylbenzenes, specific examples of which include Ipsol 150 (a petroleum-based solvent manufactured by Idemitsu Kosan Co., Ltd.), Hisol 100 (a petroleum-based solvent manufactured by JX Nippon Oil & Energy Corporation), and HAWS (a petroleum-based solvent manufactured by Shell Chemicals Japan Ltd.).

[0028] It is also possible to further blend various conventionally known additives such as a stain-resistant agent, a silane coupling agent, a pot life extender (curing retarder), a release agent, a strength deterioration inhibitor, and a drying inhibitor into the B liquid containing a polyisocyanate compound as the main component.

[0029] The urethane-curing organic binder for foundry molds according to the present invention, which is composed of parts A and B obtained in this manner, is mixed with foundry sand in the same manner as in the conventional method to form a foundry sand composition for molding a urethane-based gas-curing mold.

[0030] Specifically, for example, in the production of a gas-hardening mold by the cold box method, the organic foundry binder (Liquids A and B) according to the present invention is first mixed with foundry sand to produce a foundry sand composition (mixed sand) in which the surface of the foundry sand is coated with the organic foundry binder. Specifically, the organic binders, Liquid A (a solution containing a polyol compound as its main component, a reaction product of a basic silane compound and hydrofluoric acid, and adjusted to a water content of 0.1 to 15 wt %) and Liquid B (a solution containing a polyisocyanate compound as its main component, preferably also containing a higher fatty acid ester), as well as various desired additives, are thoroughly mixed with the foundry sand to coat the surface of the foundry sand with Liquids A and B, which serve as the organic foundry binders, to produce the foundry sand composition.

[0031] In producing such a foundry sand composition, the organic binder components A and B are prepared separately in advance, because a polyaddition reaction (urethane reaction) begins to occur gradually from the stage of mixing them. These components are usually mixed with the foundry sand during kneading. The kneading and mixing operations are carried out using a conventional continuous or batch mixer, preferably at temperatures ranging from -10°C to 50°C.

[0032] The foundry sand to be mixed with the organic foundry binder of the present invention may be any refractory sand conventionally used for foundries, whether natural or artificial. Examples include silica sand, olivine sand, zircon sand, chromite sand, alumina sand, ferrochrome slag, ferronickel slag, converter slag, mullite-based artificial particles (e.g., "Cerabeads" available from Itochu Ceratec Corporation), alumina-based artificial particles, and various other artificial particles, as well as recycled or recovered sand. One or more of these may be used in combination. Among these, natural silica sand (including recycled sand) with a high silica content is particularly preferred.

[0033] Generally, molding sand preferably has an AFS index of 30 to 100, more preferably 40 to 90, and even more preferably 50 to 70. If the AFS index is less than 30, the particle size of the refractory aggregate (refractory particles) becomes too large, which adversely affects thermal conductivity and may degrade the mold properties, further resulting in problems such as a deterioration in the casting surface. On the other hand, if the AFS index exceeds 100, the particle size of the refractory aggregate (refractory particles) becomes too small, which may result in problems such as an increase in the generation of lumps, which are agglomerates of the refractory particles, when kneaded with a resin binder, making it difficult to fully improve thermal conductivity, and further problems such as a deterioration in gas permeability, which may lead to gas defects in the casting.

[0034] The foundry sand composition obtained as described above is then shaped in a mold such as a die that will give the desired shape, and then a catalyst gas for hardening is passed through the foundry sand composition to accelerate hardening, thereby producing a gas-hardened mold. Examples of catalyst gases include conventionally known tertiary amine gases such as triethylamine, dimethylethylamine, and dimethylisopropylamine, as well as cyclic nitrogen compounds, pyridine, and N-ethylmorpholine, and at least one of these is appropriately selected and used in the usual amount range.

[0035] When producing the desired self-hardening mold by the room-temperature self-hardening method, the molding sand composition is first produced by coating the surface of the molding sand with organic binders (Liquids A and B), just as in the case of the gas-hardening mold described above. During the kneading process, a curing catalyst is further mixed into the molding sand composition used in the room-temperature self-hardening method, along with the organic binder of the present invention. Examples of such a curing catalyst include bases, amines, metal ions, and the like, which are commonly used in the well-known Ashland process.

[0036] Furthermore, in preparing the foundry sand composition that will give the gas-hardening mold or self-hardening mold described above, the amounts of liquid A and liquid B that are preferably used are such that the amounts of the main components, the polyol compound and the polyisocyanate compound, are about 0.3 to 5.0 parts by mass, and preferably about 0.4 to 3.0 parts by mass, per 100 parts by mass of the foundry sand. The blending ratio of the polyol compound to the polyisocyanate compound is not particularly limited, but liquid A and liquid B are generally combined so that the ratio of polyol compound to polyisocyanate compound is 4:6 to 6:4 by mass.

[0037] Thus, the strength of the gas-hardening molds and self-hardening molds produced as described above is comparable to or even superior to that of molds produced using conventional organic binders containing solvents such as aromatic hydrocarbons. Furthermore, the use of the urethane-hardening organic binder for foundry molds according to the present invention advantageously improves the environment during the mold-making process and reduces the environmental impact during casting using the resulting molds. Furthermore, the use of aliphatic hydrocarbons derived from plants, for example, contributes significantly to achieving carbon neutrality.

[0038] The present invention will be clarified in more detail by showing some representative examples of the present invention below, but it goes without saying that the present invention is not limited in any way by the description of such examples. Furthermore, it should be understood that in addition to the following examples and the above-mentioned specific description, various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art, as long as they do not deviate from the spirit of the present invention.

[0039] - Preparation of Phenolic Resin Solution (Solution A) - 50 parts by mass of phenol and 50 parts by mass of orthocresol (phenol / orthocresol = 50 / 50), 42.2 parts by mass of 92% by mass paraformaldehyde, and 0.15 parts by mass of zinc naphthenate as a divalent metal salt were charged into a three-necked reaction flask equipped with a reflux condenser, a thermometer, and a stirrer, and the mixture was reacted at reflux temperature for 180 minutes, followed by heating and concentration to obtain an orthocresol-modified benzyl ether-type phenolic resin having a water content of 1% or less. Next, 50 parts by mass of the resulting phenolic resin was dissolved in a solvent containing saturated fatty acid ester or methyl oleate (unsaturated fatty acid ester), aliphatic hydrocarbon, a dibasic acid ester (DBE: manufactured by DuPont USA) as a polar organic solvent serving as a plasticizer, petroleum solvents Ipzol 150 (trade name, manufactured by Idemitsu Kosan Co., Ltd.) and AF Solvent No. 4 (AF4: trade name, manufactured by ENEOS Corporation) in the proportions shown in Tables 1 to 4 below, to prepare a phenolic resin solution (Liquid A). However, for the composition of Comparative Example 4 shown in Table 4, preparation of a phenolic resin solution was attempted, but the components were not sufficiently miscible, and the final liquid mixture did not function as a solution. Therefore, preparation of the phenolic resin solution was abandoned, and subsequent experiments were discontinued.

[0040] - Preparation of Polyisocyanate Solution (Liquid B) - A polyisocyanate solution (Liquid B) was prepared by dissolving 80 parts by mass of polymeric MDI, which is a polyisocyanate compound, in a solvent consisting of saturated fatty acid ester, aliphatic hydrocarbon, and petroleum-based solvent (IPZOL 150, AF4) in the proportions shown in Tables 5 to 8 below.

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] Then, 1,000 parts by mass of Wedron sand and 5 parts by mass each of the A and B liquids prepared as described above were added to a Dalton Co., Ltd. Productgawa-type bench mixer, and the mixture was stirred and kneaded for 60 seconds to prepare foundry sand compositions (Examples 1 to 15, Comparative Examples 1 to 3).

[0050] For each of the resulting molding sand compositions, two types of mold strength were measured according to the following measurement and evaluation methods, and the skin corrosivity due to the solvent and the amount of soot expected to be generated during casting were evaluated. The measurement and evaluation results are shown in Tables 9 to 12 below.

[0051] Measurement of Mold Strength (2 Hours, 24 Hours) The kneaded molding sand composition was placed in the sand magazine of a cold box molding machine, and then this molding sand composition was filled into a mold for preparing bending strength test pieces at a gauge pressure of 0.3 MPa. Next, triethylamine gas was passed through the mold using a gas generator at a gauge pressure of 0.2 MPa for 1 second, followed by air purging at a gauge pressure of 0.2 MPa for 14 seconds. The mold was then demolded to prepare bending test pieces (molds) measuring 3 cm wide, 8.5 cm long, and 1 cm thick. The resulting test pieces were then measured for bending strength (N / cm) using a digital force gauge (manufactured by Imada Co., Ltd.) i) 2 hours after molding, and ii) after leaving them for 24 hours under low-humidity conditions of an air temperature of 25°C and a relative humidity of 40%. 2 ) is measured.

[0052] - Evaluation of skin corrosivity by solvents - Using the corrosivity category in the SDS (Safety Data Sheet) for each solvent used as a reference, judge according to the following criteria based on the percentage of corrosive solvents in the total solvent volume: ○: Does not contain solvents in corrosive category 1 or 2. △: Contains less than 25% by mass of solvents in corrosive category 1 or 2. ×: Contains 25% by mass or more of solvents in corrosive category 1 or 2.

[0053] - Amount of soot expected during casting - Test pieces were prepared from each molding sand composition using the same procedure as in the mold strength measurement described above. The resulting mold test pieces (after two hours had elapsed) were then exposed to 1,000°C in a portable electric furnace, simulating the casting process, and the amount of soot generated from the mold was evaluated. Specifically, five panelists visually evaluated the amount of soot generated according to the following criteria, using the amount of soot generated during evaluation of the mold test piece made from the molding sand composition of Comparative Example 1 as the standard. The most common evaluation among the five panelists was used as the final result, and the results were compared to the molding sand composition of Comparative Example 1 to evaluate its relative merits. ∘: Less soot generated than Comparative Example 1. Δ: The same amount of soot generated as Comparative Example 1. ×: More soot generated than Comparative Example 1.

[0054]

[0055]

[0056]

[0057]

[0058] As is clear from a comparison of the results shown in Tables 9 to 12, when organic foundry binders using specific saturated fatty acid esters and aliphatic hydrocarbons as the solvents for Liquid A according to the present invention are used, the molds obtained using these binders exhibit mold properties (mold strength) comparable to those obtained from conventional foundry resin compositions using petroleum-based solvents. Furthermore, because the foundry resin compositions of the present invention do not contain solvents of corrosive Class 1 or 2, the working environment during the preparation of the foundry sand composition and the mold-making process is advantageously improved. Furthermore, the amount of soot generated by the resulting molds is effectively reduced, thereby advantageously reducing the burden on the environment.

Claims

A urethane-curing organic binder used for molding urethane-based casting molds, which is composed of two liquids: liquid A containing a polyol compound as a main component, and liquid B containing a polyisocyanate compound as a main component, The liquid A contains a saturated fatty acid ester and an aliphatic hydrocarbon as a solvent, The saturated fatty acid ester has a boiling point of 110 to 300°C and a structure represented by the following structural formula (1): The aliphatic hydrocarbon has 6 to 20 carbon atoms. A urethane-curing organic binder for molds characterized by: (However, in the above formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms, and R 2 is a hydrocarbon group having 1 to 10 carbon atoms.

2. The urethane-setting organic binder for foundry molds according to claim 1, wherein the proportion of the aliphatic hydrocarbon in the solvent in the solution A is 1 to 50 mass %.

3. The urethane-setting organic binder for foundry molds according to claim 1, wherein the liquid A and / or the liquid B further contains a dicarboxylic acid ester.

3. A foundry sand composition comprising the urethane-curing organic binder for foundries according to claim 1 or 2 and foundry sand. 　 A mold comprising a hardened product of the molding sand composition according to claim 4.

Images